The stomatogastric ganglion (STG) of shellfish includes 30 neurons and produces pyloric rhythms. It is the common model to study central pattern generator (CPG). Regulation of pyloric rhythms not only is related to the property of single neurons in STG but also depends on the connections and property of the whole neuronal network. It has been found that transient potassium current (I(A)) and hyperpolarization-activated cation current (I(h)) exist in certain types of neurons of STG. However, roles played by these two currents in maintaining and regulating the pyloric rhythms are unknown. In the present study, in vitro electrophysiological recordings were performed on crayfish STG to examine the role played by I(A) and I(h) in regulation of pyloric rhythm. 4AP (2 mmol/L), a specific inhibitor of I(A), caused a decrease in pyloric cycle (P < 0.01), an increase in PD (pyloric dilator) ratio, a decrease in PY (pyloric) ratio (P < 0.01) and delay of phases of LP and PY firing. ZD7288 (100 μmol/L), a specific inhibitor of I(h), caused a decrease in pyloric cycle (P < 0.01), an increase in PD ratio (P < 0.01), an increase in LP (lateral pyloric) ratio (P < 0.01), a decrease in PY ratio (P < 0.01) and delay of phases of LP and PY firing. These results indicate that I(A) and I(h) play important roles in regulating pyloric rhythms in crayfish STG.
Animals ; Astacoidea ; cytology ; Ganglia, Invertebrate ; physiology ; Neurons ; cytology ; Pylorus ; innervation

OBJECTIVEto investigate the effect of deoxypodophyllotoxin (DOP) on membrane potential of dorsal unpaired median neurons (DUM, neurons) and its correlation with sodium channel.

METHODSDUM neurons were labeled with DiBAC4(3). Laser scanning confocal microscope was used to monitor the changes of membrane potential at real time on these neurons that were treated with different concentrations of the DOP. The effect of sodium channel blocker tetrodotoxin (TTX) on the changes was also observed.

RESULTSmembrane potential depolarization induced by the DOP peaked at 5 min and became stabilized after 8min. After compared with fluorescence intensity without treatment, the normalized fluorescence intensity was 69.6 ± 3.0, 72.1 ± 2.7, 77.8 ± 3.6, 86.2 ± 3.1 in cells which were treated with 1, 5, 25, 125 micromol/L DOP, respectively. These numbers were significantly lower than those from untreated control cells (P < 0.01). When DUM neurons were co-incubated with 1 micromol/L TTX for 20 min, then treated with 25 micromol/L DOP, the intensity changed to 63.6 ± 5.4, which was similar to that of the control (P > 0.05). This indicated that the effect of DOP could be completely inhibited by TTX.

CONCLUSIONDOP induced membrane depolarization of DUM neurons in the range of 1 approximately 125 micromol/L and the sodium channel should be involved in this process.

Animals ; Cells, Cultured ; Ganglia, Invertebrate ; drug effects ; physiology ; Membrane Potentials ; drug effects ; physiology ; Neurons ; drug effects ; physiology ; Periplaneta ; drug effects ; physiology ; Podophyllotoxin ; analogs & derivatives ; pharmacology ; Sodium Channels ; metabolism

The purpose of this study is to identify the electrical activity of neuron, the existence of the transition from bursting pattern to spiking pattern and the ion mechanism of the bursting pattern. The intracellular electrical activity patterns of single neurons in the stomatogastric ganglion (STG) of crayfish were recorded when the extracellular calcium concentration ([Ca(2+)](o)) or calcium-dependent potassium channel blocker tetraethylammonium concentration ([TEA](o)) were changed, using intracellular recording method. These single neurons were also functionally isolated from the ganglion by application of atropine and picrotoxin which could block the inhibitory acetylcholine synapses and glutamatergic synapses respectively. When [Ca(2+)](o) was decreased by increasing EGTA, the membrane potential of the neuron was increased, and the electrical activity patterns were changed from the resting state with lower potential value (resting state of polarization) to the bursting pattern firstly, and then to the spiking pattern, at last to the resting state with higher potential value (resting state of depolarization). When [TEA](o) was increased, the membrane potential of the neuron was increased, and the electrical activity pattern was changed from the resting state with lower potential value (resting state of polarization) to the bursting pattern firstly, and then to the spiking pattern. The duration of the burst of the bursting pattern was increased. When [Ca(2+)](o) was increased or [TEA](o) was decreased, an inverse procedure of the electrical activity pattern was exhibited. On one hand, the results indicate that a single neuron can generate various electrical activity patterns corresponding to different physiological conditions, and the regularity of the transitions between different electrical activity patterns. On the other hand, the results identify that the initiation and termination of the burst in bursting pattern are determined by calcium-activated potassium conductance, which is adjusted by intracellular calcium concentration influenced by inward calcium current. It may be the ionic mechanism of generation of the bursting pattern in a single neuron.
Action Potentials ; physiology ; Animals ; Astacoidea ; physiology ; Calcium ; metabolism ; Calcium Channels ; metabolism ; Ganglia, Invertebrate ; physiology ; Neurons ; physiology ; Potassium Channels, Calcium-Activated ; metabolism