Developmental Regulation of Intrinsic Excitability in Spinal Pain Networks

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Project Summary/Abstract Despite the high prevalence of pediatric pain, most commonly seen as musculoskeletal pain, little is known about how the immature CNS processes distinct types of noxious sensory information. In particular, the mechanisms regulating the ascending flow of nociceptive signals from the spinal cord to the brain during early life remain unclear. Since lamina I projection neurons represent an essential output of the spinal nociceptive circuit and are critical for the generation of chronic pain, a better understanding of the ionic conductances which control the intrinsic membrane excitability of these neurons during early life, and how the firing of this population shapes the maturation of synaptic inputs from different classes of sensory afferents, represents an important step towards addressing this issue. The long-term goal is to facilitate the design of evidence-based approaches to treat pediatric pain by advancing the knowledge of the developmental neurobiology of central nociceptive networks. The overall objective of this application is to identify the key factors regulating the firing of ascending projection neurons during early life and to determine the role of this activity in modulating primary afferent synapses onto these cells. The central hypothesis is that classic inward-rectifying K+ (Kir2) and NALCN Na+ leak channels jointly regulate action potential discharge in neonatal projection neurons and thereby influence the postnatal development of functionally distinct synaptic inputs from cutaneous and muscle sensory afferents. The rationale of the proposed research is that understanding the intrinsic and synaptic mechanisms that dictate the excitability of immature projection neurons (PNs) is the first step towards controlling the signaling “gain” of developing spinal nociceptive circuits, which would facilitate the design of novel strategies to alleviate pediatric pain. Guided by strong preliminary data, the central hypothesis will be tested and the overall objective of this application achieved by pursuing the following specific aims: (1) Identify the ion channels shaping the intrinsic membrane excitability of ascending spinal PNs during early life; (2) Elucidate the properties of cutaneous and muscle afferent synapses onto developing PNs; and (3) Determine the extent to which the intrinsic membrane excitability of developing PNs influences the maturation of primary afferent synaptic inputs. These aims will be accomplished by using a multidisciplinary experimental approach that includes in vitro electrophysiological, genetic and immunohistochemical techniques. The outcome of these investigations will be the first identification of which voltage-independent (i.e. “leak”) ion channels shape the intrinsic membrane excitability of neonatal spinal projection neurons, as well as the establishment of a functional relationship between the firing of these cells and the maturation of synaptic inputs from skin and muscle afferents. As a result, the proposed research is significant because it will reveal mechanisms that control ascending nociceptive transmission from the spinal cord to the developing brain, and will also yield new insight into why muscle afferents are more capable of evoking hyperexcitability within central pain circuits.