LONG-TERM SYNAPTIC TRANSFORMATION OF HIPPOCAMPAL CA1 GAMMA-AMINOBUTYRIC-ACID SYNAPSES AND THE EFFECT OF ANANDAMIDE

Evidence is presented for a distinctive type of hippocampal synaptic m odification [previously described for a molluscan gamma-aminobutyric a cid (GABA) synapse after paired pre- and postsynaptic excitation]: tra nsformation of GABA-mediated synaptic inhibition into synaptic excitat ion. This transformation persists with no further paired stimulation f or 60 min or longer and is termed long-term transformation. Long-term transformation is shown to contribute to pairing-induced long-term pot entiation but not to long-term potentiation induced by presynaptic sti mulation alone. Further support for such mechanistic divergence is pro vided by pharmacologic effects on long-term transformation as well as these two forms of long-term potentiation by Cl- channel blockers, glu tamate and GABA antagonists, as well as the endogenous cannabinoid lig and anandamide.