Synaptic plasticity and behaviour

Fast and efficient synaptic transmission depends on mechanisms that regulate both the release (exocytosis) of synaptic vesicles at the nerve terminal and their recycling (endocytosis).   We have focused on understanding the mechanisms that regulate both processes in vivo.   Using molecular and biochemical approaches, we were able to identify novel proteins and determine their role in synaptic vesicle exocytosis.   We have also shown that many of these molecules can regulate additional membrane trafficking events within the cell and are required for Notch-dependent signaling during development.   Importantly, we have shown that regulating the levels of specific proteins, known as SNARES, alters the ability of neurons to sense calcium, which is essential for neurotransmitter release and all brain function including learning and memory (Stewart et al 2000).  We have also used genetic approaches to identify additional genes that regulate synaptic plasticity and behaviour.  We found that one of these genes, nemy (no extended memory), plays and essential role in memory formation by regulating neuropeptide amidation (Iliadi et al, 2008).  We also identified mutations in ent2 (equilibrative nucleoside transporter 2) and showed that it regulates synaptic plasticity, learning and memory and ethanol sinsitivity by altering adenosine signalling at synapses (Knight et al, 2010).  Current efforts are aimed at understaning the role of neuromodulator octopamine and the neural adhesion molecule neuroligin in both synaptic function and behaviour. 

Key References :
      Knight, D., Harvey, P.J., Iliadi, K.G., Klose, M.K., Iliadi, N., Dolezelova, E., Charlton, M.P., Zurovec, M., and Boulianne, G.L. (2010). Equilibrative nucleoside transporter 2 regulates associative learning and synaptic function in Drosophila. J Neurosci 30, 5047-5057.
    Iliadi, K.G., Avivi, A., Iliadi, N.N., Knight, D., Korol, A.B., Nevo, E., Taylor, P., Moran, M.F., Kamyshev, N.G., and Boulianne, G.L. (2008). nemy encodes a cytochrome b561 that is required for Drosophila learning and memory. Proc Natl Acad Sci U S A 105, 19986-19991.
     Stewart, B.A., Mohtashami, M., Trimble, W.S. & Boulianne, G.L. (2000). SNARE Proteins contribute to calcium cooperativity of synaptic transmission. PNAS 97,13955-13960.


 

Localization of nemy in the CNS. A. b -galactosidase staining produced by insertion of a LacZ containing P-element in the 5' end of the nemy gene. B-D. A Gal4 containing P-element in the 5' end of nemy was used to drive expression of a UAS-EGFP transgene in larval (B) and adult (C and D) brains. The Gal4-UAS binary expression system can be used to examine the endogenous expression pattern of a gene when a Gal4 transcriptional activator is expressed under the control an endogenous promoter. In the larval CNS, GFP expression was observed in a pair of descending neurons (DN), neurons in the sub-eosophogeal ganglion (SEG), several midline cells (MLC) in the ventral nerve chord (VNC) as well as some lateral neurons (LN) and abdominal neurons (A8). In the adult CNS, GFP expression was observed in kenyon cells (KC) which can be seen in the posterior veiw of the CNS (C). In the anterior view (D), GFP expression was observed in the a / b , a '/ b ' and g lobes of the mushroom bodies. GFP expression was also observed in the antennal lobe (AL) and in several other nerve clusters (Ncl) and the lateral ventral neurons (LN-V).
For more detail, see Iliadi et al. (2008)
Functional analysis of ent2 mutants. We routinely use the larval neuromuscular junction to assess the effect of specific mutations on synaptic function. In this example, a mutation in the equilibrative transporter 2 (ent2) gene leads to an increase in transmitter release but a decrease in paired pulse plasticity. The traces to the left represent stimulus evoked excitatory junction potentials recorded with a sharp microelectrode in the abdominal muscles of a third-instar larvae. Pairs of stimuli are delivered to the motor axon, and the transmitter release at the axon terminal causes a depolarization of the muscle as seen. In control animals (w), the first pulse is relatively small, and the second pulse is much larger (black trace). In the ent2 mutants however, the first pulse is much larger than seen in controls, and as such the second pulse does facilitate to the same degree, and in some cases even showed depression (grey trace). We also measured calcium influx into the motor neurons using a calcium sensitive dye (Oregon-Green BAPTA-1). The image on the left shows neuromuscular junction bouons before and after a single stimulus. The increased brightness refects an increase in the concentration of calcium in the boutons. We observed a small but significant increase in the amount of calcium entering boutons in ent2 mutants (ent2-P124) compared to the control (w).
For more detail, see Knight et al. (2010)

Research

http://www.youtube.com/watch?v=kumya_ipkJU&feature=player_detailpage

We are currently using the Noldus Ethovision XT Video tracking software to record and analyse fly behaviour.  One interesting novel behaviour we have recently observed is "fainting" flies.  We recently noticed this novel behaviour in a mutant we have been studying.  When mechanically startled, wild-type flies show little change in the behaviour.  The mutants however, appear to faint for a few seconds, before resuming normal activity.  We are currently invesitgating the underlying neural pathways involved in this behaviour.  To see the fainting flies, click the you-tube link to the left.

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