Olfactory processing in the medial amygdala

Physiology 2012 (Edinburgh) (2012) Proc Physiol Soc 27, SA78

Research Symposium: Olfactory processing in the medial amygdala

P. Sah1, S. Keshavarzi1

1. Queensland Brain Institute, University of Queensland, Brisbane, Queensland, Australia.

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The medial nucleus of the amygdala (MeA), referred to as the vomeronasal amygdala, plays a key role in defensive and reproductive behaviour. It receives processed information from the associational cortical amygdala (CoA) as well as direct olfactory inputs from the accessory olfactory bulb (AO). Little is known about the processing of olfactory sensory information in the MeA. In this study we examined the physiological properties CoA and AO inputs to neurons in the posteroventral nucleus of the MeA (MePV). Whole cell recordings were made from neurons in acute coronal brain slices made from adult male GAD67-eGFP knock-in mice. Synaptic responses were evoked by electrical stimulation of the afferents in the CoA and/or in the MeA molecular layer where the axon terminals of projections from the AO are located. Cells were filled with biocytin during recording and later visualised using immunohistochemistry. Stimulation of either CoA or AO inputs evoked excitatory synaptic inputs to MeA neurones. Both CoA and AO stimulation activated dual component (AMPA/NMDA) glutamatergic synapses. In voltage clamp, AMPA-receptor mediated excitatory synaptic currents (EPSCs) evoked by stimulation of AO axons showed significantly slower kinetics as compared to those evoked by CoA stimulation. The rise times were 2.04±0.24ms vs. 0.96±0.08 ms; (n=24, p<0.001) and decay time constants were 10.1±1.35ms vs. 4.06±0.27ms (n=24, p< 0.001). Upon reconstruction of neurones, we found their dendrites extend to the molecular layer forming distal dendritic tufts. Focal pressure application of TTX (1µM) at the distal dendritic tuft that blocked the accessory olfactory synaptic input, leaving the CoA evoked responses intact (80±0.6 % block vs. 6.2±1.6% block; n=6, p<0.0001). Calcium imaging of the dendritic tree while stimulating the AO afferents revealed synaptically evoked calcium transients that were restricted to dendrites that extend to the molecular layer. These results show that MePV neurons receive convergent AO and CoA inputs at separate locations on their dendritic tree, with the AO inputs synapsing at the distal dendrites and the associational afferents from CoA synapsing mainly at the proximal dendrites. We suggest that MeA neurones process olfactory and cortical inputs using distinct dendritic compartments.



Where applicable, experiments conform with Society ethical requirements.

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