Abstract: Objective To explore the inhibitory component of the compound postsynaptic potentials(PSPs) in Mauthner cell's ventral dendrite.Methods Direct stimulation the skin of crucian carp,change the stimulus strength and the stimulus frequency or inject hyperpolarizing currents to the ventral dendrite through the Cl^- filled microelectrode or drop strychnine to the surface of medulla,microelectrode were used to record the change of postsynaptic potentials in the ventral dendrite.Results The PSP amplitudes were stimulus strength-and frequency-and Cl^- dependent within some limits.After dripping strychnine on the brain of crucian carp,the PSP amplitudes enhance greatly,even action potentials can break out.Conclusion It suggests that the afferent pathways from skin to M-cells contain both excited and inhibitory components,the inhibitory neurons project not only to the soma but also to the ventral dendrite,and the neurotransmitter released may be glycine.

Key words: Mauthner cell, Cl^-, strychnine, ventral dendrite, postsynaptic potentials, inhibition