Light and electron microscopic immunocytochemical evidence that delta sleep-inducing peptide and gonadotropin-releasing hormone are coexpressed in the same nerve structures in the guinea pig median eminence

Luteinizing hormone releasing hormone (LHRH) neurons maintained in nasal explants decrease LHRH messenger ribonucleic acid levels after activation of GABA(A) receptors

Inhibition of the LHRH system appears to play an important role in preventing precocious activation of the hypothalamic-pituitary-gonadal axis. Evidence points to gamma-aminobutyric acid (GABA) as the major negative regulator of postnatal LHRH neuronal activity. Changes in LHRH messenger RNA (mRNA) levels after alterations of GABAergic activity have been reported in vivo. However, the extent to which GABA acts directly on LHRH neurons to effect LHRH mRNA levels has been difficult to ascertain. The present work evaluates the effect of GABAergic activity, via GABA(A) receptors, on LHRH neuropeptide gene expression in LHRH neurons maintained in olfactory explants generated from E11.5 mouse embryos. These explants maintain large numbers of primary LHRH neurons that migrate from bilateral olfactory pits in a directed manner. Using in situ hybridization histochemistry and single cell analysis, we report dramatic alterations in LHRH mRNA levels. Inhibition of spontaneous synaptic activity by GABA(A) antagonists, bicuculline (10(-5) M) or picrotoxin (10(-4) M), or of electrical activity by tetrodotoxin (TTX, 10(-6) M) significantly increased LHRH mRNA levels. In contrast, LHRH mRNA levels decreased in explants cultured with the GABA(A) receptor agonist, muscimol (10(-4) M), or KCl (50 mM). The observed responses suggest that LHRH neurons possess functional pathways linking GABA(A) receptors to repression of neuropeptide gene expression and indicate that gene expression in embryonic LHRH neurons, outside the CNS, is highly responsive to alterations in neuronal activity.

Frog prohormone convertase PC2 mRNA has a mammalian-like expression pattern in the central nervous system and is colocalized with a subset of thyrotropin-releasing hormone-expressing neurons

The prohormone convertase (PC2) is expressed in the mammalian central nervous system (CNS) and has been shown to play an important role in the processing of certain neuropeptide precursors and prohormones at paired basic residues. Amphibian PC2 cDNA was recently cloned for the frog Xenopus laevis, and both its sequence and its pituitary expression pattern were shown to be very similar to those of mammalian PC2. To investigate further the function of PC2 in the vertebrate CNS, we used in situ hybridization histochemistry to localize the distribution of cells expressing PC2 mRNA in the frog brain and the spinal cord. The distribution of PC2-expressing cells was also compared with that of cells expressing thyrotropin-releasing hormone (TRH) mRNA or peptide. PC2-expressing cells were detected in specific nuclei that were widely distributed in the frog CNS. In forebrain, telencephalic PC2 mRNA was found in the olfactory bulb, pallium, striatum, amygdala, and septum, and diencephalic PC2 mRNA was seen in the preoptic area, thalamus, and hypothalamus. More posteriorly, PC2 cells were localized to midbrain tegmentum, the torus semicircularis, and the optic tectum, as well as the cerebellum, brainstem, and spinal cord. Despite this wide distribution steady-state levels of PC2 mRNA were clearly different in various brain nuclei. Regions with higher levels showed good correspondence to areas shown by others in frog to contain large numbers of neuropeptide-expressing cells, including TRH cells. On the other hand, not all brain areas with high levels of TRH mRNA had high levels of PC2 mRNA. Localization studies combining in situ hybridization and immunocytochemistry showed that, at least in optic tectum and brainstem, PC2 mRNA and pro-TRH peptide coexist. These findings suggest that pro-TRH is processed by PC2 in some, but possibly not all, brain regions. Thus, different converting enzymes may be involved in pro-TRH processing in different brain regions.

Gonadotropin-releasing hormone (GnRH) neurons in the hypogonadal mouse elaborate normal projections despite their biosynthetic deficiency

This study was undertaken to determine whether gonadotropin-releasing hormone (GnRH) neurons in the mutant hypogonadal (hpg) mouse can establish axonal connections with their target despite their failure to synthesize and secrete the GnRH neuropeptide. Normal and hpg males received intraperitoneal injections of the retrograde tracer Fluoro-Gold. This tracer does not cross the blood-brain-barrier and hence is taken up only by neurons in the central nervous system whose axons terminate on fenestrated capillaries, such as the capillaries of the median eminence. The brains of the injected animals were processed for in situ hybridization to visualize GnRH transcribing cells. In 3 hpg males 64.1 +/- 5.6% of GnRH transcribing cells contained Fluoro-Gold, while 55.8 +/- 6.4% of the cells in 3 normal males had Fluoro-Gold. Thus, we have demonstrated that secretory-deficient GnRH neurons can establish axonal connections with their primary secretory target, the median eminence. We conclude that the capability of GnRH neurons to recognize and interact with their target is not dependent upon their neurosecretory function.

Characterization of the release and metabolism of delta sleep-inducing peptide (DSIP) in the rat brain

In the present study, we examined whether delta sleep-inducing peptide (DSIP) was (1) secreted from neurons on depolarization and (2) degraded by membrane-associated peptidases. Incubation of DSIP with rat brain membrane resulted in the degradation of DSIP with liberation of tryptophan, an N-terminal amino acid of DSIP. Bestatin and puromycin, aminopeptidase inhibitors, significantly inhibited the degradation of DSIP and release of tryptophan. The releases of immunoreactive DSIP-like substance (irDSIP) from rat brain slices and synaptosomes were significantly stimulated by high K(+)-evoked depolarization. The released irDSIP was coeluted with native DSIP on gel filtration chromatography. High K(+)-evoked release of irDSIP did not show extracellular Ca(2+)-dependency. This Ca(2+)-independency suggests that the secretory pathway of DSIP may be different from that of other neurotransmitters. These results demonstrate that DSIP is released from nerve endings on depolarization and inactivated by membrane-associated puromycin-sensitive aminopeptidase. Therefore, DSIP may serve as a neuropeptide-like material in the central nervous systems.

Production and immunohistochemical application of monoclonal antibodies against delta sleep-inducing peptide

Monoclonal antibodies were produced following immunization of rats with delta sleep-including peptide (DSIP). The spleen cells of the rats were fused with the myeloma cell line SP2/0. The supernatants of hybridomas were screened on a solid-phase immunoassay using dot-immunobinding of DSIP and some DSIP fragments. The supernatants of six stable producer clones were found to react with DSIP. From this procedure it was also deduced that all these monoclonal antibodies recognized epitope(s) of the penta carboxy-terminal region of DSIP (DSIP5-9). Application of these monoclonal antibodies to rat median eminence sections gave a strong immunolabelling of a large population of fibres and terminal-like structures, mainly localized through the lateral areas. Elution-restaining experiments using a monoclonal antibody to DSIP and a polyclonal antiserum to luteinizing hormone-releasing hormone (LHRH) showed that the patterns of immunoreactivity respectively visualized overlap almost completely. Although numerous LHRH-immunoreactive neuronal elements were also easily demonstrated in the median eminence of the mouse, the hamster and the gerbil species, incubation of sections with monoclonal antibodies to DSIP failed to give any immunoreaction. Taken together these data argue for the independence of the DSIP/LHRH immunolabelling systems. Furthermore, it was demonstrated that DSIP5-9-related epitopes detected in the rat median eminence have no counterpart in the three other rodent species investigated. These species differences may reflect the fact that the carboxy-terminal sequence of the nonapeptide DSIP originally discovered in the rabbit is not conserved in all rodent species.

Immunohistochemical localization of delta sleep-inducing peptide (DSIP) in the brain and pituitary of the cartilaginous fish Scyliorhinus canicula

The distribution of delta sleep-inducing peptide (DSIP) in the brain and pituitary of the cartilaginous fish Scyliorhinus canicula was investigated using the indirect immunofluorescence technique. Delta sleep-inducing peptide-like immunoreactive cell bodies were mainly observed in the nucleus lateralis tuberis of the hypothalamus. Immunolabeled perikarya were also distributed in the nucleus lobi lateralis hypothalami and in the dorso-lateral wall of the recessus posterioris. Most of these cells, located in the subependymal layers of the infundibulum and lateral lobes, had the typical aspect of cerebrospinal fluid-contacting elements. The DSIP-like immunoreactive fibers were localized in the basal telencephalon, within the regions of the nucleus interstitialis commissurae anterioris and the nucleus entopeduncularis. A dense network of DSIP-positive fibers was seen throughout the midcaudal hypothalamus, the lateral lobes, and the posterior lobe. In the pituitary, numerous DSIP-like immunoreactive cells were detected in the median lobe of the pars distalis. In particular, a high concentration of cells was seen in the dorsal wall of the median lobe, an area which is known to contain melanin-concentrating hormone (MCH)-producing cells. Comparison of the distribution of DSIP- and MCH-like immunoreactive cells revealed that the two neuropeptides are stored in the same cells of the median lobe of the pituitary. These findings provide the first evidence for the presence of a DSIP-related peptide in fish. The distribution of the immunoreactive material supports the view that DSIP may act as a neuromodulator and/or a hypophysiotropic factor. Moreover, the presence of DSIP-like immunoreactive cells in the pars distalis suggests that this peptide may exert autocrine or paracrine effect in the pituitary.

Immunohistochemical localization of delta sleep-inducing peptide-like immunoreactivity in the central nervous system and pituitary of the frog Rana ridibunda

The purpose of the present study was to investigate the distribution of delta sleep-inducing peptide in the brain and pituitary of the frog Rana ridibunda and to determine the possible effect of this nonapeptide on adrenocorticotropic hormone and corticosteroid secretion. Delta sleep-inducing peptide-like immunoreactive fibres were observed throughout the brain of the frog. These fibres generally exhibited the characteristics of glial cell processes. Scarce delta sleep-inducing peptide-positive fibres were seen in the olfactory bulb and in the periventricular areas of the telencephalon. In the diencephalon, numerous delta sleep-inducing peptide-containing processes were noted in the preoptic nucleus, the infundibular nuclei and the median eminence. A few cerebrospinal fluid-contacting cells were visualized in the ventral nucleus of the infundibulum. Delta sleep-inducing peptide-positive fibres were also observed in the mesencephalon, radiating through the different layers of the tectum. In the cerebellum, all Purkinje cells exhibited delta sleep-inducing peptide-like immunoreactivity. More caudally, numerous delta sleep-inducing peptide-positive fibres were noted in the vestibular nucleus of the rhombencephalon. A dense network of delta sleep-inducing peptide-containing fibres was seen in the pars nervosa of the pituitary. In the distal lobe, a population of endocrine cells located in the anteroventral region contained delta sleep-inducing peptide-immunoreactive material. Labelling of consecutive sections of the pituitary by delta sleep-inducing peptide and adrenocorticotropic hormone antiserum revealed that a delta sleep-inducing peptide-related peptide is expressed in corticotroph cells. The possible role of delta sleep-inducing peptide in the control of adrenocorticotropic hormone and corticosteroid release was studied in vitro, using the perifusion system technique. Administration of graded doses of delta sleep-inducing peptide (from 10(-8) to 10(-6) M) to perifused frog anterior pituitary cells did not affect the spontaneous release of adrenocorticotropic hormone. In addition, prolonged infusion of delta sleep-inducing peptide (10(-6) M) did not alter the stimulatory effect of corticotropin-releasing factor (10(-7) M) on adrenocorticotropic hormone secretion. Similarly, exposure of frog interrenal slices to delta sleep-inducing peptide did not induce any modification of spontaneous or adrenocorticotropic hormone-evoked secretion of corticosterone and aldosterone. Our results provide the first evidence for the presence of a delta sleep-inducing peptide-related peptide in lower vertebrates. The occurrence of delta sleep-inducing peptide-like immunoreactivity in specific areas of the brain suggests that the peptide may act as a neuromodulator.(ABSTRACT TRUNCATED AT 400 WORDS)

The distribution and development of delta sleep-inducing Peptide-like immunoreactivity in postnatal and prepubertal Guinea-pig brain

The distribution and development of delta sleep-inducing peptide (DSIP) in the guinea-pig brain were studied in 2- to 60-day-old animals by using the indirect immunofluorescence method. DSIP-immunoreactive perikarya were observed in the olfactory bulb and tubercle, diagonal band of Broca, septum, preoptic area, anterior and lateral hypothalamus, arcuate nucleus and hippocampus. In addition to the densest innervation of the median eminence, DSIP-immunoreactive fibres were widely localized from forebrain to mesencephalon. The field of immunoreactive fibre endings appeared to be in close association with either the blood vessels of brain, ventricles, subarachnoid space or immunolabelled perikarya. Furthermore, throughout development the topographic distribution pattern of immunolabelled neuronal elements seemed to be similar. However, a generalized increase in number, immunofluorescence intensity and varicosities of DSIP fibres was displayed with the growth. The present results provide an anatomical basis for understanding multiple actions of DSIP in the central nervous system and future research for DSIP on development.