Modified receptor internalization upon coexpression of 5-HT1B receptor and 5-HT2B receptors.
ABSTRACT Serotonin 5-HT(2B) receptors are often coexpressed with 5-HT(1B) receptors, and cross-talk between the two receptors has been reported in various cell types. However, many mechanistic details underlying 5-HT(1B) and 5-HT(2B) receptor cross-talk have not been elucidated. We hypothesized that 5-HT(2B) and 5-HT(1B) receptors each affect the others' signaling by modulating the others' trafficking. We thus examined the agonist stimulated internalization kinetics of fluorescent protein-tagged 5-HT(2B) and 5-HT(1B) receptors when expressed alone and upon coexpression in LMTK(-) murine fibroblasts. Time-lapse confocal microscopy and whole-cell radioligand binding analyses revealed that, when expressed alone, 5-HT(2B) and 5-HT(1B) receptors displayed distinct half-lives. Upon coexpression, serotonin-induced internalization of 5-HT(2B) receptors was accelerated 5-fold and was insensitive to a 5-HT(2B) receptor antagonist. In this context, 5-HT(2B) receptors did internalize in response to a 5-HT(1B) receptor agonist. In contrast, co-expression did not render 5-HT(1B) receptor internalization sensitive to a 5-HT(2B) receptor agonist. The altered internalization kinetics of both receptors upon coexpression was probably not due to direct interaction because only low levels of colocalization were observed. Antibody knockdown experiments revealed that internalization of 5-HT(1B) receptors (expressed alone) was entirely clathrin-independent and Caveolin1-dependent, whereas that of 5-HT(2B) receptors (expressed alone) was Caveolin1-independent and clathrin-dependent. Upon coexpression, serotonin-induced 5-HT(2B) receptor internalization became partially Caveolin1-dependent, and serotonin-induced 5-HT(1B) receptor internalization became entirely Caveolin1-independent in a protein kinase Cepsilon-dependent fashion. In conclusion, these data demonstrate that coexpression of 5-HT(1B) and 5-HT(2B) receptors influences the internalization pathways and kinetics of both receptors.
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ABSTRACT: Neurotransmission by serotonin (5-HT) is tightly regulated by several autoreceptors that fine-tune serotonergic neurotransmission through negative feedback inhibition at the cell bodies (predominantly 5-HT(1A)) or at the axon terminals (predominantly 5-HT(1B)); however, more subtle roles for 5-HT(1D) and 5-HT(2B) autoreceptors have also been detected. This review provides an overview of 5-HT autoreceptors, focusing on their contribution in animal behavioral models of stress and emotion. Experiments targeting 5-HT autoreceptors in awake, behaving animals have generally shown that increasing autoreceptor feedback is anxiolytic and rewarding, while enhanced 5-HT function is aversive and anxiogenic; however, the role of serotonergic activity in behavioral models of helplessness is more complex. The prevailing model suggests that 5-HT autoreceptors become desensitized in response to stress exposure and antidepressant administration, two seemingly opposite manipulations. Thus there are still unresolved questions regarding the role of these receptors-and serotonin in general-in normal and pathological states.Journal of chemical neuroanatomy 05/2011; 41(4):234-46. · 1.75 Impact Factor
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ABSTRACT: The main objective of the current study was to determine the sensitivity of the positron emission tomography (PET) radioligand [¹¹C]P943 to fenfluramine-induced changes in endogenous 5-HT in nonhuman primate brain. Fenfluramine-induced changes in 5-HT(1B) occupancy were compared to those obtained by self-block with unlabeled P943. Two baboons and 1 rhesus monkey were given preblocking or displacing doses of fenfluramine (1-5 mg/kg) or preblocking doses of unlabeled P943 (0.2 mg/kg) and imaged with [¹¹C]P943 PET. Receptor occupancy by the low dose of fenfluramine (1 mg/kg) in the baboons was 25 and 29% and by the high dose of fenfluramine (5 mg/kg) in the rhesus macaque was 42%. Receptor occupancy by P943 (0.2 mg/kg) was 68 and 86% in the baboons. PET imaging of 5-HT(1B) receptors with [¹¹C]P943 may be a useful approach for measuring changes in endogenous 5-HT in the living human brain.Synapse 04/2011; 65(10):1113-7. · 2.31 Impact Factor
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ABSTRACT: Serotonergic dysfunction is implicated in the pathogenesis of posttraumatic stress disorder (PTSD), and recent animal models suggest that disturbances in serotonin type 1B receptor function, in particular, may contribute to chronic anxiety. However, the specific role of the serotonin type 1B receptor has not been studied in patients with PTSD. To investigate in vivo serotonin type 1B receptor expression in individuals with PTSD, trauma-exposed control participants without PTSD (TC), and healthy (non-trauma-exposed) control participants (HC) using positron emission tomography and the recently developed serotonin type 1B receptor selective radiotracer [(11)C]P943. Cross-sectional positron emission tomography study under resting conditions. Academic and Veterans Affairs medical centers. Ninety-six individuals in 3 study groups: PTSD (n = 49), TC (n = 20), and HC (n = 27). Main Outcome Measure Regional [(11)C]P943 binding potential (BP(ND)) values in an a priori-defined limbic corticostriatal circuit investigated using multivariate analysis of variance and multiple regression analysis. A history of severe trauma exposure in the PTSD and TC groups was associated with marked reductions in [(11)C]P943 BP(ND) in the caudate, the amygdala, and the anterior cingulate cortex. Participant age at first trauma exposure was strongly associated with low [(11)C]P943 BP(ND). Developmentally earlier trauma exposure also was associated with greater PTSD symptom severity and major depression comorbidity. These data suggest an enduring effect of trauma history on brain function and the phenotype of PTSD. The association of early age at first trauma and more pronounced neurobiological and behavioral alterations in PTSD suggests a developmental component in the cause of PTSD.Archives of general psychiatry 09/2011; 68(9):892-900. · 12.26 Impact Factor