2.7. Sucrose Preference Test (SPT)

This test assesses signs of anhedonia-like behavior by monitoring a rat’s preference to sucrose-laced water [32,34,35,39]. An increase in the consumption of sucrose-water over plain-water is interpreted as an animal’s preference for pleasure-seeking (hedonic) behavior. Several factors can affect SPT behavior including concentration of sucrose, circadian rhythms, side-bias, and weight of the animals [42]. While we control for these variables when implementing an SPT paradigm, the possibility of OP-induced changes in the metabolic state of the animal, insulin resistance, and oxidative stress could affect SPT outcome.

Briefly, rats were habituated to having two bottles in the cage lid for three days. The bottles were fitted with ball-bearing sipper tubes that prevented fluids from leaking. Following this acclimation, rats were deprived of water but not food for a 20-h period. At the end of this period, two bottles were introduced in the cage lid and rats had a free choice of either drinking the 1% sucrose-laced solution or plain water over the next 24-h period. The positions of two bottles were switched mid-way to reduce any confounding effects produced by a side bias. Sucrose preference was calculated as a percentage of the volume of sucrose intake over the total volume of fluid intake and averaged over the testing period.