DISTRIBUTION OF SYNAPTIC ZINC IN THE DEVELOPING MOUSE SOMATOSENSORY BARREL CORTEX

Histochemical localization of synaptic zinc was examined in the somato sensory (SI) barrel cortex of mouse. The laminar distribution and dist ribution within the barrel field were described. At postnatal day 3 (P 3) and 5 (P5), very faint and uniform zinc staining was present in the lower part of the subplate. At PG, 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 weake r staining. From this postnatal age to adult, uneven patchy distributi on of synaptic zinc in layer TV could be distinguished in coronal sect ions. In tangential sections through layer IV, zinc staining showed a barrel-like pattern due to a higher zinc concentration in septa and th e surrounding cortex. Barrel sides revealed a lower zinc concentration compared with the barrel hollow. With brain maturation, the zinc stai ning 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 pr ocess of synaptic maturation of glutamatergic terminals projecting to the SI cortex. The time course of postnatal changes in terminal zinc d istribution suggests that synaptic zinc is not involved in the mechani sms of barrel formation. (C) 1997 Wiley-Liss, Inc.