Frequency modulation of neuronal theta-bursts in rabbit's septum by low-frequency repetitive stimulation of the afferent pathways.
Activity of the neurons with stable theta-bursts was recorded extracellularly in intact and hippocampectomized septum of unanesthetized chronic rabbits during low-frequency (3-17 Hz) stimulation of horizontal limb of diagonal band or lateral septal nucleus. The stimulation rarely evoked standard oligosynaptic single-spike responses in stable theta-bursting units. Instead, gradual entrainment and phase-locking of the spontaneous theta-cycles occurred. Two types of entrainment were observed: "entrainment by the pause", where interburst interval was reset by the stimuli; and "entrainment by the burst", where bursts were time-locked to the stimuli. Such reorganization of the spontaneous bursts occurred in the narrow frequency range of stimulation (from 4 Hz up to 9-12 Hz), with the best resonance following in the range of "basic" theta frequencies of the awake rabbit (5-6 Hz). With stimulation beyond the theta-range three phenomena occurred: shift of the burst frequencies to higher or lower harmonics of stimulation frequencies; complex interactions of basic background frequency with rhythm of stimulation ("beating"); return to background theta-burst frequency in spite of continuing stimulation ("escape"). The properties of the septal theta-bursting cells as presumable intrinsic bursting pacemakers are discussed.
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001931:Brain Mapping; D002682:Chinchilla; D004558:Electric Stimulation; D004569:Electroencephalography; D006624:Hippocampus / Q000502:physiology; D008474:Medial Forebrain Bundle / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012686:Septal Nuclei / Q000502:physiology; D012688:Septum Pellucidum / Q000502:physiology*; D013826:Theta Rhythm