Cholinergic facilitation and inhibition of long-term potentiation of CA1 in the urethane-anaesthetized rats.

Responses were evoked in the hippocampal CA1 field by stimulating the medial septal area (MSA) and ventral hippocampal commissure (VHC) of urethane-anaesthetized rats. Tetanic stimulation of the MSA resulted in a homosynaptic long-term potentiation (LTP) of a slow synaptic response in the hippocampus, and heterosynaptic LTP of the evoked VHC response. Both forms of LTP were blocked by MK801. Tetanization of the VHC resulted in homosynaptic LTP but did not produce heterosynaptic LTP of the evoked MSA response. Atropine pretreatment increased commissural homosynaptic LTP and unveiled a heterosynaptic LTP of MSA-evoked responses. In contrast, atropine pretreatment partially blocked the homosynaptic LTP produced by tetanization of the MSA and prevented the heterosynaptic LTP of VHC-evoked responses.