Sex-dependent role of vesicular glutamate transporter 3 in stress-regulation and related anxiety phenotype during the early postnatal period

Abstract

Stress and related disorders are in the focus of interest and glutamate is one of the most important neurotransmitters that can affect these processes. Glutamatergic neurons are characterized by vesicular glutamate transporters (VGluT1-3) among which vGluT3 is unique contributing to the non-canonical, neuromodulatory effect of glutamate. We aimed to study the role of vGluT3 in stress axis regulation and related anxiety during the early postnatal period using knockout (KO) mice with special focus on sex differences. Anxiety was explored on postnatal day (PND) 7-8 by maternal separation-induced ultrasonic vocalization (USV). Stress-hormone levels were detected 60 min after intraperitoneal lipopolysaccharide (LPS) injection 7 days later. Both genotypes gained weight, but on PND 14-15 KO mice pups had smaller body weight compared to wild type (WT). vGluT3 KO mice reacted to an immune stressor with enhanced adrenocorticotropin (ACTH) and corticosterone secretion compared to WT. Although there was a tendency for enhanced anxiety measured by more emitted USV, this did not reach the level of significance. The only sex-related effect was the enhanced corticosterone reactivity in male pups. For the HPA axis regulation in neonates vGluT3 expression seems to be dispensable under basal conditions, but is required for optimal response to immune stressors, most probably through an interaction with other neurotransmitters. Disturbance of the fine balance between these systems may result in a borderline enhanced anxiety-like behavior in vGluT3 KO pups.

Sex differences in ultrasonic vocalization and hormonal stress response of an anxious mice strain during the early postnatal period

“…Moreover, the reduced stress reactivity to an immune challenge in AX mice pups is also a reflection of a disrupted coping style. Previously LPS was able to induce significant stimulation in ACTH and corticosterone levels in adult (Lolait et al 2007) and postnatal (Balázsfi et al 2016) mice, which was replicated in our present experiments. Although HAB rats previously demonstrated a larger increase in corticosterone levels to LPS administration than LAB rats (Salome et al 2008), their stress reaction to social defeat was also diminished (Frank et al 2006), similarly to our results.…”

“…Previous studies clearly suggested an enhanced maternal separation-induced USV emission as a sign of exaggerated anxiety both in rat and mice pups (Winslow, Insel 1991;Iijima, Chaki 2005;Varga et al 2015;Balázsfi et al 2016). Moreover, rats showing higher USV at PND 10 during a 2 min test were more anxious in their adulthood as measured in open field (Brunelli, Hofer 2007).…”

“…USA; O55:B5; 100 µg/ml/kg, dissolved in saline) or saline was injected intraperitoneally (i.p.) to the same animals (n = 5-9/group) (Balázsfi et al 2016). One hour later blood samples were taken for hormone measurements (ACTH, corticosterone).…”

Immunity and ultrasonic vocalization in rodents

“…Thus, these studies are reviewed here in somewhat greater detail. No significant links between immune function and USV were found in the two publications that we could trace dealing with early postnatal immune stimulation . The few reports available on ultrasonic calling and stimulation of the immune system during experimentally induced inflammatory or autoimmune processes are mentioned below.…”

Targeting VGLUT Machinery: Implications on mGluR5 Signaling and Behavior

“…Interestingly, similar anxiety-like behaviors were noted in mice lacking VGLUT3 signaling. Deletion of VGLUT3 enhanced innate fear in newborn mice, while adult VGLUT3 -/mice elicited marked neophobia toward anxiogenic contexts (Amilhon et al, 2010;Balázsfi et al, 2016).…”