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(+)-Methamphetamine (MA) is an illicit psychostimulant that can be synthesized from the nonprescription nasal decongestant, (+)-pseudoephedrine (PE). While MA is widely abused, PE appears to have little or no abuse liability in currently available formulations. However, PE produces centrally-mediated dopaminergic effects that are linked to the reinforcing effects of MA and other illicit psychostimulants and has been reported to function as a positive reinforcer in non-human primates. There has yet to be an assessment of the relative reinforcing effects of MA and PE. Therefore, the current study compared the reinforcing potency and strength of MA and PE, alone and combined, in four rhesus monkeys that were allowed to self-administer MA (0.003-0.3 mg/kg/inj), PE (0.1-3.0 mg/kg/inj), or combinations of the two under a progressive-ratio schedule of reinforcement. (+)-Methamphetamine functioned as a positive reinforcer in a dose-dependent manner. (+)-Pseudoephedrine also functioned as a positive reinforcer, but was less potent than MA. There were no differences in maximum injections between MA, PE, or any of the combinations of the two. Dose-addition analysis and the interaction index indicated that combinations of PE and MA were either additive or sub-additive in their reinforcing effects. These results suggest that, while MA is a more potent reinforcer than PE, the two drugs are comparable in terms of reinforcing strength. However, MA and PE do not appear to interact in a manner that enhances their relative reinforcing effects.

Although taste aversion learning has been reported to be a function of a variety of factors, one that has received considerable attention is the subject's sex, wherein males generally display stronger taste aversions than females. An exception to these findings is with cocaine for which females have been shown to display greater aversions than males. Although suggestive of a Sex x Drug interaction, cocaine was administered subcutaneously (s.c.) in this report while others administered drug intraperitoneally (i.p.). Thus, there may be a Sex x Route interaction. To address the contributions of sex and route in cocaine aversions, the present study examined aversions in male and female Sprague-Dawley rats administered a range of doses of cocaine either s.c. or i.p. At the two higher doses of cocaine tested (20 and 32 mg/kg), aversions were a function of route with animals injected s.c. with cocaine displaying greater aversions than those injected i.p. Although there was no main effect of sex at either dose there was an interaction between sex and route at the 20 mg/kg dose. Specifically, s.c.-injected males displayed stronger aversions than i.p.-injected males. There were no differences between the two routes for females. Further, males displayed stronger aversions than females when injected s.c. There was no sex difference when both groups were injected i.p. This interaction was no longer evident at the highest does of cocaine (32 mg/kg). These data indicate that sex differences in aversion learning with cocaine are a function of the route of cocaine administration (and are dose specific).

The present commentary describes the availability of a database on conditioned taste aversion learning, the avoidance of fluids and foods previously associated with the aversive effects of a variety of drugs. The database includes articles as early as 1955 by Garcia and his colleagues [Science 122 (1955) 127] (reporting such avoidance in rats) and papers just published given that the database is ongoing and constantly updated. At the printing of this announcement, approximately 2600 papers are included in the database. The database allows the user to search for articles by author(s), key word(s), date, title and journal. These terms can be used as single entries or multiple combinations. Finally, the full database can be viewed by performing the search function without entering any terms in the query window. The database can be accessed at http://www.CTALearning.com.