Sensitization of norepinephrine release in medial prefrontal cortex: effect of different chronic stress protocols

Previously, we demonstrated that continuous exposure of rats to cold (5 deg rees C) for 2-3 weeks potentiates the increase in extracellular norepinephr ine in the medial prefrontal cortex produced by acute tail shock. In the pr esent study, we used in vivo microdialysis to examine whether this sensitiz ation of evoked norepinephrine release also occurs in the medial prefrontal cortex following exposure to other chronic stress protocols. Rats exposed to 30 min of intermittent foot shock (0.6 mA) each day for 14 days, did not exhibit a greater increase in extracellular norepinephrine in response to acute tail shock. To determine whether this discrepancy between cold exposu re and foot shock might be related to differences in the nature or the patt ern of exposure to the chronic stressor, we also examined the effect of int ermittent exposure to cold or continuous exposure to a foot shock protocol on tail shock-evoked norepinephrine release. Sensitized norepinephrine rele ase did not develop following either intermittent exposure to cold (5 degre es C; 4 h/day for 14 days) or continuous exposure to a foot shock protocol( 0.6 mA trains at random intervals 24 h/day for 14 days), suggesting that bo th the nature of the stressor as well as the pattern of exposure to the chr onic stressor play a role in the development of sensitized norepinephrine r elease. (C) 1999 Elsevier Science B.V, All rights reserved.