Precursor of oxytocin, a neurohypophyseal hormone that plays a key role in social interactions and neurophysin 1, its carrier protein. . [Oxytocin]: Neuropeptide hormone released by the posterior pituitary gland that plays a key role in social behavior and other biological processes, such as milk ejection (PubMed:15931222, PubMed:20538951, PubMed:21220339, PubMed:6278592). Released in response to a variety of social cues and acts by binding to oxytocin receptor (OXTR), triggering signaling that modulates neural circuits by altering ion channel activity, changing intrinsic neuronal properties and modifying synaptic transmission (both excitatory and inhibitory) (PubMed:18174156, PubMed:35241813, PubMed:35851571). Central release (direct secretion in the brain) plays essential roles in social behavior, such as maternal care, social cognition and affiliative behaviors (PubMed:15931222, PubMed:20538951, PubMed:21220339). Stressful and anxiogenic stimuli promote release of oxytocin, which acts as a powerful modulator of anxiety- and stress-related behaviors (PubMed:15931222, PubMed:20538951, PubMed:21220339). Oxytocin promotes altruism by enhancing empathy, trust and social bonding, making people more generous (PubMed:15931222, PubMed:20538951, PubMed:21220339). Can also favor parochial altruism, a social behavior involving costly helping of one's own group (in-group) that often comes with hostility or discrimination towards other groups (out-groups) (PubMed:20538951, PubMed:21220339). Modulates neural circuits related to reward, fear and social approach, encouraging care and cooperation, but can also increase guilt or aggression towards out-groups (PubMed:20538951, PubMed:21220339). Beyond its role in social behavior, plays a role in other processes, such as parturition, lactation or osteoblast differentiation, when released peripherally (secreted from the posterior pituitary gland into the bloodstream) (PubMed:6278592). Required for parturition and milk ejection by triggering and strengthening contraction of the smooth muscle of the uterus and mammary gland, respectively (PubMed:6278592). Promotes bone mass by stimulating bone formation by osteoblasts (By similarity). {ECO:0000250|UniProtKB:P35454, ECO:0000269|PubMed:15931222, ECO:0000269|PubMed:18174156, ECO:0000269|PubMed:20538951, ECO:0000269|PubMed:21220339, ECO:0000269|PubMed:35241813, ECO:0000269|PubMed:35851571, ECO:0000269|PubMed:6278592}. [Neurophysin 1]: Carrier protein that binds to and transports oxytocin from the hypothalamus to the posterior pituitary gland, protecting it from degradation and facilitating its release. . This is the function of OXT (oxytocin/neurophysin I prepropeptide, Ensembl gene identifier ENSG00000101405).