Changes in ensemble activity of hippocampus CA1 neurons induced by chronic morphine administration in freely behaving mice.
The hippocampus plays an important role in the formation of new memories and spatial navigation. Recently, growing evidence supports the view that it is also involved in addiction to opiates and other drugs. Theoretical and experimental studies suggest that hippocampal neural-network oscillations at specific frequencies and unit firing patterns reflect information of learning and memory encoding. Here, using multichannel recordings from the hippocampal CA1 area in behaving mice, we investigated the phase correlations between the theta (4-10 Hz) and gamma (40-100 Hz) oscillations, and the timing of spikes modulated by these oscillations. Local field potentials and single unit recordings in the CA1 area of mice receiving chronic morphine treatment revealed that the power of the theta rhythm was strongly increased; at the same time, the theta frequency during different behavioral states shifted markedly, and the characteristic coupling of theta and gamma oscillations was altered. Surprisingly, though the gamma oscillation frequency changed, the power of gamma lacking theta did not. Moreover, the timing of pyramidal cell spikes relative to the theta rhythm and the timing of interneuron spikes relative to the gamma rhythm changed during chronic morphine administration. Furthermore, these responses were impaired by a selective D1/D5 receptor antagonist intra-hippocampus injection. These results indicate that chronic morphine administration induced the changes of ensemble activity in the CA1 area, and these changes were dependent on local dopamine receptor activation.
Liu
F
F
Department of Neurobiology, Institute of Neuroscience, Zhejiang University School of Medicine, 388 Yu Hang Tang Road, Hangzhou 310058, PR China.
Jiang
H
H
Zhong
W
W
Wu
X
X
Luo
J
J
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D056547:CA1 Region, Hippocampal / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D004195:Disease Models, Animal; D004334:Drug Administration Schedule; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009020:Morphine / Q000008:administration & dosage*; D009415:Nerve Net / Q000502:physiology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology*; D011954:Receptors, Dopamine / Q000378:metabolism; D013826:Theta Rhythm / Q000187:drug effects / Q000502:physiology
D011954:Receptors, Dopamine; D009020:Morphine