Enhanced post-traumatic headache-like behaviors and diminished contribution of peripheral CGRP in female rats following a mild closed head injury

Abstract

IntroductionFemales are thought to have increased risk of developing posttraumatic headache (PTH) following a traumatic head injury, or concussion. However, the processes underlying this susceptibility remain unclear. We previously explored the development of PTH-like pain behaviors in a novel rat model of mild closed head injury, along with the ability of sumatriptan and an anti-calcitonin-gene-related peptide monoclonal antibody to ameliorate these behaviors. Here, we explored the development of PTH-like behaviors and the effectiveness of these headache therapies in females subjected to the same head trauma protocol. MethodsAdult female Sprague Dawley rats were subjected to a mild closed head injury using a weight-drop device. Characterization of headache and pain related behaviors included assessment of changes in cutaneous cephalic and extracephalic tactile pain sensitivity, using von Frey monofilaments. Sensitivity to headache/migraine triggers was tested by examining the effect of systemic administration of a low-dose of glyceryl trinitrate (GTN). Treatments included acute systemic administration of sumatriptan and repeated systemic administration of a mouse anti-calcitonin-gene-related peptide monoclonal antibody. Serum levels of calcitonin-gene-related peptide were measured at various time points in females and males after the head injury. ResultsFemale rats subjected to a mild closed head injury developed cutaneous mechanical hyperalgesia, that was limited to the cephalic region, and was resolved 4 weeks later. Cephalic pain hypersensitivity was ameliorated by treatment with sumatriptan, but was resistant to an early and prolonged treatment with the anti-CGRP monoclonal antibody. Following the resolution of the head injury-evoked cephalic hypersensitivity, administration of GTN produced a renewed and pronounced cephalic and extracephalic pain hypersensitivity that was inhibited by sumatriptan, but only partially by the anti-CGRP treatment. CGRP serum levels were elevated in females but not in males at 7 days post head injury. ConclusionsDevelopment of PTH-like pain behaviors following a mild closed head injury, and responsiveness to treatment in rats is sexually dimorphic. When compared to males, female rats display a prolonged state of cephalic hyperalgesia, increased responsiveness to a headache trigger, and a poorer effectiveness of an early and prolonged anti-CGRP treatment. The increased risk of females to develop PTH may be linked to enhanced responsiveness of peripheral and/or central pain pathways and a mechanism independent of peripheral CGRP signaling.