ABSTRACT
Nicotine enhances Pavlovian conditioned responses to reward-associated cues. We investigated through which nicotinic acetylcholine receptor (nAChR) subtypes nicotine acts to produce this behavioral effect to an alcohol-associated cue. Male Long-Evans rats with freely available food and water were first accustomed to drinking 15% ethanol in their home cages using an intermittent access, two-bottle choice procedure. Then the rats were given 15 Pavlovian conditioning sessions in which a 15-s audiovisual conditioned stimulus (CS) predicted the delivery of 0.2 ml of ethanol, the unconditioned stimulus (US). Each session contained 12 CS-US trials. A control group received explicitly unpaired presentations of the CS and US. We measured Pavlovian conditioned approach to the site of US delivery during presentations of the CS, accounting for pre-CS baseline activity. Before each conditioning session, rats were injected subcutaneously with nicotine (0.4 mg/kg) or saline (1 ml/kg). During nAChR antagonist test sessions, rats were first injected systemically with the ß2*-selective nAChR antagonist dihydro-beta-erythroidine (DHßE; 3 mg/kg) or the α7-selective nAChR antagonist methyllycaconitine (MLA; 6 mg/kg), followed by their assigned nicotine or saline injection before assessing their conditioned response to the alcohol-associated cue. Consistent with previous reports, nicotine enhanced the Pavlovian conditioned response to the alcohol-paired cue. DHßE attenuated this enhancement, whereas MLA did not. These results suggest that nicotine acts via ß2*, but not α7, nAChRs to amplify Pavlovian conditioned responding to an alcohol cue. These findings contribute to a growing literature that identifies nAChRs as potential targets for pharmacological treatment of co-morbid alcohol and tobacco use disorders.
ABSTRACT
Across seven experiments, the present article examined the influence of the number of part-set cues on order retention, as assessed by both reconstruction of order and serial recall tests. Historically, part-set cueing facilitation occurs when half of the items are provided as valid part-set cues on tests of order memory. Using a variety of list lengths (10 or 16), numbers of cues (0-14), and types of cues (full or partial), the present experiments showed disparate effects of the number of part-set cues on reconstruction and serial recall tasks. On reconstruction tests, a minimum number of full cues was required before part-set cueing facilitation was produced and the magnitude of facilitation increased as the number of cues increased. Generally, partial cues did not influence order retention until almost the entire list was provided as partial cues. On serial recall tests, part-set cueing facilitation was only evident with a few full cues. In contrast, part-set cueing impairment was the norm when many partial cues were provided. These results were largely consistent with predictions of the retrieval strategy disruption hypothesis, as well as with an anchoring account of part-set cueing for order.
