EFFECTS OF L-GLUTAMIC ACID AND ITS AGONISTS ON SNAIL NEURONS

The sensitivities of 22 giant neurone types of an African giant snail (Achatina fulica Ferussac) to threo-beta-hydroxy-L-glutamic acid (thre o-L-BHGA), a derivative of L-glutamic acid (L-Glu), applied by brief p neumatic pressure ejection, were examined under current clamp. The 5 n eurone types were depolarized by this compound, whereas 2 were hyperpo larized. The 4 neurone types, PON (periodically oscillating neurone), RAPN (right anterior pallial nerve neurone), d-RPLN (dorsal right pari etal large neurone) and RPeNLN (right pedal nerve large neurone) that are excited by threo-L-BHGA and one type, v-LCDN (ventral left cerebra l distinct neurone), inhibited by this compound, were selected to stud y their pharmacological features in detail. Effects of the stereoisome rs of L-Glu and threo-L-BHGA, and mammalian L-Glu receptor agonists, e jected by brief pressure, on the 5 Achatina neurone types were examine d under voltage clamp. d-RPLN produced an inward current (I-in) by L-G lu and threo-L-BHGA, whereas this neurone type was insensitive to D-Gl u and erythro-L-, threo-D- and erythro-D-BHGA. This was also excited b y AMPA, indicating that the pharmacological features of the L-GLu rece ptors in this neurone type were similar to those of the mammalian iono tropic AMPA type L-Glu receptors, RAPN produced I-in by L-Glu and thre o L-BHGA. This neurone type was also excited by quisqualic acid and ib otenic acid, indicating that the features of the L-Glu receptors were similar to those of the mammalian metabotropic L-Glu receptors. PON an d RPeNLN produced I-in by L-Glu and threo-L-BHGA. These neurone types were also excited by quisqualic acid, AMPA and ibotenic acid, indicati ng that their L-Glu receptors seemed to be in the mixed type, of the t wo types mentioned. On the other hand, v-LCDN produced an outward curr ent (I-out) by threo-L and erythro L-BHGA, but was insensitive to L-Gl u, indicating that the receptors activated by L-BHGA were not L-Glu re ceptors. This neurone type was also inhibited by quisqualic acid.