Progress 02/01/02 to 01/31/05
Outputs
In the rat brain, the ventromedial nucleus of the hypothalamus (VMH) is involved with energy metabolism, hormone release, stress and anxiety, and female reproductive behavior. Recent evidence from our laboratory indicates that the VMH also regulates maternal behavior in virgin rats as part of an inhibitory neural circuit. Our progress period indicates that the VMH also regulates maternal behavior in pregnant rats, in addition to the dorsomedial nucleus (DMH). We also found that mRNA for progesterone receptors decrease in the brain at the later stage of pregnancy, while the mRNA for estrogen receptors remain unchanged. Further results indicate that the GABAergic system may not be involved with the inhibitory circuit. These data shed light on the important modifications that occur in the female brain as she changes from being non-parental to parental at parturition. In other words, what natural neurobiological events control both female disinterest and interest in young?
This unusual plasticity that underlies normal physiological development - as well as the development of maternal behavior - provides an interesting model that will contribute more broadly to an understanding of both natural and unnatural behavioral responses in rats and other mammals, including humans.
Impacts
The results of these studies have implications for how a virgin female makes the transition from nulliparous (nonmaternal) to pregnant to parous (immediately maternal). Little is known of the mechanisms that exist initially to suppress or inhibit the display of maternal behavior. Our findings have added to our understanding of the normal interplay between the areas in the brain that are involved in the regulation of maternal behavior.
Publications
- Mann, P.E. and Babb, J.A. Neurotoxic lesions of the hypothalamus advance the onset of maternal behavior in primigravid rats. Mother and Infant: Perinatal Influences on Health, 2003, Montreal, Canada.
- Mann, P.E. and Babb, J.A. Neurotoxic lesions of the dorsomedial and ventromedial nuclei of the hypothalamus advance the onset of maternal behavior in primigravid rats. Soc. Neuroscience Abstracts, 2003, 29, San Diego, CA.
- Mann, P.E. and Babb, J.A. Hormone receptor mRNA expression during late pregnancy in rats. Soc. Neuroscience Abstracts, 2004, 30, New Orleans, LA.
- Mann, P.E. and Bridges, R.S. Progesterone metabolites and the inhibition of maternal behavior in primigravid rats: a possible role for neurosteroids? Soc. Neuroscience Abstracts, 2005, 31, Washington, D.C.
- Mann, P.E. and Babb, J.A. Disinhibition of maternal behavior following ventromedial hypothalamic lesions in virgin rats, 2004, 1025, 51-58.
- Mann, P.E. and Babb, J.A. Neural steroid hormone expression in pregnant rats. Accepted for publication with minor revisions, Molecular Brain Research, 2005.
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Progress 01/01/03 to 12/31/03
Outputs
As of now, the following experiments were performed: 1) The objective of the first experiment was to determine whether the timing of VMH neurotoxic lesions is crucial for the display of fast latency maternal behavior in estrogen-primed, ovariectomized, virgin rats. The results indicate that only a 7-day interval between lesion and maternal behavior testing stimulated fast-latency maternal behavior. Determining the timing between neural insult and the change in subsequent behavior has significant impact on future experimental planning and helps in understanding the underlying neural mechanism involved. 2) The objective of this experiment was to determine if chronic infusions of the neurotransmitter gamma amino-butyric acid (GABA) would stimulate fast latency maternal behavior in ovariectomized, estrogen-primed, virgin rats. GABA infusions failed to stimulate a rapid onset maternal behavior, although there was a trend at the highest dose. In addition, GABA infusions did
not affect the percentage of females responding maternally on each test day, although, again, there was trend for a higher percentage of females to display maternal behavior on test day 5. These results indicate that GABAergic neurons in the VMH may not be involved in the inhibition of maternal behavior in virgin rats. 3) The objective of this study was to determine if either DMH or VMH lesions would advance the onset of maternal behavior in first-time pregnant rats. The results indicate that lesioning the DMH stimulates rapid onset maternal behavior. In addition, there were significant differences in the median latencies to display maternal behavior following VMH lesions. These results demonstrate, for the first time, that both the DMH and VMH are involved in the inhibition of maternal behavior in first-time pregnant rats.
Impacts
The results of these studies have implications for how a virgin female makes the transition from nulliparous (nonmaternal) to pregnant to parous (immediately maternal). Little is known of the mechanisms that exist initially to suppress or inhibit the display of maternal behavior. Our findings have added to our understanding of the normal interplay between the areas in the brain that are involved in the regulation of maternal behavior.
Publications
- Mann, P.E. and Babb, J.A. Neurotoxic lesions of the hypothalamus advance the onset of maternal behavior in primigravid rats. Mother and Infant: Perinatal Influences on Health, 2003, Montreal, Canada.
- Mann, P.E. and Babb, J.A. Neurotoxic lesions of the dorsomedial and ventromedial nuclei of the hypothalamus advance the onset of maternal behavior in primigravid rats. Soc. Neuroscience Abstracts, 2003, 29, 728.7.
- Mann, P.E. and Babb, J.A. Disinhibition of maternal behavior following neurotoxic lesions of the hypothalamus in primigravid rats. Brain Research, in press, 2004.
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