Resumo

The posterodorsal medial amygdala (MePD) has receptors for gonadal hormones that modulate the display of reproductive behaviors in rats. The density of dendritic spines in the MePD is sexually dimorphic, and the cyclic variation in plasma levels of ovarian steroids changes the number of these spines. Electrophysiological results suggest that the MePD activity is different between male and female rats according to the brain hemisphere studied. The aim of this work is to study the NMDAR1, NMDAR2B, Narp, GAD65 and GAD67 mRNA expression in males and females along the estrus cycle in the right and left MePDs. The RNA was isolated from the MePD of both hemispheres of adult male and female rats at three stages of the sexual cycle (diestrus, proestrus, estrus, n = 6); each n formed by a pool of 3 MePDs. The levels of NR1, NR2B, Narp, GAD65 and GAD67 transcript were quantified by real time PCR (qRT-PCR). For statistical analyses it was used the analysis of variance for repeated measures and the Tukey post hoc test (statistical significance set as p < 0.05). There were no significant statistical differences for the hemispherical laterality in the expression of NR1 [F (1.18) = 0.18; p = 0.67], NR2B [F (1.19) = 0.01; p = 0.94], Narp [F (1.19) = 0.28; p = 0.60], GAD65 [F (1.20) = 0.71; p = 0.41], and GAD67 [F (1.20) = 2.96; p = 0.10] mRNAs. There were no statistical differences on the NR2B mRNA levels between groups [F (3.2) = 0.97, p = 0.42]. However, male MePDs showed higher level of GAD65 mRNA than females. Females in estrus presented more GAD65 mRNA than females in diestrus and proestrus [F (3.2) = 41.13, p < 0.001]. Females in estrus showed higher level of mRNA GAD67 than males, which is higher than females in diestrus and proestrus [F (3.2) = 109.58, p < 0.001]. The levels of NMDAR1 and Narp mRNAs was higher in females in estrus than in males and females in proestrus and diestrus [F (3.2) = 4.18, p = 0,018; and F (3.2) = 12.65, p < 0.001, respectively]. Males presented higher levels of both GADs than females during the three sexual phases studied. We suggest that there are dimorphic pathways behind the sexual behavior, where the MePD may have an antagonist role. During the estrus phase there is the lowest estrogen and progesterone concentration on serum, coincident with the ovulation and sexual activity in rats. In females in estrus the levels of GADs and NMDARs and Narp are higher. So, the female hormones might directly or indirectly decrease the exprection of these genes, regulating the MePD function and the sexual behavior. GABA production decreased in MePD neurons can result in a lesser inhibition of the sexual behavior on females in estrus compared with what happens in the other cycle phases. The higher production of mRNAs for excitatory receptor proteins by these neurons during the estrus phase might cause higher activity in the MePD. The levels of these proteins are currently been measured by ELISA method on the same samples.