title: Validation and scopolamine-reversal of latent learning in the water maze utilizing a revised direct platform placement procedure.
abstract: The Morris water maze is routinely used to explore neurobiological mechanisms of working memory. Humans can often acquire working memory relevant to performing a task by mere sensory observation, without having to actually perform the task followed by reinforcement. This can be modeled in the water maze through direct placement of a rat on the escape platform so that it can observe the location, and then assessing the subject's performance in swimming back to the platform. However, direct placement procedures have hardly been studied for two decades, reflecting a controversy about whether direct placement resulted in sufficiently rapid and direct swims back to the platform. In the present study, utilizing revised training methods, a more comprehensive measure of trajectory directness, a more rigorous sham-trained control procedure and an optimal placement-test interval, rats swam almost directly back to the platform in under 4s, significantly more quickly and directly than sham-trained subjects. Muscarinic cholinergic mechanisms, which are inactivated by scopolamine, are essential to memory for standard learning paradigms in the water maze. This experiment determined whether this would also be true for latent learning. ANOVA revealed significant negative effects of scopolamine on both speed and accuracy of trajectory, as well as significant positive effects of direct placement training vs. sham-training. In a probe trial, placement-trained animals without scopolamine spent significantly more time and path length in the target quadrant than trained rats with scopolamine and sham-trained rats without scopolamine. Scopolamine impairments are likely due to effects on memory, since the same dose had little effect on performance with a visible platform. The revised direct placement model offers a means of further comparing the neural mechanisms of latent learning with those of standard instrumental learning.
authors.affiliation: University of Houston-Clear Lake, Houston, TX 77058, USA. Electronic address: malin@uhcl.edu.
authors.forename: David H
authors.initials: DH
authors.lastname: Malin
authors.affiliation: University of Houston-Clear Lake, Houston, TX 77058, USA.
authors.forename: Krystal L
authors.initials: KL
authors.lastname: Schaar
authors.affiliation: University of Houston-Clear Lake, Houston, TX 77058, USA.
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Izygon
authors.affiliation: University of Houston-Clear Lake, Houston, TX 77058, USA.
authors.forename: Duyen M
authors.initials: DM
authors.lastname: Nghiem
authors.affiliation: University of Houston-Clear Lake, Houston, TX 77058, USA.
authors.forename: Sikirat Y
authors.initials: SY
authors.lastname: Jabitta
authors.affiliation: University of Houston-Clear Lake, Houston, TX 77058, USA.
authors.forename: Mallori M
authors.initials: MM
authors.lastname: Henceroth
authors.affiliation: University of Houston-Clear Lake, Houston, TX 77058, USA.
authors.forename: Yu-Hsuan
authors.initials: YH
authors.lastname: Chang
authors.affiliation: University of Houston-Clear Lake, Houston, TX 77058, USA.
authors.forename: Jenny M
authors.initials: JM
authors.lastname: Daggett
authors.affiliation: University of Houston-Clear Lake, Houston, TX 77058, USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Ward
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D008297:Male; D018782:Maze Learning / Q000187:drug effects*; D008570:Memory, Short-Term / Q000187:drug effects; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D011597:Psychomotor Performance / Q000187:drug effects; D051381:Rats; D020318:Rats, Long-Evans; D015203:Reproducibility of Results; D012601:Scopolamine / Q000494:pharmacology*; D013550:Swimming
chemical_list: D018727:Muscarinic Antagonists; D012601:Scopolamine
keywords: Direct placement; Latent learning; Muscarinic; Rat; Scopolamine; Water maze; Working memory