Story posted October 23, 2003
The goldfish in the photograph at a recent faculty seminar isn't wearing a cowboy hat, but it does sport a white, pointed cap. Not a fashion statement, the cap is essential to Richmond Thompson's research into brain chemicals and social behavior. With a nod to a Clint Eastwood western, Thompson, assistant professor of psychology and neuroscience, began his tale of "The Good the Bad and the Sexy: How Brain Chemistry Affects Social Judgments."
Thompson studies the related peptides vasotocin and isotocin. Vasotocin is present in all non-mammalian verebrates and is closely related to vasopressin, which is found in most mammals. Fish also have isotocin, which is very similar to oxytocin found in mammals. All are neurochemicals found in the brain. Most of Thompson's work focuses on vasotocin.
"In general, this peptide seems to be associated with social control in all species, but it does so in specific ways," Thompson said.
People often ask Thompson why he studies fish, and the answer he gave is simple: "I can't go into your brains so easily and do all the things I need to do to figure out how it works."
Fish are also a good candidate for studying social interaction. "They're a highly social species: they form schools, and they get really stressed out if they're left alone."
Finally, studying the same system in many animals provides important context. Because of its relationship to social behavior, insight into vasotocin could have implications for research into the role of the mammalian form of the peptide, vasopressin, in autism and aggression. Though a vasotocin/vasopressin system exists in many kinds of animals, the neurochemicals do different things in each species. For example, in finches, vasotocin stimulates aggression (as does vasopressin in hamsters); in newts, it stimulates mating behavior; and in fish Thompson's work indicates it inhibits social affiliation. But all of these instances involve "Social Judgment"
"I'm playing a little fast and loose with the term social judgment," Thompson said. Essentially it means, "the propensity to approach or withdraw from another individual."
But back to the pointed cap.
Bowdoin lab technician James Walton developed a method of surgically attaching the cap to the fish. The cap is attached to a tube that goes directly into its brain, so that Thompson and Walton can apply different peptides to the brain and observe the results.
Fish rely on olfactory cues for mating behavior, so by blocking the olfactory cues, Thompson is able to eliminate mating behavior, and observe only general social behavior among the fish.
For the first vasotocin experiment, a fish was placed in a tank with a glass wall separating him from a stimulus fish. Thompson wanted to see how long the subject fish stayed by the glass near the stimulus fish, indicating social interest. In the first experiment the subject fish was a male and the stimulus fish was another male, not known to the first. Thompson and Walton observed that when vasotocin was injected into the fish's brain, the fish became less social compared to when the same fish had saline injected into the brain. But they wanted to know more about exactly why that was happening.
"What we noticed when we ran all these tests is there's a lot of difference in
individual sociality," Thompson said.
As there are with people, there seem to be social fish and asocial fish, so Thompson wanted to find out if vasotocin affected different types of fish differently. Another series of tests revealed that in the asocial fish, vasotocin doesn't have much effect, but that in social fish vasotocin has a huge effect.
"The vasotocin is basically wiping out their social behavior," Thompson said.
But because all of the stimulus fish involved were male, Thompson knew that some might argue that vasotocin was simply masking aggression. To counter this, he decided to test the fish using female fish as stimulus fish. He continued to see vasotocin accompanied by social inhibition with female stimulus fish. Thompson believes this supports the idea that vasotocin blocks general social behavior and not aggression.
Still, there was another matter to consider - since they were injecting chemicals into a fish's brain.
"Are we really inhibiting social behavior, or are we just whacking the fish out," Thompson asked. "It's one thing to put something in the brain and see it's effect on behavior; it's another to say, do those brain systems affect normal behavior?"
For example, Thompson said, if he gave an audience member a beer, it would likely have an effect. But the brain doesn't produce beer, so what would that show about normal brain function?
To get at vasotocin's role in brain chemistry, Thompson wanted to go into the brain and block normal vasotocin, not just add additional vasotocin. He found that when you took an asocial fish and blocked the vasotocin, the fish became a social fish. The combined experiments seem a pretty clear indication that vasotocin in the brain has to do with how social the fish are. Asocial fish probably have a higher level of vasotocin in their brains.
Thompson has also studied isotocin. People usually think of vasopressin and oxytocin in mammals as being sort of a yin and yang. They are linked, but they are thought to produce opposite effects on processes that control social behavior. There isn't much direct evidence for that, however, this played out for vasotocin and isotocin, in Thompson's fish: Vasotocin inhibited social behavior and isotocin stimulated it, which suggests that sociability is a result of some balance between the two.
Because of observations he made in other research with newts, Thompson also wondered if olfactory cues would affect social approach in fish and whether they worked through the vasotocin system.
Thompson has found that, when presented with a model of a female newt that has been coated with female scent, the male newt will attempt to mate with the female model, but not when presented with an unscented model. Thompson found that exposure to a pheremone changed the electrical activity in the newt's brain and affected its mating behavior. Because similar effects have been observed when vasotocin is put in the newt brain, Thompson believes that the pheremone stimulates the release of vasotocin. This was supported in another experiment, in which blocking the vasotocin in the newt's brain prevented the pheremone from making the male newt responsive to the female's physical cues.
Thompson believes that olfactory cues and vasotocin could likewise be linked in fish. When he put "male scented" water into the fish tank, it made other male fish less social, the same effect he got by infusing vasotocin into the brain. He therefore thinks that the olfactory cues could affect the level of vasotocin in fish brains, as it does in newts. Next Thompson plans to test whether blocking the vasotocin will mask the effect of the male-scented water, which would demonstrate vasotocin's role as a link between social stimuli and behavioral responses.
All of this work involves observing the effects of vasotocin, but Thompson has also been looking at the production and transport of peptides in the brain. Thompson is able to observe various brain chemicals by using fluorescent molecules. These molecules attach to antibodies that attach to the vasotocin, so Thompson can observe the movement of vasotocin by following the fluorescent colors. While vasotocin is produced in only one place in a fish's brain, Thompson has observed that it is released in two places, an area known as the dorsal motor vagus nucleus, which regulates the autonomic nervous system, and a different part of the brain responsible for monitoring the signals sent back from the body. Since he knows the behavioral effects of vasotocin, and he knows areas in the brain in which it is released, the next step is discovering if the vasotocin is affecting behavior by changing the body's responses or by changing the way the brain reacts to the body's responses.