Mapping of Morphine-Induced Gene Expression Pattern in the Adult Zebrafish Brain.

Morphine is a potent analgesic opiate commonly used in treating pain, and it is also a substance of abuse and highly addictive. Hence, it is vital to discover the action sites of morphine in the brain to increase its efficacy of treatment. In the present study, we aimed at identifying comprehensive neuroanatomical locations that are sensitive to morphine in the adult zebrafish (). We performed hybridization to localize the mu opioid receptor ( gene and to map the morphine sensitive brain areas using neuronal PAS domain-containing protein 4a (a), an early gene marker. Real-time PCR was used to detect changes in mRNA levels of and a in control and acute morphine treated fish (2 mg/L; 20 min). Intense positive signals were seen in the telencephalon, preoptic area, habenula, hypothalamic area and periventricular gray zone of the optic tectum. Acute morphine exposure significantly increased and mRNA levels in the medial zone of dorsal telencephalon (Dm), ventral region of the ventral telencephalon (Vv), preoptic area, and in the hypothalamus but a decrease in and signals in the dorsal habenula. This study provides a detailed map of localization in the brain, which includes previously unreported in the habenula of teleost. Presence of oprm1 in multiple brain sites implies multiple action targets of morphine and potential brain functions which could include reward, cognitive and negative emotions.