摘要:

The effect of rostral deafferentation of the medial basal hypothalamus (MBH) on delta-9-tetrahydrocannabinol (THC)-induced changes in serum prolactin (PRL) concentrations was investigated in female rats having retrochias-matic frontal cuts that transected the rostral hypothalamus. Cuts dorsal to the hypothalamus were produced in the same plane in other animals in order to control for possible effects of the surgical procedure or dorsal brain damage. All animals were ovariectomized 28–35 days after stereotaxic surgery to obviate potential confounding effects of differences in ovarian function between groups. Unlesioned rats were ovariectomized to provide a positive control group for THC inhibitory activity. At least 4 weeks after ovariectomy, animals were treated intravenously with THC (0.5 or 1.0 mg/kg body weight) or vehicle at the midpoint of a 110-min experimental period during which blood samples were obtained at 10-min intervals via indwelling atrial cannulae. Serum PRL concentrations were determined by radioimmunoassay and cut locations were confirmed histologically. When administered to ovariectomized animals without brain lesions, THC suppressed serum PRL concentrations from the average treatment level within 30 min (p < 0.05), and PRL levels remained suppressed for the remainder of the posttreatment sampling period. Treatment with the vehicle alone was without effect. Animals with retrochiasmatic plane cuts that did not transect the rostral hypothalamus similarly displayed PRL suppression in response to THC administration (p < 0.05). In contrast, THC administration to animals having retrochiasmatic cuts complete to the base of the brain produced a prompt PRL rise which peaked 10 min after treatment (p < 0.05) and then declined to, but not significantly below, the average pretreatment PRL level. The PRL rise (5-fold) following treatment with 1 mg THC/kg body weight was greater than that which followed treatment with 0.5 mg/kg body weight (p < 0.01). Serum PRL was not increased by treatment with the vehicle alone. These results indicate that transections of the rostral hypothalamus which separated the suprachiasmatic region from the MBH resulted in an apparent reversal of the acute effect of THC on serum PRL concentrations in that the sustained PRL inhibition that typically followed THC administration to unlesioned rats was converted to an abrupt, albeit brief PRL rise without evidence of subsequent suppression below pretreatment levels. While the mechanism of the THC-induced PRL rise remains unknown, the absence of PRL suppression in animals with rostral deafferentation of the MBH suggests that THC does not inhibit PRL secretion by directly promoting the release of PRL-inhibiting factor from median eminence nerve terminal

ISSN:0028-3835    

DOI:10.1159/000124646

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Long-term 17β-estradiol (E2) treatment in rats decreases tuberoinfundibular dopaminergic (TIDA) neuronal function. The objective of this study was to determine if the decline in TIDA function after E2 treatment in Fischer 344 (F344) rats is sustained long after removal of E2. Ovariectomized (OVX) F344 rats were each implanted with an E2-containing or empty Silastic capsule for 4 weeks; the capsule was then removed, and 26 weeks later acute experiments were performed. Release of 3H from median eminence tissue in vitro in response to electrical stimulation after 3H-DA accumulation was not different between E2-treated rats and OVX controls, even though serum prolactin (PRL) was 4-fold greater in E2-treated animals. Acute administration of apomorphine hydrochloride, a DA receptor agonist, at 2 doses, reduced serum PRL values as much in E2-treated animals as in OVX control rats. Injection of morphine sulfate or nomifensine maleate, which directly influence TIDA neurons, resulted in nonsignificant serum PRL responses in animals long after E2 withdrawal as compared to the greater response in OVX control rats. To further evaluate TIDA neuronal function, OVX non-E2-treated rats and animals 26 weeks after E2 withdrawal received a 3-day E2 challenge which increased the stimulation-evoked release of 3H from the median eminence tissue in vitro 2-fold in OVX control rats but had no effect in rats given E2 26 weeks previously. The difference in the stimulation-evoked release occurred in the presence of similar circulating serum PRL levels in the two groups as a result of the 3-day E2 treatment. These data indicate that TIDA neurons exhibit a decreased responsiveness to most stimuli after long-term withdrawal from chronic E2 treatment, even though the E2-treated anterior pituitary was fully responsive to the dopaminergic agonist, apomorphine. Thus, E2 administration to OVX F344 rats for 4 weeks appears to result in a permanent decline in TIDA neuronal function. The mechanism(s) responsible for this permanent effect of E2 is not known at present

ISSN:0028-3835    

DOI:10.1159/000124647

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Prompted by immunohistochemical reports of prolactin-like immunoreactivity in cell bodies within the rat hypothalamus, a study was undertaken to quantitate the immunologic and biologic activity of this material. Hypothalamic concentrations of prolactin-like immunoreactivity averaged 402 ± 23 pg/mg of protein (n = 30). 97% recovery of rat prolactin standards added to homogenates of hypothalamus insured that neuronal tissue, as prepared for these studies, did not interfere with the radioimmunoassay of rat prolactin. Examination of the elution profile from Sephadex G-75 columns of the prolactin-like immunoreactivity in hypothalamic extracts showed that the majority of hypothalamic prolactin-like substance was of a larger molecular size than pituitary prolactin. While increasing amounts of brain extract progressively displaced more I125 prolactin from antibody-binding sites, the displacement curve produced by adding hypothalamic extract was not parallel to that produced by the addition of increasing amounts of anterior pituitary prolactin standards of rat origin. Hypothalamic extracts from hypophysectomized animals, analyzed for biologic activity in the Nb2 lymphoma cell assay, revealed prolactin-like bioactivity, but the bioactivity/immunoactivity (B/I) ratios for hypothalamic extracts were significantly lower than the B/I ratios for pituitary prolactin (0.71 ± 0.04 for pituitary, vs. 0.19 ±0.06 in the hypothalamus; p < 0.001). Hypophysectomy, which led to the expected fall in serum prolactin to undetectable levels, and restraint stress, which resulted in a statistically significant 4-fold rise in serum prolactin, caused no change in prolactin concentrations in the hypothalamus, indicating that brain prolactin-like substance is regulated independently of pituitary prolactin and circulating serum prolactin leve

ISSN:0028-3835    

DOI:10.1159/000124648

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Peptides derived from pro-dynorphin and pro-vasopressin precursors coexist within neurosecretory vesicles of magnocellular neurons in the rat hypothalamus projecting to the posterior pituitary. The secretory activity of these neurons can be stimulated using physiological manipulations known to increase plasma vasopressin levels, such as dehydration and salt-loading. With chronic osmotic challenge, the mRNAs for both pro-dynorphin and pro-vasopressin increase in parallel in the supraoptic and paraventricular nuclei of the hypothalamus, but not within the nonmagnocellular suprachiasmatic nucleus cell groups projecting elsewhere than the neural lobe. The results indicate an example of coordinate regulation of mRNA expression for coexisting peptides within the brain.

ISSN:0028-3835    

DOI:10.1159/000124649

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The site of inhibitory action of glucocorticoids on the hypothalamic corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) was studied using a combination of glucocorticoid implantation and immunohistochemistry. Adrenalectomy increased the number and the staining intensity of the neurons containing CRF-like immunoreactivity in the anterior and medial parvicellular subdivisions of the paraventricular nucleus (PVN) and induced the appearance of AVP-like immunoreactivity in the same cell population. These effects of adrenalectomy were inhibited only by those dexamethasone implants which were placed close to the PVN. Unilateral implantation of dexamethasone into the PVN inhibited the adrenalectomy-induced changes in CRF and AVP immunostaining only on the implanted side. Dexamethasone implants placed into the hippocampus decreased the effect of adrenalectomy in the PVN while similar implants into the amygdala and cerebral cortex were ineffective. These results suggest that the primary site of glucocorticoid feedback inhibition on the hypothalamic secretagogues of adrenocorticotropin is the PVN.

ISSN:0028-3835    

DOI:10.1159/000124650

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The distribution of vasopressin (VP) and oxytocin (OT) neurons in the rat supraoptic (SON), paraventricular (PVN), and accessory magnocellular (AMN) nuclei was studied by localizing both peptides on the same section with a double immunocytochemical staining procedure employing specific monoclonal antibodies (MAB). This procedure allows us to visualize the distribution of one cell type relative to the other. In the rostral SON, VP cells lie dorsal and medial to the OT cells. Near the mid-point of the nucleus along its rostral-caudal length, there is a transition zone in which the two cell types are mixed. Proceeding caudalward, the relative locations of OT and VP cells are exchanged so that most of VP cells are located in the ventral and medial sector of the nucleus, whereas the OT cells are situated dorsal and lateral. However, there is no absolute segregation of the two types of cells anywhere in the nucleus. In the anterior part of the PVN a rostral group (rPVN) of cells composed of a medial portion and a lateral wing can be recognized. Nearly all of the cells in the rPVN are oxytocin-containing. The rPVN is separated from the next group, the middle PVN (mPVN), by a cell poor zone of about 100–150 µm. The mPVN contains both OT and VP neurons. As one proceeds caudally, the OT cells extend in the rostrocaudal direction from an anterior and ventromedial location, forming a shell around a core of VP neurons. In the most caudal PVN (cPVN), a triangular cell group characterized by fusiform cells with long-beaded processes can be distinguished from the more rounded cells of the remaining PVN. Many fusiform cells in the cPVN appear to send their axons to the posterior perifornical nucleus and the nucleus of the medial forebrain bundle. Other fusiform cells of the cPVN are oriented in a rostral-caudal plane and are situated more medially in this subdivision. The dendrites of these cells project into the mPVN while their posterior processes, most of which also appear to be dendrites, project caudally along a medial rou

ISSN:0028-3835    

DOI:10.1159/000124651

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The possible implication of the amygdaloid central nucleus (ACE) of the rat in the control of ACTH secretion in response to immobilization stress was assessed. The ACTH secretion, in response to stress and/or bilateral lesions of the ACE, was correlated with the serotoninergic activity in specific hypothalamic and amygdaloid nuclei. Bilateral lesions of the ACE produced a striking decrease of plasma ACTH levels in response to stress. However, basal plasma ACTH levels measured between 7 and 11 a.m. were identical in both control and lesioned groups. Stress, applied to intact animals, did not modify the serotoninergic activity in any of the following areas: hypothalamic paraventricular (PVH), ventromedial (VMH) and dorsomedial (DMH) nuclei; the anterior hypothalamic area (AHA); the lateral part of the basal amygdaloid nucleus (ABL), the amygdaloid medial (AME) and cortical (ACO) nuclei. However, lesion of the ACE increased the serotoninergic activity in all these structures except for the VMH. Immobilization stress applied to lesioned animals decreased the serotoninergic activity to control levels in the PVH, AHA and DMH and decreased the activity to below control levels in the VMH. The serotoninergic activity remained at an increased level in the glucocorticoid receptor-rich areas of the amygdala, namely the AME, ACO and ABL nuclei. These results provide evidence for a stimulatory role of the central nucleus of the amygdala in the control of ACTH secretion. Moreover, they substantiate an implication of the amygdaloid complex in the control of the delayed negative feedback of glucocorticoids on ACTH secretion via interaction with the serotoninergic system.

ISSN:0028-3835    

DOI:10.1159/000124652

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The site of action of the inhibitory effect of somatostatin (SRIF) on its own release was studied by: (1) measuring SRIF release in vitro from tissue preparations containing either the proximal (periventricular hypothalamus) or the distal (median eminence) portions of the hypothalamic SRIF neurons, and (2) immunocytochemical investigation of the interconnections occurring between SRIF neuronal elements in these hypothalamic regions. In vitro, a biologically active, but noncross-reacting SRIF analog (D-Trp8 SRIF) in the RIA, inhibited 25 mM K+ induced SRIF release from anterior periventricular hypothalamic tissues. The inhibitory effect of D-Trp8 SRIF was dose-dependent, maximal at 10–7M, and restricted to this anterior region, since median-eminence SRIF release was not modified by the presence of D-Trp8 SRIF. Additionally, LHRH release from anterior periventricular hypothalamus was unchanged in the presence of D-Trp8 SRIF. In the periventricular nucleus, perikarya and dendrites of labeled SRIF neurons showed frequent apposition of their limiting membranes. Classical synapses were also observed between SRIF-containing axonal processes and labeled perikarya or dendrites. Although membrane appositions between neighboring SRIF axons frequently occurred in the median eminence, no synaptic-like SRIF-SRIF connections could be detected at this level. The data demonstrate a direct inhibitory action of a SRIF agonist on the anterior periventricular hypothalamic release of the peptide. This effect correlates well with the occurrence of SRIF-SRIF synapses in this region; suggesting that SRIF exerts a negative feedback in the control of its own release through autoreceptors located on the perikarya or dendrites of SRIF-containing neuron

ISSN:0028-3835    

DOI:10.1159/000124653

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Sexual differentiation of the rat brain is affected by certain compounds administered during the neonatal period. We evaluated the effects of exposure to THC during the critical period of sexual differentiation of the female rat brain on postpubertal estrous cycles and brain neurotransmitter levels. Newborn female rats were injected either with vehicle (oil) or with different doses of THC (0.38; 1.9 or 3.8 mg/100 g) subcutaneously during the first 5 days after birth. The rats were examined daily by vaginal lavage smears from 3 to 10 months of life for phases of estrous cyclicity. The animals were then sacrificed and the anterior hypothalamus preoptic area (AHPOA) and medial basal hypothalami (MBH) were collected, processed and the methionine-enkephalin (met-enkephalin), β-endorphin-like immunoreactivity (β-end LI), LHRH and substance-P were measured by radioimmunoassays. In addition, serum LH and prolactin levels were measured by radioimmunoassay. Compared with the control rats, the rats perinatally exposed to THC exhibited either constant metestrus diestrus type vaginal smears or irregular estrous cycles. In the THC-treated animals, the met-enkephalin and β-end LI levels were lower in the AHPOA and higher in the MBH. The LHRH levels of THC-treated rats were significantly lower in the MBH. The substance-P levels were significantly lower in the AHPOA of THC treated animals. In the THC-treated rats, serum LH was low but, the prolactin levels were not significantly different from the control animals. Results indicate that perinatal exposure to THC has long-lasting inhibitory effects on postpuberal reproductive function, perhaps by permanently altering the normal functional associations of those neuronal groups in the diencephalon concerned with the regulation of gonadotrophin secreti

ISSN:0028-3835    

DOI:10.1159/000124654

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Earlier work established that neural secretion of luteinizing hormone-releasing hormone (LH-RH) and the resultant release of pituitary gonadotropins could be facilitated by activating α-receptors of a central noradrenergic (NA) system. The present study emphasizes that central NA mechanisms may also inhibit LH release largely through activation of β-adrenergic receptor

ISSN:0028-3835    

DOI:10.1159/000124655

出版商:S. Karger AG    

年代:1986

数据来源: Karger