Indoleamine neurons and their processes in the normal rat brain and in chronic diet‐induced thiamine deficiency demonstrated by uptake of 3H‐Serotonin

Abstract

Indoleamine structures in the brains of normal, pair-fed control, and thiamine deficient rats are selectively localized by autoradiography following monoamine oxidase inhibition and simultaneous intraventricular infusion of ³H-5HT (10⁻⁵ m) and cold d–1 norepinephrine (10⁻⁴ m). The locations of indoleamine neurons and their plexuses are comparable in the normal and control animals and are enumerated and mapped in detail. In addition to numerous labeled neurons in the raphe and reticular formation of pons and medulla, there are indoleamine neurons in several hypothalamic nuclei, in the mammillary, habenular, and interpeduncular nuclei. Labeled axonal plexuses occur in almost all areas of the brain but certain regions in spinal cord, medulla, midbrain, diencephalon, basal ganglia, and hippocampus are particularly rich. Thiamine deficiency causes lack of label in almost all indoleamine neurons and their processes in the midbrain and medulla; only a few dystrophic cells with hypertrophied axons are seen. In the diencephalon more indoleamine neurons and their axonal plexuses are visualized in these uptake studies. The periventricular regions of spinal cord, medulla, midbrain and diencephalon, the mammillary nuclei, habenular nuclei, and cerebellum – areas richly innervated by indoleamine axons in the normal brain – are the most severely affected. The ventricular and leptomeningeal indoleamine structures are preserved, however, and individual axons may hypertrophy. It remains to be resolved whether these changes reflect disturbances in the ability of certain indoleamine neurons to take up and retain ³H-5HT or true neuronal degeneration.