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. Author manuscript; available in PMC: 2006 Jul 4.
Published in final edited form as: Eur J Neurosci. 2005 Jul;22(1):195–200. doi: 10.1111/j.1460-9568.2005.04195.x

Fig. 2.

Fig. 2

Effects of injection speed on the development of sensitization to the reinforcing effects of cocaine. Animals responded on a PR schedule maintained by cocaine (1.5 mg/kg per injection) delivered over 5 s for one session (data points over ‘5 s’), and over the subsequent 14 sessions; responding was maintained by cocaine delivered over different durations (5, 25 or 50 s; n = 6-7 per group). Symbols represent mean (± SEM) breakpoints. Asterisks indicate significant differences between 5-s and the 25- and 50-s groups; ‘+’ symbols represent significant differences from the first day of PR testing (P < 0.05). The highest injection speed (i.e. shortest duration) resulted in sensitization, whereas longer durations failed to result in sensitization.