EXPRESSION OF A CALMODULIN-DEPENDENT PHOSPHODIESTERASE ISOFORM (PDE1B1) CORRELATES WITH BRAIN-REGIONS HAVING EXTENSIVE DOPAMINERGIC INNERVATION

Cyclic nucleotide-dependent protein phosphorylation plays a central ro le in neuronal signal transduction. Neurotransmitter-elicited increase s in cAMP/cGMP brought about by activation of adenylyl and guanylyl cy clases are downregulated by multiple phosphodiesterase (PDE) enzymes. In brain, the calmodulin (CaM)-dependent isozymes are the major degrad ative activities and represent a unique point of intersection between the cyclic nucleotide- and calcium (Ca2+)-mediated second messenger sy stems. Here we describe the distribution of the PDE1B1 (63 kDa) CaM-de pendent PDE in mouse brain. An anti-peptide antiserum to this isoform immunoprecipitated approximate to 30-40% of cytosolic PDE activity, wh ereas antiserum to PDE1A2 (61 kDa isoform) removed 60-70%, demonstrati ng that these isoforms are the major CaM-dependent PDEs in brain. Quan tification of PDE1B1 immunoreactivity on immunoblots indicated that st riatum contains 3-17-fold higher levels of PDE1B1 than other brain reg ions, with lowest immunoreactivity in cerebellum. In site hybridizatio n demonstrated high levels of PDE1B1 mRNA in the caudate-putamen, nucl eus accumbens, and olfactory tubercle. Moderate mRNA levels were obser ved in dentate gyrus, cerebral cortex, medial thalamic nuclei, and bra instem, whereas negligible mRNA was detectable in the globus pallidus, islands of Calleja, substantia nigra, and ventral tegmental area. Imm unocytochemistry confirmed that the majority of PDE1B1 protein was loc alized to the caudate-putamen, nucleus accumbens, and olfactory tuberc le. Within the caudate-putamen, PDE1B1 immunoreactivity was ubiquitous , while PDE1AS immunostaining was restricted to a minor subset of stri atal neurons. The expression of PDE1B1 protein and mRNA correlate stro ngly with areas of the brain that are richest in dopaminergic innervat ion; indeed, there are strikingly similar distributions for PDE1B1 and D-1 dopamine receptor mRNAs. Since D-1 receptor binding activates ade nylyl cyclase, and striatal neurons lack CaM-sensitive forms of cyclas e, the high amount of this PDE implies an important physiological role for Ca2+-regulated attenuation of cAMP-dependent signaling pathways f ollowing dopaminergic stimulation.