0105 EXTRACELLULAR DISCHARGE ACTIVITY PROFILES OF PARAFACIAL ZONE NEURONS ACROSS SLEEP-WAKE CYCLE IN RATS

Abstract

Recent studies suggest that medullary parafacial zone (PZ) plays a role in sleep regulation. GABAergic/glycinergic neurons in the PZ express sleep-associated fos-immunoreactivity. Cell-body-specific lesions as well as genetic disruption of GABAergic/glycinergic transmission from PZ cause sustained waking and suppression of both nonREM and REM sleep, whereas, activation of these neurons increases nonREM sleep and suppresses both waking and REM sleep. The discharge activity profiles of PZ neurons across spontaneous sleep wake cycles, especially during transitions from waking to nonREM sleep and from nonREM to REM sleep are unknown. The present study determined the extracellular discharge activity profiles of PZ neurons across spontaneous sleep-wake cycle in freely behaving rats. Adult Sprague-Dawley rats were surgically implanted with EEG and EMG electrodes for chronic recording of sleep-wake states. Five pairs of 20µm microwires were implanted through the barrel of a mechanical microdrive into the PZ for recording extracellular activity of PZ neurons across its dorsal-ventral extent. All recordings were conducted early in the light phase of a 12:12 light-dark cycle. Following isolation of single units, the discharge activity was recorded through 3–5 sleep-wake cycles. Extracellular discharge activity profiles of 45 neurons in the PZ were recorded across sleep-wake cycle. Based on their nonREM/wake, nonREM/REM, and REM/wake discharge ratios and a minimum 25% change criterion, a majority of neurons (n=24) were sleep-active including neurons that exhibited increased discharge during both nonREM and REM, nonREM only, or REM sleep only. The nonREM/REM and nonREM-sleep active neurons exhibited sustained discharge during the entire nonREM sleep episode with only small changes during wake to nonREM sleep transitions. Wake-active neurons (n=13) constituted second largest neuronal group and included both wake-REM and wake-active neurons. State-indifferent neurons (n=8) constituted 18% of the recorded neurons. Our preliminary findings show that a majority of neurons in the rat PZ are sleep-active. These sleep-active neurons, however, do not seem to anticipate transitioning of sleep-wake state. These findings are consistent with a role of the PZ in sleep regulation, especially its maintenance. VA Merit Awards, BX000936 (Alam), BX003520 (McGinty) and BX00155605 (Szymusiak), and R01 DA034748, BX001753 (Siegel).