Dopamine D, Receptors in the Rat Brain: Autoradiographic Visualization Using a High-Affinity Selective Agonist Ligand
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The Journal of Neuroscience, May 1987, 7(5): 1352-l 380 Dopamine D, Receptors in the Rat Brain: Autoradiographic Visualization Using a High-Affinity Selective Agonist Ligand C. Charuchinda,” P. Supavilai, M. Karobath, and J. M. Palacios Preclinical Research, SANDOZ LTD., CH-4002 Basle, Switzerland The non-catechol, selective dopamine D,-agonist compound component, one of the guanine-nucleotide binding proteins, a 3H-205-502 was used to localize dopamine D, receptors by G protein, to form what is called the “ternary complex” (Wreg- autoradiography after in vitro labeling of brain sections. The gett and Seeman,1983). This complex has beenparticularly well characteristics of the binding of this ligand to tissue sections characterized for dopamine D, receptors (Wreggett and de Lean, were those expected from the labeling of dopamine D, re- 1984) in the pituitary. ceptors. The binding of 3H-205-502 was inhibited selectively Some of theseligands have been usedfor the autoradiographic and stereospecifically by dopamine D, agents but not by localization of dopamine receptors after in vivo or in vitro la- dopamine D, compounds. beling (Palaciosand Wamsley, 1984; Kuhar et al., 1986; Palacios The autoradiographic localization of 3H-205-502 binding and Pazos, 1987). The most widely usedligand is 3H-spiperone, sites showed high densities of dopamine D, receptors in a ligand with limited receptor selectivity that, besidesdopamine areas such as the glomerular layer of the olfactory bulb, the D, and 5-HT, receptors, also binds with high affinity to a rec- nucleus accumbens, caudate-putamen, olfactory tubercle, ognition site without a known pharmacological role, the “spi- the lateral septum, and the islands of Calleja. Besides these rodecanone binding site” (Palacios et al., 1981; Altar et al., dopamine-innervated areas the substantia nigra and the 1985a, b). More recently, several 3H- and 1251-labeledbenzam- ventral tegmental area also showed important receptor den- ides have been introduced as selective D, ligands and utilized sities. Other areas where dopamine D, receptor binding was in receptor localization. These include ‘H-sulpiride (Jastrow et found were the stratum lacunosum-moleculare of the hip- al., 1984; Gehlert and Wamsley, 1985), 1251-sulpride(Martres pocampus, bands of labeling in the molecular layer of the et al., 1985a, b), 3H-(-)-D0 710 (Sokoloffet al., 1985), and 3H- 9th and 10th lobules of the cerebellum, and several com- eticlopride (Kiihler et al., 1986). A novel pyrroloisoquinoline, ponents of the visual system. 3H-R0 22-13 19 (piquindone; Nakajima and Iwata, 1984) has This distribution presents similarities and differences with also been used in autoradiographic experiments (Neck et al., previously reported distributions of dopamine D, receptors 1986). Finally, autoradiographic localization of dopamine re- visualized autoradiographically using 3H-labeled agonists and ceptors has been investigated with some 3H-labeled agonists, antagonists. In view of the high affinity, guanine nucleotide although satisfactory results have been obtained only with 3H- insensitivity, and dopamine D, selectivity of this agonist li- N-n-propylnorapomorphine (Fuxe et al., 1983; Scatton et al., gand, it is suggested that dopamine D, receptors exist in 1984; Dubois and Scatton, 1985; Dubois et al., 1986), 3H-apo- different states in different areas. 3H-205-502 appears to be morphine (Bouthenet et al., 1985) being a poor ligand. Recently, a new and useful tool for the study of dopamine D, receptors. 2 new non-catechol dopaminergic agonists with high affinity and selectivity for dopamine D, receptors have been described Many different radiolabeled moleculeshave been used to study (Closseet al., 1985; A. Closse,unpublished observations). These dopamine D, receptorsin the mammalian nervous system(See- ligands (&)205-50 1 [=(?)-N,N-diethyl-N’-[(3a,4a(u, lop)- 1,2,3, man, 1981; Creeseet al., 1983). The development of these dif- 4,4a, 5,lO,lOa - octahydro - 7 - hydroxy - 1 - propyl - 3 - benzo[g] ferent radioligands has been justified by their lack of pharma- quinolinyl]sulfamide] and the 6-hydroxy counterpart analog, cological selectivity for dopamine receptors or their subtypes- compound 205-502, are members of a new family of recently D, and D, (Kebabian and Calne, 1979)-and becauseof the synthesized dopamine agonistsstructurally related to apomor- poor technical properties of some of these ligands (i.e., high phine and to dopaminomimetic ergolines (Nordmann and nonspecific binding or poor chemical stability). The use of ra- Petcher, 1985). They exceed the receptor specificity of apo- diolabeled dopamine agonistshas presented special problems morphine, being selective D, agonists,and, as the ergolines,are becauseof the postulated existence of different affinity statesof long-lasting potent agonists. We have now used one of these the dopamine receptors (Creeseet al., 1984).3H-Agonists appear ligands, 3H-205-502, to visualize dopamine D, receptors in the to label predominantly a high-affinity state of the dopamine D, rat brain. receptor characterized by its high affinity for a third membrane Materials and Methods Rats (male Wistar, 180-250 g) were sacrificed by intracardial perfusion Received July 14, 1986; revised Oct. 30, 1986; accepted Nov. 10, 1986. with phosphate-buffered saline containing 0.1% formalin, after pento- We wish to thank Dr. D. Coward for a critical reading of the manuscript. barbital anesthesia (50 mg/kg). The brains were removed and frozen in Correspondence should be addressed to J. M. Palacios at the above address. liquid nitrogen. Tissue sections, 10 pm thick, were cut using a micro- a Submitted in partial fulfillment of the Ph.D. thesis, Faculty of Graduate Stud- tome-cryostat (Leitz 1720, from Leitz, Wetzlar, F.R.G.), mounted onto ies, Mahidol University, Bangkok, Thailand. gelatin-coated microscope slides and stored at -20°C until used. Copyright 0 1987 Society for Neuroscience 0270-6474/87/051352-09$02.00/O Slide-mounted rat brain sections were preincubated for 30 min in The Journal of Neuroscience, May 1987, 7(5) 1353 Table 1. Pharmacology of ‘H-205-502 binding to sections of the rat striatum Comnounds Dopamine agonists Dopamine 804.3 + 86.7 (3) Apomorphine 38.1 k 6.6 (3) Bromocriptine 28.1 zk 2.2 (3) LY 171 555 333.0 k 59.9 (3) (+)N-Propylnorapomorphine 1493.0 f 370.0 (3) (+)3-PPP 4485.0 2 913.0 (3) (-)3-PPP 386.3 f 61.5 (3) 'H-205-502 (nM) 205-501 50.9 t 1.8 (4) 205-502 5.5 + 0.6 (6) Figure 1. Concentration dependence of the binding of 3H-205-502 to rat brain striatal sections. SKF38393 6170.0 + 251.0 (3) Dopamine antagonists Spiperone 0.38 k 0.06 (3) 170 mM Tris-HCl buffer, pH 7.5, at room temperature, then incubated (+)Butaclamol 7.0 2 0.7 (3) for 90 min at room temperature in 170 mM Tris-HCl buffer, pH 7.5, (-)Butaclamol 15,000.0 * 1899.0 (3) with various concentrations (for saturation experiments) or 1 nM 3H- YM-09 15 l-2 0.47 + 0.02 (3) 205-502 and drugs as indicated. At the end of the incubation the slides were washed twice (1 min each) in 170 mM Tris-HCl buffer at 4°C. For SCH 23390 1977.0 k 700.0 (3) biochemical studies of 3H-205-502 binding, tissue was wiped from the Q Means f SEM. slide using a Whatman GF/B glass filter fiber and radioactivity deter- mined by liquid scintillation counting. Specific binding was calculated as the difference in radioactivity bound in the presence and absence of The specificity and selectivity of 3H-205-502 for dopamine 1 ELM (+)butaclamol. After the washing period, tissues were dried with cold air, and au- D, receptors were then examined. The binding of 3H-205-502 toradiograms were generated by apposing the labeled tissue to ‘H-Ul- to rat striatal sections was inhibited with high affinity by several trofilm (LKB, Sweden) as described by Unnerstall et al. (1982). Exposure dopamine agonists (Table l), including dopamine itself, apo- period was 60 d at 4°C. Brain gray and white matter standards containing morphine, bromocriptine, and the selective dopamine D, ago- known amounts of a nonvolatile 3H-labeled compound were exposed nist 205-501, unlabeled 205-502, and quinpirole (compound to the film along with the labeled tissue sections. Films were analyzed using a computerized image-analysis system that provides values of LY 17 1555; Tsuruta et al., 1981; Hahn et al., 1983). In contrast, receptor densities expressed in fmol/mg protein. Four to six bilateral the selective dopamine D, agonist SKF 38393 (Molloy and measurements were made per nucleus at the level described in each Waddington, 1984) showed only low affinity for the sites labeled animal, and the mean value was calculated. Values of “specific binding” by 3H-205-502. The inhibition of 3H-205-502 by dopamine for each rat were obtained by subtracting the nonspecific binding from agonists was stereospecific, with (+)iV-propylapomorphine and the total value. The mean value from equivalent areas in different an- imals was calculated. Results reported in this study are from at least 2 (+)3PPP showing affinities in the micromolar range (Table 1). separate experiments, involving tissues from 3 animals per experiment. Dopamine D, receptor antagonists were also potent displacers Brain nuclei were identified and named using the rat brain atlas of of 3H-205-502 binding. Again, the displacement was stereose- Paxinos and Watson (1982). lective, as shown by the differences in affinities exhibited by the 3H-205-502 (107 Ci/mmol) was synthesized and labeled by Dr. R. Voges of the Biopharmaceutical Department, Sandoz Ltd. (Basle, Swit- d- and l-stereoisomers of sulpit-ide and by (+) and (-) buta- zerland). Other chemicals or drugs were of commercial origin or kindly clamol. Selective D, antagonists such as YM-0915 l-2 (Grewe provided by the original manufacturers.