摘要:

AbstractIn rats, the release of growth hormone (GH) is inhibited during electrical stimulation of the periventricular nucleus but after the end of stimulation, there is a rebound ‘hypersecretion’ of GH. We examined the responses of arcuate neurones in pentobarbitone‐anaesthetized male rats, following electrical stimulation of the periventricular nucleus to test the hypothesis that the effects of periventricular nucleus stimulation on GH secretion are mediated via effects upon GH‐releasing hormone (GRF) neurones in the arcuate nucleus. The electrical activity of 2 groups of arcuate neurones were analysed before, during and after periventricular nucleus stimulation (10 Hz, 5 min, 0.5 mA biphasic, 0.5/1.0 ms): a) putative neurosecretory cells which were antidromically identified (AD) as projecting to the median eminence (n = 53) and b) non‐neurosecretory cells, identified by their spontaneous ‘bursting’ pattern of activity (n = 29). During stimulation predominantly inhibitory responses were observed in both AD and bursting cell groups. Of the 39 AD cells which were spontaneously active, 25 were inhibited during the periventricular nucleus stimulation, and 10 of these showed a rebound hyperactivation following the end of stimulation. Fifteen bursting cells were inhibited during stimulation and 4 of these displayed a rebound hyperactivation following the end of stimulation. Additional evidence was sought for the identity of these cells by testing their response to electrical stimulation of the basolateral amygdala (which has previously been shown to increase plasma GH concentration without influencing the release of other pituitary hormones). Six of the 10 AD cells which displayed the inhibition/rebound response to periventricular nucleus stimulation were also excited following electrical stimulation of the basolateral amygdala. We conclude that 1) electrical stimulation of the periventricular nucleus and the basolateral amygdala exert predominantly inhibitory and excitatory effects respectively upon the activity of arcuate neurones but for neither site were the effects of stimulation exclusively upon GRF neurones, and 2) the rebound hypersecretion of GH following PeN stimulation is likely to involve the rebound activation of arc

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00594.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractVasopressin (VP) and oxytocin (OT) are released within the hypothalamic nuclear region in response to direct microdialysis with hypertonic solutions. Experiments were performed to determine whether systemic osmotic stimulation causes changes in intranuclear peptide release within the supraoptic nucleus (SON). A hypertonic sodium chloride solution was injected intraperitoneally (ip) or intravenously (iv) and microdialysis techniques were used to simultaneously monitor central and peripheral peptide release in urethane anesthetized rats. Systemic osmotic stimuli elicited increases in intranuclear peptide release which were delayed and long‐lasting, occurring over a 2.5 h period. In contrast, plasma peptide levels peaked at 30‐min after the stimulus. The results demonstrate that increased plasma sodium elicits an increase in VP and OT release into the extracellular space of the hypothalamic SON. The different patterns of peptide release in plasma and brain point toward the possibility of independently regulated release into the different compartme

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00595.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe present studies assessed hypothalamic‐pituitary‐adrenal (HPA) responses following immune activation with endotoxin (ip) in three‐day old Long Evans rats. Marked plasma corticosterone (B), adrenocorticotrophic hormone (ACTH) responses and biphasic fluctuations in plasma glucose were maximal at a dose of 0.05 mg/kg. HPA responses peaked between 3–5 h following immune challenge and plasma ACTH and B responses were greater in female than in male rat pups. Plasma levels of corticosterone binding globulin (CBG) were reduced in males and substantially increased in females during the peak HPA response. Changes in plasma glucose were biphasic with slight increases when ACTH and B levels were maximal, but hypoglycemia was evident once plasma B levels returned to resting values. Endotoxin challenge reduced median eminence corticotropin‐releasing hormone (CRH) levels at times corresponding with elevated HPA activity, and prior icv injection of the CRH antagonist, a‐helical CRH, significantly attenuated elevations in plasma ACTH and B. In addition, α‐helical CRH pretreatment completely blocked endotoxin‐induced changes in plasma CBG in both males and females. These findings support the view that endotoxin‐induced HPA activation in the neonate

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00596.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe leporidae (rabbit and hare)pituitary intermediate lobe(IL)differs from that of other mammals by its neuroendocrine regulation. In particular, it is not submitted to the classic dopaminergic inhibitory control, which has been considered as a repressive factor for the expressionof glucocorticoid receptors (GR) in the mammalian IL. Hence, the present experiments aimed at examining the rabbit IL for the possible existence of GR. Using both immunocytochemistry and binding studies with (3H)‐dexamethasone, we localized GR in the nuclei of IL cells and showed the presence of saturable and high‐affinity type II receptor sites, with Kd∼3.9nM. Also, exposure of cultured IL cells to 10 nM dexamethasone (DEX) resulted in the blockade of melanocyte‐stimulating hormone(αMSH) secretion stimulated by oxytocin (OT). Importantly, the inhibitory effect was reversed by a 100‐fold excess of the glucocorticoid antagonist RU 38486. This is the first study which clearly demonstrates in a mammalian IL, namely the rabbit, the presence of functional GR, involved in the negative regulation of the melanotrophic activity of

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00597.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractWe previously reported that direct osmotic stimulation of the supraoptic nucleus (SON) of rats via a microdialysis probe produces a robust ‘rebound’ release of endogenous vasopressin (AVP) into the extracellular fluid of this hypothalamic nucleus (1). We now demonstrate in a combined microdialysis and push‐pull perfusion study that this intranuclear release is accompanied by increased AVP release in the septum. Simultaneous monitoring of intranuclear release and behavioral performance in the same animal indicated a significant correlation between the amount of endogenously released AVP and improved social memory based on the olfactory discriminative capacities of adult male rats. This memory improvement was partially blocked by local administration of a AVP V1receptor antagonist either into the SON or septum. These findings indicate that direct osmotic stimulation of the supraoptic nucleus, which increases intracerebral vasopressin release, improves the acquisition and/or processing of olfactory stimuli. Thus, the endogenous neuropeptide fulfills one of the major criteria for being causally involved as a neurotransmitter/neuromodulator in behavioral perfor

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00598.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractHypothalamo‐pituitary inhibition of reproductive function during undernutrition is well known, however, the physiological mechanisms leading to suppression of gonadotrophin secretion are not clear. A variety of studies have indicated that testicular negative feedback on LH secretion is enhanced during food restriction. To evaluate directly the suppression by endogenous androgens on hypothalamic GnRH pulse generator activity during food restriction and examine the mechanism underlying the increased testicular steroidal feedback, we examined (1) circulating bioactive LH (bLH) levels in response to selective cerebral androgen blockade by intraventricular administration of an androgen receptor antagonist (hydroxyflutamide, SCH 16423) and (2) the binding capacity and affinity of androgen receptors in medio‐basal hypothalamus, pituitary and prostate during undernutrition of intact mature male rats. Hydroxyflutamide (20 μg in 10μl vehicle), but not vehicle alone, markedly increased bLH levels in both food restricted andad‐libfed rats. However, the faster (geometric mean 11.4 vs 27.7 min) and greater (47.2 vs 21.9 ng/ml) increase in bLH level in food restricted compared with ad‐lib fed controls demonstrates an enhanced sensitivity to blockade of androgenic negative feedback during undernutrition. Food restriction increased androgen receptor binding capacity in pituitary (3.36 vs 0.77fmol/mg protein) but not in medio‐basal hypothalamus or prostate while binding affinity was unchanged by undernutrition in all 3 tissues. These studies reveal that undernutrition both enhances tonic, androgen receptor‐mediated feedback suppression of GnRH secretion and increases in pituitary (but not hypothalamic) androgen receptor numbers to cause inhibition of

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00599.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractMale rats treated with reserpine were motionless and ingested only a few of ten consecutive intraoral injections of a 1 M solution of sucrose. While injection of apomorphine, a dopamine agonist, stimulated locomotion and stereotyped sniffing in reserpinized rats, it did not reactivate ingestive responses. The non‐competitive N‐methyl‐D‐aspartate receptor antagonist MK801, however, stimulated locomotion as well as ingestion suggesting involvement of glutamate in the suppressive effect of resperpine on ingestive responses. A series of experiments was therefore undertaken to investigate the possible physiological role of glutamate in feeding.For this purpose, we used Grill's intraoral intake test, in which the rat is infused intraorally with a sucrose solution and the amount ingested measured. In untreated rats, MK801 dose‐dependently facilitated ingestion of the sucrose solution and antagonized inhibition of ingestion by cholecystokinin octapeptide. Administration of cholecystokinin octapeptide or ingestion of sucrose increased the concentration of glutamate in the nucleus of the solitary tract, a brain stem relay transmitting sensory information from the gastrointestinal tract to the forebrain. MK801 was found to bind specifically to this brain area and block the elevation of glutamate and dopamine levels which occurred after treatment with cholecystokinin octapeptide in this neural site. Together these data suggest that dopamine and glutamate may interact within the nucleus of the solitary tract in controlling ingestive

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00600.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractInsulin‐like growth factors (IGFs) regulate the autocrine/paracrine growth of neuroblastomas. The IGFs bind to specific binding proteins (IGFBPs) which modulate their biological activity. We investigated, by Western ligand blotting (WLB), the presence of IGFBPs and their possible modulation by retinoic acid (RA), IGF‐I, IGF‐II and truncated Des(1‐3)IGF‐l in conditioned medium (CM) of the human neuroblastoma SK‐N‐BE(2) cell line. We demonstrated the presence of two IGFBPs, with MW 37 kDa and 25 kDa. Following immunoprecipitation, they turned out to be IGFBP‐2 and ‐4, respectively. The RA‐induced differentiation in SK‐N‐BE(2) cells was accompanied by a marked reduction of the intensity of both IGFBP bands after 48 h (32% and 24% of control, respectively) and 72 h (2% and 0% of control, respectively) incubation. The addition of exogenous IGFs, which did not induce cell differentiation, did not change the IGFBP pattern significantly, except for the truncated form of IGF‐I, which induced a marked decrease in both the 37 kDa and 25kDa bands after 72 h incubation (45% and 18% of control, respectively). These findings suggest that IGFBPs have a role in RA‐induced differentiation i

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00601.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractUsing extracellular recordings from brainstem slicesin vitro, it was demonstrated that a high proportion (38/56) of neurones in the dorsal vagal complex of dioestrus, virgin female rats exhibit an excitatory response to [Arg8]‐vasotocin (AVT). Pharmacological characterization suggests that these responses cannot be entirely explained by interaction with either of the currently known classes of central receptors for oxytocin (OT) and vasopressin (V1a). Comparison of the responses with those to the OT receptor‐specific agonist [Thr4,Gly7]‐OT (TGOT), showed that not all neurones that responded to TGOT also responded to AVT (3/27). Furthermore, while the effects of 10−7M TGOT could be blocked either by the broad‐spectrum antagonist d(CH2)5[d‐Tyr(OEt)2,Val4,Cit8]‐vasopressin or by the selective OT receptor antagonist d(CH2)5[Tyr(Me)2,Thr4,Orn8,Tyr‐NH29]‐vasotocin, these peptides did not completely block the responses to AVT, indicating that AVT is unlikely to act through the central OT receptor. The responses to AVT and [Arg8]‐vasopressin (AVP) indicated the presence of at least 2 classes of receptor with which these agonists could act. Of 42 neurones tested with both AVP and AVT, none responded to AVP in the absence of a response to AVT, while 7/42 responded to AVT without a response to AVP. This might be explained by AVP acting through only the V1receptor, while AVT acts through both the V1and its own novel class of receptor. This was substantiated by the fact that two OT/V1receptor antagonists, d(CH2)5[d‐Tyr(OEt)2,Val4,Cit8]‐VP and d(CH2)5|Tyr(Me)2,Tyr‐NH29]‐AVP, were unable to block completely all the responses to AVT at a dose which suppressed responses to both AVP and TGOT. These data suggest that, in addition to activation by OT and AVP, neurones in the mammalian central nervous system are able to be excited by AVT, possibly involving its own

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00602.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractSexual behaviour in most female mammals is regulated by oestrogen, often acting synergistically with progesterone. Moreover, the most important neural site of action for oestradiol is the ventromedial nucleus. In the female musk shrew,Suncus murinus, testosterone (T) activates sexual behaviour. Virgin females first engage in copulatory behaviour many hours in advance of follicular development and ovulation, when plasma oestradiol levels are very low. Testosterone, produced by the ovaries and the adrenal glands, must be aromatized centrally to oestradiol to initiate sexual behaviour. To identify the neural sites of action for T, ovariectomized females received unilateral hormone implants containing testosterone propionate. Hormone pellets were placed in 1 of several brain sites including the medial preoptic area and the dorsalmedial hypothalamus (DMH). Implants in either of these 2 sites, but not in the lateral preoptic area, internal capsule, nor anterior hypothalamus stimulated the induction of sexual behaviour. Hormone implants in the ventrolateral hypothalamus resulted in partially receptive animals. Immunocytochemistry was employed to determine which steroid receptors were present in the 2 behaviourally active sites. The medial preoptic area (MPO) and the dorsal and ventromedial hypothalamus both contain many cells that express oestrogen receptor immunoreactivity. A smaller subset of neurons in these regions are immunoreactive for androgen receptors. In summary, testosterone can act specifically in either the MPO or the DMH to induce female sexual behaviour. Both sites contain cells that express oestrogen and androgen receptors. Thus, testosterone may work via one or both of these steroid receptors to regulate behaviour. The results of these studies, and data collected previously, show that female sexual behaviour in this species is regulated by T and that this steroid can induce full sexual behaviour in 2 specific neural sites. Both of the sites of action identified in this experiment are critical for the expression of sexual behaviour in other species. The MPO has been shown to regulate male sexual behaviour via the aromatization of T to oestradiol in rodents and birds. The DMH is just dorsal to the ventromedial nucleus (VMN) which is essential for the regulation of sexual behaviour in female rodents. Further work is needed to determine if the neural circuitry for sexual behaviour in the musk shrew involves either the MPO or the VMN, if both areas are essential, or perhaps, the 2 regions regulate different aspects of female sexual behaviour.

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00603.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY