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Dopamine receptors in the rat frontal cortex: An autoradiographic study
Brain Research, 177 (1979) 279-285
279
© Elsevier/North-Holland Biomedical Press
D O P A M I N E RECEPTORS IN T H E RAT F R O N T A L CORTEX: AN A U T O R A D I O G R A P H I C STUDY
L. CHARLES MURRIN and MICHAEL J. KUHAR* Departments of Pharmc cology and Experimental Therapeutics and Psychiatry and the Behavioral Sciences The Johns Hopkins University School of Medicine, Baltimore, Md. 21205 (U.S.A.)
(Accepted February 22nd, 1979)
SUMMARY Literature findings indicated that injection of low doses of [3H]spiperone results in a labelling of dopamine receptors in rat brain, but also in a labelling of serotonin receptors. Administration of pipamperone, a drug with serotonergic properties, to animals treated with [aH]spiperone reduced the serotonergic component of the binding and permitted an easier identification of dopamine receptor binding. At the level of Forceps Minor, there were elevated levels of receptors in the deeper layers of the cingulate cortex, in the region above the rhinal sulcus and in an area dorsal to the accumbens. This distribution is in agreement with the results of other biochemical, histochemical and electrophysiological studies. INTRODUCTION Biochemical ~,26-29, histochemicall,2,11, ls-2x and electrophysiological4 studies indicate the presence of a dopaminergic projection from the midbrain to the rat frontal cortex. In general, frontal cortical dopamine terminal systems are found in the deeper layers of the anterior cingulate cortex, in the deeper layers of the cortex dorsal to the corpus callosum and in the dorsal rhinal sulcus 2,11,18,21. A useful marker for dopaminergic projections is the localization of dopamine receptors by binding methodsS, 24. By utilizing [3H]spiperone, a neuroleptic drug with very high affinity for dopamine receptorsT,S,16, it is possible to label dopamine receptors in intact tissues after in vivo administrationg,12,18,15, a6. Because of this favorable distribution, it is possible to localize dopamine receptors in histological sections at the light microscopic level utilizing autoradiographic methodslO,al,la, 2,~. A difficulty with this in vivo labelling-autoradiographic approach is that [aH]spiperone * To whom correspondence should be addressed at: Department of Pharmacology, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Md. 21205, U.S.A.
Fig. 1. Autoradiographic localization of [3H]spiperone (SP) in rat cingulate cortex. Treatment of animals with pipamperone (PP) reduces the serotonergic component of binding and leaves the dopamine receptor binding relatively intact. See text for details. A and B show layer I of cingulate cortex from rats given SP and PP (B). PP causes a marked reduction in binding in layer I (more than a 7 0 ~ reduction after subtracting tissue background densities measured over the anterior commissure) but not in layer VI (Only a 5 10 ~ reduction) (C and D). See right side of Fig. 3 for general location of the micrographs. Bar -- 20 t~m. See text for discussion.
281 is not totally selective for dopamine receptors; it seems to bind to serotonin receptors as well6,17. However, by treatment of animals with pipamperone or LSD (serotonergic antagonists), it is possible to greatly attenuate the serotonergic component of [aH]spiperone binding and hence more selectively label dopamine receptorsXT,23. In this study, we have utilized pipamperone-treated animals and [3H]spiperone injections to localize dopamine receptors in the frontal cortex at the light microscopic level by autoradiographic methods. METHODS Male, Sprague-Dawley rats (175-225 g) were utilized. Five hundred #Ci/kg of [3H]spiperone (26.4 Ci/mM, New England Nuclear) were administered by tail vein injection into rats in 0.3 ml of 0.9 ~o saline. One hour later, pipamperone (1 mg/kg) was given. After pipamperone administration, the animals were sacrificed and the frontal cortical areas were prepared for autoradiographic studies as previously describedl2,1~. Because of the relatively low level of dopamine receptors in these areas, 3 month exposures were required. When cutting the tissues, we focused on the area of the frontal cortex containing the Forceps Minor, at about the level of A 10300 #m according to Konig and Klippe114 since other studies focused at this level and we would be able to compare our results to those of earlier workers. In some animals, both pipamperone and pimozide were given to displace [3H]spiperone from dopamine receptors as well. RESULTS In tissues from animals that were not treated with pipamperone, the autoradiographic localization of [aH]spiperone showed a fairly wide distribution of binding sites in the frontal cortex. Notable was the enrichment of binding sites in the more superficial layers of the cortex. However, treatment with pipamperone caused a depletion of autoradiographic grain densities in these more superficial layers while only minimally affecting the grain density in the deepest layers (Fig. 1). These findings are in agreement with the notion that serotonergic fibers tend to appear in layers I and II in the cerebral cortex 21. Blocking these serotonergic sites with pipamperone thus increased the specificity for dopamine receptors. Accordingly, we focused our analysis on tissues from animals treated with pipamperone. When animals were given pimozide (5 mg/kg), a more selective dopamine receptor blocker 17, along with pipamperone, the levels of radioactivity in the frontal cortex were reduced even further than in those with pipamperone alone (data not shown). This is evidence that the [aH]spiperone remaining after pipamperone administration is associated with dopamine receptors. However, one cannot completely rule out that the [aH]spiperone displaced by pimozide is also binding, in part, to a nondopaminergic receptor. At the levels of Forceps Minor, there were high densities of dopamine receptor in the deeper layers of the cingulate cortex, in the area above the rhinal suleus and in the area immediately dorsal to the nucleus accumbens (Figs. 2 and 3). These cingulate,
Fig. 2. Autoradiographic localization of SP in cortex from PP-treated rats. A : outer edge of rhinal sulcus area. B: rhinal sulcus area. C: region just above nucleus accumbens. D: the anterior commissure. See right side of Fig. 3 for location of micrographs. The high densities of autoradiographic grains marking dopamine receptors in B and C are contrasted with the low density in A and D. See text for discussion. Bar -- 20/tm.
283
B HIGH
~LOW
Fig. 3. Schematic diagram showing distribution of dopamine receptors in the frontal cortex. The data is taken from animals administered SP and PP. Abbreviations: FMI, forceps minor; a, nucleus accumbens; CAA, anterior commissure (pars anterior) ; TOL, lateral olfactory tract. The level shown is A 10300 from Konig and KlippeP4. Highest densities of dopamine receptors (left side) were observed in cingulate, suprarhinal and supra-accumbal areas. The high densities of receptors in nucleus accumbens which were previously reported 12are not shown. See text for further discussion. The rectangles on the right side show the location of the micrographs presented in Figs. 1 and 2. The correspondence is as follows: 1, Fig. 1A and B; 2, Fig. 1C and D; 3, Fig. 2A; 4, Fig. 2B; 5, Fig. 2C; 6, Fig. 2D. suprarhinal and supra-accumbal localizations were accompanied by other areas showing somewhat lower densities. These somewhat lower density areas were found in the dorsal cortex but also in the deep layers, in the area between the supra-accumbal and suprarhinal groups and also in an area immediately beneath the Forceps Minor (Figs. 2 and 3). Notable was the lack of high densities of receptors in the dorsal cortex above the forceps, and the background level of autoradiographic grains over white matter areas such as the anterior commissure. We also had tissues from more anterior areas. At the level of about A11050 # m according to Konig and KlippeP 4 there were still elevated densities in the suprarhinal, cingulate, in the supra-accumbal regions. Thus, these fields of dopamine receptors appear to extend for at least some distance in the rostrocaudal direction in the frontal cortical area. DISCUSSION The distribution of dopamine receptors found in this study is in agreement with the reported distribution of dopamine-containing fibers and terminals by histochemistry 1,2,11,1s-21. We did not find receptors in layers I, II and III where Lindvall et al. zl and Lewis et al. TM describe dopaminergic fibers. However, these fibers in the superficial layers are found in more caudal areas, near the genu of the corpus callosum. A possible discrepancy appears to be the lack of receptors dorsal to the Forceps Minor, an area enriched in dopamine-containing fibers 21. However, the fiber density there is low and the numbers of synapses by the dopamine fibers in these areas may be quite low and just below the limit of our detection by our autoradiographic approach. Moreover, biochemical studies showed relatively low dopamine content 3,
284 dopamine-sensitive adenylate cyclase3, 3° and [3H]dopamine uptake 27 in this region as well. These same biochemical parameters were high in the areas showing high levels o f dopamine receptors in this study3, zT. Further, the iontophoretic study of Bunney and Aghajanian 4 are also in agreement with our results in that dopamine sensitive cells in cingulate cortex are found mainly in layers V and VI and that the cells in layers II and I I I show little sensitivity to dopamine. Thus, there is an excellent general agreement between our results and those in other studies. The main interest in cortical dopaminergic systems stems from the apparent involvement o f these systems in mental disorders such as schizophrenia11, ~5. The data presented in this study indicates the feasibility o f using a histochemical approach to study dopamine receptors, and extends our knowledge of dopamine terminal fields in the frontal cortex. ACKNOWLEDGEMENT The authors acknowledge the technical assistance o f Mrs. N a o m i Taylor and Ms. D e b r a Niehoff, the clerical assistance of Princie Campbell and Carol Kenyon, the helpful suggestions o f Dr. M a r k Molliver in the preparation o f the manuscript, the gift of pipamperone and pimozide f r o m Janssen Pharmaceutics and the support of U S P H S G r a n t M H 25951 and the M c K n i g h t Foundation. M.J.K. is the recipient of R S D A A w a r d M H 00053. REFERENCES 1 Berger, B., Tassin, J. P., Blanc, G. Moyne, M. A. and Thierry, A. M., Histochemical confirmation for dopaminergic innervation of the rat cerebral cortex after destruction of ascending noradrenergic pathways, Brain Research, 81 (1974) 332-337. 2 Berger, B. Thierry, A. M., Tassin, J. P. and Moyne, M. A., Dopaminergic innervation of the rat prefrontal cortex: a fluorescence histochemical study, Brain Research, 186 (1976) 133-145. 3 Bockaert, J., Premont, J., Glowinski, J., Tassin, J. P. and Thierry, A. M., Topographical distribution and characteristics of dopamine and fl-adrenergic sensitive adenylate cyclases in the rat frontal cerebral cortex, striatum and substantia nigra. In E. Costa and G. L. Gessa (Eds.), Advan. Biochem - - PsychopharmacoL, Vol. 16, Raven Press, New York, 1977, pp. 29-37. 4 Bunney, B. S. and Aghajanian, G. K., Dopamine and norepinephrine innervated cells in rat prefrontal cortex: pharmacological differentiation using microiontophoretic techniques, Life Sci., 19 (1976) 1783-1792. 5 Creese, I., Burt, D. R. and Snyder, S. H., Dopamine receptor binding differentiation of agonist and antagonist states with 3H-dopamine and 8H-haloperidol, Life Sci., 17 (1975) 993-1002. 6 Creese, I. and Snyder, S. H., 3H-Spiroperidol labels serotonin receptors in rat cerebral cortex and hippocampus, Europ. J. Pharmacol., 49 (1978) 201-202. 7 Creese, I., Schneider, R. and Snyder, S. H., aH-Spiroperidol labels dopamine receptors in Pituitary and Brain, Europ. J. Pharmacol., 46 (1977) 377-381. 8 Fields, J. Z., Reisine, T. D. and Yamamura, H. I., Biochemical demonstration of dopaminergic receptors in rat and human brain using [aH]spiroperidol, Brain Research, 136 (1977) 578-584. 9 Hollt, V., Czlonkowski, A. and Henry, A., The demonstration in vivo of specific binding sites for neuroleptic drugs in mouse brain, Brain Research, 130 (1977) 176-183. 10 Hollt, V. and Schubert, P., Demonstration of neuroleptic receptor sites in mouse brain by autoradiography, Brain Research, 151 (1978) 149-153. 11 Hokfelt, T., Ljungdahl, A., Fuxe, K. and Johansson, O., Dopamine nerve terminal in rat limbic cortex: aspects of the dopamine hypothesis of schizophrenia, Science, 184 (1974) 177-179. 12 Klemm, N., Murrin, L. C. and Kuhar, M. J., Neuroleptic and dopamine receptors: autoradiographic localization of [3H]spiperone in rat brain, Brain Research, 169 (1979) 1-9.
285 13 Kuhar, M. J., Murrin, L. C., Malouf, A. T. and Klemm, N., Dopamine receptor binding in vivo: the feasibility of autoradiographic studies, Life ScL, 22 (1978) 203-210. 14 Konig, J. R. and Klippel, R. A., The Rat Brain. A Stereotaxic Atlas of the Forebrain and Lower Parts of the Brain Stem, Krieger, New York, 1963. 15 Laduron, P. and Leysen, J., Specific in vivo binding of neuroleptic drugs in rat brain, Biochem. PharmacoL, 26 (1977) 1003-1007. 16 Laduron, P. M., Janssen, P. and Leysen, J. E., Spiperone" a ligand of choice for neuroleptic receptors. 2. Regional distribution and in vivo displacement of neuroleptic drugs, Biochem. PharmacoL, 27 (1978) 317-321. 17 Leysen, J. E., Niemegeers, C. J. E., Tollenaere, J. P. and Laduron, P. M., Serotonergic component ofneuroleptic receptors, Nature (Lond.), 272 (1978) 169-171. 18 Lewis, M. S., Molliver, M. E., Morrison, J. H. and Lidou, H. G. W., Complementarity of dopaminergic and noradrenergic innervation in anterior cingulate cortex of the rat, Brain Research, 164 (1979) 328-333. 19 Lidbrink, P., Jonsson, G. and Fuxe, K., Selective reserpine resistant accumulation of catecholamines in central dopamine neurons after dopa administration, Brain Research, 67 (1974) 439-456. 20 Lindvall, O., Bjorklund, A., Moore, R. Y. and Stenevi, U., Mesencephalic dopamine neurons projecting to the neocortex, Brain Research, 81 (1974) 325-337. 21 Lindvall, O., Bjorklund, A. and Divac, I., Organization of catecholamine neurons projecting to the frontal cortex in rat, Brain Research, 142 (1978) 1-24. 22 Moore, R. Y., Halaris, A. E. and Jones, B. E., Serotonin neurons of the midbrain raphe: ascending projections, J. comp. NeuroL, 180 (1978) 417-438. 23 Murrin, L. C., Klemm, N. and Kuhar, M. J., Autoradiographic localization of dopamine and neuroleptic receptors in the rat brain using 3H-spil~erone. In E. Usdin and I. Kopin (Eds.), Proc. Fourth Int. Catecholamine Symposium, Raven Press, 1979, in press. 24 Seeman, P., Chan-Wong, M., Tedesco, J. and Wong, K., Brain receptors for antipsychotic drugs and dopamine: direct binding assays, Proc. nat. Acad. Sci. (Wash.), 72 (1975) 4376-4380. 25 Snyder, S. H. Banerjee, S. P., Yamamura, H. I. and Greenberg, D., Drugs, neurotransmitters and schizophrenia, Science, 184 (1974) 1243-1253. 26 Tassin, J. P., Thierry, A. M., Blanc, G. and Glowinski, J., Evidence for a specific uptake of dopamine by dopaminergic terminals of the rat cerebral cortex, Naunyn-Schmiedeberg's Arch. exp. Path. Pharmak., 282 (1974) 239-244. 27 Tassin, J. P., Stinus, L., Simon, H., Blanc, G., Thierry, A. M., LeMoal, M., Cardo, B. and Glowinski, J., Distribution of dopaminergic terminals in rat cerebral cortex. In E. Costa and G. L. Gessa (Eds.), Advanc. Biochem.-PsychopharmacoL, VoL 16, Raven Press, New York, 1977, pp. 21-28. 28 Thierry, A., Blanc, G., Sobel, A., Stinus, L. and Glowinski, J., Dopaminergic terminals in rat cortex, Science, 182 (1973) 499-501. 29 Thierry, A. M., Hirsch, J. C., Tassin, J. P., Blanc, G. and Glowinski, J., Presence of dopaminergic terminals and absence of dopaminergic cell bodies in the cerebral cortex of the cat, Brain Research, 79 (1974) 77-88. 30 Von Hungen, K. and Roberts, S., Adenylate-cyclase receptor for adrenergic neurotransmitters in rat cerebral cortex, Europ. J. Biochem., 36 (1973) 391-401.
279
© Elsevier/North-Holland Biomedical Press
D O P A M I N E RECEPTORS IN T H E RAT F R O N T A L CORTEX: AN A U T O R A D I O G R A P H I C STUDY
L. CHARLES MURRIN and MICHAEL J. KUHAR* Departments of Pharmc cology and Experimental Therapeutics and Psychiatry and the Behavioral Sciences The Johns Hopkins University School of Medicine, Baltimore, Md. 21205 (U.S.A.)
(Accepted February 22nd, 1979)
SUMMARY Literature findings indicated that injection of low doses of [3H]spiperone results in a labelling of dopamine receptors in rat brain, but also in a labelling of serotonin receptors. Administration of pipamperone, a drug with serotonergic properties, to animals treated with [aH]spiperone reduced the serotonergic component of the binding and permitted an easier identification of dopamine receptor binding. At the level of Forceps Minor, there were elevated levels of receptors in the deeper layers of the cingulate cortex, in the region above the rhinal sulcus and in an area dorsal to the accumbens. This distribution is in agreement with the results of other biochemical, histochemical and electrophysiological studies. INTRODUCTION Biochemical ~,26-29, histochemicall,2,11, ls-2x and electrophysiological4 studies indicate the presence of a dopaminergic projection from the midbrain to the rat frontal cortex. In general, frontal cortical dopamine terminal systems are found in the deeper layers of the anterior cingulate cortex, in the deeper layers of the cortex dorsal to the corpus callosum and in the dorsal rhinal sulcus 2,11,18,21. A useful marker for dopaminergic projections is the localization of dopamine receptors by binding methodsS, 24. By utilizing [3H]spiperone, a neuroleptic drug with very high affinity for dopamine receptorsT,S,16, it is possible to label dopamine receptors in intact tissues after in vivo administrationg,12,18,15, a6. Because of this favorable distribution, it is possible to localize dopamine receptors in histological sections at the light microscopic level utilizing autoradiographic methodslO,al,la, 2,~. A difficulty with this in vivo labelling-autoradiographic approach is that [aH]spiperone * To whom correspondence should be addressed at: Department of Pharmacology, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Md. 21205, U.S.A.
Fig. 1. Autoradiographic localization of [3H]spiperone (SP) in rat cingulate cortex. Treatment of animals with pipamperone (PP) reduces the serotonergic component of binding and leaves the dopamine receptor binding relatively intact. See text for details. A and B show layer I of cingulate cortex from rats given SP and PP (B). PP causes a marked reduction in binding in layer I (more than a 7 0 ~ reduction after subtracting tissue background densities measured over the anterior commissure) but not in layer VI (Only a 5 10 ~ reduction) (C and D). See right side of Fig. 3 for general location of the micrographs. Bar -- 20 t~m. See text for discussion.
281 is not totally selective for dopamine receptors; it seems to bind to serotonin receptors as well6,17. However, by treatment of animals with pipamperone or LSD (serotonergic antagonists), it is possible to greatly attenuate the serotonergic component of [aH]spiperone binding and hence more selectively label dopamine receptorsXT,23. In this study, we have utilized pipamperone-treated animals and [3H]spiperone injections to localize dopamine receptors in the frontal cortex at the light microscopic level by autoradiographic methods. METHODS Male, Sprague-Dawley rats (175-225 g) were utilized. Five hundred #Ci/kg of [3H]spiperone (26.4 Ci/mM, New England Nuclear) were administered by tail vein injection into rats in 0.3 ml of 0.9 ~o saline. One hour later, pipamperone (1 mg/kg) was given. After pipamperone administration, the animals were sacrificed and the frontal cortical areas were prepared for autoradiographic studies as previously describedl2,1~. Because of the relatively low level of dopamine receptors in these areas, 3 month exposures were required. When cutting the tissues, we focused on the area of the frontal cortex containing the Forceps Minor, at about the level of A 10300 #m according to Konig and Klippe114 since other studies focused at this level and we would be able to compare our results to those of earlier workers. In some animals, both pipamperone and pimozide were given to displace [3H]spiperone from dopamine receptors as well. RESULTS In tissues from animals that were not treated with pipamperone, the autoradiographic localization of [aH]spiperone showed a fairly wide distribution of binding sites in the frontal cortex. Notable was the enrichment of binding sites in the more superficial layers of the cortex. However, treatment with pipamperone caused a depletion of autoradiographic grain densities in these more superficial layers while only minimally affecting the grain density in the deepest layers (Fig. 1). These findings are in agreement with the notion that serotonergic fibers tend to appear in layers I and II in the cerebral cortex 21. Blocking these serotonergic sites with pipamperone thus increased the specificity for dopamine receptors. Accordingly, we focused our analysis on tissues from animals treated with pipamperone. When animals were given pimozide (5 mg/kg), a more selective dopamine receptor blocker 17, along with pipamperone, the levels of radioactivity in the frontal cortex were reduced even further than in those with pipamperone alone (data not shown). This is evidence that the [aH]spiperone remaining after pipamperone administration is associated with dopamine receptors. However, one cannot completely rule out that the [aH]spiperone displaced by pimozide is also binding, in part, to a nondopaminergic receptor. At the levels of Forceps Minor, there were high densities of dopamine receptor in the deeper layers of the cingulate cortex, in the area above the rhinal suleus and in the area immediately dorsal to the nucleus accumbens (Figs. 2 and 3). These cingulate,
Fig. 2. Autoradiographic localization of SP in cortex from PP-treated rats. A : outer edge of rhinal sulcus area. B: rhinal sulcus area. C: region just above nucleus accumbens. D: the anterior commissure. See right side of Fig. 3 for location of micrographs. The high densities of autoradiographic grains marking dopamine receptors in B and C are contrasted with the low density in A and D. See text for discussion. Bar -- 20/tm.
283
B HIGH
~LOW
Fig. 3. Schematic diagram showing distribution of dopamine receptors in the frontal cortex. The data is taken from animals administered SP and PP. Abbreviations: FMI, forceps minor; a, nucleus accumbens; CAA, anterior commissure (pars anterior) ; TOL, lateral olfactory tract. The level shown is A 10300 from Konig and KlippeP4. Highest densities of dopamine receptors (left side) were observed in cingulate, suprarhinal and supra-accumbal areas. The high densities of receptors in nucleus accumbens which were previously reported 12are not shown. See text for further discussion. The rectangles on the right side show the location of the micrographs presented in Figs. 1 and 2. The correspondence is as follows: 1, Fig. 1A and B; 2, Fig. 1C and D; 3, Fig. 2A; 4, Fig. 2B; 5, Fig. 2C; 6, Fig. 2D. suprarhinal and supra-accumbal localizations were accompanied by other areas showing somewhat lower densities. These somewhat lower density areas were found in the dorsal cortex but also in the deep layers, in the area between the supra-accumbal and suprarhinal groups and also in an area immediately beneath the Forceps Minor (Figs. 2 and 3). Notable was the lack of high densities of receptors in the dorsal cortex above the forceps, and the background level of autoradiographic grains over white matter areas such as the anterior commissure. We also had tissues from more anterior areas. At the level of about A11050 # m according to Konig and KlippeP 4 there were still elevated densities in the suprarhinal, cingulate, in the supra-accumbal regions. Thus, these fields of dopamine receptors appear to extend for at least some distance in the rostrocaudal direction in the frontal cortical area. DISCUSSION The distribution of dopamine receptors found in this study is in agreement with the reported distribution of dopamine-containing fibers and terminals by histochemistry 1,2,11,1s-21. We did not find receptors in layers I, II and III where Lindvall et al. zl and Lewis et al. TM describe dopaminergic fibers. However, these fibers in the superficial layers are found in more caudal areas, near the genu of the corpus callosum. A possible discrepancy appears to be the lack of receptors dorsal to the Forceps Minor, an area enriched in dopamine-containing fibers 21. However, the fiber density there is low and the numbers of synapses by the dopamine fibers in these areas may be quite low and just below the limit of our detection by our autoradiographic approach. Moreover, biochemical studies showed relatively low dopamine content 3,
284 dopamine-sensitive adenylate cyclase3, 3° and [3H]dopamine uptake 27 in this region as well. These same biochemical parameters were high in the areas showing high levels o f dopamine receptors in this study3, zT. Further, the iontophoretic study of Bunney and Aghajanian 4 are also in agreement with our results in that dopamine sensitive cells in cingulate cortex are found mainly in layers V and VI and that the cells in layers II and I I I show little sensitivity to dopamine. Thus, there is an excellent general agreement between our results and those in other studies. The main interest in cortical dopaminergic systems stems from the apparent involvement o f these systems in mental disorders such as schizophrenia11, ~5. The data presented in this study indicates the feasibility o f using a histochemical approach to study dopamine receptors, and extends our knowledge of dopamine terminal fields in the frontal cortex. ACKNOWLEDGEMENT The authors acknowledge the technical assistance o f Mrs. N a o m i Taylor and Ms. D e b r a Niehoff, the clerical assistance of Princie Campbell and Carol Kenyon, the helpful suggestions o f Dr. M a r k Molliver in the preparation o f the manuscript, the gift of pipamperone and pimozide f r o m Janssen Pharmaceutics and the support of U S P H S G r a n t M H 25951 and the M c K n i g h t Foundation. M.J.K. is the recipient of R S D A A w a r d M H 00053. REFERENCES 1 Berger, B., Tassin, J. P., Blanc, G. Moyne, M. A. and Thierry, A. M., Histochemical confirmation for dopaminergic innervation of the rat cerebral cortex after destruction of ascending noradrenergic pathways, Brain Research, 81 (1974) 332-337. 2 Berger, B. Thierry, A. M., Tassin, J. P. and Moyne, M. A., Dopaminergic innervation of the rat prefrontal cortex: a fluorescence histochemical study, Brain Research, 186 (1976) 133-145. 3 Bockaert, J., Premont, J., Glowinski, J., Tassin, J. P. and Thierry, A. M., Topographical distribution and characteristics of dopamine and fl-adrenergic sensitive adenylate cyclases in the rat frontal cerebral cortex, striatum and substantia nigra. In E. Costa and G. L. Gessa (Eds.), Advan. Biochem - - PsychopharmacoL, Vol. 16, Raven Press, New York, 1977, pp. 29-37. 4 Bunney, B. S. and Aghajanian, G. K., Dopamine and norepinephrine innervated cells in rat prefrontal cortex: pharmacological differentiation using microiontophoretic techniques, Life Sci., 19 (1976) 1783-1792. 5 Creese, I., Burt, D. R. and Snyder, S. H., Dopamine receptor binding differentiation of agonist and antagonist states with 3H-dopamine and 8H-haloperidol, Life Sci., 17 (1975) 993-1002. 6 Creese, I. and Snyder, S. H., 3H-Spiroperidol labels serotonin receptors in rat cerebral cortex and hippocampus, Europ. J. Pharmacol., 49 (1978) 201-202. 7 Creese, I., Schneider, R. and Snyder, S. H., aH-Spiroperidol labels dopamine receptors in Pituitary and Brain, Europ. J. Pharmacol., 46 (1977) 377-381. 8 Fields, J. Z., Reisine, T. D. and Yamamura, H. I., Biochemical demonstration of dopaminergic receptors in rat and human brain using [aH]spiroperidol, Brain Research, 136 (1977) 578-584. 9 Hollt, V., Czlonkowski, A. and Henry, A., The demonstration in vivo of specific binding sites for neuroleptic drugs in mouse brain, Brain Research, 130 (1977) 176-183. 10 Hollt, V. and Schubert, P., Demonstration of neuroleptic receptor sites in mouse brain by autoradiography, Brain Research, 151 (1978) 149-153. 11 Hokfelt, T., Ljungdahl, A., Fuxe, K. and Johansson, O., Dopamine nerve terminal in rat limbic cortex: aspects of the dopamine hypothesis of schizophrenia, Science, 184 (1974) 177-179. 12 Klemm, N., Murrin, L. C. and Kuhar, M. J., Neuroleptic and dopamine receptors: autoradiographic localization of [3H]spiperone in rat brain, Brain Research, 169 (1979) 1-9.
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