Effects of repeated ayahuasca administration on behaviour and c-Fos expression in male rats exposed to the open field.

Considering the long-lasting effects of ayahuasca on the brain and emotional processing, the objective of this study was to evaluate the behavioural and neurobiological effects of repeated ayahuasca administration in an animal model of exploratory behaviour related to novel-environment anxiety. Male Wistar rats received water, 120, 240, 480 or 3600 mg/kg of resuspended freeze-dried ayahuasca by gavage once a day for 30 days; there was also a non-manipulated homecage group. One hour after the last administration, animals were placed individually in the open field for 20 min. We analysed the weight gain, the behavioural response through a stochastic analysis, and c-Fos immunoreactive levels in the hippocampus, amygdala, pre-frontal and barrel field cortex. Ayahuasca at 120 mg/kg increased ambulation, and at 3600 mg/kg decreased vertical exploration and reduced weight gain. Aya3600 had higher c-Fos expression in regions of the hippocampus and infralimbic cortex than homecage, water or aya120 groups. Water-receiving animals had less c-Fos expression in the anterior basolateral amygdala than others groups. Our results show different behavioural effects of ayahuasca: a stimulant-like effect in small doses, and decreased activity in extreme high-dose, probably due to adverse effects. Higher activation of areas involved in emotional processing and the serotonergic pathway adds to the neurobiological literature on repeated/chronic ingestion of ayahuasca. Our data do not support an anxiolytic effect of repeated ayahuasca related to exploring new anxiogenic-environment but suggest that low ayahuasca doses should be further studied. The absence of severe impairment and behavioural syntax alteration reinforce ayahuasca safety.