Anatomical Studies of the Spinocervical Tract of the Rat

The retrograde transport of horseradish peroxidase (HRP) was used to identify and examine the cells of origin of the spinocervical tract (SCt) in the rat. Initially, precise data on the boundaries of the rat lateral cervical nucleus (LCn) were gathered after injecting HRP into the ventrobasal thalamus. These data indicated that the LCn of the rat is restricted to a region on the extreme lateral edge of the dorsalmost portion of the lateral funiculus (DLf) within spinal segment C₂ Following small iontophoretic injections of HRP that were restricted to this area, labeled SCt neurons were found in the ipsilateral nucleus proprius at all levels of the spinal cord but were most numerous in the cervical enlargement. Lesion studies indicated that the overwhelming majority of SCt axons ascend to the LCn within the DLf. In an attempt to determine whether our injection techniques labeled a significant number of cells through axons of passage, HRP injections were made in the DLf ventral to the LCn. Such injections labeled, presumably through axons of passage, cells in several areas of the spinal cord gray matter, including a large number in the contralateral marginal zone Injections in areas immediately rostral to the LCn labeled 20% or less of the total number of cells within the enlargements that were labeled by injections into the LCn. Thus, the majority of cells labeled by injections of HRP into the LCn were labeled through preterminal fibers or terminals themselves. The cells of origin of the SCt in the rat are similar in location to those in the cat but far fewer in number.     

Medial, intralaminar, and lateral terminations of lumbar spinothalamic tract neurons: a fluorescent double-label study

A dorsolateral spinothalamic tract (DSTT), consisting primarily of lamina I neurons, was confirmed in the cat lumbar spinal cord by the use of thalamic injections of fluorescent dyes combined with selective thoracic spinal cord lesions. In addition, collateralization of spinothalamic tract (STT) terminations to medial, lateral, and intralaminar thalamic regions was investigated by injections of two different fluorescent dyes into pairs of these regions. The results of this study indicate that less than 15% of cat lumbar STT neurons collateralize to more than one of the thalamic regions evaluated. Lumbar lamina I cells project to the lateral and to the medial thalamus (13% collateralize to these two regions) and have only a scant projection to the intralaminar thalamus. Lumbar laminae IV-VI STT cells are very few in cat and demonstrate almost no collateralization to multiple thalamic areas. Neurons of laminae VII-X project equally to the three thalamic regions evaluated, and approximately 10-14% of cells from this laminar group collateralize to any two of the thalamic sites evaluated.     

Descending monoaminergic pathways in the primate spinal cord.

The distribution of monoamine axons and terminals within the spinal cord of a primate (Macaca mulatta) was studied with the Falck-Hillarp histofluorescence technique for the demonstration of biogenic amines. Catecholamine and indoleamine varicosities appeared qualitatively similar to those previously reported for the rat although the indoleamine terminals were difficult to visualize and were not studied in great detail. Catecholamine fibers innervate the substantia gelatinosa, marginal layer, intermediolateral cell column, ventral horn and the region surrounding the central canal. The location of monoamine axons, as revealed by spinal cord ligation, corresponds to that in the rat and cat with the exception of the dorsolateral region of white matter where fluorescent axons are not visible in the primate.     

Anatomical organization of motoneurons and interneurons in the mudpuppy (Necturus maculosus) brachial spinal cord: the neural substrate for central pattern generation

The isolated brachial spinal cord of the mudpuppy is useful for studies of neural networks underlying forelimb locomotion, but information about its anatomy is scarce. We addressed this issue by combining retrograde labeling with fluorescent tracers and confocal microscopy. Remarkably, the central region of gray matter was aneural and contained only a tenuous meshwork of glial fibers and large extracellular spaces. Somata of motoneurons (MNs) and interneurons (INs), labeled retrogradely from ventral roots or axons in the ventro-lateral funiculus, respectively, were confined within a gray neuropil layer abutting the white matter borders, while their dendrites projected widely throughout the white matter. A considerable fraction of labeled INs was found contralaterally with axons crossing beneath a thick layer of ependyma surrounding the central canal. Dorsal roots (DRs) produced dense presynaptic arbors within a restricted dorsal region containing afferent terminations, within which dorsally directed MN and IN dendrites mingled with dense collections of synaptic boutons. Our data suggest that a major fraction of synaptic interactions takes place within the white matter. This study provides a detailed foundation for electrophysiological experiments aimed at elucidating the neural circuits involved in locomotor pattern generation.     

Localization and distribution patterns of nicotinamide adenine dinucleotide phosphate diaphorase exhibiting axons in the white matter of the spinal cord of the rabbit

The funicular distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-exhibiting axons was examined in the white matter of the rabbit spinal cord by using horizontal, parasaggital, and transverse sections. Four morphologically distinct kinds of NADPHd-exhibiting axons (2.5–3.5 m in diameter) were identified in the sulcomarginal fasciculus as a part of the ventral column in the cervical and upper thoracic segments and in the long propriospinal bundle of the ventral column in Th3–L3 segments. Varicose NADPHd-exhibiting axons of the sympathetic preganglionic neurons, characterized by widely spaced varicosities, were found in the ventral column of Th2–L3 segments. A third kind of NADPHd-positive ultrafine axons, 0.3–0.5 m in diameter with numerous varicosities mostly spherical in shape, was identified in large number within Lissauer's tract. The last group of NADPHd-exhibiting axons (1.0–1.5 m in diameter) occurred in the Lissauer tract. Most of these axons were traceable for considerable distances and generated varicosities varying in shape from spherical to elliptical forms. The majority of NADPHd-exhibiting axons identified in the cuneate and gracile fascicles were concentrated in the deep portion of the dorsal column. An extremely reduced number of NADPHd-exhibiting axons, confirmed by a computer-assisted image-processing system, was found in the dorsal half of the gracile fascicle. Axonal NADPHd positivity could not be detected in a wide area of the lateral column consistent with the location of the dorsal spinocerebellar tract. Numerous, mostly thin NADPHd-positive axonal profiles were detected in the dorsolateral funiculus in all the segments studied and in a juxtagriseal portion of the lateral column as far as the cervical and lumbar enlargements. A massive occurrence of axonal NADPHd positivity was detected in the juxtagriseal layer of the ventral column all along the rostrocaudal axis of the spinal cord. The prominent NADPHd-exhibiting bundles containing thick, smooth, nonvaricose axons were identified in the mediobasal and central portion of the ventral column. First, the sulcomarginal fasciculus was found in the basal and medial portion of the ventral column in all cervical and upper thoracic segments. Second, more caudally, a long propriospinal bundle displaying prominent NADPHd positivity was localized in the central portion of the ventral column throughout the Th3–L3 segments.     

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.     

Ascending and descending projections of the lateral vestibular nucleus in the rat

The tracer neurobiotin was injected into the lateral vestibular nucleus in rat and the efferent fiber connections of the nucleus were studied. The labeled fibers reached the diencephalon rostrally and the sacral segments of the spinal cord caudally. In the diencephalon, the ventral posteromedial and the gustatory nuclei received the most numerous labeled fibers. In the mesencephalon, the inferior colliculus, the interstitial nucleus of Cajal, the nucleus of Darkschewitch, the periaqueductal gray matter and the red nucleus received large numbers of labeled fibers. In the rhombencephalon, commissural and internuclear connections originated from the lateral vestibular nucleus to all other vestibular nuclei. The medioventral (motor) part of the reticular formation was richly supplied, whereas fewer fibers were seen in the lateral (vegetative) part. In the spinal cord, the descending fibers were densely packed in the anterior funiculus and in the ventral part of the lateral funiculus. Collaterals invaded the entire gray matter from lamina IX up to lamina III; the fibers and terminals were most numerous in laminae VII and VIII. Collateral projections were rich in the cervical and lumbosacral segments, whereas they were relatively poor in the thoracic segments of the spinal cord. It was concluded that the fiber projection in the rostral direction was primarily aimed at sensory-motor centers; in the rhombencephalon and spinal cord, fibers projected onto structures subserving various motor functions.     

Hrp-labeled sources of descending propriospinal pathways in cats

Unilateral injections of horseradish peroxidase into the cat spinal cord at different segmental levels revealed a laminar distribution of spinal interneurons that are sources of ipsilateral and contralateral propriospinal pathways of different lengths. The majority of the long pathways connecting cervical and lumbar segments are formed by neurons located in the central quadrants (laminae VII and VIII) bilaterally; a few such neurons also are present in the marginal layer and in lateral zones at the base of the dorsal horn (ipsilaterally). The zones containing numerous propriospinal neurons forming short (extending over a few segments) connections were more extensive. In the lumbar portion neurons which were sources of short uncrossed pathways tended to be concentrated in the lateral areas of the base of the dorsal horn, intermediate zone, and ventral horn, whereas sources of crossed pathways were concentrated in the ventromedial zones of gray matter. In the cervical portion "short" propriospinal neurons forming both ipsilateral and contralateral projections were concentrated in the lateral zones of gray matter. Neurons of the marginal layer and substantia gelatinosa and neurons of intermediolateral sympathetic nuclei also were sources of descending propriospinal pathways. Some propriospinal axons were intermediate in length. The distribution of neurons with axons of this kind largely coincided with the distribution of neurons that were sources of long propriospinal pathways. The connection between the spatial distribution of different groups of propriospinal neurons and the organization of the synaptic inputs into them, and also correlation between the morphological and functional characteristics of these neurons are discussed.     

Distributional pattern of serotonin-immunoreactive nerve fibers in the lateral geniculate nucleus of the rat,cat and monkey (Macaca fuscata)

Summary The distribution of serotonin-containing nerve fibers in the lateral geniculate nucleus (LGN) of the rat, cat, and monkey (Macaca fuscata) was studied by use of the peroxidase-antiperoxidase method and an antiserum against serotonin. In all three species, the pattern of fibers was denser in the ventral portion of the LGN (LGNv) than in the dorsal nuclear portion (LGNd). In the LGNd of rat, serotonin-immunoreactive fibers were evenly distributed in the form of a dense network, but in cat and monkey there were marked regional differences. Serotonin-immunoreactive elements were most numerous in the C complex and medial interlaminal nucleus of cat, and in the S layer and interlaminar zones of Macaca fuscata.Supported by a grant from the Ministry of Education, Science, and Culture of Japan (No. 57214028)     

Distribution of trigeminothalamic and spinothalamic lamina I terminations in the cat

The distribution in the thalamus of terminal projections from lamina I neurons of the trigeminal, cervical, and lumbosacral dorsal horn was investigated with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in the cat. Iontophoretic injections were guided by single- and multi-unit physiological recordings. The injections in particular cases were essentially restricted to lamina I, whereas in others they spread across laminae I-III or laminae I-V. The trigemino- and spinothalamic (TSTT) terminations were identified immunohistochemically. In all cases, regardless of the level of the injections, terminal fibers were consistently distributed in three main locations: the submedial nucleus; the ventral aspect of the basal ventral medial nucleus and ventral posterior nuclei; and, the dorsomedial aspect of the ventral posterior medial nucleus. The terminal fields in the submedial nucleus and the ventral aspect of the ventral posterior group were topographically organized. Terminations along the ventral aspect of the ventral posterior group extended posterolaterally into the caudal part of the posterior nucleus and anteromedially into the ventromedial part of the ventral lateral nucleus. In several cases with trigeminal lamina I injections, a terminal labeling patch was observed within the core of the ventral posterior medial nucleus. In cases with spinal lamina I injections, terminations were also consistently found in the lateral habenula, the parafascicular nucleus, and the nucleus reuniens. Isolated terminal fibers were occasionally seen in the zona incerta, the dorsomedial hypothalamus, and other locations. These anatomical observations extend prior studies of TSTT projections and identify lamina I projection targets that are important for nociceptive, thermoreceptive, and homeostatic processing in the cat. The findings are consistent with evidence from physiological (single-unit and antidromic mapping) and behavioral studies. The novel identification of spinal lamina I input to the lateral habenula could be significant for homeostatic behaviors.     

Distribution of trigeminothalamic and spinothalamic lamina I terminations in the cat

The distribution in the thalamus of terminal projections from lamina I neurons of the trigeminal, cervical, and lumbosacral dorsal horn was investigated with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in the cat. Iontophoretic injections were guided by single- and multi-unit physiological recordings. The injections in particular cases were essentially restricted to lamina I, whereas in others they spread across laminae I–III or laminae I–V. The trigemino- and spinothalamic (TSTT) terminations were identified immunohistochemically. In all cases, regardless of the level of the injections, terminal fibers were consistently distributed in three main locations: the submedial nucleus; the ventral aspect of the basal ventral medial nucleus and ventral posterior nuclei; and, the dorsomedial aspect of the ventral posterior medial nucleus. The terminal fields in the submedial nucleus and the ventral aspect of the ventral posterior group were topographically organized. Terminations along the ventral aspect of the ventral posterior group extended posterolaterally into the caudal part of the posterior nucleus and anteromedially into the ventromedial part of the ventral lateral nucleus. In several cases with trigeminal lamina I injections, a terminal labeling patch was observed within the core of the ventral posterior medial nucleus. In cases with spinal lamina I injections, terminations were also consistently found in the lateral habenula, the parafascicular nucleus, and the nucleus reuniens. Isolated terminal fibers were occasionally seen in the zona incerta, the dorsomedial hypothalamus, and other locations. These anatomical observations extend prior studies of TSTT projections and identify lamina I projection targets that are important for nociceptive, thermoreceptive, and homeostatic processing in the cat. The findings are consistent with evidence from physiological (single-unit and antidromic mapping) and behavioral studies. The novel identification of spinal lamina I input to the lateral habenula could be significant for homeostatic behaviors.     

Spinal projections from the rhombencephalon in the toad

Rhombencephalic cell groups projecting to the spinal cord are demonstrated following single pressure injections and/or iontophoretic ejections of HRP solution in either cervical or lumbar enlargements of the toad spinal cord. A group uptake and transport of HRP were obtained with both application techniques, when sufficiently long survival times (8-11 days) were used. Following injections in the cervical cord labeled cells are located mostly in the ventral nucleus of the VIIIth nerve and in the medial zone of the rhombencephalic reticular formation, i.e. the nucleus reticularis inferior, medius and superior. Following injections in the lumbar enlargement the majority of labeled cells are situated in the caudalmost portion of the ventral nucleus of the VIIIth nerve and in the nucleus reticularis inferior. These observations indicate that in the toad the main supraspinal descending pathways from the rhombencephalon originate in the ventral nucleus of the VIIIth nerve and the medial zone of the reticular formation, and that both these pathways are somatotopically organized.     

Experimental morphological study of endings of propriospinal fibers of the lateral funiculus in the cat cervical spinal cord

The distribution and ultrastructure of terminals of the propriospinal fibers of the lateral funiculus in the cervical segments of the cat spinal cord were studied by the experimental degeneration method. A preliminary lateral hemisection of the spinal cord was carried out 5–6 months earlier at the level of segments C2 or C3 to destroy all the long descending pathways; the lateral funiculus was then divided at the level of C4 or C5. It was shown by the method of Fink and Heimer that terminals of descending and ascending propriospinal pathways damaged by the second division are distributed in the gray matter ipsilaterally in the lateral zones of Rexed's laminase V–VII and also in the dorsolateral motor nuclei. An electron-microscopic study showed that the synapses of the degenerating terminals are mainly axo-dendritic in type and account for 14.5% of the total number of terminals counted. Residual synaptic vesicles in these terminals were spherical in shape. The mean diameter of the degenerating myelinated propriospinal fibers in the lateral funiculus was 10±3 µ. The results of this investigation were compared with those of electrophysiological investigations of the function of propriospinal neurons.     

Microtubule-associated protein 2 within axons of spinal motor neurons: associations with microtubules and neurofilaments in normal and beta,beta'-iminodipropionitrile-treated axons

We have examined the distribution of microtubule-associated protein 2 (MAP2) in the lumbar segment of spinal cord, ventral and dorsal roots, and dorsal root ganglia of control and beta,beta'-iminodipropionitrile- treated rats. The peroxidase-antiperoxidase technique was used for light and electron microscopic immunohistochemical studies with two monoclonal antibodies directed against different epitopes of Chinese hamster brain MAP2, designated AP9 and AP13. MAP2 immunoreactivity was present in axons of spinal motor neurons, but was not detected in axons of white matter tracts of spinal cord and in the majority of axons of the dorsal root. A gradient of staining intensity among dendrites, cell bodies, and axons of spinal motor neurons was present, with dendrites staining most intensely and axons the least. While dendrites and cell bodies of all neurons in the spinal cord were intensely positive, neurons of the dorsal root ganglia were variably stained. The axons of labeled dorsal root ganglion cells were intensely labeled up to their bifurcation; beyond this point, while only occasional central processes in dorsal roots were weakly stained, the majority of peripheral processes in spinal nerves were positive. beta,beta'- Iminodipropionitrile produced segregation of microtubules and membranous organelles from neurofilaments in the peripheral nervous system portion and accumulation of neurofilaments in the central nervous system portion of spinal motor axons. While both anti-MAP2 hybridoma antibodies co-localized with microtubules in the central nervous system portion, only one co-localized with microtubules in the peripheral nervous system portion of spinal motor axons, while the other antibody co-localized with neurofilaments and did not stain the central region of the axon which contained microtubules. These findings suggest that (a) MAP2 is present in axons of spinal motor neurons, albeit in a lower concentration or in a different form than is present in dendrites, and (b) the MAP2 in axons interacts with both microtubules and neurofilaments.     

Primary projections of the trigeminal nerve in two species of sturgeon: Acipenser oxyrhynchus and Scaphirhynchus platorynchus

Horseradish peroxidase histochemical studies of afferent and efferent projections of the trigeminal nerve in two species of chondrostean fishes revealed medial, descending and ascending projections. Entering fibers of the trigeminal sensory root project medially to terminate in the medial trigeminal nucleus, located along the medial wall of the rostral medulla. Other entering sensory fibers turn caudally within the medulla, forming the trigeminal spinal tract, and terminate within the descending trigeminal nucleus. The descending trigeminal nucleus consists of dorsal (DTNd) and ventral (DTNv) components. Fibers of the trigeminal spinal tract descend through the lateral alar medulla and into the dorsolateral cervical spinal cord. Fibers exit the spinal tract throughout its length, projecting to the ventral descending trigeminal nucleus (DTNv) in the medulla and to the funicular nucleus at the obex. Retrograde transport of HRP through sensory root fibers also revealed an ascending bundle of fibers that constitutes the neurites of the mesencephalic trigeminal nucleus, cell bodies of which are located in the rostral optic tectum. Retrograde transport of HRP through motor root fibers labeled ipsilateral cells of the trigeminal motor nucleus, located in the rostral branchiomeric motor column.     

The Glutamatergic Neurons in the Spinal Cord of the Sea Lamprey: An In Situ Hybridization and Immunohistochemical Study

Glutamate is the main excitatory neurotransmitter involved in spinal cord circuits in vertebrates, but in most groups the distribution of glutamatergic spinal neurons is still unknown. Lampreys have been extensively used as a model to investigate the neuronal circuits underlying locomotion. Glutamatergic circuits have been characterized on the basis of the excitatory responses elicited in postsynaptic neurons. However, the presence of glutamatergic neurochemical markers in spinal neurons has not been investigated. In this study, we report for the first time the expression of a vesicular glutamate transporter (VGLUT) in the spinal cord of the sea lamprey. We also study the distribution of glutamate in perikarya and fibers. The largest glutamatergic neurons found were the dorsal cells and caudal giant cells. Two additional VGLUT-positive gray matter populations, one dorsomedial consisting of small cells and another one lateral consisting of small and large cells were observed. Some cerebrospinal fluid-contacting cells also expressed VGLUT. In the white matter, some edge cells and some cells associated with giant axons (Müller and Mauthner axons) and the dorsolateral funiculus expressed VGLUT. Large lateral cells and the cells associated with reticulospinal axons are in a key position to receive descending inputs involved in the control of locomotion. We also compared the distribution of glutamate immunoreactivity with that of γ-aminobutyric acid (GABA) and glycine. Colocalization of glutamate and GABA or glycine was observed in some small spinal cells. These results confirm the glutamatergic nature of various neuronal populations, and reveal new small-celled glutamatergic populations, predicting that some glutamatergic neurons would exert complex actions on postsynaptic neurons.     

Afferent and efferent components of the facial nerve in a frog,Rana pipiens

Summary The seventh cranial nerve in Rana pipiens is a slender nerve with limited peripheral distribution. We investigated the afferent and efferent components of this nerve by labeling its major branch, the hyomandibular, with horseradish peroxidase. The efferent portion of the seventh nerve originates from a small cell group in the upper medulla which contains two subdivisions. Afferent fibers carried in nerve VII travel in the solitary tract and the dorsolateral funiculus. The solitary component consists of a small number of ascending fibers that reach the level of the trigeminal nucleus and a large descending component that terminates slightly caudal to the obex in the commissural nuclei of the solitary complex. Afferent fibers also descend in the dorsolateral funiculus; many of these fibers cross dorsal to the central canal in the lower medulla. Most of the fibers in the dorsolateral funiculus terminate in the ipsilateral and contralateral dorsal horns and in nuclei of the dorsal column. A few ipsilateral fibers reach lower thoracic levels of the spinal cord.     

Projection of cervical dorsal root fibers to the medulla oblongata in the brush-tailed possum, Trichosurus vulpecula

This study describes the projection of cervical spinal afferent nerve fibers to the medulla in the brush-tailed possum, a marsupial mammal. After single dorsal roots (between C2 and T1) were cut in a series of animals, the Fink-Heimer method was used to demonstrate the projection fields of fibers entering the CNS via specific dorsal roots. In the high cervical spinal cord, afferent fibers from each dorsal root form a discrete layer in the dorsal funiculus. The flattened laminae from upper cervical levels are lateral and those from lower cervical levels are medial within the dorsal columns. All afferent fibers at this level are separated from gray matter by the corticospinal fibers in the dorsal funiculus. All cervical roots project throughout most of the length of the well-developed main cuneate nucleus in a loosely segmentotopic fashion. Fibers from rostral roots enter more lateral parts of the nucleus, and fibers from lower levels pass to more medial areas; but terminal projection fields are typically large and overlap extensively. At more rostral medullary levels, fibers from all cervical dorsal roots also reach the external cuneate nucleus. The spatial arrangement here is more complex and more extensively overlapped than in the cuneate nucleus. Rostral cervical root fibers reach ventral and ventrolateral areas of the external cuneate nucleus and continue to its rostral pole; more caudal root fibers project to more dorsal and medial regions within the nucleus. These results demonstrate that projection patterns of spinal afferents in this marsupial are similar to those seen in the few placental species for which detailed data concerning this system are available.     

Effectiveness of ascending synaptic influences from various spinal funiculi on reticulospinal neurons in cats

Activity of reticulospinal neurons evoked by stimulation of the ventral, ventrolateral, dorsolateral, and dorsal funiculi of the spinal cord was recorded extracellularly in cats anesthetized with chloralose. Responses of 57 reticulospinal neurons, of which 22 projected into the ventral funiculus, 20 into the ventrolateral, and 15 into the dorsolateral, were studied. The functional properties (conduction velocity and refractory period) and the location of the neurons of the above-mentioned groups in the medulla did not differ appreciably. The most effective synaptic activation of all neurons was observed during stimulation of the dorsal and dorsolateral funiculi. Responses to stimulation of the dorsal funiculus had the lowest threshold. These responses arose in reticulospinal neurons of the ventral and ventrolateral funiculi after the shortest latent period. The effectiveness of synaptic influences from the dorsal and dorsolateral funiculi was identical in the group of neurons of the dorsolateral funiculus. Correlation between activity evoked by stimulation of the dorsal funiculus in reticulospinal neurons and peripheral nerves indicated that the responses appeared in these cells to stimulation of muscular (groups I and II) and cutaneous (group II) afferent fibers. The results indicate that impulses from low-threshold muscular and cutaneous afferents, which effectively activate reticulospinal neurons, are transmitted along ascending pathways of the dorsal funiculi.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 254–263, May–June, 1979.     

The projection of spinocerebellar neurons from the sacrococcygeal region of the spinal cord in the cat. An experimental study using anterograde transport of WGA-HRP and degeneration.

The projection from the sacro-coccygeal region of the spinal cord to the cerebellum was studied by two different techniques in the cat. In five cats wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) was injected caudal to a preceding unilateral cordotomy at the sacral level, aimed at interrupting the spinocerebellar tracts on one side completely, and the distribution of WGA-HRP labeled mossy fibers and mossy fiber terminals was studied in the cerebellum. In three additional cats, degenerating fibers were examined in Fink-Heimer stained sections following unilateral transection of the lateral and ventral funiculi at L7 or S3 level. In the WGA-HRP experiments the labeled mossy fiber terminals were located bilaterally in lobules I-V. Most of them were found in the anterior part of lobule II. In addition, labeled terminals were observed in sublobule VIIIB and in pars copularis of the paramedian lobule, contralateral to the cordotomy. The terminals in the anterior lobe were concentrated in longitudinal zones parallel to the mid sagittal plane. In lobule II, the terminals were most abundant in the superficial, apical parts of the folia. Some presumed terminals were also seen in the cerebellar nuclei. Labeled fibers were found contralateral, but not ipsilateral to the cordotomy in the superior and inferior cerebellar peduncles, as well as in the spinal cord rostral to the cordotomy. The results of the degeneration experiments were the same as those of the WGA-HRP experiments with regard to the detailed projections in the cerebellar cortex. This is strong support against the possibility that WGA-HRP labeled cerebellar mossy fiber terminals, following WGA-HRP injections in the spinal cord, would represent terminals of collaterals of retrogradely labeled neurons. It also lends strong support in favour of WGA-HRP as a reliable anterograde tracer for studying cerebellar cortical projections of spinocerebellar neurons in the cat.