Drinking microstructure analysis of direct controls of water intake in male and female rats

Measures of rodent drinking (lick) patterns are used to test how various manipulations affect fluid intake. Decades of research indicate that manipulating the satiating potency of a stimulus affects the number of licking bursts whereas manipulating the hedonic value of the solution affects the size of the licking bursts or rate of licking. This type of analysis has been largely applied to manipulations that modulate drinking that is already occurring (i.e., indirect controls or modulators of intake), but there is a dearth of studies with detailed measures of licking in response to stimuli that are primary drivers of intake (i.e., direct controls). A better understanding of licking behavior in response to direct controls of fluid intake could provide insight into how drinking is stimulated. Accordingly, we analyzed lick patterns after varying doses of primary drivers (direct controls) of intake, angiotensin II, hypertonic saline, or carbochol, in male and female rats. As expected, all treatments dose-dependently increased licks for water. Analysis of licking patterns revealed dose-related increases in burst number after treatment with all stimuli, but dose did not predict burst size or lick rate. Together with previous work on licking patterns these data suggest that direct controls of water intake are more related to processes associated with satiety than to changes in hedonic value of the consumed substance.