Recovery of function is associated with increased spine density in cortical pyramidal cells after frontal lesions and/or noradrenaline depletion in neonatal rats

Abstract

Rats were given medial frontal lesions at 7 days of age and were tested as adults on tests of forelimb use, forelimb tactile sensitivity, tongue use, hindleg use, and in a spatial navigation task. The brains were processed with a modified Golgi-Cox procedure and dendritic arborization and spine density was measured. The animals showed recovery only on the spatial task and this was associated with an increase in the number of spines per unit length of dendrite. We also reanalyzed Golgi-Cox stained material from an experiment in which animals were depleted of cortical noradrenaline (NA) in infancy and then given frontal lesions on day 7. The NA depletion blocked the recovery from frontal lesions. Analysis of dendritic morphology showed that in otherwise intact rats, NA depletion decreased dendritic arbor but increased spine density to the level of frontal operates. Depleted frontal-operates showed no additional increase in spine density and also showed a decrease in dendritic arborization. These results suggest that recovery from neonatal cortical injury and from neonatal noradrenaline depletion may be supported by changes in both the dendritic arborization and the spine density in the remaining cortex.