Cre expression during postnatal development. Immunohistochemical localization of Cre. At P0 (a-c) and P3 (d-f), striatal Cre is restricted to the patch compartment (arrowheads). Expression in layer VI of the cortex is present already at birth. Transient and very weak expression is visible in the CA1 hippocampal region (a,d,g) and in layer IV of the cortex (c,f,i). At P6 (g-i), striatal Cre expression starts in the matrix compartment (asterisk), between the patches (arrowheads). Expression in CA1 and cortex layer IV disappears progressively. Magnification: (a,b,d,e,g,h) 50×; (c,f,i) 100×.