The hallucinogenic "club drugs" 3,4-methylenedioxymethamphetamine (MDMA) and 5-methoxy-N, N-diisopropyltryptamine hydrochloride (Foxy), albeit to different degrees, remain popular as recreational drugs. Much is known about MDMA including observations that in comparison to female rodents, males appear to be more sensitive to the toxic effects associated with abuse. Less is known about the possible sex differences associated with the abuse of Foxy, especially when the consequences of its use are examined during the neuropsychological development period of adolescence. In the present study, adolescent male and female rats were given multiple doses of MDMA, Foxy, or saline across a series of 48-hr "weekends" under conditions approximating that of a rave. Behavioral testing occurred in adulthood when the rats were 131 days old and had been drug free for 66 days. Assessments included general activity, passive avoidance, and a series of Morris water maze spatial and nonspatial memory tasks. Depending on task demands, the performance of MDMA-treated rats was inferior to that of the Foxy-treated rats and saline controls. The performance of both drug groups was comparable and inferior to that of control rats on a spatial learning set task. Generally, greater impairments were observed in MDMA-treated rats than the Foxytreated rats. Sex differences were observed on some but not all spatial tasks with MDMA-treated males performing significantly worse than similarly treated female rats. The results are in the context of putative sex-mediated differences in sensitivity to MDMA or Foxy and the disruptive effects of these drugs to central serotonergic systems that may contribute to cognitive deficits.
Using animal models, there is considerable evidence suggestive of a variety of learning and memory impairments after MDMA exposure (Able, Gudelsky, Vorhees, & Williams, 2006; Arias-Cavieres et al., 2010; Compton, Selinger, Westman, & Otero, 2011; Sprague, Preston, Leifheit, & Woodside, 2003; Vorhees, Reed, Skelton, & Williams, 2004; Vorhees, Schaefer, & Williams, 2007; Vorhees et al., 2009). Similarly, MDMA appears to affect adversely prospective or working memory, as well as executive functioning in humans (Fox, Toplis, Turner, & Parrott, 2001; Heffernan, Jarvis, Rodgers, Scholey, & Ling, 2001; Heffernan, Ling, & Scholey, 2001; McCann et al., 2008; Wareing, Fisk, & Murphy, 2000). Unfortunately, declines in measures of executive function and decision-making ability persist even after abstinence from MDMA use (Zakzanis & Campbell, 2006).
Lacking the safeguards associated with legal pharmaceutical manufacturing, consumer MDMA varies widely in potency and the presence of highly undesirable impurities (Gimeno, Besacier, Bottex, Dujourdy, & Chaudron-Thozet, 2005). Further, MDMA as well as its associated analogs share biochemical similarities to that of compounds identified as stimulants as well as neurotoxins including methamphetamine, amphetamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and paraquat (Karuppagounder et al., 2014).
As a class of drugs, indolealkylamines (IAA) are chemical derivatives of 5-hydroxytryptamine (serotonin, Jiang, Shen, & Yu, 2014), a major neurotransmitter implicated in a variety of processes ranging from attention and cognition to dreaming and pain regulation (Carlson, 2013). While some IAAs are used for medical or religious purposes (Carod-Artal, 2015), they are also considered a major class of substances with abuse potential and classified under the Controlled Substances Act. Among these is 5-methoxy-N,N-diisopropyltryptamine (5- MeO-DIPT or Foxy; Skelton et al., 2009) placed under Schedule I of the Controlled Substances Act in 2004 (DEA, 2004). The actions of the US Drug Enforcement Administration were in response to the recognition that Foxy, with properties similar to other tryptaminergic hallucinogens (Shulgrin & Carter, 1980), led recreational users of MDMA and other compounds to experiment with this drug.
In rodent models, Foxy-associated deficits have been reported (Compton et al., 2006; Compton, Dietrich, Selinger, & Testa, 2011; Compton, Selinger et al., 2011; Skelton et al., 2009). These reports lend credence to the observations that the response deficits primarily implicated compromised attentional processes and response perseveration. Considered an indicator of impaired cognition and associated with a disruption in the ability to change appropriately behavior(s) as task demands change, response perseveration is considered distinct from motor or motivational deficits. As such, response perseveration involves a maladaptive change in executive function (Pettenuzzo et al., 2003).
Adolescent drug use is associated with higher levels of dependence in adulthood (Gilvarry & McArdle, 2007). When exposed to substances with additive properties, younger adults are more likely than older adults to develop addictions (Karuppagounder et al., 2014). Further, when compared to adult mice, adolescent mice show a greater sensitivity to the reinforcing effects associated with MDMA (Procopio-Souza et al., 2014).
In rats, the developmental phase of adolescence includes the period from the 21st postnatal day (PND) until PND 60, with mid adolescence and late adolescence spanning PNDs 34 to 46 and 46 to 59, respectively (Tirelli, Laviola, & Adriani, 2000). The two periods are considered analogous to periadolescence and late adolescence/early adulthood (Tirelli et al., 2003). Using this framework as a model of rodent development, comparative evaluation and extrapolation to humans is possible (Spear, 2000). In the present study, the use of adolescent rats allowed us to examine further the developmental consequences associated with two drugs of abuse at various points in cognitive and biological development.
Considerable evidence exists suggesting that MDMA produces degeneration of 5-hydroxytryptamine (5-HT) nerve endings in multiple areas of the brain in both experimental animals and humans (see Green, Meehan, Elliott, O'Shea, & Colado, 2003). While the research is more limited, a similar possibility is associated with the use of Foxy (Compton Dietrich et al., 2011; Compton Selinger et al., 2011). The available research examining the effects MDMA monoaminergic neurotoxicity in adolescent rodents is both limited and contradictory. For example, adolescent animals appear to be less sensitive to the neurotoxic effects of MDMA than their adult counterparts (Kelly, Ritchie, Quate, McBean, & Olverman, 2002; Meyer, Grande, Johnson, & Ali, 2004; Piper, 2007) with young (PND 39) adolescent rats spared of any serotonergic neurotoxicity (Fone et al., 2002). In the Fone et al. study, MDMA did impact behavior in adulthood. Conversely, recurrent exposure of 10 mg/kg of MDMA during late adolescence adversely affected the behavior of abstinent rats with a concomitant decrease in 5-HT levels in multiple areas of the brain (Cox et al., 2014). This is consistent with other reports, some of which also examined the effects of Foxy (e.g., Compton, Selinger et al., 2011; Skelton, Williams, & Vorhees, 2006; Skelton et al., 2009). Where both were examined, developmental exposure of Foxy and MDMA produced long-term changes in learning and memory performance. Nonetheless, MDMA and Foxy appear to produce dissociable effects (Skelton et al., 2009). Returning to MDMA neurotoxicity, recently reported that many MDMA mediated effects associated with binge exposure comprise not only effects to 5-HT axon terminals but also to other measured hippocampal cell markers such as alterations to GABAergic activity and neurofilament proteins (Garcia-Cabrerizo & Garcia-Fuster, 2015).
In addition to the consideration of exposure during adolescence, there is evidence suggestive of sex differences associated with some of the toxic effects attributed to MDMA (Allott & Redman, 2007). Among humans, women report greater levels of dizziness, sadness and sedation, and symptoms of psychosis (de Sola et al., 2008; Kolbrich et al., 2008; Pardo-Lozano, et al., 2012; Parrott et al., 2011). Although such differences could reflect a male advantage in drug disposition (Pardo-Lozano, et al., 2012) such as faster 5-HT synthesis and larger reserves of 5-HT (Sakai et al., 2006), male and female users of MDMA have different patterns of consumption and it is likely that a number of factor may influence any putative sex difference (Allott & Redman, 2007).
If present, such differences have implications. Evidence of a sex difference in lifetime MDMA use among US teens has been reported with higher levels of use observed among female adolescents, even after controlling for factors such as population density, race, and income (Wu et al., 2010). While data from the Monitoring the Future study suggests a decline in use among high school students (Johnston, O'Malley, Miech, Bachman, & Schulenberg, 2014), an estimated 12.80% of adults between the age of 18 and 25 have used MDMA with a significant increase between 2012 and 2013 reported for those 26 years of age or older (http://www.drugabuse.gov/national-survey-drug-use-health).
Additional support is found in rodent models. For example, male mice were far more susceptible to the lethal effects of a large dose of MDMA (80 mg/kg) than female mice (Cadet, Ladenheim, Baum, Carlson, & Epstein, 1994). In rats, Koenig and colleagues found markedly different survival rates between male and female rats, with a clear survival advantage associated with the latter sex (Koenig et al., 2005). Similarly, MDMA LD50 was found to be 2.4-times lower in male rats than in female rats, with a concomitant increase in hyperthermia detected in male rats (Fonsart et al., 2008). MDMA-mediated hyperthermia, especially under the conditions of high ambient temperatures found at raves is well known to have lethal consequences (Dafters, 1994, 1995; Gordon, Watkinson, O'Callaghan, & Miller, 1991; Parrott, 2013). Conversely, Allott and Redman (2006) have noted that reports of low sodium levels in the blood resulting from the excessive consumption of water (hyponatremia; Hartung, Schofield, Short, Parr, & Henry, 2002) as a strategy to combat hyperthermia is more common among female users (see Budisavlijevic, Stewart, Sahn, & Plath, 2003; Rosenson, Smollin, Sporer, Blanc, & Olson, 2007).
When compared to MDMA, less reliable information is available about the specific effects and consequences associated with the use of Foxy. However, previous reports about the consequences associated with its use (Ikeda, Sekiguchi, Fujita, Yamadera, & Kog, 2005; Wilson, McGeorge, Smolinske, & Meatherall, 2005) as well as toxicological investigations (Meatherall & Sharma, 2003; Sitaram, Lockett, & Blackman, 1987; Smolinske, Rastogi, & Schenkel, 2005) animal models to ascertain putative central nervous system effects (Compton, Dietrich et al., 2011; Compton et al., 2006; Compton, Selinger et al., 2011; Jing et al., 2015; Nagai, Nonaka, & Kamimura, 2007; Nakagawa & Kaneko, 2008; Skelton et al., 2009), and sexual dimorphic effects, if any, the conditions of exposure warrant further consideration of the effects of this drug.
The goal of the present study investigation was to examine further the effects of MDMA or Foxy on cognitive processes using a model more representative of the recreational use of MDMA or Foxy during adolescence. Thus, the protocol used in the present study included a series of "weekend" exposures under auditory and visual conditions (e.g., dance music, flashing lights) and ambient temperatures normally associated with adolescent raves. In addition, the question of sex differences was explored through inclusion of both male and female rats of comparable age as part of the experiment. Although there is evidence of persistent deficits following adolescent exposure of these two compounds (Compton, Selinger et al., 2011; Skelton et al, 2009), including one report of MDMA associated deficits in a rodent rave paradigm (McAleer, Schallert, & Duvauchelle, 2013), no reports are available specifically examining the consequences of MDMA or Foxy under the conditions more typical of adolescent human use at rave events.