NORADRENERGIC MODULATION OF MIDBRAIN DOPAMINE CELL FIRING ELICITED BYSTIMULATION OF THE LOCUS-CERULEUS IN THE RAT

Electrical stimulation techniques were employed in the chloral hydrate anaesthetized male rat to evaluate if the pontine noradrenergic nucle us locus coeruleus can influence the activity of midbrain dopamine neu rons in the ventral tegmental area and zona compacta, substantia nigra . Single-pulse locus coeruleus stimulation evoked an excitation, follo wed by an inhibition, of the electrical activity of single midbrain do pamine neurons. Neither of these responses were observed in animals pr etreated with reserpine, implicating noradrenaline as a mediator. The alpha1-adrenoceptor antagonist prazosin decreased the excitation, whil e other adrenoceptor antagonists were without general effect. Burst-ty pe stimulation produced only a more long-lasting inhibition. The influ ence from the locus coeruleus on midbrain dopamine neurons could be im portant in behavioural situations involving novelty and reward, and mi ght also be of importance for the actions of psychotropic drugs.