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Circadian modulation in the rat acoustic startle circuit
1Department of Psychology, University of Toronto, Ontario, Canada.
Behavioral Neuroscience
|February 1, 1995
Summary
The acoustic startle reflex (ASR) in rats is stronger at night. This study found the circadian modulation occurs later in the neural pathway, possibly at spinal interneurons or motoneurons.
Area of Science:
- Neuroscience
- Chronobiology
- Physiology
Background:
- The acoustic startle reflex (ASR) shows significant daily fluctuations.
- Previous research indicates ASR is modulated by the circadian system, with higher amplitudes during the subjective night.
Purpose of the Study:
- To pinpoint the location of circadian modulation within the primary ASR neural circuit.
- To differentiate between central and peripheral circadian influences on the ASR.
Main Methods:
- Rats were subjected to acoustic and electrical stimulation to evoke the ASR.
- Stimulation was delivered via electrodes implanted within the primary ASR circuit.
- ASR amplitudes were measured across different phases of the circadian cycle under constant conditions.
Main Results:
- Circadian modulation of ASR was observed, with greater amplitudes during subjective night.
- Both acoustically and electrically evoked startle responses showed this nocturnal enhancement.
- Electrical stimulation at the ventral lateral lemniscus and medial longitudinal fasciculus revealed amplified responses during subjective night.
Conclusions:
- Circadian modulation of the ASR is not confined to early brainstem processing.
- The data suggest a site of modulation exists after the caudal pontine reticular formation.
- Potential locations for this modulation include spinal interneurons, motoneurons, or the neuromuscular junction.