Male NMRI mice: Mice were injected i.p. with EMPA (1, 3, 10, 30, 100, 300 mg·kg−1, n= 8 mice per dose). Male Wistar rats: one hour after the dark period onset, rats were injected i.p. with EMPA (3, 10, 30 mg·kg−1, n= 8 rats per dose) and immediately placed into the activity monitoring chambers.

The distribution and abundance of in vitro binding sites of [3H]EMPA (1 nmol·L−1), measured by quantitative autoradiography and image analysis, was investigated in coronal rat brain sections. A high density of specific binding was observed in many brain regions including the limbic cortices, hippocampus, striatum and hypothalamic nuclei. Non-specific binding (NSB), determined in the presence of 10 µmol·L−1 Cp-5, a selective OX2 receptor antagonist.