Potentiation of central reward by localised perfusion of acetylcholine and 5-hydroxytryptamine

Abstract

THERE is considerable evidence that the ascending cate-cholaminergic systems of the brain¹ are involved with behaviour that is contingent on reward. Much of this evidence concerns the variables which influence intracranial self-stimulation behaviour². Because the anatomical and neurochemical correlates of self-stimulation are specified, evaluation of the catecholamine hypothesis should ideally involve the manipulation or measurement of neurochemical activity within restricted regions of the brain. We have made a first step in determining the neurochemical code of the excitatory input to the dopaminergic systems which originate in the ventral mesencephalon (VM) and which are thought to play a part in intracranial self-stimulation³. A technique well suited for this purpose is push–pull perfusion with which exogenous putative neuro-transmitters can be administered to discrete regions of the brain by way of the perfusion medium. Using this technique it was possible to establish dose–response relationships between self-stimulation of the medial forebrain bundle (MFB), through which fibres of the catecholaminergic systems pass, and perfusion of ⁵-hydroxytryptamine (5-HT) or acetylcholine (ACh) in the VM.