Effects of cocaine on monoamine uptake as measured ex vivo

Abstract

The increase in extracellular dopamine (DA) following cocaine administration plays a major role in cocaine abuse. In vitro, cocaine binds to DA transporters (DAT) and blocks DA uptake. Moreover, cocaine can increase extracellular DA concentration as measured by in vivo neurochemical methods. The present study examined the effects of cocaine and other drugs on DA, NE and 5-HT uptake using an ex vivo assay. Rats were injected i.v. with saline or drug and sacrificed at various time points after injections. Brains were dissected for regional monoamine uptake studies ex vivo. In most brain regions, cocaine given in vivo blocked monoamine uptake as expected. [ 3 H]DA uptake in nucleus accumbens was inhibited with an ED 50 = 22.3 μmol/kg. Cocaine fully inhibited [ 3 H]NE uptake (ED 50 = 4.58 μmol/kg) in the occipital cortex and partially inhibited [ 3 H]5-HT uptake (33% at 30 μmol/kg) in the midbrain. However, under the same conditions [ 3 H]DA uptake in the striatum was not inhibited after injections of cocaine up to 56 μmol/kg.. Although the mechanism for this discrepancy is unclear, DA binding and uptake sites may be distinct and/or there may be regional differences in DA transporters. KeywordsCocaine; Monoamine uptake; Ex vivo; Striatum; Nucleus accumbens Cocaine blocks the uptake of monoamine neurotransmitters in vitro, with about equal potency for the three major monoamines, dopamine (DA), norepinephrine (NE), and serotonin (5-HT) [22]. Further, it is widely held that the behavioral effects of cocaine are related to the increase in extraneuronal levels of monoamine neurotransmitters in the CNS [2,18]. A substantial body of data implicates blockade of CNS dopamine (DA) reuptake by dopamine transporters (DAT) as a primary mechanism in the abuse-related effects of cocaine [34,35].In vivo assays also indicate that cocaine can increase the extracellular levels of monoamines. Research with in vivo microdialysis has demonstrated an increase in monoamine concentrations in rat striatum and nucleus accumbens following cocaine administration [19], and in monkey striatum as well [29]. Experiments utilizing in vivo electrochemistry have reported that systemic administration of cocaine can decrease the clearance of locally-applied dopamine in Address all correspondence to: Zhixia Wang, M.D., Department of Psychiatry and Human Behavior, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS, USA 39216, Phone: (601) 815-1022 FAX (601) 984-5899, E-mail: ZWang@psychiatry.umsmed.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. [4,38], suggesting that bloc...

Electrophysiological evaluation of the time-course of dopamine uptake inhibition induced by intravenous cocaine at a reinforcing dose

“…These values coincide with ∼2.5 min onset latencies in appearance of [ 11 C]-cocaine specific binding in human striatum after iv injection (Fowler et al, 1989). Using another ex vivo approach, reliable inhibition of DA uptake in the ventral striatum was found 5 min post-injection only at high cocaine doses (10 mg/kg, iv), while no changes were seen in dorsal striatum at this time point (Wang et al, 2007). Weak inhibition of DA uptake in the dorsal striatum, however, was found in this study at 15 th post-injection min.…”

“…Previous attempts to measure brain cocaine levels after iv administration produced quite contrasting results. For example, [ 3 H] cocaine has been detected in striatal tissue one min after iv injection (10 mg/kg), peaking at ∼1.2 μM levels at 5 th min (Wang et al, 2007). If these estimates are accurate, brain cocaine levels after 1 mg/kg iv injection should be lower than ED 50 (0.3-0.8 μM; Hennings et al, 1999;Rothman et al, 2001), only bordering the range for minimal effecting DA uptake.…”

Critical role of peripheral drug actions in experience‐dependent changes in nucleus accumbens glutamate release induced by intravenous cocaine

“…; Wang et al . ). Even when using a more sensitive approach by combining DA iontophoresis with fast‐cyclic voltammetric DA detection, i.v.…”

“…Although cocaine's interactions with brain monoamine transporters appear essential for mediating its reinforcing properties (Ritz et al 1987;Wise and Bozarth 1987), DA uptake inhibition in the NAc ex vivo (when any contribution of DA release is excluded) is only detected at high doses (5-10 mg/kg, i.v. ; Pogun et al 1991; Stathis injection (Stathis et al 1995;Wang et al 2007). Even when using a more sensitive approach by combining DA iontophoresis with fast-cyclic voltammetric DA detection, i.v.…”

Simultaneous quantification of monoamine neurotransmitters and their biogenic metabolites intracellularly and extracellularly in primary neuronal cell cultures and in sub-regions of guinea pig brain

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