Morphine alters the structure of neurons in the nucleus accumbens and neocortex of rats.

Rats were given repeated injections of 10 mg/kg of morphine and were then left undisturbed for 24-25 days before their brains were processed for Golgi-Cox staining. Prior exposure to morphine decreased the complexity of dendritic branching and the number of dendritic spines on medium spiny neurons in the shell of the nucleus accumbens and on pyramidal cells in the prefrontal and parietal cortex. It is suggested that some of the long-term behavioral consequences of repeated exposure to morphine may be due to its ability to reorganize patterns of synaptic connectivity in the forebrain.