Neuroarchitecture of the central complex of the desert locust: Intrinsic and columnar neurons

Abstract

The central complex is a group of neuropils in the center of the insect brain. It consists of four major subunits: the upper and lower divisions of the central body (CBU, CBL), the protocerebral bridge (PB), and the paired noduli. A distinctive feature of the central complex is a modular architecture characterized by rows of 16 columns, intersected in the central body by stacks of layers. Evidence from locusts suggests that the central complex plays a major role in sky compass orientation. To understand signal processing in this brain area further, we have analyzed the morphologies of columnar neurons of the central complex of the locust Schistocerca gregaria. Intracellular dye fills revealed 21 types of columnar neurons that connect columns of different subunits, three types of pontine neurons linking pairs of columns within the CBU, and one amacrine cell. Most neurons appeared to be part of isomorphic sets with cell type-specific heterolateral projection patterns. Evaluation of arborization areas and neuron polarity suggests that these neurons are either intrinsic to the central complex or provide output to the lateral accessory lobes (LALs) or anterior lip region. No direct connections were found between the CBU and CBL. Instead, neurons of either subdivision were connected with the PB, but projected to non-overlapping regions in the LALs and to different layers of the noduli. This study provides novel insights into the functional organization of the central complex, especially with respect to its likely role in right-left signal matching and decision making.

Widespread Sensitivity to Looming Stimuli and Small Moving Objects in the Central Complex of an Insect Brain

“…Nomenclature of cell types from Homberg (1994), Müller et al (1997), Homberg et al (1999), and Heinze and Homberg (2009). In two cases it was unclear whether we recorded from a GFS or a colabeled intrinsic neuron of the CBU (PoU1 neuron, respectively, PoU2 neuron; Heinze and Homberg, 2008). In one case it was unclear whether we recorded from a CPU1 or a colabeled PoU1 neuron.…”

“…The labeled neurons were made visible for confocal laser scanning microscopy (Leica TCS-SP5; Leica Microsystems) by treatment of the brains with Cy3-conjugated streptavidin (Dianova). The detailed procedure is described in Heinze and Homberg (2008). The anatomy of novel neurons was analyzed in detail.…”

“…The anatomy of novel neurons was analyzed in detail. For this, brains were sectioned as described by Heinze and Homberg (2008). Briefly, brains were embedded in gelatin/albumin and then sectioned in slices of 130 m with a vibratingblade microtome (Leica VT1200 S, Leica Microsystems).…”

“…The terminals of TUx (Fig. 2B) were concentrated in layer IIb of the CBU as defined by Heinze and Homberg (2008). Its primary neurite could be traced into the cell cortex adjacent to the inferior medial protocerebrum between the antennal lobe and the medial lobe of the mushroom body, but the soma was lost during tissue processing.…”

“…A candidate brain structure for mediating directional movements is the central complex (CC). The CC comprises a group of neuropils spanning the brain midline and consists of the protocerebral bridge (PB), the upper and lower divisions of the central body (CBU, CBL), and the paired noduli (Homberg, 1987;Heinze and Homberg, 2008). In many insects studied, the CC is dominated by visual input : in locusts it holds an internal representation of sky compass directions (Heinze and Homberg, 2007), and in flies and cockroaches it plays a key role in spatial orientation during walking and climbing (Neuser et al, 2008;Triphan et al, 2010;Ritzmann et al, 2012).…”