title: Postnatal rat nigrostriatal dopaminergic neurons exhibit five types of potassium conductances.
abstract: 1. We have investigated the electrical properties of neurons acutely dissociated from the substantia nigra zona compacta (SNZC) of the postnatal rat with whole cell patch-clamp recordings. Retrogradely labeled nigrostriatal neurons were identified with the use of rhodamine-labeled fluorescent latex microspheres. Over 90% of the rhodamine-labeled neurons in the SNZC demonstrated formaldehyde/glutaraldehyde-induced catecholamine fluorescence, indicating that they were dopaminergic (DA) neurons. 2. DA neurons had 15-20 microns ovoid or fusiform-shaped cell bodies with 2-3 thick proximal processes. Labeled neurons generated spontaneous action-potential activity in both regular and irregular patterns. These cells exhibited input resistances of 300-600 M omega and action-potential amplitudes of 60-80 mV. Locally applied dopamine inhibited the spontaneous activity of these neurons by hyperpolarizing the cells. 3. Outward currents were examined with voltage-clamp recordings using a tetrodotoxin (TTX)-containing medium. In all DA cells, depolarizing voltage commands activated several components of outward current depending on the holding potential of the cell. When cells were held at -40 mV (or more positive), voltage steps activated a sustained outward current. If the membrane potential was held more negative than -50 mV, a rapidly activating and inactivating component of outward current response could also be detected. 4. From a hyperpolarized holding potential (-90 mV) the transient outward current activated with depolarizing commands to -55 mV, peaking within 5 ms. The current inactivated with a monoexponential time constant of 53 +/- 4 (SE) ms. At more positive holding potentials (-40 mV) the steady-state inactivation of the current could be removed by applying a conditioning hyperpolarizing prepulse. In response to a fixed depolarizing voltage step, half-maximal inactivation occurred at about -65 mV. The transient current was blocked by 4-aminopyridine (4-AP). 5. The sustained outward currents were isolated by holding the cells at -40 mV. Two components of sustained outward current were distinguished by their sensitivity to the calcium channel blockers Co2+ (5 mM) and/or Cd2+ (200 microM). The current remaining in the presence of Co2+/Cd2+ was activated by depolarizing voltage commands more positive than -40 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Laboratory of Neurophysiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: N L
authors.initials: NL
authors.lastname: Silva
authors.forename: C M
authors.initials: CM
authors.lastname: Pechura
authors.forename: J L
authors.initials: JL
authors.lastname: Barker
mesh_terms: D000200:Action Potentials; D000818:Animals; D003342:Corpus Striatum / Q000166:cytology / Q000254:growth & development / Q000502:physiology*; D008564:Membrane Potentials; D009431:Neural Conduction; D011188:Potassium / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013378:Substantia Nigra / Q000166:cytology / Q000254:growth & development / Q000502:physiology*
chemical_list: D011188:Potassium