Pharmacology and regulation of the neuronal dopamine transporter.

The dopamine transporter, a member of the family of Na+,Cl(-)-dependent transporters, mediates uptake of dopamine into dopaminergic neurons by an electrogenic, Na(+)- and Cl(-)-transport-coupled mechanism. Dopamine and blockers of uptake such as cocaine probably bind to both shared and separate domains on the transporter, which can be influenced dramatically by the presence of cations. Regulation of the dopamine transporter occurs both by chronic occupancy with blocker and by acute effects of D2 dopamine receptors or second messengers such as diacylglycerol (protein kinase C) and arachidonic acid.

Characterization of [125I]RTI-121 binding to dopamine transporter in vitro.

Aim: To characterize the binding of [125I]3 beta-(4-iodophenyl) tropane-2 beta-carboxylic acid isopropyl ester (RTI-121) to the dopamine transporter (DAT) under physiologically relevant conditions.

Methods: [125I]RTI-121 was used to label the DAT on fresh rat striatum synaptosomal membranes in artificial cerebrospinal fluid (ACSF) at 37 degrees C.

Results: [125I]RTI-121 binding reached equilibrium within 3 min and remained at its plateau value for at least 9 min.

Comparison of the clinical diagnostic value between pleural needle biopsy and analysis of pleural effusion.

Background: Many diseases are manifested by pleural effusion. Chest echo-guided thoracentesis and pleural biopsy are the two major procedures in diagnosing pleural effusion, but the validity is still under debate. To compare the diagnostic value of echo-guided pleural biopsy with pleural effusion analysis, we designed this retrospective study.

Binding of the [125I]3 beta-(iodophenyl)tropan-2 beta-carboxylic acid isopropyl ester to the dopamine transporter at a physiologically relevant temperature: mutually exclusive binding and different ionic requirements for various uptake blockers and substrates.

The present study describes the binding of cocaine analog [125I]3 beta-(iodophenyl)tropan-2 beta-carboxylic acid isopropyl ester ([125I]RTI-121), a highly selective ligand for the dopamine transporter (DAT), to rat striatal synaptosomal membranes at 37 degrees C. Saturation analysis of [125I]RTI-121 binding revealed a single binding site with similar affinity for RTI-121 at both 50 and 134 mM NaCl. However, the density of binding sites was reduced at 134 mM NaCl.

Intrategmental infusion of cocaine decreases dopamine release and enhances norepinephrine release in the medial prefrontal cortex.

We evaluated the effects of local cocaine infusion into the A10 (ventral tegmental area), the cell body of the mesocorticolimbic dopaminergic pathway, on the extracellular concentrations of dopamine and norepinephrine in the medial prefrontal cortex, one of its terminal fields. A 1-ml Hamilton syringe was used to infuse a cocaine solution, either 20 or 200 microM, into the ventral tegmental area of anesthetized rats for 120 min through a microdialysis probe. The pure artificial cerebrospinal fluid (0 microM cocaine) infusion served as a control and a lidocaine (100 microM) infusion was administered to prevent the local anesthetic effect of cocaine.

[3H]WIN 35,428 [2 beta-carbomethoxy-3 beta-(4-fluorophenyl)tropane] binding to rat brain membranes. Comparing dopamine cell body areas with nerve terminal regions.

Potential differences between somatodendritic acid and axonal dopamine transporters were examined by comparing the binding constants of [3H]WIN 35, 428 [2 beta-carbomethoxy- 3 beta-(4-fluorophenyl)tropane] binding to membranes prepared from the rat ventral mesencephalon, containing A9 and A10 dopamine cell bodies, and from the nucleus accumbens. Saturation analysis of [3H]WIN 35,428 binding, in the presence of compounds to occlude norepinephrine and serotonin transporters, was performed by both the "unlabeled" method (varying unlabeled ligand) and "labeled" method (varying radioligand). The density of binding was substantially lower in the ventral mesencephalon than in the nucleus accumbens, but the binding affinity was only slightly different.

Amygdala kindling of forebrain seizures and the occurrence of brainstem seizures in genetically epilepsy-prone rats.

Forebrain seizures were kindled in rats by daily electrical stimulation of the amygdala. Genetically epilepsy-prone rats scoring 9 (GEPR-9s) on the seizure severity scale during audiogenic seizure (AGS) screening ("brainstem seizure-experienced") required fewer stimulations to achieve fully kindled seizures (forelimb clonus with rearing and falling) than control rats. AGS-naive GEPR-9s required an intermediate number of stimulations, indicating a role for both genetic predisposition and previous acoustically evoked brainstem seizure experience.

Differential effects of chloral hydrate and pentobarbital sodium on a cocaine level and its catecholamine response in the medial prefrontal cortex: a comparison with conscious rats.

Adult male Sprague-Dawley rats anesthetized with chloral hydrate and pentobarbital sodium were used as two different treatment groups. Conscious rats were used as a control group. By using baseline (precocaine) concentration as 100%, after cocaine administration (3.

Monoamine interactions measured by microdialysis in the ventral tegmental area of rats treated systemically with (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin.

The effect of (+/-)-8-hydroxy-2-(di-n-propyl-amino)tetralin (8-OH-DPAT), a selective serotonin 5-HT1A agonist, on levels of extracellular norepinephrine (NE), dopamine (DA), and 5-HT (measured simultaneously) was investigated by microdialysis in the ventral tegmental area (VTA) of freely moving rats, and their behavioral activity was monitored. At 50 micrograms/kg s.c.

Autoregulation and monoamine interactions in the ventral tegmental area in the absence and presence of cocaine: a microdialysis study in freely moving rats.

Extracellular levels of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) were measured simultaneously by microdialysis in the ventral tegmental area (VTA) of conscious rats, and locomotor activity was monitored. Extracellular NE, DA and 5-HT was increased by both local infusion (30 microM) and i.p.

Effects of locally applied cocaine, lidocaine, and various uptake blockers on monoamine transmission in the ventral tegmental area of freely moving rats: a microdialysis study on monoamine interrelationships.

Microdialysis was used to compare the effect of local perfusion of cocaine with that of functionally similar compounds on extracellular norepinephrine, dopamine, and serotonin (measured simultaneously) in the ventral tegmental area of freely moving rats. Tetrodotoxin (1 microM) potently inhibited both basal and cocaine-induced dialysate monoamine outputs. The local anesthetic lidocaine produced little or no effect on the monoamine output, whereas all uptake blockers tested (at 0.

Facilitation of amygdala kindling development and kindled seizures by metaphit.

The effect of metaphit (a phencyclidine analogue with an acylating isothiocyanate) on kindling development and kindled seizures from amygdala was investigated in rats pretreated once with metaphit. Administration of a single dose of metaphit (10 or 20 mg/kg intraperitoneally i.p.

GBR 12909 and 12935 block dopamine uptake into brain synaptic vesicles as well as nerve endings.

GBR 12909 and 12935, commonly used as potent neuronal dopamine uptake blockers, also inhibit dopamine uptake into brain synaptic vesicles. The concentrations required for the latter activity (34-45 nM) are one order of magnitude higher than those required for inhibiting neuronal uptake of dopamine (1-6 nM). In contrast, the two activities differ by three orders of magnitude for cocaine (137 microM versus 0.

Differential effects of chloral hydrate and pentobarbital sodium on cocaine-induced electroencephalographic desynchronization at the medial prefrontal cortex in rats.

We evaluated the effects of two anesthetics on the cocaine-induced electroencephalographic (EEG) desynchronization in male, Sprague-Dawley rats. One group was anesthetized with chloral hydrate (400 mg/kg, i.p.

Dopamine and serotonin release-regulating autoreceptor sensitivity in A9/A10 cell body and terminal areas after withdrawal of rats from continuous infusion of cocaine.

The effects of dopamine (DA) and 5-hydroxytryptamine (5-HT) autoreceptor agents on electrically induced [3H]DA and [3H]5-HT release from superfused slices of striatum, nucleus accumbens and ventral mesencephalon (VM) containing A9 and A10 neurons were investigated in rats made tolerant to the stimulatory effect of cocaine on locomotor behavior by a 14-day continuous infusion of cocaine (29 mg/kg/day) by s.c. implanted osmotic minipumps followed by a 7-day drug-free period.

[3H]dopamine and [3H]serotonin release in vitro induced by electrical stimulation in A9 and A10 dopamine regions of rat brain: characterization and responsiveness to cocaine.

The present study investigated [3H]dopamine (DA) and [3H]5-hydroxytryptamine (5-HT) release evoked by electrical stimulation in superfused ventral mesencephalon (VM) slices containing A9 and A10 DA neurons. Electrically induced [3H]DA release from VM was, at least, of two origins: one was from DA somatodendrites, regulated by DA autoreceptors, and increased by DA uptake blockers; another was from 5-HT terminals, modulated by 5-HT autoreceptors, and could be minimized by the copresence of fluoxetine during the labeling of the slices. Release of both origins was Ca(++)-dependent and tetrodotoxin-sensitive.

Increased heart microsomal Na(+) K(+)-transporting ATPase activity by tetrandrine in spontaneously hypertensive rats.

In spontaneously hypertensive rats (SHR), the heart microsomal Na+, K(+)-ATPase showed a reduced activity with a higher Ca2+ sensitivity and lower responsiveness to K+. After SHR were treated with tetrandrine (Tet, ig 30 mg.kg-1, qd x 30 d) or when the microsomes obtained from SHR hearts were incubated with various concentrations of Tet, the myocardial Na+,K(+)-ATPase showed a higher activity with a decreased Km for K+, or ATP and an increased Vmax for K+.