Two distinct inhibitory responses of cultured, mammalian spinal neurones to ibotenic acid.

Ibotenic acid, a structural analogue of glutamic acid, was applied to mouse spinal neurones grown in dissociated cultures. This amino acid evoked two inhibitory responses in addition to an excitatory response. Both inhibitory responses were manifested by membrane hyperpolarization and decreased input resistance. However, one was long-lasting (in excess of periods of 1 h) in comparison with the other. The latter response was likely a consequence of an increased chloride conductance and was sensitive to the gamma-aminobutyric acid antagonists bicuculline and picrotoxin whereas the former response was insensitive to these drugs. The ionic mechanism of this long-lasting response has yet to be elucidated.