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Injections of Algesic Solutions into Muscle Activate the Lateral Reticular Formation: A Nociceptive Relay of the Spinoreticulothalamic Tract.

Panneton WM, Gan Q, Ariel M - PLoS ONE (2015)

Bottom Line: Immunolabeled neurons, many of them catecholaminergic, were found bilaterally in the nucleus tractus solitarii, the gracile nucleus, the A1 area, the CVLM and RVLM, the superior salivatory nucleus, the nucleus locus coeruleus, the A5 area, and the nucleus raphe magnus in the pons.The external lateral and superior lateral subnuclei of the parabrachial nuclear complex were consistently labeled in experimental data, but they also were labeled in many control cases.Few immunolabeled neurons were found in the medial reticular formation, however, but the rostroventromedial medulla was labeled consistently.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacological and Physiological Science, Saint Louis University, St. Louis, MO, United States of America.

ABSTRACT
Although musculoskeletal pain disorders are common clinically, the central processing of muscle pain is little understood. The present study reports on central neurons activated by injections of algesic solutions into the gastrocnemius muscle of the rat, and their subsequent localization by c-Fos immunohistochemistry in the spinal cord and brainstem. An injection (300 μl) of an algesic solution (6% hypertonic saline, pH 4.0 acetate buffer, or 0.05% capsaicin) was made into the gastrocnemius muscle and the distribution of immunolabeled neurons compared to that obtained after control injections of phosphate buffered saline [pH 7.0]. Most labeled neurons in the spinal cord were found in laminae IV-V, VI, VII and X, comparing favorably with other studies, with fewer labeled neurons in laminae I and II. This finding is consistent with the diffuse pain perception due to noxious stimuli to muscles mediated by sensory fibers to deep spinal neurons as compared to more restricted pain localization during noxious stimuli to skin mediated by sensory fibers to superficial laminae. Numerous neurons were immunolabeled in the brainstem, predominantly in the lateral reticular formation (LRF). Labeled neurons were found bilaterally in the caudalmost ventrolateral medulla, where neurons responsive to noxious stimulation of cutaneous and visceral structures lie. Immunolabeled neurons in the LRF continued rostrally and dorsally along the intermediate reticular nucleus in the medulla, including the subnucleus reticularis dorsalis caudally and the parvicellular reticular nucleus more rostrally, and through the pons medial and lateral to the motor trigeminal nucleus, including the subcoerulear network. Immunolabeled neurons, many of them catecholaminergic, were found bilaterally in the nucleus tractus solitarii, the gracile nucleus, the A1 area, the CVLM and RVLM, the superior salivatory nucleus, the nucleus locus coeruleus, the A5 area, and the nucleus raphe magnus in the pons. The external lateral and superior lateral subnuclei of the parabrachial nuclear complex were consistently labeled in experimental data, but they also were labeled in many control cases. The internal lateral subnucleus of the parabrachial complex was labeled moderately. Few immunolabeled neurons were found in the medial reticular formation, however, but the rostroventromedial medulla was labeled consistently. These data are discussed in terms of an interoceptive, multisynaptic spinoreticulothalamic path, with its large receptive fields and role in the motivational-affective components of pain perceptions.

No MeSH data available.


Related in: MedlinePlus

Summary diagram illustrating the multisynaptic spinoreticulothalamic tract.Data that provide components of this tract were garnered from several independent neuroanatomical studies including primary afferent projections of the GCM to lumbar spinal cord (purple lines; [34]) projections from the cmVLM (green lines; [28]), projections from the LRF (blue lines; [29]), and the data presented herein (red lines). We propose this multisynaptic pathway utilizes mostly very small fibers and is important for diffuse deep pain, including that from both muscles and viscera. We also suggest all central neurons part of this system will have very large receptive fields and respond to various multimodal stimuli. Although the multisynaptic path is drawn on the right side only, the projections from all sources are bilateral.
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pone.0130939.g008: Summary diagram illustrating the multisynaptic spinoreticulothalamic tract.Data that provide components of this tract were garnered from several independent neuroanatomical studies including primary afferent projections of the GCM to lumbar spinal cord (purple lines; [34]) projections from the cmVLM (green lines; [28]), projections from the LRF (blue lines; [29]), and the data presented herein (red lines). We propose this multisynaptic pathway utilizes mostly very small fibers and is important for diffuse deep pain, including that from both muscles and viscera. We also suggest all central neurons part of this system will have very large receptive fields and respond to various multimodal stimuli. Although the multisynaptic path is drawn on the right side only, the projections from all sources are bilateral.

Mentions: A pattern of central neuronal activation after injections of algesic solutions into the deep GCM was observed that differs from the pattern elicited after injections of algesic chemicals into the skin. Most spinal neurons with c-Fos activated after muscle injections of algesic solutions were found in deep laminae of the spinal cord (e.g., laminae IV-V, VI, VII and X) versus the more superficial location (laminae I- II) found after noxious cutaneous stimulation. In the brainstem, the amount of neuronal activation after muscle injection was substantial in the LRF, an area often ignored in contemporary studies of cutaneous pain. While the functional role of these neurons only can be speculated with the neuroanatomical assays used herein, preliminary electrophysiological studies [33] suggest that LRF neurons respond to algesic stimulation of muscles, to stimulation of the nasal mucosa with noxious vapors, and to stimulation of high threshold skin mechanoreceptors. Also, receptive fields of LRF neurons are large, sometimes responsive throughout the body. Thus, interoceptive sensations induced by noxious muscle stimulation may not be carried by the spinothalamic tract, but by the spinoreticulothalamic tract (Fig 8).


Injections of Algesic Solutions into Muscle Activate the Lateral Reticular Formation: A Nociceptive Relay of the Spinoreticulothalamic Tract.

Panneton WM, Gan Q, Ariel M - PLoS ONE (2015)

Summary diagram illustrating the multisynaptic spinoreticulothalamic tract.Data that provide components of this tract were garnered from several independent neuroanatomical studies including primary afferent projections of the GCM to lumbar spinal cord (purple lines; [34]) projections from the cmVLM (green lines; [28]), projections from the LRF (blue lines; [29]), and the data presented herein (red lines). We propose this multisynaptic pathway utilizes mostly very small fibers and is important for diffuse deep pain, including that from both muscles and viscera. We also suggest all central neurons part of this system will have very large receptive fields and respond to various multimodal stimuli. Although the multisynaptic path is drawn on the right side only, the projections from all sources are bilateral.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4496070&req=5

pone.0130939.g008: Summary diagram illustrating the multisynaptic spinoreticulothalamic tract.Data that provide components of this tract were garnered from several independent neuroanatomical studies including primary afferent projections of the GCM to lumbar spinal cord (purple lines; [34]) projections from the cmVLM (green lines; [28]), projections from the LRF (blue lines; [29]), and the data presented herein (red lines). We propose this multisynaptic pathway utilizes mostly very small fibers and is important for diffuse deep pain, including that from both muscles and viscera. We also suggest all central neurons part of this system will have very large receptive fields and respond to various multimodal stimuli. Although the multisynaptic path is drawn on the right side only, the projections from all sources are bilateral.
Mentions: A pattern of central neuronal activation after injections of algesic solutions into the deep GCM was observed that differs from the pattern elicited after injections of algesic chemicals into the skin. Most spinal neurons with c-Fos activated after muscle injections of algesic solutions were found in deep laminae of the spinal cord (e.g., laminae IV-V, VI, VII and X) versus the more superficial location (laminae I- II) found after noxious cutaneous stimulation. In the brainstem, the amount of neuronal activation after muscle injection was substantial in the LRF, an area often ignored in contemporary studies of cutaneous pain. While the functional role of these neurons only can be speculated with the neuroanatomical assays used herein, preliminary electrophysiological studies [33] suggest that LRF neurons respond to algesic stimulation of muscles, to stimulation of the nasal mucosa with noxious vapors, and to stimulation of high threshold skin mechanoreceptors. Also, receptive fields of LRF neurons are large, sometimes responsive throughout the body. Thus, interoceptive sensations induced by noxious muscle stimulation may not be carried by the spinothalamic tract, but by the spinoreticulothalamic tract (Fig 8).

Bottom Line: Immunolabeled neurons, many of them catecholaminergic, were found bilaterally in the nucleus tractus solitarii, the gracile nucleus, the A1 area, the CVLM and RVLM, the superior salivatory nucleus, the nucleus locus coeruleus, the A5 area, and the nucleus raphe magnus in the pons.The external lateral and superior lateral subnuclei of the parabrachial nuclear complex were consistently labeled in experimental data, but they also were labeled in many control cases.Few immunolabeled neurons were found in the medial reticular formation, however, but the rostroventromedial medulla was labeled consistently.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacological and Physiological Science, Saint Louis University, St. Louis, MO, United States of America.

ABSTRACT
Although musculoskeletal pain disorders are common clinically, the central processing of muscle pain is little understood. The present study reports on central neurons activated by injections of algesic solutions into the gastrocnemius muscle of the rat, and their subsequent localization by c-Fos immunohistochemistry in the spinal cord and brainstem. An injection (300 μl) of an algesic solution (6% hypertonic saline, pH 4.0 acetate buffer, or 0.05% capsaicin) was made into the gastrocnemius muscle and the distribution of immunolabeled neurons compared to that obtained after control injections of phosphate buffered saline [pH 7.0]. Most labeled neurons in the spinal cord were found in laminae IV-V, VI, VII and X, comparing favorably with other studies, with fewer labeled neurons in laminae I and II. This finding is consistent with the diffuse pain perception due to noxious stimuli to muscles mediated by sensory fibers to deep spinal neurons as compared to more restricted pain localization during noxious stimuli to skin mediated by sensory fibers to superficial laminae. Numerous neurons were immunolabeled in the brainstem, predominantly in the lateral reticular formation (LRF). Labeled neurons were found bilaterally in the caudalmost ventrolateral medulla, where neurons responsive to noxious stimulation of cutaneous and visceral structures lie. Immunolabeled neurons in the LRF continued rostrally and dorsally along the intermediate reticular nucleus in the medulla, including the subnucleus reticularis dorsalis caudally and the parvicellular reticular nucleus more rostrally, and through the pons medial and lateral to the motor trigeminal nucleus, including the subcoerulear network. Immunolabeled neurons, many of them catecholaminergic, were found bilaterally in the nucleus tractus solitarii, the gracile nucleus, the A1 area, the CVLM and RVLM, the superior salivatory nucleus, the nucleus locus coeruleus, the A5 area, and the nucleus raphe magnus in the pons. The external lateral and superior lateral subnuclei of the parabrachial nuclear complex were consistently labeled in experimental data, but they also were labeled in many control cases. The internal lateral subnucleus of the parabrachial complex was labeled moderately. Few immunolabeled neurons were found in the medial reticular formation, however, but the rostroventromedial medulla was labeled consistently. These data are discussed in terms of an interoceptive, multisynaptic spinoreticulothalamic path, with its large receptive fields and role in the motivational-affective components of pain perceptions.

No MeSH data available.


Related in: MedlinePlus