ISSN:0028-3835    

DOI:10.1159/000126504

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

We have previously shown that the abilities of the two native goldfish GnRHs, salmon GnRH (sGnRH) and chicken GnRH II (cGnRH II), to stimulate gonadotropin (GtH) secretion and elevate intracellular Ca2+ levels are mimicked by the protein kinase C (PKC) stimulators, 1,2-dioctanoylglycerol (DiC8) and 12-O-tetradecanoyl phorbol-13-acetate (TPA). The ability of PKC inhibitors to attenuate GnRH-stimulated GtH secretion was also demonstrated. In the present study, the involvement of PKC was examined through the reduction of cellular PKC levels by prolonged preincubation of the cells with TPA (TPA desensitization). TPA pretreatment reduced the levels of PKC in fish pituitary cells as measured by immunoblotting (Western blot). Pretreatment of dispersed goldfish pituitary cells in static culture with TPA abolished the GtH responses to sGnRH, cGnRH II and ionomycin, and drastically reduced TPA-and DiC8-stimulated GtH release, but had no major effect on forskolin-induced GtH release. TPA pretreatment also reduces the cell content of GtH in goldfish pituitary cells. Interestingly, treatment with all of the pharmacological secretagogues tested led to a decrease in cellular contents of GtH, however, the two native GnRHs had no such effect. In rapid column perifusion experiments (1-min fractions), the GtH responses induced by both native GnRHs were characterized by an initial acute increase in hormone secretion followed by a ‘plateau’ phase which is smaller in magnitude relative to the initial phase. TPA pretreatment of perifused cells greatly reduced both the peak and plateau phases of sGnRH- and cGnRH II-stimulated GtH secretion; TPA-induced GtH release is also greatly attenuated. In contrast, forskolin-stimulated GtH release was enhanced by TPA desensitization. The ability of fors-kolin to stimulate GtH release at similar (in static culture) or enhanced (in column perifusion) levels following TPA desensitization, despite a reduction in cell content of GtH, strongly indicates that the reduced GtH response to sGnRH and cGnRH II following TPA pretreatment is not due to a simple reduction in the availability of releasable GtH. Additionally, the magnitude of decreases in cellular contents of GtH was not sufficient to totally account for the inhibition of GnRH action observed in the PKC-depleted cells. These results strongly suggest that PKC plays an important role in both acute and prolonged GnRH-stimulated GtH secretion in the goldf

ISSN:0028-3835    

DOI:10.1159/000126505

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

In order to evaluate the participation of amino acid neurotransmitters (AANT) in pubertal development, we measured the preoptic release rates of glutamate (Glu), aspartate (Asp), homocysteic acid (HCA), γ-aminobutyric acid (GABA), glycine (Gly), and taurine (Tau) in female rats aged 26, 35 and 42 days. Push-pull cannulae were implanted in the preoptic area (POA) after reinforcing the os calvarium by cementing a slightly curved 2-mm thick polyethylene plaque. Four days later, 120-min perfusion experiments (0–90 min: artificial CSF; 90-120 min: CSF containing 50 mM KC1) were performed. Amino acid concentrations were measured in 15-min fractions after derivatization with phenylisothiocyanate, using reverse-phase high-performance liquid chromatography and UV detection. Rats aged 42 days showed significantly (p < 0.01) higher preoptic Asp release rates, as compared to 26-day-old rats; Glu output increased significantly (p < 0.05) in animals aged 35 and 42 days, as compared to 26-day-old rats. No significant changes in HCA release were observed. Preoptic release rates of GABA, Gly and Tau were significantly higher in 26-day-old animals as compared to 35-day-old (GABA, p < 0.05) and 35- and 42-day-old rats (Gly, Tau, p < 0.01). Basal release of Asp, Glu, HCA, Tau and GABA, but not of Gly, was significantly stimulated (p < 0.05) by KC1 in all age groups. It is suggested that in peripubertal female rats, increased preoptic Asp and Glu release rates and decreased GABA and Tau output might enhance luteinizing hormone-releasing hormone secretion. This effect could be one of the mechanisms leading to the first preovulatory LH sur

ISSN:0028-3835    

DOI:10.1159/000126506

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

The reuptake of dopamine into nerve terminals is the primary mechanism of inactivation of this neurotransmitter in the synaptic cleft. We report sex differences and estrous cycle variations of rat striatal dopamine uptake sites. During the estrous cycle, peak density of striatal dopamine uptake sites labelled with [3H]GBR-12935 occurred in the morning of proestrus in coincidence with peak dopamine, serotonin, dihydroxyphenylacetic acid and 5-hydroxytryptophan levels pointing to a presynaptic effect of gonadal hormones. Striatal homovanillic acid and 5-hydroxyindoleacetic acid levels as well as [3H]GBR-12935 binding affinity remained unchanged throughout the estrous cycle. The density of [3H]GBR-12935 striatal binding sites was lower in ovariectomized rats compared to intact female rats during the estrous cycle, whereas it was similar in gonadectomized male rats, intact male rats and ovariectomized rats. Binding affinity was in general similar for all the groups of rats examined. The affinity of dopamine for striatal [3H]GBR-12935 binding sites was similar in males and ovariectomized females, and did not change during the female estrous cycle. In summary, striatal dopamine uptake site density was lower in male compared to intact female rats and was shown to fluctuate during the female estrous cycle. These results suggest that gonadal hormones could influence the activity of psychoactive drugs acting on neuronal dopamine uptake sites.

ISSN:0028-3835    

DOI:10.1159/000126507

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

The onset of puberty is heralded by an increase in pulsatile LHRH release. Since neuropeptide Y (NPY) has been implicated as a major regulator in the control of pulsatile LHRH release in mature monkeys, we have hypothesized that maturational changes in the NPY neuronal system play an important role in puberty. To test this hypothesis, three experiments were conducted in female rhesus monkeys using a push-pull perfusion method. In the first experiment, changes in NPY release in the stalk-median eminence (S-ME) during puberty were determined in 9 prepubertal, 7 early pubertal and 8 midpubertal monkeys. NPY and LHRH levels were measured in aliquots of the same perfusate samples obtained from the S-ME. NPY release was pulsatile in all three groups. Mean NPY release and pulse frequency increased significantly from the prepubertal through the midpubertal stage. These developmental changes in NPY release were parallel to those observed for LHRH release in the same monkeys. In order to examine whether NPY infusion into the S-ME influences LHRH release during puberty, in the second experiment, NPY (10-6 or 10-8M) or vehicle was infused into the S-ME for 10 min at 90-min intervals in 5 prepubertal and 9 midpubertal monkeys. In the midpubertal stage, infusion of NPY at doses of 10-8 and 10-6M resulted in significant (p < 0.01) increases in LHRH release, while vehicle administration had no effect. In contrast, in prepubertal monkeys, neither NPY nor vehicle infusion altered LHRH release. In order to test whether endogenous NPY plays a role in the maintenance of pulsatile LHRH release, in the third experiment, a specific antiserum to NPY (aNPY) was infused into the S-ME of 6 prepubertal and 8 midpubertal monkeys. Infusion of aNPY (1:100, 1:1,000 dilution) significantly suppressed LHRH release in midpubertal but not prepubertal monkeys. The results are summarized as follows. (1) In prepubertal monkeys, NPY release is low, and the presence of NPY in the S-ME does not influence LHRH release. (2) At the onset of puberty, NPY release begins to increase, and NPY probably starts to stimulate LHRH release. (3) In the midpubertal period, NPY release increases further, and NPY in the S-ME is highly stimulatory to LHRH release. (4) Immunoneutralization of endogenous NPY suppresses pulsatile LHRH release during the midpubertal period but not the prepubertal period, suggesting that a developmental change in the sensitivity of the LHRH neurosecretory system to NPY occurs sometime after the onset of puberty, and that endogenous NPY is important for pulsatile LHRH release during puberty. It is concluded that the regulation of LHRH release by NPY is a contributing factor for the onset of puberty in female rhesus monkeys.

ISSN:0028-3835    

DOI:10.1159/000126508

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

A series of experiments were conducted to elucidate the role of the ovary in incubation behavior-associated luteinizing hormone (LH) suppression. Ovariectomy (Ovx) increased (p induced LH in incubating hens, but enhanced the LH response in laying hens. Serum LH and prolactin (Prl) were unaffected by Ovx, and nest deprivation (ND) decreased Prl levels (p < 0.05) with no effect on serum LH of incubating turkeys. However, serum LH increased (p < 0.05) and Prl decreased in Ovx-ND birds. Prl mRNA abundance (11.9 ± 1.2 ng/µg total RNA) decreased following Ovx (3.4 ± 0.4ng/µg total RNA) or ND (3.6 ± 0.5 ng/µg total RNA). Nest deprivation increased LHβ mRNA (2.5-fold) which was further increased (4.8-fold) by Ovx. Hypothalamic GnRH-I and GnRH-II contents increased (p < 0.05) in Ovx-ND turkeys. We conclude that serum LH suppression during incubation behavior requires ovarian participation acting synergistically with elevated Prl and/or nesting stimulus on hypothalamic GnRH, and that the concentration fo LHβ mRNA may be a limiting factor in LH s

ISSN:0028-3835    

DOI:10.1159/000126509

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

Stimulation of the rat hypothalamopituitary-adrenal axis during stress involves activation of central α1-adrenergic receptors. The subpopulation of corticotropin-releasing hormone (CRH) neurosecretory cells that contains vasopressin (VP) is selectively activated by several types of stress (immobilization, hypoglycemia, and intracerebroventricular, i.c.v., colchicine), and is located in a catecholamine-rich area of the hypothalamic paraventricular nucleus. Therefore, we tested the hypothesis that the CRH+/VP+ subpopulation is selectively activated by central α1-adrenergic receptors. The α1-agonist methoxamine or vehicle alone was injected i.c.v. after habituation of rats to daily injections of vehicle through a chronic i.c.v. cannula. Activation of the CRH+/VP+ and CRH+/VP-subpopulations was measured by quantifying depletion of neurosecretory vesicles from immunocytochemically identified axons in the external zone of the median eminence. The habituated, vehicle-injected sham control group had normal levels of plasma ACTH and corticosterone, but possessed a significantly higher proportion of VP-containing CRH axons than naive animals. This change is similar to what was observed previously in rats subjected to repeated daily stress. I.c.v. methoxamine caused elevations of plasma ACTH and corticosterone and significant depletions of vesicles from the CRH+/VP+ axons at 1 and 2 h after injection, compared to the sham control group. The CRH+/VP-axons, however, displayed significant accumulations of neurosecretory vesicles at the same times after 300 µg methoxamine, compared to the sham control group. After 100 µg methoxamine, there was no change in the CRH+/VP-axons, compared to the sham control group. We interpret the accumulation of vesicles in the VP-deficient CRH neurosecretory axons after 300 µg i.c.v. methoxamine to reflect inhibition of this subpopulation after central α1-adrenergic receptor activation. The results demonstrate for the first time that central catecholamines induce release of both CRH and VP in the portal capillary plexus. These findings support the hypothesis that stress induces release of catecholamines from axons projecting to the paraventricular nucleus, thus activating α1-adrenergic receptors that selectively stimulate the VP-containing subpopulation of CRH neurosecretor

ISSN:0028-3835    

DOI:10.1159/000126510

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

In the present study we characterized the negative feedback effect of exogenous and endogenous glucocorticoids (GC) on the responses of the hypothalamo-pituitary-adrenal (HPA) axis to neural stimuli in male rats. Dexamethasone (Dex) was injected intraperitoneally at a dose of 0.5-4.0 µg/100 g BW and rats were exposed to photic or acoustic stress 3.5 h later. The serum ACTH and corticosterone (CS) responses to these stimuli were inhibited in a dose-dependent manner by Dex, such that the stress-induced response was completely abolished at a Dex dose of 4.0 µg/100 g BW. Injection of Dex (4.0 µg/100 g BW i.p.) did not affect the content of CRF-41 at the median eminence under basal conditions but prevented the depletion in CRF-41 content following acoustic and photic stimulation observed in vehicle-treated animals. Pretreatment with a subcutaneous injection of corticosteroid type I receptor antagonist RU-28318 (5 mg/100 g BW) did not affect the inhibition of the stress-induced adrenocortical response exerted by Dex; in contrast the type II receptor antagonist RU-38486 (5 mg/100 g BW) completely abolished the inhibitory effect of Dex following both types of neural stimuli. To investigate the role of type I and type II corticosteroid receptors in mediating the feedback effect of endogenous GC, the two receptor antagonists were injected intracerebroventriculary (100 ng/100 g BW). RU-28318 did not affect the response to photic stress at 10, 30 or 90 min following the stress, whereas RU-38486 caused a significant increase (∼40%) in serum ACTH and CS at all three time points tested. We conclude that the response of the HP A axis induced by neural stimuli is sensitive to inhibition by Dex, which is mediated by a reduction of CRF-41 release from the median eminence. In addition, the feedback effect exerted by exogenous or endogenous GC following neural stress appears to be mediated by type II GC recep

ISSN:0028-3835    

DOI:10.1159/000126511

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

Recently, we reported that rats exposed to a single and short session of inescapable footshocks showed alterations in behavioural response to environmental stimuli which developed progressively over a week and remained present for at least 28 days. The aim of the present study was to investigate whether these behavioural changes were accompanied by alterations in the brain-pituitary-adrenal axis. Male Wistar rats were subjected to 10 inescapable footshocks (S) of 6 s duration and 1 mA intensity during a period of 15 min. Control rats (C) were placed in the shock apparatus for 15 min without receiving shocks. The effects of these experimental procedures were studied 14 days later. Exposure to shocks did not affect basal plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone (CORT). However, the novelty-induced ACTH response was increased in S rats as compared to C rats whereas the CORT response did not differ between C and S rats. The ACTH content of the anterior pituitary gland and adrenal weight were not affected by exposure to inescapable footshocks 14 days earlier. Quantitative immunocytochemistry of vasopressin (AVP) and corticotropin-releasing factor (CRF) in the external zone of the median eminence showed that prior footshock exposure increased the AVPi stores to 167% as compared to C rats, whereas CRFi content was not changed. In addition, S rats showed increased mineralocorticoid (MR) and glucocorticoid (GR) receptor binding capacity in the hippocampus as compared to C rats, whereas affinities were not affected. We conclude that a single and short session of inescapable footshocks has long-lasting effects on brain-pituitary-adrenal functioning concomitant with behavioural alterations.

ISSN:0028-3835    

DOI:10.1159/000126512

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

The potential roles of central and peripheral 5-HT3 receptors in the secretion of prolactin, adrenocorticotropic hormone (ACTH), corticosterone and renin was investigated. Male rats received the 5-HT3 antagonist ondansetron (0, 0.1 or 1 mg/kg i.p.), 30 min prior to injections of the serotonin (5-HT) releaser, p-chloroamphetamine (PCA; 0, 3 or 8 mg/kg i.p.). Blood samples were collected 60 min after PCA for radioimmunoassays of plasma prolactin, ACTH, corticosterone and renin concentrations. PCA significantly elevated secretion of each of these hormones. Pretreatment with the 5-HT3 antagonist, ondansetron, significantly attenuated the PCA-induced elevation of prolactin secretion, suggesting that 5-HT3 receptors contribute to the serotonergic stimulation of prolactin secretion. Ondansetron did not modify effects of PCA on ACTH, corticosterone or renin secretion. To determine whether the 5-HT3 receptor role in prolactin secretion is mediated in the brain, the endocrine effects of intracere-broventricular (i.e.v.) injections of 5-HT (30 µg/kg) or the 5-HT3 agonist, 2-methylserotonin (1 20 or 200 µg/kg) were evaluated. Both 5-HT and 2-methyl-serotonin significantly elevated plasma prolactin levels 15 min postinjection. However, ondansetron (1 mg/kg i.p.) did not antagonize these actions. Both 5-HT and 2-methylserotonin also increased plasma ACTH and corticosterone concentrations. Finally, 5-HT suppressed, while 2-methylserotonin stimulated renin secretion. None of the hormonal effects of i.c.v. injected 5-HT or 2-methylserotonin were altered by ondansetron. Thus, the results suggest that peripheral, but not central 5-HT3 receptors are involved in the stimulation of prolactin secretion. Furthermore, 5-HT3 receptors do not mediate the serotonergic stimulation of ACTH, corticosterone, or renin secretio

ISSN:0028-3835    

DOI:10.1159/000126513

出版商:S. Karger AG    

年代:1993

数据来源: Karger