Effect of cooling on spike trains from skin receptors

Quantitative characteristics of the afferent flow in a cutaneous nerve during cooling of the skin in cats were determined by the cross-correlation method. Lowering the skin temperature by 10°C with different gradients of cooling led to the appearance of activity in A-, A-, and C-fibers. The first fibers to become excited were C-fibers, followed in turn by A-fibers, a group of slowly-conducting A-fibers, and a group of fast-conducting A-fibers. The latent period of excitation of the C-fibers remained unchanged whatever the rate of skin cooling, whereas in A-fibers it increased with slowing of the rate of fall of temperature. The level of maximal activity neither in A- nor in C-fibers depended on the gradient of skin cooling, but in all the groups of fibers mentioned the time taken to reach the maximum of activity decreased with an increase in the rate of cooling.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii State University, Gor'kii. Translated from Neirofiziologiya, Vol. 12, No. 4, pp. 405–412, July–August, 1980.     

Afferent activity in thin myelinated and unmyelinated cutaneous nerve fibers during mechanical stimulation of skin receptors

Afferent activity in thin myelinated and unmyelinated cutaneous nerve fibers was analyzed by an impulse collision method and by methods improving the signal-to-noise ratio in the record of the antidromic action potential. The following groups were distinguished among the thin myelinated and unmyelinated nerve fibers on the basis of the results of investigation of conduction velocities, thresholds of electrical excitation, and response to mechanical stimulation: A ₁ (conduction velocity 30-14 m/sec) — a relatively larger number of these fibers conducts excitation in response to weak mechanical stimulation; A ₂ (14–4.0 m/sec) — the receptors of these fibers are more easily excited by a strong stimulus; a group of "mixed" fibers, containing myelinated and unmyelinated nerve fibers (4–2 m/sec), conducting excitation in response to both types of mechanical stimulation; C₁ (2.0–1.0 m/sec) — a fairly large number of these unmyelinated fibers conducts impulses in response to weak mechanical stimulation; C₂ (1.0–0.15 m/sec) the majority of fibers of this group is connected with receptors requiring strong mechanical stimulation for their excitation.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii State University, Gor'kii. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 67–75, January–February, 1976.     

Investigation of the frequency distribution of natural activity in a mixed nerve trunk by the colliding impulse method

the theory of the colliding impulse method of determining the discharge frequency spectrum and the distribution of fibers by frequency in a mixed nerve trunk is examined. Using the double impulse method, a modification of the colliding impulse method, afferent A-fibers of the aortic nerve in the cat were investigated. Only 61% of these fibers were found to be activated in the initial phase of cardiac ejection when the arterial pressure was 120 mm Hg. Most of the active fibers functioned with a frequency of about 115 spikes/sec.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 6, No. 3, pp.318–327, May–June, 1974.     

Activity of myelinated fibers under heat and burn influences on the skin

The dynamics of the activity of myelinated fibers of a cutaneous nerve under heat and burn influences on hair-covered skin was investigated in acute experiments on cats using the method of cross-correlation functions. Under heat influence on the skin the total activity of the nerve was reduced chiefly at the expense of the rapidly conducting myelinated fibers, whereas in the case of painful heating of the skin the A fibers were activated. The results obtained make it possible to solve the problem of the heat-information code from the standpoint of the flow "pattern" theory.S. M. Kirov Medical Institute, Ministry of Health of the Russian Federation, Nizhnii Novgorod. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 567–577, September–October, 1992.     

Mechanism for sympathetic modulation of activity of cutaneous receptors (with Aδ fibers)

The afferent flow in A fibers from cutaneous receptors was studied in acute experiments with cats. A decline in the number of fibers activated during adequate receptor stimulation was observed at 5 and 35 sec after the excitation of sympathetic efferents. Similar changes in the afferent flow were recorded in identical time intervals after the preliminary stretching and cooling of the skin. The results obtained indicate that the quantitative characteristics of afferent flow during the first 30 sec after stimulation of the sympathetic chain are primarily due to the change in the mechanical state of the tissues surrounding the receptors.N. I. Lobachevskii Institute of Mathematics and Cybernetics, Gor'kii University. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 517–521, July–August, 1985.     

Functional differentiation of superior laryngeal nerve afferents in cats

Electrophysiological characteristics of superior laryngeal nerve fibers and reflex responses in respiratory motor nerves and the recurrent nerve were investigated in acute experiments on cats under superficial pentobarbital anesthesia. Analysis of the compound action potential in the superior laryngeal nerve revealed three distinct groups of afferent fibers subserving different functions: group A, responsible for proprioceptive mechanisms of coordination of activity of the laryngeal muscles; group A(₃), responsible for feedback mechanisms between the receptor apparatus of the mucous membrane and muscles of the larynx and bulbar respiratory neurons, and group A, responsible for the development of protective respiratory reflexes.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 777–783, November–December, 1984.     

Neurophysiological study of bulbar projections of different groups of superior laryngeal afferents

The projections of superior laryngeal afferents to bulbar neuronal structures were investigated using ortho- and antidromic testing during acute experiments on cats anesthetized with Nembutal. It emerged that endings of the most excitable (group A) afferent fibers were mostly distributed ipsilaterally within the solitary tract nucleus, the adjoining portion of the lateral tegmental field, and the rostral section of the retrofacial nucleus. High threshold (group A and A) afferent fibers also terminate in these nuclei, but are distributed over a wider area than low-threshold afferent projections in the solitary tract nucleus and the lateral tegmental field. The reverse applied to the retrofacial nucleus. Terminals of high threshold (group A) afferents extended to the caudal trigeminal nerve spinal tract nucleus, and possibly to the dorsal motor nucleus of the vagus nerve at obex level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 81–90, January–February, 1988.     

Effect of vibrostimulation frequency upon skin mechanoreceptors innervated by Aβ-, Aδ, and C-fibers

Vibrostimulation of skin from the crus of the cat at frequencies of 10, 30, and 50/sec evokes a response of mechanoreceptors innervating group A and A fibers to the presentation of each vibrostimulus. The higher the frequency of vibrostimulation, the more clearly manifest are changes in on- and off-responses on a neurogram recorded from the n. saphenus branch. These changes are a result of a decrease in the number of impulses evoked by each vibratory beat. Mechanoreceptors innervated by fibers of group C are not excited as a result of vibrostimulation at these frequencies. After preliminary vibrostimulation, a portion of the mechanoreceptors innervated by C-fibers do not respond to presentation of a mechanical test stimulus (stretching of the skin); the higher the frequency of vibrostimulation, the smaller is the number of reacting receptors.Kirov Medical Institute, Nizhny Novgorod. Translated from Neirofiziologiya, Vol. 24, No. 1, pp. 20–27, January–February, 1992.     

Microelectrophysiological analysis of representation of different groups of splanchnic afferent fibers in posterior and anterior hypothalamic structures in cats

Responses of anterior and posterior hypothalamic neurons to stimulation of different groups of splanchnic afferent fibers were studied by simultaneous recording of hypothalamic unit activity and the compound action potential of the splanchnic nerve in cats anesthetized with chloralose and pentobarbital and immobilized with succinylcholine. Most "visceral" neurons of both the posterior (51.8%) and anterior hypothalamus (52.7%) were found to be activated during excitation of splanchnic nerve fibers of the A group. Some selectivity of the influence of the fast-conducting fraction of fibers of the A group on the posterior zones of the hypothalamus and of the more slowly conducting fraction on the anterior zones was found. An essential contribution to the activation of hypothalamic neurons was shown to be made by the slowest conducting afferent fibers of the A group, whose range of conduction velocities overlaps that of group B fibers. Afferent discharges ascending along these fibers evoked responses in 27.6% of "visceral" neurons of the posterior and in 31.6% of neurons of the anterior zones of the hypothalamus. Afferent systems of splanchnic nerve fibers of the A and C groups also were shown to participate in activation of hypothalamic "visceral" neurons.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 14, No. 5, pp. 453–461, September–October, 1982.     

Study of neuronal organization of the “gastric” region in the dorsal motor nucleus of the vagus nerve

The peculiarities of neuronal electrical activity in the dorsal motor nucleus (0.5–2.0 mm rostrally to the obex) were investigated in acute experiments on cats, using the microelectrode technique, under conditions of stimulation of the gastric vagal branches. In the gastric region of the nucleus, two groups of cells responding to nerve stimulation were identified: preganglionic parasympathetic neurons antidromically activated by such stimulation, and cells excited orthodromically with the involvement of afferent fibers of the vagus nerve.Neirofiziologiya/Neurophysiology, Vol. 25, No. 3, pp. 190–196, May-June, 1993.     

Intensity and frequency dependence of laryngeal afferent inputs to respiratory hypoglossal motoneurons

Mifflin, Steven W. Intensity and frequency dependenceof laryngeal afferent inputs to respiratory hypoglossal motoneurons. J. Appl. Physiol. 83(6):1890-1899, 1997.Inspiratory hypoglossal motoneurons (IHMs)mediate contraction of the genioglossus muscle and contribute to theregulation of upper airway patency. Intracellular recordings wereobtained from antidromically identified IHMs in anesthetized,vagotomized cats, and IHM responses to electrical activation ofsuperior laryngeal nerve (SLN) afferent fibers at various frequenciesand intensities were examined. SLN stimulus frequencies <2 Hz evokedan excitatory-inhibitory postsynaptic potential (EPSP-IPSP) sequence oronly an IPSP in most IHMs that did not change in amplitude as thestimulus was maintained. During sustained stimulus frequencies of5-10 Hz, there was a reduction in the amplitude of SLN-evokedIPSPs with time with variable changes in the EPSP. At stimulusfrequencies >25 Hz, the amplitude of EPSPs and IPSPs was reduced overtime. At a given stimulus frequency, increasing stimulus intensityenhanced the decay of the SLN-evoked postsynaptic potentials (PSPs).Frequency-dependent attenuation of SLN inputs to IHMs also occurred innewborn kittens. These results suggest that activation of SLN afferentsevokes different PSP responses in IHMs depending on the stimulusfrequency. At intermediate frequencies, inhibitory inputs areselectively filtered so that excitatory inputs predominate. At higherfrequencies there was no discernible SLN-evoked PSP temporally lockedto the SLN stimuli. Alterations in SLN-evoked PSPs could play a role inthe coordination of genioglossal contraction during respiration,swallowing, and other complex motor acts where laryngeal afferents areactivated.

     

Selective stimulation of jugular ganglion afferent neurons in guinea pig airways by hypertonic saline

Pedersen, Karen E., Sonya N. Meeker, Margerita M. Riccio,and Bradley J. Undem. Selective stimulation ofjugular ganglion afferent neurons in guinea pig airways by hypertonicsaline. J. Appl. Physiol. 84(2):499-506, 1998.We evaluated the ability of hyperosmolar stimulito activate afferent nerves in the guinea pig trachea and main bronchiand investigated the neural pathways involved. By usingelectrophysiological techniques, studies in vitro examined the effectof hyperosmolar solutions of sodium chloride (hypertonic saline) onguinea pig airway afferent nerve endings arising from either vagalnodose or jugular ganglia. The data reveal a differential sensitivityof airway afferent neurons to activation with hypertonic saline.Afferent fibers (both A and C fibers) with cell bodies located injugular ganglia were much more sensitive to stimulation with hypertonicsaline, compared with afferent neurons with cell bodies located innodose ganglia. Additional studies in vivo demonstrated that inhalationof aerosols of hypertonic saline induced plasma extravasation in guineapig trachea that was mediated via tachykininNK₁ receptors. Identification of adifferential sensitivity of guinea pig airway afferent nerves tohypertonic saline leads to the speculation that airway responses tohyperosmolar stimuli may result from activation of afferent neuronsoriginating predominantly from the jugular ganglion.

     

Response characteristics of Herbst corpuscles in the interosseous region of the pigeon's hind limb

The Herbst corpuscle, found only in birds, is one of the morphologically distinct types of lamellated sensory nerve endings. Its response properties were studied electrophysiologically in anesthetized pigeons by recording from: (A) afferents emerging from single Herbst corpuscles located in the interosseous region of the shank, (B) from vibration-sensitive cells found in the dorsal root ganglia near the lumbosacral enlargement of the spinal cord, and (C) from nerve fibers dissected out of the sciatic nerve. Vibration-sensitive cells in the dorsal root ganglia and in sciatic nerve fibers exhibited properties that were very similar to those found at the Herbst corpuscle itself. All three recording approaches indicated that Herbst corpuscles are vibration-sensitive mechano-receptors with broad bandpass tuning curves. With all approaches, the lowest threshold always fell in the frequency range between 400 and 800 Hz. The value of the threshold, however, varied with the method, being as low as 0.08 m with method C and as high as 1 m with method A. Regardless of method, these neurons exhibited no spontaneous activity, and their firing displayed a special sensory coding pattern at high stimulus amplitude: the nerve impulses were phase locked to the stimulus cycle, exhibiting a 1:1 relationship with it up to a frequency of 500 Hz. Comparison of these data with prior behavioral data suggests that the Herbst corpuscle peripheral mechanoreceptors are part of a vibratory sensory system which acts as a warning device, given attentive behavior.Abbreviations AP action potential - INTH interspike interval histogram     

The depressor trochanteris motoneurones and their role in the coxo-trochanteral feedback loop in the stick insect Carausius morosus

The innervation pattern of the coxal part of the depressor trochanteris muscle is described. This muscle is located inside the coxa cavity and is innervated by motoneurones contained in nerve C2. Serial sections of nerve C2 reveal that nerve C2 contains 3 large neurones (8, 5, and 3 m in diameter) in addition to many small neurones. In extracellular nerve recordings from nerve C2 3 large spikes could be recorded, which can easily be classified according to their amplitudes. Combined intracellular muscle recordings and extracellular nerve recordings revealed the physiological characteristics of these motoneurones, which are referred to here as the fast depressor trochanteris (FDTr) motoneurone and the spontaneously active slow depressor trochanteris (SDTr) motoneurone. The third motoneurone could be identified as an inhibitory motoneurone. Because this motoneurone was also found in nerves nl2, nl3, nl5 and in nerve C1 (to the levator trochanteris muscle) it is referred to here as the common inhibitor (CI) motoneurone.The hypothesis that the trochanteral hairplate (trHP) is the only effective feedback transducer for the coxo-trochanteral control loop (Schmitz 1984, 1986) is confirmed by the nerve recordings from nerve C2, because no reflex response was measured after ablation of the trHP. In addition, shaving the trHP reduces the activity of the spontaneously active SDTr motoneurone.The frequency responses of the excitatory depressor motoneurones show that the spontaneous activity of the SDTr motoneurone is modulated by the stimulus over a wide range of stimulus frequencies up to 100 Hz and that the FDTr motoneurone is reflexly activated during the same phase of the stimulus as the SDTr motoneurone. Up to 20 Hz the maximum of the motoneurone activity leads the maximum of the movement by about 60 to 80 deg. This shows that nonlinear highpass filter properties of the coxotrochanteral control system, described on the basis of force measurements in an earlier paper (Schmitz 1986), can be found already on the level of the motoneurones.     

Some characteristics of the afferent flow during noxious stimulation of the skin

Quantitative characteristics of the afferent impulse flow in a cat cutaneous nerve during stimulation of the skin with acid, needles, and pins were studied by a cross-correlation method. The appearance of a nociceptive response served as the test of noxious stimulation. Mechanical and chemical noxious stimuli, acting directly on the nerve fiber, activate the same peripheral channels as weak tactile stimuli exciting receptors. Spike trains under these circumstances differed in the absolute and relative numbers of active A and C fibers and the duration of activity in them. The nociceptive response is brought about through marked predominance of activity in C fibers compared with A fibers and through its long duration in both types of fibers but, in particular, in C fibers. An optical correlometer can be used to investigate activity of a whole nerve.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii Gor'kii State University. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 168–176, March–April, 1976.     

Responses of neurons of different hypothalamic structures to stimulation of tooth pulp and Aß afferents in the cat sciatic nerve

The response of neurons of different hypothalamic structures to stimulation of painful tooth pulp afferents and painless sciatic nerve Aß afferents was investigated during acute experiments on cats. It was found that 80.7%, 81.5%, and 71.4% of neurons of the posterior, tuberal, and anterior hypothalamus respectively, responded to stimulation of the tooth pulp. Shortest latency of response was recorded in the posterolateral hypothalamus. Latency of response was shorter in the lateral than in the medial structures throughout the hypothalamus. A distinct prevalence of excitatory response was found in neurons of the posterior area and an almost equal proportion of excitatory and inhibitory response in neurons of the tuberal and anterior hypothalamus. A high degree of convergence between noxious and nonnoxious somatic afferents were discovered in hypothalamic neurons: 85.8% of those studied responded to stimulation of the sciatic nerve Aß afferents. The comparable unidirectional response pattern of hypothalamic neurons to stimulation of tooth pump painful afferents and painless sciatic nerve Aß fibers point to the nonspecific nature of the response observed in the mainstream population of multisensory hypothalamic neurons. A small population of unimodal nociceptive neurons (14.2%) was found in the hypothalamus. Nociceptive responses of anterior hypothalamic neurons were distinguished by their long refractory phase, lasting 200–500 msec, and their low rate of reproduction during rhythmic stimulation of tooth pulp (1.5–2 Hz). Neuronal organization of the nociceptive hypothalamic afferent system is discussed together with the role of convergent and specific "nociceptive" neurons in the shaping of thalamic regulatory functions.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 171–180, March–April, 1986.     

Sensory and sympathetic nerve fibers undergo sprouting and neuroma formation in the painful arthritic joint of geriatric mice

Introduction

Although the prevalence of arthritis dramatically increases with age, the great majority of preclinical studies concerning the mechanisms that drive arthritic joint pain have been performed in young animals. One mechanism hypothesized to contribute to arthritic pain is ectopic nerve sprouting; however, neuroplasticity is generally thought to be greater in young versus old nerves. Here we explore whether sensory and sympathetic nerve fibers can undergo a significant ectopic nerve remodeling in the painful arthritic knee joint of geriatric mice.

Methods

Vehicle (saline) or complete Freund's adjuvant (CFA) was injected into the knee joint of 27- to 29-month-old female mice. Pain behaviors, macrophage infiltration, neovascularization, and the sprouting of sensory and sympathetic nerve fibers were then assessed 28 days later, when significant knee-joint pain was present. Knee joints were processed for immunohistochemistry by using antibodies raised against CD68 (monocytes/macrophages), PECAM (endothelial cells), calcitonin gene-related peptide (CGRP; sensory nerve fibers), neurofilament 200 kDa (NF200; sensory nerve fibers), tyrosine hydroxylase (TH; sympathetic nerve fibers), and growth-associated protein 43 (GAP43; nerve fibers undergoing sprouting).

Results

At 4 weeks after initial injection, CFA-injected mice displayed robust pain-related behaviors (which included flinching, guarding, impaired limb use, and reduced weight bearing), whereas animals injected with vehicle alone displayed no significant pain-related behaviors. Similarly, in the CFA-injected knee joint, but not in the vehicle-injected knee joint, a remarkable increase was noted in the number of CD68⁺ macrophages, density of PECAM⁺ blood vessels, and density and formation of neuroma-like structures by CGRP⁺, NF200⁺, and TH⁺ nerve fibers in the synovium and periosteum.

Conclusions

Sensory and sympathetic nerve fibers that innervate the aged knee joint clearly maintain the capacity for robust nerve sprouting and formation of neuroma-like structures after inflammation/injury. Understanding the factors that drive this neuroplasticity, whether this pathologic reorganization of nerve fibers contributes to chronic joint pain, and how the phenotype of sensory and sympathetic nerves changes with age may provide pharmacologic insight and targets for better controlling aging-related joint pain.     

Single unit activity in the peripheral lateral line system of the cichlid fishSarotherodon niloticus L.

Summary The activities of single afferent fibers were recorded in the trunk lateral line nerve of the cichlid fishSarotherodon niloticus L. Using both electrophysiological recordings and neuroanatomical tracing techniques, the number, arrangement, and innervation of superficial (SNs) and canal (CNs) neuromasts were determined. Both, SNs and CNs, are innervated by several afferent fibers of different diameters and efferent fibers. The CNs and SNs are neuronally separated: afferent fibers which innervate both CNs and SNs were not found. Whereas the single CN is innervated by a separate set of afferent fibers, fibers innervating the SNs within rows often branched to reach all or several SNs. The SNs within a row were thus considered to form a functional unit. With the exception of SNs on the tail fin, functional units of neuromasts were in general topographically restricted to single scales.The majority of lateral line units had resting activity. On the basis of the time interval distribution of the resting activity, 4 types of units were classified: these were labelled irregular (type I), regular (type II), bimodal (type III) and silent (type IV). Type I was the most common type of resting activity (obtained in 47.8% of the recorded units). Units with this resting activity type were identified as afferents innervating either SNs or CNs. Units with resting activity of type II represented mostly afferents of CNs if their mean activity was high (around 40 imp/s). If the mean activity of this type was below 20 imp/s the units were unresponsive to local water movements and at least some were identified as efferent fibers. Resting activity of type III was found only in units originating from CNs. Only 4% of the units were silent (type IV). These units were often identified as injured neuromasts. Units originating from CNs show higher mean resting activity than those from SNs. For both SN and CN units, the mean discharge rate of the resting activity correlated with the sensitivity to stimulation for sinusoidal water movements.During stimulation of the neuromasts by sinusoidal water movements of small amplitude and different frequencies, the response characteristics of SN and CN units were determined by linear frequency analysis under steady state conditions. Most units responded linearly to small stimulus amplitudes. In this amplitude range the units' resting activity was modulated according to the stimulus frequency. Small stimulus amplitudes proportionally changed the amount of modulation but did not alter the phase of the response. CN and SN units that responded linearly produce differing frequency responses. Whereas CNs were most sensitive at frequencies of up to 200 Hz (center frequencies between 100 and 200 Hz), the center frequencies of SNs were distributed between 10 and 70 Hz with a maximum number at about 30 Hz. Bode plots for many CN and SN units indicated that the neuromasts were sensitive to the acceleration component of the water movement.The functional significance of the differences between the two types of lateral line neuromasts (SNs and CNs) were discussed.Abbreviations SN superficial neuromast - CN canal neuromast     

Fine structure and innervation of the avian adrenal gland

Summary Apart from cholinergic nerve fibers, which make up the main part of efferent fibers to the avian adrenal gland (Unsicker, 1973b), adrenergic, purinergic and afferent nerve fibers occur. Adrenergic nerve fibers are much more rare than cholinergic fibers. With the Falck-Hillarp fluorescence method they can be demonstrated in the capsule of the gland, in the pericapsular tissue and near blood vessels. By their green fluorescent varicosities they may be distinguished characteristically from undulating yellow fluorescent ramifications of small nerve cells which are found in the ganglia of the adrenal gland and below the capsule. The varicosities of adrenergic axons exhibit small (450 to 700 Å in diameter) and large (900 to 1300 Å in diameter) granular vesicles with a dense core which is usually situated excentrically. After the application of 6-hydroxydopamine degenerative changes appear in the varicosities. Adrenergic axons are not confined to blood vessels but can be found as well in close proximity of chromaffin cells. Probably adrenergic fibers are the axons of large ganglion cells which are situated mainly within the ganglia of the adrenal gland and in the periphery of the organ and whose dendritic endings show small granular vesicles after treatment with 6-OHDA.A third type of nerve fiber is characterized by varicosities containing dense-cored vesicles with a thin light halo, the mean diameter (1250 Å) of which exceeds that of the morphologically similar granular vesicles in cholinergic synapses. Those fibers resemble neurosecretory and purinergic axons and are therefore called p-type fibers. They cannot be stained with chromalum-hematoxyline-phloxine. Axon dilations showing aggregates of mitochondria, myelin bodies and dense-cored vesicles of different shape and diameter are considered to be afferent nerve endings. Blood vessels in the capsule of the gland are innervated by both cholinergic and adrenergic fibers.Supported by a grant from the Deutsche Forschungsgemeinschaft (Un 34/1).     

Transneuronal degeneration in the Rolando substance of the primate spinal cord evoked by axotomy-induced transganglionic degenerative atrophy of central primary sensory terminals

Summary Transection of the sciatic nerve in Rhesus monkeys and the consequent transganglionic degenerative atrophy (TDA) of central terminals of primary afferents result in transneuronal degeneration of substantia gelatinosa (SG) cells. Severe degeneration is characterized by an increased electron density of the nucleus and by conspicuous shrinkage of the cytoplasm, mitochondrial swelling, dilation of cisterns of the rough-surfaced endoplasmic reticulum, accumulation of free ribosomes and an electron-dense material in the cytoplasm. In the mild form, dilation of cisternal elements of the endoplasmic reticulum, swollen mitochondria and accumulation of free ribosomes takes place. About 10% of SG cells in segment L₅ undergo the severe form whereas the rest shows signs of the mild form. Cytoplasmic alterations that occur during transneuronal degeneration seem to start at the level of subsurface cisterns. Dendrites and axons of transneuronally degenerating SG cells also show a conspicuous electron density. By analyzing the synaptic relationships of such darkened dendrites, connections in the upper dorsal horn can be deciphered. Modular units of the primary nociceptive analyzer that evaluate noxious and innocuous inputs on the basis of thin versus thick (AC/A) afferent activity and subjecting them to descending control appear to be recruited from structurally dispersed elements of synaptic glomeruli. These are arranged alongside dendritic processes of large antenna cells which relay impulses to projection cells of the spinothalamic tract.