Oxytocin is a peptide hormone synthesized by hypothalamic neuroendocrine neurons and released mainly from the neurohypophysis, with a central role in the physiology of pregnancy, labor and breastfeeding. Although traditionally described as the hormone that supports uterine contraction and milk ejection, oxytocin represents a highly informative model of integration between sensory signals, autonomic circuits and peripheral endocrine response. Its action is mediated through a specific, extensively regulated receptor, whose density and sensitivity vary substantially over time and across tissues, allowing the body to coordinate reproductive events that require temporal precision and functional robustness.
From a neuroendocrine perspective, oxytocin is a paradigm of how the hypothalamus can translate peripheral stimuli into rapid, stereotyped and biologically effective endocrine responses. Nipple suckling and cervical and vaginal distension are examples of sensory inputs that activate afferent circuits capable of triggering synchronized discharges of oxytocinergic neurons, leading to episodic release of the hormone into the systemic circulation. In parallel, oxytocin also acts as a central neuromodulator, contributing to the coordination of reproductive and affiliative behaviors and to the regulation of autonomic and affective components of the maternal response. Understanding the biochemistry, neuronal organization and physiology of oxytocin secretion therefore allows a deeper interpretation of the functioning of the hypothalamic-neurohypophyseal axis and of the general principles of neuroendocrine communication.
Oxytocin is a nonapeptide composed of nine amino acids and is structurally related to vasopressin. The molecule has an intramolecular disulfide bridge between two cysteine residues, which determines a cyclic configuration essential for three-dimensional stability and high receptor-binding specificity. Its structural similarity to vasopressin, due to minimal differences in amino acid sequence, illustrates how point variations can generate profoundly different receptor profiles and biological functions, making oxytocin an instructive example of structure-function relationships in peptide hormones.
From a genetic perspective, oxytocin is encoded by the OXT gene, located on chromosome 20 in humans, close to the vasopressin gene. As with other neurohypophyseal hormones, the hormone is not synthesized directly as a free peptide, but as part of a preprohormone, prepro-oxytocin, which includes a carrier protein called neurophysin I. This biosynthetic organization reflects an evolutionarily conserved strategy that links synthesis, folding, storage and axonal transport, ensuring that the active peptide is correctly packaged and available for secretion.
Processing of the precursor occurs in the endoplasmic reticulum and Golgi apparatus of oxytocinergic neurons, through proteolytic cleavage and post-translational modifications that lead to formation of the active nonapeptide and neurophysin I. Neurophysin I binds oxytocin inside dense-core secretory vesicles and facilitates its trafficking along the axon toward the neurohypophysis. The presence of neurophysin is not merely a transport detail, but a structural element required for the efficiency of the entire neurosecretory system, in which the site of synthesis and the site of release are spatially separated.
From a physicochemical perspective, oxytocin has a short plasma half-life and is degraded by circulating peptidases. Under physiological conditions, this characteristic makes temporal control of secretion essential, since the biological effect is maintained by pulses or transient increases in release rather than by stable and persistent levels. Its short duration of action is consistent with the need for rapid and reversible responses during events such as milk ejection or the contractile dynamics of labor.
The biochemistry of oxytocin therefore highlights an architecture typical of hypothalamic peptide hormones, in which the active peptide is the final result of a complex and regulated biosynthetic chain. This chain is not accessory, but determines the very possibility of precise neuroendocrine control, both in terms of peptide availability and in terms of the ability to release it rapidly in response to sensory and physiological signals.
The neurons that synthesize oxytocin mainly belong to the class of magnocellular neurons of the hypothalamus, organized into well-defined nuclei and closely associated with neurohypophyseal function. The main sites of synthesis are the supraoptic nucleus and the paraventricular nucleus, where oxytocinergic and vasopressinergic populations coexist with distinct physiological characteristics and firing patterns. This nuclear organization allows robust control of secretion, with the possibility of inter-neuronal synchronization required for large-amplitude endocrine responses, such as those needed during breastfeeding and the active phase of labor.
Anatomically, oxytocinergic neurons send their axons along the hypothalamic-hypophyseal tract to the neurohypophysis, where axon terminals are arranged in contact with fenestrated capillaries. At this site, oxytocin is released directly into the systemic circulation, clearly distinguishing this system from the hypothalamic-pituitary portal system. The vascular arrangement and the fenestrated nature of neurohypophyseal capillaries ensure rapid entry into the circulation, consistent with the need for immediate peripheral effects.
A crucial element of oxytocinergic neuron physiology is their ability to generate synchronized discharges and to respond to afferent stimuli with characteristic activity patterns. During suckling, for example, neuronal activity can organize into episodic discharges that produce pulsatile hormone release, with timing suitable for effective milk ejection. This synchronization capacity does not depend only on classical synaptic connections, but also on paracrine, glial and functional coupling mechanisms between neurons within the magnocellular nuclei.
In addition to the neurohypophyseal projection, a proportion of oxytocinergic neurons, especially in the paraventricular nucleus, has central projections toward areas involved in autonomic regulation, stress modulation and behavioral processing. This dual dimension, peripheral endocrine and central neuromodulatory, helps explain why oxytocin is associated with integrated responses involving visceral physiology, maternal behavior and affective components of reproduction.
Overall, oxytocinergic neurons constitute a highly specialized system in which nuclear organization, synchronization capacity and endocrine and central projections converge to produce rapid, coordinated and adaptive responses. Understanding this organization is essential for interpreting oxytocin physiology and its clinical relevance in conditions in which the neuroendocrine coordination of reproduction is altered or requires therapeutic support.
Oxytocin synthesis occurs in the cell bodies of hypothalamic magnocellular neurons through transcription of the OXT gene and translation of the prepro-oxytocin precursor. After entry into the endoplasmic reticulum, the precursor undergoes folding and the initial stages of processing; it is then transferred to the Golgi apparatus, where it is packaged into dense-core secretory vesicles together with neurophysin I. This packaging creates a stable complex that protects the peptide and allows its maturation during axonal transport.
Transport to the neurohypophysis occurs by axonal transport, with progressive maturation of vesicles and completion of the proteolytic cleavages required to generate the active nonapeptide. This pathway emphasizes that the neurohypophyseal system is a true distributed functional unit, in which synthesis and secretion occur at different but tightly integrated sites. The availability of oxytocin in neurohypophyseal terminals therefore reflects both hypothalamic synthesis and the dynamics of vesicle transport and mobilization.
Oxytocin release in the neurohypophysis is a calcium-dependent exocytotic process triggered by depolarization of axon terminals. Increased frequency of action potentials in oxytocinergic neurons raises intracellular calcium and induces vesicle fusion with the membrane, releasing the hormone into the extracellular compartment and allowing rapid entry into the bloodstream. The speed of the circuit permits a close correspondence between sensory stimulus and peripheral endocrine response.
A distinctive feature of oxytocin secretion is its ability to assume a highly effective episodic pattern. In particular, during breastfeeding, secretion may show pulses associated with episodes of milk ejection, while during labor it may increase progressively and in coordination with contractile dynamics. This secretory behavior reflects the structure of the afferent circuit and the property of magnocellular neurons to synchronize their activity, producing transient concentration increases that, despite a short half-life, are sufficient to generate marked peripheral effects.
Peripheral secretion is accompanied by a central dimension of oxytocin availability, linked to release in synapses and specific brain circuits. Although central dynamics and compartmentalization are distinct from endocrine dynamics, the coexistence of these two dimensions contributes to creating an integrated response in which visceral and behavioral components are coordinated. Overall, oxytocin synthesis, transport and release delineate a system designed for rapid, synchronized and reversible responses, consistent with the physiological requirements of reproduction.
The effects of oxytocin are mediated by the oxytocin receptor (OXTR), a G protein-coupled receptor with predominant coupling to Gq, capable of activating phospholipase C and increasing intracellular levels of inositol trisphosphate and diacylglycerol. The increase in intracellular calcium represents the central functional step for activation of smooth muscle contraction, particularly in the uterus and in mammary myoepithelial cells. This signaling pattern makes oxytocin a powerful activator of mechano-functional events that require rapidity, such as contraction and expulsion.
Receptor distribution is extensively regulated and varies substantially according to physiological state. In the uterus, receptor density increases markedly toward the end of pregnancy, with pronounced sensitization of the myometrium to oxytocin. This increase is not a quantitative detail, but a determining element in the transition toward a phase in which the contractile response becomes effective and coordinated. In parallel, the decidua and other compartments of the reproductive tract may also express OXTR, contributing to complex modulation of the labor response.
In the breast, OXTR is expressed on myoepithelial cells surrounding the alveoli and lactiferous ducts. Activation of the receptor induces a coordinated contraction that produces milk ejection, distinct from milk production, which depends mainly on prolactin. This functional distinction is essential for understanding how oxytocin acts as the acute effector of the ejection reflex, linking nipple stimulation to an immediate mechanical event.
The OXTR receptor is also expressed in numerous regions of the central nervous system and in extra-reproductive tissues, suggesting a broader role of oxytocin as a neuromodulator and local paracrine regulator. Receptor signaling may involve, in addition to calcium, pathways that modulate gene expression and cellular plasticity, with effects that can emerge over longer time scales. In this sense, oxytocin combines the ability to rapidly activate effector functions with the possibility of influencing circuits and tissues through slower adaptations.
An important aspect of receptor physiology is the presence of mechanisms of desensitization and sensitivity regulation, which depend on the duration of exposure and intensity of the stimulus. These mechanisms have relevant functional implications because they help define the response under conditions of prolonged stimulation, as in sustained contractile dynamics. Regulation of the receptor and signaling pathways is therefore an integral part of the effectiveness and biological safety of the oxytocin system.
The uterine action of oxytocin is one of its best-known physiological effects and is expressed mainly through activation of OXTR on the myometrium. The increase in intracellular calcium in smooth muscle cells induces contraction, while activation of complementary pathways may modulate fiber coordination and propagation of electrical activity. However, the contractile response does not depend exclusively on oxytocin concentration, but on myometrial sensitivity, which varies with gestational age and with endocrine and local tissue remodeling.
Toward the end of pregnancy, increased OXTR density and changes in the uterine microenvironment make the uterus more reactive. This phenomenon contributes to the transition from a phase of contractile quiescence to a phase in which contraction can become effective and coordinated. Labor progression also depends on the interaction between oxytocin and local mediators, including those that modulate cervical ripening and the physiological inflammatory response of childbirth. From this perspective, oxytocin acts as an amplifier and coordinator of a system that integrates endocrine and paracrine signals.
A fundamental physiological concept is that labor is accompanied by feedback circuits that can potentiate oxytocin secretion. Cervical and vaginal distension activates sensory afferents that stimulate oxytocinergic neurons, further increasing secretion and promoting more effective contractions. This positive circuit, although controlled and limited by the overall physiology of the system, represents a crucial mechanism for understanding labor progression, in which contractile intensity and afferent stimulation reinforce each other.
The function of oxytocin in labor is therefore not reducible to an isolated contractile effect, but is embedded in a regulatory network that includes receptor sensitization, peripheral signals and central circuits. Its effectiveness depends on timing, receptor density, myometrial coordination and cooperation with local mediators. This complexity explains why the same hormone concentration may produce different responses at different times of pregnancy and in different clinical contexts.
Oxytocin is essential for the milk ejection reflex, the process that allows milk transfer from the alveoli to the ducts and then to the nipple. Suckling activates sensory afferents that reach the hypothalamus and induce synchronized discharges of oxytocinergic neurons, with episodic hormone release into the circulation. Oxytocin rapidly reaches the mammary gland and binds to the OXTR receptor on myoepithelial cells, inducing a coordinated contraction that increases intraductal pressure and promotes milk emission.
This reflex is an example of rapid neuroendocrine integration, in which the peripheral stimulus generates a hormonal response with short and reproducible latency. The episodic component of release is physiologically advantageous because it produces effective contractions despite a short half-life, allowing fine and reversible control. The distinction between milk ejection, dependent on oxytocin, and milk production, mainly supported by prolactin, clarifies how the body separates control of milk synthesis from control of its mobilization, coordinating the two processes according to breastfeeding requirements.
The sensitivity of the ejection reflex can be modulated by contextual factors. Acute stress, pain and emotional conditions can interfere with the neuroendocrine response, modifying the effectiveness of release and therefore the perception of milk “let-down”. This modulation reflects integration between limbic circuits, autonomic circuits and hypothalamic nuclei, making clear that oxytocin acts within a broader neurophysiological context than the simple nipple-neurohypophysis-breast circuit.
Overall, the mammary action of oxytocin shows how the hypothalamic-neurohypophyseal axis can translate sensory stimuli into coordinated endocrine outputs and how the peripheral response critically depends on neuronal synchronization and the presence of functional receptors. This model is also useful for understanding other neuroendocrine reflexes and the way peripheral afferent signals are transformed into effective endocrine responses.
Oxytocin secretion is regulated by a set of neurophysiological mechanisms that differ, in logic and timing, from those typical of hypothalamic hormones released into the portal system. In the neurohypophyseal oxytocin system, the critical variable is not only the mean hormone level, but the ability of magnocellular neurons to generate synchronized discharges in response to well-defined afferent stimuli. This principle is particularly evident in breastfeeding, where the ejection reflex requires rapid and intermittent releases, and in labor, where secretion can increase dynamically and in coordination with the progression of cervicovaginal distension and contractile activity.
The sensory afferents that modulate oxytocin secretion are among the best-known examples of reflex neuroendocrine circuits. Nipple stimulation during suckling activates afferent fibers that ascend to the brainstem and, through polysynaptic connections, reach the hypothalamus, facilitating discharge of oxytocinergic neurons. Similarly, distension of the cervix and birth canal activates an afferent circuit that contributes to increasing magnocellular neuron activity and reinforcing peripheral secretion. These circuits show how the hypothalamus can integrate somatic inputs into rapid endocrine outputs, with latency compatible with the physiology of mechanical events such as contraction and ejection.
A central aspect of regulation is the ability of oxytocinergic neurons to shift from tonic activity to highly coordinated phasic activity. This transition cannot be attributed to a single mechanism, but emerges from the interaction of excitatory and inhibitory synaptic inputs, glial modulation, local paracrine signals and intrinsic membrane properties of magnocellular neurons. In the supraoptic nucleus and paraventricular nucleus, anatomical proximity and the presence of microcircuits favor synchronization, making it possible to release enough oxytocin to produce clear peripheral effects despite its short half-life.
Regulation is also sensitive to contextual signals that modulate hypothalamic circuits. Acute stress, fear and pain may alter firing patterns and interfere with the physiology of milk ejection, while conditions of relaxation and safety can favor a more efficient response. This modulation reflects integration between limbic and autonomic circuits and magnocellular nuclei, confirming that oxytocin secretion is part of a global neuroendocrine response and not a purely peripheral reflex.
Taken together, the mechanisms regulating oxytocin secretion show a control model in which temporality and neuronal coordination are as decisive as the amount secreted. This architecture allows rapid and reversible responses, suited to physiological events that require temporal precision and functional robustness, and makes oxytocin a paradigm of reflex neuroendocrinology.
In addition to its peripheral endocrine component, oxytocin has a central dimension of release and neuromodulatory action that contributes to shaping behaviors and autonomic responses associated with reproduction and care. In the central nervous system, oxytocin can be released from paraventricular projections toward different brain areas and act on OXTR receptors expressed in circuits involved in social processing, affectivity and stress regulation. This component should not be interpreted as separate from peripheral physiology, but as part of an integrated response that coordinates visceral and behavioral aspects of reproduction.
Central oxytocin release is conceptually distinct from neurohypophyseal release. The neurohypophysis represents a dedicated route for entry into the circulation, while the central dimension involves local diffusion and neuromodulatory action on synaptic and paracrine scales. This distinction is essential for understanding why some effects attributed to oxytocin, such as anxiety modulation or facilitation of affiliative responses, are not reducible to changes in plasma levels. Receptor distribution and compartmentalization of release make it plausible that central physiology follows its own dynamics, while maintaining functional correlations with reproductive state.
In neuroendocrine models of motherhood, central oxytocin contributes to facilitating the maternal response, stress tolerance and behavioral adaptation to the postpartum period. This effect emerges from modulation of limbic and hypothalamic circuits that integrate neonatal sensory signals, emotional inputs and autonomic responses. Oxytocin therefore acts as a mediator that makes breastfeeding and caregiving processes coherent, supporting not only the mechanical component of milk ejection but also the global organization of the maternal response.
The central action of oxytocin also includes effects on autonomic functions, such as regulation of vagal tone and modulation of neurovegetative responses associated with contact, suckling and social interactions. From this perspective, oxytocin lies among the mediators that link sensory signals and relational context to measurable physiological changes, contributing to a functional state that facilitates breastfeeding and caregiving. The complexity of the circuits involved and interindividual variability make this dimension an area of major pathophysiological interest, while requiring caution in the interpretation of experimental and translational results.
Overall, central oxytocin is an example of how a single peptide can operate simultaneously as a peripheral hormone and neuromodulator, integrating reproductive events with behavioral and autonomic adaptations. This dual nature significantly broadens the physiological meaning of the hormone, making it an intersection point between endocrinology, neuroscience and reproductive physiology.
Oxytocin interacts with stress response systems, particularly with the hypothalamic-pituitary-adrenal axis, through a network of neuroendocrine connections involving hypothalamic nuclei and limbic circuits. Although it is not a “stress hormone” in the classical sense, oxytocin can modulate neurovegetative reactivity and central processing of stressful stimuli, contributing to a state that, in specific physiological contexts such as the postpartum period, favors emotional stability and maternal function. The most coherent physiological interpretation is that oxytocin participates in an adaptive balance between activation and containment of stress, modulating thresholds and responses in a context-dependent manner.
During the peripartum period and breastfeeding, the body undergoes a phase of neuroendocrine remodeling in which the stress response can be modulated. In this context, central and peripheral oxytocin participates in a system that supports care and breastfeeding, reducing interference from excessive autonomic responses. This does not imply uniform suppression of stress, but a reorganization of the response according to biological priorities, with potential involvement of receptor mechanisms and plasticity of hypothalamic circuits.
Oxytocin also interacts with other hypothalamic and monoaminergic mediators that influence reproductive function and autonomic responses. Its neuromodulatory action can influence circuits that regulate attention, motivation and caregiving behaviors, favoring coherence between internal state and environmental demands. In this view, oxytocin function is not isolated, but embedded in a mosaic of signals that define complex neuroendocrine states.
The interaction with the stress response is also relevant in the physiology of labor: pain, anxiety and sympathetic activation can influence contractile dynamics and perception of the event. Through its ability to coordinate uterine contraction and central responses, oxytocin is among the mediators that contribute to the robustness of the process, despite individual variability and contextual modulations. This integration clarifies why oxytocin physiology is broader than its peripheral action and why its effects can be influenced by psychophysical conditions.
Oxytocin physiology is characterized by marked variability that reflects the specific requirements of reproductive phases and changes in receptor sensitivity in target tissues. Pregnancy represents the context in which regulation of the OXTR receptor assumes decisive importance: the uterus shifts from a state of relative contractile quiescence to a progressively more reactive state, in which receptor density and myometrial responsiveness increase. This transition is essential to make coordinated labor contractions possible and highlights that the response to oxytocin critically depends on the biological context of the target tissue.
In the peripartum period, oxytocin secretion and receptor sensitivity contribute not only to the active phase of labor, but also to placental delivery and the reduction of postpartum bleeding, through the promotion of effective uterine contractions. Postpartum dynamics also include the initiation of breastfeeding, in which oxytocin becomes essential for milk ejection. The puerperium is therefore a phase in which oxytocin function is intensely engaged on multiple fronts and in which neuroendocrine regulation must coordinate mechanical, autonomic and behavioral responses.
During breastfeeding, oxytocin secretion is typically associated with suckling episodes, with releases that may repeat several times during a feed. The physiology of the ejection reflex is influenced by experience, stimulation frequency and emotional context, with circuit plasticity that can improve response efficiency over time. In parallel, the peripheral response depends on the integrity of mammary tissue and the presence of functional receptors on myoepithelial cells.
Variability related to sex and age is more complex and depends on receptor distribution and central oxytocin function. In non-reproductive conditions, oxytocin continues to be produced and may contribute to autonomic and behavioral modulations, but the magnitude and functional significance vary considerably. This interindividual and intercontextual variability makes oxytocin a physiological system in which the receptor and circuit components are often more decisive than the absolute concentration of the peptide.
Overall, the physiological variability of oxytocin highlights a general principle of neuroendocrinology: the effect of a hormone depends not only on secretion, but on the competence of the target tissue, defined by receptor density, intracellular signaling state and interactions with local mediators. This principle is particularly evident in the transition from pregnancy to labor and the puerperium, where the same molecule can assume different roles within a short time frame through integrated remodeling of circuits and tissues.
Although oxytocin is mainly associated with reproductive functions, the presence of the OXTR receptor in extra-reproductive tissues suggests broader roles in integrated physiology. In the cardiovascular field, effects on autonomic modulation and potential influences on vascular tone and cardiac function have been described, with a complexity that depends on the region and physiological context. The most cautious and physiologically coherent interpretation is that oxytocin may contribute to favorable autonomic regulatory states, especially in conditions in which the neuroendocrine system is oriented toward care and stability, but that its action does not represent a primary cardiovascular axis comparable to classical ones.
In the metabolic field, oxytocin has been linked to hypothalamic circuits that integrate feeding behavior, satiety and energy balance. The presence of receptors in brain areas and the ability to modulate autonomic and behavioral responses make a contribution of oxytocin to the coordination between emotional state, feeding and energy adaptations plausible. Again, physiology should be interpreted as integration with broader networks and not as monofactorial control.
At the gastrointestinal level, receptor distribution and autonomic interactions suggest possible influences on motility and visceral functions in specific contexts. However, in human physiology the definition of a dominant role remains less clear than for reproductive functions, and clinical relevance depends on the quality of evidence and context. This does not reduce the conceptual value of the oxytocin system as a bridge between sensory signals, autonomic circuits and visceral response, but it requires an interpretative approach based on solid evidence and pathophysiological coherence.
Overall, the possible extra-reproductive roles of oxytocin reinforce the view of the hormone as a component of a broad neuroendocrine network capable of influencing complex functional states. The core of its physiology, however, remains the labor-breastfeeding axis and the associated central modulation, which represent the context in which oxytocin function is most clearly defined and biologically indispensable.
From a pharmacological perspective, oxytocin is a relevant example of how exogenous administration can interact with a physiological system strongly dependent on receptor sensitivity, signal timing and tissue context. Exogenous oxytocin acts by binding to the OXTR receptor and partly reproducing contractile and myoepithelial effects; however, the response depends on the degree of receptor expression and the state of the myometrium or mammary tissue. This concept is crucial because labor physiology is not simply a function of hormone concentration, but the result of a progressively sensitized tissue and a network of local mediators.
Prolonged administration may be associated with phenomena of receptor desensitization and changes in responsiveness, consistent with the general physiology of G protein-coupled receptors. This property helps explain why the response may change over time and why pharmacological management requires a balance between efficacy and safety. The distinction between episodic physiological release and potentially more continuous pharmacological exposure is an important conceptual element in interpreting possible effects and limitations of therapy.
Oxytocin receptor antagonists have been developed to modulate uterine contractility in specific contexts. Their rationale derives from the role of oxytocin in supporting contractions and from the possibility of reducing contractile activity through receptor blockade. In this field as well, efficacy depends on the physiological context of the myometrium and on the presence of non-oxytocinergic contractile mediators, confirming that the labor system is multifactorial and that oxytocin is an important but not exclusive element.
Overall, oxytocin pharmacology emphasizes that clinical action does not always coincide with physiology. Physiology operates in a context of synchronous signals, afferent feedback and receptor remodeling, while pharmacological administration introduces an external input that can interact with these mechanisms differently. This distinction is fundamental for a rational approach and to avoid reductionist interpretations of the clinical response.
These principles, while remaining general, are sufficient to place oxytocin pharmacology within its physiological framework, avoiding the transformation of a highly contextual hormone into a simple contractile agent devoid of regulation.
Oxytocin represents one of the best examples of neuroendocrine integration because it combines, within a single system, the ability to generate immediate peripheral effects, such as uterine contraction and milk ejection, with the ability to modulate central circuits that support behaviors and autonomic states coherent with reproduction. This dual dimension emerges from the structure of the magnocellular system, the projection to the neurohypophysis and the presence of central paraventricular projections, creating a network in which endocrine and neural components cooperate rather than proceeding in parallel.
Oxytocin biochemistry, with its short half-life and high receptor specificity, is compatible with fine temporal control. Regulation of secretion, based on sensory afferents and neuronal synchronization, allows rapid and reproducible releases. Receptor distribution, especially its regulation in the term myometrium and mammary tissue during breastfeeding, makes target tissues capable of robust responses when necessary. The central component, by modulating stress and affiliative states, contributes to maintaining a neurophysiological context favorable to maternal function and care.
Overall, the oxytocin system shows how the hypothalamus can coordinate complex events in which mechanics, behavior and homeostasis interact. Understanding this integration provides an interpretative key for reproductive physiology and for the general principles of neuroendocrinology, in which a peptide can act as a peripheral signal and as a central modulator, with effects that depend on temporality, context and receptor plasticity.