INVOLVEMENT OF NMDA RECEPTORS AND VOLTAGE-DEPENDENT CALCIUM CHANNELS ON AUGMENTATION OF LONG-TERM POTENTIATION IN HIPPOCAMPAL CA1 AREA OF MORPHINE-DEPENDENT RATS

The involvement of NMDA receptors and voltage-dependent calcium channe ls on augmentation of long-term potentiation (LTP) was investigated at the Schaffer collateral-CA1 pyramidal cell synapses in hippocampal sl ices of morphine dependent rats, using primed-bursts tetanic stimulati on. The amplitude of population spike was measured as an index of incr ease in postsynaptic excitability. D,L-AP5 and nifedipine were used as NMDA receptor antagonist and voltage-dependent calcium channel blocke r, respectively. The amount of LTP of orthodromic population spike amp litude was higher in slices from dependent rats. Perfusion of slices f rom control or dependent rats with ACSF containing either D,L-APS (25 mu M) or nifedipine (10 mu M) and delivering tetanic stimulation, show ed that D,L-APS completely blocked LTP of OPS in slices from both cont rol and dependent rats, while nifedipine attenuated the amount of LTP of OPS in dependent slices and had no effect on control ones. The resu lts suggest that the enhanced LTP of OPS in the CA1 area of hippocampa l slices from morphine dependent rats is primarily induced by the NMDA receptors activity and the voltage-dependent calcium channels may als o be partially involved in the phenomenon. (C) 1998 Elsevier Science B .V. All rights reserved.