Biomedical Engineering Reference
In-Depth Information
typically accompanied by an increase in intracellular Ca
2+
concentrations. Moreover,
genetic probes are continuously expressed in vivo, which facilitates long-term and
repeated measurements in genetically specifi ed neurons. On the other hand, the
main advantage of electrode recordings—the enormously high sensitivity and very
high temporal resolution—cannot be reached using Ca
2+
imaging.
Electrophysiological recordings and optical imaging of Ca
2+
activity have, there-
fore, both advantages and limitations, and the electrode and genetic probes represent
complementary tools to study the property of a neural circuit.
It should also be noted that Ca
2+
imaging is not the only way of monitoring
correlates of neural activity. Indicators reporting other aspects of neuronal function
have been used in
Drosophila
as well. SynaptopHluorin is a genetically encoded
sensor of neurotransmitter release and monitors the intravesicular change in pH
value associated with vesicle fusion to the membrane (Miesenbock et al.
1998
; Ng
et al.
2002
). Alternatively to fl uorescence sensors, GFP-aequorin is a Ca
2+
-sensitive
bioluminescent photoprotein for probing the different dynamic aspects of Ca
2+
sig-
naling (Martin et al.
2007
). In this case no excitation light is required and intracel-
lular Ca
2+
infl ux is directly refl ected in photon emission. Although aequorin offers a
large dynamic range, less than one photon is generated per aequorin molecule, so
that the bioluminescence is very dim and diffi cult to visualize with good spatial
resolution. A neuromodulator sensor called “Tango” has been recently developed,
which can be used to visualize sites of neuromodulation (Inagaki et al.
2012
).
7.4
Experimental Design
7.4.1
Fly Strains
A large collection of driver and responder strains are available from the stock centers
for
D. melanogaster
.
Bloomington
Drosophila
Stock Center, Indiana University, USA.
Drosophila
Genetic Resource Center, Kyoto Institute of Technology, Japan.
7.4.2
Preparation for Imaging the Brain
The
Drosophila
brain is small enough to image large parts of its circuitry simultane-
ously. A major hindrance is, however, the pigmented cuticular exoskeleton that cov-
ers the fl y's body surface. Parts of the cuticular head capsule have to be removed to
