The effects of microstimulation and microlesions in the ventral and dorsal respiratory groups in medulla of cat

Abstract

The responses in respiratory outflow resulting from microstimulation and successive microlesions of the dorsal (DRG) and ventral (VRG) respiratory groups of neurons in the brainstem were studied in anesthetized, paralyzed, artificially ventilated cats. Microstimulation (2 to 120 Hz; 5 to 50 PA; 100 pet pulse duration) at almost every point within the DRG or VRG produced a bilateral short latency inhibition of phrenic nerve activity which had an onset latency of 4 to 9 msec and a duration of 4 to 25 msec. This global stereotyped phrenic inhibition was elicited by single pulses and often was accompanied by a postinhibitory excitation. In 48 % (g2/193) of the stimulation trials, trains of stimulus pulses during inspiration decreased the duration of inspiration. In 25 % of the expiratory microstimulation trials, expiratory duration was increased and in ll%, expiration was shortened markedly by trains of pulses. Single shocks delivered to the right VRG or DRG produced a short latency excitation in the ipsilateral recurrent laryngeal nerve (RRL). This RRL excitation had an onset latency of 2 to 5 msec and a duration of 3 to 15 msec. Evidence suggests that the RRL excitation is due to a paucisynaptic activation of expiratory motoneurons in the caudal VRG. This activation is synchronous with the inhibition of inspiratory neurons in DRG and VRG