Neurotransmission through sympathetic ganglia of spontaneously hypertensive rats

Transmission of neuronal activity was assessed by recording preganglionic and postganglionic compound action potentials in superior cervical ganglia isolated from adult spontaneously hypertensive rats (SHR), Wistar-Kyoto (WKY) rats, and Wistar rats as well as young SHR and WKY rats to determine if previously observed alterations of membrane excitability, synaptic transmission, or both, have an effect on the transmission of preganglionic activity in SHR. Single stimuli induced more postganglionic neurons to fire over a wide range of preganglionic stimulation intensities in superior cervical ganglia from adult SHR as compared with those from adult normotensive controls. Short stimulation trains confirmed that SHR are able to maintain this greater number of active postganglionic neurons during low-frequency stimulation (1-20 Hz). However, by the end of a train of high-frequency stimulation (70-100 Hz) fewer neurons fired in ganglia from SHR compared with those from normotensive controls. These differences in transmission were not observed in the young rats. The results from the present study demonstrate that physiological frequencies of preganglionic activity are more effectively transmitted through sympathetic ganglia from adult SHR compared with those from normotensive controls, and this enhanced transmission through ganglia may contribute to the elevated sympathetic activity and the consequent hypertension seen in this model.