The effects of neocortical ectopias on Lashley III water maze learning in New Zealand Black mice.

Approximately 50% of New Zealand Black (NZB) mice ectopic NZB mice demonstrated learning impairments in have neocortical ectopias, which are misplaced clusters of the Lashley maze when compared to non-ectopic controls. neurons located in layer I of cortex [17,18]. Previous We used a water version of the Lashley III maze that experiments have found that ectopias in NZB mice were can be learned by the use of extra-maze cues or by related to differences in learning [5,15]. This has been memorizing the chain of correct left and right turns [7]. A shown to be the case for BXSB/MpJ mice as well [1– total of 38 NZB/BINJ (21 male and 17 female) mice were 4,6,9–11,19]. Specifically, left-pawed ectopic NZB mice given six trials per day (three trials in the morning and learned a simple water escape task better than leftand three in the afternoon, separated by at least 4 h) for 5 days right-pawed non-ectopics, that, in turn, learned better than [9]. The inter-trial interval for the three trials was |10 min. right-pawed ectopics [5]. In addition, NZB ectopics were A learning index (number of correct entries divided by less active in a small activity chamber, escaped faster in a total number of entries) was calculated and the number of non-spatial water T-maze, and were poorer in several forward, forward T-choice, forward cul-de-sac entry, and measures of spatial Morris maze learning [15]. backward errors were counted. Mice were transcardially Another learning task in which NZB mice have been perfused with physiological saline and 10% formalin, and tested is the Lashley III water maze [7]. This is a relatively their brains were examined for the presence of neocortical complex maze, containing cul-de-sacs that the animal has ectopias. to learn to avoid, and T-choices where the animal has to Of the 38 mice, 19 (50%) were non-ectopic and 19 learn to make the correct left or right turn. The mice are (50%) were non-ectopic. Table 1 shows the Lashley maze given two widely spaced trials per day over several days. learning measures for the two groups. Ectopics had lower However, NZB mice, regardless of ectopia status, were learning index scores, made more forward errors, made reported to be poor learners in the Lashley maze, even with more forward cul-de-sac entries, and tended to make more extra training trials [14], making learning comparisons backward errors, than non-ectopics (F’s(1,36)55.82, 4.87, between ectopic and non-ectopic mice meaningless. ReTable 1 cently, however, we have been able to obtain proficient Lashley III water maze behavioral means6S.E. for ectopic and nonLashley maze learning in NZB mice by giving the mice ectopic NZB mice extra training trials spaced more closely in time [9]. This Measure Ectopic Non-ectopic enabled us to compare NZB ectopics to non-ectopics in (n519) (n519) Lashley maze learning. In the present study, we found that Learning index 0.4760.01 0.5360.01*