Alterations in the rewarding value of intracranial self-stimulation following uncontrollable stressors : assessment in a current-intensity paradigm.


Bowers, Wayne J. (Wayne Joseph)




The effects of uncontrollable shock on intracranial self-stimulation (ICSS) from the nucleus accumbens (Nas), substantia nigra (SN) and the ventral tegmental area (VTA) were assessed in a rate-independent decreasing rate-intensity paradigm. Exposure to inescapable shock resulted in response depressions in ICSS from the Nas and VTA with a resulting shift in the rate-intensity function to the right while no changes were noted in animals responding from the SN. Increasing the current intensity eliciting ICSS 30 uA above the threshold current did not eliminate the stressor-induced response depressions noted in the Nas. In fact, the reductions in ICSS from the Nas were more pronounced. Inescapable shock failed to exert an effect on ICSS from either the Nas or the SN among mice without prior experience in the rate-intensity paradigm. Response reductions following inescapable shock among mice responding from the VTA were found to be considerably more pronounced than those noted in the Nas. These data were taken to suggest that uncontrollable stressors alter the rewarding/motivational value of ICSS in the Nas and VTA but not the SN. The present findings are consistent with the proposition that the alterations in reward value of ICSS following uncontrollable stressors are subserved by region-specific alterations in DA neuronal activity. It is suggested that, since altered DA neuronal activity has been demonstrated in human depressives and a decreased ability to experience pleasure is a prominent feature of depressive symptomology, stressor-induced alterations in DA activity may be responsible for these depressive symptoms. It is concluded that the paradigm employed here could be particularly beneficial in the testing of antidepressant drugs for their efficacy in alleviating the affective component of depressive symptomatology.


Stress (Physiology)




Carleton University

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