Hippocampal, hypothalamic and striatal tissue were dissected from the brains of mice that had been behaviourally assessed in the novelty place preference test, and they were subjected to quantitative PCR analysis for the transcript expression of selected gene candidates. Expression levels of the GABAAα3 receptor subunit (t=−2.85, P<0.025, df=14) (a) and the 5-HT2A receptor (t=−2.33, P<0.05, df=14) (b) genes in the hippocampus were significantly decreased in Igf2-P0 KO mice (N=8) compared with Igf2-P0 WT (N=8), but there were no significant differences in the expression of the GABAAα2 receptor subunit (t=0.02, not significant (n.s.), df=14) (c) or for 5-HT1A receptor message (t=0.52, n.s., df=14) (d). These effects were regionally specific, as evidenced by equivalent hypothalamic expression of GABAAα3 receptor subunit (t=0.78, n.s., df=14) (e) and striatal expression of 5-HT2A receptor message (t=0.34, n.s., df=14) (f) between Igf2-P0 KO and Igf2-P0 WT. No differences were observed in the expression of any of these genes, in any brain region, between Igf2-total WT and Igf2-total KO mice (N=7) and WT (N=11) (hippocampus: GABAAα3 t16=1.22, 5-HT2At16=−1.61, GABAAα2 t14=0.77 and 5-HT1At16=−0.54; hypothalamus: GABAAα3 t15=0.84, striatal 5-HT2At12=−1.51; all n.s). Data are mean±s.e.m., *significant difference from control (α<0.05), all P-values were adjusted with Bonferroni correction for multiple comparison testing.