Biomedical Engineering Reference
In-Depth Information
(a)
(b)
(c)
(e)
(d)
FIGURE 6.2
(a-d) Phase contrast micrographs of living multipolar neurons on microelectrode arrays. Electrode recording
craters in A and D are identified by white arrows. (e) Neurofilament antibody stain of multi-polar neuron. Inserts
show synaptic boutons. (bar; 40 µm, spinal cord culture, 48 d.i.v.). White bars represent 40 µm.
networks reorganize in a nonrandom manner [1] to form dynamic systems where the
overall spontaneous activity patterns and, moreover, the pharmacological response pro-
files are reproducible. Extensive pharmacological data have shown that all basic synaptic
mechanisms as well as key receptors and channels are retained in culture. In fact, even
tissue specificities, characteristic of the parent tissue region, are being documented in cul-
ture [2, 3, 4]. Although responses from such networks must be considered as “cell culture
correlates” to the changes observed in animals, such in vitro responses are repeatable and
can be quantified. Given this level of data, it is not surprising that serious efforts are now
underway to use such systems for investigations of neurotoxicity and cytotoxicity, and
for exploiting their properties for environmental toxicology, drug development, and even
in defense scenarios as broadband biosensors. Judging from toxicological investigations
performed till date, NNBS respond to a diverse array of compounds that attack neural
life support systems or alter the behavior or performance of mammals. These compounds
include bacterial toxins, metabolic poisons, toxic metals, neuropharmacological com-
pounds, hallucinatory drugs, and epileptogenic agents. The recognition that neurobe-
havioral changes can have profound impacts on operational readiness of deployed forces
drives the military-related interests in broadly sensitive biosensors for neuroactive
compounds [5, 6].
It is important to emphasize that pharmacological and toxicological investigations
address primarily receptor-dependent mechanisms. Response measurements to global
exposure of neural tissue to specific test compounds require stable, spontaneous activity,
but not necessarily specific circuitry. Numerous recent articles have demonstrated the his-
totypic responses of primary cultures where EC
50
values virtually overlap with those
obtained from animal experiments. Such cultures develop in vitro, stabilize, and are incor-
porated into recording chambers without injury to the existing circuitry. This avoids prob-
lems of deafferentation and trans-synaptic degeneration. The virtual monolayer allows
rapid, uniform pharmacological exposure of all cells and the extraction of massive spike-
pattern information. Added to the optical accessibility and general longevity, primary cul-
tures should no longer be considered a second choice to brain slices. These experimental
systems have matured and provide a rich environment for a large number of investigative
