Abstract
An alerting sound elicits the Acoustic Startle Response (ASR) that is dependent on the sound volume and organisms’ state, which is regulated by neuromodulatory centers. The locus coeruleus (LC) neurons respond to salient stimuli and noradrenaline release affects sensory processing, including auditory. The LC hyperactivity is detrimental for sensorimotor gating. We report here that priming microstimulation of the LC (100-ms at 20, 50, and 100 Hz) attenuated the ASR in rats. The ASR reduction scaled with frequency and 100 Hz-stimulation mimicked pre-exposure to a non-startling tone (prepulse). A rapid (~ 40 ms) EEG desynchronization following the LC stimulation suggested that the ASR reduction was due to elevated cortical arousal. The effects of LC stimulation on the ASR and EEG were consistent with systematic relationships between the ASR, awake/sleep state, and the cortical arousal level; for that matter, a lower ASR amplitude corresponded to a higher arousal level. Thus, the LC appears to modulate the ASR circuit via its diffuse ascending projections to the forebrain saliency network. The LC modulation directly in the brainstem and/or spinal cord may also play a role. Our findings suggest the LC as a part of the brain circuitry regulating the ASR, while underlying neurophysiological mechanisms require further investigation.
Highlights
An alerting sound elicits the Acoustic Startle Response (ASR) that is dependent on the sound volume and organisms’ state, which is regulated by neuromodulatory centers
Our present study demonstrated that a brief phasic locus coeruleus (LC) activation shortly preceding a startle-eliciting sound reduced the magnitude of the ASR in spontaneously behaving rats
The ASR attenuation by preceding LC activation was accompanied by a change of the EEG spectral components that were indicative of higher cortical arousal
Summary
An alerting sound elicits the Acoustic Startle Response (ASR) that is dependent on the sound volume and organisms’ state, which is regulated by neuromodulatory centers. An alerting stimulus can induce an eye blink, contraction of the facial, neck, and skeletal muscles as well as various visceral reactions These innate startle reflexes, which are triggered by abrupt environmental changes, initiate more complex forms of adaptive response from orienting and e xploration[1] to defensive b ehaviors[2]. We mimicked the LC phasic response by applying a mild electric current to the LC cell b odies[32] and paired the LC stimulation with the startling sound. We report that phasic LC activation paired with a startle-eliciting sound attenuated the ASR to the same extent as the auditory prepulse
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