Stereotypy scores as a measure of intensity over time (A) following first injection and (B) at 14 days of withdrawal, in response to a challenge of 2.5 mg/kg, i.p. amphetamine (sensitized and non-sensitized groups), or saline. (Amphetamine-sensitized: N=10, non-sensitized: N=6, saline: N=16; means ± S.E.M. are shown for all groups).