Characterizing Sex Differences in Depressive-Like Behavior and Glial Brain Cell Changes Following Peripheral Nerve Injury in Mice

Chronic pain and depression are intimately linked; the combination of the two leads to higher health care costs, lower quality of life, and worse treatment outcomes with both conditions exhibiting higher prevalence among women. In the current study, we examined the development of depressive-like behavior in male and female mice using the spared nerve injury (SNI) model of neuropathic pain. Males displayed increased immobility on the forced-swim test - a measure of depressive-like behavior - 2 weeks following injury, while females developed depressive-like behavior at 3-week. Since the pathogenesis of chronic pain and depression may involve overlapping mechanisms including the activation of microglial cells, we explored glial cell changes in brain regions associated with pain processing and affect. Immunohistochemical analyses revealed that microglial cells were more numerous in female SNI mice in the contralateral ventral anterior cingulate cortex (ACC), a brain region important for pain processing and affect behavior, 2-week following surgery. Microglial cell activation was not different between any of the groups for the dorsal ACC or nucleus accumbens. Analysis of astrocyte density did not reveal any significant changes in glial fibrillary acidic protein (GFAP) staining in the ACC or nucleus accumbens. Overall, the current study characterized peripheral nerve injury induced depression-like behavior in male and female mice, which may be associated with different patterns of glial cell activation in regions important for pain processing and affect.

Cage-lid hanging behavior as a translationally relevant measure of pain in mice

ABSTRACT

The development of new analgesic drugs has been hampered by the inability to translate preclinical findings to humans. This failure is due in part to the weak connection between commonly used pain outcome measures in rodents and the clinical symptoms of chronic pain. Most rodent studies rely on the use of experimenter-evoked measures of pain and assess behavior under ethologically unnatural conditions, which limits the translational potential of preclinical research. Here, we addressed this problem by conducting an unbiased, prospective study of behavioral changes in mice within a natural homecage environment using conventional preclinical pain assays. Unexpectedly, we observed that cage-lid hanging, a species-specific elective behavior, was the only homecage behavior reliably impacted by pain assays. Noxious stimuli reduced hanging behavior in an intensity-dependent manner, and the reduction in hanging could be restored by analgesics. Finally, we developed an automated approach to assess hanging behavior. Collectively, our results indicate that the depression of hanging behavior is a novel, ethologically valid, and translationally relevant pain outcome measure in mice that could facilitate the study of pain and analgesic development.

Revealing brain mechanisms of mTOR-mediated translational regulation: Implications for chronic pain

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mTOR is a major regulator of protein translation.

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mTOR serves an important role in neural plasticity.

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mTOR signalling in the brain as a pathology for neurological disorder is known.

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mTOR signalling in the brain as a chronic pain mechanism is understudied.

In the spinal cord, altered protein transcription and translation have received a lot of recent attention for their role in neural plasticity, a major mechanism leading to the development of chronic pain. However, changes in brain plasticity are also associated with the maintenance of pain symptoms, but these cellular mechanisms remain less clear. The mechanistic/mammalian target of rapamycin (mTOR) is a master regulator of protein synthesis, and controls several neuronal functions, including neural plasticity. While aberrant changes in mTOR signaling are associated with sensitization of the pain pathway (sensory neurons and spinal cord), there are various nervous system diseases that have pain as a comorbidity and altered mTOR activity in the brain. Here, we provide a brief review of mTOR changes in the brain that are associated with some neurological disorders and focus on how these changes may be relevant to the pain of the underlying condition and chronic pain itself.

Validation of the Greek version of the Severe Respiratory Insufficiency questionnaire

BACKGROUND

The Severe Respiratory Insufficiency (SRI) questionnaire is a multidimensional, well-validated tool for the assessment of health-related quality of life (HRQL) in patients with severe chronic respiratory failure (CRF), due to a variety of underlying disorders. The aim of this study was to validate the SRI questionnaire in the Greek language (Gr-SRI).

METHODS

Reliability and validity analyses were performed for the Gr-SRI using data of 136 consecutive patients with CRF, due to chronic obstructive pulmonary disease (COPD) or non-COPD respiratory diseases (kyphoscoliosis, obesity-hypoventilation, and post-tuberculosis sequelae). Sixty-three patients (46.3 %) were under long-term oxygen therapy (LTOT), while 73 (53.7 %) under long-term non-invasive mechanical ventilation at home (HMV), either with or without LTOT.

RESULTS

Cronbach's alpha was high for the Summary Score of the SRI (0.86) showing high internal consistency, comparable to that of the original German version. The results of the principal component analysis on the SRI Summary Score produced a one-factor construct with a variance of 54 %, which confirmed a single Summary Score for the Greek SRI also. The highest and the lowest scores were detected in Respiratory Complaints and Physical Functioning subscales, respectively. The SRI was capable of discriminating COPD patients and non-COPD patients, with COPD patients having lower mean SRI scores, but no difference was observed between COPD patients under HMV or LTOT.

CONCLUSIONS

Greek SRI has high psychometric properties qualifying its use for HRQL assessment in patients with CRF. HIPPOKRATIA 2017, 21(4): 186-190.