Effects of synthetic peptides on giant neurones identified in the ganglia of an African giant snail (Achatina fulica Férussac). IV

1. The previous papers (Ku et al., 1986; Kim et al., 1987; Yongsiri et al., 1987) reported the effects of the synthetic peptides, i.e. Met-enkephalin, substance P, neurotensin, oxytocin, Arg-vasopressin, proctolin, FMRFamide, ranatensin C etc., on about 20 identifiable giant neurones of an African giant snail (Achatina fulica Férussac). 2. In the present study, the effects of the same peptides on the following Achatina neurones, other than those of the previous papers, were investigated: v-RPLN, v-LPSN, v-VNAN, v-VLN, r-VMN, l-VMN, v-l-VOrN and d-RCDN. 3. Of the neurones tested here, v-RPLN (ventral-right parietal large neurone) was excited slightly by Met-enkephalin, excited markedly by oxytocin, and inhibited by FMRFamide, at 10(-4) M. 4. Of these effects, those of oxytocin and FMRFamide were undoubtedly the direct effects on the neurone tested, whereas those of Met-enkephalin were probably due to the synaptic activations. 5. Another neurone, v-LPSN (ventral-left parietal large neurone), was affected by oxytocin and ranatensin C at 10(-4) M. The two substances sometimes showed similar simple excitatory effects, in other cases biphasic (excitation followed by inhibition) effects, and in a few cases almost no effect. 6. The rest of the neurones tested were not sensitive at all to any of the peptides examined.     

Pharmacological characteristics of four giant neurons identified in the cerebral ganglia of an African giant snail (Achatina fulica Férussac)

Two giant neurons, d-RCDN (dorsal-right cerebral distinct neuron) and d-LCDN (dorsal left cerebral distinct neuron), with a diameter of about 100 microns, were found symmetrically on the dorsal surface of the cerebral ganglia of an African giant snail (Achatina fulica Férussac). They showed spontaneous spike discharges at a stable frequency. Two giant neurons, v-RCDN (ventral-right cerebral distinct neuron) and v-LCDN (ventral-left cerebral distinct neuron), (diameter, approx. 150 microns) were identified on the ventral surface of the same ganglia. No spontaneous spike discharges were evident. Both d-RCDN and d-LCDN were equally inhibited by dopamine, octopamine, 5-hydroxytryptamine and histamine. Acetylcholine sometimes showed inhibitory effects, but they were not so stable. No substance having excitatory effects on the neurons was found. Both v-RCDN and v-LCDN were equally excited by octopamine, 5-hydroxytryptamine, GABA and acetylcholine and inhibited by dopamine and beta-hydroxy-L-glutamic acid.     

Effects of synthetic biologically active peptides on giant neurones identified in the left buccal ganglion of an African giant snail (Achatina fulica Férussac)

1. The effects of synthetic biologically active peptides, including Met-enkephalin, substance P, oxytocin, Arg-vasopressin, proctolin and FMRFamide, on the following four buccal neurones were examined: d-LBAN (dorsal-left buccal anterior neurone), d-LBMN (dorsal-left buccal medial neurone), d-LBCN (dorsal-left buccal central neurone) and d-LBPN (dorsal-left buccal posterior neurone). These peptides were examined at 10(-4) M. 2. Oxytocin excited d-LBAN and slightly excited d-LBCN, while this inhibited d-LBMN. Arg-vasopressin excited slightly d-LBAN and d-LBCN, but this had some times no effect. FMRFamide inhibited d-LBAN, and slightly inhibited d-LBCN. 3. No direct synaptic connection from the two ventral cerebral giant neurones, v-LCDN and v-RCDN, to the four buccal giant neurones was found, though the two cerebral neurones innervate the cerebro-buccal connectives.     

Axonal pathways of giant neurons identified in the right parietal and visceral ganglia in the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac)

• 1.1. The axonal pathways of thirteen giant neurons identified in the right parietal and the visceral ganglia, found in the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac), were investigated by intracellular injections of Lucifer Yellow, with regard to their axonal projections into the following six peripheral nerves: lap n (left anterior palliai nerve), lpp n (left posterior palliai nerve), int n (intestinal nerve), anal n (anal nerve), rpp n (right posterior palliai nerve) and rap n (right anterior palliai nerve).
• 2.2. These projections were confirmed by the recording of the axonal responses from the nerves.
• 3.3. On the dorsal surface of the right parietal ganglion, the following four giant neurons were identified: PON (periodically oscillating neuron), TAN (tonically autoactive neuron), RAPN (right anterior palliai neuron), and d-RPLN (dorsal-right parietal large neuron).
• 4.4. The PON axonal pathways projected into int n; those of TAN into all of the nerves examined; those of RAPN into lap n, lpp n, int n, anal n and rap n.; and those of d-RPLN into pd nn (pedal nerves) through the pedal ganglia, lpp n, anal n, rap n and sometimes lap n.
• 5.5. On the dorsal surface of the visceral ganglion, the following four giant neurons were also identified: VIN (visceral intermittently firing neuron), FAN (frequently autoactive neuron), INN (intestinal nerve neuron) and d-VLN (dorsal-visceral large neuron).
• 6.6. The VIN axonal pathways, which had no branch into the six nerves examined, went to both the right and the left pedal ganglia, sending a branch into the cerebro-pleural connective; those of FAN projected into lap n, anal n and rap n, and sometimes into lpp n and rpp n; those of INN into int n; and those of d-VLN into pd nn, lap n, lpp n, anal n and rap n.
• 7.7. On the ventral surface of the right parietal ganglion, v-RPLN (ventral-right parietal large neuron) was identified. The axonal pathways went to pd nn, lap n, lpp n, anal n and rap n.
• 8.8. On the ventral surface of the visceral ganglion, the four giant neurons, v-VNAN (ventral-visceral noisy autoactive neuron), v-VLN (ventral-visceral large neuron), r-VMN (right-visceral multiple spike neuron) and 1-VMN (left-visceral multiple spike neuron) were identified.
• 9.9. The axonal pathway of v-VNAN projected into rpp n and rap n; those of v-VLN into pd nn, lap n, anal n, rap n and sometimes to lpp n; those of r-VMN into int n and rpp n; and those of 1-VMN also into int n and rpp n.
• 10.10. The present morphologial investigations of the giant neurons confirmed well the identifications of the neurons previously studied. The axon of the neurons examined here, except for VIN, projected into some of the peripheral nerves, while the VIN axon extended into the cerebro-pleural connective.
• 11.11. The five neurons, PON, TAN, v-VNAN, r-VMN and 1-VMN, formed fine axonal arborizations terminating at the neuropile, while the arborizations of the other neurons were not clearly observed.
• 12.12. Although the anatomical structures of the portion examined of the suboesophageal ganglia are asymmetrical, three pairs of symmetrically-situated neurons, d-RPLN and d-VLN, v-RPLN and v-VLN, and r-VMN and 1-VMN, were found, indicating the existence of symmetrical components in the ganglia.

     

Further study of effects of synthetic peptides on identifiable giant neurones of an African giant snail (Achatina fulica Férussac)

1. Effects of the following peptides at 10(-4) M on identifiable giant neurones of Achatina fulica Férussac were examined: physalaemin, eledoisin, bradykinin, neurokinin A, neurokinin B, neuromedin B, gastrin releasing peptide decapeptide (neuromedin C), gastrin releasing peptide (14-27), cholecystokinin tetrapeptide, cholecystokinin octapeptide, thyrotropin releasing hormone, Arg-vasotocin, gamma-melanocyte stimulating hormone. 2. The six neurones tested were as follows: PON (periodically oscillating neurone), TAN (tonically autoactive neurone), RAPN (right anterior pallial neurone), d-RPLN (dorsal-right parietal large neurone), VIN (visceral intermittently firing neurone) and d-VLN (dorsal-visceral large neurone). 3. Of the peptides examined, only Arg-vasotocin at 10(-4) M produced the excitatory effects on PON, VIN and d-VLN. Physalaemin showed slight inhibitory effects on TAN; this substance was sometimes almost ineffective on the neurone. 4. The other peptides examined were completely ineffective on all of the neurones tested.     

Further study of effects of synthetic peptides on identifiable giant neurones of an african giant snail (Achatina fulica Férussac)

• 1.1. Effects of the following peptides at 10⁻⁴ M on identifiable giant neurones of Achatina fulica Férussac were examined: physalaemin, eledoisin, bradykinin, neurokinin A, neurokinin B, neuromedin B, gastrin releasing peptide decapeptide (neuromedin C), gastrin releasing peptide (14–27), cholecystokinin tetrapeptide, cholecystokinin octapeptide, thyrotropin releasing hormone, Arg-vasotocin, γ-melanocyte stimulating hormone.
• 2.2. The six neurones tested were as follows: PON (periodically oscillating neurone), TAN (tonically autoactive neurone), RAPN (right anterior pallial neurone), d-RPLN (dorsal-right parietal large neurone), VIN (visceral intermittently firing neurone) and d-VLN (dorsal-visceral large neurone).
• 3.3. Of the peptides examined, only Arg-vasotocin at 10⁻⁴ M produced the excitatory effects on PON, VIN and d-VLN. Physalaemin showed slight inhibitory effects on TAN; this substance was sometimes almost ineffective on the neurone.
• 4.4. The other peptides examined were completely ineffective on all of the neurones tested.

     

Identification and pharmacological characteristics of giant neurones situated in the buccal ganglia of an African giant snail (Achatina fulica Férussac)

1. The following four giant neurones were identified on the dorsal surface of the left buccal ganglion of an African giant snail (Achatina fulica Ferussac): d-LBAN (dorsal-left buccal anterior neurone), d-LBMN (dorsal-left buccal medial neurone), d-LBCN (dorsal-left buccal central neurone) and d-LBPN (dorsal-left buccal posterior neurone). The axonal pathways of the neurones were studied by the intracellular injection of Lucifer Yellow; their pharmacological characteristics with respect to common putative neurotransmitters were also investigated.2. The axonal pathways of d-LBAN and d-LBCN were simple, innervating some left lateral buccal nerves or the left accessory connective buccal nerve. On the other hand, those of d-LBMN and d-LBPN were much more widespread, projecting not only to the left buccal nerves, but also to the right buccal nerves through the buccal commissure.3. No direct axonal pathway from any of the four buccal neurones tested to the other ganglioncomplexes through the cerebral buccal connectives was demonstrated.4. The pharmacological characteristics of the four neurones tested were not identical. Only 5-hydroxytryptamine excited all of the neurones, whereas dopamine, l-epinephrine and acetylcholine inhibited all of them. However, the other effective substances, such as dl-octopamine, GABA, l-homocysteic acid, erythro-β-hydroxy-l-glutamic acid and histamine, were either excitatory or inhibitory according to the neurone.     

Neurotransmitters of giant neurons in the African giant snail, Achatina fulica Férussac. IV. Supplemental results

Following the previous works, we identified recently the twelve giant neurones in the ganglia of an African giant snail (Achatina fulica Férussac), by the pharmacological study of their sensitivities to putative neurotransmitters and derivatives, and by the morphological investigation of their axonal pathways due to the intracellular injection of Lucifer Yellow. The neurones studied were: TAN-2, TAN-3, BAPN, LPPN, LBPN and LAPN in the right parietal ganglion; RPeNLN and LPeNLN in the pedal ganglia; and d-LBAN, d-LBMN, d-LBCN and d-LBPN in the left buccal ganglion.     

Pharmacological characteristics of the two largest neurons symmetrically situated in the suboesophageal ganglia of an African giant snail (Achatina fulica férussac)

1. Pharmacological characteristics of the two largest neurons, r-PLN (right-parietal large neuron) and d-VLN (dorsal-visceral large neuron), situated symmetrically on the anterior-dorsal surface in the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac), were determined.2. Of the catecholamines examined, dopamine (DA) showed marked but complex effects on the two neurons. DA produced a transient excitation followed by either hyperpolarization or depolarization of the neuromembranes. L-Norepinephrine produced a slight depolarization of the neurons.3. 5-Hydroxytryptamine (5-HT) produced marked excitation of both neurons. Bufotenine showed the same effects, but they were weaker than those of 5-HT.4. Histamine showed inhibatory effects on the two neurons examined, whereas L-histidine had rather slight or no excitatory effects.5. Of the amino acids examined, L-homocysteic acid (L-HCA) and erythro-β-hydroxy-L-glutamic acid had marked excitatory effects on r-PLN and d-VLN. L-Homocysteine sulfinic acid also showed the excitatory effects, but they were weaker than those of L-HCA. Glycine and L-methionine had slight excitatory effects on both neurons, whereas L-aspartic acid, L-glutamic acid and GABA had none.6. Acetylcholine (ACh) exhibited marked and complex effects on r-PLN and d-VLN. In trials, ACh produced either excitation or inhibation of both neurons. Propionylcholine and butyrycholine had slightly less effect, producing a slight inhibation of r-PLN and either excitation or inhibation of d-VLN in trials.     

Histological and pharmacological investigations of the two symmetrically situated giant neurons, RPeNLN and LPeNLN, identified on the anterior surface of the pedal ganglia of an African giant snail (Achatina fulica Férussac)

Morphological and pharmacological investigations were made of two giant neurons, RPeNLN (right pedal nerve large neuron) and LPeNLN (left pedal nerve large neuron), situated symmetrically on the anterior surface of the pedal ganglia of an African giant snail (Achatina fulica Férussac). The two neurons (about 250-300 microns in diameter) were the largest ones identified in the ganglia of the snail species. The axonal pathways of the two neurons were symmetrical; of their four main axonal branches, the three main branches innervated the ipsilateral pedal nerves, whereas the last main branch projected to the contralateral pedal nerves. The pharmacological features of the two neurons were very similar. Both were inhibited markedly by dopamine [minimum effective concentrations (MECs): 3 X 10(-6)-10(-5) M], DL-octopamine (MECs: 2 X 10(-6)-2 X 10(-5) M), 5-hydroxytryptamine (MEC: 3 X 10(-6) M), GABA (MEC: 3 X 10(-4) M), L-homocysteic acid (MECs: 3 X 10(-5)-10(-4) M) and erythro-beta-hydroxy-L-glutamic acid (MEC: 3 X 10(-5) M). Acetylcholine showed varied effects, either excitatory or inhibitory, on the two neurons examined. No substances were found to have any marked excitatory effects on the neurons.     

Catecholamines in the sub-esophageal ganglia and the hemolymph of the giant African snail (Achatina fulica Férussac) determined by gas chromatography]

The content of three catecholamines (dopamine, L-norepinephrine and L-epinephrine) in the subesophageal ganglia and the hemolymph of Achatina fulica Férussac was measured by a gas chromatograph with electron capture detector. The dopamine content of the ganglia was 4.3 +/- 0.9 mug/g. L-Norepinephrine and L-epinephrine in the ganglia were not detected. The three catecholamines in the hemolymph were also not detected.     

Identification and pharmacological characteristics of the two giant neurons, v-RPLN and v-VNAN, on the ventral surface in the suboesophageal ganglia of the African giant snail (Achatina fulica Férussac)

Two giant neurons, v- RPLN (ventral-right parietal large neuron) and v- VNAN (ventral-visceral noisy autoactive neuron), were identified on the ventral surface in the caudal part of the suboesophageal ganglia of the African giant snail (Achatina fulica F erussac ), and their pharmacological features to the common putative neurotransmitters and their related substances were examined. The giant neuron examined, v- RPLN , is situated in front of the exit of the right anterior pallial nerve in the right parietal ganglion. The neuron, which is 250-300 microns in diameter, one of the largest neurons in the ganglia, was usually silent without spontaneous firing. The neuron was excited by L-norepinephrine (L-NE), DL-octopamine (DL-OA), 5-hydroxytryptamine (5-HT), L-homocysteic acid (L-HCA) and erythro-beta-hydroxy-L-glutamic acid (erythro-L- BHGA ); and inhibited by dopamine (DA), GABA, acetylcholine (Ach) and its related substances. Another giant neuron examined, v- VNAN , is situated very close to the right side of the exit of the right posterior pallial nerve in the visceral ganglion. The neuron is elliptical and about 150 micron in diameter. It showed spontaneous firing highly modified by the synaptic influences. DA, 5-HT, glycine (Gly), GABA and its related substances, L-HCA, erythro-L- BHGA , and Ach and its related substances all had the direct (not via synaptic influences) excitatory effects on the neuromembrane examined. Some of them, for example, L-NE, 5-HT and Ach and its related substances caused transient excitation of the neuron, probably due to the synaptic influences, immediately after their application. No substance producing any inhibition of the neuron could be found in the present study.     

Pharmacological characteristics of three silent giant neurons, v-LPSN, v-1-VOrN and v-VLN, identified on the ventral surface in the left parietal and the visceral ganglia of the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac)

Three giant neurons, named v-LPSN, v-1-VOrN and v-VLN, were identified on the ventral surface of the left parietal ganglion and the visceral ganglion in the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac). They lacked the spontaneous spike discharges in the normal state. The pharmacological features of the three neurons, in relation to the principal common neurotransmitter substances and their derivatives were examined. The v-LPSN (ventral-left parietal silent neuron) (diameter: about 130 microns) is situated in the left parietal ganglion close to the visceral ganglion. The neuron was excited by histamine (the minimum effective concentration [MEC]: 3 X 10(-4) M) and inhibited slightly by acetylcholine (Ach) and its related substances. The v-1-VOrN (ventral-left-visceral oral neuron) (diameter: about 130 microns) is situated in the left and oral part of the visceral ganglion. The neuron was inhibited markedly by dopamine (DA) (MEC: 3 X 10(-4) M) and slightly by Ach and its related substances. No substance producing a marked excitation of the neuron has been found yet. The v-VLN (ventral-visceral large neuron) (diameter: about 300 microns) is found in the centre of the visceral ganglion. The neuron was excited by L-norepinephrine (MEC: 10(-4) M), DL-octopamine (MEC: 2 X 10(-4) M), 5-hydroxytryptamine (MEC: 10(-4) M) and beta-hydroxy-L-glutamic acid (MEC: 10(-4) M) and inhibited by DA (MEC: 10(-4) M), GABA (MEC: 3 X 10(-5) M) and Ach (MEC: 10(-4) M). L-Epinephrine showed varied effects (MEC: 10(-4) M), which were either excitatory or inhibitory.     

The effect of amino acids on the excitability of identified autoactive giant neurons of Achatina fulica Férussac]

Effects of the following amino acids were examined on the electrical activity of the two giant neurones (PON and TAN) identified in the subesophageal ganglia of Achatina fulica Férussac : L-Asp, L-Thr, L-Ser, L-Glu, L-Pro, Gly, L-alpha-Ala, beta-Ala, L-cysteine, L-cystine, L-Val, L-Met, L-Ileu, L-Leu, L-Tyr, L-Phe, L-Lys, L-His, L-Arg, L-Cit, L-Try, GABA and GABOB. Among these substances, we observed an inhibitory effect of GABA and GABOB on the TAN excitability. GABA showed stronger effect on the TAN than GABOB. This effect of GABA was due to producing hyperpolarization on the TAN membrane. GABA showed a slight excitatory effect on the PON. The effect of GABOB on the PON was very weak and unstable.     

Comparison of antagonistic effects of several drugs on calcium current in a giant neuron of an African snail (Achatina fulica Férussac)

Antagonistic effects of several drugs on the calcium current (ICa) of a giant neurone, PON (periodically oscillating neurone), of an African snail (Achatina fulica Ferussac) were compared under the voltage clamp. According to their IC50 values and the confidence limit at 95%, the order of effectiveness of the drugs was: brovincamine, verapamil greater than or equal to isoperisone, eperisone, d-diltiazem greater than or equal to vincamine, l-diltiazem, tolperisone. Their IC50 values were assumed to be the dissociation constants of Ca2+ channels in the resting state (Kr). Voltage dependence of these drugs was examined by measuring the steady-state inactivation curves. From the results obtained, the dissociation constants of the channels in the inactivated state (Ki) and the Kr/Ki ratio were calculated for each drug. The order of Ki values of these drugs was: isoperisone, brovincamine, verapamil less than or equal to eperisone, l-diltiazem, d-diltiazem, tolperisone. The use dependence of the drugs was also examined by measuring the further decrease of ICa amplitude caused by high frequent stimulations. We observed that verapamil, brovincamine, d-diltiazem and l-diltiazem were use dependent, whereas eperisone, tolperisone and isoperisone were not.     

Penetrable and impenetrable anions into the GABA-activated chloride channel on the postsynaptic neuromembrane of an identifiable giant neurone of an African giant snail (Achatina fulica Férussac).

1. GABA produced the chloride-dependent membrane hyperpolarization of an identifiable giant neurone (the TAN, tonically autoactive neurone) of Achatina fulica Férussac.2. The penetrability of various foreign anions into the GABA-activated chloride channel on the TAN postsynaptic membrane was studied by observing whether the reversal of GABA effect on the TAN membrane potential appeared with the replacement of the physiological medium solution by isotonic foreign anion solutions.3. Halogenide (Cl⁻, Br⁻, I⁻), halogenate and perhalogenate (ClO₃⁻, ClO₄⁻, BrO₃⁻), nitrate (NO₃⁻) and thiocyanate (SCN⁻)anions were penetrable into the GABA-activated chloride channel on the TAN neuromembrane, but aliphatic carboxylate (CH₃COO⁻, CH₃CH₂COO⁻) (excluding formate), halogenoacetate (ClCH₂COO⁻, CCl₃COO⁻, BrCH₂COO⁻), sulfate (SO₄²⁻) and succinate (OOCCH₂CH₂COO²⁻) anions were not penetrable into the chloride channel.4. The penetrability of formate (HCOO⁻) and benzoate (C₆H₅COO⁻) anions could not be clearly determined.5. The results of our research into the inhibitory response to GABA of an identifiable molluscan neurone were very similar to those of IPSP and inhibitory response to acetylcholine obtained by using different neurones.     

Decreases of action potential amplitudes, in sodium-free and calcium-free conditions, of identifiable giant neurons of an African giant snail (Achatina fulica Férussac)--I. The right parietal ganglion

Decreases of the action potential amplitude in sodium- and calcium-free states were observed with respect to the four giant neurons, PON (periodically oscillating neuron), Tan (tonically autoactive neuron), RAPN (right anterior pallial neuron) and d-RPLN (dorsal-right parietal large neuron), identified in the right parietal ganglion of the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac). The decrease of the PON action potential amplitude, caused in the sodium-free state, was observed to be 25.4 +/- 2.1% (23.0 +/- 2.0 mV), expressed by M +/- SE, while that of the calcium-free state was 35.0 +/- 2.1% (30.9 +/- 1.7 mV). Then, the two ionic dependencies of the PON action potential were estimated to be about 40-50% on sodium and 50-60% on calcium. The decrease of the TAN action potential in the sodium-free state, was observed to be 20.7 +/- 1.2% (18.8 +/- 1.3 mV), whereas that of the calcium-free state was 42.2 +/- 2.7% (39.0 +/- 2.2 mV), indicating that the two ionic dependencies were 30-40% on sodium and 60-70% on calcium. The decrease of the RAPN action potential in the sodium-free state, was 45.8 +/- 3.7% (40.3 +/- 3.1 mV), whereas that of the calcium-free state was 21.7 +/- 2.5% (17.8 +/- 2.0 mV), indicating that the two ionic dependencies were about 70% on sodium and about 30% on calcium. The decrease of the d-RPLN action potential in the sodium-free state was found to be 17.6 +/- 2.4% (15.2 +/- 1.8 mV), whereas that of the calcium-free state was 23.1 +/- 1.4% (20.8 +/- 1.4 mV), indicating that the two ionic dependencies were 40-50% on sodium and 50-60% on calcium. The action potential amplitudes of all the neurons tested were decreased in both sodium-free and calcium-free states. However, their ionic dependencies were estimated to vary from 70% on sodium (30% on calcium) to 30% on the sodium (70% on the calcium), according to the neurons tested.     

Histological and pharmacological investigations of the two symmetrically situated giant neurons,RPeNLN and LPeNLN,identified on the anterior surface of the pedal ganglia of an african giant snail (achatina fulica férussac)

• 1.1. Morphological and pharmacological investigations were made of two giant neurons, RPeNLN (right pedal nerve large neuron) and LPeNLN (left pedal nerve large neuron), situated symmetrically on the anterior surface of the pedal ganglia of an African giant snail (Achatina fulica Férussac).
• 2.]2. The two neurons (about 250–300 μm in diameter) were the largest ones identified in the ganglia of the snail species. The axonal pathways of the two neurons were symmetrical; of their four main axonal branches, the three main branches innervated the ipsilateral pedal nerves, whereas the last main branch projected to the contralateral pedal nerves.
• 3.]3. The pharmacological features of the two neurons were very similar. Both were inhibited markedly by dopamine [minimum effective concentrations (MECs): 3 × 10⁻⁶-10⁻⁵M], dl-octopamine (MECs: 2 × 10⁻⁶-2 × 10⁻⁵M), 5-hydroxytryptamine (MEC: 3 × 10⁻⁶M), GABA (MEC: 3 × 10⁻⁵ M), l-homocysteic acid (MECs: 3 × 10⁻⁵-10-10⁻⁴M) and erythro-β-hydroxy-l-ghitanuc acid (MEC: 3× 10⁻⁵M). Acetylcholine showed varied effects, either excitatory or inhibitory, on the two neurons examined. No substances were found to have any marked excitatory effects on the neurons.

     

Effects of N-beta-phenylpropionyl-L-tyrosine and its derivatives on the excitability of an identifiable giant neuron of Achatina fulica férussac

1. Previously the authors demonstrated the inhibitory effects of the two aromatic amino acid derivatives, N-beta-phenylpropionyl-L-Tyr (critical concentration (c.c.), 3 x 10(-7) - 10(-6) M) and N-beta-phenylpropionyl-L-Trp (c.c., 10(-6) M) on the excitability of an identifiable giant neuron, TAN (tonically autoactive neuron), of Achatina fulica Férussac. The effects of the derivatives of the two inhibitory compounds on the same neuron are examined in the present study. 2. N-beta-Cyclohexylpropionyl-L-Tyr (c.c., 3 x 10(-8) - 10(-7) M) and N-beta-cyclohexylpropionyl-L-Trp (c.c., 10(-6) M) had marked inhibitory effects, whereas N-beta-p-methyl-phenylpropionyl-L-Tyr had none. 3. N-gamma-Phenylbutyroyl-L-Tyr and N-phenylacetyl-L-Tyr, in which the chain length of the phenyl group is different, had no effect. 4. N-beta-Phenylpropionyl-N-methyl-L-Tyr, in which the imino group of the peptide bond is methylated, had no effect. 5. N-beta-Phenylpropionyl-L-Tyr (c.c., 3 x 10(-7) - 10(-6) M) and N-beta-phenylpropionyl-L-Tyr methylester (c.c. 1-3 x 10(-6) M) had marked inhibitory effects, suggesting that their carbonyl group acts as a proton acceptor. 6. N-beta-Phenylpropionyl-L-p-hydroxyphenylglycine, in which the chain length of the hydrogen binding group is shorter, had no effect. 7. N-beta-Phenylpropionyl-L-3,4-dihydroxy-Phe (c.c., 3 x 10(-6) M), N-beta-phenylpropionyl-L-3-nitro-Tyr (c.c., 3 x 10(-5) M) and N-beta-phenylpropionyl-L-p-amino-Phe (c.c., 3 x 10(-5) - 10(-4) M) had inhibitory effects, weaker than that of N-beta-phenylpropionyl-L-Tyr. N-beta-Phenylpropionyl-L-p-chloro-Phe and N-beta-phenylpropionyl-L-p-nitro-Phe showed the same effect only at high concentrations.