The name is absent



638


FRANZ ET AL.

TABLE I

SUMMARY OF EFFECTS OF KNIFE CUTS ON PLACENTOPHAGIA, ONSET OF MATERNAL BEHAVIORS, AND
NESTBUILDING IN PRIMIPAROUS AND BIPAROUS RATS

Behavior

MPO cuts

MFB cuts

ASYM cuts

Primiparous

Biparous

Primiparous

Biparous

Primiparous

Biparous

Placentophagia

Incomplete

Complete

Incomplete

Incomplete

Incomplete

Complete

Retrieving

Never

Never

Delayed

Immediate

Delayed

Immediate

Crouching

Delayed

Immediate

Delayed

Immediate

Delayed

Immediate

Pup-Iicking

Delayed

Immediate

Delayed

Immediate

Delayed

Immediate

Nestbuilding

Never

Never

Never

Never

Delayed

Delayed

feeding and drinking behavior, did not influence the timing of
onset or duration of parturition, and did not affect the viabil-
ity of offspring, (c) Although this longitudinal system is in-
volved in producing the rapid onset of periparturitional be-
havior, it does not appear to be necessary for the gradual
onset of pup-directed maternal behavior and Ofnestbuilding.
Many of the primiparae with asymmetrical cuts, which se-
vered the longitudinal system bilaterally, displayed full ma-
ternal responsiveness after 5 days of continuous exposure to
foster pups, (d) The lateral connections of the medial preop-
tic area, but not those which pass through the posterior me-
dial forebrain bundle, appear to be essential for the elicita-
tion by foster pups of maternal retrieving and nestbuilding.
After 5 days of continuous exposure to pups, primiparae
with medial preoptic area cuts licked and crouched over
pups, but did. not retrieve pups or build nests, (e) Prior in-
gestion of placenta, as a nonpregnant nullipara, did not pre-
vent the disruption Ofparturitional placentophagia by hypo-
thalamic knife cuts, (f) Prior parturitional experience
protected placentophagia and pup-directed maternal behav-
ior, but not nestbuilding, from disruption after damage to the
longitudinal system found to be necessary for the rapid onset
of these behaviors during the first parturition, (g) The role of
this system in controlling nestbuilding in biparous rats is
limited to the production of its rapid onset, just as it is in
primiparous rats, (h) The lateral connections of the medial
preoptic area continue to play an important role in mediating
retrieving and nestbuilding, even in rats with prior parturi-
tional experience.

It is important to note the parallels between the present
findings, that a longitudinal neural system is involved in the
production of immediate maternal responsiveness in primi-
parous but not in biparous rats, and previous work indicating
the importance Ofprepartum hormonal changes for the rapid
onset of maternal behavior in primiparous but not in bipar-
ous rats [32,34]. It is possible that the effects of knife cuts on
periparturitional behaviors in primiparous rats were not
produced directly, by disrupting a neural system specifically
involved in producing rapid onset, but were produced indi-
rectly by preventing the changes in gonadal hormone secre-
tions thought to be necessary for immediate maternal re-
sponsiveness. Although this latter possibility cannot be ruled
out, it seems unlikely, because eliminating the prepartum
estrogen increase or progesterone decline would have influ-
enced the time of onset or duration of parturition [4,9].

A reasonable alternative explanation for the parallels be-
tween the effects of knife cuts and the effects of hormonal
manipulations is that the cuts disrupted a neural system that
ascends through the MFB and acts in synergy with estrogen
on medial preoptic area neurons to produce the rapid onset
of maternal responsiveness in parturient primiparae, but that
neither the functional integrity of this neural system nor the
presence Ofestrogen is necessary during the second parturi-
tion. This suggestion is consistent with previous findings that
the medial preoptic area is the neural site on which estrogen
acts to facilitate the onset of maternal behavior (for review,
see [ I3]), and with evidence from electrophysiological exper-
iments demonstrating both direct and indirect input from fi-
bers in the posterior medial forebrain to cells in the medial
preoptic area [48]. On the other hand, these results do not
preclude the possibility that the behavioral effects were
produced by a disruption of MPO efferents [42].

Nestbuilding was the only component Ofperiparturitional
behavior that failed to appear immediately in biparous rats
with asymmetrical cuts. The reason for this is unclear, but
one possibility is that asymmetrical cuts disrupted hypotha-
lamic mechanisms of temperature regulation [27] and
thereby affected maternal nestbuilding indirectly [41].

One of the aims of the present experiments was to deter-
mine whether the neural systems mediating placentophagia
overlap with those mediating maternal behavior. The results
of Experiment 1 suggest that a longitudinal neural system
does, in fact, participate in the control of both pup-directed
maternal behavior and placentophagia; hypothalamic cuts
that prevented the rapid onset of maternal behavior also re-
duced the likelihood that a rat would eat all her delivered
placentas. It is important to note, however, that cuts did not
eliminate parturitional placentophagia, nor did they affect
the proportion of rats that ate donor placenta presented one
hour after delivery. Primiparae with cuts apparently found
placenta to be a palatable substance, since all but one ate
some of their delivered placenta, but they lacked the moti-
vation to eat all.

These data suggest the possibility that placentophagia is
governed by two independent processes, one which involves
an attraction to placenta, a simple willingness to consider
placenta as an ingestible substance, and the other which
produces the complete and enthusiastic consumption of
placentas, membranes, and fluids that emerge at delivery.
Only this latter process was disrupted by the knife cuts that
prevented the rapid onset of pup-directed maternal behavior
and nestbuilding.



More intriguing information

1. The name is absent
2. Monetary Discretion, Pricing Complementarity and Dynamic Multiple Equilibria
3. Business Cycle Dynamics of a New Keynesian Overlapping Generations Model with Progressive Income Taxation
4. Do imputed education histories provide satisfactory results in fertility analysis in the Western German context?
5. Quality Enhancement for E-Learning Courses: The Role of Student Feedback
6. REVITALIZING FAMILY FARM AGRICULTURE
7. Learning-by-Exporting? Firm-Level Evidence for UK Manufacturing and Services Sectors
8. Structure and objectives of Austria's foreign direct investment in the four adjacent Central and Eastern European countries Hungary, the Czech Republic, Slovenia and Slovakia
9. The name is absent
10. Innovation and business performance - a provisional multi-regional analysis
11. The name is absent
12. On Social and Market Sanctions in Deterring non Compliance in Pollution Standards
13. The name is absent
14. Party Groups and Policy Positions in the European Parliament
15. Regional science policy and the growth of knowledge megacentres in bioscience clusters
16. Non-causality in Bivariate Binary Panel Data
17. A Hybrid Neural Network and Virtual Reality System for Spatial Language Processing
18. Labour Market Flexibility and Regional Unemployment Rate Dynamics: Spain (1980-1995)
19. Examining the Regional Aspect of Foreign Direct Investment to Developing Countries
20. TOWARD CULTURAL ONCOLOGY: THE EVOLUTIONARY INFORMATION DYNAMICS OF CANCER