摘要:

Extracellular recordings from medial hypothalamic neurons in pentobarbital-anesthetized male Sprague-Dawley rats were evaluated during electrical stimulation in the ipsilateral and contralateral dorsal hippocampus/fimbria region. Similar short latency orthodromic (excitatory or inhibitory) responses were noted from both ipsilateral and contralateral stimulation sitps indicating a bilateral projection. 14.5% of neurons responded to both stimuli, usually with a similar pattern of response. When neurons were also tested with ipsilateral basal or corticomedial amygdala stimulation, 21.5–22.8% of cells displayed orthodromic responses to both the hippocampus and the amygdala stimulus. 12.5% of medial hypothalamic tuberoinfundibular neurons also responded orthodromically to the hippocampal stimulus; a preceding stimulus to the amygdala could block this response in two of three tuberoinfundibular cells. These observations provide preliminary electrophysiological analysis of the functional connectivity of hippocampal and amygdala afferents to medial hypothalamic neurons that may underlie the influence of these extrahypothalamic regions on adenohypophyseal secretion

ISSN:0028-3835    

DOI:10.1159/000123255

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The effect of melatonin treatment on the weight and volume of gonads and accessory sex organs of sham-operated and pinealectomized lizards (Calotes versicolor) was examined during the different phases of the annual gonadal cycle of the animal. Melatonin injections to sham-operated lizards inhibited gonadal activity during the progressive (April–May), reproductive (June–July) and early regression (September–October) phases of the cycle, but had no effect on the atrophied gonad present during the inactive and early progressive phases. Pinealectomy increased the weight and volume of the gonads and accessory sex organs at all phases of the gonadal cycle. Melatonin treatment in pinealectomized lizards counteracted the effect of pinealectomy. It is concluded that melatonin is antigonadotropic in this species of tropical l

ISSN:0028-3835    

DOI:10.1159/000123256

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The levels of dynorphin-(1-13), leucine enkephalin, β-endorphin and vasopressin immunoreactivity (ir-DYN, ir-1-ENK, ir-β-END, ir-VP) have been determined in the anterior and in the neurointermediate lobes of the pituitary of rats subjected to a variety of manipulations. Dehydration of rats by 5 days enforced imbibition of a 2% solution of NaCl resulted in a significant decrease in the levels of ir-DYN, ir-l-ENK and ir-VP, but not in those of ir-β-END in the neurointermediate lobe of the pituitary. In contrast, substitution of drinking water by a solution containing 20 μg/ml dexamethasone for 5 days produced a significant increase in the neurointermediate pituitary content of ir-DYN, ir-l-ENK and ir-VP, whereas levels of ir-β-END remained unaffected. This treatment, however, resulted in a significant fall in the ir-β-END content of the adenopituitary without changing levels of ir-DYN in this structure. Adrenalectomy was associated with a significant decrease in the ir-DYN, ir-VP and ir-l-ENK content of the neurointermediate lobe of the pituitary and a pronounced elevation in the ir-β-END but not ir-DYN content of the adenohypophysis. These observations are indicative that the regulation mechanisms of the functional state of particular endorphins differ between the anterior and neurointermediate lobes of the pituitary. The concomitant alterations in levels of ir-DYN, ir-l-ENK and ir-VP detected suggest that a common or similar mechanism of regulation may exist for these peptides. A common biosynthetic origin, however, appears to be unlikely, since Brattleboro rats which are unable to synthesize vasopressin possess unchanged ir-DYN- and ir-1-ENK levels in the pit

ISSN:0028-3835    

DOI:10.1159/000123257

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

In castrated male rats, gonadal steroid treatment raises the medial basal hypothalamic (MBH) LHRH levels and suppresses LH release. We have now examined whether the steroid-induced MBH LHRH response could occur concomitantly with normal pituitary LH secretion. Of the various concentrations tested, serum estradiol-17β (E2) levels in the range of 9–16 pg/ml consistently and selectively stimulated the accumulation of LHRH in the MBH after a long latency period of 60–72 h. These low E2 levels did not suppress LH release at any time interval. Serum LH levels and the episodic pattern of LH secretion were similar to those of castrated control rats. It is unlikely that enhanced pituitary sensitivity in E2-treated rats may have compensated for a decrease in LHRH release since the LH response to exogenous LHRH was similar in E2-treated and control rats. These studies show that dissociation of the feedback effects on the MBH LHRH and pituitary gland LH release may be obtained with low serum concentrations of E2 in male rats; low E2 levels stimulate LHRH accumulation in the MBH by mechanisms which may not involve inhibition of LHRH rel

ISSN:0028-3835    

DOI:10.1159/000123258

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

In order to investigate the role of central dopaminergic receptors in the control of vasopressin release and in cardiovascular regulation, the effects of intracerebroventricular administration of dopamine (DA) and bromocriptine (BC), a specific DA agonist, were compared in the anesthetized dog. The drugs were infused over a 20-min period into a lateral ventricle. DA brought about a transient decrease in mean arterial blood pressure, a slight increase in heart rate toward the end of the experiment, and a suppression of vasopressin release. BC increased heart rate and decreased blood pressure to a greater extent than did DA, and doubled the plasma vasopressin concentration. The increase in vasopressin secretion preceded the fall in blood pressure, and was, therefore, due to a direct central action of BC. Although in these circumstances it is difficult to determine the true role of dopaminergic neurons in the control of vasopressin release, there is some reason to believe that this role may be expressed by the actions of BC under the present experimental conditions.

ISSN:0028-3835    

DOI:10.1159/000123259

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Temporal alterations in plasma prolactin levels caused by the administration of 2-hydroxyestradiol and 2-hydroxyestrone (100 μg/kg) into the right atrium of freely-moving conscious male rats were examined. The catechol estrogens were given in a single bolus via an indwelling cannula and plasma prolactin concentration was monitored by taking blood samples every 2 min. A pulsatile elevation of plasma prolactin occurred approximately 4 h after the injection of 2-hydroxyestradiol and a small increase was also observed when it was administered to rats bearing a Silastic capsule containing estradiol. 2-Hydroxyestrone had no effect in untreated male rats but produced a 5- to 6-fold elevation in plasma prolactin level 4 h after its administration to rats implanted with estradiol. It is proposed that 2-hydroxyestrone suppresses the action of estradiol on prolactin secretion from the pituitary and that the accumulated hormone is released when the concentration of this catechol estrogen falls below a critical level. A longer latent period was required to produce an elevation in plasma prolactin levels by 2-hydroxyestradiol than by estradiol

ISSN:0028-3835    

DOI:10.1159/000123260

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The effect of sonicated suspensions of phosphatidylserine (PS), an acidic phospholipid, was investigated on prolactin secretion utilizing in vivo and in vitro approaches. Acute and chronic administration of PS reduced plasma prolactin levels during different phases of circadian rhythms. The phospholipid was able to inhibit the plasma prolactin surge, which occurs in cycling female rats on the afternoon of proestrus. The time course of PS on prolactin secretion was characterized by a short latency (15 min) and a long duration of action (6 h). In rats with hypothalamic deafferentation PS partially reduced the increase of circulating prolactin induced by pre-treatment with α-methyltyrosine. An inhibition of prolactin release was observed if anterior pituitary glands were incubated in presence of PS. This effect was prevented by the addition of the dopamine antagonist sulpiride to the medium. In conclusion, PS decreases prolactin secretion both in vivo and in vitro. The inhibition of the hormone secretion appears to be due to the action of PS at the level of the pituitary; however, a concomitant stimulatory action on the turnover of the tuberoinfundibular neurons cannot be ruled out

ISSN:0028-3835    

DOI:10.1159/000123261

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Three experiments were conducted using intracranial infusion of kainic acid (KA) to lesion the medial septal (MS) neurons and dorsal hippocampal (DH) neurons in 25-day-old female rats. Rats of experiment 1 were allowed to develop until vaginal opening (VO) after which vaginal lavages were taken to monitor the vaginal cycle. Rats of experiment 2 received estradiol benzoate (EB) subcutaneously immediately after KA infusion. Blood was obtained at 11.00 and 16.00 h, 2 days after EB and measured for luteinizing hormone (LH) by radioimmunoassay. Rats of experiment 3 received MS KA lesions and 2 days later tested for pituitary responsiveness to LHRH-induced LH release. In experiment 1, MS KA-lesioned rats exhibited a significant delay in VO when compared to the sham-lesioned or the unoperated control groups. Hippocampal KA-lesioned rats in contrast, showed no difference in the age of VO from the control groups. Septal KA-lesioned rats also showed disrupted vaginal cycles after the onset of puberty. In experiment 2, all the EB-treated animals exhibited the expected rise in serum LH on the afternoon 2 days following EB with the exception of the septal KA-lesioned rats. In every case, KA infusion into the medial septum abolished the ability of EB to induce an LH increase at 16.00 h 2 days after EB administration. DH KA lesion on the other hand had no effect on the EB-induced LH increase. The block of LH secretion by MS KA infusion shown in experiment 2 is not a result of decreased pituitary gland sensitivity to LH-releasing hormone (LHRH) as shown in experiment 3. These results indicate that MS neurons play a vital role in the feedback mechanism whereby EB induces an LH increase in the prepuberal female rat, and that they play a role in the timing of VO.

ISSN:0028-3835    

DOI:10.1159/000123262

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The capacity of haloperidol (Haldol) to block luteinizing hormone (LH) release and ovulation was investigated with particular reference to its effectiveness during the ‘critical period’ on the afternoon of proestrus in normal, cycling female rats. Haldol was injected subcutaneously at 13.30 h in one of five dosage levels (0.125, 0.25, 0.5, 1.0, or 4.0 mg/kg), or at 09.30 h in a single dose of 1.0 mg/kg. Control animals received the corn oil vehicle at 13.30 or 09.30 h. Blood samples were taken by means of intra-atrial catheters which had been implanted on the day prior to Haldol treatment. Oviducts were examined for the presence of ova at 10.00 h on the day following the experiment (estrus). Haldol was found to be ineffective at 13.30 h when given at dosage levels which were shown by previous authors, and in the present experiment, to be capable of blocking LH release and ovulation after injection at 09.30 h. Although LH levels and the numbers of ova released were inversely related to the dose of Haldol administered at 13.30 h, well-defined LH surges were still present and the occurrence of ovulation was not significantly inhibited. Haldol was found to block LH release and ovulation, however, when injected at 13.30 h at the highest dosage level (4.0 mg/kg). The fact that low doses of Haldol blocked in the morning but not in the afternoon indicates that the morning blockade must be mediated by a secondary action of the drug which required a certain period of time to be effective. The blockade by the high dose of Haldol in the afternoon, however, was probably due to a direct action on LH releasing mechani

ISSN:0028-3835    

DOI:10.1159/000123263

出版商:S. Karger AG    

年代:1981

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000123264

出版商:S. Karger AG    

年代:1981

数据来源: Karger