Effects of morphine tolerance and dependence on the fast excitatory synaptic transmission in sympathetic ganglia of rats

Aim: To study effects of morphine tolerance and dependence on the fast excitatory synaptic transmission in sympathetic ganglia of rats. Methods: The isolated sympathetic ganglia, superior cervical ganglia (SCG), were made from control and morphine tolerant and dependent rats respectively. Effects of morphine tolerance and dependence on the fast excitatory synaptic transmission in rat sympathetic ganglia were studied by means of intracellular recording technique. Results: 1 Morphine (0.1-1.0 mmol · L-1) reversibly inhibited the amplitude of the fast excitatory postsynaptic potentials (f-EPSPs) in SCG neurons of control rats. 2 Compared with control group, inhibitory effects of morphine (0.5 mmol · L-1 and 1.0 mmol · L-1) on f-EPSPs in SCG neurons of morphine tolerant and dependent rats were obviously decreased; 3 Naloxone (0.1 mmol · L -1), which had no significantly effect on f-EPSPs in SCG neurons of control rats, could reversibly facilitate the amplitude of f-EPSPs in SCG neurons of morphine tolerant and dependent rats; 4 No significant difference of RMP and Rm was founded between SCG neurons of control and morphine tolerant and dependent rats. Conclusion: The morphine tolerant and dependent of the fast excitatory synaptic transmission in rat sympathetic ganglia has been formed in morphine tolerant and dependent rats.