Plasma hormonal profiles and dendritic spine density and morphology in the hippocampal CA1 stratum radiatum, evidenced by light microscopy, of virgin and postpartum female rats.

Successful reproduction requires that changes in plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), oxytocin (OT), estrogen (E(2)) and progesterone (P(4)) occur together with the display of maternal behaviors. Ovarian steroids and environmental stimuli can affect the dendritic spines in the rat hippocampus. Here, studying Wistar rats, it is described: (a) the sequential and concomitant changes in the hormonal profile of females at postpartum days (PP) 4, 8, 12, 16, 20 and 24, comparing to estrous cycle referential values; (b) the dendritic spine density in the stratum radiatum of CA1 (CA1-SR) Golgi-impregnated neurons in virgin females across the estrous cycle and in multiparous age-matched ones; and (c) the proportion of different types of spines in the CA1-SR of virgin and postpartum females, both in diestrus. Plasma levels of gonadotrophins and ovarian hormones remained low along PP while LH increased and PRL decreased near the end of the lactating period. The lowest dendritic spine density was found in virgin females in estrus when compared to diestrus and proestrus phases or to postpartum females in diestrus (p<0.03). Other comparisons among groups were not statistically significant (p>0.4). There were no differences in the proportions of the different spine types in nulliparous and postpartum females (p>0.2). Results suggest that medium layer CA1-SR spines undergo rapid modifications in Wistar females across the estrous cycle (not quite comparable to Sprague-Dawley data or to hormonal substitutive therapy following ovariectomy), but persistent effects of motherhood on dendritic spine density and morphology were not found in this area.

Neonatal handling increases fear and aggression in lactating rats.

Neonatal handling reduces fear in male and cycling female rats, but increases maternal aggressive behavior against intruders to the nest area. Present study aimed to analyze the effects of neonatal handling on the maternal aggressive behavior and the activity in the open field with a predator of lactating rats on the 8th and the 18th postpartum days (periods of high and low aggressiveness). As pups, animals were divided into two groups: nonhandled (no neonatal manipulation) and handled (handling for 1 min during the first 10 days after delivery). As adults, females of both groups were impregnated and tested against a male intruder for aggressive behavior and in the open field with a cat inside a wire-meshed cage. Results showed that on the 8th day frequency of aggressive behaviors of handled females was higher than that of the nonhandled ones, but on the 18th day, no significant difference was detected. Surprisingly, in the open field test, handled females showed decreased locomotion and increased freezing on the 8th day compared to the nonhandled ones. The opposite relationship between increased aggressiveness with reduced fear is observed in the nonhandled control females in early and late lactation periods. However, neonatal handling abolishes this relationship. Apparently, the increased aggressiveness in neonatal handled lactating females does not depend on a decrease in fear. Our findings support the hypothesis that long lasting effects of early life stimulation is a dynamic function depending on the behavioral system and the period of life analyzed. Moreover, they caution the relationship between aggressive behavior and fear.