Region-specific adenosinergic modulation of the slow-cortical rhythm in urethane-anesthetized rats.

Slow cortical rhythm (SCR) is a rhythmic alternation of UP and DOWN states during sleep and anesthesia. SCR-associated slow waves reflect homeostatic sleep functions. Adenosine accumulating during prolonged wakefulness and sleep deprivation (SD) may play a role in the delta power increment during recovery sleep. NREM sleep is a local, use-dependent process of the brain. In the present study, direct effect of adenosine on UP and DOWN states was tested by topical application to frontal, somatosensory and visual cortices, respectively, in urethane-anesthetized rats. Local field potentials (LFPs) were recorded using an electrode array inserted close to the location of adenosine application. Multiple unit activity (MUA) was measured from layer V-VI in close proximity of the recording array. In the frontal and somatosensory cortex, adenosine modulated SCR with slow kinetics on the LFP level while MUA remained mostly unaffected. In the visual cortex, adenosine modulated SCR with fast kinetics. In each region, delta power increment was based on the increased frequency of state transitions as well as increased height of UP-state associated slow waves. These results show that adenosine may directly modulate SCR in a complex and region-specific manner which may be related to the finding that restorative processes may take place with varying duration and intensity during recovery sleep in different cortical regions. Adenosine may play a direct role in the increment of the slow wave power observed during local sleep, furthermore it may shape the region-specific characteristics of the phenomenon.