NPY and Anxiety: In this test the NPY KO mice displayed an anxious phenotype which corroborates the behavioural features seen in the EPM: NPY KO decreased the time spent in the central area (21.6 ± 4.4% vs. 36.9 ± 3.1%) and the number of central area entries (13.9 ± 2.2 vs. 45.4 ± 3.2), suggesting elevated anxiety levels (Fig. 2a,b).