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Distribution and axonal projections of neurons coexpressing thyrotropin‐releasing hormone and urocortin 3 in the rat brain
Author(s) -
Wittmann Gábor,
Füzesi Tamás,
Liposits Zsolt,
Lechan Ronald M.,
Fekete Csaba
Publication year - 2009
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.22180
Subject(s) - thyrotropin releasing hormone , biology , urocortin , stria terminalis , medicine , endocrinology , population , nucleus , hypothalamus , colocalization , neuroscience , forebrain , hormone , central nervous system , receptor , environmental health
Thyrotropin‐releasing hormone (TRH) decreases food intake when administered intracerebroventricularly or into the ventromedial hypothalamus. However, it is unknown which population of TRH neurons exerts this anorexigenic function. In the rostral perifornical area, the pattern of TRH‐expressing neurons is reminiscent of the distribution of neurons expressing urocortin3 (Ucn3) that also inhibits feeding when injected into the hypothalamic ventromedial nucleus (VMN). Since colocalization of TRH and Ucn3 may help to identify feeding‐related TRH neurons, the putative coexpression of the two peptides was examined using fluorescent in situ hybridization combined with immunofluorescence. Almost all (95.5 ± 0.2%) Ucn3‐immunoreactive neurons in the perifornical area expressed pro‐TRH mRNA, while 50.2 ± 1.6% Ucn3 neurons were double‐labeled in the bed nucleus of the stria terminalis (BNST). Only a few Ucn3/pro‐TRH neurons were found outside these two areas. The distribution of axons containing both Ucn3 and TRH was examined by dual immunofluorescence. Ucn3/TRH fibers heavily innervated the VMN. In addition, high densities of double‐labeled axons were observed in the lateral septal nucleus, posterior division of the BNST, medial amygdaloid nucleus, amygdalohippocampal area, and ventral hippocampus, forebrain areas associated with psychological stress and anxiety. We conclude that Ucn3 and TRH are coexpressed in a discrete, continuous population of neurons in the perifornical area and BNST, making Ucn3 a neurochemical marker to define a distinct subset of TRH neurons. The distribution of their axons suggests that Ucn3/TRH neurons may coordinate feeding and behavioral responses to stressful stimuli. J. Comp. Neurol. 517:825–840, 2009. © 2009 Wiley‐Liss, Inc.