The motornervous system ofAscaris: electrophysiology and anatomy of the neurons and their control by neuromodulators

Abstract

Analysis of the electrical properties of neurons in the motornervous system of Ascaris sutom suggests that it is largely an analogue system. The motorneurons do not conduct action potentials and they release transmitter tonically at their normal resting potential; transmitter release is increased or decreased as a continuous function of membrane potential. Despite extensive physiological descriptions of the electrical properties of the neurons and their synapses, as well as morphological descriptions of the synaptic circuitry of the system, the predicted activities of the neurons in the circuit differ from those observed by direct recording in semi-intact behaving animals. We conclude that the description of the circuit is incomplete. There are several possibilities for the missing elements, including chemical, proprioceptive, and additional neuronal components. Recently, attention has been focussed most heavily on the intercellular chemical signalling systems; in addition to those mediated by classical neurotransmitters, a surprisingly complex array of neuropeptides has been identified. One family of these peptides, the AF peptides, has been analyzed in detail. It comprises at least 20 peptides, and they fall into sequence-related subfamilies. One of these subfamilies, containing 6 peptides, is encoded by a single transcript, suggesting that the AF peptides are under multiple genetic control. All AF peptides tested have potent activity on the motornervous system and/or on muscle. There are multiple physiological activities, and cellular localization studies show multiple patterns of cellular expression. Studies on Panagrellus and Caenorhabditis emphasize the diversity of this family and its genetic control.

Neuromuscular function in plant parasitic nematodes: a target for novel control strategies?

“…Firstly, there are those FLPs that have been repeatedly identified in a wide range of nematode species such that they appear to be ubiquitous throughout the phylum. Examples of such FLPs include KSAYMRFamide and KHEYLRFamide, which we have identified in both G. pallida and H. glycines and which have previously been found in C. elegans , P. redivivus (Maule et al 1994 a, b), A. suum (Davis & Stretton, 1996), and the sheep roundworm, Haemonchus contortus (Keating et al 1995 ;Marks et al 1999). Others have speculated that the highly conserved nature of these FLPs suggests some common function critical to nematode neurobiology and also draw attention to the fact that these FLPs are multiply encoded on their own flp genes and are usually the most abundant FLPs in nematode extracts .…”

Isolation and Preliminary Biological Assessment of AADGAPLIRFamide and SVPGVLRFamide from Caenorhabditis elegans

“…For instance, flp-1 gene knockout revealed multiple phenotypic changes in Caenorhabditis elegans (6). To date, FaRPs have been isolated from four species of nematodes, including the free-living organisms C. elegans (7-11) and Panagrellus redivivus (12)(13)(14) and the parasites Haemonchus contortus (15,16) and Ascaris suum (17)(18)(19)(20). Of these, four homologous FaRPs have been isolated from both free-living and parasitic species.…”

El nematodo Caenorhabditis elegans como modelo para evaluar el potencial antihelmíntico de extractos de plantas

“…El modelo nematodo C. elegans es todavía más útil para evaluar el potencial antihelmíntico de un extracto, porque comparte características morfológicas, genéticas y neurológicas con los nematodos parásitos (77,83,84) . Incluso se ha reportado que algunos nematodos, como Ascaris suum, que no son tan cercanos filogenéticamente a C. elegans, tienen alta similitud en la neuromusculatura y en los neurotransmisores (84,85) .…”

“…Incluso se ha reportado que algunos nematodos, como Ascaris suum, que no son tan cercanos filogenéticamente a C. elegans, tienen alta similitud en la neuromusculatura y en los neurotransmisores (84,85) . Esto es relevante, debido a que el mecanismo de acción de varios de los antihelmínticos implica aspectos relacionados con la motilidad.…”