496
ENGWALL AND KRISTAL
[11,12]. The relative difficulty seen when inducing aver-
sions to non-novel substances has been attributed to the
learned safety hypothesis of Kalat and Rozin [3]. If an
animal ingests a novel substance and suffers no subsequent
malaise, the animal learns that the substance is safe to
consume. The strength of this learned safety increases as a
function of the exposure to the ingested substance prior to
TAC.
If placentophagia can be considered a normal ingestive
behavior, then its incidence should be modifiable by the
application of TAC. Animals with little previous safe
exposure to placenta should avoid the substance after it has
been paired with toxicosis. On the other hand, if placento-
phagia is controlled by mechanisms other than those
controlling feeding, or if gustatory cues are unimportant, or
if placenta is a prepotent or unique stimulus, TAC should
be ineffective in modifying placentophagia. The present
research sought to determine the extent to which the
incidence of placentophagia could be altered by the taste
aversion techniques. The questions asked were: (a) is
placentophagia during a nonpregnant state susceptible to
TAC? (b) Could an aversion acquired during a nonpregnant
condition modify placentophagia during a subsequent
parturition? (c) Could an aversion be conditioned with
equal effectiveness in both nonpregnant and parturient
conditions? (d) Would prior parturitional experience with
placenta alter the induction and expression of a taste
aversion to placenta?
P L ACE N TO P H AG 1A P R ETEST
All animals were given a placentophagia pretest to insure
that they all belonged to the population of animals that
exhibit placentophagia during a nonpregnant state [6].
Since it had been observed that animals that eat placenta
during the nonpregnant state continue to do so reliably
∣6∣, any decrease in the response to placenta could then be
attributed to the expression of a taste aversion to placenta.
METHOD
Animals
One hundred eighty-three Long-Evans female rats
(Charles River Breeding Laboratories) were used in the
placentophagia prestest. The females were approximately
60 to 75 days old upon their arrival in the laboratory and
were all virgins with no known previous exposure to
placenta. Females were housed in 18 × 18 × 24 cm wire
mesh cages and maintained on a 14 hr on; IO hr off light
cycle with the on-phase beginning at 6:00 a.m. (EST).
Charles River Rat/Mouse/Hamster Formula and water were
available ad lib, except as indicated below.
Procedure
After I week of colony residence, daily vaginal smears
were obtained until normal estrous cyclicity was confirmed.
Each female was then given the placentophagia pretest [6∣.
At 10:00 a.m. on the first day of testing, females were
moved to a quiet, well lighted testing room, and placed in a
16 × 16 X 48 cm clear plastic cage, with a wire mesh grid
covering the floor (test cage). Water was available, but no
food. Two hr later, the water was removed. Fifteen min
later, each female received a 15 min exposure to donor
placenta. Donor placenta for the pretest and Experiments I
and 2 was removed surgically from CO,-killed females on
Day 21 of pregnancy, and frozen in 6 ml glass vials along
with a few drops of physiological saline. Immediately prior
to presentation, the vials were warmed in a hot water bath,
to about 37oC. Each female was given 2 whole placentas in
a small specimen dish. After the 15 min exposure period
and after the female’s response to placenta was recorded,
vaginal smears were taken and the females returned to wire
mesh cages. The testing procedure was terminated when a
female ate placenta, or after 3 successive daily tests. Only
females that ate placenta during the pretest were used for
subsequent experiments.
EXPERIMENT I
Experiment 1 was designed to examine whether a
conditioned taste aversion to placenta, produced in virgin
females, would be expressed as an aversion to placenta
during the first parturition. Since the females in Experi-
ment I had no parturitional experience at the onset of
conditioning, their previous experience with placenta was
limited to the exposure obtained during the pretest.
METHOD
Animals
The animals were 20 virgin Long-Evans rats (90-100
days old) that had exhibited placentophagia in the pretest.
Procedure
Taste aversion conditioning. Females were randomly
assigned to 1 of 2 groups: Group C (contingent) and Group
CP (noncontingent-pregnant). One week after the pretest,
females in Group C (n = 15) were subjected to TAC. On Day I
of the conditioning procedure, females were moved to
the testing room and placed in plastic cages with wire mesh
grid inserts covering the cage floors. Animals in Group C
were food deprived for 2½ hr and water deprived for 15
min prior to the presentation of donor placenta. Immedi-
ately after 15 min of exposure to placenta, those females
that consumed placenta were given an injection of 0.15 M
LiCl solution (20 ml∕kg body weight, i.p.). Vaginal smears
were then obtained and the females were returned to their
home cages. Food and water were removed for a 2 hr
period following the injection to minimize any possible
interfering effects of ingestion while malaise developed.
Beginning on the next day (Day 2). vaginal smears were
were obtained daily to assess the effects of LiCI on estrous
cyclicity. The females were then tested for an acquired
aversion to placenta for 3 consecutive days (Days 4, 5 and
6). The criterion was abstention from placentophagia on all
3 days. Females failing to reach criterion after the first
pairing of LiCLinduced illness with placentophagia were
given additional pairings until criterion was reached. As a
control for the effects of LiCl injections per se, Group CP
(n = 5) were presented with empty dishes during the
conditioning and test trials. Aftera 15 min exposure to the
empty dish, the females were given an injection of LiCL
Two such injections of LiCI were administered in a
temporal sequence which approximated the procedure used
with Group C.
Mating. Upon reaching criterion. Group C was divided
into 2 subgroups: Subgroup CP (contingent-pregnant, n =
7) and Subgroup CP (contingent-nonpregnant, n = 8).
Within 1 week after reaching criterion, each female in
Subgroup CP and Group CP (but not Subgroup CP) was