Abstract
Recent experiments indicate that LTP in afferent inputs to the lateral nucleus of the amygdala serves an essential function in the process of fear conditioning, model of associative learning. It remains unclear, however, how the information that is contained in the specific afferent input activity is preserved during fear learning. To address this issue, we recorded activity in two independent inputs implicated in auditory fear conditioning, a direct pathway from the auditory thalamus and indirect from the auditory cortex, which converge on the same neuron. Pairing of presynaptic stimulation of either cortical or thalamic input with action potential evoked in a postsynaptic cell by depolarizing current injections through the recording electrode led to LTP in either pathway, when GABA A receptors were blocked. With GABA A receptor-mediated inhibition present, the EPSP-spike induction protocol failed to induce LTP in the thalamic pathway, while LTP in the cortical pathway was diminished but still could be observed. The analysis of input-output curves for both monosynaptic EPSP and disynaptic IPSP recorded in convergent inputs revealed that feedforward inhibition is enhanced in thalamic pathway when compared to cortical input. The stronger inhibitory drive in thalamic pathway decreases activation of NMDA receptors and thus affects the induction of LTP at thalamo-amygdala synapses. These results suggest that the differential inhibitory control of synaptic transmission at convergent inputs may contribute to spatial specificity of LTP in fear conditioning pathways. [J Physiol Sci. 2007;57 Suppl:S154]
