Some unusual effects of alpha 2-adrenergic drugs on cortical high voltage spindles in rats

The dose-response curves for a number of alpha-adrenergic drugs were investigated to estimate a possible role of the alpha 2/alpha 1 selectivity of these drugs on the incidence of cortical high voltage spindles (HVS), reflecting level of vigilance. The alpha 2 antagonists yohimbine (0.25-4 mg/kg) and idazoxan (0.5-4 mg/kg), but not atipamezole induced a biphasic effect on the incidence of HVS in rats. This effect of relatively small doses of yohimbine and idazoxan should be taken into consideration when using these drugs as alpha 2 antagonists in behavioral and neurophysiological tests. On the other hand the linearity of the dose-response curve for atipamezole (0.01-4 mg/kg) indicates that this drug is a good candidate for use in such tests.