Biomedical subjects

J Schouenborg

Publications and source records attributed to J Schouenborg.

33 records · Page 2Linked to original sources

PubMed1994

Sensorimotor transformation in a spinal motor system.

To use sensory information from the skin to guide motor behaviour the central nervous system must transform sensory coordinates into movement coordinates. As yet, the basic principles of this crucial neural computation are unclear. One motor system suitable as a model for the study of such transformations is the spinal withdrawal reflex system. The spatial organization of the cutaneous input to these reflexes has been characterized, and we now introduce a novel method of motion analysis permitting a quantitative analysis of the spatial input-output relationship in this motor system. For each muscle studied, a "mirror-image" relationship was found between the spatial distribution of reflex gain for cutaneous input and the pattern of cutaneous unloading ensuing on contraction. Thus, there is an "imprint" of the movement pattern on this motor system permitting effective sensorimotor transformation. This imprint may indicate the presence of a learning process which utilizes the sensory feedback ensuing on muscle contraction.

Animals↗

PubMed1993

Nociceptive C fibre input to the primary somatosensory cortex (SI). A field potential study in the rat.

In the present study, noxious thermal stimulation of the skin with short pulses of CO2-laser radiation was used to identify a cutaneous nociceptive C fibre input to SI and investigate the organization of this input in halothane-nitrous oxide anaesthetized rats. Noxious CO2-laser stimulation of the glabrous skin of the hindpaw consistently evoked late surface positive field potentials in SI (average onset latency 226 ms, peak latency 296 ms). It was demonstrated that these late potentials were evoked by an input from nociceptive C fibres, using a combination of latency measurements, anodal block of A fibre conduction and graded intensities of stimulation. Compared to the tactile evoked potentials in SI, the nociceptive C fibre evoked potentials were more widespread and exhibited a crude somatotopical organization. Intracortically, both tactile and nociceptive C fibre evoked potentials reversed polarity and exhibited a peak negativity in laminae III-IV. The nociceptive C fibre evoked potentials exhibited an additional peak negativity in laminae V-VI. The latter potential had a different time course as compared to the nociceptive C fibre potential evoked in laminae III-IV. In conclusion, an input from cutaneous nociceptive C fibres to SI was demonstrated for the first time in animal experiments. The input to SI from tactile receptors and cutaneous C nociceptors were differently organized.

Animals↗

PubMed1993

Multiple spinal pathways mediate cutaneous nociceptive C fibre input to the primary somatosensory cortex (SI) in the rat.

In the present study, partial lesions of the lower thoracic spinal cord in rats anaesthetized with halothane and nitrous oxide were made in order to elucidate which of the spinal funiculi mediate a nociceptive C fibre input to SI. Field potentials evoked by noxious CO2-laser stimulation were recorded in the left SI. Nociceptive C fibre input from the right hindpaw to SI was propagated by the dorsal funiculi (DF) and the left and right lateral funiculi (LLF and RLF, respectively). Nociceptive C fibre input from the left hindpaw was propagated by LLF and RLF, but not DF. Input from the hindpaws mediated by LLF and RLF caused widespread surface positive potentials throughout most of SI, although potentials in the hindlimb area tended to be larger than those in other areas of SI. Input from the right hindpaw mediated by DF caused surface positive potentials mainly in the hindlimb area of SI. Intracortically, the field potentials reversed polarity in the superficial laminae and had maximal negative amplitudes in laminae III-IV (input transferred by DF and LLF) and in laminae V-VI (input transferred by LLF and RLF). It is concluded that there are multiple spinal pathways which can transfer information from cutaneous nociceptive C fibres to SI in the rat. These ascending pathways seem to activate partly different thalamo-cortical systems.

Animals↗

PubMed1992

Functional organization of the nociceptive withdrawal reflexes. II. Changes of excitability and receptive fields after spinalization in the rat.

The spatial organization of the cutaneous input to hindlimb withdrawal reflexes was studied in spinalized, decerebrated, unanesthetized rats. Reflex activity in plantar flexors of the digits, pronators of the foot, dorsiflexors of the digits, and/or the ankle and flexors of the knee was recorded with electromyographic techniques for up to 12 h after spinalization. Graded mechanical (pinch) and thermal stimulation (CO2 laser) of the skin were used. Reflexes were absent ("spinal shock") during approximately 10-20 min after spinalization. The reflex thresholds for pinch and CO2 laser stimulation then decreased considerably during the following 5-8 h. After this time, even mild pressure (less than 0.1 N/mm2) on the skin was sufficient to evoke a reflex in most muscles. During the period from about 0.5-3 h after spinalization, the nociceptive receptive field of each muscle usually corresponded to the area of the skin withdrawn by the muscle. Maximal responses were evoked from the area of the receptive field maximally withdrawn. During this period, responses to innocuous pinch were evoked mainly from the most sensitive area of the receptive fields. Concomitant with the decrease in reflex thresholds, the nociceptive receptive fields expanded for all muscles, often to include areas of the skin not withdrawn by the muscles. For most muscles, reflexes on tactile stimuli were eventually elicited from the entire receptive fields. The receptive fields for thermonociceptive and mechanonociceptive inputs were similar in most muscles. The interossei muscles were exceptional in that they responded very weakly to thermal stimulation. It is concluded that there are neuronal networks in the spinal cord that translate cutaneous nociceptive and tactile input into a withdrawal. However, the control exerted by descending pathways is necessary to maintain a functionally adequate excitability in these reflex pathways and an appropriate size for their receptive fields.

Animals↗

PubMed1991

Topography and nociceptive receptive fields of climbing fibres projecting to the cerebellar anterior lobe in the cat.

1. The cutaneous receptive fields of 225 climbing fibres projecting to the forelimb area of the C3 zone in the cerebellar anterior lobe were mapped in the pentobarbitone-anaesthetized cat. Responses in climbing fibres were recorded as complex spikes in Purkinje cells. 2. A detailed topographical organization of the nociceptive climbing fibre input to the C3 zone was found. In the medial C3 zone climbing fibres with receptive fields covering proximal and/or lateral parts of the forelimb projected most medially. Climbing fibres with receptive fields located more medially on the forelimb projected successively more laterally. The sequence of receptive fields found in the lateral C3 zone was roughly the reverse of that in the medial C3 zone. Climbing fibres with receptive fields restricted to the digits projected preferentially to the caudal part of the forelimb area, whereas those with receptive fields covering both proximal and ventral areas of the forearm projected to more rostral parts. 3. The representation of the forelimb was uneven. Receptive fields with a focus on the digits or along the lateral side of the forearm dominated. 4. The proximal borders of the receptive fields were located close to joints. The area from which maximal responses were evoked was usually located eccentrically within the receptive field. Based on spatial characteristics the receptive fields could be divided into eight classes, which in turn were tentatively divided into subclasses. Similar subclasses of receptive fields were found in different cats. This classification was further supported by the results of a quantitative analysis of eighty-nine climbing fibres. The receptive fields of these climbing fibres were mapped with standardized noxious stimulation. 5. Climbing fibres terminating within sagittal strips (width, 100-300 microns; length, greater than 1 mm) had receptive fields which belonged to the same subclass. There were commonly abrupt changes in receptive fields between such microzones. Most classes of receptive fields were found in both the medial and the lateral parts of the C3 zone. However, receptive fields with a focus on the ventral side of either the metacarpals, the wrist or the forearm were found only in the medial part of the C3 zone. Furthermore, the class of receptive fields restricted to the lateral side of the upper arm and shoulder was only found in the lateral part of the C3 zone. 6. In the discussion, it is proposed that climbing fibres projecting to each microzone carry information from spinal multireceptive reflex arcs acting on a single muscle or a group of synergistic muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

The postsynaptic dorsal column pathway mediates cutaneous nociceptive information to cerebellar climbing fibres in the cat.

1. The location in the spinal cord of the pathway mediating cutaneous nociceptive C fibre input to climbing fibres projecting to the forelimb area of the C3 zone in the cerebellar anterior lobe was investigated in pentobarbitone-anaesthetized cats. Lesions of the spinal cord at the segmental level of C3 sparing the dorsal funiculi (DF preparation) or lesions of the ipsilateral and part of the contralateral dorsal funiculi were made. 2. In the DF preparation, the cutaneous input to climbing fibres projecting to the C3 zone was the same as in cats with an intact spinal cord. Also, the topography of tactile and nociceptive receptive fields and the distribution of A- and C fibre-evoked climbing fibre field potentials was similar to that in cats with an intact spinal cord. 3. In cats with an initially intact spinal cord the cutaneous nociceptive C fibre input and the topographically well organized tactile input to the C3 climbing fibres disappeared following a lesion of the ipsilateral and part of the contralateral dorsal funiculi. Following this lesion the receptive fields of the climbing fibres became indistinct and only irregular responses were evoked on skin stimulation. 4. It is concluded that the cutaneous nociceptive C fibre input from the forelimb to climbing fibres projecting to the C3 zone is mediated by the ipsilateral dorsal funiculus. Since cutaneous C fibres terminate exclusively in the spinal cord close to their entrance zone the postsynaptic dorsal column pathway must be part of this spino-olivocerebellar pathway.

Animals↗

PubMed1990

Functional organization of the nociceptive withdrawal reflexes. I. Activation of hindlimb muscles in the rat.

1. The organization of the nociceptive hindlimb withdrawal reflexes was investigated in 93 halothane/nitrous oxide anesthetized rats. Electromyographical techniques were used to record reflex activity in single motor units. 2. Most of the hindlimb muscles were activated by noxious mechanical stimulation of the skin of the ipsilateral hindlimb. These were the plantar flexors of the digits, the pronators of the paw, the dorsiflexors and the plantar flexors of the ankle, the flexors of the knee, the flexors of the hip and the adductors. By grading the stimulus intensity it was shown that all these muscles received input from cutaneous nociceptors. 3. Noxious stimulation of the skin failed to activate the obturator, knee extensors and m. tibialis posterior and, in most rats tested, m. semimembranosus and m. adductor magnus. The plantar flexors of the ankle, while exhibiting a clear nocireceptive field in all rats tested, had a high threshold and responded much more weakly than the dorsiflexors of the ankle. Thus, responses in muscles which oppose gravity in the standing position were either very weak or absent. 4. The present study shows that each of the activated hindlimb muscles has a highly organized nocireceptive field on the skin, which is related to the withdrawal movement caused by the muscle itself. Each of the muscles normally causes the withdrawal of its receptive field when the foot is on the ground. The skin area most effectively withdrawn, in this situation, corresponds to the most sensitive area of the nocireceptive field. However, with the exception of the plantar flexors of the digits and/or the ankle, each of the hindlimb muscles also withdraws the major parts of their receptive fields when the foot is off the ground. The locations of the nocireceptive fields were independent of the position of the hindlimb. These characteristics of the nociceptive withdrawal reflexes are the basis for their "local sign" (Sherrington 1906). 5. The threshold and the time course of reflex activation were different in different muscles. However, muscles with a similar action; the plantar flexors of the digits, the pronators of the paw, the dorsiflexors of the digits, the flexors of the knee and the adductors, respectively, had similar thresholds and time courses. Furthermore, the threshold and latency of activation of each muscle increased towards the border of its nocireceptive field, reflecting a decreasing sensitivity. These findings explain the progressive recruitment of muscles during increasing strength of noxious stimulation, termed "irradiation" (Sherrington 1906).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Long-lasting neuronal activity in rat dorsal horn evoked by impulses in cutaneous C fibres during noxious mechanical stimulation.

The responses of 44 nociceptive neurones in the lumbar dorsal horn evoked by controlled mechanical stimulation of the skin, with or without conduction block in myelinated afferent fibres, were studied in the halothane-anaesthetized rat, in order to evaluate the effects of impulses in cutaneous nociceptive C fibres on dorsal horn neurones. Continuous non-noxious pinch of the skin evoked a short-latency discharge (mean latency 15 ms) in all the 13 class 2 neurones (i.e. neurones responding to both non-noxious and noxious stimulation of the skin) tested. The short-latency discharge was followed by weak prolonged activity in 6 neurones. Following noxious pinch of the skin a prominent late discharge (peak latency 150 ms-2 s) was evoked, which in all but two class 2 neurones outlasted the stimulation period (5-10 s). The discharge evoked by noxious pinch in class 3 neurones (i.e. neurones responding to noxious stimulation only) did not usually outlast the stimulation period. In all but two nociceptive neurones tested (n = 26) the late activity evoked by noxious pinch remained, albeit at a lower frequency in some neurones, during a conduction block in A fibres2,3. Hence this late discharge is probably mainly generated by impulses in nociceptive C fibers. It is concluded that nociceptive C fibres have an important role in sustaining long-lasting activation of class 2 neurones during noxious stimulation of the skin and that long-lasting discharges in these neurones indicates tissue damage to their receptive fields.

Afferent Pathways↗

PubMed1987

Climbing fibres projecting to cat cerebellar anterior lobe activated by cutaneous A and C fibres.

1. Climbing fibre responses evoked on stimulation of the ipsilateral superficial radial nerve were examined in the forelimb area of the C3 zone in the barbiturate-anaesthetized cat. Climbing fibre responses were recorded in sixty-five Purkinje cells and as field potentials from the surface of the cerebellum. 2. In addition to the previously described A beta-fibre-evoked climbing fibre response, late climbing fibre responses were consistently evoked in all Purkinje cells studied when C fibres were stimulated. The latencies of the A beta- and C-fibre-evoked climbing fibre responses were 11-20 ms and 110-220 ms, respectively. In most experiments climbing fibre responses with an intermediate latency (20-30 ms) were evoked. It was demonstrated that this response depended on A delta fibres. 3. The long-latency climbing fibre response generated by electrical stimulation at C-fibre strength was evoked also during selective anodal block of conduction in A fibres (Brown & Hamman, 1972). Hence, impulses in C fibres were sufficient for generation of climbing fibre responses. 4. The distribution within the forelimb area of the C3 zone of the A beta- and C-fibre-evoked climbing fibre field potential was similar. No climbing fibre response was evoked in this area of the C3 zone by stimulation of A and C fibres in the contralateral superficial radial nerve or in the plantar nerves of the hind limbs. 5. It can be concluded that climbing fibres projecting to the forelimb area of the C3 zone in the cerebellum receive a somatotopically organized input from both A beta and C fibres.

Action Potentials↗

PubMed1987

Stimulation of cat cutaneous nociceptive C fibres causing tonic and synchronous activity in climbing fibres.

1. The input from cutaneous nociceptors to climbing fibres projecting to the forelimb area of the C3 zone in the cerebellar anterior lobe was examined in barbiturate-anaesthetized cats. Climbing fibre responses were simultaneously recorded in single Purkinje cells and as field potentials from the cerebellar surface close to these cells. 2. The cutaneous receptive field of the climbing fibres studied were located on the ipsilateral forelimb. All climbing fibres were activated by both non-noxious tactile stimulation and noxious pinch of the skin. The location of the receptive field and the distribution of sensitivity in the receptive field appeared to be identical for noxious and tactile stimuli. 3. A phasic response in the climbing fibres was evoked by either short- or long-lasting non-noxious pressure applied to their cutaneous receptive field. By contrast, all climbing fibres studied were strongly and tonically activated (up to 4-11 Hz for the duration of the stimulation) by sustained noxious pinch in the most sensitive area of their receptive fields. 4. Experiments with anodal block of impulse conduction in myelinated fibres indicated that a major input to climbing fibres during sustained noxious pinch originates from nociceptive C fibres. 5. Sustained noxious pinch of the skin evoked large field potentials on the cerebellar surface. These field potentials were evoked simultaneously with climbing fibre responses in single Purkinje cells and were due to synchronous activation of many climbing fibres. These field potentials and discharges in single climbing fibres were elicited from the same area of the skin suggesting that many of the synchronously discharging climbing fibres have the same receptive field on the skin.

Action Potentials↗

PubMed1986

Field potentials evoked in rat primary somatosensory cortex (SI) by impulses in cutaneous A beta- and C-fibres.

A projection of cutaneous C-afferent fibres to the contralateral primary somatosensory cortex (SI) was examined in the halothane-anaesthetized rat. Field potentials evoked by electrical stimulation of the right sural nerve were recorded at the surface of an intracortically within the left SI cortex. A late surface positive potential (latency 110-190 ms, mean 136 ms) was evoked by sural stimulation at a strength that activated A- and C-fibres. A selective anodal block of impulse conduction in A-fibres proximal to the stimulating electrodes showed that impulses in C-fibres generate the late potential also in the absence of a preceding A-fibre input. Stimulation of the sural nerve at two sites caused a shift in latency of the late potential corresponding to a conduction velocity of the primary afferent fibres of less than 1.0 m/s. The distribution of the C-fibre-evoked potential in SI was similar to that of the A beta-fibre evoked 'primary' potential suggesting that the investigated projection of cutaneous C-fibres to SI has a somatotopic organization.

Action Potentials↗

PubMed1986

First-order nociceptive synapses in rat dorsal horn are blocked by an amino acid antagonist.

An antagonist to amino acid evoked excitation, gamma-D-glutamylglycine (gamma-DGG) inhibits, dose-dependently, nociceptive C-fibre evoked field potentials and neuronal discharges in single nociceptive neurons in rat spinal cord. It is concluded that amino acids are possible transmitter substance(s) in nociceptive afferent C-fibres. These results might be useful for development of centrally acting analgesic drugs.

Amino Acids↗

PubMed1985

Effects of a distant noxious stimulation on A and C fibre-evoked flexion reflexes and neuronal activity in the dorsal horn of the rat.

In the halothane-anaesthetized rat, the responses of 49 neurons in the lumbo-sacral cord and the reflex discharge in the common peroneal nerve following electrical stimulation of the sural nerve were recorded in order to study possible relations between neuronal events and reflex nerve discharges. A distant noxious stimulus (to activate Diffuse Noxious Inhibitory Controls (DNIC) of Le Bars et al.) was used as a conditioning stimulus. Only the responses of neurons receiving an input from both A and C fibres were studied. The neurons were classified as class 1 (low threshold mechanoreceptive input only, n = 2), class 2 (nonnoxious and noxious inputs, n = 34) or class 3 (responding to noxious stimuli only, n = 13). During conditioning stimulation the C fibre evoked discharge was inhibited in 32 out of 34 class 2 neurons. The A fibre-evoked discharge was simultaneously inhibited in 29 of these neurons. The main effect of the distant noxious stimulation on the C fibre evoked neuronal discharge was to decrease the discharge by a constant number of spikes, independent of the level of evoked activity. Only one class 3 neuron was inhibited during conditioning stimulation and none of the class 1 cells were influenced by DNIC. During conditioning stimulation the late and prolonged C fibre evoked reflex nerve discharge (latency 160-200 ms, duration up to several hundred ms) was strongly depressed. Concomitantly, a short-lasting reflex nerve discharge appeared over the interval 115-160 ms. This released reflex nerve discharge (RR) had a constant latency. There was no simultaneous change of the A beta evoked reflex nerve discharge. After the end of the distant noxious stimulation the late C fibre evoked reflex nerve discharge (latency 160-200 ms) recovered. Concomitantly, the RR disappeared. The possibility that the class 2 neurons and the class 3 neurons are intercalated in different reflex pathways is discussed.

Animals↗

PubMed1984

Functional and topographical properties of field potentials evoked in rat dorsal horn by cutaneous C-fibre stimulation.

Extracellular field potentials in the lumbosacral dorsal horn evoked by stimulation of cutaneous C fibres in the sural nerve were explored in the halothane-anaesthetized rat. C-fibre-evoked field potentials were prominent in lamina II and lamina V of the dorsal horn. These potentials had a latency of 80-130 ms and a duration of more than 200 ms. A peak in the C-fibre-evoked field potential, termed the CI potential, with a median latency of 120 ms, range 105-150 ms, was distinguished in lamina II. The time from onset to peak of the CI potential was, on average, 13 ms when all C fibres were activated. The amplitude of the CI potential in lamina II was directly proportional to the amplitude of the C-fibre-evoked nerve volley, whereas the relation between the C-fibre nerve volley and the C-fibre-evoked field potential in lamina V was non-linear. A selective block of A fibres did not influence the amplitude of these field potentials. Following stimulation of C afferent fibres in the medial sural nerve, at frequencies higher than 0.1 Hz, the CI potential in lamina II, but not the C-fibre-evoked field potential in lamina V, was increased. There was no concomitant change of the A-fibre-evoked field potentials. The magnitude of the potentiation of the CI potential was dependent both on the frequency and the number of stimuli. Mean percentage potentiation was 200%, range 150-300%, after seventy stimulations at a frequency of 1.0 Hz. During the stimulation the CI potential increased monotonically. The decay of the potentiation of the CI potential was well described by two exponentially declining phases. There was a positive correlation between the size of the time constants of the decay and the number of stimuli during conditioning. Following noxious radiant heat (temperature 50-55 degrees C) applied to a restricted part of the skin (area 20-30 mm2) within the receptive field of the medial sural nerve for 10-20 s, the CI potential was potentiated by 50-130%. The duration of this potentiation was 3-15 min. This potentiation was somatotopically organized. By contrast, there was no effect on the amplitude of the CI potential following innocuous skin stimulation (slowly moving contact, brushing the skin, warmth 40 degrees C).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1983

Activity evoked by A- and C-afferent fibers in rat dorsal horn neurons and its relation to a flexion reflex.

The responses of 56 neurons recorded in the lumbosacral spinal cord of halothane-anesthetized rats were studied following the application of mechanical stimuli to the skin on the lateral aspect of the paw or electrical stimulation of the sural nerve. Only neurons driven by A- and C-fiber stimulation were considered. The evoked activity in a nerve supplying flexor muscles, the common peroneal nerve, was also recorded to evaluate possible relations between neuronal events and reflex discharges. To quantify the reflex output we also recorded the activity of 12 motoneurons. Four different populations of dorsal horn neurons activated by C-fibers could be distinguished. The neurons were classified on the basis of their responses to mechanical stimuli and of their location in the dorsal horn. Class 1 neurons were driven by nonnoxious stimulation only. Neurons driven by nonnoxious stimuli and noxious stimuli were denoted class 2S (superficial to the location of the maximal A-beta-fiber-evoked field potentials) or class 2D (deep to the same potential). Class 3 neurons were driven by noxious stimuli only. The functional characteristics of these four classes of neurons differed in many respects. The latency for the A-beta-fiber-evoked discharge was, on average, 2 ms longer in class 2S than in class 2D neurons, indicating a polysynaptic A-beta input to the former class of neurons. The C-fiber-evoked neuronal discharge often showed time-locked peaks of activity during the interval 120-170 ms. Such peaks of activity occurred, in general, later in class 2D neurons (mean, 157 ms) than in class 2S (mean, 137 ms) or in class 3 (mean, 140 ms), suggesting that the different classes received C-fiber input via partially different routes. The responses to repeated C-fiber stimulation also differed markedly among the four classes. After 16 single electrical stimulations (100 T (T = threshold strength for activating A-beta-afferents), 1 Hz), the C-fiber-evoked discharge in class 2D neurons was increased by 196%, whereas the corresponding value for those in classes 2S, 3, and 1 was 41, 24, and 38%, respectively. Ten of 14 class 2D neurons showed a simultaneous increase of the A-fiber-evoked discharge, indicating an increased excitability of these neurons after repeated impulses in C-fiber afferents. An early reflex discharge (latency, 6-10 ms) was evoked in the common peroneal nerve by electrical stimulation of the sural nerve.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗