Scopolamine-sensitive and resistant components of increase in cerebral cortical blood flow elicited by periaqueductal gray matter of rats.

The present study attempted to evaluate the effects of inhibition of cortical muscarinic receptors on the increase in cortical blood flow (laser-Doppler flowmetry) elicited by chemical stimulation of the periaqueductal gray matter in 28 anesthetized rats with cervical cordotomy. A new device was introduced which allowed focal cortical superfusion with scopolamine, an antagonist for muscarinic receptors, without disturbing the temperature of an exposed cortical area under study. We found that although the flow increase was attenuated by scopolamine (31.6 micromol/l to 1 mmol/l) so applied, about one third of it was resistant to the treatment. Cortical muscarinic and non-muscarinic receptor mechanisms may thus subserve the mediation of the flow increase.