Efectos del apoyo social percibido sobre el estrés materno y lactancia materna: Una revisión narrativa / Effects of perceived social support on maternal stress and breastfeeding: A narrative review

RESUMEN Introducción: Los organismos de salud recomiendan la lactancia materna exclusiva hasta los 6 meses de vida y lactancia materna (LM) continuada hasta los 2 años de edad. Objetivo: Realizar una revisión narrativa de los efectos del apoyo social sobre el estrés materno y la LM. Método: Se realizó una revisión narrativa y no sistemática en la cual se seleccionó artículos de la literatura en PubMed, Redalyc y BVS y en páginas web de entidades como la OMS y la UNICEF. Resultados: Los resultados reflejan que el escaso apoyo social se asocia con un incremento del estrés materno e impacta en el inicio y sostenimiento de la LM. El apoyo social actúa atenuando los niveles de estrés. Conclusión: Se concluye que el apoyo social es un factor que ha de ser considerado como una estrategia para disminuir los niveles de estrés materno y la promoción de la LM. Es necesario enfatizar el importante rol de los equipos de salud en torno a la promoción de la LM, especialmente en madres que ofrecen crianza monoparental, al proveer apoyo social y formación para la lactancia.

ABSTRACT Background: Health authorities recommend exclusive breastfeeding until six months of age and continued breastfeeding (BF) until two years. Objective: To conduct a narrative review of the effects of social support on maternal distress and BF. Method: A narrative and non-systematic review was conducted, selecting articles from the literature in PubMed, Redalyc, BVS, and from websites of organisations such as WHO and UNICEF. Results: The results show that low social support is associated with increased maternal stress and affects the initiation and maintenance of breastfeeding. Social support acts to reduce stress levels. Conclusion: Social support is a factor to be considered as a strategy to reduce maternal stress and promote BF. It is necessary to emphasise the role of healthcare teams in promoting BF, especially among single-parent mothers, by providing social support and breastfeeding education.

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.

The presence of chemosensory cues transmitted through the mother's milk increases the search and ingestion responses toward bitter and sour solutions.

Olfaction is of major importance during early stages of life in altricial species. This sense allows newborns to develop different behaviors that will allow them to survive. Odors tend to be associated to contextual stimuli (such as warmth); this, in turn, enables the pups to recognize when to withdraw or approach. At the same time, olfaction modulates the acceptance of aversive flavors. The increase of approach responses toward a bitter substance during early life is enhanced by stimulation with familiar, pre-exposed odors. Newborn rats exhibit heightened grasp responses toward an artificial nipple dispensing quinine, and drink more of this bitter solution, in the presence of a pre-exposed odor (lemon or the mother's odor). The present research assessed the replicability of previous results by pre-exposing the subjects to the scent through maternal milk and using solutions with different aversive tastes. Half of the subjects (3 day-old Wistar rats) were pre-exposed to lemon odor through the maternal milk (the mother had previously ingested the lemon essence via an intragastric injection); 4 h later, all the rats were evaluated in the presence of the lemon odor with an artificial nipple containing quinine, citric acid, saline solution, or water. The results showed enhanced seeking and intake of the bitter (quinine) and sour solution (citric acid). However, this did not occur when the nipple contained water or saline solution. The evidence suggests that: During the early stages of development, familiar odors regulate the acceptance of non-palatable, otherwise rejected, flavors; and that the route of transmission of the pre-exposed odor can be through air, or through food (amniotic fluid in previous studies and, in this case, breast milk), that is, via the retronasal and orthonasal routes.

Sensitive period for the acceptance of unpalatable flavors in the presence of a preexposed odor in infant rats.

It has been shown that exposure to familiar odors facilitate the acceptance of bitter flavors in preweanling rats, yet it unknown how long this phenomenon persists. This study assessed, in 9- or 15-day-old Wistar rats, the influence of a familiar scent (i.e., lemon) on the intake of and behavioral responsiveness (i.e., mouthing, paw lick, chin rub, head shake, among other taste reactivity responses) elicited by a 0.1% quinine solution. The results showed heightened quinine intake in 9-day-old rats that had been preexposed to the odor, when compared to non-preexposed controls. This result was replicated in Experiment 2, which also documented no alterations in behavioral responsiveness toward quinine in the 9-day-old rats, as a function of the pre-exposure. More importantly, 15-day-old rats exhibited no alterations in intake or behavioral responsiveness toward quinine as a function of odor pre-exposure. These results suggest that the effects of odor pre-exposure upon acceptance of bitter tastes may occur within a sensitive period for the acceptance of bitter food.

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.

Exposure to maternal odor enhances intake of a taste that mimicks the sensory attributes of ethanol.

Early exposure to ethanol increases subsequent acceptance of this drug. Little attention, however, has been devoted to the interaction of the taste of the drug with other, familiar or non-familiar, odors contingent with ethanol access, particularly early in ontogeny. This study assessed the influence of exposure to maternal odor on intake and grasp responses to an artificial nipple providing a solution (a sucrose-quinine mix) that emulates the taste of alcohol, in 4-day-old rat pups. The results showed that the mother's odor enhanced intake from and seeking responses to an artificial nipple that provided the solution that mimicked the taste of alcohol (Experiment 1). This pattern of results was not evoked by the odor of an unrelated dam (Experiment 2), nor was it observed when the nipple delivered water. The main new finding of the present study is that 4-day-old rats tested in the presence of the mother (and hence exposed to her odor cues) exhibited enhanced seeking and intake of a solution that mimics the chemosensory properties of ethanol.

Maternal Odor Exposure Modulates Acceptance of a Bitter Taste in Newborn and Infant Rats.

The acceptance of bitter, aversive, substances during early life is enhanced by stimulation with familiar, pre-exposed odors. Newborn rats exhibited heightened grasp responses toward an artificial nipple dispensing quinine, and drank more of this bitter solution, if concurrently stimulated with a lemon odor they had been exposed to shortly after birth. It yet unknown, however, if odors made familiar via normative developmental milestones also acquire modulatory influence upon seeking and intake of basic tastants. The current study assessed the influence of exposure to maternal odor on intake and grasp responses toward a surrogate nipple providing quinine, in 3-day (Experiment 1) or 12-day (Experiment 2) old, Wistar rat pups. The results revealed enhanced seeking and intake of the bitter solution, but not of water, in animals tested in the presence of the mother (and hence exposed to its odor cues), at both ages, compared to counterparts given either no explicit odor stimulation or stimulation to the odor of an unrelated dam. These results, obtained with a biologically relevant odor, are consistent with those previously found with a neutral, arbitrary odor. It seems that during the early stages of development, familiar odors regulate the acceptance of non-palatable, otherwise rejected, flavors.

Influence of prenatal pre-exposure to an odor on intake behavior of an aversive solution in newborn rats.

Early pre- or postnatal sensory experiences significantly influence flavor preference and food intake, and can induce liking for innately unpalatable flavors. Previous work found that newborn rats stimulated with an odor experienced shortly after birth exhibited heightened intake and seeking towards an artificial nipple containing quinine. This result suggests that odors made familiar trough early postnatal pre-exposure can shift the motivational value of unconditional stimuli. The objective of the current study was to assess the effect of an odor (lemon) experienced in-utero on the first intake responses towards an artificial nipple supplying quinine. The hypothesis, which was corroborated, was that stimulation with the olfactory stimulus experienced in-utero would increase the newborn's intake and grasp responses to the artificial nipple containing quinine. Exposure to the odor that had been pre-exposed in utero increased quinine intake and seeking (i.e., latency to grasp and total time in contact with the nipple, as well as number of and mean duration of nipple grasps) in 3-h-old pups. These results replicate those previously found with postnatal odor pre-exposure, and extend the phase for pre-exposure to the prenatal stage.

Consummatory succesive positive contrast produced by the downshift of an aversive solution in infant rats.

Subjects trained in successive positive contrast are usually given an appetitive stimulus of relatively low quality during a pre-shift, followed by exposure to a significantly greater quality of the same stimulus. Enhanced responsiveness to the high-quality stimulus during the post-shift phase, compared to a control group that receives the superior reward in both phases, is taken as an index of successive positive contrast. Successive positive contrast reports are rare, probably due to performance limitations inherent to the experimental protocols available. We exposed infant rats (14 days old at the start of training) to .1% or .01% quinine during 4, 10 min, trials (pre-shift phase). All animals were then given two trials of exposure to .01% quinine (post-shift phase). During the pre-shift the level of intake was greater in pups stimulated with the relatively less aversive .01% quinine solution. These animals also exhibited, compared to those stimulated with .1% quinine, lower emission of the aversive response paw treading. During the post-shift phase, the group that had been exposed to .1% quinine exhibited significantly greater intake of .01% quinine, along with a reduction in the emission of paw treading and an enhancement in paw licking, an ingestive, appetitive response. Altogether, the evidence is suggestive of the emergence of consummatory successive positive contrast during the second week of life of the rat. To our knowledge, this is the first evidence of positive contrast using an aversive solution.

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.

Change in the hedonic value of an aversive stimulus in the presence of a pre-exposed odor.

Rats exhibit a sensitive period from the time of birth until postnatal day 10 during which they develop preferences for odors even if those odors are paired with a moderately aversive stimulus. It is still unknown whether pre-exposure to an odor produces alterations on intake responses of basic tastants, and on other patterns that indicate a change in the hedonic value of reward, such as nipple grasping behavior. The current study assessed the effect of pre-exposure to an odor immediately after birth on intake responses of appetitive and aversive tastants. The objectives were to assess if 3-hour-old rats adjust their behaviors to obtain different values of appetitive and aversive rewards in the presence of a familiar odor. Specifically we wanted to determine whether the intake of saccharin or quinine, administered through the artificial nipple, increases in the presence of the familiar odor. Results showed that 3-hour-old rats differentially respond to two different concentrations of saccharin and two concentrations of quinine. In the presence of the pre-exposed odor newborn rats increased intake and grasp responses to the artificial nipple containing quinine. This effect disappeared with a higher concentration of quinine. These results suggest that the pre-exposed odor generated a change in the hedonic value of the aversive reward.

Ontogeny of consummatory successive negative contrast in rats.

Consummatory successive negative contrast (cSNC) occurs when organisms repeatedly exposed to a high-magnitude reward are suddenly given a low-magnitude reward. This results in a significant reduction in the consumption of the devalued reinforcer, at a level even below that of a group which had been always exposed to the low-magnitude reinforcer. A scarcity of animal studies assessed the expression of this phenomenon during early development. Three experiments assessed age of cSNC onset in preweanling rats. Percent body weight gained (%BWG) and taste reactions associated with reinforcement devaluation were measured. A reduction in %BWG and a significant increase in emission of aversive hedonic behaviors, indicative of cSNC, occurred on postnatal day 18 (PD 18; Experiments 1 and 2), but not on PD 14 or PD 17 (Experiments 3a and 3b). The neurobiological mechanisms underlying these effects and theoretical implications are discussed.

Efecto de contraste sucesivo negativo en la valoración emocional de imágenes / Successive negative contrast effect on the emotional evaluation of images

Se presentan dos experimentos para estudiar el efecto de la reducción del valor de incentivo sobre las respuestas de tiempo de observación y valoración de la emocionalidad de las imágenes, mediante una escala Likert. En ambos estudios un grupo de sujetos observó una serie de fotografías del Sistema Internacional de Imagen Afectiva (International Affective Picture System; IAPS) clasificadas como placenteras de alta activación (fase de precambio) y luego, placenteras de baja activación (fase de postcambio, Grupo Experimental, GE). Otro grupo observó en ambas fases solamente las imágenes placenteras de baja activación (Grupo Control, GC). No hubo efectos en el tiempo de observación de las imágenes pero sí en su valoración emocional. Durante la fase de post-cambio el GE evaluó las imágenes de baja activación como menos emocionales que el GC. El Experimento 2 replica el resultado cuando se interpone una tarea distractora entre cada ensayo de presentación de las imágenes. Estos resultados indican que la valoración afectiva de las imágenes está modulada por efectos de contraste negativo y que su mecanismo es de origen central (AU)

Two experiments were presented in which the International Affective Picture System (IAPS) was used to study the effect of the incentive value downshift upon the observation time and emotional valuation responses in humans. One group observed pleasant slides of high arousal (pre-shift phase) and then pleasant slides of low arousal (post-shift phase, Experimental Group, GE). The Control Group (GC) observed pleasant slides of low arousal in both phases. There was not an effect on the observation time measure, but a successive negative contrast (SNC) effect was found in the emotional valuation measure. During the post-shift phase, the GE evaluated the slides as less emotional than the GC. These results indicate that the affective evaluation of the images is modulated by negative contrast effect (AU)

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.

Discriminación ee sabores en procedimientos de ambios sorpresivos del reforzaddor durante la temprana ontogenia de a rata / Tastediscriminattion during the earlyontogeny of the rat in procedurres involving surprising changes in reinforcement

Este estudio evaluó la respuesta consumatoria de ratas infantes ante diferentes magnitudes de soluciones azucaradas y luego de su devaluación o extinción, con el objetivo de detectar la preferencia de las soluciones y la existencia de efectos de contraste y de magnitud del reforzamiento en la extinción. En el Experimento 1 se expuso ratas de 8-10 días postnatales (DPN) a diferentes concentraciones de sacarosa (12%, 10%, 5% ó 2%; fase de precambio) a las que se las devaluó al 2% (fase de postcambio). En el Experimento 2, dos grupos de 10-14 DPN recibieron soluciones al 12% ó 2% en la fase de precambio y 2% en la de postcambio. En ambos experimentos se observó que, durante la primera fase, el grupo 12% exhibió un mayor porcentaje de ganancia de peso que los demás grupos, pero no hubo diferencias entre los grupos en la fase de post-cambio. En el Experimento 3 se evaluó el efecto de magnitud del refuerzo en la extinción en ratas de 7-12 DPN, utilizando agua en la segunda fase. Se halló un efecto de magnitud del refuerzo en la adquisición, sin embargo, no hubo diferencias entre grupos en la segunda fase. En el Experimento 4 se utilizó un procedimiento de contraste anticipatorio (CA) con ratas de 10-16 DPN. Los animales exhibieron nuevamente un efecto de magnitud del refuerzo pero no se observó CA. Estos resultados indican que: (a) al menos desde los 8 DPN las ratas discriminan diferentes concentraciones de sacarosa y que prefieren la del 12%, y que (b) hasta la segunda semana de vida los animales consumen los reforzadores en función de su valores absolutos. Los resultados se discuten en términos de la ontogenia del aprendizaje de los efectos paradójicos del reforzamiento y su vinculación con la teoría de Amsel.

This study evaluated consummatory responses in infant rats exposed to different magnitude of reward, and after the devaluation (i.e., consummatory successive negative contrast) or omission (i.e., extinction) of reward. In Experiment 1, 8-10 post-natal days (PND) pups were intraorally infused with 12%, 10%, 5% or 2% sucrose (preshift phase, 2 daily trials). Subsequently, all groups received 2% sucrose (postshift phase). In Experiment 2, 10-14 day-old pups received 12% or 2% sucrose in 4 daily trials in the preshift phase, followed by 2% in a postshift trial. Both experiments indicated that during preshift, animals exposed to 12% sucrose exhibited higher sucrose consumption than those receiving lower concentration solutions. This phenomenon, indicative of a magnitude of reinforcement effect was not accompanied by evidence of successive negative contrast. In Experiment 3 we evaluated the magnitude of reinforcement extinction effect in 7-12 PND rats. Animals received 12% sucrose or water in preshift phase and both groups received a neutral solution (i.e., water) in the second phase. A magnitude of reinforcement acquisition effect was again observed, yet there were no differences between groups in extinction phase. In Experiment 4 we used an anticipatory contrast procedure in 10-16 PND pups. A magnitude of reinforcement, but not an anticipatory contrast effect was observed. Overall the results indicate that: (a) rats from - at least- 8 PND discriminate between different concentrations of sucrose, and (b) until the second week of life the response to rewards is mainly regulated by their absolute value and not by their relative value. Results are discussed terms of the ontogeny of paradoxical effects of reward and its relationship to Amsel's theory.

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.

Correlación entre miedo incondicionado y la primera reacción a la disminución y extinción de un reforzador apetitivo / Correlation between Unconditional Fear and the First Reaction to the Decline and Extinction of an Appetitive Reinforcer

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).

When rats have access to a 32% sucrose solution and the concentration is decreased to 4%, the animals drink less than those that were always exposed to the 4% solution. This phenomenon is called consummatory Successive Negative Contrast (cSNC) and is considered an animal model of frustration. Existing evidence shows that in a light-dark test, rats prefer to stay in the dark compartment, which suggests an unconditioned fear response to illuminated places. Two experiments were conducted in which the preference of rats in a light-dark test was assessed during a cSNC (Experiment 1) and during a Consummatory Extinction (Ec, access to an empty water tube, Experiment 2) in order to assess the correlation between the first reaction to the devaluation or to the omission of reinforcers with unconditioned fear responses to dark places. Results showed that the rats that spent more time in the dark place spent less time in contact with the water tube during the first reinforcer-devaluation trial (Experiment 1) and during the first minute of the first Ec trial (Experiment 2). The relation of these results and Amsel (1958), Gray (1987), and Flaherty's theories is discussed.

Efectos del aislamiento en la adultez sobre el dolor y la frustración / Effects of isolation on adulthood on pain and frustration

Los animales que viven aislados en la adultez presentan indicadores conductuales de estrés crónico, ansiedad e hipoalgesia. Si bien existe una amplia gama de tratamientos que evidencian las relaciones entre la frustración, el dolor y la ansiedad, pocos trabajos estudiaron el efecto que podría tener el aislamiento en la adultez sobre las respuestas de los animales ante la devaluación de incentivos. Se evaluaron ratas aisladas (Aislados) y agrupadas (Agrupados) a partir de los 60 días de edad en la sensibilidad al dolor con la prueba de la placa térmica (PT) y en el efecto de reforzamiento parcial sobre el contraste sucesivo negativo consumatorio (ERP-CSNc). En el ERP-CSNc dos grupos de animales (Aislados y Agrupados) recibieron una fase de precambio con ensayos bajo un Programa de reforzamiento continuo (RC, consumo de 32% de solución azucarada) y otros dos grupos (Aislados y Agrupados) en uno de reforzamiento parcial (RP, 50% reforzados con 32% de solución azucarada y 50% no reforzados). En la fase de postcambio los cuatro grupos recibieron soluciones de sacarosa al 4%. Se midió el tiempo que el animal permanecía en contacto con el bebedero (TB). Las ratas aisladas mostraron hipoalgesia en la PT. En el ERP-CSNc, tanto las ratas aisladas como las agrupadas entrenadas en RP mostraron el mismo grado de mayor persistencia de TB durante la fase de postcambio, respecto de los entrenados bajo RC. Estos resultados se discuten en función de trabajos previos y de los posibles mecanismos implicados (AU)

Animals isolated in adulthood present behavioral indicators of chronic stress, anxiety and hypoalgesia. While there is a wide range of treatments that demonstrate the relationship between frustration, pain and anxiety, there are few studies of the effect of isolation in adulthood on the devaluation of incentives. Isolated (ISO) and grouped (Group) rats from 60 days of age were evaluated on the hot plate test (HP) and the effect of partial reinforcement on consummatory successive negative contrast (ERP-cSNC). In the ERPcSNC, two groups of animals (ISO- Group) were given a preshift phase under a continuous reinforcement schedule (CR, 32% consumption of sugar solution) and two other groups (ISO- Group), under a partial reinforcement schedule (PR, 50% reinforced and unreinforced 32%); in postshift phase all groups received a 4% solution. Goal tracking time was measured. ISO rats showed hypoalgesia in HP. In the ERP-CSNC, both ISO and Group rats trained in PR showed greater persistence of goal tracking time during the postshift phase. These results are discussed considering previous research and the possible mechanisms involved (AU)

Psicofísica comparada: Efectos de la pérdida de incentivos en ratas normales e inyectadas con etanol / Comparative Psychophysic: Loss of incentive effects in normal rats injected with ethanol

Un problema de la Psicofísica particularmente relevante para el estudio de procesos de condicionamiento es el de la relación entre las propiedades de refuerzo y físicas de los es tímulos. Papini y Pellegrini (2006) observaron que el nivel de respuestas de consumo en ratas expuestas a una disminución sor presiva en la con centración de soluciones azucaradas resulta similar, si la razón de cambio de las soluciones (concentración post-cambio / pre-cambio) es la misma. Por ejemplo, una disminución de 32 a 4% y una de 16 a 2% produjeron niveles de consumo similares. Estos resultados son acordes a la Ley de Weber y podrían implicar el desarrollo de procesos emocionales; algo que se ha establecido mediante el estudio de drogas ansiolíticas. En situaciones experimentales análogas en las que se estudió el efecto de contraste negativo de incentivo (con una disminución de 32 a 4%) se demostró que la administración de etanol en el segundo ensayo post-cambio produce una recuperación más rápida de las respuestas deprimidas debido a una disminución del refuerzo (Becker & Flaherty, 1982), en comparación con controles que recibieron salina. En el presente trabajo se informa un experimento que involucró ocho grupos de ratas y que buscó replicar ambos fenómenos así como estudiar sus posibles interacciones. Se hallaron resultados compatibles con los datos previos, pero no se pudo concluir si el etanol afecta de manera determinante los niveles de respuesta proporcionales observados durante disminuciones de incentivo. Los resultados se discuten en términos de su implicancia para el estudio de la Psicofísica Comparada.

A psychophysical problem that might be of particular interest in current research on conditioning phenomena, and that exceeds the area of sensation and perception, concerns the reinforcing properties of stimuli and their relationships to the physical measures of the stimuli. Stimuli acting as reinforcers are operationally defined as those which have the property of changing the probability of response output of an organism if they are presented in an ordered fashion in relation to other stimuli or responses. From a biopsychological point of view the scale in which this property is measured is referred to as the stimulus incentive value. Papini and Pellegrini (2006) observed that the level of consummatory responses in rats exposed to surprising reductions in sucrose concentrations is similar if the shift ratio of the solutions (preshift / postshift concentration) is the same. For example, a 32 to 4% downshift and a 16 to 2% downshift produced similar levels of consummatory responding. Pellegrini and Papini (2007) and Pellegrini, Lopez Seal, and Papini (2008) extended this observations to measures of anticipatory behaviours of rats in studies implementing runway, autoshaping, solid food and within subjects design. These results are in agreement with the Weber´s Law. The incentive downshift situations as observed in spaced-trials conditions are interesting in psychological terms because they might imply the development of emotional processes (Amsel, 1992; Flaherty, 1996; Papini, 2002, 2003). Therefore, the aforementioned proportionality in incentive downshift situations might also imply proportional emotional responses. The evidence favoring an emotional interpretation of behavioral regulation during incentive downshifts arise mostly from studies which used drugs with anxiolitic-like effects (for example, clordiazepoxide and ethanol). For example, in similar experimental conditions it has been shown that the administration of ethanol before the second postshift trial reduces the level of response depression due to incentive downshifts (Becker & Flaherty, 1982). Here we present one experiment with eight groups of rats designed to replicate both of these findings and to study their potential interactions. Groups differed in the concentration of preshift sucrose solutions (either 32 or 16%) and postshift solution (16, 8, 4 or 2%), which implied two different downshift ratios (.125 and .25); and in the drug condition [vehicle (S), or an ip. injection of .75g/kg ethanol (E) administered 10 min. before the second postshift trial]. In short, the eight groups were labeled as follows: 32-8S, 32-8E, 32-4S, 32-4E, 16-4S, 16-4E, 16-2S, and 16-2E. Results are in agreement with previous data, indicating, first, a strong significant effect of downshift ratio F(1, 34) = 19,15, p < .0001; and second, a small but significant effect of ethanol administration on the recovery from incentive downshift F(1, 34) = 5,09, p < .031. However, these results are not conclusive regarding the possibility that ethanol administration can modify the proportionality observed in consummatory responding in incentive downshift situations. Also important is the observation that the 32-4 and 16-4 conditions differed respecting its postshift consummatory performance (32-4 < 16-4); the difference was significant [F(1, 18) = 6,71; p < .018] and is interpreted as a special case of the successive negative incentive contrast effect. In his classic writings on Adaptation Level Theory, Helson (1964, pp. 448-449), argued that "The evidence shows that reinforcing agents behave like psychophysical stimuli being scalable on continua having neutral or indifferent regions and in being subject to both series and anchor effects". Present results are in agreement with this statement and their implications for studies on Comparative Psychophysics are discussed. It is suggested that further research with alternative anxiolitic drugs and experimental designs might be of interest.

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.