ChAT+ neuron distribution in the developing somatosensory cerebral cortex of mouse. A, B: at P2 (A) and P4 (B) very few thin varicose ChAT+ fibers (arrowheads) are observed in the process of invading the developing cortex. At P4, in particular, a few cholinergic growth cones (arrowheads) can be discerned within the cortical plate (CP). C, D: from P6 (C) to P8 (D) an increasing number of fusiform (arrows) and rare multipolar (white arrows) ChAT+ cells populate the supragranular layers of developing cortex. E, F: at P16 the cholinergic neuronal population is mainly localized in the superficial portion of the cortical mantle (E) and some ChAT+ cells (arrows in F) lie near the vessel (v) walls. Scale bar: 66 μm in A; 55 μm in B; 45 μm in C; 143 μm in D; 192 μm in E; 100 μm in F.