Distribution of thyrotropin‐releasing hormone (TRH)‐containing cells and fibers in the human hypothalamus

Abstract

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 postmortem delay. Following fixation in paraformaldehyde, glutaraldehyde and picric acid, excellent staining was obtained with two different TRH antisera. Many TRH-containing neurons were present in the paraventricular nucleus (PVN), especially in the dorsocaudal part of this nucleus. They were mostly parvicellular, 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 immunoreactivity, excluding the possibility of cross-reactivity of the antiserum with neurohypophysial hormones or their precursors. In addition, TRH cells were found in the suprachiasmatic nucleus (SCN), which is the circadian clock of the brain, in the sexually dimorphic nucleus (SDN) and dorsomedially of the SON. We observed small number of TRH cells throughout the hypothalamic gray in all subjects studied. A high density of TRH-containing fibers was seen not only in the median eminence but also in other hypothalamic areas, e.g., in the ventromedial nucleus (VM) and in the perifornical area. The results generally agree with earlier data in the rat, with the exception of the absence of TRH cells in the SON. The large number of sites of TRH-containing fiber terminations on neurons suggests important physiological functions of this neuropeptide as a neurotransmitter or neuromodulator in the human brain, in addition to its role as a neurohormone in pituitary secretion of thyroid-stimulating hormone (TSH).

Melanocortin 4 receptor distribution in the human hypothalamus

“…Although most TRH-positive cells in the PVN are parvocellular, TRH expression in a small number of magnocellular neurons has been described as well (41). Although TRH immunostaining has been reported earlier in picric acid/glutaraldehyde-fixed vibratome sections, it was unsuccessful in formalin-fixed material such as we used (41) and could therefore not be incorporated in this study.…”

Activation and degeneration during aging: A morphometric study of the human hypothalamus

“…A good marker for the neuronal content of the majority of SDN neurons is not available at present. A few TRH neurons have so far been identified in this nucleus (Fliers et al, 1994). Such TRH positive neurons have also been identified in the rat (Simerly et al, 1986).…”

MECHANISMS IN ENDOCRINOLOGY: Beyond the fixed setpoint of the hypothalamus–pituitary–thyroid axis

“…In the 1990s, the first studies on the distribution of TRH neurons in the human hypothalamus appeared (9,10) showing that TRH-containing neurons and fibres are present in a number of hypothalamic nuclei, including the PVN, the SCN, which contains the circadian pacemaker of the brain acting as a biological clock, and the sexually dimorphic nucleus. The human PVN contains many spindle-shaped and spheric multipolar parvocellular TRH neurons, especially in its dorsocaudal portion, while only a small number of magnocellular neurons express TRH.…”