Effects of procaine on a central neuron of the snail, Achatina fulica Ferussac

Effects of procaine on a central neuron (RP1) of the giant African snail (Achatina fulica Ferussac) were studied pharmacologically. The RP1 neuron showed spontaneous firing of action potential. Extra-cellular application of procaine (10 mM) reversibly elicited bursts of potential. The bursts of potential elicited by procaine were not blocked after administration of (1) prazosin, propranolol, atropine, d-tubocurarine, (2) calcium-free solution, (3) ryanodine (4) pretreatment with KT-5720 or chelerythrine. The bursts of potential elicited by procaine were blocked by adding U73122 (10 microM) and the bursts of potential were decreased if physiological sodium ion was replaced with lithium ion or incubated with either neomycin (3.5 mM) or high magnesium solution (30 mM). Preatment with U73122 (10 microM) blocked the initiation of bursts of potential. Ruthenium red (100 microM) or caffeine (10 mM) facilitated the procaine-elicited bursts of potential. It is concluded that procaine reversibly elicits bursts of potential in the central snail neuron. This effect was not directly related to (1) the extra-cellular calcium ion fluxes, (2) the ryanodine sensitive calcium channels in the neuron, or (3) the PKC or PKA related messenger systems. The procaine-elicited bursts of potential were associated with the phospholipase activity and the calcium mobilization in the neuron.     

Effects of 2 water-soluble contrast media, meglumine iothalamate (Conray) and meglumine iocarmate (Dimer-X), on the electric activity of identifiable giant neurons of the African giant snail (Achatina fulica Ferussac)]

The influences of two water soluble contrast media, meglumine iothalamate and meglumine iocarmate, on the neuronal excitability and on the neuronal sensitivity to putative transmitters were examined in comparison with those of sucrose using two identifiable giant neurones of Achatina fulica Férussac (the TAN and the PON). A relatively low increase of osmotic pressure of the extracellular fluid, produced by the application of contrast media, reversed the Cl- dependent inhibition caused by a putative transmitter. The same increase of this osmotic pressure, however, did not influence the Cl- independent inhibition and the excitation of the neurone examined. The hyperpolarization of neuromembrane was caused by an increase of osmotic pressure of the extracellular fluid. Its relatively high increase was necessary to make spontaneous spike discharges disappear totally. All effects of the two contrast media, observed in this study, were due to the increase of osmotic pressure of the extracellular fluid ; no specific effect of the contrast media containing the iodine on the indicators used was observed.     

Effects of synthetic omega-conotoxin GVIA (omega-CgTX GVIA) on the membrane calcium current of an identifiable giant neurone, d-RPLN, of an African giant snail (Achatina fulica Ferussac), measured under the voltage clamp condition

1. The sodium and the calcium inward currents (INa and ICa) of an identifiable giant neurone, d-RPLN (dorsal-right parietal large neurone), of an African giant snail (Achatina fulica Férussac), were measured separately under the voltage clamp condition. 2. The effects of synthetic omega-conotoxin GVIA (omega-CgTX GVIA) on the calcium current of the neuromembrane were examined. 3. omega-CgTX GVIA is a peptide venom originally isolated from a fish-hunting marine snail (Conus geographus L.); the peptide venom has been demonstrated to block markedly calcium channels in vertebrates. 4. In the case of the d-RPLN membrane, the ICa was much larger than INa. The command voltage (Vc) to get the ICa in maximum was about 0 mV; the maximum value of ICa in a representative experimental case, was measured as approximately 0.8 microA. 5. With respect to the ICa of a molluscan giant neurone, d-RPLN, synthetic omega-CgTX GVIA at a high concentration, 5 X 10(-5) M, showed almost no effect, in spite of reporting the peptide venom affecting the ICa in vertebrate preparations.     

Homing behaviour of the giant African snail,Achatina fulica (Ferussac) (Gastropoda; Pulmonata)

Homing ability ofAchatina fulica was studied in the field by mark-recapture experiments. Snails hid in resting sites in the day and crept out in the rain or at night. Young adults dispersed for longer distance than old adults. Old adults seldom changed resting sites, while young adults changed them left almost every day. It was only young adults that the study site or came in from other areas. In transfer experiments, old adults returned to the initial resting sites in 5 days. These results suggest that old adults have a homing ability, while young adults do not show it clearly. The homing ability ofA. fulica is age-dependent. These differences may be related to the maturation pattern of the reproductive organ.     

Different effects of the replacement of extracellular sodium with lithium on the abnormal spike discharges caused by 2 convulsants, Metrazol and strychnine, on an identifiable giant neuron of the mollusc Achatina fulica Ferussac

The influences of the replacement of sodium with lithium in the extracellular medium on the abnormal spike discharges, caused by two convulsants, metrazol and strychnine, of a giant neurone (TAN, tonically autoactive neurone) identified in the suboesophageal ganglia of the African giant snail (Achatina fulica Férussac) were examined. The slow oscillations of potential caused by metrazol disappeared after this replacement. On the other hand, the abnormal action potentials caused by strychnine, as well as the normal action potentials, still remained after the removal of sodium in the medium.     

The ionic requirements for the production of action potential in Achatina fulica Ferussac neuron

The ionic requirement for the production of directly elicited action potentials of a tonically auto-active neuron (TAN) in the subesophageal ganglia of the giant African snail, Achatina fulica Ferussac, was studied electrophysiologically. Calcium free Ringer solution containing 1 mM EDTA reversibly abolished the directly elicited action potential. Verapamil (10 micrograms/ml) or cocaine (4 mg/ml) decreased both amplitude and Vmax of the action potentials. The amplitude of the action potential was also slightly decreased in sodium free choline Ringer. However, tetrodotoxin did not significantly affect either the amplitude or Vmax of the directly elicited action potentials. The results suggest that the ionic requirement for generating action potential in snail neuron is not an ordinary sodium spike. Both calcium and sodium ions may participate in carrying charges across the membrane of the action potential.     

Presence of TAN (tonically autoactive neuron) and its two analogous neurons, located in the right parietal ganglion of the suboesophageal ganglia of an African giant snail (Achatina fulica Ferussac). Morphological and electrophysiological studies

Three identifiable giant neurons, which were morphologically and pharmacologically identical, named TAN (tonically autoactive neuron), TAN-2 and TAN-3, were found in line on the dorsal surface of the right parietal ganglion in the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac). The diameters of these neurons were 150-200 microns. They showed regular spontaneous spike discharges at the rate of 30-40 per min. However, the spike discharges of the three neurons were not synchronized. For morphological studies of these neurons, Lucifer Yellow was injected into their somata by pressure. The axonal branches of the three neurons examined extended commonly into the following seven peripheral nerves: left anterior pallial, left posterior pallial, intestinal, anal, right posterior pallial, right anterior pallial and right anterior pallial accessory nerves. The sensitivities of the three neurons examined to the main neurotransmitter candidates and their derivatives were almost identical. These neurons were excited by 5-hydroxytryptamine [the minimum effective concentration (MEC): 10(-5)-10(-4) M] and histamine (MEC: 1-3 X 10(-4) M), and inhibited by dopamine (MEC: 1-3 X 10(-4) M), L-norepinephrine (MEC: 3 X 10(-4)-10(-3) M), L-epinephrine (MEC: 3 X 10(-4) M), GABA (MEC: 10(-5)-10(-4)), acetylcholine (MEC: 1-3 X 10(-4) M) and its derivatives.     

The modulation effects of d-amphetamine and procaine on the spontaneously generated action potentials in the central neuron of snail, Achatina fulica Ferussac

The modulation effects of d-amphetamine and procaine on the spontaneously generated action potentials were studied on the RP1 central neuron of giant African snails (Achatina fulica Ferussac). Extra-cellular application of d-amphetamine or procaine reversibly elicited bursts of potential (BoP). Prazosin, propranolol, atropine or d-tubocurarine did not alter the BoP elicited by either d-amphetamine or procaine. KT-5720 or H89 (protein kinase A inhibitors) blocked d-amphetamine-elicited BoP, whereas they did not block the procaine-elicited BoP. U73122, neomycin (phospholipase C inhibitors) blocked the procaine-elicited BoP, whereas they did not block the d-amphetamine-elicited BoP in the same neuron. These results suggest that BoP elicited by d-amphetamine or procaine were associated with protein kinase A and phospholipase C activity in the neuron.     

A novel cardio-excitatory peptide isolated from the atria of the African giant snail, Achatina fulica

An undecapeptide which potentiates the beat of the ventricle in the African giant snail, Achatina fulica Ferussac, was purified from the atria of the snail. Its primary structure was determined to be H-Ser-Gly-Gln-Ser-Trp-Arg-Pro-Gln-Gly-Arg-Phe-NH2. This peptide was found to have excitatory actions not only on the ventricle but also on the penis retractor muscle, the buccal muscle and the identified neurons controlling the buccal muscle movement of Achatina.     

Neuroeffector connections of multimodal neurons in the African snail (Achatina fulica)

Using a new method of animal preparation, the efferent connections of giant paired neurons on the dorsal surface of visceral and right parietal ganglia of snail, Achatina fulica, were examined. It was found that spikes in giant neurons d-VLN and d-RPLN evoke postjunctional potentials in different points of the snail body and viscerae (in the heart, in pericardium, in lung cavity and kidney walls, in mantle and body wall muscles, in tentacle retractors and in cephalic artery). The preliminary analysis of synaptic latency and facilitation suggests a direct connections between giant neurons and investigated efferents.     

Dynamics of the dominance of identified cardioregulatory neurons in the snail Achatina fulica]

9 cardioregulating neurones belonging to 5 different functional groups were studied in visceral and right parietal ganglia of the Giant African snail Achatina fulica. The neuronal network included multimodal and multifunctional cells exerting short- or long-lasting chronoionotropic effects on the cardiac electro- and mechanograms. Mechanisms of the differences in the cardioregulating effectiveness of these groups were discussed.     

High molecular weight lectin isolated from the mucus of the giant African snail Achatina fulica

To understand better the host defense mechanisms of mollusks against pathogens, we examined the anti-microbial activity of mucus from the giant African snail Achatina fulica. Hemagglutination activity of the mucus secreted by the integument of snails inoculated with Escherichia coli was observed to increase and to cause hemagglutination of rabbit red blood cells. Purification of the snail mucus lectin by sequential column chromatography revealed that the relative molecular mass of the lectin was 350 kDa. The hemagglutination activity of the lectin was Ca(2+)-dependent and was inhibited by galactose. Growth arrest tests showed that the lectin did not inhibit bacterial growth, but did induce agglutination of gram-positive and gram-negative bacteria. Tissue distribution analyses using a polyclonal antibody revealed that the lectin was expressed in the tissues of the mantle collar. The lectin isolated from the mucus of the snail appeared to contribute to its innate immunity.