SIMULTANEOUS LOCAL PRESSURE MICROEJECTION OF EXCITATORY AMINO-ACIDS AND FIELD POTENTIAL RECORDING WITH A SINGLE MICROPIPETTE IN THE HIPPOCAMPAL SLICE

The ability to use the same micropipette for simultaneous pressure mic roejection and field potential recording ('spot pressure electrode') i s described. This approach allows the use of a single electrode to rec ord bath field responses to pressure microejection of drugs (fPR) and synaptically evoked field excitatory postsynaptic potentials (fEPSP). To demonstrate this, the glutamate receptor agonists alpha-amino-3-hyd roxy-5-methyl-4-isoxazole propionate (AMPA, 100-300 mu M) and N-methyl -D-aspartate (NMDA, 1 mM) were used. Both AMPA- and NMDA-evoked fPRs e xhibited properties of postsynaptic responses. Thus, they were not sig nificantly altered by tetrodotoxin (TTX, 0.5-1 mu M), but were complet ely and reversibly blocked by an antagonist of AMPA/kainate receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 20 mu M) and D-2-amino-5- phosphonopentanoic acid (AP5, 20 mu M), respectively. The responses to micropressure-ejected AMPA were more stable and probably restricted t o a smaller locus than responses to iontophoretic AMPA ejection. Addit ionally, the AMPA and NMDA contained in the pipette (up to 500 mu M) d id not influence the fEPSP recorded with this pipette. Our results sug gest that this method might be a useful experimental tool for studying the local effects of excitatory amino acids and other compounds.