Abstract
Head direction
(HD) cells have been speculated to be part of a network mediating navigational
behavior. Previous work has shown that combined administration of serotonergic
and muscarinic antagonists eliminates hippocampal theta activity and produces
navigational deficits more severe than blockade of either neurotransmitter
system alone. The authors sought to assess this effect on the directional
characteristics of HD cells. HD cells were recorded from the anterior dorsal
thalamus of Long-Evans rats before and after administration of the serotonergic
antagonist methiothepin, the muscarinic antagonist scopolamine, both drugs, or
saline. Combined drug administration produced HD cells with preferred directions
that drifted within recording sessions. In addition, cells showed shifts in the
preferred directions at the start of a session relative to the position of the
major landmarks, suggesting that combined drug administration led to deficits in
landmark control of the HD system. Single drug exposures to methiothepin or
scopolamine did not noticeably affect the directional characteristics of HD
cells. This finding that navigation-impairing drugs can disrupt the HD signal
provides further evidence that this network plays an important role in
navigational behavior.