Parental Deprivation Induces N-Methyl-D-Aspartate-Receptor Upregulation in Limbic Brain Areas of Octodon degus: Protective Role of the Maternal Call

An optimal coordination between parents and their offspring involves a sequence of reciprocal behaviors to ensure the adequate care of the young, which is critical for a healthy physical, emotional, and social development. Parental deprivation, particularly an impaired child-mother attachment, induces lasting changes in emotional as well as in cognitive capacities in later life. We assessed in the South American precocial species, Octodon degus, whether alterations of glutamatergic function of the limbic system induced by parental deprivation may be a neural correlate for such behavioral changes. Further, we analyzed whether the mother's voice can protect from separation-induced changes of brain function. Changes of N-methyl-D-aspartate (NMDA) receptor expression were examined in the following three groups of 2-week-old Octodon degus pups: (I) control animals who remained undisturbed with the family; (II) animals who were repeatedly separated from the family and individually placed in an unfamiliar environment for behavioral analysis (open field); and (III) animals who were treated like the group described under (II) but were presented with maternal vocalizations during separation. Relative to those in the control group I, the animals in group II showed an upregulation of NMDA receptor density in the (a) anterior cingulate, prelimbic, infralimbic, and anterior insular cortices; (b) CA1/stratum radiatum; (c) CA1/stratum lacunosum moleculare and CA3/stratum radiatum; and (d) in the basomedial amygdaloid nucleus. Presentation of the maternal call during the separation period (group III) suppressed the separation-induced NMDA receptor upregulation in all regions. The results demonstrate that early life events can influence the expression of transmitter receptors and that maternal behavior, acting to control the pup's socio-emotional environment, is a key factor for regulating such developmental events.