Invited Symposium: Maternal Behaviour
Maternal behavior (MB) ensures that immature individuals will survive to adulthood. Mother rats provide their pups with heat, food and cares specifically aimed to their survival immediately after parturition. MB includes pronurturant activities, such as nest building, retrieval and licking, which precede prolonged periods of quiescent nursing. In the rat, maternal care is under hormonal control (see Numan, 1994. for Review). However, continuous exposure to pups can elicit this behavior after several days in virgin females and naive male rats (Rosenblatt, 1967).
The sexually dimporhic Vomeronasal System (VNS) (Segovia and Guillamón, 1993; 1996) is implicated in the control of MB (Fleming et al., 1979). Electrolytical lesions of structures of the VNS, have been proved to alter MB (Del Cerro et al., 1991; Izquierdo et al., 1992). Administration of Picrotoxine (a GABAa antagonist) during early postnatal periods has resulted in morphological alterations of the Accessory Olfactory Bulb (AOB), a structure belonging to the VNS, as well as in the induction of MB (Segovia et al., 1996). Olfactory imput from the AOB reaches the Ventral Bed Nucleus of the Stria Terminalis (BNST) (Winans and Scalia, 1975; Davis et al., 1978) and from this nucleus direct projections to the Medial Preoptic Area (MPA) are sent (De Olmos and Ingram, 1972). Neurons of the MPA and the BNST express c-fos immunoreactivity in maternally behaving virgin and postpartum (Numan and Numan, 1994).
On the other hand, environmental prenatal stress (EPS) is considered a teratogenic agent, that induces hormonal changes in the pregnant mother and her pups (Ward, 1980), as well as deficiencies in the performance of induced MB in prenatally stressed female rats (Pérez-Laso et al., 1997). So, EPS increases stress-induced corticosterone secretion peak in preweaning rats (Peters, 1982; Takahashi et al., 1988) and attenuates habituation over repeated exposure to stress in the adult (Fride et al., 1986).
Since EPS may cause changes in hormonal plasmic levels, as well as alterations in maternal behavior, in this work we study wheter EPS treatment may cause changes in progesterone, corticosterone and estradiol plasmic levels and a long-lasting effect on the induction of MB, and wheter these changes are realted with c-fos-like immunoreactivity of the AOB mitral cells, in virgin female rats when adult.
Materials and Methods
MATERNAL BEHAVIOR TEST:
STATISTICAL ANALYSIS OF DATA:
BEHAVIOR. - The percentage of PS3-F rats that became maternal was significantly lower than that of CF group (p<.0000). (Fig. 1).
- The PS3-F obtained too lower nest building scores than CF group (p<.0000). (
However, no significant differences were found between non-maternal CF and PS3-F female rats.
Discussion and Conclusion
Our results clearly demonstrate that environmental prenatal stress has induced elevated plasmic corticosterone levels in the PS3-F group. These results are in agreement with the findings of Makino et al. (1994), who demonstrated that stress during pregnancy increases corticosterone levels in the pregnant mother and her fetuses, mainly in female pups.
The fact that progesterone and corticosterone levels resulted increased after PS3 treatment, but estradiol level did not, might suggest that PS3 primed the metabolic reduction pathway in decrement of the aromatization pathway.
Th poor nest building scores obtained by the PS3-F group and the absence of animals becoming maternal, in this group too, correlates with their increase of corticosterone and their decrease of estradiol levels.
Moreover, the fact that there was a correlation between c-fos expression and the display of maternal behavior indicates tha c-fos expression is dependent of the maternal behavior performance, rather than of the stress and/or the hormonal level changes.
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*This study has been supported by DGYCIT PB96.0107-C03-02.
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|Rodríguez-Martín, J.L.; Pérez-Laso, C.; Barona, M.L.; Ortega, E.; Guillamón, A.; Segovia, S.; Del Cerro, M.C.R.; (1998). Activation Of Fos-Like Immunoreactivity In The Accesory Olfactory Bulbs Folowing Induction Of Maternal Behavior In Prenatally Stressed Rats.. Presented at INABIS '98 - 5th Internet World Congress on Biomedical Sciences at McMaster University, Canada, Dec 7-16th. Invited Symposium. Available at URL http://www.mcmaster.ca/inabis98/cruzrdelcerro/rodriguez-martin0816/index.html|
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