The effects of an alpha-adrenergic agonist or antagonist on sleep during blockade of catecholamine synthesis in the cat.

The effects of clonidine (CLO) and phentolamine (PHE) on the sleep-waking cycle in the cat treated with alpha-methyl-p-tyrosine (AMPT) were investigated with continuous 16--24 h polygraphic recordings. For the evaluation of possible cholinergic interactions in the paradoxical sleep (PS) increasing effect of AMPT, an atropine pretreatment was given to a group of cats receiving AMPT. Results were compared with those from previous experiments with PHE and atropine. When given alone, AMPT (150 mg/kg) decreased waking and increased deep slow wave sleep. Consistent with other reports PS was enhanced. These results support the hypothesis that moderate inhibition of catecholaminergic transmission favors the execution of PS in the cat. Previous studies have shown that CLO inhibits and PHE increases PS in the cat. In the present study administration of AMPT (150 mg/kg) did not alter the effect of CLO (0.01 mg/kg) or PHE (20 mg/kg) on PS; if anything, a slight potentiation was observed. These results support the view that stimulation of alpha 2-adrenoceptors is of major importance in the effect of CLO on PS and that in certain situations blockade of these receptors by PHE may contribute to its PS increasing action. The increase in PS induced by AMPT was moderate when compared with PS increase after injection of PHE (20 mg/kg) which enhances significantly both the number of PS episodes and their mean length. Atropine at a small dose of 0.075 mg/kg reverses the effect of PHE on PS, whereas it did not affect the sleep pattern induced by AMPT.