Unbiased Stereology. Three‐Dimensional Measurement in Microscopy.

A Systematic Nomenclature for the Insect Brain

http://chittkalab.sbcs.qmul.ac.uk/2009/ChittkaNivenCurrBiol09.pdf

Are Bigger Brains Better

A striking commonality across insects and vertebrates is the recurring presence of parallel olfactory subsystems, suggesting that such an organization has a highly adaptive value. Conceptually, two different categories of parallel systems must be distinguished. In one, specific sensory organs or processing streams analyze different chemical stimuli (segregate parallel systems). In the other, similar odor stimuli are processed but analyzed with respect to different features (dual parallel systems). Insects offer many examples for both categories. For example, segregate parallel systems for different chemical stimuli are realized in specialized neuronal streams for processing sex pheromones and CO2. Dual parallel streams related to similar or overlapping odor stimuli are prominent in Hymenoptera. Here, a clear separation of sensory tracts to higher-order brain centers is present despite no apparent differences regarding the classes or categories of olfactory stimuli being processed. In this paper, we review...

/pdf/parallel-olfactory-systems-in-insects-anatomy-and-function-2n72xkhg69.pdf

Parallel Olfactory Systems in Insects: Anatomy and Function

https://www.cell.com/cell/pdf/S0092-8674(10)00891-3.pdf

Profiling by Image Registration Reveals Common Origin of Annelid Mushroom Bodies and Vertebrate Pallium

In most insects with olfactory glomeruli, each side of the brain possesses a mushroom body equipped with calyces supplied by olfactory projection neurons. Kenyon cells providing dendrites to the calyces supply a pedunculus and lobes divided into subdivisions supplying outputs to other brain areas. It is with reference to these components that most functional studies are interpreted. However, mushroom body structures are diverse, adapted to different ecologies, and likely to serve various functions. In insects whose derived life styles preclude the detection of airborne odorants, there is a loss of the antennal lobes and attenuation or loss of the calyces. Such taxa retain mushroom body lobes that are as elaborate as those of mushroom bodies equipped with calyces. Antennal lobe loss and calycal regression also typify taxa with short nonfeeding adults, in which olfaction is redundant. Examples are cicadas and mayflies, the latter representing the most basal lineage of winged insects. Mushroom bodies of another basal taxon, the Odonata, possess a remnant calyx that may reflect the visual ecology of this group. That mushroom bodies persist in brains of secondarily anosmic insects suggests that they play roles in higher functions other than olfaction. Mushroom bodies are not ubiquitous: the most basal living insects, the wingless Archaeognatha, possess glomerular antennal lobes but lack mushroom bodies, suggesting that the ability to process airborne odorants preceded the acquisition of mushroom bodies. Archaeognathan brains are like those of higher malacostracans, which lack mushroom bodies but have elaborate olfactory centers laterally in the brain.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/cne.21948

Ground plan of the insect mushroom body: functional and evolutionary implications.

Malacostracan crustaceans and dicondylic insects possess large second-order olfactory neuropils called, respectively, hemiellipsoid bodies and mushroom bodies. Because these centers look very different in the two groups of arthropods, it has been debated whether these second-order sensory neuropils are homologous or whether they have evolved independently. Here we describe the results of neuroanatomical observations and experiments that resolve the neuronal organization of the hemiellipsoid body in the terrestrial Caribbean hermit crab, Coenobita clypeatus, and compare this organization with the mushroom body of an insect, the cockroach Periplaneta americana. Comparisons of the morphology, ultrastructure, and immunoreactivity of the hemiellipsoid body of C. clypeatus and the mushroom body of the cockroach P. americana reveal in both a layered motif provided by rectilinear arrangements of extrinsic and intrinsic neurons as well as a microglomerular organization. Furthermore, antibodies raised against DC0, the major catalytic subunit of protein kinase A, specifically label both the crustacean hemiellipsoid bodies and insect mushroom bodies. In crustaceans lacking eyestalks, where the entire brain is contained within the head, this antibody selectively labels hemiellipsoid bodies, the superior part of which approximates a mushroom body's calyx in having large numbers of microglomeruli. We propose that these multiple correspondences indicate homology of the crustacean hemiellipsoid body and insect mushroom body and discuss the implications of this with respect to the phylogenetic history of arthropods. We conclude that crustaceans, insects, and other groups of arthropods share an ancestral neuronal ground pattern that is specific to their second-order olfactory centers.

Neuronal organization of the hemiellipsoid body of the land hermit crab Coenobita clypeatus: Correspondence with the mushroom body ground pattern

Copepods are a diverse and ecologically crucial group of minute crustaceans that are relatively neglected in terms of studies on nervous system organization. Recently, morphological neural characters have helped clarify evolutionary relationships within Arthropoda, particularly among Tetraconata (i.e., crustaceans and hexapods), and indicate that copepods occupy an important phylogenetic position relating to both Malacostraca and Hexapoda. This taxon therefore provides the opportunity to evaluate those neural characters common to these two clades likely to be results of shared ancestry (homology) versus convergence (homoplasy). Here we present an anatomical characterization of the brain and central nervous system of the well-studied harpacticoid copepod species Tigriopus californicus. We show that this species is endowed with a complex brain possessing a central complex comprising a protocerebral bridge and central body. Deutocerebral glomeruli are supplied by the antennular nerves, and a lateral protocerebral olfactory neuropil corresponds to the malacostracan hemiellipsoid body. Glomeruli contain synaptic specializations comparable to the presynaptic "T-bars" typical of dipterous insects, including Drosophila melanogaster. Serotonin-like immunoreactivity pervades the brain and ventral nervous system, with distinctive deutocerebral distributions. The present observations suggest that a suite of morphological characters typifying the Tigriopus brain reflect a ground pattern organization of an ancestral Tetraconata, which possessed an elaborate and structurally differentiated nervous system.

The minute brain of the copepod Tigriopus californicus supports a complex ancestral ground pattern of the tetraconate cerebral nervous systems

Electron microscopical observations of the hemiellipsoid bodies of the land hermit crab Coenobita clypeatus resolve microglomerular synaptic complexes that are comparable to those observed in the calyces of insect mushroom bodies and which characterize olfactory inputs onto intrinsic neurons. In an adult hermit crab, intrinsic neurons and one class of efferent neurons originate from neuronal somata of globuli cells covering the hemiellipsoid bodies. Counts of their nucleoli show that about 120,000 globuli cells supply each hemiellipsoid body in an adult hermit crab. This number is comparable to the number of globuli cells supplying mushroom bodies of certain insects, such as honey bees and cockroaches. Counts of axons in tracts leading from the olfactory lobes to the hemiellipsoid bodies resolve 20,000 afferent axons, however, an order of magnitude greater than known for any insect. These afferent axons provide numerous swollen varicosities, each presynaptic to many small profiles, and thus comparable to the microglomeruli that characterize insect mushroom body calyces. Also, common to mushroom bodies and hemiellipsoid bodies are arrangements of intrinsic neurons, afferent neurons containing dense core vesicles, and systems of serial synaptic complexes that relate to postsynaptic profiles of efferent neurons. Together, the ultrastructural organization of the hemiellipsoid bodies of C. clypeatus supports the proposition that this center may share a common origin with the insect mushroom body despite obvious divergent evolution of overall shape. J. Comp. Neurol. 520:2847–2863, 2012. © 2012 Wiley Periodicals, Inc.

Fine structural organization of the hemiellipsoid body of the land hermit crab, Coenobita clypeatus.

Neuronal modifications that accompany normal aging occur in brain neuropils and might share commonalities across phyla including the most successful group, the Insecta. This study addresses the kinds of neuronal modifications associated with loss of memory that occur in the hemimetabolous insect Periplaneta americana. Among insects that display considerable longevity, the American cockroach lives up to 64 wk and reveals specific cellular alterations in its mushroom bodies, higher centers that have been shown to be associated with learning and memory. The present results describe a vision-based learning paradigm, based on a modified Barnes maze, that compares memory in young (10-wk old), middle-aged (30-wk old), and aged adults (50-wk old). We show that not only is the performance of this task during the 14 training trials significantly decremented in aged cockroaches, but that aged cockroaches show significant impairment in successfully completing a crucial test involving cue rotation. Light and electron microscopical examination of the brains of these different age groups reveal major changes in neuron morphology and synaptology in the mushroom body lobes, centers shown to underlie place memory in this taxon.

/pdf/the-effect-of-age-on-a-visual-learning-task-in-the-american-39u9iaplkp.pdf

Sheena Brown

Papers

Ground plan of the insect mushroom body: functional and evolutionary implications.

Neuronal organization of the hemiellipsoid body of the land hermit crab Coenobita clypeatus: Correspondence with the mushroom body ground pattern

The minute brain of the copepod Tigriopus californicus supports a complex ancestral ground pattern of the tetraconate cerebral nervous systems

Fine structural organization of the hemiellipsoid body of the land hermit crab, Coenobita clypeatus.

The effect of age on a visual learning task in the American cockroach.