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R E Fyffe

Publications and source records attributed to R E Fyffe.

51 records · Page 3Linked to original sources
PubMed1983

Receptive field organization and response properties of spinal neurones with axons ascending the dorsal columns in the cat.

Micro-electrode recordings were made from single post-synaptic axons in the dorsal columns of cats anaesthetized with chloralose and paralysed with gallamine triethiodide. The recordings were made from the L5 segment and the axons were shown to project to the upper cervical level. Forty-eight units were recorded and the axons had conduction velocities of 22-61 ms-1, averaging 38.3 ms-1. Excitatory receptive fields were complex in many units, being made up of clearly defined, separate, low and high threshold areas. The receptive fields were often discontinuous. Only a few units behaved as if they received excitatory input from a single class of mechanoreceptors. A minority (13%) of units had labile, excitatory receptive fields that expanded in size during the recording period. About 40% of the units had inhibitory receptive fields. These were of two main types: either small and within or adjacent to the excitatory field, or large and separated from or adjacent to the excitatory field. The great majority of units had resting discharges upon isolation and these consisted of single impulses or bursts of impulses at short intervals separated by longer, irregular periods. The time course of inhibition produced by electrical stimulation of cutaneous nerves suggested presynaptic inhibitory components to the inhibition. Some inhibitory curves were very prolonged with maxima at about 100 ms and total durations of up to 400 ms. The complexity of the receptive field organization in these dorsal horn neurones is discussed, as is their possible significance as input neurones to the dorsal column nuclei.

Action Potentials↗
PubMed1983

Effects of dorsal root section on spinocervical tract neurones in the cat.

1. In nine cats, dorsal roots L(6) and L(7) were sectioned under pentobarbitone anaesthesia using strict aseptic precautions. In two cats all lumbosacral roots except L(6) were sectioned under similar conditions. 27-75 days after the dorsal rhizotomies, under chloralose anaesthesia, neurones of the spinocervical tract (s.c.t.) were recorded electrophysiologically both extracellularly and intracellularly, their response properties and receptive fields were analysed, and they were injected with horseradish peroxidase (HRP). Twenty-five cells were recorded extracellularly and twenty were recorded intracellularly and stained with the enzyme.2. Of the twenty neurones stained with HRP, one was located in caudal L(5), eleven in L(6) and eight in L(7). Five cells had no receptive field, either before or after current injection, two cells had no field before injection but after current injection responded to either electrical stimulation of peripheral nerve or to brusque tapping on the limb; six neurones responded only to tapping before current injection and two of these showed a more clearly defined receptive field after current injection; six neurones had a receptive field and responded with impulses to hair movement and/or pressure within a well-defined area but this area was surrounded by skin from which excitatory post-synaptic potentials could be elicited; only one neurone had an apparently normal receptive field.3. Of the twenty-five neurones recorded extracellularly, eleven had no receptive field, four responded only to tapping on the limb, three had receptive fields consisting of an area of low threshold plus an area responding to brusque or noxious mechanical stimulation, and seven neurones had apparently normal receptive fields.4. Neurones with no observable receptive fields were either silent with no resting activity, or had very low rates of background activity consisting of isolated single impulses or short bursts of impulses. No neurones in de-afferented segments had high rates of background activity.5. There were no alterations in the normal somatotopy of the dorsal horn. All fifteen s.c.t. neurones injected with HRP and which had a localizable receptive field had fields appropriately located in the somatotopic map. There were no electro-physiological signs of inappropriate connexions.6. The dendritic trees of fifteen neurones injected with HRP were reconstructed. With the exception of one cell which appeared grossly disorganized (but which was the one cell with an apparently normal receptive field), there were no obvious differences between the dendritic trees of de-afferented cells and normal cells from the same and other cats. Their dendritic trees had similar rostro-caudal, medio-lateral and dorso-ventral extents to normal cells, and appeared to exhibit similar degrees of branching. There was a suggestion that de-afferented neurones had rather more of their dorsally-directed distal dendrites invading lamina II than normal cells, but the sample size was too small to make this more than a possibility.7. It is concluded that after dorsal rhizotomy, s.c.t. neurones lose part or all of their afferent input and that within 75 days do not show any signs of new or inappropriate connexions.

Action Potentials↗
PubMed1982

Fine structure of spinocervical tract neurones and the synaptic boutons in contact with them.

Acute electrophysiological experiments were performed on 7 adult cats and spinocervical tract (SCT) neurones were identified and injected intracellularly with horseradish peroxidase (HRP). At the conclusion of experiments regions of spinal cord were prepared for light and electron microscopy. SCT neurones were studied in thick sections and areas of interest were prepared from the same material for electron microscopy. The general ultrastructural features of SCT neurones were categorised and particular attention was paid to axon terminals contacting SCT dendrites. These terminals were found to be of two varieties: those containing clear circular vesicles and an occasional granular vesicle (63% of total) and those containing elongated agranular vesicles (37% of total).

Animals↗
PubMed1982

Ultrastructure of hair follicle afferent fibre terminations in the spinal cord of the cat.

In acute electrophysiological experiments on anaesthetized cats, single identified hair follicle afferent fibres were injected with horseradish peroxidase (HRP). The HRP was injected from an intra-axonal microelectrode in the lumbosacral spinal cord. One to six hours after injection the animals were perfused and the tissue prepared for light and electron microscopy (EM). Axon collateral arborizations containing HRP reaction product were identified in thick sections under the light microscope and the same tissue then cut on the ultramicrotome for EM study. The terminal branches of the collaterals kept their myelin sheaths until they were 0.45-1.0 micron in diameter, just before they formed synaptic boutons. Synaptic boutons (1.0-4.0 microns in diameter) were usually of the en passant variety and made contact with dendrites. The contacts were asymmetrical (Type I) and contained round, clear synaptic vesicles of 35-60 nm diameter. Both the non-myelinated portion of the terminal axon and the synaptic boutons received axo-axonic contacts. These axo-axonic boutons contained clear (agranular) vesicles irregular in profile.

Afferent Pathways↗
PubMed1981

Direct observations on the contacts made between Ia afferent fibres and alpha-motoneurones in the cat's lumbosacral spinal cord.

1. The enzyme horseradish peroxidase was injected into identified lumbosacral alpha-motoneurones and Group Ia afferent fibres in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. Subsequent histological examination allowed the determination of (a) the extent of the motoneuronal dendritic trees, (b) the number and location of Ia synapses upon the motoneurones. 2. alpha-motoneurones had seven to eighteen primary dendrites and each produced daughter branches up to the fourth to the sixth order. At dendritic bifurcations Rall's 3/2 Power Law was obeyed. There was little or no dendritic tapering up to about 800 micrometers from the soma. Beyond this distance, however, there was considerable tapering. 3. Horseradish peroxidase injections revealed that motoneuronal dendrites are much longer than previously thought. Individual dendrites could be traced for up to 1600 micrometers from the soma and dendritic trees were usually 2-3 mm from tip to tip. Nearly all the motoneurones had dendrites that entered the white matter of the cord. Dendrites could also reach as far dorsally as laminae V and VI. 4. Ia synapses upon motoneuronal somata were examined in cords counterstained with cresyl violet or methylene green. About 10% of Ia boutons in lamina IX were on somata and each Ia collateral terminated on 3.66 motoneuronal somata or the most proximal (30 micrometer) dendrites, with on average about two contacts per motoneurone. 5. Ten Ia afferent fibre-motoneurone pairs were injected with horseradish peroxidase. The following conclusions were drawn: (i) only one collateral of any given Ia axon makes contact with a motoneurone even though other collaterals from the same axon might pass through the dendritic tree, (ii) usually all contacts made between a Ia fibre and a motoneurone are at about the same geometrical distance from the soma, even when on different dendrites, (iii) between two and five contacts are made upon the dendritic tree (average 3.4) at distances of between 20 and 820 micrometers from the soma. 6. The results are discussed in relation to previous anatomical and electrophysiological work.

Animals↗
PubMed1981

Spinal cord collaterals from axons of type II slowly adapting units in the cat.

1. The morphology of single axons, and their collaterals, of Type II slowly adapting mechanoreceptors situated at the claw bases was studied. Intra-axonal injections of horseradish peroxidase were made into the axons near their entrance to the lumbosacral spinal cord of anaesthetized cats. The morphology was revealed by subsequent histochemistry. 2. Nine Type II axons were stained. All but one bifurcated into ascending and descending branches upon entering the cord. Eighty-nine collaterals arose from the axons at a mean spacing of about 570 micrometers. 3. The collaterals formed plate-like arborizations usually about 500-600 micrometers wide in the transverse plane but only 100-300 micrometers thick in the longitudinal axis of the cord. The terminal arborizations were in laminae III-VI. 4. Synaptic boutons in laminae III and IV were more numerous than in laminae V and VI. Boutons en passant were common in laminae III and IV and arranged in series of three to six, whereas in deeper laminae only two or three boutons formed a series de passage. 5. The morphology of the slowly adapting Type II collateral is discussed. 6. Some general principles of the organization of cutaneous afferent fibres in the lumbosacral cord are presented.

Animals↗
PubMed1981

Form and function of dorsal horn neurones with axons ascending the dorsal columns in cat.

1. Extracellular and intracellular recordings were made from dorsal horn neurones sending their axons through the dorsal columns in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. 2. Seventeen neurones were injected with horseradish peroxidase through the intracellular micro-electrode, recovered from the histological material and shown to send their axons into the dorsal columns. 3. The cells had axonal conduction velocities of 30--47 ms-1; excitatory receptive fields that usually showed multireceptive characteristics, often including input from sensitive mechanoreceptors in glabrous skin; a third of the sample had a marked subliminal fringe to the excitatory field; inhibitory fields were usually situated proximal to the excitatory field and contiguous with it. 4. The cells were located in laminae III, IV and medial V. Dorsal cells had restricted dendritic trees that ascended in an essentially cylindrical volume of tissue through lamina II and often into I; cells intermediate in depth had more primary dendrites than the others, usually dorsally directed into lamina II, and a more extensive rostro-caudal development; deep, medial cells had dendritic trees that radiated extensively from the cell body but were restricted to the transverse plane. Two cells had axons that ascended the dorsolateral funiculus for a few mm before re-entering the dorsal horn, crossing it and reaching the dorsal columns. Collaterals were given off the axons in the grey matter, in the dorsolateral funiculus and the dorsal columns. 5. The form and function of the neurones are discussed.

Animals↗
PubMed1980

The density, distribution and topographical organization of spinocervical tract neurones in the cat.

1. In acute experiments, detailed grids of micro-electrode recordings were made from spinocervical tract (s.c.t.) cells in the lumbosacral cord of anaesthetized cats. These grids provided electrophysiological data on the location, distribution, density and somatotopic organization of s.c.t. neurones.2. In acute experiments lasting up to 48 hr, retrograde labelling of s.c.t. cells was carried out by injecting horseradish peroxidase into the lateral cervical nucleus in anaesthetized cats. The aim was to flood the nucleus with the enzyme so that all s.c.t. neurones would be labelled in order to provide an independent check on the location, density and distribution data obtained in the electrophysiological experiments.3. The electrophysiological and the anatomical experiments were sometimes performed on the same animal.4. The electrophysiological and anatomical results were in excellent agreement. (a) S.c.t. cells are located mainly in ipsilateral laminae III, IV and V. About 25% are in lamina III, 60% in lamina IV and 10% in lamina V. There are a few cells in laminae I, II and VI making up the remaining 5%. (b) There are about 550-800 s.c.t. cells in the lumbosacral enlargement (L4-S2 inclusive) on each side of the cord. Most cells are in L7-S1 where there are twenty to forty s.c.t. neurones in each millimetre length of cord.5. Many marginal (lamina I) cells were labelled with the retrograde horseradish peroxidase method and a few cells on the contralateral side in laminae III-V and VII-VIII were also labelled. The marginal cells formed 12-18% of labelled cells on the side of injection and, in addition, a similar absolute number of marginal cells was labelled on the side contralateral to the injection. The possible identity of these neurones is discussed.6. S.c.t. cells form a sheet of neurones across the dorsal horn. The sheet is organized somatotopically in a way which resembles the representation of the hind limb dermatomes in the dorsal columns (Werner & Whitsel, 1967). There is a relative enlargement of the L6-S1 dermatomes which encroach upon their neighbouring cord segments. The gradient of the map is very steep in the mediolateral direction but gradual in the rostrocaudal direction. The detailed somatotopic maps generated in the present work have revealed that s.c.t. cells are arranged so that their receptive fields form longitudinal columns and cells within the columns have overlapping fields.

Animals↗
PubMed1980

Projections from Pacinian corpuscles and rapidly adapting mechanoreceptors of glabrous skin to the cat's spinal cord.

1. Single axons innervating Pacinian corpuscles and rapidly adapting mechanoreceptors of the foot and toe pads were injected with horseradish peroxidase near their entrance to the lumbosacral spinal cord in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. Subsequent histochemistry revealed the morphology of the intra-spinal parts of the axons. 2. All Pacinian corpuscle axons that could be traced into the dorsal root bifurcated upon entering the cord into ascending and descending branches. All Pacinian corpuscle axons gave rise to collaterals that entered the dorsal horn. 3. The collaterals of Pacinian corpuscle afferent fibres had a distinctive morphology. They provided two regions of termination, a larger dorsal region in laminae III and IV and a smaller ventral region in laminae V and VI. Within the dorsal region the terminal axons ran mainly in the longitudinal axis of the cord and carried many boutons en passant. Within the ventral region the axons ran dorso-ventrally in the transverse plane of the cord and although carrying some boutons en passant also gave rise to clusters of boutons. 4. The collaterals of rapidly adapting afferent fibres had a distinctive morphology different from that of the Pacinian corpuscle afferent fibre collaterals. The termination region of rapidly adapting afferents was limited almost exclusively to lamina III, with only slight extension into lamina IV. Boutons were mainly of the en passant type and terminal axons were generally orientated within the longitudinal axis of the cord. 5. The morphology of the afferent fibre collaterals is discussed in relation to the physiology of the dorsal horn.

Animals↗
PubMed1979

The morphology of group Ib afferent fibre collaterals in the spinal cord of the cat.

1. The enzyme horseradish peroxidase (HRP) was injected into single Ib muscle afferent fibres in anaesthetized cats. Subsequently, histochemistry allowed the morphology of the axons and their collaterals in the lumbosacral spinal cord to be determined. 2. Eleven Ib axons were stained, seven from lateral gastrocneminus-soleus, one from medial gastrocnemius and three from muscles innervated by the posterior tibial nerve. Ten of the axons were traced into the dorsal roots and all but one (from the posterior tibial nerve) bifurcated upon entering the cord. Between 5.1 and 9.9 mm of each axon was stained and the fibres gave off eighty-four collaterals at intervals of 100-2300 micron, at an average spacing of about 900 micron. The spacing between collaterals on the (finer) descending axon branches was generally less than the intervals between collaterals on ascending branches. 3. All Ib collaterals had a characteristic morphology. The collaterals coursed cranially on a direct path through the dorsal horn to lamina IV or V before branching. They arborized widely in the intermediate region, mainly in lamina VI and in the dorsal part of lamina VII. Occasionally, less extensive arborizations were seen more dorsally in lamina IV and V. The rostro-caudal extent of individual collateral arborizations was limited to 200-400 micron and there was no overlap between adjacent collaterals. Each terminal arborization gave rise to 56-384 boutons, mainly of them 'en passant' type. 4. The results are discussed in relation to previous anatomical and electrophysiological studies.

Animals↗
PubMed1978

The morphology of group Ia afferent fibre collaterals in the spinal cord of the cat.

1. The enzyme horseradish peroxidase (HRP) was injected into single Ia muscle afferent fibres in anaesthetized cats. Subsequent histochemistry allowed the morphology of the axons and their collaterals in the lumbosacral spinal cord to be determined. 2. Fifteen Ia axons were stained, four from medial gastrocnemius, four from lateral gastrocnemius-soleus and seven from muscles innervated by the posterior tibial nerve. All thirteen axons that could be traced into the dorsal roots bifurcated upon entering the cord. Between 4 and 11 mm of axons were stained and they gave off eighty seven collaterals over distances between 3 and 9 mm. Collaterals were given off at intervals of 100-2600 micron at an average spacing of about 1000 micron. 3. All Ia collaterals had a characteristic morphology. After leaving the parent axon they ran ventrally to lamina VI and then ventrolaterally to the motor nuclei. The collaterals coursed cranially from their point of origin to the motor nuclei so that their lamina VI terminations were about 100-300 micro caudal to their terminations in motor nuclei. Terminal arborizations were limited to three sites; lamina VI (the intermediate region), lamina VII (the Ia inhibitory interneurone region) and lamina IX (the motor nuclei). The three sets of terminals had characteristic arborizations and bouton arrangements. 4. The results are discussed in relation to previous anatomical studies. In particular the present results suggest that a single Ia collateral makes contact with many more motoneurones than has previously been suggested in fact with fifty to sixty rather than with about ten.

Animals↗