Corticotropin-releasing factor in the olivocerebellar tract of rats: demonstration by light- and electron-microscopic immunohistochemistry and in situ hybridization histochemistry.

The presence of corticotropin-releasing factor (CRF) in the olivocerebellar system was demonstrated in rats by light- and electron-microscopic immunohistochemistry, as well as by in situ hybridization histochemistry. CRF-like immunoreactivity was present in each portion of the olivocerebellar system: In colchicine-treated rats, CRF-immunostained cells were found in each nuclei and subunit of the inferior olive. After surgical transection of the medullary portion of the olivocerebellar tract, CRF-immunostaining accumulated in inferior olive neurons contralateral to the lesion. In situ hybridization histochemistry indicated that CRF mRNA is transcribed in inferior olive neurons for translation to CRF precursor, whereas CRF mRNA was depleted contralateral to the lesion. CRF-immunopositive fibers of the olivocerebellar tract were demonstrated ipsilateral to the transection due to an accumulation in the proximal portion of transected axons. CRF-immunopositivity was demonstrated in climbing fibers in the molecular layer of the cerebellum at both light- and electron-microscopic levels. CRF-immunostained nerve terminals (climbing fiber varicosities) established synaptic contact with dendritic spines of the Purkinje cells. These three observations provide morphological evidence suggesting that CRF might serve as a neurotransmitter in the olivocerebellar system.