DIFFERENTIAL DISTRIBUTION OF MESSENGER-RNA ENCODING CAMP-SPECIFIC PHOSPHODIESTERASE ISOFORMS IN THE RAT-BRAIN

We studied the distributions of four different cyclic AMP-specific pho sphodiesterase isoform mRNAs (APDE1-4) and compared them with that of 63 kDa calmodulin-stimulated phosphodiesterase (CPDE) in the rat brain by in situ hybridization histochemistry using specific radiolabeled o ligonucleotides. The distribution patterns were unique for all the APD E isoforms examined here. Although no significant signals for APDE1 co uld be detected anywhere in the rat brain, all other isoforms were exp ressed ubiquitously but unevenly and showed overlapping distribution p atterns. Among all the APDE isoforms studied here, APDE3 showed the st rongest and the most extensive expression. Its distribution pattern im plies that it may modulate different cellular processes associated wit h learning and memory. Compared to APDE3, the levels of expression of APDE2 and APDE4 were weaker, the latter showing the weakest expression . Our study suggests that different isoforms of APDE are expressed tog ether in the same class of neurons implying complex interactions among different signaling pathways, thereby mediating distinct and specific functions.