Electrophysiological properties of the isolated vestibulocerebellar complex of the frog in vitro

Parameters of the electrical activity of the isolated vestibulocerebellar complex of the frog were studied under in vitro conditions. In the region of the vestibular nucleus (nc. VIII), in the presence of stimulation of the stato-acoustic nerve (n. VIII), responses from efferent vestibular neurones and from unidentified (probably vestibulospinal) neurones were recorded. The latent periods of their excitatory postsynaptic potentials (EPSPs, 1.4-2.2 ms) were indicative of mono- and disynaptic connection. Inhibitory postsynaptic potentials (IPSPs) were also observed. Stimulation of the auricular lobe of the cerebellum evoked monosynaptic IPSPs, an EPSP-IPSP complex or pure EPSPs in nc. VIII, the latter probably by way of collaterals to the cerebellum. The inhibitory character of the effect of efferents from the cerebellum to the neurones of nc. VIII was demonstrated in the focal synaptic potential and in spontaneous and evoked unit activity. If n. VIII was stimulated, both focal and unit extra- and intracellular responses characteristic of activation of the Purkinje cells by mossy (MF) or climbing (CF) afferent fibres were recorded in the cerebellar cortex. The electrophysiological picture indicates that both synaptic transmission and the functional manifestations of the individual neurones are preserved in the tested preparation.     

Quantitative electron-microscopy analysis of cranial nerves III, IV, and VI and of the extrinsic eye muscles in fog.

A comparative study of the quantitative data of the frog extraocular muscles and the cranial nerves that innervate them was performed. Oculorotatory muscles contain muscle fibres of at least 4 types which are arranged in heterogeneous layers. The zonal arrangement of the muscles does not occur on the cross-sections in the vicinity of muscle insertions. In these regions only two muscle fibre types are present and the total number of fibres is smaller by 70% than in the central region of the muscle. Most numerous are muscle fibres in the rectus inferior muscle, while the smallest number of fibres is found in rectus interior muscle. Three distinct types of nerve fibres are distinguished according to the following criteria: occurrence and thickness of myelin sheath, fibre diameter and ratio "g". The fibres with thin myelin sheaths indicate small diameters (1-5--6- mum) and their ratio "g" equals 0-82 +/- 0-08. They constitute about 30% of the myelinated fibres in the nerve supply of the oculorotatory muscles and about 14% in the supply of the retractor bulbi muscle. Both the value of the ratio "g" and a greater number of these fibres in the nerve supply of the muscles that contain slow contracting muscle fibres indicate that they are rather slow conducting nerve fibres. The range of the diameters of the fibres with thick myelin sheaths is greater (3-5--13-5 mum) and their "g" equals 0-66 +/- 0-06. These fibres constitute about 70% of the myelinated ones in the nerve supply of the oculorotatory muscles and 86% in the supply of the retractor bulbi muscles. The value of the ratio "g" in these fibres indicates that they are fast contracting ones. The smallest diameters are found in the myelinated fibres (0-5--1-7 mum). These fibres occur frequently in all the examined nerves; they constitute 36--47% of the total number of all the nerve fibres. The frog extraocular muscles are characterized by an abundal nerve supply which is reflected in the low innervation ratio (1:4--1:5). On the distal cross-section of nerves the number of nerve fibres is greater than on the proximal ones. Ganglionic neurons occur sporadically around the nerves; in the nerve III synaptic contacts between two neurons were observed.     

Synaptic transmission in the sixth ganglion of the cockroach: action of 4-aminopyridine.

1. Study was made of the action of 4-aminopyridine (5 X 10(-5) M) on synaptic transmission in the last abdominal ganglion of Periplaneta americana. The 'oil-gap' technique was used to record postsynaptic events in a single giant axon. 2. 4-AP quickly increased the 'background' of postsynaptic activity, which consisted of 'spontaneous' unitary EPSPs and IPSPs. Postsynaptic spikes were also propagated. 3. Both evoked EPSPs (stimulation of cercal nerve XI) and evoked IPSPs (stimulation of cercal nerve X) were greatly increased in amplitude although their duration (half-time) was unaltered. 4. 4-AP triggered presynaptic action potentials in the cercal nerves (recorded with external electrodes). These 'antidromic' potentials appeared singly or sometimes repetitively, especially after electrical stimulation of the cercal nerves. They were often in monosynaptic correlation with unitary EPSPs. 5. Neither the resting potential nor the postsynaptic membrane resistance was modified. 6. There were no changes in the equilibrium potentials of the ions involved in postsynaptic events. 7. The results may be essentially explained by an increase in transmitter release after 4-AP treatment, which may be partly the result of a rise in presynaptic terminal excitability, and partly the result of a lengthening of the presynaptic action potentials.     

A study of pre- and postganglionic fibres in the intestinal nerve (Remak's nerve) of the chicken

Summary The mean peak CV's of two electrophysiologically defined groups of fibres in the intestinal nerve of the chicken have been determined.One group of fibres is constituted by the processes of enteric cholinergic neurones which project along the side branches of the intestinal nerve and synapse within the nerve trunk. These preganglionic fibres have a mean peak CV (at 40 °C) of 0.31 m·s^–1.The other group is made up of fibres of postganglionic neurones which project orally along the nerve trunk. The results suggest that some postganglionic neurones project only as far as the next ganglion whilst others project beyond the next two ganglia for distances greater than 5 mm. The postganglionic fibres have a mean peak CV (at 40 °C) of 0.71 m·s^–1.These figures demonstrate that both pre- and postganglionic fibres are unmyelinated. The temperature coefficient (Q₁₀) for the CV of unmyelinated fibres in the intestinal nerve was 1.57.Abbreviations CAP compound action potential - CV conduction velocity - Q ₁₀ temperature coefficient     

Morphological and electrophysiological consequences of unilateral pre- versus postganglionic vestibular lesions in the frog

The combined removal of the labyrinthine sense organs and of the ganglion of Scarpa on one side (postganglionic section) resulted in a degeneration of afferent fibres in the eighth nerve of the frog (Rana temporaria) within 2–4 days. If the eighth nerve was sectioned more peripherally (preganglionic section) and its distal part was removed together with the labyrinthine organs degeneration of afferent fibres was absent or restricted to very few fibres. Electrical stimulation of vestibular afferents in vitro evoked monosynaptic field potentials in the ipsilateral and via commissural fibres di-and polysynaptic field potentials in the contralateral vestibular nuclei. Afferent-evoked field potentials recorded on the intact side of chronic frogs ( 60 days) with a preor postganglionic lesion and afferent-evoked field potentials recorded on the operated side of chronic frogs with a preganglionic lesion had amplitudes that were very similar to those recorded in control frogs. Commissurally evoked field potentials recorded on the operated side of chronic frogs with preor postganglionic lesions were significantly increased (by about 90%) with respect to control amplitudes. In both groups the time-course of this increase was very similar, started between 15 and 30 days and saturated for survival periods longer than 60 days. Unilateral inactivation of vestibular afferents, but not degeneration, is the likely common denominator of the central process leading to the reported neural changes. A reactive supersensitivity of central vestibular neurons on the operated side for glutamate as a possible mechanism is unlikely, since converging afferent and commissural inputs are both glutamatergic and only one of them, the commissural input, was potentiated. Comparison of the time-courses of neural changes in the vestibular nuclei and postural recovery in the same individuals excludes a causal relation between both phenomena.Abbreviations HL hemilabyrinthectomy - VNC vestibular nuclear complex - HRP horseradish peroxidase - N. VIII eighth nerve - N. IX ninth nerve     

GABA-mediated synaptic inhibition of projection neurons in the antennal lobes of the sphinx moth,Manduca sexta

Responses of neurons in the antennal lobe (AL) of the moth Manduca sexta to stimulation of the ipsilateral antenna by odors consist of excitatory and inhibitory synaptic potentials. Stimulation of primary afferent fibers by electrical shock of the antennal nerve causes a characteristic IPSP-EPSP synaptic response in AL projection neurons. The IPSP in projection neurons reverses below the resting potential, is sensitive to changes in external and internal chloride concentration, and thus is apparently mediated by an increase in chloride conductance. The IPSP is reversibly blocked by 100 microM picrotoxin or bicuculline. Many AL neurons respond to application of GABA with a strong hyperpolarization and an inhibition of spontaneous spiking activity. GABA responses are associated with an increase in neuronal input conductance and a reversal potential below the resting potential. Application of GABA blocks inhibitory synaptic inputs and reduces or blocks excitatory inputs. EPSPs can be protected from depression by application of GABA. Muscimol, a GABA analog that mimics GABA responses at GABAA receptors but not at GABAB receptors in the vertebrate CNS, inhibits many AL neurons in the moth.     

EPSPs of masseter motoneurons evoked by stimulation of low-threshold infraorbital nerve afferents in cat

Stimulation of the infraorbital nerve at strengths 1.4–2.5 times higer than the threshold of excitation of A fibers in cats anesthetized with chloralose and pentobarbital evoked EPSPs with an amplitude up to 3.0 mV and a duration of 9–15 msec in 69% of masseter motoneurons after 1.5–3.0 msec. These EPSPs were complex and formed by summation of simpler short-latency and long-latency EPSPs. The short-latency EPSPs appeared in response to infraorbital nerve stimulation at 1.1–1.5 thresholds and had a slow rate of rise (2.5–4.5 msec, mean 3.7±0.4 msec), low amplitude (under 2.0 mV), and short duration (5–6 msec). Their latent period varied from 1.5 to 3.0 msec (mean 2.1±0.2 msec). The shortness of the latent period and its constancy during stimulation of the nerve at increasing strength, and also the character of development of facilitation and inhibition of the EPSP during high-frequency stimulation suggests that these EPSPs are monosynaptic. The slow rate of rise suggested that these EPSPs arise on distal dendrites of the motoneurons. Long-latency EPSPs appeared 7–9 msec after stimulation of the infraorbital nerve at 1.1–1.5 thresholds. Their amplitude reached 1.5–2.0 mV and their duration 7–9 msec. The long duration of the latent period combined with low ability to reproduce high-frequency stimulation (up to 30/sec) points to the polysynaptic origin of these EPSPs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 6, pp. 583–591, November–December, 1977.     

High extracellular concentrations of potassium and rubidium modulate the synaptic transmission in the frog labyrinth

High extracellular K or Rb levels (20 mM) produce an increase in the resting EPSP and spike frequencies recorded intra cellularly from single fibres of the posterior nerve in the isolated frog labyrinth. The afferent discharge facilitation proved to be inversely related to the fibre's initial resting activity. The K effect is systematically larger than the Rb effect. High sensitive and scarcely sensitive units may be identified with respect to K and Rb action. The present findings suggest that, according to previous models of hair cell functioning, the K and Rb effects are mediated by a raise in intracellular Ca concentration which sustains an increased transmitter release at the cyto-neural junction.     

Neuronal expression of peripherin,a type III intermediate filament protein,in the mouse hindbrain

Peripherin is a 57 kDa Type III intermediate filament protein associated with neurite extension, neuropathies such as amyotrophic lateral sclerosis, and cranial nerve and dorsal root projections. However, knowledge of peripherin expression in the CNS is limited. We have used immunoperoxidase histochemistry to characterise peripherin expression in the mouse hindbrain, including the inferior colliculus, pons, medulla and cerebellum. Peripherin immunolabelling was observed in the nerve fibres and nuclei that are associated with all cranial nerves [(CN) V–XII] in the hindbrain. Peripherin expression was prominent in the cell bodies and axons of the mesenchephalic trigeminal nucleus and the pars compacta region of nucleus ambiguus, and in the fibres that comprise the solitary tract, the descending spinal trigeminal tract and the trigeminal and facial nerves. A small proportion of peripherin positive fibres in CN VIII likely arise from cochlear type II spiral ganglion neurons. Peripherin positive fibres were also observed in the inferior cerebellar peduncle and folia in the intermediate zone of the cerebellum. Antibody specificity was confirmed by absence of labelling in hindbrain tissue from peripherin knockout mice. This study shows that in the adult mouse hindbrain, peripherin is expressed in discrete neuronal subpopulations that have sensory, motor and autonomic functions.     

Distribution of FMRFamide-like immunoreactivity in the nervous system of the slug Limax maximus

Summary The distribution of FMRFamide-like immunoreactive neurons in the nervous system of the slug Limax maximus was studied using immunohistochemical methods. Approximately one thousand FMRFamide-like immunoreactive cell bodies were found in the central nervous system. Ranging between 15 m and 200 m in diameter, they were found in all 11 ganglia of the central nervous system. FMRFamide-like immunoreactive cell bodies were also found at peripheral locations on buccal nerve roots. FMRFamide-like immunoreactive nerve fibres were present in peripheral nerve roots and were distributed extensively throughout the neuropil and cell body regions of the central ganglia. They were also present in the connective tissue of the perineurium, forming an extensive network of varicose fibres. The large number, extensive distribution and great range in size of FMRFamide-like immunoreactive cell bodies and the wide distribution of immunoreactive fibres suggest that FMRFamide-like peptides might serve several different functions in the nervous system of the slug.     

Ultrastructural localization of monoamines in the epidermis of Lumbricus terrestris (L.)

Summary Receptor cells in the epithelium and the basiepithelial nerve net of the prostomium of Lumbricus terrestris were investigated with electron microscope with special regard to the presence of monoamines. The receptor cells are found in groups of about 40 intermingled with supportive cells. After pretreatment with -methyl-noradrenaline and fixation with potassium permanganate a few receptor cells in each group and some nerve fibres in the basiepithelial nerve net contain small granular vesicles (about400 Å) characteristic for monoaminergic neurons. The distribution and relative number of these receptor cells and nerve fibres coincide well with previous reports on fluorescent receptor cells and varicose fibres. That the monoamine-storing small granular vesicles not are visualized until pretreatment with -methyl-noradrenaline is in accordance with recent microspectrofluorometric analysis, which shows that dopamine is the only primary monoamine present in the epithelium.In the epithelium there are occasional receptor cells and nerve fibres containing large vesicles (1000–1800 Å) which resemble the neurosecretory vesicles in the central nervous system. Photoreceptor cells having an intracellular cavity with microvilli and cilia have infrequently been observed at the base of the epithelium.No synapses on the mucous cells have been noticed. Nor have any synaptic specializations been observed in the basiepithelial nerve net. The morphological conditions necessary for the existence of possible axo-axonal synapses are briefly discussed.This work was supported by grants from the Helge Ax: son Johnson Foundation and the Magn. Bergvall Foundation.     

Cytochemical studies of hydrogen peroxide production in the tadpole tail of Rana japonica during metamorphic climax

Summary The degeneration of tadpole tail tissue was investigated cytochemically by localizing the sites of hydrogen peroxide production. A cerium perhydroxide precipitation method was used. No reaction product was found in resting macrophages and intact muscle fibres during premetamorphosis. In the metamorphosis phase, extensive cerium precipitates were visualized on the outer surface of the plasma membrane of phagocytotic macrophages, fibroblasts, neutrophils, epidermal cells, muscle fibres, notochordal cells, nerve cells and capillary endothelial cells. The reaction products were localized on those parts of the plasma membranes of the macrophages that were in contact with those of adjoining cells. When catalase were added, the amount of deposits decreased. -Tocopherol and indomethacin, but not dexamethasone, significantly inhibited the formation of the reaction products. These findings are taken to indicate that active oxygen is produced on the plasma membrane of activated macrophages and may play a role in the degeneration of the tail tissue.     

Monosynaptic connections mediate resistance reflex in crayfish (Procambarus clarkii) walking legs

Summary In crustacean walking legs, the coxo-basipodite chordotonal organ (CB) composed of about 50 sensory cells, evokes a resistance reflex in the levator (Lev) and depressor (Dep) muscles responsible for the movements of the coxo-basipodite joint where it is located. Mechanical stimulation of the CB strand and electrical stimulation of its sensory nerve have been performed along with systematic intracellular recordings from CB terminals (CB T) and levator (Lev) or depressor (Dep) motoneurons (MNs) in order to study their connections. Measurements of conduction times in the CB nerve demonstrated different pools of sensory fibres, the fastest of which reach the ganglion in 2.5 ms. During imposed movements to the CB strand, intracellularly recorded Lev or Dep MN display EPSPs that are correlated to spikes in the CB nerve, their delays are incompatible with a polysynaptic pathway. Systematic stimulation of the CB nerve demonstrates that about 4 to 8 CB fibres are connected with each Lev or Dep MN. Classical tests for monosynaptic connections indicate that EPSPs occurring between 3 ms and 6 ms correspond mainly to monosynaptic connections with CB T, whereas IPSPs (the latencies of which are above 12 ms) are polysynaptic. In spite of the high selectivity of the CB T onto MNs, eight simultaneous intracellular recordings of coupled CB T and MN (out of more than 300 MNs penetrated) have allowed a direct measurement of synaptic delays (less than 1 ms). The functional significance of these results is discussed in relation to the proprioceptive control of locomotor movements.Abbreviations CB Coxo-basipodite chordotonal organ - CB n CB sensory nerve - CB T CB sensory terminal - Dep depressor - Lev levator - MN motoneuron     

Ultrastructure of free nerve endings in respiratory and squamous epithelium on the rat nasal septum

The distribution of nerve fibres in the mucosa of the nasal septum of the rat was investigated by means of transmission electron microscopy on transverse and tangential ultrathin sections. Near the basement membrane of respiratory and squamous epithelium, a rather dense network of unmyelinated nerve fibres occurs. Some fibres in the respiratory epithelium ascend between the epithelial cells to reach up to the tight junctions. These fibres appeared in transverse sections to end as hooks or boutons, sometimes with branches. These shapes resemble the free nerve endings that are considered to act as nociceptors. The small intraepithelial fibres, with diameters of about 0.5–1 m, contain both dense granules and clear vesicles comparable to synaptic vesicles. Substance P was found in dense granules in basal fibres; vasoactive intestinal peptide was absent throughout the epithelium. Acetylcholinesterase activity was observed closely associated with the basal fibres; the apical fibres showed little if any activity. Membrane specializations pointing to an efferent function as well as structures usually associated with mechanoreceptive functions were lacking in both respiratory and squamous epithelium.Part of this work was presented at the Annual Conference of the Netherlands Society for Electron Microscopy, 28–29 Nov 1985, Wageningen, The Netherlands. See Spit BJ and Hendriksen EGJ (1986) Ultramicroscopy 19:102–103     

THE ROLE OF WATER IN THE STRUCTURE OF PERIPHERAL NERVE MYELIN

In the study of the drying kinetics of nerve fibres, at least five "phases" of water evaporation can be distinguished. A consideration of the accompanying changes in low-angle x-ray diffraction patterns permits a tentative identification of the "phases" and a quantitative interpretation of the data in terms of the water distribution in nerve fibres. These results suggest that the myelin sheath of frog sciatic nerve contains 40 to 50 per cent water, and it is suggested further that the greater part of this water is "organised" in relation to the hydrophilic groups of the lipide and protein components.     

Remarkable adrenergic nerves in the exocrine pancreas

Summary The adrenergic nerves in the pancreas of mice, rats, guinea-pigs, rabbits, and cats were investigated with the fluorescence method of Falck and Hillarp. The relations between the adrenergic fibres and the vessels were studied by the injection of india ink into the vessels.Besides the normal manifestation of adrenergic fibres at the large vessels, some vessels of capillary size were also accompanied by adrenergic fibres. These fibres had a very weak fluorescence, and showed up regularly only when the animal had been treated with Nialamide and L-DOPA or dopamine to increase the catecholamine content of the adrenergic fibres. The weakness of the fluorescence is perhaps due to low transmitter concentration or to small size of the nerve fibres, or to both. A rough estimate indicated that either the transmitter concentration of the nerve fibre is at least approximately 100 times below that seen in adrenergic nerves in other tissues, or that the radius of the varicosities of the nerve fibres is less than 0.2 . Neither alternative has previously been recognized.The secretory acini of the pancreas seem to lack a direct adrenergic supply. In the intrapancreatic ganglia, non-fluorescent nerve cells were reached by adrenergic terminals. No adrenergic nerve cells were detected in the pancreas of rats and cats. Small intensely fluorescent catecholamine-containing cells were observed in connexion with the intrapancreatic ganglia of rats.The research reported in this document has been sponsored by the Air Force Office of Scientific Research under grant AF EOAR 67-15 through the European Office of Aerospace Research (OAR), United States Air Force, by the United States Public Health Service (grant NB 06701-01) by the Swedish Medical Research Council (project B 67-12X-712-02A), and by the Faculty of Medicine, University of Lund, Sweden.     

The structure of the nerve fibre layer and neurocord in the enteropneusts

Summary The nerve fibre layer and the neurocord of the Enteropneusts Saccoglossus horsti, Harrimania kupfferi and Ptychodera flava have been examined with the electron microscope. The nerve fibres vary in diameter between 0.15 to 10 m. The majority of the fibres are of the smaller diameters. The nerve fibre layer is intraepidermal, and is divided by processes running radially from the epithelial cells to the basement membrane that separates the nerve fibre layer from the muscle cells.The cells of origin of these nerve fibres are situated mainly in the innermost layers of the epidermal cells. The nerve fibre profiles contain numerous vesicles of very varied diameter and contents, together with larger granular inclusions that are also found in the nerve cell bodies.Morphologically recognisable synapses are rare, but the majority of fibres are in intimate contact with one another. Sometimes the mass of fibres is divided into bundles by the epithelial cell processes. The majority of giant fibres are situated near to the basement membrane of the neurocord. The giant fibres also have a varied content of vesicles as well as neurofilaments and neurotubules.The central canal in Ptychodera flava and the remnants of the central canal in Saccoglossus horsti are both lined by columnar cells that bear microvilli as well as cilia with the typical 9 + 2 pattern of tubules. Scattered amongst these cells are mucus secreting cells which open into the cavity of the canal.I (P.N.D.) should like to thank Professor J. Z. Young, F. B. S. for much advice and encouragement. Dr. R. Bellairs generously provided the electron microscope facilities, and Dr. R. Newell kindly collected and identified the Saccoglossus specimens. Mr. R. Moss, Mrs. J. Hamilton and Mr. A. Aldrich gave excellent technical and photographic assistance.     

Removal of the Schwann sheath from the giant nerve fiber of the squid: An electron-microscopic study of the axolemma and associated axoplasmic structures

Summary Surgical thyroidectomies were used as means of altering the thyroid state of adult recipients to study the possible influence of thyroid hormones on fibre formation in irides by immature noradrenaline neurons of the locus coeruleus grafted to the eye. Whole-mount preparations of irides were analysed using fluorescence histochemistry according to Falck-Hillarp, subjectively estimating on a blind basis the number of fibres, their pattern of distribution and individual morphology in the iris dilator plate. Neurones of the locus coeruleus formed nerve fibres in irides of thyroidectomized recipients to the same extent as in controls. Distribution and fine structure of these fibres, however, differed markedly. The numerous thick axon bundles from the attachment of the brain graft, normally seen to radiate out from locus coeruleus-neurones in oculo, were almost totally lacking in the thyroidectomized group. Also, the individual nerve fibres showed abundant peripheral accumulations of fluorescent material. This appearance of the outgrowth of fluorescent fibres in the experimental group, indicative of a disturbed formation of nerve fibres during development in oculo, was abolished by reversal of the thyroid hormone deficiency using daily injections of 1-thyroxin to the recipients throughout the experiment. This strongly indicates a role for thyroxin in the process of formation of nerve fibres originating from the neurones of the locus coeruleus during perinatal development. The present paper is supportive of recent reports claiming that during the development of the CNS thyroxin plays a crucial role in tubulin assembly, and thus presumably for the ability of neurones to form processes.     

The innervation of the myometrium of the cynomolgus monkey (Macaca fascicularis)

Summary The autonomic innervation of the myometrium of Macaca fascicularis consists of bundles of unmyelinated nerve fibres running between the smooth muscle cells, and is therefore considered to be of the fascicular (= unitary) type. Close contacts between nerve fibres and smooth muscle fibres were not found. Modification of the chromaffin method according to Tranzer and Richards made it possible to visualize the heterogeneity of the nerve fibres in a single bundle. The following fibre types were found to coexist: (1) noradrenergic fibres containing synaptic vesicles with a dense granule, (2) cholinergic fibres containing empty synaptic vesicles, and (3) non-adrenergic noncholinergic (NANC) fibres containing only or predominantly large dense-cored vesicles, which do not react with this method. Noradrenergic fibres are the most numerous (around 60%), followed by NANC fibres (30%) and cholinergic elements (around 10%). The distribution of these three types is similar in the cervix, the isthmus and the body of the uterus in pregnant and non-pregnant females.     

Effects of high calcium solutions on glutamate sensitivity of crayfish muscle fibres

Crayfish neuromuscular preparations were studied after 18--36 h exposure to high calcium solutions. As previously reported for frog neuromuscular preparations the treatment damaged the nerve terminals and decreased junctional potentials. The resting potentials and input resistances of the muscle fibres were not affected; but their sensitivity to glutamate was significantly decreased when compared to that of control muscles. After exposure to high calcium, the sensitivity to gamma-aminobutyric acid, the putative transmitter at inhibitory synapses, was increased. Apparently normal twitches were elicited by direct stimulation, and calcium spikes could still be observed in the fibres. A decreased sensitivity to glutamate was also noted in experiments carried out on denervated muscles 8 months after section of the motor axons. Possible relations between nerve terminal damage and the decrease in sensitivity to glutamate are discussed.