Abstract
Offspring interaction is among the most highly motivated behaviors in maternal mammals and is mediated by mesolimbic dopamine (DA) system activation. Disruption or loss of significant social relationships is among the strongest individual predictors of affective dysregulation and depression onset in humans. However, little is known regarding the effects of disrupted mother–infant attachment (pup removal) in rat dams. Here, we tested the effects of permanent pup removal in rat dams, which were assigned to one of three groups on postpartum day (PD) 1: pups; pups removed, single-housed; or pups removed, co-housed with another dam who also had pups removed; and underwent a behavioral test battery during PD 21–23. In vivo electrophysiological recordings of ventral tegmental area (VTA) DA neurons were performed on PD 22 and 23 in a subset of animals. Pup removal did not impact sucrose consumption or anxiety-like behavior, but increased passive forced swim test (FST) coping responses. Pup-removal effects on social behavior and VTA activity were sensitive to social buffering: only single-housed dams exhibited reduced social motivation and decreased numbers of active DA neurons. Dams that had pups removed and were co-housed did not exhibit changes in social behavior or VTA function. Moreover, no changes in social behavior, FST coping, or VTA activity were found in socially isolated adult virgin females, indicating that effects observed in dams are specific to pup loss. This study showed that deprivation of species-expected social relationships (pups) during the postpartum precipitates an enduring negative affect state (enhanced passive coping, blunted social motivation) and attenuated VTA DA function in the dam, and that a subset of these effects is partially ameliorated through social buffering.
Highlights
The mother–infant attachment bond is among the strongest social attachments formed by mammals [1]
This study tested the impact of pup removal on maternal affect and ventral tegmental area (VTA) activity during the late postpartum period, and whether these effects could be modulated by social support, as modeled by co-housing with an age- and experience-matched conspecific
We showed that pup removal induces long-lasting alterations in a subset of affect-related behaviors associated with depressionrelated phenotypes as well as blunted mesolimbic DA function
Summary
The mother–infant attachment bond is among the strongest social attachments formed by mammals [1]. Mother–infant attachment is an adaptive and reciprocal process consisting of dynamic and complex behavioral and physiological interactions, which are facilitated by sensory and thermotactile cues embedded within the mother–infant dyad [2, 3]. Pup Removal Effects in Dam removal of these processes may negatively affect both members in the dyad [4]. Since human depression often entails loss of or disruption of significant social relationships [8, 9], animal models based on depression-like responses to disrupted mother–infant attachment are useful to study neural correlates associated with and/or contributing to these outcomes. Less is known about the consequences of disrupting mother– infant attachment in the rat dam
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