(177) Electrophysiological properties of neuropeptide Y Y1 receptor-expressing neurons in the substantia gelatinosa of mouse spinal cord

NPY reduces behavioral signs of acute and chronic pain, in part through activation of the NPY Y1-receptor (Y1R). However, the cellular mechanism of Y1R-mediated analgesia remains unclear. One outstanding question is whether they are expressed in inhibitory and/or excitatory neurons, and where they fit within the dorsal horn microcircuity of pain transmission and pain control. Behavioral pharmacology and targeted neurotoxin studies from our laboratory suggest that Y1R-expressing neurons are excitatory. Furthermore, we report that Y1Rs co-exist with multiple markers of excitatory neurons including Tlx3, but not with inhibitory marker of spinal interneurons, PAX2. Preliminary single-cell PCR experiments in Y1-expressing neurons using GAD67 and vGlut2 probes suggest that Y1-neurons are GABAergic neurons. To further characterize Y1R-expressing neurons we used patch-clamp electrophysiology to obtained firing pattern of spinal cord lamina II Y1-neurons from lumbar L4/L5 segment of adult Y1R-eGFP mice. In Y1R-positive cells, the majority of cells exhibited initial bursting/phasic firing (87%). However, 76 % of these neurons exhibited delayed firing when current injection were applied from hyperpolarizing potentials below -80 mV. These numbers did not significantly change in the spared nerve injury mice models. The delayed firing pattern in of the Y1-neurons coincided with rapid A-type potassium currents. Firing property and single-cell PCR experiments of Gad67 and vGluT2 expressing neurons are currently underway to demonstrate once for all whether Y1R-eGFP neurons express glutamate and/or GABA. On administration of NPY we observed that NPY induced outward current in voltage clamp mode and hyperpolarizing shift of the resting membrane potential by ∼10 mV. DRS evoked action potentials were abolished by application of NPY suggesting that NPY inhibits the excitability of Y1R-expressing interneurons in dorsal horn. Taken together, our data suggest that endogenous spinal NPY produces analgesia by altering a complex dorsal horn microcircuit in the dorsal horn that includes interneurons that express Y1R.