On the number of neurons in the dentate gyrus of the rat.

We have estimated the number of dentate granule cells in Sprague-Dawley and Wistar rats at 1, 4 and 12 months of age. In Sprague-Dawley rats the number of granule cells is relatively constant throughout this period at about 1 million. In Wistar rats, on the other hand, there is a progressive increase in the number from about 700,000 at 1 month to 1 million at 4 months; thereafter the number declines to about 800,000 at 1 year. Estimates of the numbers of cells in the polymorphic zone that can be stained immunohistochemically for somatostatin, cholecystokinin, vasoactive-intestinal peptide, and glutamic acid decarboxylase show no appreciable differences in the two strains.