Author: Rasadi Sajeewa Rajakaruna Moradana Gamage
Moradana Gamage, Rasadi Sajeewa Rajakaruna, 2024 Investigation of heat acclimation mechanisms involvement in dopamine brain system in the preoptic area of rats in a hot environment , Flinders University, College of Medicine and Public Health
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Introduction: As global warming worsens, heat-related illnesses such as heatstroke are becoming a major problem. It has long been known that heat acclimation is an effective way to prevent heatstroke. However, the brain mechanisms involved in the heat acclimation have barely been elucidated. Previous research has demonstrated that acute heat exposure increases dopamine levels in brain regions, including the preoptic area and the dorsomedial hypothalamus, the main nucleus in brain circuitry for thermoregulation. In addition, it has been suggested that the dopamine system in the brain is involved in thermoregulation. This study investigated whether dopamine in the preoptic area, the thermoregulatory centre, contributed to heat acclimation.
Method: This study used Sprague-Dawley male rats and investigated the effects of the disruption of dopaminergic input to the preoptic area on heat acclimation. For this disruption, dopaminergic fibres in the preoptic area were destroyed by a neurotoxin (a chemical conjugate of antibody to the dopamine transporter and the protein synthesis-inactivating protein, saporin; DAT-SAP) microinjected into the preoptic area. IgG-SAP was used for control. A telemetry probe (TA-F40, Data Science International) was implanted intraperitoneally to measure body temperature and locomotor activity. All preparatory surgical procedures were performed under general anaesthesia with isoflurane. After a week of recovery from surgery, rats were kept in an environment of 22°C for a week and then in an environment of 32°C for four weeks. Acute heat exposure was also performed before and after the 4 weeks to determine whether heat acclimation had been established. During the four weeks of heat exposure, body temperature was measured continuously, water intake was measured daily, and body weight was measured once a week. After the heat exposure experiment, the salivary glands, adrenal glands, and thymus were collected and weighed. The institutional animal ethics committee at Flinders University approved all the experimental procedures.
Results: During 4 weeks of heat exposure, body temperature in the 12-hour-dark phase significantly increased in both IgG-SAP and DAT-SAP treated animal groups. Between these two groups, there was no significant difference in drinking water consumption during the heat exposure and in the weight of the salivary glands, adrenal glands, and thymus glands after the exposure. In both groups, the rise in body temperature caused by acute heat exposure was suppressed after 4 weeks.
Conclusion: These results suggest that dopaminergic inputs to the preoptic area are not involved in heat acclimation. Caution is, however, needed when drawing this conclusion. Due to time constraints, it was impossible to check whether the neurotoxin had destroyed the dopamine fibres thoroughly. Therefore, it remained uncertain whether DAT-SAP was administered within the POA or whether DAT-SAP had acted usually. It is essential to clarify this point in the future. In addition, research that focuses on dopamine in brain regions other than the POA region is also necessary.
Keywords: Dopamine, Preoptic Area, Heat Acclimation, Body Temperature, Heat Exposure
Subject: Biotechnology thesis
Thesis type: Masters
Completed: 2024
School: College of Medicine and Public Health
Supervisor: Associtate Professor Yoichiro Ootsuka