In the peacock blenny, Salaria pavo, a species with courtship sex-role reversal, smaller, younger males mimic the courtship behavior and the nuptial coloration of females in order to get access to nests during spawning and to parasitize egg fertilization from nest-holder males. Later in their life, sneakers transform both morphologically and behaviorally into nest-holder males. In the present paper we investigate the activational role of 11-ketotestosterone (KT), the most potent androgen in most teleost species, to promote the switch between tactics in sneaker males of S. pavo. Sneakers were implanted either with KT or with control (i.e. castor oil) silastic implants. A week after implantation they were subjected to a set of behavioral tests and morphometric measurements. KT treatment promoted the differentiation of secondary sex characters, such as the anal glands, and inhibited the expression of female courtship behavior. KT-treated sneakers also showed a trend toward less frequent display of female nuptial coloration. There was no effect of KT treatment on the expression of typical nest-holder male behavior. Finally, there was no effect of KT treatment on the number or soma size of arginine vasotocin neurons in the preoptic area, which are often associated with the expression of vertebrate sexual behavior. Thus, KT seems to play a key role in mating tactic switching by inhibiting the expression of female courtship behavior and by promoting the development of male displaying traits (e.g. anal glands). The lack of a KT effect on behavior typical of nest-holding males and vasotocinergic preoptic neurons suggests that a longer time frame or other endocrine/social signals are needed for the initiation of these traits in males that are switching tactics.
In rhesus macaque males, lower than average cerebrospinal fluid (CSF) concentrations of the principle metabolite of serotonin, 5-hydroxyindoleacetic acid (5-HIAA), have been linked to impulsivity, involvement in escalated aggression, failure to elicit consort relationships, production of fewer sperm plugs, and a relatively early age of mortality. Given these potential fitness costs, we performed two studies aimed at elucidating the effects of CSF 5-HIAA on reproduction. Study 1 retrospectively evaluated over a four-year period, the relative reproductive outcome for pairs of adult male rhesus macaques (n = 15) who lived in social groups and who differed in concentrations of CSF 5-HIAA. Study 2 examined the relationship between CSF 5-HIAA and sperm motility and density (n = 12), as a potential mechanism for maintaining variability in CSF 5-HIAA. For Study 1, an average measure from two CSF 5-HIAA samples was calculated for the two males who were present during the time when conception most likely took place (offspring birth date -165 +/- 14 days). Within-pair comparisons of CSF 5-HIAA concentrations between the sire and the non-successful male were drawn for each of the 72 offspring in the study. We found that while sires were typically the male with relatively higher CSF 5-HIAA within the pair, there were no absolute differences in CSF 5-HIAA between males who sired at least one offspring (sires) and those who failed to reproduce (non-sires). Furthermore, while absolute age was not predictive of reproductive outcome, sires with relatively high CSF 5-HIAA also tended to be also relatively older than their competitors. By contrast, for the males with relatively low CSF 5-HIAA who reproduced, sires were relatively younger than the non-sires. These differences in reproductive outcome for males differing in CSF 5-HIAA could not be explained by variability in sperm quantity or quality as we did not find evidence of a relationship between CSF 5-HIAA and either sperm measure. The results of this study suggest that as serotonergic function affects many aspects of behavior and survivorship, it might also be associated with reproductive outcome and different life-history strategies for males differing in concentrations of CSF 5-HIAA.
The neurohormone melatonin is an important signal for both time of day and time of year in many seasonally breeding animals. High densities of melatonin receptors have been found in the suprachiasmatic nucleus, median eminence, and the pituitary gland in almost all mammals investigated so far, and lower densities of melatonin receptors have also been localized to other brain regions varying in a species-specific fashion. Because species-specific differences in receptor distributions have been correlated with differences in behavior and ecology, a comparative study of how melatonin receptors are distributed in vertebrate brains can be useful to the understanding of the functional organization of neural circuits controlling daily and seasonal behaviors. In this study, we localized and characterized melatonin binding sites in the brain of the Mexican free-tailed bat (Tadarida brasiliensis) using in vitro autoradiography with 2-[(125)I]iodomelatonin. Tadarida brasiliensis is a nocturnal insectivorous mammal that seasonally migrates, reproduces once a year, and exhibits documented sexual dimorphisms in seasonal reproductive behaviors, most notably in courtship vocalizations. Prominent 2-[(125)I]iodomelatonin binding was found in the median eminence, suprachiasmatic nuclei, and hippocampus, similar to that observed in other mammals. High densities of binding were also localized to structures of the basal ganglia, including the caudate nucleus, putamen, and nucleus accumbens, a feature commonly observed in songbirds but not in mammals. Saturation analysis indicated that the observed binding sites had an affinity for melatonin typical of the binding properties for the Mel(1a) receptor subtype. We conclude that melatonin receptor distributions in the Mexican free-tailed bat brain appear to show similarities with the reproductive and circadian systems of other mammals and the basal ganglia of songbirds.
The roles that the pineal gland and its hormone melatonin play in the regulation of circadian rhythmicity and photoperiodism vary among vertebrate species. Recently, putative sites of melatonin action have been elucidated in several avian and mammalian species by application of in vitro binding of a radioiodinated melatonin agonist, 2[125I]iodomelatonin (IMEL) and autoradioradiography. These studies in mammals, birds and reptiles have indicated profound differences in the distribution of IMEL binding between these diverse groups, suggesting that these large differences in binding may reflect differences in melatonin function. The present study was performed to determine systematically whether the variance in IMEL binding among avian species corresponds to changes in circadian organization and/or phylogenetic relationships. The distribution of specific IMEL binding was determined in the brains from birds belonging to 14 different species in 5 Orders (Psittaciformes, Passeriformes, Columbiformes, Galliformes and Anseriformes) using in vitro binding, autoradiography and computer-assisted image analysis. The distribution was compared to a similar study in 3 species of turtles as an outgroup. The data indicated IMEL binding in retinorecipient structures of the circadian, tectofugal, thalamofugal and accessory optic visual pathways in all avian species. Relay nuclei and integrative structures of the tectofugal, thalamofugal, accessory optic, and limbic systems, however, bound the hormone to varying degrees. In turtles, binding was observed in retinorecipient structures of the thalamofugal visual pathway and in retinorecipient and integrative areas of the tectofugal visual pathway. No binding was observed in the pineal gland, tuberal hypothalamus or adenohypophysis in any avian or testudine species. This distribution is drastically different from that observed in mammals, where binding predominates in the pars tuberalis of the adenohypophysis and in the suprachiasmatic nucleus, suggesting that the circadian system may influence a wide array of sensory and integrative functions in birds and reptiles through the circadian secretion of melatonin, but that this capacity has been lost in mammals.
Previous studies on the dopaminergic modulation of visuomotor functions in amphibians showed that the dopamine agonist apomorphine (APO) alters prey-catching strategies. After systemic administration of APO in common toads Bufo bufo, prey-oriented turning and locomotion was attenuated whereas snapping toward prey was facilitated in a dose dependent manner. With systemic APO administration, toads which had previously been hunting, that is pursuing prey, behaved in a waiting position, that is sitting motionless and waiting for prey. This suggests that APO facilitates the ingestive component and inhibits the orientational and locomotory components of prey capture. To help unravel the cerebral sites of action of APO, the present study employs the (14)C-2-deoxyglucose method to compare the rate of local glucose utilization in 41 brain structures. The retinal projection fields - e.g. superficial optic tectum, pretectal nuclei, and anterior dorsal thalamic nucleus - showed an elevation in glucose utilization due to APO-induced increases in retinal output. The medial tectal layers and the ventral striatum, both involved in visuomotor functions related to prey-oriented turning and locomotion, displayed APO-induced decreases in glucose utilization. APO-induced increases in glucose utilization were observed in the medial reticular formation and the hypoglossal nucleus which participate in the motor pattern generation of snapping. APO-induced increases in glucose utilization were also detected in the nucleus accumbens and the ventral tegmentum (mesolimbic system) as well as in the ventromedial pallium ('primordium hippocampi') and the septum, both of which belonging to the limbic system. These structures contribute to motivational level control and may be responsible for the APO-induced elevation of the snapping rate. Various other structures revealed APO-induced increases in glucose utilization. These structures include the olfactory bulb, lateral pallium, suprachiasmatic nucleus, nucleus of the periventricular organ, and the nucleus of the solitary tract. The lateral amygdala displayed APO-induced decreases in glucose utilization. The APO-induced alterations in local cerebral glucose utilization are evaluated with reference to the distribution of dopaminergic structures, and this is compared with similar data obtained in the rat by other authors. A neural network explaining the APO-induced behavioral syndrome in the common toad is discussed.
In this study we examine the size of primary sensory areas in the neocortex and the cellular composition of area 17/V1 in three rodent groups: laboratory nocturnal Norway rats (Long-Evans; Rattus norvegicus), wild-caught nocturnal Norway rats (R. norvegicus), and laboratory diurnal Nile grass rats (Arvicanthis niloticus). Specifically, we used areal measures of myeloarchitecture of the primary sensory areas to compare area size and the isotropic fractionator method to estimate the number of neurons and nonneurons in area 17 in each species. Our results demonstrate that the percentage of cortex devoted to area 17 is significantly greater and the percentage of cortex devoted to S1 is significantly smaller in the diurnal Nile grass rat compared with the nocturnal Norway rat groups. Further, the laboratory rodent groups have a greater percentage of cortex devoted to auditory cortex compared with the wild-caught group. We also demonstrate that wild-caught rats have a greater density of neurons in area 17 compared to laboratory-reared animals. However, there were no other clear cellular composition differences in area 17 or differences in the percentage of brain weight devoted to area 17 between nocturnal and diurnal rats. Thus, there are differences in primary sensory area size between diurnal versus nocturnal and laboratory versus wild-caught rat groups and cellular density between wild-caught and laboratory rat groups. Our results demonstrate that the differences in the size and cellular composition of cortical areas do not fit with what would be expected based on brain scaling differences alone, and have a consistent relationship with lifestyle and sensory morphology.
Ocular morphology was examined in larval, juvenile and adult F. varium. There was a 26-fold increase in eye size from 0.28 mm in the smallest larva (5.0 mm in length) to a maximum diameter of 7.2 mm in a 110 mm long adult. Larval fish had pure cone retinae at hatching, however, putative rod precursor cells were also present. Juvenile and adult fish had a duplex retina with cones arranged in a square mosaic in which 4 equal double cones surrounded a central single cone. Hypertrophy of cone ellipsoids with increasing eye size resulted in maintenance of a closely packed array in fishes of all sizes. Theoretical sensitivity, assessed in terms of convergence of rods:bipolars, rod density, and photoreceptor outer segment length, increased during the juvenile phase but was constant across the adult size range. Angular density of cones increased with increasing eye size such that theoretical spacial acuity was poor in smallest fish (1 degree 8') and improved to an asymptotic value of about 9' in adults. Behavioural acuity of a 1-day-old larva determined using the optokinetic response (29 degrees), was very much poorer than histological estimates (1 degree 8'). Behavioural acuity improved to 4 degrees 18' at 14 days of age, compared to a theoretical value of 54'. An estimate of Matthiessen's ratio based on histological measurements suggests that the larval eye is initially strongly myopic, and grows into focus. Development of the retractor lentis muscle was first apparent 7 days after hatching with the result that larval eyes are incapable of accommodative lens movements to correct for a refractive error. This apparent myopia is thought to account for at least part of the mismatch between theoretical and behavioural spatial acuity.
Ludwig Mauthner was only 19 years old when he published his discovery of the colossal fibers in the spinal cord of fishes which now bear his name. Based on Mauthner's works, archival material, and contemporary sources we provide a summary of his life and work as neuroanatomist and ophthalmologist in imperial Austria. In the years 1859-1863 Mauthner published four papers on the structure of the central nervous system in vertebrates. His first report on fishes contains the original description of a 'colossal myelinated nerve fiber' on each side of the central canal, extending through the entire spinal cord. Another, more general, treatise on 'the morphological elements of the nervous system' (published in 1863) summarizes his neurohistological studies of various vertebrates. It includes a classification of nerve cells based on their (histochemical) reaction to carmine. The main findings were soon shown to be artefactual; the paper had a long-range impact, however, because it provoked fruitful controversy among contemporary neuroanatomists. Mauthner published several monographs and numerous articles in ophthalmology, a newly developing branch of medicine that he chose for his later career. After abruptly resigning from a professorship at Innsbruck University, he opened a private practice in Vienna and continued lecturing in his field. He became a noted eye-surgeon, was elected Assistant Director of the Vienna 'Allgemeine Poliklinik', and in 1894 became Professor and Chair of Ophthalmology at the University of Vienna. Mauthner unexpectedly died on the night following the formal announcement of his appointment.
Julia Barlow Platt was a comparative embryologist and neurobiologist who was primarily interested in segmentation of the head in vertebrates. She was born on September 14, 1857 in San Francisco, California. Platt grew up in Burlington, Vermont, attended the University of Vermont and began graduate studies at Harvard University. Her nine years as a graduate student were spent on two continents with some of the most influential comparative zoologists of the time. Platt's remarkable scientific accomplishments over a ten year period include a description of axial segmentation currently used in the staging of chick embryos and the first description of a separate anterior head segment in Squalus embryos. Her most controversial study identified ectodermal cells in Necturus embryos that gave rise to head cartilage and dentine, a discovery which was the impetus for the reassessment and modification of the germ layer concept. She was one of the first women to 'matriculate' at a German university and receive a Ph.D. degree. Platt played a pioneer role in opening opportunities for other women who followed her. Platt was one of the first women neuroscientists. Among her contributions, she distinguished dorsolateral placodes, epibranchial placodes, and the first stages of lateral line organs in Necturus, and she described nerve fibers originating in the spinal cord and extending to the notochord in Branchiostoma (= Amphioxus). After receiving a Ph.D. degree in Freiburg, Germany in 1898, Platt was unable to secure a suitable teaching position and, as a result, her scientific career came to an end. She retired to Pacific Grove, California, where she pursued civic duty with the same vigor and energy she had dedicated to scientific research. We provide a sketch of her remarkable life and work as a comparative embryologist, neuroscientist and civic leader.
Vocalization behaviors of anuran amphibians are universally sexually dimorphic. Usually, only male frogs give an advertisement call, while female frog calls are limited to a soft and simple release call which is specifically suppressed at mating. In a very few species, however, female frogs also give mating vocalizations. We examined possible mechanisms for control of this rare heterotypical behavior. At the peripheral level, most differences in temporal and spectral characteristics between female mating calls and the calls of conspecific males related directly to sexual dimorphisms in laryngeal and oblique muscle morphology. At the neural and hormonal level, we first developed an integrated model for control of vocalizations, based primarily on male frog data. When this model is applied to females, female mating vocalizations were most similar to male advertisement calls, rather than being modified release calls. Females may have conscripted preexisting androgen-sensitive neural pathways typically used only by males but present in both sexes. Female mating calls have been heard only during courtship and amplexus. Androgen levels in females at this time are significantly higher than even those levels in males. Because this situation is common in frogs, female mating vocalizations likely evolved independently multiple times. Character optimization suggests that mate location is the most common biological role for female mate calling, but the particular aspects of reproductive biology vary widely across species.
We investigated the neuroanatomy and physiology of the complex tibial organ of an atympanate ensiferan, the Gryllacridid Ametrus tibialis. This represents the first analysis of internal mechanoceptors in Gryllacridids. The complex tibial organ is tripartite consisting of a subgenual organ, intermediate organ and a homologue organ to the crista acustica of tympanate ensiferan taxa of Tettigoniidae, Haglidae, and Anostostomatidae. The crista homologue contains 23 +/- 2 receptor neurons in the foreleg. It is associated with the leg trachea and found serially in all three thoracic leg pairs. Central projections of the sensory nerve of the complex tibial organ bifurcate in two lobes in the prothoracic ganglion, which do not reach the midline. The axonal endings project into the mVAC, the main vibratory-auditory neuropile of Ensifera. Recordings of the tibial nerve show that the tibial organ is sensitive to vibrational stimuli with a minimum threshold of 0.02 to 0.05 ms(-2) at 200-500 Hz, but rather insensitive to airborne sound. The main function of the tibial organ is therefore vibration sensing, although the specific function of the crista homologue remains unclear. The presence of the crista acustica homologue is interpreted in phylogenetic context. Because ensiferan phylogeny is unresolved, two alternative scenarios can be deduced: (a) the crista homologue is a precursor structure which was co-opted as an auditory system and represent a morphologically highly specialized structure before acquisition of its new function; (b) a previously functional tibial ear is evolutionary reduced but the neuronal structures are maintained. Based on comparison of neuroanatomical details, the crista acustica homologue of A. tibialis could present the neuronal complement of an ear evolutionary precursor structure, which was successively made sensitive to airborne sound by elaboration of cuticular tympana, auditory spiracle and trachea for sound propagation.
Space sickness is generally considered a variant of motion sickness although not fully proved as such. Understanding space sickness requires objective and quantitative characterization of the disorder. Vomiting is a quantifiable physiological event performed by the respiratory muscles which generate the pressures that evacuate the gut. Vomiting from all causes is coordinated by the vomiting center in the medulla oblongata. The emetic chemoreceptor trigger zone (CTZ) in the area postrema is thought to be an indispensable element in the afferent pathway of motion sickness. About 30 potential neurotransmitters exist in the vomiting control mechanism which includes at least eight chemical transmission steps through the reflex pathway of motion sickness. Individual synaptic transmitters do not likely mediate specific functions, but particular combinations of those transmitters might well serve distinct functions. Adaptation to the cause of space sickness probably results from readjustment of a cerebellar circuit or of a humoral factor acting on the CTZ, rather than from stimulus-receptor desensitization. Space sickness must, for purposes of investigation, be treated as a unique disorder engendered by weightlessness until proved equivalent to any emetic syndrome that occurs on earth.
Over the last decade, the intellectual reputation of birds has been greatly rehabilitated, notably by the studies of Nicky Clayton and coworkers on New Caledonian crows [Clayton, 2007] and the work of Irene Pepperberg and coworkers on African grey parrots [Pepperberg, 2002]. This realization stands quite in contrast to the prior and long-standing view that avian behavior, even the seemingly impressive vocal abilities of parrots for example, was merely driven by rote learning and hardwired stereotypical behavioral routines [Reiner et al., 2004]. This older view was reinforced by the other old notion that the avian telencephalon is largely hypertrophied basal ganglia and is nearly devoid of a neural region that could perform the cognitive operations carried out by the mammalian cerebral cortex [Reiner et al., 2004]. However, the work of Karten and Hodos  beginning nearly 50 years ago, on the organization and function of the avian forebrain, had long shown that the avian telencephalon is not an overgrown basal ganglia, and that it possesses a large region that is functionally akin to the mammalian neocortex [Karten and Hodos, 1970; Karten et al., 1973]. Karten  noted in his theoretical writings that this territory within the avian telencephalon, which encompasses the Wulst, dorsal ventricular ridge (DVR) and arcopallium, possesses the neuron types and connectivity characteristic of the mammalian neocortex, and can thus perform as the neural substrate for cognition. The Wulst, DVR and arcopallium, however, are arrayed as nuclei rather than as layers, which is why earlier neuroanatomists had thought that the nuclear avian telencephalon is largely equivalent to the nuclear basal ganglia of mammals.
During the 2008 Karger Workshop considerable progress was made towards defining a model or structural plan, valid for the prosencephalon of all vertebrates. The presentations demonstrated that the following features, which are valid for tetrapods, also hold true for most groups of fish: (1) The diencephalon proper is clearly composed of three neuromeres, p1-p3; (2) in the pallium four, rather than three, fundamental longitudinal zones can be distinguished; (3) during ontogenesis, numerous GABA-ergic elements migrate tangentially from the subpallium to the pallium.
Ecological studies on feral populations of mice, fish and birds elucidate the functional significance of phenotypes that differ individually in their behavioral and neuroendocrine response to environmental challenge. Within a species, the capacity to cope with environmental challenges largely determines individual survival in the natural habitat. Recent studies indicate that individual variation within a species may buffer the species for strong fluctuations in the natural habitat. A conceptual framework will be presented that is based on the view that individual variation in aggressive behavior can be considered more generally as a variation in actively coping with environmental challenges. Highly aggressive individuals adopt a proactive coping style whereas low levels of aggression indicate a more passive or reactive style of coping. Coping styles have now been identified in a range of species and can be considered as trait characteristics that are stable over time and across situations. The dimension of coping style seems to be independent of an emotionality dimension. Hence, in the analysis of the proximate mechanisms of stress and adaptation, one has to consider the possibility that the mechanisms which determine the type of stress response might be independent from those underlying the magnitude of the response. The two coping styles differ in a number of important neurobiological and neuroendocrine systems. For example, proactive males differ significantly from reactive males in the homeostatic control of serotonergic activity resulting in completely opposite dose response relationships of various serotonergic drugs. The results so far show that proactive coping is characterized by a strong inhibitory control of the 5-HT neuron via its somatodendritic 5-HT(1A) autoreceptor. It is hypothesized that the regulation of serotonin release is causally related to coping style rather than emotionality. Understanding the functional individual variation as it occurs in nature and the underlying neurobiology and neuroendocrinology is fundamental in understanding individual vulnerability to stress related disease.
Based on retrograde labeling from the high cervical spinal cord, the inter- and intra-laminar distributions of tectospinal tract (TST) somata within the tectum of 23 mammals and one reptile are described. The results show that TST somata are found only in the intermediate and deep layers. Although more TST somata are usually found in the intermediate layer, there are no useful relationships for predicting the number in one layer given the number in the other. The ratio of numbers of TST somata in the intermediate relative to the deep layer varies widely, from 0:1 (in rabbits) to over 8:1 (in marmosets). Within both layers the majority of TST somata (> 80%) are found in the lateral half of the tectum--the area subversing the lower visual field. In contrast, the variation between temporal and nasal visual fields is adequately accounted for by the animal's 'visual axis'--the azimuth of its field of best vision. In general, the present results uphold the idea that the significance of the TST somata, and perhaps of the tectospinal tract itself, is to be found in directing the head so that the retinal area of best vision can be brought to bear on stimuli either almost outside, or about to pass outside, of the area of best vision. The larger and possibly universal predominance of TST somata subserving the lower visual field suggests that the tectospinal tract may be primarily concerned with adjusting the step dimensions of the forelegs to accommodate obstacles to normal progression.
Most swimming vertebrates, particularly fishes and amphibians, avoid predators by producing an escape behavior initiated by a single action potential in one of a pair of cells, the Mauthner cells, located in the hindbrain. The most prominent feature of this behavior is a rapid, forceful bend of body and tail which leads to a characteristic C bend (stage 1) early in the escape. The spinal output of the Mauthner cell is largely responsible for this bend. Each Mauthner cell sends an axon down the length of the spinal cord on the side opposite the soma. When one Mauthner axon fires, it massively excites the ipsilateral musculature by (1) monosynaptic excitation of the large primary motoneurons that innervate the fast white muscle fibers and (2) polysynaptic excitation of motoneurons which is most likely mediated through an identified class of descending interneurons. While motoneurons on the side of the C bend are excited, excitation of those on the opposite side is blocked by inhibition of primary motoneurons and descending interneurons. This inhibition is mediated by commissural interneurons that are electrotonically coupled to the Mauthner axon and cross the spinal cord to monosynaptically inhibit cells on the opposite side. They inhibit not only primary motoneurons and descending interneurons, but also the commissural inhibitory interneurons on the opposite side. The inhibition of contralateral primary motoneurons and descending interneurons prevents motor activity on the side opposite the C bend from opposing that bend, while the inhibition of commissural interneurons prevents them from interfering, via their inhibitory connections, with excitation of motoneurons on the side of the bend. The spinal network responsible for the bend has several similarities with the spinal network for swimming in other anamniotic vertebrates, including lampreys and embryonic frogs. These similarities reveal important, primitive features of axial motor networks among vertebrates.
For prey capture in the dark, the barn owl Tyto alba has evolved into an auditory specialist with an exquisite capability of sound localization. Adaptations include asymmetrical ears, enlarged auditory processing centers, the utilization of minute interaural time differences, and phase locking along the entire hearing range up to 10 kHz. Adaptations on the molecular level have not yet been investigated. Here, we tested the hypothesis that divergence in the amino acid sequence of the voltage-gated K(+) channel Kv3.1 contributes to the accuracy and high firing rates of auditory neurons in the barn owl. We therefore cloned both splice variants of Kcnc1, the gene encoding Kv3.1. Both splice variants, Kcnc1a and Kcnc1b, encode amino acids identical to those of the chicken, an auditory generalist. Expression analyses confirmed neural-restricted expression of the channel. In summary, our data reveal strong evolutionary conservation of Kcnc1 in the barn owl and point to other genes involved in auditory specializations of this animal. The data also demonstrate the feasibility to address neuroethological questions in organisms with no reference genome by molecular approaches. This will open new avenues for neuroethologists working in these organisms.
The visual callosal neurons and the connections between the two cerebral hemispheres in hamsters have been shown to be important for visual functions, but little is known about the detailed morphology of these neurons. In this study, we have used techniques based on retrograde transport of a fluorescent tracer, Granular Blue, and intracellular injection of Lucifer Yellow in fixed brain slices to identify the laminar distribution and dendritic morphology of the visual callosal neurons in the 17/18a border region of the adult golden hamster. The cells giving rise to the callosal projections were morphologically heterogeneous, although they were all spiny neurons. Most were pyramidal cells, but some were stellate cells. They were located in layers II-VI, with cells concentrating in three bands: (1) in the middle three fifths of layer II/III; (2) in layer IV, and (3) in the middle three fifths of layer V. In layer II/III and layer V, the great majority of the cells were pyramidal or star pyramidal neurons. In layer IV, about half were stellate neurons and the rest pyramidal or star pyramidal neurons. In layer VI, they consisted mostly of modified pyramidal cells. The soma areas of the pyramidal and star pyramidal neurons in all the layers ranged from 52 to 335 micron 2 with a mean of 148 micron 2 (n = 92; SD = 64.4). In general, these cells gave rise to 3-5 basal dendrites.(ABSTRACT TRUNCATED AT 250 WORDS)
This study compares a whole brain of the dwarf sperm whale (Kogia sima) with that of a common dolphin (Delphinus delphis) using high-resolution magnetic resonance imaging (MRI). The Kogia brain was scanned with a Siemens Trio Magnetic Resonance scanner in the three main planes. As in the common dolphin and other marine odontocetes, the brain of the dwarf sperm whale is large, with the telencephalic hemispheres remarkably dominating the brain stem. The neocortex is voluminous and the cortical grey matter thin but expansive and densely convoluted. The corpus callosum is thin and the anterior commissure hard to detect whereas the posterior commissure is well-developed. There is consistency as to the lack of telencephalic structures (olfactory bulb and peduncle, olfactory ventricular recess) and neither an occipital lobe of the telencephalic hemisphere nor the posterior horn of the lateral ventricle are present. A pineal organ could not be detected in Kogia. Both species show a tiny hippocampus and thin fornix and the mammillary body is very small whereas other structures of the limbic system are well-developed. The brain stem is thick and underlies a large cerebellum, both of which, however, are smaller in Kogia. The vestibular system is markedly reduced with the exception of the lateral (Deiters') nucleus. The visual system, although well-developed in both species, is exceeded by the impressive absolute and relative size of the auditory system. The brainstem and cerebellum comprise a series of structures (elliptic nucleus, medial accessory inferior olive, paraflocculus and posterior interpositus nucleus) showing characteristic odontocete dimensions and size correlations. All these structures seem to serve the auditory system with respect to echolocation, communication, and navigation.
The distribution of proliferating cells in the midbrain, thalamus, and telencephalon of adult bullfrogs (Rana catesbeiana) was examined using immunohistochemistry for the thymidine analog 5-bromo-2'-deoxyuridine (BrdU) and DNA dot-blotting. At all time points examined (2 to 28 days post-injection), BrdU-labeled cells were located in ventricular zones at all levels of the neuraxis, but with relatively more label around the telencephalic ventricles. Labeled cells, some showing profiles indicative of dividing and migrating cells, were present in brain parenchyma from 7 to 28 days post-injection. These labeled cells were particularly numerous in the dorsal and ventral hypothalamus, preoptic area, optic tectum, and laminar and principal nuclei of the torus semicircularis, with label also present, but at qualitatively reduced levels, in thalamic and telencephalic nuclei. Double-label immunohistochemistry using glial and early neural markers indicated that gliogenesis and neurogenesis both occurred, with new neurons observed particularly in the hypothalamus, optic tectum, and torus semicircularis. In all brain areas, many cells not labeled with BrdU were nonetheless labeled with the early neural marker TOAD-64, indicating that these cells were postmitotic. Incorporation of DNA measured by dot-blotting confirms the presence of DNA synthesis in the forebrain and brainstem at all time points measured. The pattern of BrdU label confirms previous experiments based on labeling with (3)H-thymidine and proliferating cell nuclear antigen showing cell proliferation in the adult ranid brain, particularly in hypothalamic nuclei. The consistent appearance of new cells in the hypothalamus of adult frogs suggests that proliferative activity may be important in mediating reproductive behaviors in these animals.
The distribution of the growth associated protein GAP-43 has been described in the brain and spinal cord of rats and other placental mammals but not marsupials. In order to provide such information, we employed a monoclonal antibody to immunostain for GAP-43 in the central nervous system of adult and developing opossums, Didelphis virginiana. The GAP-43 immunoreactivity was widely distributed in the brain of adult opossums, but it was particularly dense within specific layers of the olfactory bulb and hippocampal formation, layer I of the cerebral cortex, the bed nucleus of the stria terminalis, the nucleus accumbens, the striatum, the amygdala, the septum, the olfactory tubercle, medial parts of the preoptic area and diencephalon, the substantia nigra, the ventral tegmental area, the periaqueductal grey matter, the interpeduncular nucleus, the periventricular grey, the molecular layer of the cerebellum, the superior central nucleus, the basilar pons, the dorsal vagal and solitary nuclei, and laminae I and II of the spinal trigeminal nucleus. Immunoreactivity for GAP-43 was also present within the spinal cord, where it was densest within laminae I, II, IX, and X and within the intermediolateral cell column. In most areas of the brain and some areas of the spinal cord, an inverse correlation existed between the location of GAP-43 and myelin. Immunostaining for GAP-43 was found throughout most of the central nervous system during early development, but it decreased with age in a regionally specific manner until the adult pattern was reached. Our results suggest that the distribution of GAP-43 in opossums is similar in many respects to that reported in rats and that it is developmentally regulated.
Growth-associated protein-43 is typically expressed at high levels in the nervous system during development. In adult animals, its expression is lower, but still observable in brain areas showing structural or functional plasticity. We examined patterns of GAP-43 immunoreactivity in the brain of the bullfrog, an animal whose nervous system undergoes considerable reorganization across metamorphic development and retains a strong capacity for plasticity in adulthood. Immunolabeling was mostly diffuse in hatchling tadpoles, but became progressively more discrete as larval development proceeded. In many brain areas, intensity of immunolabel peaked at metamorphic climax, the time of final transition from aquatic to semi-terrestrial life. Changes in intensity of GAP-43 expression in the medial vestibular nucleus, superior olivary nucleus, and torus semicircularis appeared correlated with stage-dependent functional changes in processing auditory stimuli. Immunolabeling in the Purkinje cell layer of the cerebellum and in the cerebellar nucleus was detectable at most developmental time points. Heavy immunolabel was present from early larval stages through the end of climax in the thalamus (ventromedial, anterior, posterior, central nuclei). Immunolabel in the tadpole telencephalon was observed around the lateral ventricles, and in the medial septum and ventral striatum. In postmetamorphic animals, immunoreactivity was confined mainly to the ventricular zones and immediately adjacent cell layers. GAP-43 expression was present in olfactory, auditory and optic cranial nerves throughout larval and postmetamorphic life. The continued expression of GAP-43 in brain nuclei and in cranial nerves throughout development and into adulthood reflects the high regenerative potential of the bullfrog's central nervous system.
We have shown previously that GAP-43, a growth associated protein characteristically present in growing and regenerating axons, is relatively abundant in the spinal cord of adult opossums. In the present study, we combined the orthograde transport of the fluorescent marker Fluoro-Ruby with immunofluorescence for GAP-43 to determine if any of it is present within descending spinal axons. When Fluoro-Ruby was injected into the red nucleus and midbrain tegmentum, the medial pontine or medullary reticular formation, the medullary raphe or the lateral vestibular nucleus, axons were labeled in the expected areas of the spinal cord, but in most cases none showed evidence for GAP-43. In two of the four cases with rubral injections, however, a few labeled axons within the rubrospinal tract showed GAP-43 immunofluorescence, and in one case with an injection of the gigantocellular reticular nucleus and adjacent raphe, labeled axons within lamina IX immunostained for the protein. Since serotoninergic neurons are present within the gigantocellular reticular nucleus and adjacent raphe, and axons of the same phenotype are abundant within lamina IX, we asked whether serotoninergic axons contain GAP-43. When sections of the spinal cord were immunostained for both serotonin and GAP-43, many axons within lamina IX showed evidence for both substances. Such axons appeared to contact presumptive motoneurons. In cases with Fluoro-Ruby injections of the forelimb motor cortex, labeled axons were present within the pyramidal tract, and some of them showed evidence for GAP-43.
Although early comparative studies supported hypotheses that ecological demands selected for primate cognition, later work indicated that social demands were more important. One difference between earlier and later studies is that earlier studies scaled brain structures by (A) taking residuals from an interspecific regression of the brain structure in question on body mass, whereas later studies scaled them by (B) taking residuals from an interspecific regression of the brain structure in question on another brain structure or by (C) taking ratios of the brain structure in question to another brain structure. We conducted a series of comparative tests to explore the possibility that the different methods are responsible for the discrepancy between earlier and later studies. Specifically, we tested the ability of a social variable - group size - and an ecological variable - home range size - to explain variation in the non-V1 isocortex (isocortex minus primary visual cortex) when this structure was scaled with the three different methods. In multiple regression analysis, group size was a better predictor of the non-V1 isocortex with method (B). With methods (A) and (C), however, results were ambiguous: either home range size or group size explained more of the variation, depending on the inclusion of outliers, the use of independent contrasts, and whether home range size was scaled relative to body mass. We examine the three scaling methods and find no reasonable basis for preferring any of them. Hence, our results do not allow a distinction between social and ecological hypotheses. The general implications of our study are that (1) previous comparative studies are inconclusive and (2) further research is needed to develop a scaling method where relative measures of brain structure size are demonstrated to correspond with behavioral performance.
Although it seems highly likely that mammalian isocortex evolved from a structure resembling reptilian telencephalic cortex, it has been uncertain if this occurred by the laminar differentiation of three-layered reptilian cortex into six-layered mammalian isocortex without the addition of new cell types or by laminar differentiation with the addition of new cell types. To distinguish between these two possibilities, immunohistochemical techniques were used to study turtles to see if the same major neuronal cell types, as defined by neurotransmitter or neuropeptide content, present in mammalian isocortex are also present in the specific part of reptilian cortex thought to be the forerunner of at least parts of isocortex, namely the dorsal cortex. Neurons containing the following substances are the major transmitter-specific types of neurons known to be present in mammalian isocortex: cholecystokinin-8 (CCK8), vasoactive intestinal polypeptide (VIP), acetylcholine, substance P (SP), neuropeptide Y (NPY), somatostatin (SS), LANT6, enkephalin, GABA and glutamate (GLUT). In turtles, only those of the above substances that are found in large numbers of neurons in layers V-VI in mammalian isocortex, irrespective of whether they are also present in layers II-IV (i.e. SP, NPY, SS, LANT6, GABA and GLUT), were present in neurons in dorsal cortex. The neurons containing these substances in dorsal cortex in turtles were generally highly similar in morphology to their counterparts in mammalian isocortex. In contrast, neurons labeled for CCK8, VIP or acetylcholine, which are mainly found in neurons of layers II-IV of mammalian isocortex, were absent or extremely rare in dorsal cortex. The absence or paucity of neurons labeled for these latter substances in dorsal cortex in turtles did not reflect an overall staining failure of the antisera used since the same antisera yielded excellent labeling of neurons, fibers and terminals in many other brain regions in turtles. Thus, dorsal cortex in turtles appears to lack several of the major cell types characteristic of layers II-IV of mammalian isocortex, but possesses a number of the major cell types characteristic of layers V-VI of isocortex. The findings support and extend a previous suggestion by Ebner , based on hodological data, that dorsal cortex in turtles may lack the types of neurons found in the more superficial layers of mammalian isocortex.(ABSTRACT TRUNCATED AT 400 WORDS)
The 5α-reductase (5αR) enzyme converts testosterone to 5α-dihydrotestosterone. This local metabolism within the brain is important for the full expression of male sexual behavior in many species, including green anole lizards. Two isozymes of 5αR exist and little is known about their specific distributions. We conducted in situ hybridization for both isozymes in intact male and female green anole brains during the breeding (BS) and non-breeding (NBS) seasons. 5αR1 mRNA was only detected in the brainstem, while 5αR2 was expressed in specific areas throughout the brain. As our primary interest was evaluating the potential role of 5αR in forebrain regulation of reproductive behavior, we quantified 5αR2 expression in the preoptic area, amygdala (AMY), and ventromedial hypothalamus (VMH). More 5αR2 cells were detected during the NBS than BS in the AMY, and the density of these cells was greater in females than males. In the VMH, the right side contained more 5αR2 cells than the left, an effect driven by a lateralized increase in the NBS. These data expand understanding of the distribution and potential roles of both isozymes in the adult brain, and differences in expression patterns between mammals and birds suggest that they may have been co-opted for different functions later in evolution.
The arcuate nucleus is a prominent cell group in the human hindbrain, characterized by its position on the pial surface of the pyramid. It is considered to be a precerebellar nucleus and has been implicated in the pathology of several disorders of respiration. An arcuate nucleus has not been convincingly demonstrated in other mammals, but we have found a similarly positioned nucleus in the C57BL/6J mouse. The mouse arcuate nucleus consists of a variable group of neurons lying on the pial surface of the pyramid. The nucleus is continuous with the ventrolateral part of the principal nucleus of the inferior olive and both groups are calbindin positive. At first we thought that this mouse nucleus was homologous with the human arcuate nucleus, but we have discovered that the neurons of the human nucleus are calbindin negative, and are therefore not olivary in nature. We have compared the mouse arcuate neurons with those of the inferior olive in terms of molecular markers and cerebellar projection. The neurons of the arcuate nucleus and of the inferior olive share three major characteristics: they both contain neurons utilizing glutamate, serotonin or acetylcholine as neurotransmitters; they both project to the contralateral cerebellum, and they both express a number of genes not present in the major mossy fiber issuing precerebellar nuclei. Most importantly, both cell groups express calbindin in an area of the ventral hindbrain almost completely devoid of calbindin-positive cells. We conclude that the neurons of the hindbrain mouse arcuate nucleus are a displaced part of the inferior olive, possibly separated by the caudal growth of the pyramidal tract during development. The arcuate nucleus reported in the C57BL/6J mouse can therefore be regarded as a subgroup of the rostral inferior olive, closely allied with the ventral tier of the principal nucleus.
Three distinct opioid precursors have been identified in the central nervous system of mammals: proopiomelanocortin (POMC), proenkephalin, and prodynorphin. These precursors are derived from separate genes, synthesized in distinct neurons, and yield unique sets of opioid end products. This review will discuss the general mechanisms involved in the biosynthesis of neuropeptide precursors and consider the roles of posttranscriptional and posttranslational processing mechanisms in the generation of multiple sets of end products from a single gene. In addition, techniques that can be used for isolating and characterizing neuropeptide genes, mRNAs, and end products will be reviewed. These introductory comments will serve as the framework for a discussion of the phylogeny of the opioid precursors in the major groups of non-mammalian vertebrates.
Three hypotheses have been elaborated based upon the examination of afferent projections to the diencephalon of six vertebrate classes: the first, that the target diencephalic areas should be considered homologous in all the classes; the second, that olfaction does not dominate the sensory input to the telencephaIon or diencephalon in nonmammalian forms as previously thought, but that a strong case can be made that vision does; and the third, that overlap can be inversely correlated with specialization more readily than with a hypothetical evolutionary position.
Arthropods with segmented abdomens show similar abdominal positioning behaviors. It has been possible to gain some understanding of the neural basis of these behaviors in lobsters and crayfish using standard intracellular and dye-filling techniques. Typically crayfish and lobsters have six abdominal segments each controlled by a set of flexor and extensor tonic muscles. Each segment has a dozen tonic motor neurons controlled in turn by a large number of interneurons. A similar set of phasic muscles, motor neurons and interneurons control a fast system. The fast components underlie such behaviors as escape and swimming. Lucifier-filled microelectrodes were used to stimulate, record and dye-fill the motor neurons and interneurons of the tonic systems. It was soon apparent that all of these neurons are identifiable. These data allowed us to determine how many interneurons served in a circuit generating a behavior, while the use of pairs of electrodes permitted the study of synaptic interactions between interneurons. Interneurons involved in abdominal positioning produced either flexion (flexion producing interneurons or FPI), extension (EPI) or inhibition (I). Significantly, FPIs tended to synaptically excite other FPIs and inhibit EPIs. In turn EPIs excited other EPIs and inhibited FPIs. As a result, impaling and stimulating an FPI, for example, tended to recruit others and their combined activity evoked a natural-looking behavior. The inhibition between FPI and EPI and vice versa tended to account for the reciprocity seen between the two behaviors in all experiments. Finally the synaptic connections between EPI-EPI on FPI-FPI were found to be essentially invariable. Thus repeated stimulation of an FPI or the stimulation of this same FPI in another preparation, at another time, gave essentially the same overall behavior such that the stimulation of one FPI or EPI could evoke a wide spread output resembling a normal behavior.
The abducens nucleus in carpet sharks is not a discrete delimited nucleus, as the dendrites of the motoneurons extend into the reticular formation and the medial longitudinal fasciculus. Injections of horseradish peroxidase (HRP) designed to trace the inputs to these neurons are therefore difficult to confine to this system alone. Despite this problem a consistent finding from injection of HRP in the area of the abducens nucleus is the retrograde labelling of a column of cells in the contralateral octaval nuclei. The column of cells is predominantly in the ventral portion of the descending octaval nucleus, but does straddle the entrance of nerve VIII, extending into the caudal part of the ascending octaval nucleus. Labelled cells correspond in location and morphology to those cells receiving input from horizontal canal afferent fibers, confirming the trineuronal nature of the horizontal vestibulo-ocular reflex arc in elasmobranch fishes.
The location of principal and accessory motoneurons and principal interneurons of the nucleus abducens was determined in the caspian terrapin (Mauremys caspica) by means of horseradish peroxidase histochemical tracing. Enzyme injections were made into the ipsilateral lateral rectus and retractor bulbi muscles and into the contralateral oculomotor nucleus. Labeled principal abducens motoneurons formed a cluster of cells in the rhombencephalon, under the IVth ventricle and adjacent to the medial longitudinal fascicle. The accessory abducens motoneurons were located more deeply in the rhombencephalon and more ventrolaterally than the principal motoneurons forming a compact aggregation of neurons. The principal interneurons of abducens nucleus were arranged as a cluster of cells under the floor of the IVth ventricle and more lateral than the principal motoneurons, with no intermingling.
An in vitro brain stem preparation from turtles exhibits a neural correlate of eyeblink classical conditioning during pairing of auditory (CS) and trigeminal (US) nerve stimulation while recording from the abducens nerve. The premotor neuronal circuits controlling abducens nerve-mediated eyeblinks in turtles have not been previously described, which is a necessary step for understanding cellular mechanisms of conditioning in this preparation. The purpose of the present study was to neuroanatomically define the premotor pathways that underlie the trigeminal and auditory nerve-evoked abducens eyeblink responses. The results show that the principal sensory trigeminal nucleus forms a disynaptic pathway from both the trigeminal and auditory nerves to the principal and accessory abducens motor nuclei. Additionally, the principal abducens nucleus receives vestibular inputs, whereas the accessory nucleus receives input from the cochlear nucleus. The late R2-like component of abducens nerve responses is mediated by the spinal trigeminal nucleus in the medulla. Both the principal sensory trigeminal nucleus and the abducens motor nuclei receive CS-US convergence and therefore both, or either, might be considered potential sites of synapse modification during in vitro abducens conditioning. Further data are required to determine the role of the principal sensory trigeminal nucleus in in vitro conditioning.
Indices of cerebral development were computed for 23 different species in order to assess their capacity to accurately reflect differences in learning ability. The resulting correlations between index values and performance on a variety of tasks strongly suggest that this approach may offer the best type of continuum for the comparative study of learning. It was further suggested that if the index proposed by Jerison were expanded to reflect possible neuronal connections, a more powerful measure might be obtained.
What examples of convergence in higher-level complex cognitive characteristics exist in the animal kingdom? In this paper I will provide evidence that convergent intelligence has occurred in two distantly related mammalian taxa. One of these is the order Cetacea (dolphins, whales and porpoises) and the other is our own order Primates, and in particular the suborder anthropoid primates (monkeys, apes, and humans). Despite a deep evolutionary divergence, adaptation to physically dissimilar environments, and very different neuroanatomical organization, some primates and cetaceans show striking convergence in social behavior, artificial 'language' comprehension, and self-recognition ability. Taken together, these findings have important implications for understanding the generality and specificity of those processes that underlie cognition in different species and the nature of the evolution of intelligence.
To investigate the role of the corpus cerebelli in the control of sustained swimming or cruising in goldfish, Carassius auratus, we conducted experiments examining the effects of partial ablation of the corpus cerebelli (CC) on swimming performance against constant water flow at various speeds. Ten out of 15 CC-ablated fish successfully maintained sustained swimming against water flow even at the highest speed tested (3.0 body lengths per second). This result showed that the CC is not crucial for generating the simple swimming motor pattern, although some effects of the surgical operation itself on the capability of the sustained swimming were found in both sham-operated and CC-ablated fish. However, we found that both tail-beat amplitude and frequency in CC-ablated goldfish tended to be greater than that of control fish at the same swimming speeds. The thrust index (square of the value obtained by multiplying the tail beat frequency (Hz) by twice the tail beat amplitude (mm)) was significantly larger in CC-ablated fish than in control fish at higher swimming speeds (> or =2.0 body length per second). This result suggests that CC-ablated goldfish produced more thrust by tail beats than control fish to maintain sustained swimming at higher speeds. We concluded that in goldfish the CC plays no major role in the posture control and generation of simple forward swimming movement, although the integrity of the CC is important for execution of normal swim gait.