Changes in Multiple Unit Activity of the Brain During the Estrous Cycle

Abstract

Electrical activity of the brain during the critical period in the rat was examined throughout the estrous cycle, using chronically implanted macro-micro electrodes. Slight circadian rhythms were observed in the basal level of the integrated multiple unit activity (MUA) in the basal hypothalamus and forebrain limbic area. In addition to these changes, a gradual increase of MUA in the basal hypothalamus was observed during the evening of diestrus day 2, while there was no change in the forebrain limbic preoptic area. However, a characteristic elevated pattern of MUA appeared for 12 to 25 min during the critical period (2 p.m. to 4 p.m.), both in the basal hypothalamus and forebrain limbic preoptic area, i.e., in the arcuate nucleus (ARC), ventromedial hypothalamic nucleus (VMH), medial preoptic area (MPO), septum (SEPT), amygdala (AMYG) and bed nucleus of stria terminalis (BST). The episodes of the characteristic pattern were also observed in the basal hypothalamus on the afternoons of diestrus day 2 and estrus, as well as in the forebrain limbic preoptic area on the day of estrus. To determine the possible relationship between the characteristic pattern and gonadotrophin release, electrochemical stimulation was applied to the areas of the brain where the characteristic pattern was observed during the critical period. Ovulation could be induced by stimulation of the ARC, MPO, SEPT, AMYG, and BST, but not by stimulation of the reticular formation (RF) and hippocampus (HPC). Furthermore, the results shed light on the facilitatory and inhibitory effects of progesterone on ovulation and the onset of the critical period.

Effect of Electrical Stimulation of the Medial Preoptic Area on Hypothalamic Multiple Unit Activity in Relation to LH Release

“…It has been well substantiated that these hormones are liberated when a neural surge occurs. And after intravenous injections of LH , FSH and subcutaneous injection of progesterone under the estrogen base (Terasawa and Sawyer, 1970;Kawakami et al, 1971) increases of MUA with latency of 15 to 45 min lasting 2 to 3 hr were observed.…”

On Circulating Sex Steroids During the Estrous Cycle and the Early Pseudopregnancy in the Rat with Special Reference to its Luteal Activation

“…Recently, applying the anesthesia at different times of day throughout the estrous cycle, Okamoto et al, (1972) have clarified that the ovulation is delayed by one day when the anesthesia is given at a limited time band (1200-1600) of any day in the cycle except the day of estrus. In this connection, Kawakami et al (1970) have found an increase of polyneuronic activity in the arcuate neucleus of the hypothalamus from 1300 to 1700 every afternoon in the cycling rat. These findings are suggestive of the existence of periodical excitation in CNS which may correlate with some daily rhythmic change for hypothalamo-hypophysial activity concerning gonadotrophin secretions during the cycle.…”

Hormonal Therapies: Progesterone

“…15 In adult experimental animals, the thresholds of limbic seizures in female rats fluctuate during the estrus cycle inversely to serum estradiol levels. 16 Physiological doses of estradiol activate spike discharges 5,6,17,18 and lower the thresholds of seizures induced by electroshock, kindling, pentylenetetrazol, kainic acid, ethyl chloride, and other agents and procedures. [17][18][19][20][21][22] In rabbits, topical brain application, as well as intravenous systemic administration, of estradiol produces a significant increase in spontaneous electrically recorded paroxysmal spike discharges.…”