Anxiolytic effects of rapid amygdala kindling, and the influence of early life experience in rats

The incidence of psychiatric disturbances is elevated in temporal lobe epilepsy (TLE) patients. Early life stressful events are believed to have a major impact on mental health later in life, and increasing evidence suggests that such stresses may also promote a vulnerability to TLE. This study investigated whether subjecting rats to early life stress exacerbated mood and cognitive disturbances associated with the development of epilepsy. On postnatal days 2–14, rat pups were separated from their dams for either 180 min/day (handling and maternal separation – HMS180, modelling early life stress) or 15 min/day (control handling and maternal separation – HMS15). At 7 weeks, rats were implanted with a bipolar electrode into the left amygdala. Following recovery, one group of rats from each litter underwent rapid amygdala kindling (RAK) epileptogenesis, while another underwent sham kindling. One week following this, rats were subjected to behavioural tests assessing anxiety and cognition. HMS180-exposed rats kindled faster than HMS15 rats (p < 0.0001). RAK induced a potent anxiolytic effect as evidenced by increased % time spent in the open arms of the elevated plus maze, compared with sham kindled rats (p < 0.0001). This anxiolytic effect was also observed in the open field task, as evidenced by increased time spent in the inner area (p = 0.010). Neither RAK nor maternal separation had any effect on cognitive function in the Morris water maze. We conclude that maternal separation stress accelerates limbic epileptogenesis in adult rats, and that RAK induces potent anxiolytic effects that are not influenced by such early life stressful events.