KAINIC ACID SEIZURES IN THE RAT - DIFFERENTIAL EXPRESSION OF CHROMOGRANIN-A, CARBOXYPEPTIDASE-H AND PEPTIDYLGLYCINE ALPHA-AMIDATING MONOOXIGENASE IN SUBFIELDS OF THE HIPPOCAMPAL-FORMATION

Using in situ hybridization histochemistry concentrations of mRNAs enc oding chromogranin A (ChA), carboxypeptidase H (CPH) and peptidylglyci ne alpha-amidating monooxigenase (PAM) have been investigated in the h ippocampus after kainic acid (KA)-induced limbic seizures in the rat. Increased concentrations (by 150 %) of ChA and CPH mRNAs were found in the granule cell layer 24 h after KA injection. At the same time PAM mRNA levels were only slightly elevated (by 50 %). Whereas the increas es in CPH and PAM transcripts were only transient, ChA mRNA concentrat ions in the granule cell layer were elevated up to 2 months after the initial seizures. In contrast, in the pyramidal cell layers of all hip pocampal subfields (CA1 to CA3) ChA mRNA concentrations were significa ntly reduced (by 40-70 %) 1-60 days after KA. PAM and CPH messages wer e slightly reduced in the pyramamidal cell layer of CA1 but not in CA2 and CA3. The experiments demonstrate that KA-induced limbic seizures cause sustained changes in the expression of ChA mRNA. At the same tim e the expression of two enzymes involved in post-translational process ing of neuropeptides, PAM and CPH, becomes only transiently altered. S ynthesis of ChA may be regulated differently in the strata granulosum and pyramidale during epileptic seizures.