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The type I Ca(2+)-sensitive adenylyl cyclase has been implicated in several forms of synaptic plasticity in vertebrates. Mutant mice in which this enzyme was inactivated by targeted mutagenesis show deficient spatial memory and altered long term potentiation (Wu, Z. L., Thomas, S. A., Villacres, E. C., Xia, Z., Simmons, M. L., Chavkin, C., Palmiter, R. D., and Storm, D. R. (1995) Proc. Natl Acad Sci. U. S. A. 92, 220-224). Long term potentiation in the CA1 region of the rat hippocampus develops during the first 2 weeks after birth and reaches maximal expression at postnatal day 15 with a gradual decline at later stages of development. Here we report that Ca(2+)-stimulated adenylyl cyclase activity in rat hippocampus, cerebellum, and cortex increases significantly between postnatal days 1-16. This increase appears to be due to enhanced expression of type I adenylyl cyclase rather than type VIII adenylyl cyclase, the other adenylyl cyclase that is directly stimulated by Ca2+ and calmodulin. Type I adenylyl cyclase mRNA in the hippocampus increased 7-fold during this developmental period. The developmental expression of Ca(2+)-stimulated adenylyl cyclase activity in mouse brain was attenuated in mutant mice lacking type I adenylyl cyclase. Changes in expression of the type I adenylyl cyclase during the period of long term potentiation development are consistent with the hypothesis that this enzyme is important for neuroplasticity and spatial memory in vertebrates.

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