Distinctive nicotinic acetylcholine receptor functional phenotypes of rat ventral tegmental area dopaminergic neurons

Abstract

Dopaminergic (DAergic) neuronal activity in the ventral tegmental area (VTA) is thought to contribute generally to pleasure, reward, and drug reinforcement and has been implicated in nicotine dependence. nAChRs expressed in the VTA exhibit diverse subunit compositions, but the functional and pharmacological properties are largely unknown. Here, using patch-clamp recordings in single DAergic neurons freshly dissociated from rat VTA, we clarified three functional subtypes of nAChRs (termed ID, IID and IIID receptors) based on whole-cell current kinetics and pharmacology. Kinetic analysis demonstrated that comparing to ID, IID receptor-mediated current had faster activation and decay constant and IIID receptor-mediated current had larger current density. Pharmacologically, ID receptor-mediated current was sensitive to the α4β2-nAChR agonist RJR-2403 and antagonist dihydro-β-erythroidine (DHβE); IID receptor-mediated current was sensitive to the selective α7-nAChR agonist choline and antagonist methyllycaconitine (MLA); while IIID receptor-mediated current was sensitive to the β4-containing nAChR agonist cytisine and antagonist mecamylamine (MEC). The agonist concentration-response relationships demonstrated that IID receptor-mediated current exhibited the highest EC 50 value compared to ID and IIID receptors, suggesting a relatively low agonist affinity of type IID receptors. These results suggest that the type ID, IID and IIID nAChR-mediated currents are predominately mediated by activation of α4β2-nAChR, α7-nAChR and a novel nAChR subtype(s), respectively. Collectively, these findings indicate that the VTA DAergic neurons express diversity and multiplicity of functional nAChR subtypes. Interestingly, each DAergic neuron predominantly expresses only one particularly functional nAChR subtype, which may have distinct but important roles in regulation of VTA DA neuronal function, DA transmission and nicotine dependence.

Cannabinoid CB 2 receptors modulate midbrain dopamine neuronal activity and dopamine-related behavior in mice

“…We first examined the effects of the selective CB 2 R agonist JWH133 on DA neuronal firing using perforated patch-clamp recording in single dissociated VTA DA neurons. Identification of DA neurons was based on three criteria (30,31): electrophysiology [DA neurons exhibit low spontaneous firing rates (FRs; 1-3 Hz) with long action potential (AP) duration and a distinctive H-current], pharmacology [DA neuronal firing is inhibited by DA or by a D 2 receptor agonist (e.g., quinpirole)], and IHC staining (recorded neurons are TH-positive) (Fig. S6).…”

“…Individual group comparisons were carried out using the Student NewmanKeuls method. In addition, paired t tests were used to analyze some electrophysiological data, as described previously (30,31). FRs and burst firing were determined every 10 s, as described previously (57,58).…”

Local Application of Drugs to Study Nicotinic Acetylcholine Receptor Function in Mouse Brain Slices

“…For example, the expression of I h current, resting membrane potential, spontaneous firing rate, and cell size are typical measures used to characterize DA neurons 2,7,8,16,17 . Using our method, it is also possible to characterize neurons based on their response to locally-applied nicotine or ACh 18,19 . For example, the superior colliculus (SC) is a heterogeneous and relatively uncharacterized brain area with extremely high expression of various nAChRs, including those that contain α6 subunits 20 .…”

Double target concept for smoking cessation

“…Interestingly, GABAergic neurons located in the VTA likely express relatively-simple nAChR subtypes, mainly (α4) 2 (β2) 3 -nAChRs [6] and these α4β2nAChRs contribute to cholinergic modulation of GABA tonic release onto DA neurons [9] . Recently, we have characterized three functional subtypes (ID, IID, IIID) of nAChRs in VTA DA neurons [7] that may mediate nicotine reward and dependence. For example, nicotine, in the same concentrations and time ranges as obtained from cigarette smoking, enhances glutamatergic excitation in the VTA DA neurons by increasing glutamate release via stimulating presynaptic α7-nAChRs [10] .…”

“…Dopaminergic (DA) neurons in the VTA express diverse nAChR subunits, including α3-α7 and β2-β4 [2][3][4][5][6][7] , which can combine to form at least two pharmacologically distinct nAChR subtypes. One of these functionally distinct nAChRs is homomeric α7-nAChRs, which are mainly expressed on glutamatergic presynaptic terminals, where they mediate nicotine-induced increase of glutamate release onto DA neurons [6] .…”