Sexual dimorphism in the bed nucleus of the stria terminalis, medial preoptic area and suprachiasmatic nucleus in male and female tree shrews

Abstract

Sex differences in behaviour partly arise from the sexual dimorphism of brain anatomy between males and females. However, the sexual dimorphism of the tree shrew brain is unclear. In the present study, we examined the detailed distribution of vasoactive intestinal polypeptide‐immunoreactive (VIP‐ir) neurons and fibres in the suprachiasmatic nucleus (SCN) and VIP‐ir fibres in the bed nucleus of the stria terminalis (BST) of male and female tree shrews. The overall volume of the SCN in male tree shrews was comparable with that in females. However, males showed a significantly higher density of VIP‐ir cells and fibres in the SCN than females. The shape of the VIP‐stained area in coronal sections was arched, elongated or oval in the lateral division (STL) and the anterior part of the medial division (STMA) of the BST and oval or round in the posterior part of the medial division of the BST (STMP). The volume of the VIP‐stained BST in male tree shrews was similar to that in females. The overall distribution of VIP‐ir fibres was similar between the sexes throughout the BST except within the STMA, where darkly stained fibres were observed in males, whereas lightly stained fibres were observed in females. Furthermore, male tree shrews showed a significantly higher intensity of Nissl staining in the medial preoptic area (MPA) and the ventral part of the medial division of the BST than females. These findings are the first to reveal sexual dimorphism in the SCN, BST and MPA of the tree shrew brain, providing neuroanatomical evidence of sexual dimorphism in these regions related to their roles in sex differences in physiology and behaviour.

Histochemical Characterization of the Dorsal Raphe-Periaqueductal Grey Dopamine Transporter Neurons Projecting to the Extended Amygdala

“…Consistent with this, VIP innervations from the DR-PAG region to the BNST, which was not specified as DAT+/VGlut2+, have been reported in several studies ( Petit et al, 1995 ; Kozicz et al, 1998 ). This VIP signal in the BNST exhibits sexual dimorphism in humans, finches, and tree shrews ( Zhou et al, 1995 ; Chung et al, 2002 ; Goodson et al, 2006 ; Ni et al, 2022 ). Yu et al (2021) reported that the manipulation of DA DR-PAG neuronal activities induced different behavioral modulations between male and female mice, which might be because of the sexual dimorphism of VIP fibers in BNST, originating from the VIP subpopulation of DA DR-PAG neurons.…”

Sex‐specific differences in the circadian pattern of action potential firing by rat suprachiasmatic nucleus vasopressin neurons

“…22 Because VP release from SCN neurons is activity dependent, 19,20 these observations suggested there might be differences in the firing pattern of SCN VP neurons in the two sexes. Indeed, sexually dimorphic features of the SCN have been reported in several species, [28][29][30][31][32][33][34] including humans, 35 and sex differences in circadian physiology are well documented. [35][36][37][38][39][40] Therefore, the goal of this study was to characterize and compare the circadian profiles of electrical activity in identified SCN VP neurons of male and female rats.…”