Furukawa Y, Kotegawa T, Tsutsui K
Faculty of Integrated Arts and Sciences, Hiroshima University, Japan.
J Exp Zool. 1995 Oct 1;273(2):96-103. doi: 10.1002/jez.1402730203.
We have recently isolated three opioid peptides, i.e., Met- and Leu-enkephalins and Met-enkephalin-Arg6-Phe7, from the avian brain. In the present study, therefore, effects of these endogenous opioid peptides on the electrical activity of preoptic and hypothalamic neurons of the adult male Japanese quail were examined using a brain slice preparation. All of the three opioid peptides inhibited the spontaneous firing activities of subsets of neurons in the preoptic area and the paraventricular nucleus in the hypothalamus. Threshold concentrations for the inhibitory action were between 10(-7) and 10(-6) M in Met- and Leu-enkephalins and approximately 10(-6) M in Met-enkephalin-Arg6-Phe7, respectively. In a few cells in these brain areas, however, Leu-enkephalin rather potentiated the spontaneous activities, resulting in an increase of firing rates or a decrease of interburst intervals. The inhibitory effect of Met-enkephalin was completely blocked by naloxone, an opioid receptor antagonist, but not affected by bicuculline, a gamma-aminobutyric acid A (GABAA) receptor antagonist. These results suggest that there are functional opiate receptors in subsets of preoptic/hypothalamic neurons and that one of their main physiological functions in these areas is an inhibition of neuronal activities. Because these brain regions are considered to be involved with the regulation of a variety of male reproductive behaviors, opioid peptides may regulate some reproductive behavior through the mechanism that provokes such an inhibition.
我们最近从禽脑中分离出了三种阿片肽，即甲硫氨酸脑啡肽、亮氨酸脑啡肽和甲硫氨酸脑啡肽-精氨酸6-苯丙氨酸7。因此，在本研究中，我们使用脑片标本研究了这些内源性阿片肽对成年雄性日本鹌鹑视前区和下丘脑神经元电活动的影响。这三种阿片肽均抑制视前区和下丘脑室旁核中部分神经元的自发放电活动。甲硫氨酸脑啡肽和亮氨酸脑啡肽产生抑制作用的阈值浓度分别在10^(-7)至10^(-6) M之间，甲硫氨酸脑啡肽-精氨酸6-苯丙氨酸7的阈值浓度约为10^(-6) M。然而，在这些脑区的少数细胞中，亮氨酸脑啡肽反而增强了自发放电活动，导致放电频率增加或爆发间期缩短。甲硫氨酸脑啡肽的抑制作用被阿片受体拮抗剂纳洛酮完全阻断，但不受γ-氨基丁酸A（GABAA）受体拮抗剂荷包牡丹碱的影响。这些结果表明，视前区/下丘脑神经元的部分细胞中存在功能性阿片受体，且它们在这些区域的主要生理功能之一是抑制神经元活动。由于这些脑区被认为参与多种雄性生殖行为的调节，阿片肽可能通过引发这种抑制作用的机制来调节某些生殖行为。
