A comparison of the effect of kainate and some related amino acids on locomotor activity in cockroaches and electrical activity recorded from locust ventral nerve cord.

The ED50 for loss of righting behaviour of cockroaches induced by kainate (43 mumol/kg body weight) indicated the toxicity of kainate to be much greater than would have been predicted from the excitatory action of this amino acid at insect skeletal muscle fibres. N-Methyl-D-aspartate had little effect on righting behaviour (ED50 greater than 3500 mumol/g body weight). Electrical recordings from the locust ventral nerve cord showed kainate (0.1-2 mM) to have a depolarizing action on neurons within the metathoracic ganglion. The depolarizing action of kainate was partially resistant to tetrodotoxin. The kainate-induced abolition of rostrally evoked potentials recorded in the abdominal connectives from the metathoracic ganglion suggests that the giant fibres are sensitive to kainate. Domoic acid was 46 times more potent than kainate. The lack of effect of N-methyl-D-aspartate (2 mM), dihydrokainate (2 mM), quisqualate (2 mM) and L-glutamate (20 mM) on nerve cords in the present experiments suggests that the kainate receptors in this preparation show a chemical selectivity comparable to that observed at vertebrate central neurones.