Yu. V. Panchin

Pannexins and gap junction protein diversity

Abstract.Gap junctions (GJs) are composed of proteins that form a channel connecting the cytoplasm of adjacent cells. Connexins were initially considered to be the only proteins capable of GJ formation. Another family of GJ proteins (innexins) were first found in invertebrates and were proposed to be renamed pannexins after their orthologs were discovered in vertebrates. The lack of both connexins and pannexins in the genomes of some metazoans suggests that other, still undiscovered GJ proteins exist. In vertebrates, connexins and pannexins co-exist. Here we discuss whether vertebrate pannexins have a nonredundant role in animal physiology. Pannexin channels appear to be suited for ATP and calcium signaling and play a role in the maintenance of calcium homeostasis by mechanisms implicating both GJ and nonjunctional function. Suggested roles in the ischemic death of neurons, schizophrenia, inflammation and tumor suppression have drawn much attention to exploring the molecular properties and cellular functions of pannexins.

Control of locomotion in marine mollusc Clione limacina. I. Efferent activity during actual and fictitious swimming.

Summary1.The marine mollusc Clione limacina swims by making rhythmic movements (with a frequency of 1–5 Hz) of its two wings. Filming demonstrated that the wings perform oscillatory movements in the frontal plane of the animal. During both the upward and downward movements of the wing, its posterior edge lagged behind the anterior one, i.e. the wing plane was inclined in relation to the longitudinal axis of an animal. As a result of this inclination, the wing oscillations in the frontal plane produce a force directed forwards. 2.In restrained animals with the body cavity opened (a whole-animal preparation), the wing position, electrical activity in the wing nerve and activity of two identified efferent neurons (1A and 2A) were recorded during locomotory wing movements. There were two bursts of activity in the wing nerve during the locomotory cycle, the first one corresponding to the excitation of efferent neurons controlling the wing elevation, and the second one, to the excitation of efferent neurons controlling the lowering of the wing. Neurons 1A and 2A fired reciprocally at the beginning of the phase of elevating and lowering the wing, respectively. During excitation of one of the neurons, an IPSP appeared in its antagonist. 3. A pair of isolated pedal ganglia of Clione was capable of generating the locomotory rhythm (“fictitious swimming”). In fictitious swimming, as in actual swimming, there were two bursts of activity in the wing nerve per locomotory cycle, and the 1A and 2A neurons fired reciprocally. Homologous neurons from the left and right ganglia fired inphase. A single pedal ganglion was also capable of generating the locomotory rhythm. 4.Serotonin (10-5–10-6 M) increased the locomotor activity both in the whole-animal preparation and in the isolated pedal ganglia.

Control of locomotion in marine mollusc Clione limacina II. Rhythmic neurons of pedal ganglia

Summary1.Activity from neurons in isolated pedal ganglia of Clione limacina was recorded intracellularly during generation of rhythmic swimming. To map the distribution of cells in a ganglion, one of two microelectrodes was used to monitor activity of the identified neuron (1A or 2A), while the second electrode was used to penetrate successively all the visible neurons within a definite area of the ganglion. In addition, pairs of neurons of various types were recorded in different combinations with each other. Intracellular staining of neurons was also performed. 2.Each ganglion contained about 400 neurons, of which about 60 neurons exhibited rhythmic activity related to a swim cycle. These rhythmic neurons were divided into 9 groups (types) according to axonal projections, electrical properties and the phase of activity in a swim cycle. Three types of interneurons and six types of efferent neurons were distinguished. 3.Type 7 and 8 interneurons generated only one spike of long (50–150 ms) duration per swim cycle. Type 7 interneurons discharged in the phase of the cycle that corresponded (in actual swimming) to the dorsal movement of wings (D-phase). Type 8 interneurons discharged in the opposite phase corresponding to the ventral movement of wings (V-phase). With excitation of type 7 interneurons, an IPSP appeared in the type 8 interneurons, and vice versa. Neuropilar branching of these neurons was observed in the ipsilateral ganglion. In addition, they sent an axon to the contralateral ganglion across the pedal commissure. 4.Efferent neurons (i.e. the cell sending axons into the wing nerve) generated spikes of 1–5 ms duration. Type 1 and 3 neurons were excited in the D-phase of a swim cycle and were inhibited in the V-phase. Type 2 and 4 neurons were excited in the V-phase and inhibited in the D-phase. Type 10 neurons received only an excitatory input in the V-phase, while type 6 neurons received only an inhibitory input in the D-phase. 5. Type 12 interneurons were non-spiking cells, they generated a stable depolarization (“plateau”) throughout most of the V-phase. 6. Neurons of the same type from one ganglion (except for type 6) were electrically coupled to each other. There were also electrical connections between most neurons firing in the same phase of the cycle, i.e. between types 3 and 7, as well as between types 2, 4 and 8. Type 7 interneurons from the left and right ganglia were electrically coupled, the same was true for type 8 interneurons.

Control of locomotion in marine mollusc Clione limacina III. On the origin of locomotory rhythm

Summary1. Neurons from the isolated pedal ganglia of the marine mollusc Clione limacina were recorded from intracellularly during generation of the locomotory rhythm. Polarization of single type 7 or type 8 interneurons (which discharge in the D-and V-phases of a swim cycle, respectively) strongly affected activity of the rhythm generator. Injection of depolarizing and hyperpolarizing current usually resulted in shortening and lengthening of a swim cycle, respectively. A short pulse of hyperpolarizing current shifted the phase of the rhythmic generator. The same effect could be evoked by polarization of efferent neurons of types 2, 3 and 4 which are electrically coupled to interneurons. On the contrary, polarization of types 1, 6 and 10 efferent neurons, having no electrical connections with interneurons, did not affect the locomotory rhythm. 2. A number of observations indicate that type 7 and 8 interneurons constitute the main source of postsynaptic potentials that were observed in all the “rhythmic” neurons of the pedal ganglia. Type 7 interneurons excited the D-phase neurons and inhibited the V-phase neurons; type 8 interneurons produced opposite effects. 3. Tetrodotoxin eliminated spike generation in all efferent neurons of the pedal ganglia, while in interneurons spike generation persisted. After blocking the spike discharges in all the efferent neurons, type 7 and 8 interneurons were capable of generating alternating activity. One may conclude that these interneurons determine the main features of the swim pattern, i.e., the rhythmic alternating activity of two (D and V) populations of neurons. 4. Both type 7 and type 8 interneurons were capable of endogenous rhythmic discharges with a period like that in normal swimming. This was demonstrated in experiments in which one of the two populations of “rhythmic” neurons (D or V) was inhibited by means of strong electrical hyperpolarization, as well as in experiments in which interaction between the two populations, mediated by chemical synapses, was blocked by Co2+ ions. 5. Type 7 and 8 interneurons were capable of “rebound”, i.e. they had a tendency to discharge after termination of inhibition. 6. V-phase neurons exerted not only inhibitory but also excitatory action upon D-phase neurons, the excitatory action being longer than the inhibitory one. 7. The main experimental findings correspond well to the model of rhythm generator consisting of two half centres possessing endogenous rhythmic activity. The half-centres exert strong, short duration inhibitory and weak long duration excitatory actions upon one another. The behaviour of such a model is considered and compared with that of the locomotor generator of Clione.

Analysis of the Central Pattern Generator for Swimming in the Mollusk Clionea

Abstract: The pteropod mollusk Clione limacina swims by rhythmic movements of two wings. The central pattern generator (CPG) for swimming, located in the pedal ganglia, is formed by three groups of interneurons. The interneurons of the groups 7 and 8 are of crucial importance for rhythm generation. They are endogenous oscillators capable of generating rhythmic activity with a range of frequencies typical of swimming after extraction from the ganglia. This endogenous rhythmic activity is enhanced by serotonin. The interneurons 7 and 8 produce one prolonged action potential (about 100 ms in duration) per cycle. Prolonged action potentials contribute to determining the duration of the cycle phases. The interneurons of two groups inhibit one another determining their reciprocal activity. The putative transmitters of groups 7 and 8 interneurons are glutamate and acetylcholine, respectively. Transition from one phase to the other is facilitated by the plateau interneurons of group 12 that contribute to termination of one phase and to initiation of the next phase. Maintaining the rhythm generation and transition from one phase to the other is also promoted by postinhibitory rebound. The redundant organization of the swimming generator guarantees the high reliability of its operation. Generation of the swimming output persisted after the inhibitory input from interneurons 8 to 7 had been blocked by atropine. Activity of the swimming generator is controlled by a set of command neurons that activate, inhibit or modulate the operation of the swimming CPG in relation to a behaviorally relevant context.

Control of locomotion in marine mollusc Clione limacina. VI. Activity of isolated neurons of pedal ganglia.

SummaryIn the pteropodial mollusc Clione limacina, the rhythmic locomotor wing movements are controlled by the pedal ganglia. The locomotor rhythm is generated by two groups of interneurons (groups 7 and 8) which drive efferent neurons. In the present paper, the activity of isolated neurons, which were extracted from the pedal ganglia by means of an intracellular electrode, is described. The following results have been obtained: 1. Isolated type 7 and 8 interneurons preserved the capability for generation of prolonged (100–200 ms) action potentials. The frequency of these spontaneous discharges was usually within the limit of locomotor frequencies (0.5–5 Hz). By de- or hyperpolarizing a cell, one could usually cover the whole range of locomotor frequencies. This finding demonstrates that the locomotor rhythm is indeed determined by the endogenous rhythmic activity of type 7 and 8 interneurons. 2. Type 1 and 2 efferent neurons, before isolation, could generate single spikes as well as high-frequency bursts of spikes. These two modes of activity were also observed after isolating the cells. Thus, the bursting activity of type 1 and 2 neurons, demonstrated during locomotion, is determined by their own properties. Type 3 and 4 efferent neurons generated only repeated single spikes both before and after isolation. 3. The activity of the isolated axons of type 1 and 2 neurons did not differ meaningfully from the activity of the whole cells. Furthermore, in the isolated pedal commissure, we found units whose activity (rhythmically repeating prolonged action potentials) resembled the activity of type 7 and 8 interneurons. These units seemed to be the axons of type 7 and 8 interneurons. Thus, different parts of the cell membrane (soma and axons) have similar electric properties.

Control of locomotion in marine mollusc Clione limacina IV. Role of type 12 interneurons

Summary1. Type 12 interneurons in pedal ganglia of Clione limacina exerted a strong influence upon the locomotor generator during “intense” swimming. These neurons generated “plateau” potentials, i.e. their membrane potential had two stable states: the “upper” one when a neuron was depolarized, and the “down” one, separated by 30–40 mV. The interneurons could remain in each state for a long time. Short depolarizing and hyperpolarizing current pulses, as well as excitatory and inhibitory postsynaptic potentials, could transfer the interneurons from one state to another. 2. When the pedal ganglia generated the locomotory rhythm, type 12 neurons received an EPSP and passed to the “upper” state in the V2-phase of a locomotor cycle. They remained at this state until the beginning of the D1-phase when they received an IPSP and passed to the “down” state. The EPSP in type 12 neurons was produced by type 8d neurons, and the IPSP by type 7 neurons. 3. Type 12 neurons exerted inhibitory influences upon many neurons active in the V1 and V2 phases, and excitatory influences upon the D-phase interneurons (type 7). 4. The functional role of type 12 neurons was to limit the activity of neurons discharging in the V-phase of a locomotory cycle. In addition, they enhanced the excitation of the D-phase neurons and promoted, thus, the transition from the V-phase to the D-phase.

Control of locomotion in marine mollusc Clione limacina. X: Effects of acetylcholine antagonists

The swimming central pattern generator (CPG) of the pteropod mollusc Clione limacina is located in the pedal ganglia. It consists of three groups of interneurons (7, 8, and 12) which generate the rhythmical activity and determine the temporal pattern of the motor output, that is, phasic relations between different groups of motor neurons supplying dorsal (group 1 and 3 motor neurons) and ventral (group 2 and 4 motor neurons) muscles of the wings. In this work peripheral and central effects of acetylcholine (ACh) antagonists on the swimming control in C. limacina has been studied. The ACh antagonist atropine blocked transmission from the wing nerves to wing muscles, while gallamine triethiodide (Flaxedil), d-tubocurarine, and α-bungarotoxin did not affect the neuromuscular transmission. In the pedal ganglia, the ACh antagonists atropine and gallamine triethiodide blocked inhibitory postsynaptic potentials (IPSPs) produced by group 8 interneurons onto group 7 interneurons and motor neurons of groups 1 and 3. d-Tubocurarine and α-bungarotoxin did not affect IPSPs produced by group 8 interneurons. Although atropine and gallamine triethiodide blocked IPSPs produced by group 8 interneurons in antagonistic neurons, these drugs did not influence excitatory postsynaptic potentials (EPSPs) produced by group 8 interneurons onto group 12 interneurons. The main pattern of the swimming rhythm with an alternation of two phases of the swimming cycle persisted after elimination of inhibitory connections from group 8 interneurons to antagonistic neurons by the ACh antagonists. This suggests that there are redundant mechanisms in the system controlling C. limacinas swimming. This redundancy ensures reliable operation of the system and contributes to its flexibility.

Multiple effects of an identified proprioceptor upon gastric pattern generation in spiny lobsters

Abstract1.Using deafferented preparations of the stomatogastric nervous system of spiny lobsters (Panulirus interruptus), we stimulated the central soma of the Anterior Gastric Receptor neuron (AGR) and analyzed sensorimotor integration in the gastric central pattern generator during rhythm production.2.Driving AGR to spike tonically at lower frequencies (10–20 /s) accelerated the gastric rhythm, while higher frequencies (>30 /s) suppressed it.3.Shorter spike trains in AGR evoked phase-dependent resetting of the gastric rhythm. Repetitive trains could entrain rhythms to both longer and shorter cycle periods. Some pattern-generating effects are consistent with effects upon the lateral gastric neuron, an influential member of the gastric mill network.4.AGR affected the burst intensity of many of the gastric neurons in specific, complex ways. Some powerstroke motor neurons were excited because AGR activated excitatory, premotor interneurons (E cells). However, AGR also activated parallel, seemingly inhibitory inputs, whose mechanism remains unclear. Still other effects on motor neurons may be mediated partly by synaptic interactions within the network.5.AGR adjusts the timing, strength and coordination of bursts in the motor innervation of all three teeth of the gastric mill, and may act to optimize the force of chewing to different consistencies of food.

Non-synaptic interaction between neurons in molluscs

Abstract 1. Isolated pedal ganglia of the pteropodial mollusc, Clione limacina , generate a locomotory rhythm. In 30% of the pedal ganglia preparations the locomotory rhythm was not regular, i.e. the locomotor generator worked in “bursts” alternating with periods of low activity. 2. The “locomotor bursts” were caused by spontaneous activation of command neurons located in the pedal ganglia. 3. A single neuron was extracted from burst-generating preparations by means of the intracellular microelectrode and then its soma was put back, into the initial place between the ganglion cells. Twenty-five percent of the isolated neurons renewed the bursts-related changes in their activity after the insertion into the ganglion. The neurons which were originally excited during the “locomotor bursts” continued to be excited after isolation, while those which were inhibited continued to be inhibited during the bursts. 4. It is suggested that the command neurons controlling the locomotor generator can exert action on the target cells in the absence of morphological synapses.