Biomedical subjects

T G Deliagina

Publications and source records attributed to T G Deliagina.

At least 19 recordsLinked to original sources

PubMed2001

Heterogeneity of the population of command neurons in the lamprey.

The effects of signals transmitted from the brain to the spinal locomotor networks by a population of command neurons are determined by specific functional projections of each individual neuron. To reveal these projections, we used a simple vertebrate model, the lamprey, in which responses of the spinal networks to spikes in single reticulospinal axons were detected by using the spike-triggered averaging of the motoneuronal activity. We found that individual neurons exert a uniform effect on the segmental motor output along the whole extent of their axons. Twenty different patterns of effect, that is, combinations of influences on the segmental motoneuron pools, were found. The widespread projections and heterogeneity of the population of command neurons present a basis for formation of different gross motor synergies.

Action Potentials↗

PubMed2001

Non-undulatory locomotion in the lamprey.

The lamprey (a lower vertebrate, cyclostome), in addition to ordinary swimming, is also capable of crawling. Here we describe crawling forward in a narrow U-shaped tunnel. A rapid movement along the tunnel was evoked by stimulating the tail. The muscle activity responsible for propulsion was confined to the area around the body bend. Muscles on the inner (concave) side were activated when approaching the turn, and inactivated on the top of the arc. Muscles on the outer (convex) side were co-active with their antagonists, but also active in the area of straightening of the body bend. This pattern of muscle activity propagated along the body. The role of central and reflex mechanisms in the generation of locomotor movements is discussed.

Animals↗

PubMed2001

Modeling postural control in the lamprey.

A phenomenological model of the mechanism of stabilization of the body orientation during locomotion (dorsal side up) in the lamprey is presented. The mathematical modeling is based on experimental results obtained during investigations of postural control in lampreys using a combined in vivo and robotics approach. The dynamics of the model agree qualitatively with the experimental data. It is shown by computer simulations that postural correction commands from reticulospinal neurons provide information sufficient to stabilize body orientation in the lamprey. The model is based on differences between the effects exerted by the vestibular apparatus on the left and the right side.

Animals↗

PubMed2000

Crossed reciprocal inhibition evoked by electrical stimulation of the lamprey spinal cord.

Activation of a motoneuron pool is often accompanied by inhibition of the antagonistic pool through a system of reciprocal inhibition between the two parts of the neuronal network controlling the antagonistic pools. In the present study, we describe the activity of such a system in the isolated spinal cord of the lamprey, when a tonic motor output is evoked by extracellular stimulation (0.5-1 s train of pulses, 20 Hz) of either end of the spinal cord. With two electrodes symmetrically positioned in relation to the midline, stimulation with either of them separately elicited prolonged (1-5 s) ipsilateral ventral root activity. Activity could be abolished by stronger, simultaneously applied, stimulation of the contralateral side of the cord, suggesting that reciprocal inhibition between hemisegments operates when a tonic motor output is generated. Simultaneous stimulation of both sides of the spinal cord with a single electrode with a large tip (300-400 microm in diameter), positioned over the anatomical midline, elicited inconsistent right-side, leftside, or bilateral ventral root responses. A minor displacement (10-20 microm) to the left or right from the midline resulted in activation of ipsilateral motoneurons, whereas the contralateral motoneurons were silent. These findings indicate that a small asymmetry in the excitatory drive to the left and right spinal hemisegments can be further amplified by reciprocal inhibition between the hemisegments. Longitudinal splitting of the spinal cord along the midline resulted in reduced reciprocal inhibition between the hemisegments separated by the lesion. The reduction was proportional to the extent of the split. The inhibition was abolished when the split reached nine segments in length. From these experiments, the longitudinal distribution of the commissural axons responsible for inhibition of contralateral motor output could be estimated.

Animals↗

PubMed2000

Neuronal mechanisms for the control of body orientation in clione II. Modifications in the activity of postural control system.

The marine mollusk Clione limacina, when swimming, can stabilize different body orientations in the gravitational field. The stabilization is based on the reflexes initiated by activation of the statocyst receptor cells and mediated by the cerebro-pedal interneurons that produce excitation of the motoneurons of the effector organs; tail and wings. Here we describe changes in the reflex pathways underlying different modes of postural activity; the maintenance of the head-up orientation at low temperature, the maintenance of the head-down orientation at higher temperature, and a complete inactivation of the postural mechanisms during defense reaction. Experiments were performed on the CNS-statocyst preparation. Spike discharges in the axons of different types of neurons were recorded extracellularly while the preparation was rotated in space through 360 degrees in different planes. We characterized the spatial zones of activity of the tail and wing motoneurons and the CPB3 interneurons mediating the effects of statocyst receptor cells on the tail motoneurons. This was done at different temperatures (10 and 20 degrees C). The "fictive" defense reaction was evoked by electrical stimulation of the head nerve. At 10 degrees C, a tilt of the preparation evoked activation in the tail motoneurons and wing retractor motoneurons contralateral to the tilt and in the wing locomotor motoneurons ipsilateral to the tilt. At 20 degrees C, the responses in the tail motoneurons and in the wing retractor motoneurons occurred reversed; these neurons were now activated with the ipsilateral tilt. In the wing locomotor motoneurons the responses at 20 degrees C were suppressed. During the defense reaction, gravitational responses in all neuron types were suppressed. Changes in the chains of tail reflexes most likely occurred at the level of connections from the statocyst receptor cells to the CPB3 interneurons. The changes in gravitational reflexes revealed in the present study are sufficient to explain the corresponding modifications of the postural behavior in Clione.

Animals↗

PubMed2000

Activity of reticulospinal neurons during locomotion in the freely behaving lamprey.

The reticulospinal (RS) system is the main descending system transmitting commands from the brain to the spinal cord in the lamprey. It is responsible for initiation of locomotion, steering, and equilibrium control. In the present study, we characterize the commands that are sent by the brain to the spinal cord in intact animals via the reticulospinal pathways during locomotion. We have developed a method for recording the activity of larger RS axons in the spinal cord in freely behaving lampreys by means of chronically implanted macroelectrodes. In this paper, the mass activity in the right and left RS pathways is described and the correlations of this activity with different aspects of locomotion are discussed. In quiescent animals, the RS neurons had a low level of activity. A mild activation of RS neurons occurred in response to different sensory stimuli. Unilateral eye illumination evoked activation of the ipsilateral RS neurons. Unilateral illumination of the tail dermal photoreceptors evoked bilateral activation of RS neurons. Water vibration also evoked bilateral activation of RS neurons. Roll tilt evoked activation of the contralateral RS neurons. With longer or more intense sensory stimulation of any modality and laterality, a sharp, massive bilateral activation of the RS system occurred, and the animal started to swim. This high activity of RS neurons and swimming could last for many seconds after termination of the stimulus. There was a positive correlation between the level of activity of RS system and the intensity of locomotion. An asymmetry in the mass activity on the left and right sides occurred during lateral turns with a 30% prevalence (on average) for the ipsilateral side. Rhythmic modulation of the activity in RS pathways, related to the locomotor cycle, often was observed, with its peak coinciding with the electromyographic (EMG) burst in the ipsilateral rostral myotomes. The pattern of vestibular response of RS neurons observed in the quiescent state, that is, activation with contralateral roll tilt, was preserved during locomotion. In addition, an inhibition of their activity with ipsilateral tilt was clearly seen. In the cases when the activity of individual neurons could be traced during swimming, it was found that rhythmic modulation of their firing rate was superimposed on their tonic firing or on their vestibular responses. In conclusion, different aspects of locomotor activity-initiation and termination, vigor of locomotion, steering and equilibrium control-are well reflected in the mass activity of the larger RS neurons.

Animals↗

PubMed2000

Responses of reticulospinal neurons in intact lamprey to vestibular and visual inputs.

A lamprey maintains the dorsal-side-up orientation due to the activity of postural control system driven by vestibular input. Visual input can affect the body orientation: illumination of one eye evokes ipsilateral roll tilt. An important element of the postural network is the reticulospinal (RS) neurons transmitting commands from the brain stem to the spinal cord. Here we describe responses to vestibular and visual stimuli in RS neurons of the intact lamprey. We recorded activity from the axons of larger RS neurons with six extracellular electrodes chronically implanted on the surface of the spinal cord. From these multielectrode recordings of mass activity, discharges in individual axons were extracted by means of a spike-sorting program, and the axon position in the spinal cord and its conduction velocity were determined. Vestibular stimulation was performed by rotating the animal around its longitudinal axis in steps of 45 degrees through 360 degrees. Nonpatterned visual stimulation was performed by unilateral eye illumination. All RS neurons were classified into two groups depending on their pattern of response to vestibular and visual stimuli; the groups also differed in the axon position in the spinal cord and its conduction velocity. Each group consisted of two symmetrical, left and right, subgroups. In group 1 neurons, rotation of the animal evoked both dynamic and static responses; these responses were much larger when rotation was directed toward the contralateral labyrinth, and the dynamic responses to stepwise rotation occurred at any initial orientation of the animal, but they were more pronounced within the angular zone of 0-135 degrees. The zone of static responses approximately coincided with the zone of pronounced dynamic responses. The group 1 neurons received excitatory input from the ipsilateral eye and inhibitory input from the contralateral eye. When vestibular stimulation was combined with illumination of the ipsilateral eye, both dynamic and static vestibular responses were augmented. Contralateral eye illumination caused a decrease of both types of responses. Group 2 neurons responded dynamically to rotation in both directions throughout 360 degrees. They received excitatory inputs from both eyes. Axons of the group 2 neurons had higher conduction velocity and were located more medially in the spinal cord as compared with the group 1 neurons. We suggest that the reticulospinal neurons of group 1 constitute an essential part of the postural network in the lamprey. They transmit orientation-dependent command signals to the spinal cord causing postural corrections. The role of these neurons is discussed in relation to the model of the roll control system formulated in our previous studies.

Action Potentials↗

PubMed2000

Asymmetrical effect of GABA on the postural orientation in Clione.

The marine mollusk Clione limacina, when swimming, normally stabilizes the vertical body orientation by means of the gravitational tail reflexes. Horizontal swimming or swimming along inclined ascending trajectories is observed rarely. Here we report that GABA injection into intact Clione resulted in a change of the stabilized orientation and swimming with a tilt of approximately 45 degrees to the left. The analysis of modifications in the postural network underlying this effect was done with in vitro experiments. The CNS was isolated together with the statocysts. Spike discharges in the axons of two groups of motoneurons responsible for the left and right tail flexion, as well as in the axons of CPB3 interneurons mediating signals from the statocyst receptors to the motoneurons, were recorded extracellularly when the preparation was rotated in space. Normally the tail motoneurons of the left and right groups were activated with the contralateral tilt of the preparation. Under the effect of GABA, the gravitational responses in the right group of motoneurons and in the corresponding interneurons were dramatically reduced while the responses in the left group remained unchanged. The most likely site of the inhibitory GABA action is the interneurons mediating signals from the statocysts to the right group of tail motoneurons. The GABA-induced asymmetry of the left and right gravitational tail reflexes, observed in the in vitro experiments, is consistent with a change of the stabilized orientation caused by GABA in the intact Clione.

Action Potentials↗

PubMed2000

Postural control in the lamprey: A study with a neuro-mechanical model.

The swimming lamprey normally maintains the dorsal-side-up orientation due to activity of the postural control system driven by vestibular organs. Commands for postural corrections are transmitted from the brain stem to the spinal cord mainly by the reticulospinal (RS) pathways. As shown in previous studies, RS neurons are activated by contralateral roll tilt, they exhibit a strong dynamic response, but much weaker static response. Here we test a hypothesis that decoding of these commands in the spinal cord is based on the subtraction of signals in the left and right RS pathways. In this study, we used a neuro-mechanical model. An intact lamprey was mounted on a platform that restrained its postural activity but allowed lateral locomotor undulations to occur. The activity in the left and right RS pathways was recorded by implanted electrodes. These natural biological signals were then used to control an electrical motor rotating the animal around its longitudinal axis toward the stronger signal. It was found that this "hybrid" system automatically stabilized a normal orientation of the lamprey in the gravitational field. The system compensated for large postural disturbances (lateral tilt up to +/-180 degrees ) due to wide angular zones of the gravitational sensitivity of RS neurons. In the nonswimming lamprey, activity of RS neurons and their vestibular responses were considerably reduced, and the system was not able to stabilize the normal orientation. However, the balance could be restored by imposing small oscillations on the lamprey, which elicited additional activation of the vestibular organs. This finding indicates that head oscillations caused by locomotor movements may contribute to postural stabilization. In addition to postural stabilization, the neuro-mechanical model reproduced a number of postural effects characteristic of the lamprey: 1) unilateral eye illumination elicited a lateral tilt ("dorsal light response") due to a shift of the equilibrium point in the vestibular-driven postural network; 2) removal of one labyrinth resulted in a loss of postural control due to an induced left-right asymmetry in the vestibulo-reticulospinal reflexes, which 3) could be compensated for by asymmetrical visual input. The main conclusion of the present study is that natural supraspinal commands for postural corrections in the roll plane can be effectively decoded on the basis of subtraction of the effects of signals delivered by the left and right RS pathways. Possible mechanisms for this transformation are discussed.

Animals↗

PubMed1999

Role of glutamate receptor subtypes in the lamprey respiratory network.

The respiratory role of glutamate receptors was investigated in the isolated lamprey brain preparation by analyzing the changes in respiratory activity induced by bath application of specific antagonists of ionotropic and metabotropic glutamate receptors. The results show that these antagonists differentially affect the pattern of breathing and provide the first evidence that both ionotropic and metabotropic glutamate receptors are involved in neurotransmission within the lamprey respiratory network.

2-Amino-5-phosphonovalerate↗

PubMed1999

Neuronal mechanisms for the control of body orientation in Clione I. Spatial zones of activity of different neuron groups.

The marine mollusk Clione limacina, when swimming, can stabilize different body orientations in the gravitational field. Here we describe one of the modes of operation of the postural network in Clione-maintenance of the vertical, head-up orientation. Experiments were performed on the CNS-statocyst preparation. Spike discharges in the axons of different types of neurons were recorded extracellularly when the preparation was rotated in space through 360 degrees in different planes. We characterized the spatial zones of activity of the tail and wing motor neurons as well as of the CPB3 interneurons mediating the effects of statocyst receptor cells on the tail motor neurons. It was found that the activity of the tail motor neurons increased with deviation of the preparation from the normal, rostral-side-up orientation. Their zones of activity were very wide ( approximately 180 degrees ). According to the zone position, three distinct groups of tail motor neuron (T1-T3) could be distinguished. The T1 group had a center of the zone near the ventral-side-up orientation, whereas the zones of T2 and T3 had their centers near the left-side-up and the right-side-up positions, respectively. By comparing the zone of activity with the direction of tail bending elicited by each of the groups, one can conclude that gravitational reflexes mediated by the T1, T2, and T3 groups will evoke turning of the animal toward the head-up orientation. Two identified wing motor neurons, 1A and 2A, causing the wing beating, were involved in gravitational reactions. They were activated with the downward inclination of the ipsilateral side. Opposite reactions were observed in the motor neurons responsible for the wing retraction. A presumed motor effect of these reactions is an increase of oscillations in the wing that is directed downward and turning of Clione toward the head-up orientation. Among the CPB3 interneurons, at least four groups could be distinguished. In three of them (IN1, IN2, and IN3), the zones of activity were similar to those of the three groups (T1, T2, and T3) of the tail motor neurons. The group IN4 had the center of its zone in the dorsal-side-up position; a corresponding group was not found among the tail motor neurons. In lesion experiments, it was found that gravitational input mediated by a single CPB3 interneuron produced activation of its target tail motor neurons in their normal zones, but the strength of response was reduced considerably. This finding suggests that several interneurons with similar spatial zones converge on individual tail motor neurons. In conclusion, because of a novel method, activity of the neuronal network responsible for the postural control in Clione was characterized in the terms of gravitational responses in different neuron groups comprising the network.

Animals↗

PubMed1998

Analysis of the central pattern generator for swimming in the mollusk Clione.

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.

Animals↗

PubMed1998

Control of spatial orientation in a mollusc.

The main function of postural nervous mechanisms in different species, from mollusc to man, is to counteract the force of gravity and stabilize body orientation in space. Here we investigate the basic principles of postural control in a simple animal model, the marine mollusc Clione limacina. When swimming, C. limacina maintains its vertical orientation because of the activity of the postural neuronal network. Driven by gravity-sensing organs (statocysts), the network causes postural corrections by producing tail flexions. To understand how this function occurs, we studied network activity by using a new method. We used an in vitro preparation that consisted of the central nervous system isolated with the statocysts. Output signals from the network (electrical activity of tail motor neurons) controlled an electrical motor which rotated the preparation in space. We analysed the activity of individual neurons involved in postural stabilization under opened or closed feedback loop. When we closed this artificial feedback loop, the network stabilized the vertical orientation of the preparation. This stabilization is based on the tendency of the network to minimize the difference between the activities of the two antagonistic groups of neurons, which are driven by orientation-dependent sensory inputs.

Animals↗

PubMed1998

Differential effects of the reticulospinal system on locomotion in lamprey.

Specific effects of stimulating different parts of the reticulospinal (RS) system on the spinal locomotor pattern are described in lamprey. In the in vitro brain stem and spinal cord preparation, microstimulation in different areas of the reticular formation was performed by ejecting a small amount of -glutamate from a micropipette. These areas were distributed over the four reticular nuclei of the brain stem: the mesencephalic reticular nucleus (MRN) and the anterior, middle and posterior rhombencephalic reticular nuclei (ARRN, MRRN, and PRRN, respectively). To prevent synaptic spread of excitation within the brain stem, the synaptic transmission was blocked by using a low Ca2+, high Mn2+ physiological saline in the brain stem pool. "Fictive" locomotion was evoked by applying N-methyl--aspartate (NMDA) to the spinal cord. Rhythmical discharges of motoneurons were recorded bilaterally in the midbody area, from the ventral roots that had been subdivided in dorsal and ventral branches, supplying the dorsal and ventral part of the myotome, respectively. Two major effects of brain stem stimulation were elicited: a change in the frequency of the locomotory rhythm and an induction of asymmetry (left/right, dorsal/ventral) in the segmental motor output. Approximately 50% of the stimulated sites evoked a change in locomotor frequency. In the PRRN almost all effective sites evoked an increase in frequency (10-50%). In the other nuclei, increase and decrease (10-30%) were observed equally frequently. Most of the stimulated sites (50-80%) in any reticular nucleus evoked asymmetry in the segmental motor output. Distortion of the segmental output symmetry was classified into eight categories by comparing the intensity of locomotor bursts in the dorsal and ventral branches of the two ventral roots, ipsilateral and contralateral to the stimulated side. These categories differed in the direction of the body flexion, which would be evoked during normal swimming: ipsilateral (I), contralateral (C), dorsal (D), ventral (V), ipsilateral and dorsal (ID), ipsilateral and ventral (IV), contralateral and dorsal (CD), and contralateral and ventral (CV). The different categories were not equally represented in each nucleus and across the nuclei. The most pronounced categories for each nucleus were as follow. In MRN: I (33%); ARRN: C (44%); MRRN: rostral part, I (36%) and caudal part, CV (42%); and PRRN: rostral part, I (40%) and caudal part, IV (35%). Other categories were also present but less common in each nucleus. To examine if the effects of brain stem stimulation were uniform along the spinal cord, recordings were performed from distal parts of the cord. Stimulation of a given point in the brain stem produced similar pattern of effects in 59% of cases and different patterns in 41% of cases. The main conclusion of the present study is that the proportion of RS neurons with different influences on the spinal locomotor network differs significantly among different parts of the reticular formation of the lamprey. The specificity of RS influences may represent a basis for modifications of the segmental locomotor output necessary for the control of equilibrium and steering during locomotion.

Animals↗

PubMed1997

Pattern generation.

Central pattern generators are neuronal ensembles capable of producing the basic spatiotemporal patterns underlying 'automatic' movements (e.g. locomotion, respiration, swallowing and defense reactions), in the absence of peripheral feedback. Different experimental approaches, from classical electrophysiological and pharmacological methods to molecular and genetic ones, have been used to understand the cellular and synaptic bases of central pattern generator organization and reconfiguration of generator operation in behaviorally relevant contexts. Recently, it has been shown that the high reliability and flexibility of central pattern generators is determined by their redundant organization. Everything that is crucial for generator operation is determined by a number of complementary mechanisms acting in concert; however, various mechanisms are weighted differently in determining different aspects of central pattern generator operation.

Animals↗

PubMed1997

Visual pathways for postural control and negative phototaxis in lamprey.

The functional roles of the major visuo-motor pathways were studied in lamprey. Responses to eye illumination were video-recorded in intact and chronically lesioned animals. Postural deficits during spontaneous swimming were analyzed to elucidate the roles of the lesioned structures for steering and postural control. Eye illumination in intact lampreys evoked the dorsal light response, that is, a roll tilt toward the light, and negative phototaxis, that is a lateral turn away from light, and locomotion. Complete tectum-ablation enhanced both responses. During swimming, a tendency for roll tilts and episodes of vertical upward swimming were seen. The neuronal circuitries for dorsal light response and negative phototaxis are thus essentially extratectal. Responses to eye illumination were abolished by contralateral pretectum-ablation but normal after the corresponding lesion on the ipsilateral side. Contralateral pretectum thus plays an important role for dorsal light response and negative phototaxis. To determine the roles of pretectal efferent pathways for the responses, animals with a midmesencephalic hemisection were tested. Noncrossed pretecto-reticular fibers from the ipsilateral pretectum and crossed fibers from the contralateral side were transected. Eye illumination on the lesioned side evoked negative phototaxis but no dorsal light response. Eye illumination on the intact side evoked an enhanced dorsal light response, whereas negative phototaxis was replaced with straight locomotion or positive phototaxis. The crossed pretecto-reticular projection is thus most important for the dorsal light response, whereas the noncrossed projection presumably plays the major role for negative phototaxis. Transection of the ventral rhombencephalic commissure enhanced dorsal light response; negative phototaxis was retained with smaller turning angles than normal. Spontaneous locomotion showed episodes of backward swimming and deficient roll control (tilting tendency). Transections of different spinal pathways were performed immediately caudal to the brain stem. All spinal lesions left dorsal light response in attached state unaffected; this response presumably is mediated by the brain stem. Spinal hemisection impaired all ipsiversive yaw turns; the animals spontaneously rolled to the intact side. Bilateral transection of the lateral columns impaired all yaw turns, whereas roll control and dorsal light response were normal. After transection of the medial spinal cord, yaw turns still could be performed whereas dorsal light response was suppressed or abolished, and a roll tilting tendency during spontaneous locomotion was seen. We conclude that the contralateral optic nerve projection to the pretectal region is necessary and sufficient for negative phototaxis and dorsal light response. The crossed descending pretectal projection is most important for dorsal light response, whereas the noncrossed one is most important for negative phototaxis. In the most rostral spinal cord, fibers for lateral yaw turns travel mainly in the lateral columns, whereas fibers for roll turns travel mainly in the medial spinal cord.

Animals↗

PubMed1997

The role of tonic vestibular input for postural control in rats.

Removal of a vestibular organ deprives the ipsilateral vestibular nuclei of tonic excitatory inflow from vestibular afferents, and thus evokes a central asymmetry, that is imbalance between tonic activity of the left and right vestibular nuclear complexes. In the present study, the effect of the central asymmetry upon a function of different motor systems was investigated in the freely behaving rats subjected to unilateral or bilateral labyrinthectomy (UL or BL). In four sets of experiments the following results have been obtained. 1. Seven UL-evoked symptoms (which reflect impairment of different motor systems) were qualitatively characterized. The short-lasting symptoms were: (1) body twisting, (2) rolling, (3, 4) extension of the fore- and hindlimb contralateral to UL, and (5) circling. These symptoms disappeared in a fixed order during recovery from anesthesia. During of expression of the symptoms was very short (< 1 hour) with the Halothan anesthesia and much longer (approximately 8 hours) with the chloral hydrate anesthesia. The long-lasting symptoms were (6) spontaneous ocular nystagmus, that persisted for 3 days after UL, and (7) head roll tilt, that persisted for at least several weeks after UL. 2. In BL-animals, stimulation of one of the 8th nerves was performed (by means of an implanted electrode; pulses 0.3 ms, 50 Hz, current up to 400 microA). By increasing gradually the strength of the stimulating current, we could evoke all the UL-symptoms but generally in the order (7-->1) which was the reverse as compared to the order of disappearance of the corresponding symptoms during recovery after UL (1-->7). These findings suggest that different symptoms need different levels of the central asymmetry for their appearance, and these levels also determine the order of disappearance of the symptoms during recovery from UL. 3. In UL-animals, by stimulating the 8th nerve on UL-side with a properly adjusted current (200-400 microA) we could immediately abolish all the symptoms except (6), which was, however, considerably reduced. This finding suggests that stimulation of the 8th nerve in UL-rats restores the central symmetry, which results in a concerted disappearance of almost all symptoms. In addition to the intermediate effects, stimulation of the 8th nerve in UL-animals resulted in a long-lasting effect, that is a reduction of the head roll tilt which persisted for at least 10 days after stimulation. 4. In BL-animals bilateral stimulation of the 8th nerve resulted in restoration of the muscular tone, and in considerable improvement of the control of the head position.

Anesthetics, Inhalation↗

PubMed1996

Control of locomotion in the marine mollusc Clione limacina. XI. Effects of serotonin.

The locomotor activity in the marine mollusc Clione limacina has been found to be strongly excited by serotonergic mechanisms. In the present study putative serotonergic cerebropedal neurons were recorded simultaneously with pedal locomotor motoneurons and interneurons. Stimulation of serotonergic neurons produced acceleration of the locomotor rhythm and strengthening of motoneuron discharges. These effects were accompanied by depolarization of motoneurons, while depolarization of the generator interneurons was considerably lower (if it occurred at all). Effects of serotonin application on isolated locomotor and non-locomotor pedal neurons were studied. Serotonin (5 x 10(-7) to 1 x 10(-6) M) affected most pedal neurons. All locomotor neurons were excited by serotonin. This suggests that serotonergic command neurons exert direct influence on locomotor neurons. Effects of serotonin on nonlocomotor neurons were diverse, most neurons being inhibited by serotonin. Some effects of serotonin on locomotor neurons could not be reproduced by neuron depolarization. This suggests that, along with depolarization, serotonin modulates voltage-sensitive membrane properties of the neurons. As a result, serotonin promotes the endogenous rhythmical activity in neurons of the C. limacina locomotor central pattern generator.

Animals↗