Reed Carroll - Academia.edu (original) (raw)
Papers by Reed Carroll
Current Biology, 1995
Background: One of the principal mechanisms by which G-protein-coupled receptors evoke cellular r... more Background: One of the principal mechanisms by which G-protein-coupled receptors evoke cellular responses is through the activation of phospholipase C (PLC) and the subsequent release of Ca 2+ from intracellular stores. Receptors that couple to pertussis toxin (PTX)-insensitive G proteins typically evoke large increases in PLC activity and intracellular Ca 2 + release. In contrast, receptors that use only PTX-sensitive G proteins usually generate weak PLC-dependent responses, but efficiently regulate a second effector enzyme, adenylyl cyclase. For example, in many cell types, agonist binding by the m4 muscarinic acetylcholine receptor (m4 receptor) results in a strong inhibition of adenylyl cyclase and very little stimulation of PLC activity or release of intracellular Ca 2+. We have investigated whether the weak, PTX-sensitive stimulation of PLC activity by the m4 receptor can play a significant role in the generation of cellular responses. Results: We report here that PTX-sensitive Ca 2+ release mediated by the m4 receptor in transfected Chinese hamster ovary cells is greatly enhanced when endogenous purinergic receptors simultaneously activate a PTX-insensitive signaling pathway. Furthermore, m4-receptor-induced transcription of the c-fos gene (a Ca 2 +-sensitive response) is similarly potentiated when purinergic receptors are coactivated. These enhanced m4-receptor-dependent Ca 2 + responses do not require an influx of external Ca 2+ , and occur in the absence of detectable purinergic-receptorstimulated Ca 2+ release; they apparently require the activation of both PTX-sensitive and PTX-insensitive G-protein pathways. Measurements of phosphoinositide hydrolysis indicate that the enhancement of m4-receptormediated Ca 2 + signaling by purinergic receptors is due to a synergistic increase in agonist-stimulated PLC activity. Conclusions: These studies demonstrate that the potency of m4-receptor-mediated PLC signaling is highly dependent upon the presence or absence of other PLCactivating agonists. The ability of the m4 receptor to evoke a strong, but conditional, activation of PLC may allow this type of receptor to participate in a coincidence-detection system that amplifies simultaneous PLC-activating signals through a mechanism involving crosstalk between PTXsensitive and PTX-insensitive G-protein pathways.
Current Opinion in Neurobiology, 2011
Experience-dependent modifications of neural circuits and function are believed to heavily depend... more Experience-dependent modifications of neural circuits and function are believed to heavily depend on changes in synaptic efficacy such as LTP/LTD. Hence, much effort has been devoted to elucidating the mechanisms underlying these forms of synaptic plasticity. While most of this work has focused on excitatory synapses, it is now clear that diverse mechanisms of long-term inhibitory plasticity have evolved to provide additional flexibility to neural circuits. By changing the excitatory/inhibitory balance, GABAergic plasticity can regulate excitability, neural circuit function and ultimately, contribute to learning and memory, and neural circuit refinement. Here we discuss recent advancements in our understanding of the mechanisms and functional relevance of GABAergic inhibitory synaptic plasticity.
Development of Patient-Specific Neurons in Schizophrenia Using Induced Pluripotent Stem Cells
Journal of Neurogenetics, 2011
Induced pluripotent stem cell (iPSC) technology has the potential to transform regenerative medic... more Induced pluripotent stem cell (iPSC) technology has the potential to transform regenerative medicine. It also offers a powerful tool for establishing in vitro models of disease, in particular, for neuropsychiatric disorders where live human neurons are essentially impossible to procure. Using iPSCs derived from three schizophrenia (SZ) patients, one of whom has 22q11.2del (velocardiofacial syndrome; VCFS), the authors developed a culture system to study SZ on a molecular and cellular level. SZ iPSCs were differentiated into functional, primarily glutamatergic neurons that were able to fire action potentials after ∼8 weeks in culture. Early differentiating neurons expressed a number of transcription factors/chromatin remodeling proteins and synaptic proteins relevant to SZ pathogenesis, including ZNF804A, RELN, CNTNAP2, CTNNA2, SMARCA2, and NRXN1. Although a small number of lines were developed in this preliminary study, the SZ line containing 22q11.2del showed a significant delay in the reduction of endogenous OCT4 and NANOG expression that normally occurs during differentiation. Constitutive expression of OCT4 has been observed in Dgcr8-deficient mouse embryonic stem cells (mESCs); DGCR8 maps to the 22q11.2-deleted region. These findings demonstrate that the method of inducing neural differentiation employed is useful for disease modeling in SZ and that the transition of iPSCs with 22q11.2 deletions towards a differentiated state may be marked by subtle changes in expression of pluripotency-associated genes.
Current Opinion in Neurobiology, 2011
Experience-dependent modifications of neural circuits and function are believed to heavily depend... more Experience-dependent modifications of neural circuits and function are believed to heavily depend on changes in synaptic efficacy such as LTP/LTD. Hence, much effort has been devoted to elucidating the mechanisms underlying these forms of synaptic plasticity. Although most of this work has focused on excitatory synapses, it is now clear that diverse mechanisms of long-term inhibitory plasticity have evolved to provide additional flexibility to neural circuits. By changing the excitatory/inhibitory balance, GABAergic plasticity can regulate excitability, neural circuit function and ultimately, contribute to learning and memory, and neural circuit refinement. Here we discuss recent advancements in our understanding of the mechanisms and functional relevance of GABAergic inhibitory synaptic plasticity.
Proceedings of the National Academy of Sciences, 2012
Proceedings of the National Academy of Sciences, 2010
Ca 2+ /Calmodulin protein kinase IIα (CaMKIIα) has a central role in regulating neuronal excitabi... more Ca 2+ /Calmodulin protein kinase IIα (CaMKIIα) has a central role in regulating neuronal excitability. It is well established that CaMKIIα translocates to excitatory synapses following strong glutamatergic stimuli that induce NMDA-receptor (NMDAR)-dependent longterm potentiation in CA1 hippocampal neurons. We now show that CaMKIIα translocates to inhibitory but not excitatory synapses in response to more moderate NMDAR-activating stimuli that trigger GABA A-receptor (GABA A R) insertion and enhance inhibitory transmission. Such moderate NMDAR activation causes Thr286 autophosphorylation of CaMKIIα, which our results demonstrate is necessary and sufficient, under basal conditions, to localize CaMKIIα at inhibitory synapses and enhance surface GABA A R expression. Although stronger glutamatergic stimulation coupled to AMPA receptor insertion also elicits Thr286 autophosphorylation, accumulation of CaMKIIα at inhibitory synapses is prevented under these conditions by the phosphatase calcineurin. This preferential targeting of CaMKIIα to glutamatergic or GABAergic synapses provides neurons with a mechanism whereby activity can selectively potentiate excitation or inhibition through a single kinase mediator.
The EMBO Journal, 1998
Several types of transmembrane receptors regulate cellular responses through the activation of ph... more Several types of transmembrane receptors regulate cellular responses through the activation of phospholipase C-mediated Ca 2ϩ release from intracellular stores. In non-excitable cells, the initial Ca 2ϩ release is typically followed by a prolonged Ca 2ϩ influx phase that is important for the regulation of several Ca 2ϩsensitive responses. Here we describe an agonist concentration-dependent mechanism by which m3 muscarinic acetylcholine receptors (mAChRs) differentially regulate the magnitude of the release and influx components of a Ca 2ϩ response. In transfected Chinese hamster ovary cells expressing m3 mAChRs, doses of the muscarinic agonist carbachol ranging from 100 nM to 1 mM evoked Ca 2ϩ release responses of increasing magnitude; maximal Ca 2ϩ release was elicited by the highest carbachol concentration. In contrast, Ca 2ϩ influx was maximal when m3 mAChRs were activated by moderate doses (1-10 μM) of carbachol, but substantially reduced at higher agonist concentrations. Manipulation of the membrane potential revealed that the carbachol-induced Ca 2ϩ influx phase was diminished at depolarized potentials. Importantly, carbachol doses above 10 μM were found to couple m3 mAChRs to the activation of an inward, monovalent cation current resulting in depolarization of the cell membrane and a selective decrease in the influx, but not release, component of the Ca 2ϩ response. These studies demonstrate, in one experimental system, a mechanism by which a single subtype of G-protein-coupled receptor can utilize the information encoded in the concentration of an agonist to generate distinct intracellular Ca 2ϩ signals.
Rapid redistribution of glutamate receptors contributes to long-term depression in hippocampal cultures
Synaptic strength can be altered by a variety of pre- or postsynaptic modifications. Here we test... more Synaptic strength can be altered by a variety of pre- or postsynaptic modifications. Here we test the hypothesis that long-term depression (LTD) involves a decrease in the number of glutamate receptors that are clustered at individual synapses in primary cultures of hippocampal neurons. Similar to a prominent form of LTD observed in hippocampal slices, LTD in hippocampal cultures required NMDA receptor activation and was accompanied by a decrease in the amplitude and frequency of miniature excitatory postsynaptic currents. Immunocytochemical analysis revealed that induction of LTD caused a concurrent decrease in the number of AMPA receptors clustered at synapses but had no effect on synaptic NMDA receptor clusters. These results suggest that a subtype-specific redistribution of synaptic glutamate receptors contributes to NMDA receptor-dependent LTD.
FEBS Letters, 1993
stimulation of the m3 or m2 muscarinic receptor expressed in Xenopus lurris oocytes Induces eithe... more stimulation of the m3 or m2 muscarinic receptor expressed in Xenopus lurris oocytes Induces either a fast transient or slowly oscillating calcmm-sensitive chloride current. The speed of these currents reflects the efficiency of receptor coupling to guanine nucleotide-bmding proteins and phosphatidylinositol (PI) turnover. Point mutations of the m3 receptor were made in a region of the third cytoplasmic loop to test whether receptor function relied on an a-helical structure of the G protein-coupling domain. Prolme substitution for glutamate at position 257 disrupted the m3 response. Also, smgle alanine msertions between residues 259 and 260 disrupted the m3 receptor-stimulated response while double alanme insertions at this site had no effect. Based on these results, we suggest that a region of the third cytoplasmic loop of the m3 receptor possesses an amphipathic a-helical conformation. Xenopus oocyte; G protem-coupling. Amphipathic a-helix; Seven transmembrane-spannmg receptors, Mastoparan
Current Biology, 1995
Background: One of the principal mechanisms by which G-protein-coupled receptors evoke cellular r... more Background: One of the principal mechanisms by which G-protein-coupled receptors evoke cellular responses is through the activation of phospholipase C (PLC) and the subsequent release of Ca 2+ from intracellular stores. Receptors that couple to pertussis toxin (PTX)-insensitive G proteins typically evoke large increases in PLC activity and intracellular Ca 2 + release. In contrast, receptors that use only PTX-sensitive G proteins usually generate weak PLC-dependent responses, but efficiently regulate a second effector enzyme, adenylyl cyclase. For example, in many cell types, agonist binding by the m4 muscarinic acetylcholine receptor (m4 receptor) results in a strong inhibition of adenylyl cyclase and very little stimulation of PLC activity or release of intracellular Ca 2+. We have investigated whether the weak, PTX-sensitive stimulation of PLC activity by the m4 receptor can play a significant role in the generation of cellular responses. Results: We report here that PTX-sensitive Ca 2+ release mediated by the m4 receptor in transfected Chinese hamster ovary cells is greatly enhanced when endogenous purinergic receptors simultaneously activate a PTX-insensitive signaling pathway. Furthermore, m4-receptor-induced transcription of the c-fos gene (a Ca 2 +-sensitive response) is similarly potentiated when purinergic receptors are coactivated. These enhanced m4-receptor-dependent Ca 2 + responses do not require an influx of external Ca 2+ , and occur in the absence of detectable purinergic-receptorstimulated Ca 2+ release; they apparently require the activation of both PTX-sensitive and PTX-insensitive G-protein pathways. Measurements of phosphoinositide hydrolysis indicate that the enhancement of m4-receptormediated Ca 2 + signaling by purinergic receptors is due to a synergistic increase in agonist-stimulated PLC activity. Conclusions: These studies demonstrate that the potency of m4-receptor-mediated PLC signaling is highly dependent upon the presence or absence of other PLCactivating agonists. The ability of the m4 receptor to evoke a strong, but conditional, activation of PLC may allow this type of receptor to participate in a coincidence-detection system that amplifies simultaneous PLC-activating signals through a mechanism involving crosstalk between PTXsensitive and PTX-insensitive G-protein pathways.
Current Opinion in Neurobiology, 2011
Experience-dependent modifications of neural circuits and function are believed to heavily depend... more Experience-dependent modifications of neural circuits and function are believed to heavily depend on changes in synaptic efficacy such as LTP/LTD. Hence, much effort has been devoted to elucidating the mechanisms underlying these forms of synaptic plasticity. While most of this work has focused on excitatory synapses, it is now clear that diverse mechanisms of long-term inhibitory plasticity have evolved to provide additional flexibility to neural circuits. By changing the excitatory/inhibitory balance, GABAergic plasticity can regulate excitability, neural circuit function and ultimately, contribute to learning and memory, and neural circuit refinement. Here we discuss recent advancements in our understanding of the mechanisms and functional relevance of GABAergic inhibitory synaptic plasticity.
Development of Patient-Specific Neurons in Schizophrenia Using Induced Pluripotent Stem Cells
Journal of Neurogenetics, 2011
Induced pluripotent stem cell (iPSC) technology has the potential to transform regenerative medic... more Induced pluripotent stem cell (iPSC) technology has the potential to transform regenerative medicine. It also offers a powerful tool for establishing in vitro models of disease, in particular, for neuropsychiatric disorders where live human neurons are essentially impossible to procure. Using iPSCs derived from three schizophrenia (SZ) patients, one of whom has 22q11.2del (velocardiofacial syndrome; VCFS), the authors developed a culture system to study SZ on a molecular and cellular level. SZ iPSCs were differentiated into functional, primarily glutamatergic neurons that were able to fire action potentials after ∼8 weeks in culture. Early differentiating neurons expressed a number of transcription factors/chromatin remodeling proteins and synaptic proteins relevant to SZ pathogenesis, including ZNF804A, RELN, CNTNAP2, CTNNA2, SMARCA2, and NRXN1. Although a small number of lines were developed in this preliminary study, the SZ line containing 22q11.2del showed a significant delay in the reduction of endogenous OCT4 and NANOG expression that normally occurs during differentiation. Constitutive expression of OCT4 has been observed in Dgcr8-deficient mouse embryonic stem cells (mESCs); DGCR8 maps to the 22q11.2-deleted region. These findings demonstrate that the method of inducing neural differentiation employed is useful for disease modeling in SZ and that the transition of iPSCs with 22q11.2 deletions towards a differentiated state may be marked by subtle changes in expression of pluripotency-associated genes.
Current Opinion in Neurobiology, 2011
Experience-dependent modifications of neural circuits and function are believed to heavily depend... more Experience-dependent modifications of neural circuits and function are believed to heavily depend on changes in synaptic efficacy such as LTP/LTD. Hence, much effort has been devoted to elucidating the mechanisms underlying these forms of synaptic plasticity. Although most of this work has focused on excitatory synapses, it is now clear that diverse mechanisms of long-term inhibitory plasticity have evolved to provide additional flexibility to neural circuits. By changing the excitatory/inhibitory balance, GABAergic plasticity can regulate excitability, neural circuit function and ultimately, contribute to learning and memory, and neural circuit refinement. Here we discuss recent advancements in our understanding of the mechanisms and functional relevance of GABAergic inhibitory synaptic plasticity.
Proceedings of the National Academy of Sciences, 2012
Proceedings of the National Academy of Sciences, 2010
Ca 2+ /Calmodulin protein kinase IIα (CaMKIIα) has a central role in regulating neuronal excitabi... more Ca 2+ /Calmodulin protein kinase IIα (CaMKIIα) has a central role in regulating neuronal excitability. It is well established that CaMKIIα translocates to excitatory synapses following strong glutamatergic stimuli that induce NMDA-receptor (NMDAR)-dependent longterm potentiation in CA1 hippocampal neurons. We now show that CaMKIIα translocates to inhibitory but not excitatory synapses in response to more moderate NMDAR-activating stimuli that trigger GABA A-receptor (GABA A R) insertion and enhance inhibitory transmission. Such moderate NMDAR activation causes Thr286 autophosphorylation of CaMKIIα, which our results demonstrate is necessary and sufficient, under basal conditions, to localize CaMKIIα at inhibitory synapses and enhance surface GABA A R expression. Although stronger glutamatergic stimulation coupled to AMPA receptor insertion also elicits Thr286 autophosphorylation, accumulation of CaMKIIα at inhibitory synapses is prevented under these conditions by the phosphatase calcineurin. This preferential targeting of CaMKIIα to glutamatergic or GABAergic synapses provides neurons with a mechanism whereby activity can selectively potentiate excitation or inhibition through a single kinase mediator.
The EMBO Journal, 1998
Several types of transmembrane receptors regulate cellular responses through the activation of ph... more Several types of transmembrane receptors regulate cellular responses through the activation of phospholipase C-mediated Ca 2ϩ release from intracellular stores. In non-excitable cells, the initial Ca 2ϩ release is typically followed by a prolonged Ca 2ϩ influx phase that is important for the regulation of several Ca 2ϩsensitive responses. Here we describe an agonist concentration-dependent mechanism by which m3 muscarinic acetylcholine receptors (mAChRs) differentially regulate the magnitude of the release and influx components of a Ca 2ϩ response. In transfected Chinese hamster ovary cells expressing m3 mAChRs, doses of the muscarinic agonist carbachol ranging from 100 nM to 1 mM evoked Ca 2ϩ release responses of increasing magnitude; maximal Ca 2ϩ release was elicited by the highest carbachol concentration. In contrast, Ca 2ϩ influx was maximal when m3 mAChRs were activated by moderate doses (1-10 μM) of carbachol, but substantially reduced at higher agonist concentrations. Manipulation of the membrane potential revealed that the carbachol-induced Ca 2ϩ influx phase was diminished at depolarized potentials. Importantly, carbachol doses above 10 μM were found to couple m3 mAChRs to the activation of an inward, monovalent cation current resulting in depolarization of the cell membrane and a selective decrease in the influx, but not release, component of the Ca 2ϩ response. These studies demonstrate, in one experimental system, a mechanism by which a single subtype of G-protein-coupled receptor can utilize the information encoded in the concentration of an agonist to generate distinct intracellular Ca 2ϩ signals.
Rapid redistribution of glutamate receptors contributes to long-term depression in hippocampal cultures
Synaptic strength can be altered by a variety of pre- or postsynaptic modifications. Here we test... more Synaptic strength can be altered by a variety of pre- or postsynaptic modifications. Here we test the hypothesis that long-term depression (LTD) involves a decrease in the number of glutamate receptors that are clustered at individual synapses in primary cultures of hippocampal neurons. Similar to a prominent form of LTD observed in hippocampal slices, LTD in hippocampal cultures required NMDA receptor activation and was accompanied by a decrease in the amplitude and frequency of miniature excitatory postsynaptic currents. Immunocytochemical analysis revealed that induction of LTD caused a concurrent decrease in the number of AMPA receptors clustered at synapses but had no effect on synaptic NMDA receptor clusters. These results suggest that a subtype-specific redistribution of synaptic glutamate receptors contributes to NMDA receptor-dependent LTD.
FEBS Letters, 1993
stimulation of the m3 or m2 muscarinic receptor expressed in Xenopus lurris oocytes Induces eithe... more stimulation of the m3 or m2 muscarinic receptor expressed in Xenopus lurris oocytes Induces either a fast transient or slowly oscillating calcmm-sensitive chloride current. The speed of these currents reflects the efficiency of receptor coupling to guanine nucleotide-bmding proteins and phosphatidylinositol (PI) turnover. Point mutations of the m3 receptor were made in a region of the third cytoplasmic loop to test whether receptor function relied on an a-helical structure of the G protein-coupling domain. Prolme substitution for glutamate at position 257 disrupted the m3 response. Also, smgle alanine msertions between residues 259 and 260 disrupted the m3 receptor-stimulated response while double alanme insertions at this site had no effect. Based on these results, we suggest that a region of the third cytoplasmic loop of the m3 receptor possesses an amphipathic a-helical conformation. Xenopus oocyte; G protem-coupling. Amphipathic a-helix; Seven transmembrane-spannmg receptors, Mastoparan