Cerebellar monoamine nerve terminals, a new type of afferent fibers to the cortex cerebelli

Summary

The monoamine innervation of the cerebellum of the rat has been studied by both in vivo and in vitro techniques using the histochernical fluorescence method for the demonstration of catecholamines (CA) and certain tryptamines. By way of a pharmacological approach using inter alia protriptyline, which acts mainly by blocking the membrane pump of the noradrenaline (NA) neurons, evidence was obtained that CA nerve terminals in the cerebellum mainly represent NA nerve terminals. These were found to innervate practically all parts of the cerebellar cortex with a patchy innervation pattern and with an innervation of especially the anterior and posterior lobes. The terminals mainly seem to make axodendritic contacts in the molecular and granular layers without any strict localization of the terminal plexus to any special plane of the cerebellar folia. The fibers enter the cerebellum via the inferior cerebellar peduncle and run in the white matter of the cortex cerebelli. Incubation studies with 6-hydroxytryptamine indicate that there exists also a 5-hydroxytryptamine (5-HT) innervation of the cortex cerebelli, although not as pronounced as the NA innervation. The 5-HT nerve terminals are very fine, varicose fibers and innervate mainly the molecular layer, especially of the anterior lobe. The terminals run mainly in the transverse plane of the folium parallel to the surface. Thus, the pattern of innervation of these 5-HT afferents is different from that of the NA nerve terminals. In the uvula, structures which may represent the “rosettes” of the mossy fibers or golgi axon terminals in the granular layer take up and accumulate monoamines after incubation with amine in vitro. The exact nature of these structures remains to be elucidated.The cerebellar nuclei receive a very low to low degree of innervation of NA and 5-HT nerve terminals.