Biomedical subjects

V Critchlow

Publications and source records attributed to V Critchlow.

At least 37 records · Page 2Linked to original sources

PubMed1976

Sex differences in the effects of surgical isolation of the medial basal hypothalamus on linear growth and plasma growth hormone levels in the rat.

The effects of surgical isolation of the medial basal hypothalamus (MBH) on linear growth and plasma growth hormone (GH) levels were studied in adult male and female rats. Whereas MBH isolation resulted in reduced linear growth in males, increased growth resulted in females. These effects were apparent in males 4 weeks after surgery and in females at 10 weeks. The altered growth rates persisted throughout the 28 weeks of the study. MBH isolation in both sexes led to increased food intake, obesity, and atrophy of reproductive tract organs. Non-stress plasma GH levels were unchanged at 4 weeks in both sexes but were elevated at 10 and 26 weeks in females and at 19 and 26 weeks in males. Serial samples of tail vein blood were obtained at 4-h intervals for 44 h from MBH-isolated and shamoperated females at 17 weeks postoperatively, and from similar groups of males at 19 weeks. GH levels were elevated in MBH-isolated rats of both sexes during the afternoons and evenings. Only sham-operated females showed evidence of a 24-h rhythmicity in circulating GH levels. The amplitudes of trough to peak excursions were similar in MBH-isolated and control females, but these excursions were reduced in MBH-isolated males. Although opposite effects on linear growth were noted in the two sexes, the resulting growth rates of operated males and females were similar, suggesting that MBH isolation disrupts mechanisms that normally regulate sex-specific growth patterns. Despite the sex difference in growth responses, MBH isolation caused an eventual increase in plasma GH levels in both sexes. Therefore, it is unlikely that the sex difference in growth responses is attributable exclusively to corresponding changes in circulating GH levels. A reduction in levels of circulating gonadal steroids may be an important factor. The elevations in plasma GH levels observed in both sexes suggest that MBH isolation interferes with mechanisms which inhibit GH secretion.

Animals↗

PubMed1976

Extrahypothalamic control of stress-induced inhibition of growth hormone secretion in the rat.

The aim of these experiments was to determine whether the telencephalon is essential for stress-induced suppression of plasma GH levels and, if so, which telencephalic structures are involved. In the first study, the telencephalon was completely removed from adult female rats by suction; intact and sham-operated rats served as controls. At 24 h after surgery, blood samples were collected at the initiation of and 15 min after a 3-min immobilization-blood withdrawal stress procedure and used for determining non-stress and stress plasma levels of GH, respectively. GH was measured by radioimmunoassay. In contrast to the normal stress-induced decrements in GH levels observed in controls, this response was blocked and stress caused a paradoxical increase (P less than 0.01) in GH levels in telencephalon-ablated rats. These results suggested that the telencephalon is essential for stress-induced inhibition of GH secretion. Therefore, the several components of the telencephalon were ablated individually in additional experiments to determine the structure(s) involved. Placement of large, bilateral lesions in the amygdala or complete removal by suction of hippocampus, septum or striatum did not interfere with the normal GH response to stress at 24 h after surgery. However, removal of the preoptic region duplicated the effects of complete telencephalon ablation i.e., the normal stress-induced decrement was not only blocked but also reversed. These findings suggest that the preoptic region is essential for mediating inhibition of GH secretion in response to immobilization-blood withdrawal stress and that other telencephalic structures are not essential for this neuroendocrine response.

Amygdala↗

PubMed1975

Absence of a circadian rhythm in persisting corticosterone fluctuations following surgical isolation of the medial basal hypothalamus.

To determine whether the circadian rhythm in pituitary-adrenal function is abolished after interruption of neural connections of the medial basal hypothalamus (MBH), corticosterone patterns were examined in individual adult female rats following surgical isolation of the MBH (MBHI rats). Non-stress plasma corticosterone levels were assessed fluorometrically in blood samples obtained from a tail vein of each rat at 4-h intervals for 44 h, 7-8 weeks after surgery. The highest corticosterone levels for most intact and sham-operated controls were obtained in samples collected at the period of light-dark transition. Individual MBHI rats demonstrated steroid excursions of normal amplitude that were not linked with time of day; these patterns appeared asynchronous and devoid of a 24-h cycle. The data indicate that major excursions in plasma corticosterone levels persist following surgical interruption of connections of the MBH, but circadian rhythmicity is abolished.

Adrenal Glands↗

PubMed1975

Effects of stress on plasma corticosterone and growth hormone levels in rats with median eminence-pituitary islands.

The effects of stress on plasma corticosterone and growth hormone (GH) were determined in adult female rats 24 h after forebrain removal in order to study the anatomical substrate essential for stress-induced alteration of pituitary function. Rats with median eminence-pituitary islands (MEPI) showed significant increments in plasma corticosterone levels 15 min after immobilization-blood withdrawal stress. Rats with basal hypothalamic-pituitary islands (BHPI) showed comparable increments, suggesting that the presence of hypothalamic tissue in addition to median eminence did not enhance the steroid response. A subsequent study demonstrated that MEPI rats are capable of a 2nd response, 6 h after the first. MEPI rats also showed a significant 50% increase in plasma GH levels 15 min after immobilization-blood withdrawal. In a final experiment, MEPI rats showed corticosterone but not GH responses to immobilization applied without blood withdrawal. These data offer further evidence that some stressful stimuli can alter pituitary functions under short-term conditions in the absence of hypothalamic or other forebrain neurons.

Animals↗

PubMed1974