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Receptor and cellular mechanisms of antipsychotic drugs Guo, Ningning
Abstract
The mechanisms contributing to the atypical clinical profile of clozapine remain uncertain. To address this question, Fos-immunostaining in combination with drug manipulation, brain lesions and in situ hybridization histochemistry were used to examine neurotransmitter systems involved in the effects of antipsychotic drugs. This research program employed these techniques (1) to determine receptor mechanisms mediating clozapine-induced c-fos expression in the forebrain and (2) to characterize the phenotypes of neurons targeted by clozapine and the typical antipsychotic haloperidol. In the first experiment, scopolamine, a muscarinic receptor antagonist, attenuated haloperidol-induced Fos immunoreactivity in the striatum. This suggests that haloperidolinduced Fos induction in the striatum is modulated by muscarinic cholinergic mechanisms, and that the antimuscarinic action of clozapine may contribute to its failure to increase Fos induction in the striatum. 5,7-dihydroxytryptamine lesions of the medial forebrain bundle or 6- hydroxydopamine lesions of the dorsal noradrenergic bundle produced extensive serotonin and noradrenaline depletions in the forebrain, respectively. However, neither type of lesion affected clozapine-induced c-fos expression in the rat forebrain, suggesting that neither serotonergic nor noradrenergic mechanisms are involved in this action of clozapine. 7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OHDPAT), a D3 receptor-preferring agonist, attenuated clozapine-induced c-fos expression in the nucleus accumbens (NAc), lateral septum (LSN) and the major island of Calleja (ICjM), without affecting the medial prefrontal cortex (mPFC). Quinpirole, which has similar affinities for D3 and D4 receptors, produced a small but significant attenuation of clozapine's effects in the mPFC and blocked clozapine's actions in the ICjM, NAC and LSN. Given the different affinities of quinpirole and 7-OHDPAT for D2, D3 and D4 receptors, these data suggest that clozapine-induced c-fos expression in the ICjM, NAc and LSN is due to its antagonist actions at D3 receptors, while antagonist actions at D4 receptors may contribute, in part, to the Fos induction in the mPFC. In situ hybridization for D3 receptor mRNA confirmed that most of the clozapineinduced Fos positive neurons in the ICjM, and the majority in the NAc and LSN express D3 receptor mRNA. In contrast, haloperidol-induced Fos positive neurons rarely expressed D3 mRNA in any brain region. Further studies demonstrated that clozapine increased c-fos expression in both enkephalin (Enk) and dynorphin (Dyn) containing neurons in the NAc and LSN. Haloperidol also increased c-fos expression in Enk and Dyn neurons, albeit in a different pattern. This suggests that while some Enk and/or Dyn neurons targeted by clozapine express D3 receptors, others do not.
Item Metadata
Title |
Receptor and cellular mechanisms of antipsychotic drugs
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1996
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Description |
The mechanisms contributing to the atypical clinical profile of clozapine remain
uncertain. To address this question, Fos-immunostaining in combination with drug
manipulation, brain lesions and in situ hybridization histochemistry were used to examine
neurotransmitter systems involved in the effects of antipsychotic drugs. This research
program employed these techniques (1) to determine receptor mechanisms mediating
clozapine-induced c-fos expression in the forebrain and (2) to characterize the phenotypes of
neurons targeted by clozapine and the typical antipsychotic haloperidol.
In the first experiment, scopolamine, a muscarinic receptor antagonist, attenuated
haloperidol-induced Fos immunoreactivity in the striatum. This suggests that haloperidolinduced
Fos induction in the striatum is modulated by muscarinic cholinergic mechanisms,
and that the antimuscarinic action of clozapine may contribute to its failure to increase Fos
induction in the striatum.
5,7-dihydroxytryptamine lesions of the medial forebrain bundle or 6-
hydroxydopamine lesions of the dorsal noradrenergic bundle produced extensive serotonin
and noradrenaline depletions in the forebrain, respectively. However, neither type of lesion
affected clozapine-induced c-fos expression in the rat forebrain, suggesting that neither
serotonergic nor noradrenergic mechanisms are involved in this action of clozapine.
7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OHDPAT), a D3 receptor-preferring
agonist, attenuated clozapine-induced c-fos expression in the nucleus accumbens (NAc),
lateral septum (LSN) and the major island of Calleja (ICjM), without affecting the medial
prefrontal cortex (mPFC). Quinpirole, which has similar affinities for D3 and D4 receptors,
produced a small but significant attenuation of clozapine's effects in the mPFC and blocked clozapine's actions in the ICjM, NAC and LSN. Given the different affinities of quinpirole
and 7-OHDPAT for D2, D3 and D4 receptors, these data suggest that clozapine-induced c-fos
expression in the ICjM, NAc and LSN is due to its antagonist actions at D3 receptors, while
antagonist actions at D4 receptors may contribute, in part, to the Fos induction in the mPFC.
In situ hybridization for D3 receptor mRNA confirmed that most of the clozapineinduced
Fos positive neurons in the ICjM, and the majority in the NAc and LSN express D3
receptor mRNA. In contrast, haloperidol-induced Fos positive neurons rarely expressed D3
mRNA in any brain region. Further studies demonstrated that clozapine increased c-fos
expression in both enkephalin (Enk) and dynorphin (Dyn) containing neurons in the NAc and
LSN. Haloperidol also increased c-fos expression in Enk and Dyn neurons, albeit in a
different pattern. This suggests that while some Enk and/or Dyn neurons targeted by
clozapine express D3 receptors, others do not.
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Extent |
17462692 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-03-16
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0087829
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1996-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.