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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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Differentiation of the low-threshold inputs to lamina I neurons from low-threshold inputs to lamina III neuronsA, raw responses from a single lamina III spinoparabrachial neuron showing collision of the first antidromic impulse in a train of 3 (150 Hz, upper trace) when an orthodromic impulse (asterisk, lower trace) occurred within the critical interval. The arrowhead indicates the point at which the first antidromic response should have occurred. B, stimulus–response curves from the population of lamina I neurons and the single ‘wide dynamic range’ lamina III neuron to graded velocity brushing. Note how evoked discharge increases for the lamina III neuron. C, same data as in B but transformed logarithmically.
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fig04: Differentiation of the low-threshold inputs to lamina I neurons from low-threshold inputs to lamina III neuronsA, raw responses from a single lamina III spinoparabrachial neuron showing collision of the first antidromic impulse in a train of 3 (150 Hz, upper trace) when an orthodromic impulse (asterisk, lower trace) occurred within the critical interval. The arrowhead indicates the point at which the first antidromic response should have occurred. B, stimulus–response curves from the population of lamina I neurons and the single ‘wide dynamic range’ lamina III neuron to graded velocity brushing. Note how evoked discharge increases for the lamina III neuron. C, same data as in B but transformed logarithmically.

Mentions: Serendipitously, recordings were also made from two spinoparabrachial neurons located in lamina III, one of which was a ‘wide dynamic range’ neuron, as it responded to both low-threshold brushing stimuli and to noxious stimuli; the other neuron was a nociceptive-specific cell. The response of the lamina III ‘wide dynamic range’ neuron to graded brushing is compared to that of the lamina I spinoparabrachial neuron population in Fig. 4. As can be clearly seen, in both linear and logarithmic plots, the firing rate of the lamina III cell increases smoothly as brush velocity increases, whereas the firing of lamina I neurons shows the inverse behaviour. This comparison confirms that the diminishing response of lamina I neurons to increasing velocity brushing is not simply due to the method of stimulus delivery.


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

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

Differentiation of the low-threshold inputs to lamina I neurons from low-threshold inputs to lamina III neuronsA, raw responses from a single lamina III spinoparabrachial neuron showing collision of the first antidromic impulse in a train of 3 (150 Hz, upper trace) when an orthodromic impulse (asterisk, lower trace) occurred within the critical interval. The arrowhead indicates the point at which the first antidromic response should have occurred. B, stimulus–response curves from the population of lamina I neurons and the single ‘wide dynamic range’ lamina III neuron to graded velocity brushing. Note how evoked discharge increases for the lamina III neuron. C, same data as in B but transformed logarithmically.
© Copyright Policy
Related In: Results  -  Collection

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

fig04: Differentiation of the low-threshold inputs to lamina I neurons from low-threshold inputs to lamina III neuronsA, raw responses from a single lamina III spinoparabrachial neuron showing collision of the first antidromic impulse in a train of 3 (150 Hz, upper trace) when an orthodromic impulse (asterisk, lower trace) occurred within the critical interval. The arrowhead indicates the point at which the first antidromic response should have occurred. B, stimulus–response curves from the population of lamina I neurons and the single ‘wide dynamic range’ lamina III neuron to graded velocity brushing. Note how evoked discharge increases for the lamina III neuron. C, same data as in B but transformed logarithmically.
Mentions: Serendipitously, recordings were also made from two spinoparabrachial neurons located in lamina III, one of which was a ‘wide dynamic range’ neuron, as it responded to both low-threshold brushing stimuli and to noxious stimuli; the other neuron was a nociceptive-specific cell. The response of the lamina III ‘wide dynamic range’ neuron to graded brushing is compared to that of the lamina I spinoparabrachial neuron population in Fig. 4. As can be clearly seen, in both linear and logarithmic plots, the firing rate of the lamina III cell increases smoothly as brush velocity increases, whereas the firing of lamina I neurons shows the inverse behaviour. This comparison confirms that the diminishing response of lamina I neurons to increasing velocity brushing is not simply due to the method of stimulus delivery.

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