Influence of parental deprivation on the behavioral development in Octodon degus: Modulation by maternal vocalizations

Abstract

Repeated separation from the family during very early stages of life is a stressful emotional experience which induces a variety of neuronal and synaptic changes in limbic cortical areas that may be related to behavioral alterations. First, we investigated whether repeated parental separation and handling, without separation from the family, leads to altered spontaneous exploratory behavior in a novel environment (open field test) in 8-day-old Octodon degus. Second, we tested whether the parentally deprived and handled animals display different stimulus-evoked exploratory behaviors in a modified open field version, in which a positive emotional stimulus, the maternal call, was presented. In the open field test a significant influence of previous emotional experience was found for the parameters of running, rearing, and vocalization. Parentally deprived degus displayed increased horizontal (running) and vertical (rearing) motoric activities, but decreased vocalization, compared to normal and handled controls. The presentation of maternal vocalizations significantly modified running, vocalization, and grooming activities, which in the case of running activity was dependent on previous emotional experience. Both deprivation-induced locomotor hyperactivity together with the reduced behavioral response towards a familiar acoustic emotional signal are similar to behavioral disturbances observed in human attachment disorders.

THE EFFECTS OF PRE-WEANING SOCIAL ISOLATION AND MOTHER’S PRESENCE ON THE OBJECT EXPLORATION BEHAVIOR OF INFANT <i>OCTODON DEGUS</i>

“…Braun et al (2003) suggest that isolation enhances anxiety about novel environments and modifies sensitivity to emotional stimulation, such as the mother's voice. We carried out the novel object exploration test in the home cage.…”

“…However, if anxiety is stronger than curiosity, exploratory behavior will be suppressed. Following the theory of Braun et al (2003), it is possible that our isolated group pups experienced increased sensitivity to anxiety by the isolation experience. This might have suppressed exploratory behavior to the novel object, and simultaneously decreased the anxiety-buffering effect of the mother.…”

“…Even short-term social separation from mothers and siblings (from P8 to P10, twice a day, each time for 3 min) resulted in an upregulation of dopaminergic and serotonergic receptor density in the hippocampus (Ziabreva, Poeggel, Schnabel, & Braun, 2003). Braun et al (2003) used neonatal degus and examined the effects of parental separation on exploratory behavior and vocalization in an open field, which was a novel environment for the pups. Pups were repeatedly placed in isolated cages from P1 to P7, three times a day, each time for 1 hr.…”

“…Non-deprived individuals showed less activity and more vocalization, whereas there was no effect of maternal calls on either activity or vocalization in deprived individuals, who showed high motoric activity and less vocalization. Braun et al (2003) suggested that the separation experienced early in life altered the behavioral response to a novel environment and reduced sensitivity and/or attention toward emotional signals, such as maternal calls. These studies show that early experience of family separation produces changes in emotion-and cognition-related brain regions and neuronal transmissions in degu pups.…”

“…We used the object exploration test rather than the open field test used by Braun et al (2003) and Colonnello et al (2011) to endorse a clearer interpretation of the relationship between activity level and emotionality. In the open field, high and low levels of anxiety suppress exploration whereas intermediate level increases it (Archer, 1973).…”