Physiological Properties of Neurons in Bat Entorhinal Cortex Exhibit an Inverse Gradient along the Dorsal-Ventral Axis Compared to Entorhinal Neurons in Rat.
Medial entorhinal cortex (MEC) grid cells exhibit firing fields spread across the environment on the vertices of a regular tessellating triangular grid. In rodents, the size of the firing fields and the spacing between the firing fields are topographically organized such that grid cells located more ventrally in MEC exhibit larger grid fields and larger grid-field spacing compared with grid cells located more dorsally. Previous experiments in brain slices from rodents have shown that several intrinsic cellular electrophysiological properties of stellate cells in layer II of MEC change systematically in neurons positioned along the dorsal-ventral axis of MEC, suggesting that these intrinsic cellular properties might control grid-field spacing. In the bat, grid cells in MEC display a functional topography in terms of grid-field spacing, similar to what has been reported in rodents. However, it is unclear whether neurons in bat MEC exhibit similar gradients of cellular physiological properties, which may serve as a conserved mechanism underlying grid-field spacing in mammals. To test whether entorhinal cortex (EC) neurons in rats and bats exhibit similar electrophysiological gradients, we performed whole-cell patch recordings along the dorsal-ventral axis of EC in bats. Surprisingly, our data demonstrate that the sag response properties and the resonance properties recorded in layer II neurons of entorhinal cortex in the Egyptian fruit bat demonstrate an inverse relationship along the dorsal-ventral axis compared with the rat.


CONCLUSIONS
As animals navigate, neurons in medial entorhinal cortex (MEC), termed grid cells, discharge at regular spatial intervals. In bats and rats, the spacing between the firing fields of grid cells changes systematically along the dorsal-ventral axis of MEC. It has been proposed that these changes could be generated by systematic differences in the intrinsic cellular physiology of neurons distributed along the dorsal-ventral axis of MEC. The results from our study show that key intrinsic physiological properties of neurons in entorhinal cortex of the bat and rat change in the opposite direction along the dorsal-ventral axis of entorhinal cortex, suggesting that these intrinsic physiological properties cannot account in the same way across species for the change in grid-field spacing shown along the dorsal-ventral axis.
Graduate Program for Neuroscience and james.heys@northwestern.edu hasselmo@bu.edu.
James G
JG
Heys
Graduate Program for Neuroscience and.
Christopher F
CF
Shay
Departments of Biology and.
Katrina M
KM
MacLeod
Kavli Institute for Systems Neuroscience & Centre for Neural Computation, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim 7491, Norway.
Menno P
MP
Witter
Psychology, University of Maryland, College Park, Maryland 20742, and.
Cynthia F
http://orcid.org/0000-0001-6916-0000
CF
Moss
Graduate Program for Neuroscience and Department of Psychological and Brain Sciences, Center for Systems Neuroscience, Boston University, Boston, Massachusetts 02215, james.heys@northwestern.edu hasselmo@bu.edu.
Michael E
ME
Hasselmo
D000818:Animals; D002685:Chiroptera; D018728:Entorhinal Cortex / Q000166:cytology / Q000502:physiology*; D005260:Female; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D009924:Organ Culture Techniques; D051381:Rats; D020318:Rats, Long-Evans; D013045:Species Specificity
entorhinal cortex; grid cell; h current