Experimental hyperphenylalaninemia: Dendritic alterations in motor cortex of rat

Rats were injected i.p. daily from postnatal days 3 through 82 with a combination of the phenylalanine hydroxylase inhibitor p-chlorophenylalanine (60 mg/kg) plus phenylalanine (300 mg/kg), resulting in a significant hyperphenylalaninemia of 5.36 mg 100 ml. Control rats were saline injected. Golgi-Cox-stained layer V pyramidal and layer IV stellate neurons from cortical area 4 were measured using a computerized dendrite tracking system. Basal and oblique dendritic segments of layer V pyramidal cells in animals with hyperphenylalaninemia were fewer in number, shorter, branched closer to the cell soma or apical shaft, and branched less frequently than did dendrites in control animals. Fewer differences were found for layer IV stellate cells. These data suggest that in human hyperphenylalaninemia which is not severe enough to satisfy the classification criterion for phenylketonuria of 16.5 mg 100 ml plasma there may be undetected alterations in the morphology of cortical dendrites.