Innexin Gap Junctions

Morphology of the adult brain: mushroom body neurons

Bright-field image of a Drosophila adult brain showing the mushroom bodies in green (GFP)

Figure legend: The Drosophila mushroom bodies. A whole adult cephalic ganglion is shown and consists of optic lobes (OL) on each side of the brain. The mushroom bodies (MBs) in the image above express UAS-mCD8:GFP (green) under the transcriptional control of enhancer trap line 201Y-GAL4.

Image identifying the parts of a single mushroom body

Figure legend: Mushroom body (corpora pedunculata) morphology. A close-up view of a single mushroom body (MB) expressing UAS-mCD8:GFP (white) under the transcriptional control of 201Y-GAL4. This enhancer trap line reveals most of the structural features of the MBs although it only drives reporter expression in a subset of MB neurons. Each MB is composed of approximately 2500 Kenyon cell bodies located near the dorsal-posterior surface of the brain. These extend axons toward the anterior of the brain where they bifurcate; one branch following a dorsal path to form the α lobes and the sister branch extending medially, forming the β lobes. Some axons do not bifurcate and extend medially into the γ lobes. Input into the MB neurons is received at a specialized dendritic zone called the calyx, located just below the Kenyon cell bodies. Between the calyx and the lobes, the MB axons are arranged parallel to each other in a tightly packed tract called the pedunculus.

The complexity of the brain makes it one of the the hardest tissues in which to map gap junctions to specific cell types. Focusing on a single structure within the brain and then extrapolating from these observations is one way to reduce brain complexity sufficiently to obtain a rough idea of innexin distribution amongst cell types. The mushroom bodies (MBs) are a component of the olfactory processing and associative learning circuit (Heisenberg, 2003, Connolly et al, 1996) and there are a number of reasons to focus attention on these structures:

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