GABAergic mechanisms in the pedunculopontine tegmental nucleus of the cat promote active (REM) sleep.

The pedunculopontine tegmental nucleus (PPT) has been implicated in the generation and/or maintenance of both active sleep (AS) and wakefulness (W). GABAergic neurons are present within this nucleus and recent studies have shown that these neurons are active during AS. In order to examine the role of mesopontine GABAergic processes in the generation of AS, the GABA(A) agonist muscimol and the GABA(A) antagonist bicuculline were microinjected into the PPT of chronic cats that were prepared for recording the states of sleep and wakefulness. Muscimol increased the time spent in AS by increasing the frequency and duration of AS episodes; this increase in AS was at the expense of the time spent in wakefulness. A decrease in PGO density during AS was also observed following the microinjection of muscimol. On the other hand, bicuculline decreased both AS and quiet sleep and increased the time spent in wakefulness. These data suggest that GABA acts on GABA(A) receptors within the PPT to facilitate the generation of AS by suppressing the activity of waking-related processes within this nucleus.