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Modulation of CNS dopamine receptors by peptides
02784846183 $o.ao + so Copyci@ht0 1983 PertJ6”DXl Pnrss Ltd.
MOD~~ON
OF CNS OPT
-0RS
BY PEpTiDEs
RAM K. MISHRA NeuropharmacologyLaboratory, Departments of Psychiatry and Neurosciences McMaster University, Hamilton, Ontario, Canada
(Final form, June 1983)
Abstract MISHRA, RAM K.: Modulation of CNS dopamine receptors by peptides, Prog. NeuroPsychopharmacol.& Biol. Psychiat. 1983, 7 (4-6):437-442. L-prolyl-L-leucyl-glycinamide(PLG), when administered concurrentlywith neuroleptic drug, blocked the development of dopamine receptor supersensitivityboth at the behavioral and biochemical level. 2. Chronic administratronof haloperidol resulted in development of cholecystokinin (CCK) receptor supersensitivityin the mesolimbic regions of the brain. There was no change in equilibrfum dissociation constant (KD) for CCK binding. 3. The results are discussed in relation to modulation of dopamine receptor by peptides and possible models of fnteraction of peptides wPth dopamine receptors are proposed.
1.
Keywords: cholecystokinin,dopamine receptors, prolyl-leucyl-glycinamide,tardive dyskinesia Abbreviations: cholecystokinin (CC@, dopamine (DA), L-prolyl-L-leucyl-glycinamide(PLG)
Introduction The most dramatic advance in neurosciences in the past five years has been the recognition of the importance of peptides as neurotransmittersand neuromodulators,both within the central nervous system and in the peripheral nervaus system. In recent years the presence of many peptides and their receptors or bindi‘ngsites have been identified in the central nervous system. The summary is presented in Table 1.
Table 1 Peptides and Their Binding Sites and/or Receptors Pound in the Central Nervous System Peptides found in CNS
Receptors in CNS
Thyrotropin releasing hormone (TRH) Somatostatin Prolyl-Leucyl-Glycinamide Prolactin Rndorphins and enkephalins Cholecystokinin (CCK) Insulin Vasoactive intestinal peptide (VIP) Rombesin Substance P Neurotensin
Various brain regions Various brain regions Various brain regions Pituitary gland Various brain regions Various brnin regions Various brain regions Various brain regions Various brain regions Various brain regions Various brain regions
437
438
R.K. Plishra
Biochemical, hiatochemical and irmaunochemical data demonstrated the co-existence of peptides with the classical neurotransmitters,suggesting the role of peptides in modulation of synaptic transmission. In this paper, some of the studies carried out in our laboratory on the modulatory effect of prolyl-leucyl-glycinamideand cholecystokininon dopamine receptors in the striatum and mesolimic regions of the brain are described.
Methods The experimental animals used were male Sprague-Dawleyrats weighing between ZOO-250 gms. Drug treatment, estimation of locomotor activity and 3IFspiroperidolbinding assays were performed as previously described (Chiu et al 1981. Marshall h Mishra 1980).
Results Effect of PLG on Locomotor Activity: PLG (10 mg/kg) given for 21 days along with haloperidol caused a significant blockade (Table 2) of haloperidol induced locomotor activity. The locomotor activity was measured after all groups of animals were challenged with apomorphine.
Table 2 Effect of Apomorphine on Locomotor Activity of Rats Treated with PLG and Haloperidol Gouts/hour Mean + SE24 768 + 40 710 7 36 10117 97 798 3 54
Treatment Group saline PLG haloperidol PLG + haloperidol apomorphine PLG 10 mg/kg halperidol 3mg/kg
Effect of PLG on Haloperidol Induced Supersensitivityof Dopamine Receptors: The results obtained in this series of experiments are shown in Table 3.
Table 3 Blockade of Haloperidol (HAL)-inducedincrease in specific 3H-spiroperidolbinding by PLG Treatment Group N
B max fmoles/mg Prot.
Kd (fi)
0.22 2 0.07 215 + 21 saline 6 0.24 + 0.09 512 + 32* HAL 6 0.28 7 0.05 304 i 16 PLG 6 0.21:0.02 330 f 18 PLG and HAL 6 (*p>.Ol) The various groups of animals received various drugs for 21 days. The dose of haloperidol was 3 mg/kg/day and PLG was administered 10 mg/kg/day. The animals were sacrificed 5 days after the last injection and 3H-spiroperidolbinding was carried out on striata.
Modulation of DA receptors by peptides
439
As can be seen from Table 3, simultaneous administration of PLG at lOmg/kg or even at 1-2 mg/kg (data not shown) with haloperidol antagonized the elevation in specific 3R-spiroperidol binding produced by long-term administration of neuroleptic drugs. Supersensitivityof Dopamine and Chole!&stokinin:(C@) Receptors in MesolifnbicRegions The effect of long term treatment of neuroleptic drug on CCK binding was examined in the mesolimbic regions of the rat brain. CCK and dopamine have shown to co-exist in the neuron projecting to mesolimbic regions of the brain. The results shown in Fig. 1 indicates a significant increase in CCK binding sites upon chronic administration of halperidol.
800
1251-CCK Binding T
3H-Sph Binding
r--
lluu
400
400
200
200
100
100
0
Fig. 1. C: control; N: described in Table 3.
C
C
N
N
0
neuroleptic treated. The protocol for drug treatment was same as
The CCK binding to mesolimbic membrane preparation was carried out according to method of Praissman et al (1983). The nonspecific binding was estimated by incubating the membranes with 100 fold excess unlabelled CCK-8. The specific binding constituted about 60%.
Discussion Although PLG was originally reported to potentiate the effect of L-DOPA, the results of the present study demonstrate that PLG when administered in low doses along with the neuroleptic drugs, effectively antagonize the development of dopamine receptor supersensitivity both at behavioral and biochemical level. (Tables 2-3). The possible mode of action of PLG is proposed in Fig. 2.
440
R.K. Mishra
PLO-BINDING SITES I
DOPAMINERGIC NEURON CELL BODY PRESY NAPTIC TERMINAL
POST SYNAPTIC NEURON
Fig. 2. PLG can interact with D-l or D-2 receptors through its own specific binding sites at the postsynaptic neuron or PLG can interact with the dopamine autoreceptors at the presynaptic neuron causing release of dopamine and thus the dopamine can then down regulate the receptors, alternatively, PLG can interact at the cell body level causing increased synthesis of dopamine. The results presented in this study and presented elsewhere in detail (Mishra et al 1983), support the notion that PLG has a modulatory effect on dopamine receptors in the central nervous system and the PLG and its enzymatically stable analogues should be considered as potential prophylactic and therapeutic agents in the treatment of various neuropsychiatric disorders associated with the development of dopamine receptor supersensitivity. The long-term blockade of dopamine receptors with haloperidol caused an increase in the number of both dopamine and CCK receptors in the mesolimbic regions of the rat brain. The possible mechanism of the development of CCK receptors supersensitivityis the disinhibition of the CCK release and subsequent depletion of CCK in the tissue which results in the development of observed supersensitivity (Fig. 1). This hypothesis can be further tested by lesion studies of dopaminergic neurons projecting to the limbic regions. In any case, the increase in CCK as well as in dopamlne receptors following neuroleptic treatment for a long time, is of additional interest because the peptfdergic supersensitivitywas induced towards a peptide (CCK) that co-exist and released from the same neuron as the dopamine whose receptors were blocked. Thus, CCK may contribute to the therapeutic or side effects of antipsychotic drugs. A speculative mechanfsm of action of CCK is shown in Fig. 3.
Modulation of DA receptors by peptides
441
CCK
I
0
I)
RELEASE
DA DOPAMlNERGlC/CHOLECYSTOKlNlN NEURON
Fig. 3. The common localization of dopamine and CCK in mesolimbic regions suggest that two such co-transmitterscould modulate each other's release by interaction at the cell body level, or once release, modulate different effects on the same post-synaptic neuron. Such dual modulation might be highly advantageous in the case where neurotransmitterhas the purpose of creating both short and long-term post-synaptic changes. CAMS (cyclic mp)
Conclusion The results obtained with PLG on neuroleptic drug induced dopaminergic supersensitivity at both behavioral and biochemical level suggest that PLG and its stable analogues should be considered as potential therapeutic agents in the treatment of neurological disorders associated with abnormal dopaminergic neurotransmission. The results obtained with CCK receptor binding suggest that a similar situation may occur with other co-existing peptideneurotransmitterpairs. It is therefore important to investigate any alterations in affinity or maximum binding sites to co-existing neuromodulatore that may develop upon treatment with various types of central nervous system active drugs.
Acknowledgement This study was supported by the Ontario Mental Health Foundation and the Parkinson Foundation of Canada. Reference8 CHIU, S. PAULOSE, C.S. and MISRRA, R.K. (1981). Neuroleptic drug-induced dopamine receptor supersensitivity: Antagonism by L-prolyl-L-leucyl-glycinamide. Science, 214: 1261-1262. MARSHALL, A.M. and MISRRA, R.K., (1980). Dopamine - sensitive adenylate cycloee and dopaminelneurolepticreceptor binding: Effect of Neuroleptic drugs. Adv. Biochem.
442
R.K. Mishra
Psychopharmacol. 24: 153-157. MISHRA, R.K., CHIU, S., CHIU, P. and MISHRA, C.P. (1983). Pharmacology of L-prolyl-Lleucyl-glycinamide(PLG): A review. Methods and Findings in Exptl. & Clin. Pharmacol. 5, 203-233. PRAISSMAN, M., MARTINEZ, P.A., SALADINO, C.F., GEROWITZ, J.M., STEGGLES, A.W., and FINKELSTEIN, J.A. (1983) Characterizationof cholecystokininbinding sites in rat cerebral cortex using a 125 I-CCK-8 probe resistant to degradation. J. Neurochem. 40: 14061413.
Inquiries and reprint requests should be addressed to: Dr. Ram K. Mishra NeuropharmacologyLaboratory McMaster University Hamilton, Ontario
MOD~~ON
OF CNS OPT
-0RS
BY PEpTiDEs
RAM K. MISHRA NeuropharmacologyLaboratory, Departments of Psychiatry and Neurosciences McMaster University, Hamilton, Ontario, Canada
(Final form, June 1983)
Abstract MISHRA, RAM K.: Modulation of CNS dopamine receptors by peptides, Prog. NeuroPsychopharmacol.& Biol. Psychiat. 1983, 7 (4-6):437-442. L-prolyl-L-leucyl-glycinamide(PLG), when administered concurrentlywith neuroleptic drug, blocked the development of dopamine receptor supersensitivityboth at the behavioral and biochemical level. 2. Chronic administratronof haloperidol resulted in development of cholecystokinin (CCK) receptor supersensitivityin the mesolimbic regions of the brain. There was no change in equilibrfum dissociation constant (KD) for CCK binding. 3. The results are discussed in relation to modulation of dopamine receptor by peptides and possible models of fnteraction of peptides wPth dopamine receptors are proposed.
1.
Keywords: cholecystokinin,dopamine receptors, prolyl-leucyl-glycinamide,tardive dyskinesia Abbreviations: cholecystokinin (CC@, dopamine (DA), L-prolyl-L-leucyl-glycinamide(PLG)
Introduction The most dramatic advance in neurosciences in the past five years has been the recognition of the importance of peptides as neurotransmittersand neuromodulators,both within the central nervous system and in the peripheral nervaus system. In recent years the presence of many peptides and their receptors or bindi‘ngsites have been identified in the central nervous system. The summary is presented in Table 1.
Table 1 Peptides and Their Binding Sites and/or Receptors Pound in the Central Nervous System Peptides found in CNS
Receptors in CNS
Thyrotropin releasing hormone (TRH) Somatostatin Prolyl-Leucyl-Glycinamide Prolactin Rndorphins and enkephalins Cholecystokinin (CCK) Insulin Vasoactive intestinal peptide (VIP) Rombesin Substance P Neurotensin
Various brain regions Various brain regions Various brain regions Pituitary gland Various brain regions Various brnin regions Various brain regions Various brain regions Various brain regions Various brain regions Various brain regions
437
438
R.K. Plishra
Biochemical, hiatochemical and irmaunochemical data demonstrated the co-existence of peptides with the classical neurotransmitters,suggesting the role of peptides in modulation of synaptic transmission. In this paper, some of the studies carried out in our laboratory on the modulatory effect of prolyl-leucyl-glycinamideand cholecystokininon dopamine receptors in the striatum and mesolimic regions of the brain are described.
Methods The experimental animals used were male Sprague-Dawleyrats weighing between ZOO-250 gms. Drug treatment, estimation of locomotor activity and 3IFspiroperidolbinding assays were performed as previously described (Chiu et al 1981. Marshall h Mishra 1980).
Results Effect of PLG on Locomotor Activity: PLG (10 mg/kg) given for 21 days along with haloperidol caused a significant blockade (Table 2) of haloperidol induced locomotor activity. The locomotor activity was measured after all groups of animals were challenged with apomorphine.
Table 2 Effect of Apomorphine on Locomotor Activity of Rats Treated with PLG and Haloperidol Gouts/hour Mean + SE24 768 + 40 710 7 36 10117 97 798 3 54
Treatment Group saline PLG haloperidol PLG + haloperidol apomorphine PLG 10 mg/kg halperidol 3mg/kg
Effect of PLG on Haloperidol Induced Supersensitivityof Dopamine Receptors: The results obtained in this series of experiments are shown in Table 3.
Table 3 Blockade of Haloperidol (HAL)-inducedincrease in specific 3H-spiroperidolbinding by PLG Treatment Group N
B max fmoles/mg Prot.
Kd (fi)
0.22 2 0.07 215 + 21 saline 6 0.24 + 0.09 512 + 32* HAL 6 0.28 7 0.05 304 i 16 PLG 6 0.21:0.02 330 f 18 PLG and HAL 6 (*p>.Ol) The various groups of animals received various drugs for 21 days. The dose of haloperidol was 3 mg/kg/day and PLG was administered 10 mg/kg/day. The animals were sacrificed 5 days after the last injection and 3H-spiroperidolbinding was carried out on striata.
Modulation of DA receptors by peptides
439
As can be seen from Table 3, simultaneous administration of PLG at lOmg/kg or even at 1-2 mg/kg (data not shown) with haloperidol antagonized the elevation in specific 3R-spiroperidol binding produced by long-term administration of neuroleptic drugs. Supersensitivityof Dopamine and Chole!&stokinin:(C@) Receptors in MesolifnbicRegions The effect of long term treatment of neuroleptic drug on CCK binding was examined in the mesolimbic regions of the rat brain. CCK and dopamine have shown to co-exist in the neuron projecting to mesolimbic regions of the brain. The results shown in Fig. 1 indicates a significant increase in CCK binding sites upon chronic administration of halperidol.
800
1251-CCK Binding T
3H-Sph Binding
r--
lluu
400
400
200
200
100
100
0
Fig. 1. C: control; N: described in Table 3.
C
C
N
N
0
neuroleptic treated. The protocol for drug treatment was same as
The CCK binding to mesolimbic membrane preparation was carried out according to method of Praissman et al (1983). The nonspecific binding was estimated by incubating the membranes with 100 fold excess unlabelled CCK-8. The specific binding constituted about 60%.
Discussion Although PLG was originally reported to potentiate the effect of L-DOPA, the results of the present study demonstrate that PLG when administered in low doses along with the neuroleptic drugs, effectively antagonize the development of dopamine receptor supersensitivity both at behavioral and biochemical level. (Tables 2-3). The possible mode of action of PLG is proposed in Fig. 2.
440
R.K. Mishra
PLO-BINDING SITES I
DOPAMINERGIC NEURON CELL BODY PRESY NAPTIC TERMINAL
POST SYNAPTIC NEURON
Fig. 2. PLG can interact with D-l or D-2 receptors through its own specific binding sites at the postsynaptic neuron or PLG can interact with the dopamine autoreceptors at the presynaptic neuron causing release of dopamine and thus the dopamine can then down regulate the receptors, alternatively, PLG can interact at the cell body level causing increased synthesis of dopamine. The results presented in this study and presented elsewhere in detail (Mishra et al 1983), support the notion that PLG has a modulatory effect on dopamine receptors in the central nervous system and the PLG and its enzymatically stable analogues should be considered as potential prophylactic and therapeutic agents in the treatment of various neuropsychiatric disorders associated with the development of dopamine receptor supersensitivity. The long-term blockade of dopamine receptors with haloperidol caused an increase in the number of both dopamine and CCK receptors in the mesolimbic regions of the rat brain. The possible mechanism of the development of CCK receptors supersensitivityis the disinhibition of the CCK release and subsequent depletion of CCK in the tissue which results in the development of observed supersensitivity (Fig. 1). This hypothesis can be further tested by lesion studies of dopaminergic neurons projecting to the limbic regions. In any case, the increase in CCK as well as in dopamlne receptors following neuroleptic treatment for a long time, is of additional interest because the peptfdergic supersensitivitywas induced towards a peptide (CCK) that co-exist and released from the same neuron as the dopamine whose receptors were blocked. Thus, CCK may contribute to the therapeutic or side effects of antipsychotic drugs. A speculative mechanfsm of action of CCK is shown in Fig. 3.
Modulation of DA receptors by peptides
441
CCK
I
0
I)
RELEASE
DA DOPAMlNERGlC/CHOLECYSTOKlNlN NEURON
Fig. 3. The common localization of dopamine and CCK in mesolimbic regions suggest that two such co-transmitterscould modulate each other's release by interaction at the cell body level, or once release, modulate different effects on the same post-synaptic neuron. Such dual modulation might be highly advantageous in the case where neurotransmitterhas the purpose of creating both short and long-term post-synaptic changes. CAMS (cyclic mp)
Conclusion The results obtained with PLG on neuroleptic drug induced dopaminergic supersensitivity at both behavioral and biochemical level suggest that PLG and its stable analogues should be considered as potential therapeutic agents in the treatment of neurological disorders associated with abnormal dopaminergic neurotransmission. The results obtained with CCK receptor binding suggest that a similar situation may occur with other co-existing peptideneurotransmitterpairs. It is therefore important to investigate any alterations in affinity or maximum binding sites to co-existing neuromodulatore that may develop upon treatment with various types of central nervous system active drugs.
Acknowledgement This study was supported by the Ontario Mental Health Foundation and the Parkinson Foundation of Canada. Reference8 CHIU, S. PAULOSE, C.S. and MISRRA, R.K. (1981). Neuroleptic drug-induced dopamine receptor supersensitivity: Antagonism by L-prolyl-L-leucyl-glycinamide. Science, 214: 1261-1262. MARSHALL, A.M. and MISRRA, R.K., (1980). Dopamine - sensitive adenylate cycloee and dopaminelneurolepticreceptor binding: Effect of Neuroleptic drugs. Adv. Biochem.
442
R.K. Mishra
Psychopharmacol. 24: 153-157. MISHRA, R.K., CHIU, S., CHIU, P. and MISHRA, C.P. (1983). Pharmacology of L-prolyl-Lleucyl-glycinamide(PLG): A review. Methods and Findings in Exptl. & Clin. Pharmacol. 5, 203-233. PRAISSMAN, M., MARTINEZ, P.A., SALADINO, C.F., GEROWITZ, J.M., STEGGLES, A.W., and FINKELSTEIN, J.A. (1983) Characterizationof cholecystokininbinding sites in rat cerebral cortex using a 125 I-CCK-8 probe resistant to degradation. J. Neurochem. 40: 14061413.
Inquiries and reprint requests should be addressed to: Dr. Ram K. Mishra NeuropharmacologyLaboratory McMaster University Hamilton, Ontario