Increases in the density of parvalbumin-immunoreactive neurons in anterior cingulate cortex of amphetamine-withdrawn rats: evidence for corticotropin-releasing factor in sustained elevation.

We previously reported synchronization of pyramidal neurons within prefrontal cortex of rats repeatedly exposed to amphetamine (AMPH). To test the hypothesis that cortical synchronization may be related to changes in local GABA signaling, we used antibodies specific for parvalbumin (PV), calbindin D28k (CB) and calretinin (CR) as selective labels for three distinct GABA interneuron classes in the anterior cingulate cortex (ACC) of similarly treated rats. We observed a selective increase in the density of PV-immunoreactive (ir), but not CB-ir or CR-ir, neurons in the ACC of AMPH-treated rats at both 1 day and 7 day withdrawal. Increased density of PV-ir GABA interneurons in the ACC at 1 day withdrawal was reproduced in rats repeatedly injected with apomorphine or with SKF-38393. Thus, the critical role of DA receptors during AMPH exposure is evident. However, DA receptor activation did not appear to account for the PV up-regulation in AMPH-treated rats at 7 day withdrawal. Significantly higher numbers of pericellular basket-like puncta immunoreactive for corticotropin-releasing factor (CRF) were observed in the ACC of AMPH rats at 7 day withdrawal. Combined dual immunofluorescence and confocal microscopy further revealed that CRF-ir puncta made possible pericellular contacts on PV-ir (not CB-, CR- or glutamate-ir) cell bodies. A potential cellular mechanism seems to emerge that CRF-ir terminals, that may be underdetected under normal conditions due to low activity levels, may be functionally activated during psychostimulant withdrawal, thereby altering local GABAergic signaling.