(A) Intrahippocampal infusion of adenosine or A3 receptor agonist immediately after a late nonreinforced retrieval hinders recent but not late spatial memory retention, as measured 24 h and 5 d after infusion. Male Wistar rats with infusion cannulas implanted into the CA1 region of the dorsal hippocampus were trained for 5 d in the spatial version of the MWM. Five days after the last training session, the animals were subjected to a 60-sec probe test in the absence of the escape platform. Immediately after this first test, the animals received intrahippocampal bilateral infusions (black arrow) of either saline solution (saline), 10 nmol of adenosine (A 10 nmol), A1 (ago A1), A3 (ago A3), or A1 plus A3 (ago A1 + A3) receptor agonists (10 nmol for each agonist). Memory retention was assessed in successive 60-sec probe tests carried out either 24 h or 5 d after the first test. Data are expressed as means (±SD) of the percentage of swimming time spent in the target quadrant. (Dots) Individual value for each rat, (dashed line) theoretical mean of 25% of test time spent in the target quadrant at random. (**) P < 0.01, (***) P < 0.001 versus respective saline groups; one-way ANOVA: test 24 h after the first test, F(4,34) = 6.255; test 5 d after the first test, F(4,34) = 1.142; Dunnett's posttest; n = 7–10 per group. (B) The amnesic effect on late reconsolidation induced by the intrahippocampal infusion of adenosine is blocked by A1 and A3 receptor antagonists. Male Wistar rats with infusion cannulas implanted into the CA1 region of the dorsal hippocampus were trained for 5 d in the spatial version of the MWM. Five days after the final training session, the animals were subjected to a 60-sec probe test in the absence of the escape platform. Immediately after this first test, the animals received intrahippocampal bilateral infusions (black arrow) of either saline solution (saline), 10 nmol of adenosine (A 10 nmol), or 10 nmol of adenosine plus A1 (A + antag A1) or A3 (A + antag A3) receptor antagonist (50 nmol for each antagonist). Memory retention was assessed in successive 60-sec probe tests carried out either 24 h or 5 d after the first test. Data are expressed as means (±SD) of the percentage of swimming time spent in the target quadrant. (Dots) Individual value for each rat, (dashed line) theoretical mean of 25% of test time spent in the target quadrant at random. (*) P < 0.05 versus respective saline groups; one-way ANOVA: test 24 h after the first test, F(3,38) = 3.247; test 5 d after the first test, F(3,38) = 0.4823; Dunnett's posttest; n = 7–18 per group.
