Relations between acetylcholine release and electrophysiological characteristics of theta rhythm: a microdialysis study in the urethane-anesthetized rat hippocampus.
In urethane-anesthetized rats, recording electrodes were implanted in the left dorsal hippocampus and a dialysis probe was placed in the contralateral dorsal or ventral hippocampus. Samples of extracellular acetylcholine (ACh) levels were assessed at 10-min intervals over a period of 30 min using microdialysis with high-performance liquid chromatography with electrochemical detection. EEG was recorded during the same period and amplitude, frequency, and duration of theta rhythm were calculated for each of the three 10-min intervals. Data were analyzed using the two-tailed Spearman rank-order correlation test. A positive and high rank correlation coefficient (rho = 0.90, p < 0.01, n = 8) was seen between the average ACh outflow in the dorsal hippocampus and the average theta amplitude, both being calculated for the entire collection period. A lower but statistically significant positive correlation (rho = 0.59, p < 0.01) between dorsal hippocampus ACh output and theta amplitude was also found when the couples of values collected for the 30-min period were pooled (n = 20). In contrast, frequency and duration of theta were not significantly correlated with dorsal hippocampus ACh release. Also, no statistically significant correlation (p > 0.05) was found between ACh output in the ventral hippocampus and theta parameters. Because changes in hippocampal ACh outflow are believed to be the reflection of changes in number and/or level of activity of cholinergic afferents to the dorsal hippocampus, our present findings support the view that, at least in the dorsal hippocampus of the urethane-anesthetized rat, the septohippocampal cholinergic projection regulates the theta amplitude but not frequency. Finally, the possibility that ACh outflow increase and tonic release in the hippocampus is not a sufficient condition to induce and maintain theta in the urethane-anesthetized rat is discussed.
Monmaur
P
P
Laboratoire de Psychopharmacologie et Processus Cognitifs, Université Paris VII, France.
Collet
A
A
Puma
C
C
Frankel-Kohn
L
L
Sharif
A
A
D000109:Acetylcholine / Q000378:metabolism*; D000758:Anesthesia; D000818:Animals; D004569:Electroencephalography; D004594:Electrophysiology; D006624:Hippocampus / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D051381:Rats; D017208:Rats, Wistar; D013826:Theta Rhythm; D014520:Urethane
D014520:Urethane; D000109:Acetylcholine