INHIBITORY TRANSMISSION IN CIRCADIAN PACEMAKERS OF DROSOPHILA

FRENKEL, L; MURARO, NI; BERNABO, G; HERMANN-LUIBL C; HELFRICH-FÖRSTER C; CERIANI, MF

Big Sky, Montana

Congreso; Biannual Meeting for the Society for Research on Biological Rhythms; 2014

Society for Research on Biological Rhythms

The small ventral lateral neurons (sLNvs) constitute the major pacemaker in Drosophila´s brain. Under constant conditions they guide the temporal organization of daily locomotor activity. Aside from PDF-(pigment dispersing factor)-filled vesicles, they also contain small clear vesicles putatively packed with a fast neurotransmitter potentially involved in synchronizing the circadian network. Here we show the results of a screen aimed at identifying this neurotransmitter by evaluating the locomotor activity pattern after disrupting either membrane or vesicular neurotransmitter transporters function within PDF neurons. We found that interfering with glycine transporter expression increases period length in almost an hour without affecting rhythmicity. A decrease in intracellular glycine availability accounts for the period lengthening phenotype, as disrupting glycine synthesis has a similar effect. Moreover, daily oscillations in PDF levels at the sLNvs axonal termini are decreased under such conditions, suggesting an interaction between both communication systems. The pursuit of glycinergic targets by immunohistochemistry revealed that PDF neurons express a glycine receptor. In fact, bath-applied glycine abrogates bursting of PDF+ neurons, which is consistent with the expected inhibitory effect mediated by a neurotransmitter-gated Cl- channel. Whether glycinergic transmission entails cluster synchronization remains to be explored. In support of such possibility, downregulation of the glycine receptor in PDF neurons decreases rhythmicity. Interestingly, disrupting glycinergic transmission in a subset of dorsal CRY+ neurons also impairs behavioral rhythmicity, suggesting that glycine is also involved in transmitting information to other clock clusters. This is the first evidence reporting a role for glycinergic transmission in the Drosophila brain. Our results highlight the similarities between vertebrate and invertebrate clocks also at the circuitry level.