Biomedical subjects

F Rage

Publications and source records attributed to F Rage.

28 records · Page 2Linked to original sources

PubMed1996

Neuroendocrine and autonomous mechanisms underlying thermoregulation in cold environment.

This review focuses on the central regulation of thermoregulatory responses with special attention to the participation of thyrotropin-releasing hormone (TRH) in both autonomous and endocrine responses to a cold environment. Besides a direct projection of TRH neurons from paraventricular nuclei (PVN) to the median eminence, and the subsequent activation of the thyroid axis, there are direct projections from the PVN to the autonomic preganglionic neurons controlling autonomous responses. There projections convey information to peripheral targets involved in thermogenesis through the dorsal vagal complex and the spinal cord, for parasympathetic and sympathetic neurotransmissions respectively. Furthermore, cold exposure increases TRH mRNA levels in the PVN but also in dorsal motor and caudal raphe nuclei, thus providing strong evidence for a functional link between autonomous and neuroendocrine systems involved in thermoregulation. The review also focuses on neuroendocrine regulation of cold-induced TRH/TSH release associated with modifications in somatostatin release, with special reference to the participation of several central neurotransmitters (catecholamines, serotonin or GABA) or the influence of sex steroids.

Animals↗

PubMed1995

Characterization of spontaneous and N-methyl-D-aspartate-induced calcium rise in rat cultured hypothalamic neurons.

The effect of N-methyl-D-aspartate (NMDA) on intracellular calcium concentration ([Ca2+]i) was analyzed in cultured hypothalamic neurons using the Ca(2+)-sensitive fluorescent dye Fura-2. The resting [Ca2+]i in silent neurons ranged between 35 and 100 nM and regular spontaneous [Ca2+]i oscillations were observed in 37% of neurons. Such [Ca2+]i oscillations were blocked by tetrodotoxin (TTX--the sodium channel blocker), and reduced by the voltage-sensitive calcium channel blockers omega-conotoxin (omega-CTX-GVIA) (N-type) and nifedipine (L-type). NMDA increased [Ca2+]i transients and MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d')cyclohepten-5,10-imine hydrogen] reduced them, in a dose-response manner. The amplitude of the NMDA-induced [Ca2+]i rise increased with increasing external Ca2+ concentrations, and was completely abolished in Ca(2+)-free medium. The role of intracellular calcium was tested by addition of intracellular Ca2+ mobilizers. In the presence or absence of external Ca2+, 2,5-di(tert-buty)-1,4-benzohydroquinone) (tBuBHQ) (25 microM) evoked a robust [Ca2+]i rise in NMDA-sensitive neurons. Preincubation (20 min) with tBuBHQ completely abolished the NMDA-induced [Ca2+]i response. Caffeine (10 mM), thapsigargin (25 microM), and ryanodine (10 microM) did not elicit any Ca2+ transients. Nifedipine and omega-CTX-GVIA did not modify NMDA-induced [Ca2+]i transients. NMDA-induced [Ca2+]i rise was not altered by 0.1 microM TTX but at 1 microM it was reduced by 20%. These data show that hypothalamic neurons in culture respond to NMDA in a dose-dependent manner by a rise in [Ca2+]i and that this response is mediated by NMDA receptor-gated channel. In addition, [Ca2+]i rise is dependent on the presence of extracellular Ca2+, and also seems to involve mobilization of Ca2+ from tBuBHQ-sensitive intracellular stores.

Animals↗

PubMed1994

Synchronous development of spontaneous and evoked calcium-dependent properties in hypothalamic neurons.

The development of various related parameters was compared in hypothalamic neurons grown in primary culture. We measured: (i) low- and high-voltage-activated calcium currents; (ii) spontaneous and N-methyl-D-aspartate (NMDA)-induced fluctuations of intracellular calcium concentration; (iii) basal and NMDA- or potassium-evoked somatostatin release. Spontaneous calcium fluctuations appeared after 5 days in culture and increased progressively in amplitude and frequency over the next 8 days studied. Basal release of somatostatin was not detectable in 3 day-old cultures and reached a plateau at day 5. Responses evoked by exogenous stimulations (voltage-activated calcium currents, agonist-induced intracellular calcium rise and somatostatin release) appeared early in culture, increased in amplitude during 7-10 days and then stabilized. We conclude that, in hypothalamic neurons, the main neuronal functions develop in synchrony over a limited period of time.

Animals↗

PubMed1994

Rapid changes in somatostatin and TRH mRNA in whole rat hypothalamus in response to acute cold exposure.

Acute cold stimulus induces activation of the thyreotropic axis characterized by a rapid increase in plasma thyrotropin (TSH). Since pituitary TSH release is mainly regulated by two hypothalamic hormones: thyrotropin-releasing hormone (TRH) and somatostatin, the aim of this study was to analyse whether changes in the steady state mRNA levels and peptide content of these neurohormones occur under acute cold stimulation in rats. Northern blot analysis of hypothalamic somatostatin mRNA levels after 15, 30, 60 or 180 min of cold exposure revealed a 2.0-fold increase after 15 min at 4 degrees C. This augmentation was followed by a return to control values at 30 min. However, the hypothalamic content of somatostatin was not significantly modified at any cold exposure time. TRH mRNA showed a similar pattern to somatostatin, with a 2.5-fold increase after 15 min at 4 degrees C. In contrast, hypothalamic TRH content was significantly decreased after 15 min cold exposure, returning to control values at 30 min. The increase in mRNA levels was specific for the two hypothalamic hormones, since there was no concomitant variation in GAPDH mRNA used as negative control. These results suggest that the organism is quickly aroused by cold stimulus, triggering rapid activation in transcription of the two neurohormones involved in the regulation of the thyreotrope axis. Since the peptide contents did not show the same pattern, a quantitative change in transcription or in mRNA stability does not appear to be a prerequisite for increased peptide expression, suggesting that somatostatin and TRH gene expressions could be regulated at translational or post-translational steps.

Animals↗

PubMed1994

GABAA and NMDA receptor activation controls somatostatin messenger RNA expression in primary cultures of hypothalamic neurons.

GABAA receptors mediate the inhibition of somatostatin gene expression and NMDA receptors mediate its stimulation. The aim of this study was to determine whether the two major neurotransmitters in the central nervous system (GABA and glutamate) could interact to control somatostatin mRNA content in primary cultures of hypothalamic neurons. Neurons were incubated for 15 min on days 3, 5, 7 or 11 of culture with Mg(2+)-free medium containing either NMDA (20 microM) or bicuculline (50 microM) to investigate the ontogenesis of somatostatin somatostatin secretion in response to NMDA and GABA. We found that NMDA significantly elicited somatostatin release from day 3, and bicuculline-induced release was observed from day 5. An ontogenetic study of somatostatin mRNA levels revealed that it steadily increased up to day 5 (6-fold) and a slight but nonsignificant decrease was observed on day 7 which stabilized until day 13. Experiments were thus carried out on day 11 of culture. Pharmacological manipulations of the two types of receptors (NMDA and GABAA) were performed to study the effect of the interaction on somatostatin mRNA accumulation. Time-course studies revealed the optimal time of action of the neurotransmitters (20 h). Our results demonstrated that bicuculline-induced mRNA accumulation was not additive with that elicited by NMDA after 20 h of incubation. In contrast, (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d')cyclohepten-5,10-imine hydrogen (MK-801) at 10 microM completely abolished the stimulatory effect of bucuculline during the same time period. In addition, muscimol was unable to decrease somatostatin mRNA levels when NMDA receptors were blocked by MK-801.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Presence but not synthesis of thyrotrophin-releasing hormone in rat salivary glands detected by radioimmunoassay and northern blot analysis.

Thyrotrophin-releasing hormone (TRH) is one of the ubiquitous peptides first isolated from hypothalamus. This study sought to examine if it could also be detected in rat submandibular salivary glands, as can other neurogastrointestinal peptides. Radioimmunoassay of submandibular gland homogenates revealed TRH-like immunoreactivity in all samples from male rats (637.34 pg/gland +/- 166.17, n = 15). In contrast, Northern blot analysis to determine whether the peptide was locally synthesized in the glands failed to detect TRH mRNA. Consequently, the presence of TRH in the glands (as revealed by radioimmunoassay) could be associated with binding to presumptive TRH receptors in the mediation of physiological activities.

Animals↗

PubMed1993

Stimulatory effect of N-methyl-D-aspartate on somatostatin gene expression in cultured hypothalamic neurons.

The aim of the present study was to determine whether N-methyl-D-aspartate (NMDA) stimulates somatostatin gene function in primary cultures of hypothalamic neurons. Neurons were either shortly (for 3, 8, 24 and 72 h) or chronically (for 11 days) exposed to NMDA (20 microM). Medium and cellular somatostatin contents were determined by radioimmunoassay, and steady-state preprosomatostatin mRNA levels by Northern blot analysis with an oligonucleotide probe. DNA content was measured as a cellular viability control. After 8 h incubation, NMDA induced a significant 2-fold increase in somatostatin mRNA accumulation, with a maximal 4-fold increase after 24 h incubation. A significant and dose-dependent (1.7-fold and 2.5-fold at 20 and 100 microM, respectively) stimulatory effect was also observed after chronic treatment. The kinetic patterns for medium and cellular somatostatin contents were similar to those obtained for somatostatin mRNA levels. Total DNA content was not modified under any experimental condition. The augmentations in cellular somatostatin and somatostatin mRNA determined after 24 h or chronic exposure to NMDA were blocked by (+)-5-methyl-10.11-dihydro-5H-dibenzo(a,d')cyclohepten-5,10-imine hydrogen maleate (MK-801), an NMDA receptor antagonist. MK-801 alone significantly (P < 0.05) reduced somatostatin mRNA. The stimulatory effect of NMDA on somatostatin mRNA was specific since it was not accompanied by any change in glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA. After immunostaining with a specific antibody against somatostatin, no difference was observed in the number of immunostained neurons detected in control and NMDA exposed groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

GABA inhibition of somatostatin gene expression in cultured hypothalamic neurones.

GABAA receptors mediate the inhibition of somatostatin release in hypothalamic neurones. To study the possible effect of GABA on somatostatin biosynthesis, somatostatin and preprosomatostatin mRNA levels were evaluated after exposure of hypothalamic neurones to muscimol or bicuculline. Muscimol (50 microM) decreased preprosomatostatin mRNA levels, by 25% after 4 h and 30% after 24 h treatment. Bicuculline (50 microM and 100 microM) increased preprosomatostatin mRNA levels by 1.4 and 1.5 fold after 4 h and by 1.3 and 1.7 fold after 24 h treatment. Somatostatin content was not modified after muscimol or bicuculline exposure. Total DNA content, used to control cellular viability, was not modified under any experimental conditions. Our findings suggest that the GABAergic inhibition of mRNA levels could be a consequence of the GABA inhibition of somatostatin release, thus allowing limited changes in peptide steady-state levels.

Actins↗

PubMed1992

NMDA receptor activation stimulates phospholipase A2 and somatostatin release from rat cortical neurons in primary cultures.

We have recently shown that glutamate exerts a stimulatory action on somatostatin secretion in cortical neurons essentially through NMDA receptor sites. Here, we investigated whether arachidonic acid release could be modified after NMDA receptor activation in cortical neurons in primary culture. We also studied whether pharmacological manipulation of phospholipase A2 could modify somatostatin release. We found that both glutamate and NMDA (N-methyl-D-aspartate) stimulated [3H]arachidonic acid release. NMDA-evoked arachidonic acid release was inhibited by MK-801 and TCP (two NMDA receptor-type antagonists), or by mepacrine, an inhibitor of phospholipase A2. NMDA-induced somatostatin release was inhibited by MK-801, mepacrine and by another phospholipase A2 inhibitor, p-bromophenacylbromide (pBPB). However, responses to NMDA were unaffected by H7, NDGA (nordihydroguaiaretic acid), indomethacin or by RHC 80267 (inhibitors of protein kinase C, lipooxygenase, cyclooxygenase and diacylglycerol lipase, respectively). Mepacrine (greater than or equal to 100 microM) decreased NMDA-stimulated phosphatidylinositol (PI) hydrolysis and at higher concentrations (250 microM) was also able to inhibit basal release whereas pBPB had no effect in the range of concentrations tested. Neomycin (which inhibits phosphatidylinositol metabolism by binding strongly and selectively to inositol phospholipids) reduced by 30% the NMDA-stimulated somatostatin release, although chronic treatment of neurons with the phorbol ester 12-myristate, 13-acetate (PMA) had no effect on this response. Melittin, an activator of phospholipase A2, was able to stimulate both arachidonic acid release and somatostatin secretion. High-performance liquid chromatography (HPLC) analysis of tritiated metabolites released from cortical neurons under basal or NMDA-stimulated conditions revealed that [3H]arachidonic acid was the only metabolite detectable. Furthermore, external addition of arachidonic acid increased somatostatin secretion. Our results show a correlation between the two parameters studied.

Animals↗

PubMed1992

Gamma-aminobutyric acid-glutamate interaction in the control of somatostatin release from hypothalamic neurons in primary culture: in vivo corroboration.

Recent studies have provided new data on the neuroendocrine role of glutamate (the major excitatory neurotransmitter) on somatostatin release. The neuroendocrine role of gamma-aminobutyric acid (GABA) (the major inhibitory neurotransmitter) on this same secretion, is also well established. Our objective was thus to investigate whether GABA and glutamate, which have opposite neurotransmission signals, could interact in the control of hypothalamic somatostatin release. Pharmacological manipulations of the two types of receptors were performed in vitro on primary cultures of hypothalamic neurons secreting somatostatin. We found that tonic release of somatostatin was reduced by 76% in the presence of tetrodotoxin (TTX) and was regulated by endogenous secretion of glutamate and GABA. CGS 19755, a highly selective N-methyl-D-aspartate (NMDA) receptor antagonist, significantly reduced tonic somatostatin secretion whereas it was strongly increased by picrotoxin and bicuculline, two GABAA antagonists. When CGS 19755 was applied with picrotoxin, somatostatin release was the same as levels obtained in the control group with TTX. GABA reduced tonic somatostatin release (in the presence or absence of TTX), and glutamate-stimulated secretion in a dose-dependent manner. Picrotoxin stimulation of tonic somatostatin release was additive with that obtained after glutamate stimulation and was also dose-dependent. This interaction was also studied in vivo in unanesthetized rats bearing a push-pull cannula stereotaxically implanted into the median eminence. Ip injected CGS 19755 (an antagonist that can freely permeate the blood-brain barrier) completely blocked the peak secretion of somatostatin observed after ip picrotoxin administration, whereas there was no significant effect when it was injected alone. These findings corroborated our in vitro data and allow us to postulate that GABA and glutamate interact in the control of somatostatin.

Animals↗