Basal forebrain microinjections of L-3,3′,5-triiodothyronine modify sleep in hypothyroid rats

Male rats were injected bilaterally with various doses of L-3,3′,5-triiodothyronine (T₃) into basal forebrain areas. The electroencephalogram (EEG), electromyogram (EMG) and brain temperature (Tbr) were then measured in 8-h studies. In the medial preoptic area (MPA), a 4 μg dose of T₃ caused significant elevations in REM sleep as compared to control injections. In the median preoptic nucleus (MnPO), both 2 and 4 μg doses of T₃ significantly inhibited non-REM sleep. Injections to the diagonal band of Broca did not alter EEG-defined sleep. Influences on Tbr were not significant for any of the treatments. Since these effects of T₃ were demonstrated after acute injections, the data are consistent with possible non-genomic actions of thyroid hormones in adult brain.