Chapter 4 The distribution of corticotropin-releasing factor (CRF), CRF binding sites and CRF1 receptor mRNA in the mouse cerebellum

Abstract

The purpose of the present study is to determine the distribution of CRF containing afferents, and correlate these findings with the distribution of CRF binding sites and the neuronal localization of mRNA for the CRF1 receptor in the cerebellum of a single species, the mouse. Corticotropin releasing factor (CRF) has been localized within climbing fibers and mossy fibers throughout the cerebellar cortex of the mouse using immunohistochemistry. CRF immunoreactive, axonal varicosities also are present within all four of the cerebellar nuclei. 125I-labeled CRF binding sites are evident throughout all three layers of the cerebellar cortex (molecular, Purkinje and granule cell layers), but are not seen within the cerebellar nuclei. In situ hybridization histochemistry was employed using an antisense riboprobe corresponding to the full length sequence of the rat mRNA for the CRF1 receptor. Positive signal is present throughout the cerebellum in Purkinje cells and the granule cell layer. CRF1 receptor mRNA also is expressed within all four of the cerebellar nuclei. Further experiments are required to reconcile the lack of CRF binding sites in the cerebellar nuclei with the positive mRNA receptor expression and the presence of immunoreactive axonal varicosities. In previous physiological experiments, iontophoretic application of CRF enhances spontaneous as well as quisqualate-induced activity of Purkinje cells in slice preparations of the mouse cerebellum. When the results of the anatomical techniques are compared to the physiological data, there is convergent evidence to suggest that CRF influences the firing rate or responsiveness of Purkinje cells directly via release of the peptide from the climbing fiber system and indirectly via the mossy fiber-granule cell-parallel fiber circuit. Taken together, these anatomical and physiological data provide strong evidence to suggest that, in the adult cerebellum, CRF functions as a neuromodulator.