mopey voles -- 2/14/18

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Today's selection - - from The Chemistry Between Us by Larry Young, PhD, and Brian Alexander. Prairie voles often bond for life, and when they are separated they appear to go through withdrawal:

"To investigate the rodent version of getting hugs, and what happens in the absence of hugs from a bonded partner, [German scientist Oliver] Bosch took virgin males and set them up in vole apartments with roommates -- either a brother they hadn't seen in a long time or an unfamiliar virgin female. As males and females are wont to do, the boy-girl roommates mated and formed a bond. After five days, he split up half the brother pairs, and half the male-female pairs, creating what amounted to involuntary vole divorce. Then he put the voles through a series of behavioral tests. ...

"All these tests, commonly used to test lab animals for depression, showed that if you separate a pair-bonded male vole from his mate, you'll get a very mopey vole who uses what's called passive-stress coping to deal with the overwhelming anxiety of partner loss. 'When the separation takes place, this is what causes the animals to feel so bad,' Bosch explains. 'We found this increased depressive behavior and that tells us the animal is not feeling well.' He doesn't mean 'under the weather,' he means the divorced voles are emotionally miserable. ...

"To explain the physiology behind this passive depression state in the separated voles, Bosch checked their chemistry. The males separated from their mates had much higher levels of corticosterone, a stress chemi­cal, in their blood than did any of the other groups, including voles sepa­rated from their brothers. Their HPA [hypothalamic/pituitary/adrenal] axis was working so hard, their adrenal glands weighed more. Bosch nailed CRF's [corticotropin-releasing factor] role in driving both the HPA axis overdrive and the mopey behavior by blocking CRF recep­tors in the voles' brains. When he did, the divorced voles no longer hung limply from the sticks. They didn't float for as long in the water. They still remembered their mates, and were still bonded to them; they just didn't worry about it when they left them.

"But here's the strange thing: both the voles who stayed with their fe­male mates and the voles who were forced to split from the females had much more CRF in the BNST [bed nucleus of stria terminalis] than did males who lived with, or were separated from, their brothers. In other words, loads of this stress-related hormone were being pumped in both the voles who got depressed after separation and voles who were still happily bonded and didn't show signs of passive-stress coping.

"'Bonding itself produces high CRF,' Bosch says. 'But this does not mean the system is also firing.' There is something fundamental about living with a mate that results in more CRF stress hormone in the brain, but that also prevents the engagement of the HPA stress axis as long as the mates stay together.

"For humans, falling in love, ... you're lured into a relationship, enjoy its pleasures, and then, over time, those plea­sures fade and compulsion takes over. 'It is a quite similar situation, you know, to when a person at first has the high feeling in a relationship, the CRF is silent, and the dopamine reward is taking over,' Bosch says. 'You feel high. Everything is cool. Everything is nice. Then, after a while, nature makes sure you still want to stay with a partner. And this system makes you feel sick as soon as you leave the mate. This is the idea of the whole story.'

"We ask if he believes this means the voles are returning because they are still positively motivated to be with their partners -- the 'liking' phase -- or because they want the misery of the separation to stop -- the 'wanting' phase. They want the misery to stop, he answers. 'We have this normal together, whatever that normal is. And the bad feeling forces you to come back.'

"[George] Koob, [chairman of the Committee on the Neurobiology of Addictive Disorders at the Scripps Research Institute] agrees. The CRF system is there, he explains, to signal that a loss has occurred and we need to do something about it. Likewise, when rats are taken off drugs, and their brains tested in real time for CRF levels, he finds a large boost in CRF in the relevant reward regions. When alco­holic rats denied booze are given the same CRF-blocking drug Bosch used in the voles, they stop drinking excessively even if given access to alcohol, and they don't show the same passive-stress coping."

author:	Larry Young, PhD, and Brian Alexander
title:	The Chemistry Between Us: Love, Sex, and the Science of Attraction
publisher:	Current, Published by the Penguin Group
date:	Copyright 2012 by Larry J. Young and Brian Alexander
pages:	198-202