摘要:

Estrogen target neurons are numerous in the medial preoptic/anterior hypothalamic area (MPO/AH) of the female rat brain, and they are thought to play a crucial role in reproductive functions. This brain region is also known to contain high concentrations of the inhibitory transmitter gamma-aminobutyric acid (GABA) and of its synthesizing enzyme glutamate decarboxylase (GAD). Since it is known that GABA is involved in the regulation of gonadotropin release from the pituitary gland it has been proposed that estrogen feedback may be mediated by this transmitter. Here we show, by a combined method of estrogen autoradiography and GAD immunocytochemistry, that estrogen-receptive neurons of GABAergic nature exist in the MPO/AH.

ISSN:0028-3835    

DOI:10.1159/000124500

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The effect of dehydration on dopamine (DA) release from the neural and intermediate lobes of the rat pituitary gland after electrical stimulation of the pituitary stalk was studied in vitro. The amount of DA released from pituitary lobes of dehydrated rats (no water for 72 h), in which the hormone secretion from the hypophysis, especially the neural lobe, is known to be greatly enhanced, was significantly higher when compared with that from control tissues. In control and dehydrated rats the evoked DA release from the intermediate lobe was higher than that from the neural lobe. After dehydration, the stimulus-evoked DA release from the neural lobe increased by more than 200%, whereas that from the intermediate lobe increased by only 60%, indicating a preferential activation of the DA system of the neural lobe. There was a decrease in DA released per pulse from the combined neuro-intermediate lobe of control rats with increasing number of stimulation pulses. In contrast, DA release per pulse from the neuro-intermediate lobe of dehydrated rats showed a tendency to increase with increasing number of pulses. As the availability of newly synthesized DA is believed to be the limiting factor for transmitter release, the present observations suggested a higher in vitro DA synthesis rate in the tissues from dehydrated rats. This agrees with in vivo results of Alperand his colleagues who found an increased accumulation of L-3,4-dihydroxyphenylalanine (DOPA) in neuro-intermediate lobes of dehydrated rats after inhibition of DOPA-decarboxylase.

ISSN:0028-3835    

DOI:10.1159/000124501

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Previous research has shown that electrolytic lesions of the anterior arcuate nuclei combined with anterior hypothalamic deafferentation (AHD) blocked pulsatile luteinizing hormone (LH) release in the ovariectomized rat, but that neither lesion was sufficient by itself. This led to the hypothesis that two separate neural pathways were capable of effecting pulsatile LH secretion, which was tested in another way in the present study. Newborn rats were injected with monosodium glutamate (MSG), a treatment which damages the arcuate nuclei, or NaCl of the same osmolarity as a control. As adults, the rats were gonadectomized and 2 weeks later, AHD or sham AHD was performed. One week after that, the rats were catheterized, and small blood samples were taken every 5 min for 3 h. Plasma was assayed for LH by radioimmunoassay. Neither MSG alone, AHD alone, nor the combination affected the number of animals with pulsatile LH patterns. In female rats, MSG treatment slightly decreased pulse frequency, while AHD depressed mean LH levels in male rats. No differences were seen in LH pulse amplitude. These results suggest either that MSG spares those neurons of the arcuate nuclei which are important for LH secretion, that electrolytic lesions of the arcuate nuclei destroy fibres of passage which are important for LH release, or that functional reorganization of the systems controlling LH release occurs following neonatal MSG treatment.

ISSN:0028-3835    

DOI:10.1159/000124502

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Sympathetic nerves innervate smooth muscle cells in the theca externa of Graafian follicles and induce contraction of the follicle wall. The interaction of prostaglandins (PGs) with the function of this neuromuscular complex has been elucidated by the use of isolated strips from the protruding part of the wall of bovine ovarian follicles. PGF2α contracts the strips, and it also potentiates the contractile response to electrical field stimulation of the nerves, but it has no effect on noradrenaline-induced contractions. PGE1 and PGE2 have direct relaxatory actions on the strip preparation (previously given an active contraction by carbamylcholine) and in high doses they, therefore, reduce the contractile response induced by noradrenaline. In low doses not affecting the noradrenaline response, PGE1 and PGE2 both decrease the amount of contraction induced by electric nerve stimulation, indicating an inhibitory action of the PGEs on the transmitter release. It is suggested that the role of PGs in the process of ovulation might, at least partly, be mediated by their interactions with smooth muscle cells and their sympathetic innervation in the wall of the Graafian follicle

ISSN:0028-3835    

DOI:10.1159/000124503

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

In order to assess the effect of pinealectomy (Px) on the diurnal rhythmicity of gamma-aminobutyric acid(GABA) high affinity binding to cerebral cortex membranes, groups of intact, Px or sham Px rats (subjected to surgery 15 days earlier) were killed at six different time intervals during the 24-hour cycle. GABA binding was estimated by Scatchard analysis of 3H-GABA binding to cerebral cortex membranes prepared from individual brains; only one type of binding site with dissociation constant (KD) about 20–50 nM and site number (Bmax) about 200–500 fmol/mg protein was apparent in the assay conditions employed. In intact and sham Px rats Bmax attained minimal values at night and increased during daylight. Px increased generally Bmax and disrupted its normal diurnal rhythmicity, a peak in Bmaa being observed at midnight. A significant decrease of GABA high affinity binding affinity was detected at morning hours in intact rats and at late scotophase and morning hours in Px and sham Px rats. Bmax of GABA high affinity binding in Px rats attained maximal values by 5–10 days after surgery and decreased somewhat 5 days later. Sham Px rats exhibited a transient increase in Bmax up to 10 days after surgery, returning to normal values by the 15th day. Superior cervical ganglionectomy increased binding affinity up to 15 days after surgery without affecting Bmax. The minimal melatonin effective dose to counteract Px-induced increase of GABA high affinity binding was 25 µg/kg body weight when given 3 h before sacrifice. Melatonin activity on GABA binding did not depend upon a direct effect on the binding sites, as shown in vitro. These results suggest a link between pineal function, melatonin secretion and GABA receptor activity i

ISSN:0028-3835    

DOI:10.1159/000124504

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

In order to investigate mechanisms underlying the ovarian steroid action on hypothalamic luteinizing hormone-releasing hormone (LHRH) neurons, LHRH and a higher immunoreactive molecular form (MW 1,800 daltons) of the decapeptide were immunoassayed with antibodies of different specificities in hypothalamic subcellular fractions, after molecular sieve filtration on Biogel P4 columns equilibrated with 0.2 Nacetic acid containing 0.02% sodium azide. The study was performed in ovariectomized (OVX), ovariectomized estradiol-implanted (OVX + E2) or OVX -l- E2 progesterone-treated rats (OVX + E2 + P). The animals were killed before or during the circadian luteinizing hormone (LH) surge. The amount of LHRH-like immunoreactivity recovered from the synaptosomal fraction was slightly increased in OVX + E2-implanted animals but very markedly augmented in OVX + E2 + P-treated rats. In contrast, the higher molecular form recovered from a high-speed supernatant was markedly decreased in OVX + E2 + P-treated rats when compared to the other groups. At the time of maximal LH release induced by E2 + P administration, hypothalamic LHRH was markedly depleted, whereas the larger molecular form was notably augmented. The data suggest that ovarian steroids not only influence release of hypothalamic LHRH but also the processing of LHRH precursor forms.

ISSN:0028-3835    

DOI:10.1159/000124505

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

In order to establish the in vivo specificity of the mineralocorticoid recognition system of the rat brain, we investigated the potencies of aldosterone (ALDO) and corticosterone (CORT) in suppressing salt intake in adrenalectomized (ADX) rats. Increasing doses of ALDO (25, 50 and 100 ng/h), administered by Alzet minipump, suppress salt intake in a two-bottle preference test. CORT in doses up to 50 µg/h failed to mimic this effect of ALDO or to block it. Using the 50 µg/h dose of CORT, we demonstrated that the forebrain uptake of 3H-ALDO in vivo is suppressed by 60–75% when measured by isolation of cell nuclei or by quantitative autoradiography. The suppression is especially marked in the hippocampal formation, amygdala and septum, sites which also accumulate high levels of 3H-CORT. The uptake of 3H-ALDO by ADX rat forebrain can be suppressed approximately 95% by infusion of a specific antimineralocorticoid, RU 28318, at a dose of 50 µg/h. This dose also blocks ALDO action on salt intake. Lower doses of RU 28318 fail to block ALDO action or brain 3Η-ALDO uptake. We conclude that: (1) ALDO is at least 500-fold more potent in vivo than CORT as a mineralocorticoid. (2) High uptake of 3H-ALDO in vivo by hippocampal formation, amygdala and septum in ADX rats is due in large part to binding to sites preferentially suppressed by CORT. The 3H-ALDO uptake (ca. 30%) after suppression by stress levels of CORT shows a regional distribution in which uptake is slightly higher in circumventricular structures than in hippocampal formation, septum or amygdala. (3) The action of ALDO to suppress salt intake in ADX rats is, at least in part, a central action of the ho

ISSN:0028-3835    

DOI:10.1159/000124506

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Anterior pituitary quarters were incubated in vitro and the release of β-endorphin-like (β-End-IR) and adrenocorticotropin-like immunoreactivity (ACTH-IR) was determined. The effect of phospholipase A2 as well as the effect of various compounds known to influence arachidonic acid metabolism under certain conditions were examined. Phospholipase A2 increased the release of β-End-IR and ACTH-IR. This effect was reversible, concentration-dependent (1–400 ng/ml) and inhibited in calcium-free medium and in the presence of CoCl2 (5 mM) or phospholipase A2 inhibitors (p-bromophenacylbromide, 21 µM; mepacrine, 1 mM). The phospholipase A2-induced β-End-IR release was accompanied by the release of prostaglandin E2. Inhibition of cyclooxygenase activity by indomethacin (14 or 140 µM) did not change β-End-IR release induced by phospholipase A2 (5 ng/ml). The effects of blockers of lipoxygenase (nordihydroguaiaretic acid, NDGA; AA861) or lipoxygenase plus cyclooxygenase (BW755C; eicosatetraynoic acid, ETYA) on phospholipase A2-induced release of β-End-IR were diverse. BW755C (up to 250 µM) and AA861 (up to 100 µM) produced no effect. However, NDGA or ETYA inhibited phospholipase A2-induced β-End-IR release. NDGA (100 µM) produced a maximum inhibition by about 40% (p < 0.05), whereas ETYA (100 µM) produced a maximum inhibition by about 85% (p < 0.001). These data are consistent with the view that phospholipase A2 releases endogenous arachidonic acid which is transformed into products which stimulate ACTH and β-endorphin release from the corticotrophs; the metabolizing enzyme (possibly a lipoxygenase or epoxygenase) is sensitive to NDGA and esp

ISSN:0028-3835    

DOI:10.1159/000124507

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Chronic estrogen treatment has been shown to produce a marked reduction in anterior pituitary angiotensin II (AII) receptor density. In order to determine whether this effect is generalized, we studied the effect of chronic estradiol treatment on AII receptor density in the anterior pituitary gland, adrenal cortex and mesenteric artery of ovariectomized (OVX) rats. Treated rats were injected daily with 25 µg of estradiol valerate while controls received only the vehicle. Binding affinity and density of AII receptors were measured using the AII antagonist [125I]-Sar1Ile8 AII ([125I]-SARILE). Following 7-, 14- or 28-day treatments, AII receptor density decreased by approximately 80% in the anterior pituitary; 30% in the adrenal cortex and remained the same in mesenteric artery particulate fractions. In all 3 target tissues, dissociation constants (KD) for binding of [125I]-SARILE were in the nanomolar range and were the same between control and treated rats. Using conscious rats, estradiol treatment for 7 days was also shown to block the release of aldosterone by low dose infusions of AII (10 ng/min, 30 min). Plasma AII and plasma renin activity were also the same or slightly decreased following estradiol treatments. This study suggests that estrogens may be important modulators of the AII receptor and may be directly involved in modulating target cell responsiveness to AII as expressed through differential down-regulation of AII receptors

ISSN:0028-3835    

DOI:10.1159/000124508

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Intraventricular (i.c.v.) administration of β-endorphin (β-END) has been shown to suppress lordosis behavior in ovariectomized (OVX) estrogen-progesterone (EP) primed rats, but the behavioral specificity of this effect is not known. Using OVX EP-primed rats, the present study assessed the effect of i.c.v. β-END on proceptive behavior as well as on lordosis (receptive) behavior, and attempted to discern whether the sexual effects were secondary to generalized nonspecific behavioral effects. Doses of 0.5–4 µg β-END (human) significantly suppressed lordosis behavior. Doses of 1 and 4 µg were used in experiments which measured proceptive behaviors (presentations and ear wiggling), and both doses abolished or nearly abolished the display of these behaviors. Administration of inactive peptide (a protein digest) had no effect on sexual behavior. Neither 1 nor 4 µg β-END elicited measurable catalepsy. In a series of tests for responsiveness to general somatosensory stimuli, 1 µg had no effect on responsiveness while 4 µg had minor effects, even though sexual activity was severely diminished after both doses. Blood pressure was unaltered by infusion of β-END (1 µg), although there was a significant reduction in heart rate. When open field behavior was tested in conjunction with sexual behavior, ambulation and rearing were significantly decreased after β-END treatment as compared with saline treatment. However, simple linear correlation tests showed a lack of correlation between the changes in open field behavior and the changes in sexual behavior, indicating that the effects of β-END on the two types of behavior may be unrelated. These results extend previous observations by more fully characterizing the effect of i.c.v. β-END on sexual behavior of the female rat. Although the sexual effects of β-END are not completely specific, the results indicate that the sexual suppression is not secondary to a generalized behav

ISSN:0028-3835    

DOI:10.1159/000124509

出版商:S. Karger AG    

年代:1986

数据来源: Karger