Re-examining the ontogeny of the context-preexposure facilitation effect in the rat

PISANO, MARÍA VICTORIA; PAGLINI, GABRIELA; ARIAS GRANDÍO, CARLOS

Washington D.C.

Congreso; 44 TH Annual Meeting of the International Society for Developmental Psychobiology; 2011

International Society for Developmental Psychobiology

Capability to acquire context conditioning does not emerge until weaning, at least when the defining features of the context lack explicit and salient olfactory cues. According to recent studies the so-called context-preexposure facilitation effect (CPFE) is not observed until postnatal day 23 (PD23). In these studies the foot-shock intensity employed was relatively high (1.5 mA) and context conditioning was inferred exclusively from a single behavioral measure (percentage of freezing). In adult rats studies employing a less intense foot-shock (1 mA) showed evidences of contextual fear conditioning in the immediate-shock condition. The present study examined the CPFE on PD17 and PD23 by means of the analysis of multiple dependent variables, including fecal boli and an exhaustive ethogram of the behavioral repertoire of the rat. The experimental design was defined by three between-group factors: age (PD17 or PD23), preexposure (preexposed or non-preexposed) and foot-shock (0, 0.5 or 1.5 mA). In the present study we observed comparable levels of freezing than those reported by other authors using similar parameters. Additionally, the CPFE was limited to one dependent variable (freezing), and it was detected at both ages. However, evidences of fear were found in a number of dependent variables regardless the pre-exposure treatment. Interestingly, fear responses were expressed not only in the training context, but also they were generalized to an alternative environment. These results may have important implications for the analysis of the ontogeny of contextual fear conditioning