Modeling the effects of low toxin levels in food on feeding: dose-dependent reduction of fluid intake by low levels of lithium chloride

Patterns of ingestion of rats during chronic oral administration of lithium chloride

Chronic lithium administration to rodents is used to explore the potential neural mechanisms of mood stabilization, as well as to model the side effects of chronic lithium on multiple organ systems. Oral administration of lithium in the maintenance diet or drinking water is convenient, but lithium can acutely affect intake and it can mediate acquisition of conditioned taste aversions (CTA). We compared ad libitum food and fluid intake by male rats with LiCl or NaCl solutions as their sole source of fluid across 20 days, with a commonly used dosage of LiCl (24 mM: 1 g / L LiCl). To quantify the pattern of intake, rats were housed in cages equipped with lickometers to detect licks and infrared photobeams to detect food access with 6-s resolution. To determine if rats formed a CTA to LiCl, they were subsequently tested with access to NaCl. Rats showed an immediate avoidance of the LiCl solution, as seen on the first day of access by an increased latency to initiate drinking and a decreased size of drinking bouts. Rats showed a differential response to LiCl vs. NaCl after as few as 5 licks. Chronic consumption of LiCl solution led to significantly decreased food and fluid intake compared to baseline, with concomitant weight loss. The decreased intake was realized by marked changes in the pattern of drinking and feeding bouts: a decrease in per-lick volume and a decrease in licks per drinking bout, and an increase in feeding bout duration resulting in an overall decrease in eating rate. Conversely, chronic NaCl access led to an increase in drinking bout number and licks/bout. The avoidance of LiCl was likely a combination of toxic effects of ingested LiCl and rapid acquisition of a learned aversion to the taste of LiCl, as shown by an extinguishable generalized aversion to NaCl solution during subsequent NaCl test days. The marked effect of chronic oral LiCl on ingestion may impact the oral dosing of lithium as well as the rat's metabolic status.

Pavlovian discrimination in rats using voluntary exposure to a lithium chloride procedure

In a conditioned taste aversion (CTA) procedure, the consumption of a flavor is followed by the administration of a toxin (e.g. lithium chloride, LiCl), resulting in the future avoidance of the flavor. CTA studies typically make use of forced-exposure paradigms where a volume of the toxin dependent upon the weight of the animal is injected. The use of forced paradigms can be problematic when extended training is required, such as in stimulus discrimination training involving similar flavors, since the animals can be exposed to a high amount of the toxin. In the present study we confirmed the viability of an alternative voluntary-exposure paradigm that more closely mimics natural conditions and is more considerate of the welfare of the animals as a useful tool for investigating discrimination training. In three experiments, rats received free access to either a flavor (sucrose in Experiments 1a and 1b, and saccharin in Experiment 2) or a compound of the flavor mixed with LiCl. The presence of LiCl in the compound induced post-consumption illness. Rats acquired an aversion to the flavor + LiCl compound, thus reducing both their consumption of, and exposure to, LiCl, and gradually increased their consumption of the flavor alone. The present paradigm is more similar to natural conditions than the forced-exposure paradigm as it allows the animals to experience a direct relationship between the amount of the flavor consumed and the magnitude of the illness induced by the toxin.