DISTRIBUTION OF THYROTROPIN-RELEASING-HORMONE (TRH)-CONTAINING CELLS AND FIBERS IN THE HUMAN HYPOTHALAMUS

In the present study, we describe for the first time the distribution of thyrotropin-releasing hormone (TRH)-containing cells and fibers in the human hypothalamus using brain material obtained with a short post mortem delay. Following fixation in paraformaldehyde, glutaraldehyde a nd picric acid, excellent staining was obtained with two different TRH antisera. Many TRH-containing neurons were present in the paraventric ular nucleus (PVN), especially in the dorsocaudal part of this nucleus . They were mostly paricellular, but a few magnocellular TRH-positive neurons were observed as well. The PVN also contained a dense network of TRH fibers. The supraoptic nucleus (SON) did not show any TRH immun oreactivity, excluding the possibility of cross-reactivity of the anti serum with neurohypophysial hormones or their precursors. In addition, TRH cells were found in the suprachiasmatic nucleus (SCN), which is t he circadian clock of the brain, in the sexually dimorphic nucleus (SD N) and dorsomedially of the SON. We observed small numbers of TRH cell s throughout the hypothalamic gray in all subjects studied. A high den sity of TRH-containing fibers was seen not only in the median eminence but also in other hypothalamic areas, e.g., in the ventromedial nucle us (VM) and in the perifornical area. The results generally agree with earlier data in the rat, with the exception of the absence of TRH cel ls in the SON. The large number of sites of TRH-containing fiber termi nations on neurons suggests important physiological functions of this neuropeptide as a neurotransmitter or neuromodulator in the human brai n, in addition to its role as a neurohormone in pituitary secretion of thyroid-stimulating hormone (TSH). (C) 1994 Wiley-Liss, Inc.