Quantitative autoradiography of [3H]sulpiride binding sites in rat brain

A technique has been developed to investigate [3H]sulpiride binding in rat brain sections using quantitative autoradiography and tritium-sensitive film. Binding was saturable and reversible with very low nonspecific binding. [3H]Sulpiride bound to an apparent single population of sites in striatum with a Kd of 3.2 nM and Bmax of 447 fmol/mg protein. Binding sites were localized in the lamina glomerulosa of the olfactory bulb, nucleus accumbens, olfactory tubercle, striatum and substantia nigra.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24695/1/0000114.pd

Properties of D2 dopamine receptor autoradiography: High percentage of high-affinity agonist sites and increased nucleotide sensitivity in tissue sections

[3H]Spiroperidol (spiperone) binding in the presence of mianserin, a serotonin (5-HT2) receptor antagonist, was characterized in rat brain using quantitative autoradiography. All binding parameters were directly determined from film densities. Competition and kinetic studies revealed that [3H]spiroperidol binds to a site having characteristics of the dopamine, D2, receptor in striatum. The general binding parameters were similar to values obtained in homogenate and swabbed section studies except as related to agonist binding and guanine nucleotide sensitivity. Competition studies with dopamine revealed biphasic competition curves with a Kh of 8.23 nM and a Kl of 12.3 [mu]M. The percentage of high-affinity sites was 90%. Guanine nucleotides (1 [mu]M guanylyl-imidodiphosphate) completely converted the high-affinity site to a low-affinity site. Quantitative regional distribution studies revealed high binding in striatum, olfactory tubercle and nucleus accumbens, with lower binding in other dopamine innervated regions including frontal and cingulate cortex. [3H]Spiroperidol was also found to bind to a spirodecanone site with an anatomical localization distinct from the dopamine and serotonin systems and in a region (entorhinal cortex) not previously reported. This report provides a detailed pharmacologic and regional characterization of [3H]spiroperidol binding to D2 receptor in rat brain using quantitative autoradiography to determine all binding parameters. This report also demonstrates an increased percentage of sites in the high-affinity state of the D2 receptor in tissue sections and increased affinity of the guanine regulatory protein for guanine nucleotides.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26042/1/0000115.pd

Basal ganglia and cerebral cortical distribution of dopamine D1- and D2-receptors in neonatal and adult cat brain

Quantitative receptor autoradiography was performed on neonatal and adult cat brains. Serial sections through the basal ganglia were assayed for D1- and D2-dopamine receptors and acetylcholinesterase (AChE) staining. The neonatal basal ganglia revealed patches of increased D1-receptor density that frequently overlapped with patches of increased AChE staining, while the D2-receptor distribution was more homogeneous. The adult basal ganglia revealed a mild amount of heterogeneity for both the D1- and D2-receptors, varying from 10 to 25%, with little correspondence to the marked heterogeneity seen with AChE staining. A distinct laminar distribution of the D1-receptor, without significant D2 binding, was seen in the cerebral cortex.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26835/1/0000395.pd

Iodine-125 and fluorine-18 labeled aryl-1,4-dialkylpiperazines: Potential radiopharmaceuticals for in vivo study of the dopamine uptake system

A series of fluorine-18 and iodine-125 labeled aryl-1,4-dialkylpiperazine analogs, derivatives of GBR 12935, were synthesized as radiotracers for positron emission tomography or single photon emission computerized tomography imaging of the brain based on their affinity for the presynaptic dopamine reuptake system. High specific activity fluorine-18 tracers were prepared by nucleophilic aromatic substitution reactions; iodine-125 tracers were prepared by isotopic exchange reactions. In vitro competitive binding studies demonstrated that iodine substitution is tolerated in the 4-position of the phenyl ring of the phenalkylpiperazine group. In vivo regional brain biodistribution studies in mice indicated no selectivity of the radioiodinated ligands for the dopamine reuptake site, with striatum/cerebellum concentration ratios of 1. Similar negative results with the new fluorine-18 derivatives demonstrated that in vivo selectivity for the dopamine reuptake site appears to be critically dependent on the carbon chain length between the piperazine ring and the solitary aromatic ring. These studies suggest that development of new radiopharmaceuticals based on the GBR 12935 structure cannot be based solely on considerations of in vitro binding affinities.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30090/1/0000461.pd

Heterogeneous distribution of dopamine D1 and D2 receptors in the human ventral striatum

The distribution of dopamine D1 and D2 receptors was examined in the human ventral striatum using in vitro quantitative autoradiography. Both D1 and D2 receptors have a markedly heterogeneous distribution, that includes regional differences in binding for the D1 receptor and a pattern of smaller heterogeneities for both receptors. The latter heterogeneities in D1 and D2 binding are interrelated and, in addition, appear to be related to inhomogeneities in the acetylcholinesterase histochemistry and cellular density of the ventral striatum. The present data indicate that in the human ventral striatum the ratio between D1 and D2 receptors varies widely from one area to another

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