The objective of this proposal is to establish and characterize the functional role of synaptically-releasable zinc, contained in synaptic vesicles (vesicular zinc), at glutamatergic synapses of the amygdala circuitry implicated in auditory fear conditioning. Our recent findings indicate that zinc transporter-3 (ZnT-3), serving as a marker for zinc-containing neurons, is expressed in the lateral amygdala and the TE3 area of the auditory cortex, conveying the auditory conditioned stimulus (CS) information to the lateral nucleus of the amygdala (LA) during fear conditioning, thus suggesting a potential role for vesicular zinc in regulation of synaptic functions in fear conditioning pathways. Results of our experiments with Zn2+ chelators imply that vesicular Zn2+ can control the induction of spike timing-dependent long-term potentiation (LTP) at cortico-amygdala synapses. We now propose a detailed electrophysiological analysis of the role of vesicular Zn2+, releasable in the course of synaptic activation, in synaptic transmission and plasticity in cortical and thalamic inputs to the LA, delivering auditory CS information to the amygdala during fear conditioning, in slices from ZnT-3 knockout and control mice. These genetically modified mice with targeted disruption of the ZnT-3 gene lack vesicular zinc. Both the compound and unitary postsynaptic responses will be recorded with whole-cell patch-clamp techniques and analyzed to estimate the effects of ZnT3 ablation on synaptic transmission and plasticity in the amygdala. We will also explore whether ZnT-3 knockout mice compensate for the lack of vesicular zinc by decreased GABAergic inhibition of principal neurons in the LA, assaying inhibitory neurotransmission in slices from control and ZnT-3 knockout mice. Our hypothesis is that the ability of glutamatergic synapses in fear conditioning pathways to undergo LTP can be controlled by vesicular Zn2+, released at activated synapses during LTP- inducing stimulation. The proposed studies will improve our understanding of the mechanisms of synaptic plasticity which could underlie the acquisition of fear memory. A better knowledge of the cellular mechanisms of fear-related behaviors will permit the rational development of novel therapeutic treatments for posttraumatic stress disorder, generalized anxiety, and other disorders implicating the fear system of the brain.
The proposed studies will improve our understanding of the mechanisms of synaptic plasticity which may underlie the acquisition of fear memory. A better knowledge of the cellular mechanisms of fear-related behaviors will permit the rational development of novel therapeutic treatments for posttraumatic stress disorder, generalized anxiety, and other disorders implicating the fear system of the brain.
