James S. King

A neuroanatomical analysis of spinal cord injury in the rhesus monkey (Macaca mulatta).

Thirteen rhesus monkeys were subjected to impacts of either 200, 300, 400, oe 500 g-cm, on the dorsal surface of the spinal cord (Allen 1911). Six monkeys served as controls to determine the results of transection of the cord as well as the optimal survival time, and 2 additional subjects underwent the operative procedures only. Most of the animals were sacrificed 1 week postoperatively and the brains and spinal cords were processed by the Fink and Heimer (1967) technique for degenerating axons. Two contrils and 1 experimental subject, sacrificed at 1 week, were prepared for electron-microscopic analysis...

Cerebello-olivary fibers: Their origin, course and distribution in the North American opossum

SummaryAlthough degeneration techniques suggest that cerebello-olivary fibers are limited in their origin and distribution, horseradish peroxidase and autoradiographic experiments make it clear that they arise within all cerebellar nuclei and project to most, if not all, areas of the contralateral inferior olive. Autoradiographic preparations show that cerebello-olivary fibers are highly ordered and suggest that the dentate nucleus projects primarily to the principal olive, the interpositus anterior relays particularly heavy to the dorsal accessory nucleus and the interpositus posterior distributes extensively to the medial accessory complex. Evidence for a small projection from the fastigial nucleus to the caudal medial accessory nucleus is also available. However, it appears clear that neither the dentate nor the interpositus nuclei project to just one subdivision of the olive. For example, although dentate fibers end extensively within the principal nucleus some of them also distribute to portions of the medial accessory nucleus and perhaps the dorsal accessory nucleus as well. The medial accessory olive is particularly complex and at rostral levels receives input from both interposed and dentate nuclei, whereas more caudally it receives a projection from the fastigial nucleus. Olivary fibers from both the interposed and dentate nuclei traverse the brachium conjunctivum descendons and distribute primarily to the rostral 2/3 to 3/4 of the olive, whereas those from fastigial neurons take a different route and end more caudally. Experiments utilizing horseradish peroxidase as a retrograde tracer suggest that cerebello-olivary fibers from both the interpositus anterior and dentate nuclei take origin from a population of generally small neurons.

An experimental light and electron microscopic study of cerebellorubral projections in the opossum, Didelphis marsupialis virginiana

Abstract The origin, course and distribution of cerebellorubral fibers was studied in the opossum by employing the Fink-Heimer technique. Many of the cerebellorubral fibers may be collaterals of an axon which continues to the thalamus. The majority of cerebellorubral fibers arise in the nucleus interpositus and distribute throughout the red nucleus, but they are most numerous in the caudal one-third. The interpositorubral fibers appear to be topographically organized. The only other cerebellar input to the red nucleus takes origin within the lateral cerebellar nucleus and distributes exclusively to a small dorsal rostral portion. Electron microscopic analysis of the red nucleus following either cerebellectomy, hemicerebellectomy or stereotaxic lesions in nucleus interpositus and nucleus lateralis, reveals that axon terminals of cerebellorubral fibers mainly contact the somata and proximal dendrites of giant and large-medium nerve cells. Many of the terminals on the somata and proximal dendrites reside in depressions of the plasma membrane. In addition to direct axosomatic contacts, these large boutons also synaptically contact small appendages which arise from the cell body. The majority of the terminals are large and ovoid (2–4 μm × 5–10 μm) or elongate (1 μm × 10–12 μ) and, after lesions that encroach upon the interpositus nucleus, undergo a filamentous type of degeneration followed by electron dense degeneration and glial investment. Lesions restricted to the lateral nucleus result in electron dense degeneration of small (1–3 μm) axon terminals which primarily contact the somata and proximal dendrites of large-medium neurons.

A light and electron microscopic study of corticorubral projections in the opossum,Didelphis marsupialis virginiana

Summary The origin, course and distribution of corticorubral fibers was studied in the opossum by employing the Fink-Heimer and Nauta techniques. The majority of corticorubral fibers arise from the motor-sensory forelimb cortex. Some also take origin from the motor-sensory hindlimb cortical area. No definite somatotopic organization of corticofugal fiber distribution could be established within the red nucleus. Regardless of the location of the lesion in the motor-sensory limb cortex, the greatest amount of fiber degeneration within the red nucleus was in its rostroventral portion. The majority of the degenerating fibers in the caudal one-fourth of the nucleus were located laterally. Following cortical ablations, study of the red nucleus with the electron microscope revealed that the axon terminals of corticorubral fibers show an electron-dense type of degeneration. The synaptic profiles are small (1–2 μm) and appear in two different forms based on the type of synaptic vesicles found in the degenerating axon terminals. The most common postsynaptic surfaces are small diameter (1–3 μm) dendrites. Some spines and proximal dendritic trunks are also postsynaptic to the degenerating endings. Golgi preparations reveal that the giant neurons are restricted to the caudal medial one-fourth of the nucleus whereas large-medium sized neurons are numerous and found throughout the nucleus. Small neurons are few in number. It is suggested that most of the corticorubral axon terminals contact the distal dendrites of large-medium sized neurons.

The organization of projection neurons in the opossum red nucleus

Abstract The opossum red nucleus is populated by neurons encompassing a considerable size range. The largest neurons (giant neurons, 45–70 μm) are restricted to its caudal, medial third, whereas those in the large-medium category (25–40 μm) are located throughout the nucleus. The smallest neurons (less than 20 μm) are relatively achromatic and few in number, but are also scattered throughout the nucleus. Evidence from both retrograde and orthograde degeneration studies shows that rubrospinal fibers arise from both giant and large-medium neurons in the caudal third of the nucleus and from large-medium neurons in its rostral two-thirds (mainly the ventral part). Neurons in the medial part of the caudal red nucleus (giant neurons particularly) contribute relatively few fibers to contralateral brain stem nuclei, whereas, large-medium neurons residing in its rostral two-thirds and in the lateral extreme of its caudal third project more extensively to such areas and appear to be the main source of fibers to the chief sensory and spinal trigeminal nuclei, the facial nucleus and the parvicellular reticular formation. Some of these rubrobulbar fibers are likely collaterals of spinal axons. The experimental results further suggest that (1) rubrocerebellar axons arise from both caudal and rostral areas of the nucleus, (2) some large-medium neurons project only to the contralateral brain stem and/or cerebellum, and (3) the ipsilateral rubrobulbar bundle arises from large-medium neurons which are located within the rostral red nucleus. Previous experimental light and electron microscopic studies, together with observations made from Golgi impregnated sections, provide evidence that the small neuron is intrinsic to the nucleus. The organization of the opossum red nucleus revealed by the origin of the various descending projections is generally reflected by its cortical and cerebellar inputs and by its histochemistry.

Cellular localization of corticotropin releasing factor receptors in the adult mouse cerebellum

Corticotropin releasing factor is a 41 amino acid peptide that is present in afferent systems that project to the cerebellum. In the adult, this peptide modulates the activity of Purkinje cells by enhancing their responsiveness to excitatory amino acids. Two different types of corticotropin releasing factor receptors, designated type 1 and type 2, have been identified. The purpose of this study is to use immunohistochemistry to identify which corticotropin releasing factor receptors are present in the cerebellum of the adult mouse and to determine their cellular distribution. Receptor type 1 immunostaining is present throughout all lobules of the cerebellar cortex. Distinct labeling is present over the somas of most, if not all, Purkinje cells as well as the primary dendrites of Purkinje cells located at the base of vermal folia. In vermal lobules V, VI, VIII and IX numerous glial fibrillary acidic protein immunoreactive processes, oriented radially in the molecular layer, also are immunoreactive for receptor type 1. In the granule cell layer, scattered type 1 immunoreactive puncta are present throughout most cerebellar lobules. Receptor type 2 immunoreactive puncta are present throughout the molecular layer in all lobules. In addition, scattered basket and/or stellate cells, identified with a GABA antibody, are immunopositive for the type 2 receptor. In the Purkinje cell layer, the type 2 receptor immunolabeling is confined to the basal pole of the Purkinje cell including the initial axonal segment. In the granule cell layer, labeling is present over large cell bodies, and their initial axonal segments. These are likely to be Golgi cells, based on their co-staining with GABA. Finally, numerous elongated processes within the white matter, which are likely to be axons, also are type 2 immunoreactive. These data indicate that both types of corticotropin releasing factor receptor are present in the mouse cerebellum. However, the unique distribution of the two types of receptor strongly suggests a differential role for corticotropin releasing factor in modulating the activity of neurons, axons and glial cells via cell-specific ligand-receptor interactions.

Chapter 4 The distribution of corticotropin-releasing factor (CRF), CRF binding sites and CRF1 receptor mRNA in the mouse cerebellum

The purpose of the present study is to determine the distribution of CRF containing afferents, and correlate these findings with the distribution of CRF binding sites and the neuronal localization of mRNA for the CRF1 receptor in the cerebellum of a single species, the mouse. Corticotropin releasing factor (CRF) has been localized within climbing fibers and mossy fibers throughout the cerebellar cortex of the mouse using immunohistochemistry. CRF immunoreactive, axonal varicosities also are present within all four of the cerebellar nuclei. 125I-labeled CRF binding sites are evident throughout all three layers of the cerebellar cortex (molecular, Purkinje and granule cell layers), but are not seen within the cerebellar nuclei. In situ hybridization histochemistry was employed using an antisense riboprobe corresponding to the full length sequence of the rat mRNA for the CRF1 receptor. Positive signal is present throughout the cerebellum in Purkinje cells and the granule cell layer. CRF1 receptor mRNA also is expressed within all four of the cerebellar nuclei. Further experiments are required to reconcile the lack of CRF binding sites in the cerebellar nuclei with the positive mRNA receptor expression and the presence of immunoreactive axonal varicosities. In previous physiological experiments, iontophoretic application of CRF enhances spontaneous as well as quisqualate-induced activity of Purkinje cells in slice preparations of the mouse cerebellum. When the results of the anatomical techniques are compared to the physiological data, there is convergent evidence to suggest that CRF influences the firing rate or responsiveness of Purkinje cells directly via release of the peptide from the climbing fiber system and indirectly via the mossy fiber-granule cell-parallel fiber circuit. Taken together, these anatomical and physiological data provide strong evidence to suggest that, in the adult cerebellum, CRF functions as a neuromodulator.

The synaptic organization of the cerebello-oiivary circuit

SummarySection of the superior cerebellar peduncle just rostral to the deep cerebellar nuclei results in degenerating axon terminals within the contralateral inferior olive. The nuclear origin of this fiber system and its distribution within the subdivisions of the inferior olive were described in a companion study (Martin et al., 1976). Precise localization of these degenerating terminals within the nucleus was accomplished by the examination of 1 μ plastic sections cut from each tissue block prior to thin sectioning. Degenerating axon terminals are present in all the nuclear subdivisions and when seen with the electron microscope they frequently are localized in the previously described synaptic clusters (King, 1976). These terminals demonstrate an electron dense reaction at survival times of 2 and 3 days. By day 4, they are shrunken and irregular in shape, and typically are surrounded by astrocyte processes. Cerebello-olivary axon terminals measure 1–3 μ, contain spherical, clear synaptic vesicles and typically contact spiny appendages within the synaptic clusters (glomeruli). Thus, we have demonstrated that one of the primary axon systems which terminates within the synaptic clusters is from the cerebellar nuclei. We have yet to determine the origins of the remaining terminals within the synaptic clusters which include endings with either smaller spherical, pleomorphic or numerous dense core vesicles.

Anatomical evidence for enkephalin immunoreactive climbing fibres in the cerebellar cortex of the opossum

SummaryEnkephalin immunoreactivity is present in the cerebellum of the adult opossum within axonal arbors that resemble mature climbing fibres. In the developing cerebellum, enkephalinergic axons form pericellular nests around the perikarya of Purkinje cells in a manner which resembles developing climbing fibres seen in Golgi impregnations. Serial electron micrographs of adult climbing fibres reveal elongate enkephalin immunoreactive profiles that contain synaptic vesicles and make contact with the thorns and shafts of Purkinje cell dendrites. These results suggest that a peptide, enkephalin or an enkephalin-like substance may mediate synaptic interactions between certain populations of climbing fibres and Purkinje cells in the cerebellum of the opossum. Enkephalin immunoreactive axonal arbors, present in the molecular layer, are localized in restricted areas of vermal lobules II–VIII and X. The intermediate cortex and hemispheres are devoid of enkephalinergic climbing fibres except in restricted areas of the paramedian lobule, paraflocculus and the flocculus. In an attempt to establish the origin of enkephalin axons in the cerebellum, a double labelling technique that combines retrograde labelling of cells with horseradish peroxidase and enkephalin immunohistochemistry has been employed. Enkephalin immunoreactive neurons within specific portions of the medial accessory olive are retrogradely labelled in this paradigm. The presence of enkephalin immunoreactivity in selected climbing fibres provides evidence for chemical heterogeneity within one of the major afferent systems to the cerebellum previously thought to be uniform in its transmitter content.

The direct spinal area of the inferior olivary nucleus: An electron microscopic study

SummaryIdentification of the direct spinal areas (portions of the dorsal and medial accessory nuclei) within the opossum inferior olivary complex was accomplished by mapping the location of the terminal degeneration by the Fink-Heimer technique subsequent to cervical cord lesions. Following similar lesions, sampling of these same regions for electron microscopic study was assured by examination of transversely oriented, 1 μ plastic sections prior to thin sectioning. The first evidence of electron dense axon terminals was found at a survival time of 24 hours. At survival times of 36, 48 and 72 hours, degenerating presynaptic profiles shrink, become irregular in shape and are totally or partially surrounded by glial processes. Spinal terminals average 1–2 μ in their greatest dimension, contain round, clear synaptic vesicles and generally contact small diameter (0.4–1.8 μ) dendritic shafts or occasional spiny appendages. The spiny dendritic appendages make up the central core of the olivary glomeruli and these juxtaposed dendritic processes exhibit gap junctions. At longer survival times (5, 7 and 9 days) many presynaptic profiles with either round or pleomorphic synaptic vesicles remain normal in appearance and contact dendritic shafts or the spiny appendages within glomeruli. Afferents from other sources (possibly including intrinsic neurons) must terminate within the direct spinal portion of the nuclear complex to account for the numerous axon terminals which retain normal morphology after such long survival times.