Immunoreactive leu-enkephalin in the monkey hypothalamus including observations on its ultrastructural localization in the paraventricular nucleus

Effects of D-Ala2-D-Leu5-enkephalin, microinjected into the supraoptic and paraventricular nuclei, on urine outflow rate

The effects of D-Ala2-D-Leu5-enkephalin (DADL, a delta-opioid agonist), microinjected directly into the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei, on urine outflow rate, urinary osmotic pressure, blood pressure, heart rate, respiratory rate and rectal temperature were investigated in water-loaded and ethanol-anesthetized rats. The microinjection of DADL into both the nuclei decreased urine outflow rate in a dose-dependent manner with an increase in urinary osmotic pressure, but did not change the other recorded parameters. The DADL-induced antidiuretic effect in the SON was inhibited by naloxone, but not by atropine, phenoxybenzamine, timolol nor a vasopressin antagonist, d(CH2)5-D-Tyr(Et)VAVP. The effect in the PVN was inhibited by naloxone, atropine, timolol and d(CH2)5-D-Tyr(Et)VAVP, but not by phenoxybenzamine. These results suggest that DADL causes antidiuretic effects mediated through opioid receptors in both the SON and PVN, and the underlying mechanisms are different between them. Involvement of delta-opioid receptors in the DADL-induced antidiureses was discussed.

Ultrastructural identification of neuropeptides in the central nervous system

A number of different neuropeptides have been described within presynaptic terminals at the ultrastructural level in the central nervous system. The majority of these neuropeptides share a common morphology with one another. Terminals containing neuropeptides have a population of small, clear vesicles associated with the active zone of the synapse and a lesser number of large, granular vesicles that are located at a distance from the active site of the synapse. It is believed that the large, granular vesicles act as a mechanism for the transport/storage of the neuropeptides, while the small, clear vesicles are thought to be acting as structures responsible for the release of the neurotransmitter/neuropeptide into the synaptic cleft. The neuropeptide containing terminals most often have asymmetrical junctions associated with their presynaptic membranes, although symmetrical junctions have been described with peptide containing terminals in a number of areas in the central nervous system. Neuropeptide containing terminals contact every part of the neuronal membrane; however, the majority of synaptic contacts involve portions of the dendritic shafts. Evidence is beginning to accumulate to indicate that for certain neuropeptides there is a specific spatial arrangement to their termination along the neuronal membrane.

Ultrastructural localization of enkephalin-like immunoreactivity in developing rat cerebellum

Methionine enkephalin, an endogenous opioid peptide, participates in the regulation of growth in the developing brain. In the present study, enkephalin-like immunoreactivity was localized in the cerebellum of developing and adult rats by immunoelectron microscopy. In 10-day-old animals, enkephalin-like immunoreactivity was found in the somata of proliferating, migrating and differentiating neural cells, and was associated with the plasma membrane, microtubules, filaments, mitochondria, endoplasmic reticulum and nuclear envelope. Both neurons and glia in the cerebellum of the preweaning rat displayed a similar profile of immunoreactivity. Reaction product was also detected in the dendrites and dendritic spines of Purkinje cells where it was concentrated in postsynaptic densities. The majority of internal granule neurons in 10-day-old animals were not immunoreactive, nor were axons, glial processes and postsynaptic elements (with the exception of mossy fiber terminals). At weaning (Day 21), enkephalin-like immunoreactivity was confined primarily to the somata of Purkinje, basket and stellate neurons, and to Purkinje cell dendrites and synaptic spines. Adult rats (day 75) exhibited no enkephalin-like immunoreactivity. These results establish that enkephalin or an enkephalin-like substance can be detected during the ontogeny of both neurons and glia in the cerebellar cortex, and appears to be associated with certain structural elements.

Immunocytochemical study of Met-enkephalin-like cell bodies in the cat hypothalamus

The distribution of methionine-enkephalin-like cell bodies in the hypothalamus of the cat was studied using an indirect immunoperoxidase technique. Previously, intraventricular or intratissular injections of colchicine were carried out. Met-enkephalin-like neurons were located in all hypothalamic nuclei. The densest clusters of immunoreactive perikarya were observed in the nucleus arcuatus, median eminence, regio praeoptica and perifornical region, whereas the nucleus supraopticus and hypothalamus anterior had the lowest density. In other hypothalamic nuclei the density of methionine-enkephalin (Met-enkephalin) cell bodies was intermediate.

A Golgi study of the monkey paraventricular nucleus: neuronal types, afferent and efferent fibers

The neuronal organization of the paraventricular nucleus (PVN) was examined in Golgi impregnations of adult monkey. Results showed that at least six types of neurons could be identified in the nucleus on the basis of morphological features of the somata, dendrites, and axons. Four types of neurons with sparse to densely spined cell bodies and dendrites exhibited long axons and included large neurons (types I and II), medium-sized to large neurons (type III), and small to medium-sized cells (type IV). Axons of type I, III, and IV neurons had different diameters and were followed out of the PVN. Axon collaterals that arborized within the PVN were seen on the axons of types III and IV cells. Two types of interneurons with small somata were also found. One (type V) exhibited varicose dendrites and a profusely arborizing local axon. The other cell (type VI) had recurved dendrites with long appendages and no impregnated axon. Afferent fibers were also identified. Type 1 was a fine-caliber axon that coursed long distances in the PVN and exhibited numerous short branches. Additional observations suggested that type 1 afferents originated from the stria terminalis. The other afferent axon (type 2) was thicker and gave rise to terminal arborizations containing clusters of small swellings. The efferent fibers of the PVN were also examined in impregnations of the paraventriculosupraopticohypophysial tract. Fibers formed an extensive plexus as they coursed ventrally and passed through the lateral hypothalamus. Axons coursing more laterally in the tract were much larger than those more medially located. Our findings show a diverse organization of neuronal types within the monkey PVN with evidence for intrinsic connections through axon collaterals of efferent neurons and the locally arborizing axons of interneurons. Correlations are proposed between morphological subtypes of neurons seen in this Golgi study and the known functional output pathways of the PVN.

Fine structural studies of growth-hormone-releasing-factor (GRF)-immunoreactive neurons and their synaptic connections in the guinea pig arcuate nucleus

The fine structure of neurons containing human growth-hormone-releasing factor (hGRF) immunoreactivity located in the arcuate nucleus of the guinea pig was studied by means of the preembedding immunohistochemical technique. The perikaryon of labeled neurons was fusiform or ovoid; the nucleus was regular in shape and contained a prominent nucleolus. The main ultrastructural features of the hGRF-immunoreactive neurons were the presence of numerous labeled secretory granules (100-120 nm in diameter) and the abundance and the enlargement of the organelles involved in the synthesis of the peptides: a well-developed rough endoplasmic reticulum and a conspicuous Golgi apparatus. Synaptic inputs were observed on immunoreactive perikarya but, above all, on the labeled dendrites. The unstained presynaptic nerve endings most often contained only small clear vesicles and formed symmetrical contacts. In rare cases, the presynaptic terminals exhibited both small clear and large dense vesicles and constituted asymmetrical contacts. Immunoreactive nerve endings were also observed in this area: the synaptic boutons contained large, stained vesicles and small, unlabeled, clear vesicles. These axon terminals made synaptic contacts with unstained dendritic processes; the contacts were symmetrical. The results indicate that hGRF-immunoreactive neurons of the guinea pig arcuate nucleus present morphological features of neuroendocrine cells. Moreover, the presence of hGRF-labeled nerve endings in the arcuate nucleus itself suggests that a substance related to hGRF might be a neuromodulator, at least in this area.

Distribution of enkephalin-immunoreactive neurons in the forebrain and upper brainstem of the squirrel monkey

The distribution of enkephalin-immunoreactive neuronal profiles in the forebrain and upper brainstem of the squirrel monkey (Saimiri sciureus) was studied by means of the indirect immunofluorescence method. Numerous enkephalin-immunoreactive cell bodies and fibers were disclosed in various regions including cerebral cortex, hippocampus, caudate nucleus, putamen, nucleus accumbens, septal area, olfactory tubercle, substantia innominata, amygdala, various hypothalamic and thalamic nuclei, periaqueductal gray, midbrain reticular formation and interpeduncular nucleus. Some of the highest concentrations of enkephalin-positive fibers in the squirrel monkey brain were found in the external segment of the globus pallidus, the outer layer of the median eminence, and in the pars reticulata of the substantia nigra. Overall, the pattern of distribution of the enkephalin-immunoreactive cell bodies and fibers in the forebrain and upper brainstem of the squirrel monkey is similar to that found in the rat, except that the density of positive neuronal profiles in the entire forebrain appears much higher in monkey than in rat. Furthermore, the very dense network of enkephalin-immunoreactive fibers disclosed in the substantia nigra pars reticulata of monkey appears to be lacking in rat.

Prodynorphin peptide immunocytochemistry in rhesus monkey brain

The present study describes the immunocytochemical distribution of peptides derived from the prodynorphin precursor in the brain of the rhesus monkey (Macaca mulatta). Animals were treated with colchicine (intracerebroventricularly) prior to perfusion to enhance the observation of perikaryal immunoreactivity. Using antisera generated against dynorphin A(1-17), dynorphin B(1-13), and prodynorphin(186-208) (or bridge peptide), the anatomical distribution of dynorphin systems was mapped. The results indicate a widespread neuronal localization of immunoreactivity from the cerebral cortex to the caudal medulla. Anti-dynorphin B and anti-bridge peptide sera proved useful for the demonstration of neuronal perikarya, while the dynorphin A antiserum was best for localizing terminal projection fields. Immunoreactive perikarya are located in numerous brain loci, including the cingulate cortex, caudate nucleus, amygdala, hypothalamus (especially the magnocellular nuclei), thalamus, substantia grisea centralis, parabrachial nucleus, nucleus tractus solitarius, and other nuclei. In addition, fiber and terminal immunoreactivity are seen in varying densities in the striatum and pallidum, substantia innominata, hypothalamus, substantia nigra pars reticulata, parabrachial nucleus, spinal trigeminal nucleus, and other areas. The distribution of prodynorphin peptides in the brain of the monkey is similar to that described for the rat brain; however, significant differences also exist. Other interspecies differences in the anatomy of prodynorphin and proenkephalin neuronal systems in the monkey and human brain are further discussed.