Abstract / Summary
Abstract Background Chronic migraine is characterized by recurrent headache and persistent pain hypersensitivity, often accompanied by sensory symptoms such as photophobia. Although central sensitization within thalamic and brainstem circuits is thought to contribute to migraine chronification, the contribution of the anterior pretectal nucleus (APT), a midbrain region implicated in nociceptive and sensory processing, remains poorly understood. Methods Repeated nitroglycerin (NTG) administration was used to induce cephalic and extracephalic cutaneous mechanical hypersensitivity. Neuronal activity in the anterior and posterior APT was assessed by c-Fos immunostaining and whole-cell patch-clamp recordings. CaMKII- and GABA-immunoreactive neuronal populations in the anterior APT (aAPT) were examined by double immunofluorescence staining. Chemogenetic tools were used to selectively activate or inhibit CaMKII- or VGAT-positive aAPT neurons, and behavioral responses were assessed using von Frey mechanical withdrawal threshold testing and the light/dark box test. Results Repeated NTG administration induced sustained hind-paw and periorbital mechanical hypersensitivity and transient changes in light/dark box behavior. c-Fos expression was selectively increased in the aAPT, but not in the posterior APT (pAPT), and aAPT c-Fos density was negatively correlated with mechanical withdrawal thresholds. Patch-clamp recordings showed that aAPT neurons from NTG-treated mice exhibited increased evoked firing and spontaneous excitatory postsynaptic current frequency, whereas pAPT neurons were unchanged. c-Fos labeling was observed in both CaMKII- and GABA-immunoreactive cells in the aAPT. Chemogenetic activation of either CaMKII- or VGAT-positive aAPT neurons significantly reduced mechanical withdrawal thresholds, whereas inhibition of either population attenuated established NTG-induced cutaneous mechanical hypersensitivity. Conclusions These findings identify the aAPT as a midbrain region selectively engaged during repeated NTG-induced cephalic and extracephalic mechanical hypersensitivity. CaMKII- and VGAT-positive neuronal populations show convergent functional contributions to cutaneous mechanical hypersensitivity, supporting a role for heterogeneous aAPT neuronal populations in NTG-associated nociceptive processing.