False transmitter, 5,6-dihydroxytryptamine as a tool in selecting serotonergic Helix neurons for studies with isolated, dialysed cells

Abstract

Abstract 1. Dialysed serotonergic neurons were identified, isolated from the ganglia of 5,6-dihydroxytryptamine (5,6-DHT) treated snail, Helix pomatia L. Twenty-four to 40 days after injection of 5,6-DHT into the animal, serotonergic neurons show a specific brown pigmentation, which stays there for several weeks. After protease digestion (0.5–1.0 mg/ml for 10–12 min) the labelled neurons can be easily separated. This method ensures the reliable identification of serotonergic neurons for intracellular dialysis. 2. We showed that isolated serotonergic neurons maintain their membrane characteristics, and ion-currents can be registered under voltage clamp, just as from neurons of untreated animals. The threshold concentration of serotonin (10 −7 M) and the survival time of pigment labelled dissociated cells were the same as for the control cells. 3. Following 5-HT application, the voltage activated Ca-currents were either increased or decreased, depending on the neuron used. 4. The different responses are probably caused by different receptors on the cell membrane or by the presence of different types of Ca-channels. 5. The deactivation time constant of the Ca-current, calculated from the tail current, was also altered in the pigment labelled neuron following serotonin treatment.