Genetic control of oromotor phenotypes: A survey of licking and ingestive behaviors in highly diverse strains of mice

Abstract

In order to examine genetic influences on fluid ingestion, 20-min intake of either water or 0.1M sucrose was measured in a lickometer in 18 isogenic strains of mice, including 15 inbred strains and 3 F₁ hybrid crosses. Intake and licking data were examined at a number of levels, including lick rate as defined by mean or median interlick interval, as well as several microstructural parameters (i.e. burst-pause structure). In general, strain variation for ingestive phenotypes were correlated across water and sucrose in all strains, indicating fundamental, rather than stimulus-specific, mechanisms of intake. Strain variation was substantial and robust, with heritabilities for phenotypes ranging from 0.22 to 0.73. For mean interlick interval (MPI; a measure of lick rate) strains varied continuously from 94.3 to 127.0ms, a range consistent with previous studies. Furthermore, variation among strains for microstructural traits such as burst size and number suggested that strains possess different overall ingestive strategies, with some favoring more short bursts, and others favoring fewer, long bursts. Strains also varied in cumulative intake functions, exhibiting both linear and decelerated rates of intake across the session.

Keywords: Central pattern generator; Cumulative intake; Heritability; Lickometry; Microstructure; Taste.

Figure 1

The mean (+ or ± standard error) of the mean primary interlick interval (MPI, defined as the average interlick interval of interlick intervals shorter than 160 ms) for 18 strains of mice licking water (filled symbols) or sucrose (open bars). Strains are arranged in rank order of MPI to water. The mean of all strains is also provided (open symbol and filled bar).

Figure 2

The proportion of pauses of various lengths is shown for both the water session (A) and the sucrose session (B). The white bar indicates the proportion of interlick intervals (ILI) less than 160 ms and is equivalent to our measure of lick efficiency. Gray bars indicate the proportion of ILI between 161 ms and 1 s. Black bars indicate proportion of ILI greater than 1 s which also represent interburst intervals. (as in Figure 1); the reduction in lick efficiency as MPI increases was a significant

Figure 3

The mean (+ or ± standard error) number of licks for 18 strains of mice licking water (filled symbols) or sucrose (open bars). Strains are arranged in rank order of total licks to water. The mean of all strains is also provided (open symbol and filled bar).

Figure 4

The mean (+ or ± standard error) size of bursts (A) and number of bursts (B) for 18 strains of mice licking water (filled symbols) or sucrose (open bars). The mean of all strains is also provided (open symbol and filled bar). Strains are arranged in increasing order of total number of licks during the water session (c.f., Figure 3). Despite all strains licking significantly more to sucrose than water, some strains engaged in longer bursts of licking for water than sucrose. In many cases, this may have been an artefact of some strains licking later into the session when smaller bursts are more probable. When sucrose burst number was matched to water burst number, burst size was higher to sucrose in all strains but the FVB strain (C). Examining the largest burst (D), most strains had more sustained licking to sucrose than water.

Figure 5

The ingestive strategy of mice was quantified with the Ingestive Style Index (ISI, see Method) which takes into account both burst size and burst number (relative to the all-strain mean for these data). Positive ISI values indicate a preference for infrequent, longer bursts whereas negative ISI values indicate a preference for frequent, shorter bursts.

Figure 6

The mean time during the 20 min (1200 s) session in which mice reached 50% (open bars), 75% (gray bars), and 90% (filled bars) of their lick total when ingesting water (A) or sucrose (B). Then mean of all 18 strains is also provided. Strains are rank-ordered (lowest at the top) by the NCI Index (see Method) which quantifies the extent to which cumulative intake functions deviate from linear.

Figure 7

Cumulative intake functions for 6 selected strains that exhibited the most (FVB, A, B6) and least (BTBR, 129, PWK) linear pattern of sucrose licking. The strain mean cumulative intake function is also shown for comparison.

Figure 8

Heritability (h²) estimates for 11 ingestive phenotypes for both water (filled bars) and sucrose (open bars). Estimates of h² are displayed as means (± SD) of 18 jackknife subsamples per phenotype.