The role of catecholamines in the behavioral changes observed after lateral hypothalamic (LH) lesions was assessed by comparing LH lesioned animals with animals subjected to various treatments with 6-hydroxydopamine (6-OHDA). In agreement with previous reports, bilateral electrolytic lesions of the lateral hypothalamus (LH lesioned), intraventricular administration of 6-OHDA in monoamine oxidase inhibited animals (6-OHDA + tranylcypromine) or bilateral injections of 6-OHDA into the substantia nigra (nigral 6-OHDA) produced aphagia and adipsia. Recovery of food and water intake occurred in most animals within 10 days. Some of the nigral 6-OHDA injected animals did not, however, recover during the 3 months of the experiment. Intraventricular injections of 6-OHDA did not produce these effects unless monoamine oxidase was first inhibited. After recovery of food and water intake, the intraventricular 6-OHDA + tranylcypromine and the nigral 6-OHDA groups showed the same deficits in water regulation as were found in the LH lesioned animals: decreased daily water intake, prandial drinking, increased finickiness to quinine adulteration of drinking water, and a lack of drinking in response to hypertonic saline injections. Changes in regulation of food intake were also evident. Amphetamine anorexia was reduced in the LH lesioned and the nigral 6-OHDA groups. Amphetamine anorexia was abolished in the intraventricular 6-OHDA + MAOI animals. In contrast, the anorectic properties of fenfluramine were augmented in these groups. The results suggest that the lateral hypothalamic syndrome may to a large extent reflect the interruption of the dopaminergic nigro-striatal system. Based on tyrosine hydroxylase measures in the striatum, hypothalamus and midbrain, however, it is suggested that damage to this system cannot account for the magnitude of the behavioral changes seen after LH lesions and that other as yet unknown factors may also contribute to this syndrome. © 1973.
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