电刺激兔延髓腹侧化学敏感区和压力敏感区对呼吸、血压,的影响及其中枢递质机制

电刺激麻醉兔延髓腹侧化学敏感区头端区引起潮气量(V_T)增加,呼吸频率(f)增快;电刺激压力敏感区(中间区)则使V_T减小,f亦增快。弱刺激时,两者均产生降压反应;刺激增强可诱发双相或升压反应。在出现周期性呼吸时,电刺激化学敏感区可使呼吸节律正常化、V_T增大,而电刺激压力敏感区则导致呼吸暂停。电刺激压力敏感区时,吸气时间(TI)和呼气时间(T_E)均缩短,以T_E变化更明显;由于V_T减小和T_I缩短,V_T/T_I保持相对不变,提示吸气终止的中枢阈值降低。在准备刺激的相应局部预先应用阿托品,可使电刺激化学敏感区产生的通气增强效应翻转,而对电刺激压力敏感区引起的通气抑制无明显影响;用印防己毒素则可选择性消除电刺激压力敏感区的通气抑制和降压效应。本工作表明延髓腹侧存在两个不同的中枢机制,其中化学敏感区产生的通气增强与胆碱能系统有关;压力敏感区产生的通气减弱效应与GABA系统有关。

EFFECTS OF ELECTRICAL STIMULATION OF THE CHEMOSENSITIVE AREAS AND THE BAROSENSITIVE AREAS AT THE VENTRAL MEDULLA ON RESPIRATION AND BLOOD PRESSURE AND THE UNDERLYING NEUROTRANSMITTER MECHANISMS IN RABBITS

In 42 anesthetized rabbits, electrical stimulation to the rostral chemosensitivearea at the ventral medulla elicited increases in tidal volume and frequency, whilesimilar stimulation to the bulbar barosensitive area (the intermediate area) induceda decrease in tidal volume accompanied by a faster respiratory rate. Stimulationof either area also elicited a lowering of blood pressure or low frequency. Biphasicor pressor response appeared when a stronger stimulus was used. In animals withspontaneous periodic breathing, electrical stimulation to the chemosenstive areacould normalize the breathing pattern; however, stimulating the barosensitivearea worsened the condition, i.e. resulting in apnea. Shortening of inspiratorytime (T_I) as well as expiratory time (T_E) occurred during stimulating the baro-sensitive area. Since reduction of V_T and shortening of T_I were closely correlated,V_T/T_I tended to be in constant. This meant that central threshold value ofinspiratory off process was decreased. Local application of atropine could reverse the enhanced ventilation inducedby stimulating the chemosensitive area, but there was no significant influence onthe effects due to stimulation of barosensitive area. On the contrary, picrotoxinwhen applied locally would eliminated the ventilation and blood pressure changesevoked by stimulating the barosensitive area. It is concluded that there are two diffe-rent central neurotransmitter mechanisms relating to these two areas at the ventralmedulla: the chemosensitive area which causes hyperpnea are concerned with theactivity of the cholinergic system and activation of the GABA system is responsiblefor the depressant effect of ventilation induced by stimulating the barosensitive area.