Morphological differences between excitatory and inhibitory nerve terminals in cockroach coxal muscles

Two morphologically distinct types of neuromuscular junction on the coxal leg muscles of the cockroach, Periplaneta americana, which have been physiologically described as innervated by fast, slow and inhibitory nerve fibers, have been found. In one type of neuromuscular junction the axon terminal contains many round clear synaptic vesicles and contacts several sarcoplasmic extensions from the muscle fiber. The muscle processes adhere to the axon terminal for a short distance (short contact or SC type). The axon terminal of the other type of neuromuscular junction directly contacts the muscle fiber and no extensions of the muscle fiber are formed. The contact region is comparatively long (long contact or LC type). The nerve terminal contains many polymorphic synaptic vesicles. From a correlation of the present morphological findings and the previous physiological results, it may be suggested that the SC type of nerve terminal represents both fast and slow nerve terminals and the inhibitory terminal is of the LC type.     

The fine structure of Gromphadorhina portentosa salivary glands:duct transport system

The gross external morphology of the salivary glands of Gromphadorhina portentosa is described from light, scanning, and transmission electron microscopic observations. Various techniques, such as cryofracturing and epoxy-fracturing followed by plastic removal, were employed. Internally, the transportation system is characterized by a cuticle-lined lumen bordered by duct cells. The duct collects secretory products, some of which are reabsorbed by duct cells. Products are transported to intercalary ducts and eventually to the hypopharynx and/or salivary reservoirs. Transmission electron micrographs demonstrate distinctive morphological differences between duct cells bordering ductules and those which line expanded regions of the duct. Duct cells which surround ductules have a microvillous-lined apical border in which the cuticular coat of the lumen may be only partially developed. Duct cells in other regions may retain microvilli, or the apical plasma membrane may invaginate and vesiculate. In some cells the apical region has neither microvilli nor invaginations, but possesses two morphologically different forms of microtubules. Some duct cells are characterized by the presence of lamellar bodies in the nuclear region and/or collagenous material above the basal lamina in the area where the acinar duct becomes confluent with the intercalary duct. The plasma membranes between adjacent duct cells within acini become convoluted, forming loops filled with cytoplasm. These loops, along with contact and septate desmosomes formed between membranes, may serve dual functions: adherent mechanisms between cells and/or transportation of materials between cells.     

Neuromuscular transmission in the coxal muscles of the cockroach

The coxal muscles of the cockroach are considered to be of two kinds, ‘slow’ and ‘fast’, according to their mechanical responses. In the present investigations the electrical responses of the two kinds of muscle were examined with intracellular electrodes. It is evident from these responses that the coxal muscles are each innervated by typical ‘fast’ axons giving evoked action potentials from the muscles which are of a uniform type. The ‘slow’ muscles receive in addition a ‘slow’ axon which gives rise only to facilitating junctional potentials. The mechanical differences are due to intrinsic properties of the muscle fibres, not to differences in neuromuscular transmission mechanisms at the synaptic level.     

Sense organs on the antennal flagellum of a giant cockroach, Gromphadorhina portentosa, and a comparison with those of several other species (Dictyoptera, Blattaria)

Two kinds of tactile hairs, plain and wavy, thick-walled chemoreceptors and two types of thin-walled chemoreceptors are present on the antennal flagellum of Gromphadorhina portentosa males. These are described and their location on the antenna noted. Females of this species have plain tactile hairs and the same types of chemoreceptors as do the males but wavy tactile hairs are absent. The antennal sense organs of a few specimens of five other species of cockroaches — Periplaneta americana, Blatta orientalis, Supella longipalpa, Pycnoscelus surinamensis and Diploptera punctata — were also examined. All lacked tactile hairs but were provided with thick-walled chemoreceptors and with two types of thin-walled chemoreceptors similar to those described for Gromphadorhina portentosa.     

Group influence on water conservation in the giant Madagascar hissing-cockroach, Gromphadorhina portentosa (Dictyoptera: Blaberidae)

Abstract. . Under laboratory conditions the hissing-cockroach Gromphadorhina portentosa (Schaum) forms clusters, which appears to be an adaptive behaviour to help reduce water loss. Adults grouped together retain water nearly twice as effectively as isolated individuals. This 'group effect' complements the cockroach's large body size (small surface area to volume ratio) to lower the rate of water loss still further. Despite a modest 28% tolerance limit for weight loss during dehydration, adult females survive absolute drying conditions of 0 % relative humidity without food and free water for at least a month, showing their impressive capacity for water retention. Rates of water loss of immature adults correlate with size, and no transition temperature is detected in females. To replenish water stores, cockroaches drank liquid water; there is no evidence for water gain by water vapour absorption. The profound impact exerted by the 'group' for water conservation suggests that members of this species live huddled together in nature, particularly during the long tropical dry season in order to conserve water, and this adds to previous evidence for the existence of a probable social structure.     

Susceptibility of cockroaches (Gromphadorhina portentosa,Nauphoeta cinerea and Blaptica dubia) exposed to entomopathogenic nematodes

Cockroaches are major pests, vectors of pathogenic bacteria and induce allergies. Current control methods use chemical pesticides, but they can be ineffective and costly and there are reports of resistance in the field; hence new control methods are needed. There are conflicting reports about the susceptibility of cockroaches to entomopathogenic nematodes (EPNs); so we investigated if EPNs could kill several diverse cockroach species, including the Madagascan hissing roach (Gromphadorhina portentosa), the Lobster roach (Nauphoeta cinerea) and Blaptica dubia. Female adult cockroaches were exposed to either commercial products containing Steinernema kraussei or a combination of Heterorhabditis spp. and Steinernema spp. at 50 and 150 nematodes per cm² for 21 days. We also monitored feeding and the numbers of infective juveniles that were produced from each cockroach corpse. We found that S. kraussei were harmless to all cockroach species (at both doses) but when exposed to a mixture of Heterorhabditis spp. and Steinernema spp. B. dubia died after 6 days and its feeding was strongly inhibited. We also found that the mixture of Heterorhabditis spp. and Steinernema spp. could proliferate in the cadavers of B. dubia whilst S. kraussei could only reproduce in G. portentosa and B. dubia but not N. cinerea. In conclusion, S. kraussei was harmless to all three cockroach species but B. dubia was killed when exposed to Heterorhabditis spp. and Steinernema spp., highlighting the differences in the host range of EPNs.     

Endogenous and environmental factors influence the dietary fractionation of 13C and 15N in hissing cockroaches Gromphadorhina portentosa

Since DeNiro and Epstein's discovery that the (13)C and (15)N isotopic signatures of animals approximate those of their respective diets, the measurement of stable isotope signatures has become an important tool for ecologists studying the diets of wild animals. This study used Madagascar hissing cockroaches (Gromphadorhina portentosa) to examine several preexisting hypotheses about the relationship between the isotopic composition of an animal and its diet. Contrary to my predictions, the results revealed that the tissues of adult cockroaches raised for two generations on a diet of known isotopic composition did not demonstrate enrichment of heavy stable isotopes. Moreover, the (15)N signatures of cockroaches were neither influenced by periods of rapid growth (i.e., 300-fold increase in dry body mass over 120 d) nor by imposed periods of starvation lasting up to 80 d. The offspring born to mothers raised on known diets were enriched in (15)N. Diet-switching experiments showed that turnover times of (13)C were highly correlated with age and ranged from 9 to 10 d to 60 to 75 d in subadults and adults, respectively. Adults subjected to diet switches differed from the subadults in that the adults achieved equilibrated isotopic signatures that were shifted approximately 1.0 per thousand toward their respective original diets. Lipid fractions of adult cockroaches averaged 2.9 per thousand more depleted in (13)C than in lipid-free fractions, but no changes in (13)C were observed in aging adults. Exposure to reduced ambient temperature from 33 degrees C to 23 degrees C over 120 d did not influence isotopic signatures of tissues. Overall, the results of this study reveal that different endogenous and exogenous factors can influence the isotopic signatures of cockroaches. These findings reinforce the need to conduct controlled studies to further examine environmental factors that influence the relationships between the isotopic signatures of animals and their diets.     

Plasticity in the cockroach neuromuscular system

The retrograde transport of wheat germ agglutinin-conjugated horseradish peroxidase extracellularly injected into a leg muscle was used to identify the regenerating cockroach motor neurons that have grown an axonal branch into that muscle. At least 66% of the animals with crushed nerve roots eventually reform the original innervation pattern of this muscle with no mistakes. In spite of this apparent specificity the cockroach neuromuscular system can express plasticity as evidenced by the correction of mistakes made at early stages of regeneration. These mistakes are corrected through elimination during the time interval between 40 and 60 days after nerve crush. In addition, when the distal segments of the leg are removed, thus depriving some motor neurons of their normal target muscles, many of them form stable inappropriate axonal branches in denervated as well as fully innervated muscles. These observations are discussed in terms of possible mechanisms responsible for the specificity of the cellular interactions and in terms of their relevance to understanding the development of vertebrate neuromuscular systems.     

Comparison of synaptic vesicles of neuromuscular and nerve electroplaque junctions in Torpedo marmorata]

A morphological comparison of neuromuscular and nerve-electroplaque synapses of torpedo was performed. Synaptic vesicles are much smaller at the neuromuscular synapse. The question of the respective role of these populations is raised.     

Competition in vitro among fungi acquired from the exoskeleton of the giant Madagascar hissing-cockroach,Gromphadorhina portentosa,and its relevance to human health

Few insects have received as much public attention as the Madagascar hissing-cockroach, Gromphadorhina portentosa, coveted by children as a household pet. Recently, this insect has been linked to allergies and asthma triggered by an antagonistic external mycoflora, and some of these fungi are known to cause serious illnesses, namely Aspergillus spp., Mucor spp. and Rhizopus spp. Other cockroach species serve as carriers of medically important fungi, but G. portentosa is of special concern because it is deliberately reared in captivity. The aim of this study was to ascertain why certain types of fungi dominate the exoskeleton’s mycoflora whereas others do not. Six ascomycetes (Alternaria alternata, Aspergillus flavus, Aspergillus niger, Cladosporium cladosporioides, Penicillium glabrum, Trichoderma viride), and two zygomycetes (Mucor racemosus, Rhizopus stolonifer) initially acquired from the exoskeleton of G. portentosa, were tested for their competitive ability to inhibit one another in vitro, using the cockroach as the primary substratum. R. stolonifer, M. racemosus, and mycoparasitic T. viride grew at a significantly faster rate compared to the other taxa, and growth rates correlated positively with conidia output. Slower colony growth rates were noted prior to physical contact, suggesting that the fungi engaged in chemical antagonism. Three genera emerged that best fit the profile of exploitative competitors – Rhizopus, Mucor, Trichoderma. The latter two genera completely inhibited the growth of all fungal taxa tested and also had some capacity to grow over the mycelium of another fungus. We conclude that M. racemosus and T. viride in particular, are successful agents of G. portentosa’s mycoflora because they utilize both exploitation and interference competition to their advantage. Eliminating or reducing the simple sugar load entering the cockroach colony may be one way to tilt the composition of the mycoflora to favour strains that are less medically significant. Thus, we emphasize reduction of the antagonistic fungi at the colony (food entry) level and less so on the exoskeleton level.     

The terminal neuromuscular junctions of lower chordates

Summary The structure of the terminal neuromuscular junctions found close to the insertions of myotomal muscle fibres in teleost fish and amphibia is described, and it is concluded that in both groups, the pattern of innervation is essentially similar. Different degrees of complexity are described, both in the terminal nerve branches, and in the sub-junctional apparatus. It is suggested that the terminal pattern of innervation is an adaptation to the requirements of rapid swimming.