Evaluation of Al Exposure on Empathetic Behavior in Rat Model

Abstract

Empathy, a complex psychological attribute, is referred to as an increase in affiliation towards someone in distress with a desire to reprieve their travail. Though it is a common behavioral response in humans and other organism with advanced cognition, the underlying neural circuitry and involvement of several brain regions are not yet fully understood. The current study investigated the role of social isolation and aluminum (Al)-induced neurotoxicity on regulation of empathy. An 80-day protocol was designed to evaluate the effect of Al exposure (80 mg/kg of Al in drinking water) and isolation on empathy. Female Wistar rats (200-300g) were housed in plastic cages and acclimatized. The animals were divided into 4 groups i.e. Al exposed (n = 10), Control (n = 10), isolation only (n = 10), and Al + isolation (n = 10). The control and isolation only group were given distilled water. Behaviour tests were performed at two intervals i.e. 20 and 40 days to assess short term and long term effect of metal toxicity and isolation. The model for Empathy Behavior Test (EBT) implied use of restrainer stress method where a conspecific is trapped in a perforated container under observation by the experimental rats. Empathy response was measured through assessing the number of interactions, number of climbings, freezing behavior, and time spent in close proximity to subject rat. The EBT was performed prior to as well as after 24 h of self-experiencing the restrain stress to evaluate enhancement in empathy. Moreover, anxiety and stress levels were measured by Elevated Plus Maze (EPM) and grooming behavior (spray test). It was observed that the rats exposed to Al drinking water made significantly less number of interactions and climbings after ABSTRACT 2 long term exposure (p˂ 0.0001). However, short term Al exposure was less detrimental (p˂ 0.01). Whereas, in case of isolated rats the freezing behavior tremendously increased after long term isolation (p˂ 0.0001). Furthermore, though freezing behavior was observed after short term Al exposure, it was diminished after long term exposure. In particular, the empathetic response did not increase after self-experience of distress in both the groups as compared to their respective controls. Accompanied with these behavioral changes tremendous increase in anxiety and stress like symptoms was observed in Al exposed and isolated animals. The Al exposure and Al + isolation groups made significantly less (p˂ 0.0001) number of entries in open arms of EPM. Similarly, the number of incorrect grooming bouts were significantly higher (p˂ 0.0001) in these groups. Latency to start grooming was also observed to be increased in isolated and Al exposed group signifying the stressed condition. This study provided the evidence that empathetic behaviour is influenced by metal exposure and social isolation and may have a direct association in disrupting the neural circuitry of empathy. Moreover, isolation have a peculiar relationship with empathy as some components of empathy were increased (affective) while others decreased (cognitive). This preliminary and first-of-its-kind study highlights the significant impact of Al-induced neurotoxicity however determination of the exact neural circuitry behind subcomponents of empathy is warranted.