Synaptic organization of septal projections in the rat medial habenula: a wheat germ agglutinin-horseradish peroxidase and immunohistochemical study

The synaptic organization of septal inputs to the rat habenular complex of the dorsal diencephalon was examined employing the anterograde tracer wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). The cellular distribution of substance P (SP) and choline acetyltransferase (ChAT) immunoreactivity was also studied at the light and electron microscopic level. Following placements of tracer within the entire septum, labeled axons were observed in the stria medullaris and in the medial and lateral subnuclei of the habenula. Following injections of tracer in the nuclei triangularis and septofimbrialis of the posterior septum, the medial subnucleus was heavily labeled, whereas the lateral subnucleus was devoid of peroxidase activity. The medial subnucleus possessed labeled myelinated axons and terminals that contained clear, spherical vesicles and formed asymmetric contacts with dendritic spines and shafts. Terminals possessing WGA-HRP activity also formed non-synaptic junctions with other labeled or unlabeled terminals. SP and ChAT immunoreactivity in normal and colchicine-treated animals was confined to dendrites and somata within the medial habenula. Terminals containing clear spherical vesicles formed asymmetric synaptic contacts with these immunoreactive somatic and dendritic profiles. Based on the combined anterograde tracing and immunohistochemical data, it is proposed that septal projections provide a direct innervation to habenular neurons that contain ChAT or SP activity. These septal inputs may play an important role in the facilitation of the ChAT- and SP-positive habenular neurons, both of which provide prominent afferent inputs to the interpeduncular nucleus. Thus, neurons of the habenula and interpeduncular nucleus are under the direct and indirect influence of septal neurons within the limbic forebrain circuit.

Immunohistochemical characterization of pelvic neurons which project to the bladder, colon, or penis in rats

Retrograde-tracing and immunohistochemical techniques were used in combination to investigate the types of putative transmitters in pelvic neurons that project to the bladder, colon or penis of rats. In addition, populations of axon varicosities associated with these neurons were characterized. Subpopulations of neurons in colchicine-treated major pelvic ganglia and accessory ganglia of male rats contained immunoreactivity (IR) for tyrosine hydroxylase (TH), vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), or enkephalin (ENK), while types of immunoreactivity found in major groups of varicose axons were ENK, cholecystokinin (CCK), and somatostatin (SOM). Substance P (SP)-IR varicose axons were much less common. Bladder and colon neurons were similar in a number of ways. Many neurons contained NPY-IR (greater than or equal to 50%), fewer contained TH-IR (25-30%), and even fewer contained ENK-IR (5-15%) or VIP-IR (5-10%); many neurons were associated with baskets of ENK-IR varicosities (50-65%) and fewer neurons were surrounded by CCK- or SOM-IR varicosities (30-35%). Colon neurons differed from penis neurons in having a slightly larger proportion that contained ENK-IR (10-15%, compared with 1-3%). Penis neurons were markedly different from the other two groups in additional ways. More than 90% of them contained VIP-IR, whereas only 5-7% contained NPY-IR and none were immunoreactive for TH. Furthermore, although the proportion of penile neurons associated with many ENK-IR varicosities was similar to the bladder and colon neurons (45-50%), they were rarely seen close to CCK- or SOM-IR varicose axons. These studies describe similarities and differences in the histochemical properties of neurons which project to the bladder, colon, or penis and of the varicose axons associated with those neurons. This gives further insights into the possible transmitter mechanisms involved in the regulation of different pelvic functions.

Distribution and functional significance of Met-enkephalin-Arg6-Phe7- and Met-enkephalin-Arg6-Gly7-Leu8-like peptides in the blowfly Calliphora vomitoria. I. Immunocytochemical mapping of neuronal pathways in the brain

Neuronal pathways immunoreactive to antisera against the extended-enkephalins, Met-enkephalin-Arg6-Phe7 (Met-7) and Met-enkephalin-Arg6-Gly7-Leu8 (Met-8), have been identified in the brain of the blowfly Calliphora vomitoria. Co-localisation with other enkephalins in certain neurons suggests that a precursor similar to preproenkephalin A exists in insects and that differential enzymatic processing occurs as in vertebrates. Co-localisations of the extended-enkephalin-like peptides with other vertebrate-type peptides, including cholecystokinin and pancreatic polypeptide, also occur. The enkephalinergic pathways are specific, comprising a few groups of highly characteristic neurons and areas of neuropil. Of special interest is the finding that parts of the antennal chemosensory and the optic lobe visual systems contain Met-8 immunoreactive neurons. Within the median neurosecretory cell groups, some of the giant neurons show immunoreactivity to Met-8 and others to both Met-8 and Met-7. Fibres from these cells project to the corpus cardiacum and also to the suboesophageal ganglion, where arborisations occur in the tritocerebral neuropil. Co-localisation studies of these cells have shown that at certain terminals, one particular type of peptide is the dominant neuroregulator, whilst at other terminals, within the same cell, a different co-synthesised peptide predominates. Several groups of lateral neurosecretory cells show clearly defined enkephalinergic pathways, most of which have connections with the central body. The complex patterns of immunoreactivity seen in terminals in the different parts of the central body, suggest an important role for the enkephalin-like peptides in the integration of multimodal sensory inputs. The physiological functions of the extended-enkephalin-like peptides in the brain of Calliphora is still unknown, but the anatomical evidence suggests they may have a role similar to that in mammals, where they are thought to control aspects of feeding behaviour.

Serotoninergic projections from the midbrain periaqueductal gray to the nucleus accumbens in the rat

A combined method of retrograde tracing of horseradish peroxidase (HRP) and serotonin (5-HT) immunocytochemistry indicated that some 5-HT-like immunoreactive neurons in the midbrain periaqueductal gray (PAG) of the rat send their axons to the nucleus accumbens. These PAG neurons are mainly located in the ventromedial and ventrolateral subdivisions at the middle and caudal levels of PAG.

Origin of luteinizing hormone-releasing hormone neurons

Neurons expressing luteinizing hormone-releasing hormone (LHRH), found in the septal-preoptic nuclei and hypothalamus, control the release of gonadotropic hormones from the anterior pituitary gland and facilitate reproductive behaviour. LHRH-expressing neurons are also found in the nervus terminalis, a cranial nerve that is a part of the accessory olfactory system and which projects directly from the nose to the septal-preoptic nuclei in the brain. During development, LHRH-immunoreactivity is detected in the peripheral parts of the nervus terminalis before it is found in the brain. Using a combination of LHRH immunocytochemistry and tritiated thymidine autoradiography in fetal mice, we show that LHRH neurons originate in the medial olfactory placode of the developing nose, migrate across the nasal septum and enter the forebrain with the nervus terminalis, arching into the septal-preoptic area and hypothalamus. Clinically, this migratory route for LHRH-expressing neurons could explain the deficiency of gonadotropins seen in 'Kallmann's syndrome' (hypogonadotropic hypogonadism with anosmia).

Immunohistochemical demonstration of tyrosine hydroxylase (TH)-positive but dopamine beta-hydroxylase (DBH)-negative neuron-like cells in the pineal gland of golden hamsters

Double immunostaining for tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) in the pineal gland revealed many TH-positive but DBH-negative, neuron-like cells in golden hamsters, but not in rats and gerbils. They were scattered in the meshwork of TH- and DBH-positive nerve fibers throughout the parenchyma. Their cell bodies were oval or spindle-shaped (maximum diameter: 15-20 micron). They had sometimes one or two short cell processes. Bilateral superior cervical ganglionectomy diminished strikingly the number of TH- and DBH-positive nerve fibers, but did not affect the number of TH-positive cells.

Brainstem origin of serotonin- and enkephalin-immunoreactive afferents to the opossum's cerebellum

Previous studies have described the distribution of serotonin- and enkephalin-immunoreactive elements in the posterior lobe vermis of the opossum's cerebellum. In the present study we have used a double labeling paradigm which combines the retrograde transport of horseradish peroxidase (HRP) with serotonin and enkephalin immunohistochemistry to determine the brainstem origin of serotoninergic and enkephalinergic neurons that project to the opossum's cerebellar cortex. Subsequent to HRP injections into the posterior lobe vermis, widespread areas of the medulla and pons were found to contain retrogradely labeled neurons. Serotonin-immunoreactive somata are present primarily in the raphe nuclei and the adjacent reticular formation. Enkephalinergic neurons were numerous in the raphe nuclei, medial accessory olive, gigantocellular reticular formation, locus coeruleus, and the nucleus of the trapezoid body. However, serotoninergic neurons that project to the cerebellum were located only in the medullary pyramids and the reticular formation adjacent to the raphe. Double-labeled enkephalinergic neurons were located 1) within the medullary pyramids, 2) throughout the extent of the caudal medial accessory olive, 3) in the rostral subnucleus a of the medial accessory olive, 4) in the nucleus reticularis gigantocellularis pars ventralis, 5) in the nucleus reticularis lateralis, and 6) in the nucleus reticularis ventralis lateral to the inferior olivary complex. These results indicate that although neurons containing serotonin and enkephalin immunoreactivity may be present in some of the same pontine and medullary nuclei, those serotoninergic and enkephalinergic neurons that project to the cerebellum are present primarily in restricted and spatially separate regions of the caudal medulla.

Central serotonergic projections to the nucleus tractus solitarii: evidence from a double labeling study in the rat

Projections from several brainstem serotonergic nuclei to the nucleus tractus solitarii were investigated in the rat. Experiments were performed using a double labeling method combining retrograde radioautographic tracing and serotonin immunohistochemistry. After injection of the radioactive tracer ([3H] wheat germ agglutinin) into the lateral nucleus tractus solitarii, nerve cell bodies exhibiting both radioautographic labeling and immunostaining were detected in all the serotonergic nuclei investigated, namely the nucleus raphe magnus, the ventromedial paragigantocellular nucleus, the nuclei raphe pontis, medianus and dorsalis, the medial lemniscus and the reticulotegmental nucleus of the pons. Most of the double labeled perikarya observed were in the nucleus raphe magnus, the adjacent part of the paragigantocellular nucleus and the nucleus raphe dorsalis. Nerve cell bodies retrogradely labeled but devoid of immunostaining were also observed, together with the double labeled perikarya, within serotonergic nuclei. These results provide direct evidence that brainstem serotonergic neurons contribute to the innervation of the nucleus tractus solitarii. They indicate that the nucleus raphe magnus and the nucleus raphe dorsalis constitute two major sources of central serotonergic projections to the nucleus tractus solitarii.

Evidence for a projection from the B9 serotonergic cell group to the median raphe nucleus

Following injections of several fluorescent retrograde tracers into the median raphe nucleus large numbers of retrogradely labeled cells were observed in the ventral mesencephalic tegmentum. Subsequent immunocytochemical processing for serotonin-like immunoreactivity suggested that a large component of this projection originates from serotonergic B9 cells. Although tracer injections into the dorsal raphe did not result in similar labeling of B9 cells, evidence was obtained suggesting the existence of a small serotonergic projection from the median to the dorsal raphe.

Immunocytochemical study of the hypothalamic magnocellular neurosecretory nuclei of the snake Natrix maura and the turtle Mauremys caspica

An immunocytochemical study of the magnocellular neurosecretory nuclei was performed in the snake Natrix maura and the turtle Mauremys caspica by use of antisera against: (1) a mixture of both bovine neurophysins, (2) bovine oxytocin-neurophysin, (3) arginine vasotocin, and (4) mesotocin. Arginine vasotocin- and mesotocin-immunoreactivities were localized in individual neurons of the supraoptic and paraventricular nuclei, with a distinct pattern of distribution in both species. The same cells appeared to be stained by the anti-oxytocin-neurophysin and antimesotocin sera. The supraoptic nucleus can be subdivided into rostral medial and caudal portions. In N. maura, but not in M. caspica, neurophysin-immunoreactive neurons were found in the retrochiasmatic nucleus. No immunoreactive elements were seen in the suprachiasmatic nucleus of both species after the use of any of the antisera. A dorsolateral aggregation of neurophysin-containing cells, localized over the lateral forebrain bundle, was present in both species. Magnocellular and parvocellular neurophysin-immunoreactive neurons were present in the paraventricular nucleus of both species. In the turtle, the paraventricular neurons were arranged into four distinct layers parallel to the ependyma; these neurons were bipolar with the major axis perpendicular to the ventricle, and many of them projected processes toward the cerebrospinal-fluid compartment. In N. maura a group of large neurons of the paraventricular nucleus was found in a very lateral position. The posterior lobe of the hypophysis and the external zone of the median eminence contained arginine vasotocin- and mesotocin-immunoreactive nerve fibers. The lamina termialis of both species was supplied with a dense bundle of fibers containing immunoreactive neurophysin. Neurophysin-immunoreactive fibers were also present in the septum, some telencephalic regions, including the cortex and the olfactory tubercule, in the paraventricular organ, and the periventricular and periaqueductal gray of the brainstem.

Noradrenergic neurons with divergent projections to the motor trigeminal nucleus and the spinal cord: a double retrograde neuronal labeling study

Double retrograde axonal tracing was combined with the indirect immunofluorescence antibody method to determine whether noradrenergic neurons have divergent projections to the motor nucleus of the trigeminal nerve and the spinal cord. Rhodamine-labeled microspheres were injected into the motor trigeminal nucleus and True Blue was deposited into lumbar segments of the spinal cord. After a 10-18-day survival period, brainstem sections were processed for immunofluorescence staining of noradrenergic neurons using antibodies to rat dopamine-beta-hydroxylase. Rhodamine-labeled noradrenergic neurons were observed ipsilaterally throughout the A5 and A7 groups; the contralateral A5 and A7 groups contained few rhodamine-labeled cells. A few rhodamine-labeled noradrenergic neurons were observed in the locus coeruleus and subcoeruleus. True Blue-labeled noradrenergic neurons were identified in the A5 and A7 groups, in the ventral part of the locus coeruleus and in the subcoeruleus. Double retrogradely labeled noradrenergic neurons were observed in the A5 and A7 groups but not in the locus coeruleus and subcoeruleus. Of the total number of rhodamine-labeled noradrenergic cells, a large percentage also contained True Blue: 54% in the caudal A5 group, 59% in the rostral A5 group, and 72% in the A7 group. Of the total number of True Blue-labeled noradrenergic neurons, the percentage of double retrogradely labeled cells was 33% in the caudal A5 group, 46% in the rostral A5 group, and 56% in the A7 group. The findings of this study provide the first anatomic evidence for the existence of a prominent population of noradrenergic cells in the A5 and A7 groups with divergent projections to the motor trigeminal nucleus and the spinal cord. We propose that this subpopulation of noradrenergic neurons in the A5 and A7 groups influences motoneurons at multiple levels of the neuraxis.

A direct demonstration of the perforant pathway terminal zone in Alzheimer's disease using the monoclonal antibody Alz-50

The perforant pathway links the entorhinal cortex with the hippocampal formation and provides this structure with its major cortical input. The cells of origin of the perforant pathway are destroyed in Alzheimer's disease (AD) and a marked depletion of glutamate, the putative neurotransmitter in its terminal zone, occurs. We report that the monoclonal antibody Alz-50 recognizes an antigen in the terminal zone of the perforant pathway in AD. This observation provides direct evidence for the involvement of the perforant pathway in AD, and demonstrates that Alz-50 can be used to study neural connectivity in AD brains.

Distribution and origin of vasoactive intestinal polypeptide (VIP)-immunoreactive, acetylcholinesterase-positive and adrenergic nerves of the cerebral arteries in the bent-winged bat (Mammalia: Chiroptera)

The overall distribution and origins of vasoactive intestinal polypeptide (VIP)-immunoreactive (IR), acetylcholinesterase (AChE)-positive and adrenergic nerves in the walls of the cerebral arteries were investigated in the bent-winged bat. VIP-IR and AChE-positive nerves innervating the bat cerebral vasculature appear to arise mainly from VIP-IR and AChE-positive cell bodies within microganglia found in the nerve bundle accompanying the sympathetic nerve bundle within the tympanic cavity. These microganglia, as well as the nerve bundle containing them, do not emit catecholamine fluorescence, suggesting that they are of the cranial parasympathetic outflow, probably the facial or glossopharyngeal one. The axons from VIP-IR and AChE-positive microganglia run intermingled with sympathetic adrenergic nerves in the same thick fiber bundles, and reach the cranial cavity through the carotid canal. In addition, some of the VIP-IR fibers innervating the vertebro-basilar system, at least the basilar artery, originate from VIP-IR nerve cells located in the wall of this artery. The supply of VIP-IR fibers to the bat major cerebral arteries is the richest among mammals in that it is much greater in the vertebro-basilar system than in the internal carotid system: plexuses of VIP-IR nerves are particularly dense along the walls from the posterior ramus to posterior cerebral and basilar arteries. Small pial and intracerebral arteries of the vertebro-basilar system, especially those of the posterior cerebral artery which supply most parts of the diencephalon and cerebrum, are also richly innervated by peripheral VIP-IR fibers. This pattern corresponds well with the innervation pattern of adrenergic and AChE-positive nerves.

Origin, distribution and organization of the serotoninergic innervation in the inferior olivary complex of the rat

The serotoninergic innervation of the inferior olivary complex of the rat was studied using a specific immunohistochemical technique. Fibers and varicosities positive for serotonin were present throughout the nucleus. The densest varicosities were found in the lateral portion of the dorsal accessory olive and the caudal portion of the medial accessory olive. The rostral medial accessory olive and the principal olive were sparsely populated with labeled elements. Ultrastructurally, labeled profiles were found in close opposition to small dendrites and to olivary cell bodies, but they did not display any synaptic specialization. Labeled perikaria were found in the periolivary regions, some of them located laterally to the olivary complex are responsible for the serotoninergic innervation of the dorsal accessory olive; some others located dorsally and medially in the nucleus raphe obscurus and raphe pallidus were responsible for the innervation of the medial accessory olive.

Projection of neurotensin-like immunoreactive neurons from the lateral parabrachial area to the central amygdaloid nucleus of the rat with reference to the coexistence with calcitonin gene-related peptide

The origin of neurotensin-like immunoreactive (NTI) fibers in the central amygdaloid nucleus (AC) in the rat was examined using indirect immunofluorescence and retrograde tracing combined with immunocytochemistry. Destruction of the external subdivision of the lateral parabrachial nucleus, which contains a group of NTI neurons, resulted in a marked reduction of these fibers in the ipsilateral AC, which suggests that most of these fibers are of extrinsic origin. This was also supported by the finding that injection of fast blue dye into the AC labeled many neurons in the external subdivision of the lateral parabrachial nucleus ipsilaterally, and that simultaneous treatment with antiserum against NT stained some of these neurons. Subsequent immunohistochemical staining of alternate sections revealed that many of these NTI neurons were also labeled by calcitonin gene-related peptide antiserum.

Neuronal pathways to the rat thyroid revealed by retrograde tracing and immunocytochemistry

The distribution and origin of the nerve fibres innervating the rat thyroid were studied by immunocytochemistry, retrograde tracing and denervation experiments. Immunocytochemistry revealed nerve fibres containing noradrenaline, neuropeptide Y, vasoactive intestinal peptide, peptide histidine-isoleucine, galanin, substance P, neurokinin A and calcitonin gene-related peptide around blood vessels and follicles. Many of these transmitter candidates were found to co-exist with each other in different combinations in different subpopulations of neurons. Sympathectomy eliminated all noradrenaline- and noradrenaline/neuropeptide Y-containing fibres in the thyroid. Cervical vagotomy eliminated about 50% of the galanin-, substance P- and calcitonin gene-related peptide-containing fibres. Local denervation (removal of the thyroid ganglion and the thyroid nerve) eliminated all galanin- and substance P-immunoreactive fibres and the majority of noradrenaline-, noradrenaline/neuropeptide Y-, vasoactive intestinal peptide- and calcitonin gene-related peptide-containing fibres in the thyroid gland. Injection of True Blue into the thyroid gland labelled cell bodies in the thyroid ganglion, the laryngeal ganglion, the superior cervical ganglion, the jugular-nodose ganglionic complex, the dorsal root ganglia (C2-C5) and the trigeminal ganglion. Judging from the number of labelled nerve cell bodies, the superior cervical ganglion and the thyroid ganglion contribute most to the thyroid innervation, while the laryngeal ganglion and the trigeminal ganglion contribute least. The True Blue-labelled ganglia were examined for the presence of various populations of nerve cell bodies (only major populations are listed). The thyroid ganglion harboured neuropeptide Y, vasoactive intestinal peptide and galanin/vasoactive intestinal peptide cell bodies (in order of predominance); the laryngeal ganglion galanin/vasoactive intestinal peptide, vasoactive intestinal peptide and calcitonin gene-related peptide cell bodies; the superior cervical ganglion noradrenaline/neuropeptide Y and noradrenaline cell bodies; the jugular ganglion calcitonin gene-related peptide, substance P/calcitonin gene-related peptide and galanin/substance P/calcitonin gene-related peptide cell bodies; the nodose ganglion vasoactive intestinal peptide and vasoactive intestinal peptide/galanin cell bodies; the dorsal root ganglia (C2-C5) and the trigeminal ganglion calcitonin gene-related peptide, substance P/calcitonin gene-related peptide and galanin/substance P/calcitonin gene-related peptide cell bodies.(ABSTRACT TRUNCATED AT 400 WORDS)

The dentato-olivary projection in the rat as a presumptive GABAergic link in the olivo-cerebello-olivary loop. An ultrastructural study

It is here shown that autoradiographically labelled axon terminals of the dentato-olivary projection form a heterogeneous population. However, a majority of them constitute an even class of synapses, characterized by their small axonal size, their content in pleimorphic vesicles, and the establishment of symmetric synapses on small dendrites, about 5% of which are linked through a gap junction. The same material, used for immunocytochemistry of GABA with the postembedding technique, discloses that a majority of boutons with cytological features similar to the dentato-olivary terminals are GABA-immunoreactive, especially those synapsing on dendrites linked by gap junctions. The cerebello-olivary projection, despite its heterogeneity, thus appears as part of the GABAergic system which governs the synaptic modulation of the electrotonic coupling between olivary neurons.

The neostriatal mosaic: III. Biochemical and developmental dissociation of patch-matrix mesostriatal systems

In the previous paper (Gerfen et al., 1987) mesostriatal dopaminergic neurons were shown to be subdivided into dorsal and ventral tiers that project to the striatal matrix and patch compartments, respectively. The present study provides experimental evidence that these patch-matrix mesostriatal dopaminergic systems are biochemically and developmentally distinct. A 28 kDa calcium-binding protein (CaBP, or calbindin-D28 kDa) is expressed in dorsal tier mesostriatal dopaminergic neurons. The distribution of such neurons, located in the ventral tegmental area, dorsal tier of the substantia nigra pars compacta, and retrorubral area, matches that of dopaminergic neurons that project to the striatal matrix. Dopaminergic neurons that do not express CaBP--those in the ventral tier of the pars compacta and in the pars reticulata--are distributed in a pattern that matches the origin of the dopaminergic projection to the striatal patches. During development, dopaminergic afferents to the striatal patch compartment are in place prior to the development of those to the matrix. Injections of the neurotoxin 6-hydroxydopamine (6-OHDA) into the striatum of newborn rats result in a selective and long-lasting depletion of dopaminergic afferents in the striatal patches. The later-developing matrix projection is relatively spared by such lesions. The distribution of surviving dopaminergic neurons, labeled with tyrosine hydroxylase (TH) immunoreactivity, matches the pattern of dorsal tier neurons previously shown to provide inputs to the matrix. Surviving neurons also express CaBP immunoreactivity and have dendrites that spread mediolaterally, in the plane of the pars compacta. On the other hand, those neurons that project to the patches are selectively lesioned by the neonatal 6-OHDA striatal injections, do not express CaBP, and have dendrites that are directed ventrally into the pars reticulata.

Vestibulospinal pathway in rabbit includes GABA-synthesizing neurons

When Fast blue is injected into the rabbit spinal cord it is retrogradely transported into nerve cell bodies located in the medial and the descending vestibular nuclei. Approximately 50% of the Fast blue-positive cells also contain glutamic acid decarboxylase-like immunoreactivity. These neurons presumably synthesize gamma-aminobutyric acid (GABA) and the rabbit vestibulospinal pathway therefore contains a substantial inhibitory component.

Biochemical and radioautographic evidence for dopaminergic afferents of the locus coeruleus originating in the ventral tegmental area

The dopamine (DA) content of the locus coeruleus (LC) and the uptake of tritiated DA in the presence of desmethylimipramine into fresh vibratome sections of the LC-area were determined in control rats and in rats whose ventral tegmental area (VTA) had been destroyed by local application of 6-hydroxydopamine (6-OHDA). Destruction of the VTA reduced the DA content and the number of dopaminergic fibers visualized by radioautography in the LC area. This indicates that the DA containing afferents of the LC originate, at least partly, in the VTA.

Origin of serotonin innervation of the arcuate and ventromedial hypothalamic region

Combined fluorescence serotonin immunohistochemistry and retrograde transport labelling with Fast blue and Fluoro-gold were used to identify serotonin-immunoreactive neurons in the midbrain and pons which project to the region of the arcuate and ventrome-dial hypothalamic nuclei. Approximately 90% of doubly labelled neurons were located in the 3 major mesencephalic serotonin-containing cell groups: dorsal raphe (38%), median raphe (21%) and medial lemniscus group (29%). Within these groups, there were numerous non-retrogradely labelled serotonin-immunoreactive neurons as well as numerous non-serotonin-immunoreactive retrogradely labelled neurons. No doubly labelled neurons were observed caudal to raphe pontis although non-serotonin-immunoreactive neurons were retrogradely labelled in the more caudal raphe nuclei.

Neurotransmitters in the mammalian striatum: neuronal circuits and heterogeneity

The major input and output pathways of the mammalian striatum have been well established. Recent studies have identified a number of neurotransmitters used by these pathways as well as by striatal interneurons, and have begun to unravel their synaptic connections. The major output neurons have been identified as medium spiny neurons which contain gamma-aminobutyric acid (GABA), endogeneous opioids, and substance P. These neurons project to the pallidum and substantia nigra in a topographic and probably chemically organized manner. The major striatal afferents from the cerebral cortex, thalamus, and substantia nigra terminate, at least in part, on these striatal projection neurons. Striatal interneurons contain acetylcholine, GABA, and somatostatin plus neuropeptide Y, and appear to synapse on striatal projection neurons. In recent years, much activity has been directed to the neurochemical and hodological heterogeneities which occur at a macroscopic level in the striatum. This has led to the concept of a patch-matrix organization in the striatum.

Localization of luteinizing hormone-releasing hormone (LHRH) neurons that project to the median eminence

The neuropeptide, luteinizing hormone-releasing hormone (LHRH), is released from nerve terminals in the median eminence and carried via the hypophysial portal system to the anterior pituitary, where it stimulates the release of gonadotropins. LHRH-containing neurons are located in many different regions of the rodent brain, including olfactory, septal, preoptic, and hypothalamic structures. Since those LHRH neurons that project to the median eminence form the final common pathway for the regulation of the pituitary/gonadal axis, we wished to determine which of these cell groups are afferent to this structure. A retrograde tracer, the lectin wheat germ agglutinin (WGA), was placed directly on the exposed surface of median eminence. Following survival times of 8-13 hr, brains were prepared for the dual immunocytochemical detection of WGA and LHRH. Approximately 50% of the LHRH neurons from the level of the septal nuclei caudalward were found to contain WGA immunoreactivity and therefore to project to the median eminence. The remaining single-labeled LHRH neurons were intermingled with the double-labeled cells. The 2 populations were not distinguishable from each other on either cytological or cytoarchitectonic criteria. Those LHRH neurons that were not retrogradely labeled following an injection of tracer into the median eminence are presumed to project to other regions of the central nervous system. We conclude that the LHRH neurons that are directly involved in the regulation of reproductive function are very heterogeneous, widely scattered in telencephalic and diencephalic regions.

Synaptic organization of GABAergic neurons in the mouse SmI cortex

Immunocytochemical methods were used to examine GABAergic neurons in the barrel region of the mouse primary somatosensory cortex. GABAergic neurons occur in all layers of the barrel cortex but are more concentrated in the upper portion of layers II/III and in layers IV and VI. Nine cells in layer IV were examined with the electron microscope, and portions of their dendrites were reconstructed from serial thin sections. These cells are of the nonspiny, multipolar or bitufted varieties, and some of them have beaded dendrites. The labeled cell bodies and their reconstructed dendrites were postsynaptic at asymmetrical synapses with thalamocortical axon terminals labeled by lesion-induced degeneration and with unlabeled axon terminals. Each cell also received symmetrical synapses from GABAergic axon terminals and from unlabeled axon terminals. Our results indicate that GABAergic cell bodies and processes receive synapses from thalamocortical axon terminals but that different cells display marked differences in the proportion of thalamocortical and other synapses they receive. These results indicate that GABAergic cells form a heterogeneous population with respect to their morphologies and patterns of synaptic inputs. The synaptic sequences revealed here for GABAergic neurons represent an anatomical substrate for various inhibitory processes known to occur within the cerebral cortex.

Neurotensin in the rat median eminence: the possible sources of neurotensin-like fibers and varicosities in the external layer

The possible sources of neurotensin-like immunoreactive axons in the median eminence were studied after several experimental surgical approaches including unilateral lateral retrochiasmatic area transection, midsagittal knife cut through the median eminence, complete surgical isolation of the medial basal hypothalamus and bilateral paraventricular nucleus lesions. Both immunohistochemical and radioimmunoassay data demonstrate that neurotensin-containing neuronal somata located in the hypothalamic arcuate nuclei represent the main source of neurotensin occurring in the external zone of the median eminence of the rat: neither the complete isolation of the medial basal hypothalamus nor the transection of the major neuronal input channel to the median eminence in the lateral retrochiasmatic area altered neurotensin-like immunoreactivity in the median eminence; bilateral lesioning of the paraventricular nucleus resulted in insignificant changes of neurotensin level in the median eminence; and two days after lesioning the median eminence an increased amount of retrogradely accumulated neurotensin-like immunoreactivity was found in several perikarya of the arcuate nuclei due to the blockage of axonal transport in the transected fibers. Retrograde accumulation of neurotensin-like material in other cells scattered in the anterior hypothalamus (in the paraventricular, periventricular and anterior hypothalamic nuclei) indicates that in addition to the arcuate neurons these neurons may also participate in the neurotensin innervation of the median eminence.

Pattern formation in the striatum: developmental changes in the distribution of striatonigral neurons

The striatum of the mammalian forebrain can be divided into 2 compartments, the patches and the matrix. We have investigated embryonic events involved in the formation of these compartments in rats. Early in development, dopamine fibers from the substantia nigra selectively innervate the patches. In the perinatal striatum, we observed a close match between the distributions of striatal cell bodies with axonal projections to the substantia nigra and patches of afferent dopamine fibers. Striatal cells projecting to the nigra are first seen in the ventrolateral striatum at embryonic day (E) 17. Striatonigral cell bodies are distributed homogeneously through the striatum from E18 to 19. At E20 and until postnatal day 4, these cell bodies are organized into discrete patches. After this time, striatonigral cell bodies assume the dense and homogeneous distribution characteristic of the adult striatum. A retrograde tracer injection in the nigra at E18 (during the early period of homogeneous striatonigral distribution) produces a patchy striatonigral distribution if the embryo is not sacrificed until E21. The number of retrogradely labeled striatonigral cell bodies in a midstriatal section, at times immediately before and after the early homogeneous to patchy changeover did not differ significantly. We suggest that the neurons of the patch compartment of the striatum are born first and project to the substantia nigra first. The patch neurons only become restricted to "patchy" areas as the later-born matrix neurons migrate out into the striatum.

Corticotropin-releasing factor-containing afferents to the inferior colliculus of the rat brain

Using a modified cobalt-glucose oxidase-diaminobenzidine (Co-GOD) method in a combination of horseradish peroxidase (HRP) retrograde tracing and immunohistochemistry, a widespread localization of corticotropin releasing factor-like immunoreactive (CRFI) structures in the rat inferior colliculus (IC), and a CRFI-containing pathway from the subthalamus and the hypothalamus to the IC have been observed. By means of the modified Co-GOD method, CRFI cells were detected in almost all the subdivisions of the IC, including the dorsomedial part of the central nucleus, the ventrolateral part of the central nucleus, the pericentral nucleus and the external nucleus. Neural processes with CRFI were observed in all of the above areas. Following HRP injection into the IC, double-labeled cells which contained a homogeneous brown immunoreaction product of CRF and a granular black reaction product of retrogradely transported HRP were identified in the lateral hypothalamic area (LH), zona incerta (ZI) and perifornical hypothalamic area (PeF). These double-labeled cells provide direct evidence for CRFI projections from the LH, ZI and PeF to the IC. Thus, the present study supports the view that CRF may act as a neurotransmitter or neuromodulator in the brain.

Marked sympathetic innervation in the regions of the bundle branches shown by catecholamine histofluorescence

The distribution of sympathetic nerve fibers in the regions of the bundle branches of bovine and rat hearts was examined by the glyoxylic acid-induced method for histofluorescence demonstration of catecholamines and by acetylcholinesterase (AChE) histochemistry. The studies on the bovine heart were concentrated on the nerve fascicles, the arteries and the ganglionic cells, and showed that (1) the AChE-positive nerve fascicles that occur just outside the bundle branches show a positive catecholamine-fluorescence reaction to varying degrees, the paraarterial nerve fascicles showing a uniform reaction; (2) the AChE-positive nerve fascicles within the bundle branches contain a few, mainly varicose, sympathetic nerve fibers; (3) extensive plexuses of sympathetic nerve fibers supply the arterial branches; and (4) sympathetic nerve fibers occur close to some of the ganglionic cells. The pattern of distribution of sympathetic nerve fibers in the region of the SA node was found to be essentially the same. The studies on the rat heart showed that (1) the septal arteries that occur in the proximity of the bundle branches are accompanied by the sympathetic component of innervation; and (2) there is a substantial number of varicose sympathetic nerve fibers within the bundle branches. These observations show that there is a pronounced sympathetic innervation in bundle branch regions and suggest that the paraarterial route is the most important for sympathetic nerve fibers to reach these regions.

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.

Calcitonin gene-related peptide-like immunoreactive sensory fibers form synaptic contact with sympathetic neurons in the rat celiac ganglion

The present study demonstrates synaptic contact between calcitonin gene-related peptide (CGRP)-like immunoreactive axon terminals and sympathetic neurons in the rat celiac ganglion. Our observations suggest that sensory ganglion neurons directly regulate the sympathetic activity via synapses, because CGRP immunoreactive (CGRPI) fibers in this ganglion are supplied by the sensory ganglia.

Quantitative autoradiography of dopamine D2 sites in rat caudate-putamen: localization to intrinsic neurons and not to neocortical afferents

Dopamine D2 receptors, labeled with [3H]spiroperidol or [3H]sulpiride, show a lateral-to-medial gradient in the caudate-putamen, with a more than two-fold greater density laterally than medially. It has been thought that D2 receptors are located on at least two neuronal elements of the caudate-putamen, neurons intrinsic to this structure and axons whose cell bodies reside in the cortex. As a first step in establishing what neuronal elements underlie this heterogeneous organization of D2 receptors, we took advantage of quantitative autoradiography to examine the association of these receptors with those elements. The present findings show that the D2 sites are almost exclusively located on neurons whose somata reside in the caudate-putamen and are not located on terminals of corticostriatal axons. A detailed comparison of the distribution of histochemically identified acetylcholinesterase neurons with that of D2 receptors in serially adjoining sections suggests a common organizational pattern. The density of [3H]spiroperidol sites in rat caudate-putamen was determined after unilateral injection of the neurotoxin quinolinic acid into this structure or after ablation of neocortical regions. Quantification of the tissue damage was achieved by acetylcholinesterase histochemistry (following diisopropylfluorophosphate treatment), as well as by thionin and luxol fast staining of sections adjacent to those used for [3H]spiroperidol autoradiography. In identically treated animals, biochemical determination of the extent of tissue damage was made utilizing assays for high-affinity [3H]choline and [3H]glutamate uptake in the caudate-putamen. In quinolinic acid-injected rats, the density of D2 sites was decreased by 90-95% at the site of complete loss of large acetylcholinesterase-positive neurons. Other animals, given ablations of specific neocortical fields (medial prefrontal, motor, somatosensory) or of the entire parietal-frontal cortex of one hemisphere, showed no loss of caudate-putamen D2 sites unless the cortical ablation caused accompanying damage of the caudate-putamen. In the caudate-putamen of all animals there was a close correspondence between the D2 sites and the striatal neurons (and processes) that show strong acetylcholinesterase reactivity. We suggest that the caudate-putamen topography of D2 sites is based largely on the internal organization of this structure and may preferentially involve acetylcholine-containing intrinsic neurons.

Chemical anatomy of the hypothalamus

The neuropeptide field has witnessed considerable research interest over the past decade, and a growing body of anatomic, biochemical, and electrophysiologic data have since emerged, supporting the existence and putative neuromodulatory function of a large variety of these peptide hormones in several extrahypothalamic brain regions. It is now evident that neuropeptides not only fulfill criteria required of putative neurotransmitters, but more generally act as modulators of neuronal activity. The author discusses vasopressin and oxytocin pathways, corticotropin releasing factor, atrial natriuretic factor, thyrotropin releasing hormone, somatostatin, motilin, growth hormone releasing factor, dopamine, gonadotropin releasing hormone, and substance P.

Distribution and origins of substance P (SP)-, calcitonin gene-related peptide (CGRP)-, vasoactive intestinal polypeptide (VIP)- and neuropeptide Y (NPY)-containing nerve fibers in the pineal gland of gerbils

In the pineal gland of gerbils, substance P (SP)-, calcitonin gene-related peptide (CGRP)-, vasoactive intestinal polypeptide (VIP)- and neuropeptide Y (NPY)-containing nerve fibers were demonstrated immunohistochemically. After intrapineal injection of biotin-wheat germ agglutinin, origins of fibers were examined by the combined technique of tracing method and immunohistochemistry. It was confirmed that SP- and CGRP-fibers originated from the trigeminal ganglion, VIP-fibers from the pterygopalatine ganglion and NPY-fibers from the superior cervical ganglion.

Thyrotropin-releasing hormone-immunoreactive neurons project from the ventral medulla to the intermediolateral cell column: partial coexistence with serotonin

Projections from medullary thyrotropin-releasing hormone (TRH) containing neurons to the intermediolateral cell column (IML) of the thoracic spinal cord were studied in the rat. Lesions of the ventral medullary reticular formation nuclei, nucleus paragigantocellularis lateralis and nucleus interfascicularis hypoglossi, decreased the thyrotropin-releasing hormone immunoreactivity in the IML. The ventral horn and dorsal horn contents of TRH were also reduced in rats with nucleus paragigantocellularis lateralis lesions. Coexistence of spinal cord TRH and serotonin was evaluated and quantified in 5,7-dihydroxytryptamine-treated rats. Treatment with the serotonin neurotoxin reduced the TRH content of the IML by 45% and of the ventral horn by 92%. These data show that TRH containing neurons project from the ventral medulla to IML and that approximately one-half of these TRH neurons are also serotonergic. Comparisons of the effects of the same lesions on the substance P and TRH content of the IML show that neither the origin of the SP and TRH neuronal projections to the IML, nor their coexistence with serotonin, are identical.

Comparative aspects of the area postrema: fine-structural considerations help to determine its function

The area postrema is a circumventricular organ of the fourth ventricle of the mammalian brain. Although there are distinct gross anatomical differences in the appearance of this organ between "lower" mammals such as rodents and lagomorphs and "higher" mammals such as carnivores and primates, its fine structure is remarkably similar in all species studied. There are many suggestions in the literature for a specific function for this area of the brain, ranging from its being a chemoreceptive trigger zone for the emetic response to its being a regulatory nucleus for the sleep cycle. The present report describes some comparative studies on the ultrastructure of this organ. This information is discussed in relation to what is known about the neurochemistry of the area postrema and its connections with other brain regions and visceral structures. A suggestion is offered that our current knowledge of the area postrema is consistent with its performing many of its proposed functions in the context of a regulatory ("fine-tuning") center for many autonomic functions.

A substance P-containing hypothalamic neuronal system projects to the median eminence

Immunoreactive substance P (SPi) was measured in the various hypothalamic structures and amygdala one week after placing a cut around the medial basal hypothalamus (MBH). SPi content decreased in the stalk-median eminence (SME), anterior and posterior parts of the arcuate nucleus (inside the isolated region) as well as in the paraventricular nucleus (outside the cut), while there was no change in the posteromedial amygdaloid nucleus. We suggest that there is a tuberoinfundibular neuronal system containing SPi with cell bodies in the MBH and terminals in the SME. In addition, nerve fibers containing SPi from outside the MBH may reach both the SME and the arcuate nucleus and might influence neuroendocrine regulation.

Cholinergic and non-cholinergic projections from the rat basal forebrain revealed by combined choline acetyltransferase and Phaseolus vulgaris leucoagglutinin immunohistochemistry

A two-color fluorescence method is described for demonstrating immunohistochemically the anterogradely transported plant lectin Phaseolus vulgaris leucoagglutinin (PHAL, fluorescein isothiocyanate label) and choline acetyltransferase (ChAT, rhodamine label) on the same rat brain section. Application of this method to the study of projection neurons in the vertical and horizontal limbs of the diagonal band, the substantia innominata and nucleus basalis revealed that both cholinergic and non-cholinergic pathways followed similar trajectories to their targets. These included: projections from the vertical, and, to a lesser extent, horizontal limb of the diagonal band coursing through the dorsal fornix, alveus and fimbria to the hippocampus; fibers from the vertical and horizontal limbs of the diagonal band traveling anteriorly to the anterior olfactory nucleus, posterolaterally to the entorhinal cortex, and anterodorsally into the cingulum to the cingulate and retrosplenial, and, in some cases, the frontal and occipital cortices; projections, mostly non-cholinergic, from the substantia innominata traveling laterally to the piriform cortex and amygdala, and anteriorly to the anterior olfactory nucleus and olfactory bulb; and fibers from cells in the nucleus basalis coursing dorsally to the frontal and parietal cortices or laterally to the basolateral amygdala and piriform, insular and temporal cortices. Some axon terminations ended at right angles to the parent axon shaft in short protuberances resembling terminal boutons.

Cortical projections to the nucleus of the tractus solitarius: an HRP study in the cat

Recent evidence suggests that autonomic reflexes involving sensations such as olfaction and gustation may be cortically mediated via centripetal pathways to brainstem autonomic centers. A study was therefore undertaken to elucidate one of these pathways in greater detail. Lectin conjugated horseradish peroxidase was injected into the nucleus tractus solitarius. Following standard light microscopic histochemical procedures to reveal horseradish peroxidase activity, the distribution of retrogradely labeled neurons in the cortex was recorded. Retrogradely labeled somata were seen bilaterally in layer five of the orbital gyrus, anterior insular cortex and infralimbic cortex. In other cats, the same tracer was injected into the orbital gyrus or anterior insular cortex. Bilateral anterograde labeling was seen in various subnuclei throughout the rostrocaudal extent of the nucleus tractus solitarius, but was heaviest in rostral regions of the nucleus. Labeling was also seen bilaterally in the spinal trigeminal nucleus. The projection to the nucleus tractus solitarius could allow for cortical modulation of gustatory and visceral information which is conveyed to the brainstem via the facial, glossopharyngeal and vagus nerves.

Innervation of the adult rat cerebellar hemisphere by fibres from the ipsilateral inferior olive following unilateral neonatal pedunculotomy: an autoradiographic and retrograde fluorescent double-labelling study

A left cerebellar pedunculotomy was carried out in neonatal rats of different ages to deprive the left cerebellar hemisphere of its normal climbing fibre input. In control adult animals this is totally crossed and thus arises only from the contralateral (right) inferior olive. After pedunculotomy, only the left inferior olive was intact, the right being degenerated. The remaining olivocerebellar pathway was investigated using anterograde autoradiographic or retrograde fluorescent double-labelling techniques. The anterograde autoradiographic technique showed that, in these animals, the remaining left inferior olive had an aberrant climbing fibre projection which travelled via the intact right inferior cerebellar peduncle to the denervated left hemicerebellum. If the pedunculotomy was carried out at 3 days of age (P3), this aberrant projection closely mirrored the normal pathway to the opposite hemisphere; pedunculotomy at P7 produced a different pattern of projection; while if the operation was done at P10 there was no new projection. True blue (TB) and diamidino yellow (DY) were injected into the denervated (left) and normal (right) cerebellar hemispheres respectively. Retrograde transport of these tracers confirmed both the aberrant ipsilateral projection and the normal crossed projection from neurons in the remaining inferior olive. Most of the ipsilaterally projecting neurons were in the medial accessory olive. As none of them were double-labelled, it was concluded that the new projection is not a collateral of normally projecting olivary neurons, but arises from a separate population of cells. The significance of these findings in relation to earlier work on this system is discussed.

Histaminergic projections from the premammillary and posterior hypothalamic region to the caudate-putamen complex in the rat

Immunofluorescence, using antibodies to histamine and to histidine decarboxylase, was combined with retrograde axonal tracing by injecting Granular Blue into the caudate-putamen complex. Evidence is presented for the existence of histaminergic as well as non-histaminergic projections from the posterior hypothalamus and the premammillary region to the caudate-putamen complex. The majority of the histaminergic neurons projecting to this brain region are localized in the nuclei caudalis magnocellularis and caudalis magnocellularis postmammillaris. Roughly 20-25% of the histaminergic neurons in these cell groups innervate the caudate-putamen complex.

Simultaneous labelling of two different central nervous system pathways with horseradish peroxidase and cobalt in Gnathonemus petersii and Rana esculenta

A new and simple simultaneous labelling procedure is described that gives the possibility of studying interneuronal connections and territorial overlap of different pathways. This method uses horseradish peroxidase (HRP) labelling in combination with the cobalt-filling technique. The blue colour of the HRP reaction end-product formed from 0-tolidine (Neuroscience, 4 (1979) 1805-1852) and the dark brown of cobalt-filled neurons and their processes allow easy distinction of the two different labels. Since both markers can be transported anterogradely and retrogradely by axons, this combination of the two techniques seems to be a very useful tool for neuroanatomical research. We have tested this method in a weakly electric fish, Gnathonemus petersii, and in frog, Rana esculenta.

Somatostatin in the central nervous system: physiology and pathological modifications

Since its discovery, at the beginning of 1973, somatostatin's multiple actions, in relation to its wide anatomical distribution have been widely documented. Its biochemical pathways have been elucidated with the discovery of other molecular forms as well as the mechanisms of its neuronal release. However, no definite proof is available concerning a neurotransmitter role for any peptide of the somatostatin family other than somatostatin-14. The precise determination of the roles of somatostatin in brain are still hampered by the poor pharmacology of the peptide. New tools are badly needed and in particular a true antagonist at the receptor site. The mechanisms of action of somatostatin are now well under way at least in the pituitary model. More information should come from this model and be applied to brain cells in vitro. The greatest challenge of somatostatin brain function lies in its role in the pathophysiology of neurological diseases such as Alzheimer's dementia and Huntington's disease. Nature has been using somatostatin-related molecules since inhibitory control was first needed in cell functions. Time will tell us if somatostatin is really an old peptide involved in senile dementia.

The cholinergic innervation of the rat fascia dentata: identification of target structures on granule cells by combining choline acetyltransferase immunocytochemistry and Golgi impregnation

A monoclonal antibody against choline acetyltransferase (ChAT), the acetylcholine-synthesizing enzyme, was used to study cholinergic synapses on identified (Golgi stained) granule cells in the rat fascia dentata. Choline acetyltransferase immunocytochemistry was applied to 40-microns Vibratome sections cut perpendicular to the longitudinal axis of the hippocampus. Light microscopy revealed fine varicose ChAT-immunoreactive axons in all layers of the fascia dentata, i.e., in the stratum moleculare, the stratum granulosum, and the subgranular polymorph zone. Most fibers were observed in the vicinity of granule cell bodies where they ran mainly parallel to the granular layer. Next, the immunostained Vibratome sections were sandwiched between small pieces of Parafilm and piled to form a block that was covered with agar and Golgi stained. After that, the sections were separated by cutting away the agar and removing the Parafilm. Sections containing well-impregnated granule cells were gold-toned (Fairén et al., '77), embedded in Araldite, and subjected to ultrathin sectioning for electron microscopy. A total of 14 gold-toned granule cells were examined in the electron microscope for synaptic contacts with cholinergic afferents. Choline acetyltransferase-immunoreactive axon terminals were observed that established symmetric synaptic contacts with the cell bodies and dendritic shafts of the gold-toned identified granule cells. Two types of contact were observed on spines arising from gold-toned granule cell dendrites. Immunoreactive terminals established asymmetric synaptic contacts with the head of small spines and symmetric contacts with the stalk of large, complex spines. The boutons forming asymmetric synaptic contacts with the cup-shaped spine head of the complex spines were not found to be immunoreactive. Our results demonstrate that cholinergic fibers to the rat fascia dentata establish characteristic types of synaptic contact with different postsynaptic elements of granule cells, suggesting a complex function of this afferent system.

Localization of proopiomelanocortin mRNA in functional subsets of neurons defined by their axonal projections

In situ cDNA:mRNA hybridization is a technique that has been developed for the visualization of cDNA:mRNA hybrids in individual cells. To use this technique to answer questions of regulation in heterogeneous populations of cells in the brain, it must be combined with other procedures allowing for the identification of functional subgroups of neurons. We report here a procedure by which in situ cDNA:mRNA hybridization may be combined with retrograde axonal tracing using the fluorescent tracer fast blue. Using this technique, it now becomes possible to measure mRNA regulation in functional subsets of cells defined by their axonal projections.

An autoradiographic study of the postnatal development of pericruciate cortical projections to the neostriatum and the claustrum of the cat

The postnatal development of corticostriatal and corticoclaustral projections was traced by light-microscopic autoradiography following injections of tritiated proline and leucine into the pericruciate cortex of kittens, 2-56 days of age, and adult cats. A medial-lateral topography of the corticostriatal pathways was present at birth, with a smaller and more restricted projection arising from the lateral pericruciate region. During postnatal development, the volume of the ipsilateral caudate nucleus filled by labelled corticostriatal fibers was reduced by 30% and these projections became constricted within the dorsolateral head and body of the caudate nucleus. During the first postnatal week, terminal fields were diffuse but lacked homogeneity since irregular patches of intensely labelled elements clustered near the internal capsule. By the end of the first month, a fenestrated organization became apparent within the caudate nucleus where elongated clusters of intensely labelled fibers radiated from the internal capsule and partially or completely surrounded islands of neuropil virtually devoid of label. Pericruciate inputs were confined to the dorsal parts of the rostral putamen and claustrum and the patchy nature of these terminal fields was limited to small labelled clusters close to the capsular margins. Contralateral terminal fields were labelled less intensely and occupied areas symmetrical to those within the ipsilateral neostriatum and claustrum.

Descending serotonergic fibers in the dorsolateral and ventral funiculi of cat spinal cord

Although there is much evidence for the presence of serotonergic fibers in the spinal gray matter, there is little evidence for the location of descending serotonergic fiber tracts in the spinal white matter. Using a highly sensitive immunocytochemical technique, we localized serotonin-immunoreactive axons throughout the white and gray matter of the spinal cord. Prominent concentrations of serotonergic axons were found in the dorsolateral and ventral funiculi. It is likely that these two descending fiber tracts contribute serotonergic input to the dorsal and ventral horns, respectively.

Catecholamine innervation of the caudal spinal cord in the rat

By means of the aluminum-formaldehyde (ALFA) fluorescence technique for monoamine visualization the distribution of catecholamines was studied in the caudal spinal cord, particularly in relation to motoneurons innervating pelvic structures. In the lumbosacral cord all parts of the spinal gray matter were found to contain catecholamines. In the dorsal horn the most intense fluorescence was seen in the superficial layers. The motoneuron neuropil exhibited the most prominent catecholamine-fluorescence of the ventral horn layers. In the sixth lumbar segment, which contains the motor nuclei that innervate the pelvic striated muscles as well as one innervating muscles in the lower limb, a differential distribution of the density of catecholamine fluorescence was presented by the individual nuclei. The catecholamine fibers in the motoneuron neuropil were seen closely surrounding the motoneuron somata, suggesting the existence of axosomatic contacts, and by utilizing the fluorescent retrograde tracer True Blue in combination with the ALFA method tentative axosomatic noradrenergic synapses on identified neurons innervating small striated pelvic muscles could be visualized in the light microscope. In the intermediate gray the intermediolateral nucleus in thoracic and upper lumbar segments was the most heavily innervated area, followed by the medial lumbar sympathetic group, which contains the majority of the sympathetic preganglionic neurons innervating the pelvic organs. The parasympathetic intermediolateral nucleus in the upper sacral segments received a catecholamine innervation of moderate density. The catecholamine innervation pattern is discussed in relation to the patterns of other putative transmitters. The distribution of catecholamine fluorescence in relation to nuclei that control the pelvic organs differs from the arrangement of other transmitters in this region. The complexity of the innervation of the pelvic organs and their related striated muscles is thus further stressed.

Coexistence of neuropeptides in projection neurons of the thalamus in the cat

Coexistence of neuropeptides was suggested by double-staining immunohistochemistry in projection neurons in the thalamus of the cat; cholecystokinin (CCK)-like immunoreactivity (LI) and vasoactive intestinal polypeptide (VIP)-LI in the rostral group of the intralaminar nuclei, CCK-LI and neurotensin (NT)-LI in the anterodorsal nucleus and NT-LI and VIP-LI in the laterodorsal nucleus.