A Within-Subject Model of Hot Flash-Like Symptoms in Aged Rats

Abstract

Hot flashes are a common vasomotor symptom (VMS) experienced by postmenopausal women. In rodents, VMS-like symptoms can be assessed by monitoring tail skin temperature (TST), which reflects thermoregulatory changes. However, because the TST is highly sensitive to handling and environmental stresses, a reliable assessment requires continuous monitoring under low-stress and unrestrained conditions. In this study, we established a monitoring system for aged Wistar rats and evaluated hot flash-like symptoms using a within-subjects design across four physiological states: intact, ovariectomized (OVX), 17β-estradiol (E2) treatment, and E2 withdrawal. E2 treatment significantly decreased dark-phase TST (26.63 ± 0.26°C) compared with OVX (29.39 ± 0.18°C), and this effect was reversed upon pellet removal. We also quantified ΔTST, defined as the difference between light- and dark-phase TST, and found that E2 treatment markedly increased ΔTST, indicating an estrogen-dependent restoration of circadian TST amplitude. Because aged rats exhibit irregular estrous cycles and reduced ovarian steroidogenesis, yet remain underutilized in VMS research, this model provides a physiologically relevant platform for studying menopausal vasomotor dysfunction. By repeatedly monitoring the same individuals, inter-individual variability is minimized and reliable detection of within-subject changes is achieved with a small number of animals. These findings demonstrate that our method enables reliable long-term TST monitoring under unrestrained conditions and offers a practical and validated approach for investigating the pathophysiology of menopausal vasomotor dysfunction and for screening candidate compounds targeting hot flash-like symptoms in rodents.