Cholinergic mechanisms of the medial preoptic areas of the hypothalamus in the control of thermoregulation and the states of sleep and waking in pigeons.

Cholinergic mechanisms in the medial preoptic area of the hypothalamus were found to be involved in controlling the time characteristics of the states of sleep and waking, as well as measures of thermoregulation, in pigeons. Muscarinic and nicotinic cholinergic receptors were involved in the mechanisms maintaining waking. Activation of muscarinic cholinoreceptors in the medial preoptic area was accompanied by increases in brain temperature due to increases in peripheral vasoconstriction and decreases in the level of muscle contractile activity. Activation of nicotinic cholinoreceptors in this area led to decreases in brain temperature and increases in the level of contractile muscle activity. Comparative analysis of the results of experiments and previous studies showed that changes in brain temperature in pigeons occurring on activation of cholinoreceptors depend on the type of cholinoreceptor activated but are independent of their location in the preoptic area of the hypothalamus.