Effects of pressure stimulation of the body surface on posture and vestibulospinal reflexes

The effects of pressure stimulation of the body surface on postural activities as well as on the response gain of limb extensors to natural stimulation of labyrinth receptors were investigated in intact, as well as in decerebrate cats. In intact, unanesthetized cats, slight pressure applied symmetrically to the body surface at the chest level decreased the tonic activity of the axial (neck) and limb extensor musculature, as well as the proprioceptive reflexes induced by passive flexion of the limbs. The positive supporting reaction caused by pressure applied to the pad of the foot was also depressed. If the cats were suspended in the air by their nape, slight pressure applied to the upper part of the body greatly reduced the tonic contraction of the forelimb extensors to linear acceleration after downward movement of the animal, a response which can be attributed to stimulation of macular receptors located in the sacculus. Moreover, the prominent myotatic reflexes which occurred in all four limbs as soon as the animal touched the floor were greatly depressed, as shown by the fact that the forelimbs displayed only a slight tonic contraction of the extensor musculature during landing, while the hindlimbs collapsed under the weight of the body. In precollicular decerebrate cats there was a good postural activity in all four limbs. Moreover, the multiunit EMG activity of the medial head of the triceps brachii responded to roll tilt of the animal (at 0.15 Hz, +/- 10 degrees) leading to selective stimulation of labyrinth receptors. These responses, characterized by an increased EMG activity during side-down tilt and a decreased activity during side-up tilt, were related to animal position and not to velocity of animal displacement, and are thus attributable to stimulation of macular, utricular receptors. Slight pressure applied to the chest greatly decreased not only the postural activity of the limbs, but also the amplitude of EMG modulation and then the gain in the first harmonic component of the multiunit EMG responses of the triceps brachii to animal tilt. This reduced gain was due, in particular, to a reduced number of motor units being recruited during labyrinth stimulation, although a reduced modulation of firing rate of the active motor units should not be ruled out. However, no changes in the phase angle of the responses were observed.(ABSTRACT TRUNCATED AT 400 WORDS)     

Noradrenaline suppression of the spinal efferent component of the pressor reflexes

Noradrenaline applied to the dorsal surface of spinal cord segments C6-T1 suppressed the pressor components of the blood pressure reflexes evoked by stimulation of radial nerve afferents in anesthetized cats. Noradrenaline applied to spinal cord segments L4-S1 suppressed pressor reflexes elicited by stimulation of tibial nerve afferents. The increase in noradrenaline concentration from 0.05 to 0.2% enhanced the duration and intensity of this effect.     

Effect of tyramine on the spinal cord afferent link of pressor reflexes

In anesthetized cats, tyramine application on the dorsal surface of C6-TI spinal cord segments suppressed the pressor components of blood pressure reflexes evoked by radial nerve A sigma or A + C afferent stimulation. Tyramine application on L4-SI spinal cord segments suppressed pressor reflexes to tibial nerve stimulation. Both the degree and the rate of reflex suppression increased with the rise in tyramine concentration from I to 4%. Along with these local effects "distant" tyramine action was demonstrated: pressor reflexes to radial nerve stimulation increased when tyramine was applied on L4-SI segments, but after its application on C6-TI segments pressor reflexes to tibial nerve stimulation increased in some cats, decreased in the other ones, or remained practically unchanged.     

The effect of morphine on the input neuronal system of the spinal cord, participating in the formation of nociceptive pressor reflexes]

Effect of morphine applied to the spinal cord segments L4-S2 or C6-tI on pressor reflexes evoked by supramaximal stimulation of radial and tibial nerve with low frequency (I-2 Hz) was studied in anesthetized cats. Only pressor reflexes elicited by excitation of the tibial nerve afferents were suppressed by morphine applied to the L4-S2 segments. This effect was characterized by diminution of amplitude and steepness of the reflexes and by augmentation of their latency. Both the degree and the rate of the reflex suppression were found to enhance with increasing of morphine concentration from 0.02 to 0.5%. When applied to C6-tI segments, morphine did not suppress the pressor reflexes to the tibial nerve stimulation while reflexes to the radial nerve signals were decreased considerably. In addition to this local action of morphine, the effects resulting from it's distant action, namely, some reduction in systemic arterial pressure and an increase of pressor reflexes evoked by afferent signals entering into the spinal cord segments remote from the application region, were found to occur. All these effects were reversed by naloxone (0.2 mg/kg i. v.). It is concluded that along with attenuation of different withdrawal components of the defence reaction, action of morphine on the opiate receptors of some neurons situated near the entrance of afferent signals into the spinal cord results in suppression of the circulatory components of this reaction.     

Analysis of hemodynamic reactions induced by stimulation of the hypothalamus in alert animals

Electrical stimulation on the hypothalamus in alert cats increases the blood pressure and inhibits the baroceptor reflexes. In animals with extirpated sinocarotid and aortic nerves the pressor reactions are perversed to depressor ones at threshold stimulation of the hypothalamus. Meanwhile suprathreshold stimulation of this organ leads to emergence of depressor-pressor responses. It is suggested that inhibition of the baroceptor reflexes is one of the mechanisms of the hypertensive reaction emergence at stimulation of the hypothalamus.     

Effects of peripheral inputs from hindlimb on the monosynaptic reflex of motoneurons innervating tail muscles.

The effects of group II muscle (PBSt, GS) and cutaneous afferent (Sur, SPc, Tib) inputs from the hindlimb on the monosynaptic reflexes of motoneurons innervating tail muscles were studied in lower spinalized cats. Stimulation of the cutaneous nerves at the conditioning-test stimulus interval of about 10-20 ms facilitated and inhibited the monosynaptic reflexes of ipsilateral and contralateral tail muscles, respectively. The effects of the muscle nerve stimulation were not so prominent as those elicited by cutaneous nerve stimulation. The monosynaptic reflex was also inhibited by muscle nerve stimulation at 10-50 ms intervals. The effects of conditioning stimulation of the hindlimb peripheral nerves at short intervals were depressed or blocked by section of the ipsilateral lateral funiculus at S1 spinal segment. These findings show that the neuronal pathway from hindlimb afferents to tail muscle motoneurons passed the lateral funiculus of the spinal cord and modulates the motoneuronal activity of tail muscles.     

Defensive reflexes of the respiratory tract in dogs.

Intrapleural pressure, the tracheal air flow and tidal volume were recorded simultaneously in pentobarbital-anaesthetized dogs and changes occurring in them during defensive reflexes elicited by mechanical stimulation of the mucosa of different parts of the respiratory tract were evaluated quantitatively. The results show that, in addition to coughing and sneezing provoked by inserting a nylon fibre into the tracheobronchial region, the larynx and the nose, further respiratory reflexes described in other mammals also appear in these animals. Mechanical stimulation of the epipharynx with a fine polyvinylchloride catheter, for instance, also produces in dogs an aspiration reflex characterized by sniff-like inspiratory efforts without subsequent active expiration. Touching the vocal folds, however, produces an expiration reflex consisting of expiratory efforts without preceding inspiratory effort. The character of all these reflexes is typical and closely resembles their character in cats. Stimulation of the various parts of the respiratory tract sometimes evokes an apnoeic reaction instead of typical respiratory defensive reflexes.     

Complex perception of stimuli during conditioning

The review concerns the effects of a variety of stimuli on the reproduction of conditioned reflexes. By the literature data, during conditioning of any type, besides the single stimulus intentionally applied by an experimenter as a conditioned one, an animal perceives the whole complex of stimuli (acoustic, visual, olfactory, algesic, and other exteroceptive, proprioceptive, and interoceptive stimuli), including those of the environment and time of the day during training. Many of these stimuli are essential for the reproduction of the acquired habit. The complex of stimuli that act on an animal during the reproduction should in all parameters correspond to that perceived by the animal during training. If the complexes differ at least in one stimulus, the reproduction of the reflex may fail.     

The vegetative component of a conditioned reflex]

Defensive and alimentary conditioned reflexes were studied on normal cats and cats with neural isolation of the neocortex. The cardiac component of the conditioned reflexes is elaborated in decorticated animals at a similar rate and is as steady as in normal cats. Motor conditioned reactions in decorticated cats are difficult to elaborate. Both in normal and decorticated cats unconditioned pain stimulation evokes tachycardia, while a conditioned signal, paired with this unconditioned stimulus, produces bradicardia. Ban assumption has been made that the primary conditioned reaction consists in the appearance of a certain emotional state which changes the cardiac rhythm in a typical way.     

Kainic acid lesions to the lateral tegmental field of medulla: effects on cough, expiration and aspiration reflexes in anesthetized cats

We have tested the hypothesis that neurons of both the ventral reticular nucleus and the adjacent parts of the lateral tegmental field (LTF) may be important for the production of motor programs associated with cough, expiration and aspiration reflexes. Our studies were conducted on non-decerebrate, spontaneously breathing cats under pentobarbitone anesthesia. Dysfunction of the medullary LTF region above the obex, produced by uni- or bilateral injections of kainic acid (a neurotoxin), regularly abolished the cough reflex evoked by mechanical stimulation of both the tracheobronchial and laryngeal regions and in most cases also the expiration reflex induced from the glottal area. However, some electrical activity still occurred in the neurogram of the recurrent laryngeal nerve during probing the laryngeal and glottal regions. Interestingly, the aspiration reflex elicited from the nasopharynx regularly persisted, although with lower intensity after the LTF lesion. Nevertheless, successive midcollicular decerebration performed in four cats also abolished the aspiration reflex. These experiments demonstrate the importance of medullary LTF neurons for the normal occurrence of cough and expiration reflexes. One possible explanation for the elimination of these expulsive processes is that the blockade of the LTF neurons may remove an important source of a facilitatory input to the brainstem circuitries that mediate cough and expiration reflexes. In addition, the potential importance of the mesencephalic reticular formation for the occurrence of the aspiration reflex and the role of the LTF in modulating both the eupnoeic breathing and the blood pressure are also discussed.     

Human postural response to lower leg muscle vibration of different duration

Body lean response to bilateral vibrations of soleus muscles were investigated in order to understand the influence of proprioceptive input from lower leg in human stance control. Proprioceptive stimulation was applied to 17 healthy subjects by two vibrators placed on the soleus muscles. Frequency and amplitude of vibration were 60 Hz and 1 mm, respectively. Vibration was applied after a 30 s of baseline. The vibration duration of 10, 20, 30 s respectively was used with following 30 s rest. Subjects stood on the force platform with eyes closed. Postural responses were characterized by center of pressure (CoP) displacements in the anterior-posterior (AP) direction. The CoP-AP shifts as well as their amplitudes and velocities were analyzed before, during and after vibration. Vibration of soleus muscles gradually increased backward body tilts. There was a clear dependence of the magnitude of final CoP shift on the duration of vibration. The amplitude and velocity of body sway increased during vibration and amplitude was significantly modulated by duration of vibration as well. Comparison of amplitude and velocity of body sway before and after vibration showed significant post-effects. Presented findings showed that somatosensory stimulation has a long-term, direction-specific influence on the control of postural orientation during stance. Further, the proprioceptive input altered by soleus muscles vibration showed significant changes in postural equilibrium during period of vibration with interesting post-effects also.     

Effect of hippocampal stimulation on the feeding behavior of cats

Influence of electrical stimulation (100 cps., 1.0 ms) of medial parts of dorsal and ventral hippocampus (field CA1), and the lateral parts of dorsal and posterior hippocampus (field CA3) on general behaviour, elaboration of instrumental and manifestation of delayed reactions was studied in chronic experiments on cats. Stimulation of medial parts of dorsal and ventral hippocampus elicited a reaction of orienting reflex type to natural stimuli. Stimulation of lateral parts of dorsal and posterior hippocampus evoked arrest reactions. Medial and lateral parts of hippocampus produced different influences on elaboration of conditioned reflexes. In the first case elaboration was possible, but developed slower, while in the second case the ability to learn during stimulation was completely lost due to development of arrest reaction. Stimulation of different parts of the hippocampus disturbed delayed reactions, reducing the number of correct responses.     

Models of learning based on the plastic properties of the "placing reaction" in cats]

A possibility of functional reorganization of initial sensorimotor connections of the forepaw has been shown on seven cats. The main initial relationships between the afferent tactile input and motor output for the ulnar joint of the cat forepaw are as follows: tactile stimulation of the dorsal surface of the paw produces a flexion in the ulnar joint ("placing reaction"), and that of the ventral surface, an extension of the paw in the ulnar joint ("magnetic reflex"); simultaneous tactile stimulation of the ventral surface of the paw blocks the "placing reaction" evoked by a touch of the dorsal side. Extinction was produced of the above unconditioned connections and elaboration of a new "cross" connection consisting in that tactile stimulation of the ventral side of the paw resulted in flexion in the ulnar joint.     

Neuronal application of capsaicin modulates somatic pressor reflexes

Static contraction of skeletal muscle elicits a reflex increase in cardiovascular function. Likewise, noxious stimuli activate somatic nociceptors eliciting a reflex increase in cardiovascular function. On the basis of recent work involving spinothalamic cells in the dorsal horn, we hypothesized that the dorsal horn cells involved in the aforementioned reflexes would be sensitized by applying capsaicin (Cap) to a peripheral nerve. If correct, then Cap would enhance the cardiovascular increases that occur when these reflexes are evoked. Cats were anesthetized, and the popliteal fossa was exposed. Static contraction was induced by electrical stimulation of the tibial nerve at an intensity that did not directly activate small-diameter muscle afferent fibers, whereas nociceptors were stimulated by high-intensity stimulation (after muscle paralysis) of either the saphenous nerve (cutaneous nociceptors) or a muscular branch of the tibial nerve (muscle nociceptors). The reflex cardiovascular responses to these perturbations (contraction or nociceptor stimulation) were determined before and after direct application of Cap (3%) onto the common peroneal nerve, using a separate group of cats for each reflex. Compared with control, application of Cap attenuated the peak change in mean arterial pressure (MAP) evoked by static contraction (DeltaMAP in mmHg: 38 +/- 10 before and 24 +/- 8 after ipsilateral Cap; 47 +/- 10 before and 33 +/- 10 after contralateral Cap). On the other hand, Cap increased the peak change in MAP evoked by stimulation of the saphenous nerve from 57 +/- 8 to 77 +/- 9 mmHg, as well as the peak change in MAP elicited by activation of muscle nociceptors (36 +/- 9 vs. 56 +/- 14 mmHg). These results show that the reflex cardiovascular increases evoked by static muscle contraction and noxious input are differentially affected by Cap application to the common peroneal nerve. We hypothesize that a Cap-induced alteration in dorsal horn processing is the locus for this divergent effect on these reflexes.     

Coupling sensory inputs to the appropriate motor responses: new aspects of cerebellar function

It is known that proprioceptive signals modify the spatial organization of the postural reflexes, thus leading to body stability. The neurophysiological basis of this phenomenon are at present unknown. The present report documents that, in decerebrate cat, body-to-head rotation in the horizontal plane modified the preferred response direction to labyrinthine stimulation of the forelimb extensor triceps brachii. Such direction resulted always perpendicular to the longitudinal body axis of the animal, whatever its relative position with respect to the head could be. The rotation of the preferred response direction of the triceps was greatly reduced by functional inactivation of the ipsilateral cerebellar vermis. On the other hand, following body-to-head displacement, the preferred response directions of the corresponding P-cells tended, on the average, to rotate in the same direction and by the same angle as the body. We propose that the neck input finely tunes parallel vestibular channels, endowed with different spatial and temporal properties, impinging upon P-cells, thus modifying their responses to animal tilt and, as a consequence, the spatial properties of VS reflexes. It is possible that, by a similar mechanism, the cerebellum may contribute to the changes in reference frame occurring in sensorimotor transformations of reflex and voluntary nature.     

Reflex actions of the functional divisions in the crayfish oculomotor system

Summary The electrical responses of motor neurons in different anatomical subdivisions of the crayfish oculomotor system were examined during various kinds of experimentally manipulated sensory stimulation. Geotactic reflexes are effected by neurons in the anterior motor cluster and the medulla terminalis. Optokinetic and proprioceptive nystagmus are generated by neurons in the lateral motor cluster. This functional diversity in the major subdivisions contrasts with an intradivisional homogeneity of function, in that the different motor neurons of each all contribute to reflexes initiated by different kinds of sensory input.This research was supported by USPHS Research Grant NS 04989.     

Nitric oxide modulates presynaptic afferent depolarization of mechanosensory neurons

In crayfish, movement of the tailfan causes stimulation of exteroceptive sensory hairs located on its surface. Movement is monitored by a proprioceptor, the protopodite-endopodite chordotonal organ within the tailfan. Proprioceptive afferents provide indirect presynaptic inhibitory inputs to sensory hair afferents in the form of primary afferent depolarizations (PADs). Bath application of nitric oxide (NO) substrates, donors and scavengers, and nitric oxide synthase (NOS) inhibitors had no effect on the responses of proprioceptive afferents during imposed movements of the chordotonal organ. In contrast, the amplitude of PADs in exteroceptive hair afferents was dependent on NO levels. NO levels were altered by bath-application of the NO-precursor L-arginine, the NO donor SNAP, the NOS-inhibitor L-NAME, and the NO scavenger PTIO, while changes in PAD amplitude were measured. Application of L-arginine or SNAP resulted in consistent decreases in PAD amplitude, whereas L-NAME and PTIO induced increases in PAD amplitude. These results suggest that endogenous NO decreases inhibitory inputs to exteroceptive neurons, thus enhancing transmitter release at their output synapses.     

Bodily illusions modulate tactile perception

Touch differs from other exteroceptive senses in that the body itself forms part of the tactile percept. Interactions between proprioception and touch provide a powerful way to investigate the implicit body representation underlying touch. Here, we demonstrate that an intrinsic primary quality of a tactile object, for example its size, is directly affected by the perceived size of the body part touching it. We elicited proprioceptive illusions that the left index finger was either elongating or shrinking by vibrating the biceps or triceps tendon of the right arm while subjects grasped the tip of their left index finger. Subjects estimated the distance between two simultaneous tactile contacts on the left finger during tendon vibration. We found that tactile distances feel bigger when the touched body part feels elongated. Control tests showed that the modulation of touch was linked to the perceived index-finger size induced by tendon vibration. Vibrations that did not produce proprioceptive illusion had no effect on touch. Our results show that the perception of tactile objects is referenced to an implicit body representation and that proprioception contributes to this body representation. We also provide, for the first time, a quantitative, implicit measure of distortions of body size.     

Cholinergic mechanisms related to REM sleep. III. Tonic and phasic inhibition of monosynaptic reflexes induced by an anticholinesterase in the decerebrate cat

The depression of the postural activity induced by intravenous injection of eserine sulphate (0.1 mg/kg), an anticholinesterase, has been studied in precollicular decerebrate cats. The extensor and flexor monosynaptic reflexes elicited by single shock stimulation of the GS, P1-FDHL and DP nerves are tonically depressed during the episodes of postural atonia induced by the anticholinesterase. A further phasic depression of the monosynaptic reflexes occurs during the bursts of rapid eye movements (REM) typical of these episodes. These changes in spinal reflex activity closely resemble the tonic depression of the spinal reflexes described in the unrestrained cats during the desynchronized sleep as well as the phasic depression of the spinal reflexes characteristic of the hypnic bursts of REM. Results obtained after spinal cord section indicate that both the tonic and the phasic depression of the spinal reflexes induced by eserine are due to active inhibitory influences originating from supraspinal structures. A complete bilateral destruction of the vestibular nuclei or limited to the medial and descending vestibular nuclei abolishes not only the cholinergically induced bursts of REM, as reported in a previous paper, but also the related phasic depression of the monosynaptic reflexes. These findings can be related with previous observations showing that a bilateral lesion of the vestibular nuclei abolishes the REM bursts of desynchronized sleep, as well as the related phasic inhibition of the spinal reflexes. The tonic depression of the monosynaptic reflexes induced by the anticholinesterase, on the other hand, remains unmodified by this vestibular lesion. This depression, therefore, can be attributed to supraspinal descending inhibitory volleys originating from extravestibular structures.     

Cough, expiration and aspiration reflexes following kainic acid lesions to the pontine respiratory group in anesthetized cats

The importance of neurons in the pontine respiratory group for the generation of cough, expiration, and aspiration reflexes was studied on non-decerebrate spontaneously breathing cats under pentobarbitone anesthesia. The dysfunction of neurons in the pontine respiratory group produced by bilateral microinjection of kainic acid (neurotoxin) regularly abolished the cough reflexes evoked by mechanical stimulation of both the tracheobronchial and the laryngopharyngeal mucous membranes and the expiration reflex mechanically induced from the glottis. The aspiration reflex elicited by similar stimulation of the nasopharyngeal region persisted in 73% of tests, however, with a reduced intensity compared to the pre-lesion conditions. The pontine respiratory group seems to be an important source of the facilitatory inputs to the brainstem circuitries that mediate cough, expiration, and aspiration reflexes. Our results indicate the significant role of pons in the multilevel organization of brainstem networks in central integration of the aforementioned reflexes.