Maternal separation and social isolation modulate the postnatal development of synaptic composition in the infralimbic cortex of Octodon degus.

We analysed the influence of preweaning periodic maternal separation followed by postweaning chronic social isolation on the development of synaptic composition in the infralimbic cortex of Octodon degus, a South American species formerly classified as a caviomorph rodent but now considered to belong to Lagomorpha (rabbits). Three groups of animals were analysed: (1) control pups which remained undisturbed with their families; (2) pups which were exposed to individual periodic maternal deprivation [postnatal day 1 (P1) until P21], followed by social isolation (P22 until P45); and (3) pups which were handled daily without being removed from the families (P1 until P21) and thereafter remained undisturbed with the family (P22 until P45). The mean synaptic density and mean projected height of synapses were quantified using the "dissector" method. In the deprived group, significantly higher (up to 137.8%) mean synaptic densities were found in layer II of the infralimbic cortex compared to normal control animals. In handled pups, asymmetric shaft synapses were significantly decreased (down to 54%) compared to the control group.These results indicate that early postnatal changes in the socio-emotional environment change the number of synaptic connections in the infralimbic cortex. Since this subregion of the medial prefrontal cortex is involved in a variety of emotional behaviors and plays a role in associative learning tasks, these environmentally induced synaptic changes may be indicative, and perhaps the cause, of alterations of behavioral and cognitive capacities.