Effects of Hypercapnic Acidosis on Action Potential Properties of Locus Coeruleus Neurons from the Neonatal Rat

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Central chemosensitive neurons increase their firing rate (FR) during hypercapnia acidosis (HA). We measured changes in membrane resistance (Rin), rheobase and action potential (AP) properties of neurons in the locus coeruleus (LC) to determine which ion channels may be contributing to the CO2-induced FR response. Whole cell recordings were made from LC neurons (n=6) in brainstem slices sectioned from neonatal rats (P11–P13), superfused with artificial cerebral spinal fluid or chemical synaptic blockade medium (11.4 mM Mg2+, 0.2 mM Ca2+) with a gap junction blocker (100µM carbenoxolone). HA caused a non-significant increase in Rin (34 ± 9 M); however, blockade of chemical and electrical synapses resulted in a significant increase in Rin (87 ± 21 M, P<0.05) and HA caused an additional increase of 27 ± 22 M (P<0.05). HA had no effect on AP properties; however, synaptic blockade increased the depolarization threshold (5 ± 8 mV, P<0.05), decreased the rate of depolarization (41 ± 11 mV ms–1, P<0.05), decreased the rate of repolarization (29 ± 7 mV ms–1, P<0.05), decreased AP height (45 ± 16 mV, P<0.05), and decreased the after-hyperpolarization (24 ± 6 mV, P<0.05). The increased Rin during HA and synaptic blockade supports a role for K+ channels, but the high variability of AP properties supports the multiple factors model for chemosensitivity.

[Supported by NIH grants R01HL56683 & F32 HL80877].


Presented at the 2007 Federation of American Societies for Experimental Biology (FASEB) Science Research Conference, Washington, DC.

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