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Dopamine receptors in the denervated striatum: further supersensitivity by chronic haloperidol treatment
Brain Research, 275 (1983) 183--185
183
Elsevier
Dopamine receptors in the denervated striatum: further supersensitivity by chronic haloperidol treatment A. RECHES 1, R. H, WAGNER, V. JACKSON, E. YABLONSKAYA-ALTER and S. FAHN 1Department of Neurology, Hadassah Medical Center, Jerusalem (Israel) and Department of Neurology, College of Physicians and Surgeons, Columbia University, New York, NY 10032 (U.S.A.)
(Accepted May 10th, 1983) Key words: dopamine receptor - - striatum - - denervation - - neuroleptics
Striatal dopamine (DA) receptors up-regulate following denervation or chronic neuroleptic exposure (for review see ref. 21). Receptor increases after denervation or receptor blockade have been assumed to reflect the same underlying process5. For example, levodopa has been reported to reverse neurolepticinduced increases in striatal D A receptors in ratsT,9 and based on these data it has been asserted that levodopa affects denervated D A receptors in Parkinsonian brains in the same manner*. However, the recent demonstration that up-regulation of D A receptors in rat nucleus accumbens after denervation or receptor blockade is additive 23 suggests that this assumption may be unwarranted. We have studied the effects of chronic haloperidol exposure and denervation on striatal D A receptors. We found that effects of denervation and receptor blockade on the striatal membrane binding of the putative D2 dopamine radioligand, [3H]spiperone, were additive. As in the nucleus accumbens, D A receptor up-regulation after receptor blockade or denervation may occur through separate mechanisms.
Male Sprague-Dawley rats (170-200 g) were given free access to food and water. Unilateral destruction of the nigrostriatal pathway was performed by stereotaxic injection of 6-hydroxydopamine hydrobromide 17. At the end of the treatment schedule (Table I) rats were sacrificed and the corpora striata ipsi-and contralateral to the lesion were dissected and immediately frozen on dry-ice. Tissue was kept a t - - 7 0 °C until assayed. [3H]spiperone binding was done as previously described 18 with the following modification: tissue was homogenized in approximately 1:800 w/v ice-cold Tris-HCl buffer (50 mM, pH 7.5) containing NaCI, 120 mM; KCI, 5 mM; CaC12, 2 mM; and MgCI2, 1 mM. Specific binding was defined as the difference in total binding in the presence and absence of 1/zM (+)-butaclamol (Research Biochemicals, Wayland, MA). Protein concentrations 10 were approximately 90-120 ng/m122. An aliquot of the tissue homogenate was taken for D A determination by high-pressure liquid chromatography with electrochemical detection 16. In agreement with previous studies3,8,11-13,15,24,25,
TABLE I Drug treatment schedule
Following phase 2 the animals were screened for apomorphine (1 mg.kg-l, s.c.) induced circling behavior26. Cumulative rotations 20 min post-injection were used to rank the lesioned rats into two equally responsive groups. Rotations in lesioned rats (114 + 21) were not statisticallydifferent from rotations in lesioned rats receiving haloperidol (133 + 31). Haloperidol (2 mg.kg-l, s.c.) was given in the form of Haldol-injectable solution (McNeil, Ft. Washington, PA). Rats were sacrificed at the end of phase 4. Treatment group
n
Phase I
Phase 2 (14 days)
Phase 3 (21 days)
Phase 4 (5 days)
Lesioned Lesioned plus haloperidol
8 8
Lesioning Lesioning
No drugs No drugs
Saline Haioperidol
No drugs No drugs
0006-8993/83/$03.00 © 1983 Elsevier Science Publishers B.V.
184 TABLE II Dopamine concentration and [3H]spiperone membrane binding in rat striatum
Following phase 4 (Table I) rats were sacrificed and DA concentrations in intact and lesioned striata were determined. Results are expressed as mean + S.E.M. For [3H]spiperone binding studies, striatal membranes from each rat were assayed in triplicate at a single ligand concentration (0.2 nM). One-way analysis of variance showed significant treatments effect on [3H]spiperone binding (F = 16.16, P < 0.001). Post-hoc Duncan's multiple-range test showed that both the lesion and haloperidol treatment induced significant (P < 0.05) increases in [3H]spiperone binding compared with the control values. Binding in rats receiving combined treatments was significantly increased over levels obtained in rats receiving only one treatment (P < 0.05). Treatment group
Lesioned Lesioned plus haloperidol
Doparnine ng/mg tissue
[3H]spiperone, fmol/mg protein
lpsilateral
Contralateral
Ipsilateral
Contralateral
(}.29 + 0.07 0.19 ___0.06
5.2 + 0.50 6.2 _+0.73
447.6 _+8.4 521 _+ 11.3
349.7 + 12.9 446.8 + 22.4
unilateral destruction of the nigrostriatal pathway with 6-hydroxydopamine resulted in over 90% depletion in striatal D A levels on the lesioned side (Table II). Lesioning also induced circling behavior following apomorphine injection (legend to Table II). As previously reported, binding of [3H]spiperone was significantly increased in the 6-hydroxydopamine-lesioned striatum 3.12.24.25 or by chronic neuroleptic treatment I (Table II). [3H]spiperone binding in denervated striatum from haloperidol-treated rats was significantly higher than levels obtained in rats which were exposed to one treatment only (Table II). Scatchard analysis showed a single population of binding sites. Binding changes reflected increases in the maximal density of [3H]spiperone binding sites (Bmax) with no change in ligand affinity (Kd) (Fig. 1). Our results show that the effects of denervation and receptor blockade on D A receptors in the striaturn are additive. D A depletion after 6-hydroxydopamine injection was extensive, indicating that denervation was nearly complete. Maximal increases in D A receptor density following chronic haloperidol treatment occur in doses considerably lower than used in the current study 1. On this basis it appears unlikely that subsequent increases in the density of binding sites for [3H]spiperone would have been obtained following administration of larger amounts of 6-hydroxydopamine or higher doses of neuroleptic. Since Scatchard analysis indicates a single population of binding sites (Fig. 1) these results suggest that upregulation of striatal and nucleus accumbens 23 D A receptors following denervation or receptor blockade occur through different mechanisms. Other lines of evidence support this proposal.
Chronic ievodopa treatment decreases neurolepticinduced increases in striatal receptor densityT, 9.1s and stereotypy scores 2,6.20.27 but does not affect circling behavior in mice with unilateral 6-hydroxydopamine lesions of the substantia nigra 14. Denervation and receptor blockade additively increase D A receptors in the striatum and nucleus accumbens. Linear Scatchard analysis suggests that a single population of binding sites is affected. This suggests that up-regulation following 6-hydroxydopamine or haloperidol involve different regulatory processes. It is also possible that agonist-induced down-regulation of supersensitive receptors may require intact presynaptic D A nerve terminals.
9!
BIF63~~-~~~A '
4oo
(H')- Sp~peroneBound (fmoles/mg) Fig. 1. Representative Scatchard analysis. Membranes from individual rats were pooled and binding was assessed at various concentrations of [3H]spiperone (0.02-0.4 nM). Data were plotted according to Scatchard ]9. Bmax (fmol bound/mg protein) and K d (nM) were determined by linear regression analysis. ©, Control (Braax = 363.5; K d = 0.07) Z~, HAL (bmax = 454; Ka = 0.09), O, 6-OHDA ( B m a x = 446.8; K d = 0.07) A, HAL + 6-OHDA (Bma× = 584.2; Kd = 0.07).
185 Supported, in part, by grants from the Dystonia
ton Merritt Fellowship from the Parkinson's Disease
Medical Research F o u n d a t i o n and by a grant from
Foundation. We thank Dr. Yaakov Stern for statist-
Norman Sieden. A.R. is the recipient of the H. Hous-
ical analysis of the data.
1 Burt, D. R., Creese, I. and Snyder, S. H., Antischizophrenic drugs: Chronic treatment elevates dopamine receptor binding in brain, Science, 196 (I 977) 326--328. 2 Christensen, A. V. and Moiler, N. I., Dopaminergic supersensitivity: influence of dopamine agonists, cholinergics, anticholinergics and drugs used for the treatment of Tardive Dyskinesia, Psychopharmacologia, 62 (1979) 111-116. 3 Creese, I., Burt, D. and Snyder, S. H., Dopamine receptor binding enhancement accompanies lesion-induced behavioral supersensitivity, Science, 197 (1977) 596--598. 4 Creese, I. and Sibley, D. R., Receptor adaptation to centrally acting drugs, Ann. Rev. Pharmacol. Toxicol., 21 (1981) 357-391. 5 Emmelin, N., Supersensitivity following 'Pharmacological denervation', Pharmacol. Rev., 13 (1961) 17-37. 6 Ezran-Waters, C. and Seeman, P., L-dopa reversal of hyperdopaminergic behavior, Life Sci., 22 (1978) 1027-1032. 7 Friedhoff, A. J., Bonnett, K., Rosengarten, H., Reversal of two manifestations of dopamine receptor supersensitivity by administration of L-dopa, Res. Commun. Chem. Pathol. Pharmacol., 16 (1977) 411-423. 8 Hefti, F., Melamed, E. and Wurtman, R. J., Partial lesions of the dopaminergic nigrostriatal system in rat brain: biochemical characterization, Brain Research, 19.5 (1980) 123-137. 9 List, S. J. and Seeman, P., Dopaminergic agonists reverse the elevated 3H-neuroleptic binding in neuroleptic pretreated rats, Life Sci., 24 (1979) 1447-1452. 10 Lowry, O. H., Rosebrough, N. J., Farr, A. L. and Randall, R. J., Protein measurement with the Folin phenol reagent, J. biol. Chem., 193 (1951)265-275. 11 Mishra, R. K., Marshall, A. M. and Varmuza, S. L., Supersensitivity in rat caudate nucleus: effects of 6-hydroxydopamine on the time course of dopamine receptor and cyclic AMP changes, Brain Research, 200 (1980) 47-57. 12 Mishra, R. K., Wong, Y., Varmuza, S. L. and Tuff, L., Chemical lesion and drug induced supersensitivity and subsensitivity of caudate dopamine receptors, Life Sci., 23 (1978) 443-446. 13 Pycock, C. J., Turning behavior in animals, Neuroscience, 5 (1980) 461-514. 14 Pycock, C. J. and Marsden, C. D., Central dopaminergic receptor supersensitivity and its relevance to Parkinson's disease, J. Neurol. Sci., 31 (1977) 113-121. 15 Pycock, C. J., Tarsy, D. and Marsden, C. D., Inhibitionof
circling behavior by neuroleptic drugs in mice with unilateral 6-hydroxydopamine lesions of the striatum, Psychopharmacologia, 45 (1975) 211-219. 16 Reches, A., Jiang, D. and Fahn, S., Catechol-O-methyltransferase inhibition by U-0521 increases striatal utilization of levodopa, Naunyn-Schmiedeberg's Arch. Pharmacol., 320 (1982) 34-37. 17 Reches, A., Mielke, L. R. and Fahn, S., 3-O-methyldopa inhibits rotations induced by levodopa in rats after unilateral destruction of the nigrostriatal pathway, Neurology, 32 (1982) 887-888. 18 Reches, A., Wagner, H. R., Jiang, D., Jackson, V. and Fahn, S., The effect of chronic u-dopa administration on supersensitive pre- and postsynaptic dopaminergic receptors in rat brain, Life Sci., 31 (1982) 37-44. 19 Scatchard, G., The attractions of proteins for small molecules and ions, Ann. Acad. Sci. NY, 51 (1949)660-672. 20 Seeger, T. F., Gardner, E. L. and Bridger, W. F., Increase in mesolimbic self-stimulation after chronic haloperidol: reversal by L-dopa or lithium, Brain Research, 215 (1981) 404-409. 21 Seeman, P., Brain dopamine receptors, Pharmacol. Rev., 32 (1980) 229-313. 22 Seeman, P., Ulpian, C. and Wells, J., Dopamine receptors parameters (detected by 3H-spiperone) depend on tissue concentration, Soc. Neurosci. Abstr., 8 (1982) 718. 23 Staunton, D. A., Magistretti, P. J., Koob, G. F., Shoemaker, W. J. and Bloom, F. E., Dopaminergic supersensitivity induced by denervation and chronic receptor blockade is additive, Nature (Lond.), 299 (1982) 72-74. 24 Staunton, D. A., Wolfe, B. B., Groves, P. M. and Molinoff, P. B., Dopamine receptor changes following destruction of the nigrostriatal pathways: lack of a relationship to rotational behavior, Brain Research, 211 (1981) 315-327. 25 Thai, L., Mishra, R. K., Gardner, E. L., Horowitz, S., Varmuza, S. and Makman, M. H., Dopamine antagonist binding increases in two behaviorally distinct striatal denervation syndromes, Brain Research, 170 (1979) 381-386. 26 Ungerstedt, U., Stereotaxic mapping of the monoamine pathways in the rat brain, Acta physiol, scand., Suppl., 367 (1971) 1-48. 27 Weiner, W. J., Carvey, P., Nausieda, P. A., Goetz, C. G. and Klawans, H. L., The effect of chronic levodopa on haloperidol-induced behavioral supersensitivity in the guinea pig, Life Sci., 28 (1981) 2173-2178.
183
Elsevier
Dopamine receptors in the denervated striatum: further supersensitivity by chronic haloperidol treatment A. RECHES 1, R. H, WAGNER, V. JACKSON, E. YABLONSKAYA-ALTER and S. FAHN 1Department of Neurology, Hadassah Medical Center, Jerusalem (Israel) and Department of Neurology, College of Physicians and Surgeons, Columbia University, New York, NY 10032 (U.S.A.)
(Accepted May 10th, 1983) Key words: dopamine receptor - - striatum - - denervation - - neuroleptics
Striatal dopamine (DA) receptors up-regulate following denervation or chronic neuroleptic exposure (for review see ref. 21). Receptor increases after denervation or receptor blockade have been assumed to reflect the same underlying process5. For example, levodopa has been reported to reverse neurolepticinduced increases in striatal D A receptors in ratsT,9 and based on these data it has been asserted that levodopa affects denervated D A receptors in Parkinsonian brains in the same manner*. However, the recent demonstration that up-regulation of D A receptors in rat nucleus accumbens after denervation or receptor blockade is additive 23 suggests that this assumption may be unwarranted. We have studied the effects of chronic haloperidol exposure and denervation on striatal D A receptors. We found that effects of denervation and receptor blockade on the striatal membrane binding of the putative D2 dopamine radioligand, [3H]spiperone, were additive. As in the nucleus accumbens, D A receptor up-regulation after receptor blockade or denervation may occur through separate mechanisms.
Male Sprague-Dawley rats (170-200 g) were given free access to food and water. Unilateral destruction of the nigrostriatal pathway was performed by stereotaxic injection of 6-hydroxydopamine hydrobromide 17. At the end of the treatment schedule (Table I) rats were sacrificed and the corpora striata ipsi-and contralateral to the lesion were dissected and immediately frozen on dry-ice. Tissue was kept a t - - 7 0 °C until assayed. [3H]spiperone binding was done as previously described 18 with the following modification: tissue was homogenized in approximately 1:800 w/v ice-cold Tris-HCl buffer (50 mM, pH 7.5) containing NaCI, 120 mM; KCI, 5 mM; CaC12, 2 mM; and MgCI2, 1 mM. Specific binding was defined as the difference in total binding in the presence and absence of 1/zM (+)-butaclamol (Research Biochemicals, Wayland, MA). Protein concentrations 10 were approximately 90-120 ng/m122. An aliquot of the tissue homogenate was taken for D A determination by high-pressure liquid chromatography with electrochemical detection 16. In agreement with previous studies3,8,11-13,15,24,25,
TABLE I Drug treatment schedule
Following phase 2 the animals were screened for apomorphine (1 mg.kg-l, s.c.) induced circling behavior26. Cumulative rotations 20 min post-injection were used to rank the lesioned rats into two equally responsive groups. Rotations in lesioned rats (114 + 21) were not statisticallydifferent from rotations in lesioned rats receiving haloperidol (133 + 31). Haloperidol (2 mg.kg-l, s.c.) was given in the form of Haldol-injectable solution (McNeil, Ft. Washington, PA). Rats were sacrificed at the end of phase 4. Treatment group
n
Phase I
Phase 2 (14 days)
Phase 3 (21 days)
Phase 4 (5 days)
Lesioned Lesioned plus haloperidol
8 8
Lesioning Lesioning
No drugs No drugs
Saline Haioperidol
No drugs No drugs
0006-8993/83/$03.00 © 1983 Elsevier Science Publishers B.V.
184 TABLE II Dopamine concentration and [3H]spiperone membrane binding in rat striatum
Following phase 4 (Table I) rats were sacrificed and DA concentrations in intact and lesioned striata were determined. Results are expressed as mean + S.E.M. For [3H]spiperone binding studies, striatal membranes from each rat were assayed in triplicate at a single ligand concentration (0.2 nM). One-way analysis of variance showed significant treatments effect on [3H]spiperone binding (F = 16.16, P < 0.001). Post-hoc Duncan's multiple-range test showed that both the lesion and haloperidol treatment induced significant (P < 0.05) increases in [3H]spiperone binding compared with the control values. Binding in rats receiving combined treatments was significantly increased over levels obtained in rats receiving only one treatment (P < 0.05). Treatment group
Lesioned Lesioned plus haloperidol
Doparnine ng/mg tissue
[3H]spiperone, fmol/mg protein
lpsilateral
Contralateral
Ipsilateral
Contralateral
(}.29 + 0.07 0.19 ___0.06
5.2 + 0.50 6.2 _+0.73
447.6 _+8.4 521 _+ 11.3
349.7 + 12.9 446.8 + 22.4
unilateral destruction of the nigrostriatal pathway with 6-hydroxydopamine resulted in over 90% depletion in striatal D A levels on the lesioned side (Table II). Lesioning also induced circling behavior following apomorphine injection (legend to Table II). As previously reported, binding of [3H]spiperone was significantly increased in the 6-hydroxydopamine-lesioned striatum 3.12.24.25 or by chronic neuroleptic treatment I (Table II). [3H]spiperone binding in denervated striatum from haloperidol-treated rats was significantly higher than levels obtained in rats which were exposed to one treatment only (Table II). Scatchard analysis showed a single population of binding sites. Binding changes reflected increases in the maximal density of [3H]spiperone binding sites (Bmax) with no change in ligand affinity (Kd) (Fig. 1). Our results show that the effects of denervation and receptor blockade on D A receptors in the striaturn are additive. D A depletion after 6-hydroxydopamine injection was extensive, indicating that denervation was nearly complete. Maximal increases in D A receptor density following chronic haloperidol treatment occur in doses considerably lower than used in the current study 1. On this basis it appears unlikely that subsequent increases in the density of binding sites for [3H]spiperone would have been obtained following administration of larger amounts of 6-hydroxydopamine or higher doses of neuroleptic. Since Scatchard analysis indicates a single population of binding sites (Fig. 1) these results suggest that upregulation of striatal and nucleus accumbens 23 D A receptors following denervation or receptor blockade occur through different mechanisms. Other lines of evidence support this proposal.
Chronic ievodopa treatment decreases neurolepticinduced increases in striatal receptor densityT, 9.1s and stereotypy scores 2,6.20.27 but does not affect circling behavior in mice with unilateral 6-hydroxydopamine lesions of the substantia nigra 14. Denervation and receptor blockade additively increase D A receptors in the striatum and nucleus accumbens. Linear Scatchard analysis suggests that a single population of binding sites is affected. This suggests that up-regulation following 6-hydroxydopamine or haloperidol involve different regulatory processes. It is also possible that agonist-induced down-regulation of supersensitive receptors may require intact presynaptic D A nerve terminals.
9!
BIF63~~-~~~A '
4oo
(H')- Sp~peroneBound (fmoles/mg) Fig. 1. Representative Scatchard analysis. Membranes from individual rats were pooled and binding was assessed at various concentrations of [3H]spiperone (0.02-0.4 nM). Data were plotted according to Scatchard ]9. Bmax (fmol bound/mg protein) and K d (nM) were determined by linear regression analysis. ©, Control (Braax = 363.5; K d = 0.07) Z~, HAL (bmax = 454; Ka = 0.09), O, 6-OHDA ( B m a x = 446.8; K d = 0.07) A, HAL + 6-OHDA (Bma× = 584.2; Kd = 0.07).
185 Supported, in part, by grants from the Dystonia
ton Merritt Fellowship from the Parkinson's Disease
Medical Research F o u n d a t i o n and by a grant from
Foundation. We thank Dr. Yaakov Stern for statist-
Norman Sieden. A.R. is the recipient of the H. Hous-
ical analysis of the data.
1 Burt, D. R., Creese, I. and Snyder, S. H., Antischizophrenic drugs: Chronic treatment elevates dopamine receptor binding in brain, Science, 196 (I 977) 326--328. 2 Christensen, A. V. and Moiler, N. I., Dopaminergic supersensitivity: influence of dopamine agonists, cholinergics, anticholinergics and drugs used for the treatment of Tardive Dyskinesia, Psychopharmacologia, 62 (1979) 111-116. 3 Creese, I., Burt, D. and Snyder, S. H., Dopamine receptor binding enhancement accompanies lesion-induced behavioral supersensitivity, Science, 197 (1977) 596--598. 4 Creese, I. and Sibley, D. R., Receptor adaptation to centrally acting drugs, Ann. Rev. Pharmacol. Toxicol., 21 (1981) 357-391. 5 Emmelin, N., Supersensitivity following 'Pharmacological denervation', Pharmacol. Rev., 13 (1961) 17-37. 6 Ezran-Waters, C. and Seeman, P., L-dopa reversal of hyperdopaminergic behavior, Life Sci., 22 (1978) 1027-1032. 7 Friedhoff, A. J., Bonnett, K., Rosengarten, H., Reversal of two manifestations of dopamine receptor supersensitivity by administration of L-dopa, Res. Commun. Chem. Pathol. Pharmacol., 16 (1977) 411-423. 8 Hefti, F., Melamed, E. and Wurtman, R. J., Partial lesions of the dopaminergic nigrostriatal system in rat brain: biochemical characterization, Brain Research, 19.5 (1980) 123-137. 9 List, S. J. and Seeman, P., Dopaminergic agonists reverse the elevated 3H-neuroleptic binding in neuroleptic pretreated rats, Life Sci., 24 (1979) 1447-1452. 10 Lowry, O. H., Rosebrough, N. J., Farr, A. L. and Randall, R. J., Protein measurement with the Folin phenol reagent, J. biol. Chem., 193 (1951)265-275. 11 Mishra, R. K., Marshall, A. M. and Varmuza, S. L., Supersensitivity in rat caudate nucleus: effects of 6-hydroxydopamine on the time course of dopamine receptor and cyclic AMP changes, Brain Research, 200 (1980) 47-57. 12 Mishra, R. K., Wong, Y., Varmuza, S. L. and Tuff, L., Chemical lesion and drug induced supersensitivity and subsensitivity of caudate dopamine receptors, Life Sci., 23 (1978) 443-446. 13 Pycock, C. J., Turning behavior in animals, Neuroscience, 5 (1980) 461-514. 14 Pycock, C. J. and Marsden, C. D., Central dopaminergic receptor supersensitivity and its relevance to Parkinson's disease, J. Neurol. Sci., 31 (1977) 113-121. 15 Pycock, C. J., Tarsy, D. and Marsden, C. D., Inhibitionof
circling behavior by neuroleptic drugs in mice with unilateral 6-hydroxydopamine lesions of the striatum, Psychopharmacologia, 45 (1975) 211-219. 16 Reches, A., Jiang, D. and Fahn, S., Catechol-O-methyltransferase inhibition by U-0521 increases striatal utilization of levodopa, Naunyn-Schmiedeberg's Arch. Pharmacol., 320 (1982) 34-37. 17 Reches, A., Mielke, L. R. and Fahn, S., 3-O-methyldopa inhibits rotations induced by levodopa in rats after unilateral destruction of the nigrostriatal pathway, Neurology, 32 (1982) 887-888. 18 Reches, A., Wagner, H. R., Jiang, D., Jackson, V. and Fahn, S., The effect of chronic u-dopa administration on supersensitive pre- and postsynaptic dopaminergic receptors in rat brain, Life Sci., 31 (1982) 37-44. 19 Scatchard, G., The attractions of proteins for small molecules and ions, Ann. Acad. Sci. NY, 51 (1949)660-672. 20 Seeger, T. F., Gardner, E. L. and Bridger, W. F., Increase in mesolimbic self-stimulation after chronic haloperidol: reversal by L-dopa or lithium, Brain Research, 215 (1981) 404-409. 21 Seeman, P., Brain dopamine receptors, Pharmacol. Rev., 32 (1980) 229-313. 22 Seeman, P., Ulpian, C. and Wells, J., Dopamine receptors parameters (detected by 3H-spiperone) depend on tissue concentration, Soc. Neurosci. Abstr., 8 (1982) 718. 23 Staunton, D. A., Magistretti, P. J., Koob, G. F., Shoemaker, W. J. and Bloom, F. E., Dopaminergic supersensitivity induced by denervation and chronic receptor blockade is additive, Nature (Lond.), 299 (1982) 72-74. 24 Staunton, D. A., Wolfe, B. B., Groves, P. M. and Molinoff, P. B., Dopamine receptor changes following destruction of the nigrostriatal pathways: lack of a relationship to rotational behavior, Brain Research, 211 (1981) 315-327. 25 Thai, L., Mishra, R. K., Gardner, E. L., Horowitz, S., Varmuza, S. and Makman, M. H., Dopamine antagonist binding increases in two behaviorally distinct striatal denervation syndromes, Brain Research, 170 (1979) 381-386. 26 Ungerstedt, U., Stereotaxic mapping of the monoamine pathways in the rat brain, Acta physiol, scand., Suppl., 367 (1971) 1-48. 27 Weiner, W. J., Carvey, P., Nausieda, P. A., Goetz, C. G. and Klawans, H. L., The effect of chronic levodopa on haloperidol-induced behavioral supersensitivity in the guinea pig, Life Sci., 28 (1981) 2173-2178.