Inhibition of morphine on long-term potency (LTP) of hippocampal CA1 area induced by peripheral stimulation in rats

Objective To observe the effects of morphine on long-term potency(LTP)in hippocampal CA1 area which was induced by peripheral stimulation,and the action of hippocampus in pain modulation was also observed.Methods This experiment was performed on 25 male SD rats randomized into 5 groups.Single stimulation pulses were delivered to the sciatic nerve to evoke the hippocampal field potentials.Tetanic stimulation was used to induce hippocampal LTP.Before the titanic delivery,different doses were injected into intracerebroventricular(i.c.v)in each group.Results The electric stimulus to the sciatic nerve evoked LTP in rat hippocampal CA1 area.Intracerebroventricular injection of morphine〔(100 ng/5 μl),(l μg/5 μl)〕 inhibited C-fiber-evoked LTP in the hippocampal CA1 area,and this effect of morphine was blocked by the pretreatment with opioid receptor antagonist,Naloxone.Conclusion LTP is one of the mechanisms of the action of hippocampus in pain modulation,opioid receptor plays a significant role.Morphine can inhibit C-fiber-evoked LTP in the hippocampal CA1 area,and this effect is dependent on opioid receptor.