An intracellular study of spinocervical tract cell responses to natural stimuli and single hair afferent fibres in cats.

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SUMMARY1. In chloralose-anaesthetized cats single-unit microelectrode recordings were made from axons in the dorsal columns, at the lumbar level, identified as belonging to the postsynaptic dorsal column (PSDC) system.2. Excitatory and inhibitory receptive field arrangements of a sample of seventyfive PSDC neurones were examined in detail using natural cutaneous stimuli.3. The sample was characterized by a high degree of convergent input: 80% of units were activated by both light tactile and noxious mechanical stimuli and more than half of those examined were excited by noxious radiant heat. In addition, threequarters of the units had inhibitory receptive fields on the ipsilateral limb.4. Twenty-three units (27 %) were influenced by input from areas of both hairy and glabrous skin covering the foot and distal limb. Neurones in this group had complex receptive fields, many of which occupied several discontinuous areas of skin. Background and evoked activity of these units could frequently be inhibited by light tactile and/or noxious stimuli. Their inhibitory receptive fields occupied small areas of skin overlapping or adjacent to excitatory fields.5. Fifty-two units (73 %) had receptive fields restricted to areas of hairy skin on the thigh and upper hindlimb. Half the units in this group had coextensive low-and high-threshold excitatory areas but about one-third had a concentric receptive field organization; a high-threshold excitatory component extending beyond, or around, a central low-threshold area. The discharge of these units could be inhibited only by light tactile stimuli. Their inhibitory receptive fields covered extensive areas of skin, sometimes completely surrounding the excitatory field.6. The complex receptive field arrangements observed for neurones of the postsynaptic dorsal column system are discussed in relation to previous observations on dorsal horn neurones of other ascending tracts.

Section: Discussionsupporting

confidence: 76%

Section: Discussionmentioning

confidence: 99%

Cutaneous excitatory and inhibitory input to neurones of the postsynaptic dorsal column system in the cat.

Noble

Riddell

1988

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“…The results were obtained from the series of experiments described in the previous paper (Brown et al 1987 a). Briefly, in cats, anaesthetized with a-chloralose and paralysed with gallamine triethiodide, one micro-electrode was placed inside a lumbosacral dorsal root ganglion cell (hair follicle afferent neurone) and another micro-electrode used to record the responses of a spinocervical tract neurone, extracellularly, when the dorsal root ganglion cell was caused to fire single impulses by passing current through the intracellular electrode.…”

Section: Methodsmentioning

confidence: 99%

“…Indeed, for group II afferent fibres, one or more impulses are evoked in about 50 % of afferent fibre-s.c.t. neurone pairs in 50 % of trials (Brown, Koerber & Noble, 1987 a). It was noted, however, (Brown et al 1987 a) that trains of single hair follicle afferent impulses at rates greater than about once every 1500 ms produced less of an effect than slower rates, suggesting some sort of depression of responses.…”

Section: Introductionmentioning

confidence: 99%

Actions of trains and pairs of impulses from single primary afferent fibres on single spinocervical tract cells in cat.

Brown¹,

Koerber²,

Noble³

1987

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SUMMARY1. In cats under chloralose anaesthesia single lumbosacral dorsal root ganglion cells of hair follicle afferent fibres were stimulated intracellularly to produce trains or pairs of impulses. At the same time, single spinocervical tract (s.c.t.) neurones were recorded extracellularly, from their axons in the upper lumbar spinal cord. Afferent fibre-neurone pairs were chosen in which the receptive field of the fibre was contained within the excitatory receptive field (firing zone) of the neurone.2. Trains of impulses of 2-0 Hz were less effective in increasing the probability of s.c.t. cell firing than trains at 0-67 Hz, and this latter rate was usually less effective than trains at 0 33 Hz.3. Successive responses to individual members of a train of hair follicle afferent impulses were variable. In some pairs of units succeeding responses declined until a fairly consistent plateau was reached. In others there was no decline and the responses remained irregular.4. Pairs or short trains of impulses revealed two phenomena: over the first 5 ms or so following an impulse in a group II hair follicle afferent fibre, a second or small group of impulses produced a greater response from the s.c.t. neurone but at intervals of 25-200 ms there was a profound depression of the responses evoked by the second member of a pair of impulses. For Ad afferent fibres the early facilitation lasted for at least 25 ms.5. It is concluded that a single impulse in a single hair follicle afferent fibre from within the excitatory receptive field of a s.c.t. neurone has complex actions on transmission through that neurone. An initial excitatory influence is followed by a long-lasting depression that influences transmission through the system for at least 1500 ms. Possible mechanisms underlying this depression are discussed.

“…neurones. In one accompanying paper (Brown, Koerber & Noble, 1987a) the effects of pairs of impulses in the afferent fibre have been studied and in another (Brown, Koerber & Noble, 1987b) the analysis of the response of the s.c.t. cell has been taken to the intracellular level.…”

Section: Introductionmentioning

confidence: 99%

Excitatory actions of single impulses in single hair follicle afferent fibres on spinocervical tract neurones in the cat.

Brown¹,

Koerber²,

Noble³

1987

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SUMMARY1. In cats under chloralose anaesthesia single dorsal root ganglion cells with axons innervating hair follicles were stimulated intracellularly to produce single impulses. At the same time single spinocervical tract (s.c.t.) neurones were recorded extracellularly, from their axons in the upper lumbar cord.2. When the receptive field of the afferent fibre was contained within the impulse firing zone of the s.c.t. cell, a single afferent impulse increased the probability of firing of the neurone. In thirty-nine pairs of units, where the afferent fibre had a group II conduction velocity, coupling was very efficient and for seventeen pairs the single afferent impulse produced one or more impulses in the s.c.t. cell in at least 90 % of trials. The mean number of impulses evoked in s.c.t. cells by a single group II afferent impulse was 1-47. The latencies of the impulses ranged from 1-5 to 14-0 ms, with times to peak and total durations of 25--17'5 ms and 4'5-28'0 ms respectively. For two pairs of units where the afferent fibre had a group III conduction velocity the effectiveness of single afferent impulses was much less and the latencies, but not the durations, of the impulses were longer (12 and 17 ms).3. When the receptive field of the hair follicle afferent fibre was outside, but close to, the firing zone of the s.c.t. neurone there was no indication that single afferent impulses affected the probability of neuronal discharge for thirteen of fifteen pairs of units. Weak excitation was observed in two pairs and this was clear only when two or more afferent impulses were employed.4. There was a tendency for hair follicle afferent fibres with their receptive fields at or near the centre of the s.c.t. cell's firing zone to be most effective, producing shorter latency responses with more impulses at higher frequencies. When the afferent's field was peripherally located in the s.c.t. neurone's firing zone there was a wide range of responses but these included those with the longest latencies and very few impulses.5. The results are discussed with reference too previous work on the spinocervical tract and to the known actions of single impulses on other neuronal types.