Analysis of the microstructure of the rhythmic tongue movements of rats ingesting maltose and sucrose solutions.

Abstract

The interlick interval distribution of rats while ingesting maltose under real and sham feeding conditions and while ingesting seven concentrations of sucrose under real feeding conditions was analyzed. The analysis revealed that the licking behavior of rats is organized into bursts of licking at a high rate. These bursts occurred in clusters that were separated by brief (250-500 ms) interruptions. The clusters were separated by intervals that ranged from 500 ms to many hundreds of seconds. Sham feeding increased the length of the meal by increasing the number but not the size of the clusters. Increasing the concentration of sucrose increased monotonically the size of the clusters but varied the number of clusters as an inverted-V-shaped function. This analysis revealed the details of the central nervous system's control over ingestive behavior.

A learned flavor preference persists despite the extinction of conditioned hedonic reactions to the cue flavors

“…The mean cluster size (i.e., the mean number of licks in the clusters recorded in a single test session for each animal) was extracted from the record of licks, with a cluster being defined as a set of licks, where each lick is separated by an interlick interval of no more than 1 sec. This criterion was adopted by Spector et al (1998) to define licking, and although other criteria have been used (e.g., 0.5 sec by Davis & Smith, 1992), parametric analyses suggest that there is little practical difference between them, since most pauses greater than 0.5 sec are also greater than 1 sec (see, e.g., Davis & Smith, 1992;Spector et al, 1998). We analyzed the present data using both criteria, and although estimated bout lengths were slightly shorter with the 0.5-sec criterion, the pattern of results was virtually identical to that reported below using the 1-sec criterion.…”

“…When ingesting fluids, rats produce sustained runs of rapidly occurring rhythmic licks (referred to here as "clusters") that are separated by pauses of varying length. The mean number of licks in a cluster bears a positive, monotonic relationship to the concentration of palatable fluids, which has led to the suggestion that cluster size is an index of stimulus palatability (see, e.g., Davis & Smith, 1992;Spector, Klumpp, & Kaplan, 1998). Importantly, cluster size does not simply reflect the amount of solution consumed, since there is typically an inverted U-shaped function between concentration and total consumption, with the highest levels of consumption at intermediate concentrations of palatable solutions.…”

Modulation of food reward by adiposity signals

“…We have demonstrated that ICV insulin synergizes with a subthreshold dose of the D2 receptor antagonist raclopride to decrease activity in a 5-min sucrose lick rate task (28). This task, developed and validated by Smith and Davis (29), represents a 'pure hedonic' response of the animal to a solution, and, because of its very acute timing, does not involve any post-ingestive feedback. Smith and Davis further demonstrated the dopaminergic dependence of this task since performance is decreased with the administration of a D2 receptor antagonist (30).…”

Effects of neuropeptide Y on feeding microstructure: Dissociation of appetitive and consummatory actions.

“…These gastrointestinal effects of NPY could affect ingestive behavior. In their analysis, Lynch et al (1994) observed that NPY slowed the rate of decline in ingestion rate during the meal, which is considered to indicate reduced inhibitory feedback from the gut Davis & Levine, 1977;Davis & Smith, 1992). However, this analysis was not completed for an entire meal; therefore, it is unclear whether these ingestion rate effects were sustained or offset in later phases of the meal.…”