Ionic mechanisms of depolarization responses in Helix pomatia neurons to glutamate application

Reversal potentials of transmembrane ionic currents induced by glutamate were determined in various D neurons ofHelix pomatia. Two types of neurons were found with mean reversal potentials of –10.6±1.2 and –40.0±0.6 mV. Neurons of the first group responded under ordinary conditions to glutamate application by a volley of action potentials. Neurons of the second group did not generate action potentials under the same conditions during glutamate application. With an increase in the dose of mediator the amplitude of D responses in these neurons increased only up to a certain limit, without reaching the critical depolarization level of the cell; a fall in the external chloride ion concentration led to a decrease in their reversal potential. The possible ionic mechanisms of glutamate-dependent depolarization responses of these groups of neurons are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 572–577, November–December, 1982.     

Adaptation in Helix pomatia neurons

• 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.

     

Ionic mechanisms of the transmembrane current evoked by injection of cyclic amp into identified Helix pomatia neurons

Ionic mechanisms of the transmembrane current evoked by injection of cyclic AMP into identified neurons ofHelix pomatia were investigated by the voltage clamp method. Injection of cyclic AMP into neurons RPa3, LPa2, LPa3, and LPl1 was shown to cause the development of a two-component transmembrane (cyclic AMP) current. The current-voltage characteristic curve of the early component is linear in the region from –40 to –90 mV; the reversal potential of the early component, determined by extrapolation, lies between –5 and +20 mV; the current-voltage characteristic curve of the late component also is linear and has a reversal potential between –55 and –60 mV. A decrease in the sodium concentration in the external medium from 100 to 25 mM led to a decrease in amplitude of the cyclic AMP current and to a shift of the reversal potential for the early component by 30–32 mV toward hyperpolarization. It is suggested that the early component of the cyclic AMP current in neurons RPa3, LPa2, LPa3, and LPl1 is associated with an increase in permeability of the neuron membrane chiefly for sodium ions, whereas the late component is correspondingly connected with permeability for potassium ions. Injection of cyclic AMP also caused the appearance of a transmembrane inward current in neuron LPa8, but it was independent of the holding potential and was unaccompanied by any change in membrane permeability. It is suggested that this current may be due to a change in the activity of the electrogenic ion pump.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 526–532, September–October, 1980.     

Mechanisms of up-regulation of single calcium channels by serotonin in Helix pomatia neurons

Action of serotonin (5-HT) on single Ca(2+) channel activity was studied in identified neurons of snail Helix pomatia. Only one type of Ca(2+) channels of 5 pS unitary conductance was determined under patch-clamp cell-attached mode. Kinetic analysis have shown a monotonically declining distribution of channel open times (OT) with mean time constant of 0.2 ms. The distribution of channel closed times (CT) could be fitted by double-exponential curve with time constants 1 and 12 ms. We established that 5-HT acts on Ca(2+) channel activity indirectly via cytoplasm. 5-HT prolonged the OT (up to 0.3 ms) and shortened the CT proportionally for both constants to 0.4 and 6 ms correspondingly. A conclusion is made that enhancement of Ca(2+) macro-current by 5-HT is determined by kinetic changes, increase of the number of active channels, and increase of the probability of OT. At the same time the transmitter did not affect the unitary channel conductance.     

Investigations of the ionic mechanisms of bursting activity in Helix pomatia neurons

Steady-state current-voltage characteristics of the membrane and ionic currents arising during changes in membrane potential in bursting neurons ofHelix pomatia were studied by the voltage clamp method. The steady-state current-voltage characteristics of the membrane were shown to have a nonlinear region. Replacement of sodium ions by Tris-HC1 ions in the external solution completely abolishes this nonlinearity. Hyperpolarization of the membrane under voltage clamp conditions leads to the development of an outward current which reaches a maximum and then is inactivated. This current has a reversal potential in the region of the potassium equilibrium potential. Depolarization of the membrane to the threshold value for excitation of uncontrollable regions of the axon hillock causes the appearance of a slow inward current. After reaching a maximum, the inward current falls to zero. A model of generation of waves in a bursting neuron is suggested.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 193–202, March–April, 1978.     

Multiplicity of pacemaker zones in Helix pomatia neurons

Intracellular microelectrode recordings from neurons ofHelix pomatia revealed several local zones of action potential generation both on the soma and on some of the branches of the neurons. Under certain conditions the activity of individual loci of the neuron membrane was synchronized to produce a normal action potential. It is suggested that the somatic membrane of neurons is heterogeneous in structure and consists of separate loci of an electrically excitable membrane, incorporating active and latent pacemaker zones. Neurons ofH. pomatia are characterized by two types of action potential with different triggering mechanisms: one (synaptic) type is generated under the influence of the EPSP, the other (pacemaker) arises through activation of endogenous factors for the neuron (pacemaker potentials). The interaction between synaptic and pacemaker potentials during integrative activity of the neuron is discussed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 88–94, January–February, 1973.     

Parvalbumin-immunoreactive neurons in the brain of Helix pomatia

Parvalbumin-immunoreactive material was detected in the central nervous system of the snail, Helix pomatia. Each ganglion investigated contained parvalbumin-immunoreactive neurons. The molecular weight of Helix parvalbumin-immunoreactive material as determined by Western blots is about 40 kilodaltons. ⁴⁵Ca²⁺ overlays showed that this protein binds Ca²⁺. In contrast to vertebrates, in Helix neurons parvalbuminlike material was not colocalized with the neurotransmitter gamma-aminobutyric acid (GABA).     

Presynaptic mechanisms for intensifying reactivity of command neurons in Helix pomatia defensive behavior under the effects of vasopressin analog

This study set out to investigate presynaptic mechanisms underlying reactivity of command neurons inHelix pomatia defensive behavior under the effects of desglycine-arginine vasopressin, a vasopressin analog. Peptide perfusion was found to intensify accumulated EPSP in command neurons during stimulation of the nerve without affecting the monosynaptic connection between primary sensory and command neurons. It was concluded that parallel pathways exist for the spread of excitation from the periphery to command neurons. Properties of such pathways are described and neurons with similar properties are identified. It is in these same cells that long-term changes in spontaneous EPSP induced by application of the peptide were noted.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 723–730, November–December, 1990.     

Identification of serotonin receptors on someHelix pomatia neurons

Four types of responses to iontophoretic application of serotonin were found in neurons of the ventral aspect of the visceral ganglion ofHelix pomatia. The responses differed in size, duration, latent periods, habituation to serotonin, and response to the action of serotonin antagonists (D-tubocurarine, tryptamine, neostigmine). Each type of response was evidently connected with a particular type of serotonin receptor. A scheme of distribution of the different types of serotonin receptors in the neurons of this region is drawn up.Institute of Psychiatry, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 3, pp. 300–305, May–June, 1978.     

Sites of action potential generation in Helix pomatia neurons

The site of action potential generation in unipolar snail neurons was identified by stimulating neurons isolated together with the initial portion of the process from the neuropile. Stimulation consisted of a sinusoidal from electrical current passed along the soma-axonal axis in saline solution. No low threshold sites of action potential generation were found in 80% of test neurons using this technique. Spontaneous activity was determined by the operation of one dominant site on the neuronal process. Antidromic activation of the soma by axonal action potentials (even with simultaneous hyperpolarization of the soma) induced somatic potentials more successfully than direct somatic depolarization by the current flowing through the solution.Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow. Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 90–98, January–February, 1988.     

Effect of x-rays on the pacemaker neurons of Helix pomatia

The effect of superlethal doses of ionizing radiation on exciting and electrical properties of giant neurons of the central nervous system of Helix pomatia has been investigated. At early times following irradiation the excitability does not significantly change whereas the membrane potential, resistance and pump-induced hyperpolarization increase. At later times, a stabilization of these parameters is followed by a diminution of resistance, a decrease of membrane potential and pump-induced hyperpolarization, and even the neuron death.     

Acetylcholine responses of identified neurons in Helix pomatia--I. Interactions between acetylcholine-induced and potential-dependent membrane conductances

The influence of potential-dependent membrane conductances on amplitude and time course of acetylcholine (ACh) responses was studied. The investigations were performed on the identified neurons B1 and B3 of the buccal ganglion of Helix pomatia. The neurons B1 and B3 were depolarized by ACh. The depolarization was accompanied by a decrease of membrane resistance. An inward rectification occurring negative to the resting membrane potential (RMP) reduced the amplitude of the ACh depolarizations. An outward rectification occurring positive to the RMP consisted of two parts and ceiled the ACh responses. The early outward current reduced the amplitude and modified the time course of ACh responses. Local responses or axonal action potentials increased the amplitude of the ACh depolarizations.     

Peculiarities of orthodromic inhibition in pacemaker neurons in Helix pomatia

We used the intracellular recording method to study the effect of a group of nerves in the visceral complex on the activity of a pacemaking giantneuron located in the peripheral part of the visceral ganglion in a mollusk. Single excitations of the left and right pallial, the intestinal, and the anal nerves with electrical stimuli evoked similar responses, consisting of phases of rapid depolarization (duration 100 msec, amplitude 3–5 mV) and slower hyperpolarization (duration 400 msec, amplitude 5–8 mV). The excitation also had an aftereffect, which was expressed in inhibition of the background activity of the pacemaker for several seconds. The most interesting of the functional characteristics of that response was the effects of summation. With rhythmic excitation by stimuli of low frequency (0.5–1 c/sec) the result of summation was general hyperpolarization of the neuron and the appearance of giant inhibitory postsynaptic potentials (IPSP's) with an amplitude of 12–16 mV. With higher frequency of excitation (2–3 c/sec and upward) we observed depolarization replacing the hyperpolarization of the neuron, but IPSP's of large amplitude were absent. At the end of rhythmic excitation prolonged inhibition of the pacemaker's activity, lasting some minutes, occurred in all cases. This article discusses the possible mechanisms of that type of prolonged inhibition of the pacemaker's activity, the origin of the phases in biphasic responses, and the reasons for differences in the course of summation of biphasic postsynaptic potentials.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 426–433, July–August, 1971.     

Possible interaction between synaptic and pacemaker mechanisms of electrical activity in bursting neurons of Helix pomatia

Membrane hyperpolarization induced by short pulses of inward current, by stimulation of the anal nerve, which leads to the appearance of a long IPSP in the neuron, and developing during the appearance of spontaneous IPSPs in the neuron was investigated in neuron RPa1 ofHelix pomatia. Short-term hyperpolarization of the neuron membrane by an inward current (10 msec) led to the development of self-maintained (regenerative) membrane hyperpolarization lasting several seconds. The amplitude and duration of regenerative hyperpolarization increased with an increase in amplitude and duration of the pulse of inward current. The time course of IPSPs arising spontaneously in the neuron and in response to stimulation of the anal nerve was similar to that of regenerative hyperpolarization evoked by a pulse of inward current. It is suggested that regenerative hyperpolarization associated with activation of endogenous mechanisms of regulation of the bursting activity of the neuron may be due not only to short-term membrane hyperpolarization of the test neuron by the electric current, but also to hyperpolarization occurring during IPSP generation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 67–74, January–February, 1981.     

Interaction of serotonin and leu-enkephalin on the habituating central neurons of Helix pomatia L. in situ and in vitro

1. Habituating neurons (a, b and c) of Helix pomatia reacted to the serotonin (10(-5)-10(-4)M) with depolarization evoking oscillatory waves and burst firing at the range of -35 to -55 MP values. 2. Isolated habituating cells were hyperpolarized by serotonin and failed to generate membrane oscillation or bursting pattern. 3. Only the isolated habituating neurons reacted to the application of leu-enkephalin (10(-5)-10(-4)M) by depolarization. 4. Neither membrane oscillation nor burst firing were evoked by leu-enkephalin. 5. On the cells a, b and c leu-enkephalin modulated the serotonin effect through cyclic 3',5'-AMP system both in situ and in vitro. 6. The membrane oscillation and burst firing of the habituating cells are connected to the regulation of various rhythmic processes including pneumostoma movements.     

Pre- and postsynaptic effects of eugenol and related compounds on Helix pomatia L. neurons

We showed how eugenol blocks the synaptic transmission and gave a possible interpretation how it inhibits the excitation-contraction coupling that several authors described previously. Eugenol acts both in the pre- and postsynaptic side of the neurons. It blocks the Ca2+-currents, decreases the membrane potential of the neurons, increases the inward resistance and decreases the GABA, ACh and glutamate evoked excitatory responses in submillimolar concentration.     

Ionic mechanisms of histamine-induced responses in guinea pig intracardiac neurons

Histamine, released from mast cells, can modulate the activity of intrinsic neurons in the guinea pig cardiac plexus. The present study examined the ionic mechanisms underlying the histamine-induced responses in these cells. Histamine evokes a small membrane depolarization and an increase in neuronal excitability. Using intracellular voltage recording from individual intracardiac neurons, we were able to demonstrate that removal of extracellular sodium reduced the membrane depolarization, whereas inhibition of K+ channels by 1 mM Ba2+, 2 mM Cs+, or 5 mM tetraethylammonium had no effect. The depolarization was also not inhibited by either 10 microM Gd3+ or a reduced Cl- solution. The histamine-induced increase in excitability was unaffected by K+ channel inhibitors; however, it was reduced by either blockage of voltage-gated Ca2+ channels with 200 microM Cd2+ or replacement of extracellular Ca2+ with Mg2+. Conversely, alterations in intracellular calcium with thapsigargin or caffeine did not inhibit the histamine-induced effects. However, in cells treated with both thapsigargin and caffeine to deplete internal calcium stores, the histamine-induced increase in excitability was decreased. Treatment with the phospholipase C inhibitor U73122 also prevented both the depolarization and the increase in excitability. From these data, we conclude that histamine, via activation of H1 receptors, activates phospholipase C, which results in 1) the opening of a nonspecific cation channel, such as a transient receptor potential channel 4 or 5; and 2) in combination with either the influx of Ca2+ through voltage-gated channels or the release of internal calcium stores leads to an increase in excitability.