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F P Gibbs

Publications and source records attributed to F P Gibbs.

At least 19 recordsLinked to original sources
PubMed1987

Ultrastructural localization of glucocorticoid receptor (GR) in hypothalamic paraventricular neurons synthesizing corticotropin releasing factor (CRF).

Corticotropin releasing factor (CRF) synthesizing neurons, located in the hypothalamic paraventricular nucleus (PVN), are the main central regulators of the pituitary-adrenal cortex endocrine axis. The hormone production and release of CRF-synthesizing neurons is regulated by neuronal messages and feedback action(s) of glucocorticoids secreted by the adrenal gland. In order to characterize the latter mechanism, glucocorticoid receptor (GR)-immunoreactive (IR) sites were studied in hypothalamic paraventricular neurons of intact, long-term adrenalectomized, and adrenalectomized plus glucocorticoid treated animals, by means of ultrastructural immunocytochemical labelling. In intact animals, glucocorticoid receptor immunoreactivity was found predominantly in the nuclei of parvocellular neurons. Following adrenalectomy GR-immunoreactivity was localized in the cytoplasm of the cells, and there was a concomitant disappearance of the label from the nuclei. After corticosterone administration to adrenalectomized animals, GR-IR sites were again concentrated within the cell nuclei. Immunocytochemical double labelling studies performed on adrenalectomized plus corticosterone-replaced animals demonstrated glucocorticoid receptor-IR sites in the cell nuclei of parvocellular paraventricular neurons that expressed CRF-immunoreactivity in their cytoplasm. These ultrastructural data indicate that the intracellular location of glucocorticoid receptor is dependent on the availability of glucocorticoids by the neurons. The simultaneous expression of GR- and CRF-immunoreactivity in parvocellular paraventricular neurons supports the concept of a direct feedback action of glucocorticoids upon CRF-synthesizing neurons.

Animals↗
PubMed1986

Exercise reduces gonadal atrophy caused by short photoperiod or blinding of hamsters.

The effect of voluntary exercise upon several reproductive parameters was assessed in male Syrian hamsters. Forty-two animals were caged in five groups and then blinded: Ten housed five per plastic cage; eight housed individually in plastic cages; six housed individually in plastic cages with 15 cm exercise wheels in the cage; eight housed in Wahmann steel activity cages with 36 cm wheels locked to prevent rotation; ten housed in functional Wahmann running wheel cages. At 16 weeks after blinding, animals with access to functional running wheels had significantly larger testes (3.7 +/- 1.0 g) than those with no wheels or locked wheels (1.86 +/- 0.6 g; mean +/- SD; p less than 0.001). These results suggested that voluntary exercise reduces testicular atrophy caused by blinding. A second experiment was run in which the animals were subjected to a short photoperiod (LD 6:18) for 12 weeks instead of blinding. Similar results were obtained except that access to the small exercise wheels did not affect testicular atrophy: Mean testicular mass of animals in individual cages = 0.79 +/- 0.3 g, small wheels = 0.74 +/- 0.4 g, functional Wahmann wheels, 2.56 +/- 1.0 g, locked Wahmann wheels 0.52 +/- 0.1 g (p less than 0.01).

Animals↗
PubMed1984

Coincidence of counter-antigonadal and counter-antithyroid action of melatonin administration via the drinking water in male golden hamsters.

Administration of melatonin via the drinking water prevented the gonadal involution and the thyroid hormone depletion normally observed in blinded hamsters. Ten weeks after blinding male hamsters had plasma thyroxin levels that were 57% of controls and testis weights that were 8% of controls. Administration of melatonin (80 microgram melatonin/ml drinking water) to blinded hamsters restored thyroxin levels to 86% of controls and testis weights to 93% of controls. Dose response data showed that as little as 1.25 microgram (approximately 10 microgram/hamster/day) produced a significant effect on testis weight, whereas the lowest dose required to produce a significant increase in thyroxin levels was 10 microgram/ml. The coincidence of counter-antigonadal and counter-antithyroid actions of melatonin suggests a single site of action.

Animals↗
PubMed1984

Immunohistochemical localization of corticotropin releasing factor (CRF) in the hypothalamus of the squirrel monkey, Saimiri sciureus.

Corticotropin releasing factor immunoreactive (CRF-IR) neuronal cell bodies and fibers have been localized in both the paraventricular and supraoptic nuclei of the hypothalamus of the squirrel monkey. The major projection from these nuclei is to the median eminence and neural stem. A few CRF-IR fibers were found in the dorsal pars nervosa primarily adjacent to the pars intermedia. A rostral projection of CRF-IR fibers is associated with the suprachiasmatic nucleus and continues to septal areas. A caudally projecting bundle of fibers was observed entering the midbrain in neuropil adjacent to the aqueduct. The location of CRF-IR components is also compared with those containing vasopressin (AVP).

Animals↗
PubMed1984

The neuroanatomical and neurovascular organization of normal fetal hypothalamic explants in the third cerebral ventricle of Brattleboro rats with homozygous diabetes insipidus.

This investigation has combined microangiography, immunocytochemistry, coupled with transmission and scanning electron microscopy to discuss the neuroanatomical interactions that occur in the brains of Brattleboro rats with diabetes insipidus, following stereotaxic placement of normal fetal hypothalamic fragments into the third cerebral ventricle. Following surgical placement of 17 day post-coitus hypothalamic fragments, host rats with chronic autosomal homozygous diabetes insipidus were killed and their brains were prepared for analysis. A significant degree of explants (68%) flourished and grew in the lumen of the third cerebral ventricle of recipient hosts. Explants were rapidly invaded by host vessels from two routes. Vessels arose from the underlying mantle plexus of portal capillaries which remained fenestrated in the lower one-third of the explants and developed neurovascular (neurohemal) zones. The second source of vessels arose from bed capillaries of the adjacent paraventricular nucleus and adjacent hypothalamus. In contrast to vessels arising from the contact zone, these latter vessels remained unfenestrated. Small clusters of immunocytochemically positive neurons (neurophysin positive) were seen throughout the explants. Numerous healthy magnocellular neurons harboring numerous dense core vesicles and exhibiting multiple axosomatic and axodendritic synapses were seen throughout the neuropil of explants. Axon profiles were noted to terminate upon the abluminal basal lamina of perivascular spaces surrounding fenestrated capillaries in the lower one third of explants. None of the host animals exhibited physiological return to normal parameters of urine output, drinking behavior, and/or urine osmolarity. However the growth and development of explants in the third cerebral ventricle of DI hosts coupled with the emergence of bonafide neurovascular zones supports a potential anatomical substrate for the central delivery of neuropeptide hormones in this experimental model.

Animals↗
PubMed1983

The corticotropin releasing factor (CRF) neurosecretory system in intact, adrenalectomized, and adrenalectomized-dexamethasone treated rats. An immunocytochemical analysis.

In general, antisera generated against ovine CFR do not reveal immunopositive neuronal perikarya in the rat. If animals are adrenalectomized significant amounts of immunoreactive CFR are present in the hypothalamus. By using this model, we have visualized the CFR system of the rat. Intact, intact pretreated with dexamethasone, adrenalectomized, and adrenalectomized pretreated with dexamethasone animals were used in the present study. In adrenalectomized and adrenalectomized plus dexamethasone treated animals the CFR-immunopositive neurons were observed in the parvocellular portion of the paraventricular nucleus. Distinct pathways of CRF fibers could be seen emerging from this hypothalamic nucleus. The greatest number of these fibers exited the PVN laterally and crossed either superior to or beneath the fibers of the fornix. The fibers then turned ventrally and cascaded to form a bundle of fibers above the superio-lateral margin of the optic chiasm. They turned caudally and followed the optic tract. As these fibers reached the level of the anterior median eminence, they turned medially to run along the inferior margin of the hypothalamus and enter the median eminence. A few fibers emerged from the PVN along the periventricular margin of the third ventricle, traveled caudally in the periventricular nucleus and entered the median eminence. Adrenalectomized and adrenalectomized-dexamethasone treated rats had very dense accumulations of immunoreactive CRF in the median eminence when compared with controls. Immunoreactive neurons and fibers were also observed in the central nucleus of the amygdala in the adrenalectomized and adrenalectomized-dexamethasone treated animals.

Adrenalectomy↗
PubMed1983

Temperature dependence of the hamster circadian pacemaker.

Blind male hamsters were maintained in running-wheel cages in a LD 12:12 light-dark cycle. After regular running patterns were established hypothermia was induced by ether anesthesia, wetting of the fur with ethanol, and cooling with ice. The hamsters were kept hypothermic for 3-24 h at colonic temperatures from 10 to 20 degrees C. Following hypothermia the animals were rewarmed and replaced in their home cages. Examination of the locomotor activity records showed phase shifts (delays) in activity onset that were correlated with the temperature and duration of the hypothermia but not with the circadian time at which the hypothermia was administered. The data were interpreted to mean that the circadian pacemaker was running at a reduced rate during the hypothermic bout. Calculation of the Q10 for the rate of the clock during hypothermia produced a range from 1.08 to 1.34 depending on the method of calculation. When compared with earlier data gathered from rats under similar conditions, the hamsters circadian pacemaker appears to be better temperature compensated.

Animals↗
PubMed1983

Counterantigonadotropic effect of melatonin administered via the drinking water.

Plasma melatonin levels in Syrian hamsters were augmented by the addition of melatonin to the drinking water. Preliminary experiments in pinealectomized hamsters indicated that doses in the range of 2-5 micrograms/ml in the drinking water would produce variable levels of plasma melatonin, approximately in the physiological range (10-100 pg/ml). Two protocols were used, one to demonstrate the antigonadotropic effect of melatonin and the other to elicit the counter-antigonadotropic effect. In the antigonadotropic protocol, 100-g intact male hamsters were housed under a 14-h light, 10-h dark cycle for 10 weeks. Contrary to our hypothesis, there was no effect of melatonin in the drinking water on testis mass (dose range, 0.059-50 micrograms/ml). The counterantigonadotropic protocol involved the use of 100-g male hamsters that were blinded and housed under conditions similar to those of the first protocol. They received melatonin in concentrations ranging from 1.8-320 micrograms/ml. At 10 weeks, the blinded hamsters receiving no melatonin had the expected drop in testis mass to 0.56 g. In the range from 2.4-10 micrograms/ml melatonin, there was a highly variable response, but generally, higher doses resulted in higher testis mass. In the range of 20-320 micrograms/ml, the blind hamsters had mostly normal appearing large testes (mean, 3.3 g). The following conclusions were reached. 1) We produced the well known counterantigonadotropic effect of melatonin by administration via the drinking water ad libitum. 2) We could not produce the antigonadotropic effect by similar means.

Animals↗
PubMed1982

Species difference in circadian [14C]2-deoxyglucose uptake by suprachiasmatic nuclei.

Hamsters exhibited a circadian variation in metabolic activity determined by [14C]2-deoxyglucose uptake in the suprachiasmatic nuclei, as has been previously reported for rats. The 13-line ground squirrel, a diurnal rodent, did not show a circadian variation in metabolic activity. The data are consistent with the hypothesis that there is a basic difference in the functional organization of the suprachiasmatic nuclei in nocturnal and diurnal animals.

Animals↗
PubMed1982

LHRH pathways in rat brain: 'deafferentation' spares a sub-chiasmatic LHRH projection to the median eminence.

Localization of luteotrophic hormone-releasing hormone (LHRH) was examined by immunocytochemistry in untreated male rats and rats that received an anterior hypothalamic deafferentation. Gonadotrophic function was assessed by examining testicular weight and morphology. All of the antisera used in this study were able to reveal LHRH cell bodies and fibers. Cells from the medial preoptic area, (particularly the preoptic periventricular or median preoptic nuclei) and lateral anterior hypothalamus sent axons to the median eminence. The fiber tracts were loosely organized into (1) a tract that coursed through the organum vasculum of the lamina terminalis between the optic nerves and along the ventral surface of the optic chiasm; (2) a tract that coursed to the organum vasculum from the preoptic area and then traversed along the floor of the third ventricle; (3) a tract that coursed from the medial preoptic area to the median eminence along the lateral walls of the third ventricle; and (4) a tract that arose from the more caudal portions of the LHRH cell field in the lateral preoptic and lateral anterior hypothalamus, coursed along with the fibers of the medial forebrain bundle and turned medially at the caudal hypothalamus to enter the median eminence. An anterior cut which served most of the connections between the medial preoptic area and hypothalamus but did not penetrate through the optic chiasm served tract 3 and most of tracts 2 and 4, but spared the subchiasmatic projection (tract 1). The fibers that remained in the median eminence were sufficient to retain gonadotrophic function. This study provides an explanation for the variable effects of deafferentation and lesions of the anterior hypothalamus and preoptic area on gonadotrophic function.

Animals↗
PubMed1981

Temperature dependence of rat circadian pacemaker.

Blind female rats were maintained in running-wheel cages in a 12-h light-dark cycle. Hypothermia was induced by ether anesthesia, wetting of the fur by ethanol, and covering with ice. Rats were put in restraining cages and colonic temperatures were maintained between 20 and 32 degrees C for 3-16 h by cooling with ice and water. On recovery from hypothermia, the rats were replaced in their home wheels. Examination of the activity records showed significant phase delays associated with temperatures lower than 28 degrees C. At 20 degrees C, the phase delays indicated that the clock was running at about 64% normal speed giving a mean Q10 of 1.33, which is quite a bit higher than previously reported. It is speculated that, because the rat maintains its body temperature within narrow limits after the neonatal stage, it has lost the precise temperature compensation for the period of its biological clock that has been so well documented in other organisms.

Animals↗
PubMed1981

The half-life of melatonin elimination from rat plasma.

Tritiated or unlabeled melatonin was infused intra-arterially into unanesthetized male Sprague-Dawley rats. Blood samples were collected from the jugular vein over the next two hours and the melatonin concentrations determined in the plasma by liquid scintillation counting or by RIA. Data from the tritiated melatonin experiments gave a half-life of 23 min, and data from the RIA experiments gave a half-life of 17 min.

Animals↗
PubMed1979

Fixed interval feeding does not entrain the circadian pacemaker in blind rats.

Male and female rats were blinded by orbital enucleation at 1 or 21 days of age and were housed along with intact controls in a temperature- and light-controlled room (22 +/- 2 degrees C, LD 12:12). At 40 days of age the rats were transferred to running wheel cages connected to an event recorder and their activity patterns were monitored for the next 11--16 wk. After 4--6 wk in the running wheels, the rats were subjected to a fixed interval feeding (FIF) schedule lasting 23 days followed by 4--6 wk of ad libitum feeding and watering. Of 19 blind rats with interpretable activity records, 14 showed no change in their activity patterns associated with the FIF other than the addition of a large component of activity before and after the feeding period every day. It was concluded that, in contrast to the squirrel monkey, FIF is not an important zeitgeber for blind rats.

Age Factors↗
PubMed1978

Circadian rhythms in blinded rats: correlation between pineal and activity cycles.

The rat pineal gland exhibits diurnal rhythms in levels of N-acetyltransferase activity and its substrate serotonin. We attempted to demonstrate the endogenous nature of these changes by measuring the pineal enzyme and its substrate in rats blinded for 37 and 60 days. In order to determine the proper sampling times for these one-time, terminal measurements, the running activity rhythm of each rat was monitored continuously and the animals were killed at either midrest or midrun. Circadian changes of pineal N-acetyltransferase and serotonin were demonstrated, with enzyme levels high and substrate content low during midrun. Absolute values during each activity phase were similar to those of control rats entrained to a light cycle (LD 12:12). Levels of the pineal constituents were unrelated to local time. These results suggest that rats blinded for up to 60 days maintain their free-running pineal rhythms with undamped amplitudes and in synchronization with the activity rhythm.

Acetyltransferases↗
PubMed1976

Correlation of plasma corticosterone levels with running activity in the blinded rat.

Blinded female reats were placed in running-wheel cages to monitor the phase of their activity cycle. After approximately a month of adaptation to the wheels, jugular vein blood samples were withdrawn at the beginning and end of the running phase of activity and analyzed for plasma corticosterone. By the time blood samples were obtained, the blined rats' activity cycles had desynchronized from the lighting cycle of the room in an apparently free-running fashion, and were out of phase with each other. The corticosterone levels were high at the beginning of the running phase and low at the end: begin run corticosterone was 34.5 +/- 13, end run corticosteronewas 14.2 +/- 10 (mean +/-SD in mug/100 ml of plasma; t = 7.93, df = 82, P less than 0.001). It was concluded that blinded rats do have an adrenocortical rhythm and that it is in phase with the activity cycle of each individual rat.

Adrenal Glands↗