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Neuromodulatory neurons located in the brain can influence activity in locomotor networks residing in the spinal cord or ventral nerve cords of invertebrates. How inputs to and outputs of neuromodulatory descending neurons affect walking activity is largely unknown. With the use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and immunohistochemistry, we show that a population of dorsal unpaired median (DUM) neurons descending from the gnathal ganglion to thoracic ganglia of the stick insect Carausius morosus contains the neuromodulatory amine octopamine. These neurons receive excitatory input coupled to the legs’ stance phases during treadmill walking. Inputs did not result from connections with thoracic central pattern-generating networks, but, instead, most are derived from leg load sensors. In excitatory and inhibitory retractor coxae motor neurons, spike activity in the descending DUM (desDUM) neurons increased depolarizing reflexlike responses to stimulation of leg load sensors. In these motor neurons, descending octopaminergic neurons apparently functioned as components of a positive feedback network mainly driven by load-detecting sense organs. Reflexlike responses in excitatory extensor tibiae motor neurons evoked by stimulations of a femur-tibia movement sensor either are increased or decreased or were not affected by the activity of the descending neurons, indicating different functions of desDUM neurons. The increase in motor neuron activity is often accompanied by a reflex reversal, which is characteristic for actively moving animals. Our findings indicate that some descending octopaminergic neurons can facilitate motor activity during walking and support a sensory-motor state necessary for active leg movements. NEW & NOTEWORTHY We investigated the role of descending octopaminergic neurons in the gnathal ganglion of stick insects. The neurons become active during walking, mainly triggered by input from load sensors in the legs rather than pattern-generating networks. This report provides novel evidence that octopamine released by descending neurons on stimulation of leg sense organs contributes to the modulation of leg sensory-evoked activity in a leg motor control system.

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Tout le monde croit 9a. Rien ne le prouve puisqu' on ne peut pas les comparer." (Raymond Queneau, Les fleurs bleues)The paper seeks to shed some light on the intricate relationship that holds between comitatives and Instrumentals in the languages of the world. By way of checking the Companion Metaphor on the basis of a large crosslinguistic sample, a number of revisions are put forward as to the validity of the supposedly universal preference for comitative-instrumental syncretism. The paper demonstrates that the syncretistic patterns in which comitatives and Instrumentals participate depend upon several parameters among which areal factors are especially important. In addition, the hypothesis is put forward that the syncretistic behaviour of comitatives and instrumentals cannot be explained in terms of propositional concepts. Rather, the syncretistic preferences observed for comitatives and Instrumentals are suggestive of a feature-based explanatory model. 1

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