Interaction between somatic and vagal afferent inputs in control of ventilation in 2-week-old rabbits

Effects of saphenous nerve stimulation (SNS) on the Hering-Breuer expiratory-promoting reflex evoked by a positive tracheal pressure (PTR; 5 cmH2O) and on the diaphragmatic EMG (EMG(DI)), inspiratory (TI) and expiratory (TE) time, were studied in 16 urethane-anesthetized (1.2-1.6 g/kg, i.p.) spontaneously breathing 2-week-old rabbits. Positive P(TR) applied at the end of T(I) increased the subsequent TE to 255+/-29% (+/-S.E.; P < 0.0001) of control. SNS (1 sec train, 2 msec pulse, 6 Hz) applied at the onset of TE, shortened this TE by 42+/-3% (P < 0.0001). When SNS preceded positive PTR or positive PTR preceded SNS, the TE increased to 163+/-20 and 184+/-21% of control, respectively. These responses were not different, and smaller than that provoked by the PTR test alone (P < 0.003 and 0.05, respectively). The results show that in newborns somatic afferent stimulation attenuates the vagally mediated respiratory inhibition, whether immediately before or during the vagal stimulation.