Lucas Cuenya

Long-lasting effects of perinatal asphyxia on exploration, memory and incentive downshift.

Perinatal asphyxia remains as one of the most important causes of death and disability in children, without an effective treatment. Moreover, little is known about the long‐lasting behavioral consequences of asphyxia at birth. Therefore, the main aim of the present study was to investigate the motor, emotional and cognitive functions of adult asphyctic rats. Experimental subjects consisted of rats born vaginally (CTL), by cesarean section (C+), or by cesarean section following 19 min of asphyxia (PA). At three months of age, animals were examined in a behavioral test battery including elevated plus maze, open field, Morris water maze, and an incentive downshift procedure. Results indicated that groups did not differ in anxiety‐related behaviors, although a large variability was observed in the asphyctic group and therefore, the results are not completely conclusive. In addition, PA and C+ rats showed a deficit in exploration of new environments, but to a much lesser extent in the latter group. Spatial reference and working memory impairments were also found in PA rats. Finally, when animals were downshifted from a 32% to a 4% sucrose solution, an attenuated suppression of consummatory behavior was observed in PA rats. These results confirmed and extended those reported previously about the behavioral alterations associated with acute asphyxia around birth.

The effect of partial reinforcement on instrumental successive negative contrast in inbred Roman High- (RHA-I) and Low- (RLA-I) Avoidance rats

Frustration is an emotional response that can be induced by the sudden devaluation of a reinforcer in the presence of greater reinforcement expectancies (e.g. instrumental successive negative contrast, iSNC). This emotional response seems to be similar to anxiety and can be attenuated by previous experiences of reward loss (e.g. partial reinforcement, PR, as opposed to continuous reinforcement, CR). In this study we used iSNC and PR procedures in order to compare the performance of two strains of rats psychogenetically selected on the basis of their emotional reactivity: the inbred Roman High- (RHA-I, low anxiety) and Low- (RLA-I, high anxiety) Avoidance rats. Animals were exposed to a straight alley, where they were changed from 12 pellets in the preshift phase (presented in 100% of trials-CR vs. 50% of trials-PR) to 2 pellets in the postshift phase, or exposed to 2 pellets throughout the training. The results indicated that the iSNC only appeared in RLA-I rats exposed to CR, as opposed to RLA-I animals exposed to PR and to RHA-I rats exposed to PR or CR. These data seem to support the implication of emotional responses in both iSNC and PR situations, and indicate that the behavioral reactivity to reward loss experiences is modulated by genetic variables.

Effects of isolation in adulthood on frustration and anxiety.

In consummatory successive negative contrast (cSNC), when rats receive 32% of sweetened water and are unexpectedly exposed to 4% of the same solution, they consume less than those who received 4% regularly. In consummatory extinction (cE), rats receiving a 32% or 4% sugar solution stop lapping when presented with an empty tube. In both cases, these situations trigger an aversive emotional reaction similar to fear and anxiety called frustration or negative contrast effect. Isolation conditions in adulthood increase anxiety responses. We describe an experiment in which isolated or grouped rats in adulthood are evaluated in an elevated plus maze (EPM), in cSNC and cE. Results show that rats in groups express less anxiety and activity in EPM and more persistence in cE than isolated rats. There are no differences between the two housing conditions in cSNC. We discuss these results on the basis of frustration theories.

Ethanol facilitates consummatory extinction

Rats given access to an empty sipper tube after having obtained 32% sucrose in the same situation undergo extinction of consummatory behavior (cE). Ethanol (0.75 and 1g/kg, i.p.) accelerated cE when administered before the second extinction session. The effect was not attributable to increased activity or state-dependent reduction in consummatory behavior. These data are discussed in the context of research on the effects of ethanol on behavioral assays involving incentive downshifts.

Postweaning isolation affects responses to incentive contrast in adulthood

Adolescence is a time involving a series of changes in the use of appetitive reinforcers like food, as well as neuroendocrine changes like those taking place in the mesolimbic dopamine function. Social isolation from postnatal day 21 to 36 in rats leads to behavioral and neurophysiological alterations such as increased consumption of appetitive reinforcers. The work is focused on studying how exposure to chronic stress induced by social isolation during adolescence can have a long-lasting effect on responses to reinforcement shifts in adulthood. Two experiments were performed in rats in order to analyze the effect of adolescent isolation on the responses to unanticipated shifts in reinforcement during adulthood, in reinforcement devaluation (32-4% of sucrose solution), increase (4-32% of sucrose solution), and extinction (32-0% of sucrose solution) procedures. Adolescent isolation intensified the intake response resulting from a reinforcement increase (i.e., greater positive contrast), but had no effect on the response to reinforcement devaluation and omission. The implications of this procedure are discussed, along with the underlying behavioral and neurochemical mechanisms.

Respuestas de Frustración en Humanos

Resumen es: La frustracion es un estado emocional que se desencadena ante acontecimientos que involucran la reduccion o supresion inesperada de reforzadores apetitiv...

Consummatory suppression due to incentive downshift is not a consequence of enhanced search behavior.

Rats shifted from 32% to 4% sucrose solution consume less from the 4% solution than rats that experience only the 4% solution. This consummatory suppression, a phenomenon known as consummatory successive negative contrast (cSNC), is accompanied by an increase in other behaviors such as rearing, nose-down locomotion, ambulation, sampling new sources and grooming. Despite a large body of studies on the cSNC, it remains to be determined whether reduced consumption is part of the direct response to the reward downshift or a byproduct of the increase in alternative competing behaviors. The objective of the present study was to determine if consummatory suppression would occur when most competing behaviors are prevented from occurring. Rats were trained either with 32% or 4% sucrose solution for ten days in restrainers that limited almost all movement. On the next five days, all subjects received the 4% sucrose solution and a robust suppression in drinking in the downshifted animals was observed. These results suggest that consummatory suppression is a direct consequence of incentive downshift and not a byproduct of the increase in competing behaviors.

Complex effects of reward upshift on consummatory behavior.

Exposing rats to an upshift from a small reward to a larger reward sometimes yields evidence of consummatory successive positive contrast (cSPC), an effect that could be a suitable animal model of positive emotion. However, cSPC is an unreliable effect. Ten experiments explored the effects of an upshift in sucrose or saccharin concentration on consummatory behavior under several conditions. There was occasional evidence of cSPC, but mostly a combination of increased consummatory behavior relative to preshift reward concentrations and a reduced behavioral level relative to unshifted controls. Such a pattern is consistent with processes causing opposite changes on behavior. Reward upshift may induce processes that suppress behavior, such as taste neophobia (induced by an intense sucrose taste) and generalization decrement (induced by novelty in reward conditions after the upshift). An experiment tested the role of such novelty-related effects by preexposing animals to either the upshift concentration (12% sucrose) or water during three days before the start of the experiment. Sucrose-preexposed animals drank significantly more than water-preexposed animals during the upshift, but just as much as unshifted controls (i.e., no evidence of cSPC). These results suggest that cSPC may be difficult to obtain reliably because reward upshift induces opposing processes. However, they also seriously question the ontological status of cSPC.

Exploration of a novel object in late adolescence predicts novelty-seeking behavior in adulthood: Associations among behavioral responses in four novelty-seeking tests

UNLABELLEDnThe sensation/novelty seeking behavioral trait refers to the exploration/preference for a novel environment. Novelty seeking increases during late adolescence and it has been associated with several neurobehavioral disorders. In this experiment, we asked whether inbred Roman high- and low-avoidance (RHA-I, RLA-I) rats (1) differ in novelty seeking in late adolescence and (2) whether late adolescent novelty seeking predicts this trait in adulthood. Thirty six male RHA-I and 36 RLA-I rats were exposed to a novel object exploration (NOE) test during late adolescence (pnd: 52-59;nnnDEPENDENT VARIABLESncontact latency, contact time, contact frequency). Head-dipping (hole-board, HB), time and visits to a novel-arm (Y-maze), and latency-in and emergence latency (emergence test) were registered in adulthood (pnd: 83-105). The results showed strain differences in all these tests (RHA-I>RLA-I). Factor analysis (RHA-I+RLA-I) revealed two clusters. The first one grouped HB and emergence test measures. The second one grouped NOE and Y-maze variables. Time exploring a novel object (NOE) was a significant predictor of novel arm time (RHA-I+RLA, RHA-I); contact latency was a significant predictor of novel arm frequency (RLA-I). Present results show consistent behavioral associations across four novelty-seeking tests and suggest that late adolescent novelty seeking predicts this genetically-influenced temperamental trait in adult Roman rats.

Efecto del Haloperidol sobre el Contraste Sucesivo Positivo Consumatorio en Ratas Adultas con Aislamiento Adolescente

Las ratas expuestas a aislamiento adolescente (AA) muestran alteraciones neurologicas y conductuales en la adultez, muchas de ellas relacionadas con cambios en la respuesta ante reforzadores apetitivos. En estudios previos las ratas con AA mostraron un incremento del Contraste Sucesivo Positivo consumatorio (CSPc, i.e, mayor consumo de una solucion azucarada al 32%, 24 hs despues de tener acceso a una solucion al 4%), respecto de animales sin AA. El objetivo de este estudio fue evaluar si este efecto esta asociado a la hiperactividad dopaminergica. Se administro haloperidol a animales con AA (0.1 mg/kg, i.p.) antes de los ensayos de incremento del refuerzo y salina a un grupo control. No se hallo CSPc en los animales que recibieron haloperidol, mientras que en los sujetos con salina se observo en un ensayo. Si bien los resultados apoyan la hipotesis propuesta, es necesario realizar futuros experimentos para determinar con mayor precision el correlato neuroquimico del incremento de CSPc en animales con AA. Effect of haloperidol on consummatory successive positive contrast in adult rats with adolescent isolation. Rats exposed to adolescent isolation (AA) show neurological and behavioral disorders into adulthood, many of them related to changes in response to appetitive reinforcers. Previous studies showed an increase of consummatory Successive Positive Contrast (cSPC, i.e., increased consumption of 32% sugar solution, 24 hours after having access to 4% solution) in rats exposed to AA, in comparison to animals without AA. This study aim at evaluating whether this effect is associated with dopaminergic hyperactivity. Haloperidol (0.1 mg / kg, i.p.) was administered before animals with AA were exposed to the presentation of the increased solution (4% to 32%), while saline was administered to the control group. cSPC effect was not observed in animals receiving haloperidol, while a one trial positive contrast was expressed in animals receiving saline. These results confirm the proposed hypothesis. Although the results are promising, further experiments are needed to determine more precisely the neurochemical correlate of increased cSPC in animals with AA. Key Words:xa0Adolescent Isolation; Positive Contrast; Haloperidol; Dopamine; Rat