GABAB receptor blockade enhances theta and gamma rhythms in the hippocampus of behaving rats

Hippocampus - Tập 17 Số 4 - Trang 281-291 - 2007
L. Stan Leung1, Bixia Shen
1Department of Physiology-Pharmacology, University of Western Ontario, London, Ontario, Canada. [email protected]

Tóm tắt

AbstractThe participation of GABAB receptors in hippocampal EEG generation was studied by intracerebroventricular (icv) and intracerebral infusions of GABAB receptor antagonist p‐(3‐aminopropyl)‐p‐diethoxymethyl‐phosphinic acid (CGP35348) in freely behaving rats. During awake‐immobility, icv CGP35348 induced a theta rhythm and increased gamma waves (30–100 Hz) in the hippocampus. The immobility theta peaked at 6–7 Hz and had a theta phase in CA1 stratum radiatum of ∼160° with reference to the theta at the alveus, when compared with ∼130° during walking. Immobility theta power peaks at 6–7 Hz was also found in normal rats, and it was detected in 27% of the EEG segments during immobility. Incidence of immobility theta increased to 87.5% after 480 nmol of CGP35348 icv. Muscarinic antagonist scopolamine (5 mg/kg, ip) suppressed the induction of immobility theta and the gamma power increase after icv CGP35348. CGP35348 icv did not significantly change the hippocampal theta power at 7–8 Hz during walking (theta fundamental), but it increased power at 12–15 Hz, at the second harmonic of theta. CGP35348 icv also increased 30–50 Hz gamma power during walking. Medial septal infusion of CGP35348 (12 nmol in 0.4 μl) increased the power and the frequency of the hippocampal theta second harmonic during walking, but did not increase gamma activity. Infusion of CGP35348 (8 nmol in 0.4 μl) in the hippocampus increased the local gamma activity at 30–100 Hz, but did not induce immobility theta or affect the walking theta rhythm. In conclusion, icv GABAB receptor blockade increased an atropine‐sensitive input that generated an immobility theta rhythm, while GABAB receptor blockade of the medial septum increased atropine‐resistant theta harmonics possibly generated by apical dendritic spikes. GABAB receptor blockade may enhance cognitive task performance by activating hippocampal theta and gamma rhythms in behaving rats. © 2007 Wiley‐Liss, Inc.

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Hippocampus

Tập 17 Số 4

281-291

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