AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 4 811-R819, Copyright © 1993 by American Physiological Society
Time-dependent phrenic nerve responses to carotid afferent activation: intact vs. decerebellate rats
F. Hayashi, S. K. Coles, K. B. Bach, G. S. Mitchell and D. R. McCrimmon
Department of Physiology, Northwestern University Medical School, Chicago, Illinois 60611-3008.
The objectives were to determine 1) respiratory responses to carotid
chemoreceptor inputs in anesthetized rats and 2) whether the cerebellar
vermis plays a role in these responses. A carotid sinus nerve was
stimulated (20 Hz) with five 2-min trains, each separated by approximately
3 min. During stimulation, respiratory frequency (f), peak amplitude of
integrated phrenic nerve activity (integral of Phr), and their product (f x
integral of Phr) immediately increased. As stimulation continued, integral
of Phr progressively increased to a plateau [short-term potentiation
(STP)], but f and f x integral of Phr decreased [short-term depression
(STD)] to a value still above control. Upon stimulus termination, integral
of Phr progressively decreased but remained above control; f and f x
integral of Phr transiently decreased below baseline. After the final
stimulation, integral of Phr remained above control for at least 30 min
[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
chemoreceptor activation in rats elicits STP and LTF similar to that in
cats; the vermis may play a role in LTF. A new response, STD, was observed.
