Running head: EFFECTS OF ALCOHOL ON OBJECT RECOGNITION

Two experiments investigated effects of alcohol on the ability to recognize objects. Mice explored 2 identical objects placed in an enclosed arena. Two data collection methods, open field and automated procedure, were tested to record object exploration. In experiment 1, a novel object replaced one of the objects after 1 or 24 hours, and mice spent more time exploring the novel object at both delays. In experiment 2, we administered different doses of alcohol to mice prior to the initial exploration of the objects. Object recognition testing was then conducted 24 hours later. Results indicated that the open field method provided a more reliable measure of object exploration. Mice injected with alcohol spent roughly equal amounts of time exploring both objects, indicating that they were not able to recognize the familiar object. Together, these results suggest that alcohol impairs memory acquisition. This may be because of alcohol’s established effects on the hippocampus, a structure also known to have a role in object recognition memory. Alcohol on Object Recognition 3 Impairing Effects of Alcohol on Object Recognition Alcohol is generally known to impair memory in humans and animals. According to Browning, Hoffer, & Dunwiddie (1992), memory has two phases: acquisition and retrieval. Those with damage to certain brain structures are unable to encode new memories, and thus cannot retrieve them. Likewise, alcohol has been shown to have impairing effects on the acquisition phase. Memory is also associated with long-term potentiation (LTP), which is thought to be the method by which memories are formed and strengthened through neural circuits. Research on rats shows that acute alcohol doses prevent LTP from occurring (Browning et al., 1992; Givens & McMahon, 1995). Alcohol can interfere with LTP through various mechanisms. One way is to inhibit the release of neurotransmitters necessary to transmit information through the synaptic cleft. Another way is to inhibit the neurotransmitter receptors on the postsynaptic cell. Alcohol can also strengthen the receptor for the neurotransmitter GABA, which inhibits communication between neurons (Browning et al., 1992). To learn more about the relationship between alcohol and memory, a number of different memory tests have been used in animals. One of the more recently developed tests is the object recognition test. This test exploits the tendency of animals to prefer exploring novel objects in an environment when a familiar object is also present (Ennaceur & Delacour, 1988), and thus is not confounded by external reinforcement. Recent research indicates that alcohol intake impairs the performance of rats on the object recognition test (Ciccocioppo, Antonelli, Biondini, Perfumi, Pompei, & Massi, 2002; García-Moreno, Conejo, Capilla, García-Sánchez, Senderek, & Arias, 2002). There has not been much research on the effects of alcohol on object recognition in mice, but Ryabinin, Miller, and Durrant (2002) showed that mice injected with a high dose of alcohol Alcohol on Object Recognition 4 (2.4 g/kg) did not recognize a familiar object in an object recognition task performed at a 24hour delay. In addition, mice injected with scopolamine, a drug that blocks acetylcholine receptors, showed decreased performance on an object recognition task performed at a 3-hour delay (Dodart, Mathis, & Ungerer, 1997). Many brain regions are likely to be involved in object recognition, but most studies have focused on the hippocampus. Lesion studies in mice and rats have revealed conflicting results with respect to the importance of the hippocampus to object recognition. For example, an intact hippocampus was necessary for mice to recognize objects after a 24-hour delay, but not after a 5minute delay (Hammond, Tull, & Stackman, 2004). The hippocampus and/or amygdala were necessary for rats to recognize objects at a 10-minute delay, but not at less than a 2-minute delay (Mumby, Wood, & Pinel, 1992). In addition, rats with lesions of the hippocampus showed impaired performance on a memory recognition test at delays of longer than 10-minutes, but not at less than a 1-minute delay (Clark, Zola, & Squire, 2000). However, Stupien, Florian, and Roullet (2003) found that the CA3-region of the hippocampus, a region which receives sensory input from the external and internal environment and retrieves that information for working memory processes, was necessary for mice to respond to spatial changes but not to recognize a familiar object after a 24-hour delay. Observation of the animal’s exploration of objects requires a large time commitment from researchers, so experiment 1 will attempt to establish an automated procedure as a reliable data collection method. Previous research has used an open field to record animal behavior. This requires the researcher to use a video camera and/or stop watch, and it is very timeintensive to code and interpret the data. The automated procedure, which records behavior through breaks in infrared beams that are stored and analyzed through computer software, will eliminate the need for direct observation that researchers use in the open field. Alcohol on Object Recognition 5 The literature contains mixed results concerning the time delay between the initial exposure to the object and the subsequent test for recognition. Experiment 1 will also investigate the optimal delay to use between the initial object exploration and object recognition testing phases. Previous studies on object recognition have found that alcohol or similar drugs impair object recognition in an object recognition task at delays of 1 and 24 hours (Clark et al., 2000; Dodart et al., 1997; Hammond et al., 2004; Frick & Gresack, 2003; García-Moreno et al., 2002; Ryabinin et al., 2002; Sik, van Nieuwehuyzen, Prickaerts, & Blokland, 2003). We will also use delays of 1 and 24 hours in experiment 1, and will use the delay that yields the most significant results in the second experiment. Once the optimal time delay and data collection method is established, experiment 2 will replicate the object recognition study by Ryabinin et al. (2002). We hope to reproduce the results that mice injected with a high dose of alcohol (2.4 g/kg) do not recognize a familiar object at a 24-hour delay. As part of our hypothesis, we anticipate that mice injected with a lower dose of alcohol (1.6 g/kg) will show less impaired performance on the object recognition task than mice injected with the highest dose. In addition, we anticipate that vehicle-treated mice will recognize the familiar object after the time delay and display normal novelty-seeking behaviors.