INOSITOL 1,4,5-TRISPHOSPHATE 3-KINASE DISTRIBUTION IN THE RAT-BRAIN - HIGH-LEVELS IN THE HIPPOCAMPAL CA1 PYRAMIDAL AND CEREBELLAR PURKINJE-CELLS SUGGEST ITS INVOLVEMENT IN SOME MEMORY PROCESSES

The distribution of inositol 1,4,5-trisphosphate (InsP3) 3-kinase was studied in the adult rat brain, using polyclonal antibodies raised against the purified 50,000-Da rat brain enzyme by immunohistochemistry and Western blot, in addition to enzymatic assay. Immunohistochemically, the enzyme was detected in neurons, where it was localized in the dendrites and at the periphery of the cell bodies. Using selective toxin lesions, the highest enzyme levels were found in the dendrites of hippocampal CA1 pyramidal cells and in neurons in the dorsal portion of the lateral septum, regions both involved in long-term potentiation; and in the dendrites of Purkinje cell subpopulations in the cerebellum, a region involved in long-term depression. High levels were found in neurons in the cortex; in the anterior olfactory nucleus; in the striatum (caudate, putamen, olfactory tubercle, Calleja islets and accumbens); in the central nucleus of the amygdala; in the hippocampal dentate gyrus and in the subiculum. The enzyme was not detected in other brain regions. By Western blot, a 50,000-Da immunoreactive band was present in the cortex, caudate-putamen and cerebellum. This band was most highly stained in the hippocampus. InsP3 3-kinase activity, stimulated by calcium/calmodulin, corresponded to 6172-2638 pmol in InsP4 produced/min/mg protein in the hippocampus followed by frontal and parietotemporal cortex and cerebellum. This activity was below 400 in the brainstem and spinal cord. Taking into account the possibility of InsP3 3-kinase isoenzymes not recognized by the antibody, the existence of the highest InsP3 5-phosphatase activity in the cerebellum and the heterogeneity of the enzyme cellular distribution, the immunohistochemical results corresponded reasonably well to the Western blot and enzymatic assay.