Oxytocin
Nasally administered oxytocin has been reported to reduce fear, possibly by inhibiting the amygdala (which is thought to be responsible for fear responses). Indeed, studies in rodents have shown oxytocin can efficiently inhibit fear responses by activating an inhibitory circuit within the amygdala. Some researchers have argued oxytocin has a general enhancing effect on all social emotions, since intranasal administration of oxytocin also increases envy and "Schadenfreude". Individuals who receive an intranasal dose of oxytocin identify facial expressions of disgust more quickly than individuals who do not receive oxytocin. Facial expressions of disgust are evolutionarily linked to the idea of contagion. Thus, oxytocin increases the salience of cues that imply contamination, which leads to a faster response because these cues are especially relevant for survival. In another study, after administration of oxytocin, individuals displayed an enhanced ability to recognize expressions of fear compared to the individuals who received the placebo. Oxytocin modulates fear responses by enhancing the maintenance of social memories. Rats that are genetically modified to have a surplus of oxytocin receptors display a greater fear response to a previously conditioned stressor. Oxytocin enhances the aversive social memory, leading the rat to display a greater fear response when the aversive stimulus is encountered again.
Oxytocin treatment for postpartum depression
Intranasal (IN) administration, as opposed to more conventional routes, such as oral or intravenous infusion, offers an alternative method for drug delivery. This method is often the preferred method. Oxytocin (OT) is a neuropeptide that can be administered in this manner. IN delivery methods are gaining popularity due to the non-invasive nature of the method. IN generally does not require complicated sterile preparations, is relatively painless, and often can be administered quickly by a medical doctor, or in some cases the patient. IN maximizes the convenience and comfort of the patient, making a treatment regimen more likely to be followed. During Postpartum Depression (PPD), some women may be less likely to seek treatment if treatment is inconvenient. In addition, new mothers (especially if suffering with depression) may feel socially isolated or overwhelmed by responsibilities of caring for a new infant. IN not only provides a convenient delivery method, but is also a logical choice based on efficacy. Tissue in nasal cavities is highly vascular, providing a large surface area for absorption. Large surface areas allow for quick drug onset, meaning greater potential for the drug to reach the central nervous system without undergoing first-pass metabolism. Avoiding first-pass metabolism allows more of the drug to be available for treatment. Gastrointestinal discomfort and digestive side-effects can also be avoided by IN dosage. IN delivery allows OT to cross the blood brain barrier, expediting the drug to the central nervous system and cerebrospinal fluid. The blood-brain-barrier normally protects the brain by blocking certain chemicals and toxins from reaching the brain. Increased levels of OT can be found in salivary samples after intranasal administration of the neuropeptide. Salivary OT levels can remain higher than baseline levels four hours after dosage, suggesting that OT is still producing an active response. This may be an effective way of monitoring levels of OT levels during short-term treatment or help identify women at risk of or have a history of PPD. Though OT can be administrered intravenously (and is sometimes the appropriate method depending on the medical situation), IN administration offers many advantages that make it an ideal choice for short-term treatment.