George F. Martin

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...

Spinal projections of the gigantocellular reticular formation in the rat. Evidence for projections from different areas to laminae I and II and lamina IX

SummaryWe have used the autoradiographic method to study the organization of spinal projections from the gigantocellular reticular nucleus in the rat. Of particular note was the evidence obtained for projections to laminae I, II and IX. Reticular projections to laminae I and II arise more rostrally in Gi than those to lamina IX. Projections to laminae III–VIII and X as well as to autonomic nuclei have also been documented. Our results suggest that the gigantocellular reticular nucleus of the rat can be subdivided on connectional grounds.

An autoradiographic analysis of ascending projections from the medullary reticular formation in the rat

Ascending projections from the several nuclei of the medullary reticular formation were examined using the autoradiographic method. The majority of fibers labeled after injections of [3H]leucine into nucleus gigantocellularis ascended within Forels tractus fasciculorum tegmenti which is located ventrolateral to the medial longitudinal fasciculus. Nucleus gigantocellularis injections produced heavy labeling in the pontomesencephalic reticular formation, the intermediate layers of the superior colliculus, the pontine and midbrain central gray, the anterior pretectal nucleus, the ventral midbrain tegmentum including the retrorubral area, the centromedian-parafascicular complex, the fields of Forel/zona incerta, the rostral intralaminar nuclei and the lateral hypothalamic area. Nucleus gigantocellularis projections to the rostral forebrain were sparse. Labeled fibers from nucleus reticularis ventralis, like those from nucleus gigantocellularis, ascended largely in the tracts of Forel and distributed to the pontomedullary reticular core, the facial and trigeminal motor nuclei, the pontine nuclei and the dorsolateral pontine tegmentum including the locus coeruleus and the parabrachial complex. Although projections from nucleus reticularis ventralis diminished significantly rostral to the pons, labeling was still demonstrable in several mesodiencephalic nuclei including the cuneiform-pedunculopontine area, the mesencephalic gray, the superior colliculus, the anterior pretectal nucleus, the zona incerta and the paraventricular and intralaminar thalamic nuclei. The main bundle of fibers labeled by nucleus gigantocellularis-pars alpha injections ascended ventromedially through the brainstem, just dorsal to the pyramidal tracts, and joined Forels tegmental tract in the midbrain. With the brainstem, labeled fibers distributed to the pontomedullary reticular formation, the locus coeruleus, the raphe pontis, the pontine nuclei, and the dorsolateral tegmental nucleus and adjacent regions of the pontine gray. At mesodiencephalic levels, labeling was present in the rostral raphe nuclei (dorsal, median and linearis), the mesencephalic gray, the deep and intermediate layers of the superior colliculus, the medial and anterior pretectal nuclei, the ventral tegmental area, zona incerta as well as the mediodorsal and reticular nuclei of the thalamus. Injections of the parvocellular reticular nucleus labeled axons which coursed through the lateral medullary tegmentum to heavily innervate lateral regions of the medullary and caudal pontine reticular formation, cranial motor nuclei (hypoglossal, facial and trigeminal) and the parabrachial complex.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Developmental sequence in the origin of descending spinal pathways. Studies using retrograde transport techniques in the north american opossum (Didelphis virginiana)

The origin of descending pathways to thoracic and cervical levels of the spinal cord has been investigated with retrograde tracing techniques in a series of pouch young and adult opossums. The opossum was chosen because it is born in a very immature state, 12-13 days after conception, and has a protracted development in an external pouch. A few neurons in the pontine reticular formation and nucleus coeruleus were labeled by horseradish peroxidase (HRP) injections of the thoracic cord as early as postnatal day (PND) 3. By PND 5, similar injections labeled neurons in the same areas as well as in the medullary reticular formation, the raphe nuclei of the caudal pons and medulla, the spinal trigeminal nuclei, the vestibular complex, the accessory oculomotor nuclei and the interstitial nucleus of Cajal. When Nuclear Yellow (NY) was employed, neurons were also labeled in the red nucleus, the hypothalamus and possibly in the nucleus of the solitary tract. Regardless of the technique employed, neurons in the dorsal column nuclei were not labeled by thoracic injections until at least PND 14. Axons from the nucleus ambiguus, the fastigial and interposed nuclei of the cerebellum as well as the intermediate and deep layers of the superior colliculus reach cervical levels of the cord, where they are specifically targeted, by at least PND 17. They do not significantly overgrow those levels during development. Corticospinal axons are the last of the major descending pathways to innervate the spinal cord. Cortical neurons cannot be labeled by cervical injections of either HRP or NY until at least PND 30. Evidence for transient brainstem-spinal and corticospinal projections was obtained.

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.

Brainstem projections to the facial nucleus of the opossum. A study using axonal transport techniques

The horseradish peroxidase and autoradiographic techniques have been used to determine the origin and intranuclear termination of brainstem axons projecting to the facial nucleus of the opossum and to define networks which could be utilized in some oral-facial behaviors. Two regions of the midbrain have dense projections to the facial nucleus. One region is the ventral periaqueductal gray and adjacent interstitial nucleus of the medial longitudinal fasciculus which project bilaterally to those areas of the facial nucleus supplying auricular and cervical musculature. A second is the paralemniscal zone of the caudolateral midbrain which innervates the same areas of the contralateral facial nucleus. The red nucleus and/or the adjacent tegmentum send a less dense projection to those regions of the contralateral facial nucleus which innervate buccolabial and zygomatic muscles. The dorsolateral pons (the parabrachial complex, the nucleus locus coeruleus, pars alpha, and the nucleus sensorius n. trigemini, pars dorsalis) projects densely to those areas of the ipsilateral facial nucleus which innervate buccolabial and zygomatic musculature. In contrast, the nucleus reticularis pontis, pars ventralis, projects bilaterally to parts of the facial nucleus supplying auricular and cervical muscles. There was evidence of some rostral to caudal organization in the latter projection. Neurons in medial parts of the lateral reticular formation project bilaterally to the facial nucleus. Those within the nucleus reticularis parvocellularis and the rostral nucleus reticularis medullae oblongatae ventralis innervate areas supplying buccolabial and zygomatic muscles. Neurons in the nucleus reticularis medullae oblongatae ventralis located caudal to the obex favor regions of the facial nuclei which supply auricular and cervical muscles. Neurons in the nucleus reticularis medullae oblongatae dorsalis and lamina V of the medullary and spinal dorsal horns project ipsilaterally to the facial nucleus in a manner suggesting that information from specific cutaneous areas reaches neurons supplying the muscles deep to them. The brainstem-facial connections are discussed in relation to the functionally diverse roles served by the facial nucleus in oral-facial behavior.

A further evaluation of the origin, the course and the termination of the opossum corticospinal tract

Abstract This study documents the granular postorbital, parietal and paramarginal origin of the opossum corticospinal tracts. The details of opossum cervical cord morphology were compared with what was previously described for the cat ( Rexed 1952) and certain differences were noted. The opossum corticospinal tracts coursed in both the dorsal and lateral funiculi and ended in Rexeds laminae III through VI. The predominant areas of termination were the medial and, to a lesser extent, the lateral parts of laminae IV and V. Relatively few fibers terminated in lamina VI and the possible significance of this finding is discussed. Because of the interesting paucity of corticospinal bundles arising from the agranular preorbital area, the projections of this cortex were determined and briefly described.

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.

Corticospinal development in the North-American opossum: Evidence for a sequence in the growth of cortical axons in the spinal cord and for transient projections

The course and distribution of corticospinal axons have been traced in a series of pouch young and adult opossums using wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Cortical axons enter the spinal cord approx. 28 days after birth (40 days after conception) and, at that time, are limited to those portions of the dorsal and lateral funiculi which contain them in the adult animal. Shortly thereafter, cortical axons are also found in regions of presumptive white matter where they are not seen in older pouch young or adult opossums. Those in the dorsal and lateral funiculi reach their caudal extent, the fourth thoracic segment, approx. 38 days after birth and do not significantly overgrow that level during development. Cortical axons grow into the gray matter exclusively from the dorsal and lateral funiculi and first innervate adjacent portions of laminae IV and V. They subsequently extend into laminae III and VI, then VII, VIII and X and finally, at the cervical enlargement, the medial edge of laminae I-II and lamina IX. There is a subsequent period of development during which the density of cortical innervation in all spinal laminae, particularly in the ventral horn, appears to exceed that in the adult opossum.