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=Oxytocin=

Peripheral (hormonal) actions
Humans with autism who have the R140 allele have lower plasma levels of oxytocin in their blood compared to those with autism who do not have the allele and those without autism who have the allele. The R140 allele is a single nucleotide polymorphism (SNP) in the gene coding for CD38, which causes the amino acid arginine to be produced instead of tryptophan at codon 140 in CD38. CD38 is a transmembrane protein, which regulates the release of oxytocin.

Autism and Schizophrenia
Oxytocin has been shown to improve the symptoms of those with autism. A nasal dose of oxytocin has increased the comprehension and memory of social cues, such as tone of voice. Nasal doses of oxytocin also were noted to improve the recognition of others' emotions by their tone of voice, suggesting that oxytocin could be an effective treatment for the symptoms associated with autism.

Patients with schizophrenia have benefited from oxytocin treatment. Humans with schizophrenia typically have lower functioning verbal memory in comparison to the unafflicted population. A daily nasal dose of oxytocin has been reported to improve their scores on the CVLT test, which assesses new learning and declarative verbal memory, but not the LNS test, which assess working memory. Humans with schizophrenia have problems with exhibiting empathy for others. Oxytocin receptor SNPs have been associated with the decreased level of empathy those with schizophrenia demonstrate. The rs53576 SNP is the change of guanine base pair to an adenosine base pair in the oxytocin receptor gene. Those without the SNP are better at discerning the emotional state of others, while those with the SNP are not and have a higher risk of developing unipolar depression and an autism spectrum disorder.

Autism and schizophrenia have also been linked to mutations in genes associated with oxytocin. The rs2254298 SNP is a change in the DNA from a guanine base pair to an adenine base pair, producing a GA or AA genotype. The rs2254298 adenine SNP was determined to be beneficial for those with autism and those with schizophrenia. Humans with schizophrenia with either the GA or AA genotype have more sensitivity, sympathy, compassion, and concern for others. The rs2254298 SNP was also found to have the same affect in those with autism. Because the rs2254298 SNP has the same effect in those with schizophrenia and those with autism, there is a possibility that two disorders have a similar genetic foundation.

Memory
Oxytocin generally increases human recollection of positive (i.e. happy or surprised) human faces. Men given a nasal dose of oxytocin remember faces that are happy more frequently than faces that are angry or neutral. The increase in memory of positive faces and decrease in memory of negative or neutral faces suggests that oxytocin causes the brain to focus more heavily on positive social stimuli, while also decreasing the brain’s focus on neutral or negative stimuli.

The current findings on whether oxytocin decreases the memory of negative stimuli are contradictory. One study suggests that oxytocin increases memories of positive and negative faces and has no effect on the memory of non-social cues, such as pictures of houses and landscapes. Another finding indicates that oxytocin has a negative relationship with remembering non-social stimuli because oxytocin decreased the participants’ ability to remember pictures of houses. The impact of oxytocin on negative social stimuli has still not reached a consensus. Oxytocin decreases the human fear response. Men given oxytocin have a slower reaction time in identifying fear stricken faces. The decreased response to fearful faces can be attributed to oxytocin because oxytocin is believed to activate receptors in the amygdala that reduce fear. This conclusion is also reinforced by animal research, which reports that neuroimaging data of rats given oxytocin showed decreased activity in the amygdala, which controls the fear response in both rats and humans.

Although oxytocin is typically linked with stirring positive emotions and associations, childhood memories of parents after men and women were given oxytocin have been recalled to be more positive or negative depending on the type of childhood the person had. After oxytocin administration, those who had good childhood relationships with their mothers would recall the relationship with their mother to be more positive than they had stated before being given oxytocin. After those who had poor childhood relationships with their mothers were administered oxytocin, they recalled the relationship with their mother to be worse than they had stated before oxytocin administration. Also, when plasma levels of oxytocin in the blood were examined in women, it was found that women who had been abused by their parents when they were children had lower levels of oxytocin, while women who had positive memories of their childhood had higher levels of oxytocin. Finding that the concentration of oxytocin can vary depending on a person’s childhood suggests that in addition to having a genetic component, oxytocin levels also depend on environmental factors.

Cognition
Oxytocin is involved in human interpretation of facial expressions. Men given oxytocin are less likely to misclassify expressions of happiness or surprise, while they are more likely to misclassify expressions of anger, disgust, fear, or sadness. Oxytocin also affects how the brain comprehends the connotations of words. In one study, men given oxytocin were asked to pick out words that described themselves. Afterwards, when they were asked to remember which words they chose, they remembered the positive words more often than the negative words. The role of oxytocin in distinguishing positive and negative words was demonstrated when men were asked to classify words in categories such as relationship, sex, safety, threat, happiness, and sadness as either positive or negative. If the category was relationship, then the words would be love and hate. The participant would have to indicate which word was positive and which word was negative, and the speed at which they correctly decided this was noted. Oxytocin appeared to cause men to more quickly notice positive social words related to sexuality, bonding, and social relationships, while they recognized the nonsocial positive and negative words at the same rate.