Effect of the microiontophoretic application of acetylcholine on the formation of conditioned reactions in motor cortex neurons

In alert rabbits the activity of the motor cortex neurones was recorded with simultaneous application of acetylcholine to them in the process of defensive conditioning. Conditioned reorganization, mainly of activation type, were found in 60% of neurones. In most cases conditionally reacting cells were sensitive to acetylcholine. Ionophoretic application of the transmitter promoted the formation of conditioned neuronal responses and increased them in comparison with conditioned reactions evoked in absence of acetylcholine. It is supposed that the influence of acetylcholine on conditioned cellular process is realized due to its action on the state of excitability of the cortical neurones.     

The neuronal reactivity and interaction of the rat cerebral cortex during the microiontophoretic action of acetylcholine in a model negative learning situation]

Unit activity of 46 pairs of neurons of sensorimotor cortex of rats was studied in a model situation of habituation to repetitive microiontophoretic applications of acetylcholine (ACh). The difference between the types of reactions to ACh of two neighbouring neurons recorded by the same microelectrode was observed on 37% of cases. The difference between the dynamics of activity of neurons with similar patterns of reactions during repetitive action of stimuli was also shown. Stability of the excitatory connections between two neighbouring neurons under the conditions when one of them demonstrated the habituation to repetitive action of ACh were indicated by analysis of cross-correlation histograms.     

The spike reactions of the motor cortex neurons of old rabbits to specific stimuli

Spike reactions of motor cortex neurons to tactile and electrocutaneous stimulation of a forelimb were studied in aged (6-7-year old) rabbits. As compared with young adult animals, the neuronal reactions to afferent stimuli were rarely recorded in the motor cortex of aged rabbits (66.7 and 50%, respectively). The activation manifested in increasing firing rate over its spontaneous level was less intensive than in young animals. The neuronal reactions of aged animals were characterized by the slower activation with longer latencies and slower development of spike responses. The parameters of slow activation could be partly corrected by the iontophoretic application of acetylcholine to the soma region. Neuronal inhibition recorded in the motor cortex of aged rabbits was not markedly changed compared to inhibition reactions in young animals. It is suggested that impairment of the functional state of dendrites in aging is responsible for the changes observed.     

The effect of acetylcholine and atropine on the temporal connection in the neuronal populations of the motor cortex]

On alert non-immobilized rabbits the activity of neurones in the sensorimotor cortex was studied at pair combination of brain structures stimulations. During omission of the reinforcing stimulus at the place of its expected presentation a complicated complex develops of neurones impulses reconstructions, consisting in reproduction of responses and activity changes which by their configuration differ from them and usually appear in later terms. Direct acetylcholine application on the cortex promotes manifestation of both types of neurones activity reconstructions. But atropine application depresses mainly the second type of reconstructions. Besides, acetylcholine increases the general duration of the given conditioned effects, but atropine decreases it.     

Effect of strychnine on the neuronal reactivity of the sensorimotor cortex and the temporary connection in rabbits

On awake nonimmobilized rabbits, evoked activity was studied of the sensorimotor cortex neurons in response to stimulation of the pyramidal tract, medial lemniscus and reticular nucleus of the midbrain tegmentum by stimuli of different frequencies, and driving reaction of cortical neurons to stimulation of these brain structures by series of stimuli of increasing frequency. Conditioned reflexes were also studied, established on the basis of combination of direct stimulation of the sensorimotor cortex and electrocutaneous stimulation. Application of the cortex of low concentration of strychnine solutions (less than 1%) heightened neurons reactivity and provides for the formation of temporary connection. Application of strychnine solutions of higher concentration (greater than 1%) led to opposite effects. Interconnection of electrical and behavioural effects is discussed.     

Modulatory effects of noradrenaline on the spike activity of cat motor cortex neurons under conditions of skin electrostimulation and action of extra stimuli

Effects of iontophoretic application of ephedrine (an indirect adrenomimetic that evokes noradrenaline liberation) and obsidane (a blocker of -adrenoreceptors) on extra stimulus-related modifications of evoked unit spike activity in cortical field 4 were studied in chronic experiments on cats. Neuronal responses were evoked by skin electrostimulation (SES) of extremities; a flow of air blowing on the muzzle 1.0 sec before SES was used as the extra stimulus. In most cases, the SES-evoked unit activity was depressed by ephedrine application, whereas obsidane enhanced it. Extra stimulus-related depression of the SES-evoked responses was removed by obsidane but it did not change or become even more pronounced during ephedrine applications. It is concluded that depressive effects caused by the extra stimulus on the SES-evoked responses of cortical neurons are essentially determined by noradrenergic mechanisms.Translated from Neirofiziologiya, Vol. 25, No. 2, pp. 119–125, March–April, 1993.     

Analysis of the reactivity of the sensorimotor neurons of the rat cerebral cortex to acetylcholine

Several types of cholinoceptive neurons have been identified in rat's sensomotor cortex according to response character to ionophoretical application of acetylcholine. The neurons investigated form continuous range according to duration of the excitatory component of reaction to transmitter application. It has been suggested that the duration of this component reflects the important functional properties of the nerve cell.     

Maximization of learning speed in the motor cortex due to neuronal redundancy

Many redundancies play functional roles in motor control and motor learning. For example, kinematic and muscle redundancies contribute to stabilizing posture and impedance control, respectively. Another redundancy is the number of neurons themselves; there are overwhelmingly more neurons than muscles, and many combinations of neural activation can generate identical muscle activity. The functional roles of this neuronal redundancy remains unknown. Analysis of a redundant neural network model makes it possible to investigate these functional roles while varying the number of model neurons and holding constant the number of output units. Our analysis reveals that learning speed reaches its maximum value if and only if the model includes sufficient neuronal redundancy. This analytical result does not depend on whether the distribution of the preferred direction is uniform or a skewed bimodal, both of which have been reported in neurophysiological studies. Neuronal redundancy maximizes learning speed, even if the neural network model includes recurrent connections, a nonlinear activation function, or nonlinear muscle units. Furthermore, our results do not rely on the shape of the generalization function. The results of this study suggest that one of the functional roles of neuronal redundancy is to maximize learning speed.     

Coupled neuronal reactions of the specific and nonspecific thalamic nuclei to painful and electroacupuncture stimuli

Electric reactions of neurons of the specific (VPM) and nonspecific (CM PF) thalamic nuclei caused by noxious and electroacupuncture stimulation were studied in acute experiments on cats. About 18% of the investigated neurons demonstrated coupled reactions to afferent stimulation. The coupled reaction to either noxious or electroacupuncture stimulation had inhibitory or activating character. A hypothesis on the existence of functional units responsible for the effects of electroacupuncture analgesia with participation of inhibitory, relay neurons and interneurons is made.     

Effects of acoustic stimuli on neuronal activity in the auditory cortex of the rat

Spontaneous activity of cortical neurons exhibits alternative fluctuations of membrane potential consisting of phased depolarization called "up-state" and persistent hyperpolarization called "down-state" during slow wave sleep and anesthesia. Here, we examined the effects of sound stimuli (noise bursts) on neuronal activity by intracellular recording in vivo from the rat auditory cortex (AC). Noise bursts increased the average time in the up-state by 0.81+/-0.65 s (range, 0.27-1.74 s) related to a 10 s recording duration. The rise times of the spontaneous up-events averaged 69.41+/-18.04 ms (range, 40.10-119.21 ms), while those of the sound-evoked up-events were significantly shorter (p<0.001) averaging only 22.54+/-8.81 ms (range, 9.31-45.74 ms). Sound stimulation did not influence ongoing spontaneous up-events. Our data suggest that a sound stimulus does not interfere with ongoing spontaneous neuronal activity in auditory cortex but can evoke new depolarizations in addition to the spontaneous ones.     

The topological characteristics of rat myocardial reactivity to noradrenaline, acetylcholine and a change in the electrostimulation frequency]

Dose-dependent effects of noradrenaline (10-7-10-6M), acetylcholine (10-8-3x10-6M) and stimulation rate (0.2-2.0 Hz) were obtained in experiments on myocardium preparations of the right and left atria and ventricles in rat. Three types of topological differences of the rat myocardium reactivity were observed: between the atria and ventricles (A/V), between the right and left atria and ventricles (R/L), between the right atrium (RA) and other cardiac chambers. A/V differences were most pronounced in the reactivity to acetylcholine (the atria were more reactive), the highest R/L differences were observed in the reactivity to noradrenaline (the myocardium of the right chambers was more reactive). RA reactivity greatly exceeded reactivity of other myocardial preparations to all three test influences. Topological peculiarities of chrono-inotropism permit supposing, that inotropic effects of rate changes in vivo are able to compensate, to some extent, the regional nonuniformity of cholin- and adrenergic regulatory inotropic effects.     

Long-range neuronal circuits underlying the interaction between sensory and motor cortex

In the rodent vibrissal system, active sensation and sensorimotor integration are mediated in part by connections between barrel cortex and vibrissal motor cortex. Little is known about how these structures interact at the level of neurons. We used Channelrhodopsin-2 (ChR2) expression, combined with anterograde and retrograde labeling, to map connections between barrel cortex and pyramidal neurons in mouse motor cortex. Barrel cortex axons preferentially targeted upper layer (L2/3, L5A) neurons in motor cortex; input to neurons projecting back to barrel cortex was particularly strong. Barrel cortex input to deeper layers (L5B, L6) of motor cortex, including neurons projecting to the brainstem, was weak, despite pronounced geometric overlap of dendrites with axons from barrel cortex. Neurons in different layers received barrel cortex input within stereotyped dendritic domains. The cortico-cortical neurons in superficial layers of motor cortex thus couple motor and sensory signals and might mediate sensorimotor integration and motor learning.     

NADPH-Diaphorase reactivity and neurovascular coupling in the basal forebrain and motor cortex

Using NADPH-diaphorase histochemistry, distribution of reactive neurons in the forebrain structures and motor cortex of rats was studied. Some reactive (NO-generating) neurons are associated with microvessels and, thus, can be involved in the regulation of regional blood flow. Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 405–407, July–October, 2007.     

Effects of GABA and picrotoxin on temporary bonds in neuronal populations of the motor cortex

The paired stimulations of some brain structures (the medial lemniscus, the reticular nucleus of the midbrain tectum, and the pyramidal tract) resulted in the formation of temporary bonds in the neuronal populations of the motor cortex of the non-immobilized awake rabbits. The changes in the neuronal impulsation observed in the absence of the supporting stimuli were used as the criteria of establishment of the temporary bond. The changes consisted of the elements reproducing an initial response pattern and generation of impulse sequences that appeared later and differed in their configuration from the responses evoked by the real stimuli. The application of GABA directly to the site from which the neuronal activity was recorded blocked the former changes and significantly facilitated the latter ones. Picrotoxin antagonized the GABA effect only in relation to the late rearrangements of the impulse activity (generation of the sequences that differed from the responses evoked by stimulation).Neirofiziologiya/Neurophysiology, Vol. 26, No. 2, pp. 115–121, March–April, 1994.     

Effects of serotonin on neuronal response induced in the sensorimotor cortex by tactile and conditioned acoustic stimuli

Neuronal firing response in the sensorimotor cortex to tactile (non-conditioned) and acoustic (conditioned) stimuli was investigated in trained cats before and after iontophoretic application of serotonin and lysergide. Three functionally distinct groups of neurons were identified from the response produced by presenting tactile and acoustic stimuli. Applying serotonin was found to facilitate preliminary and residual spike response induced by tactile stimulation; it also facilitates and modulates response in many cortical neurons to conditioned stimuli. Facilitation takes the form of reduced latency of response and increased numbers of spikes in response to conditioned stimulus presentation, especially at the initial phase of response to sound and immediately after the onset of conditioned reflex motion. Additional neurons formerly unresponsive to acoustic stimuli joined in the reaction under the effects of serotonin. Changed response patterns often evolve following minor fluctuations in background activity level. It is suggested that facilitation of response following iontophoretic serotonin application in the neocortex is associated with activation of excitatory serotonin receptors (S₂). The lysergide-induced increase in background and evoked activity noted during experimentation can apparently be put down to blockade of inhibitory serotonon (S_1B) receptors.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 3, pp. 337–347, May–June, 1990.     

Recognition of visual stimuli from multiple neuronal activity in monkey visual cortex

Response patterns recorded with 30 microelectrodes from area 17 of anaesthetized monkeys are analysed. A proportion of the patterns are used to define prototype response patterns. These in turn are used to recognize the stimulus from further non-averaged response patterns. In comparison, recognition by a feedforward neural network is much slower, and slightly inferior. The excitation time structure, with a resolution of about 20 ms, is found to contribute strongly to the recognition. There is some inter-ocular recognition for oriented moving bars, and for on and off phases of switched lights, but none for colours. Generalizations over some stimulus parameters (i.e. cases of confusion) are examined: If small jerking shapes are incorrectly recognized, in general the jerk direction often is the correct one. The onset of a response can most easily be found by determining the dissimilarity relative to spontaneous activity in a sliding window.