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 microejection and field potential recording ('spot pressure electrode') is described. This approach allows the use of a single electrode to record both 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-hydroxy-5-methyl-4-isoxazole propionate (AMPA, 100-300 microM) and N-methyl-D-aspartate (NMDA, 1 mM) were used. Both AMPA- and NMDA-evoked fPRs exhibited properties of postsynaptic responses. Thus, they were not significantly altered by tetrodotoxin (TTX, 0.5-1 microM), but were completely and reversibly blocked by an antagonist of AMPA/kainate receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 20 microM) and D-2-amino-5-phosphonopentanoic acid (AP5, 20 microM), respectively. The responses to micropressure-ejected AMPA were more stable and probably restricted to a smaller locus than responses to iontophoretic AMPA ejection. Additionally, the AMPA and NMDA contained in the pipette (up to 500 microM) did not influence the fEPSP recorded with this pipette. Our results suggest that this method might be a useful experimental tool for studying the local effects of excitatory amino acids and other compounds.