Nmda as well as non-nmda receptors in the phrenic motonucleus mediate respiratory effects of carotid chemoreflex. Chitravanshi, V. C., and H. N. Sapru. Section of Neurological Surgery and Department of Pharmacology, New Jersey Medical School, Newark, NJ 07103, (U.S.A.)
APStracts 3:0216R, 1996.
An in-vivo model was used to identify the transmitter/receptor mechanisms in the phrenic motonucleus which mediate carotid chemoreceptor responses. Adult male Wistar rats, anesthetized with urethane, were fixed in a stereotaxic instrument and the blood pressure and heart rate were monitored. The rats were immobilized and artificially ventilated to maintain the end-tidal CO2 at 4.5-5%. The vagus nerves were bilaterally sectioned and a pneumothorax was produced. Activity was recorded from one of the phrenic nerves. The spinal cord was exposed from C1 to T1 levels. The dorsal and ventral roots ipsilateral to the phrenic nerve from which electrical activity was recorded, were sectioned from C2 to C6 except at C3 segment (i.e., the dorsal and ventral roots at C3 segment were left intact). The phrenic nerve bursts recorded in this preparation represented output from a portion of the phrenic motonucleus located in the ipsilateral C3 segment. Carotid chemoreceptor stimulation by N2 -inhalation increased the amplitude as well as the frequency of phrenic nerve bursts. Microinjections of a specific NMDA receptor antagonist (AP-7, 50-100 mM) into the phrenic motonucleus decreased the N2-induced increase in amplitude, but not the frequency, of phrenic nerve bursts. Like-wise microinjections of a specific non -NMDA receptor antagonist (NBQX, 0.5-1 mM) into the phrenic motonucleus decreased the N2-induced increase in phrenic nerve burst -amplitude. When AP-7 and NBQX were microinjected into the phrenic motonucleus sequentially within an interval of 5 min, a drastic reduction in the N2-induced increase in phrenic nerve burst-amplitude was observed. These observations suggest that both NMDA and non-NMDA receptors located in the phrenic motonucleus are involved in the mediation of phrenic nerve responses to the carotid chemoreceptor stimulation. 

Received 26 January 1996; accepted in final form 10 May 1996.
APS Manuscript Number R55-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96