摘要:

Central gonadotropin-releasing hormone (GnRH) injected intraventricularly (IVT) has been shown to facilitate rat sexual behavior. To elucidate the brain mechanisms of GnRH action, we have applied GnRH to hippocampal brain slices in vitro. Using intracellular recording from 40 hippocampal CA1 pyramidal neurons, we have found GnRH to elicit predominantly excitation. There are two types of excitatory responses. One is a short-latency, short-duration response and the second a long-latency, long-duration response. These responses were characteristic of GnRH and not peptides generally because angiotensin II, which also had an excitatory effect, had only long-latency, short-duration effects. The neural response to GnRH may be involved in the initiation of the behavioral response since the termination of the long-duration response coincides with the onset of the behavior.

ISSN:0028-3835    

DOI:10.1159/000124636

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Leumorphin is a 29-amino-acid peptide derived from preproenkephalin B. Intracerebroventricular (i.c.v.) injection of leumorphin through an implanted cannula into the lateral ventricle of rats dose-dependently inhibited water intake induced by water deprivation, angiotensin II (AII) and carbachol. This effect was partially reversed by intraperitoneal injection of naloxone, an opiate antagonist. Naloxone alone rather attenuated water intake. The antidipsogenic effect of leumorphin was very potent: 0.6 pmol of the peptide significantly inhibited AII-induced drinking. Dynorphin 1–17 was almost as potent as leumorphin in inhibiting drinking, whereas α-neo-endorphin and leucine-enkephalin (Leu-enkephalin) were far less effective. Leumorphin given i.c.v. dose-dependently enhanced eating and this effect was abolished by naloxone. Dynorphin was as potent as leumorphin in inducing feeding, whereas α-neo-endorphin and Leu-enkephalin had no significant activity when 6 nmol was used. General activity measured by an Automex was enhanced by i.c.v. injection of leumorphin but required larger amounts of the peptide than did drinking behavior. The very potent and specific effects of leumorphin and dynorphin on drinking behavior suggest that the antidipsogenic activity of these peptides is of physiological significance like their effect on feed

ISSN:0028-3835    

DOI:10.1159/000124637

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Acetylcholinesterase (AChE) activity, and concentrations of monoamines, monoamine metabolites and oxytocin (OT) were measured in the cerebrospinal fluid (CSF) of sheep during late pregnancy, labour, parturition, vaginocervical stimulation, lamb separation and suckling. Concentrations of AChE, 4-hydroxy-3 methoxyphenylethan-1,2-diol (MHPG) and OT were significantly elevated during labour and parturition. OT levels were also significantly raised in cycling ewes given vaginocervical stimulation. Separation of the ewes from their lambs (0.5–2 h) caused significant increases in AChE and MHPG, but not in OT. During suckling, following reunion of the ewes and lambs, concentrations of AChE and OT were significantly raised. The dopamine metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid were significantly lower in CSF during late pregnancy than during parturition and post-partum. Intravenous injections of OT which produced high circulating levels of this hormone in plasma produced significant, but very small, increases in concentrations of OT in the CSF. Our results show that in the sheep, labour, parturition, suckling and vaginocervical stimulation provoke a release of OT in the brain similar to that in the peripheral circulation. Changes in CSF levels of AChE and MHPG during labour, parturition and lamb separation, but not during vaginocervical stimulation, may be related to stress or hypertensio

ISSN:0028-3835    

DOI:10.1159/000124638

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Endogenous opioid peptides inhibit secretion of oxytocin during dehydration, hemorrhage and parturition and attenuate release of vasopressin by tail electroshock. Diverse agents were used to stimulate the hypothalamo-neurohypophysial system to investigate the hypothesis that if oxytocin (or vasopressin) release were inhibited by opioid peptides regardless of the stimulus, the site of opiate action may be in the final common pathway (i.e. the magnocellular neuron) or on pituicytes in the neural lobe. Using male Sprague-Dawley rats, we therefore investigated the effect of an opiate receptor antagonist, naloxone (5 mg/kg s.c), on the plasma concentrations of oxytocin and vasopressin elevated by various pharmacologic stimuli, including histamine (10 mg/kg i.p.), nicotine (0.15 or 1.5 mg/kg i.p.), isoproterenol (30 or 120 ug/kg i.m.) and increased [NaCl] in cerebrospinal fluid (CSF; 10 µl artificial CSF containing 1 MNaCl i.v.t.). Control animals received saline (0.85%) or artificial CSF (containing 0.16 M NaCl). Animals were decapitated 60 s (†[NaCΓJ in CSF) or 10 min after the stimulus or vehicle. Vasopressin and oxytocin were extracted from plasma and quantified by RIA. The concentrations of oxytocin and vasopressin in plasma were elevated (p < 0.05) by histamine, isoproterenol (30 and 120 αg/ kg), ↑[NaCl] in CSF, and nicotine at the higher (1.5 mg/kg) but not lower (0.15 mg/kg) dose. Naloxone increased further (p<0.05) the concentration of oxytocin in plasma after histamine, nicotine (0.15 and 1.5 mg/kg), isoproterenol (30 and 120 µg/kg) and ↑[NaCl] in CSF. Naloxone also increased (p<0.05) oxytocin concentration in controls receiving CSF or saline. Vasopressin concentration was unaffected by naloxone in either controls or after any of the stimuli. We conclude that endogenous opioid peptides inhibit release of oxytocin in vivo by an effect on the final common pathway, i.e. the magnocellular neuron or on pituicytes in the ne

ISSN:0028-3835    

DOI:10.1159/000124639

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

In male and female rats of two different age groups, we measured the arginine-vasopressin (AVP) levels in cerebrospinal fluid (CSF) collected at different times of the day. Mean values of AVP in cisternal CSF averaged across the different times of the day were higher in males than in females (p = 0.02), and in young (2 months) than in aged (12 months) rats (p = 0.03) of both sexes. The AVP levels in CSF showed a clear circadian rhythm in both young and aged male rats; the values at 07.00 h and 13.00 h were higher than those at 01.00 h and 19.00 h. The amplitude of the rhythm was smaller in females than in males. In addition, the rhythm was more pronounced in young than in aged rats of both sexes. These data suggest that both age and sex affect levels of vasopressin in CSF.

ISSN:0028-3835    

DOI:10.1159/000124640

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Abrupt increases in electrical activity can be recorded from the medial basal hypothalamus of the rhesus monkey and these bursts are correlated with a pulse of LH release from the anterior pituitary. In this study we have localized the tips of the electrodes from which such electrical activity can be recorded and have attempted to correlate the placement with the presence of immunoreactive LHRH neurons and axons. Electrodes associated with bursting activity were found as far rostral as the suprachiasmatic nucleus and as far caudal as the premammillary nuclei. The majority were found in the medial basal hypothalamus including the region of the arcuate nucleus, the retrochiasmatic zone and the dorsal aspect of the median eminence. The tips of the electrodes were associated with either LHRH neurons or axon bundles. Negative electrodes (those not associated with bursting electrical activity) which did not exit through the ventral surface of the brain nor enter the ventricle were found in the same regions of the hypothalamus as positive electrodes. Although it is tempting to associate the bursting electrical activity with the LHRH neurosecretory system, such a correlation cannot yet be made.

ISSN:0028-3835    

DOI:10.1159/000124641

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Various supra- and retrochiasmatic cuts injuring different parts of the septo-preoptico-infundibular GnRH pathway were made in adult female rats, and their effects on ovulation, median eminence (ME) GnRH content and on plasma LH and FSH levels were studied. Extended retrochiasmatic frontal cut just behind the optic chiasm, or a frontal cut in front of the suprachiasmatic nucleus presumably interrupting the whole GnRH pathway blocked ovulation, led to persistent estrus with polyfollicular ovaries, and reduced the ME GnRH content to 10 and 32%, respectively, expressed in percentage of unoperated control value. Severance of the GnRH pathway on one side or partial interruption of the pathway on the two sides in the retrochiasmatic area did not interfere with ovulation, and the ME GnRH content was 50% or more of the control value. Disconnection of the GnRH fibers coming from the septum resulted in a more than 30% decrease in the GnRH content of the ME, but did not block ovulation. Two separate symmetrical lateral cuts in the suprachiasmatic area leaving intact the presently known GnRH pathway reduced the ME GnRH content to 40% of the intact value, but did not interfere with ovulation. Plasma LH and FSH levels of the animals with different knife cuts were considerably dissociated and there were no apparent correlations between brain interventions and the concentrations of these two hormones in the blood. Our previous findings together with the present data suggest that: (1) half of the GnRH pathway, medial or lateral bundles of the pathway on the two sides are sufficient for ovulation and cyclic gonadotrophic function; (2) persistent estrus develops if the ME GnRH content is below 40% of the control value, and (3) about 60% of the ME GnRH originates outside the preoptic, supra- and retrochiasmatic region. Half of this 60 % may come from the septum and the vertical part of the diagonal band of Broca, the other half from the region in front of the preoptic area. The remaining 40% presumably arises from the preoptic (7–10%), supra- (15–20%) and retrochiasmatic region (8

ISSN:0028-3835    

DOI:10.1159/000124642

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The role of the α2-adrenergic system in regulating prolactin release has been studied in vivo in male rats. Yohimbine administration alone, at doses ranging from 0.2 to 5.0 mg/kg, resulted in a dose-releated elevation of plasma prolactin levels from a basal level of 8 ± 2 to 65 ± 6 ng/ml at the highest dose. In the same experiment clonidine, 0.2 mg/kg, suppressed basal prolactin levels to 4+ 1 ng/ml and returned prolactin levels of all animals receiving 0.2–5.0 mg/kg yohimbine to basal levels. Rats were treated with increasing doses of clonidine (0.05–1.0 mg/kg) in the presence or absence of a constant dose (1.0 mg/kg) of yohimbine. Clonidine alone at doses of 0.05 and 0.2 mg/kg again significantly suppressed prolactin levels, while a dose of 1.0 mg/kg did not (failure of high dose clonidine to suppress prolactin levels suggests an additional effect of clonidine on prolactin secretion unrelated to α2-adrenergic agonist action). All three doses of clonidine completely reversed yohimbine-induced prolactin release. Basal prolactin levels were also significantly reduced by the selective α2-adrenergic agonist UK-14,304 at a dose of 0.2 mg/kg. Yohimbine-induced prolactin release was reversed by UK-14,304 at doses of 0.2 and 1.0 mg/kg, but not at the lowest dose studied, 0.05 mg/kg. The lower potency of UK-14,304 than clonidine in this assay is consistent with the lower potency of UK-14,304 as an α2-adrenergic-agonist antihypertensive agent. Several α2-antagonists in addition to yohimbine were studied. Both Wy-26,703 and piperoxan administration resulted in elevated plasma prolactin levels; these effects were reversed by clonidine treatment. A 3-fold reduction in prolactin levels was observed in the hyperprolactinemic state of lactating rats following a 0.2 mg/kg dose of clonidine. Our data demonstrate that the α2-adrenergic system is involved in inhibiting prolactin release since (1) α2-agon-ists lower basal prolactin levels, (2) α2-antagonists elevate prolactin levels, and (3) prolactin levels not different from basal ones are observed when appropriate doses of agonists and antagonists are administered i

ISSN:0028-3835    

DOI:10.1159/000124643

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Cycling rats injected with 2-hydroxyestrone or 2-hydroxyestradiol at 09.00 or 10.00 h in the morning of proestrus do not express the normal preovulatory LH surge in the afternoon of the day. The LHRH content of the median eminence in control animals decreases sharply in the afternoon from elevated noon and morning levels. The catechol estrogen-treated rats fail to show the decrease. Thus the catechol estrogens block the LH surge at its usual time by influencing the changes in the concentration of LHRH in the median eminence on proestrus. Since the catechol estrogens have short biological half-lives, their effect on the LHRHcontent in the afternoon must originate in the morning at the time of the endogenous estradiol (E2) peak. These results have implications in the physiological processes responsible for the positive feedback of estradiol on the preovulatory LH surge in the rat.

ISSN:0028-3835    

DOI:10.1159/000124644

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

These experiments were designed to examine which aspects of basal and responsive somatotroph and lactotroph synthesis and release behavior in vitro are functions of in vivo tonic hypothalamic environment. Although we cannot specifically define in vivo hypothalamic tone, we show that spontaneous rates of hormone synthesis and release in vitro, as well as release in response to a secretagogue, are influenced by altered in vivo hypothalamic tone. This work combines in vivo destruction of hypothalamic (ventromedial [VMN] or dorsomedial [DMN]) nuclei with in vitro double-label perifusion to track hormone synthesis and release of newly synthesized and stored hormone. We demonstrate that hormone synthesis rates are greater in DMN-lesioned (DMNL) or sham-operated (SHAM) animals than in VMN-lesioned (VMNL) animals and that DMNL and SHAM synthesis rates fall with time outside the hypothalamic environment. We show that basal release of newly synthesized rGH by DMNL tissue exceeds that of SHAM, while release from VMNL tissue is less than that of SHAM. Accidental placement of small bilateral lesions between and not impinging on either the DMN or VMN nuclei did not alter newly synthesized rGH release but accelerated newly synthesized rPRL release. Although basal fractional release of stored growth hormone and prolactin was the same for the three groups, potassium ion-induced release of stored hormone was similar in DMNL or SHAM tissue, but depressed in VMNL tissue. Thus, the creation of definable hypothalamic damage in a living animal produced specific modifications in in vitro pituitary synthetic/secretory behavior, presumably by reproducibly altering hypothalamic secretion. Within the limits of the lesion technique and defined experimental options, somatotroph and lactotroph synthetic/secretory behavior predicted the hypothalamic lesion. We conclude that resting rGH and rPRL synthesis, release, as well as storage compartmentalization in vitro exhibit specific and independent variability indicative of the in vivo hypothalamic environment from which the tissue was obtained.

ISSN:0028-3835    

DOI:10.1159/000124645

出版商:S. Karger AG    

年代:1986

数据来源: Karger