Assessing the Impact of Lipopolysaccharide on Learning and Memory in Rats

The immune system and the central nervous system (CNS) have a bi-direction relationship, modulating one another.4 Proinflammatory cytokines released from CNS immune cells have an impact on cognitive processes such as learning and memory.1 Liposaccharide (LPS), a cell wall component of Gram-negative bacteria, which is used to activate proinflammatory cytokine release has been found to impact learning and memory processes, such as in the anticipatory nausea paradigm (ANP).2 Anticipatory nausea and vomiting is that which may occur before a chemotherapy treatment session begins in a patient who has had chemotherapy before. It is caused by triggers like the sights, smells or sounds of the treatment room. Here, lithium chloride (LiCl, the unconditioned stimulus) becomes associated with a context, leading to disgust behaviours surfacing when exposed to the context alone (conditioned stimulus).6 Disgust behaviours, such as conditioned gaping seen in rats, are a strong index of anticipatory nausea which are not influenced by LPS induced locomotor deficits, hence allowing a more reliable study of learning and memory. Gaping involves the repeated opening and closing of the lower mandible in rapid succession, approximately 5-7 times per bout as seen in Figure 1.3 Conditioned gaping in rats uses the same orofacial musculature and is topographically similar to vomiting in shrews and humans. As such, conditioned gaping has been established as the most quantifiable index of nausea in rats. Existing literature focuses on acquisition of conditioned nausea. However, there is little research studying the effects of LPS on the consolidation processes of anticipatory nausea