Quantitative Characterization of the Filiform Mechanosensory Hair Array on the Cricket Cercus

Crickets and other orthopteran insects sense air currents with a pair of abdominal appendages resembling antennae, called cerci. Each cercus in the common house cricket Acheta domesticus is approximately 1 cm long, and is covered with 500 to 750 filiform mechanosensory hairs. The distribution of the hairs on the cerci, as well as the global patterns of their movement vectors, have been characterized semi-quantitatively in studies over the last 40 years, and have been shown to be very stereotypical across different animals in this species. Although the cercal sensory system has been the focus of many studies in the areas of neuroethology, development, biomechanics, sensory function and neural coding, there has not yet been a quantitative study of the functional morphology of the receptor array of this important model system.We present a quantitative characterization of the structural characteristics and functional morphology of the cercal filiform hair array. We demonstrate that the excitatory direction along each hair's movement plane can be identified by features of its socket that are visible at the light-microscopic level, and that the length of the hair associated with each socket can also be estimated accurately from a structural parameter of the socket. We characterize the length and directionality of all hairs on the basal half of a sample of three cerci, and present statistical analyses of the distributions.The inter-animal variation of several global organizational features is low, consistent with constraints imposed by functional effectiveness and/or developmental processes. Contrary to previous reports, however, we show that the filiform hairs are not re-identifiable in the strict sense

<em>flp-32</em> Ligand/Receptor Silencing Phenocopy Faster Plant Pathogenic Nematodes

Restrictions on nematicide usage underscore the need for novel control strategies for plant pathogenic nematodes such as Globodera pallida (potato cyst nematode) that impose a significant economic burden on plant cultivation activities. The nematode neuropeptide signalling system is an attractive resource for novel control targets as it plays a critical role in sensory and motor functions. The FMRFamide-like peptides (FLPs) form the largest and most diverse family of neuropeptides in invertebrates, and are structurally conserved across nematode species, highlighting the utility of the FLPergic system as a broad-spectrum control target. flp-32 is expressed widely across nematode species. This study investigates the role offlp-32 in G. pallida and shows that: (i) Gp-flp-32 encodes the peptide AMRNALVRFamide; (ii)Gp-flp-32 is expressed in the brain and ventral nerve cord of G. pallida; (iii) migration rate increases in Gp-flp-32-silenced worms; (iv) the ability of G. pallida to infect potato plant root systems is enhanced in Gp-flp-32-silenced worms; (v) a novel putative Gp-flp-32 receptor (Gp-flp-32R) is expressed in G. pallida; and, (vi) Gp-flp-32R-silenced worms also display an increase in migration rate. This work demonstrates that Gp-flp-32 plays an intrinsic role in the modulation of locomotory behaviour in G. pallida and putatively interacts with at least one novel G-protein coupled receptor (Gp-flp-32R). This is the first functional characterisation of a parasitic nematode FLP-GPCR

The synaptic origins of receptive field properties in the cricket cercal sensory system

1. The synaptic connections made by identified sensory neurons were studied electrophysiologically in the cercal sensory system of the cricket (Acheta domestica).2. The results confirmed that the synaptic connections made by a particular sensory neuron were correlated with the precise topographic projection of the sensory neurons and the location of the postsynaptic dendrites within this afferent projection. Where an afferent axon overlapped the dendrites of an interneuron a monosynaptic connection was often found, where there was no overlap there was no connection.3. However, the synaptic connections expected, based on anatomical overlap, were not always detected and the present study has revealed two factors that account for this difference between expectation and reality.4. First, the synaptic connections made by a particular sensory neuron were not invariant, rather they were probabilistic. For a given sensory neuron-interneuron pair, there was a certain probability that a synapse between the two neurons would be detected in any given animal and this probability was seldom 100%.5. Second, the size of the receptor hair was directly correlated with the interneurons with which the sensory neuron formed synapses. For example, one interneuron, MGI, received input only from sensory neurons associated with small receptor hairs. In contrast, interneuron 10-3 received input from sensory neurons associated with large hairs. These results confirm the hypothesis of Shimozawa and Kanou (1984).6. Our conclusion was that two properties of the receptive fields of cricket giant interneurons, directional sensitivity and acceleration/velocity sensitivity, are the direct result of the monosynaptic inputs from sensory neurons