Relationship of the Raphe and Suprachiasmatic Nuclei to Serotonin Facilitation of Cyclic Reproductive Functions in Aging Female Rats

The female reproductive system undergoes degenerative structural changes and it accumulates severe functional deficits during aging. Although other physiological systems also degenerate to varying degrees with advancing age, normal reproductive function ceases entirely and is replaced by some type of abnormal gonadal activity in the female (Aschheim, 1976). For example, in the aged rat two or three postreproductive syndromes are recognized including constant estrus (CE) and repetitive pseudopregnancy (PSP). Symptomatically, these conditions differ in terms of ovarian morphology and endocrinology. CE is characterized by polyfollicular ovaries lacking corpora lutea, while ovaries from rats showing PSP contain many corpora lutea and the number of growing and preovulatory follicles is greatly reduced. As the result of these structural changes, sex steroid production by the ovaries of CE, PSP, and normally cycling rats differ significantly. CE ovaries hyperproduce and secrete estrogen resulting in elevated serum levels of the steroid which persist chronically (Huang et al, 1978). Since corpora lutea are lacking, progesterone production and serum content are profoundly depressed (Miller and Riegle, 1980). On the other hand serum from PSP rats contains elevated levels of progesterone and relatively little estrogen. In contrast to these senile variations, ovaries from young rats showing regular estrous cycles produce sequentially estrogen and progesterone as correlates of stages of the cycle and of the periodic presence of graffian follicles and corpora lutea.