Characterization of binding of [3H]GBR 12935 (1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)-piperazine) to membranes and to solubilized membrane extracts from terminal field regions of mesolimbic, mesocortical and nigrostriatal dopamine pathways

Altered D2 receptor and transcription factor EB expression in offspring of aggressive male rats, along with having depressive and anxiety-like behaviors

MATERIALS AND METHODS

In this study we have evaluated the behavioral mood variations, and expression of DR-D2 and TFEB genes in the amygdala and PFC of aggressive male rats' offspring.

RESULTS

Anxiety and depression-like behaviors were observed, but intra-ventricle injection of DR-D2 antagonist (Sulpiride) has shown to be efficient in reducing negative behavioral changes in offspring. Furthermore, DR-D2 gene expression was increased in the amygdala and PFC of aggressive male rats' offspring, which the injection of Sulpiride decreased it significantly. TFEB gene expression was also decreased in the amygdala and PFC of aggressive male rats' offspring, but the blockade of DR-D2 had no effect on it.

CONCLUSIONS

The current data suggests the possible influence of dopaminergic receptors D2 and TFEB genes on the behavioral changes which is modified by having an aggressive father.

Presynaptic control of serotonin on striatal dopamine function

RATIONALE

The influences of the serotonergic system on dopamine (DA) neuron activity have received considerable attention during the last three decades due to the real opportunity to improve disorders related to central DA neuron dysfunctions such as Parkinson's disease, schizophrenia, or drug abuse with serotonergic drugs. Numerous biochemical and behavioral data indicate that serotonin (5-HT) affects dopaminergic terminal function in the striatum.

OBJECTIVE

The authors propose a thorough examination of data showing controversial effects induced by striatal 5-HT on dopaminergic activity.

RESULTS

Inhibitory and excitatory effects of exogenous 5-HT have been reported on DA release and synthesis, involving various striatal 5-HT receptors. 5-HT also promotes an efflux of DA through reversal of the direction of DA transport. By analogy with the mechanism of action described for amphetamine, the consequences of 5-HT entering DA terminals might explain both the excitatory and inhibitory effects of 5-HT on presynaptic DA terminal activity, but the physiological relevance of this mechanism is far from clear. The recent data suggest that the endogenous 5-HT system affects striatal DA release in a state-dependent manner associated with the conditional involvement of various 5-HT receptors such as 5-HT(2A), 5-HT(2C), 5-HT(3), and 5-HT(4) receptors.

CONCLUSION

Methodological and pharmacological issues have prevented a comprehensive overview of the influence of 5-HT on striatal DA activity. The distribution of striatal 5-HT receptors and their restricted influence on DA neuron activity suggest that the endogenous 5-HT system exerts multiple and subtle influences on DA-mediated behaviors.

Alterations of the dopamine transporter in resting lymphocytes of patients with different psychotic disorders

The aim of our study was to investigate and compare the dopamine (DA) transporter (DAT) in resting lymphocytes of 20 psychotic patients and 20 healthy control subjects, by means of both the binding parameters (Bmax and Kd) of 3H-WIN 35,428, and the reuptake parameters (Vmax and Km) of 3H-DA. The results showed that both the Bmax of 3H-WIN 35,428 binding and the Vmax of 3H-DA reuptake of the patients were significantly lower than those of healthy subjects, while the Kd or Km did not show any change. These findings, while indicating a reduced density of the lymphocyte DAT proteins, provide further support of the role of DA in psychoses and suggest that DA alterations may not be limited to brain structures.

Dopamine transporter synthesis and degradation rate in rat striatum and nucleus accumbens using RTI-76

Intracerebroventricular injections of the irreversible dopamine transporter (DAT) inhibitor, RTI-76 [3beta-(3-p-chlorophenyl) tropan-2beta-carboxylic acid p-isothiocyanatophenylethyl ester hydrochloride], decreased DAT binding in both the striatum and nucleus accumbens as measured by both [3H]GBR12935 and by [3H]WIN35,428. This decrease was dose-related, with 100 nmol RTI-76 producing approximately a 50% decrease in both regions. The maximal inhibition of DAT binding was observed 24 h after RTI-76 injection, and binding was fully restored 7 days after injection. The DAT protein half-life determined under these conditions was about 2 days. [3H]Nisoxetine binding at norepinephrine transporters in the cortex was not altered by RTI-76 administration at any time point or dose examined.

Differential relationships among dopamine transporter affinities and stimulant potencies of various uptake inhibitors

Binding to the dopamine transporter and inhibiting dopamine reuptake are considered important factors in regulating behavioral effects of cocaine. One prominent behavioral effect of cocaine and other dopamine uptake inhibitors is the stimulation of locomotor activity. To examine the relationship between action at the dopamine transporter and behavior, the displacement of [3H]WIN 35,428 (CFT naphthalene sulfate; 2-beta-carbomethoxy-3-beta-(4-fluorophenyl)tropane-1,5-naphthalene disulfonate) binding in rat caudate putamen by cocaine and other uptake inhibitors was compared with stimulation of mouse locomotor activity. There was a significant correlation among affinities for binding and potencies for stimulating activity for cocaine and structurally similar compounds. For structurally dissimilar uptake inhibitors, however, there was no significant correlation among potencies for stimulation of activity and affinity for displacement of [3H]WIN 35,428 binding. These findings provide evidence that cocaine analogs may bind to the dopamine transporter in a manner that is fundamentally different from that for structurally dissimilar uptake inhibitors.

Studies of the biogenic amine transporters. 1. Dopamine reuptake blockers inhibit [3H]mazindol binding to the dopamine transporter by a competitive mechanism: preliminary evidence for different binding domains

The present study addressed the hypothesis that the DA transporter ligand, [3H]mazindol, labels multiple sites/states associated with the dopamine (DA) transporter in striatal membranes. Incubations with [3H]mazindol proceeded for 18-24 hr at 4 degrees C in 55.2 mM sodium phosphate buffer, pH 7.4, with a protease inhibitor cocktail. In order to obtain data suitable for quantitative curve fitting, it was necessary to repurify the [3H]mazindol by HPLC before a series of experiments. Under these conditions, we observed greater than 80% specific binding. The method of binding surface analysis was used to characterize the interaction of GBR12935, BTCP, mazindol, and CFT with binding site/sites labeled by [3H]mazindol. A one site model fit the data as well as the two site model: Bmax = 16911 fmol/mg protein, Kd of [3H]mazindol = 75 nM, Ki of GBR12935 = 8.1 nM, Ki of CFT = 50 nM and Ki of BTCP = 44 nM. The inhibitory mechanism (competitive or noncompetitive) of several drugs (GBR12935, CFT, BTCP, cocaine, cis-flupentixol, nomifensine, WIN35,065-2, bupropion, PCP, and benztropine) was determined. All drugs inhibited [3H]mazindol binding by a competitive mechanism. Although the ligand-selectivity of the [3H]mazindol binding site indicates that it is the uptake inhibitor recognition site of the classic DA transporter, the quantitative differences among the ligand-selectivities of different radioligands for the same site suggest that each radioligand labels different overlapping domains of the DA uptake inhibitor recognition site. It is likely that development of domain-selective drugs may further our understanding of the DA transporter.

The cocaine analog WIN 35,428 binds to two sites in fresh rat caudate-putamen: significance of assay procedures

Binding of the potent cocaine analog [3H]WIN 35,428 (2 beta-carbomethoxy-3 beta-(4-fluoro-phenyl)-tropane) was examined in membrane homogenates prepared from fresh rat caudate-putamen. The number of rinses of the membranes following incubation with the ligand was varied. After one wash, only a single binding site was evident. With an increasing number of washes, however, two binding sites were observed. Additional rinses, up to a total of four, led to a decrease in the number of low affinity binding sites, with no change in the number of high affinity sites. These results suggest that the methodology used in these binding assays may be important for interpretation of the results.

Cocaine and GBR12909 produce equivalent motoric responses at different occupancy of the dopamine transporter

The motoric-stimulating effect of dopamine (DA) reuptake blockers is thought to result from the increase in synaptic dopamine levels, which occurs as a consequence of blockade of DA reuptake. The present study tested measured occupancy of the DA transporter in vivo produced by behaviorally equivalent doses of the DA reuptake blockers GBR12909 (20 mg/kg), cocaine (20 mg/kg), WIN35-065-2 (1 mg/kg), and nomifensine (5 mg/kg). Two methods were used to measure in vivo occupancy of the DA transporter: a) an ex vivo method, in which the ability of whole brain supernatants, prepared from rats administered the test drugs, were tested for their ability to inhibit the reuptake of [3H]DA by striatal synaptosomes; and b) an in vivo binding assay using [3H]N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine ([3H]BTCP) to label the striatal DA transporter in vivo. Considerable data support the notion that this measurement is predictive of transporter occupancy in the nucleus accumbens. Similar results were obtained with both methods: The order of potency for apparent transporter occupancy was GBR12909 >> nomifensine > WIN35-065-2 = cocaine. These data indicate that it takes greater occupancy of the DA transporter by GBR12909 to produce behavioral effects equivalent to those produced by cocaine at lower transporter occupancy. The data of the present study suggest, therefore, that studies relating the effects of DA reuptake inhibitors on DA-mediated motoric behaviors to DA transporter occupancy might facilitate the identification of novel compounds potentially useful for the pharmacotherapy of cocaine abuse.

Evidence for mutually exclusive binding of cocaine, BTCP, GBR 12935, and dopamine to the dopamine transporter

The present study addressed the possibility that there are distinct but allosterically interacting populations of binding sites for dopamine/cocaine and BTCP/GBR (N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine/1-(2-diphenylmethox y) - ethyl]-4-(3-phenylpropyl)piperazine) (selective dopamine uptake blockers) on the dopamine transporter in the rat striatum. Dopamine uptake sites were labeled in vitro with the cocaine analog [3H]CFT (2 beta-carbomethoxy-3 beta-(4-fluorophenyl)-tropane), and the inhibition of binding by CFT or cocaine was measured. A graphic method was adopted for studying shifts in inhibitory potency resulting from the addition of a second compound. Under the conditions used, the co-presence of dopamine, GBR 12935, or BTCP decreased the inhibitory potency of CFT or cocaine to the extent predicted by a model in which all compounds bind to the same site or the binding of all compounds is mutually exclusive. No evidence for negative allosteric interactions between CFT and BTCP was found in experiments comparing inhibition of [3H]CFT binding by BTCP at a low and high concentration of [3H]CFT.

Inhibition of dopamine uptake by cocaine and nicotine: tolerance to chronic treatments

Chronic administration of cocaine (50 mg/kg/day for 7 days, s.c. via an osmotic minipump) produced tolerance to inhibition of [3H]dopamine uptake by cocaine in rat striatum but did not produce cross-tolerance to inhibition of [3H]dopamine uptake by nicotine. Chronic nicotinic treatment (6 mg/kg/day for 7 days, s.c. via an osmotic minipump), however, produced tolerance to the inhibition of [3H]dopamine uptake by nicotine and cross-tolerance to inhibition of uptake by cocaine in rat striatum. Nicotine did not inhibit uptake of [3H]dopamine in the nucleus accumbens of saline-treated animals. In this tissue, both cocaine and nicotine treatments produced tolerance to cocaine, as in striatum. Unlike the effects on [3H]dopamine uptake, chronic cocaine infusion did not have any effect on the ability of cocaine to inhibit [3H]serotonin uptake in either brain region.