Stress-mediated dysregulation of the Rap1 small GTPase impairs hippocampal structure and function.

The effects of repeated stress on cognitive impairment are thought to be mediated, at least in part, by reductions in the stability of dendritic spines in brain regions critical for proper learning and memory, including the hippocampus. Small GTPases are particularly potent regulators of dendritic spine formation, stability, and morphology in hippocampal neurons. Through the use of small GTPase protein profiling in mice, we identify increased levels of synaptic Rap1 in the hippocampal CA3 region in response to escalating, intermittent stress. We then demonstrate that increased Rap1 in the CA3 is sufficient in and of itself to produce stress-relevant dendritic spine and cognitive phenotypes. Further, using super-resolution imaging, we investigate how the pattern of Rap1 trafficking to synapses likely underlies its effects on the stability of select dendritic spine subtypes. These findings illuminate the involvement of aberrant Rap1 regulation in the hippocampus in contributing to the psychobiological effects of stress.

The effect of immersion cryotherapy on medial-lateral postural sway variability in individuals with a lateral ankle sprain.

BACKGROUND AND PURPOSE: Postural stability has been shown to be impaired after a lateral ankle sprain (LAS) and after immersion cryotherapy in healthy ankles. This study was performed to determine the effects of cryotherapy on postural stability after LAS. METHOD: A single-session, repeated measures design was used. Fifteen 18- to 29-year-old males (mean age 21.33 +/- 3.54, height 71.23 +/- 2.50 cm, mass 170.33 +/- 19.77 kg) with relatively recent grade I LAS volunteered. Medial-lateral postural sway variability was assessed during single-leg barefoot stance using a Bertec force platform. Sway was tested before cryotherapy ('Pre'), immediately after 20 minutes of lower-leg immersion cryotherapy ('Post(0)'), and 10 and 20 minutes after cryotherapy ('Post(10)' and 'Post(20)'). Both legs were tested (individually) before cryotherapy; the involved leg was tested alone after cryotherapy. The uninvolved leg served as a control. RESULTS: Postural sway variability of the involved le was significantly greater than the uninvolved le before cryotherapy (p = 0.001). Postural sway variability of the involved leg was also significantly greater than the uninvolved LE during Post(0) (p = 0.000), Post(10) (p = 0.000) and Post(20) testing (p = 0.003) with the largest increase in sway variability occurring at Post(0). CONCLUSIONS: Medial-lateral postural sway variability was greater after LAS. This effect was augmented by immersion cryotherapy.