Instability of dentate gyrus field potentials in awake and anesthetized rats.
Adult male Long-Evans rats were prepared with stimulating and recording electrodes in the perforant path and dentate gyrus, respectively. Urethane-anesthetized acute (ACU) preparations and chronically-implanted freely-moving (CHR) animals received moderate-intensity (50-75% of maximum) stimulation pulses every 15-20 s for 4-5 hr in order to assess the stability of evoked field potentials. Significant increases in both population spike amplitude (+6.3%/hr) and EPSP slope (+2.5%/hr) were seen over the course of testing in the ACU group as a whole, while the CHR group showed significant decreases in EPSP slope (-3.3%/hr) but not spike (-1.2%/hr). Thus, both preparations were unstable, though the group mean drift differed in direction. Field potential drift was also affected by body temperature and stimulation intensity; drift was significantly greater when temperature was not controlled, and responses to moderate-intensity stimulation tended to be less stable than responses to high-intensity pulses. Our results indicate that a drift of 4-6% per hour in individual subjects is common; in unheated acute preparations, drift can equal or exceed 20% per hour (3/7 cases). These findings show that response instability can pose significant problems for electrophysiological investigations of neural plasticity.
Division of Life Sciences, University of Toronto, Scarborough, Ontario, Canada.
J T
JT
Rick
N W
NW
Milgram
D000777:Anesthetics; D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology; D018891:Dentate Gyrus / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D008297:Male; D019580:Perforant Pathway / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D014851:Wakefulness
D000777:Anesthetics