Rapid toxin-induced gustatory conditioning in rats: separate and combined effects of systemic injection or intraoral infusion of lithium chloride

The present experiment examined the individual and combined effects of systemic injection and oral ingestion of lithium chloride (LiCl) on both within and across session shifts in palatability. Male rats fitted with intraoral cannulae received two conditioning days in which they were injected with either LiCl or sodium chloride (NaCl) and were then presented with brief intraoral infusions of a sucrose plus LiCl or NaCl solution. The individual taste reactivity responses during the intraoral infusions were videotaped and later analyzed for response frequency. Forty-eight hours after the second conditioning day the same sucrose plus salt solution was presented again in the absence of any injection. The present results demonstrate that systemic injections of LiCl result in profound within session and across session decreases in ingestive responding accompanied by increased active and passive aversive responses. Animals receiving LiCl by injection as well as ingestion demonstrated an exaggerated response. Rats which received LiCl only through intraoral infusions produced the same pattern of decreased ingestive responding to the sucrose plus salt flavored tastant on each test trial suggesting little or no across session conditioning effects. A two process model by which animals may regulate toxicosis is discussed. (C) 2004 Elsevier B.V. All rights reserved.