Role played by periaqueductal gray neurons in parasympathetically mediated fear bradycardia in conscious rats

Content Provider	Semantic Scholar
Author	Koba, Satoshi Inoue, Ryo Watanabe, Tatsuo Bunkyo-ku
Copyright Year	2016
Abstract	Freezing, a characteristic pattern of defensive behavior elicited by fear, is associated with a decrease in the heart rate. Central mechanisms underlying fear bradycardia are poorly understood. The periaqueductal gray (PAG) in the midbrain is known to contribute to autonomic cardiovascular adjustments associated with various emotional behaviors observed during active or passive defense reactions. The purpose of this study was to elucidate the role played by PAG neurons in eliciting fear bradycardia. White noise sound (WNS) exposure at 90 dB induced freezing behavior and elicited bradycardia in conscious rats. The WNS exposure-elicited bradycardia was mediated parasympathetically because intravenous administration of atropine abolished the bradycardia (P < 0.05). Moreover, WNS exposure-elicited bradycardia was mediated by neuronal activation of the lateral/ventrolateral PAG (l/vlPAG) because bilateral microinjection of muscimol, a GABAA agonist, into the l/vlPAG significantly suppressed the bradycardia. It is noted that muscimol microinjected bilaterally into the dorsolateral PAG had no effect on WNS exposure-elicited bradycardia. Furthermore, retrograde neuronal tracing experiments combined with immunohistochemistry demonstrated that a number of l/vlPAG neurons that send direct projections to the nucleus ambiguus (NA) in the medulla, a major origin of parasympathetic preganglionic neurons to the heart, were activated by WNS exposure. Based on these findings, we propose that the l/vlPAG-NA monosynaptic pathway transmits fear-driven central signals, which elicit bradycardia through parasympathetic outflow.
Starting Page	379
Ending Page	389
Page Count	11
File Format	PDF HTM / HTML
Alternate Webpage(s)	http://physreports.physiology.org/content/physreports/4/12/e12831.full.pdf
PubMed reference number	27335434v1
Alternate Webpage(s)	https://doi.org/10.14814/phy2.12831
DOI	10.14814/phy2.12831
Journal	Physiological reports
Volume Number	4
Language	English
Access Restriction	Open
Subject Keyword	Atropine Behavior Bradycardia Cell Nucleus Central gray substance of midbrain Fear (Mental Process) Freezing Leukocytes Microinjections Midbrain structure Muscimol Neurons Projection Defense Mechanism Structure of nucleus ambiguus
Content Type	Text
Resource Type	Article