Two cell types in rat substantia nigra zona compacta distinguished by membrane properties and the actions of dopamine and opioids

Abstract

Intracellular recordings were made from 475 rat substantia nigra zona compacta neurons in vitro. The region from which recordings were made was rich in catecholamine fluorescence. Two groups of neuron, termed principal neurons (95% of the total) and secondary neurons (5% of the total) were clearly distinguishable according to one or more of the following 4 electrophysiological properties. Secondary neurons (23 cells) (1) fired spontaneous action potentials at frequencies greater than 10 Hz, or were quiescent (30%); (2) had action potentials less than 1 msec in duration; (3) did not show time-dependent inward rectification with step hyperpolarization; and (4) had slope conductances of about 4 nS (between -75 and -90 mV). In contrast, principal neurons (1) fired spontaneous action potentials in the range 1-8 Hz, or were quiescent (33%); (2) had action potentials greater than 1 msec in duration; (3) showed pronounced time-dependent inward rectification; and (4) had steady-state membrane slope conductances of around 22 nS (between -75 and -90 mV). Secondary cells were not affected by dopamine but were hyperpolarized by baclofen, GABA, and the mu opioid receptor agonist Tyr-D-Ala-Gly-MePhe-Gly-ol (DAGO). On the other hand, dopamine and baclofen inhibited firing and/or hyperpolarized all principal cells tested, but mu or delta opioid receptor agonists had no effect. The properties of these 2 cell types broadly correspond with those described by electrophysiological studies in vivo, in which case the majority, or principal, cells are believed to be dopaminergic.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of a potassium conductance in rat midbrain dopamine neurons by intracellular adenosine triphosphate (ATP) and the sulfonylureas tolbutamide and glibenclamide

“…2A). All these properties correspond to those of dopaminecontaining SN neurons demonstrated in previous studies (Grace and Onn, 1989;Yung et al, 1991), and to those of cells presumed to be dopamine-containing in other studies (such as Lacey et al, 1989;Riiper et al, 1990~;Johnson and North, 1992;see Lacey, 1993, for review). Thus, the cells studied here are considered to be dopamine neurons.…”

“…Whole-cell patchclamp recordings from cells in SNc were made from parasagittal slices (200 pm thick) of male Wistar rat (9-12 d old) midbrain. Brain slices were prepared as previously described for coronal slices (Lacey et al, 1989) and, once transferred to a recording chamber (volume, 0.75 ml), were continuously superfused at 2 ml/min in a bicarbonate-buffered medium (pH 7.2) containing (mM) NaCl (126), KC1 (2.5), NaH,PO, (1.2), MgCl, (1.3), and CaCl, (2.4) and maintained at 33-35°C. Recordings were made with borosilicate glass pipettes of resistance of 3-5 MR containing (mM) K-gluconate (125), MgCl, (2), CaCl, (l), NaCl (lo), 1,2-bis(2-aminophenoxy)ethane-N,N,N',Nf-tetraacetic acid (BAP-TA; IO), N-(2-hydroxyethylj-piperazine-N'-2-ethanesulfonic acid (HE-PES: 10).…”

Electrophysiological effects of monoamine oxidase inhibition on rat midbrain dopaminergic neurones: an in vitro study

“…A detailed description of the methods has been published elsewhere (Lacey et al, 1989;Mercuri et al, 1994; Pharmacology (1996) 117,[528][529][530][531][532] Recordings The recording electrodes (Clark, 1-1.5 mm, thick wall), pulled by Narishige vertical and horizontal pullers, were filled with 2 M KCl or 1 M K+-acetate and 2 M K+-citrate and had a tip resistance of 40-120 MO. The signals were obtained by an amplifier (Axoclamp-2A, Axon Instruments) and were displayed on a pen recorder (Gould 2400 S) and on a digital oscilloscope (Tektronix) or saved in a tape recorder (Biologic) for off-line analysis.…”

IhChannels Contribute to the Different Functional Properties of Identified Dopaminergic Subpopulations in the Midbrain

“…To date, in vitro electrophysiological studies have considered DA midbrain neurons mainly as a single population (Pucak and Grace, 1994;K itai et al, 1999), which shows low-frequency pacemaker activity, broad action potentials followed by a pronounced afterhyperpolarization, and a pronounced sag component that is mediated by hyperpolarization-activated, cyclic nucleotide-regulated cation (I h , HC N) (for review, see Santoro and Tibbs, 1999) channels (Sanghera et al, 1984;Grace and Onn, 1989;Lacey et al, 1989;Richards et al, 1997). However, in vivo studies have highlighted f unctional differences between subgroups of DA neurons (Wilson et al, 1977;Chiodo et al, 1984;Greenhoff et al, 1988;Shepard and German, 1988;).…”