Repeated exposures to gustatory stimuli produce habituation or positive contrast effects in perinatal rats

Abstract

Adult rats exhibit a decrease in consummatory responses following repeated presentations of a taste (habituation) and an increase in consummatory responses if they experience an upward shift in the magnitude or intensity of a gustatory stimulus (e.g., sucrose or saccharin). These responses do not represent a direct sensorimotor reaction to a gustatory cue, but rather reflect a change in responding based on the memory of a previous taste. Here, we sought to determine if fetal rats could (like adults) adjust their orofacial motor responses based on a memory of recent gustatory experience. Embryonic Day 18 (E18) or Day 19 (E19) rat fetuses received oral lavage with either 0.15 or 0.30% saccharin (SAC). Subsequently, observations of orofacial movements (mouthing and licking) following oral lavage with 0.30% SAC were made 50 min later, 24 hr later, or on postnatal Day 3 (P3). Thus, some animals were in a "shifted" condition in which they first experienced a relatively low concentration of SAC and then a higher one while control rats ("nonshifted") received 0.30% SAC during both taste exposures. Fetuses exhibited evidence of both habituation (with repeated presentation of the 0.30% SAC) and positive contrast effects (PCEs) (following an upward shift in SAC concentration) when retested 50 min after their first exposure to SAC on E19. However, these animals did not exhibit PCEs 24 hr later or 5 days later (on P3). Contrast effects were not observed when the initial SAC exposure was on E18, and habituation responses were variable depending on the time interval between the taste presentations to these animals. Rats with a 5- to 6-day latency between the two taste presentations showed neither PCEs nor habituation. Our data indicate that PCEs and habituation effects emerge at different ages, and their demonstration is dependent upon the latency between the taste presentations.

Preparing for Life After Birth: Introducing the Concepts of Intrauterine and Extrauterine Sensory Entrainment in Mammalian Young

“…This would help to guide the non-milk dietary choices of the young as they approach and then pass beyond weaning. Note from a safety viewpoint that entrained preferences for attractive dietary tastes and smells (e.g., [73,208,209]), and genetically preprogrammed aversion to others [41,48,208,210], would likely act together to minimise consumption of potentially toxic compounds.…”

The effect of taste familiarity on intake and taste reactivity in infant rats

“…The taste reactivity test has been adapted to infant rats and used successfully to analyze affective reactions to different tastants in early ontogeny (Hall & Bryan, 1981;Kozlov, Varlinskaya, & Spear, 2008;Vigorito & Sclafani, 1988). In a series of studies in which reactivity to saccharine was evaluated early in ontogeny (rat fetuses and neonates) as a function of previous exposure to this stimulus, a differential taste responsiveness was observed in subjects which had been preexposed to this tastant, indicating that even at this early age, subjects are capable of detecting the novelty of a gustatory stimulus (Mickley et al, 2000(Mickley et al, , 2003. However, in these studies no clear directionality of the response was obtained, that is, in some cases a reduced reaction to saccharine was found after stimulus exposure, and in others, an increased response was reported, depending on the age of the subject (Mickley et al, 2003).…”

“…In a series of studies in which reactivity to saccharine was evaluated early in ontogeny (rat fetuses and neonates) as a function of previous exposure to this stimulus, a differential taste responsiveness was observed in subjects which had been preexposed to this tastant, indicating that even at this early age, subjects are capable of detecting the novelty of a gustatory stimulus (Mickley et al, 2000(Mickley et al, , 2003. However, in these studies no clear directionality of the response was obtained, that is, in some cases a reduced reaction to saccharine was found after stimulus exposure, and in others, an increased response was reported, depending on the age of the subject (Mickley et al, 2003). In another study with rat fetuses, no differential responsiveness to a mint flavor was found after analyzing eleven behavioral categories of the fetal response as a function of familiarity (Smotherman & Robinson, 1985).…”

Exposure to ethanol on prenatal days 19–20 increases ethanol intake and palatability in the infant rat: Involvement of kappa and mu opioid receptors

“…This has been proven not only by showing that part of the olfactory system is already functional at gestational day (GD) 16 (Pedersen, Greer, & Shepherd, ), but also behaviorally, demonstrating that the injection of a flavored substance directly into the amniotic fluid modifies subsequent fetal behavioral patterns to this stimulus, that is, the fetus recognizes the chemosensory stimulus previously experienced (Mickley, Remmers‐Roeber, Crouse, & Peluso, ; Smotherman & Robinson, ). Habituation and sensitization to chemosensory stimuli have been demonstrated in rat fetuses (Chotro & Spear, ; Mickley et al, ; Smotherman & Robinson, ), as has Pavlovian associative learning. For instance, in utero exposure to apple juice paired with a LiCl injection resulted in a postnatal reduction in preference for nipples painted with apple juice (Stickrod, Kimble, & Smotherman, ).…”