Is there a cholinergic circadian rhythm throughout the oestrous cycle related to ovulation in the rat?

Rats with a 4-day oestrous cycle were given a single dose of atropine (100, 300, 500 or 700 mg/kg body wt) at 13.00 h on the days of oestrus, dioestrus 1, dioestrus 2 or pro-oestrus and were autopsied on the next expected day of oestrus. The doses of atropine (in mg/kg body wt) necessary to block ovulation during the cycle were 300 at oestrus, 100 at dioestrus 1 or 2 and 700 at pro-oestrus. A single dose of atropine (100 mg/kg) at oestrus, dioestrus 1 or dioestrus 2 was given at 09.00, 13.00, 17.00 or 21.00 h, autopsy again being performed on the next expected day of oestrus. The ability of atropine to block ovulation appeared to have a circadian rhythm, with a maximum blockade at 13.00 h on dioestrus 1 and dioestrus 2 and a minimum at 21.00 h on the same days. Hormone replacement (human chorionic gonadotrophin at oestrus, dioestrus 1 or 2, oestradiol benzoate at dioestrus 2 or progesterone at pro-oestrus) re-established normal ovulation in rats whose ovulation was blocked with atropine (100 mg/kg) on dioestrus 1 at 13.00 h. When ovulation was blocked with atropine but no hormone replacement had been given, rats ovulated 24 h after the next expected day of oestrus. Results obtained in these experiments suggest the existence of a circadian rhythm of gonadotrophin secretion throughout the oestrous cycle and a close relationship between that rhythm and the cholinergic system.

Effects of unilateral destruction of the cervico-vaginal plexus on ovulation in the rat.

Hemidestruction of the cervico-vaginal plexus in 4- or 5-day cyclic rats were performed. After recovery, all animals had normal oestrous cycles. At oestrus itself, however, the number of ova released by lesioned animals was respectively 23% and 50% less than in the sham-operated and intact control rats. The possible participation of peripheral innervation in normal ovarian function is discussed.

Early neuronal alterations caused by experimental thinner inhalation in young rats.

Young rats were treated with thinner inhalations (50 and 100 p.p.m., v/v). The brains of treated and control animals were studied with standard techniques of light and electron microscopy and with ultrastructural cytochemical method for localization of RNA. No alterations were found in the group treated with a single session of inhalation, irrespective of the dose. Animals treated with 10 or 20 sessions showed altered neurons in cerebral cortex, caudate nucleus, hypothalamus and cerebellar cortex. More frequent alterations were: small nucleoli with loss of their reticular structure and a marked decrease of their normal granular component; diminution of perichromatin fibrils and of ribosomes. In the animals treated with high doses of thinner (20 sessions, 100 p.p.m.) a small number of neurons show an increased amount of lysosomes, autophagosomes and neurofibrillar hypertrophy. These results suggest that thinner inhalation causes an initial impairment of gene transcription and of RNA processing followed by neuronal degeneration.

Hysterectomy of the newborn guinea-pig, subsequent effects on the oestrous cycle and life span of the corpora lutea.

Longer oestrous cycles result from neonatal hysterectomy than from hysterectomy in adult life. Section and cauterization of the utero-vaginal union also prolonged the vaginal closure period up to an average of 55 days. The destruction of the mesometrium did not lengthen the oestrous cycle. Uterine autografts in hysterectomized newoborn guinea-pigs did not prevent the long cycles.