疼痛对神经分泌纤维终末影响的电镜观察

EFFECT OF PAIN ON THE NERVE ENDINGS OF NEUROSECRETORY FIBERS——AN ELECTRON MICROSCOPIC STUDY

疼痛可引起脑啡肽及垂体内啡肽的释放,已知这些内源性吗啡样物质与吗啡具有类似的镇痛作用。最近Rossier[1]用放射免疫法研究,发现垂体神经叶内有亮氨酸-脑啡肽(亮-脑啡肽L-EnK)和甲硫氨酸-脑啡肽(甲-脑啡肽M-EnK)存在,前者含量较少,后者含量较多,其比例为1:3.

The purpose of this research work is to study the influence of experimentally produced pain on the uhrastructural changes of the nerve endings of the neurosecretory fibers from hypothalamus to neurohypophysis.Twenty adult male rats,weighing 200~300 g were divided into 3 groups:(1)Six animals were stimulated through two electrodes fixed on the tail to produce somatic pain.(2)Six animals were stimulated by increasing pressure in the stomach through an air balloon to cause visceral pain.And 8 animals served as control.All the animals were sacrificed and their neurohypophysis were fixed in 40%glutaraldehyde and 1%OsOsuccessively.Sections were cut with an LKB microtome and observed under H500 electron microscope.The following conclusions were drawn from the observed results:1.The neurosecretory granules in the fibers from hypothalamus to neurohypophysis grew up to maturity by increasing in size gradually as they passing down from hypothalamus to neurohypophysis.2.Basing on the morphological exhibition of the neurosecretory granules,we get the impression that the neurosecretion might be released either by molecular dispersion or by exocytosis.3.There were a great number of discrete smooth vesicles grouped in cluster in the dilated parts of neurosecretory fibers.These vesicles had been called as"synaptic"or"synaptoid"vesicles.They might be really synaptic vesicles and containing acetylcholine.Other vesicles with irregular profile and varying in size,collapsing vesicles and vacuoles might be the residues of the neurosecretory granules after discharging their content.4.Many synaptic vesicles were concentrated at the axolemma of the dilated parts of neurosecretory fibers and the membranes were thickened and leaving a synaptic cleft.5.In the exprimental groups after pain stimulation the neurosecretory granules decreased in number and the synaptoid vesicles increased in number and the neurosecretory granules showed a wide pale halo.The number of irregular vesicles and ghost of granules were increased.This phenomenon might show that the excretion of neurosecretory material and neurotransmitters was enhanced.6.Neurohemal zones were the barrier for the neurosecretory material entering into blood.Acetylcholine,endogenous opiatelike substances and gamma-aminobutyric acid(GABA)might play a control role for neurosecretion at this site.7.This experimental results supported the action mechanism of endogenous opaitelike substance and morphine could produce an important role directly in neurohypophysis.