The organization of monoamine neurons within the brainstem of the North American opossum (Didelphis virginiana)

Primary afferent distribution pattern in the marginal zone (lamina 1) of adult monkey and cat lumbosacral spinal cord

Using Golgi preparations from adult cat and monkey the present study describes the general arborization pattern of primary afferent collaterals to the marginal layer (lamina I) of the dorsal horn. The dorsal root origin of the golgi-impregnated afferents was verified in the cat by matching the structural properties of these fibers with horseradish peroxidase (HRP)-stained primary afferents which were filled with HRP via anterograde transport through dorsal rootlets. The marginal afferents, in both the cat and the monkey, are relatively fine-caliber fibers which emanate from the dorsolateral fasciculus of Lissauer. Superficially they form a transverse plexus of fibers which runs across the surface of the dorsal horn and is especially dense in the lateral portion of the dorsal aspect of the marginal layer where lamina I is thickest. In deeper regions of the marginal layer, marginal afferents are longitudinally oriented and have collaterals within the outer zone of lamina II. In both superficial and deep regions of the marginal layer the afferents run parallel with large numbers of marginal cell dendrites. Most marginal afferents give rise to collaterals with widely spaced, round to oval "boutons en passant" and "boutons terminaux" which are 1.5-2.0 micrometers in diameter. Structural correlation with previous physiological and anatomical studies suggest that most of these fibers are finely myelinated, A-delta, high-threshold mechanoreceptive fibers.

Scattered catecholaminergic cells in the dorsolateral tegmentum caudal to locus coeruleus in cat

In the cat brain stem, extending from the caudal locus coeruleus, scattered catecholaminergic (CA) cells are distributed over a large area. This includes a periventricular region dorsolateral to the fourth ventricle corresponding to the A4 group, the white matter separating vestibular and intracerebellar nuclei, and lateral to the vestibular complex in relation to the restiform body. In all, these CA cells were found to number 122 +/- 54 (mean +/- S.D.), unilaterally.

The organization of indoleamine neurons in the brain of the rhesus monkey (Macaca mulatta)

The organization of indoleamine-containing neurons throughout the CNS of Macaca mulatta was examined with Falck-Hillarp histofluorescence and radioenzymatic biochemical techniques. Indoleamine-containing cell bodies, corresponding to the serotonin-containing groups B1 to B9, were observed within the brain stem. The pontine cell populations, however, were far more numerous than in the rat and represented caudal subpopulations of cells within the nucleus raphe dorsalis (B7) and nucleus centralis superior (B8). Additionally, the pontine indoleamine-containing cells in M. mulatta extended laterally through the tegmentum such that they were often adjacent to catecholamine-containing neurons of the locus coeruleus complex. Ascending indoleamine-containing fiber bundles, similar to those defined in nonprimate mammals, were also observed within the pons and mesencephalon. Regional differences in the distribution of serotonin within hypothalamic nuclei and other forebrain regions of M. mulatta were revealed through a highly sensitive radioenzymatic assay in conjunction with microdissection. Significant concentrations of serotonin were evident in most areas, although the levels of this neurotransmitter were much lower in the median eminence region and nucleus suprachiasmaticus than in the rat. These differences may reflect variations in the control neuroendocrine events in the two species.

Spinal projections from the medullary reticular formation of the North American opossum: heterogeneity

Retrograde and orthograde transport techniques show that the nucleus reticularis gigantocellularis pars ventralis and the nucleus reticularis gigantocellularis project the entire length of the spinal cord. Double-labelling methods show that some of the neurons in each area innervate both cervical and lumbar levels. There is evidence, however, that neurons in the lateral part of the nucleus reticularis gigantocellularis pars ventralis and the dorsal extreme of the nucleus reticularis gigantocellularis project mainly to cervical and thoracic levels. The autoradiographic method shows that the above nuclei supply direct innervation to somatic and autonomic motor columns as well as to laminae V-VIII and X. The nucleus reticularis gigantocellularis pars ventralis provides additional projections to lamina I and the outer part of lamina II. Several areas of the medullary reticular formation project mainly, and in some cases exclusively, to cervical and thoracic levels. These areas include the nucleus reticularis parvocellularis, the nucleus reticularis lateralis, the nucleus retrofacialis, the nucleus ambiguus, the nucleus lateralis reticularis, caudal parts of the nuclei reticularis medullae oblongatae dorsalis and ventralis, and the nucleus supraspinalis. Autoradiographic experiments reveal that neurons in the ventrolateral medulla, particularly rostrally (the nucleus reticularis lateralis and neurons related to the nucleus lateralis reticularis), innervate sympathetic nuclei. Our results indicate that spinal projections from bulbar areas of the reticular formation are more complicated than previously supposed. Axons from separate areas project to different spinal levels and in some cases to different nuclear targets. These data are in conformity with the evolving concept of reticular heterogeneity.

Cells of origin of pathways descending to the spinal cord in some quadrupedal reptiles

The cells of origin of pathways descending to the spinal cord have been determined in several quadrupedal reptiles, viz., the turtle Pseudemys scripta elegans and Testudo hermanni and the lizards Tupinambis nigropunctatus and Varanus exanthematicus, following a technique introduced by Kuypers and Maisky ('75). This technique was very effective in producing retrograde transport of HRP to a great many neurons in the hypothalamus and in the brain stem. Projections from the hypothalamus (the nucleus paraventricularis and the nucleus periventricularis hypothalami), the interstitial nucleus of the film, the nucleus ruber, the nucleus of Edinger-Westphal, the locus coeruleus, the subcoeruleus area, a conspicuous cell group comparable to Kuypers and Maisky's (75, '77) lateral pontine area, the magnocellular reticular formation, the ventrolateral, ventromedial, and descending vestibular nuclei, the dorsal motor nucleus of the vagus, and the nucleus of the solitary tract, reach at least as far as the lumbar intumescence. Projections from two somatosensory nuclei, i.e., the nucleus descendens nervi trigemini and the nucleus funiculi dorsalis, as well as the laminar nucleus of the torus semicircularis, have been demonstrated to at least the ninth spinal segment. The two deep cerebellar nuclei, particularly the medial cerebellar nucleus, were found to project contralaterally to the spinal cord, in the lizard Varanus exanthematicus at least as far as the seventh segment; in the turtles studied so far, only projections as far caudal as the fourth spinal segment could be demonstrated. Data on the funicular trajectory of various descending pathways could also be obtained. It seems likely that in the reptiles studied, in addition to rubrospinal and reticulospinal pathways, projections from the hypothalamus, the nucleus of Edinger-Westphal, the cell group comparable to the mammalian lateral pontine area, the locus coeruleus, and subcoeruleus area, and the nucleus of the solitary tract pass via the lateral funiculus. The pathways descending from the hypothalamus and brain stem to the spinal cord in the quadrupedal reptiles studied appear to show remarkable similarities to pathway in mammals as regards their cells of origin as well as their funicular trajectory. It seems likely that some of the projections demonstrated, viz., from the locus coeruleus, at least part of the cell group comparable to the lateral pontine area, as well as the cells in and around the dorsal motor nucleus of the vagus, are noradrenergic pathways.

Catecholamine cell groups of the cat medulla oblongata

The distribution of catecholamine-containing cells within the cat medulla oblongata has been studied using formaldehyde-glutaraldehyde fluorescence histochemistry. The diffuse ventrolateral cells (A1) were scattered around but not within the lateral reticular nucleus and no cells were found dorsal to the inferior olivary nucleus. The dorsomedial (A2) cells were scattered within the nucleus tractus solitarius with an occasional cell within the dorsal motor nucleus of the vagus. No A2 cells were found within or ventral to the hypoglossal nucleus. This description contrasts in several respects with a recently published atlas of the catecholamine-containing neurons in the cat medulla.

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 opossum

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.

Spinal projections from the mesencephalic and pontine reticular formation in the North American Opossum: a study using axonal transport techniques

The results from several experimental approaches lead to the following conclusions. The nucleus cuneiformis projects to at least lumbar levels of the spinal cord. Its axons course through the ipsilateral sulcomarginal and ventral funiculi to distribute within lamina VIII and adjacent portions of lamina VII. Neurons within the nucleus reticularis pontis (RP), particularly within more medial parts of the nucleus, project through comparable routes to the same laminae. In addition, however, neurons within the lateral and dorsolateral RP relay through the lateral and dorsolateral funiculi, ipsilaterally, and the dorsolateral funiculus, contralaterally. Axons could be traced from the dorsolateral tracts to laminae IV through VII, lamina X and, in some instances, to laminae I and II. Injections of the dorsolateral pons also label the intermediolateral cell column and an area presumed to be the sacral parasympathetic nucleus. Many of the neurons which contribute to the contralateral bundle are located adjacent to the ventral nucleus of the lateral lemniscus. The nucleus reticularis gigantocellularis projects mainly via the sulcomarginal, ventral and lateral funiculi to laminae VIII and adjacent portions of lamina VII. The nucleus reticularis gigantocellularis pars ventralis innervates the same laminae; but, in addition, projects heavily to laminae I and II, to lateral portions of laminae IV through VII; to laminae IX and X and to the intermediolateral cell column. Axons destined for laminae I and II, as well as IV through VII and X, traverse the dorsolateral funiculi as described for the cat by Basbaum et al. ('78). Neurons within the nucleus reticularis parvocellularis project to cervical levels, mainly through the ventral funiculi. In general our results show that reticulospinal projections are more complex than suggested by degeneration methods and that laminae I, II. lateral parts of laminae IV-VII, laminae IX and X, as well as the intermediolateral cell column and sacral parasympathetic nucleus are targets of axons from specific areas.

The cytoarchitecture of the interfascicular nucleus and ventral tegmental area of Tsai in the rat

The cytoarchitecture of the ventral tegmental area of Tsai (VTA) has been studied in detail in the rat with the acid of both conventional techniques and glyoxylic acid-fluorescence histochemistry. Three main dopamine containing cells groups can be distinguished: nucleus paranigralis, nucleus parabrachialis pigmentosus, nucleus linearis raphe caudalis. Nucleus parabrachialis pigmentosus lies dorsally, and nucleus paranigaralis ventrally in the VTA, while nucleus linearis continues posteriorly and medially from VTA and extends dorsally in the midline up towards the dorsal raphe nucleus. Fluorescent neurons in these three groups correspond to the A10 group. In addition to these previously described findings, the present study shows evidence for further small but cytoarchitecturally distinct dopaminergic group called the interfascicular necleus. This lies anteriorly and ventrally in the ventral tegmentum in the midline, dorsal to the rostral portion of the interpeduncular nucleus and interpeduncular fossa. The significance of these cytoarchitectural findings is discussed in relation to the known connections of the region.

The development of monoaminergic brainstem-spinal systems in the North American opossum

Evidence is presented for an early appearance of monoaminergic neurites within the spinal cord of the developing opossum. They are present within the marginal zone before hindlimb movements begin (stage I) and they start to grow into the intermediate zone by the time hindlimb movements are first observed (stage II). Monoaminergic neurites grow first into the dorsolateral intermediate zone and the intermediolateral cell column where they can be found by the beginning of stage II. Shortly thereafter, fluorescent varicosities can be traced into the area dorsal to the central canal presumed to become lamina X. Fluorescent processes extend in to the ventral intermediate zone (ventral horn) somewhat later in development. Monoaminergic axons have grown into all of the areas they occupy in the adult animal, except for laminae I and II, by the time immature hindlimb movements can be altered by cutting all brainstem projections to the lumbosacral cord (stage III). Monoaminergic innervation of laminae I and II is the last to develope, but it is present by the time thoracic transection produces complete spinal shock.

Description of an indolaminergic cell component in the cat locus coeruleus: a fluorescence histochemical and radioautographic study

Using Falck-Hillarp fluorescence histochemical and radioautographic techniques, it has been found that, in addition to the well-known catecholaminergic cells, the locus coeruleus (LC) of the cat contains a sizeable component of indolaminergic neurons. Indolaminergic cell bodies occur in all subdivisions of the LC complex. They are most numerous in the LC proper and subcoeruleus area, but are also present in the medial and lateral parabrachial, and Kölliker-Fuse nuclei. In all, the indolaminergic cells are estimated to make up 7-10% of the monoaminergic neuronal population of the LC complex. With the exception of the Kölliker-Fuse nucleus, where somewhat larger cells occur, the indolaminergic cell bodies in different parts of the LC complex share a common fluorescence histochemical appearance. They display round to fusiform shapes and measure 30 x 18 micron on the average, which makes them cytoarchitectonically similar to the small type of noradrenergic cells in the LC. The formaldehyde-induced fluorescence of the indolaminergic cells in the LC complex was analyzed microspectrofluorometrically and the recorded excitation and emission spectra (maxima at 370 and 530 nm, respectively) were found to be identical with those recorded from midline raphe neurons. No evidence of noradrenaline content was found in the indolaminergic cells of the LC. Radioautographic experiments after intratissular injections of tritiated serotonin showed that the indolaminergic cells of the LC complex possess uptake mechanisms for serotonin. Taken together these results provide strong evidence for serotonin being the transmitter of the indolaminergic neurons discovered in the LC of the cat.

The synaptic terminations of certain midbrain-olivary fibers in the opossum

The nuclear origin and distribution of midbrain-olivary fibers has been described in a previous study utilizing axonal transport techniques (Linauts and Martin, '78a). The present report extends their results to the electron microscopic level and details the postsynaptic distribution of such fibers. Lesions within the ventral periaqueductal grey and adjacent tegmentum, the red nucleus or the nucleus subparafascicularis result in electron dense axon terminals within the olive at survival times of 48, 72 and 96 hours. At 72 hours, many degenerating presynaptic profiles shrink, become irregular in shape and are totally or partially surrounded by glial processes. The principal olivary nucleus contains the majority of these profiles. However, the subparafascicular terminals are more abundant in the rostral and intermediate parts of the medial accessory nucleus and the rubral terminals are concentrated within the dorsal lamella of the principal nucleus. The nuclear location of the degenerating terminals was determined by examination of 1 micrometer plastic sections cut in the transverse plane from each block face prior to thin sectioning. Degenerating terminals were counted in three cases, one from each of the three lesion sites described above. When taken together these cases show that just over 50% of the degenerating terminals are presynaptic to spiny appendages and are located within the synaptic clusters (glomeruli) described previously (King, '76). The percentage of degenerating terminals in the glomeruli increases to 70% when the lesion is in the ventral periaqueductal grey and adjacent tegmentum. The remaining degenerating terminals contact dendritic shafts outside the astrocytic boundaries of the synaptic clusters. The synpatic vesicle populations within the degenerating terminals vary with the location of the lesion. Lesions in the ventral periaqueductal grey and the adjacent tegmentum result in the degeneration of terminals with either clear spherical vesicles or endings with both clear spherical vesicles and a variable number of large dense core vesicles. In contrast, the primary degenerative changes that occur after destruction of the red nucleus or the nucleus subparafascicularis are in terminals with clear spherical vesicles. When the synaptic complex was present in the plane of section, regardless of the site of the lesion, the degenerating terminals could be classified as Gray's type I. Thus, we have demonstrated that afferents from the mesencephalon terminate within synpatic clusters located in the principal and medial accessory (part A) subnuclei of the inferior olive. Although the mesencephalic afferents have multiple origins (Linauts and Martin, '78a), many of their synaptic terminals contact spiny appendages within the synaptic clusters. This postsynaptic site also receives cerebellar terminals (King et al., '76). The origin of presynaptic profiles within the synaptic clusters that contain clear pleomorphlic vesicles is yet to be determined.

Observations on the development of brainstem-spinal systems in the North American oppossum

The North American oppossum is born 12 to 13 days after conception and and is available for 90 days or more in an external pouch where it can be observed and experimentally manipulated. It is of particular interest that the hindlimbs of the newborn opossum are very immature and remain immobile for a week or more after birth. Degeneration techniques reveal that immature brainstem axons are present within the marginal zone of the lumbosacral cord before hindlimb movements begin (our state I) and material processed for formaldehyde induced fluorescence shows that some of them transport monoamines. Several lines of evidence suggest that part of the fluorescent axons arise within the nucleus locus coeruleus. At this early stage the electron microscope reveals that all brainstem-spinal axons are small (0.1--0.4 micrometer in diameter) and unmyelinated. By the time random hindlimb movements can be observed (stage II), brainstem axons, including those transporting monoamines, can be demonstrated to have grown into limited areas of the intermediate zone of the lumbosacral cord and to arise from most of the areas contributing to them in the adult animal (horseradish peroxidase technique). Such axons are still immature and it is not yet clear that they have formed synaptic terminals. Brainstem axons continue to grow into the intermediate zone of the lumbosacral cord for some time and come to occupy all of their adult territories before thoracic transection produces obvious change in hindlimb motility (beginning of stage III). It is still another 20 days or so before thoracic transection produces spinal shock comparable to that in the adult animal. The relatively mature use of the hindlimbs and the full expression of spinal shock correlate with changes in the technique and survival time needed to demonstrate degenerating brainstem axons in experimental material.