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Biomedical subjects

L C Krey

Publications and source records attributed to L C Krey.

At least 73 records · Page 4Linked to original sources
PubMed1981

Steroid receptor levels in intact and ovariectomized estrogen-treated rats: an examination of quantitative, temporal and endocrine factors influencing the efficacy of an estradiol stimulus.

Cell nuclear estrogen receptors and cytosol progestin receptors were measured in the pituitary gland, preoptic area and hypothalamus throughout the estrous cycle of the rat. Cell nuclear estrogen receptor levels paralleled changes in serum estradiol concentrations with highest values on proestrus and lowest on diestrus. Proestrous values were 50-60% of capacity for each tissue. Cytosol progestin receptor number in these tissues was also highest on proestrus and lowest on diestrus. With these data as a guide, Silastic capsules filled with estradiol-cholesterol mixtures were used to generate physiologic levels of estrogen receptor occupation within the brain-pituitary complex of ovariectomized rats and to examine the kinetics of estradiol stimulation of lordosis behavior and cyclic gonadotropin release. Our results indicate that the effectiveness of an estradiol stimulus to elicit lordosis or luteinizing hormone release depends on at least three factors: the magnitude of the increment in serum estradiol and brain and pituitary cell nuclear estradiol receptor levels; the duration over which these increments area maintained; and the interval from previous exposure to estrogen.

Animals↗
PubMed1980

Radioimmunoassay of brian tissue and cell nuclear corticosterone.

A combined cell fractionation-radioimmunoassay procedure is described to measure tissue and cell nuclear levels of corticosterone (CORT) in rat brain in intact animals in morning, afternoon, and following ether stress as well as in adrenalectomized animals with and without replacement therapy. Tissue and nuclear CORT are, as expected, higher in afternoon than in morning and still higher after stress. Replacement of CORT by a subcutaneous pellet and by single injection of 100 microgram CORT give tissue and nuclear levels in the afternoon range. Measurement of cell nuclear CORT in brain regions reveals a pattern in intact rats very similar to that seen in ADX rats given CORT replacement, with highest CORT concentrations in hippocampus. In ADX rats comparison of cell nuclear CORT levels by radioimmunoassay with levels obtained by scintillation counting after [3H]-CORT gives further validation of the radioimmunoassay procedure.

Adrenalectomy↗
PubMed1978

The luteinizing hormone-releasing hormone (LH-RH) neuronal networks of the guinea pig brain. I. Intra- and extra-hypothalamic projections.

In the guinea pig brain, LH-RH-containing cell bodies are located not only within the classical hypophysiotrophic area but also in the medial preoptic area, septum and olfactory tubercle. LH-RH fiber tracts project not only to the primary portal plexus in the median eminence but also throughout the limbic forebrain and limbic midbrain regions. Using radiofrequency lesions in different brain regions, the projections of LH-RH cell bodies were determined. Cells in the medial preoptic area project ot the organum vasculosum of the lamina terminalis (OVLT), the suprachiasmatic nucleus, the mammillary body complex and the ventral tegmental area. LH-RH neurons in both the medial septal nucleus and medial preoptic area project via the stria medullaris to the medial habenular nucleus and from there via the fasciculus retroflexus to the interpeduncular nucleus of the midbrain. Other LH-RH neurons in the medial septal nucleus, nucleus of the diagonal band of Broca and olfactory tubercle are congregated in small clusters around large blood vessels which penetrate into this area, and they do not appear to send axons outside their immediate vicinity. The types of LH-RH axonal terminations and the roles of these peptide-containing neurons are discussed.

Animals↗
PubMed1978

The luteinizing hormone-releasing hormone (LH-RH) neuronal networks of the guinea pig brain. II. The regulation on gonadotropin secretion and the origin of terminals in the median eminence.

Cell bodies synthesizing LH-RH are located throughout the central nervous system including the hypothalamic arcuate nucleus, the medial preoptic area and medial septal nucleus. The contribution of each of these cell groups to the LH-RH terminals in the median eminence was assessed by immunocytochemistry following placement of radiofrequency lesions in male guinea pigs. Lesions in the arcuate nucleus resulted in an almost complete absence of LH-RH fibers in the median eminence. Lesions in the medial preoptic area or suprachiasmatic nucleus produced a decrease in the amount of immunoreactivity throughout the median eminence; but there was only a small decrease in the numbers of labeled fibers, which was localized to the internal zone of the median eminence and the external zone on the ventral and lateral surfaces of the infundibular stalk. Lesions of the mammillary bodies, medial amygdaloid nucleus, septal nucleus and fornix had no effect. The effects of these lesions on pituitary gonadotropin secretion was also assessed. Only lesions in the arcuate nucleus diminished plasma concentrations of luteinizing hormone (LH) and testosterone in the male guinea pigs. Similary only arcuate lesions prevented the postcastration rise in plasma LH in ovariectomized female guinea pigs. These data strongly suggest that the arcuate nucleus is the major but not the sole source of LH-RH terminals in the median eminence, and these are responsible for the neural regulation of tonic gonadotropin secretion.

Animals↗
PubMed1978

The arcuate nucleus and the control of gonadotropin and prolactin secretion in the female rhesus monkey (Macaca mulatta).

Attempts were made to destroy selectively the arcuate nucleus with radiofrequency current in adult female rhesus monkeys as a first step in identifying the areas of the mediobasal hypothalamus (MBH) that are responsible for the neural control of gonadotropin secretion in this species. Extensive or complete destruction of the arcuate region was produced in three animals and in two of these the lesion was confined primarily to the arcuate region and the dorsal aspect of the posterior median eminence. These lesions resulted in the cessation of LH and FSH secretion and blocked the positive feedback action of estradiol on gonadotropin release but did not appear to influence grossly basal thyroid and adrenocortical function, or to abolish GH discharge in response to insulin hypoglycemia. Adenohypophysial infarcts were not observed and exogenous LHRH and TRH induced marked discharges of the appropriate anterior pituitary hormones. In two additional animals with large hypothalamic lesions, destruction of the arcuate region was incomplete. In this group only partial inhibition of gonadotropin secretion was observed. LH and FSH secretion did not appear to be influenced in one animal bearing a large MBH lesion that entirely spared the arcuate region. Although serum prolactin remained at pre-lesion control levels after placement of the two relatively discrete lesions confined to the arcuate region, unambiguous increases in the secretion of this hormone were observed when the area of destruction encompassed tissue anterior and/or dorsal to the arcuate region. These observations suggest that the arcuate region is the primary structure mediating the hypothalamic control of gonadotropin secretion in the rhesus monkey. They also suggest that, in this species, the regions of the MBH involved with the regulation of gonadotropin release and those which control prolactin secretion are anatomically distinct.

Animals↗
PubMed1977

Suprachiasmatic nuclear lesions do not abolish food-shifted circadian adrenal and temperature rhythmicity.

Daytime restriction of food and water availability in nocturnal animals phase shifts the circadian periodicity of plasma corticosteroid concentrations and body temperature. These shifted rhythms persist in animals with lesions of the suprachiasmatic nuclei who are arrhythmic under normal conditions. These findings suggest the existence of an additional "clock" that may be involved in the generation of the rhythm.

Animals↗
PubMed1975

Surgical disconnection of the medial basal hypothalamus and pituitary function in the rhesus monkey. I. Gonadotropin secretion.

In an intial attempt to localize the central components of the neuroendocrine control systems whereby estrogens regulate gonadotropin secretion, the medial basal hypothalamus (MBH) was surgically isolated from the remainder of the brain in 18 female rhesus monkeys using a modified "Halasz knife". The completeness and localization of the resulting "cuts" were verified by examinations of serial 50 mugM coronal sections through each hypothalamus. The cuts extended from the optic chiasm to the mamillary bodies and from midline to the medial aspects of the optic tracts. The MBH "ISLANDS" ISOLATED BY THESE CUTS INCLUDED THE MEDIAN EMINENCE AND ARCUATE NUCLEI AS WELL AS PORTIONS OF THE VENTROMEDIAL NUCLEI, PREMAMILLARY AREAS AND MAMILLARY BODIES. Following complete MBH isolation, 6 of 7 otherwise intact monkeys responded to an estradiol benzoate (EB) injection with large LH and FSH surges. Three of these animals also displayed spontaneous gonadotropin surges which eventuated in ovulation as evidenced by sustained elevations in circulating progesterone levels. Similar patterns of LH and FSH secretion in response to EB administration were also observed in 6 of 7 intact animals in which only the superofrontal imputs to the MBH WERE INTERRUPTED. Four of these monkeys ovulated spontaneously. Circulating gonadotropin levels fell slightly in ovariectomized monkeys following complete MBH disconnection, but the circhoral, pulsatile rhythms of gonadotropin release persisted. These animals also responded to the negative and positive feedback actions of estrogen as evidenced by initial declines in circulating LH and FSH concentrations followed by surges of these hormones at the appropriate times following the injection of EB. It would appear from these observations that the sites of the negative and positive feedback actions of estrogen on LH and FSH secretion and, therefore, the sites of the central components of the neuroendocrine systems which control tonic and surge secretion of the gonadotropic hormones in the rhesus monkey may be resident within the MBH-hypophysial unit.

Animals↗