Figure 7.

Schematic representation of the neural network proposed for a glomerulus in the honey bee (model architecture based on Fonta et al., 1993; Abel et al., 2001; Nishino et al., 2009; Meyer and Galizia, 2012; Girardin et al., 2013). Octopamine is released into the whole glomerulus in both core and cortex and acts on the GABArgic local interneurons (LNs) and on GABAergic multiglomerular projection neurons (mPNs). Each glomerulus has a uniglomerular PN (uPNs) that branches into both core and cortex areas of the glomerulus. uPNs receive excitatory synapses from ORNs in the cortex area and inhibitory synapses from hetero-multiglomerular local neurons from neighboring glomeruli in the core area. The uPNs also receive inhibitory synapses in the cortex that come from the mPNs. In the glomerulus there are GABAergic and non-GABAergic multiglomerular LNs. For simplicity, only one type of the GABAergic LNs is shown in the glomeruli; LNg (LN1 or heteroLN in Figure 1) that branches in all areas of the glomerulus (cortex and core) where it receives excitatory synapses from ORN in the cortex and inhibitory synapses in the core and sends the inhibitory output into the neighboring glomeruli. Both types of GABAergic neurons (LNs and mPNs) express AmOA1 receptors in the glomerulus. Based on our indirect evidence of AmOA1 and GABA stainings in glomeruli, we hypothesize two possible mPNs connections, one that receives excitatory synapses from ORNs in the glomerulus cortex and makes synapses in the LH as well as another that receives synaptic input from LPL and LH and makes synapses onto the processes in the cortex. Future physiological and anatomical studies will clarify the branching patterns that we proposed for mPNs.