ATTENUATED HIPPOCAMPAL LONG-TERM POTENTIATION IN BASOLATERAL AMYGDALA-LESIONED RATS

Possible involvement of the amygdaloid input in long-term potentiation (LTP) in the medial perforant path-dentate gyrus granule cell synapse s in vivo was investigated by evaluating the effects of lesions of the amygdaloid nucleus. The dentate gyrus synaptic potential evoked by lo w-frequency test stimulation did not change following lesions of the b asolateral and central amygdala. However, when tetanic stimulation (30 pulses at 60 Hz) was applied 60 min after lesioning of the ipsilatera l basolateral amygdala, the magnitude of LTP was significantly attenua ted. Since lesions of the ipsilateral central amygdala and the contral ateral basolateral amygdala did not affect the dentate gyrus LTP, the attenuation of the dentate gyrus LTP is a specific effect of acute les ions of the ipsilateral basolateral amygdala. The basolateral amygdalo id lesions significantly attenuated both LTP induced by weak (20 pulse s at 60 Hz) and strong (100 pulses at 100 Hz) tetanus, indicating that the effect of the lesions does not depend on the strength of tetanus applied to induce LTP. When the ipsilateral basolateral amygdala was d estroyed after application of tetanus, it did not affect the establish ed LTP. The attenuation of LTP was also observed after the basolateral amygdala-lesioned rats were allowed a recovery period of 2 weeks. Thi s is the first report providing evidence that the ipsilateral basolate ral amygdala modulates hippocampal synaptic plasticity in vivo.