Three‐dimensional visualization of ocellar interneurons of the orchid bee Euglossa imperialis using micro X‐ray computed tomography

Abstract

We used contrast-optimized micro X-ray computed tomography (mCT) to trace the profiles of the full complement of large ocellar L-neurons in the male orchid bee Euglossa imperialis. We find that most L-neurons collect information from either the dorsal or the ventral retinae in both median and lateral ocelli, with only three neurons associated with the median ocellus having dendritic branches in both dorsal and ventral retina. In the median ocellus, we find also L-neurons that either collect information from the left or the right half of the ocellar plexus and two neurons that have a split dendritic tree in both halves. Fourteen large L-neurons collect information from the median ocellus and six to seven L-neurons from each of the lateral ocelli. The only L-neurons that project to the contralateral protocerebrum are those that have their dendritic branches in the ventral plexi of both median and lateral ocelli. The target areas of dorsal L-neurons from the lateral ocelli include a tract of mechanosensory fibers originating in the antennae. We compare our findings with what is known from the ocellar systems of other insects, make a number of functional inferences and discuss the advantages and disadvantages of mCT scans for the purpose of tracing large neuron profiles.

The utility of micro-computed tomography for the non-destructive study of eye microstructure in snails

“…Initial studies on molluscs have also proven to be useful for examination of anatomical details in bivalves 18 . Of particular interest to this study is the soft-tissue visualisation and imaging in invertebrates, including central nervous and sensory systems 2,12,19–23 . Using synchrotron tomography, Taylor et al .…”

Ocellar structure is driven by the mode of locomotion and activity time in Myrmecia ants

“…The ocelli typically comprise three simple eyes placed in a triangular formation on the dorsal surface of the head. Each ocellus consists of a lens, an iris, a corneagenous cell layer, a dorsal retina, a ventral retina and a neuropil (Narendra et al, 2016b;Ribi et al, 2011;Ribi and Zeil, 2017;Zeil et al, 2014). In some insects, the image resolved by the ocelli is under-focused (Berry et al, 2007a;Schuppe and Hengstenberg, 1993), while in some bees and wasps, the focal plane is near the retina (Hung and Ibbotson, 2014;Kelber et al, 2011;Ribi et al, 2011;Warrant et al, 2006).…”

Micro-CT and deep learning: Modern techniques and applications in insect morphology and neuroscience

“…Although the authors also map some individual neurons and their projections into the central complex, these are visualised through classical immunostaining methods and CLSM, as no individual neurons are visible on the CT data itself ( 45 ). In contrast to this, Ribi and Zeil ( 46 ) successfully traced the origins and projection areas of all large ocellar interneurons (L-neurons) in orchid bee ( Euglossa imperialis ) brains stained with osmium tetroxide and µCT scanned at a resolution of 3 µm/voxel. Using fibre-tracing methods, the authors reconstruct the individual dendritic origins of the 27 L-neurons in the ocellar plexi (below the retinae) and follow their paths to the ipsi- or contralateral protocerebrum where they terminate within close proximity to optic (lobula) and mechanosensory (antennal lobe) interneurons.…”

“…Using fibre-tracing methods, the authors reconstruct the individual dendritic origins of the 27 L-neurons in the ocellar plexi (below the retinae) and follow their paths to the ipsi- or contralateral protocerebrum where they terminate within close proximity to optic (lobula) and mechanosensory (antennal lobe) interneurons. While identification and reconstruction of the large fibers (up to 22 µm in diameter) and their main arborizations proves unproblematic at the resolution used, the authors also acknowledge that fine arborizations and branching patterns, and thus exact connectivities, are not resolved ( 46 ).…”