Selective excitation of neurons in the mammalian spinal dorsal horn by aspartate and glutamate in vitro: correlation with location and excitatory input.

The electrical activity of mammalian dorsal horn neurons was recorded with pipette microelectrodes in an in vitro spinal cord slice preparation with dorsal roots intact. Addition of relatively low concentrations of aspartate or glutamate to the superfusion solution or through the recording pipette with small iontophoretic currents excited only a subset of neurons. The majority of these excited neurons were located in the superficial dorsal horn (Rexed's laminae I and II) and a preponderance were excited by the C-fiber components of dorsal root volleys. These findings are consistent with the idea that aspartate or glutamate may function as a synaptic mediator for some neurons terminating in the superficial dorsal horn.