Poster T11 - Neurocardiac Optogenetic Applications in Langendorff Perfused Mouse Hearts

Introduction: Balance of cholinergic and catecholaminergic activation is necessary to maintain heart health. A greater understanding of the relationship between these pathways is crucial to improving cardiac interventions. Interrogating the interaction between these pathways can be done using optogenetics via selective expression of channelrhodopsin (ChR2) in neuron populations. Optogenetics allows for the study of intrinsic release of neurotransmitters in a spatiotemporal manner that cannot be achieved using electrodes. We have developed a new approach to study interactions of the intrinsic autonomic system using selective optogenetic stimulation of intrinsic cardiac neurons in perfused mouse hearts.

Materials and

Methods: Transgenic mice were bred using Cre-lox recombination to express ChR2 in either choline acetyltransferase (ChAT) or tyrosine hydroxylase (TH) neurons throughout the body. A micro-LED (465nm) encased in a silicone elastomer was constructed for stimulating the neurons of the SA node. The micro-LED is connected to a function generator set to pulse waves at 10 Hz with a 30 ms pulse width. Hearts with confirmed expression were excised and retrogradely perfused on a Langendorff system circulating Krebs-Henseleit solution. EKG, temperature, and coronary flow rate were recorded via LabChart software. Once the heart stabilized, the micro-LED was placed on the right atria and tested for best heart rate response. Competition between cholinergic and catecholaminergic activation was investigated. Optogenetic activation of the cholinergic neurons of ChAT x ChR2 mouse hearts was combined with exogenous norepinephrine. While optogenetic activation of the catecholaminergic neurons of TH x ChR2 mouse hearts was combined with exogenous acetylcholine.

Results, Conclusions, and Discussions: Optogenetic activation of ChAT x ChR2 mice resulted in an immediate drop in heart rate. This effect continues when combined with increasing doses of norepinephrine but with decreasing intensity. Optogenetic stimulation of TH x ChR2 mice resulted in a sudden but more gradual rise in heart rate. When combined with increasing doses of circulating acetylcholine, activation results in 2° AV block. This method describes a valuable experimental tool for investigating the conduction pathways in perfused hearts and the potential interactions between cholinergic and catecholaminergic activity.

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