Role of the cholinergic mechanisms of the ventrolateral preoptic area of the hypothalamus in regulating the state of sleep and waking in pigeons.

Maintenance of waking in pigeons was found to be linked with the mechanisms of activation of muscarinic (M-) cholinergic receptors of the ventrolateral preoptic area of the hypothalamus. "Muscarinic" waking was characterized by an increase in the power of the EEG spectrum at 0.75-12 Hz and an increase in brain temperature. Activation of nicotinic (N-) cholinergic receptors in this area was associated with an increase in the duration of slow sleep, a decrease in the spectral EEG power at 0.75-7 Hz, and a decrease in brain temperature in this state; hyperactivation of these receptors led to the development of waking, where waking episodes were associated with significant decreases in brain temperature. Blockade of M-and N-cholinergic receptors resulted in changes in the sleep-waking cycle and thermoregulation which were oppose to those seen on receptor activation. It is suggested that M-and N-cholinergic receptors of the ventrolateral preoptic area of the pigeon hypothalamus are involved in regulating sleep and waking, their effects being associated with influences on the GABAergic system of this area.