andrewducker | Chemical of love

minkyboylove mentioned Oxytocin in her journal in association with orgasm, which sent me in search of more references. I'd now like to know why I've not bumped into this before!

First, infusion of oxytocin into the ventricles of the brain of virgin rats or non-pregnant sheep rapidly induces maternal behavior. Second, administration into the brain of antibodies that neutralize oxytocin or of oxytocin antagonists will prevent mother rats from accepting their pups. Other studies support the contention that this behavioral effect of oxytocin is broadly applicable among mammals.

While there is no doubt that oxytocin stimulates all of the effects described above, doubt has recently been cast on its necessity in parturition and maternal behavior. Mice that are unable to secrete oxytocin due to targeted disruptions of the oxytocin gene will mate, deliver their pups without apparent difficulty and display normal maternal behavior. However, they do show deficits in milk ejection and have subtle derangements in social behavior. It may be best to view oxytocin as a major facilitator of parturition and maternal behavior rather than a necessary component of these processes.

Which makes it sound like the receptors have to be functioning, but the oxycytin doesn't necessarily have to be produced directly.

A number of factors can inhibit oxytocin release, among them acute stress. For example, oxytocin neurons are repressed by catecholamines, which are released from the adrenal gland in response to many types of stress, including fright.

A number of studies have implicated the neurohypophyseal peptides oxytocin and vasopressin in the central mediation of complex social behaviors, including affiliation, parental care and territorial aggression. Research on a monogamous rodent, the prairie vole (Microtus ochrogaster), suggests that these neuropeptides are also involved in the control of several behaviors associated with monogamy, including pair bonding, paternal care and mate guarding. Comparative studies using several species of vole have identified species-specific patterns of oxytocin- and vasopressin-receptor expression in the brain that appear to be associated with a monogamous versus non-monogamous social structure. Molecular studies suggest that changes in the regulation of oxytocin- and vasopressin-receptor gene expression underlie these species differences in receptor distribution and might provide a mechanism for the evolution of monogamy in voles.

Most behavioral and physiological effects induced by oxytocin can be blocked by oxytocin antagonists. In contrast, the antistress effects can not, suggesting that unidentified oxytocin receptors may exist.

Sexually naive female prairie voles received a daily subcutaneous injection of 20 microg oxytocin or isotonic saline for 5 days before being placed with a sexually experienced male for 48 h. Females treated with oxytocin were significantly more likely to mate during this period than saline-treated females.

Oxytocin is a pro-social hormone that affects the brain as a result of its interactions with gonadal steroids like estrogen, progesterone, testosterone and corticosterone.

"The brain affects behavior, but behavior also affects the brain," Witt said. "The brain is very plastic and these gonadal steroids provide a certain milieu in which other chemicals, like oxytocin, can affect the brain."

Animal studies, from Witt’s lab and others, have shown that oxytocin can have dramatic effects on behavior. When the natural release of oxytocin is blocked, for instance, mothers - from sheep to rats - reject their own young.

Meanwhile, virgin female rats injected with oxytocin fawn over another female’s young, nuzzling the pups and protecting them as if they were their own.

More here and here