description
Morphine is an alkaloid from the plant extracts of opium poppy. Although morphine is highly effective for the treatment of pain, it is also known to be intensely addictive. We now know that the most important brain-reward circuit involves dopamine (DA) -containing neurons in the ventral tegmental area (VTA) of the midbrain and their target areas in the limbic forebrain, in particular, the nucleus accumbens (NAc) and frontal regions of cerebral cortex. Morphine can cause indirect excitation of VTA dopamine neurons by reducing inhibitory synaptic transmission mediated by GABAergic neurons. The chronic use of morphine is characterized by adaptive changes in neurons and neuronal communication; such adaptations (e.g., 'superactivation' of adenylyl cyclase) must underlie altered behaviour associated with morphine dependence and withdrawal syndrome, as well as drug-induced craving and relapse to drug use

external resources
NCBI:552665
KEGG:hsa05032
PUBMED:8785060
PUBMED:16581089
PUBMED:21872647
PUBMED:14625081
PUBMED:20962224
PUBMED:15661627
PUBMED:1346804
PUBMED:12859419
PUBMED:8096779
PUBMED:18349442
PUBMED:21930931
PUBMED:10066284
PUBMED:14969742
PUBMED:8987801
PUBMED:12217944
PUBMED:11750924
PUBMED:11152760

genes
ADCY1 , ADCY2 , ADCY3 , ADCY5 , ADCY6 , ADCY7 , ADCY8 , ADCY9 , ADORA1 , GRK2 , GRK3 , ARRB1 , ARRB2 , CACNA1A , CACNA1B , DRD1 , GABBR1 , GABRA1 , GABRA2 , GABRA3 , GABRA4 , GABRA5 , GABRA6 , GABRB1 , GABRB2 , GABRB3 , GABRD , GABRE , GABRG1 , GABRG2 , GABRG3 , GABRP , GABRR1 , GABRR2 , GNAI1 , GNAI2 , GNAI3 , GNAO1 , GNAS , GNB1 , GNB2 , GNB3 , GNG3 , GNG4 , GNG5 , GNG7 , GNG10 , GNG11 , GNGT1 , GNGT2 , GRK4 , GRK5 , GRK6 , KCNJ3 , KCNJ5 , KCNJ6 , KCNJ9 , OPRM1 , PDE1A , PDE1C , PDE2A , PDE3A , PDE3B , PDE4A , PDE4B , PDE4C , PDE4D , PDE7A , PDE8A , PDE1B , PRKACA , PRKACB , PRKACG , PRKCA , PRKCB , PRKCG , PDE8B , GABBR2 , GNB5 , PDE10A , PDE7B , PDE11A , GNG13 , GNG2 , GABRQ , GNG12 , GNB4 , GNG8 , SLC32A1 , ADCY4 , GABRR3 ,