家兔脑桥臂旁内侧核区微量注射吗啡对中缝大核区单位放电的影响

实验在62只家兔上进行。结果观察到,中缝大核(NRM)区562个单位中,有118个单位的自发放电频率低,放电比较规则,动作电位时程长,易被微电泳5-羟色胺所阻遏,称为A 组单位。其余444个单位的自发放电频率高,动作电位时程短,称为B 组单位。大多数 B组单位对微电泳5-羟色胺不起反应。脑桥臂旁内侧核(NPBM)区微量注射吗啡(200μg/2μl)或静脉注射吗啡(3mg/kg)后,20个A 组单位中有19个发生兴奋效应,而49个B 组单位中仅有29个发生兴奋效应,而且A组单位发生兴奋的程度也比B组单位的高。这些结果提示,NRM区的A 组单位可能是5-羟色胺神经元,吗啡对这些神经元有相对选择性的兴奋作用。 在另外11只家兔上,应用辣根过氧化物酶(HRP)逆行追踪技术观察到,NPBM 区与NRM 区有纤维联系。 本实验结果提示,静脉注射吗啡所致的呼吸抑制,可能与吗啡作用于 NPBM,通过纤维联系,引起NRM 5-羟色胺神经元兴奋有关。

EFFECTS OF MORPHINE APPLIED LOCALLY IN NUCLEUS PARABRACHIALIS MEDIALIS(NPBM)ON THE DISCHARGES OF UNITS IN THE REGION OF NUCLEUS RAPHE MAGNUS(NRM)IN THE RABBIT

Experiments were carried out on 62 lightly anaesthetized, paralyzed and ar-tificially ventilated rabbits. Spontaneous unit discharges in NRM were recorded.Of 562 NRM units, 118 exhibited a specific discharge pattern characterized byregular, low frequency firing and long action potential duration. These units wereeasily inhibited by microiontophoresis of serotonin and were classified as groupA units. In contrast, the remaining 444 units, which were classified as group Bunits, showed higher discharge frequency and shorter action potential duration.Most of the group B units were resistant to microiontophoretically applied serotonin.The effects of morphine given either systematically or locally into NPBM on thedischarges of NRM units were then examined. Nineteen out of the 20 group Aunits were excited by morphine. For group B units, however, only 29 out of 49were excited, the degree of morphine excitation being much smaller than that inthe case of group A units. It is thus suggested that the group A units in NRMare presumably serotonergic and may be selectively activated by morphine. Ina separate group of rabbits, fiber projections from NPBM to NRM were identifiedby using retrograde HRP tracing technique. The results obtained indicate thatmorphine may indirectly activate NRM serotonergic neurons via the connectionbetween NPBM and NRM and thus causes respiratory depression.