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Schematic representation of the experimental protocol. Closed bars indicate the dark period and open bars represent the light period of the 12:12 h light:dark cycle. Arrows depict the time of microinjections. R: EEG recording; Pilo: pilocarpine; EA: electroacupuncture; N: naloxone; μ-ant: μ-antagonist (naloxonazine); δ-ant: δ-antagonist (naltrindole); κ-ant: κ-antagonist (nor-binaltorphimine).
