The Role Of Parvalbumin-expressing Interneurons In The Ventrolateral Periaqueductal Gray In Migraine Pathophysiology

BackgroundThe pathophysiology of migraine remains unclear. The activation of the trigeminovascular system plays an important role. The trigeminovascular nociceptive traffic is under the modulation of endogenous descending modulation pathway. Migraine is a recurrent headache disorder manifesting in attacks lasting 4-72 hours. The endogenous descending modulation pathway may play a role in the termination of migraine. Ventrolateral periaqueductal is a key node in endogenous descending modulation pathway. Parvalbumin-expressing interneurons which are abundant in the vlPAG are critically involved in advanced computations in neuronal networks.ObjectiveTo explore the role of parvalbumin-expressing interneurons in the ventrolateral periaqueductal gray in the central modulation of migraine.Method1. Silencing the activity of Parvalbumin-expressing interneurons in the ventrolateral periaqueductal gray by using DREADD combined with the PV-Cre transgenic mice.To express the evolved human muscarinic receptor hM4Di, Cre-dependent AAV viruses were injected into the vlPAG region of PV-Cre mice bilaterally. Clozapine-N-oxide, the ligand of hM4Di, was used to silence the parvalbumin-expressing interneurons through intraperitoneal injection. This method has high temporal and spatial precision.2. Establish a model for migraine by electrical stimulation on dura mater adjacent to SSSForty-eight PV-cre mice were randomly divided into six groups (group 1,2,3, 4,5 and 6). The mice in group 1 received hM4Di injection and rizatriptan therapy before electrical stimulation on dura mater. The mice in group 2 received GFP injection and rizatriptan therapy before electrical stimulation on dura mater. The mice in group 3 received hM4Di injection and normal saline therapy before electrical stimulation on dura mater. The mice in group 4 received GFP injection and normal saline therapy before electrical stimulation on dura mater. The mice in group 5 received hM4Di injection without therapy and electrical stimulation on dura mater. The mice in group 6 received GFP injection without therapy and electrical stimulation on dura mater. Four weeks after the viruses injection into the vlPAG, the migraine model was established by electrical stimulation on dura mater adjacent to SSS. CNO was administrated by intraperitoneal injection once a day for four days.3. Behavioral analysisThe dura matter adjacent to SSS of the mice was electrically stimulated in group 1,2,3 and 4. Mice in group 5 and 6 received no electrical stimulation. Behaviour was recorded for 5 minutes after stimulation. Analyze the time of the excessive grooming, the numbers of excessive grooming and the numbers of head-flick.4. ImmunostainingGFP was used as the marker of hM4Di expression, PV-immunoreactivity as the marker of PV+interneurons and Fos-immunoreactivity as an indicator of the activated neurons in the midbrain.Results1. Among the mice received normal saline therapy before electrical stimulation on dura mater, silencing the PV+interneurons was associated with shorter excessive grooming time (1.3+0.6 vs.6.H2.0, P<0.01)2. The Fos-expressing neurons were located in the ventral tegmental area of midbrain. Among the mice received normal saline therapy before electrical stimulation on dura mater, silencing the PV+interneurons was associated with lower Fos expressing level in the midbrain (66.3+5.9 vs.110.0+4.7, P<0.05).Conclusion1. Silencing the PV+interneurons in the vlPAG plays a role in descending inhibition in migraine model mice through interaction with VTA.2. PV+ interneurons may be a target of antinociception.