Instability of Dentate Gyrus Field Potentials in Awake and Anesthetized Rats

✍ Scribed by John Th. Rick; Norton W. Milgram

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 169 KB
• Volume: 9
• Category: Article
• ISSN: 1050-9631
• DOI: 10.1002/(sici)1098-1063(1999)9:3<333::aid-hipo12>3.0.co;2-2

✦ Synopsis

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. Hippo-