Involvement of A5/A7 noradrenergic neurons and B2 serotonergic neurons in nociceptive processing:a fiber photometry study

In the central nervous system,the A6 noradrenaline(NA)and the B3 serotonin(5-HT)cell groups are well-recognized players in the descending antinociceptive system,while other NA/5-HT cell groups are not well characterized.A5/A7 NA and B25-HT cells project to the spinal horn and form descending pathways.We recorded G-Ca MP6 green fluorescence signal intensities in the A5/A7 NA and the B25-HT cell groups of awake mice in response to acute tail pinch stimuli,acute heat stimuli,and in the context of a non-noxious control test,using fiber photometry with a calcium imaging system.We first introduced G-Ca MP6 in the A5/A7 NA or B25-HT neuronal soma,using transgenic mice carrying the tetracycline-controlled transactivator transgene under the control of either a dopamineβ-hydroxylase or a tryptophan hydroxylase-2 promoters and by the site-specific injection of adeno-associated virus(AAV-Tet O(3 G)-G-Ca MP6).After confirming the specific expression patterns of G-Ca MP6,we recorded G-Ca MP6 green fluorescence signals in these sites in awake mice in response to acute nociceptive stimuli.G-Ca MP6 fluorescence intensity in the A5,A7,and B2 cell groups was rapidly increased in response to acute nociceptive stimuli and soon after,it returned to baseline fluorescence intensity.This was not observed in the non-noxious control test.The results indicate that acute nociceptive stimuli rapidly increase the activities of A5/A7 NA or B25-HT neurons but the non-noxious stimuli do not.The present study suggests that A5/A7 NA or B25-HT neurons play important roles in nociceptive processing in the central nervous system.We suggest that A5/A7/B2 neurons may be new therapeutic targets.All performed procedures were approved by the Institutional Animal Use Committee of Kagoshima University(MD17105)on February 22,2018.

A13 dopamine cell group in the zona incerta is a key neuronal nucleus in nociceptive processing

In stressful modern society, pain caused by physical and mental disorders is an increasing social health problem all over the world.Physical and mental activity depends on the state of various neurotransmitters in the central nervous system(CNS).Monoaminergic systems play important roles in regulating physiological functions including nociception.It is well known that in the CNS, there are descending pathways related to nociceptive processing known as the descending antinociceptive system(DAS).Noradrenalin and serotonin are major components of the DAS that form the locus coeruleus(LC)-spinal dorsal horn noradrenergic circuit and periaqueductal gray(PAG)-rostro ventricular medulla(RVM)-spinal dorsal horn serotonergic circuit(Jordan et al., 2008).Dopaminergic pathways also play roles in regulating nociceptive processing in the CNS.