Expression of stable and reliable preference and aversion phenotypes following place conditioning with psychostimulants

The pharmacology and neurotoxicology of synthetic cathinones

The synthetic cathinones are man-made compounds derived from the naturally occurring drug cathinone, which is found in the khat plant. The drugs in this pharmacological class that will be the focus of this chapter include mephedrone, MDPV, methcathinone and methylone. These drugs are colloquially known as "bath salts". This misnomer suggests that these drugs are used for health improvement or that they have legitimate medical uses. The synthetic cathinones are dangerous drugs with powerful pharmacological effects that include high abuse potential, hyperthermia and hyperlocomotion. These drugs also share many of the pharmacological effects of the amphetamine class of drugs including methamphetamine, amphetamine and MDMA and therefore have high potential to cause damage to the central nervous system. The synthetic cathinones are frequently taken in combination with other psychoactive drugs such as alcohol, marijuana and the amphetamine-like stimulants, creating a situation where heightened pharmacological and neurotoxicological effects are likely to occur. Despite the structural features shared by the synthetic cathinones and amphetamine-like stimulants, including their actions at monoamine transporters and receptors, the effects of the synthetic cathinones do not always match those of the amphetamines. In particular, the synthetic cathinones are far less neurotoxic than their amphetamine counterparts, they produce a weaker hyperthermia, and they cause less glial activation. This chapter will briefly review the pharmacology and neurotoxicology of selected synthetic cathinones with the aim of delineating key areas of agreement and disagreement in the literature particularly as it relates to neurotoxicological outcomes.

Effects of Serial Polydrug Use on the Rewarding and Aversive Effects of the Novel Synthetic Cathinone Eutylone

BACKGROUND

As individual synthetic cathinones become scheduled and regulated by the Drug Enforcement Administration (DEA), new ones regularly are produced and distributed. One such compound is eutylone, a novel third-generation synthetic cathinone whose affective properties (and abuse potential) are largely unknown. The following experiments begin to characterize these effects and how they may be impacted by drug history (a factor affecting reward/aversion for other drugs of abuse).

METHODS

Eutylone was assessed for its ability to induce conditioned taste avoidance (CTA; aversive effect) and conditioned place preference (CPP; rewarding effect) and their relationship (Experiment 1). Following this, the effects of exposure to cocaine or 3,4-methylenedioxymethamphetamine [MDMA] on eutylone's affective properties were investigated (Experiment 2).

RESULTS

Eutylone produced dose-dependent CTA and CPP (Experiment 1), and these endpoints were unrelated. Pre-exposure to cocaine and MDMA differentially impacted taste avoidance induced by eutylone (MDMA > cocaine) and did not impact eutylone-induced place preference.

CONCLUSIONS

These data indicate that eutylone, like other synthetic cathinones, has co-occurring, independent rewarding and aversive effects that may contribute to its abuse potential and that these effects are differentially impacted by drug history. Although these studies begin the characterization of eutylone, future studies should examine the impact of other factors on eutylone's affective properties and its eventual reinforcing effects (i.e., intravenous self-administration [IVSA]) to predict its use and abuse liability.

Pups and prolactin are rewarding to virgin female and pregnant mice

Maternal interactions with offspring are highly rewarding, which reinforces expression of essential caregiving behaviours that promote offspring survival. In rats, the rewarding effect of pups depends on reproductive state, with lactating females specifically developing strong preferences for pup-associated contexts. Whether this also occurs in mice is unknown, hence we aimed to characterise pup-related preference across reproductive states in female mice. In a conditioned place preference (CPP) test, pups were a rewarding stimulus to female mice prior to lactation, with virgin and pregnant females developing a preference for a pup-associated context. We have previously shown that lactogenic hormones, acting through the prolactin receptor (Prlr), play an important role in maternal motivation. Here, we aimed to investigate whether Prlr action is important for pup-related reward behaviour in mice. We showed that prolactin itself had a reinforcing effect in a CPP test, and that exposure to pups increased blood prolactin levels in virgin female mice. Prlr expression in CamKIIα-expressing neurons and GABAergic neurons has previously been shown to be important for different aspects of parental behaviour. However, we found that conditional Prlr deletion from either of these neuronal populations did not disrupt the development of a preference for pup-associated contexts in pregnant female mice, indicating that lactogenic action on these populations is not necessary for the rewarding effect of pups. Together, these data show that while lactogenic hormones likely contribute to a rewarding effect of pups, their action on two key neuronal populations is not necessary for this effect in female mice.