RESUMO
Abstract Introduction: Adverse or favourable rearing conditions early in life affect emotional response during adolescence. To study the effect of early rearing on emotional response, animal models such as maternal separation (MS) and social enrichment (SE) by community nesting have been useful. However, the comparison of the effect of MS and SE on anxiety-related behaviours in adolescent rats is unknown. Objective: This study aimed to assess the effects of MS and SE on the emotional response of adolescent rats exposed to the elevated plus-maze test (EPM). Method: Pregnant Wistar rats were randomly distributed into three groups according to the rearing condition. In the MS group, pups were separated daily from their dams for 180 minutes, from postnatal day (P) 2 to 14. In the SE group, two females that gave birth synchronously were housed in a cage with a litter of eight pups. Females from control standard housing (SH) were individually housed and kept with their offspring until weaning (P23). On P32, anxiety-related measures were evaluated using an EPM. Results: MS and SE increase anxiety-related behaviours and locomotion in rats exposed to the EPM. SE had sex-dependent effects on anxiety-related measures, increasing vertical activity in females and horizontal activity in males. MS but not SE increased body weight gain in female rats. Conclusion: Adverse or favourable rearing conditions early in life may result in an increased anxiety phenotype in the EPM during adolescence. It is likely that the favourable effect of SE depends on the number of dams per communal nest.
Resumen Introducción: Las condiciones de crianza adversas o favorables en etapas tempranas de la vida afectan la respuesta emocional durante la adolescencia. Para estudiar el efecto de la crianza temprana sobre la respuesta emocional, han sido útiles modelos animales como la separación materna (SM) y el enriquecimiento social (ES) mediante anidamiento comunitario. Sin embargo, se desconoce la comparación del efecto de la SM y el ES sobre las conductas relacionadas con la ansiedad en ratas adolescentes. Objetivo: Este estudio pretende evaluar los efectos de la SM y el ES sobre la respuesta emocional de ratas adolescentes expuestas al test del laberinto en cruz elevado (EPM). Método: Las ratas Wistar preñadas se distribuyeron aleatoriamente en tres grupos según la condición de crianza. En el grupo SM, las crías fueron separadas diariamente de sus madres durante 180 minutos, desde el día postnatal (P) 2 hasta el 14. En el grupo ES, dos hembras que parieron de forma sincronizada se alojaron en una caja con una camada de ocho crías. Las hembras del alojamiento estándar de control (SH) se alojaron individualmente y se mantuvieron con sus crías hasta el destete (P23). En P32, se evaluaron las medidas relacionadas con la ansiedad mediante un EPM. Resultados: La SM y el ES aumentan las conductas relacionadas con la ansiedad y la locomoción en las ratas expuestas al EPM. El ES tuvo efectos dependientes del sexo en las medidas relacionadas con ansiedad, aumentando la actividad vertical en las hembras y la actividad horizontal en los machos. La SM, pero no el ES, incrementó la ganancia de peso corporal en las ratas hembra. Conclusiones: Condiciones de crianza adversas o favorables en etapas tempranas de la vida pueden dar lugar a un fenotipo de ansiedad aumentado en el EPM durante la adolescencia. Es probable que el efecto favorable del ES dependa del número de hembras por nido comunitario.
RESUMO
Despite step-down inhibitory avoidance procedures that have been widely implemented in rats and mice to study learning and emotion phenomena, performance of other species in these tasks has received less attention. The case of the Mongolian gerbil is of relevance considering the discrepancies in the parameters of the step-down protocols implemented, especially the wide range of foot-shock intensities (i.e., 0.4-4.0 mA), and the lack of information on long-term performance, extinction effects, and behavioral patterning during these tasks. Experiment 1 aimed to (a) characterize gerbils' acquisition, extinction, and steady-state performance during a multisession (i.e., extended) step-down protocol adapted for implementation in a commercially-available behavioral package (Video Fear Conditioning System-MED Associates Fairfax, VT, USA), and (b) compare gerbils' performance in this task with two shock intensities - 0.5 vs. 1.0 mA-considered in the low-to-mid range. Results indicated that the 1.0 mA protocol produced more reliable and clear evidence of avoidance learning, extinction, and reacquisition in terms of increments in freezing and on-platform time as well as suppression of platform descent. Experiment 2 aimed to (a) assess whether an alternate protocol consisting of a random delivery of foot shocks could replicate the effects of Experiment 1 and (b) characterize gerbils' exploratory behavior during the step-down task (jumping, digging, rearing, and probing). Random shocks did not reproduce the effects observed with the first protocol. The data also indicated that a change from random to response-dependent shocks affects (a) the length of each visit to the platform, but not the frequency of platform descends or freezing time, and (b) the patterns of exploratory behavior, namely, suppression of digging and rearing, as well as increments in probing and jumping. Overall, the study demonstrated the feasibility of the extended step-down protocol for studying steady performance, extinction, and reacquisition of avoidance behavior in gerbils, which could be easily implemented in a commercially available system. The observation that 1.0 mA shocks produced a clear and consistent avoidance behavior suggests that implementation of higher intensities is unnecessary for reproducing aversive-conditioning effects in this species. The observed patterning of freezing, platform descents, and exploratory responses produced by the change from random to periodic shocks may relate to the active defensive system of the gerbil. Of special interest is the probing behavior, which could be interpreted as risk assessment and has not been reported in other rodent species exposed to step-down and similar tasks.