Long‐term retention of spatial navigation by preweanling rats

Abstract

The present study was designed to examine retention of spatial information in the immature, Fischer-344N rat using a savings paradigm. Following training to locate a hidden platform using extramaze cues, preweanling animals (17 days of age) were immediately probed by testing in the tank with the platform removed. One week later, pups (26 days of age) were given an additional four training trials immediately followed by a second probe test to examine the animals' memory for the location of the platform. Animals that received initial training at 17 days of age demonstrated significant savings of information when tested after the retention interval. These data replicate our recent report of spatial navigation capabilities in the preweanling rat, and extend those findings by demonstrating that preweanling spatial navigation performance permits more rapid and accurate navigation following a 7-day retention interval after a "reinstatement" insufficient to produce accurate navigation in maturation controls.

Comparison of developmental trajectories for place and cued navigation in the morris water task

“…The point in development at which the ability to place navigate emerges has been a matter of debate in previous literature, with estimates ranging from 17 to 21 days of age (Brown & Kraemer, 1997;Brown & Whishaw, 2000;Carman et al, 2002;Carman & Mactutus, 2001;Kraemer & Randall, 1995;Rudy & Paylor, 1988;Rudy et al, 1987;Tonkiss et al, 1993). Because nearly all these studies utilized protocols consisting of multiple, consecutive days of training, however, it is difficult to determine the precise day in development at which place navigation was first observed, particularly because the critical probe trial that assesses spatial learning is typically not administered until after the completion of training.…”

“…Although some researchers (e.g. Carman et al, 2002;Carman & Mactutus, 2001) tend to identify the day in development at which spatial navigation emerges in terms of rats' ages at the onset of training, a more conservative approach is to restrict judgment of the initial emergence of spatial learning to the final day of training and/or the day a probe trial is given. Moreover, an even less ambiguous approach for identifying the precise day in development at which place learning emerges is to administer all training and test trials within a single day, as was done in the present study as well as one previous study (Brown & Whishaw, 2000), although this approach may entail certain disadvantages such as fatigue, hypothermia, or a retardation in acquisition rate that occurs with massed compared to spaced training (Commins, Cunningham, Harvey, & Walsh, 2003;Kraemer & Randall, 1995; but see Spreng, Rossier, & Schenk, 2002 for exception).…”

“…Although several water task studies report that place learning does not emerge until between postnatal day (P) 19 and 21 (Brown & Kraemer, 1997;Kraemer & Randall, 1995;Rudy & Paylor, 1988;Rudy et al, 1987;Tonkiss, Shultz, & Galler, 1993), others assert that such ability emerges as early as P17 (Carman, Booze, & Mactutus, 2002;Carman & Mactutus, 2001). Such disparities in the age that place learning is first observed may be due to different methodologies utilized by these studies, including differences in the temporal distribution of training trials (Kraemer & Randall, 1995), the size of the swimming pool (Carman & Mactutus, 2001), whether body temperature was maintained throughout training (Brown & Whishaw, 2000), and the saliency of the distal cue environment.…”

Early learning failure impairs adult learning in rats

“…This fact may have favored learning in the younger group, as can be seen in the last two trials. Spatial learning at this age has been reported employing a procedure adapted to the pups requirements, such as a reduced size of the pool (Carman & Mactutus, 2001;Carman et al, 2002). However, using the present behavioral procedure the differences in latencies to locate the platform between both age groups were evident.…”

“…A spaced learning procedure was applied for minimizing fatigue, as proposed by Kraemer and Randall (1995). However, as it has been shown that reducing the task requirements may allow spatial learning in preweanlings (Carman & Mactutus, 2001;Carman, Booze, & Mactutus, 2002), a large circular pool was used in order to increase the difficulty of the task. Each subject received 10 blocks of training, applied in two daily sessions, morning and afternoon, during 5 consecutive days.…”