Relaxin-3/RXFP3 signalling in mouse hypothalamus: no effect of RXFP3 activation on corticosterone, despite reduced presynaptic excitatory input onto paraventricular CRH neurons in vitro

Abstract

Relaxin-3/RXFP3 signalling is proposed to be involved in the neuromodulatory control of arousal- and stress-related neural circuits. Furthermore, previous studies in rats have led to the proposal that relaxin-3/RXFP3 signalling is associated with activation of the hypothalamic-pituitary-adrenal axis, but direct evidence for RXFP3-related actions on the activity of hypothalamic corticotropin-releasing hormone (CRH) neurons is lacking. In this study, we investigated characteristics of the relaxin-3/RXFP3 system in mouse hypothalamus. Administration of an RXFP3 agonist (RXFP3-A2) intra-cerebroventricularly or directly into the paraventricular nucleus of hypothalamus (PVN) of C57BL/6J mice did not alter corticosterone levels. Similarly, there were no differences between serum corticosterone levels in Rxfp3 knockout (C57BL/6J) and wild-type mice at baseline and after stress, despite detection of the predicted stress-induced increases in serum corticosterone. We examined the nature of the relaxin-3 innervation of PVN in wild-type mice and in Crh-IRES-Cre;Ai14 mice that co-express the tdTomato fluorophore in CRH neurons, identifying abundant relaxin-3 fibres in the peri-PVN region, but only sparse fibres associated with densely packed CRH neurons. In whole-cell voltage-clamp recordings of tdTomato-positive CRH neurons in these mice, we observed a reduction in sEPSC frequency following local application of RXFP3-A2, consistent with an activation of RXFP3 on presynaptic glutamatergic afferents in the PVN region. These studies clarify the relationship between relaxin-3/RXFP3 inputs and CRH neurons in mouse PVN, with implications for the interpretation of current and previous in vivo studies and future investigations of this stress-related signalling network in normal and transgenic mice, under normal and pathological conditions.

RLN3/RXFP3 Signaling in the PVN Inhibits Magnocellular Neurons via M-like Current Activation and Contributes to Binge Eating Behavior

“…Although RXFP3 has been shown to modulate synaptic inputs to parvocellular PVN CRF neurons ( C. Zhang et al, 2017 ) and neurons of the bed nucleus of stria terminalis in mice ( Ch'ng et al, 2019 ), neither RLN3 nor a selective RXFP3 agonist influenced excitatory NMDA/AMPA or inhibitory GABA A receptor-mediated postsynaptic currents (spontaneous and miniature) recorded from PVN MNCs in our rat brain preparations. We therefore conclude that RLN3 inputs primarily act on postsynaptically located RXFP3 to modulate MNC activity in the rat.…”

Differential Level of RXFP3 Expression in Dopaminergic Neurons Within the Arcuate Nucleus, Dorsomedial Hypothalamus and Ventral Tegmental Area of RXFP3-Cre/tdTomato Mice

“…1 www.gtexportal.org/home/gene/RXFP3 Furthermore, several rodent studies have observed that relaxin-3 can influence the hypothalamic-pituitary adrenal and gonadal axes, although some of these effects may be due to relaxin-3 binding to RXFP1, rather than RXFP3 (Zhang et al, 2017;De Ávila et al, 2018).…”

The Relaxin-3 Receptor, RXFP3, Is a Modulator of Aging-Related Disease

“…Further investigation of the functions of this receptor has uncovered that RXFP3 might play a vital role in several aging-related disorders, as a connection has been found to several hallmarks of aging, such as oxidative stress and DNA damage response [24], similarly to the aging keystone GIT2 [6,7]. In addition, research by other groups has elucidated possible roles for RXFP3 in stress responses [25], anxiety [26], depression [26,27], feeding [15,[28][29][30], arousal [28], and alcohol addiction [31]. Given the plethora of possible physiological activities of RXFP3, we will next assess how RXFP3 functionality may intersect with several of the classical hallmark processes involved with the aging process (Figure 1).…”