Presence of TSH receptors in discrete areas of the hypothalamus and caudal brainstem with relevance for feeding controls-Support for functional significance.

Aims: Previous studies have shown that brain-derived thyroid-stimulating hormone (TSH) and its receptor (TSHr) are present in hypothalamic extracts. No studies investigating both the anatomical location and functional significance of putative TSHr proteins in specific central nervous system (CNS) nuclei involved in feeding controls have yet been conducted. The aim was thus to determine whether TSHr are present in nuclei associated with feeding behavior, and if such receptors may be functional.

Methods: Brain tissue from adult rats was analyzed for gene expression and receptor protein expression was investigated with immunohistochemistry and western blotting. To investigate whether putative TSHr may be functional, we evaluated food intake of rats given intraparenchymal nanoinjections of TSH into the nucleus of the solitary tract (NTS).

Results: RT-qPCR confirmed previous reports that TSHr mRNA is expressed in CNS tissues of the adult rat. Immunohistochemistry showed TSHr-immunoreactivity in the arcuate, the ventromedial, the dorsomedial, and the paraventricular hypothalamic nuclei. We also found TSHr-ir in the dorsal hindbrain to be localized to the area postrema, NTS, dorsal motor nucleus of the vagus, and the hypoglossal motor nucleus. Further protein analysis with western blotting showed 120kDa TSHr-ir proteins present in the hypothalamus and brainstem. Injections of TSH into the NTS reduced food intake similar to the positive control, urocortin.

Conclusions: These data suggest that functional TSHr are present in the caudal brainstem and hypothalamic nuclei of relevance for feeding control as a possibly uncleaved holoreceptor, and highlights a hindbrain component to central TSH inhibition of food intake.