Fig. 1.

Developing 5-HT and catecholaminergic systems target the mPFC. Sagittal cryosections of E16 (a), E18 (b), E20 (c), and P6 (d) rat brains immunostained for 5-HT (red) and TH (green) and stained with DAPI (blue) to visualize cell nuclei showing the 5-HT and the catecholaminergic developing systems. Dotted lines indicate the coronal section levels. Enlargements of coronal cryosections of E16 (e), E18 (f), E20 (g), and P6 (h) rat brains immunostained for 5-HT (red) and TH (green) and stained with DAPI (blue) showing the DR with the B7, B8, and/or B9 5-HT-positive cell clusters closely intermingled with TH-positive neurons and fibers. Enlargements of coronal cryosections of E16 (i), E18 (j), E20 (k), and P6 (l) rat brains immunostained for 5-HT (red) and TH (green) and stained with DAPI (blue) showing the rostral ventral tegmental area (rVTA) and the substantia nigra (SN) with the TH-positive cell clusters/fibers closely intermingled with 5-HT-positive neurons and fibers. Dotted lines indicate the midline. Enlargements of coronal cryosections of E16 (m), E18 (n), E20 (o), and P6 (p) rat brain immunostained for 5-HT (red) and TH (green) and stained with DAPI (blue) showing the medial forebrain bundle (MFB) with TH residing mainly in dorsal fascicles while 5-HT is present mostly within more caudal ones. Coronal (half shown) cryosections of E18 (q) and E20 (r) rat brains immunostained for 5-HT (red) and TH (green) and stained with DAPI (blue) showing the forebrain targets of both systems including the caudate putamen (CPu), the lateral septum (ls), the nucleus accumbens (Acb), and the medial prefrontal cortex (mPFC). Enlargements of the mPFC region of E18 (s) and E20 (t) rat brains showing a TH/5-HT-positive stream above the subplate (SP) and one in the marginal zone (MZ) in all three prefrontal subdomains (infralimbic, IL; prelimbic, PL; and cingulate, Cg). ls, lateral septum. Bar in a–d, 500 μm; e, 200 μm; f, 300 μm; g, 250 μm; h, 200 μm; i–l, 300 μm; m–p, 200 μm; q and r, 300 μm; s and t, 250 μm