HYPOTHALAMIC CUTS AND MATERNAL BEHAVIOR
637
IiIip-Directed Mitteriiid Beluivior and Nesthttddiiitt
Retrievinit. Figure 4 shows the cumulative percentage of
rats in each group that retrieved all four foster pups. There
were significant differences among the groups on Test 1,
F(3,61)=4.32, ∕><0.OL The percentages of rats in the MFB,
ASYM, and SHAM Groups that retrieved on this test were
significantly greater than that of the MPO Group, but were
not different from each other. At least half the rats with MFB
or ASYM cuts retrieved pups on Test 1. By contrast, only 1
of 8 rats with MPO cuts retrieved on this test, and only 2 of 8
had retrieved pups by the end of the 5-day test period.
Croiieliiiift. Figure 4 shows the cumulative percentage of
rats in each group that adopted a crouching posture over one
or more pups. There were significant differences among the
groups on Test 1, F(3,65)=4.55, p<0.01. Fewer rats in the
MPO and MFB Groups crouched over pups on this test than
in the ASYM or SHAM Groups. Despite the differences
among the groups, however, it should be noted that at least
half the rats in each of the groups crouched over pups on
Test 1, and by Test 2 the differences among the groups were
not statistically significant.
Piip-Lickinft. Figure 4 shows the cumulative percentage
of rats in each group that licked pups. There were significant
differences among the groups on Test 1, F(3,79)=7.40,
p<0.01. The percentages of rats in the MPO, ASYM, and
SHAM Groups that licked pups on this test were signifi-
cantly greater than that of the MFB Group (ps<0.05), but
were not significantly different from each other. However,
note that 50% of the rats in the MFB Group did lick pups on
Test 1, and 75% were doing so by Test 2. There were no
significant differences among the groups on Test 2,
F(3,79)<1.0.
Nestbiiilding. Figure 4 shows the cumulative percentage
of rats in each group that built nests. The effects of knife cuts
on, nestbuilding in biparous rats were similar to the effects
seen in primiparous rats. There were significant differences
among the groups on Test 1, F(3,49)=9.92,/?<0.01. The per-
centages of rats in the MPO, MFB, and ASYM Groups that
built nests on this test were significantly lower than that of
the SHAM Group but were not different from each other.
MPO or MFB cuts eliminated nestbuilding for the entire
5-day test period, but ASYM cuts only delayed the onset of
nestbuilding; more than half the rats in the ASYM Group had
built nests by Test 11.
Test for Hyperphagia
As expected, biparous rats with MFB cuts were hyper-
phagic on all 10 days of exposure to the high-fat diet. They
ate an average of 7.8% of their body weights on each day
oftesting, compared with 5.9%, 6.0%, and 5.2% for rats
with MPO, ASYM, and SHAM cuts, respectively, F(3,31)
= 12.36, p<0.01. Significant differences among the groups
were apparent as early as Day 2, F(3,51)=3.25,
∕><0.05. By Day 10, the MFB rats averaged 130% of Day 0
weight, whereas the other groups averaged 108% of Day 0
weight.
Histologieal Analysis
Examination of brain sections revealed that the MPO,
MFB, and ASYM cuts were similar in placement and extent
to those described in Experiment 1.
DISCUSSION
Almost all the biparous rats with ASYM cuts ate all their
delivered placentas, and most of them displayed immediate
retrieving, crouching, and pup-licking. These results suggest
that prior parturitional experience protects placentophagia
and pup-directed maternal behavior from being disrupted by
damage to the longitudinal system found in Experiment I to
be necessary for their rapid onset during the first parturition
(see Table 1). This does not appear to be true for nestbuild-
ing, however, since ASYM cuts delayed the onset of nest-
building in biparous rats just as they did in primiparous rats.
This suggests that the connections between the MPO and the
posterior MFB continue to play an important role in produc-
ing the rapid onset of nestbuilding, even in rats that have
gained considerable maternal experience by rearing a first
litter. But since most of the primiparous and biparous rats
with ASYM cuts eventually did build nests, these connec-
tions appear to be involved only in promoting the rapid onset
of nestbuilding at parturition.
Although MPO and MFB cuts did not affect the onset of
crouching and pup-licking in biparous rats, they did produce
profound effects on other behaviors. MPO cuts eliminated
retrieving and nestbuilding for the entire 5-day test period,
just as in primiparae. These effects were not duplicated by
ASYM cuts, and therefore cannot be attributed to the dis-
ruption of a longitudinal system, suggesting that the lateral
connections of the MPO continue to play an important role in
mediating retrieving and nestbuilding, even in rats with ma-
ternal experience.
MFB cuts in biparous rats disrupted parturitional placen-
tophagia, eliminated nestbuilding for the entire 5-day test
period, and produced hyperphagia on a high-fat diet. These
effects were not duplicated by ASYM cuts, and were similar
to the effects of MFB cuts observed in the primiparous rats
of Experiment 1. It is possible that a neural system coursing
through the posterior MFB (but not the longitudinal system
involving the MPO) participates in the control of placen-
tophagia and nestbuilding in both primiparous and biparous
rats. It remains possible, though, that the observed deficits
in placentophagia and nestbuilding may have been secondary
to knife-cut-induced alterations of ingestive behavior and
activity level.
GENERAL DISCUSSION
At the time of parturition, the female rat ingests the deliv-
ered placentas, amniotic fluid, and fetal membranes, and
begins to provide maternal care in the form of pup-licking,
nursing, nestbuilding, and retrieval of stray pups back to the
nest. The present experiments were designed to examine the
effects of hypothalamic knife cuts, with and without previ-
ous parturitional experience, on these components of peri-
parturitional behavior. The results of these experiments
showed that (a) the medial preoptic area and the posterior
medial forebrain bundle, due to the nature of the connections
between them, constitute a functional, longitudinal neural
system that is involved in producing the rapid onset of both
the ingestive and caretaking components of periparturitional
behavior in the primiparous rat. (b) The effects of severing
these connections are probably due to the direct disruption
of a neural system specifically involved in producing the
rapid onset of these behaviors, since the critical cuts that
interfered with their onset did not produce alterations in