Fluctuations in spontaneous discharge of hippocampal theta cells during sleep-waking states and PCPA-induced insomnia.
1. The spontaneous activity of hippocampal theta cells in head-restrained cats was recorded during slow-wave sleep (SWS), paradoxical sleep (PS), and the attentive state of bird watching (BW). We also recorded theta cell activity during a state of insomnia with pontogeniculoocipital (PGO) waves, which was induced by the administration of p-chlorophenylalanine (PCPA), a selective inhibitor of serotonin synthesis. 2. The time-dependent structure of fluctuations in theta cell activity was evaluated by power spectral analysis and Markovian analysis. The coefficient of variation for these time series was used as a measure of the variability of theta cell activity, which indicates the relative amplitude of fluctuations. 3. During SWS, theta cell activity showed a larger variability and a flat spectrum, i.e., low Markovian properties. During PS, this activity exhibited smaller variability and high spectral density in a low-frequency band (0.01-1.0 Hz), i.e., high Markovian properties. During BW, variability, spectral and Markovian properties were intermediate. 4. The firing pattern of theta cells during PCPA-induced insomnia was similar to that during PS. However, after the administration of either a serotonin agonist, 5-Methoxy-N,N-dimethyltryptamine, or a choline antagonist, atropine sulfate, theta cell activity no longer exhibited PS-like fluctuations, revealing instead a firing pattern similar to that during SWS. 5. During PS and PCPA-induced insomnia, not only the unit activity of theta cells, but PGO activity and theta wave frequency exhibited slow fluctuations, i.e., the high spectral density in the low-frequency band (0.01-1.0 Hz). 6. Cross-correlation analyses were performed between the fluctuations in theta cell activity, theta wave frequency, and PGO activity. These fluctuations correlated with each other during both PS and PCPA-induced insomnia. Bursts of PGO waves especially contributed to these cross-correlations. 7. These results suggest, first, that the slow fluctuations of the theta cell activity during PS and PCPA-induced insomnia is the physiological expression of the removal of aminergic influences and, secondly, that they are dependent on cholinergic mechanisms, including PGO generators.
Mushiake
H
H
Department of Neurophysiology, Tohoku University, School of Medicine, Sendai, Japan.
Kodama
T
T
Shima
K
K
Yamamoto
M
M
Nakahama
H
H
D000200:Action Potentials; D000818:Animals; D002415:Cats; D004569:Electroencephalography; D010134:Fenclonine; D005829:Geniculate Bodies / Q000502:physiology; D006624:Hippocampus / Q000502:physiology* / Q000503:physiopathology; D011149:Pons / Q000502:physiology; D012890:Sleep / Q000502:physiology*; D007319:Sleep Initiation and Maintenance Disorders / Q000139:chemically induced / Q000503:physiopathology*; D014851:Wakefulness / Q000502:physiology*
D010134:Fenclonine