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.     

Responses of neurons in the auditory cortex to sound stimuli

The evoked potential (EP) and the pulse activity of single auditory cortex neurons were recorded simultaneously in response to a click and to a tone for cats under nembutal and nembutal — chloralose anesthesia. Both extra- and intracellular taps were employed. The experiments showed that the reaction of auditory cortex neurons in response to a click lasts from 200 to 300 msec. It consists of pulse discharges from several groups of neurons. Out of 174 neurons observed 8 responded within 4 to 7 msec after a click (before the EP). One hundred and nine neurons reacted in the range from 7 to 25 msec which coincided with the initial electropositivity of the EP; 11 neurons were in the range from 40 to 100 msec and 4 were between 180 and 270 msec. Such a sequence of involvement of different neuron groups in the reaction is probably accounted for to a large extent by the time dispersion of the afferent volley. With an intracellular tap slow alterations of membrane potential were observed in the form of an EPSP with pulses together with subsequent hyperpolarization lasting 50 to 70 msec and slowly increasing depolarization that reached a maximum after 170 to 200 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 147–157, September–October, 1969.     

Effect of the microiontophoretic feed of acetylcholine and noradrenaline on the neuronal reactivity of the motor cortex to specific stimuli

In the forelimb area of the motor cortex after microiontophoretic injection of acetylcholine a group of nervous cells revealed more rapid, more stable and more effective reactions to afferent stimuli. The interrelation of impulsive activity of some of these neurons and electromyographic activity of forelimb muscles has given a possibility to propose that acetylcholine mobilizes the motor cortex for motor function regulations. The only result of noradrenaline application to motor cortex neurons was the prolongation of their responses to specific afferent stimulation.     

The morphofunctional characteristics of the neurons in the sensorimotor cortex of old rabbits during the trace assimilation of rhythm]

Extracellular neuronal activity was recorded from 460 neurons from alert young (5-7 months), middle-aged (54-65 months) and old (66-85 months) rabbits. Trace rhythmic activity of sensorimotor cortical neurons was examined after long-lasting (10-20 min) rhythmic (0.5-2 Hz) electrocutaneous stimulation of the contralateral forelimb. Spectral analysis of spike activity showed age-related differences in capability of producing a rhythm of previous stimulation in spontaneous neuronal activity. In young animals propriate rhythmic fluctuations of firing rate appeared after the first or second sessions of stimulations (on the first experimental day), in middle-aged ones--after 2-4 sessions (on the second or third days); cortical neurons in old rabbits did not exhibit trace rhythmic activity. Significant morphological changes in glial and neuronal cells were observed in sensorimotor cortex of old rabbits. It is proposed that morphological deteriorations may be the reason of the impairement of trace processes during aging.     

Slow potentials and spike unit activity of the cerebral cortex of rabbits exposed to microwaves

Unanesthetized rabbits exposed to 12.5-cm microwaves at a field intensity of 40 mW/cm2 in the region of the head showed an increase in the number of slow waves and spindle-shaped firings in the EEG and a change in the discharge frequency of neurons in the visual cortex in 41-52% of the cases. An enhancement of the evoked response of visual cortex neurons to light was observed in 61% of the cases and a facilitation of the driving response in 80% of all cases. It is concluded that the evoked response is a more sensitive indicator of the microwave effect than background activity. The effects of the fields were most distinctly observed with the driving response.     

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.     

Selectivity of visual cortical neurons of rabbits to magnitude of moving stimuli

Unit responses of the rabbit visual cortex were investigated in relation to size of visual stimuli moving in their receptive field. With an increase in size of the stimulus in a direction perpendicular to the direction of movement ("width" of the stimulus) an initial increase in the intensity of the unit response through spatial summation of excitory effects is followed by a decrease through lateral inhibition. This inhibition is observed between zones of the receptive field which behave as activating when tested by a stimulus of small size. Each neuron has its own "preferred" size of stimuli evoking its maximal activation. No direct correlation is found between the "preferred" stimulus size and the size of the receptive field. With a change in stimulus size in the direction of movement ("length" of the stimulus) the responses to stimuli of optimal size may be potentiated through mutual facilitation of the effects evoked by the leading and trailing edges of the stimulus and weakened in response to stimuli of large size. The selective behavior of the neurons with respect to stimulus size is intensified in the case of coordinated changes in their length and width. It is postulated that the series of neurons responding to stimuli of different "preferred" dimensions may constitute a system classifying stimuli by their size.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 636–644, November–December, 1972.     

Unpleasant visual stimuli increase the excitability of spinal motor neurons

Abstract

Purpose: In physical therapy for post-stroke patients, we often experience cases in which unpleasant emotions cause abnormal muscle tonus. Previously, we suggested that the magnitude of spinal motor neuron excitability was correlated with the grade of muscle tonus. Therefore, spinal motor neuron excitability was considered to be a useful index to evaluate the influence of unpleasant emotions on muscle tonus. In this study, we investigated whether unpleasant emotions evoked by visual stimuli affected the excitability of spinal motor neurons.

Materials and Methods: The F-waves, an indicator of spinal motor neuron excitability, were measured in 19 healthy adult volunteers. Firstly, for the rest trial, F-waves were measured during relaxation to determine the baseline of spinal motor neuron excitability. Following the rest trial, the unpleasant trial was conducted in which F-waves were measured while the subjects viewed an unpleasant picture for 1?min. After the unpleasant trial, F-waves were measured during relaxation. For the control condition, F-waves were measured while the subjects viewed a neutral picture instead of the unpleasant picture. The recorded F-wave data were analysed for persistence and the F/M amplitude ratio.

Results: Persistence and the F/M amplitude ratio were significantly greater during the unpleasant trial than during the rest trial. In the control condition, there was no significant difference in persistence and the F/M amplitude ratio compared with the three trials.

Conclusions: Our findings indicate that unpleasant emotions may affect spinal motor neuron excitability. Therefore, learning how to control emotions should be important aspect of physical therapy.