Temporal and anatomical considerations involved in the effects of amygdaloid lesions on prolactin secretion in ovariectomized estrogenized rats.

Plasma prolactin (PRL) levels were investigated in chronically catheterized control, sham-lesioned, and amygdala (AMYG)-lesioned rats under a variety of conditions. Ovariectomized (OVX) rats injected with 0.5 mg of polyestradiol phosphate (PEP) exhibited a circadian rhythm of PRL secretion characteristic of proestrus rats. Small bilateral lesions of the central AMYG area had no effect on this pattern of PRL secretion in animals bled over a 24-h period, 1 week following lesioning. A second group of rats bearing lesions or sham lesions of the corticomedial AMYG nuclei were studied at 1, 2 and 3 weeks following surgery and PEP treatment. PEP produced a significant afternoon surge of PRL in controls at weeks 1 and 2 but not week 3. Lesions of the corticomedial AMYG nuclei had no effect on basal PRL, but significantly blunted the afternoon surge occurring at weeks 1 and 2. The effect of a larger lesion encompassing a greater proportion of the corticomedial AMYG was examined in another group of rats at 6 weeks post-lesion and 2 weeeks after PEP injection. This lesion significantly decreased PRL levels compared to controls at 5 of 6 time periods examined over a 24-h period. The effect of this lesion on PRL secretion in non-estrogenized OVX rats was also examined. There was no difference in the low, non-fluctuating 24-h PRL levels of control and lesioned rats bled at 3 or 4 weeks post-lesion.