Differential emotional experience induces elevated spine densities on basal dendrites of pyramidal neurons in the anterior cingulate cortex of Octodon degus

It appears likely that, in analogy to the synaptic development of sensory and motor cortices, which critically depends on sensory or motor stimulation (Rosenzweig and Bennett, 1996), the synaptic development of limbic cortical regions are modulated by early postnatal cognitive and emotional experiences. The very first postnatal experience, which takes place in a confined and stable familial environment, is the interaction of the newborn individual with the parents and siblings (Gray, 1958). The aim of this quantitative morphological study was to analyze the impact of different degrees of juvenile emotional experience on the synaptic development in a limbic cortical area, the dorsal anterior cingulate cortex, a region which is involved in the perception and regulation of emotions. We study the precocious trumpet-tailed rat (Octodon degus) as the animal model, because, like human babies, this species is born with functional visual and acoustic systems and the pups are therefore capable of detecting even subtle environmental changes immediately after birth (Reynolds and Wright, 1979; Poeggel and Braun, 1996; Braun et al., 2000; Ovtscharoff and Braun, 2001). The results demonstrate that already a subtle disturbance of the familial environment such as handling induced significantly elevated spine densities on the basal dendrites of layer III cortical pyramidal neurons. More severe disturbances of the emotional environment, such as periodic parental deprivation with or without subsequent chronic social isolation, resulted in an elevation of spine densities of similar magnitude as seen after handling and in addition, altered spine densities confined to specific dendritic segments were observed in these groups. These observations unveil the remarkable sensitivity of the dorsal anterior cingulate cortex towards environmental influences and behavioral experiences during phases of postnatal development. The behavioral consequences of these experience-induced synaptic changes still need to be analyzed further to assess if they are beneficial or detrimental to the animals cognitive and emotional capacities in later life.