The distribution and morphological characteristics of serotonergic cells in the brain of monotremes.

The distribution and cellular morphology of serotonergic neurons in the brain of two species of monotremes are described. Three clusters of serotonergic neurons were found: a hypothalamic cluster, a cluster in the rostral brainstem and a cluster in the caudal brainstem. Those in the hypothalamus consisted of two groups, the periventricular hypothalamic organ and the infundibular recess, that were intimately associated with the ependymal wall of the third ventricle. Within the rostral brainstem cluster, three distinct divisions were found: the dorsal raphe nucleus (with four subdivisions), the median raphe nucleus and the cells of the supralemniscal region. The dorsal raphe was within and adjacent to the periaqueductal gray matter, the median raphe was associated with the midline ventral to the dorsal raphe, and the cells of the supralemniscal region were in the tegmentum lateral to the median raphe and ventral to the dorsal raphe. The caudal cluster consisted of three divisions: the raphe obscurus nucleus, the raphe pallidus nucleus and the raphe magnus nucleus. The raphe obscurus nucleus was associated with the dorsal midline at the caudal-most part of the medulla oblongata. The raphe pallidus nucleus was found at the ventral midline of the medulla around the inferior olive. Raphe magnus was associated with the midline of the medulla and was found rostral to both the raphe obscurus and raphe pallidus. The results of our study are compared in an evolutionary context with those reported for other mammals and reptiles.

Ontogenesis of embryonic porcine ventral mesencephalon in the perspective of its potential use as a xenograft in Parkinson's disease.

Human fetal neural dopaminergic tissue can be transplanted and can ameliorate neurological deficiencies in patients with Parkinson's disease (PD). Donor tissue from other species has been used experimentally for several years in animal experiments and is now being considered an attractive alternative, particularly from a donor species that breeds in large litters, e.g., the pig. We have studied the early ontogenetic development of the mesencephalic dopaminergic system in the pig, utilising an anti-tyrosine hydroxylase (TH) immunocytochemical technique, and demonstrated the earliest appearance of its cell bodies at embryonic day 20 (E20). We compared the porcine data with those of human fetal development, as revealed by the same technique. Embryonic dopaminergic cell groups resembling the A8, A9, and A10 of the rat are present in the pig and differentiate into the homologous cell groups of human, although interesting quantitative differences are apparent. In the pig, prolonged presence of immature characteristics of TH-immunoreactive (TH-i.r.) cell bodies was observed, notwithstanding the early outgrowth of TH-i.r. axons into the ganglionic eminence. In the human, on the other hand, cell divisions and maturation of dendrites have progressed to a further degree than in the pig, before such distinct outgrowth of axons takes place. In pig embryos of 28 days, cells in the ventral mesencephalon had differentiated into TH containing neurons, which indicates their potential to synthesize dopamine. In spite of their differentiation, these cells still showed immature morphological features (rounded cell bodies with undifferentiated, short processes). Dopamine synthesis by these cells was demonstrated in previous studies by the high performance liquid chromatographic technique (HogenEsch et al. [1993] Can. J. Neurol. Sci. 20(suppl. 4):P.S. 235). In a separate paper, we have described that these porcine 28-day dopaminergic cells retain their potential for development and outgrowth in culture (van Roon et al. [1995] Res. Neurol. Neurosci. 7:199-205). We conclude that the ventral mesencephalon in pig embryos of 28 days is a potential source of dopaminergic neurons to be used as a xenograft in PD.

Afferent connections of the anterior thalamus in rabbits.

This study was designed to determine whether axons of cholinergic dorsal tegmental neurons terminate on cells in the anterior thalamus in rabbits as in other species, and to localize projecting tegmental cells for future studies of their contributions to anterior thalamic learning-relevant neuronal activity. The distribution of retrogradely labeled neurons was examined following injections of wheat germ agglutinin horseradish peroxidase (WGA-HRP) centered in the anterior ventral (AV) thalamic nucleus. The results confirm past findings in rabbits indicating projections to anterior thalamus from the mammillary nuclei, the posterior cingulate cortex, presubiculum and postsubiculum. Demonstrated for the first time in rabbits were projections from the lateral dorsal and the pedunculopontine tegmental nuclei, locus coeruleus, dorsal raphe nucleus, Gudden's dorsal tegmental nucleus, pretectum and reticular thalamic nucleus.

An experimental re-evaluation of the primary visual system of the European chameleon, Chamaeleo chameleon.

The retinofugal projections of the chameleon were investigated by means of autoradiography, horseradish peroxidase and fluorescent techniques after intraocular injection of tracers. An ipsilateral contingent of visual fibers and projections is absent. The retinal fibers decussate completely in alternating fascicles at the optic chiasma and course to terminate in two hypothalamic nuclei (nucleus suprachiasmaticus and nucleus opticus periventricularis hypothalami posterior), six thalamic nuclei (nucleus ovalis, nucleus geniculatus lateralis dorsalis partes lateralis and medialis, nucleus geniculatus lateralis ventralis, lateral part of nucleus dorsolateralis anterior, and nucleus ventrobasalis), four pretectal nuclei (nucleus griseus tectalis, nucleus lentiformis mesencephali, nucleus geniculatus pretectalis and nucleus posterodorsalis), the optic tectum (stratum griseum et fibrosum superficiale) and the tegmental nucleus opticus tegmenti. Our findings are, in general, compatible with previous descriptions of the primary visual system in other species of lizards. However, they indicate three features particular to chameleons: first, the total absence of an ipsilateral retinofugal projection; second, the existence of an additional hypothalamic visual center located in the posterior mediodorsal hypothalamus; and third, the large size of nucleus opticus tegmenti. These features are discussed in terms of the taxonomic position of chameleons with respect to other lizards.

Pattern of organization of primary visual pathways in the European lizard Podarcis sicula Rafinesque.

Central visual pathways are similarly organized in all vertebrates, although differences are also evident in the distribution of retinofugal axons in mammals, birds and reptiles. We traced the retinofugal projections in the European lizard Podarcis sicula Rafinesque and compared our observations with previous findings in other reptilian species, as well as in mammals and in birds, in order to contribute to the understanding of similarities and differences in the pattern of organization of visual pathways in these vertebrate classes. Either HRP or 3H-proline injections were placed into one eye. No differences in staining pattern were observed between HRP and 3H-proline experiments. Prominent retinofugal projections were observed to the thalamic nuclei nucleus dorsolateralis, nucleus geniculatus lateralis dorsalis, nucleus geniculatus lateralis ventralis and nucleus geniculatus lateralis ventralis, pars ventralis. In the hypothalamus the suprachiasmatic nucleus, and in the pretectum nuclei geniculatus pretectalis, lentiformis mesencephali and posterodorsalis contained detectable amounts of labeled terminals. Retinal fibers were distributed to layers 14 and 12 of the optic tectum and terminated in layers 13, 11, and 8. Labeled fibers were also present in the basal optic tract, and terminals were located in the nucleus of the basal optic tract. Ipsilateral retinofugal fibers were detected in the optic tract, and terminals were observed in the same thalamic and pretectal nuclei which receive crossed projections. No terminals in the ipsilateral tectal layers could be demonstrated. Compared to the crossed projection, the ipsilateral retinofugal contingent was very small. These results confirm and extend data from previous studies in reptiles and are consistent with the distribution of retinofugal fibers found in other vertebrates. The presence of ipsilateral retinofugal projections represents a common feature of the organization of visual pathways in reptiles, although its importance for binocular interactions remains to be elucidated.

Excitotoxic lesions of the pedunculopontine tegmental nucleus of the rat. I. Comparison of the effects of various excitotoxins, with particular reference to the loss of immunohistochemically identified cholinergic neurons.

The pedunculopontine tegmental nucleus (PPTg) has been shown to have cholinergic connections with the thalamus and basal ganglia. The ability of various doses of the excitotoxins (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) (AMPA), folate, ibotenate, kainate, N-methyl-D-aspartate (NMDA), quinolinate and quisqualate to make lesions in the PPTg was examined, with particular reference to their ability to destroy cholinergic neurons identified using choline acetyltransferase (ChAT) immunohistochemistry. All of the toxins induced convulsive activity on recovery from surgical anesthesia and all except folate made lesions in the PPTg and surrounding structures. The size of the lesions was computed following examination of Cresyl violet stained sections. The largest lesions were made by kainate = AMPA greater than NMDA = ibotenate greater than quisqualate = quinolinate. All of the toxins destroyed cholinergic neurons, higher doses producing greater loss than lower. The ratio of cholinergic cell loss to general neuronal loss (assessed by Cresyl violet staining) was also computed, revealing marked differences between the toxins. Statistical analysis showed that there were significant differences between excitotoxins in terms of this ratio, but these were accounted for by the low dose of quinolinate (24 nmol) producing a significantly greater ratio of damage (12.18:1) than every other toxin. (Next highest ratio: quisqualate 60 nmol, 6.22:1.) Between the other toxins (kainate, AMPA, ibotenate, quisqualate, NMDA and the high dose of quinolinate) there were no statistically significant differences. Intense calcium deposits (stained by Alizarin red) were found frequently and often defined the borders of the lesion. Tyrosine hydroxylase immunohistochemistry revealed axons running below and into the area of lesioned tissue suggesting strongly that fibers were undamaged by the lesions. We conclude that in the PPTg, different excitotoxins make discriminably different lesions, both quantitatively and qualitatively. Unlike excitotoxic lesions in the basal forebrain quinolinate, not quisqualate, made the most selective lesions of cholinergic neurons and, unlike excitotoxic lesions in the septal nuclei, non-myelinated fibers were spared by ibotenate. The implications of these data for research into brainstem mechanisms of Parkinson's disease are discussed.

Properties of "possibly" cholinergic neurons ascending from the rat ponto-mesencephalic area: comparison with noradrenergic and serotonergic neurons.

In urethane-anesthetized rats single neuronal activity was recorded in the laterodorsal tegmental nucleus, which has a dense complement of cholinergic neurons. In many experiments neuronal activity was recorded also in the dorsal raphe and locus coeruleus for comparison. In each experiment two to five active sites were marked with pontamine sky blue, deposited from the recording electrode ionophoretically and located histologically. Most neurons of the laterodorsal tegmental nucleus responded antidromically to stimulation of either one or more of the following sites: medial frontal cortex, medial septal nucleus, lateral geniculate nucleus or superior colliculus. Conduction velocities of their axons, estimated from latencies of antidromic responses, were within the range of unmyelinated fibers. Most of them gave rise to broad spikes (positive stroke, greater than 1.0 msec; negative stroke, greater than 3.0 msec), resembling monoaminergic neurons. Others generated brief spikes (positive and negative strokes, less than 0.8 and less than 2.2 msec). The former are probably cholinergic. Some neurons in the laterodorsal tegmental nucleus had rather regular spontaneous firing at a low rate (0.2-5 Hz), while others were not spontaneously active. Their response to noxious stimulation (tail pinch) was different from neuron to neuron, but that most frequently encountered was limited to phasic excitation, in contrast to locus coeruleus neurons which showed phasic excitation followed by mild tonic excitation; and to dorsal raphe neurons likely to be suppressed. Upon repetition of tail pinch the response of laterodorsal tegmental nucleus neurons tended to become weak or disappear while a desynchronized pattern continued to appear in the EEG in each occasion. Thus, putative cholinergic neurons, which constitute a major group in the laterodorsal tegmental nucleus, have properties similar to those of monoaminergic neurons, except for the phasic and decrementing nature of their response to tail pinch. The cholinergic, noradrenergic, and serotonergic ascending projections seem likely to subserve different roles in regulating activity of the forebrain.

Contralateral pallidothalamic and pallidotegmental projections in primates: an anterograde and retrograde labeling study.

Unilateral injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) in the internal segment of the pallidum (GPi) of the squirrel monkey (Saimiri sciureus) led to anterograde labeling of fibers ipsilaterally in the following thalamic nuclei: ventral anterior (VA), ventral lateral (VL), centromedian (CM), and lateral habenula (Hbl). The labeled fibers reached these ipsilateral thalamic nuclei by coursing along or through the ansa lenticularis, the lenticular and thalamic fasciculi, and the Forel's fields. They arborized profusely in VA/VL nuclei where they displayed small glomerule-like formations. Numerous labeled fibers also occurred in the CM. Most of them were long, varicose and gave rise to shorter fibers that formed a dense terminal field covering a large portion of the CM. A small but dense terminal field composed of delicate fibers and extremely fine terminals was noted in the Hbl. A large contingent of labeled fibers were seen to cross the midline, principally at the rostral pole of the CM and in the supramammillary decussation, to reach the contralateral thalamus where they arborized profusely in the VA/VL and CM nuclei, but not in the Hbl. The patterns of termination of these contralateral pallidothalamic fibers were strikingly similar to those observed ipsilaterally. Other anterogradely labeled fibers were also noted bilaterally in the pedunculopontine nucleus (TPP) and ipsilaterally in the external segment of the pallidum (GPe) and in the putamen. Complementary, double-labeling, retrograde studies involving the injection of nuclear yellow in the VA/VL and CM nuclei and Fast blue in the TPP, confirmed the existence of contralateral pallidothalamic and pallidotegmental projections. The number of retrogradely labeled cells in the contralateral GPi amounted approximately to 10-20% that in the ipsilateral GPi. These experiments further indicated that contralaterally projecting pallidothalamic neurons exhibited a high degree of axonal collateralization, the majority of its neurons projecting also to the contralateral TPP. Cells retrogradely labeled with the tracer injected into the thalamus were also encountered bilaterally in the thalamic reticular nucleus. Taken together, the results of these anterograde and retrograde investigations indicate that the contralateral pallidothalamic projection involves a relatively small population of GPi neurons, but that these neurons arborize extensively in their contralateral thalamic targets. Furthermore, the presence of retrogradely labeled cells in the ipsi- and contralateral reticular thalamic nucleus indicates that the VA/VL and CM nuclei, which receive a massive input from the GPi, are under the bilateral influence of this perithalamic nucleus. Such contralateral projections could play a major role in the subcortical organization of the bilateral aspect of normal basal ganglia function.(ABSTRACT TRUNCATED AT 400 WORDS)

Organization of the visual system in larval lampreys: an HRP study.

The organization of the visual system of larval lampreys was studied by anterograde and retrograde transport of HRP injected into the eye. The retinofugal system has two different patterns of organization during the larval period. In small larvae (less than 60-70 mm in length) only a single contralateral tract, the axial optic tract, is differentiated. This tract projects to regions in the diencephalon, pretectum, and mesencephalic tegmentum. In larvae longer than 70-80 mm, there is an additional contralateral tract, the lateral optic tract, which extends to the whole tectal surface. In addition, ipsilateral retinal fibers are found in both small and large larvae. Initially, the ipsilateral projection is restricted to the thalamus-pretectum, but it reaches the optic tectum in late larvae. Changes in the organization of the optic tracts coincide with the formation of the late-developing retina and consequently, the origin of the optic tracts can be related to specific retinal regions. The retinopetal system is well developed in all larvae. Most retinopetal neurons are labeled contralaterally and are located in the M2-M5 nucleus of the mesencephalic tegmentum, in the caudolateral mesencephalic reticular area and adjacent ventrolateral portions of the optic tectum. Dendrites of these cells are apparent, especially those directed dorsally, which in large larvae extend to the optic tectum overlapping with the retino-tectal projection. These results indicate that in lampreys, visual projections organize mainly during the blind larval period before the metamorphosis, their development being largely independent of visual function.

Subcortical afferents to the interstitial nucleus of Cajal: an anatomical retrograde tracing study in the rabbit.

Organization of brainstem projections to the interstitial nucleus of Cajal (INC) in the rabbit has been studied using the method of retrograde transport of horseradish peroxidase or wheat germ agglutinin-horseradish peroxidase conjugate. Injections of tracers into INC resulted in bilateral labelling in the medial terminal nucleus of the accessory optic tract, medial region of the zona incerta, vestibular nuclei (superior, medial, inferior), rostral portion of the prepositus nucleus and several nuclei of the pontine and medullary reticular formation. Retrograde labelling on the contralateral side was noted in all 4 deep cerebellar nuclei, the lateral vestibular nucleus, group Y, the rostral interstitial nucleus of the medial longitudinal fascicle, INC and mesencephalic reticular formation dorsal and lateral to the red nucleus. Cells of origin for the ipsilateral afferents of INC were found only in the nucleus of the posterior commissure. These data are discussed in relation to other morphological and physiological studies of afferent connectivity of INC in other species.

Basal forebrain and mesopontine tegmental projections to the reticular thalamic nucleus: an axonal collateralization and immunohistochemical study in the rat.

Using a double fluorescence retrograde labeling procedure, the present study sought to determine the degree to which basal forebrain and mesopontine tegmental neurons have axons that innervate both the reticular thalamic nucleus and the cerebral cortex. Immunofluorescence for choline acetyltransferase, somatostatin, and the calcium-binding protein parvalbumin was also performed to elucidate the neurochemical identity of basal forebrain and mesopontine tegmental inputs to the reticular thalamic nucleus. A significant portion (10-15%) of neurons in the basal forebrain and mesopontine tegmentum that were retrogradely labeled from the reticular thalamic nucleus were also found to be retrogradely labeled from the cortex. Many of these neurons stained positively for choline acetyltransferase. Of the basal forebrain neurons retrogradely labeled from the reticular thalamic nucleus, approximately 20% were found to be immunoreactive to choline acetyltransferase, whereas none was stained for somatostatin. A larger portion (up to 50%) of the basal forebrain neurons that were retrogradely labeled from the reticular thalamic nucleus were parvalbumin-immunoreactive, and some of these were also retrogradely labeled from the cortex. These results suggest that a subpopulation of cholinergic and non-cholinergic neurons in the basal forebrain and the mesopontine tegmentum may influence simultaneously the activity of neurons in the reticular thalamic nucleus and the cerebral cortex.

Neural associations of the substantia innominata in the rat: afferent connections.

The afferent connections of the substantia innominata (SI) in the rat were determined employing the anterograde axonal transport of Phaseolus vulgaris leucoagglutinin (PHA-L) and the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), in combination with histochemical procedures to characterize the neuropil of the SI and identify cholinergic cells. Both neurochemical and connectional data establish that the SI is organized into a dorsal and a ventral division. Each of these divisions is strongly affiliated with a different region of the amygdala, and, together with its amygdalar affiliate, forms part of one of two largely distinct constellations of interconnected forebrain and brainstem cell groups. The dorsal SI receives selective innervation from the lateral part of the bed nucleus of the stria terminalis, the central and basolateral nuclei of the amygdala, the fundus of the striatum, distinctive perifornical and caudolateral zones of the lateral hypothalamus, and caudal brainstem structures including the dorsal raphe nucleus, parabrachial nucleus, and nucleus of the solitary tract. Projections preferentially directed to the ventral SI arise from the medial part of the bed nucleus of the stria terminalis, the rostral two-thirds of the medial nucleus of the amygdala, a large region of the rat amygdala that lies ventral to the central nucleus, the medial preoptic area, anterior hypothalamus, medialmost lateral hypothalamus, and the ventromedial hypothalamus. Both SI divisions appear to receive afferents from the dorsomedial and posterior hypothalamus, supramammillary region, ventral tegmental area, and the peripeduncular area of the midbrain. Projections to the SI whose selectivity was not determined originate from medial prefrontal, insular, perirhinal, and entorhinal cortex and from midline thalamic nuclei. Findings from both PHA-L and WGA-HRP experiments additionally indicate that cell groups preferentially innervating a single SI division maintain numerous projections to one another, thus forming a tightly linked assembly of structures. In the rat, cholinergic neurons that are scattered throughout the SI and in parts of the globus pallidus make up a cell population equivalent to the primate basal nucleus of Meynert (Mesulam et al.: Neuroscience 10:1185-1201, '83). PHA-L-filled axons, labelled from lectin deposits in the dorsal raphe nucleus, peripeduncular area, ventral tegmental area, or caudomedial hypothalamus were occasionally seen to approach individual cholinergic neurons int he SI, and to contact the surface of such cells with axonal varicosities (putative synaptic boutons.(ABSTRACT TRUNCATED AT 400 WORDS)

Separate non-cholinergic descending projections and cholinergic ascending projections from the nucleus tegmenti pedunculopontinus.

A substantial population of cells from the nucleus tegmenti pedunculopontinus was demonstrated to have descending projections to the spinal cord using fluorescent retrograde axonal tracers. Double-labeling studies showed that separate perikarya in this region have descending versus ascending projections. The distributions of the cell bodies with ascending or descending projections were spatially distinct, but partially overlapping. Some ascending, but not the descending, projections were cholinergic.

The crossed nigrostriatal projection decussates in the ventral tegmental decussation.

Horseradish peroxidase (HRP) tract-tracing techniques were used in 44 rats in order to establish the site of decussation of the crossed nigrostriatal projection. Somata in both the ipsilateral and the contralateral ventromedial mesencephalon were labelled after injection of HRP into the caudate nucleus. In agreement with previous studies, contralateral labelling constituted about 3% of the ipsilateral labelling. Midsagittal transection of the mesodiencephalic junction did not prevent the contralateral labelling. However, mid-sagittal transection of the ventral mesencephalon, or selective 6-hydroxydopamine (6-OHDA) lesions of the ventral tegmental decussation did prevent the contralateral labelling. Moreover, 6-OHDA lesions of the substantia nigra ipsilateral to the horseradish peroxidase injection also prevented contralateral labelling. We conclude that the crossed nigrostriatal projection decussates in the ventral tegmental decussation, and that this projection is susceptible to damage by standard 6-OHDA lesions located on the opposite side to the origin of the crossed pathway.

The origins of cholinergic and other subcortical afferents to the thalamus in the rat.

The origins of the cholinergic and other afferents of several thalamic nuclei were investigated in the rat by using the retrograde transport of wheat germ agglutinin conjugated-horseradish peroxidase in combination with the immunohistochemical localization of choline acetyltransferase immunoreactivity. Small injections placed into the reticular, ventral, laterodorsal, lateroposterior, posterior, mediodorsal, geniculate, and intralaminar nuclei resulted in several distinct patterns of retrograde labelling. As expected, the appropriate specific sensory and motor-related subcortical structures were retrogradely labelled after injections into the principal thalamic nuclei. In addition, other basal forebrain and brainstem structures were also labelled, with their distribution dependent on the site of injection. A large percentage of these latter projections was cholinergic. In the brainstem, the cholinergic pedunculopontine tegmental nucleus was retrogradely labelled after all thalamic injections, suggesting that it provides a widespread innervation to the thalamus. Neurons of the cholinergic laterodorsal tegmental nucleus were retrogradely labelled after injections into the anterior, laterodorsal, central medial, and mediodorsal nuclei, suggesting that it provides a projection to limbic components of the thalamus. Significant basal forebrain labelling occurred only with injections into the reticular and mediodorsal nuclei. Only injections into the reticular nucleus resulted in retrograde labelling of the cholinergic neurons in the nucleus basalis of Meynert. The results provide evidence for an organized system of thalamic afferents arising from cholinergic and noncholinergic structures in the brainstem and basal forebrain. The brainstem structures, especially the cholinergic pedunculopontine tegmental nucleus, appear to project directly to principal thalamic nuclei, thereby providing a possible anatomical substrate for mediating the well-known facilitory effects of brainstem stimulation upon thalamocortical transmission.

Some anatomical observations on the projections from the hypothalamus to brainstem and spinal cord: an HRP and autoradiographic tracing study in the cat.

The hypothalamus is closely involved in a wide variety of behavioral, autonomic, visceral, and endocrine functions. To find out which descending pathways are involved in these functions, we investigated them by horseradish peroxidase (HRP) and autoradiographic tracing techniques. HRP injections at various levels of the spinal cord resulted in a nearly uniform distribution of HRP-labeled neurons in most areas of the hypothalamus except for the anterior part. After HRP injections in the raphe magnus (NRM) and adjoining tegmentum the distribution of labeled neurons was again uniform, but many were found in the anterior hypothalamus as well. Injections of 3H-leucine in the hypothalamus demonstrated that: The anterior hypothalamic area sent many fibers through the medial forebrain bundle (MFB) to terminate in the ventral tegmental area of Tsai (VTA), the rostral raphe nuclei, the nucleus Edinger-Westphal, the dorsal part of the substantia nigra, the periaqueductal gray (PAG), and the interpeduncular nuclei. Further caudally a lateral fiber stream (mainly derived from the lateral parts of the anterior hypothalamic area) distributed fibers to the parabrachial nuclei, nucleus subcoeruleus, locus coeruleus, the micturition-coordinating region, the caudal brainstem lateral tegmentum, and the solitary and dorsal vagal nucleus. Furthermore, a medial fiber stream (mainly derived from the medial parts of the anterior hypothalamic area) distributed fibers to the superior central and dorsal raphe nucleus and to the NRM, nucleus raphe pallidus (NRP), and adjoining tegmentum. The medial and posterior hypothalamic area including the paraventricular hypothalamic nucleus (PVN) sent fibers to approximately the same mesencephalic structures as the anterior hypothalamic area. Further caudally two different fiber bundles were observed. A medial stream distributed labeled fibers to the NRM, rostral NRP, the upper thoracic intermediolateral cell group, and spinal lamina X. A second and well-defined fiber stream, probably derived from the PVN, distributed many fibers to specific parts of the lateral tegmental field, to the solitary and dorsal vagal nuclei, and, in the spinal cord, to lamina I and X, to the thoracolumbar and sacral intermediolateral cell column, and to the nucleus of Onuf. The lateral hypothalamic area sent many labeled fibers to the lateral part of the brainstem and many terminated in the caudal brainstem lateral tegmentum, including the parabrachial nuclei, locus coeruleus, nucleus subcoeruleus, and the solitary and dorsal vagal nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

The anatomical organization of retinal projections in the shark Scyliorhinus canicula with special reference to the evolution of the selachian primary visual system.

The retinal projections of the shark Scyliorhinus canicula were investigated using both the degeneration technique after eye removal and the radioautographic method following the intraocular injection of various tritiated tracers (proline, leucine, fucose, adenosine). The results showed contralateral projection via different optic tract components (TOM, AOT, TOm, TOl, ROVm, RODm) to various areas and nuclei of the hypothalamus (NSC), thalamus (NODLAT, NODMAT, NTTOM, NOVT, NODPT), pretectum (NOPC, NOCPd, NOCPv), tectum (SFGS, SGI) and mesencephalic tegmentum (AOTMd, NOTMv). Ipsilateral retinal projections were found to arborize within 7 distinct zones at the hypothalamic (NSC), thalamo-pretectal (NODLAT, NTTOM, NOVT, NOPC, NOCpd) and tectal (SFGS) levels. A comparison of the data with those previously obtained in different species of elasmobranchs and batoids indicate the existence of a common and consistent pattern of organization of the primary visual system in all selachians. Many of the discrepancies reported in studies on the organization of selachian retinal projection may be listed to methodological differences and/or interspecies variations in the cytoarchitecture of the different visual centers. Moreover, a comparison of the primary visual system of more primitive squalomorph sharks with that of the more advanced galeomorph sharks and batoids suggests that this system evolved through an increase in the neuronal density of the target structures and transformations in the dendritic configurations of the postsynaptic neurons rather than through an increase in the total number of projection zones.

Afferent projections to the interpeduncular nucleus in the rat, as studied by retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase.

We examined the afferent projections to the subnuclei of the interpeduncular nucleus (IPN) in the rat by means of retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). We observed locations of retrogradely labeled cells following injections of WGA-HRP into the IPN, and distributions of anterogradely labeled fibers and terminals within the IPN following injections into the areas that contain cells of origin of afferents. Results of the retrograde and anterograde experiments have clarified the detailed organization of the IPN afferents. A part of the nucleus incertus, located dorsomedial to the dorsal tegmental nucleus, projects to the contralateral half of the rostral subnucleus of the IPN; the pars caudalis of the dorsal tegmental nucleus projects sparsely to the rostral lateral, dorsal lateral, lateral, caudal, and apical subnuclei predominantly contralaterally; the laterodorsal tegmental nucleus, to most of the subnuclei predominantly contralaterally; the ventromedial central gray rostral to the dorsal tegmental nucleus and lateral to the dorsal raphe nucleus projects to the rostral lateral and dorsal lateral subnuclei predominantly contralaterally; the median raphe nucleus, substantially to all subnuclei; the medial habenular nucleus, in a topographic manner, to the rostral, central, and intermediate subnuclei, to the rostral lateral and lateral subnuclei predominantly ipsilaterally, and to the dorsal lateral subnucleus predominantly contralaterally; the supramammillary nucleus and areas around the origin of the mammillothalamic tract and near the third ventricle project sparsely to the ventral part of the rostral subnucleus and to the central, lateral, caudal and apical subnuclei; the nucleus of the diagonal band, sparsely to the rostral, central, dorsal lateral, caudal, and apical subnuclei. These differential projections of the afferents to the subnuclei of the IPN may reflect its complex functions within the limbic midbrain circuit.

Cholinergic systems in the rat brain: III. Projections from the pontomesencephalic tegmentum to the thalamus, tectum, basal ganglia, and basal forebrain.

The ascending cholinergic projections of the pedunculopontine and dorsolateral tegmental nuclei, referred to collectively as the pontomesencephalotegmental (PMT) cholinergic complex, were investigated by use of fluorescent tracer histology in combination with choline-O-acetyltransferase (ChAT) immunohistochemistry and acetylcholinesterase (AChE) pharmacohistochemistry. Propidium iodide, true blue, or Evans blue was infused into the anterior, reticular, mediodorsal, central medial, and posterior nuclear areas of the thalamus; the habenula; lateral geniculate; superior colliculus; pretectal/parafascicular area; subthalamic nucleus; caudate-putamen complex; globus pallidus; entopeduncular nucleus; substantia nigra; medial septal nucleus/vertical limb of the diagonal band area; magnocellular preoptic/ventral pallidal area; and lateral hypothalamus. In some animals, separate injections of propidium iodide and true blue were made into two different regions in the same rat brain, usually a dorsal and a ventral target, in order to assess collateralization patterns. Retrogradely transported fluorescent labels and ChAT and/or AChE were analyzed microscopically on the same brain section. All of the above-delimited targets were found to receive cholinergic input from the PMT cholinergic complex, but some regions were preferentially innervated by either the pedunculopontine or dorsolateral tegmental nucleus. The former subdivision of the PMT cholinergic complex projected selectively to extrapyramidal structures and the superior colliculus, whereas the dorsolateral tegmental nucleus was observed to provide cholinergic input preferentially to anterior thalamic regions and rostral portions of the basal forebrain. The PMT cholinergic neurons showed a tendency to collateralize extensively.