[Show abstract][Hide abstract] ABSTRACT: Recently published work and emerging research efforts have suggested that the olfactory system is intimately linked with the endocrine systems that regulate or modify energy balance. Although much attention has been focused on the parallels between taste transduction and neuroendocrine controls of digestion due to the novel discovery of taste receptors and molecular components shared by the tongue and gut, the equivalent body of knowledge that has accumulated for the olfactory system, has largely been overlooked. During regular cycles of food intake or disorders of endocrine function, olfaction is modulated in response to changing levels of various molecules, such as ghrelin, orexins, neuropeptide Y, insulin, leptin, and cholecystokinin. In view of the worldwide health concern regarding the rising incidence of diabetes, obesity, and related metabolic disorders, we present a comprehensive review that addresses the current knowledge of hormonal modulation of olfactory perception and how disruption of hormonal signaling in the olfactory system can affect energy homeostasis.
Chemical Senses 07/2012; 37(9):769-97. · 3.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Previous studies have demonstrated that olfactory-driven behaviors in rats are influenced by short-term caloric restriction, partly through the modulation of olfactory sensitivity by appetite-modulating hormones or peptides such as insulin and leptin. Here, we addressed the issue of a long-term modulation of their neuroendocrine status by evaluating the effect of chronic food restriction in rats following a limitation of the duration of daily food intake to 2 h (SF) instead of 8 h (LF) on the expression of insulin and leptin system in the olfactory mucosa and bulb and on olfactory behaviors. This restriction resulted in a one-third reduction in the daily food intake and a 25% reduction in the body weight of SF rats when compared to controls, and was accompanied by lower levels of triglycerides, glucose, insulin and leptin in SF rats. Under these conditions, we observed a modulation of olfactory-mediated behaviors regarding food odors. In addition, restriction had a differential effect on the expression of insulin receptors, but not that of leptin receptors, in the olfactory mucosa, whereas no transcriptional change was observed at the upper level of the olfactory bulb. Overall, these data demonstrated that long-term changes in nutritional status modulate olfactory-mediated behaviors. Modulation of insulin system expression in the olfactory mucosa of food restricted rats suggests that this hormone could be part of this process.
Hormones and Behavior 05/2012; 62(2):120-7. · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Neuropeptide Y (NPY) plays an important role in regulating appetite and hunger in vertebrates. In the hypothalamus, NPY stimulates food intake under the control of the nutritional status. Previous studies have shown the presence of NPY and receptors in rodent olfactory system, and suggested a neuroproliferative role. Interestingly, NPY was also shown to directly modulate olfactory responses evoked by a food-related odorant in hungry axolotls. We have recently demonstrated that another nutritional cue, insulin, modulates the odorant responses of the rat olfactory mucosa (OM). Therefore, the aim of the present study was to investigate the potential effect of NPY on rat OM responses to odorants, in relation to the animal's nutritional state. We measured the potential NPY modulation of OM responses to odorant, using electro-olfactogram (EOG) recordings, in fed and fasted adult rats. NPY application significantly and transiently increased EOG amplitudes in fasted but not in fed rats. The effects of specific NPY-receptor agonists were similarly quantified, showing that NPY operated mainly through Y1 receptors. These receptors appeared as heterogeneously expressed by olfactory neurons in the OM, and western blot analysis showed that they were overexpressed in fasted rats. These data provide the first evidence that NPY modulates the initial events of odorant detection in the rat OM. Because this modulation depends on the nutritional status of the animal, and is ascribed to NPY, the most potent orexigenic peptide in the central nervous system, it evidences a strong supplementary physiological link between olfaction and nutritional processes.
PLoS ONE 01/2012; 7(9):e45266. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: All olfactory epithelium cells, including rapidly self-renewing olfactory sensory neurons (OSN), are continuously subjected to external airborne aggressions. We hypothesized that the apical part of rat olfactory epithelia (AOE) could be the site of a local translation to be able to respond rapidly to external stimuli. We purified significant amounts of mRNAs from AOE. Sequencing of the cDNA library identified 348 mRNA species. Of these, the 220 AOE transcripts encoding proteins with known biological functions were classified in functional groups. The main functional class (40%) coded for defense, detoxification, anti-oxidant stress and innate immunity. Other classes comprised mRNAs encoding functions for neuronal metabolism and life (19%), nuclear transcription control (15%), cell survival and proliferation (13%), RNA processing and translation (12%). They did not contain any known members of the olfactory transduction pathway. The expression of a sub-set of AOE transcripts was investigated in sub-cellular AOE fractions highly enriched in ciliated dendrites and in AOE fractions after forced hemilateral OSN-specific degeneration. All the mRNAs tested were found to be: i) present in enriched ciliated dendrite preparations ii) down-regulated after OSN degeneration iii) co-purified with polysomal fractions, suggesting their commitment to local translation. We provide strong evidence that the extreme apical side of the olfactory epithelium expresses a unique transcriptome, whose function is not related to olfaction but mainly to defense and survival. The possible local translation of this transcriptome is demonstrated, in supporting cells as well as in olfactory neuron ciliated dendrites.
Brain research 08/2011; 1405:1-14. · 2.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The mammalian olfactory mucosa (OM) is continually renewed throughout life. Owing to their position in the nasal cavity, OM cells are exposed to multiple insults, including high levels of odourants that can induce their death. OM regeneration is therefore essential to maintain olfactory function, and requires the tight control of both cell death and proliferation. Apoptosis has been implicated in OM cell death. Olfaction is one of the senses involved in food intake and depends on individual nutritional status. We have previously reported the influence of hormones related to nutritional status on odour perception and have shown that the OM is a target of insulin and leptin, two hormones known for their anti-apoptotic properties. In the present study, we investigated the potential anti-apoptotic effect of these metabolic hormones on OM cells. Both Odora cells (an olfactive cell line) and OM cells treated with etoposide, a p53 activity inducer, exhibited mitochondrial-dependent apoptosis that was inhibited by the pan-caspase inhibitor zVAD-fmk. Insulin, but not leptin, impaired this apoptotic effect. Insulin addition to the culture medium reduced p53 phosphorylation, caspase-3 and caspase-9 cleavage, and caspase-3 enzymatic activity induced by etoposide. The apoptotic wave observed in the OM after interruption of the neuronal connections between the OM and the olfactory bulb by bulbectomy was impaired by intranasal insulin treatment. These findings suggest that insulin may be involved in OM cellular dynamics, through endocrine and/or paracrine-autocrine effects of circulating or local insulin, respectively.
Journal of Neuroendocrinology 07/2011; 23(7):627-40. · 3.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The olfactory system is regulated by several nervous and hormonal factors, and there is a growing body of evidence that some of these modulations already take place in the olfactory mucosa (OM). We recently suggested that, among others, vasoactive peptides might play multifaceted roles in different OM cells. Here we studied the effect of the vasoconstrictive peptide endothelin (ET) in the rat OM. We identified different components of the ET system both in the olfactory mucosa and in long-term primary culture of OM cells, composed of olfactory sensory neurons (OSNs) lying on a blend of non-neuronal OM cells (nNCs). We demonstrated that ET receptors are differentially expressed on OM cells, and that ET might be locally matured by the endothelin-converting enzyme ECE-1 located in OSNs. Using calcium imaging, we showed that ET triggers robust dose-dependent Ca2+ responses in most OM cells, which consist of a transient phase, followed, in nNCs, by a sustained plateau phase. All transient responses depended on intracellular calcium release, while the sustained plateau phase also depended on subsequent external calcium entry. Using both pharmacology and spotting lethal (sl/sl) mutant rats, lacking functional ETB receptors, we finally demonstrated that these effects of ET are mediated through ETB receptors in OSNs and ETA receptors in nNCs.The present study therefore identifies endothelin as a potent endogenous modulator of the olfactory mucosa; specific endothelin-mediated Ca2+ signals may serve distinct signaling functions, and thereby suggest differential functional roles of endothelin in both neuronal and non-neuronal OM cells.
[Show abstract][Hide abstract] ABSTRACT: Although odorant-binding proteins (OBP) are one of the most abundant classes of proteins in the mammalian olfactory mucus, they have only recently been ascribed a functional role in the detection of odorants by olfactory neurons. Among the three OBPs described in the rat, OBP-1f is mainly secreted by the lateral nasal glands (LNG) and Bowman's glands, and its expression is transcriptionally regulated by food deprivation in the olfactory mucosa, but not in LNG. Therefore, mucus composition might be locally regulated by hormones or molecules relevant to nutritional status. Our aim has been to investigate the mechanisms of such physiological regulation at the cellular level, through both the examination of OBP-1f synthesis sites in the olfactory mucosa and their putative regulation by leptin, a locally acting satiety hormone. Immunohistochemical observations have allowed the identification of a novel population of OBP-1f-secreting cells displaying morphological and functional characteristics similar to those of epithelial mucous cells. Ultrastructural analyses by both transmission and scanning electron microscopy has enabled a more complete cytoarchitectural characterization of these specialized olfactory mucous cells in their tissue environment. These globular cells are localized in discrete zones of the olfactory epithelium, mainly in the fourth turbinate, and are often scattered from the basal to the apical surface of the epithelium. They contain numerous small droplets of mucosubstances. Using an in-vitro-derived model of olfactory mucosa primary culture, we have been able to demonstrate that leptin increases the production of mucus by these cells, so that they constitute potential targets for the physiological modulation of mucus composition by nutritional cues.
Cell and Tissue Research 09/2009; 338(1):53-66. · 3.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Food odours are major determinants for food choice, and their detection depends on nutritional status. The effects of different odour stimuli on both behavioural responses (locomotor activity and sniffing) and Fos induction in olfactory bulbs (OB) were studied in satiated or 48-h fasted rats. We focused on two odour stimuli: isoamyl acetate (ISO), as a neutral stimulus either unknown or familiar, and food pellet odour, that were presented to quiet rats during the light phase of the day. We found significant effects of nutritional status and odour stimulus on both behavioural and OB responses. The locomotor activity induced by odour stimuli was always more marked in fasted than in satiated rats, and food odour induced increased sniffing activity only in fasted rats. Fos expression was quantified in periglomerular, mitral and granular OB cell layers. As a new odour, ISO induced a significant increase in Fos expression in all OB layers, similar in fasted and satiated rats. Significant OB responses to familiar odours were only observed in fasted rats. Among the numerous peptides shown to vary after 48 h of fasting, we focused on orexins (for which immunoreactive fibres are present in the OB) and leptin, as a peripheral hormone linked to adiposity, and tested their effects of food odour. The administration of orexin A in satiated animals partially mimicked fasting, since food odour increased OB Fos responses, but did not induce sniffing. The treatment of fasted animals with either an orexin receptors antagonist (ACT-078573) or leptin significantly decreased both locomotor activity, time spent sniffing food odour and OB Fos induction in all cell layers, thus mimicking a satiated status. We conclude that orexins and leptin are some of the factors that can modify behavioural and OB Fos responses to a familiar food odour.
[Show abstract][Hide abstract] ABSTRACT: Food odours are major determinants for food choice; their detection is influenced by nutritional status. Among different metabolic signals, insulin plays a major role in food intake regulation. The aim of the present study was to investigate a potential role of insulin in the olfactory mucosa (OM), using ex vivo tissues and in vitro primary cultures. We first established the expression of insulin receptor (IR) in rat olfactory mucosa. Transcripts of IR-A and IR-B isoforms, as well as IRS-1 and IRS-2, were detected in OM extracts. Using immunocytochemistry, IR protein was located in olfactory receptor neurones, sustentacular and basal cells and in endothelium of the lamina propria vessels. Moreover, the insulin binding capacity of OM was quite high compared to that of olfactory bulb or liver. Besides the main pancreatic insulin source, we demonstrated insulin synthesis at a low level in the OM. Interestingly 48 h of fasting, leading to a decreased plasmatic insulin, increased the number of IR in the OM. Local insulin concentration was also enhanced. These data suggest a control of OM insulin system by nutritional status. Finally, an application of insulin on OM, aiming to mimic postprandial insulin increase, reversibly decreased the amplitude of electro-olfactogramme responses to odorants by approximately 30%. These data provide the first evidence that insulin modulates the most peripheral step of odour detection at the olfactory mucosa level.
Journal of Neuroendocrinology 09/2008; 20(10):1176-90. · 3.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The molecular mechanisms underlying odorant detection have been investigated using the chip based SPR technique by focusing on the dynamic interactions between transmembrane Olfactory Receptor OR1740, odorant ligands and soluble Odorant-Binding Protein (OBP-1F). The OR1740 present in the lipid bilayer of nanosomes derived from transformed yeasts specifically bound OBP-1F. The receptor preferential odorant ligand helional released bound OBP-1F from the OR-OBP complex, while unrelated odorants failed to do so. OBP-1F modified the functional OR1740 dose-response to helional, from a bell-shaped to a saturation curve, thus preserving OR activity at high ligand concentration. This unravels an active role for OBPs in olfaction, in addition to passive transport or a scavenger role. This sensorchip technology was applied to assessing native OBP-1F in a biological sample: rat olfactory mucus also displayed significant binding to OR1740 nanosomes, and the addition of helional yielded the dissociation of mucus OBP from the receptor.
Lab on a Chip 06/2008; 8(5):678-88. · 5.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Neuroanatomical data show that olfactory mucosa (OM) is a possible place for interactions between nutrition and smell. A combination of differential display mRNA analysis together with a macroarray screening was developed to identify transcripts that are differentially expressed in rat OM following food deprivation. Using this method, backed on a stringent statistical analysis, we identified molecules that fell into several Gene Ontology terms including cellular and physiological process, signal transduction, and binding. Among the 15 most differentially expressed molecules, only one was upregulated, but 14 were downregulated in the fasted state among which was, unexpectedly, odorant-binding protein 1F (OBP-1F). Because of its potential relevance to olfactory physiology, we focused our further analysis on OBP-1F using in situ hybridization, quantitative polymerase chain reaction, and western blot analysis. OBP-1F was highlighted in the lateral nasal glands, but its expression (mRNA and protein) did not change following food deprivation. Only the minor fraction of OBP-1F mRNA expressed by the OM itself was downregulated following 48 h fasting. Altogether, our results suggest that the fine transcriptional control of OBP-1F in the OM following food deprivation could be efficient only at the local level, close to its site of secretion to participate in the perireceptor events of the olfactory signal reception.
Chemical Senses 10/2007; 32(7):697-710. · 3.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Orexins A and B (OxA and OxB) are multifunctional neuropeptides implicated in the regulation of energy metabolism, wakefulness but also in a broad range of motivated behaviours. They signal through two G-protein-coupled receptors: orexin receptor 1 and 2 (Ox1R and Ox2R). The orexins and their receptors are present at all levels of the rat olfactory system: epithelium, bulb, piriform cortex but their signalling mechanisms remain unknown. We have studied orexins signal transduction pathways in the rat olfactory mucosa (OM) and in the Odora cell line derived from olfactory sensory neurons and heterologously expressing Ox1R or Ox2R. We have demonstrated by western blot and RT-PCR that multiple components of adenylyl cyclase (AC) and phospholipase C (PLC) signalling pathways were identical in OM and Odora cells. OxA and OxB induced a weak increase in IP3 in OM; they induced a significant rise in cAMP and IP3 in Odora transfected cells, suggesting the activation of AC and PLC pathways. Both OxA and OxB induced intracellular calcium elevation and transient activation of MAP kinases (ERK42/44) in Odora/Ox1R and Odora/Ox2R cells. These results suggest the existence of multiple orexins signalling pathways in Odora cells and probably in OM, corresponding to different possible roles of these peptides.
[Show abstract][Hide abstract] ABSTRACT: Leptin is an adipocyte-derived cytokine that regulates body weight mainly via the long form of the leptin receptor (Ob-Rb). Leptin and its receptors are expressed in several tissues, suggesting that leptin might also be effective peripherally. We hypothesized that, as shown in taste cells, leptin and its receptors isoforms (Ob-Rs) could be present in the rat olfactory mucosa (OM). Using RT-PCR, light and electron microscopy immunohistochemistry (ICC), we found that different isoforms of the receptor were expressed in OM and localized in sustentacular cells and in a subpopulation of maturating neurons; in addition, immunoreactivity was also present in differentiated neurons and enriched at the cilia membranes, where the odorants bind to their receptors. Moreover, using RT-PCR, ICC and RIA measurements, we showed that leptin is synthesized locally in the olfactory mucosa. In addition, we demonstrate that fasting causes a significant enhanced transcription of both leptin and Ob-Rs in rat OM by quantitative RT-PCR data. Altogether, these results strongly suggested that leptin, acting as an endocrine or a paracrine factor, could be an important regulator of olfactory function, as a neuromodulator of the olfactory message in cilia of mature olfactory receptors neurons (ORN), but also for the homeostasis of this complex tissue, acting on differentiating neurons and on sustentacular cells.
Brain Research 02/2007; 1129(1):130-41. · 2.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Orexin A and B are involved in feeding behaviors, and recently fibers containing these peptides were found in the rat olfactory bulb. These fibers, which originate from the lateral and posterior hypothalamus and the perifornical area, are distributed in the glomerular, mitral cell, and granule cell layers. Orexin receptors are mainly expressed by mitral cells. In the present study, RT-PCR experiments were done to determine orexin receptor expression during the early postnatal life of rats, and immunocytochemical experiments were performed to further clarify the structural and ultrastructural localization of orexin receptors in the olfactory bulb. Furthermore, a functional electrophysiological approach examined the action of orexin A on mitral cell excitability and spontaneous activity using in vitro patch-clamp techniques. RT-PCR results show that mRNA of the two type receptors, type 1 orexin receptors and type 2 orexin receptors, are expressed in the olfactory bulb of rat from 10 d to the adult stage. At the same ages, immunocytochemical data show that orexin 1 receptors are localized in the cell bodies of periglomerular, mitral/tufted, and granule cells. Immunoreactivity was also demonstrated in mitral/tufted cell dendrites arborizing in the glomerulus and mitral/tufted and granule cell processes running in the external plexiform layer. Functionally, orexin A produced either a direct, tetrodotoxin-insensitive depolarization in one group of mitral cells (7%), or, in another group (30%), an indirect, tetrodotoxin-sensitive hyperpolarization. Both actions were mediated by type 1 orexin receptors because the response was antagonized by SB-334867-A, a selective antagonist. Mitral cell recordings performed under bicuculline [gamma-aminobutyric acid (GABA)A receptor antagonist], indicate that the orexin-induced indirect hyperpolarization was partly mediated through GABA(A) receptors. Because granule cells and periglomerular cells express orexin receptors and are GABAergic cells, they could be both involved in this hyperpolarization. Other mechanisms, which could support an indirect hyperpolarization of mitral cells through dopamine interneuron solicitation, are proposed. Our results provide data that should allow us to better understand neural communication and regulation mechanisms between the hypothalamic feeding centers and the olfactory bulb.
[Show abstract][Hide abstract] ABSTRACT: The olfactory epithelium (OE) is composed of olfactory sensory neurons (OSNs) and sustentacular cells; it lies in the nasal cavity where it is protected by a thin mucus layer. The finely regulated composition of this mucus provides OSN with a suitable ionic environment. To maintain the functional integrity of the epithelium despite permanent physical, chemical and microbial aggressions, both OSNs and surrounding sustentacular cells are continuously renewed from globose basal cells. Moreover, the sense of smell is involved in so numerous behaviours (feeding, reproduction, etc.) that it has to cross-talk with the endocrine and neuroendocrine systems. Thus, besides its sensory function, the olfactory epithelium is thought to undergo a lot of complex regulatory processes. We therefore studied the effects of various neuropeptides on primary cultures of Sprague-Dawley rat olfactory epithelium cells. We found that arginine-vasopressin (AVP) triggered a robust, dose-dependent calcium increase in these cells. The cell response was essentially ascribed to the V1a AVP receptor, whose presence was confirmed by RT-PCR and immunolabelling. In the culture, V1a but not V1b receptors were present, mainly localized in neurons. In the epithelium, both subtypes were found differentially distributed. V1a-R were localized mainly in globose basal cells and at the apical side of the epithelium, in the area of the dendritic knobs of OSNs. V1b-R were strongly associated with Bowman's gland cells and globose basal cells. These localizations suggested potential multifaceted roles of a hormone, AVP, in the olfactory epithelium.
European Journal of Neuroscience 09/2004; 20(3):658-70. · 3.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Orexin-A and -B, also known as hypocretins, are two neuropeptides acting on feeding and sleep. They are specific ligands for two different receptors belonging to the G-protein coupled receptors family. Orexin fibers and orexin receptor neurons have been previously described in the forebrain olfactory system. Using immunocytochemistry, we showed that both orexin-A and -B as well as their receptors were present at different levels of the olfactory system, from the nasal mucosa to nuclei of the amygdala. A punctuated staining for orexins and their receptors was detected at the apical part of the olfactory epithelium; in the lamina propria of the mucosa, the staining was localized around olfactory nerves. At the ultrastructural level, olfactory neurons and supporting cells were found immunoreactive for orexins and their receptors. The labeling was localized in dendritic knobs and cilia of neurons, in the apical part and microvilli of supporting cells. The finding of immunolabeled cisternae of reticulum strongly suggests a local synthesis of both peptides and receptors, confirmed by RT-PCR experiments. In forebrain and amygdala regions, we detected numerous orexin fibers. Orexin receptors were present in mitral-tufted cells of the bulb and in many neuronal perikarya in the anterior olfactory nuclei, piriform cortex and amygdala nuclei. Altogether, these results show that orexins and their receptors are present at all levels of the olfactory system, from cilia where odors bind to their receptors to central regions where integration of olfactory signals occurs. They suggest a possible modulation of olfactory perception by these neuropeptides.
Brain Research 02/2003; 960(1-2):48-61. · 2.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nitric oxide (NO) is involved in the transmission of light information to suprachiasmatic nuclei (SCN). By immunocytochemistry, we showed that both neuronal and endothelial NO synthase isoforms (nNOS and eNOS) were present in the SCN of rats and hamsters. nNOS-immunoreactive neurons were located mainly around the SCN with only a few nNOS neurons within the nucleus. By double-label immunocytochemistry, we also found, within the population of SCN glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes, a subpopulation of eNOS-immunoreactive astrocytes. Using Western blot analysis, we detected in SCN protein extracts eNOS and nNOS proteins having the expected 140 and 150 kDa molecular weights, respectively. By in situ hybridization of a 2.4-kb murine eNOS probe, mRNA for eNOS was located in the SCN of rats and hamsters. The transcript was further identified by detection of a RT-PCR product of the predicted size, after amplification of total RNA with primers specific for eNOS. In the SCN and cerebellum, the size of the mRNA for nNOS, detected with a rat probe on Northern blot, was approximately 10.5 kb, corresponding to that previously published. In the same tissues, we found two transcripts, one weakly expressed at approximately 4.0 kb and another more strongly expressed at approximately 2.6 kb, both hybridizing with two non-overlapping murine and rat eNOS probes. These results suggested the existence in the SCN of alternate transcripts for eNOS. We propose that two pathways could link light stimuli and NO release in the SCN: one involving N-methyl-D-aspartate (NMDA) receptors and nNOS in neurons; the other linking alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and eNOS in astrocytes.
European Journal of Neuroscience 03/2000; 12(2):649-61. · 3.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To investigate the action of melatonin on the reproductive system, the effect of prolonged versus short-term exposure to melatonin on the release of gonadotrophin releasing hormone (GnRH) was examined in hypothalamic explants of male mink sacrificed in July, September or November. Mediobasal hypothalamic (MBH) explants including the pars tuberalis (PT) were incubated for 1 night with or without melatonin (10(-8) M) for 8 hr or 16 hr and the release of GnRH was then measured. The next day, the explants were incubated further but in a melatonin free buffer, and the release of GnRH was measured with increasing time. Half of the July and September explants had melatonin binding sites quantified by autoradiography. In November, a 16-hr exposure to melatonin induced a significant increase in the release of GnRH during the night, compared with control or 8-hr melatonin exposure. This increase persisted for at least 45 min after the withdrawal of melatonin, suggesting a stimulatory effect of melatonin on the synthesis of GnRH; this effect was apparent in July, September and November. In September, the density of melatonin binding in the PT was significantly lower in the explants incubated for 16 hr with melatonin, compared with those incubated for 8 hr. Thus, in vitro, a long exposure to melatonin, mimicking a single long night, stimulates the release and synthesis of GnRH in parallel with a decrease in the density of melatonin binding in the PT. These effects seem to depend heavily on the duration of exposure to melatonin.
Journal of Pineal Research 02/1999; 26(1):17-27. · 7.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Prolonged exposure of adult Syrian hamsters to short days decreases LH and FSH circulating levels within 2-4 weeks, then induces testicular regression. After 18 weeks of short days, the testis size and gonadotropin levels increase spontaneously. This study investigated whether these phases of photosensitivity and photorefractoriness corresponded to variations of in vitro GnRH release. Male hamsters were either kept under long days (LD 16:8) or transferred to short days (SD 6:18) and sacrificed from 2-26 weeks after transfer. To separate the effects of testis feedback from a possible direct photoperiodic drive on the hypothalamus, males were bilaterally castrated, kept under LD or transferred to SD, and sacrificed from 2-14 weeks after transfer. Hypothalamic explants were incubated in a saline buffer for three periods of 15 min and exposed to KCl (60 mM) for 15 min. The return to basal values was followed for six periods of 15 min, then the explants were stimulated with copper complexed equimolarly with histidine (Cu/His, 200 microM) and prostaglandin E2 (PGE2, 10 microM). At the end of the incubation period, the concentration of GnRH remaining in the explants was measured. In intact males, GnRH release in vitro increased significantly between 2 and 4 weeks after transfer to short days; it returned to values similar to LD ones between 6 and 12 weeks, during the phase of testis involution. At the beginning of photorefractoriness (SD 14-18), it increased transiently and returned to values similar to LD ones from SD 20, during the testis spontaneous recrudescence. After castration, the in vitro GnRH release decreased significantly under LD and SD. The transfer of castrated hamsters to SD resulted in transient increases of GnRH release (SD 4, 8 and 14), and in a progressive loss of the explant's ability to release GnRH in vitro. These results showed a photoperiodic regulation of in vitro GnRH release and a testis feedback effect on this release. They demonstrated an inverse relationship between the readily releasable pool of GnRH and the circulating levels of gonadotrophins at the beginning of photosensitive and photorefractory phases and after castration.
Journal of Neuroendocrinology 06/1998; 10(5):343-51. · 3.33 Impact Factor