Effects of chronic mild stress on apomorphine induced behavioral sensitization in different brain regions of rats in relation to serotonin change

Muhammad Farhan, Darakshan Jabeen Haleem


Background: The impacts of unpredictable stressors have influence on neurochemical and behavioral parameters in laboratory animals. Stress induced behavioral changes particularly those associated with anxiety like behavior may activate topographically organized mesolimbic cortical serotonergic system. This study was designed to investigate the influence of unpredictable stress on behavioral and neurochemical parameters in apomorphine treated rats.

Methods: Initially, the animals were divided into two groups as Unstressed and stressed (uncontrollable chronic mild stress or UCMS). Both groups of animals were subdivided into two groups; i.e. saline and apomorphine administrated animals at dose 1.0 mg/kg. Behavioral manipulations was observed by monitoring the locomotor activity and exploratory activity. Neurochemical estimation of 5-hydroxytryptamine (5-HT) was done by High performance liquid chromatography (HPLC).  Animals were decapitated 24hr post apomorphine injection and different regions of brain (dorsal and ventral striatum), of animals were collected and stored at -70°C.

Results: This preclinical study showed that the UCMS induced hypophagia were promoted in apomorphine administrated animals. Apomorphine induced hyperlocomotion were more prominent in unstressed animals than that of stressed groups.  It implies that apomorphine is effective in the retrieval from UCMS induced depressive symptoms in rats. Neurochemical study showed decreased level of 5-HT in unstressed animals than stressed animals in response to apomorphine administration.

Conclusion: This study, therefore establish the relation between stress and addiction at behavioral as well as neurochemical level to better understand the idea whether intolerable stress promotes addiction.

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