Recent studies in humans have demonstrated that holding a warm cup of coffee, as opposed to a cold cup of coffee, increases pro-social behavior, without any conscious awareness by the individual of the effects of temperature on their behavior. Although the mechanisms involved have not been defined, these findings suggest that there are mechanisms through which sensation of warm temperature in the skin can affect social behavior. Preliminary data from the Lowry laboratory suggest that a subpopulation of neurons in the brainstem that produce the brain chemical serotonin may be responsible for the effects of temperature on social behavior. Furthermore, these preliminary data suggest that a temperature-sensitive protein, temperature-activated transient receptor potential (TRP) ion channel 4 (TRPv4), may be responsible for sensing temperature changes in the skin that lead to activation of serotonergic neurons. The PI will test the hypotheses that (1) the neuronal activity of a subset of serotonergic neurons in the brain responds to increases in temperature via mechanisms involving TRPv4 activation, and (2) activation of TRPv4 leads to decreased anxiety-related behaviors and, conversely, increases in social interaction. Anatomical, electrophysiological, pharmacological, and behavioral approaches will be used to investigate the role of a subset of serotonergic neurons in both sensing temperature and regulating behavior. Warm temperature is expected to activate a subset of serotonergic neurons projecting to brain structures involved in regulation of social behavior. This activation of serotonergic neurons by warm temperature is also expected to be dependent on activation of the temperature-sensitive channel TRPv4. This research will provide new information relevant to the effects of thermal stimuli on a highly conserved neurotransmitter system, the serotonergic system, and on emotional and social behavior, new information that has application across vertebrate and invertebrate taxa. This project will provide valuable training opportunities for graduate and undergraduate students as well as incorporating outreach and research mentoring for underrepresented high school students in the nearby community.
We have found that exposure to warm temperature activates specific subsets of serotonergic neurons in the brainstem, including subsets of serotonergic neurons implicated in control of cognitive and affective function. In addition, we have found that exposure to warm temperature can alter emotional behavior, as evidenced by increased proactive emotional coping behavior. Supporting a close relationship between thermosensory systems and emotional behavior, we have found that increased body temperature is highly correlated with proactive emotional coping behavior during stress exposure. These findings support an emerging consensus that thermosensory signals have not only thermoregulatory and discriminative functions (i.e., allowing us to determine the relative warmth of a thermal stimulus), but also have affective and cognitive functions. These findings provide a hypothetical framework for harnessing afferent thermosensory systems, either using thermal signals or pharmacological approaches, to modulate affective and cognitive function. These findings are likely to stimulate further studies of the affective and cognitive functions of thermosensory systems. Indeed, clinical studies are currently underway to evaluate the potential for infrared whole body heating for the treatment of major depressive disorder and post-traumatic stress disorder. This work contributed to the training of high school, undergraduate, graduate, and postdoctoral trainees, including underrepresented minority students. Furthermore, this award supported outreach activities to high school students, including Native American and other underrepresented minority students.
