Src‐protein tyrosine kinases are required for cocaine‐induced increase in the expression and function of the NMDA receptor in the ventral tegmental area

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Abstract
Cocaine‐induced long‐term potentiation of glutamatergic synapses in the ventral tegmental area (VTA) has been proposed as a key process that contributes to the development of addictive behaviors. In particular, the activation of ionotrophic glutamate NMDA receptor (NMDAR) in the VTA is critical for the initiation of cocaine sensitization. Here we show that application of cocaine both in slices andin vivoinduced an increase in tyrosine phosphorylation of the NR2A, but not the NR2B subunit of the NMDAR in juvenile rats. Cocaine induced an increase in the activity of both Fyn and Src kinases, and the Src‐protein tyrosine kinase (Src‐PTKs) inhibitor, 4‐amino‐5‐(4‐chlorophenyl)‐7‐(t‐butyl)pyrazolo[3,4‐d]pyrimidine (PP2), abolished both cocaine‐induced increase in tyrosine phosphorylation of the NR2A subunit and the increase in the expression of NR1, NR2A, and NR2B in the VTA. Moreover, cocaine‐induced enhancement in NMDAR‐mediated excitatory post‐synaptic currents was completely abolished by PP2. Taken together, these results suggest that acute cocaine induced an increase in the expression of NMDAR subunits and enhanced tyrosine phosphorylation of NR2A‐containing NMDAR through members of the Src‐PTKs. This in turn, increased NMDAR‐mediated currents in VTA dopamine neurons. These results provide a potential cellular mechanism by which cocaine triggers NMDAR‐dependent synaptic plasticity of VTA neurons that may underlie the development of behavioral sensitization.