| CPG-neural networks composed of a series of neurons and synapses, has ability of spontaneously producing rhythmic, patterned neural outputs in the absence of sensory feedback or patterned central input-exist. The rhythmic motor patterns of CPG depend on the nature of the network and external conditions on network regulation. Invertebrate preparations (lobster and locust) have always played a important role in the studies because of easily maintaining activities in vitro of these preparations, clearly anatomically distributed nervous systems, large neurons which are easily identified from different animals of the same species, and fixed neural synaptic connections and the populations. In vitro rhythmic motor patterns remain unchanged, and extracellular recordings from nerves which is distinguished firing of the various types of neurons has the fundamental rhythmicity.The crustacean stomatogastric ganglion (STG) is a central pattern generator network that sits on top of the crustacean stomach and controls the movements of the pylorus and gastric mill. The STG of lobster contains about 30 neurons, and controls the movements of the lobster's stomach. The stomatogastric ganglion(STG) contains two networks, one controlling the teeth of the gastric mill (the gastric CPG) and one controlling the pyloric filter apparatus (the pyloric CPG). The complete pyloric circuit consists of 14 neurons, one of which is an interneuron (AB) and the rest of which are motor neurons (PD, PY, LP, IC, VD). The roles and importance of cellular properties in the network and the synaptic connectivity are important in lives. Some of the inputs to the STG normally fire in bursts. However, their potentiation and acceleration of the output pattern are also produced by tonic stimulation of the nerve. The primary projection from the STG is the dorsal ventricular nerve (dvn). The dvn quickly splits into two medial ventricular nerve (mvn) and further down into lateral ventricular nerve (lvn). The lvn that consists of the LP, PY, and PD from the pyloric circuit is used to recording in vitro.Food has been macerated by the gastric millpasses into the pyloric region where it is filtered, kneaded further, and then passed on into the gut. Recording from the pyloric muscles in intact show a three-phase activity pattern which reflects stomach activities. In the pyloric system the driver neurons (PD/AB) put strong inhibitory synapses on the remaining "follower" neurons so that during driver activity, followers are shut off. After driver bursts terminate spontaneously, followers are free to fire in a sequence which is determined partly by their synaptic connections and partly by their cellular properties. The synchronous recording in vivo shows the same phase between AB and PD neurons. The identical result was recorded between IC and LP neurons, VD and PY neurons.At present, the research in sensory neural system is more than in motor neural system. The purpose of this work is to reinforce the research of STG in crayfish. Three-phase rhythms were recorded in normal condition and in condition of TEA being as blocker of the Ca2+-dependent potassium currents (IK(ca)) in STG of crayfish, chosen as experimental model in this paper.The main results are as follows:The recording of three-phase rhythm in normal condition of STG neuronsThree-phase rhythm composed of the firings generated by PD, LP and PY pyloric neurons in sequence, recorded in the stomatogastric ganglion (STG) of spiny lobster in normal condition. The rhythm pattern forms low frequency and high amplitude of the LP neurons, low frequency and low amplitude of the PY neurons, high frequency and lower amplitude of the PD neurons discharge. LP neuron does not start to discharge until PD neurons being resting. The three-phase rhythm shows the specfic forms and sequence.The change of three-phase rhythm under the influence of TEAThe Ca2+-dependent potassium currents (IK(ca)) plays a part in STG during spontaneous firing of neurons. The firing rhythm pattern was changed in condition of TEA, that bursting pattern was altered from homogeneous to being resting period. The firing patterns of LP and PY neurons were changed under the influence of 30 mmol/L TEA, while the firing sequence corresponding to each neuron of the three-phase rhythm did not change. The period of three-phase rhythm and the firing duration of PY neuron were decreased significantly (P<0.01). The firing duration of LP neuron was increased significantly (P<0.05). The interspike intervals of LP and PD neurons were decreased significantly (P<0.05).The change of mean phases corresponding to the three-phase rhythm under the influence of TEAThe mean phases corresponding to the three-phase rhythm were changed in condition of 30 mmol/L TEA. The phase of PY neuron was decreased significantly (P<0.01), the phase of LP neuron and resting were increased significantly (P<0.01) in the three-phase rhythm under the influence of TEA. |
PDF Full Text Request