Detecting drug effects on short-term memory function using a combined delayed matching and non-matching to position task

Operant delayed non-matching-to-position (DNMTP) and delayed matching-to-po sition (DMTP) have become standard techniques to investigate drug effects o n short-term memory function in rats. However, these two tasks are normally conducted in isolation. Using two standard drugs, the 5HT(1A) agonist 8-hy droxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), and the muscarinic antagoni st scopolamine, this study looked at a two-choice operant task that essenti ally involved a mixed DNMTP/DMTP paradigm. Thus, DNMTP trials were interspe rsed with DMTP trials in a random sequence for the duration of a session. 8 -OH-DPAT (0.03 mg/kg) slightly but significantly improved response accuracy in a delay-dependent fashion during DMTP but not DNMTP trials. The highest dose of 8-OH-DPAT (0.1 mg/kg) impaired accuracy during DNMTP trials indepe ndent of delay and had no significant effect during DMTP trials. Scopolamin e (0.1 mg/kg) produced delay-dependent deficits in accuracy during DMTP tri als but delay-independent impairments during DNMTP trials. Because both 8-O H-DPAT and scopolamine produced delay-dependent: effects with DMTP trials t ypes and either had no effect (8-OH-DPAT) or produced delay-independent imp airments (scopolamine) during DNMTP trials types, it is suggested that DMTP trials had a greater dependence on short-term working memory function than DNMTP trials that probably relied more on positional (mediating) strategie s for solving the task. Therefore, we believe that this mixed DNMTP/DMTP ta sk offers greater potential for more reliable and discerning interpretation of data regarding short-term memory function in rodents than either of the paradigms performed in isolation. (C) 2000 Elsevier Science Inc.