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

Background Damage to the adult central nervous system often leads to long-term disruptions in function due to the limited capacity for neurological recovery. The central nervous system of the Mediterranean field cricket, Gryllus bimaculatus, shows an unusual capacity for compensatory plasticity, most obviously in the auditory system and the cercal escape system. In both systems, unilateral sensory disruption leads the central circuitry to compensate by forming and/or strengthening connections with the contralateral sensory organ. While this compensatory plasticity in the auditory system relies on robust dendritic sprouting and novel synapse formation, the compensatory plasticity in the cercal escape circuitry shows little obvious dendritic sprouting and instead may rely on shifts in excitatory and inhibitory synaptic strength. Results In order to better understand what types of molecular pathways might underlie this compensatory shift in the cercal system, we used a multiple k-mer approach to assemble a terminal ganglion transcriptome that included ganglia collected one, three, and 7 days after unilateral cercal ablation in adult, male animals. We performed differential expression analysis using EdgeR and DESeq2 and examined Gene Ontologies to identify candidates potentially involved in this plasticity. Enriched GO terms included those related to the ubiquitin-proteosome protein degradation system, chromatin-mediated transcriptional pathways, and the GTPase-related signaling system. Conclusion Further exploration of these GO terms will provide a clearer picture of the processes involved in compensatory recovery of the cercal escape system in the cricket and can be compared and contrasted with the distinct pathways that have been identified upon deafferentation of the auditory system in this same animal.

GABA-like immunoreactivity of an identified nonspiking local interneurone in the crayfish terminal abdominal ganglion

Using an antiserum directed against -aminobutyric acid (GABA) to label neurones with GABA-like immunoreactivity, approximately 70 central neurones (68±9; mean ± s.e.m., N=9) were labelled in the terminal abdominal ganglion of the crayfish Procambarus clarkii. This mean number of neurones with GABA-like immunoreactivity represents approximately 10 % of the total number of neurones in the terminal ganglion. A combination of intracellular staining using Lucifer Yellow and immunocytochemical staining revealed that an identified nonspiking local interneurone (the local directionally selective interneurone, LDS) showed GABA-like immunoreactivity.

The initiation of pre-ecdysis and ecdysis behaviors in larval Manduca sexta: the roles of the brain, terminal ganglion and eclosion hormone.

Each larval molt of Manduca sexta culminates in the sequential performance of pre-ecdysis (cuticle loosening) and ecdysis (cuticle shedding) behaviors. Both behaviors are thought to be triggered by the release of a peptide, eclosion hormone (EH), from brain neurons whose axons extend the length of the nervous system. EH bioactivity appears in the hemolymph at the onset of pre-ecdysis behavior, and EH injection can trigger pre-ecdysis and ecdysis behaviors prematurely. The present study examined the effects of removing or disconnecting portions of the central nervous system prior to the time of EH release on the initiation of pre-ecdysis and ecdysis behaviors at the final larval molt. We found that the initiation of pre-ecdysis abdominal compressions at the appropriate time required the terminal abdominal ganglion (AT) but not the brain; the initiation of pre-ecdysis proleg retractions at the appropriate time required neither the AT nor the brain; the initiation of ecdysis at the appropriate time usually required the brain but did not require the AT; and premature pre-ecdysis (but not ecdysis) could be elicited in isolated abdomens by injection of EH. Finally, pre-ecdysis behavior performed by brainless larvae was not associated with the normal elevation of EH bioactivity in the hemolymph or the normal loss of EH immunoreactivity from peripheral neurohemal release sites.

ACTIVITY OF GIANT INTERNEURONES AND OTHER WIND-SENSITIVE ELEMENTS OF THE TERMINAL GANGLION IN THE WALKING CRICKET

Using intracellular recording techniques in stationary walking crickets (Gryllus bimaculatus), we have investigated the relationship between locomotion and the activity of interneurones ascending from the terminal ganglion. Nine different types of giant interneurones (GI) were characterized during walking and standing. One third of them reduced their activity, while the others enhanced their spike rate, during walking. These physiological properties were strictly correlated with morphological characteristics such as axon position in the longitudinal tracts of the terminal ganglion. In general, ventral GIs reduced and dorsal GIs increased their spike frequency during walking. In some of them, there was a weak but significant correlation between the spike rate and translational speed, but no correlation with rotational speed. In all GIs except 10-3a, the changes in activity occurred at the start of walking. In GI 10-3a, an increase in membrane potential and spike rate was observed before the start of locomotion. Therefore, an intrinsic mechanism within the central nervous system operating on GI 10-3a is suggested. Additionally, the activities of filiform hair receptors and of previously undescribed small ascending interneurones (SAI) have been studied during walking. About 80 % of the receptors slightly increased their spike rate during walking, while one SAI became more active during walking and another one was hardly affected. The physiological properties of ascending interneurones are discussed with respect to their modulation and particular function during walking.

Ectopic sensory neurons in mutant cockroaches compete with normal cells for central targets

The cercus of the first instar cockroach, Periplaneta americana, bears two filiform hairs, lateral (L) and medial (M), each of which is innervated by a single sensory neuron. These project into the terminal ganglion of the CNS where they make synaptic connections with a number of ascending interneurons. We have discovered mutant animals that have more hairs on the cercus; the most typical phenotype, called “Space Invader” (SI), has an extra filiform hair in a proximo-lateral position on one of the cerci. The afferent neuron of this supernumerary hair (SIN) “invades the space” occupied by L in the CNS and makes similar synaptic connections to giant interneurons (GIs). SIN and L compete for these synaptic targets: the size of the L EPSP in a target interneuron GI3 is significantly reduced in the presence of SIN. Morphometric analysis of the L afferent in the presence or absence of SIN shows no anatomical concomitant of competition. Ablation of L afferent allows SIN to increase the size of its synaptic input to GI3. Less frequently in the mutant population, we find animals with a supernumerary medical (SuM) sensillum. Its afferent projects to the same neuropilar region as the M afferent, makes the same set of synaptic connections to GIs, and competes with M for these synaptic targets. The study of these competitive interactions between identified afferents and identified target interneurons reveals some of the dynamic processes that go on in normal development to shape the nervous system.