Limbs vs. Jaws: Can They Be Compared?

Current experimental research on mammalian limb muscle structureand function is compared to that on mammalian jaw muscles. Twomajor areas of comparison are stressed: structural and functional.Comparisons of limbs and jaws are made from the point of viewof the impact of recent studies on simple mechanical modelsof limb/jaw muscle function. Limb muscle structure is comparedto jaw muscles at the level of muscle architecture, muscle histochemicaland motor unit properties, and the organization of motor unitsinto neuromuscular compartments. Such comparisons reveal thatalthough limb muscles and jaw muscles might be organized insimilar ways, fundamental differences exist, both in terms ofmuscle structure and the functional conclusions which have beenbased on studies of muscle structure. The comparisons also demonstratethat much recent evidence from structural studies have had littledirect impact on simple models of muscle function but a muchlarger influence on the assumptions of the models. Comparisonsof limb/jaw muscle function from kinematic and EMG studies,indicate that many masticatory strategies are used by differentmammals but the basic problems of posture and locomotion havebeen met with essentially similar solutions, even among diversemammalian groups. The results of such comparisons demonstratethat both limb and jaw muscle function are sufficiently complexthat new or re-vitalized models are needed if the relationshipbetween structure and function are ever to be understood.     

Olfactory sensitivity in tsetse flies: a daily rhythm

The diurnal tsetse Glossina morsitans morsitans bites especially in early morning and late afternoon; around midday feeding is at a low. In laboratory apparatus that measures the amount of locomotion under constant conditions over the photophase, the flies display a similar patterning of activity levels. The profile of daily rhythms for G. morsitans reported in the literature includes a number of motor and sensory motor systems that fluctuate cophasically. Lacking is a study on the patterning of the senses' response levels. In this paper we present the first instance of a daily modulation in the sense of smell. We stimulated the antennae with concentration series of host-derived odours and measured the spiking rate of cells at different times during the photophase. The concentration-response curves suggest that the sensitivity of antennal olfactory cells flows in parallel with the other daily rhythms. This was also reflected in electroantennograms (EAGs). The electroantennography was extended to G. fuscipes fuscipes, whose level of spontaneous locomotor activity--instead of following a U- shaped pattern--rises gradually over the photophase. Again, the EAGs appeared to parallel the species' locomotor activity. What we believe happens is that the organism tones down the sensitivity of its odour receptors during periods of anticipated inactivity for reasons of economy.      

The Products and Pathways of Glucose Catabolism in Herpetomonas muscarum ingenoplastis and Herpetomonas muscarum muscarum

ABSTRACT. The products and pathways of glucose catabolism in the insect trypanosomatids Herpetomonas muscarum ingenoplastis and Herpetomonas muscarum muscarum have been studied with the aim of elucidating how both organisms are able to proliferate well under aerobic and anaerobic conditions. When incubated in medium containing glucose as the only exogenous carbon source, catabolism was found to be fermentative in both cases. Acetate was a major product of both organisms while H. m. ingenoplastis produced more ethanol and propionate and less succinate than H. m. muscarum . Ethanol production by H. m. ingenoplastis decreased both under anaerobic conditions and in the presence of elevated CO₂ concentrations, whereas succinate and propionate release by this organism were greater in high CO₂ and anoxia, respectively. Succinate production by H. m. muscarum was greatest under anaerobic conditions in elevated CO₂ whereas propionate was only a minor product. The same four products were released during growth of the organisms in complex medium, but the relative proportions differed suggesting that other substrates were being used. Both organisms contained enzymes of the glycolytic and pentose phosphate pathways, but while all activities of the TCA cycle were present in H. m. muscarum . NAD-linked isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, succinate CoA synthase and succinate dehydrogenase were not detected in H. m. ingenoplastis . Fumarate reductase activity was present in both organisms. The data presented suggest that CO₂-fixation and reverse flux through the TCA cycle may be important factors that enable the organisms to undergo anaerobiosis.