The cytochrome P-450 (P-450) content of different regions of the rat brain was measured after partial purification of the enzyme from homogenates, and the quantitative contribution of P-450b,e and P-450c,d to brain P-450 was assessed by Western immunoblotting and immunohistochemistry using rabbit antibodies raised against purified hepatic P-450b and P-450c, respectively). P-450 could be quantitated by its reduced CO difference spectrum after chromatography of homogenates on p-chloroamphetamine-coupled Sepharose. The yield of P-450 from whole brain was 90 +/- 19 pmol/g of tissue, which is approximately 1% of the level in liver microsomes from control rats. The amount of P-450 recovered from homogenates of olfactory lobes, hypothalamus, thalamus, striatum, cerebral cortex, and brainstem varied between 40 and 100 pmol/g of tissue. The cerebellum was a region of exceptionally high P-450 content, with yields of up to 400 pmol/g whereas the substantia nigra yielded only 16-20 pmol/g. Immunohistochemical studies with anti-P-450b and anti-P-450c revealed intense staining of a limited number of cells in the cerebellum with both antibodies and in the thalamus only with anti-P-450c. In the cerebellum, both anti-P-450b and anti-P-450c stained the Bergmann glial cells together with their radial processes. Individual glial cells in the granular cell layer were also stained. There was no staining of Purkinje cells. In the thalamus, anti-P-450b gave weak staining of certain astroglia, but with anti-P-450c, there was intense staining of neuronal somata.(ABSTRACT TRUNCATED AT 250 WORDS)