Vulnerability to stressor-induced disturbances in self-stimulation from the dorsal and ventral A10 area: Differential effects of intraventricular D-Ala(2)-Met(5)-enkephalinamide, D-Ala(2), N-Me-Phe(4), Gly-Ol(5)-enkephalin, and D-Pen(2), D-Pen(5)-enkephalin administration

D-Ala(2)-Met(5)-enkephalinamide (DALA) (1.0 mu g/mu l) was administered int raventricularly to mice responding for electrical stimulation from the dors al or ventral aspects of the VTA immediately prior to footshock (Experiment 1). Predictably, footshock reduced self-stimulation from the dorsal but no t the ventral VIA immediately, 24, and 168 h following the stressor. Intrav entricular DALA administration effected a partial attenuation of stressor-i nduced self-stimulation reductions from the dorsal VTA immediately and 24 h post-stressor, Deficits appeared among DALA-Shocked mice responding for br ain stimulation from the ventral VTA during comparable test intervals. The long-term depressant influence of footshock on self-stimulation from the do rsal VTA was abolished among DALA-treated mice and DALA-associated reductio ns in self-stimulation from the ventral A10 region among stressed mice were not evident 1 week later. Administration of D-Ala(2), N-Me-Phe(4), Gly-Ol( 5)-enkephalin (DAGO) (0.01 mu g/mu l) or D-Pen(2), D-Pen(5)-enkephalin (DPD PE) (1.0 mu g/mu l) intraventricularly prior to footshock effected an immed iate and a delayed antagonism, respectively, of the stressor on self-stimul ation from the dorsal VTA, which persisted for 1 week. Prophylactic adminis tration of 0.001 mu g/mu l DAGO or 0.01 mu g/mu l DPDPE prior to the stress or failed to influence self-stimulation from the ventral VTA (Experiment 2) , Administration of 0.01 mu g/mu l DAGO or 1.0 mu g/mu l DPDPE among mice r esponding for brain stimulation from the dorsal VTA following footshock pro duced a weak therapeutic effect immediately poststressor, but effected prot racted amelioration of footshock-induced reductions of self-stimulation fro m the dorsal VTA (Experiment 3), Taken together, mu, delta and mu-delta act ivation influenced self-stimulation differentially from the dorsal and vent ral VTA according to the temporal order of opioid peptide challenge relativ e to stressor imposition, These data are discussed with respect to stressor s, motivational alterations, and the putative modulating influence of endog enous enkephalin activity in subareas of the VTA. (C) 1998 Elsevier Science Inc.