Effects of acute microinjections of the thyroid hormone derivative 3-iodothyronamine to the preoptic region of adult male rats on sleep, thermoregulation and motor activity

• The preoptic regions of adult male rats were injected with 0.3, 1, 3, or 10 μg T1AM.
• nREM sleep was decreased in the 24 h following injection of 1 or 3 μg T1AM.
• Doses of 1 or 10 μg T1AM caused hypothermia, but rats recovered within 24 h.
• Locomotor activity increased after administration of 0.3 or 3 μg T1AM.
• Changes in sleep behavior and core body temperature induced by T1AM were independent.

The decarboxylated thyroid hormone derivative 3-iodothyronamine (T1AM) has been reported as having behavioral and physiological consequences distinct from those of thyroid hormones. Here, we investigate the effects of T1AM on EEG-defined sleep after acute administration to the preoptic region of adult male rats. Our laboratory recently demonstrated a decrease in EEG-defined sleep after administration of 3,3′,5-triiodo-l-thyronine (T3) to the same brain region. After injection of T1AM or vehicle solution, EEG, EMG, activity, and core body temperature were recorded for 24 h. Sleep parameters were determined from EEG and EMG data. Earlier investigations found contrasting systemic effects of T3 and T1AM, such as decreased heart rate and body temperature after intraperitoneal T1AM injection. However, nREM sleep was decreased in the present study after injections of 1 or 3 μg T1AM, but not after 0.3 or 10 μg, closely mimicking the previously reported effects of T3 administration to the preoptic region. The biphasic dose–response observed after either T1AM or T3 administration seems to indicate shared mechanisms and/or functions of sleep regulation in the preoptic region. Consistent with systemic administration of T1AM, however, microinjection of T1AM decreased body temperature. The current study is the first to show modulation of sleep by T1AM, and suggests that T1AM and T3 have both shared and independent effects in the adult mammalian brain.