Endogenous opioids regulate dendritic growth and spine formation in developing rat brain.

Continuous blockade of endogenous opioid-opioid receptor interaction by opioid antagonists from birth to day 10 increased neuronal maturation in the rat brain. The lengths of oblique dendrites of pyramidal cells in the cerebral cortex and basilar dendrites of the hippocampus were increased from controls by 136 and 51%, respectively, whereas the concentrations of spines in these cells were increased 183 and 69%, respectively. Total dendritic length of spiny branches of cerebellar Purkinje neurons was 65% greater than controls, and spine concentration of granule cells in the dentate gyrus was increased by 76%. Thus, endogenous opioids exert a remarkable influence on the timetable and magnitude of dendritic elaboration and spine formation, and serve as an important trophic influence in the regulation of neuro-ontogeny.