Differential role of noradrenaline and dopamine for intracranial self-stimulation in the lateral hypothalamus in rats

Rats were implanted a electrode into the lateral hypothalamus for self-stimulation (SS) and a cannula into the lateral ventricle ipsilaterally for drug treatment. After stable SS was established, each rat was injected 6-OHDA (10 μg/5 Ill/injection) or 6-OHDA (same dosage) with desmethylimipramine (DMI)-pretreatment on 10 consecutive days through the implanted cannula. 6-OHDA treated rats showed gradual decrease in SS rate as daily SS testings proceeded, whereas DMI+6-OHDA treated rats showed no significant changes in SS rates through the entire course of testing except on the first day of drug administration. The degree of catecholamine depletion was assessed by a biochemical fluorescent method using yoked rats of each group. 6-OHDA caused a significant depletion of NE content in the cortex and the hypothalamus, whereas DMI+6-OHDA decreased DA contents significantly in the cortex and the caudatus. The obtained results for changes in SS rates in the two groups were discussed in terms of Herberg et al. s hypothesis that in SS, DA and NE played complementary roles by being involved in the motivation and reinforcement.