Sleep states alter ventral medullary surface responses to blood pressure challenges

Ventral medullary surface (VMS) activity declines during rapid eye movement (REM) sleep, suggesting a potential for reduced VMS responsiveness to bloo d pressure challenges during that state. We measured VMS neural activity, a ssessed as changes in reflected 660-nm wavelength light, during presser and depressor challenges within sleep/waking states in five adult, unrestraine d, unanesthetized cats and in two control cats. Phenylephrine elevated bloo d pressure and elicited an initial VMS activity decline and a subsequent ri se in VMS activity in all states, although the initial decline during quiet sleep occurred only in rostral placements. Phasic REM periods elicited a m omentary recovery from the evoked activity rise, and arousals diminished th e overall elevation in activity. A sodium nitroprusside depressor challenge increased VMS activity more in REM sleep than in quiet sleep, with the inc rease being even less in waking. Enhanced responses to depressor challenges during REM sleep suggest a loss of dampening of evoked activity during tha t state; state-related differential baroreflex sensitivity may result from sleep-waking changes in VMS responses to blood pressure challenges.