Western blotting analysis of phosphorylation of CREB and upstream kinases in the nucleus accumbens following test injections of saline or 20 mg/kg of cocaine. Data represent mean ± SEM (N = 8 rats per group) phosphorylation levels for CREB (a, b), CaMKIV (c, d), ERK (e, f), CaMKII (g, h) and GluR1 serine-845 (i, j) in rats that received test injections in Paired or Non-paired environments. # p < 0.01: compared to rats that received saline test injections following repeated administration of either saline or cocaine. * p < 0.05: compared to rats that received cocaine test injections following repeated saline administration.