Dendrite spikes recorded extracellularly from dorsal horn neurones

(1) Extracellular action potentials were recorded from laminae IV--VI dorsal horn cells, using multibarrel carbon fibre micro electrodes. The amplitude and shape of the extracellular spike, the receptive field, and the response to iontophoretic glutamate ion, were investigated for each cell. (2) Of the 172 units isolated, 48 (28%) could be recorded from over a range of microelectrode tip depths greater than 100 micrometers. The sensitivity of these 'trackable' cells to glutamate was investigated at different depths; 13/48 (27%) had zones where they were insensitive to glutamate. (3) From the data on spike shapes and glutamate sensitivity, it is argued that dendritic spikes can occur in these cells.