Abstract
The ability of an animal to navigate its environment remains one of the most critical elements of survival. Head direction (HD) cells, abundantly found in various rat brain regions, are thought to play a key role in spatial orientation and navigation. This study examined the effect of bilateral reversible inactivation of the dorsal tegmental nucleus (DTN), a structure critical to the functioning of the HD cell network, on performance on the Morris Water Maze (MWM) task. Female rats that had received surgical implantation of bilateral cannulas into DTN, along with an unoperated group, were trained across four days to locate a hidden platform in a pool of opaque water. On the fifth (test) day, implanted rats either received an infusion of muscimol or saline, and (along with the nonsurgical group) were tested on their ability to locate the hidden platform. Surprisingly, no significant effect of muscimol infusion was found on the time to locate the platform on test day, although a no-platform probe trial provided evidence that DTN inactivation increased the use of a nonspatial strategy for finding the platform. While these findings suggest that adaptive strategies may somewhat mitigate the effect of DTN inactivation on performance in the MWM, the overall weak effect that was found casts doubt on the effectiveness of muscimol infusion into DTN as a method of inactivating the HD system, either because of the limitations inherent in the technique, an absence of endogenous binding sites for muscimol in the structure, DTN not being necessary for the task, or the existence of functional redundancy in the HD network.