Oxytocin activity in the hypothalamus: from intracellular signalling to anxiety-like behaviour
Final Report Abstract
Given the rising interest in the neuropeptide oxytocin (OXT) as potential treatment option in human psychopathologies such as autism, anxiety disorders and schizophrenia the molecular and neuronal mechanisms underlying the behavioural effects of OXT need to be revealed in detail. Therefore, our overall aim was to identify the intracellular pathways that are coupled to the hypothalamic OXT receptor. Moreover, we aimed to determine how OXT modulates the activity of these pathways specifically within the paraventricular nucleus of the hypothalamus to reduce anxiety-like behaviour. In the project "Oxytocin activity in the hypothalamus: from intracellular signalling to anxiety-like behaviour" we could specifically show that central administration of OXT in male rats activates the MAP kinase pathway within neurons of the PVN as reflected by increased phosphorylated MEK1/2 (pMEK1/2) and CaMKII levels. As OXT can also bind to the vasopressin receptor especially at high concentrations, we also proved for the specificity of these OXT effects using the highly specific OXT receptor agonist TGOT; indeed, also TGOT induced a robust MEK and CaMKII phosphorylation. Given our previous findings that the brain OXT system is highly activated in the peripartum period with increased OXT synthesis and release and high levels of OXT receptor binding especially in limbic regions, we next studied whether the MAP kinase pathway is altered in lactation. Indeed, we found that pMEK1/2 levels were higher in the cytosolic fraction of lactating than in virgin rats under basal conditions without OXT treatment, and that the increased pMEK1/2 level is likely due to increased phosphorylation, rather than to increased MEK synthesis during lactation. To our surprise, central infusion of OXT did only increase the activation of this pathway in virgin, but not in lactating rats. This important finding suggests (i) that OXT receptor-coupled signalling is based on similar mechanisms in males and females, and (ii) that synthetic OXT cannot further increase OXT receptor-coupled signalling in lactation due to the availability of high amounts of endogenous OXT in the extracellular fluid (ceiling effect). However, we found sex-dependent differences in the pathway leading to CREB phosphorylation in the PVN: In contrast to males, central OXT did not activate the CREB-regulating MAP kinase p38 of virgin female rats in the PVN, although the transcription factor CREB was found to be activated in both males and females by OXT. This suggests the involvement of a differential sex-dependent yet unknown factor in females. One of the aims was to study the target genes of OXT receptor coupled signalling. In this context we focused on the hypothalamic expression of the anxiogenic neuropeptide corticotrophin releasing factor (CRF), which also plays a major role in the stress response. We could demonstrate both in vitro as well as in vivo that OXT delayed the stress-induced increase in CRF hnRNA level and, in parallel, OXT likewise delayed the plasma ACTH response to restraint stress. Subsequent series of in vitro studies revealed the important involvement of the transcription factor CRTC3 (Torc) mediating the effects of OXT on stress-induced CRF expression. Specifically, OXT prevented CRTC3-binding to the promoter of the CRF gene as revealed by ChIP analyses. The final aim was to assess whether the identified MAP kinase pathway is essential for the OXT-induced anxiolysis within the PVN. Importantly, we could demonstrate (i) that local infusion of synthetic OXT into the PVN reduced anxiety-like behaviour in male and virgin female, but not in lactating rats. (ii) Local pre-treatment with the MEK1/2 inhibitor, U0126 prevented the anxiolytic effect of OXT in virgins indicating the involvement of this pathway in OXT-mediated anxiolysis. (iii) In contrast, MEK1/2 inhibition alone (without OXT treatment) increased basal anxiety in lactating rats indicating that endogenous OXT also signals via this pathway in lactation to exert its anxiolytic effect. Our results provide important information regarding the neuronal OXT receptor-coupled effects. They also indicate that the level of endogenous OXT essentially determines the effectiveness of OXT treatment as seen in lactation. This may have far reaching consequences for the use of OXT as treatment option in humans.
Publications
- Chronic icv oxytocin attenuates the pathological high anxiety state of selectively bred Wistar rats. Neuropharmacology 2010; 58(1):56-61
Slattery DA, Neumann ID
- Bridging the gap between GPCR activation and behaviour: oxytocin and prolactin signalling in the hypothalamus. J Mol Neurosci 2011; 43(2):200-208
Van den Burg EH, Neumann ID
- Central administration of oxytocin receptor ligands affects cued fear extinction in rats and mice in a timepoint-dependent manner. Psychopharmacology 2012; 223(2):149-58
Toth I, Neumann ID, Slattery DA
(See online at https://doi.org/10.1007/s00213-012-2702-4) - Differential contribution of hypothalamic MAPK activity to anxiety-like behaviour in virgin and lactating rats. PLoS One 2012;7(5): e37060
Jurek B, Slattery DA, Maloumby R, Hillerer K, Koszinowski S, Neumann ID, van den Burg EH
(See online at https://doi.org/10.1371/journal.pone.0037060) - RGS2 mediates the anxiolytic effect of oxytocin. Brain Res 2012; 1453:26-33
Okimoto N, Bosch OJ, Slattery DA, Pflaum K, Matsushita H, Wei FY, Ohmori M, Nishiki T, Ohmori I, Hiramatsu Y, Matsui H, Neumann ID, Tomizawa K
(See online at https://doi.org/10.1016/j.brainres.2012.03.012) - The brain oxytocin and vasopressin systems in anxiety and depression: Link to Sociality. Trends in Neurosciences 2012; 35 (11): 649-659
Neumann ID, Landgraf R
- Differential effects of baclofen and oxytocin on the increased ethanol consumption following chronic psychosocial stress in mice. Addict Biol 2013; 18:66-77
Peters S, Slattery DA, Flor PJ, Neumann ID, Reber SO
- Increased brain and plasma oxytocin after nasal and peripheral administration in rats and mice. Psychoneuroendocrinology 2013; 38(10):1985-93
Neumann ID, Maloumby R, Beiderbeck DI, Lukas M, Landgraf R
(See online at https://doi.org/10.1016/j.psyneuen.2013.03.003) - Brain Oxytocin in Social Fear Conditioning and Its Extinction: Involvement of the Lateral Septum. Neuropsychopharmacology 2014 [Epub ahead of print]
Zoicas I, Slattery DA, Neumann ID
(See online at https://doi.org/10.1038/npp.2014.156) - Oxytocin regulates stress-induced crf gene transcription through CREB-regulated transcription coactivator 3. J Neurosci 2 September 2015, 35 (35) 12248-12260
Jurek B, Slattery DS, Yuichi Hiraoka, Ying Liu, Katsuhiko Nishimori, Aguilera G, Neumann ID, van den Burg E
(See online at https://doi.org/10.1523/JNEUROSCI.1345-14.2015)
