PHA-L injections in IL cortex of mice. (A) Representative site of IL injection of PHA-L; PHA-L–like positive neurons and neuropil deposits are well-defined in IL, and PHA-L–like immunoreactive positive neurons (red) are counterstained with DAPI. This assessment of injection accuracy was carried out for all seven mice per genotype per age, and all of the injections were within the IL and did not overlap with neighboring regions, such as the prelimbic prefrontal cortex. (B) Bar graph showing numbers of PHA-L–positive cell bodies in IL in different genotypes and ages based on stereological estimation of cell density using the fractionator estimation method. There were no main effects of age [F(1,36) = 0.0273; P = 0.789] or genotype [F(2,36) = 0.453; P = 0.639] and no age by genotype interaction [F(2,36) = 0.309; P = 0.736]. Data are presented as means ± SEMs.