Electrical Synapses of the dentate gyrus do not change morphine state-dependent learning

Morphine exerts some of its effects via gap junctions. In this study, the effect of blocking the electrical synapses of the dentate gyrus was evaluated on morphine state-dependent learning.

Male rats weighing 200-250g were used. The passive avoidance task was used to evaluate memory. Two guide cannulas were implanted in the dentate gyrus, stereotaxically. In an experiment, animals received different doses of morphine, post-training and 24 hours later memory retrieval was evaluated. In another experiment, animals received morphine (7.5 mg/kg), post-training. One day later, 30 min before the test, different doses of morphine was injected. In another experiment, animals received quinine (100µM, 1mM and 10mM) in the test day and 40 min later memory retrieval was evaluated. In the last experiment, animals were injected with morphine (7.5 mg/kg), post-training. In the test day, different doses of quinine and 10 min later morphine (7.5 mg/kg) were injected.

Post-training injection of morphine (0.5, 2.5, 5, 7.5 mg/kg) impaired memory retrieval dose-dependently. Also, morphine induced a state-dependent memory. Blocking the electrical synapses of the dentate gyrus did not prevent the development of morphine state-dependent memory.

It seems that closing of the electrical synapses of the dentate gyrus does not affect memory retrieval induced by morphine on the test day.