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Biomedical subjects

W J Roberts

Publications and source records attributed to W J Roberts.

At least 37 records · Page 2Linked to original sources
PubMed1986

Clustering of primary afferent fibers in peripheral nerve fascicles by sensory modality.

The spatial organization of cutaneous afferent fibers in the cat saphenous nerve was studied by recording from functionally identified units in split filaments. It was found that within each fascicle, fibers tend to be clustered together with others of like modality; they are not randomly distributed. These results suggest that the sensory modality of primary afferent neurons is determined prior to their innervation of the skin.

Adaptation, Physiological↗
PubMed1985

Sympathetic activation of unmyelinated mechanoreceptors in cat skin.

In single unit recordings from the saphenous nerve in anesthetized cats, afferent units were functionally identified as unmyelinated (C) mechanoreceptors. All units responded to stimulation of the sympathetic trunk with a repetitive discharge which was maintained throughout the period of stimulation. This discharge was asynchronous with respect to efferent activity and was unaffected by brief occlusion of the arterial blood supply. The mechanism underlying the strong excitatory action of the sympathetic system on these afferents is not known although changes in blood flow and temperature can be ruled out. It is suggested that the primary function of these afferents may be to signal conditions within the skin for regulatory purposes rather than to encode external mechanical events.

Animals↗
PubMed1985

Sympathetically induced changes in the responses of slowly adapting type I receptors in cat skin.

The effects of sympathetic efferent activity on slowly adapting Type I receptors in the hairy skin of cats were studied by recording from single afferent units in the saphenous nerve. Stimulation of the sympathetic trunk at 10 Hz had predominantly excitatory effects, which were seen in some units as the development of a background discharge in the absence of overt mechanical stimulation, or in most other units as a reduction in the threshold for mechanical activation. These effects generally persisted throughout the 3-min period of sympathetic stimulation (SS). The percentage of afferent units that began to discharge during SS was significantly greater in female cats than in males (53% vs. 19%). An increase in the force exerted by the skin on the stimulus probe was also observed during SS. Several tests were conducted to assess possible neurochemical and mechanical mechanisms of action. Administration of the alpha-adrenergic blocking agent phentolamine produced a marked reduction in the sympathetic effects. However, histochemical analysis of sections from the touch domes showed no catecholamine fluorescence near the sensory fibers. Cessation of local blood flow just prior to SS, produced by occlusion of the descending aorta, had no apparent effect on the sympathetically induced changes in afferent activity. It was concluded that sympathetic activity has an excitatory action on most Type I afferents in the cat. Because this sympathetic action is neither replicated nor altered by aortic occlusion, it appears not to be mediated by changes in blood flow. It also appears not to be mediated by direct neurotransmitter action on the sensory receptor, because no catecholamine fluorescence was observed, yet the action was blocked by an alpha-adrenergic blocker. It is likely, therefore, that this sympathetic action is mediated by some unidentified mechanical response within the skin.

Adaptation, Physiological↗
PubMed1985

Sympathetic activation of A-delta nociceptors.

Primary afferent units in the saphenous nerve of cats, functionally identified as A-delta myelinated nociceptors, were tested for their responses to stimulation of the sympathetic trunk. The units were subdivided functionally into A-mechano-heat receptors (AMHs), which respond to both noxious heat and pressure, and high-threshold mechanoreceptors (HTMs), which respond only to pressure. No units of either subdivision were activated by sympathetic stimulation (SS) prior to noxious heating of their receptive fields. However, six of the seven AMH units with the highest mechanical thresholds (greater than 5 g von Frey) were activated by SS alone (10 Hz) after they had been sensitized by noxious heating of their receptive fields. Sensitized AMH units with lower mechanical thresholds (less than 5 g) were generally not activated by SS alone (1 of 22 units), and their responses to warming of their receptive fields were not altered by SS. The excitatory sympathetic action on AMH units was abolished by alpha- but not beta-andrenergic blockade in the two units tested. HTMs were unresponsive to SS even after repeated noxious heating of their receptive fields (15 units tested). The results of this study indicate that relatively high rates of sympathetic efferent activity (10 Hz) can induce firing in a small population of AMH receptors in damaged skin, specifically those units with high mechanical thresholds. This sympathetically evoked activity might trigger or exacerbate pain associated with skin damage; however, functional conclusions are difficult to draw, because of the scarcity of such units and the fact that the responses in some were brief and of low firing rates.

Animals↗
PubMed1983

Behavioral test of tolerance for aversive mechanical stimuli in sympathectomized cats.

Cats were studied behaviorally to determine their suitability as an animal model for the post-sympathectomy hyperalgesia reported to occur in humans. For this study a device and methodology were developed which allow humane testing of tolerance for intense mechanical stimulation of the hindlegs. Behavioral tolerance was measured quantitatively before and after unilateral sympathectomy. The results from this preliminary study of 6 cats are remarkably similar to those reported for humans; 1 of the 6 cats showed a decreased tolerance on the sympathectomized side which was delayed in onset and of limited duration. The new methodology appears to provide relatively stable, quantitative measures of tolerance for aversive stimulation, and the cat shows promise as an animal model for post-sympathectomy hyperalgesia.

Animals↗
PubMed1982

Histochemical evidence for sympathetic innervation of hair receptor afferents in cat skin.

The goal of the present study was to demonstrate histochemically fine catecholamine-containing sympathetic nerve fibers which might be associated with hair receptor afferent fibers in cat skin. Positive results would be consistent with the hypothesis that the sympathetically mediated desensitization of hair afferents, observed in this an earlier studies, is mediated by direct neurotransmitter release onto the afferent fibers. Activity in single primary afferent fibers was recorded electrophysiologically during mechanical stimulation of hairs and electrical stimulation of the lumbar sympathetic trunk in anesthetized cats. The mechanical threshold for activation was seen to increase markedly during low-frequency sympathetic stimulation. Fresh-frozen sections of skin from cat hindleg were treated with glyoxylic acid for detection of fluorescent catecholamines. Fluorescent fibers were observed in association with hair follicles as well as with arterioles and arrector-pili muscles. Subsequent silver staining of the identical skin sections revealed that the fine catecholamine-containing fibers located near hair follicles were closely associated with hair receptor afferent fibers. The results of hair receptor sensitivity is mediated by direct neurotransmitter release onto the afferent fibers.

Adrenergic Fibers↗
PubMed1981

Sympathetic modulation of mechanoreceptor sensitivity in frog skin.

1. Sympathetic effects on the mechanical sensitivity of frog cutaneous mechanoreceptors were examined in vivo. 2. Functionally identified units were tested with repetitive mechanical stimuli of threshold intensity during electrical stimulation of the sympathetic trunk. 3. Sympathetic activity resulted in increased sensitivity for three classes of afferents; slowly adapting compression receptors, slowly adapting stroke receptors, and rapidly adapting stroke receptors. Decreased sensitivity was produced in the fourth class, rapidly adapting compression receptors. 4. Preliminary tets of several possible modes of sympathetic influence indicated that blood flow changes, changes in probe-skin coupling and changes in tissue compliance could not account for the observed changes in receptor sensitivity. Na+ and Cl- ions, secreted by cutaneous mucous glands were found to be possible contributors to the decreased sensitivity of rapidly adapting compression receptors. Direct neurotransmitter action on the receptors, a likely mechanism of sympathetic action, was not tested. 5. The data indicate that systematic changes in cutaneous sensibility occur with modest changes in sympathetic efferent activity. Possible mechanisms of these sympathetic effects are discussed.

Action Potentials↗
PubMed1981

Sympathetically induced changes in the responses of guard hair and type II receptors in the cat.

1. Sympathetic effects on the activity of single guard hair receptors and slowly adapting, type II mechanoreceptors were studied in anaesthetized cats. 2. Spontaneous activity in type II receptors and mechanically evoked activity in both type II and guard hair receptors was recorded both without and with electrical stimulation of the lumbar sympathetic trunk. 3. Almost all guard hair receptors were desensitized by sympathetic stimulation, the mean effect being an increase in threshold to 2.2 times the unconditioned value. 4. One third of the more slowly adapting guard hair units showed sympathetically induced spontaneous activity. 5. These sympathetic effects on guard hair receptors appear not to be related to pilomotor responses or to changes in central arterial pressure. 6. Individual type II receptors were found to be excited by skin stretch along one of two axes: either parallel or perpendicular to the long axis of the leg. Intermediate orientations were not observed. 7. 'Perpendicular' units showed marked increases in resting discharge but no change in mechanical sensitivity during sympathetic stimulation. 'Parallel' units were unaffected. 8. The sympathetic effect appeared not to be related to changes in blood pressure or skin tension. 9. It is suggested that the location and orientation of stretch sensitivity of these receptors make them well suited for detection of limb movements; however, no satisfactory functional explanation was found for the pronounced sympathetic facilitation of only one subset of the receptors.

Action Potentials↗
PubMed1976

Climbing fiber responses of cerebellar Purkinje cells to passive movement of the cat forepaw.

The activity of cerebellar Purkinje cells during controlled and passive movement of the forepaw was studied in the cat. Burst responses characteristic of activation by climbing fibers were observed in Purkinje cells in lobules Vb and Vc of the cerebellar vermis and paravermis. The climbing fiber responses followed the onset of a movement with a latency ranging from 20 to 60 msec depending upon movement type and amplitude. Responsive Purkinje cells were localized in a well defined parasagittal strip very near the paravermal vein in lobules Vb and Vc. Cells within the responsive strip responded with identical response probabilities and latencies for any particular type of movement presentation. Responses were independent of starting paw position and direction of movement. Climbing fiber responses could be evoked by extremely small movements with most cells responding to displacements of 50 mum. The latencies and probabilities for climbing fiber responses were inversely related to movement amplitude with latencies as long as 80 msec for very small displacements.

Animals↗
PubMed1976

Effects from the vestibulospinal tract on transmission from primary afferents to ventral spino-cerebellar tract neurones.

Convergence of vestibulospinal and segmental effects onto spinal interneurones which project to the ventral spino-cerebellar tract (VSCT) neurones has been studied by intracellular recording in VSCT cells. The disynaptic Ia IPSPs evoked in a group of VSCT neurones from the quadriceps nerve are monosynaptically facilitated by the vestibulospinal tract while there was no facilitation of Ia IPSP evoked from a flexor nerve. These results support the view that Ia inhibition to VSCT cells and motoneurones is mediated by common interneurones. The disynaptic inhibition evoked in other VSCT cells from the vestibulospinal tract is facilitated by volleys in the contralateral flexor reflex afferents (FRA) or bilaterally from the FRA. It is postulated that these actions are mediated by collaterals of the interneurones responsible for the analogous effects in motoneurones. Findings are reported suggesting that the monosynaptic vestibulospinal EPSP in VSCT cells in most cases is collateral to the excitatory input to the last order interneurones of reflex pathways from the FRA to motoneurones and only exceptionally to the corresponding input to Ia inhibitory interneurones. In many VSCT cells the vestibulospinal tract evoked disynaptic EPSPs which are facilitated from the FRA; the functional significance of this action is uncertain. The results are consistent with the hypothesis that VSCT neurones signal information on interneuronal transmission to motoneurones.

Afferent Pathways↗
PubMed1976

Transfer characteristics between EMG activity and muscle tension under isometric conditions in man.

The relationship between motor unit activity and a voluntarily produced, sinusoidally modulated isometric tension was evaluated as a function of the modulation frequency. These date are reported in terms of the gain and phase difference of the motor activity (input) and tension (output) relationship, the gain being the logarithmic ratio of the amplitudes of the output and input sinusoids. It was found that an increase in the modulation amplitude of the motor unit activity was required to produce the same amount of modulation of the output tension as the modulation frequency was increased. For example, the modulation amplitude of the activity is about twice as much at 2 Hz as at 0.25 Hz and about 4 times as much at 5 Hz. It was also found that the maximum tension which could be produced voluntarily during brief jerks at 5 Hz was the same as the maximum sustained tension which could be attained. This latter finding emphasizes the importance of recruitment and especially synchronization of motor unit activity to the gradation of output tension.

Action Potentials↗
PubMed1975

Effects on the ventral spinocerebellar tract neurones from Deiters' nucleus and the medial longitudinal fascicle in the cat.

Effects from the vestibulospinal tract (VST) and from fibres descending in the medial longitudinal fascicle (MLF) on the cells of origin of the ventral spinocerebellar tract (VSCT) have been studied with intracellular recording. Out of 110 VSCT neurones, the VST evoked monosynaptic EPSPs in 27, di- or polysynaptic EPSPs in 56 and disynaptic IPSPs in 26. In 93 tested VSCT cells, MLF stimulation evoked monosynaptic EPSPs in 26, monosynaptic IPSPs in 2, di- or polysynaptic EPSPs in 25 and disynaptic IPSPs in 21. Convergence of monosynaptic EPSPs from VST and MLF was found in a small proportion of cells whereas the two descending pathways evoked reciprocal effects in another small group of neurones. Convergence of monosynaptic EPSPs from VST or MLF and from group I afferents was also modest. In 9 VSCT neurones there was convergence of monosynaptic excitation and disynaptic inhibition from the vestibulospinal tract and the same pattern from MLF was recorded in 9 neurones. The results are discussed in view of the hypothesis that VSCT neurones carry information on the interneuronal ttransmission in the spinal cord.

Action Potentials↗
PubMed1972

An electrophysiological demonstration of the axonal projections of single spinal interneurones in the cat.

1. Single interneurones excited from group Ia afferents and located in the ventral horn of the spinal cord in the cat were activated antidromically by stimulation of their axons with one micro-electrode while recording extracellularly close to their somas with a second micro-electrode. The interneurones studied were those which, according to previous indirect evidence, should mediate the reciprocal Ia inhibition of motoneurones.2. Two subgroups of these interneurones were studied: those excited from group Ia afferents in the quadriceps (Q) and posterior bicepssemitendinosus (PBSt) nerves. Most of them could be activated from a number of separate loci in the PBSt and Q motor nuclei respectively and from the ventral or lateral funiculi.3. The location of the axonal branches and the extent of their branching in the motor nuclei were reconstructed by comparing the latencies of the responses and the thresholds (0.1-5 muA) for antidromic activation of single interneurones from different electrode positions in a number of tracks, having previously established the relation between the threshold and the distance from the stimulated fibres. For the main branches in the white matter the conduction velocity was found to be about 70 m/sec.4. The axonal projections of the investigated interneurones were found to be fully consistent with the hypothesis that they mediate reciprocal inhibition of motoneurones.

Action Potentials↗
PubMed1972

Synaptic actions of single interneurones mediating reciprocal Ia inhibition of motoneurones.

1. The investigation was aimed at defining the function of the interneurones which, according to indirect evidence, mediate the reciprocal Ia inhibition of motoneurones (Hultborn, Jankowska & Lindstrom, 1971 b) by studying their direct synaptic actions. These actions were tested by recording post-synaptic potentials in motoneurones following spike activity of single interneurones activated by iontophoretic application of glutamate. The interneurones were found to produce unitary monosynaptic IPSPs in those motoneurones in which disynaptic IPSPs are evoked by the group Ia afferents which monosynaptically excite the interneurones.2. Unitary IPSPs were found in more than 80% of the motoneurones impaled in the immediate vicinity of the axonal branches of the investigated Q interneurones in the PBSt motor nucleus. It is estimated that each interneurone might inhibit about every fifth PBSt motoneurone. The amplitudes of the unitary IPSPs ranged between 8 and 220 muV and were 10-200 times smaller than the maximal Ia IPSPs evoked in the same motoneurones.3. The synaptic delay in the generation of unitary IPSPs was measured in relation to the spike potentials recorded from the terminal branches of interneurones in the immediate vicinity of the impaled motoneurones. The synaptic delays ranged between 0.28 and 0.42 msec.4. From chloride reversal tests and an analysis of the time course of the unitary IPSPs it was concluded that the terminals of the investigated interneurones make synaptic contact predominantly on the soma and/or on the proximal parts of the dendrites of the motoneurones, their distribution being, however, not quite uniform.

Action Potentials↗