Regulation of headache response and transcriptomic network by the trigeminal ganglion clock.

OBJECTIVE: To characterize the circadian features of the trigeminal ganglion in a mouse model of headache. BACKGROUND: Several headache disorders, such as migraine and cluster headache, are known to exhibit distinct circadian rhythms of attacks. The circadian basis for these rhythmic pain responses, however, remains poorly understood. METHODS: We examined trigeminal ganglion ex vivo and single-cell cultures from Per2::LucSV reporter mice and performed immunohistochemistry. Circadian behavior and transcriptomics were investigated using a novel combination of trigeminovascular and circadian models: a nitroglycerin mouse headache model with mechanical thresholds measured every 6 h, and trigeminal ganglion RNA sequencing measured every 4 h for 24 h. Finally, we performed pharmacogenomic analysis of gene targets for migraine, cluster headache, and trigeminal neuralgia treatments as well as trigeminal ganglion neuropeptides; this information was cross-referenced with our cycling genes from RNA sequencing data to identify potential targets for chronotherapy. RESULTS: The trigeminal ganglion demonstrates strong circadian rhythms in both ex vivo and single-cell cultures, with core circadian proteins found in both neuronal and non-neuronal cells. Using our novel behavioral model, we showed that nitroglycerin-treated mice display circadian rhythms of pain sensitivity which were abolished in arrhythmic Per1/2 double knockout mice. Furthermore, RNA-sequencing analysis of the trigeminal ganglion revealed 466 genes that displayed circadian oscillations in the control group, including core clock genes and clock-regulated pain neurotransmitters. In the nitroglycerin group, we observed a profound circadian reprogramming of gene expression, as 331 of circadian genes in the control group lost rhythm and another 584 genes gained rhythm. Finally, pharmacogenetics analysis identified 10 genes in our trigeminal ganglion circadian transcriptome that encode target proteins of current medications used to treat migraine, cluster headache, or trigeminal neuralgia. CONCLUSION: Our study unveiled robust circadian rhythms in the trigeminal ganglion at the behavioral, transcriptomic, and pharmacogenetic levels. These results support a fundamental role of the clock in pain pathophysiology. PLAIN LANGUAGE SUMMARY: Several headache diseases, such as migraine and cluster headache, have headaches that occur at the same time each day. We learned that the trigeminal ganglion, an important pain structure in several headache diseases, has a 24-hour cycle that might be related to this daily cycle of headaches. Our genetic analysis suggests that some medications may be more effective in treating migraine and cluster headache when taken at specific times of the day.

Clock-Modulating Activities of the Anti-Arrhythmic Drug Moricizine.

Dysregulated circadian functions contribute to various diseases, including cardiovascular disease. Much progress has been made on chronotherapeutic applications of drugs against cardiovascular disease (CVD); however, the direct effects of various medications on the circadian system are not well characterized. We previously conducted high-throughput chemical screening for clock modulators and identified an off-patent anti-arrhythmic drug, moricizine, as a clock-period lengthening compound. In Per2:LucSV reporter fibroblast cells, we showed that under both dexamethasone and forskolin synchronization, moricizine was able to increase the circadian period length, with greater effects seen with the former. Titration studies revealed a dose-dependent effect of moricizine to lengthen the period. In contrast, flecainide, another Class I anti-arrhythmic, showed no effects on circadian reporter rhythms. Real-time qPCR analysis in fibroblast cells treated with moricizine revealed significant circadian time- and/or treatment-dependent expression changes in core clock genes, consistent with the above period-lengthening effects. Several clock-controlled cardiac channel genes also displayed altered expression patterns. Using tissue explant culture, we showed that moricizine was able to significantly prolong the period length of circadian reporter rhythms in atrial ex vivo cultures. Using wild-type C57BL/6J mice, moricizine treatment was found to promote sleep, alter circadian gene expression in the heart, and show a slight trend of increasing free-running periods. Together, these observations demonstrate novel clock-modulating activities of moricizine, particularly the period-lengthening effects on cellular oscillators, which may have clinical relevance against heart diseases.

Trigeminal Autonomic Cephalalgias.

The trigeminal autonomic cephalalgias (TACs) are a group of primary headache syndromes all marked by unilateral headache and ipsilateral cranial autonomic features. The TACs include cluster headache, paroxysmal hemicrania, short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing, and hemicrania continua. Pathophysiology includes the trigeminal pain system, autonomic system, hypothalamus, and more recently an identified role for the vagus nerve. Diagnosis is made after looking at headache frequency, duration, and accompanying symptoms. Each TAC has its own unique treatment, which is discussed in depth.

Emerging relevance of circadian rhythms in headaches and neuropathic pain.

Circadian rhythms of physiology are the keys to health and fitness, as dysregulation, by genetic mutations or environmental factors, increases disease risk and aggravates progression. Molecular and physiological studies have shed important light on an intrinsic clock that drives circadian rhythms and serves essential roles in metabolic homoeostasis, organ physiology and brain functions. One exciting new area in circadian research is pain, including headache and neuropathic pain for which new mechanistic insights have recently emerged. For example, cluster headache is an intermittent pain disorder with an exceedingly precise circadian timing, and preliminary evidence is emerging linking several circadian components (eg, Clock and Nr1d1) with the disease. In this review, we first discuss the broad metabolic and physiological relevance of the circadian timing system. We then provide a detailed review of the circadian relevance in pain disease and physiology, including cluster headache, migraine, hypnic headache and neuropathic pain. Finally, we describe potential therapeutic implications, including existing pain medicines and novel clock-modulating compounds. The physiological basis for the circadian rhythms in pain is an exciting new area of research with profound basic and translational impact.

Thalamocortical connections of functional zones in posterior parietal cortex and frontal cortex motor regions in New World monkeys.

Posterior parietal cortex (PPC) links primate visual and motor systems and is central to visually guided action. Relating the anatomical connections of PPC to its neurophysiological functions may elucidate the organization of the parietal-frontal network. In owl and squirrel monkeys, long-duration electrical stimulation distinguished several functional zones within the PPC and motor/premotor cortex (M1/PM). Multijoint forelimb movements reminiscent of reach, defense, and grasp behaviors characterized each functional zone. In PPC, functional zones were organized parallel to the lateral sulcus. Thalamocortical connections of PPC and M1/PM zones were investigated with retrograde tracers. After several days of tracer transport, brains were processed, and labeled cells in thalamic nuclei were plotted. All PPC zones received dense inputs from the lateral posterior nucleus and the anterior pulvinar. PPC zones received additional projections from ventral lateral (VL) divisions of motor thalamus, which were also the primary source of input to M1/PM. Projections to PPC from rostral motor thalamus were sparse. Dense projections from ventral posterior (VP) nucleus of somatosensory thalamus distinguished the rostrolateral grasp zone from the other PPC zones. PPC connections with VL and VP provide links to cerebellar nuclei and the somatosensory system, respectively, that may integrate PPC functions with M1/PM.