Abstract
RATIONALE: The development of sensitization to amphetamine (AMPH) is dependent on increases in excitatory outflow from the medial prefrontal cortex (mPFC) to subcortical centers. These projections are clearly important for the progressive enhancement of the behavioral response during drug administration that persists through withdrawal. OBJECTIVES: The objective of this study was to identify the mPFC subcortical pathway(s) activated by a sensitizing regimen of AMPH. MATERIALS AND METHODS: Using retrograde labeling techniques, Fos activation was evaluated in the predominant projection pathways of the mPFC of sensitized rats after a challenge injection of AMPH. RESULTS: There was a significant increase in Fos-immunoreactive cells in the mPFC, nucleus accumbens (NAc), basolateral amygdala (BLA), and lateral hypothalamus (LH) of rats treated repeatedly with AMPH when compared to vehicle-treated controls. The mPFC pyramidal neurons that project to the LH but not the NAc or BLA show a significant induction of Fos after repeated AMPH treatment. In addition, we found a dramatic increase in Fos-activated orexin neurons. CONCLUSIONS: The LH, a region implicated in natural and drug reward processes, may play a role in the development and persistence of sensitization to repeated AMPH through its connections with the mPFC and possibly through its orexin neurons.