Interaction between postpartum stage and litter age on maternal caregiving and medial preoptic area orexin

Abstract

Most maternal caregiving behaviors change across lactation to match the developmental needs of the continuously aging offspring. However, it is mostly unknown whether the dams' postpartum stage or litter age is the primary driving force of these changes. In this study, postnatal day 1 and 8 litters were cross-fostered or in-fostered to postpartum day 1 or 8 dams. Five days later, undisturbed observations of maternal caregiving behaviors were performed on the subsequent two days. We found a main effect of dams' postpartum stage on the frequency that mothers spent with the pups and displayed erect postures over them (hovering over and kyphosis), although it was mostly driven by an interaction between postpartum stage and litter age: early-postpartum dams were in contact with younger litters and in erect postures more often with younger litters compared to later-postpartum dams with younger litters. Additionally, there was an interaction between postpartum stage and litter age on the litter weights because older litters living with later-postpartum dams were heavier than older litters living with early-postpartum dams. There was also an interaction between postpartum stage and litter age on the dams' bodyweight, with early-postpartum dams living with younger litters weighing the least and later-postpartum dams living with younger litters weighing the most. Because activity of the neuropeptide, orexin, within the medial preoptic area (mPOA) has been implicated in maternal nursing and other caregiving behaviors, we measured mPOA levels of orexin-A but it was not affected by postpartum stage or litter age (nor was there an interaction). However, high orexin-A was negatively associated with the frequency of contact with pups and the display of erect postures. These results indicate that changes in caregiving across lactation are driven by endogenous factors in the dams, age-related cues they receive from offspring, and interactions between these factors.

Low Daytime Light Intensity Disrupts Male Copulatory Behavior, and Upregulates Medial Preoptic Area Steroid Hormone and Dopamine Receptor Expression, in a Diurnal Rodent Model of Seasonal Affective Disorder

“…Brains were cut into 200-μm sections and bilateral 1-mm diameter micropunches (Harris Micropunch, Electron Microscopy Sciences, Pennsylvania, PA, USA) were made to obtain the mPOA and NAC. Tissue was processed and qtPCR run as described previously (Grieb et al, 2018). Briefly, tissue punches were homogenized by pulsed sonication in RLT Plus buffer (Qiagen, Germantown, MD, USA) containing β-mercaptoethanol.…”

Psychological and neurobiological mechanisms underlying the decline of maternal behavior

“…As the maternal behavior decline reflects the dynamic interplay between the female and the young, this approach considers both factors in a 2 × 2 complete factorial design with pup characteristics (young vs. old pups) and maternal condition (early vs. late postpartum) as two independent factors (Table 1). Grieb et al (2018) used this paradigm and demonstrated that changes in maternal behavior across postpartum are elicited by what they called the "endogenous factors" in the dams and age-related sensory cues they receive from offspring, and their interactions. One major difference between this approach and those used to in the study of the onset and maintenance of maternal behavior is that the female's behaviors reflecting their withdrawal and rejection of the pups will also be recorded, in addiction to maternal behavior, so we will have two sets of dependent measures (Reisbick et al, 1975), indicative the activity of the "approach" and "withdrawal" systems.…”

“…In the latter case, the age of testing pups can be kept the same day by day, or be advanced by one day at a time throughout the testing period. Subjects could be tested in a variety of different behavioral tasks, such as home-cage maternal behavior testing (Grieb et al, 2018), conditioned place preference (or aversion) (Wansaw et al, 2008), pup preference (Gao et al, 2020;Wu et al, 2018), and operant responding for pups or pup-related cues (Lee et al, 2000) to assess the motivational mechanisms underlying the maternal behavior decline.…”

Raising overlapping litters: Differential activation of rat maternal neural circuitry after interacting with newborn or juvenile pups

“…Interestingly, maternal behaviour dynamically changes throughout the progression of the postpartum period, adjusting to the characteristics and the physiological needs of the pups, and this adaptation has been attributed to functional modifications in the maternal circuitry . Thus, the transient inactivation of the mPOA in early postpartum, when maternal behaviour is maximal, abolishes its expression, whereas inactivation of this area on postpartum days 13‐14, when the maternal response is reduced, augments its expression .…”

“…15 Moreover, lactating rats that choose a chamber previously associated with pups over one associated with cocaine, in a conditioned place preference test, exhibit an elevation of c-Fos-like immunoreactivity expression within the infralimbic (IL) and the cingulated (Cg1) subregions of the mPFC. 16 Interestingly, maternal behaviour dynamically changes throughout the progression of the postpartum period, adjusting to the characteristics and the physiological needs of the pups, [17][18][19][20] and this adaptation has been attributed to functional modifications in the maternal circuitry. 19,21 Thus, the transient inactivation of the mPOA in early postpartum, when maternal behaviour is maximal, abolishes its expression, whereas inactivation of this area on postpartum days 13-14, when the maternal response is reduced, augments its expression.…”