βarr1 KO mice show deficits in the acquisition and extinction of cocaine self-administration.

<p><b>A)</b> The number of cocaine infusions earned by βarr1 KO mice (KO: n = 21) during the first 5 days of FR1 was lower than WT mice (WT: n = 22; p < 0.01). <b>B)</b> This difference in infusions earned was no longer present by the last three days of FR1 (WT: n = 22, KO: n = 19), FR2 (WT: n = 14, KO: n = 13) or FR5 (WT: n = 13, KO n = 11). <b>C, D</b> and <b>E.</b> Analysis of the number of within-session active lever presses during the fifth day of FR1 (<b>C</b>), the first day of FR2 (<b>C</b>) and FR5 (<b>D</b>) showed no effect of genotype. <b>F)</b> However, βarr1 KO mice (WT: n = 4, KO: n = 6) showed more persistent total lever pressing during the early phase of extinction (days 1–3; p < 0.01), but not thereafter (days 4–5). <b>G)</b> This effect was also seen during the first day of extinction when KO mice showed more persistent lever pressing during the first 90 min of this 120-min session.