Neuron Activity in the Pedunculopontine Nucleus during an Operant Conditioned Defensive Reflex

The activity of 109 neurons in the compact and diffuse zones of the pedunculopontine nucleus was studied in freely mobile rabbits during the acquisition and performance of a defensive operant conditioned reflex. A total of 47% of the neurons recorded showed responsive properties to the conditioned stimulus, which is evidence for the involvement of the pedunculopontine nucleus in operant learning. A significant predominance of excitatory conditioned reflex responses to the conditioned stimulus was demonstrated, showing that the nature of the influence of the pedunculopontine nucleus on projection structures during learning is mostly excitatory. The main patterns of cell responses to the conditioned stimulus were identified, these reflecting the nature of the influence of the conditioned stimulus on neuron activity, the structure of the behavioral act, and the properties of the reinforcement, suggesting a relationship between the pedunculopontine nucleus and the processes of attention, motor learning, and reinforcement. A significant decrease in the reactivity of neurons in the pedunculopontine nucleus to the conditioned stimulus as a result of specialization due to learning was demonstrated. Differences in the associative reactive properties of the compact and diffuse zones of the pedunculopontine nucleus to the conditioned stimulus were identified, which is evidence for the functional heterogeneity of this formation and suggests a leading role for the cholinergic compact zone in operant defensive behavior.     

Changes in the Signal Value of a Conditioned Stimulus during Acquisition of a Conditioned Two-Way Avoidance Reflex in Rats

Neuroscience and Behavioral Physiology -     

Extinction of a Conditioned Defensive Reflex in Cats after Lesioning of the Entopeduncular Nucleus

Neuroscience and Behavioral Physiology -     

Analysis of the Dynamics of Interneuronal Functional Connections during Conditioned Reflex Activity

The dynamics of interneuronal functional connections were studied in the prefrontal cortex of dogs performing a task consisting of unforeseen remodeling of movement conditioned reflexes. An original method was used to find and classify the temporal patterns of linked spikes coming from several simultaneously recorded neurons. This procedure showed that in 33 pairs of neurons (87% of the total number of pairs showing interneuronal functional connections), parts of the conditioned reflex program were associated with behaviorally significant changes in the functional relationship between the neurons. In different behavioral situations, linked activation of a given pair of cells was restricted to different stages of the performance of the conditioned reflex task. In 17 pairs of neurons, the periods of switching of interneuronal functional connections, i.e., the intervals in which linked spikes were absent during all stages of task performance, were seen only in a particular behavioral context different from the situation in which these same cells generated linked discharges. The specific characteristics of different methods of analyzing the dynamics of interneuronal functional connections in conditions of a dynamic behavioral context and multifactorial determination of conditioned reflex activity are discussed.     

Duration of Retention of Changes in the Electrical Characteristics of Command Neurons During Acquisition of a Conditioned Defensive Reflex in Snails

Neuroscience and Behavioral Physiology -     

Electrophysiological Studies of the Effects of Chronic Administration of Caffeine on the Formation of a Conditioned Defensive Reflex in the Common Snail

Chronic administration of caffeine to common snails increased the rate of formation of a conditioned defensive reflex. When daily caffeine injections were given immediately after the training procedure, the conditioned defensive reflex was acquired more quickly than when caffeine injections were given before the training procedure started. Chronic caffeine administration to both trained and untrained snails led to depolarization changes in the membrane potential and reductions in the threshold potential of defensive behavior command neurons in common snails. Comparative studies showed that addition of caffeine to the solution bathing the mollusk nervous system resulted in decreases in the threshold potential of command neurons in both intact and trained snails; there was, however, no change in the membrane resting potential. Translated from Zhurnal Vysshei Nervnoi Deyatel’nosti imeni I. P. Pavlova, Vol. 58, No. 2, pp. 202–208, March–April, 2008.     

Dopaminergic Modulation of Spike Activity in Sensorimotor Cortex Neurons in a Conditioned Reflex

Changes in the spike conditioned reflex reactions of sensorimotor cortex neurons during microion-tophoretic application of agonists and antagonists of glutamatergic and GABAergic transmission and their modulation by dopamine were studied. A paradoxical reaction is described, consisting of facilitation of spike responses evoked by antagonists of ionotropic glutamate transmission, which was blocked by GABA. This is evidence for the active involvement of inhibition in organizing the excitatory responses of neurons in the conditioned reflex. Application of the metabotropic glutamate transmission antagonist MCPG was accompanied by sharp suppression of the baseline and evoked activity of cortical neurons, along with increases in the latency of spike responses and conditioned reflex movement. Dopamine was found to reverse the effect of blocking metabotropic glutamate receptors and to normalize neuron activity, which is evidence for the stabilizing role of dopamine in the functioning of neocortical neurons.Translated from Zhurnal Vysshei Nervnoi Deyatel’nosti, Vol. 54, No. 4, pp. 495–507, July–August, 2004.     

Dynamics of Postischemic Changes in the Microcirculation in the Rat Cerebral Cortex

Neuroscience and Behavioral Physiology - Postischemic changes in the circulation appear primarily in the microcirculatory system. There are few studies of the cerebral microcirculation after...     

Effects of the Serotonin Precursor 5-Hydroxytryptophan and the Neurotoxic Analog 5,7-Dihydroxytryptamine on the Formation of a Conditioned Defensive Reflex in the Common Snail

We report here our studies on the effects of the metabolic serotonin precursor 5-hydroxytryptophan and the neurotoxic analog 5,7-dihydroxytryptamine on the acquisition of a conditioned defensive reflex and post-training electrophysiological parameters of defensive behavior command neurons in snails. Injections of 5-hydroxytryptophan into snails via the sinus node led to acceleration of the acquisition of the conditioned defensive reflex. Snails injected with 5,7-dihydroxytryptamine did not form the conditioned reflex; subsequent injection of 5- hydroxytryptophan prevented this blockade. While 5-hydroxytryptophan prevented the action of 5,7-dihydroxytryptamine at the behavioral level, no such effect was seen at the level of the electrical properties of command neurons.     

Electrophysiological Studies of the Effects of 5,6-Dihydroxytryptamine on the Acquisition of a Conditioned Defensive Reflex in Snails

The role of serotonin in the membrane properties of identified neurons was studied during acquisition of a conditioned defensive reflex. Serotonin deficiency was created using the neurotoxic serotonin analog 5,6-dihydroxytryptamine (5,6-DHT). Injection of 5,6-DHT was found to prevent decreases in the membrane and threshold potentials of command neurons during acquisition of the conditioned reflex as compared with snails given 5,6-DHT without training. Common snails recovered the ability to acquire the conditioned reflex two weeks after a second 5,6-DHT injection.     

The Effects of Changes in Extracellular Calcium Concentrations on the Electrical Properties of Command Neurons after Acquisition of a Defensive Conditioned Reflex in Snails

Studies of the electrical characteristics of the command neurons of a defensive reflex showed that the membrane potential showed no significant changes in response to changes in the calcium concentration in the perfusing solution in either intact or trained snails. Increases in the calcium ion concentration in intact snails were accompanied by increases in the threshold potential, from 14 ± 0.7 mV at 2.5 mM Ca²⁺ to 21.8 ± 0.9 mV at 20 mM Ca²⁺. The threshold potential in trained snails decreased in response to both increases and decreases in calcium concentrations, from 16.8 ± 0.6 mV (physiological saline containing 10 mM Ca²⁺) to 13.3 ± 0.6 mV at 20 mM Ca²⁺ and 11.8 ± 0.8 mV at 2.5 mM Ca²⁺. The critical depolarization level changed correspondingly: in intact snails, this decreased with increases in calcium concentration, while in trained snails it increased in response to both increases and decreases in the calcium concentration. __________ Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 54, No. 6, pp. 801–805, November–December, 2004.     

NMDA-Dependent and NMDA-Independent Neural Processes in the Bicucculline-Disinhibited Motor Cortex of the Cat during the Acquisition and Reproduction of a Conditioned Paw-on-Support Placing Reflex

Neuron activity was recorded in the motor area of the cat cortex during acquisition of an operant conditioned reflex consisting of placing the forepaw on a support in conditions of local disinhibition by spontaneous diffusion of the GABA_A receptor blocker bicucculline from the recording micropipette. The conditioned signal was electrical stimulation of the parietal cortex with a train of 3–5 impulses. Addition of 2-amino-5-phosphopentanoic acid (APV), an NMDA glutamate receptor blocker, led to disappearance of the secondary excitatory components (in the poststimulus interval 30–120 msec) from neuronal responses in the disinhibited cortex both to the indifferent (before training) and the conditioned stimulation of the parietal cortex, while excitatory reactions associated with elevation and placing of the paw on the support showed no significant change in the presence of APV. Acquisition of the operant conditioned reflex was accompanied by an increase in the amplitude (p < 0.006) and duration (p < 0.00002) of secondary responses and decreases in their latent periods (p < 0.00002). In some cases – in fixed conditioned reflexes – secondary responses to conditioned stimulation in the disinhibited cortex were transformed into trains of epileptiform discharges. The hypothesis that changes in neuronal reactions in the disinhibited cortex during learning are based on increases in the efficiency of horizontal (collateral) connections between pyramidal neurons in layers II and III of the cortex is discussed.     

The Effects of Activation of Glutamate Ionotropic Connections of Neurons in the Sensorimotor Cortex in a Conditioned Reflex

Changes in conditioned reflex spike activity of neurons in the sensorimotor cortex were studied during microiontophoretic application of agonists and antagonists of glutamate and GABAergic transmission. The results of these experiments showed that the glutamate ionotropic receptors (AMPA and NMDA) of neurons in the sensorimotor cortex were intensely activated by the arrival of a conditioned signal in the cortex. This response included not only large pyramidal neurons of the deep cortical layers, but also the surrounding inhibitory interneurons. The existence of constant tonic inhibitory regulation of the activity of large pyramidal neurons by the surrounding inhibitory cells was demonstrated, along with the active involvement of this inhibition in organizing the excitatory responses of neurons in the sensorimotor cortex during a conditioned reflex.     

Modulation of the Spike Activity of Neocortex Neurons during a Conditioned Reflex

Experiments were conducted on cats to study the effects of iontophoretic application of glutamate and a number of modulators on the spike activity of neurons in the sensorimotor cortex during a conditioned reflex. These studies showed that glutamate, as well as exerting a direct influence on neuron spike activity, also had a delayed facilitatory action lasting 10–20 min after iontophoresis was finished. Adrenomimetics were found to have a double modulatory effect on intracortical glutamate connections: inhibitory and facilitatory effects were mediated by 1 and 2 adrenoceptors respectively. Although dopamine, like glutamate, facilitated neuron spike activity during the period of application, the simultaneous facilitatory actions of glutamate and L–DOPA were accompanied by occlusion of spike activity, and simultaneous application of glutamate and haloperidol suppressed spike activity associated with the conditioned reflex response. Facilitation thus appears to show a significant level of dependence on metabotropic glutamate receptors which, like dopamine receptors, are linked to the intracellular medium via Gi proteins.     

Activity of Neurons in the Pedunculopontine Nucleus during a Food-Related Operant Conditioned Reflex

The activity of 91 neurons in the compact and diffuse zones of the pedunculopontine nucleus of freely mobile rabbits was studied during performance of a food-related operant conditioned reflex. A total of 37.4% of the neurons recorded showed reactivity to the conditioned stimulus, which is evidence that the pedunculopontine nucleus is involved in operant learning. A significant predominance of excitatory responses to the conditioned stimulus and to food reinforcement was demonstrated. The main patterns of cell responses were identified, these reflecting the nature of the effect of the conditioned stimulus on neuron activity, the structure of the behavioral act, and the properties of the reinforcement, and demonstrating a relationship between the pedunculopontine nucleus and the processes of attention, motor learning, and reinforcement. Differences were seen in the associative reactive properties of the compact and diffuse zones of the pedunculopontine nucleus to the conditioned stimulus and reinforcement, which is evidence for the functional diversity of this formation and suggests a leading role for the cholinergic compact zone in food-related operant learning and reinforcement, the diffuse zone having a leading role in food-related classical conditioned-reflex learning.     

Involvement of Cingulate Cortex in the Formation of Defensive Behavior in Rats

Changes in behavior patterns in rats during electric stimulation of the ventromedial hypothalamus (the center of defensive behavior) and cingulate cortex were studied. Electric stimulation of the frontomedial cingulate cortex reduced the latency for anxiety and escape reactions during electric stimulation of the ventromedial hypothalamus. Electrolytic destruction of the frontomedial cingulate cortex substantially increased the threshold of escape behavior during stimulation of the ventromedial hypothalamus. These findings demonstrate the involvement of the frontomedial cingulate cortex into the development of defensive (anxiety and escape) behavior in rats.     

Functional Asymmetry of the Frontal Cortex and Lateral Hypothalamus of Cats During an Operant Food-Related Conditioned Reflex

The extent of correlation and the latency of evoked potentials to sound, recorded bilaterally in the frontal cortex and lateral hypothalamus of cats, were studied at different stages of the acquisition of an operant food-related reflex and during sudden transfer to 30% food reinforcement. High correlation coefficients between the evoked responses of the cortex and hypothalamus with left-sided dominance were seen in conditions of high levels of food motivation at the beginning of each experiment and in conditions of the high-probability appearance of the acquired conditioned reflex throughout the rest of the experiment. Comparison of the peak latencies of the early positive (P55-80) components of evoked potentials on the right and left sides showed that shorter latent periods were seen in the cortex on the left side at all behavioral stages, while this occurred (on the left side) in the hypothalamus only when the conditioned reflex was unfixed, while after fixation of the reflex and provision of 30% reinforcement, shorter latent periods were seen on the right side. It is concluded that the high level of left-sided correlation of evoked potentials in the hypothalamus was associated with the motivational and motor components of purposive behavior and was not associated with the emotional tension of the animals provoked by the disruption of the food reinforcement stereotype.     

The Dynamics of Morphological Measures and Lipid Peroxidation during Aging of the Cerebral Cortex in Humans

Neuroscience and Behavioral Physiology -     

Reflection of an Orienting Reflex in the Phases of Evoked Potentials in the Rabbit Visual Cortex and Hippocampus during Substitution of Stimulus Intensity

Experiments on conscious rabbits were performed using the oddball paradigm, in which a rare (deviant) and common (standard) stimuli were of the same color but different intensities. Deviant stimuli were of lesser intensity. Recordings were made of evoked potentials induced by series of uniform deviant stimuli (without using standard stimuli), which were presented at the beginning and end of stimulation. Visual evoked potentials recorded in response to deviant stimuli in the visual cortex and hippocampus showed increases in the amplitudes of phases, shifted towards positivity as compared with responses to standard stimuli and uniform deviant stimuli at the beginning and end of stimulus blocks. Significant changes affected phases P1 and P2 of visual evoked potentials in the cortex and phases P1, N1, and P2 in the hippocampus. The most significant increase in evoked potentials in the cortex was seen for the P2 peak (P130). It is suggested that changes in responses to oddball-deviant stimuli result from an orienting reflex to rare, unexpected stimuli and that the P2 (P130) peak in the cortex is associated with transmission of information regarding changes in the intensity of the light. The amplitude of this peak was shown to be decreased in responses to uniform deviant stimuli at the beginning and end of stimulus blocks. It was also demonstrated that the clearest and most contrasting changes in visual evoked potentials in responses to deviant and standard stimuli were seen with the smallest differences in intensity between these types of stimulus, this reflecting increases in the orienting reflex at threshold differences.