The effects of scopolamine and cues to forget on pigeons' memory for time

Development and characterization of an automated behavioral assessment platform for the Göttingen minipig

The Göttingen minipig is fast becoming the standard for assessing dermal chemical hazards because, like most swine, its skin is predictive of human skin response and because this strain's smaller size makes laboratory manipulations and husbandry easier. Unfortunately, standard behavioral tests and apparatus have not been developed for behavioral assessments of this swine strain. Indeed, computer-controlled automated behavioral testing procedures are much needed. The present research advanced this goal by producing a home-cage behavioral testing system that could accommodate minipigs of various sizes (ages). An aluminum frame housed three levers for recording operant responses, and LEDs above and below each lever served as discriminative stimuli. A commercially available food pellet dispenser was attached to a specialized pellet receptacle capable of measuring pellet retrieval. Two behavioral tests were selected and adapted from our commonly used non-human primate behavioral assessments: delayed match-to-sample (a memory test) and temporal response differentiation (a time-estimation test). Minipigs were capable of learning both tests and attaining stable performance. Next, scopolamine was used to validate the sensitivity of the behavioral tests for gauging behavioral perturbations in this swine strain. Scopolamine dose-effect functions were comparable to those observed in other species, including non-human primates, wherein 37.5 µg/kg of scopolamine (administered intramuscularly) reduced responding approximately 50%. Thus, we were successful in developing the apparatus and automated operant behavioral tests necessary to characterize drug safety in this swine strain. This capability will be valuable for characterizing chemical agent toxicity as well as the safety and efficacy of medical countermeasures.

The effects of scopolamine on memory for time in rats and pigeons

In Experiment 1, pigeons were trained to match short (2 s) and long (8 s) sample durations to red and green comparison stimuli and red and green samples to vertical and horizontal line comparisons. They received injections of scopolamine hydrobromide (0.02 mg/kg), scopolamine methylbromide (0.02 mg/kg), or saline, and the delay interval was manipulated (0, 1, 3, and 9 s). In Experiment 2, rats were trained to discriminate short (2 s) or long (12 s) durations of house-light illumination using a choice procedure. During the test phase of each trial, the left and right levers were presented with the cue light on above one of them (cued lever) while the other was off (uncued lever). For half of the rats, the correct response following the short sample was to press the cued lever, whereas following the long sample, it was to press the uncued lever. This was reversed for the remaining rats. The rats received injections of scopolamine hydrobromide (0.15 mg/kg), scopolamine methylbromide (0.15 mg/kg), or saline, and the delay interval was manipulated (0, 1, 3, and 9 s). In pigeons, scopolamine equivalently disrupted both temporal and nontemporal memory. Memory for time, in both rats and pigeons, was significantly poorer following scopolamine injections than following methylscopolamine or saline injections. No choose-short effect was observed in either rats or pigeons during saline test sessions. The data indicate that central cholinergic blockade in both pigeons and rats disrupts the accuracy of delayed temporal discriminations. However, scopolamine does not appear to accelerate the rate at which memory for temporal events is foreshortened.

The effects of scopolamine, diazepam, and lorazepam on working memory in pigeons: an analysis of reinforcement procedures and sample problem type

Two groups of pigeons were trained on a delayed-matching-to-sample (DMTS) task with both identity and symbolic problems, that had either a) specific outcomes correlated (differential group) or b) outcomes uncorrelated (nondifferential group), for each correct sample-choice sequence. After reaching a criterion of 90% correct at the 0 s delay, subjects were tested under saline, methylscopolamine (0.03 mg/kg), scopolamine (0.007, 0.015, 0.03 mg/kg), diazepam (0.0, 1.0, 1.75, 2.5 mg/kg), and lorazepam (0.0, 0.5, 0.75, 1.0 mg/kg) at delays of 0 to 8 s. Scopolamine, diazepam, and lorazepam at all doses impaired performance in the nondifferential group; however, in the differential group, the medium and high doses of both scopolamine and lorazepam, and only the high dose of diazepam impaired performance. The differential outcomes procedure, relative to the nondifferential procedure, enhanced retention in the non-drug state and under these amnestic drugs. Impairments observed in the differential group were a result of decreased performance only on samples correlated with a secondary reinforcer (flashing hopper light); there was no decreased performance on samples correlated with a primary reinforcer (grain). Neither group showed any differences in performance as a function of identity versus symbolic problems in a nondrug or drug state.