Characterization of identifiable neurones in the head ganglia of the parasitic nematode Ascaris suum: a comparison with central neurones of Caenorhabditis elegans

Abstract

Intracellular recordings have been made from neurones in the head ganglia of Ascaris. The neurones had low resting membrane potentials of -21 +/- 9 mV (n = 78) and a relatively high input resistance (e.g. 25 M omega for a 100 microns cell). In all cases the intracellular location of the recording electrode was verified by injection of the fluorescent marker, 5,6-carboxyfluorescein (CBXF). To ascertain whether or not the low membrane potential was due to impalement damage, the same neurone was recorded from using two microelectrodes. The membrane potential following the first impalement by a 20 M omega 3 M KCl electrode was -38 mV and following the second impalement by a 80 M omega CBXF (for subsequent intracellular labelling) electrode was decreased to -34 mV. Input resistance of these cells was estimated using both single and two electrode intracellular recording techniques and in both cases yielded a relatively high value for the size of cell (e.g. 25 M omega for a 100 microns cell). Neurones labelled by intracellular injection of the fluorescent marker 5,6-carboxyfluorescein were morphologically simple and lacked extensive arborizations. The dorsal ganglion is a discrete structure consisting of only 3 neurones. Here we compare the morphological properties of these neurones to those described in the dorsal ganglion of Caenorhabditis elegans. The whole mount preparation of Ascaris ganglia thus provides a useful model to study the functional properties of neurones in nematode central nervous system and presents the possibility to assess central sites of action for anthelmintics.