Amygdaloid inhibition of maternal behavior in the nulliparous female rat

Abstract

In the first experiment, the effects of lesions of (1) the amygdala, (2) its major efferent projection system, the stria terminalis or (3) other non-limbic brain sites on the induction of maternal behavior in the nulliparous female rat were investigated. Animals sustaining lesions of either the amygdala or the stria terminalis became maternal more rapidly than did control animals. In the second study the effects of lesions to different portions of the amygdala on both maternal and fear responding were investigated. It was found that animals sustaining damage to the corticomedial amygdaloid nuclei became maternal more quickly than did animals sustaining either basolateral amygdaloid damage or no amygdaloid damage. Also in comparison to lesioned controls, animals with lesions of the amygdala showed reduced ‘fearfulness’ on a number of fear-mediated tasks. The third study attempted to interrelate fear responsiveness and maternal behavior by observing nulliparous animals with amygdaloid or stria terminalis lesions for their responses to unfamiliar foster pups placed daily into their preferred nesting quadrant. While control animals actively avoided pups placed into their nest sites (by moving their nest site to another quadrant of the cage), animals with amygdaloid lesions or lesions of the stria terminalis, did not. These results are interpreted to mean that nulliparous females generally do not respond maternally to pups because these females are, in general, more neophobic than parturient females and they tend to find pups and their novel odors, aversive. This aspect of their behavior is likely mediated by the amygdala. These data are discussed in terms of their relevance to the rapid maternal responsiveness normally shown by the female at parturition.