PDE1B is a calcium dependent cyclic nucleotide phosphodiesterase that is highly expressed in the striatum. Male and female wildtype (WT) and homozygous knockout mice (KO) mice were tested in a functional observational battery, as well as in a variety of behavioral assays including spontaneous locomotor activity, measures of pain sensitivity (hot plate and tail flick), anxiety (elevated plus maze), learning and memory (passive avoidance) and depression (forced swim test). No differences in were observed between WT and KO mice in any of these assays except for locomotor activity. As previously reported (Chapin et al., SFN 2001), female KO mice showed significantly higher levels of baseline spontaneous locomotor activity compared to the female WT mice. KO mice also showed an exaggerated locomotor response to an acute methamphetamine (1 mg/kg) challenge. However, in additional studies, no differences in stimulant-induced locomotor activity were found between male or female WT and KO mice after PCP administrati...