122 • Alternatives to Animal Use in Research, Testing, and Education 
hibitory toward seeded enamel growth in culture 
(56). In virology, infected cell nuclei isolated from 
a hamster cell line were used to study influenza 
virion RNA replication (16). In metabolic studies, 
the inhibition of chick -embryo -derived collagen 
fibril formation by glucose suggests a direct rela- 
tionship between excess glucose and poor wound 
healing observed in people with diabetes mellitus 
(126). One of the most unique uses of subcellular 
fractions involves the bringing together of mixed 
species systems in biochemical studies of protein 
transport across intercellular membranes. For ex- 
ample, researchers studying intracellular protein 
translocation used dog pancreatic microsomes, bo- 
vine pituitary and rabbit reticulocyte messenger 
RNA, bacterial nuclease, and a wheat germ cell- 
free system to elucidate the structure of the sig- 
nal recognition particle (213). 
Human Tissues and Cells 
Cultured human fetal lung cells have been found 
to be excellent hosts to support the developmental 
cycle of a protozoan parasite that causes severe, 
persistent, life-threatening diarrhea in immuno- 
deficient patients . There has been no effective ther- 
apy for this illness, so the in vitro system offers 
an opportunity to study the parasite’s behavior, 
development, and metabolism and provides a po- 
tential method for screening therapeutic agents 
(50). 
Virologists and oncologists have been very quick 
to take advantage of new human in vitro culture 
systems. For example, an embryonal carcinoma 
cell line from the stem cells of a teratocarcinoma 
is being used to study cytomegalovirus replication 
(83). Lysis of herpes simplex virus (HSV) type 2 is 
being investigated using human monocytes (117), 
and HSV latency is studied by using isolated neu- 
rons obtained from human fetuses (220). 
The use of postmortem material from humans 
has significance in many areas of biomedical re- 
search, but particularly in neurology . Investigators 
studying the unconventional slow-virus diseases 
use brain tissue from humans with Creutzfeldt- 
Jakob disease and from animals with scrapie (144). 
Postmortem material from schizophrenics has pro- 
vided evidence for two distinct categories of that 
disease (181), and temporal lobe structures from 
Alzheimer patients have revealed specific patho- 
logical cellular patterns in the brain hippocampal 
formation (104). 
Examples of the use of human tissue for investi- 
gations aimed at human treatment can today be 
drawn from every discipline of biomedical re- 
search. Advances in in-vitro culture methods are 
likely to increase this use further. Postmortem tis- 
sue use is likely to continue. 
In vertebra tes 
Invertebrates represent over 90 percent of non- 
plant species on the earth. Although their body 
structure is much less similar to humans than is 
vertebrate body structure, invertebrate anatomy, 
physiology, and biochemistry offer avenues for 
new approaches that have been only partially 
explored. 
Caenorhabditis elegans, a 1 millimeter roundworm, 
is of intense interest to developmental biologists. 
As they have traced this nematode’s complete cell 
lineage, it offers an unprecedented opportunity 
for the study of individual living cells (38). 
Other terrestrial invertebrates are used in many 
disciplines of biomedical research. For example, 
flies, bees, earthworms, and leeches are involved 
in various aspects of anatomy, physiology, and bio- 
chemistry (5,33). Ants and bees are used in vision 
research (4). Fruit flies are well known for their 
participation in genetic studies. Age-related meta- 
bolic changes in other insects are being investi- 
gated for possible use in aging research (184). 
Marine invertebrates represent an important, 
largely untapped research resource. One commen- 
tator (190) has suggested that the lack of opportu- 
nity by medical scientists to learn marine biology 
and the failure of marine biologists to learn pathol- 
ogy have combined to leave marine species over- 
looked. A notable exception to the underuse of 
marine invertebrates is neurobiology. The coelen- 
terates, including hydra, corals, anemones, and 
jellyfish, have helped scientists understand primi- 
tive nervous system biochemistry. Lobsters and 
squid have contributed to knowledge of brain anat- 
omy and physiology, and the grazing snail and cray- 
fish have broadened understanding of cell biol- 
ogy (33). 
