Nonassociative Learning in Expiratory Inhibition of Inspiratory Motor Output: An Experimental and Modeling Study

The present study is to characterize the habituation and re-sensitization in the inspiratory inhibition produced by the Botzinger complex (Bot.C) and the modulation effects of raphe pallidus (RP) and locus coeruleus (LC). Experiments were done on urethane anaesthetized, vagotomized, paralyzed and artificially ventilated rabbits. Electrical stimulation of the Bot.C (25 muA, 80 Hz, 15 sec) caused inspiratory inhibition that became gradually adapted with the continuation of the stimulation. At the offset of this stimulation, the phrenic discharge showed temporary rebound increase in amplitude. The adaptation-rebound response pattern resembled a neural differentiator. Pre-stimulation of the RP or LC (50 muA, 80 Hz, 10 sec) facilitated the adaptation of Bot.C´s inspiratory inhibition and the post-stimulus rebound. The results indicate the existence of nonassociative learning (habituation and re-sensitization) in the inspiratory inhibition circuit and the modulation of this nonassociative learning by RP and LC