Emergence of an egocentric cue guiding and allocentric inferring strategy that mirrors hippocampal brain-derived neurotrophic factor (BDNF) expression in the Morris water maze

Abstract

From insects to humans, successful navigation relies on retained representations of spatial relations. These representations are thought to depend on the hippocampal formation, particularly those that are independent of the navigator (allocentric representations). The Morris water maze is a simple and popular task often used to assess spatial navigation. But how animals navigate toward and retain information regarding the location of the goal in this task remains unclear. We provide a comprehensive account of how the water maze is accomplished behaviourally. Our findings suggest that animals solve the task using distal cues via an initial view-matching strategy that is supported by egocentric guidance. Through increased training, however, an emergence of an egocentric-guiding strategy combined with the animal's greater ability to infer the hidden platform's location (via allocentric extrapolation) emerges. We also demonstrate that behavioural changes, towards a more allocentric strategy, are reflected in increases in hippocampal brain-derived neurotrophic factor.

Hippocampal contribution to vector model hypothesis during cue-dependent navigation

“…A repeated measures ANOVA showed an overall effect for Quadrant (F (3,18) ¼ 9.41, P , 0.001), with subsequent Bonferroni-corrected tests revealing that animals spent significantly more time in the NE quadrant (35.04 + 5.9%) compared to the SW (12.01 + 2.84%, P , 0.01) and SE quadrants (10.08 + 2.96%, P , 0.05). In contrast, the white bars in Figure 1C show that the Far CR group followed the cues and searched mainly in the SW quadrant, with a repeated measures ANOVA revealing an overall significant effect for Quadrant (F (3,18) Harvey et al 2008). Initially, both groups swam at the pool side in a thigmotaxic fashion that decreased with time.…”

“…Measures of retention included mean percentage time (of the 60 sec) spent swimming by groups in each of the four quadrants of the pool. While a 24-h retention test has been used by many research groups, we have traditionally found, over years of testing, the use a 7-d probe test to be a more robust measure of retention (e.g., Commins et al 2003;McGauran et al 2004;McGauran et al 2005;Harvey et al 2008). …”

“…These observed behaviors were analyzed for every training trial, under a number of categories including: percentage time spent (of total time in the pool) of each behavior, and the frequency of each behavior at individual locations in the maze (i.e., 0˚-360˚). Examples of such behaviors included thigmotaxis, direct movement, and turns toward and away from the cues (see Harvey et al 2008 for more details). Thigmotaxis was characterized by the animal moving almost exclusively at the periphery of the maze.…”

“…Turns within 67%-100% were in the "far" zones. The mean number and location of turns for each animal was then assessed (adapted from Harvey et al 2008).…”

BDNF controls object recognition memory reconsolidation

“…Brain-Derived Neurotrophic Factor (BDNF) is a member of the neurotrophin family of growth factors essential for synapse formation and maintenance (Cowansage, LeDoux, & Monfils, 2010;Panja & Bramham, 2014). In the rat hippocampus, BDNF mediates spatial and recognition memory formation (Francis et al, 2012;Furini et al, 2010;Harvey et al, 2008;Petzold, Psotta, Brigadski, Endres, & Lessmann, 2015;Silhol, Arancibia, Maurice, & Tapia-Arancibia, 2007) and is sufficient for reconsolidation of fear extinction . Thus, we wondered whether this neurotrophin also maintains the recognition memory trace upon reactivation.…”