Oxytocin receptor ligand binding in embryonic tissue and postnatal brain development of the C57BL/6J mouse

Abstract

Oxytocin (OXT) has drawn increasing attention as a developmentally relevant neuropeptide given its role in the brain regulation of social behavior. It has been suggested that OXT plays an important role in the infant brain during caregiver attachment in nurturing familial contexts, but there is incomplete experimental evidence. Mouse models of OXT system genes have been particularly informative for the role of the OXT system in social behavior, however, the developing brain areas that could respond to ligand activation of the OXT receptor (OXTR) have yet to be identified in this species. Here we report new data revealing dynamic ligand-binding distribution of OXTR in the developing mouse brain. Using male and female C57BL/6J mice at postnatal days (P) 0, 7, 14, 21, 35, and 60 we quantified OXTR ligand binding in several brain areas which changed across development. Further, we describe OXTR ligand binding in select tissues of the near-term whole embryo at E18.5. Together, these data aid in the interpretation of findings in mouse models of the OXT system and generate new testable hypotheses for developmental roles for OXT in mammalian systems. We discuss our findings in the context of developmental disorders (including autism), attachment biology, and infant physiological regulation.

Summary: Quantitative mapping of selective OXTR ligand binding during postnatal development in the mouse reveals an unexpected, transient expression in layers II/III throughout the mouse neocortex. OXTR are also identified in several tissues in the whole late embryo, including the adrenal glands, brown adipose tissue, and the oronasal cavity.

Keywords: adrenal gland; autism; autoradiography; experience-dependent plasticity; kidney; neocortex; oronasal cavity; oxytocin.

Figure 1

Receptor autoradiography in C57BL/6J mice at several post-natal ages and coronal levels reveals brain areas of OXTR ligand binding, and the lack of specific OXTR ligand binding in OXTR KO brain assessed at P60.(A) accessory (a) and main (b) olfactory bulbs (B) neocortex (c), septum (d), claustrum (e), endopiriform cortex (f), piriform cortex (g), diagonal band of Broca (h), (C) bed nucleus of the stria terminalis (i), ventral caudatoputamen (j), (D) periventricular thalamus (k), CA3 hippocampus (l), central amygdala (m), medial amygdala (n), hypothalamus (o). Scale bar = 1 cm.

Figure 2

Quantification of receptor autoradiography for OXTR in C57BL/6J mice demonstrates transient developmental profiles. OXTR binding with highly selective OXTR ligand is evident in (A) the CA3 of the dorsal hippocampus, (B) the septum, and (C) the neocortex sampled at S1. For all three brain regions, there was a main effect of age. In the septum and the hippocampus, this was driven by the difference in binding between P0 and P14–P21. In the neocortex, the main effect of age was stronger and driven substantially by the peak at P14. ^*p < 0.05.

Figure 3

OXTR ligand binding in the neocortex is prominent in layer II/III. (A) OXTR is abundant in neocortical layers II/III at P14. (B) Nissl counterstain of section in (A). (C) OXTR is pseudo-colored red in a composite image of panels (A) and (B), which indicates that OXTR is prominent in layers II/III but not in layer IV or VI. OXTR is present in upper layer V. There is significantly reduced neocortical OXTR in P60 mice (D) which are only slightly above tissue background compared to OXTR KO P60 neocortex (E). (F) Quantification of OXTR binding demonstrates the transient ligand binding of OXTR in upper layers across post-natal development.

Figure 4

OXTR ligand binding (A) followed by post-processing with Nissl staining (B) reveals tissue specificity of OXTR in E18.5 embryos. Pseudocolor (OXTR in red) composite (C). Olfactory turbinates/nasal epithelium (a and b), mandible (c), tongue (d), genitourinary tract (e), dermis (f), kidney (g), adrenal gland (h), brown adipose tissue (i).