The relationship between dendritic growth of cortical neurons and the ontogeny of conditioned and unconditioned reflex control.

Suppression of an infantile reflex (circling behavior) to electric shock in a straight-alley escape problem increased as a function of age and trials in male Swiss-Webster mice trained at 7, 9, or 11 days of age and retested 24 h later. Twenty-four hours retention of prior training, indicated by the superior performance of trained subjects relative to yoked-shock and age controls, was not evident until 9 days of age. Analyses of Golgi--Cox preparations of parieto-temporo-preoccipital cortices, taken immediately following testing, revealed that behavioral development was paralleled by age-related changes in apical, oblique, and basilar dendritic networks and number of apical dendritic spines of layer V pyramidal cells. Correlations between behavioral and histological measures, indicated no consistent association of retention capacity with any of the physiological measures. However, basilar dendritic growth was significantly correlated with unconditioned reflex control as well as initial learning ability.