(246) Determining the Role of Presynaptic Ca2+ Signaling in the Spinal Cord in Pain Sensitization

Chronic neuropathic pain affects approximately 10% of the population and only a minority of patients experience satisfactory relief of their pain with currently available pharmaceutics. As most previous reports focused primarily on the post-synaptic signaling of the first sensory synapse via patch-clamp recordings, we aim to address a gap in the current knowledge about the potential role of presynaptic Ca2+ signaling in central sensitization following neuropathic injury. Utilizing a novel ex vivo intact spinal cord preparation, a mouse line that expresses GCaMP specifically in the sensory neurons, and multiphoton microscopy to image presynaptic Ca2+ signaling, we are able to evaluate presynaptic Ca2+ signaling in the spinal cord isolated from mice that underwent either spared nerve injury (SNI) or sham surgery. Behavioral testing was used to confirm development of mechanical allodynia in SNI (but not sham) mice prior to presynaptic Ca2+ imaging. Presynaptic [Ca2+]cyt changes were induced by dorsal root stimulation, bradykinin, and capsaicin. The effects of modulatory neurotransmitters, such as dopamine, were also tested for their ability to regulate [Ca2+]cyt in central processes of sensory afferent neurons. Preliminary results quantifying frequency and duration of presynaptic [Ca2+]cyt transients indicate that neuropathic injury alters basal Ca2+ signaling and responsiveness to sensory modulators.