Static and Dynamic Measurements of Neurotransmitters in Drosophila Brain

Abstract

Neurotransmitters, the substances neurons use for communication, and their precursors and metabolites are of obvious importance for the wellbeing of the individual and when the neurotransmitter balance is off it can lead to catastrophic suffering as in the addiction to drugs or in neurodegenerative diseases. By understanding how neurons communicate with the environment, treatment may be found to aid in the symptoms of unbalance. Drosophila melanogaster, the fruit fly, has been shown to be an excellent model for understanding neuronal processes and behaviors. Although the adult fly has a simpler nervous system than those of vertebrates, it is capable of higher-order brain functions, including aversive and appetitive learning, and recalling learned information from prior experiences. Invertebrate models, such as Drosophila melanogaster have been used previously to investigate neurochemical changes in the CNS associated with drug addiction as well as in the of study of neurodegenerative diseases such as Alzheimer’s disease, Huntington’s disease, and Parkinson’s disease by Drosophila mutants. Many of the neurotransmitters associated with these diseases occur in minute amounts and can be difficult to detect in the small volume of the fly brain. As such, it is essential to develop analytical tools for these unique biological systems that can be quickley performed and accurately analyses the neuronal substances as well as requiring extremely small sample volume. Capillary electrophoresis and in vivo voltammetry are two methods that meet these requirements.

In Paper I a new separation scheme for capillary electrophoresis was devised to allow resolution of 23 neurotransmitters, metabolites, and precursors. In fly homogenates a focus on six of the substances thought to be involved in the response to alcohol were identified. In Paper II the removal of the cuticles and eyes leaving only the brains further enhanced the separation profile of neurotransmitters from Paper I. In Paper III a method for sample preparation by freeze drying the Drosophila brains was presented. The use of freeze-dried samples offers a way to preserve the biological sample while making dissection of the tiny brain samples easier and faster. This provides more concentrated samples and with that higher signals and better detection limits. In Paper IV the effect of cocaine on the dopamine transporter was shown to be reduced by the ADHD drug methylphenidate using in vivo voltammetry.