Lack of alpha2-adrenoceptor autoregulation of noradrenaline release in rat nucleus accumbens slices.

The role of release-inhibitory alpha2-adrenoceptors on or near noradrenergic nerve terminals was investigated in slices of rat nucleus accumbens and medial prefrontal cortex, representing major projection areas of mesocorticolimbic dopamine neurons. As expected, the electrically evoked release of [3H]noradrenaline from superfused medial prefrontal cortex slices was strongly inhibited (to about 25% of control values) by exogeneous noradrenaline and by the alpha2-adrenoceptor agonist oxymetazoline, while blockade of alpha2-adrenoceptors with phentolamine or rauwolscine caused a large increase (to almost 250% of control values) in neurotransmitter release. In striking contrast and much to our surprise, these drugs did not at all affect the electrically evoked release of [3H]noradrenaline from nucleus accumbens slices. These results indicate that alpha2-adrenoceptor autoregulation of noradrenaline release may not be a major feature of noradrenergic varicosities in rat nucleus accumbens. Thus, the functioning or presence of these receptors may vary with the brain region innervated by locus coeruleus neurons and may not represent a ubiquitous feature of noradrenergic neurons.