Parallel processing in the honeybee olfactory pathway: structure, function, and evolution

Animals face highly complex and dynamic olfactory stimuli in their natural environments, which require fast and reliable olfactory processing. Parallel processing is a common principle of sensory systems supporting this task, for example in visual and auditory systems, but its role in olfaction remained unclear. Studies in the honeybee focused on a dual olfactory pathway. Two sets of projection neurons connect glomeruli in two antennal-lobe hemilobes via lateral and medial tracts in opposite sequence with the mushroom bodies and lateral horn. Comparative studies suggest that this dual-tract circuit represents a unique adaptation in Hymenoptera. Imaging studies indicate that glomeruli in both hemilobes receive redundant sensory input. Recent simultaneous multi-unit recordings from projection neurons of both tracts revealed widely overlapping response profiles strongly indicating parallel olfactory processing. Whereas lateral-tract neurons respond fast with broad (generalistic) profiles, medial-tract neurons are odorant specific and respond slower. In analogy to “what-” and “where” subsystems in visual pathways, this suggests two parallel olfactory subsystems providing “what-” (quality) and “when” (temporal) information. Temporal response properties may support across-tract coincidence coding in higher centers. Parallel olfactory processing likely enhances perception of complex odorant mixtures to decode the diverse and dynamic olfactory world of a social insect.     

Influence of homologous n-alkanoic acids on functional properties of isolated skeletal muscles. I. Muscle contraction]

1.The contractility of isolated muscles of the frog (and in some instances of the rat) was investigated at room temperature in Ringer's solutions containing homologous alkanoic acids (100 mM C4 to 0.4 mM C10). 2. Free fatty acids decrease the contraction amplitudes evoked by direct stimulation. The effects increase with concentration, exposure, and chain length of the fatty acids. In Ringer's solution the changes are totally or partly reversible. 3. The depression of contraction amplitude induced by free fatty acids is removed by small concentrations of caffeine (2--5 mM) in Ringer's solution. 4. Interactions of fatty acids with different structures of skeletal muscle (mitochondria, sarcolemma and membranes of sarcoplasmic vesicles) are discussed. The distinct effect of fatty acids on stimulated muscles and the importance of membranes in the regulation of the calcium ion concentration in the cytoplasm suggest that fatty acids interact with membrane lipids.     

Interruption of searching movements of partly restrained front legs of stick insects,a model situation for the start of a stance phase?

Stick insects (Cuniculina impigra) possessing only one foreleg with restrained coxa performed searching movements. A force transducer was introduced as an obstacle into the plane of movement of femur or tibia. Depending on where it was introduced and whether it was touched for the first time during an upward or a downward movement, different kinds of behaviour of the leg were released. For these different movements, the forces applied to the obstacle and the electrical activity of the depressor, levator, retractor and protractor muscles are described. In addition the alterations occurring after ablation of several sense organs including the trochanteral campaniform sensilla are mentioned. The described movements were similar to the corresponding behaviours during walking at the end of swing phase and the beginning of stance phase. Therefore there is some probability that results obtained by this experimental paradigm can also be applied to the swing-stance transition.     

Plasma hyaluronan concentration: no circadian rhythm but large effect of food intake in humans

This study was designed to determine if a circadian rhythm in plasma hyaluronan concentration [HA] exists in the absence of physical activity, and if plasma [HA] is associated with feeding in human subjects. Five persons were studied under standardized conditions, blood samples being taken between 0600 and 2200 hours at 30-min intervals. Any orthostatic challenge and muscle activity was abolished by immobilization by a 6° head-down bed-rest, and the effect of a quasi-continuous ingestion of energy compared a normal, three-portion diet of equivalent energy content or to fasting. Reproducibility of HA profiles on two consecutive half-days was also studied. A highly sensitive immunoassay was used to determine plasma [HA]. The data indicated that without physical activity and without food ingestion, [HA] was unchanged and displayed no diurnal rhythm. In addition, we observed that [HA] increased after the first food intake, peaking after 60 min, and concluded from our results that without ingestion of a larger meal, and sessions of postural or muscle activity, no circadian plasma [HA] rhythm exists. Accepted: 10 June 1998     

A decomposable continuous immune network

Immune systems serve to detect evolutionarily unprecedented invasors. One way is to have a universal set of recognition molecules. Such an overlapping set of recognition molecules is necessarily self-detecting. When all recognition molecules are cell-bound, a second, passport or histocompatibility, recognition signal can be used to discriminate between invaded and non-invaded cell surfaces. Soluble molecules, by contrast, cannot be protected, nor can they obey a protecting signal. This implies certain constraints for universal humoral immune systems. A set of differential equations embodying those constraints is provided. It corresponds to an input-determined continuous automaton. One testable implication: rate sensitivity of the primary immune response.