Descending control of nociception: specificity, recruitment and plasticity

Descending control of nociception: specificity, recruitment and plasticity

2009 April ; 60(1): 214–225 | M. M. Heinricher, I. Tavares, J.L. Leith, and B. M. Lumb
The dorsal horn of the spinal cord is a critical site for the regulation of nociceptive transmission, influenced by both local and supraspinal mechanisms. Descending control of spinal nociception originates from various brain regions, including the periaqueductal gray (PAG) and rostral ventromedial medulla (RVM) system, and the dorsal reticular nucleus (DRt) and ventrolateral medulla (VLM). The PAG-RVM system preferentially suppresses nociceptive inputs mediated by C-fibers while preserving sensory-discriminative information conveyed by A-fibers. The RVM contains ON-cells and OFF-cells, which are differentially recruited by higher structures to enhance or inhibit pain. Dynamic shifts in the balance between pain-inhibiting and facilitating outflows from the brainstem play a crucial role in setting the gain of nociceptive processing, which can be altered in different behavioral, emotional, and pathological states. Descending facilitation of spinal nociception is a major contributor to central sensitization and the development of secondary hyperalgesia, indicating a shift towards facilitation in the transition from acute to chronic pain. The PAG-RVM system is also involved in coordinating survival strategies, with selective descending control of noxious inputs to suppress distracting input and preserve sensory-discriminative information. The RVM's ON-cells and OFF-cells exert bidirectional control over dorsal horn function, with the balance between these populations affecting nociceptive threshold. Higher centers, such as the amygdala and prefrontal cortex, also influence the RVM, providing a neural substrate for the influence of cognitive and emotional factors on pain. The DRt and VLM, located in the caudal medulla, are involved in descending control of dorsal horn nociceptive processing, with the DRt facilitating and the VLM inhibiting nociceptive responses. Understanding how descending control systems interface with dorsal horn nociceptive processes and how they are recruited to effect changes in the priority of pain relative to other behaviors is essential for comprehending pathological pain states.The dorsal horn of the spinal cord is a critical site for the regulation of nociceptive transmission, influenced by both local and supraspinal mechanisms. Descending control of spinal nociception originates from various brain regions, including the periaqueductal gray (PAG) and rostral ventromedial medulla (RVM) system, and the dorsal reticular nucleus (DRt) and ventrolateral medulla (VLM). The PAG-RVM system preferentially suppresses nociceptive inputs mediated by C-fibers while preserving sensory-discriminative information conveyed by A-fibers. The RVM contains ON-cells and OFF-cells, which are differentially recruited by higher structures to enhance or inhibit pain. Dynamic shifts in the balance between pain-inhibiting and facilitating outflows from the brainstem play a crucial role in setting the gain of nociceptive processing, which can be altered in different behavioral, emotional, and pathological states. Descending facilitation of spinal nociception is a major contributor to central sensitization and the development of secondary hyperalgesia, indicating a shift towards facilitation in the transition from acute to chronic pain. The PAG-RVM system is also involved in coordinating survival strategies, with selective descending control of noxious inputs to suppress distracting input and preserve sensory-discriminative information. The RVM's ON-cells and OFF-cells exert bidirectional control over dorsal horn function, with the balance between these populations affecting nociceptive threshold. Higher centers, such as the amygdala and prefrontal cortex, also influence the RVM, providing a neural substrate for the influence of cognitive and emotional factors on pain. The DRt and VLM, located in the caudal medulla, are involved in descending control of dorsal horn nociceptive processing, with the DRt facilitating and the VLM inhibiting nociceptive responses. Understanding how descending control systems interface with dorsal horn nociceptive processes and how they are recruited to effect changes in the priority of pain relative to other behaviors is essential for comprehending pathological pain states.
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