Ch. 8 — Alternative to Animal Use in Testing • 179 
transmitter chemicals, the formation of syn- 
apses, and the conduction of impulses (7). 
Although tissue and organ cultures may approx- 
imate more closely the physiology of the human 
or whole-animal model, they are more difficult to 
manipulate than cell cultures (see ch. 6). Sophisti- 
cated equipment must be used to monitor and con- 
trol the environment and to perfuse the sample 
with nutrients. Where the sample is more than 
a few cell layers thick, uniform delivery of the test 
substance, nutrients, and oxygen is difficult, as is 
the removal of waste products. Cell differentia- 
tion can usually be maintained in tissue and or- 
gan cultures, albeit with some difficulty (50). 
Human placentas have proved quite useful in 
testing the ability of a drug to cross the placenta 
from mother to fetus. There are certain logistical 
problems with this method, however. The placenta 
must be transferred to the perfusion apparatus 
within 5 minutes after it is eliminated from the 
uterus, and it is only useful for about 3 hours af- 
terward (77). 
Nonanimal Organisms 
There are a variety of nonanimal organisms that 
can replace some animals in testing, ranging from 
plants to single-celled organisms to invertebrates. 
All of these can respond to certain noxious stimuli, 
and some may experience pain. However, many 
commentators believe that they do not experience 
pain or suffering in the same way that animals do, 
particularly in those cases where there is no brain 
or neural tissue (90). The use of such organisms, 
which has never been controlled under any Fed- 
eral or State law, is regarded as a replacement for 
animals in this report. 
Micro-organisms 
In recent years, increased emphasis has been 
placed on the use of bacteria and fungi to meas- 
ure certain genotoxic effects. A major advantage 
of these organisms is that they can be cultivated 
much more easily and quickly than most animal 
or human cells. Their genetic makeup is simple 
compared with that of animals and humans and 
the fact that a great deal is known about it facili- 
tates their use, particularly in toxicological re- 
search leading to new methods (74). A change in 
genetic material is relatively easy to detect and 
characterize. Fungal systems have been shown to 
be especially useful in mutagenicity testing and 
seem to be more sensitive than bacteria (126), per- 
haps at the expense of falsely indicating a hazard. 
Other species that have proved useful include slime 
molds, algae, and protozoa (74). 
Protozoa, although rather primitive overall, fre- 
quently have specialized functions that mimic those 
of humans. For example, the cilia of protozoa re- 
spond to smoke or phenols as do the cilia in the 
human bronchial tube (5). Various protozoans have 
been used in toxicity testing of cigarette smoke. 
Protozoans are currently being evaluated for use 
in screening tests for carcinogenesis, mutagene- 
sis, and reproductive toxicity (93). 
Invertebrates 
Invertebrates have made major contributions in 
biomedical research because certain aspects of 
their physiology are sufficiently similar to that of 
mammals (74). Although models for toxicity test- 
ing require greater similarity to animals or more 
thorough characterization of differences than 
models for research, invertebrates offer exciting 
possibilities. 
Of the invertebrates, insects offer the greatest 
selection of models, there being over 2 million spe- 
cies from which to choose (74). Among them, the 
fruit fly, Drosophila melanogaster, is the best un- 
derstood. Procedures have been developed for de- 
tecting mutagenicity (18), as well as teratogenic- 
ity (11) and reproductive toxicity (93). 
The sea urchin has long been a favored test 
organism for basic reproductive research (74). Con- 
sequently, the mechanisms and procedures of 
testing this invertebrate can easily be developed 
and performed. The sea urchin model for fertili- 
zation and development can be used in screening 
for reproductive toxicity, teratogenicity, and muta- 
genicity. Nematodes, annelids, and mollusks are 
also used for alternative mutagenesis testing re- 
gimes and, additionally, mollusks are used in the 
area of reproductive toxicology. Sponges, mollusks, 
crustaceans, and echinoderms are being used in 
metabolism studies, as understanding metabolite 
formation in nonmammalian species can lend in- 
sight to interspecies variation (93). 
