Electrophysiological effects of tachykinin agonists on sympathetic ganglia of spontaneously hypertensive rats

This study investigated the cellular basis for the enhanced ganglionic responsiveness to NK1 agonists in the spontaneously hypertensive rat (SHR) in comparison to their normotensive counterpart, the Wistar-Kyoto (WKY) rat. Rats for in vivo studies were anesthetized with pentobarbital and treated with chlorisondamine (10.5 micromol/kg). Extracellular recordings from the external carotid nerve showed a greater responsiveness of decentralized SHR superior cervical ganglia (SCG) to intravenous injection of SP (32 nmol/kg). Blood pressure and heart rate were increased in SHRs, whereas WKY rats responded with a decrease in blood pressure and only slight tachycardia. Membrane properties of SCG neurons, as shown by intracellular microelectrode recordings, were similar between strains. Picospritzer application of the NK1 agonist GR-73632 (100 microM, 1 s) evoked slow depolarization and increased neuron excitability. Spontaneous firing was evoked only in some neurons. Depolarization amplitudes were similar between strains; however, the NK1 agonist depolarized a greater number of neurons in hypertensive rats. In conclusion, SHRs are more responsive to ganglion stimulation by NK1 agonists due to a greater number of responsive cells within the SCG rather than an enhanced responsiveness of individual neurons.