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.

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.

Condicionamiento de lugar en ratas y etanol / Place conditioning in rats and ethanol

Uno de los procedimientos usados con animales no humanos para conocer el valor hedónicode las drogas es el condicionamiento de lugar (CL) en el cual se evalúa la preferencia oaversión hacia un contexto asociado previamente con una droga, inferido por el tiempode permanencia en ese lugar, en comparación con otro asociado a un vehículo (salina). Eneste trabajo informaremos sobre distintos aparatos, procedimientos, medidas dependientesutilizadas en el CL y los resultados principales hallados con el uso de etanol. Finalmentese presenta un experimento de CL con ratas en el cual se utilizó un diseño intra-intersujeto.Consistió en tres fases: (1) pre-test, preferencia de las ratas hacia dos contextos: lugarnegro (LN) y lugar blanco (LB); (2) condicionamiento, cada animal del grupo experimentalrecibió ensayos alternados de etanol (dosis 0.5 g/kg) asociados al contexto no preferidoy solución salina al preferido; los del grupo control, recibieron salina asociado a amboscontextos; (3) post-test igual al pre-test. En ambas pruebas se midió el tiempo de permanenciade las ratas en cada contexto. Los animales tratados con etanol revirtieron lapreferencia de lugar, mientras los del grupo salina no la modificaron. De este estudio seinfiere que bajo la dosis utilizada, el etanol tiene un valor hedónico positivo(AU)

One of the most common procedures used toassess the hedonic value of a drug is the conditioned place (CP) which explores thepreference or the aversion towards a previously drug paired context. In this paper wereport on the different apparatus, procedures and dependant measures used on CP and themain results found using ethanol. Finally we present a CP between-within subjects experimenton rats. The experiment consisted in three phases: (1) Pre-Test, we measured the animal’spreference towards both contexts black place (BP) and white place (WP); (2) Conditioning,each animal received ethanol (dose: 0.5g/kg, i.p.) paired with the non preferred contextand saline paired with the preferred context on alternate trials. A control group receivedvehicle in both contexts; (3) Post-Test same as pre-test. In both tests the time spent in eachcontext was measured. The ethanol treated group reversed its place preference, whereasthe saline group kept its initial preference. From this study we inferred that under thisdose, ethanol has a positive hedonic value(AU)