The Effects Of Serotonin And Fluoxetine On Neurotransmission In Crayfish Superficial Extensor Muscle

Abstract

Serotonin (5-HT) has been shown to cause an increase in transmitter release in the opener muscle and tailfan muscles of the crayfish. Despite the readily accessible muscles associated with the abdominal posture of the crayfish, no study has investigated the effects of serotonin at the neuromuscular junction in the superficial extensor muscle in the tail of the crayfish. Similarly, no research to date has studied the effects of selective serotonin reuptake inhibitors (SSRIs) in the crustacean or any invertebrate system. In this study, measurement of EJP amplitude in postsynaptic bundles of the superficial extensor muscle was made with intracellular microelectrodes during application of serotonin and fluoxetine. Serotonin (1?M, 10 ?M and 25 ?M) caused a decrease in both presynaptic stimulus threshold and EJP amplitude. Stimulus threshold either returned or surpassed control stimulus level when serotonin was replaced with standard Ringers solution or fluoxetine (10 ?M). EJP amplitude was significantly increased when fluoxetine (10 ?M) was added to the 10 ?M serotonin solution. These findings suggest that serotonin has the opposite effect on neurotransmission in the superficial extensor muscle than in the opener or tailfan muscle of the crayfish. It further suggests that this serotonin mediated reduction of neurotransmission may be blocked by the addition of fluoxetine.