TIME-DEPENDENT PHRENIC-NERVE RESPONSES TO CAROTID AFFERENT ACTIVATION- INTACT VS DECEREBELLATE RATS

The objectives were to determine 1) respiratory responses to carotid c hemoreceptor inputs in anesthetized rats and 2) whether the cerebellar vermis plays a role in these responses. A carotid sinus nerve was sti mulated (20 Hz) with five 2-min trains, each separated by approximatel y 3 min. During stimulation, respiratory frequency (f), peak amplitude of integrated phrenic nerve activity (integral Phr), and their produc t (f X integral Phr) immediately increased. As stimulation continued, integral Phr progressively increased to a plateau [short-term potentia tion (STP)], but f and f X integral Phr decreased [short-term depressi on (STD)] to a value still above control. Upon stimulus termination, i ntegral Phr progressively decreased but remained above control; f and f x f integral Phr transiently decreased below baseline. After the fin al stimulation, integral Phr remained above control for at least 30 mi n [long-term facilitation (LTF)]. Repeated 5-min episodes of isocapnic hypoxia also elicited STP, STD, and LTF. Vermalectomy lowered the CO2 -apneic threshold and eliminated LTF. In conclusion, carotid chemorece ptor activation in rats elicits STP and LTF similar to that in cats; t he vermis may play a role in LTF. A new response, STD, was observed.