Effect of selective protein kinase C inhibitor on synaptic plasticity of command neurons of defensive behaviour during sensitization in snails

Polymyxin B (proteinkinase C inhibitor) effects on nociceptive sensitization of semiintact preparation were investigated in LP11 and RP11 snail neurons. It was found that application of sensitizing stimuli to control snail head initiated neural membrane depolarization, increase its excitability as well as depression of neural responses evoked by sensory stimulation during short-term stage. Polymyxin B application suppressed neural responses evoked by sensitizing (nociceptive) stimuli. At the same time changes in neural membrane excitability as well as neural responses evoked by tactile stimulation of snail foot or chemical stimulation of snail head were similar with ones in control snails. Polymyxin Bdid does not change the depression of neural responses evoked by tactile stimulation of snail head during short-term stages of sensitization but significantly suppressed facilitation of neural responses evoked by tactile stimulation of snail head during long-term stage of sensitization. It was suggested that proteinkinase C is involved in regulation of nociceptive mechanisms as well as in plasticity selective induction mechanisms in command neuron synaptic inputs activated by tactile stimulation of snail head.     

Selective involvement of opioids in mechanisms of synapse-specific plasticity in Helix lucorum snail during sensitization acquisition

Effects of met-enkephalin (opioid peptide) and naloxone (opioid antagonist) on nociceptive sensitization were studied in L-RP11 Helix neurons. In control snails sensitizing stimulation produced reversible membrane depolarization and depression of neural responses evoked by sensory stimuli during the short-term stage of sensitization and facilitation of these responses at the long-term stage. Met-enkephalin (10 but not 0.1 microM) suppressed the neural responses evoked by nociceptive stimuli. Sensitizing stimulation during metenkephalin application prevented the facilitation of neural responses evoked by tactile stimulation of snail head, whereas facilitation of neural responses evoked by chemical stimulation of head or tactile stimulation of foot were similar to that in control sensitized snails. Sensitizing stimulation during met-enkephalin and/or naloxone application prevented the facilitation of neural responses evoked by chemical stimulation of snail head, whereas responses evoked by tactile stimulation of snail head or foot were facilitated (as in neurons of control sensitized snails). Opioids are suggested to be involved in regulation of nociceptive mechanisms and selective induction of long-term plasticity in L-RP11 neural inputs activated by tactile of chemical stimulation of snail head.     

Learning-related long-term synaptic facilitation in snails: Possible mechanisms of long-term memory formation

The long-term changes in the electrical activity of command neurons related to sensitization and elaboration of associative defensive behavioral habit (food rejection) were studied inHelix snail. The long-term effects consisted of facilitation of synaptic components in neuronal responses to the test stimulations. Variations were found in the dynamics of long-term synaptic facilitation of responses to the applied chemical and tactile stimuli in the course of sensitization, as well as dependence of the degree of long-term facilitation of responses to the test stimulation at the site of its application with respect to the site of the sensitizing stimulation (site-specific sensitization). After conditioning, the synaptic response of command neurons to the conditioning stimulation appeared approximately 30 min later than did the long-term sensitization in these cells. The minimum duration of long-term synaptic facilitation of responses to the test stimulation varied from 1 h (for tactile stimulation) to 3 h (for chemical stimulation). The maximum duration of effects exceeded 4 h. It is suggested that the observed features of the synaptic plasticity in command neurons during learning are based on the selective regulation of synaptic inputs by specific protein regulators, whose lifespan does not exceed 1 h to 3 h.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 383–389, September–October, 1993.     

Selectivity of opioid peptide effects on excitability and various sensory inputs in LPl1 and PPl1 command neurons participating in defensive behavior of the snail Helix lucorum

Opioid peptides effects on neural membrane as well as neural responses evoked by sensory stimuli with different modality and site of application, were investigated in L-RPII command neurones of defensive behaviour of semi-intact preparation in the land snail Helix lucorum. Met-enkephalin (10 uM) application onto the snail CNS increases membrane excitability and produces facilitation of neural responses evoked by quinine solution (0.5%) application onto snail head and depression of reactions evoked by tactile stimulation of the head. Met-enkephalin in dose of 0.1 uM initiates only a depression of neural responses evoked by tactile stimulation of the head. Leu-enkephalin (10 uM) application suppresses neural reactions evoked by tactile stimulation of the head. Membrane excitability and neural responses evoked by quinine application onto the snail head do not change after leu-enkephalin administration. Effects appear 10-20 min after initiation of the peptide application. Initial neural responses were observed 15-30 min after CNS washing with Ringer solution. In addition, facilitation of neural responses evoked by chemical stimulation of the snail head was found 30-50 min after leu-enkephalin washing. Peptides do not change neural responses evoked by tactile stimulation of the snail foot. Neural effects of peptides were prevented by simultaneous naloxon administration (50 uM). Experimental results show selective opioid peptides' effects on excitability and plasticity of L-RPII neural inputs with site- and modality-specifics.     

Effect of cyclic AMP on the excitation and response of command neurons responsible for the snail defensive behavior caused by sensory stimulation]

Extraneuronal application of db-cAMP or intraneuronal injection of cAMP were found to increase the neural membrane excitability and synaptic facilitation in neural responses to sensory stimulation of Lpl1 and Rpl1 neurones. The db-cAMP exerted no effects on neural responses to tactile stimulation of the snail foot or mantle. The intraneuronal injection of cAMP produced synaptic facilitation only in neural responses to quinine application to the snail head. The findings suggest the cAMP selective involvement in postsynaptic mechanisms of inducing the long-term facilitation transient stage.     

Antagonists of NMDA glutamate receptors selectively affect synaptic mechanisms of the nociceptive sensitization in the snail

The effects of N-methyl-D-aspartate (NMDA) glutamate receptor antagonists on the mechanisms of nociceptive sensitization were studied in LPl1 and RPl1 neurons of the semiintact preparation of a Helix lucorum snail. Application of sensitizing stimuli on the head part of the control preparation led to a depolarization of the membrane and increase in its excitability. A depression of responses of neurons evoked by tactile or chemical sensory stimulation during the short-term period and significant facilitation of responses during the long-term period of sensitization were observed. Sensitization performed under conditions of application of NMDA antagonists (AP5 or MK801) produced similar changes in membrane potential, membrane excitability, and neuronal responses evoked by tactile stimulation of the head or foot. However, the chemical stimulation of the head under these conditions evoked a significant depression of responses during the short- and long-term sensitization periods. The results suggest that the NMDA glutamate receptor antagonists selectively affect the plasticity induction mechanisms of the command neuron synaptic inputs, which mediate the chemical sensory stimulation from the snail's head.     

Transformation of the afferent tactile signal into a motor command in the cat motor cortex

Activity of 112 neurons of the precruciate motor cortex in cats was studied during a forelimb placing reaction to tactile stimulation of its distal parts. The latent period of response of the limb to tactile stimulation was: for flexors of the elbow (biceps brachii) 30–40 msec, for the earliest reponses of cortical motor neurons about 20 msec. The biceps response was observed 5–10 msec after the end of stimulation of the cortex with a series of pulses lasting 25 msec. Two types of excitatory responses of the neurons were identified: responses of sensory type observed to each tactile stimulation of the limb and independent of the presence or absence of motion, and responses of motor type, which developed parallel with the motor response of the limb and were not observed in the absence of motion. The minimal latent period of the responses of motor type was equal to the latent period of the sensory responses to tactile stimulation (20±10 msec). Stimulation of the cortex through the recording microelectrode at the site of derivation of unit activity, which increased during active flexion of the forelimb at the elbow (11 stimuli at intervals of 2.5 msec, current not exceeding 25 µA), in 70% of cases evoked an electrical response in the flexor muscle of the elbow.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 115–123, March–April, 1977.     

Effect of zif268 early gene antisense oligonucleotide on mechanisms of synapse-specific plasticity

It was found that nociceptive sensitization was followed by long-term facilitation of synaptic responses evoked by chemical sensory stimulation of the snail "head", tactile stimulation of the snail "head" and foot in LP11 command neuron of defence behavior in snail Helix lucorum. Sensitizing stimulation during the intracellular injection of antisense olygonucleotide immediate early gene zif268 resulted in a selective suppression of synaptic facilitation in LP11 neuron responses evoked by tactile and chemical stimulation of the snail "head". At the same time, development of synaptic facilitation of responses in the LP11 neuron evoked by tactile stimulation of the foot was the same as in control sensitized snails. The results suggest that immediate early gene zif268 is selectively involved in the mechanisms of specific regulation of plasticity of the synaptic "input" of LP11 neuron from sensory receptors of the snail "head".     

Critical role of intracellular calcium in plasticity mechanisms of defense behavior command neurons LPl1 and PPl1 of Helix lucorum during nociceptive sensitization

The role of intracellular calcium in changes in excitability and responses of defense behavior command neurons LP11 and PP11 of Helix lucorum to sensory stimulation was investigated in semi-intact preparation of a snail during nociceptive sensitization. It was found that application of sensitizing stimuli onto the snail's head initiated membrane depolarization, increase in its excitability as well as depression of neural responses evoked by sensory stimuli in short-term period of sensitization and significant facilitation of neural responses in long-term period of sensitization. To elucidate the contribution of LP11 and PP11 neurons in plasticity rearrangements involved in the mechanisms of sensitization, we applied sensitizing stimuli during strong hyperpolarization of the neurons or after intracellular injection of calcium chelators. Application of sensitizing stimuli during hyperpolarization of the neurons suppressed the increase in membrane excitability and depressed the neural responses evoked by chemical stimulation of snail's head i.m. short- and long-term periods of sensitization. At the same time, synaptic facilitation of neural responses evoked by tactile stimulation of snail's head and foot was observed, which was similar to synaptic facilitation in the control sensitized snail. Intracellular injection of EGTA or BARTA (calcium chelators) before sensitization suppressed synaptic facilitation in neural responses evoked by sensory stimulation. Under these conditions, the increase in excitability was more pronounced then in the control snail neurons. The experimental results suggest the changes in neural responses evoked by sensory stimulation in sensitized snails involve postsynaptic calcium-dependent mechanisms of plasticity in LP11 and PP11 neurons.     

Effects of calcium channel blockers on spino-bulbo-spinal reflexes evoked by activation of the high-threshold and low-threshold somatic afferents

Effects of the calcium channel blockers nifedipine and verapamil on spino-bulbo-spinal (SBS) reflexes were studied in rats anesthetized with a mixture of urethane and chloralose; the reflexes evoked by activation of the high-threshold and low-threshold (tactile) somatic afferents were tested. The blockers were microinjected into then. reticularis gigantocellularis, the main structure where the SBS reflexes are relayed. Nifedipine (10^–4 M) evoked fast (with a latency of 1–2 min) and significant (20%–60%) suppression of both the high-threshold and low-threshold SBS reflexes. The reflexes recovered within 40 to 90 min. Lower concentrations of nifedipine (10^–5 M) either did not modify both types of the SBS reflexes (in 25% of experiments) or facilitated these reflexes by 16%–40% within 15–20 min. Microinjections of verapamil affected the SBS reflexes in a similar manner, but the effects were shorter. Possible ways by which the L-type calcium channels are involved in the transmission of afferent impulsation of different modalities (nociceptive and non-nociceptive) are discussed.Neirofiziologiya/Neurophysiology, Vol. 26, No. 4, pp. 270–275, July–August, 1994.     

Selective effect of the antibody to protein SMP-69 on activity of the defence behavior command neurons in grape snail

Effects of antibody against serotonin-modulated protein SMP-69 on defence behavior command neurons L-RP11 were studied in semi-intact preparation of snail Helix lucorum. An increase in membrane excitability as well as selective facilitation of neural responses evoked with chemical sensory stimulation of the snail head (0.25-0.5% quinine solution) were determined 1-1.5 hours after antibody application to the neurons. The antibody did not change neural responses evoked with tactile stimulation of the snail head. These effects were similar to those found in L-RP11 neurons after serotonin or cAMP applications as well as after nociceptive sensitization of the snail. It was suggested that protein homologically related the SMP-69 in mammalians was involved in mechanisms of excitability as well as long-term specific plasticity regulation of L-RP11 neurons synaptic inputs from the head chemoreceptors in snail Helix lucorum.     

Effect of protein synthesis inhibitors on neuronal mechanisms of sensitization inHelix snail

A sensitizing treatment with 5–10% quinine solution causes short-term (lasting 50–70 min) and long-term (lasting several hours) changes in the activity of the command neurons for defensive behavior (LPl1 and PPl1) in the snailHelix lucorum. The short-term effects are characterized by a depolarizing shift in membrane potential, increased excitability, and an initial increase in the content of bound calcium (Ca-c) in the neurons. The long-term effects appear as facilitation of synaptic components of neuronal responses to sensory stimuli without any changes in excitability and in membrane potential, and also as a repeated increase of Ca-c content. Treatment with anisomycin or cycloheximide during sensitization acquirement prevents development of long-term sensitization.Translated from Neirofiziologiya, Vol. 25, No. 2, pp. 109–115, March–April, 1993.     

Dynamic defensive and feeding reactions to the acquisition of sensitization in edible snails]

In snails changes of defensive and alimentary behaviour and of reactions of command and modulator neurones of these kinds of behaviour were studied during elaboration of sensitization. After a single action of 50% chinine solution on mollusc's head, a short-term (during 50-70 min) and long-term (hours or days) facilitation was found of animals defensive reactions and responses of command neurones of defensive behaviour to tactile and chemical sensory stimuli. Alimentary behaviour of the snails and reactions of modulator neurones of alimentary behaviour to carrot juice presentation were inhibited in sensitized animals. Dynamics differences of defensive responses to tactile and chemical stimuli in the same sensitized animals were observed. Short-term responses facilitation under sensitization correlated chiefly with depolarization of the membrane potential of defensive behaviour neurones and with an increase of plasmatic membrane excitability. Prolonged facilitation of responses was due mainly to a change of effectiveness of synaptic transmission. The described model of sensitization elaboration can be a base for studying of molecular-cellular mechanisms, underlying the learning.     

Selective pharmacological blocking of synaptic transmission through the parasympathetic ganglia: Effects on the cardiovascular system

In acute experiments on rats and dogs, compounds IEM-1556 and IEM-1678, the blockers of transmission through the parasympathetic ganglia, reduced the negative chronotropic effect of stimulation of the vagus nerve (VN), while practically not changing the heart rate (HR). In chronic experiments on dogs, these compounds increased the HR, substantially reduced the respiratory heart arrhythmia, did not change the arterial blood pressure (AP), and reduced the chronotropic effects of VN stimulation. IEM-1556 exerted more strong and long-lasting blocking effects on vagal heart control than IEM-1678 did, but in anesthetized animals could evoke a drop in the AP. Acetylcholine, if administered during the action of the above compounds, inhibited heart activity. It is concluded that both IEM-1678 and IEM-1556 are selective parasympatholytics (although IEM-1556 may produce a side effect). The above compounds block synaptic transmission through the intracardiac parasympathetic ganglia and do not affect neuro-effector transmission in the heart.Neirofiziologiya/Neurophysiology, Vol. 28, No. 2/3, pp. 151–159, March–June, 1996.     

Effects of dopamine on background and evoked activity in interneurons of a spinal cord segment isolated from infant rats

The effects of 1·10^–5–1·10^–3 M dopamine on background and evoked interneuronal-activity was investigated during experiments on a spinal cord segment isolated from 11–18-day old infnat rats. Dopamine induced an increase in background firing activity rate in 52.5% and a reduced rate in 42.5% of the total sample of responding cells. Dopamine exerted a primarily inhibitory effect on interneuronal activity invoked by dorsal root stimulation, as witnessed by the reduced amplitude of the postsynaptic component of field potentials in the dorsal horn together with the fact that invoked activity was depressed in 66.7% of total interneurons responding to dopamine and facilitated in only 33.3% of these cells. All dopamine-induced effects were reversible and dose-dependent. Dopamine-induced effects disappeared after superfusing the brain with a solution containing 0–0.1 mM Ca²⁺ and 2 mM Mn²⁺, suggesting that this response is of transsynaptic origin. In other cells the excitatory or inhibitory action of dopamine also persisted in a medium blocking synaptic transmission; this would indicate the possibility of dopamine exerting depolarizing and hyperpolarizing effects on the interneuron membrane directly. Contrasting responses to dopamine in interneurons may be attributed to the presence of different types of dopamine receptors in the spinal cord.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 7–16, January–February, 1989.     

Unit responses of the sensomotor cortex to paired electrical stimuli

Unit responses of the sensomotor cortex to paired electrical stimulation and visual cortex, applied either simultaneously or after various delays (from 0 to 200 msec) depend on the order of application of the stimuli and on the interval between them. If stimulation of the sensomotor cortex was used in a conditioning role the response continued unchanged when the intervals between stimuli were increased to 200 msec. If, however, stimulation of the sensomotor cortex had a testing role interaction was observed between the stimuli so that responses to both first and second stimuli were blocked; this was exhibited most clearly for intervals of 40–80 msec between stimuli. The blocking effect persisted on some neurons with delays of up to 200 msec between stimuli, while the response of others to both the first and the second stimulus was restored.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 628–635, November–December, 1973.     

Responses of rabbit visual cortical neurons to intracortical electrical stimulation

Responses of rabbit visual cortical neurons to single and repetitive intracortical electrical stimulation were investigated. The stimulating electrode was located 0.7–1.2 mm away from the recording electrode. Response thresholds to single stimulation were as a rule 150–180 µA, whereas to series of stimuli they were 30–60 µA. The latent period to the first spike averaged 5–15 msec but the probability of the initial discharge was very low, namely 3–6%. With an increase in current intensity the duration of the initial inhibitory pause was increased in half of the neurons responding to it, whereas in the rest it was unchanged. After presentation of series of stimuli spontaneous activity was enhanced for a short time (4–6 sec). In about half of the cells the same kinds of discharge dynamics were observed in response to repetitive stimulation (frequency 0.25 Hz) as in responses to light, but more neurons with sensitization of discharge and fewer "habituating" neurons took part in responses to electrical stimulation. It is postulated that stimulation of a given point of the visual cortex evokes excitation of a local neuron hypercolumn and inhibition of neighboring cell columns.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 412–419, July–August, 1983.     

Neurons with visual receptive fields independent of eye position in the caudal section of the ventral bank of cat cruciate slucus

Neurons responding to tactile and visual stimulation were found in the caudal section of the cruciate slucus ventral bank in awake cats. Tactile receptive fields were located on the face, mainly around the mouth. Visual stimuli evoked a response when presented close to the tactile receptive field. It was found that the visual responses of these bimodal neurons located in layer VI of the cortex display spatial consistency. The position of these visual receptive fields remained constant through saccadic eye movements, while still linked to the tactile receptive field.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neifofiziologiya, Vol. 18, No. 6, pp. 800–805, November–December, 1986.