Comparing immune activation (lipopolysaccharide) and toxin (lithium chloride)-induced gustatory conditioning: lipopolysaccharide produces conditioned taste avoidance but not aversion

Abstract

Feeding and drinking typically involve both appetitive and consummatory behaviors. Appetitive behaviors include those behaviors produced by an animal prior to the actual consumption, such as approach movements, whereas consummatory behaviors (such as licking and chewing) are involved in the actual consumption of food. The present research compared the gustatory conditioning effects of bacterial lipopolysaccharide (LPS) and lithium chloride (LiCl) in two different paradigms, conditioned taste avoidance and conditioned taste aversion which differentially affect the appetitive and consummatory components of feeding. Male rats were implanted with intraoral cannulae and habituated to a water deprivation schedule and afterwards received two conditioning days (Days 1 and 4). Each conditioning day consisted of 1 h access to a novel sucrose solution (0.3 M) immediately followed by a systemic injection of LPS (200 μg/kg), LiCl (0.15 M, 3 meq) or NaCl vehicle. Conditioned taste aversion was assessed using the taste reactivity test on Day 7, where orofacial and somatic responses were videotaped and analyzed during 3 brief (1 min) exposures to the sucrose solution. Conditioned taste avoidance was assessed on Days 8 and 9 using a two-bottle preference test (sucrose versus water). Animals conditioned with LiCl displayed typical aversive-like responses in the taste reactivity paradigm evidenced by significant reductions in positive ingestive responses ( P<0.05) and an increase in active aversive responses ( P<0.05) relative to controls. Furthermore, LiCl treatment resulted in conditioned avoidance of sucrose in the two-bottle preference test characterized by a decreased sucrose preference ( P<0.05). Conditioning with LPS produced a reduced sucrose preference ( P<0.05) relative to controls, comparable to the avoidance seen in LiCl-treated rats. In contrast, conditioning with LPS resulted in similar positive ingestive responses to intraorally infused sucrose as seen in controls. The present results demonstrate that LPS treatment produces conditioned avoidance but not aversion and suggest that LPS can selectively condition the appetitive aspects of feeding whereas the consummatory behaviors remain unaffected.