Research has found that it’s more startling to hear a single loud sound than a soft sound followed by a loud sound. This neurological phenomenon is called pre-pulse inhibition and exists so that the body can adapt to loud stimuli when it is supplied with a warning. Pre-pulse inhibition itself is not a particularly essential brain function, but deficits in pre-pulse inhibition have been correlated to other neurological disorders, including schizophrenia, attention deficit disorder (ADD) and obsessive-compulsive disorder (OCD).
Allison Reeder ’14 has been awarded a science summer research grant to study pre-pulse inhibition in rats under the direction of Stone Professor of Psychology and Director of the Hamilton College Neuroscience Program Douglas Weldon. Reeder, a mathematics and neuroscience dual concentrator, is researching the roles of specific neurotransmitters in the brain as they pertain to pre-pulse inhibition, with a focus on the chemicals dopamine and serotonin. A better understanding of the relationship between pre-pulse inhibition and related disorders could result in the development of antipsychotic drugs that target the pre-pulse inhibition system but also treat the various symptoms of schizophrenia, ADD and OCD.
Reeder’s research involves 42 rats which are either injected with various chemicals designed to affect brain receptors or a harmless saline control solution. The experimental group of rats is injected with a dopamine receptor antagonist and a serotonin receptor antagonist. The dopamine receptor antagonist is known to cause a deficit in pre-pulse inhibition, while the serotonin receptor antagonist is suspected of reducing the deficit in pre-pulse inhibition caused by the previously administered drug. After being injected with the two antagonists or a control solution, the rats undergo a waiting period to allow the drugs to take effect.
The rats are then individually placed in a device known as a startle chamber. The chamber administers a series of startling stimuli (loud noises) followed by a series of non-startling stimuli paired with subsequent startling stimuli (soft noises followed by loud noises). The chamber then creates a stimulus free environment. The startle chamber measures the height that the rats jump as each series of stimuli is administered in order to determine if each rat’s pre-pulse inhibition is impeded by the administered drug. The rats are finally placed in an open space where their motor activity is recorded by a tracking camera and a program called AnyMaze. Reeder runs 58 individual trials for all 42 of the rats.
Despite Reeder’s initial hypothesis, the serotonin receptor antagonist she administered does not seem to be correlated with a reduction in the effect of the dopamine receptor antagonist. In fact, Reeder’s data indicates that the serotonin receptor antagonist may even cause the opposite effect, and increase the level of pre-pulse inhibition.
Although the drugs Reeder administered did not have the desired effect, her research can hardly be called a failure. The data she has collected will aid researchers in understanding the relationship between dopamine and serotonin in pre-pulse inhibition and may still lead to discoveries pertinent to neurological disorder research. Regardless of her results, Reeder believes that “this research will help [her] future career goals because it has confirmed [her] interest in neuroscience.” She hopes to attend medical school or a neuroscience graduate program and says that her time studying pre-pulse inhibition at Hamilton will prove useful in her future research endeavors.
Reeder is a graduate Kearsarge Regional High School (N.H.)
