Beyond reproduction: the role of progesterone in neuropathic pain after spinal cord injury

Therapeutic potential of progesterone in spinal cord injury-induced neuropathic pain: At the crossroads between neuroinflammation and N-methyl-D-aspartate receptor

In recent decades, an area of active research has supported the notion that progesterone promotes a wide range of remarkable protective actions in experimental models of nervous system trauma or disease, and has also provided a strong basis for considering this steroid as a promising molecule for modulating the complex maladaptive changes that lead to neuropathic pain, especially after spinal cord injury. In this review, we intend to give the readers a brief appraisal of the main mechanisms underlying the increased excitability of the spinal circuit in the pain pathway after trauma, with particular emphasis on those mediated by the activation of resident glial cells, the subsequent release of proinflammatory cytokines and their impact on N-methyl-D-aspartate receptor function. We then summarize the available preclinical data pointing to progesterone as a valuable repurposing molecule for blocking critical cellular and molecular events that occur in the dorsal horn of the injured spinal cord and are related to the development of chronic pain. Since the treatment and management of neuropathic pain after spinal injury remains challenging, the potential therapeutic value of progesterone opens new traslational perspectives to prevent central pain.

Effect of Exercises on Central and Endocrine System for Pain Modulation in Primary Dysmenorrhea

Dysmenorrhea is the term for describing complex menstrual flow and painful spasmodic cramps during menstruation, and pain without any pathology is considered Primary Dysmenorrhea (PD). It is the most frequent ailment among women of all ages and races. The pain is dull and throbbing in character and occurs in the lower back and abdomen. Symptoms commonly appear 6 to 12 months after menarche, with the most significant incidence in the late teen and early twenties. Physical exercise is nearly a new non-medical intervention to relieve PD associated pain. Aerobics, stretching and Resistive exercises for 8-12 weeks, either supervised or unsupervised, relieves pain. Exercises are believed to cause hormonal changes in the uterine lining, which reduces PD symptoms. Researchers have presumed different pain-relieving methods, ranging from non-opioids to opioids to hormonal for variations in pain sensitivity. Exercise-induced analgesia provides the central pathway as the primary mechanism for pain reduction while, another way to reducing pain in PD may be a hormonal interaction. The hormonal changes causing exercise-induced pain modulation during the menstruation cycle is not clearly understood and the interaction and activation of all the central and endocrine components, which is a complex mechanism, is also not explained clearly. This study briefly reviews the physiological mechanism of Exercise-induced analgesia and its potent roles in controlling the pathogenesis of PD for pain relief.

Neural stem cell transplantation inhibits glial cell proliferation and P2X receptor-mediated neuropathic pain in spinal cord injury rats

P2X4 and P2X7 receptors play an important role in neuropathic pain after spinal cord injury. Regulation of P2X4 and P2X7 receptors can obviously reduce pain hypersensitivity after injury. To investigate the role of neural stem cell transplantation on P2X receptor-mediated neuropathic pain and explore related mechanisms, a rat model of spinal cord injury was prepared using the free-falling heavy body method with spinal cord segment 10 as the center. Neural stem cells were injected into the injured spinal cord segment using a micro-syringe. Expression levels of P2X4 and P2X7 receptors, neurofilament protein, and glial fibrillary acidic protein were determined by immunohistochemistry and western blot assay. In addition, sensory function was quantitatively assessed by current perception threshold. The Basso-Beattie-Bresnahan locomotor rating scale was used to assess neuropathological pain. The results showed that 4 weeks after neural stem cell transplantation, expression of neurofilament protein in the injured segment was markedly increased, while expression of glial fibrillary acidic protein and P2X4 and P2X7 receptors was decreased. At this time point, motor and sensory functions of rats were obviously improved, and neuropathic pain was alleviated. These findings demonstrated that neural stem cell transplantation reduced overexpression of P2X4 and P2X7 receptors, activated locomotor and sensory function reconstruction, and played an important role in neuropathic pain regulation after spinal cord injury. Therefore, neural stem cell transplantation is one potential option for relieving neuropathic pain mediated by P2X receptors.

Daily Fluctuations of Progesterone and Testosterone Are Associated With Fibromyalgia Pain Severity

The purpose of this longitudinal blood sampling study was to examine relationships between sex hormones and fibromyalgia pain. Eight women meeting case definition criteria for fibromyalgia provided venous blood samples and reported their fibromyalgia pain severity over 25 consecutive days. All women exhibited normal menstrual cycles and were not taking oral contraceptives. Cortisol, and the sex hormones estradiol, progesterone, and testosterone, were assayed from serum. A linear mixed model was used to determine if fluctuations of sex hormones were associated with changes in pain severity. In the entire sample, day to day changes in progesterone (P = .002) as well as testosterone (P = .015) were significantly and inversely correlated with pain severity. There was no relationship between estradiol and pain (P = .551) or cortisol and pain (P = .633). These results suggest that progesterone and testosterone play a protective role in fibromyalgia pain severity. Sex and other hormones may serve to increase as well as decrease fibromyalgia pain severity.

PERSPECTIVE

Sex hormones fluctuate normally in women with fibromyalgia, but may still contribute to pain severity.

Hormonal therapy in traumatic spinal cord injury

Traumatic spinal cord injuries are major health problems and the underlying pathophysiological events and treatment strategies are currently under investigation. In this article, we critically reviewed the literature investigating the effects of estrogen, progesterone, and human chorionic gonadotropin on spinal cord damage or preservation following traumatic spinal cord injury. The National Library of Medicine database was searched through December 2016 using PubMed for articles addressing the clinical relevance of the hormones to improve neural structural integrity following traumatic spinal cord injury. It was found that each of these hormones, through varied mechanisms, could serve to reduce the harmful effects associated with spinal cord injury, and could aid in restoring some function to the injured spinal cord in the animal models. The most striking effects were seen in the reduction of inflammation commonly linked to injury of the central nervous system. The effects of human chorionic gonadotropin administration following spinal cord injury have received far less attention than those of either estrogen or progesterone, and additional inquiry could be of general benefit. In this article, we discussed the outstanding questions and suggested future directions for further investigation.