John S. Edwards

Neurogenesis in adult insect mushroom bodies.

The occurrence of neurogenesis in mushroom bodies of adult insects belonging to several orthopteroid and coleopteran families is described. Using injections of 5‐bromo, T2′‐deoxy we showed that neuroblasts, which are progenitors of Kenyon cells during preimaginal instars continue to divide in adult Acheta domesticus. Their progeny constitute a central column in mushroom body cortices of 3‐week‐old females. Other Gryllidae, Gryllus bimaculatus and Gryllomorpha dalmatina, show the same pattern of neuroblast activity and migration of their progeny. Immunocytochemical staining of glial cells failed to reveal any immunoreactivity, either in proliferating regions or in the resulting cells.

Postembryonic Development and Regeneration of the Insect Nervous System

Publisher Summary Developmental changes in the anatomy of the nervous and muscular system of many insects have been described, however apart from the experimental studies of muscle development and regression little is known of the morphogenetic mechanisms in either muscle or nerve, and of these, the nervous system is the less understood. The postembryonic development of the insect nervous system is especially relevant to recent developments in neuroembryology and questions of the nature of neural specificity. Advances in knowledge of the ontogeny of the nervous system, which have been made almost exclusively with vertebrates, stress the capacity of differentiating neurons for forming complex and specific connections during early stages. This chapter also describes patterns of development in the nervous system, the source of neurons and glia, post embryonic development of the brain and sense organs of the head, cell death in the developing nervous system, and regeneration in the nervous system.

Mechanisms of freezing tolerance in an Antarctic midge, Belgica antarctica

ABSTRACT. The larvae and adults of Belgica antarctica were studied in an attempt to identify the mechanism of low temperature adaptation that enables this species to survive in the Antarctic. Larvae are freezing‐tolerant during the austral summer and elaborate a complex of cryoprotectants including erythritol, glucose, sucrose and trehalose. Adults are freezing‐susceptible and lack adequate quantities of cryoprotectants. Maintenance on artificial diets indicated that cryoprotectant profiles have food‐source and temperature‐dependent components. In addition, direct utilization of dietary cryoprotectants is suggested.

Embryonic development of an insect sensory system, the abdominal cerci ofAcheta domesticus

Summary1.The embryonic development of the abdominal cerci of the house cricketAcheta domesticus is described from scanning and transmission electron microscope data.2.A staged description of externally visible events in embryogenesis is tabulated as a context for describing the chronology of embryonic development of the abdominal cerci.3.Three phases of cercal development are distinguished: differentiation of the cercal anlagen and secretion of the first embryonic cuticle; elongation of the cercus culminating in the secretion of the second embryonic cuticle after completion of a continuous epidermis at the time of dorsal closure; and differentiation of functional sensilla on the third embryonic (first instar) cuticle.4.The first axon profiles appear in the cercus immediately before elongation of the cercus. These axons have dendrites with ciliary configuration in the lumen of the cercus. Glial cells associated with the pioneer axons may precede the axons in occupying dorsal and ventral luminal midlines of the cerci.5.Trichoid sensilla appear in the integumet following apolysis of the second embryonic cuticle.6.Axons are added to the dorsal and ventral pioneer fibre bundles shortly before sensilla become apparent.7.The majority of sensory axons traverse the cercus during the final 15% of embryonic development.8.The sensilla of the first instar cercus do not achieve their final orientation until the cercal cuticle is expanded following eclosion from the second embryonic cuticle that encloses the hatchling until it reaches a free surface.9.The role of the pioneer fibres in establishing a pathway for the functional sensillar neurons is discussed in relation to other studies of sensillar development in insects.

The protocerebral neurosecretory system and associated cerebral neurohemal area of Acheta domesticus

SummarySix principal types of neurons are recognized in the median neurosecretory-cell group of the pars intercerebralis in the house cricket, Acheta domesticus. Four of the six cell types are neurosecretory neurons. The majority of the 900 cells contain granules 1500–3000 Å in diameter and are designated as type I. These neurons, which are associated with the nervus corporis cardiaci I (NCCI), undergo asynchronous secretory cycles.Two cell types (II and IV), which contain 700–1600 Å granules, terminate in a neurohemal area on the ventral median surface of the brain, a site not previously recognized as neurohemal in insects. Neurosecretory axons that lie within and below the perineurial sheath in the cerebral neurohemal area contain typical synaptoid figures, but no evidence of exocytosis was found. A single pair of neurosecretory cells (type III) has been recognized only from light microscope sections.Two distinct types of vesicle-bearing axons occur in protocerebral neuropile. The majority contain electron-dense and dense-cored vesicles 600–1000 Å in diameter. Some axons contain granules of type I cells and may be collaterals or loops of NCCI axons.

Phenology and life history of Belgica antarctica, an Antarctic midge (Diptera: Chironomidae)

ABSTRACT. 1 An account of the life‐history with emphasis on phenology and number of instars is presented for Belgica antarctica Jacobs, the southernmost holometabolous insect. 2 Contrary to earlier reports, Belgica has four instars, in common with most other chironomids. Mean head capsule lengths varied between different populations but no overlap was found between discrete size classes of successive instars. 3 Belgica overwinters in all four instars. 4 Relative frequency of different instars from samples taken through the season indicates that a 2‐year life‐span is the commonest pattern. 5 Emergence of adults is relatively synchronous. Belgica exhibits protandry, which may be established at the time of pupation.

Projection of sensory neurons from a homeotic mutant appendage, Antennapedia, in Drosophila melanogaster

Central projections of sensory neurons from homeotic mutant appendages (Antennapedia) of Drosophila melanogaster were compared with those of wild-type antennae and wild-type legs by means of degeneration and cobalt backfilling methods. Sensory axons originating from wild-type thoracic legs terminate within the ventral ipsilateral half of the corresponding neuropile segment and do not project to the brain. Sensory fibers from the third antennal segment (AIII) of wild-type animals project into the ipsilateral antennal glomerulus (AG) and to a lesser extent into the contralateral AG, whereas those from the second antennal segment terminate principally within the ipsilateral posterior antennal center. The sensory terminals of femur, tibia, and tarsi of the homeotic leg show a distribution very similar to that of the homologous wild-type antennal segment AIII, differing to a minor degree only in the size and precise localization of terminals within the antennal glomeruli. No degenerating axons were evident in ultrastructural examination of neck connectives after removal of homeotic legs. It is thus very improbable that any sensory fibers of the homeotic leg project to normal leg projection areas in the thoracico-abdominal ganglion. Several alternative explanations are offered for the apparent retention of antennal specificity by axons from the transformed appendage.

Neural Regeneration: Delayed Formation of Central Contacts by Insect Sensory Cells

Correlated anatomical and electrophysiological results demonstrate that sensory neurons, which differentiate de novo within the epidermis of regenerate abdominal cerci of crickets, enter the terminal ganglion and form functional central connections even when regeneration of the cerci is delayed through the greater part of postembryonic development. Stimulation of regenerate cerci evokes activity in giant interneurons which is normal by several physiological criteria.

The projection of neuroendocrine fibers (NCC I and II) in the brains of three orthopteroid insects

Neuronal projections from neuroendocrine tracts (nervi corpori cordiaci I and II) in the brains of the locust (Schistocerca vaga), cricket (Acheta domesticus), and cockroach (Periplaneta americana) were studied using reconstructions of silver‐intensified cobalt chloride preparations. Collaterals from the NCC I in these species branch extensively in the dorsal protocerebral neuropile, anterior to the stalk of the corpora pedunculata and ventral to its calyces. Other fibers project from the NCC I bilaterally into the medial protocerebral neuropile, anterior to the central body, and posterior to the beta lobes. NCC II collaterals arborize in the medial, dorsal, and lateral protocerebral neuropile, their region of projection partially overlapping with that of the NCC I. Several NCC II fibers terminate in the superior arch of the central body in Acheta but not in the other two species. Tritocerebral cells filled through the NCC I branch in the medial tritocerebral neuropile in all three species, but most extensively in Schistocerca. No NCC fibers were seen to penetrate any part of the corpora pedunculata, protocerebral bridge, olfactory glomeruli, ocellar tracts, or optic lobes.

Fine structure of degenerating abdominal motor neurons after eclosion in the sphingid moth, Manduca sexta.

SummaryUltrastructural aspects of the natural degeneration of a group of six motor neurons in the fourth abdominal ganglion of Manduca sexta are described. These motor neurons innervate intersegmental muscles that degenerate and disappear immediately after adult eclosion. The first detectable changes in the cell bodies appear 12 h after eclosion and include disruption of the endoplasmic reticulum and an increase in the size and number of lamellar bodies. At 32 h the nuclear membranes rupture, and the membranous and granular cytoorganelles segregate in different parts of the cell. At that stage the surrounding glial cells participate in the digestion of material from the degenerating neurons. From 72 h onward the remaining neuronal structures become disrupted, and are finally transformed into a single, large lamellar body (residual body) within the glial profile. The degeneration pattern differs significantly from that of embryonic vertebrate neurons.