Light and electron microscopic immunocytochemistry of GRF-like immunoreactive neurons and terminals in the rat hypothalamic arcuate nuclues and median eminence

Growth hormone-releasing factor (GRF) synthesizing neuronal perikarya and terminals were investigated by light and electron microscopic immunocytochemistry using rat hypothalamus. Immunoreactive neuronal perikarya were located mainly in the ventrolateral part of the arcuate nucleus. They contained well developed cell organella such as mitochondria and rough surfaced endoplasmic reticulum with some expansion. They also contained immunoreactive dense granules (80-120 nm in diameter). On the surface of the immunoreactive neuronal perikarya were frequently found non-immunoreactive axo-somatic synapses. Therefore, the GRF-like immunoreactive neurons were assumed to receive neuronal inputs from other neurons on their neuronal soma. In the external layer of the median eminence large numbers of immunoreactive terminals were distributed particularly around the capillaries of the portal vessel. Electron microscopic immunocytochemistry revealed large numbers of immunoreactive terminals containing immunoreactive dense granules, synaptic vesicles and mitochondria in the vicinity of the basement membrane of the pericapillary space of the portal vessel. Therefore, we concluded that GRF-like immunoreactive substances are released into the portal capillaries from the nerve terminals, which originate from the neuronal perikarya in the ventrolateral part of the arcuate nucleus, and act on growth hormone release in the anterior pituitary. We also suggest that GRF-like immunoreactive neurons have abundant terminal arborization in the external layer of the median eminence.     

Light and electron microscopic immunocytochemistry of β-endorphin/β-LPH-like immunoreactive neurons in the arcuate nucleus and surrounding areas of the rat hypothalamus

β-Endorphin/β-LPH-like immunoreactive neurons in the hypothalamic arcuate nucleus and its surrounding areas were visualized by light and electron microscopic immunocytochemistry. Immunoreactive processes were found in the vicinity of the pia mater, in the lateral part of the external layer of the median eminence and near the lateral wall of the third ventricle. Neuronal perikarya contained immunoreactive dense granules as well as developed cell organellae. They received neuronal inputs from other neurons through axoplasmic and axodendritic synapses. Immunoreactive neuronal processes containing dense granules and mitochondria were found as preterminal elements on non-immunoreactive neuronal soma and dendrites. Immunoreactive processes also make intimate contact with capillaries in the arcuate nucleus near the median eminence.     

Light and electron microscopic immunocytochemistry of neurotensin-like immunoreactive neurons in the rat hypothalamus

Neurotensin-like immunoreactive neuronal perikarya, fibers and terminals in the rat hypothalamus, particularly in the arcuate nucleus, the paraventricular nucleus and the median eminence, were investigated by light and electron microscopic immunocytochemistry. The main distributional areas of immunoreactive neuronal perikarya were found to be the arcuate nucleus, the periventricular nucleus and the paraventricular nucleus by light microscopic immunocytochemistry. Immunoreactive neuronal perikarya showed a characteristic distributional pattern in the arcuate nucleus. In the paraventricular nucleus they were distributed in both the magnocellular and parvocellular portions. A large number of immunoreactive terminals were observed throughout the external layer of the median eminence, particularly its lateral portion. A moderate number of immunoreactive terminals were also observed in the internal layer of the median eminence. By electron microscopic immunocytochemistry immunoreactive neuronal perikarya both in the arcuate and paraventricular nuclei showed generally well-developed cell organelles such as mitochondria, r-ER, and Golgi complex. In addition, immunoreactive dense granules were dispersed throughout the perikarya. A large number of immunoreactive terminals containing immunoreactive dense granules, clear vesicles and mitochondria were observed in the vicinity of pericapillary spaces of the external layer of the median eminence. This observation strongly suggests that neurotensin-like immunoreactive substance is released into the portal capillaries.     

Immunocytochemical demonstration of dynorphin(PH-8P)-like immunoreactive elements in the human hypothalamus

PH-8P (dynorphin[1-8])-like immunoreactive neuronal perikarya, processes, and terminals located within the human hypothalamus were investigated by the avidin-biotin peroxidase complex (ABC) immunocytochemical procedure. Immunopositive neurons were distributed throughout the hypothalamus. The distributional pattern was found to be similar to that in other mammalian species by the use of antisera against dynorphin. A large number of immunoreactive neuronal perikarya were detected in the supraoptic nucleus (SON) and the magnocellular portion of the paraventricular nucleus (PVN). Their processes appeared to project to the posterior pituitary via the internal layer of the median eminence and their distribution seemed to be less dense than in other mammalian species. PH-8P and vasopressin were colocalized in the neuronal perikarya in the human SON unlike the colocalization of these peptides in the rat SON and PVN. There were a few immunoreactive terminals in the external layer of the median eminence; their immunoreactive substances may be released into the portal veins to act on anterior pituitary cells. In addition, PH-8P-like immunoreactive neurons in the human hypothalamus may project to the extrahypothalamic area.     

Reciprocal synaptic relationships between angiotensin II-containing neurons and enkephalinergic neurons in the rat area postrema

A preembedding double immunostaining technique was used to study synaptic relationships between angiotensin-II-like immunoreactive and enkephalin-like immunoreactive neurons in the rat area postrema. The angiotensin-II-like immunoreactive neurons were detected by silver-gold intensification of the DAB reaction results while the enkephalin-like immunoreactive neurons were detected by simple ABC-DAB reaction. The synaptic relationships were reciprocal between the two neurons. Most of the synapses found between these two neurons were the presynaptic enkephalin-like immunoreactive axon terminals that made synapses on the angiotensin-II-like immunoreactive perikarya and dendrites. Both the axo-somatic and axo-dendritic synapses were symmetrical. However, although angiotensin-II-like immunoreactive axon terminals also made synapses on enkephalin-like perikarya and dendrites, the axo-somatic synapses were symmetrical, while the axo-dendritic synapses were asymmetrical. The present results confirm the presence of angiotensin-II-like immunoreactive neurons in the area postrema and suggest that these angiotensinergic neurons in the area postrema may play a role in the regulation of blood pressure via coordinated synaptic interactions with enkephalinergic neurons.     

Distribution patterns of individual medial lemniscal axons in the ventrobasal complex of the monkey thalamus

Somatostatin-immunoreactive neurons in the rat neostriatum were studied by correlated light and electron microscopy using the peroxidase-antiperoxidase immunocytochemical technique. Immunoreactivity was localized in neuronal perikarya and processes. The perikarya were of spindle or fusiform shape (average length 16.9 microns) and were found in all parts of the neostriatum. From each neuron there arose two to four straight immunoreactive dendritelike processes, which could frequently be traced as far as about 130 microns from their perikaryon. Immunoreactive varicose axonlike processes were occasionally found, some of which were proximal axons of identified immunoreactive cells. Nine of the light microscopically identified neurons showing somatostatin-immunoreactivity were studied in the electron microscope; two of them had proximal axons with varicosities. Each neuron had an oval or elongated nucleus, which was always indented. These morphological features correspond well to those of certain "medium-size aspiny" neurons classified by Golgi studies. Although the immunoreactive endproduct was diffusely located throughout the neuron, it was characteristically located in the saccules and large granules (diameter 133 nm) of the Golgi apparatus, and large immunoreactive vesicles of similar size to those in the Golgi apparatus frequently occurred in all parts of axon. Very little synaptic input was found on the perikarya and dendrites of somatostatin-immunoreactive neurons. The perikarya and proximal dendrites received both symmetrical and asymmetrical synaptic input, while the distal dendrites usually received boutons that formed asymmetrical contacts. The somatostatin-immunoreactive boutons contained pleomorphic electron-lucent vesicles (diameter 39.3 nm) and a few large immunoreactive granular vesicles; these boutons always formed symmetrical synapses. Their postsynaptic targets were dendritic shafts, spines, and unclassified dendritic profiles. On the other hand, the varicosities of identified proximal axons of somatostatin-positive neurons did not form typical synapses, since they lacked clusters of small vesicles, but some of them were in direct apposition (via membrane specializations) to unlabelled perikarya or dendrites. It is concluded that somatostatin is a useful marker for a particular type of neuron in the neostriatum. The presence of somatostatin immunoreactivity in synaptic boutons is consistent with the view that somatostatin could be a neurotransmitter in the neostriatum.     

Glutamate decarboxylase-immunoreactive structures in the rat neostriatum: a correlated light and electron microscopic study including a combination of Golgi impregnation with immunocytochemistry

An antibody to glutamate decarboxylase has been used in a light and electron microscopic study of the neostriatum of rats that had received intracerebral injections of colchicine. In the light microscope, neuronal perikarya and small punctate structures that displayed immunoreactivity were found. The perikarya could be divided into two classes based on their sizes: small-to-medium-sized and large. Proximal dendrites, axon initial segments, and axon collaterals were occasionally stained. When the nuclei of the neurons were visible, they possessed indentations. The immunoreactive punctate structures were spread evenly throughout the neostriatum but occasionally were associated with immunoreactive and nonimmunoreactive perikarya. When the same sections were examined in the electron microscope, the small-to-medium-sized immunoreactive perikarya were found to be similar in morphology and synaptic input to a class of Golgi-impregnated neuron that has been previously shown to accumulate locally administered, radiolabelled gamma-aminobutyric acid. Neurons with the ultrastructural characteristics of typical striatonigral neurons did not display immunoreactivity. As neurons in this pathway probably contain gamma-aminobutyric acid, it is possible that our procedure or our antibody does not stain all gamma-aminobutyric-acid-containing structures in the neostriatum. A total of 404 immunoreactive punctate structures were examined by correlated light and electron microscopy or by electron microscopy alone. They were identified as immunoreactive axonal boutons and each of them, when examined in serial sections, displayed typical synaptic specialisations. Membrane specialisations were always of the symmetrical type. At least five distinct targets of the immunoreactive terminals were identified: neurons that were themselves immunoreactive for glutamate decarboxylase; the immunoreactive terminals made synaptic contact with all parts of the neurons examined, i.e., perikarya, proximal dendrites, and axon initial segments. Neurons identified by Golgi impregnation of the same sections as medium-sized and densely spiny; the immunoreactive terminals made contact predominantly with the perikarya and dendritic shafts. Large neurons found only in the ventral caudate-putamen, whose somata and dendrites were ensheathed in immunoreactive terminals. Medium-sized nonimmunoreactive perikarya that possessed nuclear indentations. Large nonimmunoreactive perikarya that had the typical structural features of striatal cholinergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ultrastructure and synaptic organization of luteinizing hormone-releasing hormone (LHRH) neurons in the anestrous ewe

Electron microscopic immunocytochemistry was employed to examine the ultrastructure of luteinizing hormone-releasing hormone (LHRH) neurons and their projections to the median eminence in the sheep brain. LHRH perikarya in the preoptic area of anestrous ewes are less innervated than nonimmunoreactive cells in the same sections, but still receive numerous synaptic inputs, primarily onto distal dendrites and small somatic protuberances. Axon terminals synapsing upon LHRH cells contain a combination of clear spherical vesicles and larger dense-core vesicles. Interestingly, LHRH cell bodies and dendrites are almost entirely surrounded by glial processes. These processes intervene between immunoreactive elements that at a light microscopic level appear to be in contact with each other. Thus no evidence was obtained at the ultrastructural level for contacts among adjacent LHRH cells or dendrites in the preoptic area. Synaptic inputs onto LHRH cell bodies and dendrites appear to penetrate this glial sheath. In contrast to the absence of contacts among LHRH cells in the preoptic area, individual LHRH terminals in the median eminence are often clustered in direct plasma membrane contact. Comparisons between animals of differing reproductive status are needed to determine whether alterations in synaptic inputs, glial ensheathment, or LHRH-LHRH appositions, may underlie seasonal changes in the activity of LHRH neurons.     

Immunohistochemical evidence for synaptic connections between neuropeptide Y-containing axons and periventricular somatostatin neurons in the anterior hypothalamus in rats

By employing a pre-embedding double immunolabeling technique, we examined light and electron microscopically synaptic associations between neuropeptide Y (NPY)-containing axons and somatostatin (SRIH)-containing neurons in the anterior periventricular area (APV) of the rat hypothalamus. For light microscopy, the immunoreactions for NPY and SRIH were visualized with silver-gold and diaminobenzidine (DAB), respectively, and the reverse labeling was used for electron microscopy. Light microscopy disclosed many brown SRIH perikarya surrounded by several black beads of NPY fibers in the APV. In electron microscopy, immunoreactive SRIH neurons revealed silver-gold particles scattered throughout the cytoplasm and accumulated in the Golgi area and the secretory granules. SRIH perikarya and dendritic processes indicated synaptic associations with DAB-labeled NPY fiber terminals and immunonegative fibers. NPY presynaptic terminals possessed numerous small clear vesicles and a few dense core visicles; vesicular membranes and cores were labeled with DAB chromogen. Both the pre- and postsynaptic membranes were thickened equally to be a symmetric synapse. These findings suggest that NPY neurons are involved in the regulation of growth hormone secretion from the pituitary by affecting periventricular SRIH neurons.     

Fine structure of histaminergic neurons in the caudal magnocellular nucleus of the rat as demonstrated by immunocytochemistry using histidine decarboxylase as a marker

The morphology of histamine-containing neurons in the caudal magnocellular nucleus was light and electron microscopically examined by means of peroxidase-antiperoxidase (PAP) immunocytochemistry with histidine decarboxylase (HDC) as a marker. HDC-like immunoreactive (HDCI) neurons had large (25–30 μm in diameter) perikarya from which two to four primary dendrites arose. The perikarya had a nearly round nucleus and well-developed Golgi apparatus in addition to a large number of mitochondria and rough endoplasmic reticulum. Immunoreactive endproducts were found diffusely throughout the perikarya, dendrites, and axons. HDCI neurons made synaptic contact with nonreactive axon termminals on the perikarya and dendrites. In addition, the HDCI neurons very frequently formed puncta adherentia with neuronal elements, either HDCI or nonreactive, or glial cells. Most of the HDCI axon terminals serially observed under electron microscopy did not exhibit typical synaptic contact in the caudal magnocellular nucleus. These findings suggest the nonsynaptic release of histamine in the caudal magnocellular nucleus.     

The fine structural organization of tyrosine hydroxylase immunoreactive neurons in rat arcuate nucleus

The fine structure of the tyrosine hydroxylase (TH) immunoreactive neurons of the hypothalamic arcuate nucleus was examined by means of immunocytochemistry [peroxidase-antiperoxidase (PAP) method], utilizing an antibody against TH. Immunolabeled axon terminals were observed infrequently and were located predominantly in the lateral region, whereas numerous labeled perikarya and dendrites were found throughout the nucleus. The labeled terminals, containing primarily clear and occasionally dense core vesicles, were never observed in synaptic contact. On the other hand, unlabeled axon terminals were frequently seen synapsing on labeled dendrites. In addition, the labeled dendrites were often seen in direct apposition to other neuronal elements such as both labeled and unlabeled perikarya. In contrast, unlabeled dendrites were never seen apposed to labeled perikarya. Labeled dendrites also occurred in direct contact with one another and with unlabeled dendrites. Moreover, numerous labeled dendrites were encountered along tanycytic processes. Dendrites engaged in tanycytic appositions were occasionally partially encompassed by thin sheaths emanating from the tanycytic process. The extensive contact made by the labeled dendritic profiles on both labeled perikarya and dendrites suggests that tubero-infundibular dopaminergic (TIDA) cells may communicate with each other by means of dendritic release of dopamine. The presence of appositions between labeled dendrites and both unlabeled perikarya and dendrites suggests that the TIDA system also influences other neuronal populations through its dendrites. Finally, the dendrotanycytic relationship suggests that the TIDA system may play some role in the regulation of tanycytic function.     

GABA-like immunoreactivity in the tuberomammillary nucleus: an electron microscopic study in the rat

The organization of GABAergic elements in the histaminergic tuberomammillary nucleus has been examined by using antibodies against gamma-aminobutyric acid (GABA) and light and electron microscopy. Most neuronal perikarya of the ventral subgroup of the tuberomammillary nucleus were GABA immunoreactive (GABA-i). The morphology of the GABA-i perikarya was similar to the morphology of histaminergic perikarya described by Hayashi et al. ('84: J. Comp. Neurol. 229: 223-241) and Wouterlood et al. ('86: J. Comp. Neurol. 252:227-243). The GABA-i perikarya were contacted by relatively few terminals. The mean bouton covering ratio of GABA-i perikarya was 6.1%, whereas the mean bouton covering ratio for GABA-i dendrites in the tuberomammillary nucleus was 31%. Some of the presynaptic terminals were GABA-i. In addition, GABA-i perikarya and dendrites formed close contacts that never presented synaptic specializations. These results suggest that neurons of the histaminergic tuberomammillary nucleus contain the neurotransmitter GABA. Furthermore, GABA may act as a modulator of cellular processes within the tuberomammillary nucleus.     

Septal efferent axon terminals identified by anterograde degeneration show multiple sites for modulation of neuropeptide Y-containing neurons in the rat dentate gyrus

The ultrastructure and cellular associations of septal efferent terminals identified by anterograde degeneration with neurons containing neuropeptide Y (NPY) in the rat dentate gyrus were examined quantitatively. For this, the septal complex (i. e., medial septal and diagonal band nuclei) of adult male rats was injected with the neurotoxin ibotenic acid (1%; 150 nl) and following a 2–4-day survival period, the hippocampal formation was processed for the electron microscopic immunocytochemical demonstration of NPY using the avidin-biotin complex method. Terminals with the morphological characteristics of anterograde degeneration, in particular an increase in osmiophilia, and neurons containing NPY-like immunoreactivity (NPY-LI) were most abundant in the hilus of the dentate gyrus. In this region, degenerating terminals (n = 109) were usually small (0.2–0.4 μm in diameter) and formed both asymmetric and symmetric synapses with small (distal) dendrites. The degenerating terminals contacted either single NPY-containing (19%) perikarya or dendrites or unlabeled (48%) perikarya or dendrites. Some degenerating terminals contacted the same perikarya or dendrites as an NPY-containing terminal (11%); these neurons were either immunoreactive for NPY or unlabeled. The remaining degenerating terminals were either directly apposed without glial intervention to unlabeled and NPY-labeled terminals (11%) or lacked associations with any neuronal processes in the plane of section analyzed (11%). The findings demonstrate that ibotenic acid injections in the septal complex can identify septal efferent terminals by degeneration and provide cellular substrates for the direct synaptic regulation as well as presynaptic modulation of hippocampal NPY-containing neurons by septal efferent terminals. © 1993 Wiley-Liss, Inc.     

Ultrastructural localization of tyrosine hydroxylase immunoreactivity in the rat diagonal band of Broca.

The present study sought to establish the cellular basis for the catecholaminergic (i.e., noradrenaline and dopamine) modulation of neurons in the horizontal limb of the diagonal band of Broca (HDB) in the rat brain. The light and electron microscopic localization of antigenic sites for a polyclonal antibody directed against the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH), were examined in the HDB using a double-bridged, peroxidase-antiperoxidase method. By light microscopy, numerous punctate, varicose processes with intense TH-immunoreactivity (TH-I) were detected in the HDB. Additionally, a few small, bipolar, or multipolar TH-immunoreactive neurons were observed. Ultrastructural analysis of single sections revealed that the TH-labeled processes were axons and axon terminals. Axons (n = 134) with TH-I were primarily unmyelinated. Terminals with TH-I (n = 169) were 0.3-1.4 microns in diameter and contained many small, clear vesicles and 0-5 larger dense-core vesicles. The types of associations (i.e., asymmetric synapses, symmetric synapses, and appositions which lacked a membrane specialization in the plane of section analyzed) formed by the TH-labeled terminals were quantitatively evaluated. The TH-labeled terminals: (1) formed associations with unlabeled perikarya and dendrites (134 out of 169), (2) were closely apposed without glial intervention to unlabeled and TH-labeled terminals (11 out of 169), or (3) had no neuronal associations in the plane of section analyzed (24 out of 169). The relatively rare (n = 4) associations with unlabeled perikarya were mostly characterized by symmetric synaptic specializations. The majority of the TH-labeled terminals were associated with the shafts of small dendrites (66% of 134). Moreover, most of the associations on dendrites and dendritic spines were further characterized by asymmetric synaptic specializations; however, many were also appositions without any apparent glial intervention in the plane of section analyzed. Additionally, the TH-labeled terminals were often associated with only one dendrite, which, in the same plane of section, was sparsely innervated by other terminals. Astrocytic processes usually surrounded the portions of the terminals and dendrites not involved in the region of association. The TH-immunoreactive perikarya were small (7-12 microns), ovoid, and had an indented nucleus with some heterochromatin. Their scant cytoplasm contained mitochondria, Golgi complexes, and endoplasmic reticulum. A few immunoreactive dendrites, presumably derived from the local neurons, were also detected. Both TH-immunoreactive perikarya and dendrites were associated primarily with unlabeled terminals, although a few terminals with TH-I also contacted them.(ABSTRACT TRUNCATED AT 400 WORDS)     

Electron microscopic immunocytochemical evidence for the existence of bidirectional synaptic connections between growth hormone-releasing hormone- and somatostatin-containing neurons in the hypothalamus of the rat

Synaptic contacts between growth hormone-releasing hormone (GHRH)- and somatostatin-containing neurons were demonstrated in the rat hypothalamus by a double-staining immunocytochemical method at the electron microscopic level. Somatostatin-immunoreactive nerve terminals synapse on GHRH-positive dendrites and cell bodies in the arcuate nucleus. A fine network of GHRH-immunopositive nerve terminals was observed at the light microscopic level in the rostral part of the periventricular nucleus and in the dorsal part of the arcuate nucleus around somatostatin-containing neuronal elements. With the electron microscope synaptic contact between GHRH-containing nerve terminals and somatostatin-containing dendrites are demonstrated. The reciprocal innervation between GHRH- and somatostatin-containing neurons that project to the median eminence and regulate growth hormone secretion must allow them to coordinate their activities.     

Ultrastructure of luteinizing hormone-releasing hormone (LHRH) neurons and their projections in the golden hamster

Seasonal breeding mammals exhibit a reversible annual cycle of fertility, and thus represent valuable models for investigating the organization of luteinizing hormone-releasing hormone (LHRH) neurons which mediate the neuroendocrine control of reproduction. Electron microscopic immunocytochemistry was used to examine the ultrastructure of LHRH neurons and their projections in a seasonal breeder, the golden hamster, housed under photoperiodic conditions which are reproductively stimulatory. LHRH perikarya in the diagonal band, medial septum, and preoptic area were bipolar or unipolar cells which possessed nuclei with prominent indentations and multiple nucleoli. LHRH reaction product within these cells was associated with neurosecretory granules and the rough endoplasmic reticulum (RER), particularly those portions of RER adjacent to the outer nuclear envelope. LHRH cell bodies and dendrites in the hamster received an extremely limited amount of synaptic input; of a total of twenty-five cells analyzed, we found only five instances of morphologically identified synapses onto immunoreactive dendrites. Occasionally close somatic appositions were seen between LHRH cells and non-immunoreactive neurons, and in one instance between two LHRH somas. In the organum vasculosum of the lamina terminalis (OVLT), LHRH fibers appeared as isolated strings of varicosities. In contrast, within the median eminence immunoreactive axonal profiles were frequently bundled together in fascicles although synaptic specializations were not observed between individual axons. The existence of contacts between LHRH axons in the median eminence, coupled with the extreme paucity of synaptic inputs onto LHRH neurons in this species, suggests that the median eminence may be a site where neural or hormonal signals could influence the coordinated release of LHRH from cells of dispersed origin.     

Localization of Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) in the Hypothalamus-Pituitary System in Rats: Light and Electron Microscopic Immunocytochemical Studies

The localization of pituitary adenylate cyclase-activating polypeptide (PACAP) in the hypothalamus-pituitary system in rats was examined in light and electron microscopic immunocytochemistry using a specific antiserum to synthetic PACAP 1–38 (R0831). In light microscopic study, intensely PACAP-immunostained perikarya were observed in the supraoptic and paraventricular magnocellular nucleus in the hypothalamus. In the median eminence, many immunoreactive nerve fibers were observed in the internal layer, but a few immunoreactive terminals were noticed in the external layer. In the pituitary gland, numerous immunoreactive nerve fibers were observed in the posterior lobe. In the intermediate lobe, moderately immunostained cells were observed, but in the anterior lobe no immunostained cells were noticed. In electron microscopic study, PACAP-immunoreactivity was examined by avidin-biotin peroxidase complex method. In the perikarya of the supraoptic and paraventricular magnocellular nucleus, DAB-reaction products were distributed diffusely in the cytoplasmic matrix, frequently attaching to the rough-surfaced endoplasmic reticulum. In the nerve terminals of the posterior lobe, reaction products were observed among the secretory granules, but sometimes upon them. In the cells of the intermediate lobe, reaction products were also distributed in the cytoplasmic matrix.     

Ultrastructural localization of neuropeptide Y-like immunoreactivity in the rat hippocampal formation.

Neuropeptide Y (NPY) has been implicated in the modulation of hippocampal neuronal activity and in the pathophysiology of several neurological disorders involving the hippocampal formation. Thus, this study examines the light and electron microscopic immunoperoxidase labeling of a rabbit polyclonal antibody against porcine NPY in single sections through each lamina of the CA1 and CA3 regions of the hippocampus and the dentate gyrus (DG) of normal adult rats. By light microscopy, the majority of perikarya with intense NPY-like immunoreactivity (NPY-LI) were located in stratum oriens of CA1 and CA3 of the hippocampus and in the hilus of the DG. Fine varicose processes with NPY-LI were found in all layers of the hippocampal formation, but were densest in the outer third of the molecular layer of the DG. The density of NPY-labeling was greater in the ventral portion of the hippocampal formation. By electron microscopy, most NPY-containing perikarya in all three hippocampal regions were: small (8-12 microns) or medium-sized (12-18 microns) and elongated; or medium-sized and round. A dense accumulation of NPY-LI was commonly observed within the individual saccules of Golgi complexes and some rough endoplasmic reticulum in the cytoplasm. Perikarya and dendrites with NPY-LI usually were directly apposed to other neuronal processes (mostly terminals) and lacked astrocytic appositions. The majority of terminals in contact with NPY immunoreactive neurons were unlabeled and synapsed with the shafts of large and small dendrites. In CA1 and CA3 of the hippocampus, the types of synapses formed by the unlabeled terminals were not significantly different; however, more asymmetric synapses than symmetric synapses were formed by the unlabeled terminals on the shafts of small NPY-labeled dendrites in the DG. The terminals with NPY-LI (0.25-1.2 microns) contained many small, clear vesicles and 0-2 large, dense-core vesicles. The types of synapses (i.e., asymmetric and symmetric) and distribution of NPY-labeled terminals on the targets were remarkably similar in each lamina of the hippocampal subregions. The NPY-labeled terminals usually synapsed with one unlabeled perikaryon or dendrite. However, others synapsed either (1) with two unlabeled perikarya or dendrites simultaneously or (2) with one NPY-containing perikaryon or dendrite. Most of the terminals with NPY-LI formed symmetric junctions with the shafts of small (distal) dendrites.(ABSTRACT TRUNCATED AT 400 WORDS)     

Electronmicroscopic study of somatostatin-containing neurons in rat arcuate nucleus with special reference to neuronal regulation

After an intraventricular administration of colchicine, the arcuate nucleus of rat hypothalamus was examined light and electron microscopically by pre-embedding immunohistochemistry for somatostatin. The arcuate nucleus exhibited numerous immunoreactive cell bodies and dense networks of immunoreactive fibers. The fibers appeared to surround immunonegative cell bodies. The immunoreactive cell bodies were multipolar in shape and projected immunoreactive processes to some extent. The immunoreactive cell bodies and fibers received synaptic contacts by immunonegative fiber terminals containing a large number of synaptic clear vesicles. Similarly, immunoreactive somatostatin fibers appeared to terminate upon other immunonegative cell bodies and fibers. The immunoreactive presynaptic terminals contain several labeled granules and numerous synaptic vesicles. In close proximity to these immunolabeled terminals, non-labeled presynaptic fibers. This suggests that in the arcuate nucleus neurons regulated by somatostatin neurons are also under the control of other types of neurons.     

GRF immunoreactive neurons in the paraventricular nucleus of the rat: an immunohistochemical study with monoclonal and polyclonal antibodies

Our study demonstrates a complex GRF neuronal system within the rat hypothalamus. Using both high affinity polyclonal and high specificity monoclonal antibodies to rat (r) GRF, we have substantiated evidence for immunoreactive GRF (GRF-i) perikarya in the parvocellular portion of the paraventricular nucleus. Other hypothalamic areas containing rGRF-positive perikarya include the lateral arcuate nucleus, lateral hypothalamus, perifornical area and dorsomedial nucleus. GRF-i neuronal terminals were seen in the external zone of the median eminence, more rostrally in the periventricular nucleus, and near the suprachiasmatic nucleus and more caudally in the dorsomedial nucleus and ventral premammillary nucleus.