Abstract
Low frequency stimulation of the vagal pulmonary stretch receptor (PSR) afferents promotes central inspiratory activity (vagal inspration-promoting (VIP) reflex, Takano and Kato, J. Physiol., 1999, 2003). P2X receptors modulate excitatory synaptic transmission in the nucleus of the solitary tract (NTS), where the PSR afferents terminate, in a manner sensitive to pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; Kato and Shigetomi, J. Physiol., 2001). To elucidate the role of P2X receptors in the VIP reflex, PPADS was microinjected into the NTS in anesthetized rabbits. The vehicle was injected into the NTS contralateral to the PPADS injection. Effects of afferent stimulation of the vagus nerve ipsilateral to PPADS injection (il-stim) and contralateral (cl-stim) on the phrenic nerve rhythm were compared. Unilateral microinjection of PPADS (20 nmole/side/rabbit) significantly reduced the shortening effects of il-stim at a low fre-quency (5-40 Hz) on respiratory cycle (TTOT) and expiratory time (TE) for 60-120 min, whereas the effects of cl-stim and the expiratory prolonging effects of il-stim and cl-stim at a higher frequency (100-160 Hz) were not affected. These results suggest that the ATP-P2X receptor-mediated signaling in the NTS is involved in the respiratory responses to low frequency afferent inputs via vagus afferents. [Jpn J Physiol 54 Suppl:S111 (2004)]
