Chronic voluntary nicotine drinking enhances nicotine palatability in rats.

Abstract

The response of rats to nicotine solutions was examined with the brief-exposure, taste reactivity test and a two-bottle, 24-hr preference test. In Experiment 1, naive nondeprived rats were administered intraoral infusions (0.8 ml infused during 1 min) of distilled water and 1 microgram/ml, 5 micrograms/ml, 10 micrograms/ml, 25 micrograms/ml, 50 micrograms/ml, and 100 micrograms/ml nicotine. The oral motor, taste reactivity (TR) responses of the rats were recorded during the infusion. Nicotine solutions up to a concentration of 50 micrograms/ml elicited a number of ingestive TR responses similar to that by water. Ingestive responses significantly decreased and aversive TR responses significantly increased in response to 100 micrograms/ml nicotine. On the basis of these results, two-bottle preferences for water versus 1 microgram/ml, 5 micrograms/ml, and 0 microgram/ml (water control group) nicotine were measured in three groups of naive rats. Rats initially showed an equal preference for 0 microgram/ml and 1 microgram/ml nicotine. After 16 days of exposure, however, rats developed a significant preference for 1 microgram/ml nicotine. The preference ratio for 5 micrograms/ml nicotine significantly increased during the experiment, but the preference ratio remained significantly less than that for 1 microgram/ml and 0 microgram/ml nicotine solutions. Last, TR responses elicited by intraoral infusions of 1 microgram/ml and 5 micrograms/ml nicotine were then measured in these rats having had the two-bottle experience. Rats showing a two-bottle preference for the 1 microgram/ml nicotine solution displayed significantly more ingestive TR responses to 1 microgram/ml and 5 micrograms/ml nicotine than did the control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Peculiar Vulnerability to Nicotine Oral Self-administration in Mice during Early Adolescence

“…Yet, present results do indicate that such a preference was highly stable during the whole 12-day-long experiment. In agreement with the considerations put forward by other authors (Zellman et al 1985;Flynn et al 1989), it seems likely that, following the first drinking sessions, the taste of nicotine became also associated with post-oral reinforcement. As a consequence, the preference for the drug solution and its taste did not vanish.…”

“…At lower concentrations, the acute reaction to the taste of nicotine is reported to be "neutral." It has also been shown that, following a period of free-choice drinking between nicotine and water, a nicotine solution is able to elicit more ingestive responses than tap water, suggesting an increase in the immediate palatability of nicotine (Flynn et al 1989). From these results, authors have concluded that nicotine palatability is enhanced because of its pairing with positive post-oral reinforcement, a similar result being also evident with morphine solutions (Zellner et al 1985).…”

“…Nicotine solutions are generally reported to be bitter. In laboratory rats, however, nicotine is reported to elicit aversive responses (as assessed in the taste-reactivity test) only when the concentration is around 50 mg/l or more (Flynn et al 1989). At lower concentrations, the acute reaction to the taste of nicotine is reported to be "neutral."…”

“…Animals are provided with the possibility of a free choice between two bottles, containing either a vehicle or a nicotine solution. The nicotine solutions generally fail to be preferred to water in this paradigm when the two bottles are left continously available 24 h per day (Le Houezec et al 1989;Flynn et al 1989). Results are negative in various rat and mouse strains, even when attempts have been made to try to mask the NIC bitter taste by means of a sweetened solution as a vehicle (Smith and Roberts 1995;Meliska et al 1995;Robinson et al 1996).…”

“…In order to address this point, a number of methods could be used (for literature see Flynn et al 1989;Berridge 2000). Among these possibilities, the assessment of behavioral pharmacological effects of oral nicotine was chosen.…”