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Abstract: DCX-immunoreactive (DCX+) cells occur in the piriform cortex in adult mice and rats, but also in the neocortex in adult guinea pigs and rabbits. Here we describe these cells in adult domestic cats and primates. In cats and rhesus monkeys, DCX+ cells existed across the allo- and neocortex, with an overall ventrodorsal high to low gradient at a given frontal plane. Labeled cells formed a cellular band in layers II and upper III, exhibiting dramatic differences in somal size (5–20 μm), shape (unipolar, bipolar, multipolar and irregular), neuritic complexity and labeling intensity. Cell clusters were also seen in this band, and those in the entorhinal cortex extended into deeper layers as chain-like structures. Densitometry revealed a parallel decline of the cells across regions with age in cats. Besides the cellular band, medium-sized cells with weak DCX reactivity resided sparsely in other layers. Throughout the cortex, virtually all DCX+ cells co-expressed polysialylated neural cell adhesion molecule. Medium to large mature-looking DCX+ cells frequently colocalized with neuron-specific nuclear protein and γ-aminobutyric acid (GABA), and those with a reduced DCX expression also partially co-labeled for glutamic acid decarboxylase, parvalbumin, calbindin, β-nicotinamide adenine dinucleotide phosphate diaphorase and neuronal nitric oxide synthase. Similar to cats and monkeys, small and larger DCX+ cells were detected in surgically removed human frontal and temporal cortices. These data suggest that immature neurons persist into adulthood in many cortical areas in cats and primates, and that these cells appear to undergo development and differentiation to become functional subgroups of GABAergic interneurons. [Copyright &y& Elsevier]

Abstract: Doublecortin-immunoreactive (DCX+) cells were detected across the allo- and neo-cortical regions in the adult guinea pig cerebrum, localized to layer II specifically at its border with layer I. The density of labeled cells declined with age, whereas no apparent apoptotic activity was detectable over the cortex including layer II. DCX+ cells varied in somal size, labeling intensity, nuclear appearance, and complexity of processes. These cells were often arranged in clusters with cells of similar morphology sometimes packed tightly together. They exhibited complete colocalization with polysialylated neural cell adhesion molecule (PSA-NCAM) and neuron-specific type III β-tubulin (TuJ1). Medium to large-sized DCX+ cells had well-developed neuritic processes, and expressed neuron-specific nuclear protein (NeuN). Large mature-looking cells with weak DCX reactivity invariably displayed heavy NeuN reactivity, implicating a transitional stage of these labeled cells. These “transitional” cells also consistently exhibited weak reactivity for γ-aminobutyric acid (GABA), glutamate decarboxylase (GAD67), β-nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) and neuronal nitric oxide synthase (nNOS), suggestive of them being young GABAergic/nitrinergic interneurons. Our data indicate that DCX+ cells exist widely in the adult guinea pig cerebral cortex, with a predominant localization in upper layer II. The morphological variation and differential expression of neuronal markers in these cells implicate that they might be developing neurons, and that they are probably differentiating into GABAergic interneurons. This population of cells might be involved in interneuron plasticity in the adult mammalian cerebral cortex. [Copyright &y& Elsevier]