Prenatal morphine exposure enhances seizure susceptibility but suppresses long-term potentiation in the limbic system of adult male rats

The present study examined the effects of prenatal morphine exposure on NMD A-dependent seizure susceptibility in the entorhinal cortex (EC), and on ac tivity-dependent synaptic plasticity at Schaffer collateral and perforant p ath synapses in the hippocampus. During perfusion with Mg2+-free ACSF, an e nhancement of epileptiform discharges was found in the EC of slices from pr enatally morphine-exposed male rats. A submaximal tetanic stimulation (2X50 Hz/l s) in control slices elicited LTP at the Schaffer collateral-CA1 syna pses, but neither LTP nor LTD was evoked at the perforant path-DG synapses. Tn slices from prenatally morphine-exposed adult male rats, long-term pote ntiation of synaptic transmission was not observed at Schaffer collateral-C A1 synapses, while the submaximal tetanus now elicited frank LTD of synapti c EPSPs at perforant path synapses. These data suggest that prenatal morphi ne exposure enhances the susceptibility of entorhinal cortex to the inducti on of epileptiform activity, but shifts long-term plasticity of hippocampal synapses in favor of LTD. (C) 2000 Elsevier Science B.V. All rights reserv ed.