- Email: [email protected]
Postsynaptic localization of 5-HT1D receptor binding sites in human caudate
OPERATE
NEUROL~Y
113,28-30
(1991)
Postsynaptic Localization of 5HT, D Receptor Binning Sites in Human Caudate JOSEPH Department
of Neurology,
GONZALEZ-HEYDRICH H-3160,
Stanford
AND STEPHEN
University
Stanford,
MATERIALS
California
943054235
AND
METHODS
Radioligand binding studies were performed using human autopsy brain tissue obtained from the National Neurological Research Bank in Los Angeles, CA and included subjects with Huntington’s disease and individuals who died of nonneurological diseases. The mean -t SD ages of the subjects were 65 z!z8 years for the Huntington’s cases and 78 + 6 years for the control cases. Tissue samples were rapidly frozen at autopsy within 24 h of death and stored at -70°C until needed. On the day of study, the samples were thawed in 50 mM Tris-HCl buffer. For determination of 5-HT,n receptors, experiments were performed according to the method of Heuring and Peroutka using tissue samples obtained from the caudate nucleus and frontal cortex from each subject (10). For 5-HT,n receptor binding studies, assays were performed in the presence of 100 nM &OHDPAT and 100 I& mesulergine. For the determination of [3H]paroxetine-labeled 5-HT transporter binding sites, caudate nucleus samples from Huntington’s and control cases were prepared according to the methods of Habert et a2. (7). The number of sites (B,,) and their aflinity (EC,) were determined by the Rosenthal variation of the Scatchard analysis. The statistical comparison of the Bm,, and the KD values between control and Huntington’s disease cases were performed using a Student’s paired t test.
INTRODUCTION
The 5hydroxytryptaminein (&HT,,) receptor binding site appears to function as a terminal autoreceptor modulating the release of 5-HT and other neurotransmitters (11). Binding to this site is regulated by guanine nucleotides (8,9) and mediates the inhibition of adenylate cyclase (12). Recent work has tried to determine the location of the 5-HT,, receptor within the synapse, Waeber and Palacios reported decreased binding to 5HT,, receptors in the substantia nigra, globus pallidus, and caudate nucleus in Huntington’s disease brains using a single concentration of 3H-5-HT (21). These results were interpreted by the authors as indicating that a significant number of 5-HT,, receptors are located on the intrinsic neurons of the striatum postsynaptic to the 5-HT afferents to the caudate. The present study seeks to confirm and extend the findings of Waeber and Palacios by performing saturation studies to determine if the observed decrease in binding to the 5-HT,, receptor is due to a change in affinity or a change in density of receptor sites and by looking to see if the decrease in binding could be accounted for by a loss of 5-HT termi-
RESULTS Saturation studies of 3H-5-HT binding to 5-HT,, receptor binding sites were performed in caudati and frontal cortex membrane preparations obtained from 28
Inc. resewed.
Center,
nals in the caudate in Huntington’s disease. Thus, in the following study we measured the saturation binding parameters of 5-HT,,, receptor binding sites in the caudate nucleus and frontal cortex of individuals with Huntington’s disease and of individuals with no known neurological disease. In addition, the density of 5-HT uptake sites labeled by [3H]paroxetine was determined in the caudate of control and Huntington’s disease brains.
5-hy~oxyt~t~ine~o (5HT,,) receptor binding sites were quantified by saturation studies in the postmortem caudate nucleus and frontal cortex of individuals with Huntington’s disease and control individuals with no known neurological disease. ‘H-5-HT was used as the radioligand in the presence of 100 n&f &OHDPAT and 100 r&f mesulergine in order to restrict radioligand binding to 5-HT,, receptors. No alteration in Kn value was detected in Huntington’s disease as compared to control brain tissue. However, the density (B-J of the 5-HT,o site was significantly decreased (P < 0.01) in the caudate, but not the frontal cortex, of Huntington’s disease versus control individuals. By contrast, no significant difference was found in B,,,= or Kn of [SH]paroxetine binding between control and Huntington’s caudates. These data suggest that a significant number of caudate 5-HT,, receptors are located on the intrinsic neurons of the striatum as opposed to 5-HT nerve terminals. 8 1991 Academia Press, Inc.
0014~4886/91$3.00 Copyright 0 1991 by Academic Press, All rights of reproduction in any form
Medical
J. PEROUTKA
POSTSYNAPTIC
TABLE
1
Saturation Parameters of 5-HT,, 5-HT,,
Tissue
Source
Caudate Control Huntington’s Frontal Cortex Controi Huntington’s
HUMAN
KD WW
Receptors
Binding
sites
(pmol/g
Banax tissue)
2.6 zk 0.3 2.0 AI 0.6
11 r+2 4.5 -+ 2’
3.4 + 0.6 3.6 + 0.6
6.5 f 1 6.6 + 2
Note. Radioligand studies were performed as described under Materials and Methods. Data shown are the means it standard errors of three experiments, each performed using tissues taken from different individuals (i.e., n = 3 subjects per condition). * P < 0.01 versus control values.
control individuals with no known neurological diseases and individuals with Huntington’s disease. As shown in Table 1, no significant differences exist between the K, values in the various conditions (P > 0.05 by Student’s t test). By contrast, the B, of 5-HT,n receptor binding sites in Huntin~on’s disease in~~duals is si~fi~antly reduced from control levels in caudate (P < 0.01) but not frontal cortex, membrane preparations. In order to assess whether the decrease in 5-HT,n receptor binding sites in Huntington’s disease caudates could be secondary to a loss of presynaptic 5HT fibers, [3H]paroxetine-labeled 5-HT transporter sites were measured in the caudate membranes of control (n = 6) and Huntin~on’s disease in~viduals (n = 6). There was no significant difference in E3H]paroxetine binding parameters between the control (B,, = 15 rt 4, KD = 0.63 * 0.2) and Huntington’s disease (B,, = 20 f 7, KD
= 0.60 f 0.2). DISCUSSION
The major finding of the present study is that a significant number of 5-HT,, receptor binding sites in the caudate are located postsynaptically to 5-HT nerve terminals. This conclusion is supported by the fact that the neurons of the caudate which degenerate in Huntington’s disease are nonserotonergic intrinsic neurons (13). Moreover, the observation that [3H]paroxetine-labeled 5-HT uptake sites are not decreased in Huntin~on’s disease caudate indicates that serotonergic inputs from the raphe nucleus are intact. The principle deficit in Huntington’s disease is a loss of intrinsic striatal neurons (19) with preservation of 5-HT projections to the striatum from the raphe nucleus (13), This anatomical deficit offers an opportunity to clarify the location of the 5-HT,n receptor in humans
5-HT,,
29
RECEPTORS
by comparing the saturation properties of the 5-HT,, receptor with that of a 5-HT presynaptic marker (i.e., the 5HT transporter labeled by [3H]paroxetine). Physiologic data suggest that the &HT,n receptor is the human 5HT terminal autoreceptor (4) and, therefore, is located on the presynaptic terminal of 5-HT neurons. However, in experiments done before the &I-IT, receptor subtypes could be distinguished from one another, lesions of projections from the raphe nucleus in the rat produced increases in total 5-HT, receptor binding sites (17). If the majority of 5-HT,, receptor binding sites were located on presynaptic 5HT terminals, then a decrease in density would be expected. Moreover, previous human postmortem brain studies, also done before the 5-HIT, receptor subtypes could be distinguished from one another, demonstrated a loss of 5-HT, receptor sites in the putamen in Huntington’s disease (1,Z). While this work was in progress, Waeber and Palacios reported a decrease in binding to 5-HT,, receptors in the substantia nigra, globus pallidus, and caudate nucleus in Huntington’s disease brains (21). As in the present study, these results were interpreted by the authors as indicating that a significant number of 5-HT,n receptors are located on the neurons intrinsic to the striatum. In the present study, unlike in that of Waeber and Palacios, saturation studies were performed in order to determine if the observed changes result from a decrease in the affinity andfor density of the 5-HT,n receptor in Huntington’s disease. In addition, the present study found no decrease in the density of 5-HT terminals in Huntington’s disease caudate. Thus, our results cannot be explained by a loss of the 5-HT afferents to the caudate in Huntington’s disease. In summa~, a growing body of evidence suggests that some, but not all, 5-HT,, receptor binding sites are located postsynaptically to 5-HT terminals. This observation agrees with physiological studies showing that 5-HT terminal receptor can also modulate the release of other neurotransmitters such as acetylcholine (5, 14, 15), dopamine (3, 20), norepinephrine (6), and glutamate (18, 16). The observation that a component of the 5-HT system (basal ganglia 5-HT,, receptor binding sites) are altered in Huntington’s disease may have implications for the understanding of the pathophysiology of both its motor and psychiatric abnormalities. These observations also suggest that selective 5-HT receptor agents may be worthy of study as possible therapeutic agents in the treatment of Huntington’s disease.
ACKNOWLEDGMENTS This National (S.J.P.)
work was supported in part by the Stanley Foundation and Institutes of Health Grants NS 12151-15 and NS 23560-04 and National Institutes of Health Grant 5T32 NS 07280-05
30
GONZALEZ-HEYDRICH
(J.G-H). The Anne Schmidt
authors thank for technical
Mary Keller assistance.
for editorial
assistance
AND and
REFERENCES 1.
CROSS, A. J., G. P. REYNOLDS, 1986. Brain serotonin receptors &em. znt. 9: 431-435.
2.
ENNA, S. J., J. P. BENNETT, D. B. BYLUND, S. H. SNYDER, E. D. BIRD, AND L. L. IVERSEN. 1976. Alterations of brain neurotransmitter receptor binding in Huntington’s chorea. Bruin Res. 116: 531-537.
3.
ENNIS, C., J. D. KEMP, AND B. Cox. 1981. Characterization of inhibitory 5hydroxytryptamine receptors that modulate dopamine release in the striatum. J. Neurochem. 36: 1515-1520. GALZIN, A. M., P. BLIER, J. P. CHODKIEWJCZ, M. F. POIFUER, H. Loo, F. X. Roux, A. REDONDO, A. LISTA, R. RAMDINE, AND S. Z. LANCER. 1988. Pharmacological characterization of the serotonin (5-HT) autoreceptor modulating the electrically evoked release of [‘HI-5-HT from slices of human frontal cortex. Sot. Neurosci. Abstr. 14: 313. GILLET, G., S. AMMOR, AND G. FILLION. 1985. Serotonin inhibits acetylcholine release from rat striatum slices: Evidence for a presynaptic receptor-mediated effect. J. Neurochem. 45: 16871691.
4.
5.
6.
L. M. HEWITT, in Huntington’s
AND P. SLATER. disease. Neuro-
10.
HEURING, R. E., AND S. J. PEROLVKA. 1987. Characterization of a novel ‘H-5-hydroxytryptamine binding site subtype in bovine brain membranes. J. Neurosci. 7: 894-903.
11.
HOYER, D. 1989. 5-Hydroxytryptamine receptors and effector coupling mechanisms in peripheral tissues. In Peripheral Actions of&HT. (J. R. Fozard, Ed.), pp. 72-98. Oxford Univ. Press.
12.
HOYER, D., AND P. SCHOEF~R. 1988. 5-HT,, receptor-mediated inhibition of forskolin-stimulated adenylate cyclase activity in calf substantia nigra. Eur. J. Pharmacol. 147: 145-147. KISH, S. J., K. SHANNAK, AND 0. HORNYKIEWICZ. 1987. Elevated serotonin and reduced dopamine in subregionally divided Huntington’s disease striatum. Ann. Neurol. 22: 386-389.
13.
14.
MAUR.A, G., AND M. RAITERI. 1986. Cholinergic terminals in rat hippocampus possess 5-HT,, receptors mediating inhibition of acetylcholine release. Eur. J. Phurmacol. 129: 333-337.
15.
MAURA, G., A. RICCHE’ITI, AND M. RAITERI. 1986. Serotonin inhibits the depolarization-evoked release of endogenous glutamate from rat cerebellar nerve endings. Neurosci. Lett. 67: 218222.
16.
MAURA, G., E. ROCCATAGLIATA, M. ULIVI, AND M. RAITERI. 1988. Serotonin-glutamate interaction in rat cerebellum: Involvement of 5-HT, and 5-HT, receptors. Eur. J. Phurmucol. 145: 31-38. &urn, M., AND E. AZMITIA. 1988. Selective destruction of the serotonergic fibers of the fornix-fimbria and cingulum bundle increases 5-HT, but not 5-HT, receptors in rat midbrain. Eur. J. Pharmucol. 90: 3’77-384.
17.
GOTHERT, M., P. KOLLECKER, N. ROHM, AND H.-R. ZERKOWSKI. 1986. Inhibitory presynaptic 5-hydroxytryptamine (5-HT) receptors on the sympathetic nerves of the human saphenous vein. Naunyn Schmiedeberg’s Arch. Pharmacol. 332: 317-323.
18.
HABERT, E., D. GRAHAM, L. TAHRAOIJI, Y. CLAUSTRE, LANGER. 1985. Characterization of [3H]paroxetine binding cortical membranes. Eur. J. Phurmacol. 118: 107-114.
19.
S. Z. to rat
HARRINGTON, M. A., AND S. J. PEROIJTKA. 1990. Differential modulation of 5-hydroxytryptaminein binding sites by GTP and GTPgammaS. Bruin Res., 506: 172-174. HERRICK-DAVIS, K., M. TITELER, S. LEONHARDT, R. STRUBLE, AND D. PRICE. 1988. Serotonin 5-HT,, receptors in human prefrontal cortex and caudate: Interaction with a GTP binding protein. J. Neurochem. 51: 1906-1912.
PEROUTKA
20.
21.
RAITERI, M., G. MAURA, G. BONANNO, AND A. PI~ALUGA. 1986. Differential pharmacology and function of two 5-HT, receptors modulating transmitter release in rat cerebellum. J. Pharmucol. Exp. Ther. 237: 644-648. SANBERG, P. R., AND J. T. COYLE. 1984. Scientific approaches to Huntington’s disease. CRC Crit. Rev. Clin. Neurol. 1: l-44. SHAFUF, N. A. 1985. Serotonin, (5HTi) receptors modulate striatal dopaminergic transmission: Studies on uptake, release, and receptor mechanisms. ZRCS Med. Sci. 13: 368-369. WAEBER, C., AND J. M. PALACIOS. 1989. Serotonin-1 receptor binding sites in the human basal ganglia are decreased in Huntington’s chorea but not in Parkinson’s disease: A quantitative in vitro autoradiography study. Neuroscience 32: 337-347.
NEUROL~Y
113,28-30
(1991)
Postsynaptic Localization of 5HT, D Receptor Binning Sites in Human Caudate JOSEPH Department
of Neurology,
GONZALEZ-HEYDRICH H-3160,
Stanford
AND STEPHEN
University
Stanford,
MATERIALS
California
943054235
AND
METHODS
Radioligand binding studies were performed using human autopsy brain tissue obtained from the National Neurological Research Bank in Los Angeles, CA and included subjects with Huntington’s disease and individuals who died of nonneurological diseases. The mean -t SD ages of the subjects were 65 z!z8 years for the Huntington’s cases and 78 + 6 years for the control cases. Tissue samples were rapidly frozen at autopsy within 24 h of death and stored at -70°C until needed. On the day of study, the samples were thawed in 50 mM Tris-HCl buffer. For determination of 5-HT,n receptors, experiments were performed according to the method of Heuring and Peroutka using tissue samples obtained from the caudate nucleus and frontal cortex from each subject (10). For 5-HT,n receptor binding studies, assays were performed in the presence of 100 nM &OHDPAT and 100 I& mesulergine. For the determination of [3H]paroxetine-labeled 5-HT transporter binding sites, caudate nucleus samples from Huntington’s and control cases were prepared according to the methods of Habert et a2. (7). The number of sites (B,,) and their aflinity (EC,) were determined by the Rosenthal variation of the Scatchard analysis. The statistical comparison of the Bm,, and the KD values between control and Huntington’s disease cases were performed using a Student’s paired t test.
INTRODUCTION
The 5hydroxytryptaminein (&HT,,) receptor binding site appears to function as a terminal autoreceptor modulating the release of 5-HT and other neurotransmitters (11). Binding to this site is regulated by guanine nucleotides (8,9) and mediates the inhibition of adenylate cyclase (12). Recent work has tried to determine the location of the 5-HT,, receptor within the synapse, Waeber and Palacios reported decreased binding to 5HT,, receptors in the substantia nigra, globus pallidus, and caudate nucleus in Huntington’s disease brains using a single concentration of 3H-5-HT (21). These results were interpreted by the authors as indicating that a significant number of 5-HT,, receptors are located on the intrinsic neurons of the striatum postsynaptic to the 5-HT afferents to the caudate. The present study seeks to confirm and extend the findings of Waeber and Palacios by performing saturation studies to determine if the observed decrease in binding to the 5-HT,, receptor is due to a change in affinity or a change in density of receptor sites and by looking to see if the decrease in binding could be accounted for by a loss of 5-HT termi-
RESULTS Saturation studies of 3H-5-HT binding to 5-HT,, receptor binding sites were performed in caudati and frontal cortex membrane preparations obtained from 28
Inc. resewed.
Center,
nals in the caudate in Huntington’s disease. Thus, in the following study we measured the saturation binding parameters of 5-HT,,, receptor binding sites in the caudate nucleus and frontal cortex of individuals with Huntington’s disease and of individuals with no known neurological disease. In addition, the density of 5-HT uptake sites labeled by [3H]paroxetine was determined in the caudate of control and Huntington’s disease brains.
5-hy~oxyt~t~ine~o (5HT,,) receptor binding sites were quantified by saturation studies in the postmortem caudate nucleus and frontal cortex of individuals with Huntington’s disease and control individuals with no known neurological disease. ‘H-5-HT was used as the radioligand in the presence of 100 n&f &OHDPAT and 100 r&f mesulergine in order to restrict radioligand binding to 5-HT,, receptors. No alteration in Kn value was detected in Huntington’s disease as compared to control brain tissue. However, the density (B-J of the 5-HT,o site was significantly decreased (P < 0.01) in the caudate, but not the frontal cortex, of Huntington’s disease versus control individuals. By contrast, no significant difference was found in B,,,= or Kn of [SH]paroxetine binding between control and Huntington’s caudates. These data suggest that a significant number of caudate 5-HT,, receptors are located on the intrinsic neurons of the striatum as opposed to 5-HT nerve terminals. 8 1991 Academia Press, Inc.
0014~4886/91$3.00 Copyright 0 1991 by Academic Press, All rights of reproduction in any form
Medical
J. PEROUTKA
POSTSYNAPTIC
TABLE
1
Saturation Parameters of 5-HT,, 5-HT,,
Tissue
Source
Caudate Control Huntington’s Frontal Cortex Controi Huntington’s
HUMAN
KD WW
Receptors
Binding
sites
(pmol/g
Banax tissue)
2.6 zk 0.3 2.0 AI 0.6
11 r+2 4.5 -+ 2’
3.4 + 0.6 3.6 + 0.6
6.5 f 1 6.6 + 2
Note. Radioligand studies were performed as described under Materials and Methods. Data shown are the means it standard errors of three experiments, each performed using tissues taken from different individuals (i.e., n = 3 subjects per condition). * P < 0.01 versus control values.
control individuals with no known neurological diseases and individuals with Huntington’s disease. As shown in Table 1, no significant differences exist between the K, values in the various conditions (P > 0.05 by Student’s t test). By contrast, the B, of 5-HT,n receptor binding sites in Huntin~on’s disease in~~duals is si~fi~antly reduced from control levels in caudate (P < 0.01) but not frontal cortex, membrane preparations. In order to assess whether the decrease in 5-HT,n receptor binding sites in Huntington’s disease caudates could be secondary to a loss of presynaptic 5HT fibers, [3H]paroxetine-labeled 5-HT transporter sites were measured in the caudate membranes of control (n = 6) and Huntin~on’s disease in~viduals (n = 6). There was no significant difference in E3H]paroxetine binding parameters between the control (B,, = 15 rt 4, KD = 0.63 * 0.2) and Huntington’s disease (B,, = 20 f 7, KD
= 0.60 f 0.2). DISCUSSION
The major finding of the present study is that a significant number of 5-HT,, receptor binding sites in the caudate are located postsynaptically to 5-HT nerve terminals. This conclusion is supported by the fact that the neurons of the caudate which degenerate in Huntington’s disease are nonserotonergic intrinsic neurons (13). Moreover, the observation that [3H]paroxetine-labeled 5-HT uptake sites are not decreased in Huntin~on’s disease caudate indicates that serotonergic inputs from the raphe nucleus are intact. The principle deficit in Huntington’s disease is a loss of intrinsic striatal neurons (19) with preservation of 5-HT projections to the striatum from the raphe nucleus (13), This anatomical deficit offers an opportunity to clarify the location of the 5-HT,n receptor in humans
5-HT,,
29
RECEPTORS
by comparing the saturation properties of the 5-HT,, receptor with that of a 5-HT presynaptic marker (i.e., the 5HT transporter labeled by [3H]paroxetine). Physiologic data suggest that the &HT,n receptor is the human 5HT terminal autoreceptor (4) and, therefore, is located on the presynaptic terminal of 5-HT neurons. However, in experiments done before the &I-IT, receptor subtypes could be distinguished from one another, lesions of projections from the raphe nucleus in the rat produced increases in total 5-HT, receptor binding sites (17). If the majority of 5-HT,, receptor binding sites were located on presynaptic 5HT terminals, then a decrease in density would be expected. Moreover, previous human postmortem brain studies, also done before the 5-HIT, receptor subtypes could be distinguished from one another, demonstrated a loss of 5-HT, receptor sites in the putamen in Huntington’s disease (1,Z). While this work was in progress, Waeber and Palacios reported a decrease in binding to 5-HT,, receptors in the substantia nigra, globus pallidus, and caudate nucleus in Huntington’s disease brains (21). As in the present study, these results were interpreted by the authors as indicating that a significant number of 5-HT,n receptors are located on the neurons intrinsic to the striatum. In the present study, unlike in that of Waeber and Palacios, saturation studies were performed in order to determine if the observed changes result from a decrease in the affinity andfor density of the 5-HT,n receptor in Huntington’s disease. In addition, the present study found no decrease in the density of 5-HT terminals in Huntington’s disease caudate. Thus, our results cannot be explained by a loss of the 5-HT afferents to the caudate in Huntington’s disease. In summa~, a growing body of evidence suggests that some, but not all, 5-HT,, receptor binding sites are located postsynaptically to 5-HT terminals. This observation agrees with physiological studies showing that 5-HT terminal receptor can also modulate the release of other neurotransmitters such as acetylcholine (5, 14, 15), dopamine (3, 20), norepinephrine (6), and glutamate (18, 16). The observation that a component of the 5-HT system (basal ganglia 5-HT,, receptor binding sites) are altered in Huntington’s disease may have implications for the understanding of the pathophysiology of both its motor and psychiatric abnormalities. These observations also suggest that selective 5-HT receptor agents may be worthy of study as possible therapeutic agents in the treatment of Huntington’s disease.
ACKNOWLEDGMENTS This National (S.J.P.)
work was supported in part by the Stanley Foundation and Institutes of Health Grants NS 12151-15 and NS 23560-04 and National Institutes of Health Grant 5T32 NS 07280-05
30
GONZALEZ-HEYDRICH
(J.G-H). The Anne Schmidt
authors thank for technical
Mary Keller assistance.
for editorial
assistance
AND and
REFERENCES 1.
CROSS, A. J., G. P. REYNOLDS, 1986. Brain serotonin receptors &em. znt. 9: 431-435.
2.
ENNA, S. J., J. P. BENNETT, D. B. BYLUND, S. H. SNYDER, E. D. BIRD, AND L. L. IVERSEN. 1976. Alterations of brain neurotransmitter receptor binding in Huntington’s chorea. Bruin Res. 116: 531-537.
3.
ENNIS, C., J. D. KEMP, AND B. Cox. 1981. Characterization of inhibitory 5hydroxytryptamine receptors that modulate dopamine release in the striatum. J. Neurochem. 36: 1515-1520. GALZIN, A. M., P. BLIER, J. P. CHODKIEWJCZ, M. F. POIFUER, H. Loo, F. X. Roux, A. REDONDO, A. LISTA, R. RAMDINE, AND S. Z. LANCER. 1988. Pharmacological characterization of the serotonin (5-HT) autoreceptor modulating the electrically evoked release of [‘HI-5-HT from slices of human frontal cortex. Sot. Neurosci. Abstr. 14: 313. GILLET, G., S. AMMOR, AND G. FILLION. 1985. Serotonin inhibits acetylcholine release from rat striatum slices: Evidence for a presynaptic receptor-mediated effect. J. Neurochem. 45: 16871691.
4.
5.
6.
L. M. HEWITT, in Huntington’s
AND P. SLATER. disease. Neuro-
10.
HEURING, R. E., AND S. J. PEROLVKA. 1987. Characterization of a novel ‘H-5-hydroxytryptamine binding site subtype in bovine brain membranes. J. Neurosci. 7: 894-903.
11.
HOYER, D. 1989. 5-Hydroxytryptamine receptors and effector coupling mechanisms in peripheral tissues. In Peripheral Actions of&HT. (J. R. Fozard, Ed.), pp. 72-98. Oxford Univ. Press.
12.
HOYER, D., AND P. SCHOEF~R. 1988. 5-HT,, receptor-mediated inhibition of forskolin-stimulated adenylate cyclase activity in calf substantia nigra. Eur. J. Pharmacol. 147: 145-147. KISH, S. J., K. SHANNAK, AND 0. HORNYKIEWICZ. 1987. Elevated serotonin and reduced dopamine in subregionally divided Huntington’s disease striatum. Ann. Neurol. 22: 386-389.
13.
14.
MAUR.A, G., AND M. RAITERI. 1986. Cholinergic terminals in rat hippocampus possess 5-HT,, receptors mediating inhibition of acetylcholine release. Eur. J. Phurmacol. 129: 333-337.
15.
MAURA, G., A. RICCHE’ITI, AND M. RAITERI. 1986. Serotonin inhibits the depolarization-evoked release of endogenous glutamate from rat cerebellar nerve endings. Neurosci. Lett. 67: 218222.
16.
MAURA, G., E. ROCCATAGLIATA, M. ULIVI, AND M. RAITERI. 1988. Serotonin-glutamate interaction in rat cerebellum: Involvement of 5-HT, and 5-HT, receptors. Eur. J. Phurmucol. 145: 31-38. &urn, M., AND E. AZMITIA. 1988. Selective destruction of the serotonergic fibers of the fornix-fimbria and cingulum bundle increases 5-HT, but not 5-HT, receptors in rat midbrain. Eur. J. Pharmucol. 90: 3’77-384.
17.
GOTHERT, M., P. KOLLECKER, N. ROHM, AND H.-R. ZERKOWSKI. 1986. Inhibitory presynaptic 5-hydroxytryptamine (5-HT) receptors on the sympathetic nerves of the human saphenous vein. Naunyn Schmiedeberg’s Arch. Pharmacol. 332: 317-323.
18.
HABERT, E., D. GRAHAM, L. TAHRAOIJI, Y. CLAUSTRE, LANGER. 1985. Characterization of [3H]paroxetine binding cortical membranes. Eur. J. Phurmacol. 118: 107-114.
19.
S. Z. to rat
HARRINGTON, M. A., AND S. J. PEROIJTKA. 1990. Differential modulation of 5-hydroxytryptaminein binding sites by GTP and GTPgammaS. Bruin Res., 506: 172-174. HERRICK-DAVIS, K., M. TITELER, S. LEONHARDT, R. STRUBLE, AND D. PRICE. 1988. Serotonin 5-HT,, receptors in human prefrontal cortex and caudate: Interaction with a GTP binding protein. J. Neurochem. 51: 1906-1912.
PEROUTKA
20.
21.
RAITERI, M., G. MAURA, G. BONANNO, AND A. PI~ALUGA. 1986. Differential pharmacology and function of two 5-HT, receptors modulating transmitter release in rat cerebellum. J. Pharmucol. Exp. Ther. 237: 644-648. SANBERG, P. R., AND J. T. COYLE. 1984. Scientific approaches to Huntington’s disease. CRC Crit. Rev. Clin. Neurol. 1: l-44. SHAFUF, N. A. 1985. Serotonin, (5HTi) receptors modulate striatal dopaminergic transmission: Studies on uptake, release, and receptor mechanisms. ZRCS Med. Sci. 13: 368-369. WAEBER, C., AND J. M. PALACIOS. 1989. Serotonin-1 receptor binding sites in the human basal ganglia are decreased in Huntington’s chorea but not in Parkinson’s disease: A quantitative in vitro autoradiography study. Neuroscience 32: 337-347.