Post-synaptic inhibition of bulbar inspiratory neurones in the cat.

Abstract

Stable intracellular recordings from 36 bulbar inspiratory neurons revealed 3 centrally originating, rhythmic patterns of synaptic inhibition (i.p.s.p.). A declining pattern of i.p.s.p. accompanying the early stages of inspiration (early inspiratory inhibition) was identified in a total of 20 neurons representing examples of each of the functional classes of bulbar neurons examined, i.e., 6 R.alpha.- and 2 R.beta.-neurons of the dorsal respiratory group and 12 R.alpha.-neurons of the ventral respiratory group. A transient pattern of i.p.s.p. just preceding or coinciding with the cessation of inspiration (late inspiratory inhibition) was present in the remaining 16 neurons which were tested, representing 6 R.alpha.-neurons and 3 R.beta.-neurons of the dorsal respiratory group and 7 R.alpha.-neurons of the ventral respiratory group. An augmenting pattern of expiratory i.p.s.p. was present in all 36 neurons. Late inspiratory and expiratory i.p.s.p. in the same neurons showed a similar time course of reversal when Cl was injected or allowed to diffuse into the cells and were associated with similar increase in input conductance. Both patterns of i.p.s.p. appear to arise at or close to the cell soma. Early inspiratory i.p.s.p. required a relatively longer period of Cl injection for reversal to be accomplished. Input conductance changes were either absent or smaller than those associated with late inspiratory or expiratory inhibition. These i.p.s.p. appear to arise at more distal dendritic sites. The patterns of i.p.s.p. are discussed in relation to the mechanisms shaping the growth of central inspiratory activity, bringing this activity to an end and suppressing its redevelopment during expiration.