A presynaptic site of action within the mesencephalic reticular formation for (+)-amphetamine-induced electrocortical desynchronization.

1. Changes induced in the electrocorticogram by the bilateral perfusion of (+)-amphetamine into the mesencephalic reticular formation (MRF) have been studied in cat encéphale isolé preparations. 2. (+)-Amphetamine, applied for 5 min in the MRF, mimicked the electrocortical desynchronization induced by the perfusion of (-)-noradrenaline (NA) or (-)-alpha-methylnoradrenaline (AMNA) into the same sites. 3. Perfusion of 6-hydroxydopamine (6-OHDA) also induced desynchronization but, over the 1 h perfusion period, slow wave activity gradually returned to the electrical record. 4. Following the application of 6-OHDA the effect of (+)-amphetamine was abolished or significantly attenuated, whereas the effect of NA or AMNA was not affected. 5. The electrocortical desynchronization induced by (+)-amphetamine could be restored if its application was preceded by perfusion with NA or AMNA. 6. Fluorescence studies using AMNA indicated that 6-OHDA depleted noradrenergic nerve terminals near the cannulae tips. However, the terminals were still capable of taking up exogenously applied AMNA. 7. These results suggest that (+)-amphetamine has a presynaptic action on noradrenergic nerve terminals within the MRF.