The morphology and organisation of the central projections of tactile hair afferents from the hind leg of the locust, Schistocerca gregaria, were examined by staining individual hair afferents. Each tactile hair on the femur, tibia, and tarsus is innervated by a single sensory afferent, which projects to the ipsilateral half of the metathoracic ganglion. Afferents arborize in the ventralmost and lateral ventral association centres (vVAC and lVAC). The projections are organised somatotopically in a map with three axes, according to the position of the hair on the leg. First, proximo-distal: afferents from hairs on the proximal leg segments project more anteriorly than do those from hairs on distal leg segments. Moreover, on any given segment the afferents from the more proximal hairs project more anteriorly than do the afferents from the distal hairs. Second, antero-posterior: afferents from hairs on the posterior surface of the leg project more medially than do afferents from anterior hairs. Third, dorso-ventral: afferents from hairs on ventral parts of the leg project more ventrally than do afferents from the dorsal hairs. The afferents from posterior and anterior hairs project to an area between the central projections from dorsal hairs and ventral hairs. The position of a projection within the map is dependent upon the location of the hair on the leg and not the peripheral routes taken by the axon of its afferent to reach the ganglion.

SUMMARYElectric fields are pervasively present in the environment and occur both as a result of man-made activities and through natural occurrence. We have analysed the behaviour of cockroaches to static electric fields and determined the physiological mechanisms that underlie their behavioural responses. The behaviour of animals in response to electric fields was tested using a Y-choice chamber with an electric field generated in one arm of the chamber. Locomotory behaviour and avoidance were affected by the magnitude of the electric fields with up to 85% of individuals avoiding the charged arm when the static electric field at the entrance to the arm was above 8-10 kV m -1 . Electric fields were found to cause a deflection of the antennae but when the antennae were surgically ablated, the ability of cockroaches to avoid electric fields was abolished. Fixation of various joints of the antennae indicated that hair plate sensory receptors at the base of the scape were primarily responsible for the detection of electric fields, and when antennal movements about the head-scape joint were prevented cockroaches failed to avoid electric fields. To overcome the technical problem of not being able to carry out electrophysiological analysis in the presence of electric fields, we developed a procedure using magnetic fields combined with the application of iron particles to the antennae to deflect the antennae and analyse the role of thoracic interneurones in signalling this deflection. The avoidance of electric fields in the context of high voltage power lines is discussed.

No abstract

Extremely low frequency electromagnetic field (ELF EMF) pollution from overhead powerlines is known to cause biological effects across many phyla, but these effects are poorly understood. Honey bees are important pollinators across the globe and due to their foraging flights are exposed to relatively high levels of ELF EMF in proximity to powerlines. Here we ask how acute exposure to 50 Hz ELF EMFs at levels ranging from 20–100 µT, found at ground level below powerline conductors, to 1000–7000 µT, found within 1 m of the conductors, affects honey bee olfactory learning, flight, foraging activity and feeding. ELF EMF exposure was found to reduce learning, alter flight dynamics, reduce the success of foraging flights towards food sources, and feeding. The results suggest that 50 Hz ELF EMFs emitted from powerlines may represent a prominent environmental stressor for honey bees, with the potential to impact on their cognitive and motor abilities, which could in turn reduce their ability to pollinate crops.

1. The response properties of proprioceptive sensory neurons providing input to the local circuits controlling leg movements of the locust have been analysed by the Wiener kernel method. The proprioceptor, the femoral chordotonal organ, encodes the position and movements of the tibia about the femorotibial joint. 2. Intracellular recordings were made from sensory neurons while the apodeme of the organ was moved with a band-limited Gaussian white noise signal with a cutoff frequency of 27, 58, or 117 Hz. To define the input-output characteristics of the neurons, the first- and second-order Wiener kernels were computed by a cross-correlation between the spike response of the afferents and the white noise stimulus. 3. White noise stimulation elicited sustained spiking in 50 out of 54 afferents throughout the 20 s periods of stimulation and recording. The first-order kernels, the linear response properties, of these afferents were of six basic types that were dependent on the cutoff frequency of the white noise stimulus. These included 1) flexion-sensitive afferents that were primarily position sensitive irrespective of stimulus frequency, 2) flexion-sensitive afferents that were position sensitive at low frequencies but also coded velocity at higher frequencies, 3) flexion-sensitive afferents that coded velocity at all stimulus frequencies, 4) flexion-sensitive afferents that coded velocity at low stimulus frequencies but also acceleration at high frequencies, 5) extension-sensitive afferents that coded velocity at all stimulus frequencies, and 6) extension-sensitive afferents that coded velocity at low stimulus frequencies and acceleration at high frequencies. A seventh type contained the four remaining afferents that adapted rapidly to the stimulus within 3-5 s. These were all extension-acceleration sensitive irrespective of stimulus frequency. 4. The gain curves (produced by Fourier transform of the 1st-order kernels) and the power spectra of the linear models (produced by convolving the 1st-order kernels with the white noise) demonstrated that responses in the position-sensitive afferents are representative of a constant gain low-pass filter with a cutoff frequency of approximately 80 Hz, whereas those in the velocity- and acceleration-sensitive afferents are band passed, having peaks at 80 Hz. 5. The main nonlinearity was a signal compression in which the diagonal peak(s) of the second-order nonlinear kernels offset one or more peaks of the first-order kernels and represents a rectification or directional sensitivity of the afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

Synopsis Starting from the basis that the direction of sliding of one particle relative to another is, in general, inclined at an angle to the direction of the applied shear stress, a theory is developed to account for the difference between peak and residual stresses in terms of the volume expansion of the mass during shear. A reason is given to explain why the theory based on energy considerations cannot fully account for this difference. It is also suggested that the observed differences between the angle of sliding friction øμ (= tan−1μ) and the angle of internal friction øf are explainable in terms of the mode of failure which is itself a function of øμ. The analysis is extended to cover both direct and triaxial shear tests. Experimental results obtained from triaxial tests on samples of lead shot are presented and the pro-posed theory appears to fit these results, after several modifications have been made to them, better than the theory based on energy considerations. Tests on a set of samples lubricated with graphite are a novel feature of the experimental programme, and the results from these tests coupled with the results obtained from sliding friction tests are shown to be in general agreement with the proposed theory. Partant du fait que la direction de glissement d'une particule par rapport à une autre est, en général, inclinée a un angle en direction de l'effort de cisaillement appliqué, une théorie est developpée pour expliquer la difference entre l'effort maximum et l'effort constant en termes du volume d'expan-sion de la masse pendant le cisaillement. On donne une raison pour indiquer pourquoi la theorie basee sur des considerations d'energie ne peut pas expliquer complétement la différence. I1 est également suggéré que les différences observees entre l'angle de friction de glissement øμ(= tan−1μ) et l'angle de friction interne øf sont explicables en termes du mode de rupture, qui lui- même est fonction de øμ L'analyse est étendue pour couvrir tant les essais directs que les essais & trois axes de cisaillement. Les résultats expérimentaux obtenus par des essais a trois axes sur des echantillons de grenaille de plomb sont présentés et la théorie proposée prouve qu'elle s'accorde avec ces résultats, après y avoir apporte plusiers modifications, bien mieux que la theorie basée sur des considerations d'energie. Des expériences sur un jeu d'échantillons lubrifiés au graphite sont une nouveauté du programme expérimental et les résultats de ces expériences, ajoutes à ceux obtenus des experiences de friction de glissement, sont, dans l'ensemble, d'accord avec la theorie proposée.

No abstract

The relationships between the morphology and receptive fields of local and intersegmental interneurons that process mechanosensory information from a hindleg of the locust have been analysed. Sensory neurons from tactile hairs project to ventral areas of neuropil in the metathoracic ganglion where they form a 3-dimensional somatotopic map of a hindleg. By contrast, sensory neurons from a proprioceptor at the femoro-tibial joint (the femoral chordotonal organ) project to lateral and more intermediate areas of neuropil and have no branches in the most ventral regions of neuropil. Particular local and intersegmental interneurons respond to stimulation of specific arrays of hairs on a hindleg, or to movements of particular joints. Their receptive fields are defined, in part, by the patterns of excitatory, monosynaptic connections made by these afferents. Each interneuron has a characteristic receptive field and a characteristic morphology defined by its array of branches in the regions of neuropil containing the projections of the afferents that provide its monosynaptic inputs. Interneurons with inputs exclusively from tactile hairs have branches in the most ventral regions of neuropil, while those with exclusively proprioceptive inputs have branches only in more intermediate levels of neuropil. Interneurons with extensive receptive fields from tactile hairs also have extensive areas of branching within the ventral neuropil. Interneurons with receptive fields restricted to particular regions of the leg have branches restricted to the ventral region of neuropil containing the projections of afferents from that part of the leg. Thus, interneurons with inputs only from hairs on the tarsus have branches in the posterior region of neuropil corresponding to the projections of the tarsal afferents, while interneurons with receptive fields on the femur have branches in more anterior regions of neuropil corresponding to the projections of the femoral hair afferents. Interneurons with receptive fields on the tibia have branches in neuropil between the tarsal and femoral projections.