Nerve In Hamsters Research Articles

Differential Toxicities of Intraneurally Injected Mercuric Chloride for Sympathetic and Somatic Motor Fibers: An Ultrastructural Study

Mercury is a well-known neurotoxin but the susceptibility of autonomic nerves to mercury poisoning in vivo has seldom been studied. Our previous studies have shown that the hypoglossal nerve in hamsters contains somatic motor and postganglionic sympathetic fibers. The aim of this study was to investigate the ultrastructural changes in the nervous system following intraneural injection of mercuric chloride into the hypoglossal nerve in hamsters. Six adult hamsters were used in this study. After anesthesia, the digastric muscle on the right side was removed and the trunk of the hypoglossal nerve was exposed. Two microliters of mercuric chloride aqueous solution was injected into the main trunk of the hypoglossal nerve at the bifurcation. The contralateral hypoglossal nerve was kept intact and used as the normal control. Animals were allowed to survive for 1 or 3 days and were prepared for ammonium sulfide histochemistry and electron microscopy. Three days after injection of mercuric chloride solution, almost all unmyelinated sympathetic fibers in the hypoglossal nerve trunk were lost, whereas myelinated somatic axons were spared. Although mercury deposition in the myelin sheaths of neuronal processes was observed in the hypoglossal nucleus, the neuronal somas were intact. By contrast, degenerated neuronal processes and mercury deposition in neuronal somas were frequently found in the superior cervical ganglia. This study demonstrated an undue susceptibility of sympathetic fibers to mercury intoxication. The mechanisms that underlie the selective reaction of sympathetic fibers to mercury warrant further investigation.

Synergistic effect of optic and peripheral nerve grafts on sprouting of axon-like processes of axotomized retinal ganglion cells in adult hamsters

We investigated the sprouting response of retinal ganglion cells (RGCs) following the transplantation of peripheral nerve (PN) and/or optic nerve (ON) into the vitreous of the eye and the intraorbital transection of the optic nerve in hamsters. Our previous results showed that an intravitreal PN graft could induce sprouting of axon-like processes in axotomized RGCS [3] (Cho, E.Y. and So, K.F., Characterization of the sprouting response of axon-like processes from retinal ganglion cells after axotomy in adult hamsters: a model using intravitreal implantation of a peripheral nerve, J. Neurocytol., 21 (1992) 589–603). In this model, we have examined the effect of intravitreal ON graft on the sprouting of RGCs both following a co-transplantation of PN and ON into the vitreous and transplantation of ON alone. The present results show that sprouting is increased by more than two-fold in retinas having PN and ON grafts than a PN graft alone. However, the ON graft by itself rarely induced sprouting in RGCs. These results suggest that the ON graft enhance the number of RGCs to sprout axon-like processes in the presence of PN graft by exerting a synergistic rather than an additive effect, since ON graft alone did not induce sprouting. In addition, no diffusible inhibitory effect of ON graft on PN induced sprouting was observed.

Recovery from Facial Paralysis Following Crush Injury of the Facial Nerve in Hamsters: Differential Effects of Gender and Androgen Exposure

In recent studies, we have shown that administration of androgens to male hamsters enhances functional recovery from facial paralysis induced by facial nerve crush at the level of the stylomastoid foramen. Furthermore, we have established that the mechanism behind this enhancement of regeneration involves an acceleration of the rate of regeneration, without a shortening in the delay of sprout formation. From those studies, several unexpected findings of inherent sex differences emerged. First, intact (nongonadectomized) females have a faster facial nerve regeneration rate than males and, second, testosterone has a less dramatic effect on the rate of regeneration in females compared to males. In the present study, we explored these novel findings of sex differences in the response of motor neurons to injury. Adult intact female hamsters were subjected to right facial nerve crush axotomy at the level of stylomastoid foramen and either implanted with two or four silastic capsules containing 5α-dihydrotestosterone, or sham-implanted for controls. A group of adult intact male hamsters was also subjected to right facial nerve crush axotomy. Animals were observed daily, beginning on Day 1 postoperatively and continuing throughout a 3-week recovery period for signs of functional recovery from facial paralysis. The average day of return of each of four behavioral components (semi-blink, blink reflex, full vibrissae movement, and complete recovery) was calculated for all four experimental groups. The results indicate that intact females recover functional return of movement following crush injury significantly faster than intact males. In contrast to our previous findings in male hamsters, administration of exogenous steroids does not accelerate recovery from facial paralysis in adult female hamsters. Why these sex differences in both inherent recovery from peripheral nerve injury and in the ability of androgens to augment regeneration occur is unknown, but will be interesting to explore from a molecular perspective in future studies.

Degenerative changes of neurons in the superior cervical ganglion following an injection of Ricinus communis agglutinin-60 into the vagus nerve in hamsters

The present study describes neuronal changes in the superior cervical ganglion of hamsters following injection of Ricinus communis agglutinin-60 (RCA-60) into the ipsilateral vagus nerve in the cervical region. There were no noticeable structural changes in the ganglion 1 day after injection. Between 3 and 15 days after injection, a small number of neurons located in the caudal part of the ganglion underwent degenerative changes including disappearance of rough endoplasmic reticulum and cytoplasmic vacuolation. The structural alterations were most acute 7 days after the injection when some neurons showed signs of total vacuolation and lysis. A second phase of neuronal change occurred after longer survival periods extending from 60 to 120 days after injection. The most striking feature of such neurons was darkening of their dendrites associated with abnormally high density cytoplasm that contained mitochondria with disrupted cristae. As distinct from the early phase in which cell necrosis was observed, there was no evidence of cell death of neurons bearing darkened dendrites. Since examples of exfoliation of the affected dendrites and their phagocytosis by satellite cells were extremely rare, it is postulated that these structural alterations are probably reversible but over an extended period. The significance of the two phases of degenerative change is discussed in connection with the acute and possible chronic effects of the toxic lectin. The present study also confirms the presence of postganglionic sympathetic axons in the cervical vagus nerve.

Differential distribution of phosphorylated and non-phosphorylated neurofilaments within the retina and optic nerve of hamsters

Retinae and optic nerve sections from adult hamsters were reacted with antibodies against phosphorylated (P) or non-phosphorylated (NP) neurofilament proteins. NP epitopes were observed within ganglion cell bodies and extended into the proximal portion of the optic nerve. P epitopes became prominent within axons as they approached the optic disc and remained throughout the optic nerve. This spatial distribution appears similar to the pattern of myelination within this axonal population.

The postnatal development of the optic nerve in hamsters: an electron microscopic study

The postnatal development of the optic nerve in the golden hamster has been examined using the electron microscope. The number of the optic fibres present in the optic nerve showed an initial increase during the first day after birth but it declined afterwards and tapered off after Day 16. At its peak on postnatal Day 1, there was an average of 314,629 axons in the optic nerve but when the animal reached adulthood only 109,587 fibres remained amounting to about 65% loss of the total fibre population. The period of axon loss coincided with the appearance of large patches of degenerated profiles in the optic nerve. The occurrence of the optic fibre loss has been implied to correlate with the time when the retinal projections were undergoing a dynamic reorganization at the target sites during the process of establishing the adult patterns of retinofugal connections.

The postnatal development of the optic nerve in hamsters: an electron microscopic study.

The postnatal development of the optic nerve in the golden hamster has been examined using the electron microscope. The number of the optic fibres present in the optic nerve showed an initial increase during the first day after birth but it declined afterwards and tapered off after Day 16. At its peak on postnatal Day 1, there was an average of 314,629 axons in the optic nerve but when the animal reached adulthood only 109,587 fibres remained amounting to about 65% loss of the total fibre population. The period of axon loss coincided with the appearance of large patches of degenerated profiles in the optic nerve. The occurrence of the optic fibre loss has been implied to correlate with the time when the retinal projections were undergoing a dynamic reorganization at the target sites during the process of establishing the adult patterns of retinofugal connections.

Study of the effect of gymnemic acid on taste in hamster

Behavioral and electrophysiological experiments with 10 sweeteners have been made to test if gymnemic acid (GA) is able to block the response to sweet stimuli in single taste fibres of the chorda tympani proper nerve in hamsters. The hamster was chosen because earlier studies show that it is more sensitive to GA than any other non-human species. Since GA has been shown to affect the sweetness of many different substances, its effects were studied on an array of sweeteners. To avoid, however, the inclusion of sweeteners unpalatable to the hamster, the hamsters' liking of this array was tested with two-bottle preference technique for −24 h. It was found that acesulfam-K, fructose, glucose, sucrose and xylitol were strongly liked, while the animals showed no preference for aspartame, D-tryptophane, sodium cyclamate, sodium saccharin and thaumatin over water. The summated nerve response of these stimuli was then recorded. It was found that neither thaumatin nor aspartame elicited a response, while the other stimuli gave a good response. Finally, the sweeteners which were both preferred in the two-bottle tests and gave a nerve response were used as taste stimuli in single fibre experiments together with sodium chloride, quinine hydrochloride, citric acid and saccharin. The single fibre recordings were made before and after application of 5 mg GA for 3 min on the tongue. It was found that GA did not cause any dramatic decrease or disappearance of the responses to either the sweet or the non-sweet substances. The responses to the sweeteners, however, were more depressed than those to the non-sweet stimuli.