摘要:

The activity of the brain stem catecholaminergic (CA) cell groups of the ventrolateral (A1C1) and dorsomedial (A2C2) medulla that are known to contain primarily noradrenergic neurones (A1 and A2) and a smaller proportion of adrenergic cells (C1 and C2) as well as the noradrenergic group locus ceruleus (LC) in the dorsal pons was determined at various times up to 16 days following surgical adrenalectomy. The activity of the CA cell groups was estimated by the rate of tyrosine hydroxylation in vivo that was assessed by measuring the 3, 4-dihydroxyphenylalanine (DOPA) accumulated 20 min following administration of DOPA decarboxylase inhibitor NSD 1015. In the medullary nuclei noradrenaline content was found around 40- up to 70-fold the adrenaline content. This result was taken as evidence that the noradrenergic cells are likely to provide the main contribution to the tyrosine hydroxylation rate that we measured. Endogenous DOPA content represented between 2 and 10% of the noradrenaline content. NSD 1015 induced an accumulation of DOPA that was linear for at least 20 min and reached at this time more than 10-fold the endogenous level. While no modification of the in vivo tyrosine hydroxylation rate was observed in the LC, a significant increase was found in both medullary groups following adrenalectomy. In the A1C1 group it was detected 8 days after surgery and was then maintained with a maximum that represented up to a 60% increase over the basal value. In the A2C2 group the activation was slightly delayed and less marked. Increase in ACTH level occurred much earlier: it was about 70% of the maximal level already 4 days following adrenalectomy. The tyrosine hydroxylase activity measured in vitro with saturating concentrations of substrate and cofactors, was not affected by adrenalectomy. Daily injection of dexamethasone prevented the increase in plasma ACTH as well as the increase of the in vivo tyrosine hydroxylation rate in the medullary CA groups triggered by adrenalectomy. This activation is thus likely to be mediated by type II glucoreceptors and does not seem to involve an increase of the tyrosine hydroxylase content but rather other regulatory processes of the hydroxylation step in vivo. While the brain stem CA neurons are known to participate in the control of the hypothalamo-pituitary axis, their delayed activation following adrenalectomy suggests that they are not directly involved in the early increase in plasma ACTH level triggered by the lack of circulating corticosteroids.

ISSN:0028-3835    

DOI:10.1159/000126219

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

To investigate the role of amino acid neurotransmitters in the regulation of LH secretion in ovariectomized (ovx) rats with or without estrogen substitution, we measured the release rates of γ-aminobutyric acid (GABA), taurine, glycine, aspartate, glutamate, homocysteic acid, and also of the neurally inactive amino acids serine and glutamine in push-pull perfusate samples of the preoptic/anterior hypothalamic area (PO/AH) collected at 30-min intervals. To achieve this we had to develop a highly sensitive assay utilizing phenylisothiocyanate prederivatization which was followed by HPLC chromatography. In confirmation of our earlier results we observed again a conspicuous drop of preoptic GABA release prior to and during the time of estrogen-induced LH surge. In addition, the release rates of the excitatory amino acid neurotransmitters aspartate and glutamate in the PO/AH increased during this time. Interestingly, also secretion of taurine and glycine was increased during the LH surge, whereas preoptic release rates of serine and glutamine and of homocysteic acid, the putative endogenous ligand of the so-called N-methyl-D-aspartate receptor, remained unchanged. No such changes of amino acid neurotransmitters release rates were observed in ovx rats. This finding underlines that the changes of amino acid secretion in ovx estrogen-primed rats are likely due to the influence of the steroid rather than due to a diurnal rhythm. We conclude that GnRH neurons are under a tonic inhibitory tone exerted by GABA which is relieved during the time of the estrogen-induced LH surge. During this time, aspartate and glutamate may have additional stimulatory effects on GnRH neurons. The unchanged preoptic release rates of the neurally inactive neurotransmitters serine and glutamine give evidence for the selectivity of the observed effects

ISSN:0028-3835    

DOI:10.1159/000126220

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The effect of activation of central γ-aminobutyric acid β (GABAB) receptors on pulsatile luteinizing hormone (LH) secretion was examined in unanesthetized ovariectomized rats. Intraventricular injections of 2 or 10 µg baclofen, a selective GABAB receptor agonist, usually arrested the existing pulsatile LH secretion for a short period, then LH pulses resumed with reduced frequencies and increased amplitudes. The increase in the pulse amplitude was not necessarily accompanied by a reduction in the pulse frequency, but was observed even after nonelongated interpulse intervals in animals receiving the GABA agonist. Mean LH levels showed complex bi- and triphasic fluctuations after the central administration of high and low doses of baclofen, respectively. It was concluded that central GABAB receptors are involved in the modulatory mechanism affecting the LH pulse frequency and amplitude in the ovariectomized r

ISSN:0028-3835    

DOI:10.1159/000126221

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

In order to analyze the feedback action of prolactin (PRL) on the hypothalamus on the cellular level, we used primary cultures of rat embryonic diencephalon to measure the calcium response of individual neurons to PRL by means of fast fluorescence photometry. The cultures were subsequently stained with antibodies against the neuronal marker MAP-2, glutamic acid decarboxylase (GAD) or tyrosine hydroxylase (TH). PRL caused a rapid rise of intracellular free Ca2+ in a specific type of GABAergic neuron characterized by a spindle-shaped bipolar morphology and immunoreactivity to MAP-2 and GAD but not to TH. It is concluded that a subpopulation of hypothalamic GABAergic but not dopaminergic neurons react to PRL with a rapid increase in intracellular free Ca2+. These data are compatible with the assumption of a rapid negative feedback regulation of the secretion of PRL from the pituitary mediated by tuberoinfundibular GABAergic neurons.

ISSN:0028-3835    

DOI:10.1159/000126222

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The role of α1-adrenergic receptors in the secretion of corticotropin-releasing hormone (CRH) during stress was studied by immunohistochemical analysis of the CRH content of the median eminence (ME) after intracerebroventricular (icv) administration of the αi-adrenergic agonist, methoxamine, or the antagonist, prazosin, in rats pre treated with colchicine. Immunohistochemical staining was performed by the peroxidase technique on 40 µm free-floating sections using a polyclonal antibody specific for CRH. In the first experimental model, rats were implanted with icv cannulae and adapted to the experimental conditions by daily handling and icv injection of artificial CSF. Colchicine (75 µg) was administered through the cannulae 6 h before the experiment, conditions in which axonal transport was blocked with little change in basal immunostaining. Two hours after immobilization stress or a single injection of methoxamine (100 µg, icv), there was a marked decrease in CRH immunoreactivity throughout the ME, reflecting release of the neuropeptide into the portal circulation. The decrease in CRH immunostaining following immobilization was largely prevented by icv injection of the α1-adrenergic antagonist, prazosin. In the second experimental model, rats were sacrificed 48 h after icv colchicine injection, conditions in which colchicine acts as a stressor and causes marked depletion of irCRH from the ME. This chronic effect of colchicine was also partially prevented by administation of prazosin, 400-ng injection 5 min prior to colchicine, followed by a continuous icv mini-pump infusion of prazosin, indicating that αi-adrenergic stimulation contributes to the action of colchicine. In addition, the increase in the number and immunodensity of CRH cell bodies in the paraventricular nucleus typically observed following 48 h colchicine treatment was markedly reduced by prazosin administration, suggesting that αi-adrenergic stimulation causes an increase in peptide synthesis as well as release. These results indicate that central α1-adrenergic mechanisms are an important component in the regulation of hypothalamic CRH secretion durin

ISSN:0028-3835    

DOI:10.1159/000126223

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Insulin-like growth factor II (IGF-II) peptide, mRNA, and receptors are widely distributed in the central nervous system, yet the physiological role of IGF-II in brain remains largely unknown. In the present study, we examined the in vivo effects of central administration of recombinant human IGF-II on pulsatile GH secretion and food intake. The IGF-II preparation used was shown to stimulate 3H-thymidine incorporation in MG-63 human osteosar-coma cells in vitro. Free-moving adult male rats bearing chronic intracerebroventricular (icv) and intracardiac venous cannulae were icv administered 10 µl of either IGF-II (in doses of 300 ng and 1 µg) or the vehicle solution, and blood samples were obtained every 15 mm for 6 h. Vehicle-injected control animals exhibited the typical pulsatile pattern of GH secretion with most peak GH values greater than 100 ng/ml and trough levels less than 1.2 ng/ml. Central administration of IGF-II, at both doses, failed to alter the spontaneous 6-hour GH secretory profile; there were no significant differences in either GH peak amplitude, GH trough level, GH interpeak interval, or mean 6-hour plasma GH level, compared to vehicle-injected controls. There was also no effect of icv administered IGF-II on mean plasma glucose or insulin levels. Compared to vehicle-injected control rats, the icv injection of IGF-II (at doses of 300 ng and 1 µg) did not significantly alter 24-h food intake or body weight gain in normal feeding rats. Furthermore, IGF-II icv, at both doses, had no effect on short-term food consumption in rats exposed to a 17-h period of food deprivation. Taken together, these findings do not provide evidence to support a physiological role for IGF-II in feedback regulation of pulsatile GH secretion at the level of the brain, or in the central control of food inta

ISSN:0028-3835    

DOI:10.1159/000126224

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Brain angiotensin II (AII) receptors play a role in the regulation of luteinizing hormone release. This action is thought to involve luteinizing hormone-releasing hormone containing neurons in the preoptic-anterior hypothalamic (POAH) area of the brain. Previous studies have demonstrated a discrete locus of AII receptor binding sites and responsiveness within the POAH to microinjections of AII in the adult female rat, corresponding to the ventral portion of the bed nucleus of the stria terminalis (BSTV). To further characterize the age- and sex-dependent AII receptor binding in the BSTV and other brain regions, in vitro receptor autoradiography using 125I-sarcosine1, isoleucine8 AII (125I-SI AII) was performed on 2-, 4- and 10-week-old female and male rat brains. Rats of both sexes displayed an age-dependent increase in 125I-SI AII binding in the BSTV, as well as in the suprachiasmatic nucleus (SCh). There was no detectable difference in binding within the BSTV between the female and male of any age group. Prepubertal ovariectomy did not impair the expression of 125I-SI AII binding in the BSTV or the SCh of adult female rats. The developmental expression of AII receptors in the BSTV and SCh may therefore play a role in sexual maturation and regulation of sexual function in the rat.

ISSN:0028-3835    

DOI:10.1159/000126225

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

A significant number of pro-opiomelanocortin (POMC)-containing cells were detected in the rat median eminence (ME) by immunocytochemistry using an antibody raised against a synthetic peptide corresponding to the cleavage site between adrenocorticotropin and β-lipotropin moieties. Distribution of POMC-positive cells was restricted to the internal zone of the anterior parts of the ME. Such cells were observed as early as the 14th day of gestation in the area of the primitive ME, long before glial fibrillary acidic protein-positive cells appeared postnatally in this structure. Dissociated cell cultures obtained from the ME of 1-day-old rats produced cells immunoreactive for neurofilaments and the POMC moiety. Such cells displayed a neuronal morphology: the cell body was oval (13–18 µm) with long and fine beaded fibers. These findings clearly demonstrate the early appearance of POMC neurons in the developmental ME, a target organ of the hypothalamic infundibular neur

ISSN:0028-3835    

DOI:10.1159/000126226

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

In aggregate cell cultures of 15- to 20-day-old rat pituitary maintained in serum-free medium, luteinizing hormone-releasing hormone (LHRH) (10 nM) stimulated prolactin (PRL) release, confirming our previous results and those of others with serum-supplemented medium. Since angiotensin II (AII) stimulates PRL release and a renin-angiotensin system is expressed in gonadotrophs, LHRH stimulation of PRL release might be mediated by AIL To evaluate this hypothesis, the influence of (Sar1, Ala8)AII and (Sar1, Ile8)AII two peptide AII receptor antagonists, of DUP753, a nonpeptide and stable AII receptor antagonist, of a converting enzyme inhibitor, and of angiotensinogen on LHRH-induced PRL release was tested in various in vitro conditions of 15- to 20-day-old female rat pituitary. In aggregates maintained in serum-free medium with or without dexamethasone (DEX) and triiodothyronine (T3), or maintained in serum-supplemented medium, the effect of LHRH on PRL release was not affected by (Sar 1 Ala8)AII (0.1 µM), (Sar1, Ile8)AII (10 µM) or DUP753 (10 µM). Only a high dose (10 µM) of (Sar1, Ala8)AII attenuated the LHRH-induced PRL release. The latter attenuation was seen only with aggregates cultured in the DEX/T3 medium and not with aggregates cultured in the presence of serum. A dose of 1 or 10 nM (Sar1, Ala8) AII also failed to block the effect of LHRH used at 1 nM. In contrast, (Sar1, Ala8) AII dose dependently as well as DUP753 (10 µM) abolished the AII-induced PRL release. (Sar1, Ala8)AII also failed to affect the LHRH-induced PRL release in pituitary cell aggregates from 6-week-old male rats. However, in aggregates from both immature and 6-week-old rats, (Sar1, Ala8) AII provoked a small and statistically significant attenuation of the LHRH-induced PRL release when a 100 nMdose of LHRH was used. In freshly isolated hemipituitaries from 5-day-old rats, (Sar1, Ala8) AII (1 or 10 µM) did not affect the LHRH- (10 nM) induced PRL release. In single cells obtained by redispersion of aggregates and mounted in a Biogel P2 column, LHRH still stimulated PRL release. Again this effect could not be blocked by DUP753. Treatment of aggregate cell cultures with the angiotensin-converting enzyme inhibitor captopril or with angiotensinogen did not alter the LHRH-induced PRL release. It is concluded that AII is not the paracrine factor mediating the effect of LHRH at low nanomolar doses on PRL release, at least not through the classical AII receptor. The involvement of AII acting on a non-(Sar1Ala8) AII-sensitive receptor cannot be excluded and warrants further investig

ISSN:0028-3835    

DOI:10.1159/000126227

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Previous studies have indicated that during the estradiol- and progesterone (P4)-induced surge in luteinizing hormone (LH), the effects of opiates on behavioral, autonomic and neuroendocrine functions are altered. In the present study, we further evaluated the apparent universality of alterations in opiate-mediated function during the LH surge by investigating the effects of morphine sulfate (MS) on prolactin (PRL) secretion during both the estradiol benzoate (EB) and the EB + P4-induced LH surges. All doses of MS tested (0.5, 2.0 and 5.0 mg/kg) resulted in significant increases in PRL secretion in nonestrogen-treated animals which did not show LH/PRL surges. During the LH/PRL surge induced by EB/P4 treatment, MS caused no change in the PRL secretion, while in EB/oil treated animals, a paradoxical and dose-dependent decrease in PRL secretion was observed. The suppression of PRL was 52, 68 and 80% of baseline respectively for the 3 doses of MS. Evaluation of the time dependence of MS on PRL secretion showed that the paradoxical suppression in EB/oil-treated animals was seen only during the LH/PRL surge, occurring at 17.30 h (7.5 h post P4 injection), and not before (12.30 h) or after (23.00 h) the steroid-induced LH/PRL surge. Finally, we assessed the role of pituitary dopamine receptors on the phenomenon of MS-induced PRL suppression in EB/oil rats. Domperidone (1 mg/kg), a peripherally active D2 receptor antagonist, administered prior to the morphine challenge, attenuated the opiate-induced PRL suppression in EB/oil-treated animals suggesting that a dopaminergic mechanism is involved in this paradoxical response to morphine.

ISSN:0028-3835    

DOI:10.1159/000126228

出版商:S. Karger AG    

年代:1992

数据来源: Karger