Comparison of pre-pulse inhibition, tactile discrimination learning and barrel cortical neural response in adult male rats following chronic exposure to morphine, methadone and buprenorphine

Background and Aim : Chronic exposure to opioids is the most common treatment plan to reduce the pain. In this study, the stereotyped behaviors and cognitive functions related to different types of tactile and auditory inputs were investigated in the rats following chronic exposure to the morphine, methadone, and buprenorphine.Methods : Here, three addicted groups received morphine, methadone, and buprenorphine while the control rats received saline for 21 days. after Novel texture recognition test, the pre pulse inhibition test was performed in an acoustic startle box. Multi-unit recording technique was used to study the excitatory and inhibitory receptive fields of barrel cortical neurons.Results : Our results demonstrated that the opioid-treated groups showed stereotyped behaviors including grooming and rearing. In the behavioral level, prepulse inhibition and preference indices were not changed significantly in the opioids treated groups compared to those of the saline group as two criteria for acoustic startle reflex and tactile discrimination, respectively. In the neuronal level, chronic morphine and methadone treatment changed the response properties of the barrel cortical neurons to the whisker deflections in the experimental groups compared to the saline group.Conclusion : Thus, it was concluded that the excitatory receptive fields of neurons in the barrel cortex can be changed as a result of chronic exposure to morphine and methadone.

Keywords:

Morphine , Methadone , Buprenorphine , Startle box , Barrel cortex , Rat