Taleisnik S, Haymal B
Instituto de Investigación Médica Mercedes y Martín Ferreyra, Córdoba, Argentina.
Neuroendocrinology. 1997 Aug;66(2):114-21. doi: 10.1159/000127227.
Electrochemical and electrical stimulation of the medial preoptic area (MPA) was shown to induce release of LH in rats. Owing to differences in cytoarchitecture and neural afferents between the medial (mMPA) and lateral (lMPA) parts of the MPA, we decided to explore whether this difference in organization would distinctly influence the secretion of gonadotropin. Both parts of the MPA were electrochemically stimulated on the day of proestrus in freely behaving rats bearing chronic implanted electrodes. An anodic direct current of 100 microA was delivered for 40 s at 11.00 h and blood samples were obtained every hour until 17.00 h. Serum LH concentrations in rats stimulated in the medial part of the MPA showed a robust rise 1 h after the stimulus was applied and the values remained high up to the end of the bleeding period. All these animals ovulated. An initial rise in serum LH was also seen in rats stimulated in the lMPA but serum values thereafter returned to basal levels, significantly lower than those in the mMPA-stimulated or in control, nonstimulated rats. Only 2 rats showed full ovulation and the others failed to ovulate or had partial ovulation. Injection of the serotonin antagonist, methysergide, did not affect the response of rats stimulated in either the mMPA or lMPA. The GABA antagonist, bicuculline, had no effect on LH release evoked by lMPA stimulation but blocked the release induced by mMPA stimulation. This later blockade was partially reversed by the administration of the opioid receptor antagonist, naloxone, suggesting the existence of GABA facilitatory influences on LH release via inhibition of opioidergic inputs to the GnRH neurons. On the other hand, naloxone administration had no effect on LH release evoked by stimulation of the mMPA but partially reversed the inhibition resulting from stimulating the lMPA. These data indicate that the mMPA and lMPA have opposite effects on LH secretion and provide evidence for the possible neurotransmitters involved.
对大鼠内侧视前区（MPA）进行电化学和电刺激可诱导促黄体生成素（LH）释放。由于MPA内侧部分（mMPA）和外侧部分（lMPA）在细胞结构和神经传入方面存在差异，我们决定探究这种组织结构差异是否会显著影响促性腺激素的分泌。在自由活动且植入慢性电极的大鼠处于动情前期当天，对MPA的两个部分进行电化学刺激。在11.00 h施加100微安的阳极直流电，持续40秒，每小时采集血样直至17.00 h。刺激MPA内侧部分的大鼠血清LH浓度在刺激后1小时出现强劲上升，且在出血期结束时仍保持较高水平。所有这些动物都排卵了。刺激lMPA的大鼠血清LH也出现了初始上升，但此后血清值恢复到基础水平，显著低于mMPA刺激组或未刺激的对照组大鼠。只有2只大鼠完全排卵，其他大鼠未能排卵或部分排卵。注射5-羟色胺拮抗剂麦角新碱对mMPA或lMPA刺激的大鼠反应没有影响。GABA拮抗剂荷包牡丹碱对lMPA刺激引起的LH释放没有影响，但阻断了mMPA刺激诱导的释放。给予阿片受体拮抗剂纳洛酮可部分逆转这种后期阻断，提示存在GABA通过抑制GnRH神经元的阿片能输入对LH释放产生促进作用。另一方面，给予纳洛酮对mMPA刺激引起的LH释放没有影响，但部分逆转了lMPA刺激导致的抑制作用。这些数据表明mMPA和lMPA对LH分泌具有相反的作用，并为涉及的可能神经递质提供了证据。
