636
FRANZ ET AL.
times ate the placentas. However, rats with cuts did not eat
their placentas or lick their pups with the celerity and thor-
oughness characteristic of control rats. For example, be-
tween deliveries of individual pups, rats with cuts ignored
both pups and placentas much of the time. On the occasions
that they did attend to pups, they sniffed and licked them,
but did not engage in the vigorous grooming of pups seen in
control rats. Nor did rats with cuts build nests or gather the
pups together, even after parturition had been completed.
Instead they typically went to sleep, leaving pups scattered
about the cage, some still covered with membranes and some
with placentas still attached.
Finally, comparison of the effects of knife cuts on placen-
tophagia in females that were either placentophages or
nonplacentophages as virgins revealed that prior ingestion of
placenta, in the absence of parturitional experience, does not
prevent the disruption of parturitional placentophagia by
MPO or MFB knife cuts.
EXPERIMENT 2
A number of lines of evidence have suggested that the
experience of delivery and rearing the first litter protects
placentophagia and maternal behavior from disruption
produced by manipulation of physiological mechanisms
shown to be necessary for their occurrence during the first
parturition. In order to determine whether prior parturitional
experience influences the effects of hypothalamic knife cuts
on Periparturitional behavior, this experiment was designed
to investigate the effects of MPO, MFB, ASYM, and SHAM
cuts in biparous rats.
FIG. 4. Cumulative percentages of groups of biparous rats, after
knife-cut surgery, that displayed retrieving, crouching, pup-licking,
and nestbuilding across tests.
were no significant differences among the groups in food
intake, F(3,32)<1.O. or water intake, F(3,32)<1.O.
METHOD
Subjects '.
Experimental rats (n=36), pup-donors, and placenta-
donors were Long-Evans females, 3-6 months old, born and
raised in our laboratory (offspring of rats purchased from
Charles River Breeding Laboratories) and housed and main-
tained as described in Experiment 1.
Procedure
At the onset of the experiment, each experimental rat had
been determined, by the procedure described in Experiment
1, to be a placentophage as a nonpregnant nullipara, and had
subsequently given birth to a litter and had raised it to wean-
ing. One to two weeks after having her pups weaned at 25
days of age, each experimental rat was bred, subjected to
knife-cut surgery, and tested according to the procedures
described'in Experiment 1.
RESULTS
Postoperative Food and Water Intake
Four of 12 rats with MFB cuts were dropped from the
experiment on Day 21 of pregnancy due to extreme debilita-
tion. The mean food intakes (as percentage of body weight)
for groups of biparous rats with MPO, MFB, ASYM, and
SHAM cuts were 5.3±0.8%; 6.6±0.7%; 5.7±0.8%; 5.6±0.3%,
respectively. The mean water intakes (percentage of body
weight) for these groups were: MPO: 18.0±3.7%; MFB:
12.8±2.0%; ASYM: 14.4±1.9%; SHAM: 14.I±1.2%. There
Timing of Parturition and Condition of Offspring
There were no differences among the four groups with
respect to gestation length, F(3,32)= 1.52, p>0.05, with
27.8% of the rats in all 4 groups delivering on Day 22, 66.7%
on Day 23 and 5.5% on Day 24. Nor were there significant
differences for duration of parturition, F(3,32)<1.0, with
mean durations ranging from 1I3.8±11.1 min for the MPO
Group to 153.8± 15.4 min for the MFB Group. There were no
differences among the groups with respect to litter size,
F(3,32)< 1.0 (means ranged from 9.0± 1.3 pups for the MPO
Group to 13.9±1.3 for the SHAM Group); percentage of
each litter born alive, F(3,32)<I.0 (means ranged from
84.7± 12.7% for the ASYM Group to 92.9±3.3% for the
SHAM Group); or live pup weight, F∫3,32)<1.0 (means
ranged from 5.4±0.2 g for the SHAM Group to 6.0±0.2 g for
the MPO Group). None of the biparous rats cannibalized
their young.
Placentophagia
Almost all the rats with MPO (n=8), ASYM (n=7), or
SHAM cuts (n=13) ate all their placentas, but only two of
the eight rats with MFB cuts ate all their placentas. The
differences among the groups were statistically significant,
F(3,32)=6.66, p<0.01. The MPO, ASYM, and SHAM
Groups were not different from each other, but all were sig-
nificantly more placentophagic than the MFB Group. There
were no differences among the groups with respect to inges-
tion of donor placenta 1 hr after parturition, F(3,32)<1.0.
The percentage of each of the groups that ate donor placenta
were: MPO: 88%; MFB: 88%; ASYM: 100%; SHAM: 85%.