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Carapace and plastron sensitivity to touch and vibration n the tortoise (Testudo hemanni and T graeca)
Journal of Zoology
Abstract
Neural impulses in response to tactile stimulation of the shell were recorded from afferent nerve fibres in tortoises (T. graeca and T. hermanni). It was found that there is a mechanoreceptive innervation in the superficial layers of the shell which is sensitive to transient stimuli, particularly to vibration at frequencies up to 100 Hz. Receptive fields pertaining to single and small groups of individual afferent fibres were mapped: the fields were sharply circumscribed and distributed in relation to the scutes of the shell. The tactile innervation that was found would be consistent with a capacity for recognition and accurate localization of innocuous stimuli and may play a central role in courtship and mating behaviour.
A complete bibliography of the research publications that Devin and I used in writing our book, " Tortoises of the World. Giants to Dwarfs." To be published in April 2024 by Johns Hopkins University Press.
Shell fractures are one of the most traumatic and recurrent injuries observed in chelonians during clinical practice. The most common causes of fractures are falling, being run over by automobiles, being burned, and wild animal bites. Epoxy, acrylic resin, polyester, fiber-grass blanket, and screw fixation are among the current techniques used to treat fractures. Regarding the difficulty of fracture repair in the carapace, this case report aimed to report a procedure that is effective, less time-consuming, accessible, affordable, and safe for shell fractures in C. carbonarius. During the physical examination, the animal showed two fractures, in the dorsal region of the carapace and right lateral side of the bridge, with subcutaneous tissue exposure and loss of a small piece of dorsocranial carapace. To treat these injuries, the animal was submitted to a resin application. The procedure consists of using ethyl-cyanoacrylate associated with sodium bicarbonate, which produces a more resistant resin that is bactericidal, non-toxic, and easy to apply in a low surgery time compared to the common methods used to fix shell fractures. The resin application was successfully done, and the animal was under care for a month after the fracture reduction. It was observed that the treatment was effective, presenting reduction of the fracture. A month after the procedure, the animal showed no intercurrence. Three years after the procedure, the animal still presents part of the material still fixed to the shell, normal growth, without interference in locomotor capacity. This resin proved to be an innovative and promising alternative way to treat fractures, suggesting the development of new non-invasive approaches for several tissues and different animal species.
Changes in the structural association of skeletal traits are crucial to the evolution of novel forms and functions. In vertebrates, such rearrangements often occur gradually and may precede or coincide with the functional activation of skeletal traits. To illustrate this process, we examined the ontogeny of African hinge-back tortoises (Kinixys spp.). Kinixys species feature a moveable "hinge" on the dorsal shell (carapace) that enables shell closure (kinesis) when the hind limbs are withdrawn. This hinge, however, is absent in juveniles. Herein, we describe how this unusual phenotype arises via alterations in the tissue configuration and shape of the carapace. The ontogenetic repatterning of osseous and keratinous tissue coincided with shifts in morphological integration and the establishment of anterior (static) and posterior (kinetic) carapacial modules. Based on ex vivo skeletal movement and raw anatomy, we propose that Kinixys employs a "sliding hinge" shell-closing system that overcomes thoracic rigidity and enhances the protective capacity of the carapace. Universal properties of the vertebrate skeleton, such as plasticity, modularity, and secondary maturation processes, contributed to adaptive evolutionary change in Kinixys. We discuss a hypothetical model to explain the delayed emergence of skeletal traits and its relevance to the origins of novel form-to-function relationships.
Anesthesia and analgesia in ectotherms is a rapidly developing field, though much of the currently available information is anecdotal. A common excuse for not using analgesia in reptiles, amphibians, and fish is that these species do not have the neuroanatomic pathways sufficient for pain perception. Reptiles, amphibians and fish have the neuroanatomy necessary to perceive pain. Additionally, they possess descending modulatory pathways and express behavioral changes that would be indicative of pain in mammals. It is, therefore, logical to conclude that these species experience pain and should be provided analgesia when appropriate. Treatment of pain in reptiles, amphibians, and fish should be specific for the animal in question, and care should be taken when trying to extrapolate drug efficacy or dose.
This chapter is an overview of analgesia across vertebrates and invertebrates. It discusses a physiology of pain that can be classified anatomically as somatic or visceral pain, or temporally as acute or chronic. The chapter discusses pain management in vertebrate species, and lists commonly used analgesics in nonmammalian vertebrates and mammals. Blockade or attenuation of ascending nociceptive pathways or activation of descending antinociceptive pathways by different classes of the analgesic drugs usually provides better analgesia with fewer side effects than unimodal therapy with a single class of analgesic drugs. The chapter also discusses recognition of pain in fish, reptiles, amphibians and bird species.
Turtle shells are a form of armor that provides varying degrees of protection against predation. Although this function of the shell as armor is widely appreciated, the mechanical limits of protection and the modes of failure when subjected to breaking stresses have not been well explored. We studied the mechanical properties of whole shells and of isolated bony tissues and sutures in four species of turtles (Trachemys scripta, Malaclemys terrapin, Chrysemys picta, and Terrapene carolina) using a combination of structural and mechanical tests. Structural properties were evaluated by subjecting whole shells to compressive and point loads in order to quantify maximum load, work to failure, and relative shell deformations. The mechanical properties of bone and sutures from the plastral region of the shell were evaluated using three-point bending experiments. Analysis of whole shell structural properties suggests that small shells undergo relatively greater deformations before failure than do large shells and similar amounts of energy are required to induce failure under both point and compressive loads. Location of failures occurred far more often at sulci than at sutures (representing the margins of the epidermal scutes and the underlying bones, respectively), suggesting that the small grooves in the bone created by the sulci introduce zones of weakness in the shell. Values for bending strength, ultimate bending strain, Young's modulus, and energy absorption, calculated from the three-point bending data, indicate that sutures are relatively weaker than the surrounding bone, but are able to absorb similar amounts of energy due to higher ultimate strain values. J. Exp. Zool. 9999A:1-13, 2012. © 2012 Wiley Periodicals, Inc.
The transient suppression of motor activity in the spinal cord after a cutaneous stimulus is termed the cutaneous silent period (CSP). It is not known if CSP is due to suppression of the premotor network or direct inhibition of motoneurons. This issue was examined by intracellular recordings from motoneurons in the isolated carapace-spinal cord preparation from adult turtles during rhythmic scratch-like reflex. Electrical stimulation of cutaneous nerves induced CSP-like suppression of motor nerve firing during rhythmic network activity. The stimulus that generated the CSP-like suppression of motor activity evokes a polysynaptic compound synaptic potential in motoneurons and suppressed their firing. This compound synaptic potential was hyperpolarizing near threshold for action potentials and was associated with a substantial increase in conductance during the CSP in the motor pool. These results show that direct postsynaptic inhibition of motoneurons contributes to the CSP.
A three‐year study on reproduction in wild populations of Testudo hermanni has shown that:
( a ) sexual activity occurs between March and October, except the nesting season (May and June), and is most frequent in August and September,
( b ) tortoises are promiscuous in their mating habits, there is no evidence of mate selection in relation to size,
( c ) nest site selection is correlated to ground temperature and nesting itself mainly occurs in the early evening before dark, when the ground temperature characteristics are most indicative of a specific site's relative temperature,
( d ) incubation takes about three months and is probably temperature dependent,
( e ) most nests are preyed upon by mammalian predators within a few days after laying (> 90% being destroyed), the main cue being the smell of the eggs,
( f ) average clutch size in Greece is higher than in France, while mean egg weight in France is higher than in Greece, and there is no strong relationship between body size or weight and egg or clutch weight in either country,
( g ) in contrast to other studies, there is no apparent correlation between rainfall and reproduction parameters,
( h ) some females nest in successive years, and more than once in a year, with a laying interval of 10–20 days,
( i ) mean size of sexually active individuals is not significantly different from the mean size of adults, although nesting females are significantly bigger; the minimum size for sexually active males is about 120 mm and for females 130 mm.
The discussion examines these observations in an evolutionary context.
1.1. Percussion or electrical stimulation of the carapace in T graeca elicited responses at the ipsilateral cord dorsum. The segmental levels of inflow were identified by mapping and dorsal rhizotomy.2.2. The waveform properties of the cord dorsum potentials resembled those associated with cutaneous stimulation.3.3. The effects of local stimulation and local anaesthesia indicate that a proportion of nerve endings in the carapace are present in the superficial layers of the thecal bone.4.4. Conduction velocity of afferents from the carapace was 14.5 m/sec (mean) at 23–25°C in the ipsilateral dorsal tract and therefore in the upper range for the population of tract fibres.
1.
A scratch reflex is displayed by a low spinal turtle in response to gentle mechanical stimulation delivered to specific regions of the shell anterior to a hindlimb (Valk-Fai and Crowe, 1978, 1979). The behavior consists of a rhythmic limb movement in which the foot protracts and rubs against the stimulated patch of shell once per cycle. A brief stimulus can elicit a response composed of a small number of cycles or even a fraction of a cycle (Fig. 1); maintained rubbing of the shell can elicit a response consisting of 5–20 cycles (Fig. 2A).
2.
The scratch motor program is divisible into an A phase in which IT-KE is active and a B phase in which IT-KE is quiescent and HR-KF is active (Fig. 2B). The A phase is further divisible into an A1 phase in which IT-KE is the only active KE muscle and into an A2 phase in which all three KE muscles are active.
3.
Two variations of the scratch program exist (Figs. 3 and 4). These variations indicate that there are flexibilities in the organization of the spinal generator for turtle scratch reflex.
4.
The scratch motor program can also be expressed in a preparation immobilized by a neuromuscular blocking agent (Figs. 5 and 6). The responses in this preparation are termed the fictive scratch reflex since they occur in the absence of a real movement. One of the variations in the scratch program which was seen in preparations with a moving limb was also seen in the fictive scratch reflex (Fig. 7).
5.
The scratch motor program can also be expressed in preparations with the hindlimb enlargement deafferented via bilateral dorsal rhizotomies (Figs. 8 and 9).
6.
These observations establish that the turtle scratch reflex is centrally programmed, i.e., it is not dependent upon phasic timing cues derived from sensory feedback. Even though the reflex is centrally programmed, it is still possible to demonstrate that sensory feedback from a moving limb can modulate the scratch rhythm (Fig. 10 of this paper and Fig. 6 of Valk-Fai and Crowe, 1979).
1.
Studies upon reflex movements of the rear legs of terrapins were made on spinal preparations and chronic preparations in which the spine was transected at the D3-D4 levels.
2.
Light mechanical stimuli applied to the junctional regions between the carapace and plastron produce leg movements which bring up the foot to try and push away the cause of the stimulation.
3.
A mechanism exists in the spinal cord which enables accurate and repeatable movements to take place irrespective of the resting position of the limb prior to stimulation and the position of the stimulation.
4.
If one particular stimulation position is used for a series of stimulus-response studies, and the final resting position after one response is used as the begin position for the next one, a particular closed pathway of movement is followed by the ankle. The shape and extent of this pathway depend upon the choice of stimulation position.
5.
If the initial resting position of the ankle does not lie on such a pathway, the response consists first of all of a movement which brings it onto the pathway followed by a movement along the pathway to the target.
6.
Sometimes a response to a single stimulus consists of a series of movements around the pathway to and from the target.
7.
EMG's show bursts of activity during a movement cycle. The duration of sartorius activity depends upon the particular pathway. Semi-membranosus activity does not noticeably vary in duration.
The functional distribution of dorsal horn structures in the lumbo-sacral spinal cord of the tortoise (T. graeca, T. hermanni) was determined by surface mapping of the cord dorsum potential in the decerebrate animal. Electrical stimuli were applied to either skin, peripheral nerve, dorsal roots or dorsal tracts. It was shown that the cord dorsum potential in this reptile could be interpreted in the same way as that in the mammal; this permitted identification of the primary volley separately from the consequent activity of post-synaptic structures within the dorsal horn. The longitudinal distribution of post-synaptic activity suggested that the associated structures are not distributed uniformly along the cord but rather have concentration maxima within segments in regions just rostral to the root entry zones. Combined transverse and longitudinal mapping revealed streaming of postsynaptic activity, traced over two or three segments, towards the mid line, when proceeding rostrally from a given root entry zone. The fact that this occurred for successive roots suggests that somatotopic representation exists in the transverse plane within the dorsal horn.
The longitudinal distribution of post-synaptic activity suggested that the associated structures are not distributed uniformly along the cord but rather have concentration maxima within segments in regions just rostral to the root entry zones.
Combined transverse and longitudinal mapping revealed streaming of post-synaptic activity, traced over two or three segments, towards the mid line, when proceeding rostrally from a given root entry zone. The fact that this occurred for successive roots suggests that somatotopic representation exists in the transverse plane within the dorsal horn.
1. Intracellularly recorded responses of lumbosacral motoneurones in the tortoise are described. The preparation was decerebrate and unanaesthetized. Cells were tested by stimulation of the main branches of the ipsilateral sciatic nerve.
2. The distribution of cells according to resting membrane potential is given; highest recorded values were around 70 mV.
3. The action potential has a step on the rising phase and has a total duration in the region of 4 msec.
4. The motoneurone input resistance, measured by the spike height method, was 5‐8 MΩ.
5. Orthodromic excitation of motoneurones occurred after a central latency of 2 msec.
6. Inhibition, and inhibitory (hyperpolarizing) potentials were demonstrated. Peak amplitude of maximum response was frequently greater than 10 mV. The potentials were influenced by injected currents in a manner resembling IPSPs in mammalian motoneurones. Minimum central latency for inhibitory potentials was about 3 msec.
7. Membrane potentials and dimensions of action potentials for motoneurones in the cat are given for purposes of comparison with the tortoise.
1. The myelinated fibre spectrum of the plantar nerve of reptile consists of a unimodal distribution corresponding approximately to the delta elevation in mammalian nerve and contains a variety of receptor categories similar to those of mammals except for the obvious absence of structures related to hairs.
2. The various receptor types of reptilian skin do not fall into discrete groups on the basis of conduction velocity.
3. Only a few thermoreceptor fibres were identified but a large proportion of slowly adapting mechanoreceptors responded to rapid temperature transients.
4. Two distinct categories of slowly adapting receptors whose discharge is related to the amplitude of skin displacement have been identified and studied in detail. These two receptors can be distinguished by their patterns of discharge, and display several distinctive features including differences in resting discharge, receptive field size, threshold, response to DC polarization, etc.
5. The mathematical functions describing the response to stimuli of varying magnitude for one receptor type is markedly affected by the sequence of stimulus presentation.
Vibration‐sensitive receptors in the tortoise's shell
- Rosenberg M. E.
The anatomy of the tortoise
- Thomson J. S.