Department of Biology

Program

Evolution, Ecology & Behavior

Research Area

Behavior

Education

Ph.D., University of Washington, 1997

Awards

Ralph E. Powe Junior Faculty Enhancement Award, the Oak Ridge Associated Universities, 2006

Research Description

What is serotonin doing in the auditory system?
Most of us think of the neuromodulator serotonin in the context of its regulation of behaviors such as mood (Prozac), appetite (Phen-fen), and aggression. What is less well-known is that this neural signaling molecule is also found within sensory systems, where it helps us to filter and make sense of our complicated sensory environments. In the Hurley lab, we would like to know how serotonin is involved in the regulation of normal perception and behavior as well as in pathologies of the auditory system. Because we understand so little about these topics, this research area can accommodate many new projects and ideas.

We currently use multiple techniques in several research areas: 1) The roles that particular types of serotonin receptors play in mediating the effects of serotonin; 2) How serotonin levels fluctuate within the auditory system under different behavioral circumstances; and 3) How fluctuations in the level of serotonin affect auditory perception and behavior. These areas are described in more detail further down.

Comparative models for the study of auditory processing
We have used both echolocating bats and mice in our research. Bats are fascinating animals that make excellent models for the study of the auditory system. They rely on echolocation to navigate and catch their insect prey, but as social animals they also have a rich repertoire of communication calls. Reflecting the fact that sound is so important to them, bats have hypertrophied auditory systems that are relatively easy to study. At the same time, however, many aspects of their auditory systems are strikingly similar to those seen in other mammals, which facilitates the extrapolation of some experimental findings to other species.

More recently, we have also begun to use mice to address our experimental questions, and so far have found that serotonin acts in similar ways in mice and bats. This bolsters the idea that serotonin function is generally conserved in different species of mammal.

In both of these animal models, we study the effects of serotonin in a particular part of the auditory system called the inferior colliculus (IC). This auditory region is directly on the neural pathway leading from the ear to higher centers like the cortex, and integrates many types of auditory information. The IC is also involved in a range of important auditory-related behaviors, creating the potential for testing the role of serotonin in these behaviors in the future.

RESEARCH AREAS

1) Roles of serotonin receptors:
The release of serotonin is a neural signal that is ’received’ by many different types of transmembrane receptors. These receptors then translate the serotonin signal into neuron-specific effects. Thus, by targeting different types of neurons and having different effects on these neurons, serotonin receptors can reconfigure the auditory circuits of the brain. In keeping with these principles, we have found that activating different types of serotonin receptors in the auditory system cause different types of changes in the ways that neurons respond to sound. At least one of these receptors, the serotonin 1A receptor, also targets neurons with different response properties, in different locations of the IC. We are continuing to explore the functional consequences of the distinct roles of serotonin receptors.

2) Serotonin levels and behavioral state:
Based on the activity of neurons that deliver serotonin to the auditory system, it has been predicted that more serotonin is released in the auditory system when animals are awake and alert, and less serotonin is released during sleep cycles. In addition, it is possible that there are more transient changes in response to environmental events. However, very little is known regarding how serotonin levels fluctuate under these types of conditions. We have recently added a new technique to the lab that will allow us to directly measure serotonin levels within the auditory system, something that will help us explore the normal fluctuations in serotonin during a range of different behaviors.

3) Does serotonin affect auditory perception and behavior?
Understanding how serotonin alters the perception of sound will ultimately involve making behavioral measurements. A brand-new project we have begun in the lab aims to determine whether serotonin influences auditory learning, but many other aspects of auditory perception remain to be tested.

People: the most important resource
The work that we accomplish depends on having able and enthusiastic people from a diversity of backgrounds, so that new ideas are always coming up. Lab members from the undergraduate to the postgraduate level have made important contributions to our research! If you are interested in applying to work with me or looking into the wonderful undergraduate or graduate programs we have on the Bloomington campus, follow these links: Graduate Program in EEB, Graduate Program in Neuroscience. In the future, I expect that the pursuit of these questions will take my students and me to many different levels of analysis, ranging from ion channels to behavior, and will lead to new and interesting ideas about neuromodulator-induced plasticity in the auditory system.

Select Publications

Hurley LM, Bohorquez A, Tracy J. 2008. The serotonin 1B receptor modulates frequency response curves and spectral integration in the inferior colliculus by reducing GABAergic inhibition. J Neurophysiol. 100:1656-67.

Hurley LM, Bohorquez A, Tracy J. 2008. The serotonin 1B receptor modulates frequency response curves and spectral integration in the inferior colliculus by reducing GABAergic inhibition. J Neurophysiol. 100:1656-67.

Hall IC and Hurley LM 2007. The serotonin releaser fenfluramine alters the auditory responses of inferior colliculus neurons. Hear Res 228(1-2):82-94.

Hurley LM 2007. Activation of the serotonin 1A receptor alters the temporal characteristics of auditory responses in the inferior colliculus. Brain Res 1181:21-9.

Hurley LM 2006. Different serotonin receptor agonists have distinct effects on sound-evoked responses in inferior colliculus. J Neurophysiol. 96(5):2177-88.

Hurley LM and Pollak GD 2005. Serotonin shifts first-spike latencies of inferior colliculus neurons. J Neurosci. 2005 Aug 24;25(34):7876-86.

Hurley LM and Pollak GD 2005. Serotonin selectively modulates responses to species-specific vocalizations in the inferior colliculus. J Comp Physiol A, Apr 14 (Epub 2005 Apr 14)

Thompson AM, Hurley LM. 2004. Dense serotonergic innervation of principal nuclei of the superior olivary complex in mouse. Neurosci Lett, 168: 179-182.

Hurley LM, Devilbiss DM, Waterhouse BD 2004. A matter of focus: monoaminergic modulation of stimulus coding within mammalian sensory networks. Current Opinion in Neurobiology, 14: 488-495. (invited review)

Hurley, LM; Thompson, AM; Pollak, GD. 2002. Serotonin in the inferior colliculus. Hearing Research, 168:1-11. (review)

Klug A, Bauer EE, Hanson J, Hurley LM, Meitzen J, Pollak GD. 2002. Inhibition generates response selectivity for species-specific calls in the inferior colliculus of Mexican free-tailed bats. Journal of Neurophysiology 88: 1941-1954.

Hurley, LM and Pollak, GD. 2001. Serotonin effects on frequency tuning of inferior colliculus neurons. Journal of Neurophysiology, 85(2):828-42.

Hurley, LM and Thompson, AM. 2001. Serotonin staining in the auditory brainstem of the Mexican free-tailed bat, Journal of Comparative Neurology, 435(1):78-88.

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