Biomedical Engineering Reference
In-Depth Information
known network role is partially cut of from the network and the associated behavior is moni-
tored from some time ater the “surgery”. Note that the device only needs to ensure the
overall
viability
of the organism while the organism takes care of neuronal maintenance (e.g., recovery
from surgery). Because the exact developmental lineage of the neuron being ablated is oten
known, it may be possible to infer from these experiments general rules on how to build small
neuronal networks.
6.5.5 Olfaction
Using simple PDMS microluidic mazes assembled on agar, in 2005, the Bargmann laboratory
(Rockefeller University, New York) found out that, by modifying its olfactory preferences,
C. ele-
gans
can learn to avoid pathogenic bacteria (the worms had previously learned the taste of this
bacterial strain by eating it). he worms, placed in a central chamber approximately 1.5 cm away
from the bacteria, were consistently repelled by the pathogenic bacteria strain and attracted by
the nonpathogenic one (
Figure 6.71
).
Microluidics can also be used to design traps in which the animal can be locally perfused
and their neuronal responses imaged in real time with cellular resolution (
Figure 6.72
). he
animal is introduced into a funnel-shaped microchannel so that, as it crawls forward, it gets
stuck, sticking its nose out into a perfusion chamber. At this point, the animal is immobile and
its chemosensory neurons can be functionally imaged by calcium imaging without anesthesia
(see ASH neuron in
Figure 6.72b
) while they are perfused with various stimulants.
Figure 6.72c
shows the distinct patterns of ASH neuron response when comparing young and old (3 days
older) worms, suggesting that the functionality of sensory neurons is altered with age.
G1
Grown on OP50
Grown on OP50/PA14
a
c
B2
B1
1 mm
40
1 cm
1.5 cm
***
***
30
G2
G2
20
10
B1
B2
0
G1
Bacterium
lawn
Bacterium
lawn
150 µm
Agar substrate
Attractive learning
for OP50 (G1)
Aversive learning
for PA14 (B1)
b
d
Petri dish
Agar
substrate
Decision
area
0.08
PDMS
maze
0.04
0
Dummy chambers
not in use for these
experiments
-0.04
-0.08
FIGURE 6.71
Microluidic. “olfactory. mazes”. reveal. worm. learning. behaviors.. (From. Yun. Zhang,.
Hang. Lu,. and. Cornelia. I.. Bargmann,. “Pathogenic. bacteria. induce. aversive. olfactory. learning. in.
Caenorhabditis elegans
,”.
Nature
.438,.179-184,.2005..Adapted.with.permission.from.the.Nature.
Publishing.Group.)
