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

The present study examined the hypothesis that cholinoceptive reticular mechanisms in the gigantocellular tegmental field (FTG) of the medial pontine reticular formation cause state-dependent changes in the discharge of parabrachial neurons. In chronically implanted, unanesthetized cats, extracellular recordings were made from nonrespiratory and respiratory neurons in the parabrachial nuclear complex (PBNC) during the natural sleep-wake cycle and during the rapid eye movement (REM) sleeplike 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-induced REM sleeplike state (DCarb). Cells that decreased discharge in natural REM sleep (REM-off cells) displayed decreased discharge during both DCarb and the neostigmine-induced REM sleeplike states. The limited sample of parabrachial respiratory neurons revealed significantly diminished discharge during the cholinergically induced REM sleeplike state. 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.