PONTINE CHOLINERGIC RETICULAR MECHANISMS CAUSE STATE-DEPENDENT CHANGES IN THE DISCHARGE OF PARABRACHIAL NEURONS

The present study examined the hypothesis that cholinoceptive reticula r mechanisms in the gigantocellular tegmental field (FTG) of the media l pontine reticular formation cause state-dependent changes in the dis charge of parabrachial neurons. In chronically implanted, unanesthetiz ed cats, extracellular recordings were made from nonrespiratory and re spiratory neurons in the parabrachial nuclear complex (PBNC) during th e natural sleep-wake cycle and during the rapid eye movement (REM) sle eplike state caused by FTG microinjection of carbachol or neostigmine. PBNC cells that increased discharge during natural REM sleep (REM-on cells) revealed similar increased discharge during the carbachol-induc ed REM sleeplike state (DCarb). Cells that decreased discharge in natu ral REM sleep (REM-off cells) displayed decreased discharge during bot h DCarb and the neostigmine-induced REM sleeplike states. The limited sample of parabrachial respiratory neurons revealed significantly dimi nished discharge during the cholinergically induced REM sleeplike stat e. Thus cholinoceptive mechanisms localized to specific regions of the pontine reticular formation can cause state-dependent changes in the firing rates of respiratory and nonrespiratory neurons in the PBNC.