Neuropeptides in the posterodorsal medial amygdala modulate central cardiovascular reflex responses in awake male rats

The rat posterodorsal medial amygdala (MePD) links emotionally charged sensory stimuli to social behavior, and is part of the supramedullary control of the cardiovascular system. We studied the effects of microinjections of neuroactive peptides markedly found in the MePD, namely oxytocin (OT, 10 ng and 25 pg; n=6/group), somatostatin (SST, 1 and 0.05 μM; n=8 and 5, respectively), and angiotensin II (Ang II, 50 pmol and 50 fmol; n=7/group), on basal cardiovascular activity and on baroreflex- and chemoreflex-mediated responses in awake adult male rats. Power spectral and symbolic analyses were applied to pulse interval and systolic arterial pressure series to identify centrally mediated sympathetic/parasympathetic components in the heart rate variability (HRV) and arterial pressure variability (APV). No microinjected substance affected basal parameters. On the other hand, compared with the control data (saline, 0.3 µL; n=7), OT (10 ng) decreased mean AP (MAP50) after baroreflex stimulation and increased both the mean AP response after chemoreflex activation and the high-frequency component of the HRV. OT (25 pg) increased overall HRV but did not affect any parameter of the symbolic analysis. SST (1 μM) decreased MAP50, and SST (0.05 μM) enhanced the sympathovagal cardiac index. Both doses of SST increased HRV and its low-frequency component. Ang II (50 pmol) increased HRV and reduced the two unlike variations pattern of the symbolic analysis (P<0.05 in all cases). These results demonstrate neuropeptidergic actions in the MePD for both the increase in the range of the cardiovascular reflex responses and the involvement of the central sympathetic and parasympathetic systems on HRV and APV.

Effect of estradiol implanted in the corticomedial amygdala on the sexual behavior of castrated male rats

1. The purpose of the present investigation was to study the effect of ß-estradiol crystals implanted in the corticomedial area of the amygadaloid body on the sexual behavior of castrated male rats. 2. The animals were divided into the following groups: group I (N=9), castrated rats; group II (N=4), rats which had been castrated and stereotaxically implanted with cholesterol, both groups being used as controls; group III (N=6), castrated rats con estradiol implants. Latency to the first anogenital exploration, latency to the first mount and mount frquency were determined during the pre-castration and post-castration phases and after the material had been implanted in groups II and III in 10-min observation sessions. 3. There was diminished sexual behavior of the animals in group I without spontaneous recurrence within the period observed. Group II animals, who had undergone implantation of cholesterol, an inert substance, maintained low levels of sexual behavior (post-castration 0.8 ñ 7 vs 0.0 ñ 0.0 and 0.5 ñ 0.5 on the 6th and 9th day afther implantation, repectively). Group III animals presented a gradual increase in the number of mounts (from post-castration 1.2 ñ 0.5 to 6.5 ñ 2.7 and 4.1 ñ 1.0 on the 6th and 9th day after implantation, respectively) and a decrease of mount latency (from post-castration 431.2 ñ 55.9 to 226.1 ñ 119.6 and 51.0 ñ 28.9 on the 6th and 9th day after implantation, respectively) reaching pre-castration levels on the 6th and 9th day after ß-estradiol implantation. 4. We conclude that, under the effect of estradiol, the amygdaloid region can modulate male sexual behavior, thus injdicating a physiological role for estradiol receptors present in this area