Neuropeptide Y significantly reduced the potassium-stimulated release of [3H]norepinephrine [( 3H]NE) from slices of rat hippocampus, hypothalamus and frontal cortex but not from slices of parieto-occipital cortex. The NPY-induced inhibition of [3H]NE release from frontal cortical slices was concentration dependent, reaching statistical significance at 10 nM. The alpha 2-adrenoceptor partial agonist, clonidine, also reduced the potassium-stimulated release of [3H]NE. The combination of NPY and clonidine in hippocampal slices produced a greater reduction of stimulated [3H]NE release than either of the two compounds alone, suggesting a potentiation of their activity, whereas in frontal cortical slices, the effect was additive. When NPY and clonidine were added to frontal cortical slices, they independently produced a significant concentration-dependent reduction in forskolin-stimulated cAMP accumulation. However, NPY and clonidine combined did not produce a further reduction in forskolin-induced cAMP accumulation than either compound when used alone. These results suggest that the ability of NPY to potentiate alpha 2-adrenoceptor-induced inhibition of [3H]NE release in discrete brain regions does not depend on the reductions in cAMP.