Central neuroplasticity and decreased heart rate variability after particulate matter exposure in mice.
BACKGROUND
Epidemiologic studies show that exposure to fine particulate matter [aerodynamic diameter < or = 2.5 microm (PM(2.5))] increases the total daily cardiovascular mortality. Impaired cardiac autonomic function, which manifests as reduced heart rate variability (HRV), may be one of the underlying causes. However, the cellular mechanism(s) by which PM(2.5) exposure induces decreased HRV is not known.


OBJECTIVE
We tested the hypothesis that exposure to PM(2.5) impairs HRV by decreasing the excitability of the cardiac vagal neurons in the nucleus ambiguus. We also determined the effect of iron on PM-exposure-induced decrease in HRV.


METHODS
We measured 24-hr HRV in time domains from electrocardiogram telemetry recordings obtained in conscious, freely moving mice after 3 days of exposure to PM(2.5) in the form of soot only or iron-soot. In parallel studies, we determined the intrinsic properties of identified cardiac vagal neurons, retrogradely labeled with a fluorescent dye applied to the sinoatrial node.


RESULTS
Soot-only exposure decreased short-term HRV (root mean square of successive difference). With the addition of iron, all HRV parameters were significantly reduced. In nonexposed mice, vagal blockade significantly reduced all HRV parameters, suggesting that HRV is, in part, under vagal regulation in mice. Iron-soot exposure had no significant effect on resting membrane potential but decreased spiking responses of the identified cardiac vagal neurons to depolarizations (p < 0.05). The decreased spiking response was accompanied with a higher minimal depolarizing current required to evoke spikes and a lower peak discharge frequency.


CONCLUSIONS
The data suggest that PM-induced neuroplasticity of cardiac vagal neurons may be one mechanism contributing to the cardiovascular consequences associated with PM(2.5) exposure seen in humans.
Pham
Hai
H
Department of Pharmacology, University of California at Davis, One Shields Avenue, Davis, CA 95616, USA
Bonham
Ann C
AC
Pinkerton
Kent E
KE
Chen
Chao-Yin
CY
D000393:Air Pollutants / Q000633:toxicity*; D000818:Animals; D004562:Electrocardiography; D006339:Heart Rate / Q000187:drug effects*; D051379:Mice; D009473:Neuronal Plasticity / Q000187:drug effects*; D010316:Particle Size
D000393:Air Pollutants