Changes in maternal motivation across reproductive states in mice: A role for prolactin receptor activation on GABA neurons

The survival of newborn offspring in mammals is dependent on sustained maternal care. Mammalian mothers are highly motivated to interact with and care for offspring, however, it is unclear how hormonal signals act on neural circuitry to promote maternal motivation during the transition to motherhood. In this study we aimed to establish methods that enable us to evaluate change in maternal motivation across the reproductive life cycle in female mice. Using two behavioural testing paradigms; a novel T-maze retrieval test and a barrier climbing test, we found that pup retrieval behaviour was low in virgin and pregnant mice compared to lactating females, indicating that maternal motivation arises around the time of parturition. Furthermore, in reproductively experienced females, maternal motivation declined over time after weaning of pups. As we have previously shown that lactogenic action mediated through the prolactin receptor (Prlr) in the medial preoptic area (MPOA) is essential for the expression of maternal behaviour, we aimed to investigate the role of lactogenic hormones in promoting pup-related motivational behaviours. With GABAergic neurons expressing Prlr in multiple brain regions important for maternal behaviour, we conditionally deleted Prlr from GABA neurons. Compared to control females, lactating GABA neuron-specific Prlr knockout mice showed slower and incomplete pup retrieval behaviour in the T-maze test. Testing of anxiety behaviour on an elevated plus maze indicated that these mice did not have increased anxiety levels, suggesting that lactogenic action on GABA neurons is necessary for the full expression of motivational aspects of maternal behaviour during lactation.

Effect of methanolic crude extract of Aframomum melegueta (A.m) seeds on selected lactogenic hormones of Albino rats

The search for alternative control of excessive milk secretion associated with exclusive breast feeding necessitated this study. This study was designed to investigate the effect of methanolic crude extract of Aframomum melegueta (A.m) seed by measuring serum concentrations of selected lactogenic (prolactin, estradiol and progesterone) hormones in lactating and non-lactating Albino rats. A total of 18 non-lactating and lactating rats each were assigned into three (3) treatments of 6 rats each. Treatment 1 and 2 (controls) received 0.11 mg/kg/day of reference drug (bromocriptine) and 100 mg/kg/day of Dimethylsulfoxide (Dmso) 1 ml:9 ml of normal saline which is referred to as normal control in this study. Treatment 3 received 100 mg/kg/day of A.m methanolic crude extract. Serum samples were collected and analyzed for prolactin, estradiol and progesterone by ELISA techniques. The result obtained showed a 21.13% and 25.12% significant (P<0.05) reduction in serum concentration of prolactin for both non-lactating (26.15±0.15 ng/ml) and lactating (14.90±1.16 ng/ml) rats relative to (33.23±1.82 and 19.90±1.16 ng/ml) normal control rats but a significant (P<0.05) increase (26.15±0.15 ng/ml; 14.90±1.16 ng/ml) in serum levels of the same hormone relative to (12.56±0.89 ng/ml; 10.56±0.29 ng/ml) reference control drug (bromocriptine) in both groups. Serum estradiol levels were significantly (P<0.05) reduced by methanol extract relative to normal control rats in both groups. There was however, no significant (P>0.05) changes in serum levels of estradiol relative to reference control drugs in both rats. Serum levels of progesterone were not significantly altered in both groups relative to normal control rats. The above findings confer on the extract antilactogenic capability and hence a good alternative to bromocriptine.

Neuroendocrine regulation of maternal behavior

The expression of maternal behavior in mammals is regulated by the developmental and experiential events over a female's lifetime. In this review the relationships between the endocrine and neural systems that play key roles in these developmental and experiential processes that affect both the establishment and maintenance of maternal care are presented. The involvement of the hormones estrogen, progesterone, and lactogens are discussed in the context of ligand, receptor, and gene activity in rodents and to a lesser extent in higher mammals. The roles of neuroendocrine factors, including oxytocin, vasopressin, classical neurotransmitters, and other neural gene products that regulate aspects of maternal care are set forth, and the interactions of hormones with central nervous system mediators of maternal behavior are discussed. The impact of prior developmental factors, including epigenetic events, and maternal experience on subsequent maternal care are assessed over the course of the female's lifespan. It is proposed that common neuroendocrine mechanisms underlie the regulation of maternal care in mammals.