Cell Body Rind Research Articles

Metamorphosis and denucleation of the brain in the miniature wasp Megaphragma viggianii (Hymenoptera: Trichogrammatidae)

Holometabolan brains undergo structural and allometric changes and complex reorganizations during metamorphosis. In minute egg parasitoids, brain formation is shifted to the late larva and young pupa, due to extreme de-embryonization. The brains of Megaphragma wasps undergo denucleation, the details of which remained unknown. We describe the morphological and volumetric changes in the brain of Megaphragma viggianii (Trichogrammatidae) during pupal development with emphasis on the lysis of nuclei and show that the absolute and relative volume of the brain decrease by a factor of 5 from prepupa to adult at the expense of the cell body rind. The first foci of lysis appear during early pupal development, but most nuclei (up to 97%) are lost between pharate adult and adult. The first signs of lysis (destruction of the nuclear envelopes) occur in pupae with red eyes. The number of lysis foci (organelle destruction and increasing number of lysosomes and degree of chromatin compaction) strongly increases in pupae with black eyes. The cell body rind volume strongly decreases during pupal development (in larger insects it increases slightly or remains unchanged). Elucidation of the lysis of nuclei in neurons and of the functioning of an anucleate brain is an important objective for neuroscience.

Structure of the Brain of the Smallest Coleoptera

The structure of the brain of the smallest coleopteran, Scydosella musawasensis Hall, 1999, is described for the first time. As in other extremely small beetles, the brain of S. musawasensis displays signs of miniaturization: displacement to the thorax, compactization, and a small number and size of the neurons. The body size of the studied smallest beetle is similar to that of the minute hymenopteran Megaphragma, which has a nearly anucleate nervous system. However, the structure of the brain of the studied smallest beetle is similar to that of large representatives of the order and is characterized by a high number of nuclei in the brain and a significant volume of the cell body rind. The neuropil of S. musawasensis occupies 60% of the brain volume, confirming the neuropilar constant rule.

Outsourcing a visual neuropil – The central visual system of the median eyes of Galeodes granti Pocock, 1903 (Arachnida: Solifugae)

Only a few studies have examined the central visual system of Solifugae until now. To get new insights suitable for phylogenetic analysis we studied the R-cell (or retinula cell) projections and visual neuropils of Galeodes granti using various methods.G. granti possesses large median eyes and rudimentary lateral eyes. In this study, only the R-cells and neuropils of the median eyes were successfully stained. The R-cells terminate in two distinct visual neuropils. The first neuropil is located externally to the protocerebrum directly below the retina, the second neuropil lies in the cell body rind of the protocerebrum, and immediately adjacent is the arcuate body.This layout of the median eye visual system differs from Arachnopulmonata (Scorpiones + Tetrapulmonata). However, there are several similarities with Opiliones. In both, (1) the R-cells are connected to a first and second visual neuropil and not to any other region of the brain, (2) the first neuropil is not embedded in the cell body rind of the protocerebrum, it is rather external to the protocerebrum, (3) the second visual neuropil is embedded in the cell body rind, and (4) the second neuropil abuts the arcuate body. These findings may provide important new characters for the discussion on arachnid phylogeny.

Constant neuropilar ratio in the insect brain

Revealing scaling rules is necessary for understanding the morphology, physiology and evolution of living systems. Studies of animal brains have revealed both general patterns, such as Haller's rule, and patterns specific for certain animal taxa. However, large-scale studies aimed at studying the ratio of the entire neuropil and the cell body rind in the insect brain have never been performed. Here we performed morphometric study of the adult brain in 37 insect species of 26 families and ten orders, ranging in volume from the smallest to the largest by a factor of more than 4,000,000, and show that all studied insects display a similar ratio of the volume of the neuropil to the cell body rind, 3:2. Allometric analysis for all insects shows that the ratio of the volume of the neuropil to the volume of the brain changes strictly isometrically. Analyses within particular taxa, size groups, and metamorphosis types also reveal no significant differences in the relative volume of the neuropil; isometry is observed in all cases. Thus, we establish a new scaling rule, according to which the relative volume of the entire neuropil in insect brain averages 60% and remains constant.

Metamorphosis of the central nervous system of Trichogramma telengai (Hymenoptera: Trichogrammatidae)

During metamorphosis, the insect CNS undergoes both structural and allometric changes. Due to their extreme de-embryonization and parasitism, the formation of the CNS in egg parasitoids occurs at the late larval stage. Our study provides the first data on the morphological and volumetric changes of the CNS occurring during the pupal development of the parasitic wasp Trichogramma telengai Sorokina, 1987 (Trichogrammatidae). The prepupal–pupal development includes fusion and concentration of ganglia achieved by the loss of connectives. Volumetric analysis shows that during the pupal development the absolute body volume and CNS volume gradually decrease. The brain and thoracic synganglion slightly increase in volume during the pupal period and extremely decrease from late pupa to adult. The CNS neuropil volume increases from prepupa to adult. The mean cell diameter also decreases during the metamorphosis of the nervous system. The cell body rind volume decreases during pupal development; this decrease correlates with the decrease in the number of cells on the one hand and increase in the neuropilar volume on the other hand.

Neuroarchitecture of the central complex of the desert locust: Tangential neurons.

The central complex (CX) comprises a group of midline neuropils in the insect brain, consisting of the protocerebral bridge (PB), the upper (CBU) and lower division (CBL) of the central body and a pair of globular noduli. It receives prominent input from the visual system and plays a major role in spatial orientation of the animals. Vertical slices and horizontal layers of the CX are formed by columnar, tangential, and pontine neurons. While pontine and columnar neurons have been analyzed in detail, especially in the fruit fly and desert locust, understanding of the organization of tangential cells is still rudimentary. As a basis for future functional studies, we have studied the morphologies of tangential neurons of the CX of the desert locust Schistocerca gregaria. Intracellular dye injections revealed 43 different types of tangential neuron, 8 of the PB, 5 of the CBL, 24 of the CBU, 2 of the noduli, and 4 innervating multiple substructures. Cell bodies of these neurons were located in 11 different clusters in the cell body rind. Judging from the presence of fine versus beaded terminals, the vast majority of these neurons provide input into the CX, especially from the lateral complex (LX), the superior protocerebrum, the posterior slope, and other surrounding brain areas, but not directly from the mushroom bodies. Connections are largely subunit- and partly layer-specific. No direct connections were found between the CBU and the CBL. Instead, both subdivisions are connected in parallel with the PB and distinct layers of the noduli.

The allometry of the central nervous system during the postembryonic development of the spider Eratigena atrica

During ontogenesis, the size of a spider body, tissues and organs increases dramatically. The aim of the study was to estimate changes in the central nervous system of postembryonic stages of Eratigena atrica and compare them with the literature data on species differing in behavioural traits. Allometric analysis involved evaluation of histological slides embedded in paraffin and stained with hematoxylin and eosin. The reduced major axis regression (RMA) was applied to find allometric relationships between the volumes of the particular parts of the body. All the measured parts of the central nervous system (CNS) were negatively allometrically related to the volume of the prosoma, showing that the increment of the CNS was lower than that of the entire body. The growth of the brain was negatively allometrically related to the growth of the CNS but the increment of the subesophageal ganglion was greater than that of the CNS, exhibiting a positive allometry. Within both these structures, the increase in neuropil volume was greater than the growth of the cortex (cell body rind). Thus, in postembryonic development, the share of the subesophageal ganglion and neuropil in the total volume of the CNS increased, whereas that of the brain and cortex decreased. The mode of the CNS development in E. atrica is similar to that observed in other arthropods, including Argiope aurantia, a spider of different ecology and behaviour.

Neurons innervating the lamina in the butterfly, Papilio xuthus

The butterfly Papilio xuthus has compound eyes with three types of ommatidia. Each type houses nine spectrally heterogeneous photoreceptors (R1-R9) that are divided into six spectral classes: ultraviolet, violet, blue, green, red, and broad-band. Analysis of color discrimination has shown that P. xuthus uses the ultraviolet, blue, green, and red receptors for foraging. The ultraviolet and blue receptors are long visual fibers terminating in the medulla, whereas the green and red receptors are short visual fibers terminating in the lamina. This suggests that processing of wavelength information begins in the lamina in P. xuthus, unlike in flies. To establish the anatomical basis of color discrimination mechanisms, we examined neurons innervating the lamina by injecting neurobiotin into this neuropil. We found that in addition to photoreceptors and lamina monopolar cells, three distinct groups of cells project fibers into the lamina. Their cell bodies are located (1) at the anterior rim of the medulla, (2) between the proximal surface of the medulla and lobula plate, and (3) in the medulla cell body rind. Neurobiotin injection also labeled distinct terminals in medulla layers 1, 2, 3, 4 and 5. Terminals in layer 4 belong to the long visual fibers (R1, 2 and 9), while arbors in layers 1, 2 and 3 probably correspond to terminals of three subtypes of lamina monopolar cells, respectively. Immunocytochemistry coupled with neurobiotin injection revealed their transmitter candidates; neurons in (1) and a subset of neurons in (2) are immunoreactive to anti-serotonin and anti-γ-aminobutyric acid, respectively.

The accessory lateral eye of a diplopod, Cylindroiulus truncorum (Silvestri, 1896) (Diplopoda: Julidae)

Using electron microscopy we describe an accessory lateral eye for Cylindroiulus, a diplopod. The accessory eye is situated at the cell body rind of the optic lobes, deep inside the head, and is composed of six R-cells; a dioptric apparatus is absent. Comparison reveals that many arthropods possess accessory lateral eyes in addition to the compound eyes or lateral ocelli. Their homology and distribution among the arthropod main lineages is discussed along with characters that may be useful for reconstructing phylogeny.

Glial patterning during postembryonic development of central neuropiles in the brain of the honeybee

Glial cells are involved in several functions during the development of the nervous system. To understand potential glial contributions to neuropile formation, we examined the cellular pattern of glia during the development of the mushroom body, antennal lobe and central complex in the brain of the honeybee. Using an antibody against the glial-specific repo-protein of Drosophila, the location of the glial somata was detected in the larval and pupal brain of the bee. In the early larva, a continuous layer of glial cell bodies defines the boundaries of all growing neuropiles. Initially, the neuropiles develop in the absence of any intrinsic glial somata. In a secondary process, glial cells migrate into defined locations in the neuropiles. The corresponding increase in the number of neuropile-associated glial cells is most likely due to massive immigrations of glial cells from the cell body rind using neuronal fibres as guidance cues. The combined data from the three brain regions suggest that glial cells can prepattern the neuropilar boundaries.

Glial cells phagocytose neuronal debris during the metamorphosis of the central nervous system in Drosophila melanogaster

Using electron microscopy we demonstrate that degenerating neurons and cellular debris resulting from neuronal reorganization are phagocytosed by glial cells in the brain and nerve cord of the fruitfly Drosophila melanogaster during the first few hours following pupariation. At this stage several classes of glial cells appear to be engaged in intense phagocytosis. In the cell body rind, neuronal cell bodies are engulfed and phagocytosed by the same glial cells that enwrap healthy neurons in this region. In the neuropil, cellular debris in tracts and synaptic centres resulting from metamorphic re-differentiation of larval neurons is phagocytosed by neuropil-associated glial cells. Phagocytic glial cells are hypertrophied, produce large amounts of lysosome-like bodies and contain a large number of mitochondria, condensed chromatin bodies, membranes and other remains from neuronal degeneration in phagosomes.

Central projections of the sensory hairs on the gemma of the ant Diacamma: substrate for behavioural modulation?

In the ant genus Diacamma, all workers eclose from their cocoons with little clublike thoracic appendages, called gemmae. Whether these gemmae are mutilated determines individual behaviour, and ultimately reproductive role, in two of the three species examined. The gemmae are covered with sensory hairs, which probably serve a mechanoreceptive function. The sensory afferents arising from these hairs were stained and traced into the central nervous system (CNS). They feature widely distributed collaterals invading all three thoracic ganglia as well as the suboesophageal and the second abdominal ganglia. The multisegmental arborization pattern of the gemma afferents is very similar to that of wing-hair afferents of other ants (queens and males) or other insects in general. This implies that gemmae and wings are homologous structures. We discuss the morphology of the gemma afferents with respect to their possible involvement in the behavioural changes associated with mutilation. The neuronal processing may be modulated by (1) the decrease of sensory input onto interneurons (suggested by the afferents' extensive arborizations); or (2) by the effect of neuromodulatory substances (suggested by the finding that terminals occur within the cell body rind of the ganglion).

Glial cells in adult and developing prothoracic ganglion of the hawk moth Manduca sexta

The glial cells of the prothoracic ganglion of the hawk moth Manduca sexta were studied in histological sections of several postembryonic stages and classified according to cell morphology, size, staining properties, and topographical relationships. In general, each glial cell type was found to be confined to one of the major ganglionic domains and each of these domains (i.e., perineurium, cell body rind, glial cover of the neuropil, and neuropil) was found to comprise specific cell types. Some types of glia were recognized in both larval and later stages, but other types were found exclusively from late pupal stages. It is proposed that the higher morphological diversity expressed by the glia of the pharate adult is attained by differentiation of new cell types during metamorphosis. Before the differentiation of new cell types, extensive cell death and cell proliferation seem to occur within some glial subpopulations.