Effects of glutamic acid analogues on identifiable giant neurones, sensitive to β‐hydroxy‐L‐glutamic acid, of an African giant snail (Achatina fulica Férussac)

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Abstract
1 The effects of the seven glutamic acid analogues, .alpha.-kainic acid, .alpha.-allo-kainic acid, domoic acid, erythro-L-tricholomic acid, DL-ibotenic acid, L-quisqualic acid and allo-.gamma.-hydroxy-L-glutamic acid were examined on six identifitable giant neurones of an African giant snail (A. fulica Ferussac). 2 The neurones studied were: PON (periodically oscillating neurone), d-RPLN (dorsal-right parietal large neurone), VIN (visceral intermittently firing neurone), RAPN (right anterior pallial neurone), FAN (frequently autoactive neurone) and v-RCDN (ventral-right cerebral distinct neurone). Of these, d-RPLN and RAPN were excited by the two isomers (erythro and threo-) of .beta.-hydroxy-L-glutamic acid (L-BHGA), whereas PON, VIN, FAN and v-RCDN were inhibited. L-Glutamic acid (L-Glu) had virtually no effect on these neurones. 3 .alpha.-Kainic acid and domoic acid showed marked excitatory effects, similar to those of L-BHGA, on d-RPLN and RAPN. Their effective potency quotients (EPQs), relative to the more effective isomer of L-BHGA were 0.3 for both substances on d-RPLN, and 1 for .alpha.-kainic acid and 3-1 for domoic acid on RAPN. .alpha.-Kainic acid also had excitatory effects on FAN and v-RCDN (EPQ for both: 0.3), which were inhibited by L-BHGA but excited by .gamma.-aminobutyric acid (GABA). 4 Erythro-L-tricholomic acid showed marked effects, similar to those of L-BHGA, on VIN (EPQ: 0.3) and RAPN (EPQ: 3-1), but produced weaker effects on PON and d-RPLN (EPQ: 0.1). 5 DL-Ibotenic acid produced marked effects, similar to those of L-BHGA, on PON, VIN (EPQ for both: 1) and RAPN (EPQ:1-0.3), but had weak effects on d-RPLN (EPQ: < 0.1) and FAN (EPQ: 0.1). It had excitatory effects on v-RCDN (EPQ: 0.1). This neurone was inhibited by L-BHGA but excited by GABA. 6 L-Quisqualic acid showed the same effects as L-BHGA on all of the neurones examined (EPQ range 30-0.1). It was the most potent of the compounds tested on RAPN (EPQ: 30-10), FAN (EPQ:30) and v-RCDN (EPQ:3). 7 .alpha.-Allo-kainic acid and allo-.gamma.-hydroxy-L-glutamic acid had no obvious effect on any of the neurones examined. 8 As described above, the responses of the neurones examined to these substances varied widely. However, L-quisqualic acid generally had effects on the neurones similar to those of L-BHGA; the L-BHGA-excited neurones were also excited by .alpha.-kainic acid and domoic acid.

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