Showing papers in "Neuroendocrinology in 1975"

Reproductive capacity of aging female rats.

Abstract: Multiparous female Long-Evans rats, 20 months or older, were seen to progress from irregular estrous cycles to a constant-estrous syndrome to a series of irregular pseudopregnancies to an anestrous state. An animal in constant estrus was characterized by ovaries with well developed and sometimes cystic follicles, no corpora lutea, an estrogen-stimulated uterus, and an anterior pituitary that appeared normal. Repeatedly pseudopregnant rats had long diestrous periods of variable length, ovaries with many corpora lutea, uteri with numerous secretory glands, and anterior pituitaries that often showed hemorrhagic or small tumorous areas. Anestrous rats had small, atrophic ovaries with no obvious follicular or luteal elements, atrophic uteri, and large pituitary tumors. Twice-daily injections of L-dopa induced the resumption of regular or irregular estrous cycles in most constant-estrous but not in pseudopregnant or anestrous rats.

The Effect of Various Putative Neurotransmitters on the Release of Corticotrophin Releasing Hormone from the Hypothalamus of the Rat in vitro. I. The Effect of Acetylcholine and Noradrenaline

Abstract: The effect of various putative neuro-transmitters upon the release of corticotrophin releasing hormone (CRH) was investigated using the hypothalamus of the rat in vitro . Acetylcholi

First Geoffrey Harris Memorial Lecture. Some Recent Developments in Brain-Pituitary-Ovarian Physiology

Abstract: Figure 14 summarizes some of the brain-pituitary-ovarian relationships which we have been discussing. Neurons in the arcuate nucleus of the hypophysiotropic area produce LRH which is secreted into the proximal capillary plexus of the hypophysio-portal system in the median eminence. LRH production is modulated in the rat and possibly also in the monkey by direct input from the preoptic region and less directly by facilitatory and inhibitory projections from the amygdala, hippocampus and midbrain. Electrophysiological evidence has been presented for "ultrashort' feedback action of LRH on arcuate neurons as well as the "short' feedback loop of LH. Gonadal steroids are pictured as feeding back directly to the pituitary and to several sites in the brain where positive and negative influences are exerted on both pituitary-ovarian function and sexual behavior. Evidence has been presented that adrenergic mechanisms influence LRH release with norepinephrine facilitatory and dopamine inhibitory to the process; dopaminergic neurons may be more intimately related to the control of prolactin secretion, and some consider dopamine and prolactin inhibiting factor to be identical. Finally, immunological methods as represented by immunohistochemistry and radioimmunoassay promise further important developments in this field in the near future. I am sure that Geoffrey Harris would have been pleased with the progress made in answering the questions which he raised in his Dale lecture.

Effect of meal feeding on daily rhythms of plasma corticosterone and growth hormone in the rat.

Abstract: After rats had adapted to regular meal feeding in the morning they demonstrated an altered circadian rhythm of plasma corticosterone (B) even under the normal light-dark cycle. The altered daily rhythm of plasma B consisted of two peaks, with one peak at 08.00 h in anticipation of meal feeding and a second peak corresponding to the normal peak of plasma B prior to lights-off seen in ad libitum-fed animals. Neither peak of plasma B in the meal-fed animals achieved the magnitude of the single peak observed in control animals. In spite of some quantitative differences during certain periods of the day, after the animals had adapted to meal feeding there was no difference in the basic profile of the daily rhythm of plasma immunoactive growth hormone (GH).

Growth hormone effects on sleep and wakefulness in the rat.

Abstract: The sleep-wakefulness pattern and brain protein levels were determined in rats for 3 h following these conditions: administration of an inhibitor of protein synthesis (anisomycin), administration of several doses of rat growth hormone (GH) or thyrotropin, and administration of a combination of anisomycin + GH or thyrotropin. Anisomycin inhibited sleep and increased wakefulness, GH increased REM sleep, and thyrotropin produced no change. The combined administration of GH and anisomycin returned sleep to control levels. Anisomycin produced a time-dependent decrease in brain protein levels, GH produced changes in brain protein levels as compared to controls in the second hour only, and thyrotropin had no effect upon brain protein levels. The results are discussed in terms of the possible relationship between sleep and proteins.

Effects of Stress on Catecholamines and Tyrosine Hydroxylase Activity of Individual Hypothalamic Nuclei

Abstract: The effects of acute stress on norepinephrine (NE) and dopamine (DA) concentrations and of repeated stress on tyrosine hydroxylase (TH) activity were measured in individual hypothalamic nuclei and oth

Action of luteinizing hormone-releasing factor (LRF) in the initiation of lordosis behavior in the estrone-primed ovariectomized female rat.

Abstract: In order to evaluate the precise role of luteinizing hormone-releasing factor (LRF) in mediating the onset of sexual behavior, the specificity, time-course, and dose-response relationship of LRF-facilitated lordosis behavior were determined. Ovariectomized female rats, pretreated with estrone and LRF, displayed a pattern of lordosis behavior which differed little from that produced by estrone-progesterone. Little if any lordosis behavior was observed in response to LRF alone, estrone alone, or estrone in combination with luteinizing hormone (LH), follicle-stimulating hormone (FSH), or thyrotropin-releasing factor (TRF). Furthermore, LRF-induced lordosis behavior occurred in the absence of the adrenals, thus eliminating adrenal progesterone as a factor in facilitating the appearnce of lordosis behavior. The LRF-facilitated lordosis behavior was seen 2 h after the injection of LRF and was maintained for a total of 8 h. A minimal dose of 150 ng LRF was required to initiate the first consistent appearance of lordosis behavior; the maximum response was obtained with 500 ng. It is thus suggested that LRF is not only responsible for the ovulatory discharge of LH and subsequent ovulation, but may also play a role in the initiation of the onset of mating behavior in the female rat.

Diurnal variations in plasma corticosterone and growth hormone as corrlelated with regional variations in norepinephrine, dopamine and serotonin content of rat brain.

Abstract: Statistically significant diurnal variations in plasma growth hormone (GH) were found to occur in handled male rats. Peak GH values (at midday) appeared to be inversely correlated with the diurnal pea

Effect of Adrenocortical Hormones on Activity of the Serotoninergic System in Limbic Structures in Rats

Abstract: A single dose of corticosterone (1 mg/kg b.w. i.p.) increased the 5-hydroxytryptamine (5-HT) content in the mesencephalon, amygdala and hypothalamus. The maximum was observed at 15 min following admin

Effects of melatonin on neurotransmitter uptake and release by synaptosome-rich homogenates of the rat hypothalamus

Abstract: Preincubation of synaptosome-rich homogenates of rat hypothalamus with melatonin resulted in significant decreases of norepinephrine, serotonin, dopamine and glutamate uptake. Melatonin inhibition was noncompetitive; apparent Km's of initial uptake processes were: (2.5 +/- 0.3) x 10(-7) M for norepinephrine, (2.6 +/- 0.3) x 10(-7) M for serotonin, (2.4 +/- 0.4) x 10(-7) M for dopamine and (1.0 +/- 0.3) x 10(-7) M for glutamate. Apparent Ki's for melatonin inhibition of transmitter uptake were: 0.64 +/- 0.14 mM (norepinephrine), 0.23 +/- mM (serotonin), 0.51 +/- 0.08 mM (dopamine) and 1.21 +/- 0.10 mM (glutamate). Transmitter release evoked by increasing [K+] in medium to 30 mM was augmented by melatonin in a dose-dependent manner. Maximal effects were observed on serotonin release. Accumulation of 3H-melatonin within synaptosome-rich homogenates did not exhibit differences between 0 and 37 degrees C, indicating that the uptake of the hormone was not an active process. These results suggest that exogenously-administered melatonin may affect neurotransmitter accumulation and release in the hypothalamus by modification of the transmitter uptake mechanism rather than by competition with the transmitter for its uptake pump.

Prolactin Release Induced by Electrical Stimulation of the Hypothalamic Preoptic Area in Unanesthetized Sheep

Abstract: The hypothalamic preoptic area (POA) was electrically stimulated through permanently implanted electrodes in 4 unanesthetized sheep. Initiation of POA stimulation was followed within 10–20 min by larg

Changes in the serum levels of the gonadotrophins progesterone and estradiol during the estrous cycle of the guinea pig.

Abstract: Using heterologous radioimmunoassay systems, it has been possible to demonstrate a complete cross-reaction between partially purified preparations of guinea pig FSH and LH and the corresponding rat gonadotrophins. On this basis, radioimmuno-assays for these 2 gonadotrophins have been established and they have been used in order to study changes in blood hormonal levels during the estrous cycle. There is a serum LH peak during estrus shortly before ovulation. At ovulation, serum LH levels show a smaller increase which is maintained for 1 or 2 days. The changes in serum FSH levels do not systematically coincide with those of LH. A parallel study of the changes in serum progesterone and estradiol was also performed. The levels of estrogen increased during the pre-ovulatory period, reaching a maximum shortly before the pre-ovulatory LH peak. Progesterone does not increase until shortly thereafter.

Compensatory adrenal growth is neurally mediated.

Abstract: We have tested the possibility that compensatory adrenal growth is neurally mediated. Small unilateral electrolytic lesions were made in the ventral hypothalamus of young male rats. Subsequently, unilateral adrenalectomy was performed on the side ipsilateral or contralateral to the hypothalamic lesion. Four days later the animals were killed and the remaining adrenal was weighed; the location and extent of the hypothalamic lesions were determined. Lesions placed on the same side as adrenalectomy prevented compensatory growth of the remaining gland (p less than 0.005), while lesions on the side opposite to the removed adrenal did not interfere with compensatory adrenal growth. We conclude from these findings, and from a review of some anatomical studies, that compensatory adrenal growth is effected through a reflex that involves both afferent and efferent neural limbs.

Effect of Exposure to Cold on Hypothalamic TRH Activity and Plasma Levels of TSH and Prolactin in the Rat

Abstract: No significant change in hypothalamic TRH content was found in rats during acute (5-240 min) exposure to cold (5 degrees C), in spite of rapid and sustained elevations in plasma TSH and thyroxine. Plasma PRL rose markedly in the first 15 min, but returned to normal thereafter. Chronic exposure to cold (32 days) was characterized by elevated plasma and pituitary levels of both TSH and PRL in the presence of an unaltered hypothalamic TRH content. If increased TRH release from the hypothalamus occurs during exposure to cold, as suggested by the pituitary-thyroid stimulation, either it is compensated for by an equal rise in synthesis, or the extra amount released is negligible in comparison with the hypothalamic content of TRH. The acute PRL response to exposure to cold may be related to an acute TRH release but could also result from the accompanying stress response acting by a mechanism independent of TRH.

Stimulatory effect of prostaglandin E2 on LH release in the rat: evidence for hypothalamic site of action.

Abstract: The intravenous administration of prostaglandin E2 (PGE2; 100 µ g/rat) to immature male and female rats increased the serum level of luteinizing hormone (LH). T

Radioimmunoassayable avt and avp in adult mammalian brain tissue: comparison of normal and brattleboro rats.

Abstract: Arginine vasopressin (AVP) and vasotocin (AVT) were measured by radioimmunoassay in extracts of cerebral cortex, cerebellum, brain stem, pineal, hypothalamus, and neurohypophysis from normal Long-Evans rats. AVP was present in expected concentrations in pituitary and hypothalamus and there was no evidence of its accumulation elsewhere. AVT was not detectable in these tissues (within the limits imposed on our assay by the presence of excessive amounts of AVP) but was easily detectable in pineal tissue with a concentration of 22.4 ± 6.6 µU/gland. Extracts of neurohypophysis and pineal glands from homozygous Brattleboro rats (rats with hereditary hypothalamic diabetes insipidus) revealed the total absence of AVP and AVT. We conclude that the Brattleboro rat is incapable of synthesizing biologically active neurohypophyseal peptides which contain arginine in position 8.

The stimulatory effect on gonadotropin release of implants of estradiol or progesterone in certain sites in the central nervous system.

Abstract: The sites of stimulatory feedback of ovarian steroids on gonadotropin release were examined. In estrogen-primed ovariectomized rats, estradiol or progesterone was implanted stereotaxically into variou

Prostaglandin E2-induced release of luteinizing hormone-releasing factor (LRF).

Abstract: Prostaglandin E2 (PGE2) injected into the third ventricle (3rd V) of conscious ovariectomized rats bearing a permanent jugular cannula increased the percentage of plasma samples

Potentiation of Luteinizing Hormone Release by Estradiol at the Level of the Pituitary

Abstract: The objective of this study was to determine the influence of estradiol-17 β and/or progesterone on gonadotropin secretion at the level of the pituitary. Female rats in which the hyp

Amygdalar participation in tonic ACTH secretion in the rat.

Abstract: The role of the amygdaloid complexes in the compensatory hypersecretion of ACTH following adrenalectomy was studied in the adult male rat. Unilateral or bilateral radiofrequency or knife-cut lesions were placed in the amygdalae, their efferent pathways or the septal region. Three weeks following adrenalectomy resting plasma ACTH concentrations were measured by radioimmunoassay. Bilateral lesions of a direct medial-projecting portion of the ventral amygdalo-hypothalamic pathway blocked the compensatory hypersecretion of ACTH following adrenalectomy. A unilateral complete amygdalar lesion coupled with destruction of the same direct amygdalo-hypothalamic pathway on the opposite side had the same positive effect. In contrast, unilateral destruction of the direct amygdalo-hypothalamic projections, ablation of the septum, or bilateral destruction of the stria terminalis did not block hypersecretion of ACTH following adrenalectomy. These data suggest that the amygdalae and their direct hypothalamic projections, but not the stria terminalis or septum, are essential for the hypersecretion of ACTH following adrenalectomy. Furthermore, one amygdaloid complex appears sufficient for this effect. It is possible that the amygdalae act as a central nervous system ‘glucocorticoid-sensor’ in the modulation of ACTH secretion in the rat.

Serotoninergic control of rat growth hormone secretion.

Abstract: The ability of 5-hydroxy-L-tryptophan (5-HTP) or pentobarbital anesthesia to elevate rat serum GH levels is completely blocked by the simultaneous administration of the serotonin antagonist cyprohepta

Further studies on the maturation of the estrogen negative feedback on gonadotropin release in the female rat.

Abstract: To evaluate estrogen negative feedback in infantile female rats, 9-day-old rats were ovariectomized (OVX) and treated with different doses of estradiol benzoate (Eb, s.c. once daily for 2 days); plasm

On the presence of a MSH-release inhibiting system in the rat neurointermediate lobe.

Abstract: Rat neurointermediate lobes were superfused in vitro and showed a stable secretion rate of MSH after 30 min. MSH secretion from lobes of untreated rats was reversibly inhibited during superfusion with medium containing 45 mM K+. This inhibition could not be induced using lobes from median eminence lesioned or reserpinized rats. Superfusion with 45 mM K+ also induced release of dopamine from lobes preincubated with the labeled transmitter. It is concluded that the MSH-release inhibiting system present in the rat neurointermediate lobe may be identical to the dopaminergic arcuate-intermediate lobe system.

Effects of Iontophoretically-Applied Prolactin on Unit Activity of the Rat Brain

Abstract: The effects of prolactin and other hormones applied electrophoretically to 400 neurons in the brain were studied in rats under urethane anesthesia. 51 prolactin-activated neurons were distributed main

Facial receptive fields of trigeminal neurons: increased size following estrogen treatment in female rats.

Abstract: In order to assess the generality of previous reports of enlarged genital sensory fields following estrogen treatment, facial receptive fields of individual trigeminal ganglion neurons from ovariectomized female rats injected with estrogen were compared with fields from noninjected controls. Mechanoreceptive field boundaries were determined with a series of stimulating probes varying in diameter, and calibrated according to the force delivered at the bending point (Von Frey technique). For each single unit, the threshold receptive field was determined with the smallest stimulus probe capable of reliably activating single unit discharges. Facial receptive fields from estrogen-treated females were significantly larger in area (by a factor of 10) than fields from noninjected controls. Furthermore, the increase in field area was independent of spatial location within the facial region (normally, field size decreases in a proximal-distal direction from the body trunk), and was not affected by cutting the trigeminal nerve root. Receptive field thresholds were also significantly lowered by estrogen treatment. The fact that long-term systemic estrogen treatment influences tactile sensory fields in the facial region of females suggests that this phenomenon is not peculiar to the genital region normally contacted by the male during mating.

Immunofluorescence study of LRF-producing neurons in the cat and the dog.

Abstract: A fluorescent antibody study of LRF-producing neurons was made with antisera to synthetic LRF in normal male and female cats and dogs Specific immunoreactive perikarya have been found in the rostral hypothalamus of both species In the dog, specific immunoreactive perikarya have also been found in the pars oralis tuberi, the infundibular nucleus, the premammillary region, and even the dorsomedial and ventromedial areas and the rostral mesencephalon

Effect of intraventricular glutamate on ACTH release.

Abstract: Sodium glutamate infused into the 3rd ventricle is a potent stimulus of ACTH release, as shown by the rise in plasma corticosterone levels. Glutamate failed to consistently increase the plasma corticosterone level in rats with deafferentation of the medial basal hypothalamus (MBH). We suggest that intraventricular glutamate interferes with central nervous function outside the MBH and stimulates ACTH release via afferent neural pathways.

Inhibition of ADH release in the rat by narcotic antagonists.

Abstract: The diuretic action of two new narcotic antagonists, oxiiorphan and butorphanol, was studied in rats heterozygous for hereditary hypothalamic diabetes insipidus. Both drugs caused a prompt increase in

Effects of estrogen on neuronal excitability in the hippocampal-septal-hypothalamic system.

Abstract: The effects of electrical stimulation of the medial preoptic area (MPO) upon unit firing in the periventricular arcuate nucleus, and that of the dorsal hippocampus (DHPC) on medial septo-preoptic and

Changes in hypothalamic neurotransmitter uptake following pinealectomy, superior cervical ganglionectomy or melatonin administration to rats.

Abstract: Rats subjected to pinealectomy or to pinealectomy plus bilateral superior cervical ganglionectomy exhibited depressed serotonin uptake by hypothalamic synaptosomes; norepinephrine, dopamine or glutamate uptake was not affected by any of the surgical procedures. Treatment with melatonin resulted in inhibition of hypothalamic serotonin accumulation but it did not modify the uptake of norepinephrine, dopamine or glutamate. These data suggest a relationship between the pineal gland and the serotoninergic nerve endings of the hypothalamus.