Time-dependent phrenic nerve responses to carotid afferent activation: intact vs. decerebellate rats.
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.
Hayashi
F
F
Department of Physiology, Northwestern University Medical School, Chicago, Illinois 60611-3008.
Coles
S K
SK
Bach
K B
KB
Mitchell
G S
GS
McCrimmon
D R
DR
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002346:Carotid Sinus / Q000294:innervation*; D002531:Cerebellum / Q000502:physiology*; D003655:Decerebrate State; D004558:Electric Stimulation; D000860:Hypoxia / Q000503:physiopathology; D008297:Male; D010791:Phrenic Nerve / Q000502:physiology*; D011311:Pressoreceptors / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D013997:Time Factors