Gioia M, Bianchi R
Institute of Human Anatomy, University of Milan, Italy.
J Hirnforsch. 1995;36(3):421-31.
Enkephalins are opioid peptides which elicit an analgesic effect when injected into the periaqueductal gray matter and in particular into its caudal part. In this study we wanted to investigate the fine structure of the neurons and of the synaptic circuits involved in the enkephalin action in rats using immunocytochemical pre-embedding methods. The labelled neurons show a small-medium sized soma, with a large nucleus, an absence of an extensive granular endoplasmic reticulum and few synaptic contacts. The synapses on enkephalin dendrites are often multiple, unlabelled and show both symmetrical and asymmetrical junctions. Enkephalin axon terminals make synaptic contacts on dendrites, usually unlabelled; contacts between enkephalin elements were occasionally seen. The enkephalin synapses show a symmetrical type of junction. These data give morphological support to the physiological findings, in particular to those suggesting an inhibitory effect of enkephalin on periaqueductal gray matter cells through a post-synaptic process. The findings are discussed with respect to pain modulation taking into consideration the enkephalin synaptic complex in intrinsic circuits and the possible ending of enkephalin axons on the projective neurons of the periaqueductal gray matter.
脑啡肽是一种阿片肽，当注射到中脑导水管周围灰质，尤其是其尾部时，会产生镇痛作用。在本研究中，我们希望使用免疫细胞化学预包埋方法，研究大鼠中参与脑啡肽作用的神经元和突触回路的精细结构。标记的神经元显示出中小型的胞体，有一个大细胞核，缺乏广泛的颗粒内质网，且突触接触较少。脑啡肽树突上的突触通常是多个的，未标记，且显示出对称和不对称的连接。脑啡肽轴突终末在树突上形成突触接触，通常未标记；偶尔可见脑啡肽成分之间的接触。脑啡肽突触显示出对称类型的连接。这些数据为生理学发现提供了形态学支持，特别是那些表明脑啡肽通过突触后过程对中脑导水管周围灰质细胞产生抑制作用的发现。考虑到固有回路中的脑啡肽突触复合体以及脑啡肽轴突在中脑导水管周围灰质投射神经元上可能的终止，我们就疼痛调制对这些发现进行了讨论。
