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. 2020 Dec 14;9:e62576. doi: 10.7554/eLife.62576

Figure 24. Connections between MBONs form a multi-layered feedforward network.

Connections between MBONs, including both typical and atypical MBONs are shown, using a threshold of 30 synapses. The color of the arrow, as indicated in the color key, represents the nature and location of the synaptic connection. The number of synapses made in any given connection is indicated by the number in the arrow and the arrow thickness is proportional to that number. Numbers have been pooled for cases where there are two MBONs of the same cell type but only connections that occur in the right hemisphere are shown. The numbers within the circles indicate the MBON cell type; for example 1 represents MBON01. Typical MBONs are numbered with bold numerals. Circles are color-coded according to their neurotransmitter. (A) Axo-dendritic connections outside the MB lobes, axo-dendritic connections inside the MB lobes provided by feedforward MBONs (MBON05, MBON06, and MBON11), and the reciprocal axo-axonal connections between MBON6 and MBON11 within the MB lobes. (B) Axo-axonal synapses outside the MB lobes. Note that some MBONs, such as MBON24, form both axo-dendritic and axo-axonal connections outside the MB. Additional details of MBON05’s innervation of MBON30 are provided in Figure 24—figure supplement 1A.

Figure 24.

Figure 24—figure supplement 1. MBON30 displays an unusual pattern of innervation from other MBONs and FB neurons.

Figure 24—figure supplement 1.

(A) MBON30 receives strong input from MBON05, a feedforward glutamatergic MBON, through three distinct axo-dendritic paths: inside the γ1 and γ2 compartments (260 synapses); inside the γ3 and γ4 compartments (140 synapses); and outside the MB lobes (283 synapses). The locations of synapses used in each of these three connections are shown. Note that in the connectivity diagram in Figure 24, the arrow represents all 400 synapses that occur in either the γ1 and γ2 compartments (260) or in the γ3 and γ4 compartments (140). (B) MBON30 receives strong input from the FB mediated by the FB2-5RUB cell type which has nine columnar cells. The connection occurs inside the RUB. MBON30 is the only MBON that has input from an FB cell type among its top 10 inputs.