EFFECTS OF IONTOPHORETICALLY APPLIED ACETYLCHOLINE ON MEMBRANE-POTENTIAL AND SYNAPTIC ACTIVITY OF BULBAR RESPIRATORY NEURONS IN DECEREBRATECATS

Intracellular recordings were made from bulbar respiratory neurones of decerebrate cats, together with iontophoretic application of acetylch oline and its specific antagonists to assess cholinergic mechanisms in volved in the central respiratory network in vivo. Of 126 respiratory- related neurones impaled in the ventral respiratory group, iontophores is of acetylcholine produced depolarization in 67 cells (53%), hyperpo larization in 36 cells (29%), and no effect in the remaining 23 cells (18%). Depolarization occurred predominantly in laryngeal motoneurones (31/40) and bulbo-spinal neurones (4/5), while a comparable number of non-antidromically-activated respiratory neurones displayed either de polarization (33/81) or hyperpolarization (31/81). Acetylcholine had n o significant effect on excitatory and inhibitory postsynaptic potenti als in all types of neurones tested. Both depolarizing and hyperpolari zing effects of acetylcholine were antagonized by coiontophoresis of a tropine, but not by hexamethonium. Input resistance was increased (7/9 ) or unchanged (2/9) in depolarized cells, whereas it was unaltered in all hyperpolarized cells tested (n = 6). The present results suggest that the distribution and functions of cholinergic muscarinic receptor s are different for the laryngeal and bulbo-spinal types of respirator y neurones and the non-antidromically-activated respiratory neurones i n the cat.