A.O. Humbertson

A chronological study of mitotic activity in satellite cell hyperplasia associated with chromatolytic neurons.

SummaryAfter axotomy, spinal ganglia show an increase in the ratio of satellite cells to neurons. The objective of this study is to clarify the temporal aspects of the satellite cell hyperplasia and the role of mitotic activity in this proliferative response.The ventral rami of the fourth, fifth and sixth lumbar spinal nerves in 100 gm female rats were sectioned on the right side. Corresponding left spinal nerves were kept intact and served as controls. After axotomy, representative animals were sacrificed over a twenty day period. Six hours before sacrifice, 0.12 mg of colchicine was given intraperitoneally. Right, experimental and left, control ganglia were removed and an inventory of neurons, satellite cells, and mitotic figures was conducted.An increase in the number of satellite cells was noted on the first day after axotomy; it reached a maximum on the sixth day and disappeared by the eighteenth day. Mitotic activity was observed in all experimental ganglia, but not in the control tissue.

Projections from the brain stem reticular formation to laminae I and II of the spinal cord. Studies using light and electron microscopic techniques in the North American opposum

The horseradish peroxidase and autoradiographic methods show that laminae I and outer II are innervated by the nucleus reticularis gigantocellularis pars ventralis, and the nucleus reticularis pontis pars ventralis. Both areas contain neurons of the indolamine type and probably account for the indolamine-like varicosities which are present within laminae I and II. Degeneration materiom the above nuclei end on small dendritic shafts and spines as well as on vesicle-filled proflies. The terminals identified formed asymmetrical contacts and contained clear as well as dense-cored vesicles. No terminals were present within glomeruli. A projection to laminae I and outer II also arises within the dorsolateral pons and several ines of evidence suggest that it is catecholaminergic. The electron microscope revealed that axons from the dorsolateral pons are fairly numerous within laminae I and II, but that terminal contacts are relatively rare. Those present are asymmetrical and alternate with intermediate-sized dendrites. They contain clumps of clear, spherical vesicles as well as larger vesicles with a variety of dense cores.

Reticular and Raphe Projections to the Spinal Cord of the North American Opossum. Evidence for Connectional Heterogeneity

Publisher Summary The chapter reviews the organization of reticular and raphe projections to the opossums spinal cord and describes possible neurotransmitters or modulators employed by some of them. The opossums central nervous system is relatively generalized in comparison with that of most mammals. Corticospinal tracts exist, but they are limited and can only be traced to laminae III–VI of the cervical cord. In contrast, axons from the red nucleus and vestibular complex, as well as from several reticular and raphe nuclei, project the length of the spinal cord. Reticular and raphe neurons projecting to different levels of the spinal cord are identified by the horseradish peroxidase (HRP) technique. In a study described in the chapter, HRP was injected into the desired level of the cord where it was incorporated by axons and transported retrogradely to the parent cell bodies. The presence of HRP in reticular and raphe cells was revealed by several histochemical techniques.

Serotonergic innervation of the forebrain in the North American opossum

The forebrain distribution of axons showing serotonin-like immunoreactivity was studied in the North American opossum. Serotonergic innervation of the hypothalamus was extensive, particularly within the ventromedial nucleus, the periventricular nucleus and the rostral supraoptic nucleus. Serotonergic axons were also present within the fields of Forel and zona incerta, but they tended to avoid parts of the subthalamic nucleus. In the thalamus serotonergic innervation was dense within the midline nuclei (e.g. the central, intermediate dorsal and rhomboid nuclei) and the ventral lateral geniculate nucleus, but relatively sparse in some of the nuclei more readily associated with specific functions (e.g. the ventrobasal nucleus). Serotonergic axons innervate most areas of the rostral and dorsal forebrain. Areas containing the heaviest innervation included the interstitial nucleus of the stria terminalis and the lateral septal nucleus. Serotonergic innervation of the neocortex varied markedly from region to region and within different layers of the same regions. The retrograde transport of True Blue combined with immunofluorescence for localization of serotonin revealed that serotonergic axons within the forebrain arise mainly within the dorsal raphe and superior central nuclei, but that some originate within the midbrain and pontine reticular formation and the locus coeruleus, pars alpha. Neurons of the raphe magnus and obscurus also innervate the forebrain, but few of them are serotonergic. The use of horseradish peroxidase as a retrograde marker provided evidence that raphe projections to the forebrain are topographically organized. Our results suggest that serotonergic projections to the forebrain, like those to the spinal cord, are connectionally heterogeneous.

Development of raphe-spinal connections in the North American opossum

The Falck-Hillarp technique, serotonin (5-HT) immunohistochemistry and the retrograde transport of horseradish peroxidase (HRP) were utilized to investigate the development of raphe-spinal connections in the pouch-young opossum. The brainstem raphe and adjacent reticular formation contain 5-HT immunoreactive neurons in the newborn opossum (12 days after conception) and processes from these cells can be visualized in the marginal zone of the spinal cord. Between eight and 15 days after birth 5-HT immunoreactive varicosities begin to grow into the presumptive deep layers of the dorsal horn, the intermediolateral cell column and the ventral horn. In the latter region some of them approximate presumed motor neurons. Between 40-50 days after birth 5-HT immunoreactive varicosities appear in presumptive laminae I and II of the dorsal horn.

The brainstem origin of monoaminergic projections to the spinal cord of the North American opossum: A study using fluorescent tracers and fluorescence histochemistry

The retrograde transport of fluorescent markers has been combined with the glyoxylic acid and Falck-Hillarp techniques to identify the origin of monoamine axons within the spinal cord of the North American opossum. Catecholamine axons arise from neurons located within the ventrolateral medulla, dorsal to the superior olivary complex, within the dorsolateral and rostrolateral pons and within the periventricular nuclei of the hypothalamus. Such neurons are most numerous within the dorsolateral pons where they are found dorsal and lateral to the motor trigeminal nucleus, within the nucleus locus coeruleus pars alpha and adjacent reticular formation as well as within the ventral part of the nucleus locus coeruleus. Neurons containing the fluorescent marker and catecholamines were interspersed with others containing only the injected marker with the possible exception of the nucleus locus coeruleus. Spinal axons of the indoleamine type arise from neurons within the nuclei pallidus, obscurus and magnus raphe, the nucleus reticularis gigantocellularis, the nucleus reticularis gigantocellularis pars ventralis, the nucleus reticularis pontis pars ventralis and the nucleus dorsalis raphe. The latter nucleus only innervates rostral cervical levels. Most of the above areas also contain many non-indoleamine neurons which were labelled by the injected marker. This was particularly true of the nucleus magnus raphe and the adjacent nucleus reticularis points pars ventralis after injections of fluorescent markers into the superficial dorsal horn.

The Development of Descending Spinal Connections. Studies Using the North American Opossum

Publisher Summary This chapter discusses the development of descending spinal connections. The opossum is a good model for developmental studies. The development of the opossums nervous system is quite protracted in comparison to that of placental mammals. The opossums hindlimbs are little more than buds at birth and do not become motile for 7–10 days postnatally. The development of hindlimb motility and the influence of descending pathways on that motility can be divided into three stages: (1) stage I begins at birth (or conception) and ends when spontaneous hindlimb movements first appear (postnatal day 7–10), (2) stage II begins with the onset of hindlimb motility and ends approximately 20 days later (50–60 mm snout-rump length) when that motility can be altered by transecting the spinal cord at thoracic levels, and (3) stage III begins when hindlimb movements can first be affected by thoracic transection and continues until the animal can support its weight and ambulate (90–120 mm S-R length, estimated to have been 60–75 days in the pouch). Axons from the reticular formation, raphe nuclei, coeruleus complex, vestibular nuclei, and red nucleus invade most of the lumbosacral areas innervated in the adult animal before transecting them produces noticeable change in hindlimb motility.

Initiating factors in perineuronal cell hyperplasia associated with chromatolytic neurons

SummaryNeuronal hypertrophy and increased metabolism in nerve cells are evaluated as possible factors initiating hyperplasia of perineuronal cells. Colchicine induced neuropathy in the dorsal root ganglia is used as the model of increased neuronal metabolism.Twenty-eight female white rats weighing 100 g were divided into four groups, each animal receiving a 50 μl injection into the subarachnoid space at the lumbosacral level eight days and again three days before sacrifice. The 50 μl contained 25, 2.5 and 0.25 μg of colchicine in distilled water for the first three groups and normal saline for the last group.A Zeiss ocular with random test points was used to determine the volume of tissue occupied by perineuronal cells and nerve cells in spinal ganglia. Direct cell counts yielded the size of the population of perineuronal cells and neurons.Irreversible motor and sensory loss occurred with the high dose injection, reversible loss with the 2.5 μg injection and no loss with either the low dose or the saline injection. Chromatolytic neurons were noted in all animals receiving colchicine. Neither proliferation of perineuronal cells nor neuronal hypertrophy were observed. Neuronal hypertrophy, rather than altered neuronal metabolism, may be the initiating event in the perineuronal cell hyperplasia that frequently accompanies chromatolysis.