Cell Axons Research Articles

Corticofugal influences on postsynaptic processes in rubrospinal neurons in the cat brain

Composite and unitary EPSPs of red nucleus neurons evoked by stimulation of the sensomotor and association parietal cortex and nucleus interpositus of the cerebellum were studied in acute experiments on cats anesthetized with pentobarbital. A monosynaptic connection was shown to exist between not only the sensomotor, but also the association cortex, and rubrospinal neurons, in which unitary EPSPs appeared during stimulation of the association cortex after a latent period of 1.5–2.7 msec, with a peak rise time of 1.1–3.1 msec and an amplitude of 0.22–0.65 mV. Analysis of the temporal characteristics of the unitary EPSP suggested that synapses formed by fibers from the association cortex occupy a position nearer the soma than synapses formed by axons of sensomotor cortical cells.

Régulations aminergique et cholinergique du système caudal neurosécréteur de l'omble de fontaine, Salvelinus fontinalis, en relation avec l'osmo-iono-regulation

The innervation of the caudal neurosecretory system of the brook trout, Salvelinus fontinalis, was studied under light and electron microscopy in order to characterize its nature, distribution, and regulatory function over the activity of the caudal neurosecretory cells. A dual innervation of the cell bodies and axons of neurosecretory cells was disclosed. One type of axosomatic connection exhibited small lucent vesicles and large dense-cored granules. These boutons were identified as monoaminergic since they appeared depleted after reserpine treatment and they were selectively labeled with 5-OH-dopamine. In fish exposed to demineralized water, reserpine induced a condition that stimulated the synthetic activity of caudal neurosecretory cells, a clear reduction of this activity, according to morphometric (cell and nucleus diameters) and ultrastructural criteria (dimensions of the Golgi complex). By comparison, no significant variation of the synthetic activity was noted in freshwater-adapted trout treated with reserpine. A second type of innervation was also identified as cholinergic by histochemical localization of acetylcholinesterase. Electron microscopic analysis also revealed axosomatic and axoaxonic cholinergic synaptic connections with characteristic small 500-Å diameter lucent vesicles. The injection of fenitrothion, an anticholinesterase agent, enhanced discharge of neurosecretory material from axonal endings of caudal cells while the synthetic activity did not appear to be modified. Our findings suggest an important role of aminergic and cholinergic controls over the response of the caudal neurosecretory system of Salvelinus fontinalis during hyperosmotic adaptation.

The neural path probabilistic delay model

The neural path probabilistic delay (NPPD) algorithm models the neural network in a discrete-time manner analogous to the computer network. The four stages of the basic neuron cell component, i.e. neuron cell body, axon branches, synapse region, and dendrite trees are represented by the mathematical structures of cascaded Markov chains. A state probability transition matrix for the neuron cell is generated by a queueing model of signal interarrival and service rate probability density function (PDF) data. To obtain the delay value for the soma, the PDF functions respectively describing the rate of action potential generation at each cell body and neuron signal arrival at synaptic dendrite terminals, are subtracted and quantized horizontally. This quantization of service minus interarrival PDFs is analogous to the human nervous system encoding of action potential pulses. The specific state transition probability matrices associated with the axon, synapse, and dendrite stages are computed from experimental link structure data. Both PDF and link structure data are measured from neurons located in the specific section of the nervous system considered. An example of the NPPD measure is derived for a neural path in a segment of the cerebellar folium in the cerebellar cortex of the human brain, because a path in this area is initiated by a pain sensation stimulus to the cerebral cortex. Therefore, the motor response path delay parameters for the pain stimulus are of interest in the implementation of the robotic system.

Electrophoretic analysis of axonally transported proteins in rabbit vagus nerve.

Proteins synthesized in the nodose ganglia of rabbits were radiolabeled with 35S-methionine and the proteins present in the vagus nerve, at various times later, were analyzed by SDS (sodium dodecyl sulfate)-polyacrylamide gel electrophoresis. Three major groups of proteins were transported as waves of radioactivity within the nerve at rates of 15-17 mm/h, 12-15 mm/day, and 25-30 mm/day. The front of the fastest wave was composed of two proteins only, of apparent molecular weights 21,000 and 24,000. These were followed after a delay by a number of proteins of higher molecular weight, traveling at the same fast rate. The 25-mm/day wave contained several proteins including a major one of molecular weight 43,000 while the 12-mm/day wave was composed entirely of two proteins of molecular weights 54,000 and 56,000. These groups of slowly transported proteins are therefore similar to those transported much more slowly in other mammalian nerves, with the exception that no proteins with molecular weight similar to the neurofilament proteins could be detected. We have confirmed the dependence of slow transport for both groups of proteins on contact between cell body and axon and suggest that it may be a general phenomenon in all mammalian nerves.

Activity and structure of movement-signalling (corollary discharge) interneurons in a cockroach

1. Intracellular recordings were taken from interneurons in the thoracic nervous system of partly restrained American cockroaches during voluntary or imposed leg movements. 2. Two pairs of interganglionic interneurons were found which fired action potentials during voluntary extension movements of one segment of one leg, but rarely during imposed leg extensions or during other voluntary movements (Figs. 4, 5). Because these interneurons were active during a movement driven by specific muscles, they are designated corollary discharge (CD) neurons. 3. Intracellular staining of these CD interneurons showed that the soma and dendritic arbor of each were located in the ganglion that controlled the leg whose movement accompanied firing of the neuron. Furthermore, the soma was situated in and the dendritic arbor was confined to the half ganglion ipsilateral to the same leg, and each cell's axon left the ganglion in the ipsilateral connective (Figs. 7, 8). No other neurons having different physiological characteristics were found with these structural features. 4. It is suggested that such CD neurons may be common in insects and may help coordinate movements, and that they may represent a distinct class, possibly recognizable on structural grounds alone.

Neurons and their interconnections in the frontal cortex of monkeys

It was shown by the Golgi and Golgi-Kopsch method that pyramidal cells of layers II–IV in the frontal cortex of the monkeyMacaca rhesus have numeruous, mainly recurrent axon collaterals by means of which they form vertical connections. Pyramidal cells with ascending axons are found. Axons of stellate basket neurons unite pyramidal cells in both horizontal (modules) and vertical (micromodules) directions; depending on the direction of the axon collaterals, two groups of stellate neurons can be distinguished. Groups of 14 to 16 pyramidal cells whose apical dendrites are connected into bundles were found. Axons of pyramidal cells in layers II–IV descend in the composition of the pyramidal tract and give off collaterals which run toward the bodies and dendrites of neighboring pyramidal cells, united into the same group, forming terminal and en passant junctions. Besides bundles, special kinds of "local" cell groups with U-shaped axons are found.

Retinogeniculate terminations in cats: morphological differences between X and Y cell axons.

We injected horseradish peroxidase into single, physiologically identified, optic tract axons of X and Y cells in cats and studied their termination patterns in the lateral geniculate nucleus. All X cell axons innervate lamina A or A1 in narrow zones, and some sparsely innervate the medical interlaminar nucleus. All Y cell axons have broad terminal zones in laminae A and C (from the contralateral retina) or lamina A1 (if ipsilateral), and most innervate the medial interlaminar nucleus densely.

Competitive elimination of foreign motor innervation on autonomic neurones in the frog heart.

1. Somatic motoneurones are capable of forming functional synapses when redirected to vagotomized autonomic neurones in the frog heart. We tested if regenerating vagus nerves could reinnervate ganglion cells in the presence of foreign hypoglossal innervation and, furthermore, whether hypoglossal innervation persisted when vagal axons regenerated to the heart. 2. Simulating the redirected hypoglossus nerve produced a parasympathetic-like cardiac inhibition in the absence of vagal regeneration. However, when the vagus nerve was allowed to regenerate to the heart, vagal cardio-inhibition was restored and hypoglossal inhibition disappeared. 3. Intracellular recordings showed that 71% of the cardiac ganglion cells were innervated by hypoglossal axons before vagal regeneration, but that this value fell to less than 9% over a period of 40 weeks during vagal regeneration. 4. If the vagus nerve was prevented from regenerating to the heart, hypoglossal innervation did not decline, indicating that elimination of the foreign motor innervation was dependent upon vagal reinnervation. 5. Although hypoglossal terminals formed synapses only on the axons of parasympathetic ganglion cells, regenerating vagal fibres re-established synaptic contact both on axons as well as on neuronal perikarya. 6. The data indicate that in the frog parasympathetic cardiac ganglion, extensive synaptic remodelling can take place during reinnervation and that previously established, inappropriate inputs can be functionally eliminated by regeneration of the native nerve supply.

A study of the cerebral region of the visual system in the pulmonata

The distribution of central axons of receptor cells of the eyes and the locations of neurons sending axons into the optic nerves were studied in the cerebral ganglia of the pulmonate mollusksLymnaea stagnalis andHelix sp. by the method of axonal transport of cobalt chloride injected via the optic nerves. Afferent fibers of these nerves form terminal ramifications (chiefly dorsally) in the middle part of the cerebral ganglion. Some of them pass through the commissure to the symmetrical region of the opposite cerebral ganglion. Neurons innervating the eyes are located in several regions of both cerebral ganglia. InLymnaea they are distributed near the point of entry of the optic nerve, in the region of the commissure, the mesocerebrum, and the posterior part of the ganglion. InHelix these neurons are found in the same regions except in the posterior part of the ganglion. In electrophysiological experiments responses of neurons in these parts of the cerebral ganglion to adequate stimulation of the eye were recorded. Differences in the character of responses and also the presence of neurons indifferent to stimulation of the eye are evidence of the functional heterogeneity of these areas. This suggests that morphologically separate visual centers do not exist in the cerebral ganglion of the Pulmonata. Neurons giving specific responses to stimulation of the eye and evidently belonging to different levels of the visual system (afferent or efferent divisions) are closely connected both with each other and with cells of other functional systems.

Synaptic terminals in the dorsal lateral geniculate nucleus from neurons of the thalamic reticular nucleus: A light and electron microscope autoradiographic study

( 3H)-proline was injected in the caudodorsal part (visual segment) of the thalamic reticular nucleus to study its projection to the dorsal lateral geniculate nucleus. This was done by autoradiographic tracing of anterograde axonal transport of tritium at the light- and electron microscopic level. The results of the light-microscope autoradiography show that connections of the thalamic reticular nucleus are distributed along lines of projections in the dorsal lateral geniculate nucleus, indicating a retinotopic arrangement of this projection. The results of the electron microscope autoradiography provide direct evidence that axons of cells in the thalamic reticular nucleus terminate in the dorsal lateral geniculate nucleus as synaptic boutons that contain flattened synaptic vesicles, dark mitochondria and establish symmetrical synapses with perikarya and with proximal, intermediate and distal dendrites. They do not take part in intraglomerular synapses (as boutons with pleomorphic synaptic vesicles do) and are not postsynaptic to other vesicle-containing boutons in the dorsal lateral geniculate nucleus. The present results, taken in conjunction with physiological studies that have shown postsynaptic inhibitory effects of the thalamic reticular nucleus on dorsal lateral geniculate nucleus relay cells in the rat, establish a correlation of an inhibitory synapse with the presence of flattened synaptic vesicles in the corresponding synaptic boutons. Also, the observation that thalamic reticular nucleus terminals in the dorsal lateral geniculate nucleus avoid forming synapses with boutons containing pleomorphic vesicles, believed to be synaptic processes of interneurons, is indicative that the inhibitory effects are exerted monosynaptically on geniculate relay cells.

Signal transmission from rods to ganglion cells in rat retina after bleaching a portion of the receptive field.

1. Recordings from single axons of retinal ganglion cells in the rat's optic tract in response to small flashing test lights were used to follow the course of dark adaptation after exposing half of the receptive field to a bleaching light. 2. The recovery of log sensitivity followed an exponential time course in the exposed and unexposed half-fields. The curves had different time constants, with the exposed side taking longer to recover. 3. The time constants of recovery were increasing functions of exposure, but the rate of increase was different in the exposed and the unexposed half-fields. Direct exposure increased the time constant at a greater rate than did indirect exposure. 4. Comparison of the time constants of recovery in the exposed half-fields with those for pigment regeneration suggests that sensitivity recovers with the time course of rhodopsin regeneration. 5. Increment thresholds were determined using steady backgrounds which illuminated half of the receptive field. A greater threshold elevation was produced in the directly illuminated half-field compared with the half-field illuminated only by scattered light. Comparisons of the threshold-raising capacity of direct and indirect illumination were used to establish an 'upper bound' on the magnitude of light scatter. The time courses of the recovery of sensitivity after two different bleaches were compared. First, thresholds were measured in the unexposed half-field after a half-field bleach. Secondly the recovery of sensitivity after direct bleaching-exposure to the predetermined scatter upper bound' was measured. Recovery was more rapid in the latter case than the former, thus indicating that adaptation spreads laterally via some process other than light scattering.

Effect of intervening lesions on amino acid distributions in rat olfactory cortex and olfactory bulb.

Levels of the proposed neurotransmitter amino acids glutamate, aspartate, gamma-aminobutyric acid (GABA), and glycine were measured within the layered structures of the olfactory bulb and olfactory cortex following unilateral transections of the lateral olfactory tract or of virtually all fiber tracts of the olfactory peduncle. Distributions of the amino acids on both lesion and control sides were examined and compared by means of a mapping procedure. The results suggest: 1) Glutamate and aspartate are specifically associated with mitral (and presumably also tufted) cell axons and terminals in the piriform cortex. The distribution of aspartate in the olfactory bulb is further suggestive of a specific association of aspartate with mitral cell dendrites and somata. 2) Glutamate might be specifically associated with some centrifugal fibers traveling to the olfactory bulb in or near the anterior commissure. 3) GABA might be specifically related to some certrifugal fibers to the olfactory bulb in addition to its prominent association with granule cells of the bulb. 4) Glycine is unlikely to play a prominent neurotransmitter role in either the olfactory bulb or olfactory cortex.

Localization of hexokinase in neural tissue: electron microscopic studies of rat cerebellar cortex.

The distribution of hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) in the rat cerebellar cortex has been studied at the electron microscopic level using the peroxidase-antiperoxidase procedure. Extensive staining of cytoplasmic regions, with some increased staining at mitochondrial profiles, was seen in the cell bodies of both neurons (basket, stellate, Lugaro, Golgi, and granule cells) and astrocytes. Oligodendrocytes showed little or no detectable staining. Purkinje cell perikarya were much less intensely stained than were the perikarya of other neurons. The initial portion of the Purkinje dendrite was, like the perikaryon from which it emerged, lightly stained. More intense staining was seen in the secondary and tertiary branches of the Purkinje dendrite, but the terminal branches were devoid of stain. Granule cell dendrites were well stained in their initial portions but devoid of stain in their terminal dendritic digits which form part of the cerebellar glomeruli. In contrast to the unstained granule cell dendritic digits, the central mossy fiber nerve terminal of the glomerulus exhibited intense staining of the mitochondrial profiles and of synaptic vesicles adjacent to the mitochondria. Axons of basket cells showed intense staining in the segments adjacent to the Purkinje cell soma, while terminal twigs of the basket axons in the pinceau surrounding the (unstained) initial segment of the Purkinje axon showed markedly decreased staining intensity. These results indicate that there may be substantial variation in hexokinase levels between the various regions of neuronal processes. Hexokinase was seen at both cytoplasmic and mitochondrial locations in a variety of cells. It does not appear likely that location of hexokinase can be directly correlated with cell type, i.e., with neurons versus glia.

Glio-axonic junctional like complexes at the mauthner cell's axon cap of teleosts: A possible morphological basis for field effect inhibitions

Differentiated contacts were identified by electron microscopy between glia and axons as they enter the axon cap which surrounds the initial segment of the teleost's Mauthner cell. At these regions, the cleft of adjacent membranes is 20–25 nm wide and contains clods of electron-dense material with a pseudo-periodicity of 10–30 nm. These junctions, referred to as ‘septate-like junctions’, presumably contribute to the compartmentalization of the axon cap and, therefore, to its elevated resistivity which underlies the generation of field effect inhibitions.

The olivocerebellar system. I. Delayed and slow inhibitory effects: An overlooked salient feature of cerebellar climbing fibers

(1) Chemical destruction of the inferior olive (ION), or midline section interrupting the climbing fibers (CFs) rapidly resulted in marked modifications of Purkinje cell (P. cell) simple spike (SS) firing rate and pattern. (2) After CF deafferentation, P. cells at first about doubled their SS frequency which further increased for the next 10 min. (3) Besides the increase in the firing rate, the spike train became much more regular, which in part seemed to be linked to mass oscillations of the neuronal circuitry, as revealed by strong oscillations of background noise. (4) After ION destruction CF activity could be supplied for by juxtafastigial (JF) stimulation which reduced SS frequency again while the firing became much less regular. These effects were shown to be due to the all-or-nothing activity of the CF and not to the simultaneous stimulation of mossy fibers (MFs) or P. cell axons. Neither were they ascribable to CF collaterals. The differences between this new powerful inhibitory action of the CF system on the P.cell and the well documented pause mechanism is discussed. (5) A quantitative relationship has been established between complex spikes (CSs) and SS firing rates. A steady 2/sec CS frequency was shown to effectively silence the P.cell. (6) When CF stimulation was discontinued, an ‘off’ effect was described. It consisted of an initial rise in SS frequency developing in 9 sec, and a delayed further increase unfolding in about 10 min. (7) When CF stimulation began, an ‘on’ effect was observed, which evolved with an exponential-like kinetic of very variable time-constant seemingly depending on past history.

Dark adaptation within the receptive field centre of rat retinal ganglion cells.

1. Recordings from single axons of retinal ganglion cells in the rat's optic tract were used to determine whether bleaching a small area of the receptive field reduced sensitivity globally or locally, near the bleached photoreceptors. 2. When a suprathreshold test spot was alternated between two equally sensitive positions, the ganglion cell gave an approximately balanced response. The balance was upset if a small-spot bleach was selectively applied to one position. Recovery of the balanced condition was rapid. 3. Varying the duration of a constant illuminance bleach varied the duration of the imbalance following the bleach. 4. The recovery of sensitivity after small-spot bleaches was measured both at the location of the bleach and also at another location, initially equally sensitive. The recovery at the bleached location lagged recovery at the unbleached location; but even in the bleached location, the return of sensitivity was rapid. 5. Recovery of sensitivity after half-field bleaches was measured in the bleached and unbleached halves of the receptive field. Recovery in the bleached half lagged that in the unbleached half. 6. A comparison between the effects of a small-spot bleach and a half-field bleach of the same strength show that the duration of dark adaptation depends on the area of the bleach.

Light adaptation within the receptive field centre of rat retinal ganglion cells.

1. Responses from axons of single retinal ganglion cells in the rat's optic tract were used to measure the pooling of adaptive signals within the cells' receptive field. Computer-aided analyses of response measurements were used to evaluate sensitivity at a number of field locations. 2. A small adapting spot caused a localized decrease in sensitivity within the receptive field centre of ON- and OFF-centre ganglion cells. 2. The functions describing response versus test luminance were similar in shape for all test and adaptation configurations. This assured that, using a fixed criterion response, sensitivity determinations could be made just as well in any receptive field location and under any of the experimental conditions. 4. A concentric surround, antagonistic to the receptive field centre, was readily apparent only under conditions of light adaptation. Experiments on the local effects of small adapting spots, conducted with selective surround adaptation, showed that the non-uniform spread of adaptation within the receptive field centre was not linked to surround intrusion. 5. The possibility that the photopic mechanism intruded to contaminate these results was considered and rejected. 6. When a suprathreshold spot was alternated between two equally sensitive positions, the ganglion cell gave an approximately balanced response. An upset of this balance was produced by placing a small adapting spot at either position, thus demonstrating, in another way, the non-uniform spread of adaptation within the receptive field centre. 7. It is concluded that significant pooling of adaptation effects occurs prior to the combination of influences which contribute to the centre response of a ganglion cell.

Evidence that the different classes of relay cells of the cat's lateral geniculate nucleus terminate in different layers of the striate cortex.

Small electrophoretic injections of horseradish peroxidase (HRP) were made with recording microelectrodes in different layers of area 17 of the cat. The sizes and locations of labeled relay cells in the lateral geniculate nucleus (LGNd) were then studied. Layer I was found to receive inputs mainly from small LGNd cells (13--21 micrometer). These cells were located in the parvocellular C laminae and the MIN. Layer II and the upper portion of layer III were not found to receive LGNd afferents. Lower layer III was found to receive inputs mainly from small to medium-sized relay cells. These cells were located in the A laminae and the parvocellular C laminae. Layer IVab and the layer III--IV border region were found to receive afferents from predominantly large LGNd neurons (greater than 20 micrometers). These cells were located in alminae A, A1, C, and the MIN. Layer IVc was found to receive inputs from mostly small to medium-sized cells (15--23 micrometer). Nearly all of these cells were in the A laminae although some small cells in laminae C were observed following layer IVc injections which involved the layer IV--V border region. Layer V, away from the layer IV--V border region, was not found to receive LGNd afferents. Finally, layer VI was found to receive inputs from both large and small relay cells. These cells were all located in the A laminae. In the light of previous findings, these results suggest that the terminals of W, X, and Y cell axons are segregated within the cat's striate cortex: W cells projecting to layer 1, the deeper portion of layer III and the layer IV--V border region; X cells projecting heavily to layer IVc with a minor projection to layer VI and possibly also to lower layer III; Y cells projecting heavily to layer IVab and the layer III-IV border region with a smaller projection to layer VI.

Glycine, GABA and synaptic inhibition of reticulospinal neurones of lamprey.

1. Intracellular recordings were made from the cell bodies and axons of giant reticulospinal neurones (Müller cells) of the lamprey and the effects of a variety of putative neurotransmitters tested. Bath-applied acetylcholine, carbamylcholine, norepinephrine, dopamine, histamine and serotonin were without effect. Glycine and gamma-aminobutyric acid (GABA) hyperpolarized and reduced the input resistance of cell bodies but had no effect on the membrane conductance of axons. 2. The threshold dose of bath-applied GABA or glycine for a conductance change in somata was about 0.5 mM and the maximum effect was reached at about 10 mM. The maximum conductance change produced by glycine was always greater than that produced by GABA. 3. Replacement of the sodium in the bathing saline with lithium or choline prolonged the conductance change produced by ionophoretically applied glycine or GABA, suggesting the presence of sodium-dependent uptake systems for glycine and GABA. 4. The reversal potentials for responses to ionophoretically applied glycine and GABA average about --83 mV, the same as that for the inhibitory post-synaptic potential (i.p.s.p.) produced in Müller cells by stimulation of the ipsilateral vestibular nerve. 5. The i.p.s.p. and drug responses appeared to involve an increase in chloride conductance, since their reversal potentials were shifted appropriately by changes in either internal or external chloride. 6. Changes in extracellular potassium concentration also changed i.p.s.p. and drug reversal potentials. However, these effects could be attributed to secondary changes in internal chloride. 7. The receptors for GABA and glycine appeared to be different because of the absence of cross-desensitization and because, at doses below 20 microM, picrotoxin and bicuculline selectively blocked GABA responses while strychnine selectively blocked glycine responses. 8. At concentrations of 20 microM, strychnine eliminated the i.p.s.p. while picrotoxin and bicuculline had no effect. Further, the i.p.s.p. and glycine response of Müller cells located in the isthmic region of the midbrain had the same threshold sensitivity to strychnine. However, the glycine response of other Müller cells was more sensitive to strychnine than was the i.p.s.p. 9. We conclude that glycine is a better candidate for the inhibitory transmitter onto Müller cells than is GABA.

The structure and distribution of the cross-striated fibril and associated membranes in guinea pig photoreceptors.

Examination of longitudinally and transversely sectioned photoreceptor cells of the guinea pig retina revealed an aggregate of thin filaments forming a single cross-striated fibril coursing through the full length of the non-receptor portion of the cell. The fibril begins as the ciliary rootlet from the region of the basal body of the connecting cilium. From the basal body it passes between the mitochondria of the ellipsoid and along the Golgi zone of the myoid region of the inner segment, narrowing from an irregularly shaped bundle to a ribbon-shaped aggregate. The fibril separates into discrete strands, each curving along the nucleus, reuniting into a single bundle to pass down the cell's axon, and terminating deep within the synaptic terminal. The fibril is flanked by two separate membranous saccules, each continuous along nearly its full length. The fibril's extensive course in the guinea pig and its association with continuous membranes necessitates a reexamination of earlier proposals for the function of cross-striated filamentous structures in photoreceptor cells.