[Neural mechanisms of memory: synaptic and genomic hypotheses].

Memorizing of new facts and events means that entering signals produce definite changes within the brain. According to the commonly accepted hypothesis, traces of memory are stored through modifications in the strength of synaptic connections, resulting in formations of new patterns of neural activity. This synaptic hypothesis of memory determines the main direction of experimental studies in the field. It is shown in this review that the synaptic hypothesis can hardly explain the mechanism of long-term (often life-long) memory storage as well as memory resistance to both uncontrolled synaptic activity (epileptic seizures) and various adverse effects on the brain (anesthesia, injury, concussion, etc.). Arguments for an alternative hypothesis are given that long-term memory is mainly formed at the intraneural level through modifications of DNA molecules and associated proteins. This genomic hypothesis allows for a new approach to understanding the etiology ofAlzheimer's disease, whose initial symptom is solely memory impairment.

[Electrophysiologic study of the serotoninergic neuron C1 in the pteropod mollusk Clione]. / Elektrofiziologicheskoe issledovanie serotoninergicheskogo neirona C1 u krylonogogo molliuska Clione.

Functional characteristics of the cerebral serotoninergic neuron (C1) have been studied in the pteropod mollusc Clione limacina. The C1 neuron axon projected to the buccal ganglia and axon collaterals terminated in buccal nerves. Stimulation of the C1 neuron activated the feeding rhythm generator in the buccal ganglia. Effects developed relatively slowly and far outlasted the period of C1 neuron stimulation. The C1 neuron received synaptic feedback from buccal neurons. As a result, the C1 neuron activity was cyclically modulated with respect to feeding rhythm generation. There was a correlation between the activity of the C1 neurons and that of the locomotor generator located in the pedal ganglia. Activation of the locomotor generator, both spontaneous and evoked by stimulation of some command neurons, was accompanied by excitation of the C1 neurons. The correlation between the activities of the locomotor generator and of the C1 neurons is suggested to be one of manifestations of the feeding synergy including simultaneous activation of the locomotor and buccal systems.

[The neuronal mechanisms of the defensive reaction to stimulation of the cutaneous nerve in the freshwater snail]. / Neironnye mekhanizmy oboronitel'noi reaktsii na razdrazhenie kozhnogo nerva u presnovodnoi ulitki.

The whole body withdrawal reaction of freshwater snail Planorbarius corneus consists of two phases. In the first phase the shell is rapidly moved down to cover the head, in the second one the body is slowly retracted into the shell. The columellar muscle is involved in this behaviour. Motoneurons of the columellar muscle are identified in the cerebral, parietal and pedal ganglia. In the preparation of the central nervous system connected with the columellar muscle it is demonstrated that stimulation of the lip nerve evoked a biphasic motoneuron excitation responsible for two phases of the muscle contraction. A similar biphasic excitation of the motoneurons could arise spontaneously. This implies that the whole body withdrawal reaction is, at least partly, a fixed act generated by a central mechanism (a central program) which is triggered by a sensory stimulus. The central mechanism of the withdrawal reaction could be also activated by a depolarization of some columellar motoneurons. This suggests that the central mechanism received a feedback from the motoneurons.

[The neuronal mechanisms of the escape reaction to stimulation of the statocyst receptors in the freshwater snail]. / Neironnye mekhanizmy oboronitel'noi reaktsii na razdrazhenie retseptorov statotsistov u presnovodnoi ulitki.

Tilts of the freshwater snail Planorbarius corneus, resulting in statocyst receptor stimulation, induced the defensive reaction including pulling down of the shell, shortening of the foot, inhibition of locomotion and feeding. The preparation of the central nervous system has demonstrated that many inter- and motoneurons from different ganglia were involved in this reaction. Usually the reaction was of "all or none" manner. The repeated reaction of the second tilt could be evoked not earlier than 10-20 s after the previous one. It is concluded that the defensive reaction to statocyst receptor stimulation is a "fixed act" determined by a special central mechanism (a central program). The reactions to stimulation of statocyst receptors and skin nerve are proved to be generated by the same mechanism.

[Neural regulation of heart function in the Pteropod mollusc Clione limacina]. / Nervnaia reguliatsiia raboty serdtsa u krylonogogo molliuska Clione limacina.

The heart of the pteropodial mollusc Clione limacina is innervated by the median nerve arising from the left abdominal ganglion. Five neurons sending axons to the heart have been identified in the Clione central nervous system with retrograde cobalt or Lucifer yellow staining. Neuron H1 located in the left pedal ganglion evoked heart excitation. Three neurons H2-H4 located in the medial part of the left abdominal ganglion caused heart inhibition. Neuron H5 located in the caudal part of the left abdominal ganglion did not affect the heart. The activity of the efferent heart neurons was found to be related to the operation of the locomotor rhythm generator. Spontaneous or reflex suppression of the locomotor rhythm generation was accompanied by inhibition of neuron H1 and excitation of neurons H2-H4. Such behavior of the efferent heart neurons ensures a positive correlation between heart and locomotor activities in Clione limacina.

[Neuronal mechanisms of the generation of the feeding rhythm in the buccal ganglia of the pteropod mollusk]. / Neironnye mekhanizmy generatsii "pishchevogo ritma" v bukkal'nykh gangliiakh krylonogogo molliuska.

Two antagonistic groups of neurons, active in protractor and retractor phases of the feeding cycle, were found in the buccal ganglia of the pteropod mollusc Clione limacina. Neurons within each group are electrically coupled, while the groups inhibit one another. Each group is able to perform independent rhythmic activity. When the activity of one of the groups terminates (due to inner reasons), the other group becomes active (due to both the inner tendency of generating periodic bursts and the postinhibitory rebound).

[Growth of neurites and formation of connections in cultures of pteropodial mollusc neurons]. / Rost otroskov i obrazovanie sviazei v kul'ture neironov krylonogogo molliuska.

Dissociated neurons from the brain of pteropodial mollusc were cultivated in a 25% Leibovitz medium containing 2% of calf serum. Neurite outgrowth was observed in 1-30% of the neurons. It was maximum during the first 3 days. Neurite length reached 300 microns. Membrane potential of neurons was 40-60 mV; they generated single spikes or bursts of impulses. Intercellular connections were tested on the 3-4th days in 70 pairs of neurons with neurites overlapped. Electrical connections between the cells were observed in 20% of the pairs tested, and in 6% of pairs stimulation of one of the neurons evoked an inhibitory postsynaptic potential in the other.

[Effect of the locomotor system of the pedal ganglia of the pteropodial mollusk on anatomically isolated neurons]. / Vliianie lokomotornoi sistemy pedal'nykh gangliev krylonogogo molliuska na anatomicheski izolirovannye neirony.

The isolated pedal ganglia of the pteropodial mollusc Clione limacina generate the locomotor activity. In 30% of the pedal ganglion preparations, the locomotor rhythm was not regular, i. e. the locomotor generator worked in "bursts". These "locomotor bursts" were caused by spontaneous activations of command neurons located in the pedal ganglia. Single neurons were extracted from such preparations with an intracellular microelectrode and then their somas were put into the initial place between the ganglion cells. 25% of the isolated neurons (9 out of 35) renewed the "locomotor bursts"-related changes in the activity after the insertion into the ganglion. Neurons, originally excited during "bursts", continued to be excited after isolation, while inhibited neurons continued to be inhibited. It follows, therefore, that the command neurons can act on the target cells in the absence of morphological synapses.

[Generation of locomotor rhythms in Limacina helicina]. / Generatsiia lokomotornoi ritmiki u krylonogogo molliuska.

Two groups of neurons (motoneurons and putative interneurons), exhibiting periodic activity with the locomotory rhythm, were recorded in the pedal ganglia of the isolated nervous system of the mollusc Limacina helicina. Motoneurons periodically generated spike bursts, while interneurons generated only one prolonged (100-400 ms) action potential per cycle. Rhythmic generation persisted after blocking the spike discharges of motoneurons by means of tetrodotoxin. Rhythmic generation could be facilitated by application of serotonin.

[Activity of isolated interneurons of the pedal ganglia of the pteropodal mollusk]. / Aktivnost' izolirovannykh interneironov pedal'nykh gangliev krylonogogo molliuska.

Interneurons from pedal ganglia of marine mollusc Clione limacina continued their rhythmical discharges for many hours after isolation. A discharge frequency increased with depolarization of neurons and decreased with hyperpolarization. It is concluded that the endogenous activity of interneurons underlies generation of the locomotor pattern in mollusc pedal ganglia.

[Regeneration of neurons of the pedal ganglion of the pteropodal mollusk Clione limacina]. / Regeneratsiia neironov pedal'nogo gangliia krylonogogo molliuska Clione limacina.

In pedal ganglia of mollusc Clione limacina the growth of axons was studied in motoneurons and interneurons after transections of the wing nerve or of the pedal comissure. Neurons were stained by Lucifer Yellow. In motoneurons, neurites grown both from the transected end of the axon and from the neuron soma spread to all nerve trunks of ipsi- and contralateral ganglia. After nerve transection in the whole mollusc, wing movements restored 10 days later. In interneurons, neurites branched within the pedal ganglion or spread into cerebral ganglia but they did not extend out peripheral nerve trunks. Thus, the patterns of neurite sprouting in moto- and interneurons are different.

[Activity of propriospinal neurons of segments C3 and C4 during "fictive locomotion" in the cat]. / Aktivnost' propriospinal'nykh neironov segmentov C3 i C4 vo vremia "fiktivnoi lokomotsii" koshki.

The activity of C3-C4 propriospinal neurons was recorded during "fictitious locomotion" of forelimbs in immobilized decerebrated cats with the spinal cord transected at the lower thoracal level. The neurons were identified by the antidromic responses to stimulation of the lateral funiculus in the C6 segment. Most of the neurons (70%) were antidromically activated also from the lateral reticular nucleus. The discharge frequency of most neurons was rhythmically modulated in correlation with the motoneuron activity during "fictitious locomotion", i.e. in the absence of any rhythmical signals from the limb receptors. The cooling of the rostral area of the cervical enlargement abolished both the generation of the locomotor rhythm and the rhythmical activity of the propriospinal neurons. Therefore intraspinal mechanisms controlling the forelimb activity are the main source for rhythmical modulation of the C3-C4 propriospinal neurons.

[Motor neuron activity of the pedal ganglia of pteropod mollusks during generation of locomotor rhythms]. / Aktivnost' motoneironov pedal'nykh gangliev krylonogogo molliuska pri generatsii lokomotornogo ritma.

Activity of motoneurons from pedal ganglia of marine mollusc Clione limacina was recorded during generation of the locomotor rhythm. Motoneuron groups controlling antagonistic wing muscles are active alternatively, excitation of one group being accompanied by inhibition of the other group. Many synergetic motoneurons are electrically coupled.

[Interneuron activity of the pedal ganglia of pteropod mollusks during generation of locomotor rhythms]. / Aktivnost' interneironov pedal'nykh gangliev krylonogogo molliuska pri generatsii lokomotornogo ritma.

Activity of interneurons from isolated pedal ganglia of marine mollusc Clione limacina was recorded during generation of the locomotor rhythm. Two groups of reciprocally active interneurons were found. These neurons generate one prolonged action potential per locomotory cycle. Inhibitory interaction between the two groups was observed. The interneurons were supposed to generate the locomotor rhythm.

[Neurons of the pedal ganglia of a pteropod mollusk regulating locomotor generator function]. / Neirony pedal'nykh gangliev krylonogogo molliuska, upravliaiushchie rabotoi lokomotornogo generatora.

Neurons whose excitation affected the locomotory rhythm were recorded in the isolated pedal ganglia of the marine mollusc Clione limacina. Some of these neurons generated "plateau" potentials, i.e. they remained depolarized for a long period after termination of the initial depolarizing current. A role of the command neurons in the motor behaviour of Clione is discussed.

[Effect of serotonin and theophylline on generation of rhythmic activity in the buccal ganglia of gastropod mollusks]. / Vliianie serotonina i teofillina na generatsiiu ritmicheskoi aktivnosti v bukkal'nykh gangliiakh briukhonogikh molliuskov.

Effect of serotonin on generation of the feeding rhythm in buccal ganglia was studied in 8 species from 3 subclasses of gastropod molluscs. Serotonin (10(-5) mol/l) initiated or increased the rhythmical activity in the buccal ganglia. The effect of serotonin was potentiated with theophylline (phosphodiesterase inhibitor).

[Analysis of late components of evoked potentials arising in the paramedian lobule of the cerebellum in response to stimulation of nerves and the cerebral cortex]. / Analiz pozdnikh komponentov vyzvannykh potentsialov, voznikaiushchikh v paramediannoi dol'ke mozzhechka pri razdrazhenii kory bol'shikh polusharii i nervov.

The field potentials in response to stimulation of the cerebral sensorimotor cortex and of the limb nerves were recorded in the granular layer of the cerebellar paramedian lobule in nonanesthetized cats. The field potentials contained long-latency components, i.e. slow negative waves generated by granule cells. The long-latency component to nerve stimulation was recorded both inside and outside the projection area of the given limb, while the cerebral stimulation with a low intensity (1.8-2.5 thresholds) evoked this component in the given projection area only. The long latency component to cerebral stimulation followed higher rates and was less sensitive to the action of the barbital anaesthesia than the component following the nerve stimulation. Simultaneous cerebral and nerve stimulation evoked the long latency component equal to the sum of the separate components. It is suggested that slow conduction spinal and cerebral inputs form separate mossy fibres - granule cell pathways.

[Locomotion of Barents Sea ophiuroids]. / Lokomotsii ofiur Barentsova moria.

Locomotion of 5 species of Ophiuroids from the Barents Sea has been described--Ophiura albida, O. robusta, O. sarsi, Ophiacantha bidentata, Ophiopholis aculeata. Representatives from the genus Ophiura move by means of one or two symmertic pairs of arms which perform rhythmic rowing beats. The feet tube do not participate in their locomotion. Locomotion pattern in O. bidentata and especially O. aculeata, which have long flexible arms, is more complex. However, the analysis indicates that they replace themselves by a comparatiely limited set of standard "programmed" movements which may be used in various combinations. In locomotion of these species, the tube feet are involved which provide for the reliable contact of distal ends of the active rays with the supporting surface; due to this contact the animals can move in a straightforward direction.