Activation of neuropeptide S‐expressing neurons in the locus coeruleus by corticotropin‐releasing factor

Key points Neuropeptide S (NPS) and its cognate receptor represent a recently discovered transmitter system in the brain modulating anxiety‐ and stress‐related behaviour. Using a transgenic NPS‐EGFP‐expressing mouse line, the present study shows that NPS‐expressing neurons are situated in close proximity to corticotropin‐releasing factor (CRF)‐containing fibres at the locus coeruleus in the brain stem and express the CRF receptor 1 (CRF1). CRF depolarizes NPS neurons via activation of the CRF1 receptor through two different ionic mechanisms (a decrease in potassium and an increase in cation conductance) involving the cAMP signalling pathway. After acute immobilization stress, NPS neurons display an increased expression of c‐fos. This study identifies a mechanism by which stress‐related CRF release might activate NPS neurons in the brain stem, thereby triggering NPS release in target areas such as the amygdala, and functioning as a negative feedback control to buffer stress responsiveness. Abstract A recently discovered neurotransmitter system, consisting of neuropeptide S (NPS), NPS receptor, and NPS‐expressing neurons in the brain stem, has received considerable interest due to its modulating influence on arousal, anxiety and stress responsiveness. Comparatively little is known about the properties of NPS‐expressing neurons. Therefore in the present study, a transgenic mouse line expressing enhanced green fluorescent protein (EGFP) in NPS neurons was used to characterize the cellular and functional properties of NPS‐expressing neurons located close to the locus coeruleus. Particular emphasis was on the influence of corticotropin‐releasing factor (CRF), given previous evidence of stress‐related activation of the NPS system. Upon acute immobilization stress, an increase in c‐fos expression was detected immunocytochemically in brain stem NPS‐EGFP neurons that also expressed the CRF receptor 1 (CRF1). NPS‐EGFP neurons were readily identified in acute slice preparations and responded to CRF application with a membrane depolarization capable of triggering action potentials. CRF‐induced responses displayed pharmacological properties indicative of CRF1 that were mediated by both a reduction in membrane potassium conductance and an increase in a non‐specific cation conductance different from the hyperpolarization‐activated cation conductance Ih, and involved protein kinase A signalling. In conclusion, stress exposure results in activation of brain stem NPS‐expressing neurons, involving a CRF1‐mediated membrane depolarization via at least two ionic mechanisms. These data provide evidence for a direct interaction between the CRF and the NPS system and thereby extend previous observations of NPS‐modulated stress responsiveness towards a mechanistic level.