The Journal of Neuroscience, September 15, 1999, 19(18):8071-8082
Serotonin Differentially Modulates Responses to Tones and
Frequency-Modulated Sweeps in the Inferior Colliculus
Laura M.
Hurley and
George D.
Pollak
University of Texas, Austin, Texas 78712
Although almost all auditory brainstem nuclei receive serotonergic
innervation, little is known about its effects on auditory neurons. We
address this question by evaluating the effects of serotonin on
sound-evoked activity of neurons in the inferior colliculus (IC) of
Mexican free-tailed bats. Two types of auditory stimuli were used: tone
bursts at the neuron's best frequency and frequency-modulated
(FM) sweeps with a variety of spectral and temporal structures.
There were two main findings. First, serotonin changed tone-evoked
responses in 66% of the IC neurons sampled. Second, the influence of
serotonin often depended on the type of signal presented. Although
serotonin depressed tone-evoked responses in most neurons, its effects
on responses to FM sweeps were evenly mixed between depression and
facilitation. Thus in most cells serotonin had a different effect on
tone-evoked responses than it did on FM-evoked responses. In some
neurons serotonin depressed responses evoked by tone bursts but left
the responses to FM sweeps unchanged, whereas in others serotonin had
little or no effect on responses to tone bursts but substantially
facilitated responses to FM sweeps. In addition, serotonin could
differentially affect responses to various FM sweeps that differed in
temporal or spectral structure. Previous studies have revealed that the efficacy of the serotonergic innervation is partially modulated by
sensory stimuli and by behavioral states. Thus our results suggest that
the population activity evoked by a particular sound is not simply a
consequence of the hard wiring that connects the IC to lower and higher
regions but rather is highly dynamic because of the functional
reconfigurations induced by serotonin and almost certainly other
neuromodulators as well.
Key words:
serotonin; inferior colliculus; auditory; neuromodulation; brainstem; frequency modulation
Copyright © 1999 Society for Neuroscience 0270-6474/99/19188071-12$05.00/0
Previous Article | Next Article
