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Injections of horseradish peroxidase were made in lobules VI and VII of the cerebellar vermis (in the Cat). Serial frontal sections of the brain stem reveal that the lateral and paramedian nuclei were essentially projected onto lobule VI, and the projections from the raphe nuclei onto lobule VII.
A fluorescence histochemical and electron microscopic study of the monoaminergic cell groups in the squirrel monkey and Rhesus monkey brains has revealed the direct apposition of blood vessels to perikarya and dendrites of monoaminergic neurons. Capillaries and small arterioles or venules, ranging from 8-50 microns in diameter, showed perikarya and dendrites abutting the basement membrane without evidence of glial interposition. This neuronal-vascular relationship was present in 20% to 30% of the small vessels in the serotonergic nuclei raphe dorsalis and centralis superior and in the noradrenergic locus coeruleus. Such contacts were clearly present but observed less frequently in the dopaminergic substantia nigra pars compacta and in the serotonergic nuclei raphe obscurus, pallidus, magnus, and pontis. We postulate that monoamine-containing neurons apposed to blood vessels in certain regions of the brain may be influenced directly by hormones or other substances in blood.
The raphe nuclei of the rabbit brain stem were found in the midline and adjacent reticular formation of the medulla, pons, and mesencephalon. Nuclei raphe obscurus, pallidus, and magnus were located in the medulla. Nucleus raphe pontis and the caudal portion of nuclei raphe dorsalis and centralis superior were present in the pons. The rostral portion of nuclei raphe dorsalis and centralis superior, and nuclei linearis caudalis and intermedius were present in the msencephalon. Wings of neurons extended from the midline clusters of raphe neurons into the adjacent reticular formation. These wings of neurons contained serotonergic perikarya which were cytoarchitecturally indistinguishable from the midline neurons. A detailed localization of these nuclei is presented in atlas form. These raphe nuclei contained heterogeneous populations of neurons which varied in the size, shape and density of the cell bodies. In addition, the dendritic branching, specific orientation of dendrites, and appearance of spines were distinct for each of the raphe nuclei. Individual raphe nuclei often contained several subpopulations of neurons characterized by unique spatial configuration and orientation. The main morphological similarities of the raphe nuclei are location in or adjacent to the midline, the presence of serotonergic cell bodies in all raphe nuclei except the linear nuclei, and heterogeneous cell populations.
Time-course variations in tyrosine hydroxylase activity were measured in the locus coeruleus of the albino rat after electrolytic coagulation of either the nucleus raphe dorsalis or the nucleus raphe centralis. Highly significant increases were measured at 4 days after lesioning of the raphe dorsalis (30.33%) and the raphe centralis (81.55%) compared with control values, whereas the activity in groups A9 and A10 was unchanged at this time-point. In conjunction with other experimental evidences, an hypothesis is proposed that the catecholaminergic neurons located in the locus coeruleus are directly and/or indirectly controlled by the serotonin-containing neurons located in the anterior raphe system nuclei.
The descending projections to the spinal cord arising from the dorsolateral pontine tegmentum and brain stem raphe nuclei have been investigated by means of the horseradish peroxidase (HRP) technique. Particular attention was taken to clarify the cells of origin and the funicular trajectory of these spinal projections. After injections of HRP into the spinal cord, a significant of HRP labeled neurons were observed in the following dorsolateral pontine tegmental structures: (1) an area ventral to the nucleus cuneiformis; (2) principal locus coeruleus; (3) locus coeruleus a; (4) locuse subcoeruleus; (5) Kölliker-Fuse nucleus; and (6) nucleus parabrachialis lateralis. As a rule, the projections are ipsilateral and descendaphe-spinal projections, we have demonstrated that the nucleus raphe dorsalis also sends axons to the cervical segment of the spinal cord. Furthermore, in accord with previous reports, HRP labeled cells were also identified in the nucleus raphe magnus, pallidus and obscurus, but not in the nucleus raphe centralis superior and pontis. On the whole the present study further clarified the organization of spinal projections from the dorsolateral pons and raphe nuclei and provided some additional anatomical data for the physiology of the tegmentospinal and raphe-spinal projections.
1. The purpose of these experiments was to compare effects of electrical stimuli applied in two regions of the brain stem that are the sites of origin of descending bulbospinal systems; namely, the nucleus gigantocellularis of Brodal (7) and the nucleus raphe magnus, on the responses of lumbosacral spinothalamic neurons to mechanical stimuli. 2. In cats anesthetized with alpha-chloralose, stimulating in either of these structures with single pulses of current while the spinothalamic neuron was tonically activated by a sustained mechanical pressure resulted in an increase in the excitability of the cell followed by a prolonged suppression of its impulse activity. 3. For different neurons, the latency of the excitation ranged from 4 to 18 ms following the brain stem stimulus, while the latency of the suppression ranged from 16 to 34 ms. 4. In general, the effects of stimulating in the reticular formation and in the raphe nuclei were similar. although quantitative differences were found in the effects of each on different spinothalamic neurons. On the basis of these two studies, it is argued that the reticulospinal and raphe-spinal systems exert qualitatively similar effects on the responses of spinothalamic neurons evaluated in this experiment. 5. A comparison of the magnitudes of the suppression phase evoked from several different sites in the ipsilateral reticular formation and nucleus raphe magnus suggests that the descending systems arising from both these structures may be quite heterogeneous. 6. Stimulation of both regions of the brain stem produced a much greater suppression of the response of the spinothalamic neurons to slowly changing or sustained mechanical stimuli than to transient stimuli. It is suggested that the effects of descending systems arising both in the raphe nuclei and in the reticular formation on the responses of spinothalamic neurons to a mechanical stimulus are at least as dependent on the time course of the mechanical stimulus as they are on its intensity.
Effect of treatment with p-bromo-methamphetamine (V-111), the serotonin depleting drug, on two way avoidance conditioning (CAR) was studied in raphe lesioned male Wistar rats. Both sham lesioned and raphe lesioned animals treated with V-111 showed increased avoidance acquisition and increased number of inter-trial responses. Lesions of the raphe nuclei increased by itself the number of avoidance responses, the treatment with V-111 however produced further facilitation of avoidance acquisition. These results are discussed in terms of the role oserotonergic system in the processes of learning and retention of CAR, and direct action of V-111 on serotonergic system of the brain is suggested.
In experiments on male albino rats, after electrolytic lesions of dorsal and median mesencephalic raphe nuclei, l-DOPA and apomorphine did not exert their stimulating effect on aggressiveness and emotional reactivity, seen in control false-operated animals. The inhibitory effect of haloperidol on emotional reactivity increased after raphectomy. The stereotype behaviour elicited by dopaminergic agents and their effects on exploratory motor activity were not changed by raphectomy. It is assumed that the effects of dopamino-potentiating agents on emotional reactivity are partly mediated by their influence on serotonergic system.
Synaptogenesis was studied in the monoamine (MA) cell groups locus coeruleus (LC), dorsal and medial raphe nuclei (RN) and substantia nigra, zona compacta (SN) between day 18 of gestation and postnatal day 60 using ethanolic phosphotungstic acid (E-PTA) to visualize synaptic profiles. Nuclear area, and cellular packing density (inversely proportional to area of neuropil) were also determined. As determined using the E-PTA method, synaptogenesis begins in the neuropil of the SN first, on or before 18 days of gestation, and in the LC and RN at 19 days. Synaptogenesis on MA cell perikarya is first observed in the SN, on or before 18 days, and in the LC and RN at 20 days. The onset of somatic synaptogenesis coincides with the beginning of nuclear growth and development of the neuropil (decrease in cellular packing density) in all MA cell areas, raising the possibility of common factors in the initiation of these processes. Nonsynaptic contacts precede the appearance of synaptic profiles both in the neuropil and on the somata of the MA cells of the LC, RN and SN, and may represent precursors of mature synapses or desmosome-like contacts. Somatosomatic nonsynaptic contacts occur only prenatally between adjacent MA neurons in the LC, RN and SN. Although some synaptogenesis occurs prenatally in these MA cell groups (indiciating that these parts of the MA circuitry may be functional before birth), most of this synaptogenesis occurs postnatally and continues into adulthood. Since such synaptogenesis does not begin until 2-4 days prior to birth, whereas these neurons and their processes exhibit MA fluorescence as early as 12-14 days of gestation, they apparently are capable of synthesizing transmitter and proliferating terminals before they themselves are innervated.
The effect of electrolytic lesions of dorsal raphe nucleus (DRN) and median raphe nucleus (MRN), produced with two methods, was tested on catalepsy produced by spiperone, pimozide and haloperidol. Using two methods of evaluating catalepsy (acc. to Delini-Stula and Morpurgo and to Costall et al.) it has been found that both kinds of MRN lesions increase the catalepsy produced by neuroleptics, with the exception of the action of haloperidol as assayed with the Delini-Stula and Morpurgo method, and pimozide as assayed with the method of Costall et al. A lesion of DRN either slightly antagonized or did not influence the cataleptogenic action of neuroleptics.
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Afferent projections to the locus coeruleus from the various raphe nuclei, particularly of the midbrain (nuclei raphe dorsalis and medianus) and pons (nuclei raphe pontis and magnus), have been studied in the rat by retrograde transport methods using horseradish peroxidase (HRP). The locus coeruleus, in both its dorsomedial and ventrolateral divisions, and in its various anterior-posterior components, were injected with 0.05 microliters of horseradish peroxidase following which various structures of the brainstem, particularly the raphe nuclei, were examined for HRP reactive cells. It was found that injections in most components of the locus coeruleus were associated with HRP positive cells in varying degrees of density in the nuclei raphe dorsalis, medianus, pontis, and magnus, with considerably sparser labelling in the anterior aspects of the medullary raphe nuclei pallidus and obscurus. Labelled cells were also seen in the nuclei of the solitary tract, contralateral locus coeruleus. lateral reticular areas of the pons and midbrain, nuclei pontis oralis and caudalis, vestibular nuclei, mesencephalic nucleus of the trigeminal nerve, fastigial nuclei of cerebellum and medial parabrachial nuclei. These data, showing widespread innervation of the locus coeruleus from all raphe nuclei, as well as many other brainstem areas, in the rat support the general view of heavy innervation of the locus coeruleus from both extra-raphe and raphe nulcei. These latter raphe projections, probably serotonergic in nature, provide anatomical support for the various experiments indicating considerable regulation of locus coeruleus activities, such as phasic events of REM sleep, among other, by widespread projections from most raphe nuclei was well as several other regions of the brainstem.
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