Abstract
In an appetitively motivated procedure, we have previously reported that systemic treatment with the dopamine (DA) D1 receptor agonist SKF81297 (0.4 and 0.8mg/kg) depressed acquisition at a 2s inter-stimulus-interval (ISI), suitable to detect trace conditioning impairment. However since DA is involved in reinforcement processes, the generality of effects across appetitively- and aversively-motivated trace conditioning procedures cannot be assumed. The present study tested the effects of SKF81297 (0.4 and 0.8mg/kg) in an established conditioned emotional response (CER) procedure. Trace-dependent conditioning was clearly shown in two experiments: while conditioning was relatively strong at a 3-s ISI, it was attenuated at a 30-s ISI. This was shown after two (Experiment 1) or four (Experiment 2) conditioning trials conducted in – as far as possible – the same CER procedure. Contrary to prediction, in neither experiment was there any indication that trace conditioning was attenuated by treatment with 0.4 or 0.8mg/kg SKF81297. In the same rats, locomotor activity was significantly enhanced at the 0.8mg/kg dose of SKF81297. These results suggest that procedural details of the trace conditioning variant in use are an important determinant of the profile of dopaminergic modulation.
Highlights
Pavlovian trace conditioning procedures require the acquisition of an association between a conditioned stimulus (CS, e.g. noise) and an unconditioned stimulus (US, e.g. food or foot shock) despite the interposition of an interval of time between these events (Pavlov, 1927)
In an appetitively motivated procedure, we have previously reported that systemic treatment with the dopamine (DA) D1 receptor agonist SKF81297 (0.4 and 0.8 mg/kg) depressed acquisition at a 2-s inter-stimulus-interval (ISI), suitable to detect trace conditioning impairment (Pezze, Marshall, & Cassaday, 2015)
Trace-dependent conditioning was clearly shown in the present experiments in that while conditioning was relatively strong at the 3-s ISI, it was attenuated at the 30-s ISI
Summary
Pavlovian trace conditioning procedures require the acquisition of an association between a conditioned stimulus (CS, e.g. noise) and an unconditioned stimulus (US, e.g. food or foot shock) despite the interposition of an interval of time between these events (Pavlov, 1927). The ability to condition to the trace of the CS when it is no longer present allows animals to form associations when events, which may be causally-related, are separated in time. Trace conditioning procedures test working memory defined as the capacity to maintain ‘on line’ transitory information (Goldman-Rakic, 1996). Such working memory is likely essential for associative processes in general, and in particular when a time interval must be bridged (Gilmartin, Balderston, & Helmstetter, 2014). Trace conditioning is widely used to investigate the neural substrates of this important aspect of working memory (Cassaday, Nelson, & Pezze, 2014). Pezze et al / Learning and Motivation 55 (2016) 53–64
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