Monday afternoon at SFN there was a very interesting symposia on oxytocin and vasopressin as mediators of stress and aggression called "Oxytocin and Vasopressin: Central Regulators of Emotion". 51 years ago, the Nobel Prize was awarded to Vincent du Vigneaud for the structure of the oxytocin peptide, and research as to what it does has come a long way. A very intersting talk was by Craig Ferris (of U Mass Medical School), described under the fold. But first a little bit about oxytocin and vasopresin.
Oxytocin is a hormone and neurotransmitter which is involved in a variety of behaviors: breastfeeding, birth, pro-social behavior, bonding, and even sex! It is (mostly) manufactured in the hypothalamus and pituitary gland where it is bound to neurophysin. Its structure is very similar to vasopressin, which is another hormone---it is primarily released when the body is low on water, and causes the kidneys to reduce urine volume and conserve water. Vasopressin is also produced in the hypothalamus.
Craig Ferris of U Mass Med School first gave a talk entitled "Using Fmri to Study the Neurobiology of Vasopressin and Oxytocin. " His data was generated in rats in a 4.7T scanner Brooker system with restrained rats. Functional imaging with BOLD (blood oxygen level dependent) was utilized to compare a control period to a stimulation period.
As the restraint itself induces stress, they included an acclimation period with a simulated imagining environment to acclimate the animals.
It is known that vasopressin enhances aggressive response (Ferris et al 1999- Beh Neuro). Administration of this hormone to rats increases the number of bites and decreases bite latency. Therefore the goal was to image aggressive motivation as a model for areas of vasopressin activation and release. Their setup was very interesting. They began with a male subject rat, and housed it with a female rat for several weeks. Then in the fMRI (during the stimulation period) a male "stranger rat" was introduced to an area which contained the female cohabitant, as was within the view of the subject rat. This induced an aggression response called "piloerection" which is the arching of the rat's back to make it look bigger. This response has been linked to vasopressin release, and was therefore a good indication of when the imaging should begin. In addition, they explored whether agressive motivation could be blocked with a vasopressin receptor antagonist. The reason behind this is that in hamsters, a receptor antagonist blocks piloerection and reduces aggressive behavior.
During the imaging study, the following results were recorded (they examined 100+ areas):
1. mate + intruder = significant activity thalamus and cortical and lateral hypothalamus and a reduction in activation in presence of antagonist. Specifically, a reduction in activity in the amygdala, hypothalamus, thalamus after the antagonist was introduced.
2. Ventricular injection of vasopressin into the lateral hypothalamus resulted in an increase in aggressive motivation and thalamus/hypothalamus/amygdala activation
As for oxytocin, they wished to observe the effects of this hormone on maternal behavior in rats. Specifically, nursing suckling causes release of oxytocin, and they wished to determine whether fMRI could show areas of activation? This required that pups must be in the fMRI machine with the mother (which was a bit of a technological feat). They found that suckling activates the PVN, pituitary, trunk area of somatosensory cortex. Futhermore, their results suggest that suckling is a rewarding experience as it activates the mesolimbic dopamine system. Interestingly, artificial suction produced the exact same activation pattern as natural suckling; pups were not even in the room! Futhermore, this activation pattern could be reversed to baseline levels by administering an oxytocin antagonist.