- Email: [email protected]
D3 Receptor Relationships in Brain Coexpression, Coactivation, and Coregulation
408
J-C. Schwaru et of.
3. Vernier, P., Cardinaud, B., and Vincent, J. D. (1995).Evolution of the catecholaime receptor family. TIPS. 16,375-381. 4. Cardinaud, B., Sugamori, K. S., Coudouel, S., Vincent, J. D., Niznik, N. B., and Vernier, P. (1996).Early emergence of three dopamine D1 receptor subtypes in vertebrates: Molecular phylogenetic, pharmacological and functional criteria defining Dla, D l b and D l c receptors in european eel anguilla anguilla. f. Biol. Chem. 272, 2778-2787.
J-C.Schwartz," S. Ridray,t R. Bordet,t J. Diaz,t and P. Sokoloff* *Unite de Neurobiologie et Pharmacologie (U. 109) lnserrn Centre Paul Broca 75014 Paris, France tlaboratoire de Physiologie Faculte de Pharmacie Paris, France
D I /D3 Receptor Relationships in Brain Coexpression, Coactivation, and Coregulation The identification of the dopamine (DA) D3 receptor (D3R), a D2-like receptor (l),has represented a challenge: to which extent its functions can be differentiated from those of the much more abundant D2R? The strategy we have followed to meet this challenge has consisted of (1) identification or designing selective D3R ligands, testing them on transfected cell lines; ( 2 )characterizing the phenotype of D3R-expressing neurons in brain; and (3) assessing the responses mediated by the D3R and the regulation of its expression in brain. Using these approaches, we show that, in contrast to D2R, highly segregated from DlR, D3R is coexpressed with DlR, with which interactions are shown at the level of neurochemical responses and regulation of gene expression.
1. Coexpression of D I R and and Functional Interactions
D3R
in Ventral Striatum
We had previously identified medium-size spiny neurotensin neurons in the shell part of nucleus accumbens as D3R-expressing neurons and suggested Advances In Pharmacology, Volume 42 Copyright 0 1998 by Academic Press. All rights of reproduction in any form reserved. 1054-3589/98 $25.00
D I/D3 Receptor Relationships in Brain
409
that they respond in an opposite manner when compared with neurotensin neurons harboring D2R (2). This proposal was based on data obtained with a variety of neuroleptics with mixed D2WD3R antagonist properties, which, on acute administration, all diminish neurotensin mRNA levels in D3R-expressing neurotensin neurons (in ventromedial shell), whereas they induce opposite effects on D2R-expressing neurotensin neurons (in cone). We have now confirmed that the former effect is, as assumed, selectively related to D3R blockade, because it is reproduced by administration of nafadotride in a D3R-selective dosage. In addition, the haloperidol-induced decrease in neurotensin mRNA in ventromedial shell is prevented on coadministration of DO-897, a novel highly selective and partial D3R agonist. D3R and D1R are highly expressed in the islands of Calleja, a structure of poorly defined physiological role, receiving a sparse dopaminergic innervation from the mesencephalon (A9 or A10 neuronal groups?) and from which D2R is absent. Double hybridization studies showed D1R and D3R mRNAs to be coexpressed in a high percentage (-80%) of substance P granule cells, the major neuronal population of the islands. The opposite roles of the two receptor subtypes are shown by studies in which the effects of agonist or antagonist administration were evaluated on the expression of c-fos. Whereas SKF 38393, a D1R agonist, enhances it markedly, quinpirole, a D2R/D3R agonist, has an opposite effect; in addition, endogenous dopamine must have a tonic effect on this system, because c-fos expression is decreased and increased on treatment by SCH 23390 and nafadotride, respectively (Table I). In the ventromedial shell of nucleus accumbens, a large proportion of D3Rharboring neurons were found to coexpress D l R (63%)and substance P (71%) mRNAs. The two receptor subtypes seem to be involved in a synergistic manner in the control of the neuropeptide gene expression. In rats pretreated with reserpine (to avoid interference of changes in DA release), treatment with SKF 38390 slightly enhanced substance P mRNA levels, a change that was markedly TABLE I Interactive Responses Mediated by DI and D3 Receptors in Islands of Calleja and Ventromedial Shell of Nucleus Accumbens Treatment
Change in mRNAs (%
controls)
of ~
c-fos rnRNAs in island of Calleja +271 t- 62"" -75 2 8" -19 2 30 (NS) -75 t- 5" +222 i 76* Substance P rnRNAs in accurnbens shell +34 g:*x-
SKF 38393 (10 rng/kg) Quinpirole (1 mgkg) SKF 38393 + quinpirole SCH 23390 (0.5 rng/kg) Nafadotride (1 mglkg)
SKF 38393 (10 rng/kg) Quinpirole (lrng/kg) SKF 38393 + quinpirole SKF 38393 + quinpirole
+ nafadotride
NS, not significant. "P < 0.05; ’*I’
( 1 mg/kg)
< 0.01
-9 i 6 (NS) +190 i 53*" +63 t- 22"
4 10
J-C. Schwartz et a/.
potentiated by cotreatment with quinpirole (see Table I). It can be concluded, therefore, that although D1R and D3R are largely coexpressed, their costimulation may result in either opposite or synergistic responses according to the neuronal type and kind of response considered.
II. D I R-Mediated Ectopic Induction of D3R in Denervated Striatum The expression of the D3R in neurons of the ventral striatum is highly dependent on the dopaminergic innervation. Thus, after 6-OHDA-induced denervation, D3R mRNA levels and [3H]7-OH-DPAT binding site number are drastically reduced (by over 50%) in nucleus accumbens (3). Considering the upregulation of D2R under such circumstance, the change seems paradoxical. The depletion is not consequent to DA (or DA cotransmitter) deprivation because it is not reproduced by chronic administration of D1R and D2R antagonists, reserpine, or cholecystokinin and neurotensin antagonists. In contrast, a D3R downregulation follows administration of GABA agonists or colchicine, suggesting that accumbic D3R expression is under the positive control of a trophic factor released by DA neurons in an activity-dependent manner. By treating hemiparkinsonian rats with L-dopa under conditions leading to a sensitization of their turning behavior, we observed that D3R mRNA levels in ipsilateral nucleus accumbens progressively became enhanced over the control level. This change was accompanied unexpectedly by the appearance of the D3R signal as well as, after a few days, of D3R-binding sites in the ipsilateral dorsal striatum, an area where this receptor is normally not expressed (Fig. 1).
FIGURE I In situ hybridization of D3R rnRNAs in frontal brain sections of rats unilaterally lesionned by 6-OHDA (left) and treated for 5 days with vehicle L-dopa (60 m a g , i.p. b.i.d.) alone or together with SCH 23390 (0.5 rng/kg) or with SKF 38393 (10 mg/kg, i.p., b.i.d.). StPv, periventricular striatum; CdPu, caudate putarnen; AcSh, nucleus accumbens core; AcCo, nucleus accurnbens core; ICj, islands of Calleja.
D I/D3 Receptor Relationships in Brain
4II
The ectopic induction by L-dopa is apparently consequent to D1R stimulation, being prevented by coadministration of SCH 23390 and mimicked by administration of SKF 38393. D3R induction in the denervated striatum seems to be responsible for the sensitization to L-dopa observed in the same animals. In support, the two processes develop during and decay on interruption of L-dopa with strictly parallel time courses. In addition, the L-dopa-induced turning behavior of rats previously sensitized by repeated L-dopa is inhibited on administration of nafadotride in low dosage, compatible with a selective D3R blockade. Because nafadotride has no such effect on turning behavior in nonsensitized hemiparkinsonian rats, this strongly suggests that ectopic D3R appearance and behavioral sensitization, a so far poorly understood process, are causally related. The process might have therapeutic relevance because sensitization of the motor behavior in rats might reflect either beneficial or detrimental effects of chronic dopatherapy in parkinsonian subjects (i.e., the progressive resumption of complex motor behaviors or development of dyskinesias or psychiatric disturbances). References 1. Sokoloff, P., and Schwartz, J. C. (1995). Novel dopamine receptors half a decade later. Trends Pharmacol. Sci. 16, 270-275. 2. Diaz, J., Levesque, D., Lammers, C. H., Griffon, N., Martres, M. P., Schwartz, J. C., and Sokoloff, P. (1995).Phenotypical characterization of neurons expressing the dopamine D3 receptor in the rat brain. Neuroscience 6 5 , 731-745. 3. Leveque, D., Martres, M. P., Diaz, J., Griffon, N., Lammers, C. H., Sokoloff, P., and Schwartz, J. C. (1995). A paradoxical regulation of dopamine D3 receptor expression suggests the involvement of a n anterograde factor from dopamine neurons. Proc. Natl. Acad. Sci. U.S.A. 92, 1719-1723.
J-C. Schwaru et of.
3. Vernier, P., Cardinaud, B., and Vincent, J. D. (1995).Evolution of the catecholaime receptor family. TIPS. 16,375-381. 4. Cardinaud, B., Sugamori, K. S., Coudouel, S., Vincent, J. D., Niznik, N. B., and Vernier, P. (1996).Early emergence of three dopamine D1 receptor subtypes in vertebrates: Molecular phylogenetic, pharmacological and functional criteria defining Dla, D l b and D l c receptors in european eel anguilla anguilla. f. Biol. Chem. 272, 2778-2787.
J-C.Schwartz," S. Ridray,t R. Bordet,t J. Diaz,t and P. Sokoloff* *Unite de Neurobiologie et Pharmacologie (U. 109) lnserrn Centre Paul Broca 75014 Paris, France tlaboratoire de Physiologie Faculte de Pharmacie Paris, France
D I /D3 Receptor Relationships in Brain Coexpression, Coactivation, and Coregulation The identification of the dopamine (DA) D3 receptor (D3R), a D2-like receptor (l),has represented a challenge: to which extent its functions can be differentiated from those of the much more abundant D2R? The strategy we have followed to meet this challenge has consisted of (1) identification or designing selective D3R ligands, testing them on transfected cell lines; ( 2 )characterizing the phenotype of D3R-expressing neurons in brain; and (3) assessing the responses mediated by the D3R and the regulation of its expression in brain. Using these approaches, we show that, in contrast to D2R, highly segregated from DlR, D3R is coexpressed with DlR, with which interactions are shown at the level of neurochemical responses and regulation of gene expression.
1. Coexpression of D I R and and Functional Interactions
D3R
in Ventral Striatum
We had previously identified medium-size spiny neurotensin neurons in the shell part of nucleus accumbens as D3R-expressing neurons and suggested Advances In Pharmacology, Volume 42 Copyright 0 1998 by Academic Press. All rights of reproduction in any form reserved. 1054-3589/98 $25.00
D I/D3 Receptor Relationships in Brain
409
that they respond in an opposite manner when compared with neurotensin neurons harboring D2R (2). This proposal was based on data obtained with a variety of neuroleptics with mixed D2WD3R antagonist properties, which, on acute administration, all diminish neurotensin mRNA levels in D3R-expressing neurotensin neurons (in ventromedial shell), whereas they induce opposite effects on D2R-expressing neurotensin neurons (in cone). We have now confirmed that the former effect is, as assumed, selectively related to D3R blockade, because it is reproduced by administration of nafadotride in a D3R-selective dosage. In addition, the haloperidol-induced decrease in neurotensin mRNA in ventromedial shell is prevented on coadministration of DO-897, a novel highly selective and partial D3R agonist. D3R and D1R are highly expressed in the islands of Calleja, a structure of poorly defined physiological role, receiving a sparse dopaminergic innervation from the mesencephalon (A9 or A10 neuronal groups?) and from which D2R is absent. Double hybridization studies showed D1R and D3R mRNAs to be coexpressed in a high percentage (-80%) of substance P granule cells, the major neuronal population of the islands. The opposite roles of the two receptor subtypes are shown by studies in which the effects of agonist or antagonist administration were evaluated on the expression of c-fos. Whereas SKF 38393, a D1R agonist, enhances it markedly, quinpirole, a D2R/D3R agonist, has an opposite effect; in addition, endogenous dopamine must have a tonic effect on this system, because c-fos expression is decreased and increased on treatment by SCH 23390 and nafadotride, respectively (Table I). In the ventromedial shell of nucleus accumbens, a large proportion of D3Rharboring neurons were found to coexpress D l R (63%)and substance P (71%) mRNAs. The two receptor subtypes seem to be involved in a synergistic manner in the control of the neuropeptide gene expression. In rats pretreated with reserpine (to avoid interference of changes in DA release), treatment with SKF 38390 slightly enhanced substance P mRNA levels, a change that was markedly TABLE I Interactive Responses Mediated by DI and D3 Receptors in Islands of Calleja and Ventromedial Shell of Nucleus Accumbens Treatment
Change in mRNAs (%
controls)
of ~
c-fos rnRNAs in island of Calleja +271 t- 62"" -75 2 8" -19 2 30 (NS) -75 t- 5" +222 i 76* Substance P rnRNAs in accurnbens shell +34 g:*x-
SKF 38393 (10 rng/kg) Quinpirole (1 mgkg) SKF 38393 + quinpirole SCH 23390 (0.5 rng/kg) Nafadotride (1 mglkg)
SKF 38393 (10 rng/kg) Quinpirole (lrng/kg) SKF 38393 + quinpirole SKF 38393 + quinpirole
+ nafadotride
NS, not significant. "P < 0.05; ’*I’
( 1 mg/kg)
< 0.01
-9 i 6 (NS) +190 i 53*" +63 t- 22"
4 10
J-C. Schwartz et a/.
potentiated by cotreatment with quinpirole (see Table I). It can be concluded, therefore, that although D1R and D3R are largely coexpressed, their costimulation may result in either opposite or synergistic responses according to the neuronal type and kind of response considered.
II. D I R-Mediated Ectopic Induction of D3R in Denervated Striatum The expression of the D3R in neurons of the ventral striatum is highly dependent on the dopaminergic innervation. Thus, after 6-OHDA-induced denervation, D3R mRNA levels and [3H]7-OH-DPAT binding site number are drastically reduced (by over 50%) in nucleus accumbens (3). Considering the upregulation of D2R under such circumstance, the change seems paradoxical. The depletion is not consequent to DA (or DA cotransmitter) deprivation because it is not reproduced by chronic administration of D1R and D2R antagonists, reserpine, or cholecystokinin and neurotensin antagonists. In contrast, a D3R downregulation follows administration of GABA agonists or colchicine, suggesting that accumbic D3R expression is under the positive control of a trophic factor released by DA neurons in an activity-dependent manner. By treating hemiparkinsonian rats with L-dopa under conditions leading to a sensitization of their turning behavior, we observed that D3R mRNA levels in ipsilateral nucleus accumbens progressively became enhanced over the control level. This change was accompanied unexpectedly by the appearance of the D3R signal as well as, after a few days, of D3R-binding sites in the ipsilateral dorsal striatum, an area where this receptor is normally not expressed (Fig. 1).
FIGURE I In situ hybridization of D3R rnRNAs in frontal brain sections of rats unilaterally lesionned by 6-OHDA (left) and treated for 5 days with vehicle L-dopa (60 m a g , i.p. b.i.d.) alone or together with SCH 23390 (0.5 rng/kg) or with SKF 38393 (10 mg/kg, i.p., b.i.d.). StPv, periventricular striatum; CdPu, caudate putarnen; AcSh, nucleus accumbens core; AcCo, nucleus accurnbens core; ICj, islands of Calleja.
D I/D3 Receptor Relationships in Brain
4II
The ectopic induction by L-dopa is apparently consequent to D1R stimulation, being prevented by coadministration of SCH 23390 and mimicked by administration of SKF 38393. D3R induction in the denervated striatum seems to be responsible for the sensitization to L-dopa observed in the same animals. In support, the two processes develop during and decay on interruption of L-dopa with strictly parallel time courses. In addition, the L-dopa-induced turning behavior of rats previously sensitized by repeated L-dopa is inhibited on administration of nafadotride in low dosage, compatible with a selective D3R blockade. Because nafadotride has no such effect on turning behavior in nonsensitized hemiparkinsonian rats, this strongly suggests that ectopic D3R appearance and behavioral sensitization, a so far poorly understood process, are causally related. The process might have therapeutic relevance because sensitization of the motor behavior in rats might reflect either beneficial or detrimental effects of chronic dopatherapy in parkinsonian subjects (i.e., the progressive resumption of complex motor behaviors or development of dyskinesias or psychiatric disturbances). References 1. Sokoloff, P., and Schwartz, J. C. (1995). Novel dopamine receptors half a decade later. Trends Pharmacol. Sci. 16, 270-275. 2. Diaz, J., Levesque, D., Lammers, C. H., Griffon, N., Martres, M. P., Schwartz, J. C., and Sokoloff, P. (1995).Phenotypical characterization of neurons expressing the dopamine D3 receptor in the rat brain. Neuroscience 6 5 , 731-745. 3. Leveque, D., Martres, M. P., Diaz, J., Griffon, N., Lammers, C. H., Sokoloff, P., and Schwartz, J. C. (1995). A paradoxical regulation of dopamine D3 receptor expression suggests the involvement of a n anterograde factor from dopamine neurons. Proc. Natl. Acad. Sci. U.S.A. 92, 1719-1723.