Using optogenetics to assess neuroendocrine modulation of heart rate in Drosophila melanogaster larvae

Abstract

The Drosophila melanogaster heart has become a principal model in which to study cardiac physiology and development. While the morphology of the heart in Drosophila and mammals is different, many of the molecular mechanisms that underlie heart development and function are similar and function can be assessed by similar physiological measurements, such as cardiac output, rate, and time in systole or diastole. Here, we have utilized an intact, optogenetic approach to assess the neural influence on heart rate in the third instar larvae. To simulate the release of modulators from the nervous system in response to environmental influences, we have directed expression of channel-rhodopsin variants to targeted neuronal populations to assess the role of these neural ensembles in directing release of modulators that may affect heart rate in vivo. Our observations show that the activation of targeted neurons, including cholinergic, dopaminergic, and serotonergic neurons, stimulate the release of cardioactive substances that increase heart rate after the initial activation at both room temperature and in a cold environment. This parallels previous studies suggesting these modulators play a crucial role in altering heart rate when applied to exposed hearts and adds to our understanding of chemical modulation of heart rate in intact Drosophila larvae.

Effect of Temperature on Heart Rate for Lucilia sericata (syn Phaenicia sericata) and Drosophila melanogaster with Altered Expression of the TrpA1 Receptors

“…Dissected larval preparations allow a defined bathing environment free from hormones and peptides in the hemolymph of intact larvae or pupa. Thus, the direct effect of temperature or the addition of 5-HT could be addressed independent of other factors which may fluctuate in the hemolymph, particularly during pupation [ 35 , 36 , 37 ].…”

The Effects of Chloride Flux on Drosophila Heart Rate

“…The visceral organs were removed, keeping the heart tube intact. This dissection technique was previously used to directly assess light-sensitive ion channels and pumps as well as pharmacological agents on the heart of Drosophila larvae [58,59,60,61,62,63,64]. Pinning of the animal on its back after dissection was used to directly apply the LED lights on the caudal aspect of the heart and to allow for the exchange of the bathing saline to one containing serotonin in later steps of the procedure.…”

Feasibility of Using Adjunctive Optogenetic Technologies in Cardiomyocyte Phenotyping – from the Single Cell to the Whole Heart

“…Since successful application of optogenetics depends on production of a photocurrent large enough to trigger depolarization, expression levels can be critical determinants of experimental outcome. A number of viral [18,25,29,[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] and non-viral methods [9,10,25,29,31,32,48,[54][55][56][57][58][59][60][61][62][63] have been successfully applied to the cardiomyocyte. For in vivo cardiac application tissue tropism with adeno-associated virus (AAV) types 1 or 6 might be preferable to type 9 used in vitro [64].…”