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Adult specimens of Helix pomatia L. were kept under a 12:12 light-dark cycle (photophase: 8.00–20.00 hr) at a constant temperature (23°C) and at a constant humidity for at least 3 weeks. Subsequently, extracellular recordings from the inner lip nerve were performed at constant light over a period of at least 24 hours. Stimulations with aqueous solutions of sucrose and sodium chloride were performed every 2 hours. The results showed that the maxima of neural responses were correlated to the scotophase of the light-dark cycle, the snails were adapted to. Furthermore, in those snails that had been adapted to an inverted light-dark cycle (photophase: 20.00–8.00 hr), the periods of maximum responses were shifted to the end of the scotophase.

Simultaneous pre- and postsynaptic intracellular recordings were used to study the mechanism of presynaptic terminal recruitment in a multifunction interneurone in the snail Helix pomatia . The interneurone was presynaptic to at least 20 neurones. The synaptic efficiency was correlated with the presence of presynaptic depolarizing after-potentials (DAPs) electrotonically produced by the delayed firing of remote terminal processes. These processes have large swellings filled with neurosecretory vesicles. The terminals were recruited in a graded manner when the interneurone was fired with a prolonged current. The terminal recruitment was enhanced by stimulating various efferent nerves, which presumably activated presynaptic receptors for dopamine. A few animals (three out of 300) had two electrically coupled interneurones. Simultaneous recordings from both cells showed that the terminals could be fired independently of the soma-axon activity. The graded and local firing of the presynaptic terminals was attributed to the electrical load that the large boutons exert on electrotonically spreading presynaptic impulses.

A slow-wave model for bursting activity based on the hyperpolarization-activated outward current has been analysed by simulation of the well-known experimental data. It is shown that the slow-wave model demonstrates an increase of membrane input resistance during the development of the depolarizing phase; responds adequately to stationary de- or hyperpolarizing current; demonstrates a phenomenon of induced hyperpolarization and contingency. Change of definite model parameters selectively affects burst or interburst interval, and the period of slow-wave oscillation. It is found that the investigated model, when using the slowest process (1.5 sec) can generate persistent oscillations with a period of more than 100 sec. Introduction of variable parameters in the model simulates an initiation of slow-wave oscillation in Helix bursting neuron evoked by stimulation of identified peptidergic interneuron. The limitation of the presented model of slow-wave oscillation is discussed.

1. 1. Neuronal shape during epileptic activity was studied with confocal laser scanning microscopy and intracellular recording of identified neuronal individuals in the buccal ganglia of Helixpomatia. Simultaneous observations of single Lucifer Yellow stained fibers and epileptic activity of the same neuron were done. 2. 2. During epileptic activity, the development of several types of morphological changes were observed: local and extended swellings, constrictions, stretching of neuronal processes and release of intracellular material. 3. 3. Morphological alterations did not only occur with epileptic activity but could also appear due to extended laser exposure of fluorescent neuronal processes. 4. 4. Phototoxicity is discussed as a limiting factor for a valid interpretation of the morphological changes observed by confocal microscopy.

1. 1. The structure and topography of carbohydrate determinants on the growth cone surface membrane of the snail Helix pomatia nerve cells cultured in vitro have been characterized with a variety of gold-labelled lectins of different sugar specificity. 2. 2. Substantial differences in the pattern of carbohydrate determinants in different parts of growth cone have been revealed. On the surface membrane of organelle-poor veils complex branched sugar chains of N-type were exposed, in other parts of regenerating neuron they were absent. Maturation of veils is accompanied by accumulation of organelles within them and expression on their surface of a considerable number of nonsialylated disaccharide residues of T-F antigen (Galβ l-3GalNac) which can be related to an increased migration ability of these structures. 3. 3. The mature growth cone contains numerous N-acetylglucosamine and considerably less N-acetyllactosamine and N-acetylgalactosamine determinants. 4. 4. All the lectins studied failed to bind to the surface of growth nubbin containing clusters of subplasmalemmal vesicles. 5. 5. The fusion of primary lysosomes with the inner surface of membrane of mature dendrites was found. Decrease or complete disappearance of carbohydrate residues in the fusion region has been observed. The physiological significance of carbohydrate components in neurite growth is discussed.

1. 1. The mechanism of generation of membrane potential (MP) oscillations was studied in identified bursting neurons from the snail Helix pomatia. 2. 2. Long-lasting stimulation of an identified peptidergic interneuron produced a persistent bursting activity in a non-active burster. 3. 3. External application of calcium channel blockers (1 mM Cd2+ or 5 mM La2+) resulted in a transient increase in the slow-wave amplitude and subsequent prevention of pacemaker activity generation in bursting neurons. Application of these blockers together with endogenous neuropeptide initiating bursting activity generation, increased MP wave amplitude without prevention of bursting activity generation. 4. 4. Replacement of all NaCl in normal Ringer's solution with isoosmotic CaCl2, glucose or Tris-HCl produced a reversible block of bursting activity generation. Stationary current-voltage relation (CVR) of bursting neuron membrane has a region of negative resistance (NRR) and does not intersect the potential axis in threshold region for action potential (AP) generation in normal Ringer's solution. In Na-free solution stationary CVR is linear and intersects the potential axis near — 52 mV. 5. 5. Novel potential- and time-dependent outward (Erev = − 58 mV) current, IB, activated by hyperpolarization was found in the bursting neuron membrane. Having achieved a maximal value, this current decayed with a time constant of about 1 sec. Hyperpolarization inactivated maximal conductance, gB, responsible for IB, and depolarization abolished inactivation of gB. 6. 6. Short-lasting (0.01 sec) hyperpolarization of the bursting neuron membrane by inward current pulse induced the development of prolonged hyperpolarization wave lasting up to 10 sec. 7. 7. These results suggest that: (a) persistent bursting activity of RPal neuron in the snail Helix pomatia is not endogenous but is due to a constant activation of peptidergic synaptic inputs of these neurons; (b) Ca2+ ions do not play a pivotal role in the ionic mechanism of MP oscillations but play a determining role in the process of secretion of a peptide initiating bursting activity by the interneuron presynaptic terminal; (c) depolarizing phase of the MP wave is due to specific properties of stationary CVR and hyperpolarization phase is due to regenerative properties of hyperpolarization-activated outward current IB. The minimal mathematical version of MP oscillations based on the experimental data is presented.

1. 1. A variety of colloidal gold-labelled lectins with different sugar specificities to determine whether different nerve and glial cells of the snail Helix pomatia cultured in vitro , can be distinguished by the carbohydrates that they express was screened. The analysis of lectin binding has shown substantial differences in the carbohydrate pattern between nerve and glial cells and between the soma of monoaminergic and peptidergic neurons. 2. 2. The surface of monoaminergic and peptidergic neurons contains N -acetylglucosamine and N -acetyllactosamine determinants, and does not exhibit neuraminic acid and complex branched N -glycosyl chains. Moreover, N -acetylgalactosamine can be detected on peptidergic neuron membranes only. 3. 3. N -Acetylglucosamine residues are not present on the surface of the glial cells, and the density of the N -acetyllactosamine and/or terminal β-galactose residues is much higher here than on the surface of the nerve cells. 4. 4. These results suggest that nerve cells in the snail brain can be distinguished from glial cells by the presence of a cell-surface glycoconjugate containing terminal N -acetyl- d -glucosamine residues, whereas peptidergic neurons can be distinguished from monoaminergic neurons by the presence of a surface glycoconjugate containing terminal α-linked N -acetyl- d -galactosamine residues.

1. 1. Inhibitory innervation of the Helix heart was found to be organized by two multifunctional neurons. Mechanical stimulation of many visceral organs including the heart evokes antidromic action potentials in these cells. 2. 2. Morphological and functional analysis of these neurons showed them to be identical to previously described motoneurons and to the multifunctional interneuron V 21. 3. 3. Multifunctional neurons do not interact with one another, they receive direct outputs and inputs from the heart and to the heart. They independently mediate inhibitory cardiocardiac and viscerocardiac reflexes. 4. 4. Due to the presence of several trigger zones in these neurons the reflexes can persist following gangliotomy.

1. 1. The large ink-labelled vessels, such as the anterior aorta and the middle foot artery run over the largest groups of 5,6-dihydroxytryptamine-pigmented serotonergic cell bodies of the CNS. 2. 2. The main branching points of the vessels in the CNS perineuriurn are located over small groups of pigmented serotonergic cell bodies. 3. 3. This intimate anatomical connection suggests mutual relationship between the serotonergic cell bodies and the vessel system.

1. 1. Synaptic short-term depression could be transferred into long term depression by repetition of series of stimuli. 2. 2. The transition from short-term depression to long-term depression was blocked by puromycin. 3. 3. The majority of the transition took place during resting periods between stimulus series. 4. 4. The initiation of the transition process was 83% completed after 5 min of stimulation. 5. 5. Short- and long-term depression were quantitatively separated into their two serial sites of origin: afferent axons and synaptic terminals. 6. 6. Long sequences evoked periods with increased and variable EPSPs not conforming to depression.

1. 1. The identifiable neuron B3 in the buccal ganglion of Helix pomatia has been studied with regard to its morphological and physiological properties. The neuron is of interest in studies on experimental epileptology and on functions of small neuronal networks. 2. 2. Action potentials of neuron B3 are conducted to the kidney. 3. 3. Synaptic inputs to neuron B3 originate from several types of neurons in the buccal ganglia and from neurons situated in the wall of the pharynx. 4. 4. The functional significance of neuron B3 may consist of a transfer of information from pharyngeal feeding activities to the kidney.

1. 1. In a group of photosensitive neurons in the left parietal ganglion, the onset of light prolongs significantly (by about 40%) the duration of the action potential. 2. 2. The broadening of the action potential after the onset of light was found to be due to its calcium component and could not be induced after blocking the Ca 2+ channels by Cd 2+ and in absence of Ca 2+ in the medium. 3. 3. The onset of light induced constantly an enhancement of the calcium inward current. 4. 4. The prolongation of the action potential was time, and temperature, dependent, suggesting involvement of some second messenger in the light-induced modulation of voltage-gated channels. 5. 5. The presence of phosphodiesterase inhibitor IBMX mimics the effect of light on the action potential and on the Ca 2+ inward current.

1. 1. The connection between an identified interneuron and RPal bursting neuron from Helix pomatia L. brain was studied electrophysiologically and morphologically. 2. 2. Electrical stimulation of interneuron induced an increase or evoked bursting activity in the RPal neuron. 3. 3. The interneuron and RPal neurons were stained by CoCl 2 and NiCl 2 intracellular injections. 4. 4. The axon from interneuron had two large branches, the first branch was traced in visceral nerve and the second branch was traced in the direction of RPal axon, which in turn went into visceral nerve. 5. 5. According to these and the literature data, it is proposed that contact between interneuron and RPal neuron is axo-axonal.

1. 1. Under constant temperature and humidity conditions and a 12:12 light-dark cycle heart rates of Helix pomatia show a diurnal rhythm with minimum values at 12.00 hr and maximum values at 24.00 hr. 2. 2. Diurnal rhythm persists during estivation. 3. 3. In hibernating snails periodic fluctuations of heart rate occur which are not synchronized by the prevailing photoperiod.

1. 1. In the contents of the oesophagus and stomach, one form of acid phosphatase is found. Its electrophoretic mobility is identical to that of the multiple form 3 of acid phosphatase from the hepatopancreas. 2. 2. The enzyme is not stimulated by divalent cations. It is inhibited by molybdate, Cu2+, Hg2+. F− and tartrate L+. 3. 3. The optimum pH of the enzyme is 4.5. The Km for paranitrophenylphosphate as substrate amounts to 0.25 mM. The enzyme is stable at a temperature of up to 55°C.

1. 1. Frequency dependency of a multisynaptic EPSP in neuron F76 of Helix pomatia is described. 2. 2. Following a single EPSP, the amplitude of a second was 52% of the first recovering in time through three phases: from 0 to 4 sec after the first, no increase occurred; from 4 to 10 sec an exponential recovery was observed (τe = 2 sec) and from 10 sec, amplitude acquired full size along an exponential course of τ1 = 45 sec. 3. 3. A model is made for changes of presynaptic vesicles. The model describes EPSP amplitudes during and after trains.

1. 1. The neurons B1 through B3 in the buccal ganglia of Helix pomatia were treated systemically with pronase. 2. 2. After an application of pronase, oscillations of the resting membrane potential (RMP) disappeared irreversibly. 3. 3. Initial fluctuations of the RMP appeared which turned into a permanent depolarization. 4. 4. Action potentials were prolonged with longlasting application of pronase. 5. 5. IPSP and electrotonically mediated excitatory responses remained nearly unchanged. 6. 6. Most of the chemically mediated EPSP decreased irreversibly down to zero level. Some EPSP—especially those elicited by stimulation of the cerebrobuccal connectives—were affected only slightly. 7. 7. The relation between RMP and amplitudes of chemical EPSP was inverted.

1. 1. Complex formation between calcium, haemocyanin from Helix pomatia, d -lactate and succinate has been investigated by means of potentiometric titrations using iterative curve fitting procedures. 2. 2. Strong complexes containing more than two constituents could not be detected. 3. 3. The method proved to be useful to investigate the protein-calcium complex formation. 4. 4. The model thus derived, using acid-base and complex formation equilibria, agrees within the concentration range of 20–40 mM Ca2+ with an empirical formula of pH-dependence of calcium binding by Helix pomatia haemocyanin.

1. 1. The shell side of the mantle of Helix pomatia and H. aspersa is normally several mV positive to the other side in vivo and in vitro. 2. 2. The short circuit averages 40 μamp/cm2. It does not depend on Na, K, Ca, Mg or HCO3, but requires the presence of Cl on the shell side. 3. 3. The electrical gradient is reduced by 2,4-dinitrophenol, thiocyanate and furosemide, but not by oubain, acetazolamide or SITS. 4. 4. It is suggested that fluid leaks between the epithelial cells towards the shell in vivo and is reabsorbed by active transport of Cl. 5. 5. In H. pomatia about to secrete calcareous epiphragms the electrical potential reverses, but still requires Cl.

1. 1. A two microelectrode voltage-clamp method was used to investigate the inward and outward membrane currents of snail ventricular fibres. 2. 2. The presence of a slow Ca-sensitive inward current ( I si ) was described. This was activated at - 35 mV and peaked between 0 and + 10 mV. 3. 3. The I-V characteristic of the fully activated outward currents accompanying a 3–5 sec depolarization was N-shaped, indicating the presence of both inward and outward rectification. 4. 4. The time- and voltage-dependent outward current could be resolved into two exponentials when plotted on a semilogarithmic scale. 5. 5. The fast component had a time constant of between 0.5 and 1.2 sec, and this outward current is thought to represent a pacemaker current in a snail heart. The activation variable was 0 at −35 mV and 1 at +45 mV. 6. 6. The time constant of the other component of outward current was found to be between 2.5-4.5 sec. 7. 7. The role of different currents components are discussed.

1. 1. Intracellular injection of 2,4-DNP decreased the amplitude and frequency of the slow oscillation of membrane potential but did not eliminate spike generation. 2. 2. During lengthened interburst intervals fast oscillation with low amplitude occurred. 3. 3. Intracellularly injected CdCl 2 increased the amplitude of the slow oscillation after a transient depolarization then paroxismal activity appeared. 4. 4. Speed of the inward current decreased significantly after 2,4-DNP injection while it was not influenced by CdCl 2 . The amplitude of the inward current was decreased in both cases. 5. 5. The initial value of the outward current was decreased strongly at 2,4-DNP injection while its steady state value at CdCl 2 injection.

1. 1. Intracellular methods have been used to study the effects of barium ions on the spontaneous EPSPs of the snail brain. 2. 2. An analysis of the interspike interval histograms of various pacemaker neurones showed characteristic differences when pacemaker activity and/or EPSPs were influenced in the barium media. 3. 3. The steady-state membrane resistance decreased when slow or fast EPSPs were evoked. The slope membrane resistance increased in some neurones while it decreased when the synaptically evoked effects of the barium ions predominated. 4. 4. The amplitude and frequency of the spontaneous fast and slow EPSPs increased when barium acted. 5. 5. The spontaneous EPSPs were not unequivocally prevented in 0 Ca 2+ -30mM Mg 2+ medium. but they were highly depressed in some cases, and were again facilitated in the presence of Ba 2+ 6. 6. Na + -free (Tris or Choline) solution totally blocked the barium evoked spontaneous EPSPs, but after readmission of the sodium ions a facilitation of the transmitter release occurred. The delayed release was also increased if barium had been acting previously in the Na + -free medium. 7. 7. On the other hand K + -free solution increased the spontaneous transmitter release, and the facilitatory effect of barium ions was enhanced in the absence of potassium ions. 8. 8. Indirect and/or direct facilitatory effects of barium ions were involved in the spontaneous transmitter release depending on the doses used.

1. 1. The effects of short- and long-term temperature transition on the threshold potential for excitation (0v) and on temporal characteristics of the action potential were examined in the identified bursting neuron of the snail Helix pomatia. 2. 2. Abrupt cooling (from 25° to–0.5°C) induced a consistent and reversible increase of the threshold voltage in the Br neurons from warm acclimated animals. 3. 3. Acclimation of intact animals to low (5 °C) temperature resulted in a complete compensation in 0v. That is, threshold potential of the Br neurons from cold acclimated animals recorded at −0.5°C was not different from the value recorded at 25°C in warm acclimated neurons. 4. 4. The duration of evoked action potentials was markedly prolonged by cooling but showed no compensatory changes with acclimation.

1. 1. Transmitter mobilization and fractional release were studied in Helix pomatia. The right palliai nerve was stimulated and a synaptic potential was recorded in cell F76 in the right parietal ganglion. 2. 2. The extra- and intra-cellular pH were changed with Tris-maleate, CO2 or (NH4)2SO4. 3. 3. The time constant for the monoexponential part of mobilization decreased with reduced intracellular pH. Only a fraction of this effect could be related to an increase in the intracellular Ca-activity. 4. 4. Fractional release was reduced in low external pH, but was increased in low intracellular pH. Fractional release is affected more by changes in internal pH than external pH.

1. 1. Spontaneous withdrawal-extension sequences in the optic tentacle of Helix pomatia were modified by electrical stimulation. 2. 2. An average learning curve for a large population showed two distinct exponential phases. Forgetting occurred in two separate phases. 3. 3. Retention was followed after varying numbers of stimulations. 4. 4. Electric shocks on the foot blocked retention. 5. 5. Retention was greater in animals receiving injection of trained, compared to untrained brain material.

1. 1. A long-term learning phenomenon in the tentacle of Helix pomatia has been observed. 2. 2. Repeated mechanical stimulation of the optic tentacle led to habituation of the associated withdrawal-extension action pattern whereas repeated combined mechanical and electrical stimulation potentiated the reflex. 3. 3. The potentiation was present 40 days after four sessions of stimulations. Sessions spaced with proportionally increasing intervals were more effective than massed training. Puromycin (125 mg/ml) blocked 80% of protein synthesis as well as the long-term but not the short-term retention of potentiation. 4. 4. Contrary to observations in other preparations, the amount of water soluble proteins, notably S-100, was not affected by learning. Injections in vivo of and exposure of brain in vitro to S-100 had no effect on learning or a variety of brain potentials.

1. 1. In the identified neurons Bl, B2 and B3 of the buccal ganglia of Helix pomatia , responses to stimulation of ganglionic nerves have been studied systematically. 2. 2. The responses consisted of early depolarizations and late de- and/or hyperpolarizations which were composed of several elements: electrotonical and chemical depolarizations of short as well as long latencies and hyperpolarizations of long duration. 3. 3. Occurrence and shape of the elements depended upon the type of neuron, the stimulated nerve and the individual preparation.

1. 1. In Helix pomatia the afferents of the cardio-renal system and pneumostoma activate 70 and 35% of the reacting neurons in the visceral and right parietal ganglia, respectively. 2. 2. Two heart excitatory motoneurons received inputs from both the cardio-renal system and pneumostoma, while the other two heart excitatory motoneurons were excited only by pneumostoma afferents. 3. 3. The central neuron (V21) of the network regulating cardiorenal system can be involved into both afferent and efferent pathways. 4. 4. In the Gastropoda the neural networks regulating various organs and systems are set up from variable units. The conduction and interpretation of the information takes place in dynamic network and not at rigidly fixed pathways.

1. 1. The effects of barium ions on the stimulus evoked fast and slow EPSPs of the snail brain have been studied using intracellular methods. 2. 2. Most of the stimulus-evoked slow, fast and compound EPSPs were facilitated if barium ions were present in a calcium containing solution. 3. 3. The barium induced facilitation could be evoked by indirectly or directly depending on the barium doses. 4. 4. Raising the Mg 2+ and/or decreasing the Ca 2+ concentration in the bathing solution depressed or totally blocked the barium evoked facilitatory actions. 5. 5. Causing conduction blockage and ion deficiency, Na + -free solution abolished the stimulus evoked responses, and neither functions of the sodium ions were substituted by barium ions. 6. 6. Barium ions were, in most cases, unable to substitute for calcium ions in the stimulus evoked chemical transmission process. 7. 7. Barium ions depolarize the terminals, probably shield the membrane charges, and influence the intraterminal charge distribution, all of which may be factors of the facilitated transmitter release.

1. 1. Cobalt retrograde axonal diffusion and intracellular recordings were used to identify central neurons innervating the penis retractor muscle (PRM) of Helix pomatia . In intact brain-muscle preparations we studied the spontaneous activity of identifiable central neurones and the peripheral effector suspected to be innervated by them simultaneously. 2. 2. Central neurons sending off processes into the penis retractor nerve (PRN) were located in the cerebral ganglia, the right cerebro-pedal connective and the pedal ganglia. Four neurons located on the latero-ventral surface of the right pedal ganglion have been morphologically and electrophysiologically identified revealing the possibility of a routine recognition of individual central neurons from animal to animal. 3. 3. The four identifiable neurons could be classified by virtue of their electrophysiological properties in three types: (1) two irregular bursting cells, (2) one regular beating cell and (3) one silent cell. The firing patterns of the three active cells were found to correspond with rising phase resp. tension maintenance or relaxation of tonic contraction within the PRM. 4. 4. The two irregular bursting cells (IB cells) could be distinguished in IB cell 1 and IB cell 2 by their different burst activities in relation to the muscle behaviour. Spontaneously occurring or' intracellularly stimulated burst activities of IB cell 1 showed a correlation in time with the rising phase of strong contractions within the PRM. The bursting activities of IB cell 1 were not impaired after disconnecting brain and muscle, while the tonic contraction within the PRM was abolished. 5. 5. Spike discharge of the second irregular bursting cell (IB cell 2) accompanied muscle relaxation. Intracellular stimulation of IB cell 2 caused burst activity but failed to produce relaxation from muscle tone. After disconnecting brain and muscle IB cell 2 became silent. 6. 6. Increase in the regular beating rhythm of the third active cell could be observed during tonic muscle activity mainly during the maintained state of muscle tone. After disconnecting brain and muscle this cell fired the whole time in a very regular manner. 7. 7. From these studies it is suggested that IB cell 1 involved in generating strong contractions within the PRM. IB cell 1 seems to exert its effect directly on peripheral nervous structures without the use of centrally located interneurons possibly by a modulatory effect on the efficiency of peripheral motoneurons. I B cell 2 and the regular beating cell appeared to receive direct or indirect afferent input from the peripheral organ. The role of the silent is as yet unresolved.

1. 1. To reveal the morphology of the suboesophageal ganglia of Helix pomcitia, the connective tissue was completely removed and the preparations stained whole-mount with methylgreen-pyronin G to display the relative locations of the neurons. 2. 2. Fifteen large cells which could be recognized as individuals in at least 75% of the preparations investigated, were morphologically identified by size, position and color. 3. 3. The cells were electrophysiologically characterized with respect to spontaneous activity, synaptic input from peripheral nerves, and response to application of drugs (e.g. ACh, DA and 5-HT). 4. 4. The peripheral axonal projections of eight of the major identified cells were investigated by intracellular CoCl2 injection and by cobalt backfillings of the peripheral nerves.

1. Edible snails kept without feeding at 4°C, 97% relative humidity and with 8 hr of light per day begin to hibernate in autumn and awake again in spring. 2. In the hemolymph of covered snails the freezing-point depression and concentration of Na, K, Ca, Mg, Cl and protein are significantly higher than in the active snails of autumn and spring. 3. In the foot muscle only the Ca content changes considerably, with a decline immediately after covering. The water content falls significantly at the beginning of hibernation and the Na content at the end. 4. After Helix pomatia has covered itself in, the albumen gland contains less Na, Ca and particularly K. At the end of hibernation the content of Na and Ca has increased. Generally a loss of ions ensues, when the snails awake. 5. In the digestive gland during hibernation the water content is lower than the K content and, at the end of hibernation, Na content are higher in comparison in the active snails of autumn and spring. The Ca content decreases immediately after covering and again after waking in spring. 6. In the kidney: at no time between autumn and spring does the water, Na and Ca content change significantly. The K content is on a significantly higher level during hibernation and drops to a very low value in the active snails in spring.

1. 1. The heart of Lymnaea stagnalis produces a pressure gradient of some 6.5 cm of water between the aorta and the pulmonary vein. 2. 2. Ventricular systole is compensated partly by auricular expansion and partly by an increase m volume of the pericardial liquid; the cardiac refilling mechanism is not very efficient and certainly not as efficient as that in Helix pomatia. 3. 3. The efficiency lost in diastolic refilling is a result of the need for an efficient osmoregulatory mechanism.

1. 1. The characteristic activity pattern of the bimodal pacemaker neuron (RPal) of Helix pomatia was temporarily inhibited by synaptic input, both in isolated ganglion by electrical stimulation of nerves and in brain-heart preparation by tactile stimulation of peripheral receptors. 2. 2. Intracellular injection or extracellular application of SH blockers changed bursting of the RPal neuron. Hyperpolarizing phases were absent while the cell generated action potentials in a normal way, or, slow waving was present without generation of action potentials. 3. 3. It is suggested that slow oscillation of the membrane potential is based on an intracellular metabolic cycle, which is independent of spike generation.

1. Mechanical power measurements of snail perfused isolated ventricle were made with increasing hydrodynamic pressures of hacmolymph or physiological salines. 2. Microcalorimetry, using the Calvet apparatus, gives the total energy flux: Σ(−ΔH) where H is enthalpy, produced by the isometric beating heart. 3. The value of α = [mechanical power]/[Σ(−ΔH)] is a measurement of myocardial efficiency; it varies from 0·08 to 0·26 in haemolymph or Ringer saline. 4. Efficiency is not affected by lowering PO 2 in haemolymph but is modified by increasing K + or Ca 2+ in isotonic salines.

1. 1. The effects of photostimulation were investigated in four identified neurons in Helix pomatia subesophageal ganglia. Three of the tested photosensitive cells reacted to illumination with a depolarization and increment of frequency of spontaneously generated action potentials. One identified cell in the right parietal ganglion reacted to light with hyperpolarization. 2. 2. Analysing the dynamics of action potential frequency changes during 1 or 2 min illuminations as well as during the subsequent dark periods it was found that shortly after the onset of light the action potential frequency reached a maximum and it remained significantly higher till the light was switched off. 3. 3. Hyperpolarization of the membrane enhanced the amplitude of light evoked depolarization in all three tested depolarizing neurons. A linear change of amplitude of light evoked depolarization was observed for the range of light intensities used here. An increment of neurons reactivity to light in the course of adaptation to darkness was observed and analysed.

1. 1. The hemolymph of Helix pomatia subjected to a 1-hr temperature rise from an adaptation temperature (AT) of 20°C to 43°C shows, when examined at intervals of 1 and 24 hr after return to 20°C, at least a temporary increase in the freezing-point depression and also a rise in the concentrations of K, Ca, glucose, NPS and protein. 2. 2. In the case of lowering the temperature to 0°C only rises in glucose and NPS concentrations are found. 3. 3. After both temperature changes the pH value and Na concentration fall in the hemolymph, and in the foot muscle the LDH activity becomes greater. 4. 4. In the hemolymph of heat- (50°C) and cold-killed (−10°C) snails the concentration of K, NPS and glucose are conformably higher, and the Na concentration and pH value are lower in comparison to those at 20°C. 5. 5. The other measured values in the hemolymph generally tend at heat death to increase, however, at cold death they decrease. In the foot muscle the Na intake stands over against a greater K efflux at heat and cold death.

1. 1. Between oviposition and the late gastrula we found that the concentration of ecdysteroids is higher in diapausing eggs than in non-diapausing eggs. 2. 2. Enzymatic hydrolysis, with Helix pomatia juice, of the conjugated ecdysteroids increases the immunoreactivity of the extracts in greater proportion in diapausing eggs. 3. 3. The analysis of developmental variations of the free ecdysteroids in monovoltin strains shows the presence of a rise in ecdysone in relation to the onset of the diapause (at the gastrula stage). 4. 4. Acidic treatment with HCl which prevents the diapause is followed by an increase of free 20-hydroxy ecdysone. 5. 5. The early diapause is characterized by the loss of ecdysteroids in free-form (ecdysteroids are mainly in conjugated form), while late diapause shows an increase of free ecdysteroids in relation to the resumption of embryogenesis.

1. 1. Spike frequency adaptation has been studied on neurons of Helix pomatia subesophageal ganglia and interpreted by means of a behavioural model describing the phenomenon in neurons either silent or autorhythmic at rest. 2. 2. At low stimulating currents the initial discharge frequency F (0) is linearly related to the current strength G . 3. 3. In the linearity range F (0)/ G each neuron was characterized by means of four model parameters: the proportionality constant between F (0) and G , the decay constant of the frequency, the inhibitory current from a single nerve impulse and the decay time constant of the inhibitory current. 4. 4. The four parameters varied in different cells with a range of 0.18–4.98 Hz/nA, 1.02–3.85 sec, 0.05–0.95 nA and 1.74–22.33 see, respectively. 5. 5. Experimental results have been analyzed considering inhibitory current, electrogenie sodium pump and other proposed adaptation parameters.

1. 1. Frequency-dependent depression in neuron F76 of Helix pomatia is describable in terms of the presynaptic parameters: number of sites ready for secretion (No), fractional release (F), period of no mobilization (a), rate constants for early and late mobilization (ke and kl) (Christoffersen & Juel, Comp. Biochem. Physiol, 61A, 611–619, 1979). 2. 2. EPSP trains and model parameters have been tested as functions of Na+, Ca2+, Mg2+, (Co2+) and temperature. Na+: changed only F; Ca2+: affected F, a, ke and kl; Mg2+: influenced No and F; temperature: Q10 for the a- plus ke-period was 3.8, Q10 for kl was 2.2. 3. 3. Observed ion- and temperature-dependent parameter functions reproduced observed changes of trains.

1. 1. In Achatina —similarly to Helix pomatia —the neurones regulating cardio-renal system are scattered throughout the CNS. 2. 2. Two inhibitory motoneurones (V12, V13) and one interneurone (V21) were identified in both species. The tonic firing of cell V21 caused the stopping of the heart. 3. 3. There exists a reciprocal inhibitory relation between the inhibitory interneuron and excitatory motoneuron. 4. 4. In CNS of Achatina 5–6 cells generate periodic trains of impulses. Among them four receive inputs from the cardio-renal system. 5. 5. In the heart regulatory network paired, synchronously firing cells were discovered being coupled electrotonically or having common command. 6. 6. The heart regulatory network of Achatina is a convergent, overguaranteed one in which a hierarchial arrangement can be recognized.

1. 1. The spontaneous and electrically excited activities of the penis retractor muscle (PRM) of Helix pomatia L. were studied. 2. 2. Four distinct muscle activities were recorded in response to electrical stimulation: (a) single or a few muscle potentials correlated with phasic contractions; (b) trains of discrete muscle potentials associated with tetanic tension development; (c) high-frequency long duration bursts of muscle potentials accompanying strong prolonged contractions. On cessation of the electrical activity the muscle relaxes rapidly, and; (d) high-frequency bursts of muscle potentials accompanying only the tension development of strong prolonged contractions. On cessation of the electrical activity the muscle preparation remains still in the contracted state from which it relaxes very slowly. 3. 3. Intact PRM-nerve-brain preparations in the absence of obvious sensory input show 2 distinct spontaneously occurring muscle activities i.e. those specified in 2(a) and 2(c). 4. 4. Section of the penis nerve proximal to identified peripheral neurons leads to a loss of the muscle activity mentioned in 2(c). Spontaneous phasic muscle activity, 2(a), was unaffected by the surgical treatment. 5. 5. Tactile stimuli of the penis caused a tetanic muscle activity, similar to 2(b), in the intact as well as in the semi-intact PRM preparation indicating a peripherally mediated reflexive behaviour. 6. 6. With the exception of the muscle behaviour mentioned in 2(d) it could be demonstrated that the spontaneously occurring muscle activities and the electrically induced muscle responses show characteristic similarities. The implications of these results for the contractile activities in the PRM are discussed.

1. 1. Long lasting synaptic inhibitions (LLI) were recorded in the silent cells LPL1 and RPL1 of Helix pomatia. 2. 2. During LLI the excitability of the cell was strongly reduced. 3. 3. The membrane conductance changes during LLI were characterized using the voltage-clamp technique. 4. 4. LLI in the silent cell LPL1 is mediated by a synaptically induced inhibition of the voltage-dependent inward Ca2+ -current.

1. 1. Simple learning phenomena have been investigated in the giant neurons of the oesophageal ganglion of the snail ( Helix pomatia ), according to the classical conditioning paradigm. 2. 2. In the course of the experiments, the stimulation of the nervus analis or n. pallialis sinister was paired with an intracellular stimulation, and the formation of conditional hypo- or hyperpolarization has been observed. 3. 3. Elaboration of the conditional response required numerous pairings (60–120), and lasted only for a relatively short period of time (15–60 min). 4. 4. It was presumed that the conditional response is produced by local changes of excitability in the cell membrane. The characteristics of these learned responses (number of pairings, duration of CR, etc.) are similar to Pavlovian summation phenomena.

1. 1. The intestinal absorption of l-proline, l-lysine and l-glutamic acid has been studied by the everted sac method in vitro using the intestine of two species of pulmonates molluscs. 2. 2. l-proline was actively absorbed by the intestine of Helix pomatia, whereas l-glutamic acid and l-lysine were not. 3. 3. No active transport of l-proline, l-lysine or l-glutamic acid were detected in the intestine of Arion empiricorum. 4. 4. The regional variation in l-glutamic acid absorption was studied for the slug intestine. The S/M ratio was the same on either anterior and posterior intestine. However, this amino acid was transported by a mechanism of mediated diffusion by the posterior intestine of the slug and by simple diffusion by the anterior one.

1. 1. The mapping of the axonal branches from the Br bursting neuron of Helix pomatia was made using electrophysiological and staining methods. 2. 2. Visceral nerve stimulation at increasing intensities produced graded antidromic spikes from, at least, 12 axon branches. 3. 3. Lucifer yellow-injected cells confirmed the existence of up to 26 axon branches in the visceral nerve. 4. 4. In the visceral ganglion a second burster styled Br' shared a number of electrophysiological and morphological properties in common with the Br cell. 5. 5. The two bursters contain similar elementary neurosecretory granules. 6. 6. Br sent an axon bundle in the visceral nerve and others within the axon bundle of the Br cell. 7. 7. This anatomical structure might be the basis of the slight and slow modulation exerted by Br upon Br', which resulted in phase relationship between the two bursters.

1. 1. The LPd7 giant neurone on the dorsal surface of the left pedal ganglion of Helix pomatia has been identified as a new element in the regulation of the pneumostome movements. 2. 2. The LPd7 cell forms pre- and postsynaptic connections with a number of central neurones in the suboesophageal ganglia and also has widespread peripheral connections. 3. 3. Upon weak tactile stimulation the LPd7 neurone receives excitatory inputs from the foot and mantle collar. 4. 4. Discharge of the neurone resulted in closing movement of the pneumostome, similar to the effect of parietal giant neurones triggering the withdrawal reaction of the animal. 5. 5. However, the parietal and LPd7 cells exert their efferent reaction via parallel neural pathways.

1. 1. On the dorsal surface of the suboesophageal ganglionic mass about 50 neurones were studied which responded with IPSPs to stimulation of the four main nerves. Ba2+ depressed or totally abolished the stimulus evoked IPSPs. 2. 2. All the IPSPs eliminated by barium administration had a null potential (EIPSP) at or very near to the potassium equilibrium potential (EK) and were not chloride dependent. 3. 3. The mechanism of the barium effect on the post-synaptic membrane was a blockage of the potassium conductance induced by the unknown transmitter mediating the transmission. 4. 4. Effect of Ba2+ on IPSPs differed from that of TEA+ because barium did not show cholinoceptive specificity. Barium was able to depress potassium conductance of the post-synaptic area evoked by any kind of transmitter except for a few cases where the unknown transmitter may have antagonized this effect of barium. 5. 5. A supposed pre-synaptic effect of Ba2+ could have realized in an enhanced transmitter release on a neurone where in presence of barium, both spontaneous and stimulus evoked inhibitory responses increased. This type of PSP showed a null potential very near to the chloride equilibrium potential (Ec1).

1. 1. Fibres of the identified neurons B1 to B3 in the buccal ganglia of Helix pomatia can be divided into three types according to their diameters. 2. 2. Electrical stimulation of nerves containing the different fibres induces typical fast depolarizations in the somata of neurons B1 to B3. The appearance of these depolarizations is strictly correlated to the fibre types. 3. 3. The depolarizations are interpreted as axonal action potentials.

1. 1. The mediodorsal bodies (MDB) of the pulmonate snails Lymnaea stagnalis and Helix pomatia as well as the ovotestis of H. pomatia contain ecdysteroids. 2. 2. After in vitro incubation of isolated MDB of H. pomatia considerable amounts of immunoreactive ecdysteroids (IE) were detected in the incubation medium whereas in MDB tissue the ecdysteroid content showed no striking increase compared with controls. 3. 3. Immunoreactive ecdysteroids released by MDB into the culture medium were analyzed by HPLC and RIA and identified as ecdysone. 4. 4. We conclude that MDB have the capability of ecdysone biosynthesis and release. Thus, for the first time a gland secreting ecdysone has been found in an invertebrate species other than arthropods.