Differential Effects of Dorsal Raphe Nucleus Lesions on Pseudopregnancy Induced by Reserpine or Vaginal Stimulation in Female Rats.

Abstract

Abstract. The role of the dorsal raphe nucleus in the maintenance of pseudopregnancy induced by reserpine and/or vaginal stimulation was investigated in female rats. In order to induce pseudopregnancy, either the vagina was stimulated electrically (VS) on the day of proestrus, or 1 mg/kg b.w. reserpine (R) was injected on the day of diestrus I. In some females, both VS and R treatments (VS+R) were applied. Radiofrequency lesions were made in the dorsal raphe nucleus (DRL) 5 days after VS and 3 days after R. At the same time, the left uterine horn was traumatized in order to induce deciduoma. As a result, positive decidual responses were seen in most control and sham-control rats with VS or R-treatments. In contrast, the incidence of deciduoma in DRL females with R injection was lower than that in control and sham groups, but the incidence in DRL females with VS or VS+R was comparable to that in control and sham females. These results suggest that the dorsal raphe nucleus plays an important role in maintaining the mechanism of pseudopregnancy induced by reserpine, but not in that induced by vaginal stimulation. Key words: Dorsal raphe nucleus, Pseudopregnancy, Deciduoma, Vaginal stimulation, Reserpine, Lesion.(J. Reprod. Dev. 44: [337][338][339][340][341][342][343] 1998) electrical method [1, 2] or depletion of monoamine by drugs, such as reserpine [3,4] causes pseudopregnancy (PSP) in rats. In the PSP, the prolactin surge occurs by these artificial methods as in pregnancy [5,6] and makes a conditioning of uteri for decidual formation. These indicate an importance of the central nervous system for rat pregnancy in the first half-period. Thus, analysis of the PSP in rats may deepen our understanding of the difference of the pseudopregnancy-regulating mechanisms among species in an evolutional view. The basic regulatory mechanism for PSP involves the preoptic area (POA) and the medial basal hypothalamus (MBH) in rats, because destruction of he pregnancy is maintained by the luteal function in the first half-period of it. The corpus T luteum independently secretes progesterone responsible for the maintenance of pregnancy in many mammals such as a human. On the other hand, for progesterone secretion in this half-period of pregnancy, the stimulation of the corpus luteum by prolactin surges from the pituitary is required in the rat. Furthermore, in the rat, the onset of pregnancy requires coital stimulation as reflex ovulation. Instead of coital stimulation, artificial vaginal stimulation (VS) by mechanical or