Assessment of dopamine-sensitive behaviors in mice lacking the testosterone-responsive TRPM8 channel. University of Illinois College of Medicine at Peoria 05/01/2024 10563731 A ErdmierB SheplerH PalmisanoTE KoeltzowS Asuthkar 0.58). Finally, male TRPM8 -/- mice exhibited a robust preference for sucrose compared to wildtype mice. Additional data collection is in progress.Conclusion: TRPM8-/- mice were less active during the active phase of the day/night cycle compared to wildtype mice. However, TRPM8-/- mice exhibited increased interest in a novel object and a robust preference for sucrose, indicating increased sensitivity to motivationally-relevant stimuli. These behavioral data suggest that TRPM8 -/- mice are likely to exhibit decreased basal DA levels in reward-relevant brain areas, but that motivationally relevant stimuli likely elicit robust increases in DA.]]>

• Transient Receptor Potential Melastatin-8 (TRPM8) cation channel being a high affinity target for testosterone suggests a mechanism by which androgens can rapidly influence central nervous system activity (Asuthkar et al., 2015). • Sex differences are a signature feature of anxiety, depression and substance use, yet the identification of neurobiological mechanism to account for this dimorphism has not been meaningfully identified (Altemus et al., 2014;Bangasser & Cuarenta, 2021;Santos-Toscano et al., 2023). • In addition to its well-established role in peripheral cold sensation (Bautista et al., 2007), TRPM8 is highly expressed in the central nervous system, including the hypothalamus, and limbic and cortical regions relevant to motivated behavior.

• Male TRPM8-KO mice exhibit disrupted sexual behavior, including increased mounting, indiscriminate approach, and a prolonged latency to satiety. These behaviors were linked to altered dopamine (DA) neuron activity in the ventral tegmental area (Mohandass et al., 2020). DA exerts an essential role in a variety of motivated behaviors, including response to novelty and reinforcement learning, and is critically implicated in substance use disorders and depression. Altemus, Margaret, Nilofar Sarvaiya, and C. Neill Epperson. "Sex differences in anxiety and depression clinical perspectives." Frontiers in neuroendocrinology 35.3 (2014): 320-330. Asuthkar, Swapna, et al. "The TRPM8 protein is a testosterone receptor: I. Biochemical evidence for direct TRPM8-testosterone interactions." Journal of Biological Chemistry 290.5 (2015): 2659-2669. Bangasser, Debra A., and Amelia Cuarenta. "Sex differences in anxiety and depression: circuits and mechanisms." Nature Reviews Neuroscience 22.11 (2021): 674-684. Bautista, Diana M., et al. "The menthol receptor TRPM8 is the principal detector of environmental cold." Nature 448.7150 (2007): 204-208. Mohandass, Adithya, et al. "TRPM8 as the rapid testosterone signaling receptor: Implications in the regulation of dimorphic sexual and social behaviors." The FASEB Journal 34.8 (2020): 10887-10906.

Discussion

It is possible that the effects of TRPM8 deletion on sexual reward will translate to more global reward processes. Therefore, we subjected TRPM8 null mutant mice to a battery of tests that are sensitive to DA and/or are established rodent models of anxiety, depression, and substance abuse. We hypothesize that male mice lacking the TRPM8 gene will exhibit impairment on these measures compared to wildtype mice.

• Deletion of the TRPM8 receptor did not reliably influence spontaneous locomotor activity among either male or female mice. However, there was a trend for male TRPM8 null mutant mice to habituate to the test environment faster than wildtype mice. These findings suggest that DA is not altered under basal conditions.

• Male TRPM8 -/-mice exhibited a preference for a low concentration of sucrose; this effect was not observed among female mice. In contrast, deletion of the TRPM8 receptor resulted in decreased activity in the light-dark test, and reduced time in the anxiogenic light side of the chamber. These mice also exhibited a decreased latency to immobility in the forced swim test. Together, these findings suggest that TRPM8 may play a protective role in the etiology of anxiety and depression.

• Male TRPM8-KO mice exhibited a diminished response to amphetamine compared to wildtype, suggesting that TRPM8 may be involved in substance use disorders.

• Future research seeks to clarify the relationship of testosterone, TRPM8, and DA.

Sucrose Preference: Male TRPM8 deficient mice exhibited a preference for a low concentration of sucrose (0.1%) compared to male wildtype mice (t (10) = 2.01, p < 0.05; d = 1.00). In contrast, deletion of the TRPM8 gene had no impact on sucrose preference among females across three different concentrations.

This work is supported by the National Science Foundation: (IOS-1922428)

Spontaneous Locomotor Activity: As expected, female mice were more active than male mice across the 48 h. test (F (1,26) = 16.35, p < 0.001; Left). There were no differences between TRPM8-KO and WT mice. Inset represents cumulative activity totals. Shaded area denotes dark cycle. DA plays a role in habituating to a novel environment. Male TRPM8-KO mice exhibited a trend towards increased latency to habituate (F (1,12) = 1.60, p = 0.2; Right). Asterisks denote statistically significant differences among planned comparisons. Error bars depict SEM.

Repeated Amphetamine: On Day 1 of testing, mice were allowed 40 minutes to acclimate to the test environment (Habituation), prior to an injection of physiological Saline (3 ml/kg body weight, i.p.) prior to an injection of a low dose of Amphetamine (1.0 mg/kg). Procedures were identical for 5 subsequent days, except the dose of amphetamine was increased (3.0 mg/kg). Data analysis indicate no differences between groups during habituation or in response to saline across 6 days of testing. However, RMANOVA revealed a statistically significant main effect of test day 3 (F (5,65) = 157, p < 0.001). Error bars depict SEM.