Locus coeruleus involvement in the effects of immobilization stress on the P13 midlatency auditory evoked potential in the rat

Abstract

1. 1. Adult male rats were prepared for recording midlatency auditory evoked responses from the vertex (Vx, P13 potential) and auditory cortex (ACx, P7 potential). 2. 2. The P13 potential is the rodent equivalent of the human P1 or P50 potential, which exhibits decreased sensory gating in posttraumatic stress disorder. 3. 3. Immobilization (IMB) stress for 60 min led to a significant decrease in P13 potential amplitude and sensory gating of the potential for the first 30–40 min of 1MB. 4. 4. The effects of 1MB on the P13 potential were reduced by pre-treatment with the α-2 adrenergic receptor blocker yohimbine (YOH). 5. 5. Injections of corticotropin releasing factor (CRF) into the locus coeruleus (LC), but not injections dorsal or ventral to the LC, induced a dose-dependent decrease in P13 potential amplitude and sensory gating. 6. 6. The effects of CRF were blocked by cotreatment with the CRF receptor antagonist cehelical CRF (α-h CRF). 7. 7. The effects of IMB on the P13 potential were mimicked by injections of the α-2 adrenergic receptor agonist dexmedetomidine (DEX) into the pedunculopontine nucleus (PPN). 8. 8. The effects of DEX injections into PPN were reduced by pre-treatment with the α-2 adrenergic receptor blocker YOH. 9. 9. The effects of IMB on P13 potential amplitude and sensory gating may be mediated in part via CRF activation of LC, which sends inhibitory α-2 adrenergic projections to PPN, a major source of the P13 potential.