Motivational aspects of maternal anxiolysis in lactating rats.

RATIONALE AND OBJECTIVE: This study examines the role of maternal motivation on the reduced anxiety-like responses displayed by lactating rats in the plus maze test. RESULTS: Maternal animals, both lactating and sensitized (ovariectomized females behaving maternal after a continuous exposure to pups), displayed anxiolytic-like responses in the plus maze test in contrast to ovariectomized non-maternal rats. However, the levels of experimental anxiety were lower in lactating than in sensitized females. Pups placed in the open arms of the maze further reduced the low levels of anxiety-like behavior of both sensitized and lactating rats. Low doses of haloperidol (0.05 and 0.1 mg/kg), a dopamine antagonist, which interfere with maternal motivation but has neither anxiolytic nor anxiogenic effect in the plus maze test, significantly increased the anxiety-like responses of lactating rats. The presence of the pups in the open arms of the maze overrode the behavioral effect of haloperidol on lactating dams' anxiety-related behavior. CONCLUSIONS: These experiments show that maternity induces changes in the way the animals react to the environment, rendering them less anxious to aversive stimuli. The degree of experimental anxiolysis displayed by maternal animals varies according to their maternal motivation, which is modulated by the female's endocrine state, the pups and/or the dopaminergic system.

Experimental anxiety in the black and white model in cycling, pregnant and lactating rats.

This study demonstrates changes in experimental anxiety assessed in the black and white paradigm during various reproductive states of female rats. Low levels of experimental anxiety were observed during late proestrus and on day 17 of gestation, stages related to high progesterone (P) levels. In estrus, metestrus, diestrus and on day 21 of gestation, stages characterized by low P concentrations, high levels of experimental anxiety, similar to those exhibited by ovariectomized females, were found. No changes in experimental anxiety were observed on day 8 of lactation compared to ovariectomized females. These data are discussed from the standpoint of the putative anxiolytic-like effect of progestins.

Role of maternal behavior on aggression, fear and anxiety.

Concomitant to the expression of maternal behavior, the lactating female develops anxiolysis in the elevated plus maze test, aggression towards intruders and reduced fear in response to a sudden auditory stimulus. This study aims to determine if these behavioral changes are associated with maternal behavior independently of the endocrine status that characterizes gestation, parturition and lactation. To assess this purpose, the behavior of lactating females was compared to that exhibited by maternal and nonmaternal ovariectomized rats untreated with steroid hormones. In contrast with lactating dams, sensitized animals (rats that displayed maternal behavior after a continuous contact with young pups) did not display reduced anxiety in the plus maze test. However, the sensitized females showed behaviors characteristic of lactating rats, such as some components of maternal aggression and reduced fear, though much less intensely than dams. These results suggest that aggression and reduced fear, but not anxiolysis, partially depend on the development of maternal behavior.

Inhibitory effect of buspirone and diazepam, but not of 8-OH-DPAT, on maternal behavior and aggression.

The action of diazepam (0.0, 1.0, and 2.0 mg/kg) and the serotonergic compounds buspirone (0.0, 2.5, and 5.0 mg/kg) and 8-OH-DPAT (0.0, 0.1, and 1.0 mg/kg) on maternal behavior and aggression were studied. An activity test was made after these treatments to control for unspecific actions due to motor impairment. Diazepam and buspirone dose-dependently inhibited the expression of maternal aggression and the active components of maternal behavior such as retrieving and nest building. 8-OH-DPAT did not affect these behaviors. 8-OH-DPAT (1.0 mg/kg) provoked the serotonergic syndrome and hypothermia; however, ovariectomized animals showed more signs of the syndrome and a decrease in body temperature after 8-OH-DPAT than lactating rats. Buspirone, but not the other anxiolytics, reduced motor activity. The role of drugs acting at the serotonergic, dopaminergic, and GABA-benzodiazepine systems in the control of maternal behavior and aggression is discussed.