Temporal correlation of graded reversible inspiratory inhibition with discharge patterns of late inspiratory neurons located in the dorsal respiratory group in cats.

Respiratory neurons were recorded with microelectrodes in the medullary dorsal respiratory group of pentobarbital-anesthetized cats. The animals were ventilated with a phrenic-driven servorespirator that allowed manipulation of phasic volume feedback. By increasing or decreasing the gain of the servorespirator, graded reversible inhibition could be temporally advanced or delayed, respectively. Fourteen percent of the neurons were late inspiratory (1.I.) and received a facilitatory volume input and, hence, are classified as 1.I. beta neurons. When the time of onset of graded inhibition was advanced, the onset of firing of 1.I. beta neurons was advanced, and, similarly, when graded inhibition was delayed, the onset of 1.I. beta neuron firing was delayed. The lag between the onset of firing and the onset of graded inhibition ranged from -240 msec to +760 msec, but each neurons displayed a relatively constant lag as servorespirator gain was changed. When transient inspiratory inhibition was produced by inflating the lungs and then withdrawing volume during the graded reversible inhibitory period, the 1.I. beta neurons fired during the transient inhibitory period but decreased their firing as inspiratory activity recovered. This indicates that 1.I. beta activity is associated with graded inhibition, not with the irreversible stage of phase transition.