Oxytocin and Vasopressin

A few years ago I read Matt Ridley's book Genome and was instantly hooked on genetics and variability in our species.  Genome does a great job of covering the basics of genetics and explaining the some of the discoveries uncovered by the mapping of our 23 chromosomes in the Human Genome Project.  Genome considers the relationship of our genes to disease, intelligence, personality, and even language.  For an amateur genetic science buff like myself, this book was a real eye opener, and helped me form the structure of the evolutionary container.

During my recent vacation I took along another Matt Ridley book, The Agile Gene.  The Agile Gene departs a bit from the hard edge scientific data of Genome, and gets into the discussion of nature vs. nurture.  Ridley goes back to Darwin and William James to explain the earliest discussions of nature vs. nurture, and reminds us it wasn't that long ago that we debated whether a donkey embryo inserted into a horse for gestation would produce a horse, or a donkey.  It produces a donkey of course.

One aspect of the book that got me thinking was the discussion of human instinct, and predetermined behavior.  William James asserted that humans have more instinct than other animals.  Noted examples are babies sucking, clasping, walking, fear of loud noises, etc.  The strongest instinct, he believed, was love.   For James to be right of course, there must be some heritable trait, a physical or chemical change in our brains when we fall in love, a change that causes love, rather than being caused by.

This leads us to Dr. Tom Insel, who studied vole monogamy (yes, certain types of voles are monogamous) and the differences in the chemical makeups, and neural receptors in the voles brains.  Prairie voles are unique among mice for their faithful bonding.  They live in couples, and share the duties of caring for their young. Montane voles are more typical in that they mate frequently, and quickly separate.  They also bear their young alone, and abandon them to live on their own after a few weeks.  Insel had been studying the hormones Oxytocin and Vasopressin since the late 80's and began looking at their effects on the mice.

Oxytocin and Vasopressin are relics of our species first leaving the water.  The Vasopressin hormone  tells the kidneys to conserve water, oxytocin tells them to excrete salt.  But, and this is a big but, the hormones are polymorphic, i.e., they serve other purposes as well.  Insel discovered that the two hormones expressed themselves similarly in both sets of mice, but that the receptors in their brains for the hormones were different.  The monogamous mice had far more Oxytocin receptors in their brains than the non-monogamous mice, and that when Oxytocin or Vasopressin were injected into the brains of the voles, the traits of monogamy were enhanced.  The same injections for the non-monogamous mice produced no results because they had limited Oxytocin and Vasopressin receptors.

The point of all of this, besides the information that emotions are indeed heritable, is that our genes are polymorphic.  They serve multiple purposes, purposes that may be totally unrelated.  So, even though our mere 30,000 genes have been considered 'light' by some who initially thought the number to be closer to 100,000, the 30,000 or so we do use can have multiple disparate purposes.

Polymorphism is a standard design principle in object oriented software development, so you can see why this caught my eye.  Its also something I'll need to consider in the development of genetic algorithms, to see if I cant allow immutable genetic variables to cross-cut concerns.  Always something to work on. 

Comments

[Susan Kuchinskas]

My understanding of Insel's work is a bit different.

The theory is that the difference between monogamous and polygamous voles is not in the amount of oxytocin receptors in their brains, but in the placement of their receptors.

Monogamous species have receptors for both oxytocin and dopamine in the parts of the brain that deal with social memory. Dopamine makes sex rewarding and causes the animal to want to do it again, thereby replicating its genes.

Oxytocin reinforces social memory, so, in the case of monogamous voles, the dopamine reward of sex is tied to the sex partner.

Vasopressin seems to be a bit different in its effects on the male brain; it may be that vasopressin reinforces monogamy in males, while oxytocin does so in females.

But the difference between monogamous and polygamous is a difference of receptor distribution among brain systems.

[Bob McGinley]

Hey Susan, Thanks for the input. So your saying that its not the number of receptors, but where the receptors are located.

Interesting. So non-monogamous voles have less oxytocin receptors in the social memory area? Or they have less social memory area in general?

So is the heritable trait a social memory area with oxytocin receptors?

And here is my big question; how big a art part does the variance in oxytocin receptors in humans play in our psychology?

[Susan Kuchinskas]

Wow, that's a great question, Bob. Larry Young has found variations in an allele (formerly known as "junk dna") that seem to correlate with how much extra-pair copulation a male vole might engage in. In fact, he's found that a very large minority of supposedly monogamous male prairie voles never form a bond. Instead, they sneak around copulating with paired females when the male partner is off nibbling roots or something.