The Role of Hypothalamic Tri-Iodothyronine Availability in Seasonal Regulation of Energy Balance and Body WeightReport as inadecuate




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Journal of Thyroid ResearchVolume 2011 2011, Article ID 387562, 7 pages

Review Article

School of Biomedical Sciences, Queen-s Medical Centre, University of Nottingham Medical School, Nottingham NG7 2UH, UK

Division of Nutritional Sciences, School of Biosciences, University of Nottingham, Loughborough LE12 5RD, UK

Received 11 January 2011; Revised 7 April 2011; Accepted 27 April 2011

Academic Editor: Noriyuki Koibuchi

Copyright © 2011 Michelle Murphy and Francis J. P. Ebling. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Seasonal cycles of body weight provide a natural model system to understand the central control of energy balance. Studies of such cycles in Siberian hamsters suggest that a change in the hypothalamic availability of thyroid hormone is the key determinant of annual weight regulation. Uptake of thyroid hormone into the hypothalamus from the peripheral circulation occurs largely through a specific monocarboxylate transporter expressed by tanycyte cells lining the third ventricle. Tanycytes are the principal brain cell type expressing type II and type III deiodinases, so they control the local concentrations of T4, T3, and inactive metabolites. Type III deiodinase mRNA in tanycytes is photoperiodically upregulated in short photoperiod. This would be expected to reduce the availability of T3 in the hypothalamus by promoting the production of inactive metabolites such as rT3. Experimental microimplantation of T3 directly into the hypothalamus during short-days promotes a long-day phenotype by increasing food intake and body weight without affecting the peripheral thyroid axis. Thus, thyroid hormone exerts anabolic actions within the brain that play a key role in the seasonal regulation of body weight. Understanding the precise actions of thyroid hormone in the brain may identify novel targets for long-term pharmacological manipulation of body weight.





Author: Michelle Murphy and Francis J. P. Ebling

Source: https://www.hindawi.com/



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