Lesions of the brain and the onset of puberty in the female rat.

Abstract

Lesions of the amygdala of prepuberal female rats had no effect on the day of vaginal opening, subsequent estrus cycles, or weights of ovaries or when compared with sham-operated controls. In contrast, lesions of the supraoptic area or posterior arcuate area of the hypothalamus induced early vaginal opening. These data suggest that destruction of the amygdala, at least under the conditions of these experiments, does not induce precocious puberty in the female rat. {Endocrinology 89: 898, 1971) r I 'HERE ARE a number of reports suggesting JL a role of the amygdala in reproductive processes of the rat. In adult female rats, blockade of ovulation by a variety of methods is overcome by stimulation of the amygdala (1, 2); there is a concomitant increase in plasma LH and FSH levels, and lesions of the stria terminalis abolish this effect. Consistent with the above results are reports that lesions of the central amygdaloid nucleus and lateral portion of the stria terminalis decrease ovarian function in adult rats (3) and amygdala lesions in adult male rats decrease the weight and reduce sperm formation in the testes (4). In prepuberal rats the role of the amygdala appears to be somewhat different. Lesions of the basal and medial amygdala and stria terminalis have been reported to increase uterine weights in female rats (5-7). Early vaginal opening was also reported, but this occurred only in about 1/3 of the rats with histologically verified bilateral lesions. In one of the above reports (7), lesions of the amygdala led to increased ovarian weights. Eleven rats with stimulated uteri of 17 which had lesions of the stria terminalis also had increased ovarian weights when compared to controls (6). Consistent with the above are findings that lesions of the corticomedial amygdala in immature male rats lead to hypertrophy of sexual accessory glands (8) and that electrical stimulation of this region delays vaginal opening and ovulation in immature female rats (9). Although these results are opposite to those reported in adults, there is evidence that, in ovariectomized adult rats, lesions Received August 14,1970. Supported by USPHS Grants AM06704 and 5 FO2 HD35420. 1 USPHS Postdoctoral Research Fellow of the National Institute of Child Health and Human Development. of the amygdala raise plasma LH levels above castrate levels (10). The present experiments were performed in order to more clearly define the role of the amygdala in the control of the onset of puberty in female rats. The effects of electrolytic lesions of the amygdala and hypothalamus on the day of vaginal opening and subsequent estrous cycles were studied. Materials and Methods Immature female Sprague-Dawley rats were used. In the first experiment, these rats were lesioned when 21-22 days of age; in the second experiment, animals were lesioned when 21-23 days of age. Lesions were produced by passing anodal DC current through a unipolar platinum electrode insulated with epoxy resin except at the tip; the indifferent electrode was connected to the stereotaxic instrument. Unless otherwise specified, all lesions were produced by passing a current of 2.0 mA for 10 sec. In Experiment I (see Table 1) bilateral lesions were placed in the corticomedial (AME) and basolateral (ABL) nuclei of the amygdala and in the stria terminalis within the amygdala (ST). Other sham-lesioned animals were implanted with electrodes, but no current was passed. One group of unoperated rats served as a normal control. In Experiment II, rats received bilateral lesions in the corticomedial nucleus and stria terminalis; others received bilateral lesions in the basolateral amygdala (3.0 mA for 10 sec); 2 additional groups received midline lesions in the supraoptic area (SOA) of the hypothalamus or posterior border of the arcuate nucleus (P.ARH). As in Experiment I, some rats served as shamlesioned controls, and one group served as untreated normal controls. After the operation, all animals were placed in a light-controlled room and fed rat chow and water ad lib. Each day all rats were examined for vaginal opening. Once opened, daily vaginal smears were taken. Autopsies were performed when the rats were 48 days of age (Experiment I) or 50-52 days