TRH Neurons and Thyroid Hormone Coordinate the Hypothalamic Response to Cold

Area of Science:

• Endocrinology
• Neuroscience
• Physiology

Background:

• Thyroid hormone (TH) is crucial for mammalian thermoregulation, particularly during cold exposure.
• Cold stimulates the hypothalamus-pituitary-thyroid (HPT) axis, increasing plasma TH levels.
• Local TH metabolism in organs allows for tissue-specific thermogenic responses.

Purpose of the Study:

• To review the role of TH in cold defense.
• To highlight recent findings on centrally mediated effects of thyrotropin-releasing hormone (TRH) and TH.
• To explore the neural connections between hypothalamic TRH neurons and brown adipose tissue (BAT).

Main Methods:

• Literature review of studies on TH, TRH, and thermoregulation.
• Analysis of neuroendocrine and neural pathways involved in cold adaptation.
• Examination of studies investigating intrahypothalamic TH effects on metabolism.

Main Results:

• Hypothalamic TRH neurons connect to BAT, influencing autonomic nervous system regulation of thermogenesis.
• Intrahypothalamic TH exerts metabolic effects on BAT, liver, and heart via the autonomic nervous system.
• TH in hypothalamic nuclei like PVN suggests a central role in thermoregulation.

Conclusions:

• TH plays a significant role in central thermoregulation, acting via both neuroendocrine and neural pathways.
• The autonomic nervous system mediates TH's metabolic effects originating from the hypothalamus.
• Further research is needed to clarify the physiological relevance of neurally mediated TH effects in cold defense.