Morphological characteristics of chemosensory,visual, and statocyst pathways in the snailHelix lucorum

The following structural characteristics of the chemosensory, visual, and vestibular pathways of the snail (Helix lucorum) were demonstrated by using a variety of histological techniques. Large and small neurons of the tentacle ganglion, the bipolar cells of the olfactory nerve, and a proportion of optic tentacle bulb chemoreceptors within the olfactory nerve all send their processes to the CNS of the mollusk. Here they are divided up into numerous bundles of fibers in the neuropil of the ipsilateral cerebral ganglion. They are joined by processes from the central nervous system put out by all neurons of the protocerebrum and the cluster of cells of the commissural section of the metacerebrum. Ocular receptors do not send processes down below the enlargement of the upper optic nerve. This enlargement is also the site where processes from cells within the CNS and the nerve itself terminate. An area of arborization of processes from the visual pathway cells is located in the neuropil of the pleural portion of the metacerebrum. Hair cells of statocysts put out processes to the cerebral ganglion, whence axons of small metacerebral neurons extend towards the organ of balance. Some processes from vestibular pathway cells form an arborization zone at the ipsilateral cerebral ganglion, while others pass through the cerebral commissure to form their area of arborization in the contralateral ganglion. Processes from vestibular and visual pathway cells arborize in exactly the same area.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 7–16, January–February, 1986.     

Low-threshold region of action potential generation in the somatic membrane of molluscan neurons

Heterogeneity of the somatic membrane of subesophageal ganglionic neurons ofHelix lucorum was studied by extracellular electrical stimulation. A sinusoidal current was applied through electrodes movable relative to the preparation. The threshold of action potential generation was shown to depend on the direction of the extracellular current, so that the presence of functional heterogeneity could be demonstrated in the cell soma.Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow. Research Institute for Biological Testing of Chemical Compounds, Ministry of the Medical Industry of the USSR, Staraya Kupavna, Moscow Region. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 15–19, January–February, 1985.     

Detection and analysis of recurrent inhibition of firing motoneurons in man

During regular firing of "small" motor units, activated during weak voluntary contraction of the human soleus muscle, thick efferent fibers of n. tibialis were stimulated (a small M response was evoked, in which the small units did not participate). Peristimulus histograms of potentials of single motor units were constructed and the effect of stimulation on interspike interval duration was analyzed. The firing rate of the motor units was 4.5–7.6 spikes/sec. Stimulation of the nerve led to a sharp decrease in probability of their discharge or even complete temporary cessation of firing, i.e., it had a well marked inhibitory effect (lasting 10–20 msec). The latent period of inhibition (35–40 msec) was only a little longer than the latent period of the monosynaptic reflex of the soleus muscle. The effect of an inhibitory volley on duration of the interspike interval of the motor units depended on the time when the volley arrived during the interval. Lengthening of the interval was observed only if the inhibitory volley arrived in the second half or at the end of the interval. It is concluded that inhibition of firing of small motor units is due to Renshaw cells, activated on stimulation of axons of large motoneurons. The efficiency of a short (compared with the duration of the interspike interval) inhibitory volley reaching a motoneuron firing at low frequency characteristic of its adequate activation, is discussed.Institute for Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 88–96, January–February, 1984.     

Regeneration of pedal ganglion neurons in the sea butterfly Clione limacina

In the pedal ganglia ofClione limacina the growth of neurites is traced in motoneurons after transection of the wing nerve and in interneurons after transection of the pedal commissure. Neurons were stained intracellularly with Lucifer yellow. In the motoneurons the neurites growing from the transected end of the axon and from the neuron soma spread to all nerve trunks departing from the ipsi- and contralateral ganglia. For nerve transection in the intact mollusk, wing movements were restored 10 days after the operation. In the interneurons the growing neurites branched within the pedal ganglion or spread to the cerebral ganglia, but they never reached the periphery.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 449–455, July–August, 1985.     

Contribution of a humoral factor to postsynaptic sensitization in heterosynaptic facilitation

It was shown that heterosynaptic facilitation develops in the cerebral ganglia giant neurons of the freshwater gastropod molluskPlanorbis corn eus due to diffuse neurohumoral influences on pre- and postsynaptic structures and not local synaptic action on presynaptic mechanisms. It was also found that n-cholinergic synaptic mechanisms come under this facilitatory influence. Serotonin is the source of facilitation in neurons of bothPlanorbis corneus cerebral ganglion and those of the aplysia abdominal ganglion. Seeing that: a) conditioning stimuli facilitate the effects produced by iontophoretic acetylcholine application, as well as n-cholinergic synaptic transmission and b) the amplitude of EPSP and acetylcholine potential increase 4–6 times during facilitation when the input impedance of the post-synaptic membrane is increased by just 20%, it was deduced that the postsynaptic membrane of the giant neuron makes a significant contribution to heterosynaptic facilitation of the sensitization of n-cholinergic receptors. The part played by n-cholinergic receptors of the postsynaptic membrane in heterosynaptic facilitation and conditioned reflex habituation is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 250–259, March–April, 1986.     

Characteristics of heterosynaptic facilitation in giant neurons of the cerebral ganglion of Planorbis corneus

Experiments on giant neurons of the cerebral ganglion of the molluskPlanorbis corneus showed that heterosynaptic facilitation even if evoked by a single uncombined stimulation of the pallial nerve, is more effective than facilitation achieved by a combination of stimulations of nerves directly entering the cerebral ganglion. The intensity of facilitation does not depend on the synaptic efficiency of the heterosynaptic input for the test neuron, but on the intensity of its connection with the other neurons surrounding the giant cell (conjecturally of neurosecretory type). This fact, and also the long latent period of manifestation and achievement of the maximum of facilitation, and its nonspecificity relative to several inputs all suggest that heterosynaptic facilitation is neurosecretory in its origin. Such a mechanism of a sharp increase in the efficiency of synaptic connections in a nerve center may play an important role in the animal's nervous activity as a whole and in the formation of temporary connections in particular, although it does not reflect the specificity of the conditioned reflex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 498–507, September–October, 1980.     

Interaction between hair cells in the statocyst ofHelix lucorum

An electrophysiological study of interactions between hair cells within the statocyst ofHelix lucorum was undertaken by intracellular and extracellular recording. Analysis of the results led to the following conclusions. First, some hair cells, subtending on angle on the arc of the statocyst sphere of not more than 90°, were electrically connected; electrical synapses, moreover, possessed polar properties; the coefficient of coupling in one direction was about 10 times greater than the other. Second, some connections between hair cells which subtended an angle of not more than 90° were mixed electrochemical in character. The excitatory chemical component in this case was directed in a direction opposite to effective electrical conduction. Third, inhibitory connections were observed between statocyst receptors: monosynaptic chemical (subtending an angle of about 180°, evidently, between the hair cells) and polysynaptic weak inhibitory interactions (subtending an angle in this case of not less than 90–100° between the test neurons). Fourth, all types of connection between hair cells were observed in CNS preparations with the vestibular nerve divided close to the cerebral ganglion. This means that zones of synaptic contacts between these receptors are located not in the CNS, but close to the statocyst.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 230–239, March–April, 1985.     

Discharges of tectal neurons evoked by electrical stimulation of single retinal ganglion cells in frogs

"EEG quanta" — extracellular monosynaptic PSPs evoked by action potentials of a single axon — were recorded in the frog thalamus at a depth of 200–700 µ during electrical stimulation of the retina by single, double, or triple pulses of current of threshold strength. With an interval of 5–25 msec between consecutive stimuli, a negative spike, increasing as the microelectrode was inserted deeper, was observed at the peak of the testing EEG quanta, which were enlarged 1.5–2.5 times. It is postulated that this spike is the synchronous discharge of neuron bodies (population spike), evoked by an action potential of a single retinotectal axon. This axon branches in layers F or G. Discharges appear in neurons of layers 6–8. The possibility that the volley discharge of one class 3–5 detector excites tectal ganglion cells, whose axons mainly form the tecto-bulbospinal tract, is discussed.Research Institute of Cardiology and Laboratories of Electroencephalography and Neurocybernetics, Medical Institute, Kaunas, Lithuania. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 829–835, November–December, 1984.     

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.     

Analysis of unit activity in the cat lateral geniculate body

Spontaneous and evoked single unit activity of lateral geniculate body neurons was recorded extracellularly in acute experiments on cats. Eight groups of neurons differing in the durations of the minimal and mean interspike intervals of spontaneous unit activity, and in the latent period and duration of the first volley of spikes of evoked activity, were distinguished by analysis of the data. On the basis of this classification a scheme for interaction between neurons of the lateral geniculate body is suggested.Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 30–37, January–February, 1978.     

Neural correlates of habituation of the proleg withdrawal reflex in larvae of the hawk moth, Manduca sexta

The larval proleg withdrawal reflex of the hawk moth, Manduca sexta, exhibits robust habituation. This reflex is evoked by deflecting one or more mechanosensory planta hairs on a proleg tip. We examined neural correlates of habituation in an isolated proleg preparation consisting of one proleg and its segmental ganglion. Repeated deflection of a single planta hair caused a significant decrease in the number of action potentials evoked in the proleg motor nerve (which carries the axons of proleg retractor motor neurons). Significant response decrement was seen for interstimulus intervals of 10 s, 60 s and 5 min. Response decrement failed to occur in the absence of repetitive stimulation, the decremented response recovered spontaneously following a rest, and electrical stimulation of a body wall nerve facilitated the decremented response (a neural correlate of dishabituation). Adaptation of sensory neuron responses occurred during repeated hair deflections. However, when adaptation was eliminated by direct electrical stimulation of sensory neurons, the response in the proleg motor nerve still decreased significantly. Muscle recordings indicated that the response of an identified proleg retractor motor neuron decreased significantly during habituation training. Thus, habituation of the proleg withdrawal reflex includes a central component that is apparent at the level of a single motor neuron. Accepted: 20 December 1996     

Cerebral motoneurons mediating tentacle retraction in the land slug Ariolimax columbianus

(1) Tentacle retraction in the land slug Ariolimax columbianus can be elicited by stimulation of all nerves and connectives of the ipsi- and contralateral cerebral ganglia. (2) Six neurons in the left cerebral ganglion were classified as tentacle retraction motoneurons because their action potentials are followed one-for-one with constant delay by action potentials in the left tentacle retractor nerve and their depolarization causes retraction of the ipsilateral tentacle. The motoneurons can be identified by size, pattern of pigmentation, position, and physiological characteristics. (3) Each retractor motoneuron discharges at a rather constant rate and has more than one source of excitatory input, but no IPSPs were observed. No synaptic connections between the six retractor motoneurons were found. The nerve action potentials that correspond to each motoneurons are distinguishable by waveform and size rank. (4) Each motoneuron elicits visible contractions in a particular region of the ipsilateral retractor muscle, but the motor fields of some motoneurons overlap. Some motoneurons mediate relatively rapid contractions while others cause slower responses. (5) There is one-for-one correspondence between action potentials of the largest unit recorded extracellularly in the retractor nerve and exciatory junction potentials recorded from the retractor muscle. No evidence of a peripheral neural plexus was found in serial sections of the retractor muscle.     

Responses of an identified Helix pomatia neuron to application of peptides,mediators, prostaglandins,and cyclic nucleotides

Extracellular application of oxytocin, Lys-vasopressin, and Leu-enkephalin to neuron RPa1 ofHelix pomatia evoked the generation of pacemaker potentials and the appearance of potentiation of spike activity of bursting type, characteristic of this cell. Noradrenalin and prostaglandins of the E group had a similar action. Dibutyryl-cyclic AMP, the phosphodiesterase inhibitor papaverine, and sodium fluoride, a nonspecific activator of adenylate cyclase, also initiated or potentiated bursting discharges of the neuron. It is suggested that the effects of oxytocin, Lys-vasopressin, Leu-enkephalin, noradrenalin, and prostaglandins of the E group are mediated through intracellular processes linked with activation of adenylate cyclase by these substances, leading to an increase in the cyclic AMP content in the nerve cell.P. K. Anokhin Research Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 80–87, January–February, 1981.     

Pre- and post-synaptic actions of the cerebral ventral giant cell on buccal muscles ofPhiline

Summary The cerebral ventral giant cell ofPhiline exterts a selective presynaptic inhibitory modulatory action on the terminals of a buccal excitatory motoneuron in two buccal muscles. Other excitatory inputs to the muscles are not affected. The ventral giant cell also makes direct synaptic contacts on the fibres of the same muscles. In the retractor muscle M4, 5 the junction potentials are usually depolarising when measured in sea water, but in the fibres of M6 they may have either polarity. The mean membrane potential of the fibres of M4, 5 and M6 was –74.7±0.65 mV and –64±0.95 mV respectively. Depolarization of the muscles fibres by around 15 mV by immersion in 20 mM K saline abolished the junction potential in M4, 5 and converted the depolarizing potential in M6 to a hyperpolarizing response.It is concluded that the VGC junction potential results from an increase in membrane conductance to an ion with a reversal potential between –60 and –70 mV.     

Naloxone-dependent depression by morphine of responses of snail neurons to serotonin

Morphine, added to the extracellular solution in a concentration of 1·10^–5 M, quickly and reversibly weakens the depolarizing and hyperpolarizing responses of neurons of the snailHelix lucorum evoked by 1·10^–6 M serotonin. The inhibitory effect of morphine is completely abolished by the addition of naloxone (1·10^–5 M), suggesting that opiate receptors are involved in the process. Interaction between morphine and serotonin is noncompetitive in type, as is shown by the character of the dose-effect curves recorded during the action of serotonin before and after morphine application.Institute of Psychiatry, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 6, pp. 589–593, November–December, 1981.     

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.     

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.     

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.     

Synaptic mechanisms controlling receptor unit activity in the stretch receptor—Abdominal ganglionic chain system of the crayfish

Inhibitory control over activity of the receptor neuron was investigated in a preparation of the stretch receptor and abdominal ganglionic chain in crayfishes. Potentials were recorded intracellularly from receptor neurons and neurons of the abdominal ganglion, and extracellularly from the dorsal roots. IPSPs appeared in the receptor neuron in response to stimulation of that same neuron or of the abdominal ganglionic chain. The relationship between spikes at the input and output of the inhibitory neuron varied over a wide range depending on the functional state of the neuron. A linear relationship was established between the time before appearance of the IPSP and the duration of the interspike interval of the slowly adapting neuron (SAN) and also between the firing rate of this and the inhibitory neurons during recurrent inhibition. Factors influencing the length of the interspike interval of the SAN on the appearance of an IPSP in it were investigated. It is postulated that summation of potentials evoked by spikes of the SAN and also of potentials evoked by spikes of that neuron, together with local processes evidently of endogenous nature takes place in the inhibitory neuron. IPSPs were recorded from two neurons resistant to strychnine and blocked by picrotoxin on the receptor neuron. The structural and functional organization of the individual elements in the chain of recurrent inhibition and inhibition evoked by stimulation of the abdominal ganglionic chain is discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 323–332, May–June, 1973.