IDENTIFIABLE ACHATINA GIANT-NEURONS - THEIR LOCALIZATIONS IN GANGLIA,AXONAL PATHWAYS AND PHARMACOLOGICAL FEATURES

1. An African giant snail(Achatina fulica Ferussac), originally from E ast Africa, is now found abundantly in tropical and subtropical region s of Asia, including Okinawa in Japan. This is one of the largest land snail species in the world. Tile Achatina central nervous system is c omposed of the buccal, cerebral and suboesophageal ganglia. The 37 gia nt neurones were identified in these ganglia by the series of studies conducted over about 20 years. The identifications were made by the lo calization of these neurones in the ganglia, their axonal pathways and their pharmacological features. 2. In the left buccal ganglion, the f our giant neurones, d-LBAN, d-LBMB, d-LBCN and d-LBPN, were identified . In the left and right cerebral ganglia, d-LCDN, d-RCDN, v-LCDN and v -RCDN were identified, The suboesophageal ganglia are further composed of the left and right parietal, the visceral, the left and right pleu ral, and the left and right pedal ganglia. In the right parietal gangl ion, PON, TAN, TAN-2, TAN-3, RAPN, d-RPLN, BAPN, LPPN, LBPN, LAPN and v-RPLN were identified. In the visceral ganglion, VIN, FAN, INN, d-VLN , v-VLN, v-VAN, LVMN, RVMN and v-VNAN were identified. In the left par ietal ganglion, v-LPSN was identified. In the left and right pedal gan glia, LPeNLN, RPeNLN, d-LPeLN, d-LPeCN, d-RPeAN, d-LPeDN, d-LPeMN and d-LPeEN were identified. 3. Of the small molecule compounds tested, do pamine, 5-hydroxytryptamine, GABA, L-glutamic acid, threo- or erythro- beta-hydroxy-L-glutamic acid were effective on the Achatina giant neur ones. We suppose that these compounds act as the neurotransmitters for these neurones. 4. Of the neuroactive peptides, achatin-I (Gly-D-Phe- Ala-Asp). APGW amide (Ala-Pro-Gly-Trp-NH2) and Achatina cardioexcitato ry peptide (ACEP-1) (Ser-Gly-Gln-Ser-Trp-Arg-Pro-Gln-Gly-Arg-Phe-NH2) were proposed as neurotransmitters, because these were effective on th e Achatina giant neurones and their presence was demonstrated in the A chatina ganglia. Further, myomodulin (Pro-Met-Ser-Met-Leu-Arg-Leu-NH2) , buccalin (Gly-Met-Asp-Ser-Leu-Ala-Phe-Ser-Gly-Gly-Leu-NH2), FMRFamid e (Phe-Met-Arg- Phe-NH2). [Ser(2)]-Mytilus inhibitory peptide ([Ser(2) ]-MIP) (Gly-Ser-Pro-Met-Phe-Val-NH2), catch relaxing peptide (CARP) (A la-Met-Pro-Met-Leu-Arg-Leu-NH2), oxytocin (Cys-Tyr-Ile-Gln-Asn-Cys-Pro -Leu-Gly-NH2) and small cardioactive peptide(B) (SCFB)(Met-Asn-Tyr-Leu -Ala-Phe-Pro-Arg-Met-NH2) could also be neurotransmitters because thes e peptides were also effective on the Achatina giant neurones, though their presence in the ganglia of this animal has not yet been demonstr ated. 5. Calcium current (Ic,) was recorded from Achatina giant neuron es in the Na+ free solution con taining K+-channel blockers under volt age clamp. The Ca2+ antagonistic effects of brovincamine, verapamil, e perisone, diltiazem, monatepil, etc., were compared using the I-Ca of the Achatina neurones. 6. Almost all of the mammalian small molecule n eurotransmitters were effective on the Achatina giant neurones, sugges ting that these compounds are acting on the neurones of a wide variety of animal species. However, the pharmacological features of the Achat ina neurone receptors to these compounds were nor fully comparable to those of the mammalian receptors. For example, we proposed that beta-h ydroxy-L-glutamic acid (either threo- or erythro-) could be an inhibit ory neurotransmitter for an Achatina neurone. 7. In contrast, the Acha tina giant neurones appear to have no receptor for the mammalian neuro active peptides, except for oxytocin and Arg vasotocin. On the other h and, many neuroactive peptides were isolated from invertebrate nervous tissues, including achatin-I, a neuroexcitarory tetrapeptide having a D-phenylalanine residue.