Post‐inhibitory rebound properties of dopaminergic cells of the ventral tegmental area

Abstract

We have investigated the post-inhibitory rebound (PIR) properties of dopamine cells in the ventral tegmental area of the rat midbrain. Using microelectrodes to record intracellularly from rat cells in the midbrain slice, we found that 54% of all recorded DA cells exhibited rebound depolarization in the presence of TTX. We observed primarily two types of rebound responses distinguished by their maximum amplitude and inactivation time constant, which we have termed as the ‘slowly inactivating PIR’ and low-threshold spike (LTS). 35% of DA cells exhibited a ‘slowly inactivating PIR’ and 19% showed LTS. A subset of the latter exhibited repetitive LTS. The PIR was enhanced in high K+ medium and suppressed in low-calcium medium. Under voltage clamp conditions, inward rebound currents at the end of a hyperpolarizing voltage step were partially blocked by specific T-type channel blocker, Ni2+. Repetitive LTSs were reversibly changed to single LTS by blocking the potassium SK current.