Altogether, our observations show that UVB treatment significantly enhances the desire for male-female interaction and significantly increases the attractiveness of female mice. To validate that male preference for a UVB-treated female mouse results from sexual signals, we repeated the three-chamber test with a female subject, a UVB-treated female stimulus, and a mock-treated control female stimulus (Figures S2I–S2L). This confirmed that the observed desire for social proximity in both male and female mice results from the UVB treatment. The subject female demonstrated no difference in the latency to visit, the frequency of visits, or the total time spent near or in the zone of a wire cage containing a UVB-treated or a mock-treated male stimulus (Figures 2D and 2E; Figure S2D). Furthermore, the subject males preferred to visit and stay near the wire cage (Figure 2C, middle and right panels) and in the zone of the wire cage (Figure S2A, middle and right panels) of a UVB-treated female rather than a control female. All the experiments took place in a reverse 12-h light/dark cycle under dim, red lighting. The visual data were subsequently analyzed manually for respective behavior parameters. The males were individually housed for 24 h in a new cage with sawdust bedding; food and water were provided ad libitum. Males exhibited similar sniffing behavior during the 1-h test session regardless of the treatment the female received (Figure 1G). Next, we evaluated the effect of UVB treatment on female attractiveness by measuring anogenital sniffing behavior (Clarke and Trowill, 1971) (Figure 1F; Video S1). These results suggest that UVB treatment of females enhances their attractivity as indicated by the relative increase in male vocalization parameters. During a male-female encounter, male mice exclusively dominate the calls (frequency of 40–70 kHz), a behavior positively related to their level of sexual arousal (Kerchner, 2004). (O) Latency intromission (left panel), duration of intromission (middle panel), and total number of intromissions (right panel) by a UVB- or control-treated male on a control female. (M) Total number of anogenital sniffing events by UVB- or control-treated males on a control-treated female. In females, FSH and LH stimulate the production of estrogen and progesterone, which regulate ovulation and pregnancy (Barbieri, 2014; Rosner and Sarao, 2019). Supplementation provides a controlled and safe way to increase vitamin D without the risks of excessive sun exposure. For men with adequate vitamin D levels, the hormonal benefit of extra sun exposure may be minimal. Sunlight, specifically UVB rays, triggers the skin to synthesize vitamin D. Fortunately, taking vitamin D supplements can similarly boost vitamin D levels—and testosterone—without the risk of getting burned. Scientists suspect that when you liver processes vitamin D from the sun or food, it sends a signal to the testes to convert total testosterone into free testosterone, the unbound testosterone your body can use. Research has also established other links between sunlight and testosterone. The pituitary gland releases follicle-stimulating hormone (FHS) and luteinizing hormone (LH), the latter of which stimulates testosterone production in the testes. Pheromones are inducers of communication and behavioral responses, including sexuality and mating (Ferrero et al., 2013; Roberts et al., 2010; Stowers and Liberles, 2016; Verhaeghe et al., 2013). Axillary secretions originate from apocrine odor glands, eccrine sweat glands, and sebaceous glands located in the skin (Verhaeghe et al., 2013). Another mode of skin-brain crosstalk involves the combined neural signals from the preoptic hypothalamus and peripheral nerves that together trigger eccrine sweat glands (Stowers and Liberles, 2016). Signals from the brain to the skin include thermoregulation, sweat-gland function, blood flow, adnexal functions (Roosterman et al., 2006), and hair graying (Zhang et al., 2020). Sensory signals from the skin to the brain include temperature, touch, pain, stretch, itch, and vibration; they are sensed by skin receptors that transfer the stimuli via nerve fibers directly to the brain (Roosterman et al., 2006). All skin layers are innervated by sensory, sympathetic, and parasympathetic nerve fibers that relay signals to the brain and receive cues from it (Slominski et al., 2012). HRT helps men with hormone imbalance by replacing deficient hormones, restoring balance and vitality. If you haven’t just gotten out of a cold plunge, smaller-than-normal gonads are often a sign of hormone imbalance. "Too much ultraviolet radiation can damage the DNA in our skin cells, leading to wrinkles and even skin cancer," he says. That in turn, causes increases in LH/FSH that trigger testosterone, estradiol, and progesterone." Snagging some sun may help you boost your T levels, according to the Huberman Lab Podcast’s Andrew Huberman, Ph.D. S.T., G.S., S.M., T.Z., H.K., and G.C., investigation and formal analysis (human testosterone data).
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