Species Differences in the Immunoreactive Expression of Oxytocin, Vasopressin, Tyrosine Hydroxylase and Estrogen Receptor Alpha in the Brain of Mongolian Gerbils (Meriones unguiculatus) and Chinese Striped Hamsters (Cricetulus barabensis)

Abstract

Species differences in neurochemical expression and activity in the brain may play an important role in species-specific patterns of social behavior. In the present study, we used immunoreactive (ir) labeling to compare the regional density of cells containing oxytocin (OT), vasopressin (AVP), tyrosine hydroxylase (TH), or estrogen receptor alpha (ERα) staining in the brains of social Mongolian gerbils (Meriones unguiculatus) and solitary Chinese striped hamsters (Cricetulus barabensis). Multiple region- and neurochemical-specific species differences were found. In the anterior hypothalamus (AH), Mongolian gerbils had higher densities of AVP-ir and ERα-ir cells than Chinese striped hamsters. In the lateral hypothalamus (LH), Mongolian gerbils also had higher densities of AVP-ir and TH-ir cells, but a lower density of OT-ir cells, than Chinese striped hamsters. Furthermore, in the anterior nucleus of the medial preoptic area (MPOAa), Mongolian gerbils had higher densities of OT-ir and AVP-ir cells than Chinese striped hamsters, and an opposite pattern was found in the posterior nucleus of the MPOA (MPOAp). Some sex differences were also observed. Females of both species had higher densities of TH-ir cells in the MPOAa and of OT-ir cells in the intermediate nucleus of the MPOA (MPOAi) than males. Given the role of these neurochemicals in social behaviors, our data provide additional evidence to support the notion that species-specific patterns of neurochemical expression in the brain may be involved in species differences in social behaviors associated with different life strategies.

Vasopressin and oxytocin receptor systems in the brain: Sex differences and sex-specific regulation of social behavior

“…Sex differences in VP neurons and plasma VP concentrations have also been found in humans (Share et al, 1988; Asplund & Aberg, 1991; Van Londen et al, 1997; Ishinina et al, 1999; Miller et al, 2013; Graugaard-Jensen et al, 2014; however, see Fliers et al, 1985; Swaab et al, 2001; Gouin et al, 2012). In contrast, we found that only a few rodent species show sex differences in OT-immunoreactivity (CD mice: Häussler et al, 1990; mandarin voles: Qiao et al, 2014; Brandt’s voles: Xu et al, 2010; Mongolian gerbils and Chinese-striped hamsters: Wang et al, 2013). There is also a lack of sex differences in OT neuron size and number in humans (Fliers et al, 1985; Wierda et al, 1991; Ishunina and Swaab, 1999), and most human studies report a lack of sex differences in plasma OT (Zhong et al, 2012; Taylor et al, 2010; Grewen et al, 2005; Gordon et al, 2008; Gordon et al, 2010; Graugaard-Jensen et al, 2014; however see van Londen et al, 1997; Miller et al, 2013; Weisman et al, 2013).…”

“…In detail, VP synthesis in hypothalamic regions is similar between male and female mice (PVN and SON: Joca et al, 2013; Steinman et al, 2015), voles (PVN, SON, SCN in prairie, pine, meadow, and montane voles: Wang, 1995; Wang et al, 1996), Mongolian gerbils (PVN, medial preoptic area [MPOA], lateral hypothalamus [LH] and anterior hypothalamus [AH]: Wang et al, 2013), and Chinese striped hamsters (PVN, medial preoptic area, lateral hypothalamus and anterior hypothalamus: Wang et al, 2013). However, other rodent species show region- and social context-specific sex differences in hypothalamic VP-immunoreactivity.…”

“…Across species, most OT is synthesized in the PVN and SON, but some OT synthesizing cells are found in the accessory magnocellular nucleus of the hypothalamus (rats, humans: Fliers et al, 1985; Weirda et al, 1991; Meynen et al, 2007) or LH, AH, and MPOA (hamsters, gerbils, voles, naked mole rats: Brownstein et al, 1980; Dierickx, 1980; Rhodes et al, 1981; Swanson and Sawchenko, 1983; Wang et al, 1996; Rosen et al, 2008; Xu et al, 2010; Wang et al, 2013). OT-producing magnocellular neurons of the PVN and SON project to the posterior pituitary where OT is released into the general circulation as a hormone, in which it is involved in maternal responses such as milk ejection and uterine contractions (Fuchs and Poblete, 1970; Belin et al, 1984), in male reproductive functions such as ejaculation, in cardiovascular homeostasis, and other peripheral activities (Gimpl and Fahrenholz, 2001).…”

“…For example, females had more OT-immunoreactive neurons in the PVN, SON, and anterior hypothalamic periventricular nucleus of CD mice (Häussler et al, 1990), the PVN and SON of mandarin voles (Qiao et al, 2014), the PVN of Brandt’s voles (Xu et al, 2010), and the MPOA of Mongolian gerbils and Chinese-striped hamsters (Wang et al, 2013). …”

“…These findings further suggest that when sex differences are found in OT and in OTR, it not necessarily is in the same direction or exists in both parameters (Tables 5 and 7). For example, female mandarin voles, hamsters, and gerbils show higher OT-immunoreactivity (Wang et al, 2013; Qiao et al, 2014), while male rats and deer mice show higher OTR binding (Insel et al, 1991; Uhl-Bronner et al, 2005; Dumais et al, 2013). Importantly, both the brain region- and species- specificity of sex differences in OTR suggests that the OT system in these brain regions and species may be implicated in sex-specific regulation of social behavior.…”