Neuropeptide S: a novel regulator of pain-related amygdala

23 Amygdala plasticity is an important contributor to the emotional-affective dimension of 24 pain. Recently discovered neuropeptide S (NPS) has anxiolytic properties through 25 actions in the amygdala. Behavioral data also suggest antinociceptive effects of centrally 26 acting NPS, but site and mechanism of action remain to be determined. This is the first 27 electrophysiological analysis of pain-related NPS effects in the brain. We combined 28 whole-cell patch-clamp recordings in brain slices and behavioral assays to test the 29 hypothesis that NPS activates synaptic inhibition of amygdala output to suppress pain 30 behavior in an arthritis pain model. Recordings of neurons in the laterocapsular division of 31 the central nucleus (CeLC), which serves pain-related amygdala output functions, show 32 that NPS inhibited the enhanced excitatory drive (monosynaptic excitatory postsynaptic 33 currents, EPSCs) from the basolateral amygdala (BLA) in the pain state. Based on 34 miniature EPSC analysis the inhibitory effect of NPS did not involve a direct postsynaptic 35 action on CeLC neurons but rather a presynaptic, action potential-dependent network 36 mechanism. Indeed, NPS increased external capsule (EC)-driven synaptic inhibition of 37 CeLC neurons through a PKA-dependent facilitatory postsynaptic action on a cluster of 38 inhibitory intercalated cells (ITC). NPS had no effect on BLA neurons. High-frequency 39 stimulation (HFS) of excitatory EC inputs to ITC cells also inhibited synaptic activation of 40 CeLC neurons, providing further evidence that ITC activation can control amygdala 41 output. The cellular mechanisms by which EC-driven synaptic inhibition controls CeLC 42 output remain to be determined. Administration of NPS into ITC, but not CeLC, also 43 inhibited vocalizations and anxiety-like behavior in arthritic rats. A selective NPS receptor 44 antagonist ([D-Cys(tBu)]NPS) blocked the electrophysiological and behavioral effects of 45 NPS. Thus, NPS is a novel tool to control amygdala output and pain-related affective 46 behaviors through a direct action on inhibitory ITC cells. 47 48