Involvement of Corticotrophin-Releasing Factor and Orexin-A in Chronic Migraine and Medication Overuse Headache: Findings From Cerebrospinal Fluid

CRF regulates pain sensation by enhancement of corticoaccumbal excitatory synaptic transmission

Both peripheral and central corticotropin-releasing factor (CRF) systems have been implicated in regulating pain sensation. However, compared with the peripheral, the mechanisms underlying central CRF system in pain modulation have not yet been elucidated, especially at the neural circuit level. The corticoaccumbal circuit, a structure rich in CRF receptors and CRF-positive neurons, plays an important role in behavioral responses to stressors including nociceptive stimuli. The present study was designed to investigate whether and how CRF signaling in this circuit regulated pain sensation under physiological and pathological pain conditions. Our studies employed the viral tracing and circuit-, and cell-specific electrophysiological methods to label the CRF-containing circuit from the medial prefrontal cortex to the nucleus accumbens shell (mPFCCRF-NAcS) and record its neuronal propriety. Combining optogenetic and chemogenetic manipulation, neuropharmacological methods, and behavioral tests, we were able to precisely manipulate this circuit and depict its role in regulation of pain sensation. The current study found that the CRF signaling in the NAc shell (NAcS), but not NAc core, was necessary and sufficient for the regulation of pain sensation under physiological and pathological pain conditions. This process was involved in the CRF-mediated enhancement of excitatory synaptic transmission in the NAcS. Furthermore, we demonstrated that the mPFCCRF neurons monosynaptically connected with the NAcS neurons. Chronic pain increased the protein level of CRF in NAcS, and then maintained the persistent NAcS neuronal hyperactivity through enhancement of this monosynaptic excitatory connection, and thus sustained chronic pain behavior. These findings reveal a novel cell- and circuit-based mechanistic link between chronic pain and the mPFCCRF → NAcS circuit and provide a potential new therapeutic target for chronic pain.

Biology of Neuropeptides: Orexinergic Involvement in Primary Headache Disorders

Migraine is a very common, severe disabling condition that can last for days and strike multiple times per month. Attacks, often characterized by severe unilateral throbbing pain that is exacerbated by activity, are commonly preceded by several diverse symptoms including fatigue, irritability, and yawning. This premonitory (prodromal) phase represents the earliest identifiable feature of an attack that is a reliable predictor of ensuing headache. The diversity of these symptoms underlines the complex nature of migraine and focuses considerable attention on the hypothalamus due to its prominent role in homeostatic regulation allowing state dependent behavioral modifications. While multiple neurotransmitter and neuropeptide systems have been proposed to play a role in migraine, the current review will focus on the emerging role of the hypothalamic orexinergic system in primary headache disorders. Specifically the potential role of altered orexinergic signalling in premonitory symptomatology and the future potential of targeted orexinergic therapies that could with other approaches act during the premonitory phase to prevent the occurrence of the headache or reduce an individual's susceptibility to attacks by altering the brain's response to external and internal triggers.

Cross-talk between orexins (hypocretins) and the neuroendocrine axes (hypothalamic-pituitary axes)

Lesioning and electrical stimulation experiments carried out during the first half of the twentieth century showed that the lateral hypothalamic area (LHA) is involved in the neuroendocrine control of hormone secretion. However, the molecular basis of this phenomenon remained unclear until fifty years later when in 1998, two different laboratories discovered a new family of hypothalamic neuropeptides, the orexins or hypocretins (OX-A/Hcrt1 and OX-B/Hcrt2). Since then, remarkable evidence has revealed that orexins/hypocretins play a prominent role in regulating virtually all the neuroendocrine axes, acting as pivotal signals in the coordination of endocrine responses with regards to sleep, arousal and energy homeostasis. The clinical relevance of these actions is supported by human data showing impairment of virtually all the neuroendocrine axes in orexin/hypocretin-deficient narcoleptic patients. Here, we summarize more than ten years of knowledge about the orexins/hypocretins with particular focus on their role as neuroendocrine regulators. Understanding this aspect of orexin/hypocretin physiology could open new therapeutic possibilities in the treatment of sleep, energy homeostasis and endocrine pathologies.

Modulation of trigeminovascular processing: novel insights into primary headache disorders

Dysfunction of the descending circuitry that modulates nociceptive processing is thought to facilitate primary headache disorders such as migraine and cluster headache, either by reducing inhibition or increasing facilitation of neural signals. The identification of novel neurotransmitter systems (orexinergic, cannabinoid and dopaminergic) within this descending pathway and their interaction with 5-HT(1B/1D) (triptan) receptors provides important clues about several of the risk factors and comorbidities associated with primary headache disorders and indicates that triptans exert central as well as peripheral activity. Current research supports the early treatment of primary headache disorders in order to prevent structural changes in the brain and to minimize dysfunction in the descending modulation of pain control.

Modulation of trigeminovascular processing: novel insights into primary headache disorders

Dysfunction of the descending circuitry that modulates nociceptive processing is thought to facilitate primary headache disorders such as migraine and cluster headache, either by reducing inhibition or increasing facilitation of neural signals. The identification of novel neurotransmitter systems (orexinergic, cannabinoid and dopaminergic) within this descending pathway and their interaction with 5-HT(1B/1D) (triptan) receptors provides important clues about several of the risk factors and comorbidities associated with primary headache disorders and indicates that triptans exert central as well as peripheral activity. Current research supports the early treatment of primary headache disorders in order to prevent structural changes in the brain and to minimize dysfunction in the descending modulation of pain control.