Influx of calcium through voltage-gated channels regulates a wide variety of cellular processes including excitability and chemical synaptic transmission in the nervous system. Calcium channels are composed of multiple subunits with the 11 subunits forming the ion conducting pores. In vertebrates there are three major families of 11-subunits genes (Cav1, 2 and 3) with multiple genes/family and some redundancy in function. Drosophila has one gene per family and these have non-redundant functions, an advantage for assessing function of distinct subtypes in vivo. The cacophony (cac) gene in Drosophila, like its Cav2 vertebrate family homologues, encodes channels responsible for regulating evoked release of neurotransmitter at the NMJ. However, the properties of Cac channels have been difficult to examine directly since electrophysiological access to the presynaptic nerve terminal is limited and the cac gene has not been successfully expressed in heterologous systems. In our recent analysis of cac mutants, using a preparation we developed to record from identified neurons in brains of adult flies, we found that Cac channels underlie PLTXII- sensitive calcium currents that regulate AP-independent release of neurotransmitter at central cholinergic synapses in the antennal lobe. A second functionally distinct calcium current is also present in antennal lobe neurons. This grant proposes three aims: 1) identify channel subtypes that underlie calcium currents in specific populations of antennal lobe and mushroom body neurons in the adult brain, 2) test the hypothesis that Cac channels regulate evoked transmission and plasticity in antennal lobe and mushroom body circuits, and 3) determine how calcium channels and G-protein signaling regulate burst firing and network activity in the antennal lobe. The results of these studies should provide insights into how specific calcium channel subtypes regulate excitability, synaptic transmission, and network activity in central circuits activated during olfactory associative learning in the adult brain. Our studies include use of cac mutant flies that exhibit temperature sensitive paralysis and seizures. Mutations in the CACNA1A gene, the human homolog of cac, are linked to neurological diseases that are characterized by a broad spectrum of symptoms including ataxias and migraines. Thus knowledge of the cellular mechanisms contributing to the behavioral deficits in cac mutant flies should also contribute to understanding of human disease associated with mutant calcium channel genes.
The proposed study uses Drosophila as a model organism to determine how different calcium channel subtypes regulate activity in identified circuits in the adult brain. Knowledge of the cellular mechanisms contributing to behavioral deficits in flies with mutations in voltage-gated calcium channels should contribute to understanding of human neurological diseases associated with altered calcium channel function.
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