Generation of respiratory pattern in the rabbit -- brainstem transections revisited.

The effects of unilateral transection of the lower brainstem on the generation of central respiratory rhythm and its amplitude were studied in halothane anesthetized, vagotomized, paralyzed and artificially ventilated rabbits. Transections involving N. VII or rostral part of N. r VII elicited apneustic pattern of discharge in both phrenic nerves. Lesions made at more caudal levels (1.5-3.5 mm rostral to obex) restored a more normal pattern of discharge as far as frequency is concerned, but reduced the amplitude, particularly in the ipsilateral phrenic nerve. Sections below the obex abolished the activity of the ipsilateral phrenic n. Since classical midpontine sections did not, elicit apneustic discharge, it is possible that this pattern is produced by modifications in the number and functional connections of inspiratory-inhibitory neurons.