Ionic currents in the somatic membrane of identified T-mechanosensory neurons isolated from segmental ganglia of the medicinal leech.

Based on physiological investigations, Nicholls and Baylor (1968) identified and described three types of mechanosensory neurons in segmental ganglia of medicinal leech: T-cells receiving touch information, P-cells sensitive to changes in pressure applied on the skin, and N-cells affected by nociceptive stimuli. The electrical excitability and the passive electrical parameters of the somatic membrane of mechanosensory neurons have been thoroughly investigated (Baylor and Nicholls 1969a, b, c; Jansen and Nicholls 1973; Fuchs et al. 1981). Differences have been observed in the electrical pattern between different types of mechanosensory neurons. T-cells were found to differ from the other types of the leech neurons also by their sensitivity to some drugs that alter the function of the voltage-dependent ionic channels (Kleinhaus and Prichard 1983; Johan-sen and Kleinhaus 1985). Attempts to determine the characteristics of the different types of leech neurons under voltage-clamp conditions using single-or double-barrelled microelectrodes came up against some difficulties (Kleinhaus and Prichard 1983). We applied the methods of intracellular perfusion and voltage-clamp to study the ionic mechanisms of excitability of the somatic membrane of leech neuron under controlled external and internal ionic conditions. The experiments were carried out on type T-mechanosensory neurons isolated from segmental ganglia of medicinal leech. Ganglia from Hirudo medi-cinalis were treated with 0.3 % Pronase E, dissolved in standard leech Ringer solution (Table 1, bottom), for 20 min at 18—20 °C. After the treatment, the ganglia were transferred to the standard solution and kept there for 60 min at 4°C. Using finely sharpened metal needles, the connective tissue sheaths covering the ganglion were torn in several places as far as possible from the selected neurons and carefully removed from the glial packets with nerve cell bodies