Altered expression of delayed excitation in medial NTS neurons of spontaneously hypertensive rats.

The spontaneously hypertensive (SH) rat has an exaggerated sympathetic discharge which may result from an enhanced neuronal excitability in the central nervous system. To test this hypothesis, we examined the electrophysiological properties of neurons in the medial region of the nucleus of the solitary tract (mNTS), a central nucleus involved in the processing of baroreceptor afferent information, in SH rats and normotensive Sprague-Dawley (SD) rats. An in vitro brainstem slice preparation was used to record intracellularly from 18 neurons in 4-5-month-old SH rats and 16 neurons in 4-5-month-old SD rats. Between the two groups there was no significant differences in resting membrane potential, input resistance, and spontaneous firing frequency, or in action potential amplitude, duration, and after-hyperpolarization (AHP). There were no significant differences in spike frequency adaptation and post-tetanic hyperpolarization (PTH). Delayed excitation (DE), a manifestation of A-current, occurred in 88% in SH and SD mNTS neurons, but the duration of DE was significantly (P < 0.05) shorter in SH mNTS neurons. We propose that attenuated expression of A-current may contribute to increased sympathetic drive in SH rats.