Biology subjects

Baraibar, A. M.

Publications and source records attributed to Baraibar, A. M..

7 recordsLinked to original sources

bioRxiv2025

Astrocyte CB1 receptors drive blood-brain barrier disruption in CNS inflammatory disease

Reactive astrocytes shape central nervous system (CNS) inflammation and participate in myelin damage and repair mechanisms in multiple sclerosis (MS). Through the activation of cannabinoid CB1 receptors (CB1R) expressed by neurons and oligodendrocyte lineage cells, endocannabinoid signaling restricts neurodegeneration and promote remyelination in preclinical MS models. However, despite accumulating evidence that supports a crucial role for these receptor populations in brain physiology and pathology, the implications of astrocyte CB1R signaling in MS initiation and progression remain uncertain. Using complementary in vivo disease models, here we investigated the effects of targeted genetic deletion of astrocytes CB1R on the expression of MS-like pathology in mice. Interestingly, astrocyte-specific deletion of CB1R reduced demyelinating neuropathology, attenuated astrocyte reactivity and improved clinical deficits during the time-course of experimental autoimmune encephalomyelitis (EAE). Mice with astrocyte CB1R inactivation displayed unaltered oligodendrocyte populations both in EAE lesions and in lysolecithin-induced remyelinating spinal cord lesions, likely excluding that astrocyte CB1R modulate myelin repair processes. Conversely, inactivation of CB1R in astroglial cells restricted humoral and leukocyte parenchymal infiltration and reduced the expression of vascular effectors in EAE lesions. Finally, loss of blood-brain barrier (BBB) function induced by cortical microinjection of VEGF-A was less severe in GFAP-CB1R-KO mice. These results show that astrocyte CB1R signaling constitutes a significant pro-inflammatory mechanism in MS and bring to light a deleterious role for endocannabinoid-mediated modulation of astroglial cells with potential implications in the etiopathology and therapy of neuroinflammatory disorders.

neuroscience↗

bioRxiv2025

NEUROGLIAL CB1 RECEPTORS CONTROL NAVIGATION STRATEGIES

Navigation and memory functions are essential for survival and are regulated by the hippocampus. These processes are tightly controlled, and one of the key modulators involved is the endocannabinoid system, particularly through the cannabinoid receptor type-1 (CB1). CB1 is widely expressed in various hippocampal cell types. While it is known that CB1 participates in memory processes, its specific roles in different cell types and how these roles may differ between sexes remain unclear. This study investigates how CB1 signaling in the hippocampus, in both, cell-type-specific and sex-dependent manner, contributes to navigation and memory. To this end, we selectively deleted CB1 receptors from neurons, CAMKII-expressing neurons, and astrocytes from the hippocampus of adult male and female mice. We then assessed its effect on a broad range of behaviors, including innate emotional responses, memory, navigation, and other hippocampus-related functions such as nesting. Deletion of CB1 in CAMKII-expressing neurons produced a pronounced effect in males, leading to increased anxiety and impairments in both reference and spatial memory. These mice also showed altered performance in the Barnes maze, relying less on spatial strategies. By contrast, females were less affected by this specific deletion. Interestingly, only deletion of CB1 from astrocytes led to spatial memory impairments in females, which also showed reduced LTP and a decreased reliance on spatial strategies in the Barnes maze. In conclusion, our findings show that neuronal CB1 receptors are critical for the spatial navigation strategy in males, while astrocytic CB1 receptors play a key role in memory processes both in males and females.

neuroscience↗

bioRxiv2024

Functional differentiation of Human Dental Pulp Stem Cells into neuron-like cells exhibiting electrophysiological activity

BackgroundHuman dental pulp stem cells (hDPSCs) constitute a promising alternative for central nervous system (CNS) cell therapy. Unlike other human stem cells, hDPSCs can be differentiated, without genetic modification, to neural cells that secrete neuroprotective factors. However, a better understanding of their real capacity to give rise to functional neurons and integrate into synaptic networks is still needed. For that, ex vivo differentiation protocols must be refined, especially to avoid the use of fetal animal serum. MethodsIn this study, we sought to improve existing differentiation protocols for obtaining functional neuron-like cells from hDPSCs. We compared the effects of the absence or presence of fetal serum during the initial expansion phase as a step prior to switching cultures to neurodifferentiation media. We improved hDPSC neurodifferentiation by adding retinoic acid (RA) and potassium chloride (KCl) pulses for 21 or 60 days and characterized the results by immunofluorescence, digital morphometric analysis, RT-qPCR and electrophysiology. ResultsWe found that neural markers like Nestin, GFAP, S100{beta} and p75NTR were expressed differently in neurodifferentiated hDPSC cultures depending on the presence or absence of serum during the initial cell expansion phase. In addition, hDPSCs previously grown as spheroids in serum-free medium exhibited in vitro expression of neuronal markers such as doublecortin (DCX), neuronal nuclear antigen (NeuN), Ankyrin-G and MAP2 after neurodifferentiation. Presynaptic vGLUT2, Synapsin-I, and excitatory glutamatergic and inhibitory GABAergic postsynaptic scaffold proteins and receptor subunits were also present in these neurodifferentiated hDPSCs. Treatment with KCl and RA increased the amount of both voltage-gated Na+ and K+ channel subunits in neurodifferentiated hDPSCs at the transcript level. Consistently, these cells displayed voltage-dependent K+ and TTX-sensitive Na+ currents as well as spontaneous electrophysiological activity and repetitive neuronal action potentials with a full baseline potential recovery. ConclusionOur study demonstrates, for the first time, that hDPSCs can be differentiated to neuronal-like cells that display functional excitability and thus evidence the potential of these easily accessible human stem cells for nerve tissue engineering. Our results highlight the importance of choosing an appropriate culture protocol to successfully neurodifferentiate hDPSCs.

cell biology↗

bioRxiv2023

Autoimmune inflammation triggers aberrant astrocytic calcium signaling to impair synaptic plasticity

Cortical pathology involving inflammatory and neurodegenerative mechanisms is a hallmark of multiple sclerosis (MS) and a correlate of disease progression and cognitive decline. Astrocytes play a pivotal role in MS initiation and progression but astrocyte-neuronal network alterations contributing to gray matter pathology remain undefined. Here we measured astrocytic calcium in the experimental autoimmune encephalomyelitis (EAE) model of MS using fiber photometry in freely behaving mice and two-photon imaging ex vivo. We identified the emergence of spontaneously hyperactive cortical astrocytes displaying calcium transients of increased duration as well as dysfunctional responses to cannabinoid, glutamate and purinoreceptor agonists during acute EAE disease. Deficits in astrocyte calcium responses are associated to abnormal signaling by Gi and Gq protein coupled receptors in the inflamed cortex and are partially mirrored in cells activated with pro-inflammatory factors both in vitro and ex vivo thus suggesting cell-autonomous effects of the cortical neuroinflammatory environment. Finally, we show that deregulated astrocyte calcium activity is associated to an enhancement of glutamatergic gliotransmission and a shift of astrocyte-mediated short-term and long-term plasticity mechanisms towards synaptic potentiation. Overall our data identities astrocyte-neuronal network dysfunction as key pathological feature of the inflammatory gray matter that may contribute to MS symptomatology and clinical progression.

neuroscience↗

bioRxiv2023

A spatial threshold for astrocyte calcium surge

Astrocytes are active cells involved in brain function through the bidirectional communication with neurons, in which the astrocyte calcium signal plays a crucial role. Synaptically-evoked calcium increases can be localized to independent subcellular domains or expand to the entire cell, i.e., calcium surge. In turn, astrocytes may regulate individual synapses by calcium-dependent release of gliotransmitters. Because a single astrocyte may contact [~]100,000 synapses, the control of the intracellular calcium signal propagation may have relevant consequences on brain function by regulating the spatial range of astrocyte neuromodulation of synapses. Yet, the properties governing the spatial dynamics of the astrocyte calcium signal remains poorly defined. Imaging subcellular responses of cortical astrocytes to sensory stimulation in mice, we show that sensory-evoked astrocyte calcium responses originated and remained localized in domains of the astrocytic arborization, but eventually propagated to the entire cell if a spatial threshold of >23% of the arborization being activated was surpassed. Using transgenic IP3R2-/- mice, we found that type-2 IP3 receptors were necessary for the generation of the astrocyte calcium surge. We finally show using in situ electrophysiological recordings that the spatial threshold of the astrocyte calcium signal consequently determined the gliotransmitter release. Present results reveal a fundamental property of astrocyte calcium physiology, i.e., a spatial threshold for the astrocyte intracellular calcium signal propagation, which depends on astrocyte intrinsic properties and governs the astrocyte integration of local synaptic activity and the subsequent neuromodulation. One-Sentence SummaryThere is a spatial threshold for the astrocyte intracellular calcium signal propagation that is determined by astrocyte intrinsic properties and controls gliotransmission.

neuroscience↗

bioRxiv2023

Aluminium alters excitability by inhibiting calcium, sodium and potassium currents in bovine chromaffin cells.

Aluminium (Al3+) has long been related to neurotoxicity and neurological diseases. This study aims to describe the specific actions of this metal on cellular excitability and neurotransmitter release. Al3+ reduced intracellular calcium concentrations around 25% and decreased catecholamine secretion in a dose-dependent manner, with an IC50 of 89.1 M. Al3+ blocked calcium currents in a time- and concentration-dependent manner with an IC50 of 560 M. This blockade was irreversible, since it did not recover after wash-out. Moreover, Al3+ produced a bigger blockade on N-, P- and Q-type calcium channels subtypes (69.5%) than on L-type channels subtypes (50.5%). Sodium currents were also inhibited by Al3+ in a time- and concentration-dependent manner, 24.3% blockade at the closest concentration to the IC50 (419 M). This inhibition was reversible. Voltage-dependent potassium currents were non-significantly affected by Al3+. Nonetheless, calcium/voltage-dependent potassium currents were inhibited in a concentration-dependent manner, with an IC50 of 447 M. This inhibition was related to the depression of calcium influx through voltage-dependent calcium channels subtypes coupled to BK channels. In summary, the blockade of these ionic conductances altered cellular excitability that reduced the action potentials firing and so, the neurotransmitter release and the synaptic transmission. These findings prove that aluminium has neurotoxic properties because it alters neuronal excitability by inhibiting the sodium currents responsible for the generation and propagation of impulse nerve, the potassium current responsible for the termination of action potentials, and the calcium current responsible for the neurotransmitters release.

neuroscience↗

bioRxiv2022

SPATIAL ORGANIZATION OF NEURON-ASTROCYTE INTERACTIONS IN THE SOMATOSENSORY CORTEX

Microcircuits in the neocortex are functionally organized along layers and columns, which are the fundamental modules of cortical information processing. While the function of cortical microcircuits has focused on neuronal elements, much less is known about the functional organization of astrocytes and their bidirectional interaction with neurons. Here we show that CB1R-mediated astrocyte activation by neuron-released endocannabinoids elevate astrocyte Ca2+ levels, stimulate ATP/adenosine release as gliotransmitters, and transiently depress synaptic transmission in layer 5 pyramidal neurons at relatively distant synapses (>20 {micro}m) from the stimulated neuron. This astrocyte-mediated heteroneuronal synaptic depression occurred between pyramidal neurons within a cortical column and was absent in neurons belonging to adjacent cortical columns. Moreover, this form of heteroneuronal synaptic depression occurs between neurons located in particular layers, following a specific connectivity pattern that depends on a layer-specific neuron-to-astrocyte signaling. These results unravel the existence of astrocyte-mediated non-synaptic communication between cortical neurons, and that this communication is column- and layer-specific, which adds further complexity to the intercellular signaling processes in the cortex.

neuroscience↗