The behavioural effects of intrahypothalamic multistage versus single injections of 6-hydroxydopamine

16 micrograms of 6-hydroxydopamine were injected bilaterally into the lateral hypothalamus of male Sprague-Dawley rats in either a single injection or in a series of multistage injections over a period of 75 days. While the single injection produced behavioural deficits typical of those seen following catecholamine depletion of the forebrain, the behaviour of animals injected incrementally with the same dose was indistinguishable from that of controls. Fluorescent histochemical assessment revealed that the animals in the multistage injection group, the behaviourally unimpaired, suffered more severe depletion of forebrain catecholamines than those in the single-stage injection group. Accumulation of amines proximal to the site of drug injection was extensive only in those animals displaying behavioural deficits, that is, the group with the lesser amount of forebrain catecholamine depletion. It is suggested that the severity of deficits in consummatory and motor behaviour occurring after hypothalamic trauma is determined by a lesion's effectiveness in producing amine accumulation rather than catecholamine depletion.