Avoidance reaction and defensive reflex in the rabbit based on hypothalamic stimulation inducing strokes of the paws

In experiments on rabbits electrical stimulation of the medial hypothalamic area elicited a biphasic reaction: running during the current action and species-specific reaction of kicking the floor with the hind limbs in poststimulous period. Conditioning with acoustic stimulus led in the half of rabbits to elaboration of a habit of jumping on a safe platform in experimental model of active avoidance and to a weak conditioned reaction of kicking without running in the model of classical defensive reflex. The number of conditioned limb kicks was 7-10 times less than that of analogous responses to the reinforcing stimulus. With the increase of the number of combinations, the conditioned habit of kicking became deteriorated: the response became weaker and its latency more prolonged. The results of experiments are discussed in the light of Anokhin's theory of functional system of goal-directed behavioural act.     

Avoidance reactions to painful stimulation of another individual following destruction of the rat amygdala]

Experiments in male albino rats have shown that bilateral lesion of the amygdala does not prevent avoidance conditioning to pain stimulation of another rat, improvement of the reaction after a painful action of the experimental animal and its extinction after the discontinuation of pain stimulation of the partner. Amygdalectomy performed after elaboration of a conditioned avoidance reaction, improves or worsens it, depending on which of the two rivaling motivations (sensitivity to signals of the other animal or fear of an open field) relatively predominanted in the given animal before the operation. The facts obtained suggest that the amygdala may be classified as belonging to the system of brain structures, where the "interrupting function" of emotions is achieved directing the behaviour to meet the predominant need.     

The effect of phenamine and caffeine on caudate inhibition of conditioned reflex avoidance reactions in cats]

In cats with a preliminarily learned conditioned avoidance reaction, stimulation of the caudate nucleus inhibited behavioral response by lengthening its latency and reducing the number of conditioned reactions. Intensity of the inhibitory effect did not substantially depend on the localization of electrodes in the head or body of the nucleus and weakened within a few experimental days. D,1-amphetamine (0.5 to 4 mg/kg) and caffeine (10 to 10 mg/kg) suppressed the caudate inhibition, but the action of the drugs was manifested in different ways. The influence of large doses of d,1-amphetamine was characterized by a serious disturbance of behaviour and caudate inhibition of conditioned responses.     

Cyclic 3'',5'' AMP relay in Dictyostelium discoideum. II. Requirements for the initiation and termination of the response

The secretion of 3H-cyclic adenosine 3',5'-monophosphate (cAMP) by prelabeled and suitably differentiated Dictyostelium discoideum amoebae was elicited in a perfusion apparatus by 10(-10) to 10(-5) M [14C]cAMP stimuli of defined magnitude and duration. Exogenous stimuli evoked an immediate increase in the rate of [3H]cAMP secretion which accelerated continuously to reach a peak of up to 100 times the unstimulated rate after 2--3 min of stimulation. Withdrawal of the stimulus at any time during the response led to a rapid decline to basal levels. Furthermore, a spontaneous decline in secretion rate was observed during prolonged cAMP stimulation, with a return to basal levels after 3--8 min of stimulation. After the initial secretory event, cells did not respond further to the continued presence of external [14C]cAMP unless (a) it was interrupted by a brief recovery period or (b) the level of the stimulus was increased sufficiently. Since the second increment could follow the first at any time, continuous secretion of [3H]cAMP could be sustained for up to 30 min by progressively increasing the stimulus between 10(-10) and 10(-5) M cAMP. The total magnitude of spontaneously terminated responses depended on the size of the increment in applied cAMP, larger stimuli evoking both a more rapid acceleration and a slower deceleration in [3H]cAMP secretion rate. The integrated response to a given increment in stimulus level was apparently independent of its "shape" - i.e., the duration, magnitude, and number of sub-steps in the increment. These data support two mechanistic inferences: that amoebae respond in proportion to relative increases in extracellular cAMP concentration, but adapt to the concentration of cAMP itself. The data further suggest that the initiation and termination of the response are mediated by cellular component(s) beyond cAMP-occupied receptors.     

Neuronal correlates of changes in the defensive behavior of Helix lucorum L. during ontogeny

In experiments on the isolated nervous system, responses of the same command neurones of avoidance behaviour to electrical stimulation of the intestinal nerve were compared in adult snails (Helix pomatia) and in snails 1-20 days old. Dynamics of spike reactions of the command neurones to rhythmic nerve stimulation differed in adult and newborn snails. In the neurones of young snails, no sensitization, common in the adult animals, was observed. Study of excitatory input in the command neurones during rhythmic nerve stimulation suggests independence of habituation of synaptic input amplitude and spike response sensitization, because dynamics of habituation coincided in the young and adult snails while spike response underwent sensitization only in adult animals.     

Mechanisms of destabilization and early termination of spiral wave reentry in the ventricle by a class III antiarrhythmic agent, nifekalant

Nifekalant (NF) is a novel class III antiarrhythmic agent that is effective in preventing life-threatening ventricular tachycardia/fibrillation (VT/VF). We investigated mechanisms of destabilization and early termination of spiral-type reentrant VT by NF in a two-dimensional subepicardial myocardial layer of Langendorff-perfused rabbit hearts (n = 21) using a high-resolution optical action potential mapping system. During basic stimulation, NF (0.1 microM) caused uniform prolongation of action potential duration (APD) without affecting conduction velocity and an increase of APD restitution slope. VTs induced by direct current stimulation in the presence of NF were of shorter duration (VTs > 30 s: 2/54 NF vs. 19/93 control). During VTs in control (with visible rotors), the wave front chased its own tail with a certain distance (repolarized zone), and they seldom met each other. The average number of phase singularity (PS) points was 1.31 +/- 0.14 per 665 ms (n = 7). In the presence of NF, the wave front frequently encountered its own tail, causing a transient breakup of the spiral wave or sudden movement of the rotation center (spatial jump of PS). The average number of PS was increased to 1.63 +/- 0.22 per 665 ms (n = 7, P < 0.05) after NF. The mode of spontaneous termination of rotors in control was in most cases (9/10, 90.0%) the result of mutual annihilation of counterrotating wave fronts. With NF, rotors frequently terminated by wave front collision with the atrioventricular groove (12/19, 63.2%) or by trapping the spiral tip in a refractory zone (7/19, 36.8%). Destabilization and early termination of spiral wave reentry induced by NF are the result of a limited proportion of excitable tissue after modulation of repolarization.     

Changes in excitability in the motor cortex of the dog during switching-over conditioned escape and avoidance reflexes

Excitability of the motor cortex (projection of the foreleg), judged by the threshold of flexion reaction to its stimulation during elaboration of conditioned transswitching (CT), was studied in dogs. CT was elaborated for instrumental reflexes of escape (1-st CT variant) and avoidance (2-nd CT variant). In the 1-st variant the dog escaped from the hydrochloric acid solution, if during its administration it produced an active flexion of the foreleg in situation A and an active extension of the same leg in situation B, with a permanent action of a switch (a fan). In the 2-nd CT variant, the dog avoided the acid, if in situation A, in response to a tone of 250 Hz, it actively lifted its foreleg, and if in situation B, it actively resisted a passive lift in response to the same stimulus. In escape CT as well as in avoidance CT, there was a statistically significant difference between the thresholds of flexion reaction. The threshold was lower in situation of instrumental flexion reflex formation in comparison to the situation of extension reflex formation.     

The role of dopamine and serotonin in modulating the defensive behavior of the edible snail

Dopamine application in concentration of 10(-5)-10(-6) M into saline around the snail CNS leads to decrease of excitability of LPa7 neurone which is presynaptic in relation to defensive behaviour command neurones, and to decrease of amplitude of monosynaptic excitatory postsynaptic potential (EPSP) in the command neurones elicited by intracellular stimulation of LPa7 neurone. Besides, the dopamine causes a decrease of summated EPSP amplitude in the studied neurones in response to intestinal nerve stimulation (70% in average), a change of rest potential towards hyperpolarization for 6-8 mV, a reduction of the command neurones input resistance (20% in average). The described influences can lead to a general increase of the threshold of defensive system reaction to stimulation. Dopamine action on the defensive behaviour command neurones is significantly weakened in serotonine presence. Against the dopamine background, the efficiency of serotonine influence on the value of EPSP in command neurones in response to testing stimulus is reduced. According to the obtained data, a conclusion is made that interrelation of dopamine and serotonine concentrations can be a base for formation of behaviour choice in snail.     

Rapid corticosterone-induced impairment of amplectic clasping occurs in the spinal cord of roughskin newts (taricha granulosa)

Courtship clasping, a reproductive behavior in male roughskin newts (Taricha granulosa), is rapidly blocked by an action of corticosterone (CORT) at a specific neuronal membrane receptor. The CORT-induced impairment of clasping in behaving newts appears to be mediated partly by an elimination of clasping-related activity in medullary reticulospinal neurons. Previous studies of rapid CORT actions in Taricha have focused on the brain, so existence of CORT action in the spinal cord or peripheral nervous system has not been assessed. The present study used newts with a high cervical spinal transection to examine potential spinal or peripheral CORT effects on clasping by the hindlimbs in response to pressure on the cloaca. Spinal transection causes clasps elicited by cloacal stimulation to be very sustained beyond the termination of the eliciting stimulus. In spinally transected newts, CORT caused a dose-dependent depression in the duration as well as quality of the clasp that appeared within 10 min of injection. CORT selectively impaired the usual sustained maintenance of a clasp after termination of cloacal stimulation, but not clasp elicitation during stimulation. These effects were not produced by dexamethasone, a synthetic glucocorticoid that binds poorly to the CORT membrane receptor. The CORT effect on clasp maintenance but not clasp elicitation implies selective action on an intraspinal generator for clasping but not on sensory or efferent neuromuscular aspects of the response. These results indicate the presence in the newt spinal cord of the CORT membrane receptor that exerts functional effects distinctly different from those on the brainstem.     

Improved conditioned avoidance learning by oxytocin administration in high-emotional male Sprague-Dawley rats

OBJECTIVE: To examine anti-stress-like properties of oxytocin as a means to improve conditioned avoidance learning in a low-performing, high-emotional, stock of Sprague-Dawley male rats. METHODS: Adult male rats of two stocks of the Sprague-Dawley strain, designated Stock A and Stock B, were treated daily with oxytocin (1 mg kg(-1) s. c.) for 5 days preceding four daily conditioned avoidance acquisition sessions (approximately 20 trials per 15 min session). The Stock B animals were previously characterized as high-emotional based on [1] elevated plasma corticosterone, and lowered plasma oxytocin, levels and [2] decreased reaction time and an increased startle amplitude to an acoustic stimulation. Finally, [3] these animals were unable to acquire a conditioned avoidance response within 5 days of training. RESULTS: The Stock A animals rapidly and statistically significantly acquired the avoidance behaviour within 4 days of daily training, whereas Stock B animals did not improve over this time period. The avoidance performance of Stock B animals was markedly and statistically significantly improved by the oxytocin pre-treatment, whereas the performance of Stock A animals was not affected by the same oxytocin treatment. CONCLUSIONS: Pre-treatment with oxytocin markedly improved avoidance learning in the Stock B high-emotional animals. It is suggested that the improvement is due to previously demonstrated anti-stress-like properties of oxytocin, rendering the animals able to successfully cope with the demands of the conditioned avoidance situation.     

Response of single alpha motoneurons to high-frequency pulse trains. Firing behavior and conduction block phenomenon

Studies were conducted on 25 cats to document the discharge rates of alpha motoneurons during stimulation of the sciatic nerve at frequencies from 100 to 10,000 pulses per second (pps). In addition, the feasibility of using high-frequency pulse trains to block the conduction of action potentials was investigated. Two cuff electrodes were placed around the proximal portion of the left sciatic nerve, and recordings of antidromic potentials were taken from single fibers of the L7 ventral root. When stimulating through the more proximal electrode, discharge rates were generally equal to or were subharmonics of the stimulation rate up to 1,000 pps. Firing often decreased in rate during 3-min runs. At 2,000-10,000 pps, fibers responded briefly at rates of several hundred per second but stopped firing within seconds after stimulus initiation. After cessation of response to the high-frequency pulse train, action potentials generated at 50 pps at the more distal electrode did not propagate to the recording electrodes. The 'electrical block' so induced was maintained for up to 20 min, and recovery following termination of the pulse train was complete within 1 s.     

Extinction and amnesia in aggressive and submissive mice with various terms of agonistic interaction

Dependence of the passive avoidance retrieval on the duration of agonistic interactions was analyzed in C57BL/6J mice in procedures of extinction and amnesia during formation of aggressive and submissive behavioral stereotypes. The resistance to amnestic stimulation was lower in aggressive mice with 10-day experience of victories than in aggressive animals after 20 daily confrontations. Prolongation of extinction in aggressive mice and fast extinction in submissive animals did not depend on the number of agonistic interactions.     

Excitability of single firing human motoneurones to single and repetitive stimulation (experiment and model)

The activity of single motoneurones of m. flexor carpi ulnaris (FCU) was investigated by recording their motor unit (MU) action potentials during weak and moderate voluntary muscle contractions. The MU firing rate range was 4.5-15 imp/s. The excitability of motoneurones was tested with a number of single stimuli eliciting a monosynaptic H-reflex of low amplitude. Two different indices were defined which relate to motoneuronal excitability: the response index--the ratio of the number of responses of a motoneurone to the total number of stimuli, and the response time--the time after the last background MU discharge at which motoneurone is ready to respond to the excitatory volley. Both the response index and the response time were determined for single motoneurones at different levels of background activity. In the lower range of firing rates, the response index for all motoneurones decreased when increasing the firing rate, but it remained constant in the higher rate range. This kind of response seems to be a typical motoneuronal response to the stimulation with single stimuli. The data on the response time were used to study the excitability of the same single motoneurones to computer simulated repetitive stimulation (stimulation rate 40-100 imp/s). In this case, the excitability of each motoneurone was determined as an increment of its firing rate in response to the stimulation. For the lower firing rate range, the excitability for all motoneurones also decreased when the firing rates increased whereas a variety of slopes was obtained in the higher rate range.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mating behaviour and behavioural ecology of a Predatory Wasp,Symmorphus allobrogus (de Saussure) (Hymenoptera: Eumeninae)

This paper represents an attempt to investigate the mating behaviour of Symmorphus allobrogus, explaining the willingness of male to mount and copulate. The male displays including mode and frequency of antennation and position while copulating, the displays further comprises of intensity and frequency of rejecting behaviour. The presence of the male’s copulatory and postcopulatory courtship studies, understands the maintenance of monandry. The wasp has numerous secondary sexual characters, and the mating behaviour follows a phyletic and the specific sexual mating characters in context of sexual selection. The duration of mating phases and the number of male antennation series during precopulatory, copulatory and postcopulatory phases of mounting, differs significantly. Mating success depends mostly on the activities of male in the premounting phase and the behaviour of both sexes has a roughly equal importance for it in precopulatory phase. While during copulation, activity of male has little influence on its duration; however, behaviour of female has crucial effect, inducing its earlier termination.     

Theoretical simulation of the calcium action potential in squid giant synapse: The plateau termination

A biophysical model is proposed for the simulation of the experimentally observed calcium action potential at the squid giant synapse. It is observed that while Ca activation at the synapse is responsible for the generation of the upstroke of the action potential, a repolarizing process needs to be invoked to simulate the plateau termination and other long-time effects. Out of the likely candidates, the Ca-activated K current has been chosen as the most plausible repolarizing process. The model can reproduce all the observed features of calcium action potential excepting its behaviour after repetitive stimulation.     

Systems organization of cerebral processes in the cat during learning while undergoing electrical stimulation of the neocortex

A delayed spatial choice (DSC) was elaborated in five cats during electrical stimulation (ES) of the frontal cortical parts with a frequency of 80 imp/s. Then the task fulfillment was tested following cessation of the electrostimulation or under the action of other current frequencies (35,3 and 120 imp/s). The number of erroneous choices increased in the absence of ES or during 3 imp/s ES of the frontal parts. The effects of frequencies of 35,80 and 120 imp/s did not differ. Three cats were trained to DSC without ES. The conditioned reflexes were tested during ES of the frontal cortical parts with current frequency of 3 and 80 imp/s. Statistically significant increase of the number of erroneous responses took place in both situations. The obtained data are discussed from the point of view of the integrative activity of the cerebral structures in DSC. Its disturbance during ES of the cortical zones and dissociation (discordance) after cancellation of stimulation during which the conditioned reflex had been elaborated, point to systemic organization of brain functioning in goal-directed forms of behaviour.     

Effect of constant darkness on relearning in a Y maze and on the temporal dynamics of forced swimming in rats of different ages

Prolonged keeping of rats in darkness significantly activated them. This effect manifested itself in shortening of conditioned avoidance latency in the Y-maze against the background of relearning improvement in young (8-9 weeks) animals and its deterioration in mature (18-20 weeks) ones. In animals of various age groups the share of active swimming and the number of active attempts to leave the vessel increased with a decrease of the duration of immobilization in the structure of forced swimming. A significant increase of the number of immobilization short cycles (up to 6 s) on the actogram and a reduction in the number of more protracted immobility periods were noticed. Participation is suggested in such effect realization of biologically active pineal gland factors.     

Differential regulation of primary and memory CD8 T cell immune responses by diacylglycerol kinases

The manipulation of signals downstream of the TCR can have profound consequences for T cell development, function, and homeostasis. Diacylglycerol (DAG) produced after TCR stimulation functions as a secondary messenger and mediates the signaling to Ras-MEK-Erk and NF-κB pathways in T cells. DAG kinases (DGKs) convert DAG into phosphatidic acid, resulting in termination of DAG signaling. In this study, we demonstrate that DAG metabolism by DGKs can serve a crucial function in viral clearance upon lymphocytic choriomeningitis virus infection. Ag-specific CD8(+) T cells from DGKα(-/-) and DGKζ(-/-) mice show enhanced expansion and increased cytokine production after lymphocytic choriomeningitis virus infection, yet DGK-deficient memory CD8(+) T cells exhibit impaired expansion after rechallenge. Thus, DGK activity plays opposing roles in the expansion of CD8(+) T cells during the primary and memory phases of the immune response, whereas consistently inhibiting antiviral cytokine production.     

Effects of Na(+) and K(+) channel blockade on vulnerability to and termination of fibrillation in simulated normal cardiac tissue

Na(+) and K(+) channel-blocking drugs have anti- and proarrhythmic effects. Their effects during fibrillation, however, remain poorly understood. We used computer simulation of a two-dimensional (2-D) structurally normal tissue model with phase I of the Luo-Rudy action potential model to study the effects of Na(+) and K(+) channel blockade on vulnerability to and termination of reentry in simulated multiple-wavelet and mother rotor fibrillation. Our main findings are as follows: 1) Na(+) channel blockade decreased, whereas K(+) channel blockade increased, the vulnerable window of reentry in heterogeneous 2-D tissue because of opposing effects on dynamical wave instability. 2) Na(+) channel blockade increased the cycle length of reentry more than it increased refractoriness. In multiple-wavelet fibrillation, Na(+) channel blockade first increased and then decreased the average duration or transient time () of fibrillation. In mother rotor fibrillation, Na(+) channel blockade caused peripheral fibrillatory conduction block to resolve and the mother rotor to drift, leading to self-termination or sustained tachycardia. 3) K(+) channel blockade increased dynamical instability by steepening action potential duration restitution. In multiple-wavelet fibrillation, this effect shortened because of enhanced wave instability. In mother rotor fibrillation, this effect converted mother rotor fibrillation to multiple-wavelet fibrillation, which then could self-terminate. Our findings help illuminate, from a theoretical perspective, the possible underlying mechanisms of termination of different types of fibrillation by antiarrhythmic drugs.