Exposure to hot and cold environments increases noradrenaline release in the bed nucleus of the stria terminalis in rats

Experimental Approaches Used to Investigate Voluntary Behavioral Thermoregulatory Responses

A new behavioral test was developed to investigate the neural mechanisms of voluntary, behavioral thermoregulatory responses. The apparatus used in this test consisted of a thermostatic chamber that maintained the ambient temperature at a chosen level and two side-by-side floor plates that were placed in the thermostatic chamber and could be set to different temperatures. As the three temperatures, ambient temperature and two plate temperatures, can be controlled independently, we term this behavioral test the three-temperature (3 T) test. When the ambient temperature was 28 °C with floor plate temperatures of 25 °C and 35 °C, mice showed preference to the warm plate over the cool one. By contrast, when the ambient temperature was 40 °C, the mice showed preference to the cool plate, that is, a cool-seeking behavior. Detailed analyses of the time courses of the plate preference and core body temperature revealed that this cool-seeking behavior contributed to the regulation of body temperature. By using the 3 T test in combination with the latest in vivo imaging techniques for real-time measurement of neuronal activities and neurotransmitter releases in the brain of freely-moving animals, the neural mechanisms of voluntary, behavioral thermoregulatory responses could be elucidated in the near future.

Exposure to hot and cold environments activates neurons projecting from the paraventricular thalamic nucleus to brain regions related to approach and avoidance behaviors

Although cool- and warm-seeking behaviors for behavioral thermoregulation are considered to be appetitive/approach and aversive/avoidance behaviors, the neuronal circuits mediating such behaviors remain to be elucidated. A growing body of evidence suggests that the paraventricular thalamic nucleus (PVT) is a key brain region in a neuronal circuit that mediates appetitive/approach and aversive/avoidance behaviors. In this study, to elucidate the neuronal circuits mediating behavioral thermoregulatory responses, we examined whether neuronal pathways from the PVT to the nucleus accumbens (NAc), bed nucleus of the stria terminalis (BNST), and central nucleus of the amygdala (CeA), which are brain regions implicated in mediating appetitive/approach and aversive/avoidance behaviors, are activated during exposure to hot (38°C) and cold (8°C) environments using c-Fos immunostaining and retrograde tracing. Our results showed activation of neuronal pathways from the PVT to the NAc, BNST, and CeA during exposure to hot and cold environments, suggesting that activation of these pathways may be involved in avoidance behaviors from hot and cold environments for behavioral thermoregulation.

Effect of short- and long-term heat exposure on brain monoamines and emotional behavior in mice and rats

Heat exposure affects several physiological, neuronal, and emotional functions. Notably, monoaminergic neurotransmitters in the brain such as noradrenaline, dopamine, and serotonin, which regulate several basic physiological functions, such as thermoregulation, food intake, and energy balance, are affected by heat exposure and heat acclimation. Furthermore, cognition and emotional states are also affected by heat exposure and changes in brain monoamine levels. Short-term heat exposure has been reported to increase anxiety in some behavioral tests. In contrast, there is a possibility that long-term heat exposure decreases anxiety due to heat acclimation. These changes might be due to adaptation of the core body temperature and/or brain monoamine levels by heat exposure. In this review, we first outline the changes in brain monoamine levels and thereafter focus on changes in emotional behavior due to heat exposure and heat acclimation. Finally, we describe the relationships between emotional behavior and brain monoamine levels during heat acclimation.

Hemispheric stroke: Mood disorders

Stroke causes many forms of disability, including emotional and mood disorders. Depression is the most common of these, affecting approximately one-third of stroke patients. Other disorders like mania, bipolar disorder, anxiety disorder, or apathy may also develop following stroke, although they are less common. The development of mood and emotional disorders is dependent on the severity of brain injury, the side of injury, and hemispheric location. Whereas a left hemispheric stroke often results in depression or a catastrophic reaction with anxiety, injury to the right hemisphere has predominantly been associated with the development of emotional indifference (anosodiaphoria) or euphoria. In this chapter, we discuss the mood disorders associated with hemispheric strokes and the neuropsychological mechanisms that might account for the clinical manifestations of these affective disorders.

Exposure to hot and cold environments increases noradrenaline release in the bed nucleus of the stria terminalis in rats

AIMS

Thermoregulatory responses in homeothermic animals, including humans, are classified into involuntary autonomous and voluntary behavioral thermoregulatory responses. Although behavioral thermoregulatory responses are probably driven by positive (pleasant) and/or negative (unpleasant) emotions, the neuronal mechanisms underlying the induction of negative emotions by hot and cold environments remain poorly understood. The bed nucleus of the stria terminalis is a brain region implicated in stress responses and negative emotions, such as fear, anxiety, and aversion. Various stimuli that cause negative emotions, such as immobilization stress, fox odor, gastric distension, and inflammatory pain, increase noradrenaline release in the rat bed nucleus of the stria terminalis, especially in the ventral bed nucleus of the stria terminalis. It has been reported that the negative emotional component of pain is mediated by noradrenergic neurotransmission in the ventral bed nucleus of the stria terminalis. However, the role of intra-ventral bed nucleus of the stria terminalis noradrenergic neurotransmission in the induction of negative emotion by exposure to hot and cold environments remains to be elucidated. For the first step to address this issue, the effects of hot and cold environments on noradrenaline release in the ventral bed nucleus of the stria terminalis were examined.

METHODS

In vivo microdialysis analyses in unanesthetized, freely moving male Sprague-Dawley rats were performed to examine hot and cold environments-induced noradrenaline release in the ventral bed nucleus of the stria terminalis.

RESULTS

Exposure to hot (38°C) and cold (8°C) environments significantly increased noradrenaline release in the ventral bed nucleus of the stria terminalis.

CONCLUSIONS

The results suggest that exposure to hot and cold environments enhances noradrenergic neurotransmission in the ventral bed nucleus of the stria terminalis, which may induce negative emotion, and thereby drive avoidance behaviors, that is, escape from hot and cold environments.