Afferent fiber connections from the lower brain stem to the rat cerebellum by the horseradish peroxidase method combined with MAO staining, with special reference to noradrenergic neurons.

The origin of cerebellar noradrenaline (NA) was investigated by means of the horseradish peroxidase (HRP) method, combined with the monoamine oxidase (MAO) staining method to identify the NA neurons. The present study gives clear cut evidence that the main source for cerebellar NA in the rat is the locus coeruleus (Lc), both the dorsal and ventral parts which innervate the entire cerebral cortex and hypothalamus respectively. The present study clearly demonstrates the pontine NA neurons such as the nucleus subcoeruleus (sc) NA neurons also send their axons to the cerebellum. The fact that some neurons in the nucleus dorsalis nervi vagi and the nucleus commissuralis were labeled by HRP indicates strong possibility that A2 NA neurons also innervate the cerebellum, though direct proof was lacking in this study. Furthermore, some unknown afferent fibers to the cerebellum were found in this study. These are as follows: (1) non-noradrenergic neurons in the Sc area, (2) nucleus reticularis gigantocellularis and nucleus reticularis parvocellularis, (3) group 1 (of Meessen and Olszewski), (4) a cell group extending to the ventrolateral region of the reticular formation of the pons, (5) nucleus ambiguug, (6) nucleus nervi facialis.