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Biomedical subjects

M Wilkinson

Publications and source records attributed to M Wilkinson.

At least 325 records · Page 18Linked to original sources
PubMed1976

Dispersed cell cultures of the rat pineal: growth and morphological differentiation.

A method is described for the preparation and growth of rat pineal monolayer cultures derived from both mature and immature animals. The cultures were observed to undergo profound but reversible morphological differentiations by addition of dibutyryl-cAMP, monobutyryl-cAMP, papaverine, prostaglandins, and adenosine, and by removal of serum. Sodium butyrate and theophylline had no effect. Time-lapse photography indicated that this reversible transformation took place via a contraction-relaxation mechanism. Both colcemid and cytochalasin B inhibited the transformation. These results demonstrate that this type of morphological transformation, previously demonstrated in tumour and embryonic cell cultures, can also occur in nonembryonic, non-neoplastic tissue, and may be related to a general dedifferentiative process occurring in monolayer cultures.

Age Factors↗
PubMed1976

Ovarian control of gonadotropin secretion during induced precocious sexual maturation in the rat.

In sexually immature female rats 'primed' with a unilateral basal hypothalamic lesion on day 23 of life, a gonadotropin surge was triggered by progesterone (P) on day 26. The influence of sequential ovariectomy (OVX) on this response was studied in an attempt to elucidate the mode of action of brain lesions inducing precocious sexual maturation in this species. OVX, carried out on days 23-26, abolished or greatly reduced the LH surge, but had little effect on basal LH concentrations. In contrast, basal FSH concentrations rose rapidly after OVX. In lesioned rats, the post-castration rise of FSH could be prevented by leaving the ovaries in place during the 1st 24 or 48 h. It is concluded that the lesion-induced maturation of the positive feedback mechanism underlying the pubertal preovulatory gonadotropin surge is mediated by the ovaries. In prepubertal rats at this age, tonic FSH release, but not tonic LH release, is under tight negative feedback control.

Animals↗
PubMed1976

Synergistic effects of oestrogen and brain stimulation on precocious sexual maturation in the female rat.

Precocious activation of the pituitary-gonadal axis was induced in immature rats by unilateral electrochemical stimulation of the basal hypothalamus on day 23 of life. In response to this brain stimulus, about 50% of animals ovulated prematurely on either day 27 (96 h after stimulation) or on day 28 (120 h after stimulation), whereas less advanced stages of sexual development (increased ovarian and uterine weights, growth of ovarian follicles) were noted in the others. The combination of the brain stimulus with a single injection of 0.25 mug oestradiol benzoate on day 23 induced ovulation in 15% of rats already on day 26 (72 h after stimulation). When injected alone, this dose of oestradiol benzoate did not induce ovulation, but led to a rapid and sustained increase in the LH/FSH ratio (assessed by radioimmunoassays) in both the anterior pituitary gland and in plasma. Lower priming doses (0.05 mug and 0.125 mug) led to progressively fewer animals ovulating on day 26, but left the number ovulating on day 27 largely unaffected. In contrast, a higher dose (0.5 mug) gave an early response in 15% of the population, but severely reduced the number ovulating in a 10 day follow up period. It is concluded, in agreement with Hohlweg's early concept regarding the feedback effect of oestrogen in immature female rats, that steroid-priming facilitates the ovulatory response to brain stimulation by shifting pituitary gonadotropin output in favour of LH.

Animals↗