COMMENTARY
Reductions of p11 and 5-HT1B Receptor Availability in Limbic Brain Regions in Cocaine Dependence Per Svenningsson
R
esults from the 2012 National Survey on Drug Use and Health reported that approximately 1.6 million individuals aged 12 or over are cocaine abusers in the United States (1). In addition, cocaine abusers often have comorbid disorders, and it has been estimated that 30% to 40% of individuals suffering from drug abuse have a mood or anxiety disorder (2). The high rate of comorbidity between mood disorders and cocaine dependence suggests shared anatomical pathways and molecular mechanisms. Accordingly, it has been reported that both depression and cocaine dependence are associated with alterations in the reward circuitry of the brain, particularly in the nucleus accumbens. Accumulating evidence suggests that p11 (S100A10) plays a critical role in various aspects of depression (3). Levels of p11 are regulated in animal models of depression and in postmortem brain tissue from subjects who suffered from depression as well as by antidepressant regimens (4). Conversely, p11 regulates depression-like behaviors and/or responses to antidepressants (3,4). In particular, global p11 knockout mice show evidence of behavioral despair and anhedonia, consistent with a depressionlike phenotype (4). Likewise, focal viral transduction with RNA interference against p11 into accumbal neurons of wild-type mice causes depressive-like behaviors, whereas focal viral restoration of p11 exclusively within the nucleus accumbens of p11 knockout mice normalizes such behavioral responses (5). In this issue of Biological Psychiatry, Arango-Lievano et al. (6) hypothesized that p11 in nucleus accumbens would not only influence depression-like behaviors but also influence actions of cocaine in mice. Initially, they demonstrated that chronic intraperitoneal administration of cocaine reduced p11 messenger RNA and protein levels in the nucleus accumbens. There are two major classes of projection neurons in nucleus accumbens, which are distinguished by their expression of dopamine D1 receptors versus D2 receptors. Chronic cocaine reduced p11 in both classes of projection neurons. To determine the role of reduced accumbal p11 in cocaine dependence, combinations of mouse genetics and viral strategies were employed. p11 knockout mice showed enhanced cocaine conditioned place preference, which was reproduced by focal viral-mediated downregulation of p11 in the nucleus accumbens of wild-type mice. To distinguish the relative roles of p11 in D1 receptor- versus D2 receptorexpressing projection neurons in cocaine actions, ArangoLievano et al. (6) developed a novel Cre inducible viral vector to selectively express small hairpin RNAs against p11 downstream of a floxed STOP cassette. This new adeno-associated virus vector allows for conditional p11 gene downregulation when combined with cell-type specificity of bacterial artificial chromosome-Cre transgenic lines and the anatomical precision of stereotactic viral From the Center for Molecular Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden. Address correspondence to Per Svenningsson, M.D., Ph.D., Karolinska Institutet, Department of Clinical Neuroscience, Center for Molecular Medicine, CMML8:01, Stockholm 171 76, Sweden; E-mail: [email protected]. Received Aug 18, 2014; accepted Aug 19, 2014.
0006-3223/$36.00 http://dx.doi.org/10.1016/j.biopsych.2014.08.011
delivery. Using this sophisticated approach, it was demonstrated that specific silencing of p11 in D2-expressing projection neurons or choline acetyltransferase interneurons of nucleus accumbens did not have an effect on cocaine conditioned place preference. In contrast, specific silencing of p11 in D1-expressing projection neurons of nucleus accumbens increased cocaine conditioned place preference. These data demonstrate that p11 within D1expressing projection neurons of nucleus accumbens is a molecular determinant of cocaine dependence. p11 is an adaptor protein for several receptors and ion channels at the plasma membrane, as well as for intracellular trafficking proteins, enzymes, and transcription factors (3). p11 interacts with serotonin 1B (5-HT1B) receptors and increases their cell surface expression (4). 5-HT1B receptor knockout mice have been reported to show a shorter latency to develop selfadministration of cocaine than wild-type mice (7). However, opposite results were subsequently found with pharmacologic approaches, and it appears that compensatory changes have taken place during the development of the 5-HT1B knockout mice, which may have rendered these mice more vulnerable to cocaine (7). It has also been observed in rodent studies that dose, brain region, and treatment duration differentially influence the modulation of cocaine actions by 5-HT1B receptors. Thus, animal data on the role of 5-HT1B receptors in various aspects of cocaine dependence are complex. At the moment, the role of 5-HT1B receptors in human cocaine abuse is poorly understood. In this issue of Biological Psychiatry, Matuskey et al. (8) performed [11C]P943 positron emission tomography imaging, along with structural magnetic resonance imaging, to compare 5-HT1B receptor availability in subjects with cocaine dependence with age-matched healthy control subjects. [11C]P943 imaging was done in nine candidate regions, and after correcting for gray matter reductions in the frontal cortex of subjects with cocaine dependence, statistically significant reductions were found in the anterior cingulate cortex, frontal cortex, and hypothalamus. Interestingly, [11C]P943 imaging in patients with major depressive disorder is reduced in the ventral striatum and ventral pallidum when compared with control subjects (9). It may, therefore, turn out that reduced 5-HT1B receptor availability contributes to negative mood states observed in cocaine dependence. A caveat for the interpretation of reduced [11C]P943 binding potential is that it could be due to not only 5-HT1B downregulation but also higher levels of extracellular 5-HT. [11C]P943 has, indeed, been shown to be sensitive to endogenous 5-HT in nonhuman primates. Taken together, this issue of Biological Psychiatry presents two studies (6,8) on cocaine dependence that have examined molecular targets, p11 and 5-HT1B receptors, which have previously been shown to be downregulated in depression. Interestingly, both studies report that these molecular targets are downregulated also in response to cocaine dependence. Thus, reductions of p11 and 5-HT1B receptor availability appear to represent molecular maladaptations shared between depression and cocaine dependence. The detailed study of p11 in cocaine conditioned place preference in mice was focused on nucleus accumbens and it BIOL PSYCHIATRY 2014;76:763–764 & 2014 Society of Biological Psychiatry
764 BIOL PSYCHIATRY 2014;76:763–764 remains to be determined whether p11 plays a similar role in modulating cocaine responses in other limbic brain regions. Somewhat surprisingly, [11C]P943 imaging provided no evidence that 5-HT1B receptors are altered in the ventral striatum (i.e., nucleus accumbens of human subjects) in the cocaine addicts. However, within the same subjects, 5-HT1B receptors are reduced in regions interconnected with nucleus accumbens: hypothalamus, anterior cingulate cortex, and frontal cortex. The nucleus accumbens is, indeed, an integrative region of the reward system and receives dense glutamatergic innervation from hypothalamus, anterior cingulate, and frontal cortex. All these four regions express 5-HT1B receptors and p11 along with dopamine D1 receptors. As mentioned above, Arango-Lievano et al. (6) identified D1 receptor projecting neurons in nucleus accumbens as key mediators of the effects of p11 on cocaine reward. It is wellestablished that D1 receptors are critically involved in cocaine actions. Selective stimulation of D1 receptors is sufficient to support acquisition and maintenance of cocaine selfadministration behavior, whereas blockade of D1 receptors strongly attenuates the rewarding effects of cocaine. Moreover, optogenetic activation of D1-expressing accumbal neurons enhances cocaine conditioned place preference, whereas optogenetic activation of D2-expressing neurons in the same region attenuates cocaine conditioned place preference (10). D1 receptors are coupled to stimulatory G proteins and activate adenylate cyclase/cyclic adenosine monophosphate/cyclic adenosine monophosphate-dependent protein kinase to facilitate excitation of D1-expressing neurons. In contrast, 5-HT1B receptors are coupled to inhibitory G proteins and inhibit adenylate cyclase and neuronal excitability. The fact that both 5-HT1B receptor availability and p11 are downregulated in cocaine dependence suggests a model in which adenylate cyclase-mediated signaling and neuronal excitability are augmented in D1-expressing neurons. Based on data from pharmacologic and optogenetic experiments, such augmentation is likely to promote the development of cocaine dependence. It may therefore be beneficial to strengthen 5-HT1B signaling in D1expressing neurons to counteract cocaine dependence. Unlike alcoholism, opiate addiction, and cigarette smoking, there is currently no approved pharmacotherapy for cocaine abuse. The novel data presented here (6,8) provide a rationale for future studies of 5-HT1B receptor agonists and increased accumbal p11 against cocaine dependence, particularly when it is comorbid with depression. When designing future experiments, it shall be remembered that animal data indicate that 5-HT1B receptors have different roles depending on the stage of the
www.sobp.org/journal
Commentary cocaine addiction cycle. Moreover, selective targeting of individual molecules is rarely successful for the treatment of psychiatric disorders. A more feasible approach may be to include affinity toward 5-HT1B receptors in multireceptor compounds aimed for the treatment of cocaine dependence. Another research direction that will be interesting to follow is whether alterations of p11 levels and/or 5-HT1B receptor availability can be developed into reliable molecular biomarkers for distinct aspects of cocaine dependence that could be used for stratification or outcome measures in therapy trials. The author declares no biomedical financial interests or potential conflicts of interest. 1. Substance Abuse and Mental Health Services Administration (2013): Results from the 2012 National Survey on Drug Use and Health: Summary of National Findings. Rockville, MD: Substance Abuse and Mental Health Services Administration. NSDUH Series H-46, HHS Publication No. (SMA) 13–4795. 2. Conway KP, Compton W, Stinson FS, Grant BF (2006): Lifetime comorbidity of DSM-IV mood and anxiety disorders and specific drug use disorders: Results from the National Epidemiologic Survey on alcohol and related conditions. J Clin Psychiatry 67:247–257. 3. Svenningsson P, Kim Y, Warner-Schmidt J, Oh YS, Greengard P (2013): p11 and its role in depression and therapeutic responses to antidepressants. Nat Rev Neurosci 14:673–680. 4. Svenningsson P, Chergui K, Rachleff I, Flajolet M, Zhang X, El Yacoubi M, et al. (2006): Alterations in 5-HT1B receptor function by p11 in depression-like states. Science 311:77–80. 5. Alexander B, Warner-Schmidt J, Eriksson T, Tamminga C, ArangoLievano M, Ghose S, et al. (2010): Reversal of depressed behaviors in mice by p11 gene therapy in the nucleus accumbens. Sci Transl Med 2: 54ra76. 6. Arango-Lievano M, Schwarz JT, Vernov M, Wilkinson MB, Bradbury K, Feliz A, et al. (2014): Cell-type specific expression of p11 controls cocaine reward. Biol Psychiatry 76:794–801. 7. Castanon N, Scearce-Levie K, Lucas JJ, Rocha B, Hen R (2000): Modulation of the effects of cocaine by 5-HT1B receptors: A comparison of knockouts and antagonists. Pharmacol Biochem Behav 67:559–566. 8. Matuskey D, Bhagwagar Z, Planeta B, Pittman B, Gallezot J-D, Chen J, et al. (2014): Reductions in brain 5-HT1B receptor availability in primarily cocaine-dependent humans. Biol Psychiatry 76:816–822. 9. Murrough JW, Henry S, Hu J, Gallezot JD, Planeta-Wilson B, Neumaier JF, Neumeister A (2011): Reduced ventral striatal/ventral pallidal serotonin1B receptor binding potential in major depressive disorder. Psychopharmacology (Berl) 213:547–553. 10. Lobo MK, Covington HK 3rd, Chaudhury D, Friedman AK, Sun H, Damez-Werno D, et al. (2010): Cell type-specific loss of BDNF signaling mimics optogenetic control of cocaine reward. Science 330:385–390.
Reductions of p11 and 5-HT1B Receptor Availability in Limbic Brain Regions in Cocaine Dependence Per Svenningsson
R
esults from the 2012 National Survey on Drug Use and Health reported that approximately 1.6 million individuals aged 12 or over are cocaine abusers in the United States (1). In addition, cocaine abusers often have comorbid disorders, and it has been estimated that 30% to 40% of individuals suffering from drug abuse have a mood or anxiety disorder (2). The high rate of comorbidity between mood disorders and cocaine dependence suggests shared anatomical pathways and molecular mechanisms. Accordingly, it has been reported that both depression and cocaine dependence are associated with alterations in the reward circuitry of the brain, particularly in the nucleus accumbens. Accumulating evidence suggests that p11 (S100A10) plays a critical role in various aspects of depression (3). Levels of p11 are regulated in animal models of depression and in postmortem brain tissue from subjects who suffered from depression as well as by antidepressant regimens (4). Conversely, p11 regulates depression-like behaviors and/or responses to antidepressants (3,4). In particular, global p11 knockout mice show evidence of behavioral despair and anhedonia, consistent with a depressionlike phenotype (4). Likewise, focal viral transduction with RNA interference against p11 into accumbal neurons of wild-type mice causes depressive-like behaviors, whereas focal viral restoration of p11 exclusively within the nucleus accumbens of p11 knockout mice normalizes such behavioral responses (5). In this issue of Biological Psychiatry, Arango-Lievano et al. (6) hypothesized that p11 in nucleus accumbens would not only influence depression-like behaviors but also influence actions of cocaine in mice. Initially, they demonstrated that chronic intraperitoneal administration of cocaine reduced p11 messenger RNA and protein levels in the nucleus accumbens. There are two major classes of projection neurons in nucleus accumbens, which are distinguished by their expression of dopamine D1 receptors versus D2 receptors. Chronic cocaine reduced p11 in both classes of projection neurons. To determine the role of reduced accumbal p11 in cocaine dependence, combinations of mouse genetics and viral strategies were employed. p11 knockout mice showed enhanced cocaine conditioned place preference, which was reproduced by focal viral-mediated downregulation of p11 in the nucleus accumbens of wild-type mice. To distinguish the relative roles of p11 in D1 receptor- versus D2 receptorexpressing projection neurons in cocaine actions, ArangoLievano et al. (6) developed a novel Cre inducible viral vector to selectively express small hairpin RNAs against p11 downstream of a floxed STOP cassette. This new adeno-associated virus vector allows for conditional p11 gene downregulation when combined with cell-type specificity of bacterial artificial chromosome-Cre transgenic lines and the anatomical precision of stereotactic viral From the Center for Molecular Medicine, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden. Address correspondence to Per Svenningsson, M.D., Ph.D., Karolinska Institutet, Department of Clinical Neuroscience, Center for Molecular Medicine, CMML8:01, Stockholm 171 76, Sweden; E-mail: [email protected]. Received Aug 18, 2014; accepted Aug 19, 2014.
0006-3223/$36.00 http://dx.doi.org/10.1016/j.biopsych.2014.08.011
delivery. Using this sophisticated approach, it was demonstrated that specific silencing of p11 in D2-expressing projection neurons or choline acetyltransferase interneurons of nucleus accumbens did not have an effect on cocaine conditioned place preference. In contrast, specific silencing of p11 in D1-expressing projection neurons of nucleus accumbens increased cocaine conditioned place preference. These data demonstrate that p11 within D1expressing projection neurons of nucleus accumbens is a molecular determinant of cocaine dependence. p11 is an adaptor protein for several receptors and ion channels at the plasma membrane, as well as for intracellular trafficking proteins, enzymes, and transcription factors (3). p11 interacts with serotonin 1B (5-HT1B) receptors and increases their cell surface expression (4). 5-HT1B receptor knockout mice have been reported to show a shorter latency to develop selfadministration of cocaine than wild-type mice (7). However, opposite results were subsequently found with pharmacologic approaches, and it appears that compensatory changes have taken place during the development of the 5-HT1B knockout mice, which may have rendered these mice more vulnerable to cocaine (7). It has also been observed in rodent studies that dose, brain region, and treatment duration differentially influence the modulation of cocaine actions by 5-HT1B receptors. Thus, animal data on the role of 5-HT1B receptors in various aspects of cocaine dependence are complex. At the moment, the role of 5-HT1B receptors in human cocaine abuse is poorly understood. In this issue of Biological Psychiatry, Matuskey et al. (8) performed [11C]P943 positron emission tomography imaging, along with structural magnetic resonance imaging, to compare 5-HT1B receptor availability in subjects with cocaine dependence with age-matched healthy control subjects. [11C]P943 imaging was done in nine candidate regions, and after correcting for gray matter reductions in the frontal cortex of subjects with cocaine dependence, statistically significant reductions were found in the anterior cingulate cortex, frontal cortex, and hypothalamus. Interestingly, [11C]P943 imaging in patients with major depressive disorder is reduced in the ventral striatum and ventral pallidum when compared with control subjects (9). It may, therefore, turn out that reduced 5-HT1B receptor availability contributes to negative mood states observed in cocaine dependence. A caveat for the interpretation of reduced [11C]P943 binding potential is that it could be due to not only 5-HT1B downregulation but also higher levels of extracellular 5-HT. [11C]P943 has, indeed, been shown to be sensitive to endogenous 5-HT in nonhuman primates. Taken together, this issue of Biological Psychiatry presents two studies (6,8) on cocaine dependence that have examined molecular targets, p11 and 5-HT1B receptors, which have previously been shown to be downregulated in depression. Interestingly, both studies report that these molecular targets are downregulated also in response to cocaine dependence. Thus, reductions of p11 and 5-HT1B receptor availability appear to represent molecular maladaptations shared between depression and cocaine dependence. The detailed study of p11 in cocaine conditioned place preference in mice was focused on nucleus accumbens and it BIOL PSYCHIATRY 2014;76:763–764 & 2014 Society of Biological Psychiatry
764 BIOL PSYCHIATRY 2014;76:763–764 remains to be determined whether p11 plays a similar role in modulating cocaine responses in other limbic brain regions. Somewhat surprisingly, [11C]P943 imaging provided no evidence that 5-HT1B receptors are altered in the ventral striatum (i.e., nucleus accumbens of human subjects) in the cocaine addicts. However, within the same subjects, 5-HT1B receptors are reduced in regions interconnected with nucleus accumbens: hypothalamus, anterior cingulate cortex, and frontal cortex. The nucleus accumbens is, indeed, an integrative region of the reward system and receives dense glutamatergic innervation from hypothalamus, anterior cingulate, and frontal cortex. All these four regions express 5-HT1B receptors and p11 along with dopamine D1 receptors. As mentioned above, Arango-Lievano et al. (6) identified D1 receptor projecting neurons in nucleus accumbens as key mediators of the effects of p11 on cocaine reward. It is wellestablished that D1 receptors are critically involved in cocaine actions. Selective stimulation of D1 receptors is sufficient to support acquisition and maintenance of cocaine selfadministration behavior, whereas blockade of D1 receptors strongly attenuates the rewarding effects of cocaine. Moreover, optogenetic activation of D1-expressing accumbal neurons enhances cocaine conditioned place preference, whereas optogenetic activation of D2-expressing neurons in the same region attenuates cocaine conditioned place preference (10). D1 receptors are coupled to stimulatory G proteins and activate adenylate cyclase/cyclic adenosine monophosphate/cyclic adenosine monophosphate-dependent protein kinase to facilitate excitation of D1-expressing neurons. In contrast, 5-HT1B receptors are coupled to inhibitory G proteins and inhibit adenylate cyclase and neuronal excitability. The fact that both 5-HT1B receptor availability and p11 are downregulated in cocaine dependence suggests a model in which adenylate cyclase-mediated signaling and neuronal excitability are augmented in D1-expressing neurons. Based on data from pharmacologic and optogenetic experiments, such augmentation is likely to promote the development of cocaine dependence. It may therefore be beneficial to strengthen 5-HT1B signaling in D1expressing neurons to counteract cocaine dependence. Unlike alcoholism, opiate addiction, and cigarette smoking, there is currently no approved pharmacotherapy for cocaine abuse. The novel data presented here (6,8) provide a rationale for future studies of 5-HT1B receptor agonists and increased accumbal p11 against cocaine dependence, particularly when it is comorbid with depression. When designing future experiments, it shall be remembered that animal data indicate that 5-HT1B receptors have different roles depending on the stage of the
www.sobp.org/journal
Commentary cocaine addiction cycle. Moreover, selective targeting of individual molecules is rarely successful for the treatment of psychiatric disorders. A more feasible approach may be to include affinity toward 5-HT1B receptors in multireceptor compounds aimed for the treatment of cocaine dependence. Another research direction that will be interesting to follow is whether alterations of p11 levels and/or 5-HT1B receptor availability can be developed into reliable molecular biomarkers for distinct aspects of cocaine dependence that could be used for stratification or outcome measures in therapy trials. The author declares no biomedical financial interests or potential conflicts of interest. 1. Substance Abuse and Mental Health Services Administration (2013): Results from the 2012 National Survey on Drug Use and Health: Summary of National Findings. Rockville, MD: Substance Abuse and Mental Health Services Administration. NSDUH Series H-46, HHS Publication No. (SMA) 13–4795. 2. Conway KP, Compton W, Stinson FS, Grant BF (2006): Lifetime comorbidity of DSM-IV mood and anxiety disorders and specific drug use disorders: Results from the National Epidemiologic Survey on alcohol and related conditions. J Clin Psychiatry 67:247–257. 3. Svenningsson P, Kim Y, Warner-Schmidt J, Oh YS, Greengard P (2013): p11 and its role in depression and therapeutic responses to antidepressants. Nat Rev Neurosci 14:673–680. 4. Svenningsson P, Chergui K, Rachleff I, Flajolet M, Zhang X, El Yacoubi M, et al. (2006): Alterations in 5-HT1B receptor function by p11 in depression-like states. Science 311:77–80. 5. Alexander B, Warner-Schmidt J, Eriksson T, Tamminga C, ArangoLievano M, Ghose S, et al. (2010): Reversal of depressed behaviors in mice by p11 gene therapy in the nucleus accumbens. Sci Transl Med 2: 54ra76. 6. Arango-Lievano M, Schwarz JT, Vernov M, Wilkinson MB, Bradbury K, Feliz A, et al. (2014): Cell-type specific expression of p11 controls cocaine reward. Biol Psychiatry 76:794–801. 7. Castanon N, Scearce-Levie K, Lucas JJ, Rocha B, Hen R (2000): Modulation of the effects of cocaine by 5-HT1B receptors: A comparison of knockouts and antagonists. Pharmacol Biochem Behav 67:559–566. 8. Matuskey D, Bhagwagar Z, Planeta B, Pittman B, Gallezot J-D, Chen J, et al. (2014): Reductions in brain 5-HT1B receptor availability in primarily cocaine-dependent humans. Biol Psychiatry 76:816–822. 9. Murrough JW, Henry S, Hu J, Gallezot JD, Planeta-Wilson B, Neumaier JF, Neumeister A (2011): Reduced ventral striatal/ventral pallidal serotonin1B receptor binding potential in major depressive disorder. Psychopharmacology (Berl) 213:547–553. 10. Lobo MK, Covington HK 3rd, Chaudhury D, Friedman AK, Sun H, Damez-Werno D, et al. (2010): Cell type-specific loss of BDNF signaling mimics optogenetic control of cocaine reward. Science 330:385–390.
