Thermal gradient ring reveals thermosensory changes in diabetic peripheral neuropathy in mice

An improved conflict avoidance assay reveals modality-specific differences in pain hypersensitivity across sexes

ABSTRACT

Abnormal encoding of somatosensory modalities (ie, mechanical, cold, and heat) are a critical part of pathological pain states. Detailed phenotyping of patients' responses to these modalities have raised hopes that analgesic treatments could one day be tailored to a patient's phenotype. Such precise treatment would require a profound understanding of the underlying mechanisms of specific pain phenotypes at molecular, cellular, and circuitry levels. Although preclinical pain models have helped in that regard, the lack of a unified assay quantifying detailed mechanical, cold, and heat pain responses on the same scale precludes comparing how analgesic compounds act on different sensory phenotypes. The conflict avoidance assay is promising in that regard, but testing conditions require validation for its use with multiple modalities. In this study, we improve upon the conflict avoidance assay to provide a validated and detailed assessment of all 3 modalities within the same animal, in mice. We first optimized testing conditions to minimize the necessary amount of training and to reduce sex differences in performances. We then tested what range of stimuli produce dynamic stimulus-response relationships for different outcome measures in naive mice. We finally used this assay to show that nerve injury produces modality-specific sex differences in pain behavior. Our improved assay opens new avenues to study the basis of modality-specific abnormalities in pain behavior.

Morphological and Neurological Impairments Induced by Chronic Administration of Dimethyl Sulfoxide in Mice

We studied the influence of DMSO administered ad libitum with drinking water in concentrations of 0.01, 0.1, and 1% for 4 and 6 weeks on pain sensitivity, motor coordination, and myelin content in the corpus callosum of C57BL/6 mice. After 6-week administration, DMSO in all studied concentrations decreased myelin content in the corpus callosum. Moreover, 4-week administration of 0.1% DMSO and 6-week administration of 1% DMSO increased the latency to fall in the rotarod test by 3.1 (p<0.05) and 5.1 (p<0.001) times, respectively. After 4-week administration of DMSO in concentrations of 0.01 and 0.1%, the latency of the tail flick response increased by 2.1 (p<0.05) and 1.8 times (p<0.001), respectively. Administration of DMSO in concentrations of 0.01 and 1% for 6 weeks led to a decrease of this parameter by 2.7 (p<0.05) and 3.8 times (p<0.01), respectively. Thus, DMSO in all studied concentrations decreased myelin content in the corpus callosum of C57BL/6 mice and modified motor coordination and pain sensitivity of animals.

Thermal gradient ring for analysis of temperature-dependent behaviors involving TRP channels in mice

There are a lot of temperature-sensitive proteins including transient receptor potential (TRP) channels. Some TRP channels are temperature receptors having specific activation temperatures in vitro that are within the physiological temperature range. Mice deficient in specific TRP channels show abnormal thermal behaviors, but the role of TRP channels in these behaviors is not fully understood. The Thermal Gradient Ring is a new apparatus that allows mice to freely move around the ring floor and not stay in a corner. The system can analyze various factors (e.g., 'Spent time', 'Travel distance', 'Moving speed', 'Acceleration') associated with temperature-dependent behaviors of TRP-deficient mice. For example, the Ring system clearly discriminated differences in temperature-dependent phenotypes between mice with diabetic peripheral neuropathy and TRPV1-/- mice, and demonstrated the importance of TRPV3 in temperature detection in skin. Studies using the Thermal Gradient Ring system can increase understanding of the molecular basis of thermal behaviors in mice and in turn help develop strategies to affect responses to different temperature conditions in humans.