Gentle Mechanical Stimulation Research Articles

The cat lumbar spinal cord somatotopic map is unchanged after peripheral nerve crush and regeneration

Microelectrode recordings have been made of the activity of neurons in the left dorsal horn of the lumbar enlargement of cats in which the left sciatic and saphenous nerves had been crushed 9 months earlier. In normal animals the receptive fields of neurons in this part of the spinal cord excited by gentle mechanical stimulation of the leg are somatotopically organized in such a way that they provide a map of the hind-leg skin. Previous experiments have shown that 9 months after cutting the nerves supplying the lower half of the hind-leg this somatotopic map is lost. The present experiments show that 9 months after nerve crush the somatotopic map is restored and indistinguishable from that seen in normal animals.

Motor neuron synaptic potentials during fictive scratch reflex in turtle

1. A scratch reflex motor program, termed the ‘fictive’ scratch reflex (Stein and Grossman 1980), is displayed by an immobilized low spinal turtle in response to gentle mechanical stimulation delivered to specific regions of the shell. The fictive scratch is a cyclic program; each cycle is divisible into three phases, the A1, the A2 and the B phases (Fig. 1). Rhythmic A1 and A2 activities may be produced even when the B phase is deleted (Fig. 2). 2. Intracellular recordings from hindlimb motor neurons during the fictive scratch reveal that each motor neuron is depolarized to fire action potentials during its active period and is hyperpolarized during at least part of its quiescent period (Figs. 3–5). Moreover, the activation pattern of A1 motor neurons is the inverse of the activation pattern of B motor neurons (Figs. 3 and 5). The synaptic activation patterns of motor neurons during the A1 and A2 phases are preserved even during B phase deletions (Fig. 6). 3. A fictive flexion reflex motor program is produced in this preparation in response to gentle mechanical pressure applied to the dorsum of the foot (Figs. 7 and 8). The synergies observed in fictive flexion reflex differ from those observed during the fictive scratch reflex. 4. These data support a model for turtle of a three phase scratch generator that is asymmetrically arranged. A similar conclusion has been reached in studies of the scratch program generator in the cat (Berkinblit et al. 1978a, b). Our data also indicate that the motor neuron activation pattern of flexion reflex is different from that of scratch reflex. Therefore data obtained from turtle flexion reflex can not be utilized to construct a model of the turtle scratch generator.

Physiology and morphology of substantia gelatinosa neurons intracellularly stained with horseradish peroxidase.

Neurons in Rexed's layer II were physiologically characterized with natural and electrical stimuli applied to their cutaneous receptive fields. The neurons were then intracellularly stained with horseradish peroxidase. Three general patterns of physiological responses were found. Nociceptive specific neurons did not respond to gentle mechanical stimulation. Most responded exclusively to tissue-damaging stimuli. Some also responded to moderately heavy pressure, but these responded to noxious stimuli with an increased discharge frequency. Wide dynamic range neurons responded to both gentle mechanical stimulation and to tissue-damaging stimulation. Low-threshold mechanoreceptive neurons responded only to gentle mechanical stimulation. Some of the low-threshold mechanoreceptive neurons were innervated by primary afferents with unmyelinated axons. Excepting those low-threshold mechanoreceptive neurons with input from unmyelinated afferents, the patterns of primary afferents innervation of layer II neurons were similar to the patterns of innervation that have been found for neurons in layers I and IV-V. All but 2 of the 22 neurons that we found were recognized as being of two general morphological types. Stalked cells had their perikarya situated along the superficial border of layer II. Most of their dendrites traveled ventrally while spreading out rostrocaudally. This gave their dendritic arbors a fan-like shape. Stalked cell axons arborized largely in layer I. Islet cell perikarya were found throughout layer II. Most of their dendrites traveled rostrocaudally. Their dendritic arbors were shaped like cylinders with their long axes parallel to the long axis of the spinal cord. Islet cell axons arborized in the immediate vicinity of their dendritic territories, within layer II. Stalked cells and those islet cells whose dendritic arbors were largely contained within the superficial one-third of layer II (layer IIa) were either nociceptive specific or wide dynamic range neurons. The islet cells whose dendritic arbors were largely within the deeper two-thirds of layer II (layer IIb) were all low-threshold mechanoreceptive neurons. These observations suggest that layers IIa and IIb have different functional roles and that stalked cells and islet cells are separate and distinct components of the neural circuitry of the superficial dorsal horn.

Central program for scratch reflex in turtle

1. A scratch reflex is displayed by a low spinal turtle in response to gentle mechanical stimulation delivered to specific regions of the shell anterior to a hindlimb (Valk-Fai and Crowe, 1978, 1979). The behavior consists of a rhythmic limb movement in which the foot protracts and rubs against the stimulated patch of shell once per cycle. A brief stimulus can elicit a response composed of a small number of cycles or even a fraction of a cycle (Fig. 1); maintained rubbing of the shell can elicit a response consisting of 5–20 cycles (Fig. 2A). 2. The scratch motor program is divisible into an A phase in which IT-KE is active and a B phase in which IT-KE is quiescent and HR-KF is active (Fig. 2B). The A phase is further divisible into an A1 phase in which IT-KE is the only active KE muscle and into an A2 phase in which all three KE muscles are active. 3. Two variations of the scratch program exist (Figs. 3 and 4). These variations indicate that there are flexibilities in the organization of the spinal generator for turtle scratch reflex. 4. The scratch motor program can also be expressed in a preparation immobilized by a neuromuscular blocking agent (Figs. 5 and 6). The responses in this preparation are termed the fictive scratch reflex since they occur in the absence of a real movement. One of the variations in the scratch program which was seen in preparations with a moving limb was also seen in the fictive scratch reflex (Fig. 7). 5. The scratch motor program can also be expressed in preparations with the hindlimb enlargement deafferented via bilateral dorsal rhizotomies (Figs. 8 and 9). 6. These observations establish that the turtle scratch reflex is centrally programmed, i.e., it is not dependent upon phasic timing cues derived from sensory feedback. Even though the reflex is centrally programmed, it is still possible to demonstrate that sensory feedback from a moving limb can modulate the scratch rhythm (Fig. 10 of this paper and Fig. 6 of Valk-Fai and Crowe, 1979).

A chronic isolated tracheal segment to study airway reflexes in conscious dogs.

Airway reflexes are difficult to study in conscious animals because associated changes in ventilation alter intrathoracic airway dimensions. By studying an isolated segment of extrathoracic trachea, we have overcome this problem. In each of 2 dogs, we created surgically an isolated tracheal segment just below the larynx, sealed at one end and tapered at the other to a 3-mm opening via a skin fistula. A chronic tracheostomy was also created near the thoracic outlet. We monitored intraluminal pressure (Pseg) of the isolated segment to reflect changes in smooth muscle tone. During anesthesia, with pentobarbital, gentle mechanical stimulation of the carina, deflation of the lungs, and asphyxia for one min increased Pseg (+9 to +/- 16 cm H2O). Lung inflation and alveolar hyperventilation decreased Pseg (-9 to -16 cm H2O). Five breaths of 2 per cent histamine aerosol increased Pseg (+5 cm H2O) when resting tone was normal. We also coated lumen of the isolated segment with tantalum powder and documented roentgenologically changes in the size of the segment that reflected changes in smooth muscle tone; constriction and dilation in response to asphyxia and lung inflation, respectively, were demonstrated directly by this technique. In conscious dogs, lung inflation decreased Pseg, and carinal stimulation increased Pseg. Instillation of lidocaine hydrochloride (Xylocaine) into the isolated tracheal segment blocked cough caused by mechanical stimulation of the segment, but carinal stimulation still caused constriction of the segment under these conditions which indicated that afferent, but not effrent parasympathetic innervation of the segment had been blocked selectively. Conversely, instillation of atropine sulfate into the isolated tracheal segment blocked constriction of the segment caused by carinal stimulation, but mechanical stimulation of the segment still caused cough under these conditions, which indicated that efferent, but not afferent parasympathetic innervation of the segment had been blocked selectively. We conclude that an innervated extrathoracic tracheal segment constricts and dilates via cholinergic pathways and is suitable for the study of airway reflexes in conscious dogs.

Functional subsets of neurons in somatosensory thalamus of the cat

Functional properties of somatosensory thalamic neurons isolated within a region encompassing nucleus ventralis posterolateralis were studied in chloralose-anesthetized cats. A sample of these neurons responding to electrical stimulation of the contralateral forepaw was reconstructed by pooling data from 46 individual animals on the basis of unit spatial location. Seventy percent of the 640 neurons studied responded only to the contralateral forepaw; they had small receptive fields as determined by natural stimulation, generally on the digits and the dorsum of the paw, and 75% of this group were excited by light touch or deflection of hairs. Thirty percent of the neurons studied responded to the contralateral forepaw and to other limbs as well, their larger receptive fields often being bilateral. Approximately 50% of these wide-field neurons were excited by gentle mechanical stimulation. Some cells of this type were identified as projection neurons by virtue of their antidromic activation from the S I forepaw area of cerebral cortex. The wide-field neurons described here are not adequately explained as vestigial aberrations persisting at the feline stage in an evolutionary trend toward strictly somatotopic thalamic representation. Comparison of the dynamic response properties (latency, spikes per discharge, and frequency-following) of small- and wide-field somatosensory thalamic neurons suggests that they are activated via different input mechanisms and that each has a particular functional role in somesthesis.

Tactile projections to granule cells in caudal vermis of the rat's cerebellum.

We discovered a small tactile area in a single a folium of the uvula of the cauday vermis of the rat's cerebellum. Gentle mechanical stimulation of relatively small cutaneous receptive fields (RFs) activated multiple units in the granule cell (GC) layer in a portion of a single folium in rats anesthetized with sodium pentobarbital. The total size of this area on each side of the midline is about 1.5 mm2, yet micromapping within this tiny region using tungsten ball microelectrodes and a high puncture sampling density (about 75 punctures/mm2) revealed a highly differentiated pattern of cutaneous projections to the GC layer. All peripheral projections are ipsilateral; the two homologous areas from each side adjoining at the midline of folium 9a. The larger projection areas from cutaneous RFs are mostly from mystacial vibrissae and upper lip, but small projection sites from the remainder of the head, neck and forelimb also are present. The pattern of projections were patch-like, forming a fractured somatotopic pattern or mosaic, with some somatotopic and some nonsomatotopic features. Each RF activated units in a vertical column in the GC layer. This area has not been described in any mammal, and its functional role can now be studied.

Responses of spinocervical tract neurones to noxious stimulation of the skin.

1. Activity of single spinocervical tract neurones has been recorded in the lumbar spinal cord of chloralose anaesthetized or decerebrated cats. Reversible spinalization was produced by cold block at L3. Sensitivity of these neurones to noxious stimulation was studied by heating their cutaneous receptive fields above 40-45 degrees C. 2. Most of the units were located in lamina IV of the dorsal horn and had their receptive fields in the ipsilateral foot. All but one of the studied neurones were excited by moving hairs or by gentle mechanical stimulation of the skin. 3. Eighty-four % of the units were affected by noxious stimuli and three kinds of response were obtained: (i) 61% were excited (E-cells) by noxious heat; (ii) 19% were inhibited (I-cells); and (iii) 19% gave a mixed response reversing from excitatory to inhibitory (EI-cells). 4. E-cells had axons with a wider range of conduction velocities than the rest and also received the strongest descending inhibition from supraspinal structures. 5. The recording sites of EI-cells were located in the medial third of the dorsal horn whereas E- and I-cells were distributed over the full width of the dorsal horn. 6. The possible role of the spinocervical tract in nociception is discussed.

Climbing fibre inputs to cerebellar Purkinje cells from trigeminal cutaneous afferents and the SI face area of the cerebral cortex in the cat.

1. An investigation was made of climbing fibre (CF) activity evoked in single Purkinje cells in the cerebellum by electrical stimulation of trigeminal cutaneous afferents, the face area of the SI cortex, and the superficial radial nerve, in Nembutal-anaesthetized cats. In addition, both the extent of the cutaneous receptive fields of individual Purkinje cells on the face and the CF responses evoked in these cells by controlled natural stimulation were examined. 2. The pattern of convergence from these inputs on to individual Purkinje cells was found to be complex. DF responses were evoked in 67% of trigeminally-activated cells by electrical stimulation of more than one trigeminal branch. An excitatory CF convergence from the face area of the SI cortex was found on 68% of trigeminally activated cells; 23% also responded to stimulation of the superficial radial nerve. 3. In 81% of the Purkinje cells which were activated by trigeminal nerve stimulation, CF responses were readily elicited by gentle mechanical stimulation of the facial skin. A qualitative relationship was established between the size of the peripheral field of a Purkinje cell, and the probability of convergence on to that cell from the SI cortex. 4. Recordings were made from a limited number of Purkinje cells which were responsive to electrical stimulation of bilateral trigeminal branches and the superficial radial nerve. However, CF responses in these cells often could be elicited only by high intensity stimulation. It is suggested that these cells are analogous to, or perhaps an extension of the population of Purkinje cells described in the anterior lobe which are excited via the ventral funiculus pathway in the spinal cord only by stimulation of 'flexor reflex afferents' in bilateral limb nerves.

The response of laryngeal afferent fibres to mechanical and chemical stimuli.

1. We have recorded afferent activity from ;single fibres' dissected from the superior laryngeal nerve of anaesthetized cats.2. Units which responded to gentle mechanical stimulation of the larynx epithelium were chosen for study.3. Receptors with myelinated fibres were grouped according to their spontaneous activity. Group 1 fibres had little or no spontaneous activity: group 2 fibres had constant and continuous spontaneous activity.4. Group 1 fibres had a wide range of adaptation rates. Their conduction velocities lay between 3.0 and 30 m/sec. The receptors were generally stimulated by ammonia and distilled water and often by CS riot control agent, 5 and 10% CO(2), 200 ppm SO(2), and cigarette smoke. Histamine, phenyl diguanide, graphite dust, 100 ppm SO(2) and saline drops did not generally excite the fibres.5. Group 2 fibres were slowly adapting. Their conduction velocities ranged between 8.0 and 26.5 m/sec. Ammonia usually, and distilled water sometimes, excited these fibres while 5 and 10% CO(2) mixtures inhibited them. A minority of group 2 fibres were pH sensitive, inhibited by acids and stimulated by alkaline buffers. Cigarette smoke had complex actions, either excitation, inhibition or, at different times, both. Histamine, P.d.g., CS, SO(2), saline drops and dust had no action on these fibres.6. Recordings were made from one unmyelinated fibre (conduction velocity 1.9 m/sec) which responded to stroking of the epithelium with a thread and to histamine, P.d.g. and ammonia vapour applied to the epithelium.7. We consider the site, method of excitation and reflex actions of the different receptors described.

Epipharyngeal receptors responding to mechanical stimulation.

1. Action potentials were recorded from twenty-one afferent nerve fibres from receptors in the epipharynx in anaesthetized, paralysed cats. Sixteen of the fibres had no spontaneous discharge.2. Gentle mechanical stimulation of the epithelium of the epipharynx with a nylon fibre caused all twenty-one receptors to discharge with rapidly adapting bursts of impulses at a mean peak frequency of 197 impulses/sec.3. Stimulation with a stream of air through the epipharynx sufficient to distend the whole pharynx caused seven out of twelve receptors to discharge in rapidly adapting bursts. Stimulation with a jet of air directly on to the epithelium of the epipharynx caused seven out of nine receptors to discharge.4. Chemical stimulation of the epipharynx with ammonia vapour caused an increased discharge in only three out of twenty receptors, and intravenous histamine had no effect on the four units tested.5. It is concluded that the receptors mediate the ;aspiration reflex' elicited by mechanical stimulation of the epipharyngeal mucosa.

Experimental evaluation of the hypothesis of ligamento-muscular protective reflexes. II. A study in cat using the medial collateral ligament of the knee joint.

ABSTRACTAndersson, S. and B. Stener. Experimental evaluation of the hypothesis of ligamento‐muscular protective reflexes. II. A study in cat using the medial collateral ligament of the knee joint.Acta physiol. scand.1959.48.Suppl. 166. 27—49.—A method has been developed for effecting a large increase in the ligament's tension, without appreciably damaging its innervation during the preparatory dissection (STENER 1959). The effect of the intense afferent impulse flow, induced by this method, on motoneurones supplying muscles capable of opposing an increase in tension in the ligament was studied by myography, electromyography and monosynaptic testing. With none of these methods was it possible to detect any reflex motor effects ascribable to receptors in the ligament. On the other hand, strong reflex motor responses were obtained by gentle mechanical stimulation of extra‐ligamentary receptors within the ventromedial region of the joint (skin removed).

Observations on luminescence in sea pens (Pennatulacea)

The luminescent responses of sea pens ( Leioptilus gurneyi ) have been studied by visual observation and photo-electric recording. Light is emitted by the polyps (autozooids and siphonozooids) when the animal is excited. Gentle mechanical stimulation and electrical stimulation (condenser shocks) evoke luminescent waves which pass over the rachis at a velocity of 26·4 cm/s (20·5°C). The first luminescent wave appears after 1 to 3 shocks, depending on the condition of the animal. Subsequently, waves arise at the rate of 1/shock, and increase progressively in intensity owing to neuroeffector facilitation. On recording from re-­stricted loci (width 2 cm), the following data for temporal characteristics of flashes (from auto ­zooids) were obtained: latent period, 0·18s; total duration of flash, 1 to 1·2s; maximal intensity from first deflexion, 0·2 s; time to half-maximum, 0·1 s. Strong mechanical and prolonged electrical stimulation produce a refractory state in which the animal contracts and no longer produces luminescent waves. Slow progressive spread of luminescence can then be induced by maintained repetitive stimulation. This effect is ascribed to intemuncial facilitation overcoming fatigue in the nerve net. Certain lines of evidence indicate that light may temporarily inhibit luminescence, apparently by affecting the excitatory system. The results are related to observations made on the luminescent responses of other sea pens.