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Quantitative characterization of low-threshold mechanoreceptor inputs to lamina I spinoparabrachial neurons in the rat.

Andrew D - J. Physiol. (Lond.) (2009)

Bottom Line: Graded velocity brushing stimuli (6.6-126 cm s(-1)) were used to characterize the mechanoreceptor inputs to 'wide dynamic range' neurons in lamina I of the dorsal horn that had axons that projected to the contralateral parabrachial nucleus.The most effective tactile stimuli for activation of 'wide dynamic range' lamina I spinoparabrachial neurons were low velocity brush strokes: peak discharge occurred at a mean velocity of 9.2 cm s(-1) (range 6.6-20.4 cm s(-1), s.d. 5.0 cm s(-1)), and declined exponentially as brush velocity increased.The data indicate that C-fibres, but not A-fibres, conveyed low-threshold mechanoreceptor inputs to lamina I projection neurons.

View Article: PubMed Central - PubMed

Affiliation: Department of Oral & Maxillofacial Surgery, School of Clinical Dentistry, Claremont Crescent, Sheffield S10 2TA, UK. d.andrew@sheffield.ac.uk

ABSTRACT
It has been suggested that primary afferent C-fibres that respond to innocuous tactile stimuli are important in the sensation of pleasurable touch. Although it is known that C-tactile fibres terminate in the substantia gelatinosa (lamina II) of the spinal cord, virtually all of the neurons in this region are interneurons, and currently it is not known how impulses in C-mechanoreceptors are transmitted to higher centres. In the current study, I have tested the quantitative response properties of 'wide dynamic range' projection neurons in lamina I of the spinal cord to graded velocity brushing stimuli to identify whether low-threshold mechanoreceptor input to these neurons arises from myelinated or umyelinated nerve fibres. Graded velocity brushing stimuli (6.6-126 cm s(-1)) were used to characterize the mechanoreceptor inputs to 'wide dynamic range' neurons in lamina I of the dorsal horn that had axons that projected to the contralateral parabrachial nucleus. The most effective tactile stimuli for activation of 'wide dynamic range' lamina I spinoparabrachial neurons were low velocity brush strokes: peak discharge occurred at a mean velocity of 9.2 cm s(-1) (range 6.6-20.4 cm s(-1), s.d. 5.0 cm s(-1)), and declined exponentially as brush velocity increased. The data indicate that C-fibres, but not A-fibres, conveyed low-threshold mechanoreceptor inputs to lamina I projection neurons.

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Responses to brushing stimuliA, raw responses from a typical ‘wide dynamic range’ lamina I spinoparabrachial neuron to repeated brushing at the lowest velocity tested (6.6 cm s−1). The first, then every other response to a series of 10 stimulus repetitions are shown. A marker trace (bottom) from a photocell indicates stimulus timing. As can be seen, there is a gradual reduction in response as the stimulus is repeated, similar to primary afferent C-fibre mechanoreceptors. B, responses of the same cell to 4 other of the 10 different brush velocities that were tested. Responses to the 1st, 5th and 10th stimuli are shown, with each action potential represented by a vertical tick mark. As can be seen, increasing stimulus velocity caused a progressive reduction in response.
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fig02: Responses to brushing stimuliA, raw responses from a typical ‘wide dynamic range’ lamina I spinoparabrachial neuron to repeated brushing at the lowest velocity tested (6.6 cm s−1). The first, then every other response to a series of 10 stimulus repetitions are shown. A marker trace (bottom) from a photocell indicates stimulus timing. As can be seen, there is a gradual reduction in response as the stimulus is repeated, similar to primary afferent C-fibre mechanoreceptors. B, responses of the same cell to 4 other of the 10 different brush velocities that were tested. Responses to the 1st, 5th and 10th stimuli are shown, with each action potential represented by a vertical tick mark. As can be seen, increasing stimulus velocity caused a progressive reduction in response.

Mentions: Graded velocity brushing was used to activate low-threshold mechanoreceptors that conveyed tactile information to lamina I spinoparabrachial neurons. An example of the response of a single neuron to repeated brushing stimuli is shown in Fig. 2A. As can be clearly seen, the response to repeated stimuli, delivered at the same velocity, gradually declined over the series of 10 brush strokes; such fatigue is a characteristic feature of C-fibre mechanoreceptors in both experimental animals and humans (Bessou et al. 1971; Nordin, 1990; Vallbo et al. 1999). The responses of the same unit to brushing at increasing velocities is shown in Fig. 2B. As the velocity of the brush increased, the response of the neuron diminished. Quantitative responses to the full range of brush velocities are shown in Fig. 3A. As can be seen from these stimulus–response functions, all of the neurons were preferentially sensitive to slowly moving stimuli. Maximal discharge rates (based on inter-spike intervals) were in the range 8–73 impulses s−1 (mean 40 impulses s−1, s.d. 26 impulses s−1) and occurred at a mean brush velocity of 9.2 cm s−1 (range 6.6–20.4 cm s−1, s.d. 5.0 cm s−1). In contrast, only two neurons were activated at the highest velocity tested (126 cm s−1), and their maximal discharge rates were only 1.2 and 0.1 impulses s−1. The population stimulus–response function could be fitted with a first-order exponential decay function of the form y=ae−bx (a= 48.7, b= 0.06; r2= 0.93). Plotting the data on a logarithmic scale showed that the decline in neuronal response to increasing velocity was linear (Fig. 3B), and it could be fitted with a straight line of the form y=mx+c (m=−1.87, c= 3.33; r2= 0.93).


Quantitative characterization of low-threshold mechanoreceptor inputs to lamina I spinoparabrachial neurons in the rat.

Andrew D - J. Physiol. (Lond.) (2009)

Responses to brushing stimuliA, raw responses from a typical ‘wide dynamic range’ lamina I spinoparabrachial neuron to repeated brushing at the lowest velocity tested (6.6 cm s−1). The first, then every other response to a series of 10 stimulus repetitions are shown. A marker trace (bottom) from a photocell indicates stimulus timing. As can be seen, there is a gradual reduction in response as the stimulus is repeated, similar to primary afferent C-fibre mechanoreceptors. B, responses of the same cell to 4 other of the 10 different brush velocities that were tested. Responses to the 1st, 5th and 10th stimuli are shown, with each action potential represented by a vertical tick mark. As can be seen, increasing stimulus velocity caused a progressive reduction in response.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2821553&req=5

fig02: Responses to brushing stimuliA, raw responses from a typical ‘wide dynamic range’ lamina I spinoparabrachial neuron to repeated brushing at the lowest velocity tested (6.6 cm s−1). The first, then every other response to a series of 10 stimulus repetitions are shown. A marker trace (bottom) from a photocell indicates stimulus timing. As can be seen, there is a gradual reduction in response as the stimulus is repeated, similar to primary afferent C-fibre mechanoreceptors. B, responses of the same cell to 4 other of the 10 different brush velocities that were tested. Responses to the 1st, 5th and 10th stimuli are shown, with each action potential represented by a vertical tick mark. As can be seen, increasing stimulus velocity caused a progressive reduction in response.
Mentions: Graded velocity brushing was used to activate low-threshold mechanoreceptors that conveyed tactile information to lamina I spinoparabrachial neurons. An example of the response of a single neuron to repeated brushing stimuli is shown in Fig. 2A. As can be clearly seen, the response to repeated stimuli, delivered at the same velocity, gradually declined over the series of 10 brush strokes; such fatigue is a characteristic feature of C-fibre mechanoreceptors in both experimental animals and humans (Bessou et al. 1971; Nordin, 1990; Vallbo et al. 1999). The responses of the same unit to brushing at increasing velocities is shown in Fig. 2B. As the velocity of the brush increased, the response of the neuron diminished. Quantitative responses to the full range of brush velocities are shown in Fig. 3A. As can be seen from these stimulus–response functions, all of the neurons were preferentially sensitive to slowly moving stimuli. Maximal discharge rates (based on inter-spike intervals) were in the range 8–73 impulses s−1 (mean 40 impulses s−1, s.d. 26 impulses s−1) and occurred at a mean brush velocity of 9.2 cm s−1 (range 6.6–20.4 cm s−1, s.d. 5.0 cm s−1). In contrast, only two neurons were activated at the highest velocity tested (126 cm s−1), and their maximal discharge rates were only 1.2 and 0.1 impulses s−1. The population stimulus–response function could be fitted with a first-order exponential decay function of the form y=ae−bx (a= 48.7, b= 0.06; r2= 0.93). Plotting the data on a logarithmic scale showed that the decline in neuronal response to increasing velocity was linear (Fig. 3B), and it could be fitted with a straight line of the form y=mx+c (m=−1.87, c= 3.33; r2= 0.93).

Bottom Line: Graded velocity brushing stimuli (6.6-126 cm s(-1)) were used to characterize the mechanoreceptor inputs to 'wide dynamic range' neurons in lamina I of the dorsal horn that had axons that projected to the contralateral parabrachial nucleus.The most effective tactile stimuli for activation of 'wide dynamic range' lamina I spinoparabrachial neurons were low velocity brush strokes: peak discharge occurred at a mean velocity of 9.2 cm s(-1) (range 6.6-20.4 cm s(-1), s.d. 5.0 cm s(-1)), and declined exponentially as brush velocity increased.The data indicate that C-fibres, but not A-fibres, conveyed low-threshold mechanoreceptor inputs to lamina I projection neurons.

View Article: PubMed Central - PubMed

Affiliation: Department of Oral & Maxillofacial Surgery, School of Clinical Dentistry, Claremont Crescent, Sheffield S10 2TA, UK. d.andrew@sheffield.ac.uk

ABSTRACT
It has been suggested that primary afferent C-fibres that respond to innocuous tactile stimuli are important in the sensation of pleasurable touch. Although it is known that C-tactile fibres terminate in the substantia gelatinosa (lamina II) of the spinal cord, virtually all of the neurons in this region are interneurons, and currently it is not known how impulses in C-mechanoreceptors are transmitted to higher centres. In the current study, I have tested the quantitative response properties of 'wide dynamic range' projection neurons in lamina I of the spinal cord to graded velocity brushing stimuli to identify whether low-threshold mechanoreceptor input to these neurons arises from myelinated or umyelinated nerve fibres. Graded velocity brushing stimuli (6.6-126 cm s(-1)) were used to characterize the mechanoreceptor inputs to 'wide dynamic range' neurons in lamina I of the dorsal horn that had axons that projected to the contralateral parabrachial nucleus. The most effective tactile stimuli for activation of 'wide dynamic range' lamina I spinoparabrachial neurons were low velocity brush strokes: peak discharge occurred at a mean velocity of 9.2 cm s(-1) (range 6.6-20.4 cm s(-1), s.d. 5.0 cm s(-1)), and declined exponentially as brush velocity increased. The data indicate that C-fibres, but not A-fibres, conveyed low-threshold mechanoreceptor inputs to lamina I projection neurons.

Show MeSH
Related in: MedlinePlus