Contrasting effects of stress on medial and sulcal prefrontal cortex self-stimulation

Male Wistar rats were subjected to either 25 controllable or uncontrollable footshocks and then tested for changes in fixed-interval 5-second (FI-5) self-stimulation of the medial prefrontal cortex (MPC), sulcal prefrontal cortex (SPC) or nucleus accumbens (NAS). Controllable footshock caused a moderate facilitation of MPC self-stimulation (30% above baseline rates) but inhibited SPC self-stimulation (32% below baseline rates). Uncontrollable footshock had no effect on MPC self-stimulation but inhibited SPC self-stimulation (52% below baseline rates). An inhibition of SPC self-stimulation was also evident 24 hours following controllable or uncontrollable footshock. NAS self-stimulation was unaffected by footshock. Changes in locomotor activity were not consistently related to changes in self-stimulation following footshock. These results are discussed in terms of the different effects of mild stress on the release of reward-relevant neurotransmitters in the MPC, SPC and NAS. The possible role of stress-induced hypoalgesia in determining the stress-induced facilitation of MPC self-stimulation is also discussed.