Behavioural and neurotoxic effects of ayahuasca infusion (Banisteriopsis caapi and Psychotria viridis) in female Wistar rat

Highlights

• Ayahuasca decreased locomotion of Wistar female rats in OF and EPM tests.

• Ayahuasca treated animals were more active than controls in FS test.

• Potential antidepressant properties of ayahuasca was shown.

• Ayahuasca increase neuronal activation in serotoninergic brain areas.

Abstract

Ayahuasca, a psychoactive beverage used by indigenous and religious groups, is generally prepared by the coction of Psychotria viridis and Banisteriopsis caapi plants containing N,N-dimethyltryptamine (DMT) and β-carboline alkaloids, respectively. To investigate the acute toxicity of ayahuasca, the infusion was administered by gavage to female Wistar rats at doses of 30X and 50X the dose taken during a religious ritual, and the animals observed for 14 days. Behavioural functions were investigated one hour after dosing at 15X and 30X using the open field, elevated plus maze, and forced swimming tests. Neuronal activation (c-fos marked neurons) and toxicity (Fluoro-Jade B and Nissl/Cresyl staining) were investigated in the dorsal raphe nuclei (DRN), amygdaloid nucleus, and hippocampal formation brain areas of rats treated with a 30X ayahuasca dose. The actual lethal oral dose in female Wistar rats could not be determined in this study, but was shown to be higher than the 50X (which corresponds to 15.1 mg/kg bw DMT). The ayahuasca and fluoxetine treated groups showed a significant decrease in locomotion in the open field and elevated plus-maze tests compared to controls. In the forced swimming test, ayahuasca treated animals swam more than controls, a behaviour that was not significant in the fluoxetine group. Treated animals showed higher neuronal activation in all brain areas involved in serotoninergic neurotransmission. Although this led to some brain injury, no permanent damage was detected. These results suggest that ayahuasca has antidepressant properties in Wistar female at high doses, an effect that should be further investigated.

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-HT_2A serotonin receptor (Smith et al., 1998), an action that may be attenuated by its interaction with 5-HT_1A 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-HT_2A 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.