Figure 1.
Experimental procedures of Experiments 1–3. Each square represents a daily session, and arrows of different color represent intravenous injections of different drugs (red, nicotine; blue, NicotinePM; green, saline; and brown, HEXA). Time intervals between single (Experiment 1–3) and paired (Experiment 3; two arrows connected by a blue line) drug injections were 120 min. Time intervals between two injections in a pair (Experiment 3) were 4 min. For other details, see Materials and Methods.