Biomedical Engineering Reference
In-Depth Information
(b)
(c)
(a)
(d)
Concentration tetrodotoxin (nM)
Control
2
5
10
20
Wash
20
15
10
5
0
0
50
100
150
200
Time (min)
FIGURE 6.21
Concentration-dependent effects of tetrodotoxin for a typical spinal cord network using the NRL portable sys-
tem after shipping of network. The pharmacological sensitivity to tetrodotoxin for the portable recording system
is similar to that achieved with laboratory-based recording systems. (a) Shipping and recording chamber; (b)
shipping containers; (c) portable recording assembly; (d) Concentration-response profile of a culture shipped
from Texas to Washington, DC.
or “heat” plot, and a per-minute display of mean spike rate across the network. These are
indeed simple measures that are not intended to be exhaustive, but are sufficient to allow
a user insight into the status of the network. Off-line analysis can then be performed to
achieve spike sorting and measure other parameters such as burst dynamics, synchro-
nization, and waveform amplitude.
A typical recording medium used for monitoring NNBS activity in the portable system
consists of MEM supplemented with (in mM) 25 glucose, 40 HEPES, and 26 NaHCO
3;
, and
is allowed to equilibrate for 4 h in air before adjustment of the pH to 7.4. There is a slow
drift toward higher pH levels; however, the networks tolerate this drift very well over the
1-to-2-day time frame. Based on this protocol for aqueous-phase sample introduction
under constant flow conditions, minimal variation in mean spike rate is observed, consis-
tent with temporal stability, such that changes of >10% are readily distinguished. With this
particular formulation, the NRL group has observed stability in neuronal network func-
tion exceeding 2 days of continuous perfusion. As mentioned earlier, the system has been
successfully used off-site at a bioassay workshop [7] in Oregon and recently at the
National Oceanographic and Atmospheric Administration in South Carolina. During
these demonstrations, sensitivity has been shown for a multiplicity of neuroactive com-
pounds including tetrodotoxin, titysustoxin, brevetoxin-2, brevetoxin-3, arsenic, cyanide,
cadmium, mercury, strychnine, and the organophosphate phosdrin.
To assess the potential utility of the NNBS approach for detection of threats in aqueous
phase, one can compare the concentration-dependent inhibition by various threats to
those levels that induce lethality. For example, consider cadmium and strychnine, which
