Abstract: Here studied the mechanism of responded pattern of 33 neurons to sex pheromone in the antennal lobe (AL) of male moths Agrotis segetum.Pressure injecting 100 mmol/L GABA into AL,GABA can elicit inhibitory responses of slow hyperpolarization and long time inhibition of background spiking,alike which caused by sex pheromone in the same neuron.But GABA can not act on the excitation evoked by pheromone.Low-Cl- saline caused that the IPSP to reverse the hyperpolarization,excitation evoked by pheromone was prolonged,and the distinct separation between bursts disappeared.Bicuculline was as a GABAA receptor antagonist in vertebrates,and a water-soluble form of this agent was used for pressure ejection into the AL neuropil.Bicuculline increased the spike frequency in tested neu rons,even strengthened the excitation phase acted by pheromone,and the hyperpolarization and spike-inhibition produced by pheromone was replaced by excitation.The effect was reversible by washing in normal saline.Results indicate that the hyperpolarization is related to GABA receptor,which responds to the sex pheromone in AL neurons in the male moths Agrotis segetum.