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Biomedical subjects

S J Lisney

Publications and source records attributed to S J Lisney.

35 records · Page 2Linked to original sources
PubMed1987

Functional aspects of the regeneration of unmyelinated axons in the rat saphenous nerve.

Electrophysiological experiments have been carried out to investigate aspects of unmyelinated axon regeneration in a transected cutaneous nerve. Some comparisons with regeneration of myelinated axons in the same nerve have also been made. By 3 months after injury approximately 80% of the unmyelinated axons that had survived in the proximal stump had regenerated into the distal stump. About the same proportion of myelinated axons had regrown into the distal stump by this time. With both groups of axons there was no marked increase in the amount of regeneration across the injury site with longer recovery times. Conduction velocities in the regenerated unmyelinated axons tended to be slower across the injury site than proximally; the proximal conduction velocities did not differ from those in control nerves. The unmyelinated axons seemed to take longer to resupply the skin than did the myelinated ones, but in both cases the extent of skin innervation had reached about 60% control values by 6 months after the injury.

Animals↗
PubMed1984

The organization of saphenous nerve fibers in the dorsal roots of the rabbit and cat.

Electrophysiological experiments have been carried out on rabbits and cats to find out whether there is a relationship between the dorsal rootlet by which a particular saphenous nerve fiber passes to the spinal cord and the part of the saphenous nerve territory it supplies. Preliminary experiments were carried out to determine the extent of the saphenous nerve field in both animals and to determine the dorsal rootlets by which saphenous nerve fibers reach the cord in rabbits. Then, in experiments on rabbits and cats in which recordings were made from fiber bundles dissected from dorsal rootlets, it was found that saphenous nerve fibers in any one dorsal rootlet supplied only a limited portion of the saphenous nerve field; that there was overlap in the areas of the saphenous nerve field supplied by adjacent rootlets; and that moving caudo-rostrally through the rootlets containing saphenous fibers, the areas of skin supplied gradually moved from distal parts of the field to proximal ones. The results show that the saphenous nerve input to the spinal cord is somatotopically organized.

Animals↗
PubMed1983

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.

Animals↗
PubMed1983

Thresholds to electrical stimulation of nerves in cat canine tooth-pulp with A beta-, A delta- and C-fibre conduction velocities.

The thresholds to electrical stimulation and the conduction velocities of nerve fibres supplying the pulp of cat canine teeth have been determined. Compound action potentials and the responses of 80 single units were recorded from the inferior alveolar nerve. The properties of 4 types of coronal stimulating electrode were compared. In the single unit studies separate estimates of intradental and extradental conduction velocity of the fibres were obtained by stimulating the pulp in the crown and in the root of the tooth. The units had extradental conduction velocities ranging from 57.7 to 0.9 m . s-1 and therefore included A beta-, A delta- and C-fibres. The thresholds of the units to coronal stimulation ranged from 7 microA, 0.1 ms to 805 microA, 1.0 ms.

Afferent Pathways↗
PubMed1983

Changes in the somatotopic organization of the cat lumbar spinal cord following peripheral nerve transection and regeneration.

Glass microelectrodes were used to record the activity of neurones in the left dorsal horn of the L6 segment of the spinal cord of normal cats and cats in which the left sciatic and saphenous nerves had been cut 1 or 9 months previously. In the normal animals the receptive fields of L6 dorsal horn neurons excited by tactile stimulation of the leg were somatotopically organized, with neurones in the medial and central dorsal horn having receptive fields on the distal parts of the leg, particularly the toes, and neurones in the lateral dorsal horn having receptive fields on the proximal parts of the leg, buttock and lower back. This somatotopy has been shown before. One month after nerve section no cells responded to tactile stimulation of the distal leg and cells in the medial and central parts of the dorsal horn now had receptive fields on the proximal leg, buttock and back. There did not appear to be any somatotopic organization of these new receptive fields. Lateral dorsal horn neurones had normal receptive fields. Nine months after nerve section neurones in the medial and central parts of the lumbar dorsal horn had receptive fields on the distal leg but they showed several abnormal features and there was no evidence of a return of the somatotopic organization seen in normal animals. Lateral dorsal horn cells still had normal receptive fields.

Animals↗
PubMed1983

Coupling between fibres involved in sensory nerve neuromata in cats.

Electrophysiological evidence has been obtained for coupling between pairs of fibres involved in 2 types of neuroma of a cutaneous sensory nerve in cats. A pair of fibres was taken to be coupled when an antidromic impulse in 1 fibre evoked an orthodromic impulse in the other. The fibres involved tended to be small diameter myelinated fibres and unmyelinated fibres. The coupling between a pair of fibres was stable over periods of several hours. Some of the coupled fibres had regenerated back to the skin and formed a functional sensory ending. These coupled responses can be explained by there being ephaptic interaction between fibres within the neuroma or they may be due to activity in retrograde sprouts of regenerating nerve fibres. Ephaptic interactions between fibres in a neuroma may be part of the explanation for abnormal sensibility, particularly pain sensibility, after peripheral nerve injury.

Animals↗
PubMed1981

Coupling between chorda tympani nerve fibres in the cat.

Evidence for coupling between a small proportion of chorda tympani nerve fibres has been obtained in cats. Single chorda tympani fibres from which a response was recorded following electrical stimulation of another chorda tympani fibre were taken as being coupled to that fibre. The coupled fibres were associated with between 1 and 4 fungiform papillae on the tongue and they showed responses to gustatory, mechanical and electrical stimulation of those papillae.

Afferent Pathways↗
PubMed1981

On the number and nature of regenerating myelinated axons after lesions of cutaneous nerves in the cat.

1. Electrophysiological and anatomical techniques were used to investigate normal and regenerating sural and posterior femoral cutaneous nerve fibres in the cat. 2. One and a half years after transection of these nerves it was found that the regenerating neurones supported multiple sprouts in the distal stump of the nerve. The branching occurred at or beyond the level of the neuroma and some of the branched fibres innervated split receptive fields on the skin. 3. Counts of the number of axons in the proximal stumps of transected nerves showed that the whole original population of myelinated fibres persisted for at least 18 months. About 75% of these fibres successfully crossed the unrepaired transection site and regenerated into the distal stump of the nerve to re-form functional connexions in the skin. 4. After nerve crush all the myelinated axons regenerated. None showed signs of abnormal branching. 5. After crush the conduction velocities of the regenerated axons in the distal stump of the nerve reached nearly normal values by 6 months. After nerve transection the distal conduction velocities were reduced to 50% of normal even 18 months after the injury. 6. The implications of these findings for the recovery of function after nerve injury in man are discussed.

Action Potentials↗
PubMed1981

Changes in primary afferent depolarization of sensory neurones during peripheral nerve regeneration in the cat.

1. Micro-electrode recordings were made from normal and regenerating sural nerve fibres in cats. Increases in the excitability of the central terminals of these fibres after conditioning stimulation of other sural nerve fibres were taken as evidence for primary afferent depolarization. 2. At all recovery times studied the excitability changes seen were significantly less than those seen in control animals. Two factors contributed to the changes in primary afferent depolarization. First, the proportion of fibres that showed no evidence of primary afferent depolarization increased significantly. This proportion became smaller as recovery progressed. Secondly, where primary afferent depolarization was present, the magnitudes of the effects were slightly but significantly decreased compared with control values. 3. Excitability changes of the central terminals of sural nerve fibres were also measured after conditioning stimulation of the ipsilateral, unlesioned accessory sural nerve. One month after sural nerve transection there was a significant increase in the proportion of fibres showing no evidence of excitability changes following accessory sural nerve conditioning stimulation compared with control animals. Thus, the loss of primary afferent depolarization of regenerating sural nerve fibres was neither simply a consequence of desynchronization of the volley of impulses entering the spinal cord after conditioning stimulation of other regenerating sural fibres, nor due to fewer fibres being activated during conditioning stimulation of the lesioned nerves. 4. A possible explanation of these results is that after peripheral nerve crush or transection the central terminals of the damaged fibres retract or atrophy. Then as regeneration of the nerve proceeds, the central terminals of the fibres re-form.

Action Potentials↗
PubMed1979

Evidence for primary afferent depolarization of single tooth-pulp afferents in the cat.

1. Responses of single tooth-pulp afferents to electrical stimulation of sites in the trigeminal sensory nuclear complex were recorded from caine teeth in cats. 2. Changes in the excitability of the central terminals of a pulpal afferent after stimulation of other groups of sensory nerves were taken as evidence for changes in their polarization. 3. Electrical stimulation of nerves in other teeth resulted in raised excitability of the central terminals of pulpal afferents lasting up to 300 msec. The greatest effects were observed 30--100 msec after the conditioning stimulus. 4. Increased terminal excitability was also observed after the ipsilateral infraorbital nerve was stimulated. This occurred when only nerve fibres with conduction velocities in the A alpha range were excited. 5. Mechanical stimulation of a canine tooth produced increases in terminal excitability of pulpal afferents innervating the same tooth. 6. A similar effect was also observed after a brief pull on a group of ipsilateral mystacial vibrissae. 7. No evidence of decreases in the excitability of the central terminals of tooth-pulp afferents was obtained with any of the conditioning stimuli.

Action Potentials↗
PubMed1978

Do primary afferents from tooth-pulp cross the midline?

Compound action potentials were recorded from the pulps of canine teeth in cats during stimulation of the inferior dental nerve, trigeminal ganglion or brain stem on one side. Recordings were also made from the inferior dental nerve while stimulating the canine pulps. No evidence for pulpal fibres crossing the midline was found.

Afferent Pathways↗
PubMed1978

Branched afferent nerves supplying tooth-pulp in the cat.

1. Recordings have been made from nerve terminals in canine and third incisor teeth of cats. 2. Ninety-three tooth-pulp units in ten cats could be excited either by mechanical or electrical stimulation of adjacent mucous membrane or by electrical stimulation of the pulp of a nearby tooth. 3. Section of the trigeminal nerve centrally did not abolish these responses. 4. Results for twelve out of thirteen units tested with collision techniques indicated that the nerves were branched.

Action Potentials↗
PubMed1978

Some anatomical and electrophysiological properties of tooth-pulp afferents in the cat.

1. The responses of nerves which could be excited by electrical stimulation of the canine tooth-pulp were recorded from the trigeminal ganglion. 2. Preliminary experiments showed that the responses of mandibular canine pulpal afferents were recorded from the postero-lateral part of the trigeminal ganglion whereas the responses of maxillary canine pulpal afferents were recorded from the central part of the ganglion. 3. The conduction velocity differed in various parts of these nerves; the conduction velocity inside the tooth tended to be slower than that from the tooth to the trigeminal ganglion; the mean conduction velocity in the part of the nerve peripheral to the trigeminal ganglion was faster than that in the part central to the ganglion, and in the central part the conduction velocity decreased caudally. 4. Collision experiments combining tooth stimulation and stimulation of sites in the trigeminal sensory nuclear complex were carried out to investigate the projections of individual pulpal afferents. 5. The results of these experiments showed that some tooth-pulp afferents bifurcate and project to both the main sensory nucleus and the nucleus caudalis. For other pulpal afferents only a projection to the main sensory nucleus or the nucleus caudalis could be demonstrated. 6. Pulpal afferents that bifurcated had faster conduction velocities than those for which no bifurcation could be shown.

Afferent Pathways↗