Medial prefrontal cortex transection enhanced stress-induced activation of sympathoadrenal system in rats

The medial prefrontal cortex (mPFC) projects to the sympathetic premotor and preganglionic neurons. Besides the well described modulatory effect on the hypothalamo-pituitary-adrenal (HPA) axis activity, the mPFC also exerts modulatory effect on the activity of the sympathoadrenal system (SAS). The aim of the present study was to find out whether interruption of the anatomical interconnections between the mPFC neurons and hypothalamic, brainstem and spinal cord structures may affect the SAS and HPA axis activities determined by the plasma catecholamines (epinephrine, EPI and norepinephrine, NE) and corticosterone (CS) levels in the rats exposed to a single immobilization (IMO) stress.

The posterior transection of the mPFC was performed bilaterally by inserting a V-shaped blade into the brain of adult male Sprague Dawley rats. Sham-operated animals (controls) underwent a craniotomy only. The animals were allowed to recover for 14 days. Thereafter, the tail artery was cannulated and the animals exposed to acute IMO for 2 h. The blood samples were collected at 5, 30, 60, 120 min of the IMO. Concentrations of the plasma EPI, NE, and CS were determined by radioimmunoassay.

The IMO-induced elevation of the plasma EPI levels in the mPFC-transected rats reached statistical significance at 120 min of the IMO, when compared to controls. Similarly, plasma NE levels were significantly increased at 60 and 120 min of the IMO in the mPFC-transected animals in comparison with controls. The transection had no significant effect on the plasma CS levels.

The data indicate that the mPFC transection may enhance the IMO-induced SAS activity without affecting the activity of the HPA axis. We found that the mPFC may exert an inhibitory effect on the SAS activity in the stressed animals.