Stimulation of the hypothalamus and ovulation in the guinea‐pig

Abstract

SUMMARY1. Various methods of stimulating the hypothalamus were applied to the guinea-pig with the aim of inducing ovulation.2. Electrochemical stimulation of the hypothalamus, or gross stimulation of the brain, was ineffective.3. Electrical stimulation of the medial basal hypothalamus or rostral hypothalamus elicited gonadotrophin release.4. Despite variation of the time and intensity of stimulation, follicular luteinization was more common than the formation of new corpora lutea.5. Electrical stimulation of the medial basal hypothalamus often caused luteinization of follicles. Fewer animals responded to excitation of the rostral hypothalamus, but in those that did, ovulation occurred more frequently.6. The present observations contrast markedly with comparable. studies on the rat, where both electrochemical and electrical stimulation of the hypothalamus readily induce ovulation.

Implantation of Oestrogen in the Brain and the Induction of Ovulation in the Guinea-Pig

“…or oestradiol benzoate, perhaps because the implants, unlike the single injections, applied effective concentrations of the steroid to the hypothalamo-hypophysial system. Nevertheless, application of oestrogen to the hypothalamus, like electrical stimulation of that region (Booth & Donovan, 1974), still failed to induce formation of a full complement of new corpora lutea.…”

“…While guinea-pig ovaries contain ripe follicles capable of ovulating in response to injected gonadotrophins during late dioestrus (Dempsey, Hertz & Young, 1936), it has proved difficult to elicit this response by electrical stimulation of the hypothalamus at this stage of the oestrous cycle (Booth & Donovan, 1974). In order to avoid con¬ fusion with the approaching natural ovulation, stimulation was carried out on days 10-15, before the next expected oestrus, at a time when progesterone secretion by the corpora lutea has fallen (Feder, Resko & Goy, 1968;Challis, Heap & Ulingworth, 1971), and oestrogen secretion is just beginning to rise (Joshi, Watson & Labhsetwar, 1973).…”

Gonadotrophin secretion in the ovariectomized guinea‐pig: effects of electrical stimulation of the hypothalamus and of LH‐RH.

“…The technique of hypothalamic stimulation was based upon the work of Booth & Donovan (1974a) and the observations of Harris, Manabe & Ruf (1969), who considered that a satisfactory stimulus for the excitation of unmyelinated nerve fibres was provided by a 50 Hz alternating sine-wave current with a peak-to-peak current of 0-5-1-0 mA. Assessment of the threshold required to produce gonadotrophin release was not attempted, but it is noteworthy that the response to stimulation at 0 5 mA (Fig.…”

“…(Dey, 1943; Dey, Fisher, Berry & Ranson, 1940) or surgical cuts in or around this area of the brain (Butler & Donovan,197 1). However, attempts to induce ovulation by means of electrical or electrochemical stimulation of areas of the guinea-pig brain have met with variable success (Quinn, 1969(Quinn, , 1970(Quinn, , 1974Booth & Donovan, 1974a).…”

Effect of stimulation or lesioning of the hypothalamus upon gonadotrophin secretion in the guinea‐pig.

“…Many years ago, Dey, Fisher, Berry & Ranson (1940) showed that lesions in the anterior hypothalamus caused constant vaginal oestrus associated with highly follicular ovaries, but the changes in gonadotrophin secretion producing this effect have not been explored. However, gonadotrophin secretion in the guinea-pig is resistant to change in that electrical stimulation of the hypothalamus does not readily induce ovulation (Booth & Donovan, 1974a), and did not markedly alter the secretion ofluteinizing hormone (LH) or alter follicle-stimulating hormone (FSH) release in the spayed female (Donovan, ter Haar & Parvizi, 1977). Pre-treatment with oestrogen, progesterone or both steroids modulated the response to brain stimulation, though not to a marked degree.…”