Effects of pretraining treatment with testosterone on successive and anticipatory negative contrast

Sucrose exposure in juvenile rats produces long-term changes in fear memory and anxiety-like behavior

Sugar consumption has increased dramatically in our society, a phenomenon that is primarily associated with obesity and diabetes appearance. However, whether this overconsumption of sugar has an impact on the developing CNS remains unknown. This study investigated the long-term effects of unlimited access to sucrose using the two-bottle choice paradigm and the juvenile and adult effects were compared. Male Sprague Dawley rats had free access to water containing 10% sucrose and water during youth (PD 25-50) or adulthood (PD 75-100). Rats in the sucrose group, privileged to take sugary solution over the water. No weight differences were observed between the sucrose groups and their age-matched water controls. After treatment all animals drank only water for another 25 days. Frustration, measured as the amount of water drank after the sucrose period, was higher in young-exposed animals compared to adults. In addition, rats that consumed sucrose during youth travelled less the central zones of an open field. Sucrose consumption during youth also affected fear behavior as animals exhibited impaired extinction of fear memory compared to control, indicating that prefrontal and hippocampal function is impaired. In contrast, rats exposed to sucrose during adulthood did not behave significantly different from control on either task. The calretinin and parvalbumin GABAergic interneurons go through extensive remodeling during youth in the medial prefrontal cortex and the ventral hippocampus. Here, we found that rats exposed to sucrose during youth presented an increased expression of calretinin-immunoreactivity in the medial prefrontal cortex, but not in the ventral hippocampus, indicating that early sucrose consumption produces enduring effects on the GABA system. Altogether these results indicate that sugar overconsumption at early stages of life induces long-term effects on behaviors related to fear and anxiety in adulthood.

Social interaction with rat exposed to constant light during lactation prevents depressive-like behavior induced by constant light in adulthood

Circadian rhythm disruptions are often observed in depressed patients, and changes in the light/dark cycle promote depressive-like behavior in animal models. Prolonged exposure to constant light (LL) is known to lead to arrhythmicity of circadian locomotor activity and depressive-like behavior in rats. Interestingly, neonatal exposure to LL prevents both arrhythmicity and depressive behavior in adulthood. Arrhythmic rats under LL conditions that cohabitate with a rhythmic rat exhibit improvement in circadian rhythms. We tested whether such cohabitation also protects against LL-induced depressive-like behavior. Wistar rats were assigned to conditions of either neonatal constant light (neonatal-LL) on postnatal days 10-22 or a regular light/dark cycle (neonatal-LD). On day 45, the animals were assigned to three possible pair combinations. After a baseline sucrose preference test, half of the pairs were placed under LL conditions. Weekly sucrose preference tests were conducted to evaluate depressive-like behavior. The animals were isolated by an aluminum wall on the test day. At week 2 of LL, sucrose preference was reduced in neonatal-LD/neonatal-LD pairs of animals. At week 5, neonatal-LD/neonatal-LD pairs exhibited anhedonic-like behavior, but the pairs with at least one neonatal-LL rat did not. The LL cycle was returned to an LD cycle, and the neonatal-LD/neonatal-LD pairs exhibited a restoration of sucrose preference 2 weeks later. We conclude that social interaction can prevent depressive-like behavior induced by circadian rhythm disruption as long as one of the animals is more prone to present a strong rhythm.

Propranolol reverses open field effects on frustration

Reactivity to a reward is affected by prior experience with different reinforcer values of that reward, a phenomenon known as incentive relativity. Incentive relativity can be studied via the consummatory successive negative contrast (cSNC) paradigm, in which acceptance of 4% sucrose is assessed in animals that had been exposed to 32% sucrose. These downshifted animals usually exhibit significantly less sucrose acceptance than animals that always received the 4% sucrose solution. In previous work, we found that exploration of a novel open field (OF) before the first trial with the downshifted solution attenuated the contrast effect. The goal of the present experiments was to expand the knowledge on the effects of OF exposure on cSNC. We evaluated the effect OF exposure before the second downshift trial and assessed the mediational role of the adrenergic system in the effects of OF during the first and second trial of cSNC. The results indicate that OF applied before the first or second downshift trials exert opposite effects and that the adrenergic system is involved in the acquisition and consolidation of the OF information.

Incentive relativity in middle aged rats

Response to a reinforcer is affected by prior experience with different reward values of that reward, a phenomenon known as incentive relativity. Two different procedures to study this phenomenon are the incentive downshift (ID) and the consummatory anticipatory negative contrast (cANC), the former is an emotional-cognitive protocol and the latter cognitive one. Aged rodents, as also well described in aged humans, exhibit alterations in cognitive functions. The main goal of this work was to evaluate the effect of age in the incentive' assessment using these two procedures. The results indicated that aged rats had an adequate assessment of the rewards but their performance is not completely comparable to that of young subjects. They recover faster from the ID and they had a cognitive impairment in the cANC. The results are discussed in relation to age-related changes in memory and emotion.