Opposite effects of amphetamine self-administration experience on dendritic spines in the medial and orbital prefrontal cortex

We studied the long-term effects of amphetamine self-administration experience (or sucrose reward training) on dendritic morphology (spine density) in nucleus accumbens (Nacc), medial (MPC) and orbital prefrontal cortex (OFC), and hippocampus (CA1 and dentate). Independent groups of rats were trained under a continuous schedule of reinforcement to nose-poke for infusions of amphetamine (0.125 mg/kg/inf) or to receive sucrose pellets during 2 h daily test sessions for 14-20 days. One month after the last training session, the brains were collected and processed for Golgi-Cox staining. We found that: (i) amphetamine self-administration experience selectively increased spine density on medium spiny neurons in the Nacc and on pyramidal neurons in the MPC; (ii) in contrast, amphetamine self-administration decreased spine density in the OFC, whereas sucrose-reward training increased spine density; and (iii) both amphetamine self-administration and sucrose-reward experience increased spines in the CA1, but had no effect in the dentate gyrus. Thus, amphetamine self-administration experience produces long-lasting and regionally-selective morphological alterations in rat forebrain - alterations that may underlie some of the persistent psychomotor, cognitive and motivational consequences of chronic drug exposure.