Postpartum rats spontaneously display pup-directed behaviors and exhibit lower anxiety-related behaviors compared to nulliparous rats. The ventral bed nucleus of the stria terminalis (BSTv) is a neural site critical for dams' maternal behaviors and, in male rats, for regulating anxiety-related behaviors. Neurotransmitters modulating the BSTv in females have not been previously identified. The BSTv contains one of the highest concentrations of norepinephrine (NE) in the brain and, in male rats, the release of (NE) in the BSTv is known to increase anxiety. It is also known that NE depresses neural excitability when applied to the BSTv. Given that: 1) maternal behavior is dependent on a functional BSTv, 2) NE inhibits the BSTv, 3) NE increases anxiety in male rats, and 4) dams exhibit pup-directed care and low anxiety, I hypothesized that dams maintain naturally low levels of NE release in their BSTv that account for their maternal responsiveness and low anxiety-related behaviors. To test this hypothesis, I examined the effects of increasing NE release in the BSTv on maternal behaviors, the effects of increasing or decreasing NE release in the BSTv on anxiety-related behaviors, and the concentrations of endogenous monoamines in female rats. Yohimbine or idazoxan (alpha-2 autoreceptor antagonists that increase NE release) significantly disrupted retrieving behaviors in postpartum rats. Idazoxan, but not yohimbine, also reduced the time dams spent nursing pups. Yohimbine also decreased exploration of the open arms in an elevated plus maze (EPM) when administered systemically or within the BSTv. Idazoxan, surprisingly, did not mimic the anxiogenic effects of yohimbine. Additionally, clonidine (an alpha-2 autoreceptor agonist that decreases NE release) did not affect anxiety-related behaviors in an EPM when administered systemically or within the BSTv. Finally, the concentrations of NE, dopamine, and serotonin were measured in the BSTv, medial preoptic area (mPOA), and dorsal bed nucleus of the stria terminalis (BSTd). Numerous differences in monoamine levels were found. Some notable results include postpartum rats containing higher levels of NE and turnover of serotonin compared to postpartum rats that had their litter removed or diestrous virgins. Together, these results demonstrate that increasing NE release in the BSTv of postpartum rats disrupts maternal behavior and increases anxiety-related behaviors. Furthermore, differences in NE and serotonin may account for the behavioral differences between postpartum and virgin rats.
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