in which they receive a foot shock (Fanselow and Poulos, 2005). The human glial-chimeric mice exhibited enhanced performance in CFC throughout all 4 days of training (Fig. 6B). By just the second day, the human glial-chimeric mice exhibited substantially more rapid and robust CFC than their non-chimeric littermate controls (n=6; 6.9 ± 0.1 months of age; F = 14.8 by two-way repeated measures ANOVA, p=0.003), and continued to display enhanced CFC during the subsequent 2 days of CFC training (Fig. 6B). To exclude the possibility that a generalized increase in freezing behavior could explain the observed differences, we also examined the context-specificity of freezing responses. In these experiments, the mice were placed in a second chamber with a different floor and odor. Chimeric mice exhibited superior discrimination between the two contexts, suggesting stronger contextual learning, as opposed to a non-specific higher level of fear (n=8-13; 7.6 ± 0.1 months; p<0.05, t-test) (Fig. 6B). No differences were observed in the reaction times to foot shock between the human glial chimeras and their rag 1-null immunodeficient controls (n=5, 9.6 ± 0.95 month, F = 0.08 by two-way ANOVA, p>0.5) (Fig. S5A). Moreover, neither thermal nor mechanical sensitivity were affected by chimerization of
