摘要:

The ontogenesis of growth hormone releasing hormone (GH-RH) containing neurons in the rat hypothalamus has been studied by immunohistochemistry, using a specific anti-rat GH-RH serum. Immunoreactive fibers were first detected in the prospective median eminence on day 18 of gestation. During the subsequent 3 days, they rapidly increased in distribution and intensity of staining within this structure. On day 21, positive fibers were also visible in a plexus within the arcuate nucleus. In 1-day-old rats treated with colchicine, positive perikarya were distributed in several hypothalamic nuclei, including the arcuate nucleus, dorsomedial nucleus, basal lateral hypothalamus, and perifornical region. The distribution was similar to that previously described in adult rats. The intensity of staining in the various hypothalamic regions increased during early postnatal life to levels nearly comparable to those in adult rats by 30 days. These findings showing the early appearance of GH-RH-positive terminals in the median eminence and the wide distribution of the perikarya at an early stage of postnatal life support the view that hypothalamic GH-RH serves an important role in the regulation of growth hormone secretion during late prenatal and early neonatal periods.

ISSN:0028-3835    

DOI:10.1159/000124579

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Estrogen-2/4-hydroxylase (E-2/4-H) activity was measured by a direct product isolation assay in punch biopsy specimens obtained from nine nuclear regions from forebrain of adult male rats. Tritiated catechol estrogens were isolated from incubations of tissues with [6,7–3H]estradiol from all regions studied. The amount of 4-hydroxyestradiol (4-OH-E2) formed equaled or exceeded that of 2-hydroxyestradiol (2-OH-E2). There were significant regional differences in the amounts of catechol estrogen produced. The difference was nearly 8-fold between the arcuate-median eminence (ARC-ME) and the medial preoptic nucleus (POM), regions with the highest and lowest specific activities, respectively (37.7 ±6.2 vs. 5.1 ±0.7 pmol/mg protein/10 min 2-OH-E2, mean + SEM, n = 6). The supraoptic nucleus was the site of second highest concentrations of E-2/4-H activity (20.3 pmol 2-OH-E2/mg protein/10 min). Estrogen-2/4-H activity in the paraventricular (PVN) and periventricular (PERI) nuclear regions, though only about half that in the SON, was significantly greater than in the remaining brain areas (nucleus interstitialis striae terminalis, caudate, anterior hypothalamic and medial preoptic nuclei and cortex. The ARC-ME, the region with the highest E-2/4-H activity is where the dopaminergic neurones and terminals from the Gn-RH neurons are concentrated. The functions regulated by these two classes of neurones, the secretion of prolactin and gonadotrophins, respectively, have been the subject of most of the previous studies aimed at establishing the role of catechol estrogen formation in the hypothalamus. The SON and PVN, additional sites with high E-2/4-H activity, are the regions where the magnocellular, oxytocinergic and vasopressinergic neurones are concentrated. These neurones, though recognized targets of estrogens’ action, have not been considered previously potential sites of catechol estrogen formation or as targets of their ac

ISSN:0028-3835    

DOI:10.1159/000124580

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The modulatory actions of ovarian steroids on the norepinephrine (NE) induced alterations in luteinizing hormone (LH) secretion were examined in male and female rats. Long-term (4 weeks) castrated male and female rats bearing chronic third-ventricle cannulae were implanted with intra-atrial catheters. Animals were bled sequentially at 5- or 15-min intervals for 4–6 h, and plasma LH secretory patterns were determined by radioimmunoassay. After a 2- to 3-hour control bleeding period, castrated unprimed rats received an intracerebroventricular (ICV) infusion of 0.3 µmol of arterenol bitartrate or vehicle. Blood sampling was continued for an additional 2–3 h after infusion. In female rats NE caused a rapid and potent inhibition of episodic LH secretion which was characterized by decreases in mean plasma LH, mean pulse amplitude, and pulse frequency. Similarly, ICV infusion of NE into male rats resulted in decreased mean plasma LH and pulse frequency. In a second series of experiments, castrated male and female rats were primed with estrogen and progesterone 2 days prior to the bleeding/infusion session. Animals were bled sequentially and infused with 0.3 µmol arterenol bitartrate or vehicle during a morning or afternoon session. ICV infusion of vehicle had no effect on plasma LH in either sex regardless of the time of day. NE infusion into estrogen and progesterone primed female rats resulted in significant elevations of plasma LH during both morning and afternoon periods. In estrogen and progesterone primed male rats, NE infusion resulted in a marked facilitation of LH release, similar to that observed in female rats. In both male and female groups afternoon infusion caused a slightly greater and longer lasting elevation in plasma LH than a similar morning infusion. These data demonstrate that ICV infusion of NE results in analogous inhibition of pulsatile LH secretion in both castrated male and female rats. In addition, this inhibitory effect of ICV infusion can be reversed by prior administration of estrogen and progesterone not only in female rats, but in male rats as well. This suggests that the neural mechanisms by which ovarian steroids modulate the noradrenergic regulation of LH secretion in female rats is also present in the mal

ISSN:0028-3835    

DOI:10.1159/000124581

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The frequency-dependence of secretion of arginine vasopressin (AVP) from the mouse neural lobe in vitro was studied and found to be comparable to that reported for the rat neural lobe in vitro. For a stimulus train of 600 pulses, the secretion of AVP per pulse (i.e., facilitation) increased to a maximum at 20 Hz. Compound intracellular action potentials were recorded from the mouse neural lobe using optical recording methods and potentiometric dyes. These extrinsic optical signals reflect the true time courses of transmembrane potential changes (e.g., action potentials), and the action potentials recorded from mouse neural lobes had a duration of 5 ms; at half-maximum peak height. Optical recordings during repetitive stimulation showed that significant spike broadening occured in each subsequent spike at 10 and 16 Hz stimulation. These data are consistent with a spike broadening hypothesis of frequency-dependent facilitation in the neural lobe. However, 4-aminopyridine, a drug which causes spike broadening in neural tissues by blocking potassium channels, did not produce an increase in secretion of AVP per stimulus from the mouse neural lobe.

ISSN:0028-3835    

DOI:10.1159/000124582

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The effects of discrete lesions of the suprachiasmatic and medial preoptic nucleus on luteinizing hormone-releasing hormone (LHRH) neurons of the female rat were examined. The lesions disrupted the estrous cycle and prevented the preovulatory surge of luteinizing hormone and prolactin. Two to three months following the lesions, control and lesioned animals were perfused, the brains were sectioned, and the tissue processed for LHRH immunocytochemistry using the peroxidase antiperoxidase method and a high-titer, conformational antiserum to LHRH. Faintly stained LHRH cells were observed in the preoptic area and the basal hypothalamus at all stages of the estrous cycle. The number of immunoreactive cell bodies varied from a high of 583 cells on proestrus, to a low of 35 cells on estrus (mean ± SEM = 323 ± 59; n = 11). In contrast, the constant estrous animals with lesions showed increased intensity and number of LHRH neurons rostral, lateral and caudal to the lesion. The total number of cells ranged from 625 to 954 cells per animal (mean ± SEM = 784 ± 44; n = 8; p< 0.001 vs. controls). Moreover, all lesioned animals exhibited intense fiber stain in the median eminence region. In conclusion, these data support the hypothesis that persistent estrus is caused by destruction of neurons which directly or indirectly control LHRH neur

ISSN:0028-3835    

DOI:10.1159/000124583

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

A radioimmunoassay specific for arginine-vasopressin (AVP) was used to establish the presence of immunoreactive (ir)-AVP in extracts of anterior pituitary glands from Sprague-Dawley (SD) and Long-Evans (LE) rats (3.05 ± 1.0 and 1.66 ±0.9 ng/gland, respectively). Lower levels of ir-AVP (0.56 ±0.26 ng/gland) were detected in anterior pituitary gland extracts from rats with hereditary diabetes insipidus (Brattleboro; di/di). The anterior pituitary gland ir-AVP from each rat strain was further characterized by reverse-phase high-performance liquid chromatography (RP-HPLC). In each case the major peak of immunoreactivity co-migrated with synthetic AVP. By peroxidase-antiperoxidase immunocytochemistry, sparsely distributed cells containing ir-AVP were localized in anterior pituitary sections. Levels of ir-AVP in primary cultures of anterior pituitary cells (from SD rats) increased from 52 ± 5 pg/106 cells at 2 days in vitro to 152 ± 17 pg/106 cells at 3 days; during this period 56 ± 6 pg/ml ir-AVP was secreted into the culture medium. Fewer than 1% of the cells in these cultures were immunostainable for AVP. These data indicate that the anterior pituitary gland of the Brattleboro, Long-Evans and Sprague-Dawley rat contains ir-AVP, and that there is synthesis and secretion of this peptide in primary cultures of anterior pituitary cells in

ISSN:0028-3835    

DOI:10.1159/000124584

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

We have investigated the effects of hyperprolactinemia, produced by pituitary isografts under the kidney capsule (16–20 days), on the LH releasing action and priming effect of LH-releasing hormone (LHRH) in normal and hypogonadal (hpg) female mice. The pituitary grafts increased the plasma prolactin concentrations about 3-fold in normal intact mice and 4-fold in hpg mice. The extent of the graft-induced hyperprolactinemia was reduced by ovariectomy in normal mice, but was the same in grafted hpg compared with intact normal mice despite the absence in the hpg mice of functioning ovaries. The priming effect of LHRH could be elicited in both types of mice by giving two injections of LHRH separated by an interval of 60 min. Hyperprolactinemia did not reduce the amount of LH released in response to a first injection of LHRH, but did reduce significantly the amount of LH released (primed) in response to a second injection of LHRH. Ovariectomy significantly increased the magnitude of the releasing action of LHRH in normal mice and prevented the graft-induced reduction of LHRH priming. These results show that hyperprolactinemia in normal and hpg mice suppresses the magnitude of the priming effect of LHRH. This may be an important mechanism by which prolactin reduces gonadotropin secretio

ISSN:0028-3835    

DOI:10.1159/000124585

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Earlier work has shown that diabetic rats possess lower concentrations of brain p-tyrosine; these animals also show a decrease in the rate of accumulation of striatal DOPA after decarboxylase inhibition and an increase in striatal binding sites for dopamine. These findings suggested that diabetic rats show a reduction in the metabolism of brain dopamine. This is an investigation of the effects of streptozotocin-induced (65 mg/kg, intracardially) diabetes on rat striatal concentrations of p-tyrosine, p-tyramine, m-tyramine, dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid. Also, the effects of insulin administration (0.5–4 IU/kg, intraperitoneally) to normal and diabetic rats were studied. The onset of diabetes or effect of insulin treatment was determined by the changes produced in blood glucose. Streptozotocin produced a significant reduction in the striatal concentration of p-tyrosine, 3,4-dihydroxyphenylacetic acid and homovanillic acid observed 7 or 14 days after injection. The treatment produced a reduction in p-tyramine and an increase in m-tyramine. Insulin administration significantly increased rat striatal p-tyrosine, p-tyramine, 3,4-dihydroxyphenylacetic acid and homovanillic acid while m-tyramine was decreased. The concentrations of p-tyrosine, dopamine, 3,4-dihydroxy-phenylacetic acid and homovanillic acid in the striatum of insulin-treated diabetic rats were within the range of control values. The results indicate that streptozotocin-diabetic rats possess a reduced striatal dopamine metabolism and that this is counteracted by insulin administration. These changes are probably the consequence of changes in the availability of some amino acid precursors and in tyrosine hydroxylase activit

ISSN:0028-3835    

DOI:10.1159/000124586

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Hyperprolactinemia adversely affects reproductive functions, presumably through an effect at the hypothalamic level. Given the numerous published reports linking hypothalamic serotonin (5-hydroxytryptamine, 5HT) mechanisms to the regulation of gonadotrophin secretion, we sought to determine the effects of experimentally induced hyperprolactinemia on ovarian steroid-induced increases in serum LH levels and region-specific hypothalamic 5HT synthesis in ovariectomized rats. In the first study, bilaterally ovariectomized Sprague-Dawley rats either received two pituitary homo-grafts implanted beneath the left kidney capsule or were sham-grafted. Both groups of rats were injected subcutaneously with 5 µg/100 g of estradiol benzoate (E2) in corn oil vehicle at 08.00 h, 1 and 2 days before serum collection and 5 mg/100 g of progesterone (P) in corn oil vehicle at 07.00 h on the day of serum collection. Blood samples were collected via chronic indwelling jugular cannulae from each rat at 10.00, 12.00, 13.00, 14.00, 16.00 and 18.00 h. A statistically significant elevation in serum LH levels was detected at 13.00, 14.00 and 16.00 h. This increase in serum LH levels was significantly attenuated in rats bearing pituitary homografts, an effect attributed to the high serum PRL levels measured in these animals. In the second study, bilaterally ovariectomized Sprague-Dawley rats were divided into three experimental groups: (1) rats bearing two pituitary homografts and injected with E2 and P on the schedule and at the dosages previously described, (2) sham-grafted rats injected with E2 and P on the schedule and at dosages previously described and (3) sham-grafted rats injected with corn oil vehicle only. The rats were then injected intravenously with 10 mg/100 g of NSD-1015 6 h after P injection and 30 min prior to killing the rats. Accumulation of 5-hydroxytryptophan in various hypothalamic areas was then assayed by liquid chromatography with electrochemical detection as a relative index for the level of 5HT synthesis. Administration of these ovarian steroids produced an increase in estimated 5HT synthesis in the preoptic area-anterior hypothalamus (POA-AH) but not in the median eminence or mediobasal hypothalamus. The E2 + P-induced increase in 5HT synthesis in the POA-AH was significantly blunted in rats with pituitary homografts. Considering the postulated role a 5HT mechanism within the POA-AH plays to facilitate ovarian steroid-mediated surges in LH secretion, hyperprolactinemia may inhibit LH secretion through its attenuation of ovarian steroid stimulation of 5HT synthesis in the POA-AH

ISSN:0028-3835    

DOI:10.1159/000124587

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The effect of 5-methoxytryptoline (5-MeOT), 5-hydroxytryptoline (5-OHT) and tryptoline (Tp), putative endogenous derivatives of the tryptamines, on plasma prolactin (PRL) concentrations has been investigated in the adult male rat. The possible involvement of the hypothalamic serotonergic system has been considered in the mediation of the hormonal effect of the tryptolines. Therefore, plasma PRL levels have been evaluated in rats receiving tryptolines after different pharmacological manipulations of central serotonergic function. Although the three compounds increased the plasma titers of PRL in a dose-dependent manner and enhanced the hypothalamic content of serotonin (5HT), they appear to affect the serotonergic system through different mechanisms. In particular, 5-OHT might act at a presynaptic level, since its hyperprolactinemic effect was antagonized both by the depletion of central 5HT content after p-chlorophenylalanine and by the degeneration of serotonergic terminals after 5,7-dihydroxytryptamine. In contrast, 5-MeOT behaved as if it had a postsynaptic site of action, being counteracted by the serotonergic postsynaptic antagonists metergoline and cyproheptadine. The unsubstituted tetrahydro-β-carboline, Tp, is probably active at both pre- and postsynaptic sites. The enhancing effect of Tp on PRL secretion was antagonized by chronic treatment with p-chlorophenylalanine, while it was also maintained in 5,7-dihydroxytryptamine-lesioned rats. These findings suggest that tryptolines may play a functional role in PRL secretion by interacting with central serotonergic systems through different biochemical mechanisms

ISSN:0028-3835    

DOI:10.1159/000124588

出版商:S. Karger AG    

年代:1986

数据来源: Karger