Ultrasonic vocalization ratios reflect the influence of motivational state and amygdala lesions on different types of taste avoidance learning

Abstract

Consumption of a sweet solution (the CS) and ultrasonic vocalizations (USVs) emitted by rats were recorded in a conditioned taste avoidance paradigm. The rats’ affective states were inferred from a ratio of high to low-frequency ultrasonic calls, which have been associated with positive and negative affect, respectively. The interacting effects of deprivation state and lesions of the basolateral amygdala (BLA) on CS consumption and affective state were examined. Rats were trained during the light phase while either 23 h or 3 h water deprived by exposing them to the CS and then injecting them with LiCl or saline. They were tested by re-exposing them to the CS while either 23 or 3 h deprived. Sham-lesioned rats that received LiCl injections consumed significantly less of the CS and evidenced relatively negative affect (inferred from the USV ratio) compared to control rats that received saline injections, regardless of the deprivation state in which they were trained or tested. Rats with BLA lesions trained while 23 h deprived failed to exhibit either reduced consumption or negative affect, regardless of whether they were tested while deprived for 23 or 3 h. Identical lesions had no effect on reduced consumption or on negative affect in rats trained while 3 h deprived, regardless of whether they were tested while deprived for 3 or 23 h. The findings suggest that both reduced consumption and negative affect are the results of different learning processes in deprived (23 h) and nearly satiated (3 h, during the light phase) rats. The amygdala-dependent negative affective shift observed in deprived rats may be due to an aversive Pavlovian conditioned response that acts to suppress drinking. The amygdala-independent negative affective response and reduced consumption in nearly satiated rats could be due to a form of latent learning of a stimulus-outcome association.