Immobilization-Induced Behavioral Deficits are Attenuated But Coping with Repeated Stress Impaired in Apomorphine Injected Rats

Apomorphine a non-narcotic derivative of morphine acts as a dopamine agonist to produce psychostimulant effects. Currently, apomorphine is used in patients with advanced Parkinson’s disease, for the treatment of persistent and disabling motor fluctuations which do not respond to levodopa or dopamine agonists. There is growing evidence that Parkinson’s disease patients treated with apomorphine develop an addiction to their therapy. A likely explanation for this could be that the drug enhances mood and alleviates emotional distress. In the present study it is investigated by determining responses to stress in apomorphine treated animals. We find that anorexigenic and anxiogenic effects of 1st episode of immobilization stress observed in saline treated animals do not occur in apomorphine treated rats. Conversely, repeated immobilization stress of 2h/day for 5 days produces anorexia and anxiety like behavior in repeated apomorphine but not repeated saline treated animals. The present study reveals interesting differences in the effects of single and repeated administration of apomorphine on responses to single and repeated immobilization stress to support the notion that apomorphine reduces stress-induced anxiety but its long term use, like other drugs of abuse, impairs coping with stress to increase vulnerability to depression. It would suggest that stress can increase an individual's risk for substance abuse because these drugs inhibit stress perception but the converse is also true; substance abuse can increase a person's vulnerability to stress-related illnesses. The findings may help improve pharmacotherapy in Parkinson’s disease and treat depression and other stress related disorders when they coexist with addiction.