Fig. 8. Site-specificity of tetanus-induced plasticity in alpha lobe-extrinsic neurons. (A) Each MB consists of two halves. One half is composed of K-cells with their somata and dendrites in the median calyx (m), and another half has somata and dendrites in the lateral calyx (l). The axons of the K-cells fuse in the peduncle and send their collaterals into the alpha lobe (). There the lateral and the median sectors house the axon collaterals of the respective calyces. All alpha lobe-extrinsic neurons that we marked in the course of our study branched across the whole alpha lobe, making it very likely that they receive input from both median and lateral K-cells. (B) This Pe1 neuron responded with depression after tetanus to the lateral calyx. Depression was found for the test stimuli to both the median (filled triangles) and the lateral calyx (open triangles). The delayed augmentation effect, however, was site-specific. Only the input from the tetanized calyx augmented. (C,D) Two examples from unidentified alpha lobe-extrinsic neurons for site-specific facilitation induced by tetanus. Again the tetanus was applied to the lateral calyx, and the responses to test stimuli in the median (filled triangles) and lateral (open triangles) were monitored during successive minutes. The ordinate in the diagrams gives the number of spikes elicited by a single stimulus, and the abscissa time in min. The stimulus artefacts in B, C and D mark the test pulses.