The Indoleamine Afferent Axons to the Cerebellum

Abstract

This chapter will deal with the elucidation of the origins, course, synaptic connections, and cytology of a large system of axons from various sites in the brain stem to the cerebellar cortex and nuclei. The systems share a transmitter in common, the indoleamine serotonin, or 5-hydroxytryptamine (5HT). In attempts to learn about serotonin axons, an extensive series of experiments was executed including lengthy infusions of radioactive transmitter molecules into the ventricular system, local injections of radioactive transmitters into the cerebellum, and local injections of horseradish peroxidase (HRP). In addition to light and electron microscopy on conventional material and autoradiograms, fluorescence microscopy for endogenous amines was also carried out. The results were corroborated by means of experiments with metabolic precursors of serotonin and with neurotoxic serotonin analogs.