Subcellular distribution of corticotropin-releasing-factor-like immunoreactivity in rat central nervous system

Corticotropin-releasing-factor-like immunoreactivity (CRF-LI) was measured in a number of subcellular fractions from rat brain using a highly sensitive and specific radioimmunoassay. CRF-LI was highly enriched in the crude synaptosomal/mitochondrial fraction (P₂) relative to the homogenate, P₁, S₁, and S₂ fractions. Separation of the P₂ fraction into synaptosomal, myelin, and mitochondria-enriched subfractions on a rapid one-step sucrose gradient revealed that CRF-LI was present at higher concentrations in the synaptosomal fraction than in the mitochondrial and myelin fractions. The distribution of CRF-LI paralleled that of synapsin, a synaptic vesicle marker phosphoprotein, but not that of pyruvate dehydrogenase, a mitochondrial phosphoprotein. These results are consistent with a nerve terminal localization of CRF and a potential role for this peptide as a central nervous system neurotransmitter.