Neuroinflammation drives sex-dependent effects on pain and negative affect in a murine model of repeated mild traumatic brain injury

Abstract

The Center for Disease Control and Prevention estimates that 75% of reported cases of traumatic brain injury (TBI) are mild, where chronic pain and depression are 2 of the most common symptoms. In this study, we used a murine model of repeated mild TBI to characterize the associated pain hypersensitivity and affective-like behavior and to what extent microglial reactivity contributes to these behavioral phenotypes. Male and female C57BL/6J mice underwent sham or repeated mild traumatic brain injury (rmTBI) and were tested for up to 9 weeks postinjury, where an anti-inflammatory/neuroprotective drug (minocycline) was introduced at 5 weeks postinjury in the drinking water. Repeated mild traumatic brain injury mice developed cold nociceptive hypersensitivity and negative affective states, as well as increased locomotor activity and risk-taking behavior. Minocycline reversed negative affect and pain hypersensitivities in male but not female mice. Repeated mild traumatic brain injury also produced an increase in microglial and brain-derived neurotropic factor mRNA transcripts in limbic structures known to be involved in nociception and affect, but many of these changes were sex dependent. Finally, we show that the antiepileptic drug, gabapentin, produced negative reinforcement in male rmTBI mice that was prevented by minocycline treatment, whereas rmTBI female mice showed a place aversion to gabapentin. Collectively, pain hypersensitivity, increased tonic-aversive pain components, and negative affective states were evident in both male and female rmTBI mice, but suppression of microglial reactivity was only sufficient to reverse behavioral changes in male mice. Neuroinflammation in limbic structures seems to be a contributing factor in behavioral changes resulting from rmTBI.

NPD1/GPR37 axis protects painful traumatic brain injury and its complications

“…Next, we aimed to determine whether gliosis and neuroinflammation (6) are involved in the development of functional deficits of TBI and the protective effects of NPD1. To this end, we utilized IF to visualize astrocytes and microglia (Fig.…”

Minimally invasive serial collection of cerebrospinal fluid reveals sex-dependent differences in neuroinflammation in a rat model of mild traumatic brain injury

“…In a recent publication, Liu et al reported that males, but not females, treated with minocycline after a repeat mTBI (rmTBI) experienced an increased cold thermal threshold and decreased anxiety-like behavior. There was also sex differences in the microglial response to rmTBI as both males and females exhibited increased microglia and brain-derived neurotrophic factor (BDNF) mRNA in the anterior cingular cortex, but only males saw an increase in BDNF in the nucleus accumbens 23 . Another sex difference noted in the literature is the effect of regulatory T cells (Tregs) on microglial activation.…”