Synaptic activation of a cholinergic receptor in rat hippocampus.

Tetanic stimulation of the basal dendritic field (stratum oriens) of Ca1 area of rat hippocampal slice can produce a slow depolarization associated with an increase in input resistance, decrease in accommodating properties of the cell to a depolarizing drive and an increase in synaptic activity. These effects are enhanced by an acetylcholinesterase inhibitor, eserine, and blocked by the muscarinic antagonists, pirenzepine and atropine. The accommodating property of the cell is more sensitive to the stimulation than the membrane potential or input resistance. The effects of oriens stimulation can be obtained also in fornix-fimbria transected hippocampal slice indicating that it may activate a local cholinergic or non-cholinergic pathway. The stimulation causes a heterosynaptic enhancement of reactivity of neurons to afferent stimulation indicating that acetylcholine may cause an enhanced excitability of hippocampal neurons.