MONOAMINE LEVELS AND NEURONAL DEGENERATION IN RAT BRAIN FOLLOWING LATERAL HYPOTHALAMIC LESIONS

¹ Departments of Anatomy, Medicine (Neurology) and Pharmacology, University of Chicago, Chicago, Illinois

Unilateral section of the medial forebrain bundle in the rat lateral hypothalamus results in a decrease in the serotonin and norepinephrine content of the brain-half ipsilateral to the lesion. The decreases in monoamines first appear on the 2nd to 3rd postoperative day and continue to fall until the 12th day. Degenerating axons are first evident in the bundle on the 2nd postoperative day and increase in number until the 5th day. There is no apparent increase in the number of degenerating axons between the 5th and 12th days. After medial forebrain bundle lesions, degenerating axons can be traced anatomically to only two areas of the telencephalon, the septum and amygdala. In contrast to this restricted distribution of the severed axons, the decrease in serotonin produced by medial forebrain bundle lesions occurs throughout the telencephalon. Falls in amine are found not only in the septum and amygdala, but also in the striatum, hippocampus and cortex, telencephalic areas which do not receive a projection from the medial forebrain bundle. These findings indicate that the loss of amine occurs, in large part, as a trans-synaptic effect of the lesions in neurons one or more synapses removed from the degenerated axons of the medial forebrain bundle.

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