Responses of cultured rat cortical and spinal cord neurones to kainate (KA) have been related to the expression of KA receptor subunits revealed by single-cell reverse transcription polymerase chain reaction (RT-PCR). Semi-rapid application of KA evoked non-desensitizing responses with EC(50) values of 82 microM for cortical and 67 microM for spinal cord neurones. In the presence of concanavalin A, GYKI 53655 (100 microM) reduced responses of both types of neurone to KA by about 80% to leave a KA receptor-mediated response with an EC(50) of 4 microM on spinal cord neurones and 27 microM (P<0.001) on cortical neurones. Ultra-fast application of KA to outside-out patches of cortical neurones evoked a non-decaying response which was reduced by about 30% by GYKI 53655 to reveal a transient response that desensitized by 92.5% with a time constant (tau(des)) of 26.2 ms. Responses of spinal cord patches decayed by 47.8%. GYKI 53655 reduced the peak response by 8.3% and the residual response desensitized by 75.8%, with a tau(des) of 17.3 ms, all values being significantly smaller than for cortical neurones. Single-cell RT-PCR showed relative abundances of mRNAs for the KA receptors, GluR5, GluR6 and GluR7, of 12, 33 and 54% for cortical neurones and 38, 10 and 54% for spinal cord neurones, respectively. The relative abundances of KA1 and KA2 were 12 and 88% for cortical neurones, and 19 and 79% for spinal cord neurones, respectively. The most likely expression patterns of functional KA receptors is GluR6/KA2 for cortical neurones and GluR5/KA2 for spinal cord neurones.