Fig. 2

a The X-axis represents the dose of MK-801(mg/kg). The Y-axis represents the number of responses in 1 h of propofol self-administration. Black bars represent active nose-pokes, while gray bars represent inactive nose-pokes. Compared with the saline group, MK-801(0.1, 0.2, 0.4 mg/kg) groups have no significant differences in numbers of active nose-poke (F (3, 28) = 1.353, P > 0.05) (a) or inactive nose-poke (F (3, 28) = 0.047, P > 0.05). b The X-axis represents the dose of MK-801 (mg/kg). The Y-axis represents the number of propofol infusions in 1 h, Black bars represent the number of propofol infusions in 1 h. Compared with the saline group, a significant difference in the number of infusions per session following MK-801 administration (F (3, 28) = 4.372, P < 0.01), 0.2 mg/kg MK-801 significant increased in the number of propofol infusions (P = 0.003,P < 0.01)