κ Opioid receptors in the nucleus accumbens shell mediate escalation of methamphetamine intake. - Whitfield TW Jr; Schlosburg JE; Wee S; Gould A; George O; Grant Y; Zamora-Martinez ER; Edwards S; Crawford E; Vendruscolo LF; Koob GF (The Journal of neuroscience : the official journal of the Society for Neuroscience, 2015)