Modulation of ACh turnover in the septal-hippocampal pathway by electrical stimulation and lesioning

The septal-hippocampal cholinergic pathway of the rat was either electrically stimulated or lesioned in order to study whether or not acetylcholine turnover rate (TRACh) changes with the activity of the cholinergic neurons. Appropriate electrical stimulation of the septum selectively increased the TRACh in the hippocampus in nonanesthetized and in barbiturate-treated animals. The ACh content of the hippocampus increased by approximately 30% 1 h after fimbria lesions, but decreased by about 80% 9 days after fimbria lesions. Acute fimbria lesions decreased the TRACh in the lesioned side by approximately 85%, but the TRACh in the intact side and in the cortex was unchanged. The same was true in rats with chronic fimbria lesions. In conclusion, the hippocampal TRACh increases or decreases proportionally to the activity of the cholinergic neurons; therefore the measurement of this parameter is of particular value in understanding how postynaptic cholinergic neurons are modulated by putative neurotransmitter released from afferent nerve terminals.