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Biomedical subjects

Pablo E Castillo

Publications and source records attributed to Pablo E Castillo.

13 recordsLinked to original sources
PubMed2025

Chaperone-mediated autophagy regulates neuronal activity by sex-specific remodelling of the synaptic proteome.

Chaperone-mediated autophagy (CMA) declines in ageing and neurodegenerative diseases. Loss of CMA in neurons leads to neurodegeneration and behavioural changes in mice but the role of CMA in neuronal physiology is largely unknown. Here we show that CMA deficiency causes neuronal hyperactivity, increased seizure susceptibility and disrupted calcium homeostasis. Pre-synaptic neurotransmitter release and NMDA receptor-mediated transmission were enhanced in CMA-deficient females, whereas males exhibited elevated post-synaptic AMPA-receptor activity. Comparative quantitative proteomics revealed sexual dimorphism in the synaptic proteins degraded by CMA, with preferential remodelling of the pre-synaptic proteome in females and the post-synaptic proteome in males. We demonstrate that genetic or pharmacological CMA activation in old mice and an Alzheimer's disease mouse model restores synaptic protein levels, reduces neuronal hyperexcitability and seizure susceptibility, and normalizes neurotransmission. Our findings unveil a role for CMA in regulating neuronal excitability and highlight this pathway as a potential target for mitigating age-related neuronal decline.

Animals↗
PubMed2006

Redundant functions of RIM1alpha and RIM2alpha in Ca(2+)-triggered neurotransmitter release.

Alpha-RIMs (RIM1alpha and RIM2alpha) are multidomain active zone proteins of presynaptic terminals. Alpha-RIMs bind to Rab3 on synaptic vesicles and to Munc13 on the active zone via their N-terminal region, and interact with other synaptic proteins via their central and C-terminal regions. Although RIM1alpha has been well characterized, nothing is known about the function of RIM2alpha. We now show that RIM1alpha and RIM2alpha are expressed in overlapping but distinct patterns throughout the brain. To examine and compare their functions, we generated knockout mice lacking RIM2alpha, and crossed them with previously produced RIM1alpha knockout mice. We found that deletion of either RIM1alpha or RIM2alpha is not lethal, but ablation of both alpha-RIMs causes postnatal death. This lethality is not due to a loss of synapse structure or a developmental change, but to a defect in neurotransmitter release. Synapses without alpha-RIMs still contain active zones and release neurotransmitters, but are unable to mediate normal Ca(2+)-triggered release. Our data thus demonstrate that alpha-RIMs are not essential for synapse formation or synaptic exocytosis, but are required for normal Ca(2+)-triggering of exocytosis.

Action Potentials↗
PubMed2006

Protein kinase A regulates calcium permeability of NMDA receptors.

Calcium (Ca2+) influx through NMDA receptors (NMDARs) is essential for synaptogenesis, experience-dependent synaptic remodeling and plasticity. The NMDAR-mediated rise in postsynaptic Ca2+ activates a network of kinases and phosphatases that promote persistent changes in synaptic strength, such as long-term potentiation (LTP). Here we show that the Ca2+ permeability of neuronal NMDARs is under the control of the cyclic AMP-protein kinase A (cAMP-PKA) signaling cascade. PKA blockers reduced the relative fractional Ca2+ influx through NMDARs as determined by reversal potential shift analysis and by a combination of electrical recording and Ca2+ influx measurements in rat hippocampal neurons in culture and hippocampal slices from mice. In slices, PKA blockers markedly inhibited NMDAR-mediated Ca2+ rises in activated dendritic spines, with no significant effect on synaptic current. Consistent with this, PKA blockers depressed the early phase of NMDAR-dependent LTP at hippocampal Schaffer collateral-CA1 (Sch-CA1) synapses. Our data link PKA-dependent synaptic plasticity to Ca2+ signaling in spines and thus provide a new mechanism whereby PKA regulates the induction of LTP.

Animals↗
PubMed2006

Endocannabinoid-mediated synaptic plasticity in the CNS.

Changes in synaptic efficacy are thought to be crucial to experience-dependent modifications of neural function. The diversity of mechanisms underlying these changes is far greater than previously expected. In the last five years, a new class of use-dependent synaptic plasticity that requires retrograde signaling by endocannabinoids (eCB) and presynaptic CB1 receptor activation has been identified in several brain structures. eCB-mediated plasticity encompasses many forms of transient and long-lasting synaptic depression and is found at both excitatory and inhibitory synapses. In addition, eCBs can modify the inducibility of non-eCB-mediated forms of plasticity. Thus, the eCB system is emerging as a major player in synaptic plasticity. Given the wide distribution of CB1 receptors in the CNS, the list of brain structures and synapses expressing eCB-mediated plasticity is likely to expand.

Animals↗
PubMed2005

Blockade of calcium-permeable AMPA receptors protects hippocampal neurons against global ischemia-induced death.

Transient global or forebrain ischemia induced experimentally in animals can cause selective, delayed neuronal death of hippocampal CA1 pyramidal neurons. A striking feature is a delayed rise in intracellular free Zn(2+) in CA1 neurons just before the onset of histologically detectable cell death. Here we show that alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPARs) at Schaffer collateral to CA1 synapses in postischemic hippocampus exhibit properties of Ca(2+)/Zn(2+)-permeable, Glu receptor 2 (GluR2)-lacking AMPARs before the rise in Zn(2+) and cell death. At 42 h after ischemia, AMPA excitatory postsynaptic currents exhibited pronounced inward rectification and marked sensitivity to 1-naphthyl acetyl spermine (Naspm), a selective channel blocker of GluR2-lacking AMPARs. In control hippocampus, AMPA excitatory postsynaptic currents were electrically linear and relatively insensitive to Naspm. Naspm injected intrahippocampally at 9-40 h after insult greatly reduced the late rise in intracellular free Zn(2+) in postischemic CA1 neurons and afforded partial protection against ischemia-induced cell death. These results implicate GluR2-lacking AMPA receptors in the ischemia-induced rise in free Zn(2+) and death of CA1 neurons, although a direct action at the time of the rise in Zn(2+) is unproven. This receptor subtype appears to be an important therapeutic target for intervention in ischemia-induced neuronal death in humans.

Animals↗
PubMed2004

Double-knockout mice for alpha- and beta-synucleins: effect on synaptic functions.

An abundant presynaptic protein, alpha-synuclein, is centrally involved in the pathogenesis of Parkinson's disease. However, conflicting data exist about the normal function of alpha-synuclein, possibly because alpha-synuclein is redundant with the very similar beta-synuclein. To investigate the functions of synucleins systematically, we have now generated single- and double-knockout (KO) mice that lack alpha- and/or beta-synuclein. We find that deletion of synucleins in mice does not impair basic brain functions or survival. We detected no significant changes in the ultrastructure of synuclein-deficient synapses, in short- or long-term synaptic plasticity, or in the pool size or replenishment of recycling synaptic vesicles. However, protein quantitations revealed that KO of synucleins caused selective changes in two small synaptic signaling proteins, complexins and 14-3-3 proteins. Moreover, we found that dopamine levels in the brains of double-KO but not single-KO mice were decreased by approximately 20%. In contrast, serotonin levels were unchanged, and dopamine uptake and release from isolated nerve terminals were normal. These results show that synucleins are not essential components of the basic machinery for neurotransmitter release but may contribute to the long-term regulation and/or maintenance of presynaptic function.

Animals↗
PubMed2004

Endocannabinoid-mediated metaplasticity in the hippocampus.

Repetitive activation of glutamatergic fibers that normally induces long-term potentiation (LTP) at excitatory synapses in the hippocampus also triggers long-term depression at inhibitory synapses (I-LTD) via retrograde endocannabinoid signaling. Little is known, however, about the physiological significance of I-LTD. Here, we show that synaptic-driven release of endocannabinoids is a highly localized and efficient process that strongly depresses cannabinoid-sensitive inhibitory inputs within the dendritic compartment of CA1 pyramidal cells. By removing synaptic inhibition in a restricted area of the dendritic tree, endocannabinoids selectively "primed" nearby excitatory synapses, thereby facilitating subsequent induction of LTP. This induction of local metaplasticity is a novel mechanism by which endocannabinoids can contribute to the storage of information in the brain.

Animals↗
PubMed2004

A single in-vivo exposure to delta 9THC blocks endocannabinoid-mediated synaptic plasticity.

Endogenous cannabinoids (eCB) mediate synaptic plasticity in brain regions involved in learning and reward. Here we show that in mice, a single in-vivo exposure to Delta 9-tetrahydrocannabinol (THC) abolishes the retrograde signaling that underlies eCB-mediated synaptic plasticity in both nucleus accumbens (NAc) and hippocampus in vitro. This effect is reversible within 3 days and is associated with a transient modification in the functional properties of cannabinoid receptors.

Animals↗
PubMed2003

Heterosynaptic LTD of hippocampal GABAergic synapses: a novel role of endocannabinoids in regulating excitability.

Neuronal excitability and long-term synaptic plasticity at excitatory synapses are critically dependent on the level of inhibition, and accordingly, changes of inhibitory synaptic efficacy should have great impact on neuronal function and neural network processing. We describe here a form of activity-dependent long-term depression at hippocampal inhibitory synapses that is triggered postsynaptically via glutamate receptor activation but is expressed presynaptically. That is, glutamate released by repetitive activation of Schaffer collaterals activates group I metabotropic glutamate receptors at CA1 pyramidal cells, triggering a persistent reduction of GABA release that is mediated by endocannabinoids. This heterosynaptic form of plasticity is involved in changes of pyramidal cell excitability associated with long-term potentiation at excitatory synapses and could account for the effects of cannabinoids on learning and memory.

Animals↗
PubMed2002

Assessing the role of Ih channels in synaptic transmission and mossy fiber LTP.

Hyperpolarization-activated nonselective cation channels (Ih channels) play an important role in the control of membrane excitability and rhythmic neuronal activity. The functional relevance of presynaptic Ih channels in regulating synaptic function, however, is not well established. Recently, it has been proposed [Mellor, J., Nicoll, R. A. & Schmitz, D. (2002) Science 295, 143-147] that presynaptic Ih channels are necessary for hippocampal mossy fiber long-term potentiation (LTP). This observation challenges an alternative model that suggests presynaptic forms of LTP are caused by a direct modification of the transmitter release machinery. Here, we assess the role of Ih in hippocampal mossy fiber LTP as well as cerebellar parallel fiber LTP, forms of potentiation that share common mechanisms. Our results show that after Ih blockade neither mossy fiber LTP nor parallel fiber LTP are affected. Furthermore, Ih does not significantly modify basal excitatory synaptic transmission in the hippocampus, whereas the organic Ih blockers ZD7288 and DK-AH 269 induce a large Ih-independent depression of synaptic transmission. In summary, our results indicate that Ih-mediated persistent changes in presynaptic excitability do not underlie presynaptic forms of LTP.

Animals↗
PubMed2002

RIM1alpha forms a protein scaffold for regulating neurotransmitter release at the active zone.

Neurotransmitters are released by synaptic vesicle fusion at the active zone. The active zone of a synapse mediates Ca2+-triggered neurotransmitter release, and integrates presynaptic signals in regulating this release. Much is known about the structure of active zones and synaptic vesicles, but the functional relation between their components is poorly understood. Here we show that RIM1alpha, an active zone protein that was identified as a putative effector for the synaptic vesicle protein Rab3A, interacts with several active zone molecules, including Munc13-1 (ref. 6) and alpha-liprins, to form a protein scaffold in the presynaptic nerve terminal. Abolishing the expression of RIM1alpha in mice shows that RIM1alpha is essential for maintaining normal probability of neurotransmitter release, and for regulating release during short-term synaptic plasticity. These data indicate that RIM1alpha has a central function in integrating active zone proteins and synaptic vesicles into a molecular scaffold that controls neurotransmitter release.

Adaptor Proteins, Signal Transducing↗
PubMed2002

RIM1alpha is required for presynaptic long-term potentiation.

Two main forms of long-term potentiation (LTP)-a prominent model for the cellular mechanism of learning and memory-have been distinguished in the mammalian brain. One requires activation of postsynaptic NMDA (N-methyl d-aspartate) receptors, whereas the other, called mossy fibre LTP, has a principal presynaptic component. Mossy fibre LTP is expressed in hippocampal mossy fibre synapses, cerebellar parallel fibre synapses and corticothalamic synapses, where it apparently operates by a mechanism that requires activation of protein kinase A. Thus, presynaptic substrates of protein kinase A are probably essential in mediating this form of long-term synaptic plasticity. Studies of knockout mice have shown that the synaptic vesicle protein Rab3A is required for mossy fibre LTP, but the protein kinase A substrates rabphilin, synapsin I and synapsin II are dispensable. Here we report that mossy fibre LTP in the hippocampus and the cerebellum is abolished in mice lacking RIM1alpha, an active zone protein that binds to Rab3A and that is also a protein kinase A substrate. Our results indicate that the long-term increase in neurotransmitter release during mossy fibre LTP may be mediated by a unitary mechanism that involves the GTP-dependent interaction of Rab3A with RIM1alpha at the interface of synaptic vesicles and the active zone.

Animals↗