116 • Alternatives to Animal Use in Research, Testing, and Education 
use, since they have made previously difficult anal- 
yses more accessible to many more investigators . 
Substituting One Species 
for Another 
In some instances, laboratory mammals (e.g., ro- 
dents) or nonmammalian vertebrates can be used 
in place of companion mammals (e.g., dogs), domes- 
tic species (e.g., sheep), or primates (e.g., monkeys). 
As more information on the physiology , biochem- 
istry, and endocrinology of laboratory mammals 
and nonmammalian species accumulates and is 
demonstrated to be like or unlike that of humans, 
greater use can be made of laboratory species, 
which in turn can generate more information and 
reduce future needs for research. Comparative 
neuroscience is perhaps the most rapidly expand- 
ing field and is related to physiology, biochemis- 
try, pharmacology, developmental biology, and 
zoology (33). Some brain components have been 
found to be remarkably similar between vertebrate 
species (69). 
Economics plays a large part in the selection of 
how many and what kind of animals will be used 
in some research (see ch. 11). An investigator fol- 
lowing up on previous work will generally begin 
with the species already in use, changing only if 
money becomes scarcer or if a better model is 
clearly demonstrated. Investigators starting anew 
are likely to seek the advice of a facility veterinar- 
ian or of colleagues as to which species best fits 
their needs and to begin with the smallest accept- 
able animal. Still other researchers deliberately 
begin work with a novel animal model in order 
to create a new research niche. 
One of the principal reasons for the increased 
use of rodents in all areas of biomedical research 
has been the availability of genetically homogene- 
ous or pathogen-free strains. For some studies, 
however, a further degree of genetic definition 
is needed. These studies require that the research 
animal carry some specific genetic traits that are 
suited to the objectives of the research. Because 
of their high reproductive potential, rodents are 
ideal for this type of "custom designing” and ex- 
tensive use is being made of these animals in a va- 
riety of disciplines (109). Oncology and immunol- 
ogy are two of the more familiar areas of use (92). 
Pharmacological research using an ethanol -prefer- 
ring strain of rats has prepared the way for explo - 
ration of the genetics of alcoholism (212). Further, 
the male Lewis rat, an animal that rapidly acquires 
testicular lesions and antibodies to sperm after 
vasectomy, is a candidate for study of the rever- 
sal of vasectomy. This research could answer ques- 
tions of human concern in anatomy, physiology, 
immunology, endocrinology, and reconstructive 
surgery (100). 
Chickens and their embryos play an important 
role in developmental biology, endocrinology, 
histology, and zoology. Other current uses are in 
molecular biology, in which embryonic chicken 
brain tissue is being cultured to study the neural- 
cell adhesion molecule (193), and biochemistry, in 
which the embryonic chicken liver is being used 
to study the acquisition of hormone responsive- 
ness during embryogenesis (62). In cardiology, tur- 
keys with inherited Turkey Round Heart disease 
serve as models of cardiomyopathy (107), and tur- 
key erythrocytes are fused with amphibian eryth- 
rocytes to study receptors that mediate physio- 
logical functions in heart, smooth muscle, and 
other tissues (199). 
Frogs have long been used in anatomy, biochem- 
istry, developmental biology, physiology, and zool- 
ogy. They continue to be widely used in those dis- 
ciplines and, additionally, are currently being used 
by NASA in radiology studies (125). In dental re- 
search, frogs are used to assess digital transplants 
to augment tooth and jaw regeneration (101). The 
newt Triturus— able to regenerate its limbs, eye 
lens, tail, and spinal cord— is used in developmen- 
tal biology to explore mechanisms of organ regen- 
eration (90). Turtles are used in physiology to study, 
for example, retinal mechanisms subserving color 
vision. The cone cells of the turtle retina are espe- 
cially conducive to such research (161). 
Fish are used in research to a lesser degree than 
other vertebrates, considering that there are over 
30,000 species and their care is relatively uncom- 
plicated . It has been suggested that fish would make 
excellent subjects for nutritional research, since 
many are known to show specific vitamin deficien- 
cy symptoms (210). Physiologists have used gold- 
fish to study the implications of myelin-sheath 
resistances in demyelinating diseases (73). Rain- 
bow trout embryos are being used in oncology re- 
