Exacerbated Headache-Related Pain in the Single Prolonged Stress Preclinical Model of Post-traumatic Stress Disorder

Activation of NOP receptor increases vulnerability to stress: role of glucocorticoids and CRF signaling

RATIONALE

Recently, we demonstrated that the activation of the nociceptin/orphanin FQ (N/OFQ) receptor (NOP) signaling facilitates depressive-like behaviors. Additionally, literature findings support the ability of the N/OFQ-NOP system to modulate the hypothalamic-pituitary-adrenal (HPA) axis.

OBJECTIVES

Considering that dysfunctional HPA axis is strictly related to stress-induced psychopathologies, we aimed to study the role of the HPA axis in the pro-depressant effects of NOP agonists.

METHODS

Mice were treated prior to stress with the NOP agonist Ro 65-6570, and immobility time in the forced swimming task and corticosterone levels were measured. Additionally, the role of endogenous glucocorticoids and CRF was investigated using the glucocorticoid receptor antagonist mifepristone and the CRF1 antagonist antalarmin in the mediation of the effects of Ro 65-6570.

RESULTS

The NOP agonist in a dose-dependent manner further increased the immobility of mice in the second swimming session compared to vehicle. By contrast, under the same conditions, the administration of the NOP antagonist SB-612111 before stress reduced immobility, while the antidepressant nortriptyline was inactive. Concerning in-serum corticosterone in mice treated with vehicle, nortriptyline, or SB-612111, a significant decrease was observed after re-exposition to stress, but no differences were detected in Ro 65-6570-treated mice. Administration of mifepristone or antalarmin blocked the Ro 65-6570-induced increase in the immobility time in the second swimming session.

CONCLUSIONS

Present findings suggest that NOP agonists increase vulnerability to depression by hyperactivating the HPA axis and then increasing stress circulating hormones and CRF1 receptor signaling.

Hangover headache and its behavioral changes in rats

Objectives

The present study aims to establish and evaluate a rat model for hangover headaches caused by alcoholic drinks.

Materials and Methods

Chronic migraine (CM) model rats were divided into 3 groups, and intragastrically administered alcoholic drinks (sample A, B, or C) to simulate hangover headache attacks. The withdrawal threshold for the hind paw/face and the thermal latency of hind paw withdrawal were detected after 24 hr. Serum was collected from the periorbital venous plexus of rats in each group, and enzymatic immunoassays were used to determine the serum levels of calcitonin gene-related peptide (CGRP), substance P (SP), and nitric oxide (NO).

Results

Compared with the control group, the mechanical hind paw pain threshold was significantly lower in rats administered Samples A and B after 24 hr; however, no significant difference was observed across groups for the thermal pain threshold. The mechanical threshold for periorbital pain was only significantly reduced in rats administered Sample A. Immunoassays further indicated that serum levels of SP in the group administered Sample A were significantly higher than those in the control group; the serum levels of NO and CGRP were significantly higher in the group of rats receiving Sample B.

Conclusion

We successfully developed an effective and safe rat model for investigating alcohol drink induced hangover headaches. This model could be used to investigate the mechanisms associated with hangover headaches for the development of novel and promising candidates for the future treatment or prophylaxis of hangover headaches.

Therapeutic potential of nociceptin/orphanin FQ peptide (NOP) receptor modulators for treatment of traumatic brain injury, traumatic stress, and their co-morbidities

The nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor is a member of the opioid receptor superfamily with N/OFQ as its endogenous agonist. Wide expression of the NOP receptor and N/OFQ, both centrally and peripherally, and their ability to modulate several biological functions has led to development of NOP receptor modulators by pharmaceutical companies as therapeutics, based upon their efficacy in preclinical models of pain, anxiety, depression, Parkinson's disease, and substance abuse. Both posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) are debilitating conditions that significantly affect the quality of life of millions of people around the world. PTSD is often a consequence of TBI, and, especially for those deployed to, working and/or living in a war zone or are first responders, they are comorbid. PTSD and TBI share common symptoms, and negatively influence outcomes as comorbidities of the other. Unfortunately, a lack of effective therapies or therapeutic agents limits the long term quality of life for either TBI or PTSD patients. Ours, and other groups, demonstrated that PTSD and TBI preclinical models elicit changes in the N/OFQ-NOP receptor system, and that administration of NOP receptor ligands alleviated some of the neurobiological and behavioral changes induced by brain injury and/or traumatic stress exposure. Here we review the past and most recent progress on understanding the role of the N/OFQ-NOP receptor system in PTSD and TBI neurological and behavioral sequelae. There is still more to understand about this neuropeptide system in both PTSD and TBI, but current findings warrant further examination of the potential utility of NOP modulators as therapeutics for these disorders and their co-morbidities. We advocate the development of standards for common data elements (CDE) reporting for preclinical PTSD studies, similar to current preclinical TBI CDEs. That would provide for more standardized data collection and reporting to improve reproducibility, interpretation and data sharing across studies.

Effects of oxytocin on responses to nociceptive and non-nociceptive stimulation in the upper central nervous system

Oxytocin is known as a social bonding hormone, but it also functions as an anxiolytic or analgesic neurotransmitter. When oxytocin regulates pain or anxiousness centrally as a neurotransmitter, it is secreted by neurons and directly projected to targeted regions. Although the function of oxytocin at the spinal level is well studied, its effects at the supraspinal level are poorly understood. We aimed to investigate the effect of oxytocin at the supraspinal level in vivo using C57BL/6J (wild-type [WT]), oxytocin-deficient (Oxt^-/-), oxytocin receptor-deficient (Oxtr^-/-), and oxytocin receptor-Venus (Oxtr^Venus/+) mice lines. Response thresholds in Oxtr^-/- mice in Hargreaves and von-Frey tests were significantly lower than those in WT mice, whereas open field and light/dark tests showed no significant differences. Moreover, response thresholds in Oxt^-/- mice were raised to those in WT mice after oxytocin administration. Following the Hargreaves test, we observed the co-localisation of c-fos with Venus or the oxytocin receptor in the periaqueductal gray (PAG), medial amygdala (MeA), and nucleus accumbens (NAc) regions in Oxtr^Venus/+ mice. Furthermore, in the PAG, MeA, and NAc regions, the co-localisation of oxytocin with c-fos and gamma-aminobutyric acid was much stronger in Oxtr^-/- mice than in WT mice. However, following von-Frey test, the same findings were observed only in the MeA and NAc regions. Our results suggest that oxytocin exerts its analgesic effect on painful stimulation via the PAG region and a self-protective effect on unpleasant stimulation via the MeA and NAc regions.

Nociceptin/orphanin FQ receptor system blockade as an innovative strategy for increasing resilience to stress

The ability to successfully cope with stress is known as 'resilience', and resilient individuals are less prone to develop psychopathologies. Understanding the neurobiological mechanisms of resilience may be instrumental to improve current therapies and benefit high-risk subjects. This review summarizes the complex interplay that exists between physiological and pathological responses to stressful events and the nociceptin/orphanin FQ (N/OFQ) - N/OFQ receptor (NOP) system, including: the effects of stress in regulating N/OFQ release and NOP expression; the ability of the N/OFQ-NOP system to modulate the hypothalamic-pituitary-adrenal axis; behavioral studies; and evidence in humans correlating this peptidergic system with psychopathologies. Available findings support the view that N/OFQ signaling stimulates the hypothalamic-pituitary-adrenal axis, thus increasing stress circulating hormones and corticotropin-releasing factor signaling. Additionally, activation of the NOP receptor inhibits monoamine transmission, including 5-HT, and this may contribute to maladaptive outcomes of stress. Ultimately, the N/OFQ system seems to have an important role in stress vulnerability, and blockade of NOP signaling may provide an innovative strategy for the treatment of stress related psychopathologies.

Understanding Opioid Actions, Pain and Analgesia: A Tribute to Dr. Gavril Pasternak

This special issue is a tribute to our mentor, colleague and friend, Gavril W. Pasternak, MD, PhD. Homage to the breadth and depth of his work (~ 450 publications) over a 40 career in pharmacology and medicine cannot be captured fully in one special issue, but the 22 papers collected herein represent seven of the topics near and dear to Gav's heart, and the colleagues, friends and mentees who held him near to theirs. The seven themes include: (1) sites and mechanisms of opioid actions in vivo; (2) development of novel analgesic agents; (3) opioid tolerance, withdrawal and addiction: mechanisms and treatment; (4) opioid receptor splice variants; (5) novel research tools and approaches; (6) receptor signaling and crosstalk in vitro; and (7) mentorship. This introduction to the issue summarizes contributions and includes formal and personal remembrances of Gav that illustrate his personality, warmth, and dedication to making a difference in patient care and people's lives.