The accessory magnocellular neurosecretory system of the rostral human hypothalamus

Abstract

The morphology and neurophysin expression of the magnocellular accessory neuroendocrine system located in the rostral human hypothalamus is investigated in a series of brains obtained at autopsy. The hypothalami were fixed in formalin and embedded in paraffin, or after cryoprotection, frozen for cryostat sectioning. Paraffin sections were either stained with Luxol Fast blue or immunoreacted for neurophysin I or neurophysin II, the precursor molecule for oxytocin and vasopressin. Further, 50-μm-thick serial cryostat sections were immunoreacted with the same antibodies. Both the paraventricular and supraoptic nuclei as well as the hypothalamo-hypophysial tracts exhibited strong immunoreactivity for the neurophysin antibodies. In addition, large collections of immunoreactive accessory magnocellular nuclei and single scattered neurophysin-positive neurons were located in the preoptic region between the paraventricular and supraoptic nucleus among the hypothalamo-hypophysial nerve fibers. In addition, smaller collections of neurophysin-immunoreactive neurons were located in the basal part of this region. Among the accessory magnocellular nuclei, the classical circular nucleus was identified. Accessory magnocellular neurons were often located along the blood vessels and projections of some of these neurons penetrated the vascular endothelium. The accessory magnocellular cell bodies expressed either neurophysin I or neurophysin II immunoreactivity. Summarizing, the accessory magnocellular system in the human brain is large and differs in morphology compared to the system seen in other vertebrates. The neurons of this system contain both vasopressin and oxytocin. Some neurons of the accessory neuronal systems might secrete vasopressin or oxytocin directly into the blood stream.

Expression of vasopressin mRNA in the hypothalamus of individuals with a diagnosis of schizophrenia

“…In our immunohistochemical investigations of the accessory magnocellular neurosecretory system of the human hypothalamus (Møller et al, 2018), we found no correlation between the postmortem time and the immunoreactivity in our sections. An explanation for that several of our autopsy brains with long postmortem time has preserved protein, and mRNA might be due to the fact that the dead bodies in our study were kept cold in the morgue during most of the postmortem time, and after removal of the brains, these were immediate fixed by immersion in cold formalin.…”

“…The nona peptide, vasopressin, is a part of the hypothalamic–pituitary–adrenal axis. This hormone is located in magnocellular neurons in the human hypothalamic paraventricular nucleus of the hypothalamus (Møller et al, ; Saper, ) in which parvocellular neurons, containing corticotropin‐releasing hormone (CRH), also are located. Although the main function of vasopressin, also called the antidiuretic hormone (ADH), is the regulation of water re‐absorption in the kidney, via projections of axons to the posterior pituitary lobe and release of the hormone to the vascular system, vasopressin is also involved in regulation of cortisol from the suprarenal glands (Aguilera & Rabadan‐Diehl, ).…”

The bovine anterior hypothalamus: Characterization of the vasopressin–oxytocin containing nucleus and changes in relation to sexual differentiation

“…The nucleus circularis (NC; also called accessory supraoptic nucleus in the rat in Bodian and Maren () was clearly present in the pig, disambiguating it from the VON (van Eerdenburg & Swaab, ). It is also present in rats (Price Peterson, ), hamsters (Ferris, Axelson, Martin, & Roberge, ), cats (Caverson et al, ), dogs (Laqueur, ), and was recently reported in the human hypothalamus (Møller et al, ) and has been linked to osmotic functions in rats (Wallace & Harrell, ) and flank marking in hamsters (Ferris et al, ). We were not able to detect any NC in the bovine hypothalamus.…”

“…Originally most authors found these cells to be accessory subnuclei to the PVN and the SON (Dellmann, ; Junge, ; Koikegami, ; Morton, ; Scharrer & Scharrer, ), based on various species. Other research groups chose to consider it a different entity (Braak & Braak, ; Gadamski & Lakomy, ; Szteyn et al, ; van Eerdenburg et al, ; Vierling, , ) while later, the concept of islands being part of a supraoptico‐paraventriculo‐hypohysal system emerged (Dierickx & Vandesande, ; Marani, ; Møller et al, ; Silverman & Zimmerman, ) following the human structure of these clusters. We subscribe to the argument of van Eerdenburg et al () in that the VON is obviously related to the PVN and SCN, because of its content of AVP and OXT and cell size, and is part of the hypothalamic magnocellular neurosecretory system although in the case of the pig and cattle at least, the organization into one distinct nucleus is striking (Figures and a,b).…”

“…In the opposite way, the cells forming the VON are probably present more diffusely in other species, such as the anterobasal PVN in the rabbit (Schimchowitsch, Moreau, Laurent, & Stoeckel, ), or the anterior PVN in the cat (Caverson, Ciriello, Calaresu, & Krukoff, ). Another possibility is that the VON is a different entity from the accessory neurosecretory system, that is the more diffuse magnocellular accessory nuclei found between the SON and the PVN, the accessory neurosecretory system, in the hypothalamo‐hypophysial tract (Møller et al, ). In sheep, Vierling () described a group of cells similar to the VON although as part of the PVN, comparable to what was later described in the horse as the ventral PVN (Melrose & Knigge, ), which tends to show that the VON could be a common feature in large herbivores.…”