Dopamine Transporter Binding Sites Research Articles

Development of striatal dopaminergic function. I. Pre- and postnatal development of mRNAs and binding sites for striatal D1 (D1a) and D2 (D2a) receptors

Quantitative receptor autoradiography with iodinated ligands, quantitative in situ hybridization histochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to describe the prenatal and early postnatal ontogeny (embryonic day 14 to postnatal day 7, or E14 to P7) of striatal D1 and D2 dopamine receptor binding sites and mRNA levels, respectively, in relation to the development of dopaminergic nigrostriatal innervation. D1 dopamine receptor, measured by [ 125I]SCH23982 binding, and dopamine transporter binding sites, measured by [ 125I]RTI-55 binding, were present in low amounts beginning on E14 (2–3% and 0.3–0.6% of adult values, respectively) and increased slowly during the prenatal period. D2 receptor binding sites, measured with [ 125I]spiperone, were also detected on E14 but in higher relative quantities (17% of adult values) than D1 receptor and dopamine transporter binding sites at the same age. Other than abrupt declines in the late prenatal period for D1 and D2 receptor binding sites, all three binding sites increased throughout development and increased maximally between P7 and adulthood. On P5, both D1 and D2 receptors were functionally coupled to their respective G proteins, based on GTP-induced decreases in affinity of dopamine for [ 125I]SCH23982 and [ 125I]spiperone binding. D1 receptor mRNA was present in E14 striatal anlage, increased prenatally, declined on P0, then increased to a peak on P5, after which it declined to its lowest levels (20% of peak values) in the adult. In contrast, D2 receptor mRNA levels were present also on E14, increased to a peak on P0, declined until P5, and increased thereafter to adulthood. Anatomically, nigrostriatal innervation and D1 and D2 receptor mRNA levels increased from the medial to lateral striatal quadrants. In contrast, D1 and D2 receptor binding site ontogeny exhibited fairly homogeneous distributions from E18 to P7. D1 and D2 receptor mRNAs appear to be expressed early in prenatal development before there is any significant dopaminergic innervation. In contrast, the majority of D1 and D2 receptor binding activity, representing expressed receptor proteins, develops in the postnatal period and correlates well with the increase in dopaminergic innervation. Intrinsic genetic programming is more likely to be responsible for D1 and D2 receptor gene transcription in striatal neuroblasts and newly born neurons, while factors derived from ingrowing dopaminergic afferents may direct post-transcriptional dopamine receptor development. The dissociation between the ontogeny of dopamine receptor binding sites and mRNAs suggests that the developmental regulation of D1 and D2 receptor synthesis is independent of D1 and D2 receptor gene transcription.

Expression of dopamine transporter mRNA and its binding site in fetal nigral cells transplanted into the striatum of 6-OHDA lesioned rat

Neurological disorders in rat model of hemi-Parkinson's disease can be compensated by the transplantation of fetal nigral cells. However, the role of the dopamine transporter (DAT) in this recovery has not been clarified. To clarify this mechanism, we examined the expression of DAT in the caudate putamen (CPu) by in situ hybridization histochemistry (mRNA) and autoradiography (using the ligand [125I] beta-CIT, which labels DAT) and compared them with the recovery of motor disturbance revealed with methamphetamine-induced rotation. Models were made with the stereotaxic injection of 6-hydroxydopamine into the left side of the substantia nigra pars compacta. Cell suspensions from rat fetus (embryonic day 14-15) were transplanted into the lesioned side of CPu. Methamphetamine-induced rotation, expression of DAT mRNA, and [125I] beta-CIT binding were evaluated 2, 4 and 12 weeks after the transplantation. Methamphetamine-induced rotation recovered partly in the 2nd week and significantly in the 4th week. [125I] beta-CIT binding increased with time and the dense binding was detected 4 and 12 weeks after the transplantation. In all transplanted rats, cells expressing DAT mRNA were found in CPu. These results indicated that transplanted fetal dopaminergic cells maturated in CPu of host animals and extended nerve terminals where high density of DAT binding sites were found.

Medial Dorsal Striatum Is More Sensitive Than Lateral Dorsal Striatum to Cocaine Inhibition of Exogenous Dopamine Clearance: Relation to [ 3H]Mazindol Binding, but Not Striosome/Matrix

Previous studies have shown that acute systemic cocaine inhibits dopamine (DA) transport and thereby produces dose-dependent changes in exogenous DA clearance in the brain. This measure reflects the dynamic activity of the DA transporter. There are also differential effects of cocaine on DA clearance in dorsal and ventral striatum, and evidence from many studies suggests that even within the dorsal striatum, the interaction of cocaine with the DA transporter may not be homogeneous. A greater understanding of how cocaine interacts with the striatal DA transporter will help clarify the role of the striatum in mediating effects of cocaine. In these studies we used in vivo electrochemical recording to examine the effect of ip cocaine on exogenous DA clearance in the medial and lateral dorsal striatum with respect to both DA transporter binding sites and electrode localization to striosomes or matrix. Baseline exogenous DA clearance was different in medial and lateral dorsal striatum in the absence of cocaine. Systemic cocaine produced a more pronounced inhibition of DA clearance in medial dorsal striatum than in lateral dorsal striatum. [ 3H]Mazindol binding to DA transporters was lower in medial dorsal striatum, but was not in register with striosome or matrix compartments. There was no notable difference between cocaine's effects on DA clearance in striosome or matrix that was due to this compartmentalization. Others have demonstrated that medial dorsal striatum receives proportionally more innervation from the mesolimbic, as opposed to the nigrostriatal, DA system. Taken together, these and previous in vivo results suggest that this differential sensitivity to cocaine reflects the unique properties of the ascending mesolimbic DA projection and the lower density of DA transporters associated with it.

Effects of repeated injections of cocaine on catecholamine receptor binding sites, dopamine transporter binding sites and behavior in rhesus monkey

In order to determine if repeated injections of cocaine produced long-lasting alterations in catecholaminergic binding sites, rhesus monkeys were treated with saline (1.0 ml/15 kg) or cocaine (3.0–4.0 mg/kg) four times daily for 14 consecutive days and sacrified two weeks after the last injection. The densities of dopamine D 1 receptor binding sites, dopamine transporter binding sites and β adrenergic receptor binding sites were significantly decreased in caudate nucleus to 51%, 17% and 61% of control, respectively, two weeks after repeated cocaine injections. There were no differences in D 2 receptor binding site densities in the caudate, nor were there differences in binding sites between groups in the other brain regions examined: prefrontal cortex (D 1, D 2, dopamine transporter, β), nucleus accumbens (D 1, D 2, dopamine transporter) and substantia nigra (D 2). Behavioral observation showed that the cocaine-treated monkeys became sensitized to the repeated injections. Early in the regimen, these animals displayed stereotypic grooming, buccal movements and visual checking after each injection that differed significantly from the saline-treated animals. As the regimen progressed, the frequency of grooming decreased while the frequencies of visual tracking and splayed legs increased in a manner consistent with the development of behavioral sensitization. Together, these findings suggest that the caudate nucleus may be more sensitive than other dopamine-containing brain regions to long-lasting pre- and post-synaptic effects of repeated cocaine administration, and that the changes seen in dopaminergic neurons may be related to behavioral sensitization.