Studies on the mechanisms of learning. IV. Ontogeny of calcium channels in the rat's cortex

The sensitivity of some electrocortical potentials of rats to topically applied tetrodotoxin (TTX), manganese, lanthanum, calcium, mescaline and strychnine was followed from the age of 6 to 20 days and compared with that of adult animals. Sensitivity to TTX was relatively greater in the younger rats. In contrast, the blocking effect of Mn2+ or La3+ was small initially but increased with age. Similarly, the ability of mescaline or strychnine to give rise to giant spikes (dendritic action potentials) increased with maturation of the brain cortex. Finally, an increase in external calcium concentration depressed cortical potentials in the younger animals and had the usual increase of the mescaline or strychnine spikes in the older rats. It is concluded that the formation of calcium channels in dendritic membranes is part of the maturation process of cortical neurons and possibly related to the learning mechanisms. The depressant action of high external calcium during the first days of life was ascribed to an unspecific reduction in membrane permeability.