The focus of this proposal is on mechanisms underlying pain, in particular, the sensitization of nociceptive afferents. Specifically, I proposed to fill a critical gap in our understanding of these mechanisms by characterizing the contribution of neural activity, in particular, neural activity-dependent increases in intracellular Ca2+ in both the rapid and the longer-term sensitization of these afferents. Data from previous studies indicate that activity- dependent changes in gene expression are not only Ca2+ dependent, but dependent on the pattern of activity. Similarly, a number of ion channels that contribute to the establishment of excitability in sensory neurons are modulated by a variety of enzymes, that are themselves regulated by changes in intracellular Ca2+. In this context, I have proposed to focus on voltage-gated sodium channels (VGSCs) for a number of reasons, not the least of which include a) the essential role these channels play in neural excitability, b) evidence that both rapid post-translational modifications of these channels, and longer-term changes in channel expression, influence sensory neuron excitability, and c) because both rapid and longer-term changes in VGSCs have been shown to be Ca2+ and/or activity dependent. Finally, that the influence of activity on both rapid and longer-term changes in VGSCs properties may change in the presence of injury, is suggested by the observation that persistent inflammation results in dramatic changes in the regulation of intracellular Ca2+ in nociceptive afferents, which includes the almost complete loss of Na+/Ca2+ exchanger (NCX) activity in the sensory neuron somata. Thus, I hypothesize that dysregulation of intracellular Ca2+, particularly the decrease in NCX activity, contributes to inflammatory pain via the activity-dependent sensitization of nociceptive afferents secondary to both the rapid modulation of VGSCs, as well as longer-term changes in the pattern of expression of these channels. To test this hypothesis, I will characterize the influence of NCX blockade on rapid activity-dependent changes in the excitability and VGSC properties of mouse and human nociceptive afferents. I will then characterize the influence of NCX blockade on activity-dependent changes in transcription/translation on the excitability and VGSCs in mouse and human nociceptive afferents. The experiments proposed will not only serve as an excellent training vehicle enabling the mastery of a variety of powerful techniques and approaches, but will be the first to establish the relationship between the regulation of intracellular Ca2+ and both rapid and longer-term activity-dependent changes in afferent excitability and VGSC properties.
Pain is a significant problem because of its prevalence, its impact on those who suffer, and its economic and social consequences, all of which is exacerbated by relative absence of consistently effective treatment options. I have proposed to address this issue by identifying processes that contribute to both rapid and longer-term pain, in particular, those involved in changes in the excitability sensory neurons, which are responsible for transmitting pain from peripheral to the central nervous system. Identifying the mechanisms responsible for the changes in neuronal excitability after injury may suggest novel treatment options for pain, as well as explain the limited efficacy of current treatments.
