title: Ionic factors governing rebound burst phenotype in rat deep cerebellar neurons.
abstract: Large diameter cells in rat deep cerebellar nuclei (DCN) can be distinguished according to the generation of a transient or weak rebound burst and the expression of T-type Ca(2+) channel isoforms. We studied the ionic basis for the distinction in burst phenotypes in rat DCN cells in vitro. Following a hyperpolarization, transient burst cells generated a high-frequency spike burst of < or = 450 Hz, whereas weak burst cells generated a lower-frequency increase (<140 Hz). Both cell types expressed a low voltage-activated (LVA) Ca(2+) current near threshold for rebound burst discharge (-50 mV) that was consistent with T-type Ca(2+) current, but on average 7 times more current was recorded in transient burst cells. The number and frequency of spikes in rebound bursts was tightly correlated with the peak Ca(2+) current at -50 mV, showing a direct relationship between the availability of LVA Ca(2+) current and spike output. Transient burst cells exhibited a larger spike depolarizing afterpotential that was insensitive to blockers of voltage-gated Na(+) or Ca(2+) channels. In comparison, weak burst cells exhibited larger afterhyperpolarizations (AHPs) that reduced cell excitability and rebound spike output. The sensitivity of AHPs to Ca(2+) channel blockers suggests that both LVA and high voltage-activated (HVA) Ca(2+) channels trigger AHPs in weak burst compared with only HVA Ca(2+) channels in transient burst cells. The two burst phenotypes in rat DCN cells thus derive in part from a difference in the availability of LVA Ca(2+) current following a hyperpolarization and a differential activation of AHPs that establish distinct levels of membrane excitability.
authors.affiliation: Hotchkiss Brain Inst., Univ. of Calgary, 3330 Hospital Dr. NW, Calgary, AB, Canada T2N 4N1.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Molineux
authors.forename: W Hamish
authors.initials: WH
authors.lastname: Mehaffey
authors.forename: Reza
authors.initials: R
authors.lastname: Tadayonnejad
authors.forename: Dustin
authors.initials: D
authors.lastname: Anderson
authors.forename: Adrien F
authors.initials: AF
authors.lastname: Tennent
authors.forename: Ray W
authors.initials: RW
authors.lastname: Turner