Mechanical Stimulation Of Skin Research Articles

Electrodermal reflexes in the cat's paws elicited by natural stimulation of skin.

Electrodermal reflexes recorded from the central pads on the hind-and forepaws were elicited by natural stimulation of skin in ketamine anaesthetised cats. 2. Stimuli which excite the Pacinian corpuscles in the paws (air jet stimuli applied to the paw, vibrational stimuli produced by tapping on the experimental frame) and the cutaneous nociceptors (mechanical and thermal noxious stimuli) elicit electrodermal reflexes. Stimuli exciting hair follicle receptors on the trunk or legs or slowly adapting receptors in the feet are without effect. 3. Electrodermal reflexes elicited by non-noxious mechanical stimulation of skin in the hindpaws have a clear-cut spatial organization. Air jet stimuli can only produce them from the distal hindpaws but not from any other skin area indicating that this reflex may be organized at the spinal level. Electrodermal reflexes on noxious stimulation too have some spatial organization.

EFFECT OF MECHANICAL STIMULATION ON CELL PROLIFERATION IN MOUSE EPIDERMIS AND ON GROWTH REGULATION BY ENDOGENOUS FACTORS (CHALONES)

Mechanical stimulation of dorsal mouse skin by skin massage or removal of the horny layer results in a mutually comparable increase in DNA-labelling and mitotic activity. However, only after injury such as removal of the horny layer hyperplasia develops. This phenomenon, called "hyperplastic transformation" is characterized by a transient abolition of the epidermal G1 chalone responsiveness. There is some indication that the susceptibility to a heat labile factor, probably the epidermal G2 chalone, is not affected. Skin massage neither interferes with the responsiveness to epidermal G1 chalone nor induces "hyperplastic transformation". Mouse tail epidermis shows a "functional hyperplasia" and responds to the G1 chalone. To explain these observations, it is assumed that the epidermal stem cell population is heterogeneous consisting of G1 chalone-sensitive and G1 chalone-insensitive cells.

The neuron of the fast conducting system in hirudo medicinalis: identification and synaptic connections with primary afferent neurons.

A single neuron, located in the center of each segmental ganglion of H. medicinalis is antidromically activated by electrical stimulation of the ventral cord anteriorly and posteriorly to the ganglion, at the same threshold as the fast conducting system (FCS) and with a latency equal to the FCS conduction time. This neuron is activated trans-synaptically by tactile and photic stimulation of the skin and by stimulation of high-threshold fibres running along the cord. A spike evoked by intracellular stimulation of this neuron propagates along the FCS. Intracellular staining shows that this neuron sends two axonal branches in the anterior and posterior median connectives. Direct electrical stimulation of touch cells (T cells), as well as mechanical stimulation of the skin, lowers the threshold of and may eventually fire, the FCS neurons, not only at the level of the ganglion to which they belong, but also at the level of the neighbouring ganglia. This effect is mediated by bilateral pathwasy located in the lateral connectives. It is concluded that the FCS consists of a chain of single neurons, located in each ganglion and electrotonically coupled to each other. Touch cells project with excitatory synapses on the FCS neurons.

Reflexes in postganglionic fibres within skin and muscle nerves after mechanical non-noxious stimulation of skin.

1. Somato-sympathetic reflexes in postganglionic neurones to hairy skin and to muscle produced by mechanical non-noxious stimulation of skin were studied in cats anesthetized with chloralose. Most of the postganglionic fibres investigated were spontaneously active and had presumably vasoconstrictor function. 2. In 60% of the cutaneous postganglionic neurones stimulation of hairs induced predominantly excitation. This excitation was mostly followed by a slight depression of the spontaneous activity. In 30% of the neurones the spontaneous activity was depressed or predominantly depressed by these stimuli. 3. In most muscle postganglionic neurones the spontaneous activity was depressed by stimulation of hairs. 4. In both types of neurones the reflexes were produced by activity in hair follicle receptors with Group II afferents. Hair follicle receptors with Group III afferents most probably also contributed to this effect. Except for a slight depression of the spontaneous activity in some cutaneous postganglionic neurones by slowly adapting receptors, mechanical stimulation of other types of receptors with Group II afferents had no effect on the postganglionic neurones. 5. Reflexes in postganglionic neurones could be elicited by stimulation of hairy skin all over the body surfaces.

A study of single axons in the cat's medial lemniscus.

1. A method was developed for locating the rostral part of the medial lemniscus in anaesthetized cats and then exploring it with a micro-electrode selective for single axons. Records were made from 165 axons, all shown histologically to lie in the lemniscus.2. Almost all lemniscal axons responded at short latency to a shock through surface electrodes over the dorsal columns at C2. The great majority probably belonged to the dorsal column-lemniscal system, though some may have belonged to other (e.g. spinocervicothalamic) systems.3. Resting discharge was seen in almost all axons in the absence of any stimulation, and must have been generated almost entirely in the relevant relay nuclei, particularly since in many axons it was easily depressed or totally inhibited by appropriately placed mechanical stimulation of skin or a shock to the dorsal columns.4. For each fibre held for an adequate length of time, the receptive field, if accessible, was classified as accurately as possible. Fifty-two axons were precisely categorized in this way: many more were studied for long enough to yield useful information.5. One half (twenty-six) of the best categorized axons had receptive fields suggesting excitation by only one type of receptor: fifteen by tylotrich hairs, four by rapidly adapting tactile foot pad receptors, two by claw movement, two by cutaneous touch corpuscles and three by Type II cutaneous receptors. Rigidly held probes driven by electromechanical transducers were used to establish stimulus/response relations. Adjacent or surround inhibition was seen in nearly all these fields, except for the Type II category.6. The other half (twenty-six) of the best categorized axons showed various degrees of inter-receptive excitatory convergence. Five responded to all types of hair, twelve to hair movement and foot-pad displacement, and nine to hair movement combined with inputs from a variety of slowly adapting receptors in skin or deep tissues, thresholds for the latter ranging from light contact to noxious pressure.7. Forty axons responded with a slowly adapting discharge to joint movement, some with properties suggesting that their receptors did not lie in the joint capsule itself. The high threshold of most of these axons to dorsal column stimulation suggested that the relevant primary axons lay either deep in the dorsal column or in some other tract.8. Of axons whose receptive fields were accurately located, 88% lay in forelimb or upper trunk - the remainder in lower trunk, hind limb or tail. The forepaw accounted for 41% of the former group. Axons with receptively ;pure' properties tended to lie in central or deep parts of the main lemniscal mass at the level studied. Axons responding to joint movement tended to lie deep in the main mass and in the ventromedial lemniscal bundle. There was some clustering of axons with identical receptive properties.

Afferent connections to the fast conduction pathway in the central nervous system of the leech Hirudo medicinalis.

A burst of all-or-none action potentials, identical in size and shape, can be recorded from the ventral cord of H. medicinalis following both photic and mechanical stimulation of the skin. This response propagates both anteriorly and posteriorly from its point of origin at the same conduction velocity of about 1.3 m/sec. The action potential elicited by electrical stimulation of the cord collides by refractoriness with the action potentials elicited in response to photic and mechanical stimulation. The cord response to photic and mechanical stimulation is reversibly suppressed by perfusion with high Mg++ solutions, whereas the afferent discharges recorded from the segmental nerves remain unaffected. Lesion experiments show that the cord responses to mechanical and photic stimuli, travel along the median connective (Faivre's nerve). It is concluded that afferent impulses originating from mechanoreceptors and photoreceptors converge with chemical excitatory synapses onto a fast conducting pathway in the ventral cord. This fast conducting pathway is coextensive with the one which is excited by electrical stimulation of the ventral cord (1, 3).

Sensory cells in the spinal cord of the sea lamprey.

1. Intracellular recordings were made from dorsal cells in the spinal cord of the sea lamprey.2. Dorsal cells were excited by mechanical stimulation of the ipsilateral skin and were established as first-order sensory cells using a variety of physiological criteria. Receptive fields were mapped.3. Dorsal cells were subdivided into three functional types on the basis of their responses to mechanical stimulation of the skin. Touch (T) cells gave rapidly adapting responses to indentation of the skin. Pressure (P) cells gave slowly adapting responses to indentation of the skin. Nociceptive (N) cells gave slowly adapting responses to severe (often destructive) indentation of the skin. The three types also differed in their spontaneous activity and in their response to repeated stimulation.4. Pressure and nociceptive cells were excited by heating the skin over the receptive field. The amount of heat necessary to excite nociceptive cells was greater than that necessary for pressure cells and often left a permanent burn mark on the skin.5. The three types of dorsal cell also showed differences in resting potential, membrane time constant, spike threshold, and response to sustained depolarization.

Presynaptic and post-synaptic inhibition elicited in the cat's dorsal column nuclei by mechanical stimulation of skin.

1. Primary afferent depolarization (PAD), with a time course comparable with that of the PAD following limb nerve stimulation, was produced in the cuneate nucleus by mechanical stimulation of the skin of the ipsilateral forepaw. Brushing or blowing on hairs was as effective as any other form of stimulation and there was a rapid adaptation to a sustained stimulus. Up to 55% increase in excitability was produced by blowing on hairs.2. The P-wave and the PAD produced by mechanical stimulation were at a minimum in the rostral part of the cuneate nucleus and at a maximum 2-6 mm caudal to the obex.3. The distribution of the PAD produced in the gracile nucleus by blowing on the skin of the hind foot was studied by a technique allowing measurement of excitability changes near the terminals of single fibres. Minimal values were obtained rostral to the obex and maximal values 1-4 mm caudal to the obex, a distribution matching that previously determined for single cells subject to surround inhibition.4. Post-synaptic inhibition was produced in the cuneate nucleus by gentle blowing on the ipsilateral forepaw. Up to 20% fall in excitability occurred in populations of cells tested by direct electrical stimulation. IPSPs lasting up to 160 msec were observed in single cells following light mechanical stimulation in the immediate neighbourhood of these cells' receptive fields. Blocking of antidromic invasion of single cells was occasionally produced by mechanical skin stimulation.5. It is concluded that both pre- and post-synaptic inhibition must be concerned in the phenomenon of afferent surround inhibition, though there was no evidence to indicate their relative roles, qualitatively or quantitatively.6. It is shown that up to 20% reduction in transmission through the gracile or cuneate nucleus could be produced by blowing on the ipsilateral hind paw or forepaw respectively, measured as reduction in the area of the monophasically recorded lemniscal response. A single electrical stimulus to the skin of the contralateral forepaw reduced transmission through the cuneate nucleus by less than 5%.

Two specific feedback pathways to the central afferent terminals of phasic and tonic mechanoreceptors.

In five types of mechanoreceptor afferents of the cat's hind foot, the primary afferent depolarization (PAD) induced by mechanical skin stimulation was measured by testing the excitability of their terminations in the dorsal horn. Two types of skin stimuli were used to set up activity in distinct populations of rapidly and slowly adapting mechanoreceptors respectively.

Neuronal specification of cutaneous nerves through connections with skin grafts in the frog.

Skin grafts were rotated 180 degrees in frog tadpoles. After metamorphosis, cutaneous reflexes were tested, and the receptive fields of cutaneous nerves were mapped electrophysiologically. Accurately localized limb movements were elicited by mechanical stimulation of normal skin, or of dorsal skin reimplanted on the back after 180-degree rotation. Reflexes misdirected to the original site of the stimulated skin were elicited from dorsoventrally inverted grafts, but not from anteroposteriorly inverted grafts. In most cases, the local nerves supplied the grafts, and each nerve entered the skin within its own receptive field. This observation eliminated the possibility that misdirected reflexes were due to selective regrowth of cutaneous nerves. We concluded that cutaneous nerves formed central synaptic associations which were specified by their new terminal connections with grafted skin.

Myelinated afferent nerve fibers from the skin of the rabbit ear

Electrophysiological recordings were made by dissection and microelectrode methods from single myelinated fibers of the great auricular nerve responding to mechanical stimulation of hairs and skin. Two types of hair follicle afferent unit, both rapidly adapting, were observed: type G, conducting at 18 to 54 m/sec, excited by movement of up to six guard hairs, with amplitude thresholds of 8 to 36 μ; and type D, conducting below 18 m/sec, excited by many down hairs and guard hairs with thresholds of 2 to 30 μ. Units responding only to stimulation of the dorsal skin surface comprised a low-threshold group, excited also by movement of ventral hairs, and a high-threshold group, also excited by stimulation of the ventral skin surface. Slowly adapting mechanoreceptive units, touch corpuscles, and type T hair follicle units were not found. The innervation of rabbit car skin thus differs considerably from that of the trunk and limbs.

Presynaptic depolarization of cutaneous mechanoreceptor afferents after mechanical skin stimulation.

1. An investigation was made into the presynaptic depolarization of the spinal cord terminals of mechanoreceptor units of the hind foot of the cat after short mechanical displacement of the skin. The depolarization was measured by testing the excitability of the primary afferent fibres. 2. The following types of mechanoreceptor units were investigated: touch receptors of the central foot pad, hair follicle receptors, and touch corpuscles of the hairy skin. They were all depolarized by mechanical stimuli to the central pad or to the hairy skin. No difference has been found between receptor units which had or did not have a collateral in the dorsal columns. 3. The amount of depolarization depended on the amplitude of the mechanical stimulus. With weak mechanical pulses there was a close relation between the amplitude of the pulse and the size of the depolarization, but there was little additional increase of the depolarization with skin indentations exceeding 10 to 15 μ. No spatial facilitation could be demonstrated when two mechanical pulses were applied simultaneously. 4. The presynaptic depolarization of cutaneous mechanoreceptor afferents has a ‘surround’ pattern of organization: with mechanical pulses of constant amplitude the depolarization was largest when the pulse was applied at or close to the receptive field of the unit and decreased with increasing distance between the middle of the receptive field and the stimulus point. It seemed unimportant whether or not the unit under study was excited by the conditioning stimulus. 5. There is a discussion of the functional significance of these findings.