Substitution of the chlorine atom by a radio-iodine in position 5 in the zacopride molecule yielded [125I]iodo-zacopride that bound with high affinity (Kd = 4.3 nM) to 5-HT3 receptors in the rat central nervous system. Assays with membranes from the posterior (mainly entorhinal) cortex confirmed that the pharmacological properties and regional distribution of [125I]iodo-zacopride-specific binding sites were identical with those of 5-HT3 sites labelled by the reference radioligand [3H]zacopride. Autoradiographic investigations for the visualization and quantification of 5-HT3 receptors yielded similar results with both radioligands, but autoradiograms could be obtained after only 1-3 days of exposure of sections labelled with [125I]iodo-zacopride, instead of 4-6 months using [3H]zacopride. The highest density of 5-HT3 sites was found in the nucleus tractus solitarius followed by, in decreasing order, the dorsal motor nucleus of the vagus nerve, the superficial layers of the dorsal horn in the spinal cord, the nucleus of the spinal tract of the trigeminal nerve, and the area postrema. Significant labelling of 5-HT3 receptors was also observed in limbic areas (amygdala, hippocampus, frontal and entorhinal cortex), and to a much lower extent in the dorsal raphe nucleus, striatum, and substantia nigra. These multiple locations further support the idea that 5-HT3 receptors are probably involved in several 5-HT-mediated functions in the central nervous system.
Uptake of (18)F-dopa may be up-regulated in early PD, suggesting a compensatory increase of dopamine synthesis in surviving dopaminergic terminals. Positron emission tomography dopamine transporter ligands and (18)F-dopa give complementary information on the presynaptic status of the nigrostriatal dopaminergic system and might be associated to investigate the efficacy of neuroprotective treatments in PD.
Serotonin 5-HT1A receptors in rat hippocampal membranes were solubilized by 10 mM 3-[3-(cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS) and chromatographed on various gels in an attempt to design a relevant protocol for their (partial) purification. In particular, an affinity gel made of the 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) derivative 8-methoxy-2-[(N-propyl, N-butylamino)amino]tetralin (8-MeO-N-PBAT) coupled to Affigel 202 was specially developed for this purpose. First, studies of the effects of various compounds (detergents, lipids, reducing agents, sugars, etc.) on the specific binding of [3H]8-OH-DPAT and on the rate of heat-induced inactivation of solubilized 5-HT1A sites led to a buffer composed of 50 mM Tris-HCl, 50 microM dithiothreitol, 1 mM CHAPS, 10% glycerol, 0.1 mM MnCl2, and 50 micrograms/ml of cholesteryl hemisuccinate, pH 7.4, ensuring a high degree of stability of solubilized 5-HT1A sites, compatible with chromatographic analyses for 2-4 days at 4 degrees C. Adsorption and subsequent elution of [3H]8-OH-DPAT specific binding sites were found with several chromatographic gels, including wheat germ agglutinin-agarose, phenyl-Sepharose, hydroxylapatite-Ultrogel, diethylaminoethyl (DEAE)-Sepharose, and DEAE-Sephacel. Similarly, 8-MeO-N-PBAT-Affigel 202 allowed the adsorption and subsequent elution (by 1 mM 5-HT) of active 5-HT1A binding sites solubilized from rat hippocampal membranes. The two-step chromatography using 8-MeO-N-PBAT-Affigel 202 followed by wheat germ agglutinin-agarose gave a fraction enriched (by at least 400-fold) in 5-HT1A sites. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of this partially purified fraction revealed a major protein band with Mr close to 60,000.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.