substance dependence pathway morphine addiction pathway 2012-07-11T11:41:36Z KEGG:05032 Morphine, an effective pain killer drug, can also be extremely addictive. Activation of dopamine neurons and reduction of inhibitory synaptic transmission might be associated with the effects or morphine. Changes in neuronal responses and communication may underlie the addictive behavior. PW:0001032 pathway vpetri