Effects of habenular lesions on the substance P content of various brain regions

Activation of the neurokinin-1 receptor by substance P triggers the release of substance P from cultured adult rat dorsal root ganglion neurons

Background

Although substance P (SP) is an important primary afferent modulator in nociceptive processes, it is unclear whether SP regulates its own release from primary sensory neurons.

Results

Using a highly sensitive radioimmunoassay for SP, we have demonstrated that the activation of neurokinin-1 receptor by SP or GR73632 (a potent neurokinin-1 receptor agonist) triggered an increase of SP release from cultured adult rat dorsal root ganglion (DRG) neurons depending on the dose and exposure time within 60 min, and thereafter, the SP release level gradually decreased over 360 min. Accompanying the SP release, a significant reduction in the percentage of neurons expressing neurokinin-1 receptor on their membranes during exposure to SP (200 pg/dish) occurred time dependently (56 ± 5% and 32 ± 2% at 180 and 360 min, respectively). The GR73632-evoked (10 nM, 60 min) SP release was attenuated by several inhibitors for mitogen-activated protein kinase kinase, p38 mitogen-activated protein (MAP) kinase and cyclooxygenase-2 (COX-2), protein kinase C (PKC), respectively. In contrast, a c-Jun NH₂-terminal kinase inhibitor increased the GR73632-evoked SP release.

Conclusion

These results indicate that the neurokinin-1 receptor activation by its agonists regulates the SP release process involving the activation of MAP kinases, PKCs and COX-2 from cultured DRG neurons.

Enkephalin, dynorphin and substance P in postmortem substantia nigra from normals and schizophrenic patients

Three peptide neuromodulators that are found in high concentration in the substantia nigra: dynorphin A 1-8, met5-enkephalin-arg6-gly7-leu8 and substance P, were measured by specific radioimmunoassays in nigral tissue from normals and schizophrenics postmortem. Substance P and dynorphin were unchanged between the two groups. However, the proenkephalin-derived peptide was significantly elevated in the schizophrenic group. The immunoreactivity was identified as authentic met5-enkephalin-arg6-gly7-leu8 by high pressure liquid chromatography. The data suggest that a different set of regulatory controls exists for nigral enkephalin peptides as compared to dynorphin and substance P, and that the former system may be disordered in schizophrenia.

Substance P immunoreactivity in the rat interpeduncular nucleus: synaptic interactions between substance P-positive profiles and choline acetyltransferase- or glutamate decarboxylase-immunoreactive structures

The subnuclear and synaptic distribution of substance P immunoreactivity was examined in the rat interpeduncular nucleus at the light and electron microscope level. The nucleus possessed a prominent substance P-immunoreactive axonal plexus in the lateral and dorsomedial subnuclei, and in the dorsal cap of the rostral subnucleus. The density of substance P-immunoreactive axons in the remaining subnuclear divisions was sparse to moderate. Terminals of immunoreactive axons contained spherical vesicles and formed asymmetric contacts on dendritic processes exclusively. Immunoreactive neurons, restricted to the rostral subnucleus, possessed long, sparsely branched dendrites. Unlabelled terminals containing either spherical or pleomorphic vesicles contacted substance P-immunoreactive dendritic profiles. Axodendritic and axosomatic synapses containing substance P immunoreactivity pre- and postsynaptically were not observed. Ultrastructural evidence for synaptic relationships between substance P-containing profiles and those containing either choline acetyltransferase or glutamate decarboxylase was obtained by means of double antigen immunohistochemistry. Terminals of fasciculus retroflexus axons stained for choline acetyltransferase immunoreactivity formed asymmetric synaptic contacts with substance P-immunoreactive dendritic profiles. Few substance P-positive dendrites in the rostral subnucleus received terminals possessing glutamate decarboxylase activity. Unlabelled terminals containing either spherical or pleomorphic vesicles contacted substance P- and glutamate decarboxylase-immunoreactive dendritic profiles simultaneously. Terminals possessing either substance P or glutamate decarboxylase immunoreactivity formed synaptic contacts with dendritic processes of neurons in the lateral subnucleus. Many of the neurons within this subnuclear division contained glutamate decarboxylase. This study provides direct evidence of synaptic relationships between choline acetyltransferase-immunoreactive axons and substance P-immunoreactive dendritic profiles, and between substance P-positive axons and glutamate decarboxylase-immunoreactive dendrites. These findings reveal that two types of transmitter-specific axons of the fasciculus retroflexus innervate neuronal populations of the interpeduncular nucleus stained immunohistochemically for either substance P or glutamate decarboxylase.

Differential effects of fasciculus retroflexus lesions on serotonin, glutamate and gamma-aminobutyrate content and choline acetyltransferase activity in the interpeduncular nucleus

After placing bilateral electrolytic lesions in the fasciculus retroflexus (FR) of the rat, the endogenous content of serotonin, glutamate and gamma-aminobutyrate (GABA) as well as choline acetyltransferase activity (ChAT) were measured in the interpeduncular nucleus (IPN) at the 7th, 28th and 120th survival days. Confirming earlier results, an almost total depletion of ChAT was obtained in the IPN following complete FR lesions at any survival day studied. In such cases, the following changes were observed; 1) the serotonin level increased consistently and roughly doubled at the 120th survival day, suggesting heterotypic sprouting of serotonergic fibers and/or enhanced serotonin synthesis in the serotonergic neurons in the IPN, 2) the glutamate level decreased by approximately one-half, while the activity of high affinity uptake of glutamate remained unaltered, at the 7th survival day, suggesting a lowered glutamate formation coupled with lowered glucose utilization in the IPN, and 3) the GABA level decreased at a slower rate and reached one-third of the control at the 120th survival day, for which either transsynaptic degeneration of GABA neurons in the IPN or a suppressed metabolic rate in the GABA shunt following the lowered glutamate formation is a possible explanation.

Cellular localization of substance P- and neurokinin A-encoding preprotachykinin mRNA in the female rat brain

To determine the locations of neurons in the rat brain expressing substance P and neurokinin A mRNA, we performed in situ hybridization with a radiolabeled cRNA probe that was complementary to alpha-, beta-, and gamma-preprotachykinin mRNA. Several types of controls indicated specificity of the labeling. Brain regions containing many labeled neurons include the anterior olfactory nucleus, layer II of the olfactory tubercle, the islands of Calleja, the nucleus accumbens, the caudate-putamen, portions of the amygdala and hypothalamus, the medial habenular nucleus, nuclei of the pontine tegmentum, several raphe nuclei, several portions of the reticular formation, and the nucleus of the solitary tract. Less frequent labeled neurons were also found in many other regions of the brain. These results extend many previous immunocytochemical studies of the locations of neurons containing immunoreactive substance P, neurokinin A, and neuropeptide K.

Rat brain regional distribution and spinal cord neuronal pathway of FLFQPQRF-NH2, a mammalian FMRF-NH2-like peptide

Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2 (F-8-NH2) is a peptide, originally detected by FMRF-NH2 antisera, and subsequently isolated from bovine brain. Using a specific radioimmunoassay for F-8-F-NH2, we have examined the regional distribution and characteristics of F-8-F-NH2 immunoreactivity (IR) in rat brain, spinal cord and pituitary gland. In CNS, F-8-F-NH2-IR is highly concentrated in the spinal cord, hypothalamus and pons-medulla (368, 202 and 136 fmol per mg protein, respectively); lowest values are in the cortex and hippocampus. A modest rostrocaudal gradient of F-8-F-NH2-IR was observed; levels in the sacral cord are 50% higher than in the cervical cord. Dorsal cord content is 8 times higher than in the ventral cord. Dorsal rhizotomy failed to change F-8-F-NH2-IR in the affected regions of the spinal cord while significantly reducing substance P levels. F-8-F-NH2-IR was significantly decreased caudal to a spinal transection, indicating the presence of a descending pathway within the spinal cord. The highest concentration of F-8-F-NH2-IR (1008 fmol per mg protein) was found in the neurointermediate lobe of the pituitary, while no F-8-F-NH2-IR could be detected in the anterior lobe. Immunohistochemically, F-8-F-NH2-IR was confined to nerve terminal-like structures in the neural lobe. The anterior and intermediate lobes were devoid of immunoreactive structures. HPLC characterization of F-8-F-NH2-IR in the dorsal spinal cord, medulla-pons and pituitary revealed one major immunoreactive peak which is more hydrophobic than bovine F-8-F-NH2. In addition to this material, the hypothalamus was found to contain another, more abundant F-8-F-NH2-immunoreactive peak. Analysis of F-8-F-NH2-IR from posterior pituitary with various antisera having differing affinities for F-8-F-NH2 and gamma 1-MSH indicates that the F-8-F-NH2-IR of rat pituitary is not due to gamma 1-MSH. The high concentration of F-8-F-NH2-like peptide in the dorsal spinal cord supports a role in mediating nociceptive transmission while the localization of F-8-F-NH2-IR in the posterior pituitary suggests an additional autonomic or endocrine function.

Glutamate decarboxylase immunoreactivity in the rat interpeduncular nucleus: a light and electron microscope investigation

The distribution of immunohistochemically demonstrable glutamate decarboxylase, the synthetic enzyme for GABA, was examined in the rat interpeduncular nucleus at the light and electron microscope levels. Immunoreactive perikarya were distributed in a characteristic pattern among the subnuclear divisions. The rostral, ventral and caudal portions of the nucleus possessed numerous immunoreactive perikarya, while few immunoreactive somata were observed in the subnuclei of the dorsal aspect. A dense field of immunostained axons and terminals was also present throughout. Ultrastructural examination of glutamate decarboxylase immunoreactivity revealed numerous labelled somata, dendritic processes, axons and boutons. Axodendritic and axosomatic synapses with immunoreactive postsynaptic profiles were numerous throughout those subnuclei with large numbers of immunoreactive somata. Immunostained terminals in contact with both immunoreactive and non-immunoreactive somatic and dendritic profiles were also present. An abundance of immunostained terminals was observed in the subnuclei that possessed a sparse population of immunoreactive somata. Immunoreactive myelinated axons of unknown origin were also present. This investigation demonstrates that the rat interpeduncular nucleus possesses a large population of glutamate decarboxylase-immunoreactive neurons coextensive with a plexus of immunostained axons and terminals. The results suggest that the immunoreactive neurons give rise to axons which contribute to an intrinsic circuit interconnecting the different subnuclear divisions. These immunoreactive neurons are in receipt of non-immunoreactive afferent inputs of variable morphology, as well as projections from intrinsic immunoreactive neurons.

Analysis of the rat interpeduncular subnuclei by immunocytochemical double-staining for enkephalin and substance P, with some reference to the coexistence of both peptides

The rat interpeduncular nucleus (IPN) was immunocytochemically double-stained for enkephalin (ENK) and substance P (SP) on the same sections. On the basis of both peptidergic distribution patterns and topographic relationship, the IPN was divided into nine subnuclei and one cap: the rostral subnucleus (IP-R), the central subnucleus (IP-C), the rostral-lateral subnucleus (IP-RL), the main lateral subnucleus (IP-L), the caudal-lateral subnucleus (IP-CL), the dorsal-lateral subnucleus (IP-DL), the dorsal-medial subnucleus (IP-DM), the apical subnucleus (IP-A), the intermediate subnucleus (IP-I), and the dorsal cap (IP-Cap). As the descriptions of the IP-RL, IP-L, and IP-CL were inconsistent with previous reports, they were reevaluated; the IP-RL was proposed as the region situated in the lateral portion at rostral levels and characterized by the lack of ENK and SP immunoreactive structures, the IP-L as the region situated throughout the rostrocaudal extent in the lateral portion of the IPN and containing the highest density of SP immunoreactive fibers but no ENK immunoreactive fibers, and the IP-CL as the region situated just laterocaudal to the IP-L in the caudal pole of the IPN and containing ENK immunoreactive cells and fibers but no SP immunoreactive structures. Our results also showed that some cells in the IP-R have both ENK and SP immunoreactivity. This coexistence was observed in some small spherical cells of the IP-R, but rarely in larger oval-shaped cells, which occasionally showed only ENK immunoreactivity. In addition, paired ENK immunoreactive fiber bundles entering the IP-R were found to run just rostral to the paired SP immunoreactive columns, both of which composed parts of the interpedunculotegmental tract. A three-dimensional model representing the subnuclear organization of the IPN was proposed on the basis of the present results.

Topography of cholinergic and substance P pathways in the habenulo-interpeduncular system of the rat. An immunocytochemical and microchemical approach

The topography of cholinergic and substance P containing habenulo-interpeduncular projections has been studied in the rat. The research has been carried out by combining choline acetyltransferase and substance P immunohistochemistry to experimental lesions and biochemical assays in microdissected brain areas. In addition, computer-assisted image analysis has been performed in order to obtain quantification of immunohistochemical data. The results show that cholinergic and substance P containing neurons have a different localization in the medial habenula and project to essentially different areas of the interpeduncular nucleus. Cholinergic neurons are crowded in the ventral two-thirds of the medial habenula while substance P containing cells are exclusively localized in the dorsal part of the nucleus. In most parts of the interpeduncular nucleus, choline acetyltransferase and substance P containing fibres and terminals are similarly segregated and no overlapping is apparent except for the rostralmost and the caudalmost ends of the nucleus. Cholinergic activity is largely concentrated in the central core of the nucleus, while substance P is preferentially localized in the peripheral subnuclei of the interpeduncular nucleus. In addition, both substance P and choline acetyltransferase levels show peculiar regional variations along the rostrocaudal axis of the interpeduncular nucleus. The results of experimental lesions demonstrate that the substance P projection carried by each fasciculus retroflexus is prevailingly ipsilateral in the rostral part of the interpeduncular nucleus and becomes progressively bilateral as far as more caudal regions of the nucleus are reached. By contrast, the cholinergic projections carried by each fasciculus retroflexus intermingle more rapidly and only show a slight ipsilateral dominance in the interpeduncular nucleus. The results of the study are discussed with reference to previous anatomical and neurochemical data which, in several instances, had given rise to discrepant interpretations.

Analysis of the habenulopetal enkephalinergic system in the rat brain: an immunohistochemical study

The enkephalinergic afferent system in the rat habenula was examined by the indirect immunofluorescence method with antibodies against leucine-enkephalin. Leucine-enkephalin-like immunoreactive (L-ENKI) fibers were observed in the dorsal portion of the medial habenular nucleus (MHb), the intermediate portion of the lateral habenular nucleus (LHb), and the border zone between the MHb and the LHb (BZHb). Knife-cut studies demonstrated that almost all the fibers were supplied via the stria medullaris. Also two discrete ENKergic afferents to the MHb and the LHb were found by several kinds of lesion studies: the MHb was ipsilaterally innervated from L-ENKI neurons in "septoperiventricular area," which is the junctional area between the ventral supracommissural septum and the rostral thalamic periventricular region. The LHb was ipsilaterally innervated from L-ENKI neurons in the rostral portion of the lateral hypothalamus. Our findings also suggested that the L-ENKI fibers in the BZHb are supplied via the stria medullaris with an ipsilateral predominance and that, at the most caudal level, they arise not only from the ipsilateral stria medullaris but also from the contralateral stria medullaris via the habenular commissure.

Functional mapping of the effects of lesions of the habenular nuclei and their afferents in the rat

Through the use of the quantitative autoradiographic 2-[14C]deoxyglucose technique, we have investigated the functional significance of the habenular nuclei by the measurement of local cerebral glucose utilization (LCGU) in discrete brain areas of conscious rats following 3 kinds of lesioning. Bilateral electrolytic lesions of the habenular nuclei decreased LCGU in a limited number of well-defined brain areas (the interpeduncular nucleus, median and dorsal raphe, mammillary body and dorsal tegmental nucleus) at 7 and 14 days after lesions. These changes were also observed 180 days following lesioning except that of the dorsal tegmental nucleus. At 14 days after bilateral ibotenic acid-induced lesions of the lateral habenula, LCGU was significantly decreased in the median and dorsal raphe, mammillary body and interpeduncular nucleus. In further studies, bilateral electrolytic lesions of the stria medullaris (which conveys the major afferents to the habenula) decreased glucose use in the interpeduncular nucleus less than that observed after bilateral electrolytic lesions of the habenular nuclei. A highly significant positive correlation was observed between LCGU and choline acetyltransferase activity in the interpeduncular nucleus after all types of lesion. These results further support the view that the medial and the lateral habenula exert a major influence upon functional activity in the interpeduncular nucleus and the mesencephalic raphe nuclei, respectively.

Distribution of some peptides (substance P, [Leu]enkephalin, [Met]enkephalin) in the brain stem and spinal cord of a lizard, Varanus exanthematicus

The distribution of substance P-like and [Leu]- and [Met]enkephalin-immunoreactive cell bodies, fibers and terminal structures in the brain stem and spinal cord of a lizard, Varanus exanthematicus, was studied with the indirect immunofluorescence technique, using antibodies to these peptides. Substance P-like immunoreactive cell bodies were found in the hypothalamus, in a periventricular cell group in the rostral mesencephalon, in the interpeduncular nucleus, in and ventral to the descending nucleus of the trigeminal nerve, in and directly ventral to the nucleus of the solitary tract, scattered in the brain stem reticular formation and in the trigeminal and spinal ganglia. A rather widespread distribution of substance P-like immunoreactivity was found in the brain stem and spinal cord, mainly concentrated in striatotegmental projections related to visceral and/or taste information (nucleus of the solitary tract, parabrachial region), in the descending nucleus of the trigeminal nerve and in the dorsal horn of the spinal cord (areas I and II). In the spinal cord also around the central canal (area X and adjacent parts of area V-VI) a distinct substance P innervation was found. The ventral horn receives only a very sparse substance P innervation. The distribution of [Leu]- and [Met]enkephalin in the brain stem and spinal cord of Varanus exanthematicus is less impressive than that of substance P. Enkephalinergic cell bodies were found particularly in the caudal hypothalamus. Small populations of enkephalinergic cell bodies were found in the vestibular nuclear complex, in the nucleus of the solitary tract, in and around the descending nucleus of the trigeminal nerve and throughout the rhombencephalic reticular formation. Enkephalins are likely to be present in efferent projections of the striatum, in projections related to taste and/or visceral information (nucleus of the solitary tract, parabrachial region) and in descending pathways to the spinal cord. Enkephalinergic fibers are present in the lateral funiculus and enkephalin-immunoreactive cell bodies are found in the reticular formation, particularly the inferior reticular nucleus which is known to project to the spinal cord. In the spinal cord enkephalinergic terminal structures were found especially in the superficial layer of the dorsal horn (areas I and II) and around the central canal. The ventral horn including the motoneuron area receives only a relatively sparse enkephalinergic innervation.

Cytoarchitecture, fiber connections, and some histochemical aspects of the interpeduncular nucleus in the rat

The organization of afferent and efferent connections of the interpeduncular nucleus (IP) has been examined in correlation with its subnuclear parcellation by using anterograde and retrograde tracing techniques. Based on Nissl, myelin, and acetylcholinesterase staining five paired and three unpaired IP subnuclei are distinguished. The unpaired division includes the rostral subnucleus (IP-R), the apical subnucleus (IP-A), and the central subnucleus (IP-C). The subnuclei represented bilaterally are the paramedian dorsal medial (IP-DM) and intermediate subnuclei (IP-I) and the laterally placed rostral lateral (IP-RL), dorsal lateral (IP-DL), and lateral subnuclei (IP-L). Immunohistochemical techniques showed cell bodies and fibers and terminals immunoreactive for substance P, leu-enkephalin, met-enkephalin, or serotonin to be differentially distributed over the different IP subnuclei. Substance P-positive perikarya were found in IP-R, enkephalin neurons in IP-R, IP-A, and the caudodorsal part of IP-C, and serotonin-containing cell bodies in IP-A and the caudal part of IP-L. Efferent IP projections were studied both by injecting tritiated leucine in IP and by injecting HRP or WGA-HRP in the presumed termination areas. The results indicate that the major outflow of IP is directed caudal-ward to the median and dorsal raphe nuclei and the caudal part of the central gray substance, i.e., the dorsal tegmental region. The projection appears to terminate mainly in the raphe nuclei, around the ventral and dorsal tegmental nuclei of Gudden, and in the dorsolateral tegmental nucleus. The descending projection to the dorsal tegmental region originates in virtually all IP subnuclei, but the main contribution comes from IP-R and the lateral subnuclei IP-RL, IP-DL, and IP-L. Sparser projections to the dorsal tegmental region originate in IP-C and IP-I, whereas the contribution of IP-A is only minimal. The projections from IP-R are mainly ipsilateral and those from IP-DM are mainly contralateral. IP fibers to the median and dorsal raphe nuclei originate predominantly in IP-R and IP-DM, and to a lesser extent in IP-C, IP-I, IP-RL, and IP-DL. A much smaller contingent of IP fibers ascends to diencephalic and telencephalic regions. A relatively minor projection, stemming from IP-RL and IP-DL, reaches the lateral part of the mediodorsal nucleus, the nucleus gelatinosus, and some midline thalamic nuclei. These IP fibers follow either the habenulo-interpeduncular pathway or the mammillothalamic tract.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptides in human brain--postmortem studies

Four neuropeptides (substance P, methionine-enkephalin, neurotensin and cholecystokinin) were measured by radioimmunoassays in a number of brain regions of deceased patients with mental illnesses and controls. The most striking finding in these studies was that methionine-enkephalin concentrations in caudate nuclei of chronic paranoid schizophrenic patients were reduced relative to several control groups. Neuroleptics had no obvious effects on any of the four measured neuropeptides. These findings are not inconsistent with the hypothesis that methionine-enkephalin may be involved in some of the pathology of the schizophrenic syndrome.

Substance P in the interpeduncular nucleus of the rat: normal distribution and the effects of deafferentation

The interpeduncular nucleus (IPN) is a midbrain structure that receives its major afferents from the medial habenulae via the fasciculi retroflexi. Among the axons projecting to the IPN is a population of substance P (SP)-containing axons. The IPN has been subdivided into the central, dorsal, intermediate, rostral, and lateral subnuclei using cytoarchitectonic criteria. The distribution of SP among these subnuclei was determined by using Sternberger's ('79) peroxidase-antiperoxidase technique. In the normal IPN the rostral subnucleus can be subdivided into two sectors on the basis of SP content. The ventral sector contains a moderate amount of SP and scattered SP positive perikarya. The dorsal cap of the rostral subnucleus contains denser SP than the ventral sector and it is continuous with the SP found in the dorsal subnucleus. The lateral subnuclei contain the densest SP found in the IPN and appear as laterally placed columns that expand in size caudally. The central and intermediate subnuclei contain very sparse SP. The fasciculus retroflexus was destroyed in 30 animals unilaterally or bilaterally and animals were perfused 4 days to 3 months postoperatively. After unilateral fascicular lesion, the SP in the rostral part of the ipsilateral lateral subnucleus is almost abolished, but caudally the decrease is confined to its lateral aspect. There is no visible decrease contralateral to the lesion. SP in the rostral part of the cap of the rostral subnucleus is decreased ipsilaterally but no loss is seen contralaterally or caudally. Animals with bilateral lesions show a great decrease in staining in the dorsal cap of the rostral subnucleus and the lateral subnuclei, with no decrease seen in the central, dorsal, or intermediate subnuclei. These results confirm that the origin of most of the SP in the IPN is fasciculus retroflexus fibers, but some of the SP arises from intrinsic SP perikarya located in the ventral sector of the rostral subnucleus and some may also arise from other sources. The areas of the IPN that receive bilateral SP projections from the fasciculus retroflexus (parts of the lateral and rostral subnuclei) show evidence for replacement of SP after lesion. This replacement implies sprouting or an increase in production of SP by remaining systems.

The ultrastructure and organization of methionine-enkephalin immunoreactive profiles in the interpeduncular nucleus of the cat

An ultrastructural analysis of the dorso-intermediate (CDIZ) and dorso-median zones (CDMZ) at the caudal end of the interpeduncular nucleus was undertaken. Serial vibratome sections were stained for met-enkephalin-like immunoreactivity by using the indirect antibody peroxidase-antiperoxidase method of Sternberger, and ultrathin sections were examined electron microscopically. Met-enkephalin-like immunoreactivity was observed in two different types of somata in the two regions. The dendritic architecture of the dorso-intermediate zone was characterized by the presence of many dendritic crests. A large number of these dendritic crests were immunostained for met-enkephalin. A variety of terminals was also seen in the CDIZ and CDMZ and they are categorized according to their vesicular morphology into three classes. One class contained mainly clear round vesicles. The met-enkephalin-like immunoreactive (MELI) terminal profiles in both regions were of this class and contained small round vesicles which were less than 35 nm in diameter. These MELI terminals appeared in significant numbers, sometimes in close proximity to unlabeled somata and dendrites. The dorso-median zone had, in addition, two more classes of terminals. One class was characterized by a large number of dense-cored vesicles--class II, and the other group had a large proportion of flat clear vesicles--class III. The possible neurochemical identities of some of the unlabeled terminals in relation to the MELI dendritic structures are discussed in the light of known neurochemically established afferent projections to the CDIZ and CDMZ of the interpeduncular nucleus.

A study of afferent projections to the rat interpeduncular nucleus

Forebrain and brainstem afferents projecting to the interpeduncular nucleus (IPN) have been demonstrated in male rats by retrograde transport of fluorescent dye, "fast blue," microinjected in IPN, followed by intraventricular colchicine 48 hr prior to perfusion. The most intensely labeled cells projecting to IPN were concentrated throughout the entire rostrocaudal extent of the medial habenular nuclei. A small number of labeled medial habenular cells located dorsomedially also revealed SP immunofluorescence. Additional forebrain afferents originate from septal, hypothalamic and mammillary nuclei. Of brainstem afferents projecting to IPN, the most intensely labeled neurons were present in a circumscribed region overlying the dorsal aspect of the dorsal tegmental nucleus, an area described in the cat as the nucleus incertus [5], and which we now suggest is present in the rat. Many labeled cells in the medial aspect of this nucleus also revealed L-ENK immunofluorescence. Additional brainstem afferents include the raphe, dorsolateral tegmental nuclei and locus coeruleus. This study demonstrates both forebrain and brainstem afferents projecting to IPN and reveals an SP and L-ENK projection from the medial habenula and nucleus incertus, respectively.

Colchicine neurotoxicity demonstrates the cholinergic projection from the supracommissural septum to the habenula and the nucleus interpeduncularis in the rat

Colchicine injections in the supracommissural septum of the rat caused degeneration of several neurons in the nucleus triangularis septi and the nucleus septofimbrialis. The lesions resulted in significant decreases of choline acetyltransferase in the habenula (-34%) and in the nucleus interpeduncularis (-36%), thus demonstrating the existence of a major cholinergic projection to these nuclei from the supracommissural septum. A large fall in choline acetyltransferase was also noticed in the dorsal hippocampus as a consequence of colchicine damage to the fimbria-fornix fibers crossing the injected area.

Substance P neuronal organization in the median region of the interpeduncular nucleus of the cat: an electron microscopic analysis

The localization of substance P-like immunoreactivity in the interpeduncular nucleus using the peroxidase-antiperoxidase technique, revealed that the median region of the interpeduncular nucleus was one area rich in substance P-like immunoreactive processes. The ultrastructural characteristics of these substance P-like immunoreactive processes and their organization within the middle zone of the median region of the interpeduncular nucleus was studied. Substance P-like immunoreactivity was found in the perikaryon of small neurons, and in proximal and small dendrites. The substance P-like immunoreactive cell bodies and proximal dendrites receive a variety of unlabeled synaptic terminals. The immunoreactive small dendrites usually formed the central component of a "rosette"-like formation with unlabeled terminals. A few immunoreactive small unmyelinated axons and boutons were also present in the neuropil. The substance P-like immunoreactive boutons contained mainly small round vesicles with some large dense-core vesicles. These substance P-like immunoreactive boutons were presynaptic to unlabeled dendritic profiles, and frequently to substance P-like immunoreactive dendritic profiles. They were also seen in apposition to unlabeled boutons. Substance P-like immunoreactive boutons were not found to synapse with the crest-like dendritic processes in this part of the interpeduncular nucleus. It is suggested on the basis of morphological features, that some of the unlabeled terminals synapsing on substance P-like immunoreactive dendrities, may be cholinergic in nature.

Effect of manganese treatment on the levels of neurotransmitters, hormones, and neuropeptides: modulation by stress

Six weeks of daily intraperitoneal injection with manganese chloride (15 mg/kg body wt) reduced the normal weight gain of male Fischer-344 rats. This treatment depressed plasma testosterone and corticosterone levels, but prolactin levels were unaffected. The only significant changes in the levels of a variety of neuropeptides assayed in several regions were increases in the levels of hypothalamic substance P and pituitary neurotensin. Striatal serotonin, dopamine, and their metabolites were unchanged in manganese-exposed rats relative to saline-injected controls. However, the stress of injection combined with the effect of manganese appeared to significantly increase concentrations of striatal monoamines relative to uninjected controls.

Populations of substance P, Met-enkephalin and serotonin immunoreactive neurons in the interpeduncular nucleus of cat: cytoarchitectonics

The indirect antibody-peroxidase immunostaining method was used to study the distribution of substance P- (SPLI), Met-enkephalin- (MELI) and serotonin-like (5-HTLI) immunoreactivity within the interpeduncular nuclear complex (IPN) of the cat. Populations of immunoreactive cell bodies were found to have a distinct pattern of localization within the IPN. This distribution pattern is described as seen at 4 representative levels rostrocaudally through the IPN. SPLI cell bodies were mainly at rostral levels I, II and III especially in the median region and as a cluster of cells in the intermediate regions of the IPN. MELI cell bodies were seen at all 4 levels, confined mainly to the median and intermediate regions at levels I and II and also in the lateral regions at levels III and IV. There were few 5-HTLI cell bodies at the rostral levels I and II where they were confined to the dorsal zone of the median region, whereas at levels III and IV there were numerous cell bodies located throughout the intermediate region of the IPN. The immunoreactive cell bodies in the IPN may belong to both intrinsic and projection neurons. The distinctive neurochemical cytoarchitectonics of the IPN suggest that this region of the brain which lies along the course of major limbic pathways, may be a center of complex integrative mechanisms of neuronal activity.

The effects of p-chlorophenylalanine (PCPA) treatment on the substance P content measured in discrete brain nuclei of normal and neonatally-induced hypothyroid rats

Neonatal hypothyroidism is known to induce the accumulation of substance P and serotonin in many discrete brain nuclei of the rat. In this work, we have studied the effects of p-chlorophenylalanine (PCPA), a serotonin (5-HT) depleting drug, on the regional distribution of substance P in the brains of neonatally-induced hypothyroid and euthyroid rats. PCPA injections were given 48 and 24 h before sacrifice and the peptide content of discrete brain nuclei, removed by punches of frozen brain slices, was measured by radioimmunoassay. In hypothyroid animals, substance P levels were significantly increased in the n. paraventricularis, n. medialis thalami, n. arcuatus. n. mamillaris medialis, substantia nigra, area ventralis tegmenti, n. interpeduncularis, substantia grisea and n. dorsalis raphes. This hypothyroid-induced accumulation of substance P was completely abolished, and even reversed in some nuclei, by PCPA treatment. Interestingly, in normal rats, following PCPA treatment, the substance P level was increased in n. paraventricularis pars magnocellularis, n. ventromedialis (hypothalami), n. dorsomedialis pars dorsalis (hypothalami), n. amygdaloideus centralis, area ventralis tegmenti, substantia grisea, n. medianus raphes and n. dorsalis raphes. These results lend support to the existence of a physiological relationship between both substance P and serotonergic systems.

Experimental immunohistochemical studies on the substance P neuron system in the lateral habenular nucleus of the rat: distribution and origins

We examined the distribution and afferent projections of substance P-like immunoreactive (SPI) fibers in the lateral habenular nucleus of the rats by using the indirect immunofluorescence method. On the basis of the distribution, a dense plexus of SPI fibers in the lateral habenular nucleus (LHb) could be divided into two parts: medial (mLHb) and lateral (lLHb). The present study demonstrates that SPI fibers in the lLHb originate from SPI cells in the rostral entopeduncular nucleus (rEP) and the adjacent area, while those in the mLHb originate from SPI cells in the medial habenular nucleus. Moreover, we showed that the axons from SPI cells in the rEP reached the lLHB via the "pallidohabenular tract."

Effects of thyroid state on serotonin, 5-hydroxyindoleacetic acid and substance P contents in discrete brain nuclei of adult rats

The effects of chemical thyroidectomy produced by propylthiouracil treatment or hyperthyroidism produced by daily injections of thyroxine on the content of serotonin, its metabolite 5-hydroxyindoleacetic acid and of substance P in discrete brain nuclei of adult rats have been studied. Brain nuclei were removed by punches of frozen brain slices. The serotonin and 5-hydroxyindoleacetic acid contents were measured by high performance liquid chromatography with electrochemical detection while substance P was assayed by radioimmunoassay. The serotonin level was significantly increased in 11 nuclei of the hypothyroid and in 12 nuclei of the hyperthyroid rats. The 5-hydroxyindoleacetic acid levels were higher in 16 nuclei of the hypothyroid and 7 nuclei of the hyperthyroid animals. The state of the thyroid gland in adult rats also affected the substance P system but less consistently than the serotonin pathway. Thus, the substance P content in the brain of propylthiouracil-treated animals increased significantly in 4 nuclei while it decreased in the septum lateralis and the striae terminalis. Following the chronic thyroxine injections, the substance P level was increased in the nucleus caudatus putamen and the tractus diagonalis and was decreased in the area ventralis tegmenti. We previously reported that neonatal thyroidectomy caused a general increase of the substance P and serotonin contents in many brain nuclei of young rats. It appears that the effects of chemical thyroidectomy on mature and immature rat brain are different for the substance P system, suggesting that thyroxine plays an important role in the maturation of substance P-containing neurons.

Cholinergic and GABAergic forebrain projections to the habenula and nucleus interpeduncularis: surgical and kainic acid lesions

The forebrain cholinergic and GABAergic projections to the habenula and nucleus interpeduncularis have been investigated by means of surgical and kainic acid lesions. Bilateral transection of the stria medullaris caused a 50% decrease of choline acetyltransferase in both the habenula and nucleus interpeduncularis, and a 65% decrease of glutamate decarboxylase in the habenula. Electrolytic lesions of the posterior septum (nucleus triangularis septi and nucleus septo-fimbrialis) accounted for at least 30-40% decrease of the cholinergic parameter in the habenula and nucleus interpeduncularis. Moreover, the choline acetyltransferase decrease in the habenula appeared restricted to the medial part of the nucleus. Kainic acid injections causing very large neuronal destruction in the nucleus of the diagonal band of Broca, and more than 70% decrease of choline acetyltransferase in the dorsal hippocampus, did not affect the cholinergic parameter in either the medial or lateral habenula or nucleus interpeduncularis. Kainic acid injections in the nucleus entopeduncularis resulted in a 40% decrease of glutamate decarboxylase in the habenula. Kainic acid injections in the nucleus of the diagonal band were accompanied by a 40% decrease of glutamate decarboxylase in the medial subdivision only. The present study points at the nuclei of the posterior septum as the source of a major cholinergic projection to the habenula and nucleus interpeduncularis, and reveals a previously unsuspected GABAergic input from the nucleus of the diagonal band to the medial habenula.

Experimental and immunohistochemical studies concerning the major origins of the substance P-containing fibers in the lateral lemniscus and lateral parabrachial area of the rat, including the fiber pathways

The origins and pathways of substance P-containing fibers in the lateral lemniscus and lateral parabrachial area of the rat were investigated by means of the indirect immunofluorescence technique. Following the placement of various knife cuts or lesions, the following could be concluded: (1) The cells of origin of substance P-containing fibers in the lateral lemniscus and lateral parabrachial area are localized in the ventral reticular formation of the rhombencephalon from the level of P2.8 to P7.0 in the atlas of Palkovits and Jacobowitz; (2) The fibers from these origins pass the ventral reticular formation of the rhombencephalon to form a dense bundle; (3) the fibers turn dorsally at the mid-rhombencephalon junction to reach the lateral lemniscus and lateral parabrachial area. The present study demonstrates the linking of the functions of the parabrachial area and lateral lemniscus via substance P innervation.

Sex-related difference in substance P level in rat anterior pituitary: a model of neonatal imprinting by testosterone

There was a distinct sex-related difference in the anterior pituitary level of substance P-like immunoreactivity (SP-LI) in adult rats; the anterior pituitaries of male rats contained a higher concentration of SP-LI than those of females. Neonatal castration (day 1) resulted in a marked decrease of the SP-LI level in adult males, and this decrease in the SP-LI level was restored by neonatal testosterone replacement (days 2, 4, 6) but not by androgen replacement in adulthood. On the other hand, testosterone injection of neonatal females (days 2, 4, 6) caused a significant elevation of the SP-LI level after maturation. Ovariectomy of adult females failed to alter the SP-LI level. These results indicate that neonatal exposure to testosterone plays a critical role in the sexual differentiation of the substance P level in rat anterior pituitary.

Chemical transmission in the rat interpeduncular nucleus in vitro

We have used a rat brain-slice preparation to study the effects of some cholinomimetic and amino acid agonists and antagonists on the discharge frequency of neurones in the interpeduncular nucleus (i.p.n.), and on the response of these neurones to electrical stimulation of their main excitatory input, the fasciculus retroflexus of Meynert (f.r.m.). A high proportion of i.p.n. neurones were excited by carbachol, acetylcholine (ACh) and muscarine, but methacholine was less effective. The amino acids L-glutamate and L-aspartate were highly effective stimulants of i.p.n. neurones. The responses to ACh or carbachol were greatly reduced by the nicotinic blocking agents hexamethonium, d-tubocurarine and mecamylamine but only slightly reduced by atropine. The response to muscarine was abolished by low doses of atropine. Alpha-Bungarotoxin did not block the response of i.p.n. neurones to f.r.m. stimulation or to cholinomimetic agonists. The response of i.p.n. neurones to f.r.m. stimulation was not appreciably affected by high doses of nicotinic antagonists or atropine nor was there any enhancement of the response by physostigmine. The amino acid antagonists gamma-D-glutamylglycine (gamma DGG) and 2-amino phosphonovalerate (2-APV) were effective blockers of the response to f.r.m. stimulation and preferentially reduced responses to aspartate while having little effect on responses to glutamate or cholinomimetic agonists. It is concluded that ACh is an unlikely candidate for transmitter in this pathway despite abundant neurochemical evidence in its favour. It is more likely that the transmitter is an excitatory amino acid, probably an aspartate-like substance.

Correlation of neurochemical and behavioral effects of triethyl lead chloride in rats

Adult male Fischer-344 rats were dosed sc with 1 or 2.5 mg/kg of triethyl lead chloride (TEL) for 5 consecutive days. One week after the last dose, TEL-exposed rats had decreased Met-enkephalin in the hypothalamus, septum, and frontal cortex, while substance P was decreased in the hippocampus and frontal cortex. Dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) in the caudate nucleus were not altered by TEL nor were serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the caudate nucleus, hypothalamus, hippocampus, or frontal cortex. In a second experiment, rats were dosed with 1.75 mg/kg sc for 5 days. Subsequent assay of brain tissue indicated that TEL decreased met-enkephalin levels in the septum of rats one and seven days after cessation of dosing; effects on substance P were not observed. TEL-induced decreases in Met-enkephalin in the septum were temporally associated with increased hot plate latencies. One day after cessation of dosing with TEL, concentration of 5-HIAA in the caudate nucleus, hippocampus, frontal cortex, and brain stem, and 5-HT in the hippocampus and brain stem were increased. Biogenic amine concentrations were not affected in any other region or at any other time postdosing. A third experiment indicated that TEL-induced analgesia could be attenuated by 10 mg/kg chlordiazepoxide or 10 mg/kg of naloxone. The present results suggest that TEL-induced analgesia may be due to alterations in emotionality or reactivity to noxious stimuli, which may be associated with the alteration in delta opiate mechanism in the limbic system, such as the change of septal enkephalin neuronal activities.

The transsynaptic regulation of the septal-hippocampal cholinergic neurons

There is not yet a complete understanding of the functional interactions among various septal nuclei which regulate hippocampal function. Nevertheless, much has been learned histologically and biochemically about the major connections of the distinct areas of the septal complex and the chemical character of some of these pathways. The cholinergic septal-hippocampal pathway serves as a well defined link between these two important structures of the limbic system. Acetylcholine turnover rates in the hippocampus have been shown to increase or decrease proportionally to the activity of the cholinergic neurons originating in the septum. Moreover, these turnover rates have been shown to be modulated by intraseptal injections of agonists or antagonists of various neurotransmitters or neuromodulators which are stored in various cell groups located in the septum. By coupling this biochemical approach with techniques to study the receptor organization, greater detail concerning the transmitter and cotransmitter interactions among the various neuromodulators can be obtained.

Effect of acrylamide on neurotransmitter metabolism and neuropeptide levels in several brain regions and upon circulating hormones

The effect of acute and subchronic acrylamide treatment on levels of dopamine, serotonin, and their metabolites was determined in several brain regions of the rat. Concentrations of several neuropeptides and circulating hormones were also measured. Both a single and repeated doses of acrylamide resulted in elevated levels of 5-hydroxyindolacetic acid in all regions studied (frontal cortex, striatum, hippocampus, brain stem, and hypothalamus). Changes in regional content of other monoamines were much less pronounced. Turnover studies following pargyline blockage of monoamine oxidase, suggested results were due to increased rates of serotonin turnover in acrylamide-treated rats. Changes in neuropeptide levels were only detected in the hypothalamus where a single acrylamide treatment caused elevated levels of beta-endorphin and substance P, and in frontal cortex where met-enkephalin levels were higher after repeated acrylamide injection. Such repeated injection caused a major depression in plasma levels of testosterone and prolactin.

Distribution of substance P-like immunoreactivity in the lower brainstem of the human fetus: an immunohistochemical study

The regional distribution of substance P-like immunoreactive (SPI) structures in the lower brainstem of the human fetus was investigated using the indirect immunofluorescence technique. SPI cells were found in a number of areas including the inferior colliculus, central gray matter of the midbrain, n. laterodorsalis tegmenti, midbrain and medullary reticular formation, n. vestibularis inferior, and n. prepositus hypoglossi. An extensive network of SPI fibers of varying densities were identified throughout the lower brainstem.

Sex-related difference in the rat pituitary [Met5]-enkephalin level--altered by gonadectomy

Ontogenetic study of the rat pituitary [Met5]-enkephalin-like immunoreactivity (ME-LI) revealed that a sex-related difference in the level of this peptide began at 35 days of age. By 70 days of age, the level of male ME-LI was twice that of the female. Castration reduced the ME-LI in male rats and increased the ME-LI in female rats. These results suggest a possible role of sex hormones in regulating the pituitary enkephalin system.

Organization of the habenulo-interpeduncular connections in cats: a horseradish peroxidase study

The afferent fiber connections to the interpeduncular (IP) complex were demonstrated by the retrograde axonal transport of horseradish peroxidase (HRP) in cats. The HRP was injected into each nucleus of the IP complex, that is the central nucleus (IPC), the paramedian nucleus (IPP), the apical nucleus (IPA), and the posterior nucleus (IPN) including the outer division (IPO) and the inner division (IPI), and surrounding areas of the IP complex, using a ventral or dorsal surgical approaches. Most of the labeled neurons were in the medial habenular nucleus (MH) and each of the sub-nuclei of the IP complex was related to a specific part of the MH. Thus, the mediodorsal part of MH projected to the IPC, the medioventral part of MH projected to the IPI, the laterodorsal part of MH projected to the IPA, and the lateroventral part of MH projected to the IPP and the IPO. There were a few labeled cells in the accessory dorsal tegmental nucleus, the nucleus raphe dorsalis (RD), the nucleus centralis superior, the nucleus of the locus coeruleus, the gray matter of the floor of the fourth ventricle, and the nucleus of diagonal band of Broca, but there were no obvious patterns in the projections of these nuclei to the different sub-nuclei of the IP complex. When the area of the HRP injection involved the midbrain reticular formation adjacent to the IP complex and the nucleus reticularis tegmenti pontis (RT) but not the IP complex itself, there were many labeled cells in the lateral habenular nucleus and the medial and lateral mammillary nuclei, but there were no labeled cells in the medial habenular nucleus.

Ontogeny of substance P-containing neuron system of the rat: immunohistochemical analysis--II. Lower brain stem

Ontogeny of the substance P neuron system in the lower brain stem of the rat was investigated by means of the indirect immunofluorescence technique. Substance P-positive structures (cells and fibers) first appeared in the primordium of the ventral part of the nucleus tractus spinalis nervi trigemini (nVs), in the reticular formation between nucleus reticularis lateralis and nVs, and in the reticular formation between nVs and nucleus originis nervi facialis, respectively, at gestational day 14. After that time, substance P-positive structures made their appearance gradually in various areas of the lower brain stem. The present study demonstrates that substance P-positive structures appear at a very early ontogenetical stage, which suggests that substance P may play a role in the development of the lower brain stem in addition to its role as a neurotransmitter or neuromodulator.

The distribution of enkephalin immunoreactive fibers and terminals in the monkey central nervous system: an immunohistochemical study

Using immunohistochemical techniques, the distribution of met-enkephalin fibers and terminals was studied in the central nervous system of adult old-world monkeys. Areas which showed the greatest density of immunoreactivity included substantia gelatinosa, nucleus tractus solitarius, nucleus parabrachialis, substantia nigra, median eminence, globus pallidus (external segment), patches within the striatum and the region of nucleus accumbens and the olfactory area. Striking and discrete zones of enkephalin immunoreactive fibers and terminals which did not conform to known nuclear boundaries were observed in the latter areas. The distribution of enkephalin in the monkey is compared to what has been described in the rat central nervous system. In general, the two species are similar, however, differences were observed in some areas including the hypoglossal nucleus, substantia nigra and in the region of the nucleus accumbens and olfactory area. The results are discussed with regard to the possible functional significance of enkephalin localization in regions related to regulation of pain, mood, and autonomic function.

Experimental and immunohistochemical studies on the cerebellar substance P of the rat: localization, postnatal ontogeny and ways of entry to the cerebellum

With the indirect immunofluorescence technique, the localization (including the postnatal ontogeny) of substance P in the cerebellum, and the ways of entry of substance P-containing fibers into the cerebellum were explored. In the newborn rat cerebellum, dense fiber bands of axons with substance P-like immunoreactivity which can be traced to the lower brain stem are found. These fibers are also traceable to the developing granular cell layer. Two weeks after birth, however, substance P-containing structures seen in the cerebellum begin to decrease progressively and in the cerebellum of the adult rats, only a small amount of substance P-containing structures is observed. The present study established that substance P-containing fibers are mostly derived from extracerebellar substance P-containing cells and demonstrated the presence of three sites of entry of these substance P-containing fibers to the cerebellum, via (1) the inferior cerebellar peduncle, (2) the fasciculus uncinatus and (3) the middle cerebellar peduncle, respectively. Following deafferentation of the cerebellum, substance P-accumulating fibers are observed only ventral to the lesion (i.e. on the brain stem side), while in the cerebellum a remarkable decrease of substance P-containing fibers is seen and no substance P-accumulating fibers are found dorsal to the lesion (cerebellar side).

Ontogeny of substance P-containing neuron system of the rat: immunohistochemical analysis--I. Forebrain and upper brain stem

The ontogeny of substance P-containing neuron system in the forebrain and upper brain stem of the rat was investigated by means of the indirect immunofluorescence technique. Substance P-positive structures first appeared in the primordium of the epithalamus and the area which surrounded the commissura posterior of the rat fetus corresponding to gestational day 14 (10-12 mm embryos). On and after gestational day 14, substance P-positive structures gradually made their appearance in various areas of the forebrain and upper brain stem. Substance P-positive structures thus continued to increase in number and in density during the fetus and perinatal stage and showed histochemically maximum content at the stage between postnatal days 5 and 15. After then, substance P-positive neurons tended to decrease in number as the rats grew, while substance P-positive fibers maintained in general their strong immunoreactivity even in the adult rats. The present study demonstrates that substance P-positive structures appear at a very early ontogenetical stage. This suggests that substance P might play an important role in the development of the forebrain and upper brain stem in addition to its neurotransmitter or neuromodulator functions.

Monosodium glutamate exposure in the neonate alters hypothalamic and pituitary neuropeptide levels in the adult

Administration of monosodium glutamate (MSG) during the neonatal period in rats produced differential effects on the contents of various neuropeptides in the hypothalamus: beta-endorphin (beta-E) level was reduced by 70% while substance P (SP), neurotensin (NT) and Met5-enkephalin (ME) levels were not significantly changed (ME content of male rats was slightly reduced). The contents of ME, SP and NT in striatum and hippocampus were also unaffected by the same treatment. Male rats contain higher pituitary content of beta-endorphin-like immunoreactivity (beta-ELI) than female rats. MSG treatment reduced the pituitary content of beta-ELI and abolished the sex difference in beta-ELI level seen in the control rats. MSG treatment in the neonates by eliminating beta-E neurons while sparing ME neurons in the brain may be a useful tool for studying the different functions of these two separate opioid peptides.

Topographic atlas of somatostatin-containing neuron system in the avian brain in relation to catecholamine-containing neuron system. II. Mesencephalon, rhombencephalon, and spinal cord

With the indirect immunofluorescence technique of Coon's and collaborators, overall distribution of the somatostatin (SRIF)-positive neurons system in the avian lower brain stem was explored. Numerous cell somata containing SRIF were identified in the interpeduncular nucleus and substantia grisea centralis (GCT) at the level of the nucleus nervi trochlearis. Furthermore, a moderate number of SRIF-positive neurons were seen in the tectum opticum, nucleus tractus solitarii, and spinal cord. Scattered labeled cells were noticed in the rhombencephalon. A dense network of SRIF-positive fibers was distributed widely in the lower brain stem of birds. Their locations corresponded in many cases to the areas where SRIF-positive neurons were found. The present study also presents the distribution of the catecholamine (CA) neuron system in the avian lower brain stem. Possible interactions between SRIF and CA neurons systems are briefly discussed.

Experimental immunohistochemical studies on the amygdalofugal peptidergic (substance P and somatostatin) fibers in the stria terminalis of the rat

The amygdalofugal substance P (SP) and somatostatin (SRIF) neuron systems in the stria terminalis (ST) were investigated by means of the indirect immunofluorescence technique of Coons. SP- and SRIF-positive cells were mainly located in the area (Amc) between the central (ac) and medial (am) amygdaloid nuclei. Some extended medially into the am and laterally into the ac. Destruction of the Amc resulted in a marked reduction of SP- and SRIF-positive fibers in the ST. Furthermore, a substantial decrease in SP-positive fibers was seen in the dorsal part of the bed nucleus of the ST (stb), there was a small decrease in the SP-positive fibers in the lateral hypothalamus (LH), a significant decrease in the SRIF-positive fibers in the lateroventral part of the anterior hypothalamic nucleus (lvAH), and a small decrease in the SRIF-positive fibers in the LH. These facts indicate that the origins of a number of SP- and SRIF-positive fibers are the Amc and that the amygdalofugal SP pathway in the ST innervates stb and LH and the amygdalofugal SRIF pathway in the ST projects to lvAH and LH.

A substance P projection to the hippocampus

Electrolytic lesions of the septal area in the rat resulted in a major decrease in the activity of choline acetyltransferase in the hippocampus, consistent with the interruption of the septo-hippocampal cholinergic pathway. These lesions also significantly decreased the levels of substance P in the hippocampus. It is suggested that a substance P projection to the hippocampus arises in or passes through the septal area.

Afferent connections of the interpeduncular nucleus and the topographic organization of the habenulo-interpeduncular pathway: an HRP study in the rat

The HRP tracing method was employed to investigate the organization and afferent connections of the interpeduncular nucleus (IPN) in the rat. To study the topographical features of the different projections, a method was devised for obtaining HRP placements of limited size in different areas of the IPN. The main afferent connection of the IPN is a topographically organized projection from the medial habenula (Hb). This projection follows a reversed caudorostral pattern, terminating throughout all but the caudalmost part of the IPN. The dorsal part of the IPN receives a sparse innervation arising mainly from a narrow lateral and ventrolateral area of the medial Hb. The ventral two thirds of the IPN receives a much heavier projection, as follows: A large ventrolateral area of the medial Hb projects to the lateral part of the IPN in a completely bilateral way. An additional projection, which is predominantly ipsilateral, arises from the rostral half of the dorsolateral part of the medial Hb and terminates in the caudal IPN. The medial part of the medial Hb projects preferentially to central areas of the IPN. The projection from the lateral Hb is quantitatively much smaller but appears to be distributed to the entire length of the IPN, following a nonreversed caudorostral arrangement, with the ipsilateral projection predominating. The projections from the medial and lateral Hb to the IPN were confirmed by tracing anterogradely transported HRP as well. No reciprocal connection from the IPN to the Hb could be demonstrated. A sparse projection to the IPN with a strong ipsilateral predominance arises from the horizontal limbs of the nucleus of the diagonal band of Broca. This was the only projection observed from the septal region. Sparse projections from the premammillary and supramammillary nuclei were also demonstrated. Confirmatory data and some details of organization were also obtained for projections to the IPN from other areas, including the medial and dorsal raphe nuclei, the dorsal tegmental nucleus of Gudden, and the adjacent dorsolateral tegmental nucleus. Very small projections from the ventral tegmental nucleus and the locus coeruleus were also found.

Discrete regional distributions of thyrotropin releasing hormone (TRH) receptor binding in monkey central nervous system

Thyrotropin releasing hormone (TRH) directly influences central nervous system (CNS) function, independent of its pituitary action. Although these CNS effects have been behaviorally characterized, information is not yet available on the precise regional distribution of its receptor. TRH receptor binding was examined in the monkey CNS by the radioreceptor assay for clarifying the site of TRH action. TRH was bound to brain tissue membranes via high-affinity (Kd = 5.9 x 10(-9) M) and low-affinity (Kd = 11.2 x 10(-8) M) components. TRH receptor binding varied dramatically throughout the monkey brain, with more than 40-fold variation. The limbic system contained the greatest amount of binding. The next highest areas were the cerebral cortex, hypothalamus, interpeduncular nucleus and periaqueductal gray matter of the midbrain. Receptor binding was very low or not detectable in the medial thalamus, cerebellum, brain stem, spinal cord and white matter. These data suggest that TRH has an effect on the CNS via limbic system, cerebral cortex and midbrain.

Brain peptides as neurotransmitters

Numerous peptides appear to be neurotransmitter candidates in the brain. Some, such as the opioid peptide enkephalins, neurotensin, and substance P, were first isolaterd from the brain. Peptides, such as cholecystokinin and vasoactive intestinal polypeptide, were known as intestinal hormones and later recognized as brain constituents. Certain hypothalamic-releasing hormones, pituitary peptides, and blood-derived peptides like angiotensin II and bradykinin, may also be central neurotransmitters. The diversity of localization of these peptides throughout the brain implies a multiplicity of potential roles.