Effect of monoamine oxidase inhibitors on the concentrations of dopamine and serotonin in the striatum of the cat with and without unilateral brainstem lesions

A comparison between the effects of tranylcypromine and harmaline on the concentrations of dopamine, and serotonin in the striatum of the brain of normal cats gave the following results. Harmaline produced an increase in serotonin but not in dopamine whereas tranylcypromine increased both biogenic amines. In addition, harmaline produced its maximal effect on serotonin concentration within 1 hour whereas tranylcypromine caused an increase in both dopamine and serotonin only after a much longer period of time. In cats with unilateral brainstem lesions that interrupted the striatopetal fibers from the brainstem nuclei concerned with the elaboration of dopamine and serotonin, the administration of harmaline resulted in different effects in the two striata of the brain. Under such circumstances the concentrations of dopamine and serotonin in the striatum of the intact side of the brain were similar to those found in normal cats treated with harmaline. In cats with a complete interruption of the fibers concerned with the elaboration of the two biogenic amines, there was a complete cell loss in the corresponding brainstem nuclei, associated with a complete depletion of dopamine and serotonin in the ipsilateral striatum. This depletion was apparently unaffected by treatment with harmaline.

Autoradiography and drug localization

Autoradiography was used to follow the distribution of 1-aminocyclopentanecarboxylic acid (ACPC), its analogue 1-amino-2-methylcyelopentanecarboxylic acid, tryptamine, and a barbituric acid analogue of phenylalanine. Mice were injected with 14C-labelled compounds, and sagittal sections were exposed for autoradiography. ACPC was localized in the pancreas and also in Walker tumors. Similarly, the methyl analogue accumulated in the pancreas but was located also in the kidney. There was a high content in an Ehrlich ascites tumor. The barbiturate was found mainly in the intestine and gallbladder. Tryptamine was rapidly metabolized and excreted through the kidney. These findings add much to the information obtained by the classical techniques of biochemistry.