Conjugate inhibition in the presence of an eyelid reflex dominant in the rabbit

Conjugated inhibition was studied of the swallowing reflex during formation of dominant focus in the centre of the eye-lid reflex. In the initial period of the dominant focus formation when the dominant passed through the stage of summating reflex, the swallowing reflex was not inhibited. When the dominant turned to optimal stage, i. e. when it was reinforced by stimuli of various modalities, the swallowing reflex was conjugately inhibited. When the dominant turned to pessimal state, summation was not observed in the dominant focus, and conjugated inhibition went on. In the study of the influence of the eye-lid reflex on the swallowing one, it was found that during formation of temporary connection of the type of summating reflex a circular interaction between the centres took place.     

Electrophysiologic study of the cerebral control of swallowing

Swallowing dominant, created by serial pouring of water into rabbit's mouth cavity was tested in after-action from water supply. As a result of summation in the dominant focus of excitations elicited by stimuli of various modalities, swallowing took place. The study of swallowing dominant revealed by its stimulus which elicits its own unconditioned reflex (blinking), has shown that temporary feedback is characteristic for the dominant as well as for the conditioned reflex. Summation in the swallowing center during dominant testing by stimulation of the eye cornea takes place without conjugated inhibition of the blinking center. During discrete pouring of water into the animal's mouth, evoked potentials appear in the cortical-subcortical structures of the swallowing center. Identical potentials appear in corresponding structures before the summation swallowing. Appearance of these potentials in the electric activity of the dominant focus testifies to its readiness for summation.     

Changes in the cholinosensitivity of sensomotor cortex neurons during conditioned reflex extinction]

Characteristics of neuronal responses of the sensorimotor cortex to ionophoretically administered neuromediators (acetylcholine, L-glutamate) were studied in rabbit in the course of extinction of conditioned defensive reflex. In the majority of neurones the extinction of the conditioned reflex is accompanied by a drop of cholinosensitivity. In a number of neurones the extinction of reflexes either does not change the reaction to acetylcholine, or enhances it. The analysis of these reactions permits to assume the existence of a group of neurones directly involved in the formation, fixation and storage of the temporary connection.     

Conditioned food reflexes acquired on the basis of a dominant

By means of daily alimentary deprivation and presentation of acoustic stimuli, a hunger dominant was created in rabbits. After dominant testing by eye stimulation with air puff, when not only winking of one eye but also swallowing or chewing appeared,--the dominant was disrupted by giving food to the animal. Disruption of motivational hunger dominant led to rapid formation of stable temporary connection. At subsequent creation of hunger dominant the animal itself disrupted it by winking reaction with the significant eye. The basis of goal-directed reaction is the activation of feedback temporary connection, established at the dominant summation stage. The conditioned alimentary reflex, elaborated on the basis of dominant disruption is designated as endogenous alimentary conditioned reflex.     

Tonic component of the conditioned reflex process and its functional role

Tonic background activity of 266 neurones in the hippocampus and different neocortical areas was studied in freely moving rabbits in the process of defensive and food instrumental conditioned performance and during switching-over of instrumental and classical food and defensive reflexes. Associations of CS and reinforcement evoke background activity changes in most of recorded cortical neurones preceding the development of other conditioned manifestations. Conditioned reflex was performed only after reaching the background firing rate of almost every examined neurone optimal for its realization. The performance of different conditioned reflexes was associated with different background activity levels of cortical neurones. The above mentioned data form the experimental basis for the identification of the tonic component in conditioned process which reflects tonic character of temporary connection formation and function.     

Effect of anaesthetics on the sympathetic reflex.

i) In the awake animal, neither a late response nor a silent period could be evoked from the tibial nerve. Somatic afferentation with impulse trains failed to inhibit efferent sympathetic activity. On the other hand, vagal afferentation had an inhibitory action also in the awake animal. In the awake animal, the excitatory processes are dominant. ii) Urethan anaesthesia did not influence the sympathetic nervous processes; the reflex response were practically the same as in the awake animal. iii) Chloralose anaesthesia altered the sympathetic reflex observable in the awake animal. Somatic afferentation of low threshold voltage already elicited a late response and a silent period; in addition, a high degree of summation ability of silent periods was apparent. Thus, chloralose anaesthesia seems to raise the excitatory level of the sympathetic centres in the direction of inhibition. iv) Combined chloralose+urethan anaesthesia, under which investigations are usually performed, was seem to affect the reactivity of the sympathetic centres in the same way as did chloralose anaesthesia.     

Long-lasting inhibition of the soleus muscle H reflex related to realization of voluntary arm movements in humans

In healthy humans, we recorded the H reflex induced by transcutaneous stimulation of the tibial nerve (recording from the soleus muscle). In subjects in the lying position, we studied changes in the H reflex values after preceding voluntary arm movements realized with a maximum velocity after presentation of an acoustic signal. On the 200th to 300th msec after forearm flexion, long-lasting inhibition of the H reflex developed following a period of initial facilitation and reached the maximum, on average, 700 msec from the moment of the movement. Flexion of the contralateral upper limb in the elbow joint induced deeper inhibition than analogous movement of the ipsilateral arm. Long-lasting clear inhibition of the H reflex developed after arm flexion in the elbow joint but was slightly expressed after finger clenching. After inhibition reached the maximum, its time course was satisfactorily approximated by a logarithmic function of the time interval between the beginning of the conditioning voluntary movement and presentation of the test stimulus. Durations of inhibition calculated using a regression equation were equal to 6.6 sec and 8.5 sec after ipsilateral and contralateral elbow-joint flexions, respectively. Inhibition was not eliminated under conditions of tonic excitation of motoneurons of the tested muscle upon voluntary foot flexion. Long-lasting inhibition of the H reflex was also observed after electrical stimulation-induced flexions of the upper limb. The obtained data indicate that movements of the upper limb cause reflex long-lasting presynaptic inhibition of the soleus-muscle H reflex that can play a noticeable role in redistribution of the muscle tone during motor activity. Neirofiziologiya/Neurophysiology, Vol. 40, No. 3, pp. 221–227, May–June, 2008.     

Functional assymmetry of the cerebral cortex in cats during formation of a conditioned reflex

During elaboration of a symmetric active defensive reflex, the animal is given the opportunity to make instrumental movements with the right or left paw. On the first day of elaboration, the cats can be subdivided into three approximately equal groups: with the right preferred paw, with the left preferred paw and ambidexters. After stabilization of the reflex, motor asymmetry increases in both preferred groups, while the number of ambidexters diminishes. Unilateral electric shock producing seizures, which is applied to the "dominant" or "subdominant" hemisphere, exerts correspondingly differing influences on the subsequent reproduction of the reflex. Suppression of reproduction is more pronounced when the shock is applied to the "dominant" hemisphere. The result of repetitive application of electroshock to one and the same hemisphere is that the functions of the "dominant" hemisphere are effected by the hemisphere which was not subjected to direct electrical stimulation.     

Several mechanisms of acetylcholine participation in the processes of formation and fixation of temporary connections

Microphoretic application of acetylcholine (ACH) to the neurones of the rabbit sensorimotor cortex elicits changes of spontaneous and evoked activity which do not correlate with one another and which persist up to two minutes after the end of ACH application. Following the formation of a defensive conditioned reflex to sound, the reactions to ACH in units involved in the formation of the temporary connection are intensified as compared with their reactions before conditioning and with reactions of those neurones which did not elaborate a temporary connection. The possible mechanisms of ACH participation in the processes of elaboration and fixation of temporary connections are discussed.     

The dynamics of forming an active defensive reflex in cats]

Active defensive reflexes were elaborated in cats with pain stimulations of the forepaw by means of an electrical pricking device with a target attached to it. The elaboration was carried out during action of a flickering light used for the convenience of the EEG analysis. Repeated pain stimulation led to elaboration of an aggressive attacking reaction, chiefly manifested in the paw striking the target. At the beginning of the elaboration, passive-defensive reactions were manifest, which did not completely disappear even after formation of a stable attacking reflex. Two types of active defensive reflexes were elaborated: A-type reflex which helped the animal to get rid of the pain stimulation at the very beginning; B-type reflex which prevented the pain stimulation. The difference beteween these two types is discussed.     

The effects of neuroleptics and nialamide on defensive conditoned reflex in rats.

Experiments were carried out on male Wistar rats after development of defensive conditioned relex during 6 weeks of training. In one series of experiments chlorpromazine, haloperidol, pimozide or fluspirilene were used in doses of 0.05, 0.5 and 5.0 mg/kg intraperitoneally. In another series of experiments nialamide was given intraperitoneally in a dose of 140 mg/kg 16--18 hours before administration of one of these neuroleptics. A delay in the time of appearance of the defensive conditioned refex was observed after administration of neuroleptics in all animals. In some rats neuroleptics caused complete disappearance of the conditioned refex as well as the defensive unconditioned refex. Previous inhibition of monoamine oxidase activity obtained with nialamide increased evidently the inhibitory effect of the studied neuroleptics on the appearance of defensive conditioned reflex.     

An analysis of the neuronal processes in the activating brain systems of the rat during the acquisition of an instrumental defense reflex

In chronic experiment, a defensive conditioned reflex was elaborated in rats with electrodes implanted in the reticular oral pons nucleus, cortico-medial group of amygdalar nuclei, ventromedial hypothalamic nucleus and central grey substance of the midbrain. Synchronization of the activity of neuronal groups of emotiogenic formations in the studied brain structures, became enhanced at formation of the conditioned reflex. A dependence was revealed of the level of correlation of limbic neuronal groups activity on functional state of the reticular formation, as well as neurochemical correlation mechanisms. The increase (decrease) of coefficients of correlation of the activity of neuronal ensembles of limbic structures was accompanied by a change of evoked potentials parameters recorded in them.     

Electrophysiological study of 5,6-dihydroxytryptamine effect on defensive reflex conditioning in the snail

The role of serotonin in expression of membrane properties of identified neurons was studied during defensive reflex conditioning using the neurotoxic analogue of serotonin 5,6-dihydroxytryptamine (5,6-DHT). The defensive reflex conditioning in snails was destroyed on the second day after second injection of 5,6-DHT. Through the 1st weeks after second injection of 5,6-DHT the snails were learned but worse than snails after injection of saline solution. This result shows the recovery of snail's learning ability within 2 weeks after the second injection of 5,6-DHT. It was found that injection of 5,6-DHT prevented the decrease of membrane and threshold potentials of command neurons during defensive reflex conditioning as compared with the snails injected with 5,6-DHT without learning.     

Neuromodulation in a rat model of the bladder micturition reflex

A rat model of bladder reflex contraction (BRC) was used to determine the optimal frequency and intensity of spinal nerve (SN) stimulation to produce neuromodulation of bladder activity and to assess the therapeutic mechanisms of this neuromodulation. In anesthetized female rats (urethane 1.2 g/kg ip), a wire electrode was used to produce bilateral stimulation of the L6 SN. A cannula was placed into the bladder via the urethra, and the urethra was ligated to ensure an isovolumetric bladder. Saline infusion induced BRC. Electrical stimulation of the SN produced a frequency- and intensity-dependent attenuation of the frequency of bladder contractions. Ten-herz stimulation produced maximal inhibition; lower and higher stimulation frequency produced less attenuation of BRC. Attenuation of bladder contraction frequency was directly proportional to the current intensity. At 10 Hz, stimulation using motor threshold pulses (T(mot)) produced a delayed inhibition of the frequency of bladder contractions to 34 ± 11% of control. Maximal bladder inhibition appeared at 10 min poststimulation. High current intensity at 0.6 mA (～6 * T(mot)) abolished bladder contraction during stimulation, and the inhibition was sustained for 10 min poststimulation (prolonged inhibition). Furthermore, in rats pretreated with capsaicin (125 mg/kg sc), stimulation produced a stronger inhibition of BRC. The inhibitory effects on bladder contraction may be mediated by both afferent and efferent mechanisms. Lower intensities of stimulation may activate large, fast-conducting fibers and actions through the afferent limb of the micturition reflex arc in SN neuromodulation. Higher intensities may additionally act through the efferent limb.     

Direct cortical response in the cat motor cortex during summation

Summation was studied by a procedure close to that used in producing a conditioned reflex. Subthreshold electrical stimulation, which gave rise to a dominant focus in the cat motor cortex, was applied after photic stimulation. Under these conditions, summation occurred both when the two stimuli were applied simultaneously and when the weaker stimulus preceded the stronger one by a very short interval (tens of milliseconds). Increased excitability was characteristic of the dominant focus. An excessive increase in excitability weakened the summation reflex. Electrographically, this type of conditioning was reflected in an increase in amplitude of the primary negative wave of the direct cortical response, recorded in the motor area at a distance of 2–3 mm from the stimulation point. It is concluded from analysis of this electrophysiological phenomenon and comparison of the results with data in the literature that different mechanisms are involved in the summation process during different sequences of stimulation ("photic+electrical" and "electrical+photic").Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 293–302, November–December, 1969.     

Effect of local depression of inhibition on intercentral relations in the rat spinal cord

Changes in spinal reflexes of rats were studied after the formation of local depression of inhibition (a "determining dispatch station" of paroxysmal activity), generating an increased excitation wave, by means of tetanus toxin. Tonic and rhythmic paroxysmal activity generated in the poisoned half of the lumbar segments was shown to evoke discharges of all spinal and bulbar motoneurons with certain temporal characteristics. Depression of unit activity in the focus with glycine abolished this phenomenon. Excitation of the focus created on one side of the cervical segments evoked a pathologically increased scratch reflex of the ipsilateral hind limb, unconnected with a disturbance of inhibition of lumbar motoneurons. The focus had enhanced excitatory and inhibitory effects on monosynaptic reflexes of lumbar flexor motoneurons. The role of local depression of inhibition in the function of the nervous system is discussed.     

Effect of preliminary presentation of a future conditioned stimulus on the rate of elaboration of an instrumental defensive reflex in the rat

Preliminary presentation of future conditioned stimulus without reinforcement delayed and then accelerated subsequent elaboration of defensive conditioned reflex to this stimulus in rats. Preliminary presentation of resembling stimuli influenced the speed of conditioning in a lesser degree. It is suggested that such changes are due to formation of a local conditioned reflex to the future conditioned stimulus.     

Influence of CPAP on reflex responses to tracheal irritation in anesthetized humans

We investigated the effects of lung inflation during continuous positive airway pressure breathing (CPAP) on airway defensive reflexes in 10 enflurane-anesthetized spontaneously breathing humans. The airway defensive reflexes were induced by instillation into the trachea of 0.5 ml of distilled water at two different levels of end-expiratory pressure (0 and 10 cmH2O CPAP). The tracheal irritation at an end-expiratory pressure of 0 cmH2O caused a variety of reflex responses including apnea, spasmodic panting, expiration reflex, cough reflex, an increase in heart rate, and an increase in blood pressure. Lung inflation during CPAP of 10 cmH2O did not exert any influence on these reflex responses in terms of the types, latencies, and durations of reflex responses although the intensity of the expiration reflex and cough reflex was augmented by lung inflation. Our results suggest that the pulmonary stretch receptors do not play an important role in the mechanisms of airway defensive reflexes in humans.     

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.     

Regulation of wrist stiffness by the stretch reflex

In restoring the angular position after a displacement, the role of the muscle stretch reflex was investigated by comparing the restored angular torques and angular positions in the wrist under ischaemic and non-ischaemic conditions in normal human subjects. The wrist compliance (COM), defined as the dynamic relation between the angular position and the angular torque of the joint, was calculated to quantify the changes in the restoration of a displacement after abolishing the stretch reflex by ischaemia. The elasticity from the COM-function was found to be single most important factor controlled by the stretch reflex. The elasticity that equals the static stiffness of the system increased by more than 100%, from 0.21 Nm degree-1 with abolished reflex to 0.45 Nm degree-1 with intact reflex. Our results have shown that the stretch reflex assists in the rapid return of the limb to its original position after a mechanical displacement. When the reflex was blocked by ischaemia, the perturbation displaced the limb further away from the initial position.