CONSUMMATORY SUCCESSIVE POSITIVE CONTRAST WITH AVERSIVE SOLUTIONS IN INFANT RATS: REPLICATION AND GENERALIZATION TO A HIGHER CONCENTRATION OF A BITTER SOLUTION

Successive positive incentive contrast is typically demonstrated when a group of subjects shows a higher consumption of a reinforcer than a control group, if they were previously exposed to a similar one of lower magnitude. Recently, a similar effect was observed by lowering the concentration of a quinine solution in the experimental group. On the other hand, the presence of a familiar odor has been shown to attenuate responses elicited by aversive stimuli in infant rats. This experiment was designed to assess if the presence of a familiar odor decreases the responses elicited by an aversive solution. Two groups of rats were exposed to a consummatory positive successive contrast procedure, decreasing the concentration of a quinine solution (i.e., 0.2% - 0.01%). Half of the subjects in each group was tested in the presence of the homecage odor during the postshift phase. A positive successive contrast effect was evidenced by subjects in the experimental group, consuming more of the lower-concentration solution during the postshift phase. The presence of the odor, however, exerted no effect. Results are discussed in the context of the social buffering and positive successive contrast effects.

Regulation of the stress response by social buffering: A review across species

This review presents a critical reading of the literature on social buffering in human and non-human animals. The term social buffering has been coined to refer to an attenuation of stress responses by the presence of conspecifics. Evidence shows that the buffer seems to be specific for each stage of development, being the mother the factor that attenuates the stress responses during early development and conspecifics of the same age, later in life. An animal model of scarcity of resources revealed that when being reared by a stressed mother, the social buffering effect does not occur. The literature reviewed allows us to approach a key factor related to stress and its effects in the different stages of ontogeny.

Diferencias fenotípicas ante la devaluación y omisión de una recompensa esperada

La frustración es una respuesta comportamental, emocional y neurobiológica concomitante a la discrepancia negativa entre el refuerzo esperado y el obtenido, ya sea por la devaluación u omisión del incentivo. Los modelos animales y la comparación de cepas endocriadas han permitido estudiar la contribución de los factores genéticos a la expresión de diferencias fenotípicas en tales situaciones. El objetivo consistió en comparar cepas que difieren en su comportamiento emocional ante la devaluación (Exp 1) y omisión (Exp 2) de un refuerzo: las ratas espontáneamente hipertensas (SHR) y normotensas Wistar Kyoto (WKY). En ambos experimentos se halló que las SHR realizaron significativamente más respuestas de ingesta durante la fase de adquisición. En la fase de prueba del Exp 1, se observó una recuperación enlentecida de su respuesta. En el Exp 2 no se observaron diferencias entre cepas. La cepa emocionalmente más reactiva (SHR) no difirió con respecto a su control (WKY) en la reacción inicial ante la devaluación del refuerzo, pero mostró una recuperación enlentecida. Estos datos son congruentes con la literatura que sugiere que, ante la devaluación del incentivo, las diferencias fenotípicas se expresan con mayor facilidad en la recuperación de la respuesta (frustración secundaria).

Infant Trauma Alters Social Buffering of Threat Learning: Emerging Role of Prefrontal Cortex in Preadolescence

Within the infant-caregiver attachment system, the primary caregiver holds potent reward value to the infant, exhibited by infants' strong preference for approach responses and proximity-seeking towards the mother. A less well-understood feature of the attachment figure is the caregiver's ability to reduce fear via social buffering, commonly associated with the notion of a "safe haven" in the developmental literature. Evidence suggests this infant system overlaps with the neural network supporting social buffering (attenuation) of fear in the adults of many species, a network known to involve the prefrontal cortex (PFC). Here, using odor-shock conditioning in young developing rats, we assessed when the infant system transitions to the adult-like PFC-dependent social buffering of threat system. Rat pups were odor-shock conditioned (0.55 mA-0.6 mA) at either postnatal day (PN18; dependent on mother) or 28 (newly independent, weaned at PN23). Within each age group, the mother was present or absent during conditioning, with PFC assessment following acquisition using 14C 2-DG autoradiography and cue testing the following day. Since the human literature suggests poor attachment attenuates the mother's ability to socially buffer the infants, half of the pups at each age were reared with an abusive mother from PN8-12. The results showed that for typical control rearing, the mother attenuated fear in both PN18 and PN28 pups, although the PFC [infralimbic (IL) and ventral prelimbic (vPL) cortices] was only engaged at PN28. Abuse rearing completely disrupted social buffering of pups by the mother at PN18. The results from PN28 pups showed that while the mother modulated learning in both control and abuse-reared pups, the behavioral and PFC effects were attenuated after maltreatment. Our data suggest that pups transition to the adult-like PFC social support circuit after independence from the mother (PN28), and this circuit remains functional after early-life trauma, although its effectiveness appears reduced. This is in sharp contrast to the effects of early life trauma during infancy, where social buffering of the infant is more robustly impacted. We suggest that the infant social buffering circuit is disengaged by early-life trauma, while the adolescent PFC-dependent social buffering circuit may use a safety signal with unreliable safety value.

Correlación entre Miedo Incondicionado y la Primera Reacción a la Disminución y Extinción de un Reforzador Apetitivo

Cuando las ratas tienen acceso a una solución azucarada al 32% y luego la concentración disminuye al 4%, los animales consumen o permanecen en contacto con el bebedero menos tiempo que los animales que siempre consumieron la solución al 4%. A este fenómeno de Contraste Sucesivo Negativo consumatorio (CSNc) se le considera un modelo animal de frustración. Existe evidencia de que en una prueba de luz-oscuridad, las ratas prefieren permanecer en el compartimiento oscuro, lo que sugiere una respuesta de miedo incondicionado hacia lugares claros. Se presentan dos experimentos en los que se evaluó la preferencia de ratas en una prueba de luz-oscuridad y a un CSNc (Experimento 1) y a una Extinción Consumatoria (Ec, acceso a un bebedero vacío, Experimento 2) para evaluar la correlación entre la primera reacción a la devaluación u omisión de reforzadores con las respuestas de miedo incondicionado a los lugares oscuros. Las ratas que permanecieron más tiempo en el lugar oscuro permanecieron menos tiempo en contacto con el bebedero durante el primer ensayo de devaluación del reforzador (Experimento 1) y durante el primer minuto del primer ensayo de Ec (Experimento 2). Esos resultados se discuten en relación con las teorías de Amsel (1958), Gray (1987) y Flaherty (1996).

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.

Early Experience and Incentive Relativity in Adulthood

Human and animal studies have shown the long-lasting impact of early life experiences on the development of individual differences in stress responsiveness in later life. Despite the numerous works that evaluate the effect of early experiences on different behavioral paradigms, which for the most part are related to aversive situations, there are few studies that assess the effects on the unexpected downshift or omission of positive rewards. The purpose of this article is to present several independent lines of research into how frustration responses during adulthood may be influenced by early experiences. Very few works have been found on the subject, and in most cases the results were negative or controversial. However, more recent investigations suggest that the responses in adults to frustration or euphoria may be modulated by early experiences.

Anxiolytic-like effect of ejaculation upon frustration

In three experiments, we studied the consequences of ejaculation upon the frustrative or contrast response of male rats exposed to reward downshift situations (i.e., surprising changes from 32% to 4% sucrose solutions). Similar to what has been found after treatment with anxiolytic agents, consummatory suppression was partially reversed by previous ejaculations in a second postshift trial (Experiments 2 and 3), such a result not having been obtained in a first postshift trial (Experiment 1). Moreover, the effect of ejaculations upon males' behavior during a second postshift trial was transitory, disappearing when assessed during the third and fourth postshift trials (Experiment 3). These results are in accordance with both Amsel's (1958, 1992) frustration theory and Flaherty's (1996) multistage hypothesis of successive negative contrast; the diverse factors that are known to modulate contrast effects are considered, including an interpretation of the present data in terms of the anxiolytic-like effect of the ejaculation.