Using Kalirin conditional knockout mice to distinguish its role in dopamine receptor mediated behaviors.

BACKGROUND

Mice lacking Kalirin-7 (Kal7), a Rho GDP/GTP exchange factor, self-administer cocaine at a higher rate than wildtype mice, and show an exaggerated locomotor response to experimenter-administered cocaine. Kal7, which localizes to post-synaptic densities at glutamatergic synapses, interacts directly with the GluN2B subunit of the N-methyl-D-aspartate (NMDA; GluN) receptor. Consistent with these observations, Kal7 plays an essential role in NMDA receptor dependent long term potentiation and depression, and glutamatergic transmission plays a key role in the response to chronic cocaine. A number of genetic studies have implicated altered Kalirin expression in schizophrenia and other disorders such as Alzheimer's Disease.

RESULTS

A comparison of the effects of experimenter-administered cocaine on mice lacking all Kalirin isoforms to its effects on mice lacking only Kalirin-7 identified Kal7 as the key isoform whose deletion produces exaggerated locomotor responses to cocaine. Pretreatment of Kal7 mice with a low dose of ifenprodil, a selective GluN2B antagonist, eliminated their enhanced locomotor response to cocaine, revealing an important role for GluN2B in this behavior. Selective knockout of Kalirin in dopamine transporter expressing neurons produced a transient enhancement of cocaine-induced locomotion, while knockout of Kalirin in Drd1a- or Drd2-dopamine receptor expressing neurons was without effect. As observed in Kalirin global knockout mice, eliminating Kalirin expression in Drd2-expressing neurons increased exploratory behavior in the elevated zero maze, an effect eliminated by pretreatment with ifenprodil.

CONCLUSIONS

The cocaine-sensitive neuronal pathways which are most sensitive to altered Kalirin function may be the pathways most dependent on GluN2B and Drd2.