Regeneration of central and peripheral synaptic connections in the locomotor system of the pteropod molluscClione limacina

The neural network underlying rhythmic wing movements in the molluscClione limacina is well-studied. Two different groups of motoneurons innervate two distinct groups of wing muscles. The locomotor rhythm generated in the left and right pedal ganglia is synchronized by interneurons. When the axons of the locomotor motoneurons are crushed, numerous fine neurites sprout towards the denervated muscles and reach them in 8–15 days. At this stage motoneurons project to and synapse on not only correct but equally incorrect muscle targets. After 2 weeks of regeneration the number of incorrect neurites and synaptic connections begins to decrease and following 1.5–2 months all incorrect connections are eliminated, incorrect axons are withdrawn and the behavioral deficit is compensated. In this study the regeneration of interneurons and the growth profiles of inter- and motoneurons were also studiedin vitro. Two individually isolated pedal ganglia were co-cultured in three different configurations: a) the wing nerve stump from one ganglion was fixed against the commissural stump from another ganglion; b) the wing nerve stumps were fixed against each other; c) the commissural stumps were fixed against each other. Under the above experimental conditions we found that the interneurons were able to cross only the contact between two commissural stumps, and in this case found their original targets, restored correct connections and synchronized the rhythm in two pedal ganglia. In contrast, motoneurons were able to cross all types of contacts.     

Neuronal mechanisms of defense reaction to cutaneous nerve stimulation

A two-stage defense response was induced in the freshwater snailPlanorbarius corneus by stimulating the head. It consisted of the shell being rapidly lowered over the head and foot followed by the snail gradually withdrawing into its shell. These movements are performed by contracting the columellar muscle. Motoneurons of the columellar muscle were identified in the cerebral, parietal, and pedal ganglia. Stimulating the lip nerve was found to induce 2-stage excitation in motoneurons (responsible for the 2-stage muscular contraction) in preparations of central nervous system with the columellar muscle attached. The same 2-stage motoneuronal excitation can also occur spontaneously. This implies that defense reaction in the cell is at least partially a "fixed action" underlying a central mechanism or program and triggered by afferent stimuli. Activation of the central mechanism of defense response can also induce depolarization in certain columellar muscle motoneurons. This points to the existence of a feedback between neurons of the central mechanism and motoneurons.Institute of Research on Transmission of Information, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 786–795, November–December, 1990.     

Chemical sensitivity of Limnaea stagnalis neurons and their responses to synaptic stimulation

Responses of nerve cells to puncture, to touching the surface of the mollusk leg, osmotic stimulation, and extracellular microiontophoretic injection of acetylcholine, noradrenalin, serotonin, atropine, and propranolol were recorded intracellularly in the right parietal, left pedal, and visceral ganglia of the unisolated circumpharyngeal ring ofLimnaea stagnalis. Selective sensitivity of the neurons to the biologically active substances was observed. Results indicative of the functional differences between the various ganglia and of their neurochemical organization were obtained. Selective blocking of the unit responses to puncture of the surface of the mollusk leg by atropine or propranolol suggests that different forms of excitation reaching the central neurons evoked different and specific neurochemical processes on their subsynaptic membranes which can retain the essential informativeness of the widely different afferent volleys converging on a single nerve cell.I. M. Sechenov First Moscow Medical Institute. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 510–518, September–October, 1973.     

Serotonin-induced changes in the action of functionally distinct neurons in Helix pomatia

The effects of serotonin on the amplitude of summated EPSP in interneurons and on the duration of action potentials in sensory neurons, interneurons, and motoneurons involved in avoidance behavior were investigated in functionally distinct neurons isolated from theHelix pomatia nervous system. The duration of action potentials in sensory neurons was found to increase under the effects of serotonin (and this could underly the rise in EPSP amplitude), although that of interneuron and motoneuron spikes did not change. The functional significance of selective neuronal response to a rise in serotonin concentration is discussed, together with the mechanics underlying such effects.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 316–322, May–June, 1987.     

Electrophysiological study of serotoninergic neuron Cl in the pteropod mollusk Clione

Functional characteristics of cerebral serotoninergic neuron Cl, axons of which terminate at the buccal ganglia [7], were investigated in the pteropod molluskClione. Stimulating neuron Cl induced activation of the feeding rhythm generator located in the buccal ganglia — an effect arising after a long latency and persisting for some tens of seconds once stimulation had ended. Neuron Cl receives feedback from buccal ganglion cells and this brings about periodic modulation in ganglia activity during the generation of feeding rhythm. Activity of neuron Cl is correlated with operation of the locomotor rhythm generator located in the pedal ganglia. The firing rate of Cl neurons increased upon activation of the locomotor generator (whether spontaneous or induced by stimulating certain command neurons). The correlation found between workings of the locomotor generator and activity of Cl neurons is thought to be one of the manifestations of feeding synergy involving simultaneous activation of the locomotor and buccal apparatus.Institute for Research on Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 18–25, January–February, 1991.     

Neural control of heartbeat in the pteropod mollusk Clione limacina

The heart of the pteropod molluskClione limacina is innervated by the median nerve arising from the left abdominal ganglion. Five neurons sending axons to the heart have been identified in theClione central nervous system with retrograde cobalt or Lucifer yellow staining. Neuron H1 located in the left pedal ganglion produced an excitatory effect on heart beat. Stimulation of three neurons, H2–H4, situated in a compact group in the medial region of the left abdominal ganglion, led to inhibition of cardiac contraction, while H5, located in the caudal region of the left abdominal ganglion, did not affect heart beat. The activity of efferent cardiac neurons (ECN) was found to be related to the operation of the locomotor rhythm generator. Spontaneous or reflex depression of the latter was found to inhibit neuron H1 and activate units H2–H4. The behavior of these ECN accounts for the positive correlation between heart operation and locomotor activity inClione limacina.Institute of Research on Information Transmission, Academy of Sciences of the USSR, Moscow, M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 185–192, March–April, 1989.     

Evoked activity of spinal neurons in the early period after sciatic nerve division

The character of dorsal horn motoneurons and interneurons evoked by stimulation of the dorsal root, and activity of Renshaw cells in response to stimulation of the ventral root were studied in albino rats in the lower lumbar segments of the spinal cord 5 days after sciatic nerve division. A significant increase in the mean amplitude of excitatory postsynaptic potentials of motoneurons was observed on the side of division of the nerve. No significant change in membrane potential and in the threshold of appearance of the action potential of these motoneurons took place. The mean number of action potentials and the duration of discharge of the Renshaw cells and dorsal horn interneurons likewise were not significantly changed.Dnepropetrovsk Medical Institute, Ukrainian Ministry of Health. Translated from Neirofiziologiya, Vol. 24, No. 3, pp. 306–314, May–June, 1992.     

Responses of descending interneurons to stimulation of wind head receptors in locust

Responses of descending interneurons of the thoracic nerve chain ofLocusta migratoria L. to wind stimulation of the head receptors concerned with the activation of the insect's flight were investigated by means of extracellular microelectrode recordings from their axons. Altogether 11 types of descending effects transmitted by these interneurons to neurons of the segmental ganglia were detected. Ipsilateral and contralateral wind stimulation of the receptors can not only activate hitherto silent interneurons but also effectively modify the character of discharges from spontaneously active, discharging neurons. This influence may be either excitatory (increased spontaneous firing rate) or inhibitory (decreased rate or total abolition of spontaneous discharges). Some descending interneurons give rise not only to on-responses but also to typical off-responses to stimulation. The possible functional role of some of the observed effects in the mechanisms triggering and maintaining the insect's flight is discussed.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Biological Research Institute, Hungarian Academy of Sciences, Tihany. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 602–610, November–December, 1973.     

Electrogenesis in molluscan giant neurons after treatment with ribonuclease

Electrical activity of identified and unidentified neurons ofHelix pomatia was recorded intracellularly after incubation of the ganglia for 0.5, 1, and 2 h in ribonuclease (RNAse) solution. Histochemical and cytophotometric analysis showed that after 30 min no RNA could be found in any of the neurons studied or in the glia and neuropil of the ganglia. At these times of incubation action potentials and spontaneous and evoked postsynaptic potentials could be recorded in all the neurons studied. The response to microapplication of acetylcholine to the neuron soma or to its direct electrical stimulation remained the same as in the control. In the identified neurons the addition of RNAse and its subsequent action did not alter their electrogenesis even after incubation for 2 h. It is concluded that electrogenesis is not directly dependent on the RNA content in the neuron. The primary role of RNA is considered to be participation in the synthesis of the specific proteins responsible for synaptic transmission.I. M. Sechenov Institute of Physiology, First Medical Institute, Moscow. Faculty of Psychology, Moscow State University, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 423–428, July–August, 1972.     

Influence of the pteropod mollusk pedal ganglia locomoter system on anatomically isolated neurons

It was established during experiments on pedal ganglia generating locomotor rhythm isolated fromClione limacina, a pteropod mollusk, that this rhythm was irregular in 30% of preparations; i.e., the locomotor generator worked in bursts which alternated with periods of regular activity. Locomotor bursts were produced by excitation in command neurons located within the pedal ganglia. Single neurons were extracted from the ganglia in these preparations generating locomotor bursts by means of an intracellular microelectrode; their somata were then placed in their original sites amongst the ganglia cells. A total of 35 neurons were isolated showing changed activity during bursts. Nine of these cells renewed their erratic activity (linked to locomotor bursts) following reinsertion into the ganglion. Neurons which had initially shown an excitatory pattern during bursts continued to be excited; the same was true for inhibitory types. These observations indicate that the command neurons governing generator operation can act on target cells when morphological contact with them has been suppressed.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow; M. V. Lomonosov State University. Moscow. Translated from Neirofiziologiya, Vol. 18, No. 6, pp. 756–763, November–December, 1986.     

Functional properties of interneurons of the masticatory reflex

Interneurons of the supratrigeminal nucleus, transmitting effects from the sensory and motor branches of the trigeminal nerve to motoneurons of the muscles of mastication were investigated. Two groups of interneurons with different functional connections were found. The first group (A) contains neurons excited during stimulation of the sensory branches and the motor nerve to the digastric muscle (A₁), neurons excited during stimulation of sensory branches and high-threshold afferents of the motor nerve to the masseter muscle (A₂), and neurons excited only by low-threshold afferents of the motor nerve to the masseter muscle (A₃). Neurons of the second group (B) were activated only by sensory fibers of the trigeminal nerve. It is postulated that interneurons of group A transmit inhibitory effects to motoneurons of antagonist muscles of the lower jaw. Group B interneurons participate in the transmission of excitatory influences to motoneurons of the digastric muscle.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 150–157, March–April, 1972.     

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.     

Types of locomotion in ophiurans

Motion pictures were taken of the locomotion of two species of ophiurans living in the Sea of Japan:Ophiura sarsi vadicoa Djakonov andAmphipholis kochii Lutken.Ophiura sarsi was found to move with the aid of paddling movements of two pairs of arms: The fifth arm (passive) pointed backward. Ophiurans of this species do not use their ambulacral feet. Three main types of locomotor movements were distinguished inAmphipholis kochii, First, locomotion by the "breast stroke" method, in which one arm (the leading) points forward, two point to the side, and two backward. The two side arms are periodically carried forward, after which the disk and the remaining arms are moved with their aid. In this method waves of flexion and extension of the segments spread along the side arms. Second, displacement by pulling with the leading arm pushing with the hind arms, and third, movement by stepping movements of the ambulacral feet. These three methods of locomotion can be used either independently or in various combinations with each other. The ambulacral feet also provide the link between the active arms and the supporting surface by means of which the ophiurans can move forward.Institute of Oceanology, Academy of Sciencs of the USSR, Moscow. Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Moscow State University. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 521–528, September–October, 1976.     

Postural interneurons in the abdominal nervous system of lobster

The multisegmented abdomen of crayfish and lobster assumes a variety of postures as components of different behavioral acts. Experimentally these postures can be maintained by activating any of a number of premotor positioning interneurons. The pathways by which the motor output in two or more segments is coordinated were here investigated for a small group of identified postural interneurons whose somata lie in the 2nd abdominal ganglion (A2). Stimulation of all postural interneurons examined evokes a motor output in other abdominal ganglia through which the axon of the neuron passes as well as in the ganglion of origin (ganglion containing the neuron's cell body). The spread of motor excitation away from the originating ganglion occurs via two general pathways. In the first pathway connections to postural motoneurons are made directly by processes of the postural interneuron which pass into ganglia distal to the originating ganglion. Examples of this are shown for two flexion producing interneurons (FPIs) 201 and 301. Each of these FPIs makes monosynaptic connections with motoneurons in A2 and with a homologous set of motoneurons in A3. All postural interneurons fired a set of corollary discharge interneurons (CDIs) whose activities were recorded from the abdominal connectives. Two FPIs, 202 and 301, and a third interneuron, 503, produced motor outputs in ganglia to which they did not project. The motor specificity established in A2 by stimulation of FPIs 202 and 301 (whose axons pass caudally) was preserved in more rostral ganglia, such as A1. Therefore, different sets of CDIs can be specifically recruited to spread the same motor program that is initiated in the originating ganglion to ganglia that do not receive projections from the stimulated postural interneuron. CDIs, in addition, have the capacity to elicit motor programs in distal ganglia that are markedly different from that expressed in the ganglion of origin. For example, although 503 produced an inhibitory output in the abdominal ganglia that it innervated (A1 and A2), a flexion response was generated by it in more caudal ganglia. The caudal flexion response was mediated in part through a monosynaptic activation of FPI 201 and through other unidentified CDIs. Thus, the interneuronal circuitry for postural control is composed of numerous components, some of which have regional control over different portions of the abdominal nerve cord. Depending upon the required movement, select components are coactivated, either serially or in parallel, to effect a variety of spatially distinct positions.     

Morphological properties of neuron RPD1 in lymnaea stagnalis and its involvement in processing of polymodal sensory information

Characteristics of the right partietal ganglion neuron of the gastropod molluskLymnaea stagnalis (RPD1) were investigated by intracellular staining with Lucifer Yellow. Branches proceeding from this neuron are found in nerves of the right parietal, visceral, cerebral, and pedal ganglia of the central nervous system (CNS) as well as along peripheral nerves. Concentrations of RPD1 neurite branches were revealed in the distal, right parietal, and pleural ganglia. Electrophysiological techniques were used to investigate neuronal response to adequate stimulation of different sensory organs and cutaneous coverings (tentacles, lips, mantle, and so on). It was found that RPD1 has wide-ranging polymodal sensory input and responds to adequate stimulation of mechano-, chemo-, and photoreceptors of cutaneous coverings of the head of mantle. Stimulus application produced either subthreshold summated EPSP or a spike response in the neuron. Response in this unit during blockade of chemical synaptic transmission at peripheral and central regions of the nervous system is analyzed.A. A. Ukhtomskii Physiological Institute, A. A. Zhdanov State University, Leningrad. Translated from Neirofiziologiya, Vol. 20, No. 6, pp. 785–793, November–December, 1988.     

Involvement of calcium-binding membrane components in neurophysiological mechanics of habituation in Helix pomatia

Dynamics of binding between calcium and hydrophobic membrane components were investigated in vivo in identified neurons ofHelix pomatia while producing habituation to tactile stimuli using a fluorescent chlortetracycline probe technique. A decline in the concentration of membrane-bound calcium (Ca _b ²⁺ ) and likewise in the intensity of electrophysiological response was found in the "command" neurons of defensive behavior when applying a train of stimuli. An increase in Ca _b ²⁺ was noted in the sensory neuron studied and in the spiracle motoneurons. It proved difficult to produce habituation in these cells fulfilling standard electrophysiological criteria. Hydrophobe-hydrophil transfer of calciumbinding molecules is thought to accompany production of habituation in nerve cells.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 605–612, September–October, 1989.     

Influence of opioid peptides on nerve tissue in vitro

The influence of opioid peptides (gamma- and beta-endorphins, leu- and met-enkephalins, as well as certain synthetic analogs of enkephalin) was investigated on organotypic cultures of rat spinal and sympathetic ganglia. The cellular composition and size of the zone of growth were evaluated on the basis of intravital observations and an analysis of the specimen obtained using the method of impregnation, according to Holmes and the detection of catecholamines with glyoxylic acid. It was established that under the action of all the investigated substances that possess high affinity for opiate receptors, growth of the neurites from an explant was enhanced, and the number of glial and fibroblastoid cells in the growth zone was increased. The effect was observed most distinctly on a model of sympathetic ganglia. The tested compounds exhibited a significant growth-stimulating effect in the range of concentrations 10^–8–10^–14 M. The maximum size of the growth zone of the explants of the sympathetic ganglia in the case of a mean effective concentration of the peptides 10^–10 M by the third to fifth day of culturing was approximately 2–2.5 times this value in the control. The reaction was similar to the response of the nerve cells to nerve growth factor, used as a standard. Thus, the opioid peptides exhibit a pronounced growth effect on the structures of the nerve tissue under conditions of culture. It is suggested that this group of compounds, together with its currently well-known functions, may play a definite role in processes of the development and regenera-of nerve tissue.Institute of Experimental Cardiology, All-Union Cardiologic Science Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 550–557, July–August, 1985.     

Inhibitory effects of reticulospinal fibers of the lateral funiculus on neurons of thoracic spinal reflex pathways

Experiments on anesthetized cats with partial transection of the spinal cord showed that reticulo-spinal fibers in the ventral part of the lateral funiculus participate in the inhibition of polysynaptic reflexes evoked by stimulation of the ipsi- and contralateral reticular formation. The reticulo-fugal wave in the ventrolateral funiculus evoked comparatively short (up to 70 msec) IPSPs in some motoneurons of the internal intercostal nerve investigated and at the same time evoked prolonged (up to 500 msec) inhibition of IPSPs caused by activation of high-threshold segmental afferents. This wave also led to the appearance of IPSPs in 14 of 91 (15.5 %) thoracic spinal interneurons studied. The duration of these IPSPs did not exceed 100 msec; meanwhile, segment excitatory responses of 21 of 43 interneurons remained partly suppressed for 120–500 msec. It is concluded that the inhibitory action of the lateral reticulo-spinal system on segmental reflexes is due to several synaptic mechanisms, some of them unconnected with hyperpolarization of spinal neurons. The possible types of mechanisms of this inhibition are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 162–172, March–April, 1978.     

Excitation and inhibition in the visual center of Rana temporaria

Analysis of postsynaptic unit responses in the visual center ofRana temporaria showed that optic nerve fibers with high and low conduction velocities usually converge on a single neuron of the tectum opticum (TO). In response to stimulation of the optic nerve a complex depolarization potential consisting of 3 (or possibly 4) EPSPs was recorded in one group of neurons; these EPSPs were probably generated through excitation of several groups of afferent fibers. Either an increase or a decrease in the EPSPs can be observed in the TO neurons in response to repetitive and paired stimulation of the optic nerve. Postsynaptic inhibitory responses of some TO neurons, probably of direct and recurrent origin, are discussed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 637–643, November–December, 1971.     

Restoration of retino-tectal connections in frogs during regeneration of the optic nerve

At various times after unilateral division of the optic nerve in the frogRana temporaria L. evoked potentials in response to electrical stimulation of the optic nerve were investigated in a segment distal to the site of operation, spike activity was recorded from endings of regenerating and intertectal axons when stimuli of different shapes were placed in the field of vision, and the distribution of axonal bulbs of growth by depth in the tectum mesencephal was studied electron-microscopically. During regeneration of the axons the responses of the retinal ganglionic cells to visual stimuli retained most of their individual features. Myelinated axons of the retinal ganglionic cells regenerate first (starting on the 21st day after operation). Myelination of these fibers lags significantly behind their growth and is complete more than 100 days after the operation. Unmyelinated axons of the retinal ganglionic cells grow up toward the tectum mesencephali after myelinated axons (80 or more days after the operation). Axonal bulbs of growth in the initial periods after the operation are located close to the pial surface and the level of spread of the myelinated axons of the retinal ganglionic cells differs significantly from their normal level of localization. Intertectal connections persist after division of the nerve and are activated by visual stimuli during regeneration of the axons of the retinal ganglionic cells. Connections were found mainly between intertectal fibers terminating superficially and retinal ganglionic cells belonging to class 1 and 2 detectors. Axons of the retinal ganglionic cells grow up toward the caudal region of the tectum mesencephali later than toward the rostral region.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 611–620, November–December, 1973.