ELEVATED tph2 mRNA EXPRESSION IN A RAT MODEL OF CHRONIC ANXIETY

Abstract

Background Allelic variations in TPH2, the gene encoding tryptophan hydroxylase 2, the rate-limiting enzyme for brain serotonin (5-HT) biosynthesis, may be genetic predictors of panic disorder and panic responses to panicogenic challenges in healthy volunteers. To test the hypothesis that tph2 mRNA is altered in chronic anxiety states, we measured tph2 expression in an established rat model of panic disorder. Methods We implanted 16 adult, male rats with bilateral guide cannulae and then primed them with daily injections of the corticotropin-releasing factor (CRF) receptor agonist, urocortin 1 (UCN1, 6 fmoles/100 nl per side, n = 8) or vehicle (n = 8) into the basolateral amygdaloid complex (BL) for 5 consecutive days. Anxiety-like behavior was assessed, 24 hr prior to and 48 hr following priming, in the social interaction (SI) test. A third group (n = 7) served as undisturbed home cage controls. All rats were killed 3 days after the last intra-BL injection to analyze tph2 and slc6a4 (gene encoding the serotonin transporter, SERT) mRNA expression in the dorsal raphe nucleus (DR), the main source of serotonergic projections to anxiety-related brain regions, using in situ hybridization histochemistry. Results UCN1 priming increased anxiety-related behavior in the SI test compared to vehicle-injected controls and elevated tph2, but not slc6a4, mRNA expression in DR subregions, including the ventrolateral DR/ventrolateral periaqueductal gray (DRVL/VLPAG), a subregion previously implicated in control of panic-related physiologic responses. Tph2 mRNA expression in the DRVL/VLPAG was correlated with increased anxiety-related behavior. Conclusion Our data support the hypothesis that chronic anxiety states are associated with dysregulated tph2 expression.

Differences in Anxiety-Like Behavior within a Batch of Wistar Rats Are Associated with Differences in Serotonergic Transmission, Enhanced by Acute SRI Administration, and Abolished By Serotonin Depletion

“…Our claim that LO animals are characterized by enhanced serotonergic activity is based mainly on the observation that they display enhanced expression of the gene encoding the rate-limiting enzyme for the synthesis of serotonin, TPH2, in the region where serotonergic cell bodies are situated, the raphe nuclei, and that this increase in TPH2 expression was confirmed by means of Western-blot assessment of the TPH2 protein. Our findings are in line with previous studies showing that raphe TPH2 expression is enhanced in rodents rendered anxious by genetic modulation of nonserotonergic genes ( Jahanshahi et al, 2011 ) or by subchronic infusion of a corticotropin-releasing agent into the basolateral amygdaloid complex ( Donner et al, 2012 ). Moreover, the importance of nongenetic factors in this context is illustrated by the observations that chronic restraint stress, maternal deprivation during early life combined with social defeat at adulthood, and neonatal administration of lipopolysaccharides are all interventions that produce both anxiety-like behavior in the EPM and elevated TPH2 expression in rodents ( Chamas et al, 1999 ; Gardner et al, 2009 ; Sidor et al, 2010 ).…”

Differences in Anxiety-Like Behavior within a Batch of Wistar Rats Are Associated with Differences in Serotonergic Transmission, Enhanced by Acute SRI Administration, and Abolished By Serotonin Depletion

“…Our claim that LO animals are characterized by enhanced serotonergic activity is based mainly on the observation that they display enhanced expression of the gene encoding the rate-limiting enzyme for the synthesis of serotonin, TPH2, in the region where serotonergic cell bodies are situated, the raphe nuclei, and that this increase in TPH2 expression was confirmed by means of Western-blot assessment of the TPH2 protein. Our findings are in line with previous studies showing that raphe TPH2 expression is enhanced in rodents rendered anxious by genetic modulation of nonserotonergic genes ( Jahanshahi et al, 2011 ) or by subchronic infusion of a corticotropin-releasing agent into the basolateral amygdaloid complex ( Donner et al, 2012 ). Moreover, the importance of nongenetic factors in this context is illustrated by the observations that chronic restraint stress, maternal deprivation during early life combined with social defeat at adulthood, and neonatal administration of lipopolysaccharides are all interventions that produce both anxiety-like behavior in the EPM and elevated TPH2 expression in rodents ( Chamas et al, 1999 ; Gardner et al, 2009 ; Sidor et al, 2010 ).…”

Development×environment interactions control tph2 mRNA expression

“…The regionally specific pattern of altered tph2 mRNA expression in female rats exposed to adolescent social isolation, selectively in the DRVL/VLPAG and DRV serotonergic neurons, in this study is identical to the regionally specific pattern of altered tph2 mRNA expression following amygdala priming (Donner et al, 2012). In the amygdala priming model, the chronic anxiety-like state is dependent on disinhibition of projection neurons in the basolateral amygdala, following a reduction of local GABAergic inhibition (Rainnie et al, 2004).…”

“…A similar dissociation between control of tph2 and slc6a4 mRNA expression in the DRVL/VLPAG and DRV was found in a model of amygdala priming (Donner et al, 2012). Briefly, amygdala priming increased tph2 mRNA expression selectively in the DRV and DRVL/VLPAG subregions of the DR, while it had no effect on slc6a4 mRNA expression in these subregions (Donner et al, 2012).…”

“…A similar dissociation between control of tph2 and slc6a4 mRNA expression in the DRVL/VLPAG and DRV was found in a model of amygdala priming (Donner et al, 2012). Briefly, amygdala priming increased tph2 mRNA expression selectively in the DRV and DRVL/VLPAG subregions of the DR, while it had no effect on slc6a4 mRNA expression in these subregions (Donner et al, 2012). Characterizing mechanisms underlying selective control of tph2 mRNA expression, in the absence of changes in slc6a4 or htr1a mRNA expression, in two animal models thought to involve disinhibition of the amygdala is an important goal for future studies.…”

Crh receptor priming in the bed nucleus of the stria terminalis (BNST) induces tph2 gene expression in the dorsomedial dorsal raphe nucleus and chronic anxiety

“…One limitation of the current study is that we limited our assessment to analysis of tph2 and slc6a4 mRNA expression, and did not extend this finding to confirm effects of intra-BNST Ucn1 priming on Tph2 and Slc6a4 protein. Although, in previous studies, we have observed parallel effects of treatment, i.e., chronic administration of the glucocorticoid hormone, corticosterone, on tph2 mRNA expression, Tph2 protein expression, and Tph2 activity in the dorsomedial DR (Donner et al, 2012a;Donner et al, 2016), future studies should also evaluate Tph2 protein expression and Tph2 activity within the dorsomedial DR following intra-BNST priming.…”

Differences in Anxiety-Like Behavior within a Batch of Wistar Rats Are Associated with Differences in Serotonergic Transmission, Enhanced by Acute SRI Administration, and Abolished By Serotonin Depletion

“…Our claim that LO animals are characterized by enhanced serotonergic activity is based mainly on the observation that they display enhanced expression of the gene encoding the rate-limiting enzyme for the synthesis of serotonin, TPH2, in the region where serotonergic cell bodies are situated, the raphe nuclei, and that this increase in TPH2 expression was confirmed by means of Western-blot assessment of the TPH2 protein. Our findings are in line with previous studies showing that raphe TPH2 expression is enhanced in rodents rendered anxious by genetic modulation of nonserotonergic genes ( Jahanshahi et al, 2011 ) or by subchronic infusion of a corticotropin-releasing agent into the basolateral amygdaloid complex ( Donner et al, 2012 ). Moreover, the importance of nongenetic factors in this context is illustrated by the observations that chronic restraint stress, maternal deprivation during early life combined with social defeat at adulthood, and neonatal administration of lipopolysaccharides are all interventions that produce both anxiety-like behavior in the EPM and elevated TPH2 expression in rodents ( Chamas et al, 1999 ; Gardner et al, 2009 ; Sidor et al, 2010 ).…”

Development×environment interactions control tph2 mRNA expression

“…The regionally specific pattern of altered tph2 mRNA expression in female rats exposed to adolescent social isolation, selectively in the DRVL/VLPAG and DRV serotonergic neurons, in this study is identical to the regionally specific pattern of altered tph2 mRNA expression following amygdala priming (Donner et al, 2012). In the amygdala priming model, the chronic anxiety-like state is dependent on disinhibition of projection neurons in the basolateral amygdala, following a reduction of local GABAergic inhibition (Rainnie et al, 2004).…”

“…A similar dissociation between control of tph2 and slc6a4 mRNA expression in the DRVL/VLPAG and DRV was found in a model of amygdala priming (Donner et al, 2012). Briefly, amygdala priming increased tph2 mRNA expression selectively in the DRV and DRVL/VLPAG subregions of the DR, while it had no effect on slc6a4 mRNA expression in these subregions (Donner et al, 2012).…”

“…A similar dissociation between control of tph2 and slc6a4 mRNA expression in the DRVL/VLPAG and DRV was found in a model of amygdala priming (Donner et al, 2012). Briefly, amygdala priming increased tph2 mRNA expression selectively in the DRV and DRVL/VLPAG subregions of the DR, while it had no effect on slc6a4 mRNA expression in these subregions (Donner et al, 2012). Characterizing mechanisms underlying selective control of tph2 mRNA expression, in the absence of changes in slc6a4 or htr1a mRNA expression, in two animal models thought to involve disinhibition of the amygdala is an important goal for future studies.…”

Crh receptor priming in the bed nucleus of the stria terminalis (BNST) induces tph2 gene expression in the dorsomedial dorsal raphe nucleus and chronic anxiety

“…One limitation of the current study is that we limited our assessment to analysis of tph2 and slc6a4 mRNA expression, and did not extend this finding to confirm effects of intra-BNST Ucn1 priming on Tph2 and Slc6a4 protein. Although, in previous studies, we have observed parallel effects of treatment, i.e., chronic administration of the glucocorticoid hormone, corticosterone, on tph2 mRNA expression, Tph2 protein expression, and Tph2 activity in the dorsomedial DR (Donner et al, 2012a;Donner et al, 2016), future studies should also evaluate Tph2 protein expression and Tph2 activity within the dorsomedial DR following intra-BNST priming.…”

Differences in Anxiety-Like Behavior within a Batch of Wistar Rats Are Associated with Differences in Serotonergic Transmission, Enhanced by Acute SRI Administration, and Abolished By Serotonin Depletion

“…Our claim that LO animals are characterized by enhanced serotonergic activity is based mainly on the observation that they display enhanced expression of the gene encoding the rate-limiting enzyme for the synthesis of serotonin, TPH2, in the region where serotonergic cell bodies are situated, the raphe nuclei, and that this increase in TPH2 expression was confirmed by means of Western-blot assessment of the TPH2 protein. Our findings are in line with previous studies showing that raphe TPH2 expression is enhanced in rodents rendered anxious by genetic modulation of nonserotonergic genes ( Jahanshahi et al, 2011 ) or by subchronic infusion of a corticotropin-releasing agent into the basolateral amygdaloid complex ( Donner et al, 2012 ). Moreover, the importance of nongenetic factors in this context is illustrated by the observations that chronic restraint stress, maternal deprivation during early life combined with social defeat at adulthood, and neonatal administration of lipopolysaccharides are all interventions that produce both anxiety-like behavior in the EPM and elevated TPH2 expression in rodents ( Chamas et al, 1999 ; Gardner et al, 2009 ; Sidor et al, 2010 ).…”

Development×environment interactions control tph2 mRNA expression

“…The regionally specific pattern of altered tph2 mRNA expression in female rats exposed to adolescent social isolation, selectively in the DRVL/VLPAG and DRV serotonergic neurons, in this study is identical to the regionally specific pattern of altered tph2 mRNA expression following amygdala priming (Donner et al, 2012). In the amygdala priming model, the chronic anxiety-like state is dependent on disinhibition of projection neurons in the basolateral amygdala, following a reduction of local GABAergic inhibition (Rainnie et al, 2004).…”

“…A similar dissociation between control of tph2 and slc6a4 mRNA expression in the DRVL/VLPAG and DRV was found in a model of amygdala priming (Donner et al, 2012). Briefly, amygdala priming increased tph2 mRNA expression selectively in the DRV and DRVL/VLPAG subregions of the DR, while it had no effect on slc6a4 mRNA expression in these subregions (Donner et al, 2012).…”

“…A similar dissociation between control of tph2 and slc6a4 mRNA expression in the DRVL/VLPAG and DRV was found in a model of amygdala priming (Donner et al, 2012). Briefly, amygdala priming increased tph2 mRNA expression selectively in the DRV and DRVL/VLPAG subregions of the DR, while it had no effect on slc6a4 mRNA expression in these subregions (Donner et al, 2012). Characterizing mechanisms underlying selective control of tph2 mRNA expression, in the absence of changes in slc6a4 or htr1a mRNA expression, in two animal models thought to involve disinhibition of the amygdala is an important goal for future studies.…”

Crh receptor priming in the bed nucleus of the stria terminalis (BNST) induces tph2 gene expression in the dorsomedial dorsal raphe nucleus and chronic anxiety

“…One limitation of the current study is that we limited our assessment to analysis of tph2 and slc6a4 mRNA expression, and did not extend this finding to confirm effects of intra-BNST Ucn1 priming on Tph2 and Slc6a4 protein. Although, in previous studies, we have observed parallel effects of treatment, i.e., chronic administration of the glucocorticoid hormone, corticosterone, on tph2 mRNA expression, Tph2 protein expression, and Tph2 activity in the dorsomedial DR (Donner et al, 2012a;Donner et al, 2016), future studies should also evaluate Tph2 protein expression and Tph2 activity within the dorsomedial DR following intra-BNST priming.…”