Tripping the Light Fantastic: Modeling the Consequences of Recreational Use of MDMA or 5-MeO-DIPT in Humans Using Weekend "Rave" Exposures in Rat

Discussion In the present experiment, while dependent on task demands, the performance of MDMA-treated rats was inferior to that of the Foxy-treated and saline rats. In addition, the performance of both drug groups was comparable and inferior to that of control rats on the spatial learning set task. Nonetheless, when the data are considered collectively, greater impairments were observed in MDMA-treated rats than the Foxy-treated rats. There is considerable evidence that exposure to or recreation use of MDMA is capable of compromising cognition. Such effects lead to compromised executive control, planning deficits, perseverative behavior, and deficits in working memory (Compton, Selinger et al., 2011; Marston, Reid, Lawrence, Olverman, & Butcher, 1999; McCardle, Luebbers, Carter, Croft, & Stough, 2004; Moyano, Frechilla, & Del Rio, 2004; Parrott, 2002; Skelton et al., 2006; Skelton et al., 2009; Thompson et al., 2009; Wareing et al., 2004). The deficits in working memory have been reported to extend to spatial working memory processes (Fox, McLean, Turner, Parrott, Rogers, & Sahakian, 2002; Harper, Wisnewski, Hunt, & Schenk, 2005; Wareing, Fisk, & Murphy, 2000). However, the effects do appear to be to some degree dependent on prior experiences, with reports of a deficit in reference memory rather working memory (Vorhees et al., 2004). In addition, sex differences were observed on some but not all spatial tasks with MDMAtreated males performing significantly worse than similarly treated female rats. Justifying exclusion on the basis of the frequency and presence of an estrus cycle and accompanying hormonal fluctuations (Sharp & La Regina, 1998), often female animals were not included in physiological and psychopharmacological research (Wallinga, Gralhlmann, Granneman, Koolhaas, & Buwalda, 2011). More recently, recognition in support of the consideration of sex differences in the study of psychostimulants such as MDMA has increased following reports that female use of ecstasy has increased and remains popular (Allott & Redman, 2007). Last, in humans MDMA has a more profound impact on 5-HT in females (see McCann & Ricaurte, 2014, for a review), with subjectively more potent effects reported among female users (Liechti, Gamma, Vollenweider, 2001). Unfortunately, when sex differences were examined in animals exposed to MDMA, the results have been equivocal (Fonsart et al., 2008; Koenig et al., 2005; Palenicek, Votava, Bubenikova, & Horacek, 2005; Wallinga et al., 2011; Walker, Williams, Jotwani, Waller, Francis, & Kuhn, 2007; Wyeth et al., 2009). In some investigations no differences in MDMA mediated depletion of 5-HT and 5-HIAA (a metabolite of  5-HT) was detected, while in another study there sex differences were observed (Wallinga et al., 2011). In the Wallinga et al. investigation MDMA had a more pronounced and lasting hyperthermic effect in male rats a result that was consistent with others (e.g., Fonsart et al., 2008; Wyeth et al., 2009). Further, MDMA linked hyperthermia is associated with higher morbidity in male animals (Fonsart et al., 2008; Wallinga et al., 2011). Conversely, 5-HIAA depletion was observed only in male rats. When hyperthermic responses were equated, 5-HT depletion was higher in female animals, suggesting MDMA toxicity to 5-HT systems in female rats (Wallinga et al., 2011). Noting that the MDMA metabolite methylenedioxamphetamine was higher in male rats, Wallinga and colleagues note the normal interpretation is to postulate that the sex difference reflects higher levels of enzymatic activity associated with N-demethylation step in the pharmacokinetics of MDMA (see Fonsart et al., 2008; Meyer & Quenzer, 2013). Simply put, the higher rates of conversion to MDMA metabolites increase the vulnerability of male rats to the drug's neurotoxic effects. However, Wallinga et al. (2015) did not find a male rat disadvantage associated with 5HT depletion following MDMA exposure. Noting a small number of studies, in the Allott and Redman (2007) review of the literature the authors offered the preliminary conclusion that adult males suffer a greater impact from the acute physiological effects of MDMA while adult females are more susceptible to the both subacute and acute effects when physical and psychological indices are considered. In addition, much less is known about the effects of Foxy so any conclusion at this point would remain premature. Given the possible reasons for the reported sex differences such as hormonal differences or sex differences associated with pharmacokinetic considerations as examples (Allott & Redman, 2007), such research avenues should be explored further, especially in light of developmental considerations. Adolescence is a developmental period marked by considerable neural change (Müller & Jacobs, 2010). For example, a number of maturational changes to 5-HT neural systems during adolescence have been described (Andrade & Beck, 2010; Sturman & Moghaddam, 2011), including differential expression of 5-HT receptors with age (Whitaker-Azmitia, 2010). More generally, because adolescence is a period of anatomical and functional transformation, adolescent exposure to drugs can be particularly problematic (Smith, 2003). When adolescent MDMA exposure has been considered, evidence emerged that such exposure produced long-term decreases in 5-HT levels, including such indices as direct neurotransmitter levels, metabolites, and binding sites (Bull, Hutson, & Fone, 2003, 2004; Compton, Selinger et al., 2011; Piper, Fraiman, & Meyer, 2005; Piper & Meyer, 2004). After examining the effects at different time points in adolescent development, one group concluded that the neurotoxic and behavioral alterations associated with MDMA exposure are indeed dependent on age of exposure (Morley-Fletcher, Bianci, Gerra, & Laviola, 2002). Further, Bull et al. (2004) found reductions in hippocampal, striatum, and cortical 5-HT levels 60 days following the final MDMA exposure, a result that is consistent with work in our lab (Compton et al., 2011). Thus, although variables such as the frequency and exposure duration are important when considering the neurochemical effects associated with MDMA use (Green et al., 2003), there is considerable evidence suggestive of the importance of the developmental age of drug exposure (Teixeira-Gomes et al., 2015). Perhaps unsurprisingly, even when developmental exposure is considered, differences in the pattern and frequency of administration can influence the effects of MDMA exposure. Similar to the protocol reported here, Piper and colleagues assessed the effects of MDMA in adolescent rats through multiple dose (sc) exposures occurring every 5th day from PND 35 to 60 (Piper & Meyer, 2004). The results of Piper and Meyer revealed that prior MDMA compromised cognition even though the damage to serotonergic systems was largely absent. In a subsequent study(Piper, Vu, Safain, Oliver, & Meyer, 2006), rats were periodically exposed to MDMA between PNDs 35 to 60, followed by a single MDMA binge session or testing with the 5-hydroxytryptamine1A receptor agonist 8-OH-DPAT at PND 67. Prior MDMA exposure lead to a predicted attenuation of the neurotoxic changes that would otherwise have been expected (Piper et al., 2006). As is the case when considering the physiological consequences associated with drug use, the drug dose is a relevant variable. For example, in a recent report on the effects of daily exposure of MDMA for four days over PND 38 to 41, 5 mg/kg had no effect on behavioral measures such as anxiety and place conditioning while in with a 10 mg/kg dose, a number of effects were observed (Cox et al., 2014). Consistent with the behavioral results, monoaminergic parameters were only affected at the 10 mg/kg dose. Interestingly, no change in hippocampal 5HT levels was found following the higher MDMA exposure but 5-HT levels were reduced in the amygdala. Ultimately, the results of the animal studies reviewed here as well as the present results must be considered in light of their relevance to the effects of MDMA or Foxy on humans. While tempting to perform direct mg/kg comparisons, doing so leads to underestimates in the bioavailability of a given drug (Lin, 1998), because in small animals drug elimination rates tend to be higher than in larger animals such as humans (Green et al, 2003). Using the allometric scaling formula for interspecies comparisons (Hayes & Kruger, 2014), allows for interspecies inferences concerned with drugs of abuse - Dosehuman = Doseanimal (Weighthuman/Weightanimal)0.25, with dose and weight expressed in mg/kg and kg respectively. In addition, an adjustment of the exponent to 2/3 has been suggested (White & Seymour, 2005). Thus, calculated for a single dose of MDMA or Foxy at 5 mg/kg for a .200 kg adolescent rat would be considered equivalent to a dose in a 50 kg adolescent human of approximately 1.26 mg/kg or 63 mg of drug. While less information concerning the pharmacodynamics of Foxy is available, research with animals (Compton et al., 2006; Compton, Dietrich et al., 2011; Compton, Selinger et al., 2011; Skelton et al., 2009) and humans (Ikeda et al., 2005; Kiyota, 2004; Smolinske et al., 2005; Tanaka, Kamata, Katagi, Tsuchihashi, & Honda, 2006; Wilson et al., 2005) suggests that research with the dose used here has value. While there is support for that developmental exposure of Foxy appears to result in longterm changes that affect cognition (Compton, Dietrich et al., 2011) the effects observed here are milder than that reported and thus dissociable from effects of MDMA (Compton, Selinger, et al., 2011; Skelton et al., 2009). Arguably, at some of the observed differences in the behavioral effects associated with each drug may simply reflect the fact that the two drugs are not equipotent and/or exerts the same level of CNS effects (Skelton et al., 2009). Indeed, it would be prudent to explore this issue further. At any rate, since the MDMA and, to a lesser extent, Foxy effects seem to persist following a relatively long abstinence period, the examination of possible permanent adverse effects in cognition is reasonable. Currently, we are examining the adolescent exposure of Foxy or MDMA by conducting a longitudinal assessment of the effects of these compounds across the rodent lifespan. The developmental considerations considered here also include the specific timeframe of exposure. As an illustration of this point, consider 5-HT turnover in the rodent nucleus accumbens, part of the reinforcement system of the brain (Carlson, 2013; Teicher, 1999). Prior developmental research has shown that levels are up to four times lower in PND 30 to 40 rats than prepubescent rats or older (PND 60 to 80) rats (Teicher, 1999). 5-HT2A receptors just before the onset of adolescence are at highest level of expression in the cortex and follow a decline to adult levels (Morilak & Ciaranello, 1993). Thus, the timing of MDMA or Foxy exposure could have a variety of effects, with the long-term consequences resulting from such variables as the developmental exposure period as well as the length of exposure. Acute exposure of MDMA has been linked to a dose-dependent increase in extracellular concentration of 5-HT in a number areas of the brain including the hippocampus, cerebral cortex, and the striatum (Gough, Ali, Slikker, & Holson, 1991; Gudelsky & Nash, 1996). In addition, there is clear evidence that MDMA interferes with normal serotonergic metabolism (Leonardi & Azmitia, 1994), perhaps contributing to reported increases of serotonin efflux (Gudelsky & Yamamoto, 2008). Unfortunately, the effects of MDMA are not limited to acute exposure (Compton, Selinger et al., 2011; Green et al., 2003; Gudelsky & Yamamoto, 2003; Kish et al., 2010; Ricaurte, Yuan, & McCann, 2000). Considerable evidence exists across species that, as a consequence of repeated exposure to MDMA, there is a long-term reduction in both 5-HT concentration in the brain and reuptake sites (Ricaurte et al., 2000; Green et al., 2003; Gudelsky & Yamamoto, 2003). Thus, as Gudelsky and Yamamoto (2008) noted, the consensus was largely that MDMA exposure produced a number of 5-HT neurotoxic effects, stressing bioenergetic processes and stimulating oxidative stress (Gudelsky & Yamamoto, 2003; Darvesh & Gudelsky, 2005; Quinton & Yamamoto, 2006). Although dopaminergic effects have also been reported (Biezonski et al., 2013), such effects appear to be a consequence of MDMA serotonergic activation of 5-HT2A/C or 5-HT2B/C receptors (Gudelsky & Yamamoto, 2008). A desire for greater novelty and higher levels of sensation-seeking are often associated with adolescence (Adriani & Laviola, 2004). In one recent report (Rodríguez-Arias, Vaccaro, Arenas, Aguilar, & Miñarro, 2015), adolescent mice exposed to MDMA in adolescence produced an expected increase in sensitivity to the reinforcing effects of MDMA when tested in adulthood. However, adolescent exposure produced differing monoaminergic and behavioral effects in mice classified as either high or low sensation-seeking animals. Returning the issue of adolescent exposure of MDMA and Foxy, while there is considerable information concerned with the effects of psychostimulant exposure in adult animals, the same cannot be said for studies using adolescent animals (Teixeira-Gomes et al., 2015). This is especially true when drugs such as Foxy are considered. As such, the current literature still contains a number of gaps about the long-term consequences to the organism, brain function, and subsequent behaviors following chronic exposure to these compounds during adolescent development. In addition, because of a number of regulatory and ethical considerations, well-designed investigations involving human adolescents are rare. Where found, they are often compromised by sampling issues and confounding variables not limited to but often including polydrug use (Teixeira-Gomes et al., 2015) and the purity of the drugs used. The results reported here provide evidence and elsewhere (Compton et al., 2006; Compton, Dietrich et al., 2011; Compton, Selinger et al., 2011; Skelton et al., 2009) that there are indeed consequences, albeit somewhat different in nature, associated with the use of MDMA or Foxy including long-term alterations in aspects of learning and memory performance. Higher levels of novelty and sensation seeking are often associated with adolescence (Adriani & Laviola, 2004). Therefore, it is prudent that researchers continue to examine these drugs at different developmental time points, taking into account a number of possible sexually dimorphic effects associated with their use. Acknowledgments This research was sponsored in part by a grant from the Palm Beach Atlantic University Faculty Research Committee to Friederike S. Luetzenberg and David M. Compton. The authors would like to thank C. Garcia, P. Esquivel, and J. Luetzenberg for their assistance with the collection of data and B. Gonzalez and N. Hernandez for their assistance with the HPLC assessment of 5-HT.