Biomedical subjects

G N Orlovsky

Publications and source records attributed to G N Orlovsky.

At least 37 records · Page 2Linked to original sources

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↗

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↗

PubMed1996

Visual potentiation of vestibular responses in lamprey reticulospinal neurons.

The lamprey normally swims with the dorsal side up. Illumination of one eye shifts the set-point of the vestibular roll control system, however, so that the animal swims with a roll tilt towards the source of light (the dorsal light response). A tilted orientation is often maintained for up to 1 min after the stimulation. In present study, the basis for this behaviour was investigated at the neuronal level. The middle rhombencephalic reticular nucleus (MRRN) is considered a main nucleus for the control of roll orientation in lampreys. Practically all MRRN neurons receive vestibular and visual input and project to the spinal cord. Earlier extracellular experiments had shown that optic nerve stimulation potentiates the response to vestibular stimulation in the ipsilateral MRRN. This most likely represents a neural correlate of the dorsal light response. Experiments were carried out in vitro on the isolated brainstem of the silver lamprey (Ichthyomyzon unicuspis). MRRN cells were recorded intracellularly, and the overall activity of descending systems was monitored with bilateral extracellular electrodes. The responses to 10 Hz optic nerve stimulation and 1 Hz vestibular nerve stimulation, and the influence of optic nerve stimulation on the vestibular responses, were investigated. In most preparations, optic nerve stimulation excited practically all ipsilateral MRRN cells. After stimulation, the cell was typically depolarized and showed an increased level of synaptic noise for up to 80 s. In contralateral MRRN neurons, optic nerve stimulation usually evoked hyperpolarization or no response. Vestibular nerve stimulation evoked compound excitatory postsynaptic potentials (EPSPs) or spikes in approximately 90% of the cells, both ipsilaterally and contralaterally. A smaller subpopulation of MRRN cells (approximately 10%) received vestibular inhibition. In 26 of 48 recorded MRRN cells, the response to vestibular stimulation was potentiated after ipsilateral optic nerve stimulation. The potentiation was seen in cells receiving either excitatory or inhibitory vestibular input as an increase in EPSP amplitude/spiking (85%) and a decrease in inhibitory postsynaptic potential amplitude (15%) respectively. In most cases the vestibular responses did not return to control levels during the testing period (10-30 min), and thus the visual stimulation most likely induced long-lasting changes in the functional connectivity of the role control network, in addition to the short-lasting afteractivity. In four of the 11 cells recorded contralateral to the stimulated optic nerve, a depression of the vestibular response could be seen. In potentiated cells, single vestibular pulses often evoked longer episodes of large synaptic noise and sometimes spiking. In the latter case, the action potentials appeared with highly variable latency after each stimulation pulse. This indicates that an important mechanism underlying the potentiation may be a long-lasting increase in excitability in a pool of unidentified interneurons located either upstream of the MRRN cells, relaying vestibular and visual inputs, or downstream, providing positive feedback.

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PubMed1995

Control of locomotion in marine mollusk Clione limacina. VIII. Cerebropedal neurons.

1. The pteropod mollusk Clione limacina swims by rhythmical oscillations of two wings, and its spatial orientation during locomotion is determined by tail movements. The majority of neurons responsible for generation of the wing and tail movements are located in the pedal ganglia. On the other hand, the majority of sensory inputs that affect wing and tail movements project to the cerebral ganglia. The goal of the present study was to identify and characterize cerebropedal neurons involved in the control of the swimming central generator or motor neurons of wing and tail muscles. Cerebropedal neurons affecting locomotion-controlling mechanisms are located in the rostromedial (CPA neurons), caudomedial (CPB neurons), and central (CPC neurons) zones of the cerebral ganglia. According to their morphology and effects on pedal mechanisms, 10 groups of the cerebropedal neurons can be distinguished. 2. CPA1 neurons project through the ipsilateral cerebropedal connective to both pedal ganglia. Activation of a CPA1 by current injection resulted in speeding up of the locomotor rhythm and intensification of the firing of the locomotor motor neurons. 3. CPA2 neurons send numerous thin fibers into the ipsi- and contralateral pedal and pleural ganglia through the cerebropedal and cerebropleural connectives. They strongly inhibit the wing muscle motor neurons and, to a lesser extent, slow down the locomotor rhythm. 4. CPB1 neurons project through the contralateral cerebropedal connective to both pedal ganglia. They activate the locomotor generator. 5. CPB2 neurons also project, through the contralateral cerebropedal connective, to both pedal ganglia. They affect wing muscle motor neurons. 6. CPB3 neurons have diverse morphology: they project to the pedal ganglia either through the ipsilateral cerebropedal connective, or through the contralateral one, or through both of them. They affect putative motor neurons of the tail muscles. 7. CPC1, CPC2, and CPC3 neurons project through the ipsilateral cerebropedal connective to both pedal ganglia. They activate the locomotor generator. 8. CPC4 and CPC5 neurons project through the contralateral cerebropedal connective to the contralateral pedal ganglia. They activate the locomotor generator. 9. Serotonergic neurons were mapped in the CNS of Clione by immunohistochemical methods. Location and size of cells in two groups of serotonin-immunoreactive neurons in the cerebral ganglia appeared to be similar to those of CPA1 and CPB1 neurons. This finding suggests a possible mechanism for serotonin's ability to exert a strong excitatory action on the locomotor generator of Clione. 10. The role of different groups of cerebropedal neurons is discussed in relation to different forms of Clione's behavior in which locomotor activity is involved.

Animals↗

PubMed1995

Control of locomotion in marine mollusk Clione Limacina. IX. Neuronal mechanisms of spatial orientation.

1. When swimming freely, the pteropod mollusk Clione limacina actively maintains a vertical orientation, with its head up. Any deflection from the vertical position causes a correcting motor response, i.e., bending of the tail in the opposite direction, and an additional activation of the locomotor system. Clione can stabilize not only the vertical orientation with its head up, but also the posture with its head down. The latter is observed at higher water temperature, as well as at a certain stage of hunting behavior. The postural control is absent in some forms of behavior (vertical migrations, defensive reactions, "looping" when hunting). The postural reflexes are driven by input from the statocysts. After removal of the statocysts, Clione was unable to maintain any definite spatial orientation. 2. Activity of the neuronal mechanisms controlling spatial orientation of Clione was studied in in vitro experiments, with the use of a preparation consisting of the CNS and statocysts. Natural stimulation (tilt of the preparation up to 90 degrees) was used to characterize responses in the statocyst receptor cells (SRCs). It was found that the SRCs depolarized and fired (10-20 Hz) when, during a tilt, they were in a position on the bottom part of the statocyst, under the statolith. Intracellular staining has shown that the SRC axons terminate in the medial area of the cerebral ganglia. Electrical connections have been found between some of the symmetrical SRCs of the left and right statocysts. 3. Gravistatic reflexes were studied by using both natural stimulation (tilt of the preparation) and electrical stimulation of SRCs. The reflex consisted of three components: 1) activation of the locomotor rhythm generator located in the pedal ganglia; this effect of SRCs is mediated by previously identified CPA1 and CPB1 interneurons that are located in the cerebral ganglia and send axons to the pedal ganglia; 2) bending the tail evoked by differential excitation and inhibition of different groups of tail muscle motor neurons; this effect is mediated by CPB3 interneurons; and 3) modification of wing movements by differential excitation and inhibition of different groups of wing motor neurons; this effect is mediated by CPB2 interneurons. 4. Gravistatic reflexes in the tail motor neurons were inhibited or reversed at a higher water temperature. 5. The SRCs are not "pure" gravitation sensory organs because they are subjected to strong influences from the CNS. In particular, CPC1 interneurons, participating in coordination of different aspects of the hunting behavior, exert an excitatory action on some of the SRCs, and inhibitory actions on others.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1995

Neural networks that co-ordinate locomotion and body orientation in lamprey.

The networks of the brainstem and spinal cord that co-ordinate locomotion and body orientation in lamprey are described. The cycle-to-cycle pattern generation of these networks is produced by interacting glutamatergic and glycinergic neurones, with NMDA receptor-channels playing an important role at lower rates of locomotion. The fine tuning of the networks produced by 5-HT, dopamine and GABA systems involves a modulation of Ca2+-dependent K+ channels, high- and low-threshold voltage-activated Ca2+ channels and presynaptic inhibitory mechanisms. Mathematical modelling has been used to explore the capacity of these biological networks. The vestibular control of the body orientation during swimming is exerted via reticulospinal neurones located in different reticular nuclei. These neurones become activated maximally at different angles of tilt.

Animals↗

PubMed1995

Responses of neurons in the central cervical nucleus of the rat to proprioceptive and vestibular inputs.

Activity of neurons in the central cervical nucleus (CCN) was recorded extracellularly in decerebrate, immobilized rats. Neurons were identified by their antidromic response to electrical stimulation of the contralateral superior cerebellar peduncle. Stimulation of the ipsilateral dorsal neck muscles (m. biventer cervicis and complexus [BCC]; m. splenius [S]) by a single electric pulse evoked a short-latency (approximately 1 ms) excitatory response in the majority of CCN neurons. The response was usually followed by a period of inhibition of the resting discharge (approximately 20 ms). Stimulation of the contralateral BCC or S usually produced only inhibition of the resting discharge (approximately 20 ms). Mechanical stretching of BCC or S resulted in activation (about 100% increased firing rate) of the ipsilateral CCN neurons, lasting for the duration of the stretch. A pronounced dynamic component, i.e. an extra-excitation at the beginning of the stretch and inhibition after termination of the stretch, was also observed. Stroking and pinching of the skin in the neck region affected the tested CCN neurons, while cutaneous stimuli at other sites of the body were inefficient. Stimulation of the vestibular receptors was performed in two ways. (i) Unilateral galvanic stimulation of the labyrinths by constant current pulses through the external acoustic meatus affected all CCN neurons tested. Contralateral stimulation with negative current was found to be most efficient; it produced excitation followed by inhibition. (ii) Natural vestibular stimulation was performed by rotating the animal in the transverse plane (roll, +/- 10 degrees) or the sagittal plane (pitch, +/- 5 degrees). Sinusoidal movements (0.5-1 Hz) or trapezoid movements were applied. Sinusoidal roll tilt evoked responses in all neurons tested, with a peak discharge during contralateral rolling or at the moment of transition from the ipsi- to contralateral position. All tested CCN neurons also responded statically to roll tilt, i.e. their tonic activity increased with up to 65%, of which the majority (80%) responded in the continuously maintained contralateral roll tilt position compared to the ipsilateral. Sinusoidal pitch tilt also affected all tested neurons, although the reaction was smaller than compared to roll. They usually responded by increasing their firing rate when moving towards the nose-down position. A static response (40-60% difference in the firing rate between the extreme pitch positions) was observed in some neurons. No tested neurons showed any clear rhythmic modulation during either spontaneous or induced, real or fictive locomotion.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed1994

Defense reaction in the pond snail Planorbis corneus. I. Activity of the shell-moving and respiratory systems.

1. In the intact pond snail Planorbis corneus, tactile or electrical stimulation of the skin evoked a biphasic general defense reaction. A weak stimulation evoked only the first phase of the reaction, represented as a fast pulling of the shell towards the head. With stronger stimulation, this phase was followed by the second phase that was comprised of three components: detachment from the substrate, slow retraction of the body into the shell, and letting out of air from the lung through the pneumostome. 2. About 70 motor neurons (MNs) of the columellar muscle have been revealed in different ganglia by means of their cobalt back-filling through the cut columellar nerve. A complicated pattern of electrical coupling was found for different groups of MNs. Excitation of individual MNs, evoked by current injection, resulted in contraction of the columellar muscle (CNS-columellar muscle preparation). The strongest contraction was evoked by the cerebral MNs; fast small contraction by the parietal MNs; and slow, long-latency contraction, by the pedal MNs. 3. In the same preparation, electrical stimulation of the cutaneous (lip) nerve evoked biphasic contraction of the columellar muscle (a first phase lasting approximately 3 s, and a second phase of up to 1 min). The temporal pattern of this response was similar to that of the defense reaction in the intact animal. A weak stimulation evoked only the first phases of the reaction, while a stronger stimulation evoked both phases. The amplitude of both the first and the second phase was graded with the strength of stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1994

Defense reaction in the pond snail Planorbis corneus. II. Central pattern generator.

1. In the isolated CNS of the pond snail Planorbis corneus, spontaneous bursts of activity in the motor neurons (MNs) supplying the columellar muscle were occasionally observed. The biphasic pattern of this activity, with a shorter (3-5 s) initial burst and longer (20-40 s) subsequent burst, was similar to that of the motor output during the general ("whole-body") defense reaction. In preparations consisting of the CNS isolated with the columellar muscle or with the lung, spontaneous biphasic contractions of the muscle as well as openings of the pneumostome with a temporal pattern characteristic of the defense reaction were observed. These findings demonstrated that the efferent pattern of the defense reaction in the snail is, to a large extent, produced by a special neuronal mechanism (the central pattern generator, CPG) triggered by the sensory input, rather than generated by ongoing processing of sensory input. The CPG consists of two components responsible for generation of two phases of the defense reaction. A characteristic feature of the CPG is that the magnitude of its response depends in a graded fashion on the strength of the initial stimulus. 2. In the pleural ganglia there are at least two electrically connected interneurons (DRN1s) that play an important role in generation of the first phase of the defense reaction. Processes of the DRN1s form a ring passing through all (except pedal and buccal) ganglia. The DRN1s received an excitatory input when a peripheral nerve was stimulated. They generated action potentials of long (0.2-2 s) duration. The DRN1 from the right ganglion was studied in more detail.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1994

Defense reaction in the pond snail Planorbis corneus. III. Response to input from statocysts.

1. In the intact pond snail Planorbis corneus, a rapid tilt in any plane evoked a defense reaction consisting of a fast movement of the shell towards the head, shortening of the foot, inhibition of locomotion and of rhythmical feeding movements. This reaction was similar to the first phase of the general defense reaction of Planorbis to cutaneous stimulation. 2. A method has been developed for inclination of the isolated CNS in space (up to 90 degrees) and simultaneous intracellular recordings from different neurons. 3. The statocyst receptor cells (SRCs) responded both phasically and tonically to the tilt. The SRCs differ in their spatial zones of sensitivity. 4. Essential manifestations of the defense reaction to the input from statocysts could be observed in the in vitro preparation of the CNS isolated with statocysts. Both tilting of the CNS and electrical stimulation of individual SRCs elicited an excitatory response in numerous neurons from different ganglia, including motor neurons (MNs) of the columellar muscle. This response was of "all-or-none" nature, and could be evoked by electrical stimulation of any SRC. The response was followed by a long (10-20 s) period of refractoriness. 5. Activation of SRCs resulted also in excitation of the giant dopaminergic cell in the left pedal ganglion (related to the control of respiration), in inhibition of the feeding rhythm generator, and in inhibition of the pedal neurons responsible for activation of the ciliary locomotor system. 6. Combined stimulation of two inputs able to evoke a defense reaction, i.e., those from the statocyst and from cutaneous nerve, revealed a strong interdependence of their central effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1993

Role of dermal photoreceptors and lateral eyes in initiation and orientation of locomotion in lamprey.

The response to illumination, and the functional roles of skin photoreceptors and lateral eyes, were examined in the adult river lamprey (Lampetra fluviatilis L.). Illumination of one side of the lamprey evoked a turning movement away from the light source followed by locomotion. The lateral eyes were responsible for directing the movements away from the source of light. A selective illumination of one lateral eye consistently evoked a negative phototactic reaction, whereas a selective illumination of tail skin photoreceptors evoked locomotion, without any preferential orientation relative to the source of light. Experiments were performed by video recording the locomotor responses to localized illumination, and analyzed frame by frame. The horizontal turning movement during negative phototaxis consisted of an asymmetric laterally directed mechanical wave, of higher amplitude and lower velocity than the normal locomotory waves, which was propagated from the rostral to the caudal end of the body.

Animals↗

PubMed1993

Visual input affects the response to roll in reticulospinal neurons of the lamprey.

A body orientation with the dorsal side up is usually maintained by lampreys during locomotion. Of crucial importance for this is the vestibular-driven control system. A visual input can affect the body orientation: illumination of one eye during swimming evokes roll tilt towards the source of light. The aim of the present study was to investigate the interaction of visual and vestibular inputs in reticulospinal (RS) neurons of the brainstem. The RS system is the main descending system transmitting information from the brainstem to the spinal cord. The response of neurons in the middle rhombencephalic reticular nucleus to a unilateral non-patterned optic input was investigated, as well as the influence of this input on the response of RS neurons to vestibular stimulation (roll tilt). Experiments were carried out on a brainstem preparation with intact labyrinths and, in some cases, intact eyes. Illumination of one eye or electrical stimulation of the optic nerve (10 Hz) resulted in an activation of RS neurons preferentially on the ipsilateral side of the brainstem. The same result was obtained after ablation of the optic tectum, demonstrating that there are asymmetrical visual projections to the lower brainstem which do not involve the tectum. Stimulation of the optic nerve strongly affected the vestibular response in RS neurons. As a rule RS neurons are silent at the normal (dorsal-side-up) orientation of the brainstem and become active with contralateral roll tilt. During continuous optic nerve stimulation, however, the RS neurons on the side of stimulation fire during normal orientation of the brainstem, and the response to contralateral roll tilt increases considerably in many neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Neuronal control of swimming locomotion: analysis of the pteropod mollusc Clione and embryos of the amphibian Xenopus.

It is rare to be able to explain the behaviour of a whole animal at the level of the properties and connections of characterized CNS neurones. In a marine mollusc, Clione, and a lower vertebrate embryo, Xenopus, it is possible to make intracellular recordings during fictive swimming behaviour. This has allowed us to analyse the operation of two central pattern generators (CPGs) at the cellular level. Although the timeframes over which the two CPGs operate are different, there are significant similarities in their patterns of neural output. A detailed analysis of the neural networks involved reveals that the swimming CPGs of Clione and Xenopus have several common operating principles, which suggests that common mechanisms have evolved to perform similar tasks, despite differences in neuronal 'hardware'.

Animals↗

PubMed1993

Pharmacologically induced elements of the hunting and feeding behavior in the pteropod mollusk Clione limacina. I. Effects of GABA.

1. The pteropod mollusk Clione limacina is a predator, feeding on the small pteropod mollusk Limacina helicina. Injection of gamma-aminobutyric acid (GABA) into the hemocoel of the intact Clione evoked some essential elements of the hunting and feeding behavior, i.e., protracting the tentacles, opening the mouth, and triggering the rhythmic movements of the buccal mass. This pattern resembled that evoked by presentation of the prey: Clione grasped the Limacina by its tentacles, extracted the prey's body from the shell and then swallowed it. 2. In electrophysiological experiments, several targets of GABA action have been found: 1) direct application of GABA to isolated cerebral motor neurons projecting to the protractor muscles of tentacles resulted in their excitation; 2) GABA activated the feeding rhythm generator located in the buccal ganglia; 3) GABA exerted excitatory or inhibitory effects on the receptor cells of statocysts, the effects being mediated by the efferent input to these cells; 4) GABA suppressed the defense reaction, which is an inhibition of the locomotor activity and of tentacle motor neurons, arising in response to stimulation of the head afferents; and 5) GABA potentiated an excitatory action of the serotoninergic metacerebral cells on the feeding rhythm generator. 3. Effects of GABA on the tentacle motor neurons and the feeding rhythm generator are pharmacologically distinguishable. The action of GABA on the feeding rhythm generator was mimicked by baclofen (which activates the GABAB receptors in mammalian neurons) and was not sensitive to bicuculline (the GABAA receptor antagonist in mammals). On the other hand, bicuculline competitively inhibited the GABA-induced excitation of the tentacle motor neurons. 4. GABAergic neurons have been located in the cerebral, pedal, and buccal ganglia by means of immunohistochemical methods.

Animals↗

PubMed1993

Pharmacologically induced elements of the hunting and feeding behavior in the pteropod mollusk Clione limacina. II. Effects of physostigmine.

1. A contact of the pteropod mollusk Clione limacina with its prey (small pteropod mollusk Limacina helicina) evokes a complex pattern of hunting and feeding behavior: protraction of tentacles to seize the prey, activation of buccal apparatus to swallow the prey, activation of locomotor system (speeding up of wing beating), reversal of reaction to tactile stimulation of the head, loss of normal (vertical) orientation in space, and swimming in circles. After injection of physostigmine (PhS), the acetylcholinesterase inhibitor, into the hemocoel of intact Clione, all these manifestations of the hunting and feeding behavior could be evoked by tactile stimulation of the head, or they arose spontaneously. 2. In the preparation of the isolated CNS, the effect of PhS on the neural networks controlling different aspects of the hunting and feeding behavior was studied by recording from neurons monitoring activity of different networks (< or = 4 neurons simultaneously). Tactile stimulation of the head was mimicked by a short-term electrical stimulation of the corresponding nerve. Before PhS application, the nerve stimulation evoked elements of the defense reaction, i.e., long-lasting inhibition of all main motor control systems: the locomotor network in the pedal ganglia, the tentacle control network in the cerebral ganglia, and the network controlling radula and hook movements in the buccal ganglia. However, after PhS application, the same stimulus evoked a long-lasting bout of excitation in all the three networks accompanied by activation of the heart-exciting neuron as well as by a modification of the activity of statocyst receptor cells controlling Clione's spatial orientation (the "fictive hunting bout"). Similar hunting bouts could arise spontaneously. 3. Injection of acetylcholine (ACh) into the hemocoel of intact Clione was less effective than injection of PhS. After ACh injection, reversal of reaction to head stimulation was observed in < or = 20% of the experiments (the percentage of positive results was higher if ACh was injected into the head just over the CNS). Bath application of ACh to the isolated CNS did not produce the hunting bouts. However, a short-term local application of ACh to the cerebral ganglia in the isolated CNS resulted in activation of the main motor systems controlling locomotion, protraction of tentacles, and movements of buccal mass. 4. During spontaneous PhS-induced bouts, excitation of different networks involved in hunting behavior was sometimes not quite synchronous. Different networks could be excited in variable order over a period of up to several seconds.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗

PubMed1992

Vestibular control of swimming in lamprey. I. Responses of reticulospinal neurons to roll and pitch.

A method has been developed for recording the response of single neurons in the lamprey brainstem in vitro to natural stimulation of vestibular receptors. The brainstem dissected together with the intact vestibular apparatus could be rotated in space, in two perpendicular planes (transverse, the roll tilt, and sagittal, the pitch tilt), in one of them up to 360 degrees, and in the other one up to +/- 30 degrees. The responses of single reticulospinal (RS) neurons, in all four reticular nuclei of the brainstem, to roll and pitch were recorded extracellularly and, with small inclinations (up to +/- 45 degrees) also intracellularly. Two types of preparations were used, with and without the rostral part of the spinal cord. In the brainstem preparations, most RS neurons responded both to a definite brain orientation in space and to a change of the orientation (static and dynamic reactions). Responses to roll tilt were similar in all reticular nuclei: all cells were excited with roll tilt towards the contralateral side, this reaction was qualitatively preserved when the roll was performed in combination with different pitch inclinations. Responses to pitch tilt were less clearcut; some neurons were activated with nose-up deflection while others responded to nose-down tilt. In preparations including the spinal cord, responses of RS neurons to roll and pitch tilt differed from those in the isolated brainstem in that they were much less specific and stable. Roll and pitch tilts could trigger the spinal locomotor CPG, which, by sending "efference copy" signals back to the brainstem, produced modulation of RS neurons in relation to the locomotor rhythm.

Animals↗