Schedule-induced drinking as functions of interpellet interval and draught size in the Java macaque

Area of Science:

• Behavioral Neuroscience
• Animal Behavior
• Operant Conditioning

Background:

• Schedule-induced polydipsia is a phenomenon where intermittent access to food can lead to excessive water consumption in animals.
• Understanding the factors influencing schedule-induced drinking is crucial for comprehending behavioral regulation and potential therapeutic targets.

Purpose of the Study:

• To investigate the relationship between fixed-time (FT) food delivery intervals and water intake in Java monkeys.
• To examine the effect of varying water draught sizes on schedule-induced drinking patterns.
• To elucidate the regulatory mechanisms underlying water consumption under fixed-time schedules.

Main Methods:

• Three Java monkeys were exposed to fixed-time (FT) schedules of food reinforcement, with inter-pellet intervals ranging from 8 to 256 seconds.
• Water was concurrently available, with draught size systematically varied between 0.3 and 1.0 milliliter per lick.
• Session water intake, drinking bout initiation probability, and bout size were measured and analyzed in relation to FT values and draught size.

Main Results:

• Session water intake exhibited a bitonic relationship with the inter-pellet interval, influenced by drinking bout initiation probability and bout size.
• Drinking bout initiation probability decreased at higher inter-pellet intervals, while bout size increased with longer intervals.
• Reduced draught sizes (≤0.5 mL) primarily affected bout size, with minimal impact on total session water intake.

Conclusions:

• A volume-regulation process governs schedule-induced drinking at the session intake level in Java monkeys.
• This regulatory process is constrained at the bout level, particularly when smaller water draught sizes are available.
• Findings highlight the complex interplay between food reinforcement schedules, water availability, and behavioral regulation of fluid intake.