The Role of the Dal Neurons in Modulating Circadian Rhythms in Olfactory Short-Term Memory in Drosophila Melanogaster

Depressed short-term memory (STM) abilities during non-adaptive times of the day can significantly impact those who work occupations that require peak levels of cognitive functioning around the clock. While much work has gone into understanding the endogenous clock and circadian rhythms, there is still much to learn about the neural circuity that underlies the daily rhythms that define these regular oscillations in STM performance. The DAL neurons in the Drosophila brain are part of the circadian network and innervate the mushroom bodies (MBs), the species’ olfactory learning center, making them compelling candidates to be involved in circadian circuitry for olfactory learning. In this thesis, I investigate the DAL neurons\u27 role in mediating circadian rhythms in olfactory learning by examining their serotonergic synapses onto the α/β lobes of the MBs. An olfactory associative learning paradigm was used to measure and compare STM performance. Since the 5HT1A receptor was detected in the α/β lobes of the MBs, mutants for 5HT1A are expected to lose communication between the DAL neurons and the MBs. The 5HT1AMB09978 mutants were tested against wildtype groups, and data showed the rhythm in olfactory learning was disrupted in these mutants. These results implicated the 5HT1A receptor as necessary for circadian rhythms in olfactory STM. Mutants for 5HT1B, which was not detected in the α/β lobes, were also examined. 5HT1BMB05181 mutants retained circadian rhythms in olfactory learning, suggesting that the 5HT1B receptor does not play a role in the circadian modulation of olfactory learning. Additionally, rutabaga adenylyl cyclase (rut) was tested as a potential downstream modulator from the 5HT1A receptor. Our data confirmed that rut is necessary for wildtype olfactory learning but dispensable for the circadian rhythms in olfactory learning