Tuberomammillary histaminergic neurons are not required for behavioral responses in a Nitroglycerin-induced acute...

The investigation into the association between histamine and headache has persisted for nearly a century. Nevertheless, the functional role of the central histaminergic system in headache pathophysiology remains inadequately characterized. This study aims to elucidate the activation status of tuberomammillary nucleus (TMN) histaminergic neurons in mice during acute headache episodes and their impact on headache-related behavioral alterations. Using transgenic mouse models, immunofluorescence staining, and chemogenetic manipulation, we systematically evaluated the functionality of histaminergic neurons in acute headache. c-Fos expression analysis and calcium signaling measurements were utilized to assess TMN neuronal activation. Our findings indicated that nitroglycerin (NTG) stimulation did not significantly alter the activation level of TMN histaminergic neurons, with no statistically significant differences observed between NTG-treated and control groups (p = 0.48, p = 0.92). Furthermore, calcium probe and histamine probe techniques revealed no substantial changes in neuronal activity during acute headache phases, suggesting a non-critical role for these neurons in acute headache responses. Anatomical tracing confirmed sparse projections from TMN histaminergic neurons to the trigeminal complex (TCC), reinforcing their limited involvement in pain signal transmission. Collectively, our results challenge the purported significance of central histaminergic neurons in acute headache pathophysiology within the NTG-induced mouse model and suggest that TMN histaminergic neurons do not show detectable activation and are not required for the behavioral endpoints tested in an NTG-induced acute headache mouse model.