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  • Title: Modulation of the proestrous surge of luteinizing hormone by electrochemical stimulation of the amygdala and hippocampus in the unanesthetized rat.
    Author: Carrillo AJ, Rabii J, Carrer HF, Sawyer CH.
    Journal: Brain Res; 1977 Jun 03; 128(1):81-92. PubMed ID: 559528.
    Abstract:
    The roles played by the amygdala and hippocampus in controlling the release of pituitary luteinizing hormone (LH) were studied in the freely moving rat. Monopolar stainless steel electrodes were implanted into the corticomedial (CM) amygdala, basolateral (BL) amygdala and dorsal hippocampus of female rats. When the animal had recovered from surgery and shown two consecutive 4-day estrous cycles, a chronic atrial cannula was introduced during the afternoon of diestrus II. On the following day (proestrus) electrochemical stimulation (ECS) was applied (20--50 micronA anodal DC 120 sec) bilaterally to the amygdala or hippocampus and blood samples were taken every 90 min from 12.00 to 21.00 h for radioimmunoassay (RIA) of LH. Next day, uterine tubes were examined for ova as evidence of ovulation. ECS of the amygdala exerted two divergent influences on LH release. Stimulation of the BL amygdala at 13.45 h, just before the critical period (14.00--16.00 h), was effective in delaying and reducing the LH surge, whereas ECS of the CM amygdala at 12.00 h resulted in an early synchronization in the timing of the LH curves. All of the rats in both groups ovulated, in contrast to the results of applying ECS to the dorsal hippocampus; there the LH surge and ovulation were completely blocked in 7 out of 9 rats. Thus, in the freely moving rat, the hippocampus can exert a potent inhibitory influence on LH release whereas the amygdala plays a modulatory role in the process. Modulation of the proestrous surge of luteinizing hormone (LH) by electrochemical stimulation of the amygdala and hippocampus in the unanesthetized female rat was investigated. Monopolar stainless steel electrodes were implanted into the corticomerdial (CM) amygdala, basolateral (BL) amygdala, and dorsal hippocampus of the rats. Following recovery from surgery and 2 consecutive 4-day estrous cycles, a chronic atrial cannula was introduced during the afternoon of Diestrous 2. On the following day (proestrus) electrochemical stimulation (ECS) was applied (20-50 mcA anodal direct current 120 seconds) bilaterally to the amygdala or hippocampus and blood samples were taken every 90 minutes from 1200 to 2100 hours for radioimmunoassay of LH. The next day uterine tubes were examined for ova as evidence of ovulation. ECS of the amygdala exerted 2 divergent influences on LH release. Stimulation of the BL amygdala at 1345 hours just before the critical period (1400-1600 hours) was effective in delaying and reducing the LH surge, whereas ECS of the CM amygdala at 1200 hours resulted in an early synchronization in the timing of the LH curves. All of the rats ovulated in contrast to the results of applying ECS to the dorsal hippocampus. It is concluded that in the freely moving rat the hippocampus can exert a potent inhibitory influence on LH release whereas the amygdala plays a modulatory role in the process.
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