The distribution of putative neurotransmitters in the lateral geniculate nucleus of the rat

Selective reduction of glutamate in the rat superior colliculus and dorsal lateral geniculate nucleus after contralateral enucleation

The effects of afferent lesions on the levels of glutamate, aspartate and gamma-aminobutyric acid (GABA) in the laminae of the superior colliculus (SC) and dorsal lateral geniculate nucleus (dLGN) of the rat were studied, using microassay methods for these amino acids. The analysis was performed 12-14 days after left eye enucleation, or ablation of right visual cortical area, or both left eye enucleation and ablation of right visual cortex. Superficial gray layer (SGL) and deep layers in the SC were dissected out from the thin-sectioned, freeze-dried sample. In the dLGN, the outer and inner laminae were separately dissected. The glutamate contents in the upper half of SGL and outer lamina of dLGN contralateral to eye enucleation decreased significantly (15%). Combination of eye enucleation and visual cortical ablation further decreased the glutamate content in the upper half of the right SGL (29.3%). On the other hand, aspartate and GABA concentrations in the SC and dLGN exhibited no significant reduction after deafferentations. These results indicate that the retino-tectal and retino-geniculate pathway of the rat may be glutamatergic in nature.

An immunocytochemical analysis of the lateral geniculate complex in the pigeon (Columba livia)

The lateral geniculate complex (GL) of pigeons was investigated with respect to its immunohistochemical characteristics, retinal afferents, and the putative transmitters/modulators of its neurons. The distributions of serotonin-, choline acetyltransferase-, glutamic acid decarboxylase-, tyrosine hydroxylase-, neuropeptide Y- (NPY), substance P- (SP), neurotensin- (NT), cholecystokinin- (CCK), and leucine-enkephalin- (L-ENK) like immunoreactive perikarya and fibers were mapped. Retinal projections were studied following injections of Rhodamine-B-isothiocyanate into the vitreous. Transmitter-specific projections onto the visual Wulst and the optic tectum were studied by simultaneous double-labelling of retrograde tracer molecules and immunocytochemical labelling. The GL can be divided into three major subdivisions, the n. geniculatus lateralis, pars dorsalis (GLd; previously designated as the n. opticus principalis thalami, OPT), the n. marginalis tractus optici (nMOT), and the n. geniculatus lateralis, pars ventralis (GLv). All three subdivisions are retinorecipient. The GLd can be further subdivided into at least five components differing in their immunohistochemical characteristics: n. lateralis anterior (LA); n. dorsolateralis anterior thalami, pars lateralis (DLL), n. dorsolateralis anterior thalami, pars magnocellularis (DLAmc); n. lateralis dorsalis nuclei optici principalis thalami (LdOPT); and n. suprarotundus (SpRt). The LdOPT consists of an area of dense CCK-like and NT-like terminals of probable retinal origin. Three subnuclei (DLL, DLAmc, SpRt) were shown to project to the visual Wulst. Cholinergic and cholecystokinergic relay neurons participated in this projection. The nMOT occupies a position between the GLd and GLv and encircles the rostral pole of n. rotundus and the LA. It is characterized mainly by medium sized NPY-like perikarya which were shown to project onto the ipsilateral optic tectum. Bands of NPY-like fibers in the tectal layers 2, 4, and 7 could at least in part be due to this projection of the nMOT. Most of the antisera used revealed transmitter/modulator-specific fiber systems in the GLv which often showed a layer-specific distribution. Perikaryal labelling was only obtained with glutamic acid decarboxylase. On the basis of its chemoarchitectonics, topography, and connectional pattern, the GLd complex of pigeons is most directly equivalent to the mammalian GLd. However, although the different subdivisions of the avian GLd may represent functionally different channels within the thalamofugal pathway similar to the lamina-specific differentiation within the mammalian geniculostriate projection, direct comparison of subnuclei of birds and mammals is not justified at this time. The nMOT appears similar to the intergeniculate leaflet (IGL) and the avian GLv clearly corresponds in many features to the mammalian GLv.

Depletion of brain serotonin by 5,7-DHT modifies hamster circadian rhythm response to light

The midbrain raphe complex innervates the circadian rhythm regulating system by direct projections to the suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL). The present experiments examined the changes in circadian rhythm regulation consequent to the depletion of brain serotonin by central 5,7-dihydroxytryptamine (DHT) application. Adult male hamsters with access to running wheels were entrained to a light-dark cycle 14:10 (LD) of photoperiod, pre-treated with desmethylimipramine and given bilateral lateral ventricle infusions of 75 micrograms DHT/2.5 microliters 0.5% ascorbic acid in saline or vehicle only. Two separate experiments were performed. Four weeks after surgery, animals were transferred to either constant light (LL; Experiment 1) or constant dark (DD; Experiment 2). Animals remained in LL for 85 days, then were transferred to DD for 50 days, followed by a return to LD 14:10 for 14 days. Animals in Expt. 2 remained in DD for 55 days, were given 3 days food deprivation, then, beginning 35 days later, were periodically exposed to 30 min light pulses as a phase response curve (PRC) to light was generated. DHT treatment induced rapid appearance of advanced activity onset, delayed offset and longer duration of the nocturnal activity phase. DHT animals in LL had circadian locomotor rhythms much longer than control animals (24.43 +/- 0.04 vs 24.19 +/- 0.05 h) and normal circadian rhythmicity was rapidly lost by DHT animals in LL. There was no effect of DHT on circadian period in DD, but the DHT treated animals in DD had a larger phase delay region of the PRC than did controls and this was associated with an overall change in the temporal properties of the PRC. Serotonin immunohistochemistry showed an approximate 90% loss of cells from the dorsal raphe nucleus and decreased density of the serotonergic terminal field in the SCN and IGL. The results support the view that the serotonergic system modulates the phasic actions of light on the hamster circadian rhythm system. The data also indicate that hamsters can have a Type 0 PRC.

Immunocytochemical characterization of the suprachiasmatic nucleus and the intergeniculate leaflet in the diurnal ground squirrel, Spermophilus lateralis

The suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL) are retinorecipient structures that play important roles in the expression of circadian rhythmicity. We examined these two structures in a diurnal ground squirrel, Spermophilus lateralis, using immunohistochemical techniques, and cholera toxin-bound horseradish peroxidase. A number of immunoreactive substances are distributed within the ground squirrel SCN in a pattern similar to that reported in many other mammals. These include vasopressin, vasoactive intestinal polypeptide, serotonin, neuropeptide Y (NPY), and glial fibrillary acidic protein. The squirrel SCN differs from that of most other species examined to date in two respects. First, a dense cluster of cells containing immunoreactive L-enkephalin (L-ENK-IR) is observed in the center of the SCN. Second, there is a contralateral, but no ipsilateral, projection from the retina to the SCN. In the lateral geniculate region there is a substantial region that contains NPY-immunoreactive cells and receives a bilateral retinal projection. This region is assumed to be homologous with the IGL described in other mammals. Cells containing L-ENK-IR are distributed throughout the LGN in groups that overlap, but which have a distinctly different distribution than the more extensive groups of NPY-IR cells.

Retinal fibers make synaptic contact with neuropeptide Y and enkephalin immunoreactive neurons in the intergeniculate leaflet of the rat

Direct synapses between retinal fibers and neuropeptide Y (NPY) and/or enkephalin-immunoreactive (ENK-I) neurons were investigated in the intergeniculate leaflet (IGL) of the rat, using combined immunohistochemical and degeneration techniques. Degenerating retinal fibers terminated on dendrites of NPY-I and/or ENK-I neurons. NPY-I fibers in the IGL formed axo-dendritic synapses on non-immunoreactive dendrites. Most of them were asymmetrical synapses. ENK-I axon terminals contacted non-immunoreactive dendrites with symmetrical synapse.

Motor activity correlates negatively with free-running period, while positively with serotonin contents in SCN in free-running rats

Free-running period of blinded rats kept in a cage with a running wheel varied markedly, while it varied little in rats kept in a cage without a running wheel. The mean free-running period of the former group is significantly shorter than that of the latter. In the former, the free-running period correlated negatively with motor activity, indicating that activity affects the free-running period. In both groups, essentially similar diurnal patterns of biogenic amines and their metabolites were observed in various discrete areas in the brain examined. However, there was a significant difference between the two groups in several areas. In the SCN, 5-HT content correlated positively with motor activity, consequently correlated negatively to the free-running period at 3 out of 4 sampling times over 24 h but no such correlation was observed in other monoamines and their metabolites examined. These facts suggest that 5-HT may be associated with modification of the free-running period.

Development of substance P, Leu-enkephalin and serotonin profiles in the lateral geniculate nuclear complex of albino rat

Immunohistochemical studies for analysing the development of the profile of two peptides--substance P (SP) and Leu-enkephalin (Leu-ENK), and serotonin (SER)--have been conducted on the lateral geniculate nuclear (LGN) complex of albino rats at gestation day 18 and various postnatal age periods. SP immunoreactivity is found to increase from 1 day postnatal (DPN) up to 20 DPN and decrease thereafter, whereas the SER and Leu-ENK-immunoreactive fibres and terminals seen as occasional fibres at 1, 5, and 10 DPN are better visualized from 20 DPN and gradually increase up to 40 DPN. The possible role and significance of the changes seen in these putative neurotransmitters/neuromodulators with development are discussed.

Thalamic origin of neuropeptide Y innervation of the accessory optic nucleus of the pigeon (Columba livia)

Immunohistochemical and tracing techniques were used in combination to reveal the source of a neuropeptide Y-like immunoreactive (NPY-LI) plexus in the nucleus of the basal optic root (nBOR) of the pigeon accessory optic system. Injections of rhodamine-labeled latex microspheres into nBOR produced retrograde labeling of a population of neurons interposed between the principal optic nucleus of the dorsolateral thalamus (equivalent to the mammalian dorsal lateral geniculate nucleus) and the ventral lateral geniculate nucleus. The retrogradely labeled neurons were distributed mainly in the immediate vicinity of the lateral, dorsal, and ventral aspects of the nucleus rotundus. Immunohistochemical methods revealed many NPY-containing somata within the same intergeniculate thalamic area. Double-labeling immunohistochemical and retrograde tracing experiments evidenced that many NPY-LI neurons in the intergeniculate area contained rhodamine microspheres that had been previously injected into the ipsilateral nBOR. The projection of that general thalamic area to the nBOR was then confirmed by means of anterograde transport of Phaseolus vulgaris leucoagglutinin. In these experiments, the intergeniculate region was demonstrated to project to all divisions of the nBOR and to every other retino-recipient structure, including the suprachiasmatic nucleus. Finally, electrolytic lesions of the intergeniculate area produced a dramatic reduction in the number of NPY-LI axons and terminals within the ipsilateral nBOR and also within other retino-recipient structures. These data indicate the existence of a thalamic NPY-LI projection to the pigeon nBOR of the accessory optic system. This chemically specific projection originates from the intergeniculate area, which was shown in this study to project to all other retino-recipient structures. Thus, NPY may have a role in the functional organization of the accessory optic system and also of the avian visual system as a whole.

Destruction of the hamster serotonergic system by 5,7-DHT: effects on circadian rhythm phase, entrainment and response to triazolam

The role of the serotonergic system in the regulation of hamster circadian rhythms was analyzed using intraventricular injection of the selective neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT). Sixty days after 5,7-DHT administration, immunoreactive serotonin in the forebrain, particularly the suprachiasmatic nuclei and intergeniculate leaflets, was severely depleted in 16 animals, moderately depleted in four and only slightly affected in four. 5,7-DHT produced an immediate and sustained advance of the onset of running wheel activity relative to the 24 h light-dark (LD) cycle. Activity onset occurred 0.7 +/- 0.07 h before lights out among 5,7-DHT-treated animals compared with 0.18 +/- 0.04 h after lights out for vehicle-infused controls. This new, advanced phase angle of entrainment was maintained throughout the 60-day period of the study while the animals remained in a LD cycle, including after an 8-h phase advance of the light cycle. 5,7-DHT treatment also delayed the offset of wheelrunning in 16 of 24 animals and reduced the likelihood of a smooth pattern of reentrainment to the shifted LD cycle. The drug treatment did not affect circadian period in constant darkness, the rate of reentrainment to an 8-h phase advance or the amount of wheelrunning activity per day. In addition, 5,7-DHT treatment had no effect on the ability of triazolam, a short-acting benzodiazepine, to accelerate the rate of reentrainment to an 8-h phase advance. These observations show that ascending projections of midbrain raphe serotonin neurons participate in the regulation of the circadian activity phase but are not required for triazolam-induced acceleration of reentrainment to a phase-advanced LD cycle.

Distribution and synaptic organization of serotoninergic and noradrenergic axons in the lateral geniculate nucleus of the rat

Antisera raised against the monoamines serotonin (5-HT) and noradrenaline (NA) were employed in a study designed to provide a detailed description of the distribution, morphology, and synaptic organization of the serotoninergic and noradrenergic afferents in the lateral geniculate nucleus (LGN) of the rat. The distribution patterns of the two types of immunoreactive fibers were distinct and largely complementary to each other. NA axons were particularly concentrated in the dorsal lateral geniculate nucleus (LGd), with the ventral lateral geniculate nucleus (LGv) and the intergeniculate leaflet (IGL) receiving substantially fewer fibers. In contrast, 5-HT axons, although present throughout the LGN, were preferentially concentrated in the LGv and IGL. 5-HT and NA axon terminals and axonal varicosities, examined in single and serial ultrathin sections, formed conventional synapses in the extraglomerular neuropil. The types of synapses and the nature of the postsynaptic targets were different for the two monoamines. 5-HT afferents formed asymmetrical synapses on dendritic spines and shafts of both presumptive relay cells and interneurons but established symmetrical synapses on cell bodies. However, NA afferents formed almost exclusively symmetrical synapses on dendritic spines and shafts and made no contacts with cell bodies. The present findings suggest that the 5-HT and NA afferents of the rat LGN, which are likely to influence certain stages of visual processing, exhibit distinct organizational principles and act at restricted sites as do other classical neurotransmitter systems.

Neurotransmitters, receptors, and neuropeptides in the accessory optic system: an immunohistochemical survey in the pigeon (Columba livia)

Immunohistochemical techniques were used to survey the distribution of several conventional transmitters, receptors, and neuropeptides in the pigeon nucleus of the basal optic root (nBOR), a component of the accessory optic system. Amongst the conventional neurotransmitters/modulators, the most intense labeling of fibers/terminals within the nBOR was obtained with antisera directed against glutamic acid decarboxylase (GAD) and serotonin (5-HT). Moderately dense fiber plexuses were seen to label with antibodies directed against tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT). GAD-like immunoreactivity (GAD-LI) was found in many small and medium-sized perikarya within the nBOR. Some of the medium-sized cells were occasionally positive for ChAT-LI. Cell body and dendritic staining was also commonly seen with the two tested antisera against receptors-anti-GABA-A receptor and anti-nicotinic acetylcholine receptor. The antisera directed against various neuropeptides produced only fiber labeling within the nBOR. The densest fiber plexus staining was observed with antiserum against neuropeptide Y (NPY-LI), while intermediate fiber densities were seen for substance P (SP-LI) and cholecystokinin (CCK-LI). A few varicose fibers were labeled with antisera against neurotensin (NT), leucine-enkephalin (L-ENK), and the vasoactive intestinal polypeptide (VIP). Unilateral enucleation produced an almost complete elimination of TH-LI in the contralateral nBOR. SP-LI and CCK-LI were also decreased after enucleation. No apparent changes were seen for all other substances. These results indicate that a wide variety of chemically-specific systems arborize within the nBOR. Three of the immunohistochemically defined fiber systems (TH-LI, SP-LI, and CCK-LI fibers) were reduced after removal of the retina, which may indicate the presence of these substances in retinal ganglion cells. In contrast, the fibers exhibiting ChAT-LI, GAD-LI, 5-HT-LI, NPY-LI, NT-LI, L-ENK-LI, and VIP-LI appear to be of nonretinal origin. Two different populations of nBOR neurons exhibited GAD-LI and ChAT-LI. However, these two populations together constituted only about 20% of the nBOR neurons.

Organization of lateral geniculate-hypothalamic connections in the rat

The location and chemical identity of neurons interconnecting the lateral geniculate complex and the hypothalamus were analyzed in order to provide further information on the anatomical substrates for the entrainment of circadian rhythms. A particular objective of the study was to characterize the neurons projecting between the intergeniculate leaflet (IGL) of the lateral geniculate complex and the suprachiasmatic nucleus (SCN) and related anterior hypothalamic areas. The connectivity experiments employed five combinations of fluorescent tracer injection and were combined with immunohistochemical localization of either neuropeptide Y (NPY), met-enkephalin (mENK) or the vasoactive intestinal polypeptide (VIP)/peptide histidine isoleucine (PHI) group. IGL efferents. Injection of tracer into the SCN results in retrograde labeling of NPY-immunoreactive neurons in the IGL as would be expected from prior work. These neurons and their terminals also contain the C-flanking peptide of the NPY precursor molecule (CPON). In addition, there are two additional groups of neurons in the IGL that project either to the SCN or the contralateral IGL but do not exhibit NPY immunoreactivity. These include a substantial population of cells that project to the SCN and an even larger group of neurons which project to the contralateral IGL and contain mENK immunoreactivity. Hypothalamic efferents. Injection of tracer into the IGL results in retrograde labeling of scattered neurons throughout the SCN and immediately adjacent anterior hypothalamus ipsilaterally and also in labeling of a small number of neurons in the same areas on the contralateral side of the brain. In rare instances, individual SCN neurons appear to project to both IGLs. However, the retrochiasmatic area (RCA) contains the largest number of retrogradely labeled neurons following tracer injections into the IGL. These neurons are concentrated along the midsagittal plane and in the lateral RCA ipsilateral to the injected IGL. None of the labeled neurons in the SCN or adjacent anterior hypothalamus exhibit VIP or PHI immunoreactivity. These observations indicate that the anatomical relations between the geniculate complex and the anterior hypothalamus are more complex than previously shown. First, the geniculohypothalamic tract arises from two distinct groups of IGL neurons: one contains NPY/CPON immunoreactivity; the chemical content of the other is not characterized at the present time. Second, the commissural projection between the two IGLs is formed by a third group of neurons, and these cells contain mENK immunoreactivity. Finally, reciprocal projections from the hypothalamus to the IGL arise from neurons in the retrochiasmatic area, SCN, and adjacent anterior hypothalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

The geniculohypothalamic tract in monkey and man

The intergeniculate leaflet (IGL) of the lateral geniculate complex in rodents contains neuropeptide Y-immunoreactive (NPY-IR) neurons which project to the suprachiasmatic nucleus (SCN) of the hypothalamus. In the macaque monkey and human brain, a large portion of the pregeniculate nucleus contains NPY-IR neurons indicating that this is the primate homologue of the rodent IGL. The monkey SCN has a dense plexus of NPY-IR axons identical in location and appearance to that in rodents. As in other mammals, no NPY-IR neurons are found in the monkey SCN. In contrast, in the human SCN, the NPY-IR plexus is less dense than in the monkey and there are numerous NPY-IR neurons. This suggests that the human SCN differs in organization from that of other mammals and that the functional homologue of the mammalian geniculohypothalamic tract is local circuit NPY+ neurons within the nucleus.

Two brain nuclei controlling circadian rhythms are identified by GFAP immunoreactivity in hamsters and rats

The intergeniculate leaflet (IGL) of the lateral geniculate complex is marked by the presence of neuro-peptide Y-containing neurons that project to the suprachiasmatic nuclei (SCN) of the hypothalamus. In the present study, we demonstrate that both the IGL and SCN in the hamster and rat are specifically delineated by the presence of glial fibrillary acidic protein-like immunoreactivity. This is significantly greater than in most other diencephalic regions and is particularly dense in the hamster brain. These observations suggest that glial-neuronal interactions may participate in circadian rhythm generation and regulation.

The organization of the rat lateral geniculate body by immunohistochemical analysis of neuroactive substances

The organization of neuroactive substances in the rat lateral geniculate body (LGB) was studied with available immunohistochemical stainings. In the dorsal lateral geniculate nucleus (DLG), there existed only gamma-aminobutyric acid (GABA)-like immunoreactive neurons. Immunoreactive fiber plexuses for substance P (SP), cholecystokinin-8 (CCK) and vasoactive intestinal polypeptide (VIP) were present in the lateral margin of the DLG, just beneath the optic tract. There were immunoreactive neurons and fibers for GABA, SP, leucine-enkephalin (ENK) and neuropeptide Y (NPY) in the intergeniculate leaflet (IGL). ENK-, NPY- and SP-like immunoreactive neurons in the IGL were mainly medium-sized, and bipolar or spindle-shaped with a few dendrites oriented dorsoventrally. In the IGL, use of double-labeled immunofluorescence demonstrated that a few neurons exhibited both ENK- and SP-like immunoreactivities, and a few neurons had both GABA- and ENK-like immunoreactivities. Although the morphology of ENK-like immunoreactive neurons resembled to NPY-like immunoreactive neurons, both neurons were clearly different neurons. Many GABA-, ENK- and SP-like immunoreactive neurons and fibers were found in the ventral lateral geniculate nucleus (VLG). These immunoreactive neurons were mainly medium-sized, and bipolar in shape, while a few immunoreactive neurons were of multipolar shape. Neurons containing ENK and fibers containing SP mainly existed in the lateral half of the parvocellular part and in the medial half of magnocellular part of the VLG. In this region, about one-third of the GABA-like immunoreactive neurons contained ENK-like immunoreactivity. Many SP neurons mainly existed in the medial half of the parvocellular part of the VLG. CCK- and VIP-like immunoreactive fibers were present in the lateral half of the magnocellular part of the VLG. Immunoreactive fibers for calcitonin gene-related peptide, corticotropin-releasing factor, neurotensin and tyrosine hydroxylase were disseminated throughout the LGB. The subdivisions of the LGB were discussed, based upon the distribution of neuroactive substances.

Laminar and segregated distribution of immunoreactivities for some neuropeptides and adenosine deaminase in the superior colliculus of the rat

The distribution and morphology of adenosine deaminase, substance P, leucine-enkephalin, corticotropin-releasing factor, and calcitonin gene-related peptidelike immunoreactive cells and fibers throughout the superior colliculus of the rat were examined by means of the unlabelled-antibody peroxidase-antiperoxidase method. Adenosine deaminase immunoreactive cells were found in the stratum opticum and lower stratum griseum superficiale; substance P immunoreactive cells were localized to the upper stratum griseum superficiale, and calcitonin gene-related peptide immunolabelled neurons were situated in deeper strata. Substance P, leucine-enkephalin, and calcitonin gene-related peptide immunoreactive fibers were distributed similarly in their lamination and in their patchlike organization. Corticotropin-releasing factor immunoreactive fibers were observed evenly throughout all the strata and were fewer in the stratum griseum superficiale. These findings suggest that, as in afferent modules and segregated efferents of the mammalian superior colliculus, the cells and fibers containing neuroactive substances and neuroactive substance-related enzymes also show a segregated and laminar distribution.

Distribution of tachykinin- and enkephalin-immunoreactive fibers in the human thalamus

Sections at regular intervals through the human thalamus and alternating with those used for histochemical and cytoarchitectonic analysis in the companion paper, were stained immunocytochemically with a monoclonal antibody that recognizes tachykinins, including substance P, and with an antiserum against metenkephalin-arg-gly-leu (MERGL). Immunoreactivity for both types of molecule is found in fiber systems that enter the thalamus: (a) anteromedially, from the hypothalamus and prethalamic regions; (b) posterolaterally, from the midbrain tegmentum. No immunoreactive somata were observed in the thalamus. The chief nuclei in which dense, apparently terminal, ramifications of both sets of immunoreactive fibers are found include the posterior complex (Po, L and Sg), the intralaminar nuclei except the centre median, and a small nucleus tentatively identified as the nucleus submedius. It is significant that many of these nuclei have been implicated in pain phenomena, that most of them receive spinothalamic inputs, and that spinal cells at the origins of the tract are immunoreactive for substance P or metenkephalin. This study provides further evidence for the close similarity between nuclear delineation in the human and monkey thalami.

Dorsal raphe serotoninergic branching neurons projecting both to the lateral geniculate body and superior colliculus: a combined retrograde tracing-immunohistochemical study in the rat

Injections of HRP into the superior colliculus labelled cells in the lateral cell groups of the dorsal raphe nucleus. The cytoarchitectural features and location of these cells showed remarkable similarities with those known to project to the lateral geniculate body, and, therefore, the possible existence of branching neurons in the dorsal raphe nucleus projecting to these two visual structures was tested. Injections into the lateral geniculate body and the superior colliculus of several fluorescent tracers--namely, Fast Blue, Fluoro-Gold, propidium iodide, rhodamine-B-isothiocyanate, and Diamidino Yellow, used in different combinations, showed single- and double-labelled neurons in the lateral wings of the dorsal raphe nucleus. In order to verify the chemical nature of these cells, the tissue was processed for immunofluorescence with serotonin antibodies. The results obtained showed several triple-labelled cells exhibiting two fluorescent tracers as well as 5-hydroxytryptamine-like immunoreactivity. Some immunonegative tracer-positive cells were also observed, suggesting their nonserotoninergic nature. Finally, electrolytic lesions of the lateral wings of the dorsal raphe nucleus caused a gradual disappearance of serotonin-immunoreactive fibers in these visual areas following different survival times. This correlated well with a decrease in the serotonin content studied by high-pressure liquid chromatography. These results support a role of the serotoninergic dorsal raphe projection to the lateral geniculate body and to the superior colliculus in the processing of visual information, and they suggest that serotonin may have a coordinating influence on primary visual centers.

Cholecystokinin innervation of rat thalamus, including fibers to ventroposterolateral nucleus from dorsal column nuclei

The distribution of cholecystokinin octapeptide immunoreactive fibers and puncta in the adult rat thalamus was studied using immunocytochemical methods. Small to moderate numbers of immunoreactive fibers were present in the lateral habenular nucleus, ventral lateral geniculate nucleus, zona incerta, parataenial, mediodorsal, medioventral, and submedial nuclei, the rhomboid, paracentral, central lateral and parafascicular nuclei, and in the medial geniculate and dorsal lateral geniculate nuclei. Moderate to large numbers of cholecystokinin (CCK)-positive fibers were present in the paraventricular nuclei, the reticular nucleus, the anteroventral, anteromedial, and central medial nuclei, and in the rostral extension of the internal medullary lamina between the parataenial and anteroventral nuclei. Dense concentrations of immunoreactive fibers were also found in a principal sensory relay nucleus, the ventroposterolateral nucleus (VPL), of the ventrobasal complex. The number of CCK-positive fibers in VPL showed a marked unilateral decrease in rats which had received lesions of the contralateral gracile and cuneate nuclei. The results of this study demonstrate that CCK-immunoreactive fibers and puncta are widely distributed in the rat thalamus, and that the source of these fibers in VPL is probably the dorsal column nuclei.

Distributions of certain neuropeptides in the primate thalamus

The distributions of fibers and terminals immunoreactive for somatostatin (SRIF), neuropeptide Y (NPY), substance P (SP) and cholecystokinin octapeptide (CCK), were studied in the diencephalon of cynomolgus monkeys. Immunoreactivity for all 4 peptides is found in extrinsic afferent fibers innervating the dorsal thalamus, ventral thalamus and epithalamus. The distributions of such fibers are more extensive than previously described and include many relay nuclei in their zones of terminations. SP fibers are particularly concentrated in the ventral posteromedial nucleus. All peptides are especially concentrated in fibers in the intralaminar and reticular nuclei. Afferent fibers immunoreactive for each of the 4 peptides approach the thalamus by two pathways. An anterior route is formed by the classical periventricular system ascending from the hypothalamus to the epithalamus. A posterior pathway ascends in the lateral midbrain tegmentum and provides innervation to posterior, intralaminar, and many relay nuclei, plus the ventral thalamus. A basal forebrain pathway, containing SRIF and NPY immunoreactive fibers, enters the thalamus in association with the ansa lenticularis and SP fibers also ascend from the substantia nigra.

The innervation density of serotonergic (5-HT) fibers varies in different subdivisions of the cat lateral geniculate nucleus complex

The innervation density of serotonin (5-HT)-immunoreactive fibers, identified using an antibody to 5-HT, was found to differ in the 4 subdivisions of the cat lateral geniculate nucleus complex (LGN). The mean density (fiber length per unit area) of anti-5-HT-stained fibers was highest in the ventral LGN (0.062 micron per micron 2), moderate in the medial interlaminar nucleus (MIN) and the parvicellular C laminae of the dorsal LGN (0.039-0.040 per micron 2), and lowest in the A and magnocellular C laminae of the dorsal LGN (0.020 per micron 2). The fiber density in MIN was particularly dense along the medial edge of the nucleus, a region called the geniculate wing. The heaviest serotonin innervation is thus found in geniculate structures receiving input from W-type retinal ganglion cells and lightest in structures receiving X and Y input.

Autoradiographic mapping of [mono[125I]iodo-Tyr10, MetO17]vasoactive intestinal peptide binding sites in the rat brain

The distribution of vasoactive intestinal peptide binding sites in the rat brain was examined by in vitro autoradiography on slide-mounted sections. A fully characterized monoiodinated form of vasoactive intestinal peptide (M-[125I]VIP) previously shown to maintain in the central nervous system the full biological activity of native vasoactive intestinal peptide was used for this study. In initial kinetic and pharmacological experiments the binding of M-[125I]vasoactive intestinal peptide to slide-mounted sections was shown to be time-dependent, saturable and reversible. Association of M-[125I]VIP specific binding was maximal within 90-120 minutes. Specific binding, corresponding to approximately 50% of total binding was saturable, of high affinity (Kd of 76.6 pM) and low capacity (fmol/mg prot range). Dissociation of M-[125I]VIP was maximal at 10 minutes. Unlabeled vasoactive intestinal peptide and the two structurally related peptides "peptide-histidine-isoleucine" (PHI) and secretin competed in a concentration-dependent manner for sites labeled by M-[125I]vasoactive intestinal peptide with the following rank order of potencies: vasoactive intestinal peptide greater than PHI greater than secretin. Vasoactive intestinal peptide receptors, as revealed by quantitative autoradiography, are present at various levels of the neuraxis. High densities were observed in olfactory bulb, cerebral cortex (highest in layers I, II, IV and VI), dentate gyrus, subiculum, various thalamic and hypothalamic nuclei, superior colliculus, locus coeruleus, area postrema, subependymal layer and pineal gland. Intermediate densities were found in the amygdala, nucleus accumbens, caudate-putamen, septum, bed nucleus of the stria terminalis, CA1 to CA4 fields of the hippocampus and central gray. No specific binding of M-[125I]vasoactive intestinal peptide was observed in white matter tracts such as corpus callosum, anterior commissure, medial forebrain bundle and fornix. The mapping of M-[125I]vasoactive intestinal peptide binding sites as revealed by autoradiography on slide-mounted sections indicates an association, although not exclusive, of vasoactive intestinal peptide receptors with brain regions involved in the processing of specific sensory inputs.

Double-labeling of neuropeptide Y-immunoreactive neurons which project from the geniculate to the suprachiasmatic nuclei

A projection from the ventral geniculate area to the suprachiasmatic nuclei (SCN) has been demonstrated in rats and hamsters. Large lesions in this area of the geniculate cause a dramatic decrease in neuropeptide Y-immunoreactivity in the SCN. Since numerous neuropeptide Y-immunoreactive neurons are found in the lateral geniculate area, we and others proposed that these immunoreactive neurons project to the SCN. In the present study, neurons in the lateral geniculate area of golden hamster brains were examined for both neuropeptide Y-immunoreactivity and a retrograde tracer transported from the SCN. Two days after a pressure injection of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into the SCN of hamsters, labeled neurons were found in the intergeniculate leaflet and in the external lamina of the anterior ventral lateral geniculate nucleus (VLGN). These neurons were compared with similarly located neurons which showed immunoreactivity for neuropeptide Y. Morphometric comparisons of neuropeptide Y- and WGA-HRP-labeled neurons indicated that they were comparable in terms of soma size, number of dendrites, orientation and location. In additional hamsters, neurons double-labeled with a retrograde tracer and neuropeptide Y-immunoreactivity were localized in the intergeniculate leaflet and in the external lamina of the anterior VLGN. These results demonstrate that many neuropeptide Y-immunoreactive neurons located in both the intergeniculate leaflet and in the external lamina of the anterior VLGN project to the SCN in hamsters.

Distribution of neuropeptide Y-like immunoreactivity in the rat central nervous system--II. Immunohistochemical analysis

The distribution of neuropeptide Y-like immunoreactivity in the rat brain and spinal cord was investigated by means of the peroxidase-antiperoxidase procedure of Sternberger using a rabbit anti-neuropeptide Y serum. A widespread distribution of immunostained cells and fibres was detected with moderate to large numbers of cells in the following regions: olfactory bulb, anterior olfactory nucleus, olfactory tubercle, striatum, nucleus accumbens, all parts of the neocortex and the corpus callosum, septum including the anterior hippocampal rudiment, ventral pallidum, horizontal limb of the diagonal band, amygdaloid complex. Ammon's horn, dentate gyrus, subiculum, pre- and parasubiculum, lateral thalamic nucleus (intergeniculate leaflet), bed nucleus of the stria terminalis, medial preoptic area, lateral hypothalamus, mediobasal hypothalamus, supramammillary nucleus, pericentral and external nuclei of the inferior colliculus, interpeduncular nucleus, periaqueductal central gray, locus coeruleus, dorsal tegmental nucleus of Gudden, lateral superior olive, lateral reticular nucleus, medial longitudinal fasciculus, prepositus hypoglossal nucleus, nucleus of the solitary tract and spinal nucleus of the trigeminal nerve. In the spinal cord cells were found in the substantia gelatinosa at all levels, the dorsolateral funiculus and dorsal gray commissure in lumbosacral cord. The pattern of staining was found to be similar to that observed with antisera to avian and bovine pancreatic polypeptide, but to differ in some respects from that observed with antisera to molluscan cardioexcitatory peptide. The presence of neuropeptide Y immunoreactive fibres in tracts such as the corpus callosum, anterior commissure, lateral olfactory tract, fimbria, medial corticohypothalamic tract, medial forebrain bundle, stria terminalis, dorsal periventricular bundle and other periventricular areas, indicated that in addition to the localisation of neuropeptide Y-like peptide(s) in interneurons in the forebrain, neuropeptide Y may be found in long neuronal pathways throughout the brain.

Neuropeptide Y innervation of the hippocampal region in the rat and monkey brain

Using antibodies to neuropeptide Y (NPY) in combination with immunohistochemical techniques we have studied the distribution of cell bodies and nerve terminals containing NPY immunoreactivity (-i) in the hippocampal region of rats and monkeys (cynomolgus). In colchicine-pretreated rats a large number of NPY-positive cells are present in all areas of the hippocampal region. The NPY-i cells range in size from small (diameter across soma: 10-15 micron) to large (approximately 20 micron). Most of the NPY-i cells are situated in the hilus, in the subgranular zone of the area dentata, and in the stratum oriens of Ammon's horn. A majority of these are polymorphic cells but cells of different morphology are present in these layers as well. These include small spheroid cells and dentate pyramidal basket cells that are distinct from the polymorphic cells in the subgranular zone. The subicular complex (e.g., the subiculum, pre-, and parasubiculum) and the entorhinal area contain fewer NPY-i cells than the rest of the hippocampal region. In the dorsal parts of the pre- and parasubiculum numerous small cells are scattered throughout all layers, while in the entorhinal area the NPY-stained cells are situated primarily in the deep layers (V and VI). In the ventral part of the lateral entorhinal area large multipolar and bitufted cells are found in layers II-VI. In the untreated monkey brain NPY-positive cells are found in the hilus of the area dentata and in the deep (IV through VI) layers of both the medial and lateral entorhinal area. Fewer NPY-stained cells are present in the subicular complex and in the entorhinal area. In the monkey as well as in the rat, NPY-stained cells are present in the angular bundle and in the alveus. A dense network of NPY-i fibers innervates the entire hippocampal region in both the rat and the monkey. The hippocampal NPY-i preterminal processes are present primarily in stratum moleculare of Ammon's horn and in the outer one-third of this layer in the area dentata. The NPY-positive innervation of the dentate molecular layer is far more prominent in the monkey than in the rat brain. Numerous NPY-stained fibers are scattered in other areas as well. In all retrohippocampal structures, and in particular the entorhinal area, the NPY-i fibers form a massive network that innervates all layers to about the same extent, with the exception of the molecular layer, which is more densely innervated than the other layers.

Distributional pattern of serotonin-immunoreactive nerve fibers in the lateral geniculate nucleus of the rat, cat and monkey (Macaca fuscata)

The distribution of serotonin-containing nerve fibers in the lateral geniculate nucleus (LGN) of the rat, cat, and monkey (Macaca fuscata) was studied by use of the peroxidase-antiperoxidase method and an antiserum against serotonin. In all three species, the pattern of fibers was denser in the ventral portion of the LGN (LGNv) than in the dorsal nuclear portion (LGNd). In the LGNd of rat, serotonin-immunoreactive fibers were evenly distributed in the form of a dense network, but in cat and monkey there were marked regional differences. Serotonin-immunoreactive elements were most numerous in the C complex and medial interlaminal nucleus of cat, and in the S layer and interlaminar zones of Macaca fuscata.

Neuropeptide Y immunoreactivity in the hamster geniculo-suprachiasmatic tract

The distributions of neuropeptide Y (NPY) and avian pancreatic polypeptide (APP) immunoreactivity were examined in the suprachiasmatic nucleus and the geniculate area of male golden hamster brains. In some cases, colchicine was injected intraventricularly to aid in visualization of immunoreactive cell bodies. A group of hamsters were given bilateral or unilateral radiofrequency lesions of the geniculate area and neuropeptide Y immunoreactivity was examined in the suprachiasmatic nucleus after survival times varying between 8 and 300 days. Another group of hamsters received unilateral intraocular injections of anterograde tracers and the overlap of NPY-immunoreactive cells in the geniculate area and labeled retinal afferents was assessed. It was found that NPY- and APP-immunoreactive fibers formed a dense plexus in the ventro-lateral suprachiasmatic nucleus. NPY-immunoreactive cell bodies were observed in the intergeniculate leaflet as well as in the external lamina of the anterior portion of the ventral lateral geniculate nucleus. Unilateral lesions of the geniculate produced a relative reduction in neuropeptide Y immunoreactivity in the ipsilateral suprachiasmatic nucleus whereas bilateral lesions produced a reduction of neuropeptide Y immunoreactivity in both suprachiasmatic nuclei. All NPY-immunoreactive cells in the intergeniculate leaflet were overlapped by bilateral retinal afferents. In the ventral lateral geniculate nucleus, all NPY-immunoreactive cells were overlapped by contralateral retinal afferents; however, not all such cells were in areas receiving ipsilateral retinal afferents. These results indicate that the hamster geniculo-suprachiasmatic tract originates in part from NPY-immunoreactive cell bodies and that these cells lie in areas receiving direct retinal afferents.

Neuropeptides are present in projection neurones at all levels in visceral and taste pathways: from periphery to sensory cortex

Using combined immuno-staining and retrograde tracing techniques many of the ascending visceral and taste pathways within the rat central nervous system have been shown to be composed of a variety of neuropeptide and catecholamine synthesizing enzyme containing neurones. The pathway we examined extended from the periphery to sensory cortex and included: the nodose ganglion (periphery)----solitary nucleus (medulla)----parabrachial nucleus (pons)----ventral posterior medial nucleus (thalamus)----visceral and taste sensory areas (cortex). In the solitary nucleus of the medulla many neuronal cell bodies could be shown to be both immuno-positive for one of 6 neuropeptides including avian pancreatic peptide (APP), cholecystokinin (CCK), enkephalin (ENK), neurotensin (NT), somatostatin (SOM) and substance P (SP) or the catecholamine synthesizing enzyme tyrosine hydroxylase (TOH) and to have a projection to the parabrachial nucleus of the pons. In the parabrachial nucleus of the pons many neuronal cell bodies could be shown to be immuno-positive for one of 5 neuropeptides (CCK, ENK, NT, SOM, SP) and have a projection to the ventral posterior medial nucleus of the thalamus. In the ventral posterior medial nucleus of the thalamus several neuronal cell bodies were shown to be immuno-positive for one of 3 neuropeptides (CCK, ENK, SOM) and project to the visceral and taste sensory cortex. This is the first report of neuropeptides being present in the projection neurones of any sensory system in the central nervous system and for the first time describes an entire set of putative neurotransmitters which extends from the periphery to the sensory cortex. From previous studies it also appears that in all cases examined the relevant receptors are present in these visceral and taste relay nuclei in order for the neuropeptide or catecholamine to produce an effect upon release. Comparisons between rat and other animals suggest that a similar organization of these visceral and taste pathways may also be present in other mammals including man. Functionally these neuropeptides containing projection neurones appear to be primarily involved in relaying visceral information rather than taste information. In this capacity activation of these neurones may produce such visceral sensations as malaise, well being, hunger, satiety or thirst.