Transcriptional expression changes during compensatory plasticity in the prothoracic ganglion of the adult cricket Gryllus bimaculatus

Most adult organisms are limited in their capacity to recover from neurological damage. The auditory system of the Mediterranean field cricket, Gryllus bimaculatus, presents a compelling model for investigating neuroplasticity due to its unusual capabilities for structural reorganization into adulthood. Specifically, the dendrites of the central auditory neurons of the prothoracic ganglion sprout in response to the loss of auditory afferents. Deafferented auditory dendrites grow across the midline, a boundary they normally respect, and form functional synapses with the contralateral auditory afferents, restoring tuning-curve specificity. The molecular pathways underlying these changes are entirely unknown. Here, we used a multiple k-mer approach to re-assemble a previously reported prothoracic ganglion transcriptome that included ganglia collected one, three, and seven days after unilateral deafferentation in adult, male animals. We used EdgeR and DESeq2 to perform differential expression analysis and we examined Gene Ontologies to further understand the potential molecular basis of this compensatory anatomical plasticity. Enriched GO terms included those related to protein translation and degradation, enzymatic activity, and Toll signaling. Extracellular space GO terms were also enriched and included the upregulation of several protein yellow family members one day after deafferentation. Investigation of these regulated GO terms help to provide a broader understanding of the types of pathways that might be involved in this compensatory growth and can be used to design hypotheses around identified molecular mechanisms that may be involved in this unique example of adult structural plasticity.

Transcriptional Expression Changes During Compensatory Plasticity in the Central Nervous System of the Adult Cricket Gryllus Bimaculatus: I. Auditory System Plasticity in the Prothoracic Ganglia

Most adult organisms are limited in their capacity to recover from neurological damage. The auditory system of the Mediterranean field cricket, Gryllus bimaculatus, presents a compelling model for investigating neuroplasticity due to its unusual capabilities for structural reorganization into adulthood. Specifically, the dendrites of the central auditory neurons of the prothoracic ganglion sprout in response to the loss of auditory afferents. Deafferented auditory dendrites grow across the midline, a boundary they normally respect, and form functional synapses with the contralateral auditory afferents, restoring tuning-curve specificity. The molecular pathways underlying these changes are entirely unknown. Here, we used a multiple k-mer approach to re-assemble a previously reported prothoracic ganglion transcriptome that included ganglia collected one, three, and seven days after unilateral deafferentation in adult, male animals. We used EdgeR and DESeq2 to perform differential expression analysis and we examined Gene Ontologies to further understand the potential molecular basis of this compensatory anatomical plasticity. Enriched GO terms included those related to protein translation and degradation, enzymatic activity, and Toll signaling. Extracellular space GO terms were also enriched and included the upregulation of several protein yellow family members one day after deafferentation. Investigation of these regulated GO terms help to provide a broader understanding of the types of pathways that might be involved in this compensatory growth and can be used to design hypotheses around identified molecular mechanisms that may be involved in this unique example of adult structural plasticity.

Unravelling intra- and intersegmental neuronal connectivity between central pattern generating networks in a multi-legged locomotor system

Animal walking results from a complex interplay of central pattern generating networks (CPGs), local sensory signals expressing position, velocity and forces generated in the legs, and coordinating signals between neighboring ones. In the stick insect, in particular, intra- and intersegmental coordination is conveyed by these sensory signals. The rhythmic activity of the CPGs, hence of the legs, can be modified by the aforementioned sensory signals. However, the precise nature of the interaction between the CPGs and these sensory signals has remained largely unknown. Experimental methods aiming at finding out details of these interactions, often apply the muscarinic acetylcholine receptor agonist, pilocarpine in order to induce rhythmic activity in the CPGs, hence in the motoneurons of the segmental ganglia. Using this general approach, we removed the influence of sensory signals and investigated the putative connections between CPGs associated with the coxa-trochanter (CTr)-joint in the different segments (legs) in more detail. The experimental data underwent phase-difference analysis and Dynamic Causal Modelling (DCM). These methods can uncover the underlying coupling structure and strength between pairs of segmental ganglia (CPGs). We set up different coupling schemes (models) for DCM and compared them using Bayesian Model Selection (BMS). Models with contralateral connections in each segment and ipsilateral connections on both sides, as well as the coupling from the meta- to the ipsilateral prothoracic ganglion were preferred by BMS to all other types of models tested. Moreover, the intrasegmental coupling strength in the mesothoracic ganglion was the strongest and most stable in all three ganglia.

An interneurone of unusual morphology is tuned to the female song frequency in the bushcricket Ancistrura nigrovittata (Orthoptera, Phaneropteridae)

The interneurone AN5-AG7 of the duetting bushcricket Ancistrura nigrovittata has its soma in the seventh (penultimate) abdominal ganglion. Its major postsynaptic arborizations with dense thin branches of smooth appearance are found in the prothoracic ganglion. The branches terminate in the auditory neuropile, predominantly at the same location as those auditory receptors that respond best to the female song frequency. Correspondingly, AN5-AG7 responds preferentially to frequencies between 24 and 28 kHz, thereby matching the carrier frequency of the female response song quite well. At frequencies below 24 kHz, AN5-AG7 receives inhibition, which is sometimes seen as clear inhibitory postsynaptic potentials. At these frequencies, thresholds of excitatory postsynaptic potentials are considerably lower than spike thresholds. In contrast, above 20 kHz, the two thresholds match and they correspond to the behavioural threshold. The AN5-AG7 interneurone is more sensitive to soma-contralateral stimuli and it receives predominantly inhibition, but also some excitation, from the soma-ipsilateral ear. Response strength is not greatly affected by stimulus duration but shows prominent habituation. This habituation depends only weakly on intensity and frequency. Some AN5-AG7 interneurones show very small graded potentials and no spiking responses to any acoustic stimuli.

An auditory interneurone tuned to the male song frequency in the duetting bushcricket Ancistrura nigrovittata (Orthoptera, Phaneropteridae)

An auditory interneurone (AN1) of the bushcricket Ancistrura nigrovittata is described; it has a soma and dendrites in the prothoracic ganglion, an ascending axon and axon collaterals in the protocerebrum. As judged from morphological and physiological similarity, it is probably homologous to AN1 described in Tettigonia viridissima and to AN1 described in Gryllus bimaculatus. The occurrence and physiology of AN1 are not sex-specific. It receives predominant excitation between 12 and 16 kHz (male song frequency) and inhibition at lower frequencies and more strongly at higher frequencies. It shows optimum-type intensity/response curves. Frequency tuning and intensity-dependence compare well with female behaviour. Lesion experiments demonstrate that AN1 receives excitation and frequency-dependent inhibition from the soma-contralateral ear and inhibition from the soma-ipsilateral ear. The latter contributes to the clear left­right difference in its responses. AN1 does not obviously discriminate between temporal patterns of different behavioural effectivity. Its spiking, however, is coupled to the temporal pattern. It is hypothesized that AN1 may be involved in frequency processing by female A. nigrovittata.