Increased cardiovascular responsiveness to central cholinergic stimulation in the genetically epilepsy-prone rat

We sought to determine whether differences in cardiovascular responsiveness to central stimulation of the cholinergic system existed between the genetically epilepsy-prone and outbred Sprague-Dawley rats. We treated the unanaesthetized, restrained rats with the indirect cholinergic agonist physostigmine (25, 50, 100 and 200 micrograms kg-1, i.v.) and the direct muscarine agonist arecoline (50, 100 and 200 micrograms kg-1, i.v.). Blood pressure and heart rate were evaluated. Genetically epilepsy-prone rats demonstrated to be more susceptible to the action of physostigmine than the outbred Sprague-Dawley rats. Conversely, we did not note any difference between the two strains in the extent of the pressor response induced by arecoline. Moreover, we treated both strains with hemicholinium-3 (34.8 nmol, i.c.v.) to deplete endogenous stores of acetylcholine. This treatment did not affect the pressor response to arecoline, whereas it greatly reduced the response to physostigmine. The present results support an increased cardiovascular responsiveness to central cholinergic stimulation in the genetically epilepsy-prone rat which appears to be related to a pre-synaptic rather than a post-synaptic component.