Human divers exposed to hyperbaric pressure may suffer from cognitive and motor impairments thought to be related to high pressure effects per ce. These effects, termed high pressure neurological syndrome (HPNS), appear at pressure above 1.1 MPa. HPNS involves CNS hyperexcitability that is partially attributed to augmented responses of the glutamatergic N-methyl-d-aspartate receptor (NMDAR). NMDAR is blocked by Mg(2+) (physiologically) and by dl-2-Amino-5-phosphonopentanoic acid (AP5, pharmacologically). We have recently reported that hyperbaric pressure augments rat hippocampus NMDAR synaptic response and generates hyperexcitability. We now test pressure effects on the blockade efficacy of Mg(2+)and AP5...