Ch. 8— Alternative to Animal Use in Testing • 185 
Chick Embryo Chorioallantoic Membrane Assay 
Photo credit: Joseph Leighton, Medical College of Pennsylvania 
Typical reaction seen 3 days after certain concentrations 
of household products have been placed on the 14-day- 
old chorioallantoic membrane. The thin white plastic ring 
has an internal diameter of 10 millimeters. The area of 
injury within the ring is well defined with a distinct edge. 
All of the cells in the injured area are degenerating or 
dead. The severity of this positive lesion is quantified by 
measuring its diameter. 
get organs or tissues, but they are not a replace- 
ment for whole-animal testing. The most promising 
alternatives in the near future involve modifica- 
tions of animal use (for example, by combining 
tests), and the use of screening tests and computer 
simulation for improved experimental design. The 
screening tests with the greatest promise are for 
hepatotoxicity and neurotoxicity. 
Hepa to toxi ci ty 
Several in vitro alternatives for hepatotoxicity 
have been developed, including perfused liver 
(108), liver cell suspensions (39), and liver cell cul- 
tures (39,44). Liver perfusions can only be main- 
tained for a few hours, and with some difficulty. 
Cell cultures can retain the special functions of 
liver cells with specially prepared culture media 
(76,81). However, the cells are viable for only a 
limited period of time and do not replicate in a 
reproducible manner. Although these techniques 
have been used to study mechanisms of liver tox- 
icity, only limited attention has been given to their 
use in screening or as alternatives (91). 
Neurotoxicity 
The development of alternatives for neurotox- 
icity is more difficult than for hepatotoxicity . The 
nervous system is the most complex organ in the 
body, both in terms of structure and its function. 
Because many neurotoxins affect only one kind 
of cell, a battery of in vitro tests would probably 
be required to replace whole-animal testing— if 
anything could. Substances can also affect vari- 
ous areas differently, partly because of distribu- 
tion factors. For example, very few substances are 
able to enter the brain because of the "blood-brain 
barrier." Thus, pharmacokinetic studies will con- 
tinue to be very important. 
Some in vitro tests (41) and tests using inverte- 
brates (8) seem useful, at least for screening. As 
yet, however, the primary use of in vitro tech- 
niques has been the elucidation of mechanisms 
of known toxic effects (31). Many toxic effects to 
neural tissue have been correlated with concen- 
trations of specific chemicals in or around the cells, 
thus offering the means for developing in vitro 
tests (31). 
MUTAGENICITY 
Mutation, the change in the DNA sequence of 
genes, is a mechanism by which toxic effects may 
be initiated. If the DNA replicates, the mutation 
is passed from the mutated cell to its descendants. 
Mutation can lead to cell death or the gain or loss 
of certain functions. When it occurs in germ cells, 
38-750 O 
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