The influence of raphe nucleus lesions on fertility in the female rat

Abstract

By lesioning brain raphe nuclei, the effect of decreasing the activity of the serotoninergic (5-HT) system on the fertility of the female rat was investigated. The females were mated on the 10th day after lesioning. On both the 15th and 21st day of pregnancy the numbers of live and resorbed foetuses and the weights of placentas in the lesioned groups did nor differ statistically as compared with the control group. Interestingly, the lesioned group showed an increase in the number of ovulating cells on the one hand, and decrease in the number of implantations on the other. The data obtained strongly suggest that midbrain serotoninergic cell groups (B7, B8) inhibit ovulation and are not associated with initiation of labour in the female rat.There are many reports showing that a multitude of chemically diverse agents which have an in¬ fluence on the activity of the monoaminergic sy¬ stem also interfere in different degrees with spon¬ taneous ovulation. Brown (1967) and Kordon & Glowinski (1969) have reported that specific inhibi¬ tion of catecholamine (CA) biosynthesis by Lmethyl-p-tyrosine results in ovulation blockade. Similarily, Coppola et al. (1966) and Meyerson & Sawyer ( 1968) have shown antiovulatory effects of catecholamine depletors. Most research concerning the blocking influence of serotonin (5-HT) on ovulation has been based either on administration of exogenous 5-HT or on treatments designed to raise the endogenous 5-HT level (Kordon et al. 1968; Kordon 1969; Lippman 1968) and/or on reducing the stimulatory influence of the CA sy¬ stem. Labhsetwar (1971) suggested that the blocking influence on ovulation of CA depletors may be caused by changing the CA/5-HT balance in fa¬ vour of the 5-HT system. Carrer & Taleisnik (1970) have shown that electrochemical stimulation of a median raphe nucleus before the 'critical period' on the day of pro-oestrus results in block¬ ing of spontaneous ovulation in female rats. Labhsetwar (1971) and Kordon et al. (1971/72) have shown that the inhibition of 5-HT synthesis by administration of parachlorophenylalanine (p-CPA) also inhibits ovulation. Until now, the role that 5-HT played in the mechanism of gonadotro¬ phin release has not been explained. However, Wilson & Endersby (1979) indicate the possibility that increased 5-HT activity is required to stimulate ovulation, and that its site of action is the paraventricular nucleus. The same blocking of ovulation can be obtained not only by administration of 5-HT or of drugs that stimulate the activity of the 5-HT system, but also by p-CPA-The serotoniner-. gic neuron bodies, designated in accordance with Dahlstrom & Fuxe (1964) in groups B1-B9, are located within the brainstem raphe area. Jacobs et al. (1974) found that a dorsal or median lesion produced similar reductions (of about 50%) in hypothalamic 5-HT level. These data indicate that both raphe nuclei send serotoninergic projections into the hypothalamus. Geyer (1976) found that lesions to either B7 or Bs group produced similar reductions in hypothalamic trypt...