CHARACTERIZATION OF IDENTIFIABLE NEURONS IN THE HEAD GANGLIA OF THE PARASITIC NEMATODE ASCARIS-SUUM - A COMPARISON WITH CENTRAL NEURONS OF CAENORHABDITIS-ELEGANS

Intracellular recordings have been made from neurones in the head gang lia of Ascaris. The neurones had low resting membrane potentials of -2 1+/-9 mV (n = 78) and a relatively high input resistance (e.g. 25 M Oh m for a 100 mu m cell). In all cases the intracellular location of the recording electrode was verified by injection of the fluorescent mark er, 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 follo wing the first impalement by a 20 M Ohm 3 M KCl electrode was -38 mV a nd following the second impalement by a 80 M Ohm CBXF (for subsequent intracellular labelling) electrode was decreased to -34 mV. Input resi stance of these cells was estimated using both single and two electrod e intracellular recording techniques and in both cases yielded a relat ively high value for the size of cell (e.g. 25 M Ohm for a 100 mu m ce ll). Neurones labelled by intracellular injection of the fluorescent m arker 5,6-carboxyfluorescein were morphologically simple and lacked ex tensive arborizations. The dorsal ganglion is a discrete structure con sisting of only 3 neurones. Here we compare the morphological properti es of these neurones to those described in the dorsal ganglion of Caen orhabditis elegans. The whole mount preparation of Ascaris ganglia thu s provides a useful model to study the functional properties of neuron es in nematode central nervous system and presents the possibility to assess central sites of action for anthelmintics.