Abstract
We previously reported that parasympathetically‐mediated bradycardia in response to white noise sound (WNS) exposure in conscious rats was suppressed by muscimol, a GABAA receptor agonist, microinjected into the lateral/ventrolateral periaqueductal gray (l/vlPAG). This finding prompted us to determine if the rat l/vlPAG is activated by the WNS exposure. Rats were exposed to 30‐min WNS at 90 dB, which evoked freezing behavior, an index of fear. We examined the distribution of cells expressing Fos, a marker of neuronal activation, in the WNS‐exposed rats and control rats which had not been exposed to WNS (N=6 for each). The WNS exposure significantly (P<0.05) increased Fos positive cells in l/vlPAG, as well as dorsolateral PAG, as compared to the control. Subsequently, we investigated if Fos positive cells in the PAG after the WNS exposure in rats would be immunolabeled with cholera toxin b‐subunit, a retrograde tracer, previously microinjected into the nucleus ambiguus (NA) (N=2). Our pilot data suggested that there were neuronal projections from l/vlPAG to NA which were activated by the WNS exposure. In conclusion, the l/vlPAG‐NA pathway may play a role in evoking bradycardia in response to exposure of WNS. Supported by JSPS Kaken 26670112.
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