cocaine increases the frequency of small-amplitude GABAergic mini inhibitory postsynaptic currents (mIPSCs) in D1+ MSNs (Heiman et al., 2008). On the other hand, another group recently showed that chronic cocaine results in an opposite response with decreased frequency and amplitude of mIPSCs in the D1+ MSNs (Kim et al., 2011). However, the latter group did show diminished membrane excitability in the D1+ MSNs after chronic cocaine, which could be a reflection of enhanced GABA tone and is consistent with the field’s assessment of enhanced inhibition in the NAc after exposure to chronic cocaine. Furthermore, such differences between the two groups could simply be due to the timing of cocaine exposure and withdrawal. In general, there is a need to study glutamatergic and GABAergic function in the two MSNs in response to drugs of abuse and the field is now equipped with the resources that make such a cell-type- and region-specific study possible.
