摘要:

The enzyme which converts norepinephrine to epinephrine, phenylethanolamine N-methyltransferase (PNMT), is found in brain as well as in the adrenal medulla. PNMT activity is subject to regulation by glucocorticoids, hormones which have a diurnal rhythm. We asked (1) whether a diurnal fluctuation exists in adrenal and brain PNMT activity and (2) what relationship this fluctuation might have to the diurnal rhythm in circulating glucocorticoids. Rats were sacrificed at 4-hour intervals over a 24-hour period. The PNMT activity in the adrenals and brainstems of these animals was determined by radioenzymatic assay, and the plasma levels of corticosterone were measured by competitive protein binding. No significant temporal variation was found in adrenal PNMT activity. Brainstem PNMT activity, however, showed a distinct diurnal fluctuation in activity, with a nadir at 7 a.m. and a peak at 3 p.m. The rise in brainstems PNMT clearly preceded by several hours the circadian rise in plasma corticosterone. We conclude that the circadian rhythm in circulating corticosterone does not drive the diurnal variation in brain PNMT activity. In unstressed animals, injection of exogenous corticosterone failed to elevate brainstem PNMT activity, whereas injection of specific inhibitors of PNMT activity significantly elevated plasma corticosterone levels. These data raise the possibility that the converse is true: changes in epinephrine synthesis may modulate the diurnal rhythm in pituitary-adrenal activity.

ISSN:0028-3835    

DOI:10.1159/000123169

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

To study the effect of pinealectomy (Px) on the rhythms of serum indoles, male rats were adapted to 12L:12D for 2 weeks after which half of them were Px. The animals were decapitated at 4-hour intervals 1 week after operation. Melatonin (Mel) and N-acetylserotonin (NAS) were extracted and quantified by RIA. The concentrations of serum Mel and NAS were significantly reduced after Px, suggesting that the pineal contributes a significant amount of these to the blood. However, circadian rhythms of them were not abolished by Px, indicating the existence of extrapineal sources at least one of which is capable of secreting Mel and NAS with a diurnal rhythm. Retina is suspected to be an important source.

ISSN:0028-3835    

DOI:10.1159/000123170

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

30-day-old male rats were (1) sham-operated or subjected to (2) removal of the olfactory bulbs, (3) olfactory bulbectomy and blinding, (4) olfactory bulbectomy and pinealectomy or (5) olfactory bulbectomy, blinding and pinealectomy. Animals were exposed from 30 to 110 days of age to long-day (14 h of light per day) or short-day (8 h of light per day) photoperiods. The reproductive system of neurologically-intact rats was not affected by exposure to short days. Nor did bulbectomy affect the reproductive system of rats exposed to long days. However, bulbectomized, short-day rats had significantly lower body weights, reduced testicular and seminal vesicle weights and lower plasma testosterone levels than did bulbectomized, long-day rats. The effects of short-day exposure on bulbectomized rats were prevented by pinealectomy. Short-day exposure and blinding exerted similar effects in bulbectomized rats. The testes of rats from all groups contained elongated spermatids; blinding and short-day treatment had no effect on spermatogenesis. Neither mating behavior nor the number of young sired was influenced by photoperiod in bulbectomized or intact rats. Removal of the olfactory bulbs unmasks photoperiodic responsiveness in rats; the antigonadal effects of short-day exposure are mediated by the pineal gland in bulbectomized rats as in species traditionally designated photoperiodic. The mechanisms by which bulbectomy renders rats responsive to short days are considered.

ISSN:0028-3835    

DOI:10.1159/000123171

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Adult male mice previously isolated for 14 days, were maintained in pairs as residents and intruders. They were categorized as dominant or subordinate on the basis of initiation of attacks and of wounding. After 10 days, the amount of free cytoplasmatic testosterone receptors was determined in a part of the basal forebrain consisting of septum, diencephalon, corpus striatum, and amygdala. In addition, the plasma testosterone level and the activity of the adrenal tyrosine hydroxylase were measured. The adrenal tyrosine hydroxylase activity was increased in the dominant and the subordinate mice compared to isolated controls. Subordinates had higher tyrosine hydroxylase activities than dominants. The specific testosterone receptors in brain cytosol of dominants were freed like those of 6-day castrates despite the fact that the plasma testosterone concentration of dominants (717 ng/100 ml) was not significantly decreased compared to controls (1,003 ng/100 ml). In subordinates, the plasma testosterone content fell to 265 ng/100 ml while castrated mice showed 20–43 ng/100 ml. The amount of free testosterone specific binding sites in the brain cytosol of subordinates corresponded to that of 10-day castrates. Thus, the amount of circulating total testosterone does not seem to be the only factor determining the binding of available testosterone in brain cytoso

ISSN:0028-3835    

DOI:10.1159/000123172

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Stress of immobilization suppressed pulsatile LH release and decreased mean serum LH levels within 10 min, lasting at least for 2 h in ovariectomized rats. Anterior cuts (radius, 2 mm) at the level of the caudal border of the suprachi-asmatic nucleus, resulted in elimination of the stress-induced LH suppression. A smaller cut (radius, 1 mm) at the same level induced increased LH secretion without a period of inhibition in some rats by the stress. Extended anterior cut at the level of the border between the medial preoptic and the anterior hypothalamic area, partially inhibited the suppressive effect of the stress on LH secretion; that is, LH pulses resumed within 2 h. A more extended anterior cut at the level of the anterior border of the medial preoptic area, or a posterior or small posterior cut at the level of the midmammillary body, had no effect on the LH suppression by the stress. Basal LH levels prior to the stress were lower in the groups which had neural deafferentation in the anterior area to the mediobasal hypothalamic, but not in the groups with posterior deafferentation, compared with the sham control. Serum prolactin response to the immobilization was inhibited almost completely by an anterior, small anterior, posterior or small posterior cut. Extended anterior cuts inhibited the stress-induced prolactin release in about half of the animals, whereas a more extended anterior cut had no effect. Any kind of deafferentation except the posterior or small posterior cut failed to change basal nonstressed prolactin levels as compared to those in sham-operated rats. The rats bearing a posterior or small posterior cut had significantly lower serum prolactin levels prior to the immobilization. These results indicate that the stimulus necessary for stress-induced LH suppression and for the maintenance of the basal LH levels may reach the mediobasal hypothalamus from the anterior direction. The stress-evoked inhibitory stimulus for LH-RH release may interact, at the anterior hypothalamus-suprachiasmatic region, with the LH-RH neuron or inputs regulating the LH-RH neuron. Both neural connections from anterior and posterior directions to the medial basal hypothalamus seem to be indispensable for the stress-induced prolactin release and the input from the posterior direction for maintaining the nonstressed basal prolactin levels.

ISSN:0028-3835    

DOI:10.1159/000123173

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The appearance and relative distribution of immunoreactive gonadotropic and thyrotropic cells of the anterior pituitary of normal rat fetuses were studied by immunocytology with anti-rat luteinizing hormone serum, anti-porcine luteinizing hormone β serum, anti-bovine thyrotropic hormone serum after saturation with bovine luteinizing hormone. The thyrotropic cells appeared at 17 days of gestation. They were preferentially localized in the dorsal part of the anterior lobe. The gonadotropic cells localized in the ventral part of the same lobe, appeared 1 day later. The number of immunoreactive cells of the two populations increased until the end of gestation. In the pituitaries of 21-day-old rat fetuses encephalectomized at 16 days of gestation, the same number of gonadotropic and thyrotropic cells was observed as in control fetuses at the same age. Gonadotropic cells were also observed in rat adenohypophysial primordia explanted at 14 days of gestation and maintained in organ culture for 7 days. Thyrotropic cells were only stained when the primordia were explanted at 15 days of gestation and cultured for 6 days. No immunoreactive gonadotropic or thyrotropic cells were detected when explantation was performed before 14 days of gestation. These results clarify the problem of the role of hypothalamus on the differentiation of these two cell types

ISSN:0028-3835    

DOI:10.1159/000123174

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The ligand binding properties of muscarinic receptors present in whole hypothalamus as well as in its three regions (preoptic area, median and posterior regions) were studied in male rats and mice, as well as in female rats during various stages of the estrous cycle, using the tritiated antagonist N-methyl-4-piperidyl benzilate. Kinetic and equilibrium analysis of antagonist binding as well as competition experiments with agonists, were used to probe the nature of the binding sites and possible differences between specific muscarinic sites in the various preparations. We could detect differences in agonist binding parameters between male and female rats in the preoptic area. In female rats binding of agonist to high affinity state is characterized by a lower affinity (27 nM) than in males (3.7 nM). Secondly, the population of agonist high affinity sites at the proestrous stage is much higher than that at other stages of cycle (66 vs. 38%). In addition, the binding properties of muscarinic receptors following intracisternal 6-hydroxydopamine lesion were investigated. This treatment resulted in a decrease of about one sixth of the total muscarinic receptors in the hypothalamus. The data are best interpreted as a degeneration of existing presynaptic muscarinic receptors located on catecholamine terminals in the hypothalamus. The pre- and postsynaptic nature of the muscarinic receptors, their localization in view of their binding properties, and their possible physiological role are discussed.

ISSN:0028-3835    

DOI:10.1159/000123175

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The ligand binding properties of muscarinic receptors present in rat adenohypophysis were studied using the tritiated antagonists N-methyl-4-piperidyl benzilate, 3-quinuclidinyl benzilate, and methylscopolamine. Equilibrium analysis of antagonists binding as well as competition experiments with several agonists were used to probe the nature of binding sites. The nature of antagonist binding in the adenohypophysis points to heterogeneity of binding sites, in contrast to other brain regions, in which homogeneous populations of muscarinic receptors were detected. Some of the binding properties, e.g. affinity constants, population of high affinity agonist binding sites, etc., clearly indicated differences between male and female rats as well as differences in female rats at various stages of estrous cycle. The nature of these receptors and their possible physiological role are discussed.

ISSN:0028-3835    

DOI:10.1159/000123176

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

[3H]-[3-methyl-His2]thyrotropin releasing hormone ([3H]MeTRH) binds to sites in the sheep anterior pituitary gland which appear to be the same as those occupied by [3H]TRH and which can therefore be identified as TRH receptors. In competition experiments performed in parallel, both ligands gave the same number of binding sites, 15 pmol/g wet weight, and showed the same pharmacology for 19 TRH analogs ranging over more than 5 orders of magnitude in potency. The apparent dissociation constant of binding of [3H]MeTRH was about 3.5 nM compared to 29 nM for [3H]TRH. Kinetic experiments with [3H]MeTRH yielded a rate constant for association of 1.4 × 107M–1 min–1 and rate constants for the bi-phasic dissociation of 5 × 10–2 min–1 (fast phase) and 7 × 10–3 min–1 (slow phase). Detailed methods are described for preparation of [3H]MeTRH by reduction of the dehydroproline precursor and its purification by ion exchange and antibody affinity chromatography. The major advantage of the new ligand is that its higher affinity of binding gives relatively less nonspecific binding than is obtained with [3H]TRH, particularly in central

ISSN:0028-3835    

DOI:10.1159/000123177

出版商:S. Karger AG    

年代:1981

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000123178

出版商:S. Karger AG    

年代:1981

数据来源: Karger