Abstract
The amygdala is a brain region involved in the regulation of anxiety-related behavior. The purpose of this study was to correlate anxiety-related behavior of inbred mouse strains (BA//c, BALB/cJ, C3H/HeJ, C57BL/6J, CPB-K, DBA/2J, NMRI) to receptor binding in the amygdala. Binding site densities of receptors (NMDA, AMPA, kainate, GABAA, serotonin, muscarinergic M1-M2) were measured with quantitative receptor autoradiography using tritiated ligands. Measurements of fear-sensitized acoustic startle response (ASR; induced by footshocks), elevated plus maze (EPM) behavior and receptor binding studies showed differences between the strains except for AMPA and muscarinergic M2 receptors. Factor analysis revealed a Startle Factor with positive loadings of the density of serotonin and kainate receptors, and the amplitudes of the baseline and fear-sensitized ASRs. A second Anxiety-related Factor only correlated with the fear-sensitized ASR and anxiety parameters on the EPM but not receptor densities. There were also two General Activity Factors defined by (negative) correlations with entries to closed arms of the EPM. Because the density of NMDA and muscarinergic M1 receptors also correlated negatively with the two factors, these receptors had a positive effect on general activity. In contrast, correlations of GABAA, serotonin, and kainate receptors had the opposite sign as compared to closed arm entries. It is concluded that hereditary variations in the amygdala, particularly in kainate and serotonin receptors, play a role for the baseline and fear-sensitized ASR, whereas the general activity is influenced by many neurotransmitter receptor systems.