Basal dendrites of granule cells are normal features of the fetal and adult dentate gyrus of both monkey and human hippocampal formations.

The aim of this study was to analyze the granule cell population of the dentate gyrus both in healthy rhesus monkeys and in humans free of mental and neurological disorders. Brains of neonatal and adult rhesus monkeys as well as brains of fetal, neonatal and adult humans were impregnated with Golgi methods. The results show that a significant population of granule cells have basal dendrites in primates. Some basal dendrites curve up into the molecular layer where they have similar morphology as the apical dendrites. In contrast, other basal dendrites protrude into the hilus and they are shorter, thinner and have only a few side branches. The frequency of granule cells with basal dendrites in the human dentate gyrus is twice as much as that of the rhesus monkey. Most of these human granule cells have their basal dendrites in the hilus. This observation confirms the fact that discrepancies occur in the normal morphology of individual neurons between the rodent and primate hippocampal formations. The results indicate that basal dendrites of granule cells are not pathological as previously suggested.