Behavioural and neurotoxic effects of ayahuasca infusion (Banisteriopsis caapi and Psychotria viridis) in female Wistar rat
Introduction
Ayahuasca (or hoasca) is a psychoactive beverage traditionally used in shamanic rituals by various indigenous populations of the Amazon (McKenna, 2004). It was introduced to non-indigenous Brazilians in the 1930s, and its use by religious groups, including Santo Daime and União do Vegetal (UDV), spread beyond the Amazon borders in the 1970s (MacRae, 2004). Religious use of ayahuasca has been regulated in Brazil since 1986 in response to concerns raised by society and health authorities regarding its inadequate use, while ensuring the freedom of religious practices (CONAD, 2010). Its use has also been regulated in other countries, including the USA, Belgium and the Netherlands (Labate and Feeney, 2012, Blainey, 2014). However, ayahuasca consumption has extended beyond religious practices, and may occur in recreational contexts by people seeking the psychedelic effects of the infusion. This non-religious use is illegal in Brazil, and the material can be seized by Brazilian government authorities (Alvarenga et al., 2014).
The psychoactive properties of ayahuasca are produced by the substances present in the plants normally used to prepare the infusion: N,N-dimethyltryptamine (DMT) present in the leaves of Psychotria viridis, and β-carboline alkaloids such as harmine, harmaline and tetrahydroharmine, present in the Banisteriopsis caapi vine (MacKeena, 2004) (Fig. 1). DMT, a non-selective serotonin (5-hydroxytryptamine, 5-HT; Fig. 1) receptor agonist, elicits its effect through stimulation of the 5-HT2A serotonin receptor (Smith et al., 1998), an action that may be attenuated by its interaction with 5-HT1A receptors (Halberstadt and Geyer, 2011). However, unlike other hallucinogens, DMT is inactive when administered orally, as it is readily metabolized by monoamine oxidases (MAO) (Suzuki et al., 1981, Riba et al., 2014). β-carbolines, mainly harmine and harmaline, inhibit MAO activity (Wang et al., 2010), and therefore block the metabolic breakdown of DMT in the liver and gut. Thus, when DMT is absorbed in the gastrointestinal tract, the psychoactive properties of the ayahuasca infusion can occur (Ott, 1999, Riba et al., 2003). Furthermore, as MAO inhibitors, β-carbolines can increase the level of serotonin in the brain (McKenna et al., 1984), and are capable of inducing direct psychoactive effects (Freedland and Mansbach, 1999, Brierley and Davidson, 2012). Brierley and Davidson (2013) also suggested that harmine augments dopamine efflux via a novel shell-specific, presynaptic 5-HT2A receptor-dependent mechanism, independent of MAO inhibitory activity.
The effects and pharmacokinetics of ayahuasca in healthy volunteers after a single or two-repeated ritual doses (about 0.5–1 mg/kg bw of DMT) have been thoroughly described in the literature (Callaway et al., 1999, Riba et al., 2003, Riba et al., 2012, Barbanoj et al., 2008, Bouso et al., 2012, Santos et al., 2012). Other studies have investigated the therapeutic properties of ayahuasca, primarily to treat drug addiction (Brierley and Davidson, 2012, Thomas et al., 2013, Loizaga-Velder and Verres, 2014).
Although the ritualistic use of ayahuasca is considered to be safe (Bouso et al., 2012), a small number of case reports suggest that some individuals may be more prone to experience significant side-effects from ayahuasca intake (Santos, 2013a, Santos, 2013b). However, experimental data from studies with animals exposed to high doses of the infusion remain scarce in the literature. The present study aimed at investigating the lethal dose, the impact on behaviour, and the neurotoxic potential in female Wistar rats after acute exposure to high-dose levels of an ayahuasca infusion.
Section snippets
Animals
This study was conducted with female rats, which are normally more sensitive to acute tests than males (OECD, 2001). Healthy nulliparous female Wistar rats aged between 9 and 12 weeks were acquired from Granja RG (São Paulo, Brazil) and allowed to acclimatize for a 15-day period in the Faculty of Health Sciences of the University of Brasilia (UnB) animal house prior to study initiation. Subjects were kept individually in polypropylene cages under controlled conditions: 12 h/12 h, light/dark; 22–25
Acute toxicity
None of the first three animals treated with 30X dose (corresponding to 9 mg/kg bw DMT) died or had any morbidity signs over the 14-day study. When this test was repeated, one animal died in the first 2 h after oral gavage. Following the OECD 423/2001 protocol, the experiment was repeated at a higher dose, which in this study was the highest possible dose that could be given to the rat by gavage, 50X dose (15 mg/kg bw DMT). One of the six animals tested with 50X died (5 h and 40 min after gavage).
Discussion
Ayahuasca alkaloid profiles vary considerably, mainly due to the proportion of the plants and the method used to prepare the infusion, as well as the plant cultivars (McKenna et al., 1984, McKenna, 2004). The level of harmine present in the material used in this study (1.56 mg/mL) was similar to that reported by Callaway et al. (1999) (1.7 mg/mL) in a human pharmacokinetic study, and by Oliveira et al. (2010) (1.37 mg/mL) in toxicological studies. However, our infusion contained less DMT (0.141
Conclusions
In this study, the actual lethal dose of an ayahuasca infusion could not be determined in female Wistar rats due to the limited solubility of the lyophilized material, but showed to be higher than the 50X dose (or 15 mg/kg bw DMT). Rats exposed to 15X and 30X doses presented decreased locomotor and exploratory activities in the open field and elevated plus-maze tests, similar to fluoxetine, a known antidepressant drug. Behavior of treated rats in the forced swimming test indicated a more
Acknowledgments
We are grateful to Prof. Maria Lucília dos Santos from the Chemistry Institute at the University of Brasilia for providing the synthetized DMT. Fluoxetine was a gift from Farmacotécnica, Brazil. This work received the financial support of the Federal District Research Foundation (FAP-DF; Grant 193000358/2010). LG Motta, JA Morais and W Melo Jr were granted Master’s scholarships by the REUNI Program of the University of Brasilia.
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