Distribution of corticotropin-releasing factor in the cerebellum and precerebellar nuclei of the opossum: a study utilizing immunohistochemistry, in situ hybridization histochemistry, and receptor autoradiography.

This study reports 1) a nonhomogeneous distribution of three morphologically distinct, corticotropin-releasing factor (CRF)-immunoreactive axonal phenotypes within the cerebellum of the opossum: climbing fibers, mossy fibers, and beaded fibers within the ganglionic plexus; 2) the existence of CRF binding sites within the cerebellar cortex; and 3) the distribution of CRF-containing neurons in brainstem precerebellar nuclei identified with immunohistochemistry and in situ hybridization histochemistry. CRF-immunoreactive climbing and/or mossy fibers were identified within all cerebellar lobules. The density of CRF-immunoreactive fibers was greatest in the vermis, where longitudinal bands of intensely immunoreactive climbing and mossy fibers were interspersed with regions containing fibers demonstrating lower levels of immunolabeling. CRF-immunoreactive fibers were present within all deep cerebellar nuclei. The topography of CRF-containing cerebellar fibers is discussed with respect to possible sites of origin within the brainstem. CRF-immunoreactive neurons were identified in all nuclei of the inferior olivary complex, although the number and intensity of immunostaining of CRF-containing cells varied within and among individual nuclei. CRF-immunoreactive somata were also present in brainstem nuclei known to give rise to cerebellar mossy fibers. In situ hybridization histochemistry utilizing an 35S-labeled synthetic 48-base oligodeoxynucleotide complementary to amino acids 22-37 of rat CRF proper revealed that CRF mRNA is transcribed in precerebellar nuclei. Variation in the level of CRF mRNA was detected among inferior olivary nuclei, in correspondence with variations detected in the levels of immunostaining. Data from this study suggest that variation in the level of CRF immunoreactivity detected within cerebellar afferent fibers may correlate with the level of CRF mRNA within cell bodies of origin of the projections. In vitro receptor autoradiography, utilizing 125I-Tyro-ovine CRF, revealed correspondence between CRF binding sites and CRF-immunoreactive fibers in the cerebellar cortex. Results of this study support suggestions for CRF-mediated circuitry in the cerebellum.