Effect of amine precursors on the concentration of striatal dopamine and serotonin in cats with and without unilateral brain stem lesions

Abstract

A study of the effect of amine precursors on the concentration of dopamine and serotonin in the striata of the brains of normal cats and of cats with unilateral brain stem lesions gave the following results. The i.p. injection of dl-DOPA and of dl-5-HTP into normal cats produced a marked increase of the striatal dopamine and serotonin, respectively. The i.p. injection of dl-DOPA into cats with unilateral brain stem lesions that completely severed the nigro-striatal pathways and did not influence the depletion of dopamine in the corresponding striatum but produced a marked increase of dopamine in the striatum of the intact side. Such lesions were associated with a complete disappearance of the neurons (retrograde degeneration) in the ipsilateral substantia nigra and nucleus parabrachialis pigmentosus which are responsible for the elaboration of dopamine. The i.p. injection of dl-5-HTP into cats with unilateral brain stem lesion that interrupted the striatopetal fibers responsible for regulating the serotonin content of the striatum did not modify the complete, or nearly complete, depletion of serotonin in the corresponding striatum although it markedly increased the concentration of serotonin in the striatum of the intact side of the brain. Such lesions are associated with a retrograde cellular degeneration in some basomedial cell groups of the upper pons and lower midbrain on the side of the lesion. Consequently, the use of dopamine and serotonin precursors to compensate for a loss of those biogenic amines from the striatum as encountered in some extrapyramidal syndromes could be of value only where some functioning striatopetal neurons persist.