| Abstract: | Histochemical localization of synaptic zinc was examined in the somatosensory (SI) barrel cortex of mouse. The laminar distribution and distribution within the barrel field were described. At postnatal day 3 (P3) and 5 (P5), very faint and uniform zinc staining was present in the lower part of the subplate. At P6, subtle laminar variations emerged. At P8, these variations were clearly observed. Intense zinc staining was found in layers I, II, III, and V. Layers IV and VI showed a weaker staining. From this postnatal age to adult, uneven patchy distribution of synaptic zinc in layer IV could be distinguished in coronal sections. In tangential sections through layer IV, zinc staining showed a barrel-like pattern due to a higher zinc concentration in septa and the surrounding cortex. Barrel sides revealed a lower zinc concentration compared with the barrel hollow. With brain maturation, the zinc staining increased more intensely outside the barrel field, thus producing a progressively higher contrast between the barrel field and adjacent cortical regions. The differences in zinc staining between the barrel side and barrel hollow diminished with age but were still visible at P70. The changes in synaptic zinc distribution probably reflect the process of synaptic maturation of glutamatergic terminals projecting to the SI cortex. The time course of postnatal changes in terminal zinc distribution suggests that synaptic zinc is not involved in the mechanisms of barrel formation. J. Comp. Neurol. 386:652–660, 1997. © 1997 Wiley-Liss, Inc. |
