Cannabinoid agonist rescues learning and memory after a traumatic brain injury.

Traumatic brain injury can cause persistent challenges including problems with learning and memory. Previous studies suggest that the activation of the cannabinoid 1 receptor after a traumatic brain injury could be beneficial. We tested the hypothesis that posttraumatic brain injury administration of a cannabinoid 1 receptor agonist can rescue deficits in learning and memory. Young adult male rats were subjected to a moderately severe controlled cortical impact brain injury, with a subset given postinjury i.p. injections of a cannabinoid receptor agonist. Utilizing novel object recognition and the morris water task, we found that the brain-injured animals treated with the agonist showed a marked recovery.

Hierarchical use of cues in the missing object recognition task by rats (Rattus norvegicus).

This study investigated rats' preferences for using non-spatial and spatial cues in a missing-object recognition task. Rats were trained to find a sunflower seed under any one of four previously missing adjacent objects, the test array of a trial, after having found seeds under three of them in the 'study' array of that trial. On some trials the study and test arrays consisted of a different object at each baited food site and on other trials, of identical objects. A previously missing object's position and orientation within its array and its global position within the large foraging chamber varied over trials but not within trials. Following training, rats received interspersed non- or partially rewarded probe trials with transformed test arrays of dissociated non-spatial (object-specific) and spatial cues on test array feeders. Results from these probe trials revealed that rats preferred to search for a missing object based first on its specific non-spatial features before searching for it based on its local spatial features; that is, its local position followed by its orientation, and finally based on its global position. This hierarchical sequence for using spatial cues was preserved under the identical-objects cueing condition. Rats reversed their preferences between object-specific and local position cues, however, when novel objects replaced the same four different objects in a supplementary experiment. We discussed the implications of these findings in terms of the influence of ecological- and context-dependent factors on information use or retrieval from animals' visuo-spatial working memory.

Changing within-trial array location and target object position enhances rats' (Rattus norvegicus) missing object recognition accuracy.

Six rats were trained to find a previously missing target or 'jackpot' object in a square array of four identical or different objects (the test segment of a trial) after first visiting and collecting sunflower seeds from under the other three objects (the study segment of a trial). During training, objects' local positions within the array and their global positions within the larger foraging array were varied over trials but were not changed between segments within a trial. Following this training, rats were tested on their accuracy for finding the target object when a trial's test array was sometimes moved to a different location in the foraging arena or when the position of the target object within the test array had been changed. Either of these manipulations initially slightly reduced rats' accuracy for finding the missing object but then enhanced it. Relocating test arrays of identical objects enhanced rats' performance only after 10-min inter-segment intervals (ISIs). Relocating test arrays of different objects enhanced rats' performance only after 2-min ISIs. Rats also improved their performance when they encountered the target object in a new position in test arrays of different objects. This enhancement effect occurred after either 2- or 30-min ISIs. These findings suggest that rats separately retrieved a missing (target) object's spatial and non-spatial information when they were relevant but not when they were irrelevant in a trial. The enhancement effects provide evidence for rats' limited retrieval capacity in their visuo-spatial working memory.