Differential laminar effects of amphetamine on prefrontal parvalbumin interneurons.

The increase in excitatory outflow from the medial prefrontal cortex is critical to the development of sensitization to amphetamine. There is evidence that psychostimulant-induced changes in dopamine-GABA interactions are key to understanding the behaviorally sensitized response. The objective of this study was to characterize the effects of different amphetamine paradigms on the Fos activation of GABAergic interneurons that contain parvalbumin in the medial prefrontal cortex. Although a sensitizing, repeated regimen of amphetamine induced Fos in all cortical layers, only layer V parvalbumin-immunolabeled cells were activated in the infralimbic and prelimbic cortices. Repeated amphetamine treatment was also associated with a loss of parvalbumin immunoreactivity in layer V, but only in the prelimbic cortex. An acute amphetamine injection to naive rats was associated with an increase in Fos, but in parvalbumin-positive neurons of the prelimbic cortex, where it was preferentially induced in layer III. These data indicate that distinct substrates mediate the response to repeated or acute amphetamine treatment. They also suggest that a sensitizing amphetamine regimen directs medial prefrontal cortex (mPFC) outflow, via changes in inhibitory neuron activation, toward subcortical centers important in reward.