Résumé : The distribution of inositol 1,4,5-trisphosphate (InsP3) 3-kinase mRNA in the rat brain is reported using oligonucleotides based on a cDNA clone sequence that encodes rat brain InsP3 3-kinase and the in situ hybridization technique. Moderate levels were found in CA2-4 pyramidal neurons, in the cortex, and in the striatum. The cerebellar granule cells, thalamus, hypothalamus, brainstem, spinal cord, and white matter tracts were almost negative. The levels of InsP3 3-kinase mRNA were highest in the hippocampal CA1 pyramidal neurons, granule cells of the dentate gyrus, and cerebellar Purkinje cells. These results contrast with the lower concentration of the InsP3 receptor already reported in the hippocampus versus the Purkinje cells and suggest a special role for inositol 1,3,4,5-tetrakisphosphate in Ammon's horn.