Organization of the cortico-ponto-cerebellar pathway to the dorsal paraflocculus. An experimental study with anterograde and retrograde transport of WGA-HRP in the cat.

To reveal the organization and relative magnitude of connections from various parts of the cerebral cortex to the dorsal paraflocculus via the pontine nuclei, WGA-HRP was injected in the dorsal paraflocculus in conjunction with injection of the same tracer in various parts of the cerebral cortex in 17 cats. Termination areas of cortical fibres (anterogradely labelled) and pontine neurons projecting to the dorsal paraflocculus (retrogradely labelled) were carefully plotted in serial transverse sections. As an average of countings in ten cats, 90% of the labelled cells were found in the pontine nuclei contralateral to the injection, and the majority (70%) were located in the rostral half of the nuclei. The highest degree of overlap between anterograde and retrograde labelling was found after injections of the parietal association cortex (areas 5 and 7). In an experiment with double anterograde tracing, it was shown that both area 5 and 7 contribute substantially to the cerebral inputs to the dorsal paraflocculus. High degree of overlap also occurred after injections of several visual cortical areas (areas 17, 18, 19, 20 and the posteromedial lateral suprasylvian visual area, PMLS). Cases with injections restricted to individual visual areas indicate that they all contribute to the parafloccular input. Considerably less overlap occurred after injections of the primary sensorimotor region (SI, MI) and second somatosensory area (SII), while the supplementary motor area, the auditory cortex and gyrus cinguli probably have no or very restricted access to the dorsal paraflocculus. It is concluded that the dorsal paraflocculus has its major cortical input from the parietal association cortex and the visual cortical areas. Since all the various cortical regions studied project to largely different parts of the pontine nuclei, and overlap with neurons projecting to the dorsal paraflocculus takes place at numerous places, it follows that the pontine neurons projecting to the dorsal paraflocculus must consist of many subgroups differing with regard to their cortical input.     

Structure and localization of sympathetic neurons in the cat spinal cord

By the method of retrograde axonal transport of horseradish peroxidase (HP) structure and localization of sympathetic neurons sending axons to the cranial cervical ganglion (CCG) have been revealed ipsilaterally in the ventral horns and in 4 nuclei of the spinal cord: nucl ILp, nucl. ILf. nucl. IC, nucl. ICpe. Orientation of the neurons, their number, structure of the nuclei formed by them, degree of the CCG efferentation by the preganglionic fibres, which run from various nuclei, are different. In nucl. ILf two types of neurons have been revealed-triangle and spindle-shaped, they always orienting by their long axis in mediolateral direction. The greatest amount of HP-positive neurons are found in nucl. ILp. They form a well distinquished compact nucleus in the lateral horns. HP-labelled neurons in nucl. ILp are found at the level of segments T1-T8 with their maximal amount at the level of segments T1-T3. HP-positive neurons are detected in nucl. ILf beginning from the segment C8 up to the middle of T4, in nucl. IC-from the segment C8 up to T6, in nucl. ICpe-from the segment C8 up to T5, in the ventral horns-from the segment T1 up to T5. In rostocaudal direction from the segment C8 up to T8 the number of HP-positive neurons is decreasing, but the part of nucl. ILp neurons in the CCG efferentation, comparing to the neurons in other sympathetic structures of the spinal cord, is increasing.     

Projections of neurons of the hypothalamic locomotor region to some brainstem and spinal cord structures in the cat

Efferent projections of the thalamic locomotor region were investigated using the horseradish peroxidase technique of retrograde axonal transport. This enzyme was injected into different brain structures. Function was monitored during a micro-injection into the locomotor areas. It was found that direct descending projections from the hypothalamic locomotor region lead mainly to ipsilateral structures and reach the lumbar sections of the spinal cord. Neurons of the locomotor area of the hypothalamus make their major connections with thelocus coeruleus area and the medial brainstem reticular formation. Projections were observed from the hypothalamic locomotor region to the mesencephalic locomotor area and the locomotor strip.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 6, pp. 817–23, November–December, 1985.     

Projection to the lateral reticular nucleus from neurons located in C6-C7 segments of the spinal cord. An electrophysiological study in the cat.

Spinoreticular neurons projecting to the lateral reticular nucleus (LRN) were investigated electrophysiologically in the cervical enlargement of the cat spinal cord. Experiments were performed on alpha-chloralose anaesthetized animals. Antidromic action potentials were recorded extracellularly from cells located in C6 and C7 segments following stimulation of the ipsilateral LRN. The total sample included 50 neurons. Their cell bodies were found to be distributed in Rexed's laminae VI-VIII of the gray matter. Axonal conduction velocities ranged from 14.7 to 89.7 ms-1. Considerable differences between particular cases enabled two separate groups of slower and faster conduction to be distinguished. Values for these two groups were 14.7-44.3 ms-1 and 52.2-89.7 ms-1, respectively. Discrete differences with regard to the location of these groups were also pointed out. Such differentiation suggests that a proportion of axons from the slower conducting pool may be in fact collaterals of neurons that project to other brainstem centers or to lower levels of the spinal cord.     

Striatal projections from the lateral and posterior thalamic complexes. An anterograde tracer study in the cat

Striatal projections from the lateral intermediate (LI) and posterior (Po) thalamic complexes were studied with the anterograde tracers wheat germ agglutinin-horseradish peroxidase and Phaseolus vulgaris leucoagglutinin. Projections to the lateral part of the head and body of the caudate nucleus (CN) and to the putamen (Pu) were found to arise from the ventral parts of the caudal subdivision of the LI besides the well established sources in the intralaminar and ventral thalamic nuclei. No projections to the CN and only a few to the Pu were found to arise from the medial division of the Po. The presence of terminal and intercalated varicosities in the thalamostriatal fibers suggests that they form both terminal and en passant synapses. Thalamostriatal fibers from these thalamic sectors were unevenly distributed within the CN, with patches of either low-density innervation or with no projections at all interspersed within irregular, more densely innervated areas. The former coincided with the acetylcholinesterase-poor striosomes and the latter areas of dense projection with the extrastriosomal matrix.     

Spatial distribution of descending propriospinal tract neurons in the cat spinal cord

Quantitative estimates of the density of distribution of interneurons forming descending intersegmental connections in the cat spinal cord were obtained. Neurons were labeled by retrograde axonal transport of horseradish peroxidase injected unilaterally at different segmental levels. The mean number of labeled units per section 50 µ thick, in a given zone, was used as the measure of density. The density of distribution of the propriospinal neurons forming the longest tracts between the cervical and lumbosacral regions of the cord was found to be about half the density of distribution of neurons with short (not more than two segments) axons, and to be several times less than the corresponding value for neurons with axons of intermediate length. No marked local peaks of density of distribution of long-axon neurons were found at the level of the brachial enlargement. The number of neurons with crossed axons in most segments was close to half of the total number of propriospinal units. Zones of transverse section of the spinal cord with maximal concentrations of neurons forming direct and crossed propriospinal tracts of different lengths were determined at different levels. Correlation between the quantitative composition of propriospinal neuron populations with characteristics of influences transmitted by these populations is examined.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 96–105, January–February, 1984.     

The effect of GABA on lumbar terminations of rubrospinal neurons in the cat spinal cord

Although GABA and piperidine-4-sulphonic acid depolarize I a afferent terminations in the cat spinal cord by activation of bicuculline-sensitive GABA receptors, no evidence was obtained for a bicuculline-sensitive alteration by either gabamimetic of the electrical threshold of rubrospinal terminations in the spinal intermediate nucleus. The terminal axonal arborizations in the spinal cord of neurons in the red nucleus thus do not have GABA receptors similar to those on the cell bodies. The results are discussed in relation to the depolarizing action of GABA on some central neurons, and on neurons with peripheral cell bodies, and to probable differences in the intracellular chloride content of neurons having peripheral or central cell bodies, and thus of different embryological origin. A presynaptic depolarizing inhibitory process mediated by GABA appears to be confined to the terminals of primary afferent fibres in the mammalian central nervous system.     

Properties of axons of sympathetic preganglionic neurons in the cat lumbar spinal cord

Responses arising in ventral root filaments and antidromic discharges of single sympathetic preganglionic neurons in the lateral horn of gray matter in segment L₂ of the cat spinal cord were recorded during stimulation of the white rami communicantes in the same segment. Conduction velocities, thresholds, and refractory periods were determined for individual groups of sympathetic preganglionic fibers. Excitation was conducted more slowly along the intramedullary part of the axons of some sympathetic neurons than along the extramedullary part. In a third group of neurons studied the second antidromic discharge appeared in response to paired stimulation if the interstimulus interval was appreciably longer than their refractory period. It is postulated that axons of sympathetic preganglionic neurons in the lumber spinal cord have a thin intramedullary part and are supplied with recurrent collaterals.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 6, No. 2, pp. 143–151, March–April, 1974.     

Neuronal organization of the lateral basilar region of the cat spinal cord

The neuronal organization of the lateral basilar region (LBR) of gray matter in the cervical portion of the cat spinal cord was studied by light and electron microscopy. It was found that LBR neurons form a homogeneous group with regard to the size of their soma. The ordinary pale ultrastructure of the cytoplasm is found in 96.8% of neurons examined. The ultrastructure of the cytoplasm of the small cells (3.2%) is dark and their matrix has high electron density. Most endings on LBR neurons have spherical vesicles (of the S-type). Endings with flattened vesicles (F-type) are next in order of numerical frequency. In some endings, besides the ordinary synaptic vesicles, there are other vesicles with an osmiophilic center, and endings with a dense matrix and numerous spherical vesicles. Endings of the F-type are relatively more numerous on dendrites of LBR neurons than on their soma. Axodendritic synapses form 87.8% of the synaptic connections of the LBR, and axo-somatic synapses 9.2%. The few axo-axonal synapses are formed by small endings with small synaptic vesicles and large plaques with spherical vesicles. The latter frequently make contact with several dendrites simultaneously. The functional role of the various neuronal structures of LBR in the transmission of descending and afferent influences is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 296–302, May–June, 1972.     

Distribution of reticulospinal neurons in the chicken by retrograde transport of WGA-HRP

To determine the distribution of reticulospinal (RS) neurons in the chicken, WGA-HRP was injected into the cervical or lumbosacral enlargement either unilaterally or bilaterally. The brainstem reticular nuclei sent largely descending fibers to both the spinal enlargements. The mesencephalon (medial and lateral mesencephalic reticular formation) and the rostral pons (nucleus reticularis [n.r.] pontis oralis) project mainly to the cervical enlargement. RS neurons were mainly distributed from the pontomedullary junction to the rostral medulla including n. r. pontis caudalis and pars gigantocellularis, n. r. gigantocellularis, n. r. parvocellularis, n. r. paragigantocellularis, and n. r. subtrigeminalis. It is suggested that the majority of these neurons send axons at least as far as the lumbosacral enlargement. In the lower medulla, RS neurons were distributed in the dorsal and ventral parts of the central nucleus of the medulla.     

Synaptic links of propriospinal neurons of the lumbar section of the cat spinal cord

The distribution of propriospinal fiber terminals of the lateral funiculus in the lumbar segments of the cat spinal cord was examined by light and electron microscopy. For the selective demonstration of these terminals, preliminary hemisectioning of the brain at the boundary of the thoracic and lumbar segment, eliminating all the long descending pathways, and subsequent hemisectioning or sectioning of the lateral funiculus at the level of the third lumbar segment was carried out. It was established by staining the degenerating endings (by the Fink—Heimer method) that the terminals of the descending and ascending propriospinal fibers, which form part of the lateral and ventral funiculi, are located mainly in the lateral and medial parts of lamina VII and the dorsal section of lamina VIII, according to Rexed, as well as in the regions adjacent to the dorsolateral and ventromedial motor nuclei. A large number of these terminals is found in the corresponding regions of the gray matter on the contralateral side of the brain. Since, in the case of selective injury of the lateral funiculus the number of degenerating terminals in lamina VIII is noticeably decreased, it can be assumed that the propriospinal neuron terminals of the ventral funiculus are concentrated mainly in lamina VIII. The axons of the propriospinal neurons extend over several segments both in the ascending and in the descending directions. It was shown in an electron microscopic study of the regions in which most of the propriospinal terminals are located that these terminals are of an axo-dendritic nature and terminate in the dendrites of both inter- and motor neurons. Their degeneration can be of the "light" or "dark" type.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 401–407, July–August, 1971.     

Stabilization of intracellular recordings in the cat spinal cord using high-frequency ventilation

Stabilization of intracellular recordings by a substantial reduction of respiratory motion may be accomplished by the use of high-frequency ventilation (600-800 breaths/min). The technique is a simple one and enables maintenance of relatively constant blood gas tensions. Although the improved stability was demonstrated in experiments performed on alpha motoneurones in the thoracic spinal cord, it is anticipated that a reduced respiratory movement should benefit recordings in other spinal and supraspinal sites.