Hindlimb Suspension Does Not Influence Mechanical Sensitivity, Epidermal Thickness, and Peripheral Nerve Density in the Glabrous Skin of the Rat Hind Paw

Abstract

Our aim was to investigate the influence of microgravity on the sensitivity of the skin to mechanical stimulation, epidermal thickness, peripheral nerve density in the upper dermis, and serum levels of a stress marker in a rat hindlimb suspension (HS) model. Thirty 8-week-old male Wistar rats were randomly divided into 3 groups: HS, n=10; sham HS, n=10; control, n=10. The suspension system was attached to rat tails in both the HS and sham-HS groups, but the hindlimbs were suspended only in the HS group. The HS and sham-HS groups were treated for 4 weeks. In behavioral tests using von-Frey filaments (n=5 in each group), mechanical hypersensitivity developed in the HS and sham HS groups. Serum corticosterone levels increased significantly in the HS and sham HS groups compared to the control group, and no changes in epidermal thickness or peripheral nerve density were observed immediately after the removal of HS (n=5 in each group). These data indicated that the mechanical hypersensitivity observed in the HS group was not caused by microgravity or inactivity, but rather by restraint stress. We suggest that microgravity does not affect skin sensitivity and histology in these animals.

Animal model of simulated microgravity: a comparative study of hindlimb unloading via tail versus pelvic suspension

“…In a recent study, blood corticosterone level and hindlimb paw hypersensitivity to mechanical (von Frey hair) stimuli were observed increasing similarly in HLS rats and in rats that had tail suspension device attached but were not suspended (Tanaka et al. ). The authors had concluded that it is not microgravity or inactivity, but a restraint stress constitutes a major pathogenic factor determining changes in mechanical withdrawal thresholds in HLS‐rat.…”

Selective skin sensitivity changes and sensory reweighting following short-duration space flight

“…However, in a recent study, no histological changes in skin or peripheral nerves were found after 4 wk of unloading to account for the hypersensitivity. The authors suggest that increased stress levels in the animals may actually be the largest contributing factor to hypersensitivity (in the hind limb suspension model) (38). To our knowledge, vibration sensitivity of the skin has not been evaluated in this model.…”

Indicators of Physical Stress During Hindlimb Suspension in Wistar Rats / Indicadores De Stress Físico Durante a Suspensão Dos Membros Inferiores Em Ratos Wistar

“…Furthermore, cortisol and corticosterone are associated with acute and chronic stress 17,20 , so that elevation of their concentration shows the stressful characteristic of HS. In combination with the situational restraint stress associated to cage housing 2,21 , all these changes contribute to an overall debilitation of the animal.…”