Intrinsic properties of nucleus reticularis thalami neurones of the rat studied in vitro.

1. Neurones of the nucleus reticularis thalami of the rat were studied by intracellular recordings from in vitro slices. The resting membrane potential was -56.28 +/- 5.86 mV (mean value +/- S.D.); input resistance was 43.09 +/- 9.74 M omega; the time constant tau was 16.51 +/- 3.99 ms. At the resting membrane potential tonic firing is present, while at membrane potentials more negative than -60 mV a burst firing mode gradually prevails. 2. Prolonged depolarizing current pulses superimposed on a steady hyperpolarization consistently activated sequences of burst-after-hyperpolarization complexes. The all-or-none burst response consisted of Na+-mediated, TTX-sensitive fast action potentials superimposed on a low threshold spike (LTS). The burst was followed by a stereotyped after-hyperpolarization lasting 100-120 ms (BAHP), with a maxima -85 mV. The BAHP was blocked by Cd2+ and apamine but not by 8-Br cyclic AMP. The early component of BAHP was significantly attenuated by TEA. The oscillatory rhythmic discharges were abolished by agents which blocked the BAHP. 3. The presence of strong after-hyperpolarizing potentials (SAHP and BAHP) in RTN neurones plays a significant role in determining two different functional states, defined as tonic and oscillatory burst firing modes, respectively.