Doublecortin-expressing neurons in human cerebral cortex layer II and amygdala from infancy to 100 year-old

Abstract A cohort of morphologically heterogenous doublecortin immunoreactive (DCX+) “immature neurons” has been identified in the cerebral cortex largely around layer II and the amygdala largely in the paralaminar nucleus (PLN) among various mammals. To gain a wide spatiotemporal view on these neurons in humans, we examined layer II and amygdalar DCX + neurons in the brains of infants to 100 year-old individuals. Layer II DCX + neurons occurred throughout the cerebrum in the infants/toddlers, mainly in the temporal lobe in the adolescents and adults, and only in the temporal cortex surrounding the amygdala in the elderly. Amygdalar DCX + neurons occurred in all age groups, localized primarily to the PLN, and reduced in number with age. The small-sized DCX + neurons were unipolar or bipolar, and formed migratory chains extending tangentially, obliquely and inwardly in layers I-III in the cortex, and from the PLN to other nuclei in the amygdala. Morphologically mature-looking neurons were lightly labeled and co-expressed the neuron-specific nuclear antigen, glutamic acid decarboxylase and nicotinamide adenine dinucleotide phosphate-diaphorase. Taken together, we consider that the layer II and amygdalar DCX + neurons form a slowly developing interneuron system that supports inhibitory network plasticity in the cerebrum in an age/region-dependent manner.