Biomedical Engineering Reference
In-Depth Information
normal medium but was extended beyond 30 days in modified medium with a glutamine
dipeptide, which is known to limit glutamine degradation [28].
The long-term activity fluctuations in terms of spike and burst production are shown in the
highly time-condensed record of Figure 6.15. A frontal cortex network was used for four mor-
phine applications (between 50 and 250 min) and then left unattended for 72 h in a constant-
volume bath medium. Life support was provided by temperature control to 36
0.1ºC, 10%
CO
2
in humidified air, and 30 µl/h water addition (syringe pump) to compensate for evapo-
ration (empirically determined). The graph is representative of a general slow, gradual decay
in activity (43% for bursting in 72 h) and shorter periods of minor fluctuations. The SD of the
minute means also increases after the 3000-min mark (arrow). The long-term changes are
attributed to alterations in the medium biochemistry, as medium replacement (not shown
here) generally raises the activity to original levels, and often above those levels. Short-term
fluctuations may be caused by pH changes, as that parameter is difficult to monitor continu-
ously. Even short-term electronic noise cannot be ruled out. Alternatively, it may be generic
to spontaneous network activity. Regardless, it is readily apparent that the NNBS approach
allows long-term assessment of detailed electrophysiological function that extends far
beyond the time window permitted by any other in vitro neuronal methodology based on
dissociated cells.
50
Netwo rk #1
Netwo rk #2
Network #1
Network #2
40
30
20
10
0
1
2
3
4
5
6
7
8
9
11
12
14
15
16
17
18
19
20
21
22
23
25
27
28
32
Days in closed chamber
FIGURE 6.14
Long-term twin network experiment with dual recording array. The culture with stable glutamine (network 2)
performed better than the one in normal medium. Frontal cortex networks 69 d.i.v. at the beginning of experiment.
Spike rate per minute
Burst rate per minute
Mean rate per minute
100
2000
90
1800
80
1600
1400
70
60
1200
Spike generation
50
1000
40
800
30
600
Burst generation
20
400
10
200
0
0
0
250
500
750
1000
1250
1500 1750 2000
2250 2500
2750 3000
3250 3500
3750
4000
4400
0
5
10
15
20
250
30
35
40
45
50
55
60
65
70 hours
FIGURE 6.15
Continuous 75-h record of frontal cortex culture in a constant-volume bath medium showing spike and burst
production averaged over 58 discriminated units per minute. Pharmacological manipulation between 50 and 250
min was followed by 70 h of unattended recording except for an osmolarity check (10 µl removed) at 1250 min
(vertical line).
