Distribution of vasopressin and vasoactive intestinal polypeptide (VIP) fibers in the human hypothalamus with special emphasis on suprachiasmatic nucleus efferent projections.

Jul 14, 1997The Journal of comparative neurology

Locations of vasopressin and VIP nerve fibers in the human hypothalamus, focusing on signals from the body’s internal clock area

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Abstract

Vasopressin (VP) and vasoactive intestinal polypeptide (VIP) fibers from the human suprachiasmatic nucleus (SCN) were found to extensively branch and innervate multiple hypothalamic areas.

VP and VIP were confirmed to be present in different subdivisions of the SCN.
SCN projections primarily targeted the anteroventral hypothalamic area (AVH), sub-paraventricular nucleus (sub-PVN), ventral part of the paraventricular nucleus (PVN), and dorsomedial nucleus of the hypothalamus (DMH).
There is substantial similarity between human SCN projections and those observed in rats and hamsters.
The presence of VP and VIP fibers between the SCN and the PVN suggests a possible direct anatomical connection.
VP and VIP fibers were also detected in other hypothalamic areas that do not have established direct connections to the SCN.

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The human suprachiasmatic nucleus (SCN) is located in the basal part of the anterior hypothalamus and is considered as the biological clock that generates circadian rhythms and synchronizes the daily activity pattern with the environmental light-dark cycle. However, the mechanisms and pathways by which the SCN transmits its information to the other brain areas are unknown. Therefore, in the present study, we investigated the efferent projections of the SCN by the immunocytochemical staining of two major peptidergic SCN neurotransmitters: vasopressin (VP) and vasoactive intestinal polypeptide (VIP). It confirmed that these peptides are present in different subdivisions of the SCN. The results of this investigation show that VP and VIP fibers arising from the SCN were detected to branch extensively and hence seem to innervate the SCN itself and the central and medial part of the anteroventral hypothalamic area (AVH), the area below the paraventricular nucleus (sub-PVN), the ventral part of the paraventricular nucleus (PVN), and the dorsomedial nucleus of the hypothalamus (DMH). There appeared to be substantial congruity between the presumptive human SCN projections and those as observed by tracing in rat or hamster. Regarding the anatomical organization of the human SCN projections, the main projection areas appeared to be the AVH, the sub-PVN, the ventral part of the PVN, and the DMH. The observation that VIP and in particular VP fibers pass between the SCN and the PVN suggests that the human SCN and the PVN may have a direct anatomical connection. In addition, VP and VIP fibers were detected in several other hypothalamic areas that are not known to have clear direct connections to the SCN. The possible origin of these VP and VIP fibers is discussed.

Distribution of vasopressin and vasoactive intestinal polypeptide (VIP) fibers in the human hypothalamus with special emphasis on suprachiasmatic nucleus efferent projections.

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