PERSISTENT NA-SIZED NEOSTRIATAL NEURONS - CHARACTERIZATION USING INFRARED VIDEOMICROSCOPY AND WHOLE-CELL PATCH-CLAMP RECORDINGS( CONDUCTANCE IN MEDIUM)

1. In the present study we investigate the expression of a persistent Na+ conductance (I-NaP) in identified medium-sized neostriatal neurons . Nomarski optics and infrared videomicroscopy were used for cell visu alization and identification in thick slices (350 mu m). Current- and voltage-clamp recordings were obtained utilizing whole cell patch-clam p methodology. 2. Application of depolarizing ramp voltage commands fr om a holding potential of -70 mV induced a slow, noninactivating inwar d current that occurred before and independent of the rapidly inactiva ting sodium current that subserves action potential generation. I-NaP began to activate at potentials less negative than -70 mV and peaked a t -34 +/- 1 (SE) mV. Its average peak amplitude was -100 +/- 17 pA. I- NaP was abolished by tetrodotoxin (TTX, 0.5-1 mu M) or an Na+-free sol ution. In contrast, it was not affected by Ca2+ channel blockers. Depo larizing ramp commands also induced tetraethylammonium-sensitive outwa rd currents. 3. Dopamine (DA) (20-100 mu M) produced a significant red uction of I-NaP. 4. These results demonstrate the existence of a TTX-s ensitive persistent Na+ conductance in medium-sized neostriatal neuron s. This conductance is modulated by DA and could play a role in the ge neration of rhythmic oscillations and in supporting repetitive firing.