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1.
Commun Biol ; 7(1): 678, 2024 Jun 03.
Article in English | MEDLINE | ID: mdl-38831002

ABSTRACT

Deciphering the functional organization of large biological networks is a major challenge for current mathematical methods. A common approach is to decompose networks into largely independent functional modules, but inferring these modules and their organization from network activity is difficult, given the uncertainties and incompleteness of measurements. Typically, some parts of the overall functional organization, such as intermediate processing steps, are latent. We show that the hidden structure can be determined from the statistical moments of observable network components alone, as long as the functional relevance of the network components lies in their mean values and the mean of each latent variable maps onto a scaled expectation of a binary variable. Whether the function of biological networks permits a hierarchical modularization can be falsified by a correlation-based statistical test that we derive. We apply the test to gene regulatory networks, dendrites of pyramidal neurons, and networks of spiking neurons.


Subject(s)
Gene Regulatory Networks , Humans , Animals , Pyramidal Cells/physiology , Pyramidal Cells/metabolism
2.
Proc Natl Acad Sci U S A ; 121(24): e2311570121, 2024 Jun 11.
Article in English | MEDLINE | ID: mdl-38830095

ABSTRACT

Even a transient period of hearing loss during the developmental critical period can induce long-lasting deficits in temporal and spectral perception. These perceptual deficits correlate with speech perception in humans. In gerbils, these hearing loss-induced perceptual deficits are correlated with a reduction of both ionotropic GABAA and metabotropic GABAB receptor-mediated synaptic inhibition in auditory cortex, but most research on critical period plasticity has focused on GABAA receptors. Therefore, we developed viral vectors to express proteins that would upregulate gerbil postsynaptic inhibitory receptor subunits (GABAA, Gabra1; GABAB, Gabbr1b) in pyramidal neurons, and an enzyme that mediates GABA synthesis (GAD65) presynaptically in parvalbumin-expressing interneurons. A transient period of developmental hearing loss during the auditory critical period significantly impaired perceptual performance on two auditory tasks: amplitude modulation depth detection and spectral modulation depth detection. We then tested the capacity of each vector to restore perceptual performance on these auditory tasks. While both GABA receptor vectors increased the amplitude of cortical inhibitory postsynaptic potentials, only viral expression of postsynaptic GABAB receptors improved perceptual thresholds to control levels. Similarly, presynaptic GAD65 expression improved perceptual performance on spectral modulation detection. These findings suggest that recovering performance on auditory perceptual tasks depends on GABAB receptor-dependent transmission at the auditory cortex parvalbumin to pyramidal synapse and point to potential therapeutic targets for developmental sensory disorders.


Subject(s)
Auditory Cortex , Gerbillinae , Hearing Loss , Animals , Auditory Cortex/metabolism , Auditory Cortex/physiopathology , Hearing Loss/genetics , Hearing Loss/physiopathology , Receptors, GABA-B/metabolism , Receptors, GABA-B/genetics , Glutamate Decarboxylase/metabolism , Glutamate Decarboxylase/genetics , Receptors, GABA-A/metabolism , Receptors, GABA-A/genetics , Parvalbumins/metabolism , Parvalbumins/genetics , Auditory Perception/physiology , Pyramidal Cells/metabolism , Pyramidal Cells/physiology , Genetic Vectors/genetics
3.
Cereb Cortex ; 34(5)2024 May 02.
Article in English | MEDLINE | ID: mdl-38745556

ABSTRACT

The basic building block of the cerebral cortex, the pyramidal cell, has been shown to be characterized by a markedly different dendritic structure among layers, cortical areas, and species. Functionally, differences in the structure of their dendrites and axons are critical in determining how neurons integrate information. However, within the human cortex, these neurons have not been quantified in detail. In the present work, we performed intracellular injections of Lucifer Yellow and 3D reconstructed over 200 pyramidal neurons, including apical and basal dendritic and local axonal arbors and dendritic spines, from human occipital primary visual area and associative temporal cortex. We found that human pyramidal neurons from temporal cortex were larger, displayed more complex apical and basal structural organization, and had more spines compared to those in primary sensory cortex. Moreover, these human neocortical neurons displayed specific shared and distinct characteristics in comparison to previously published human hippocampal pyramidal neurons. Additionally, we identified distinct morphological features in human neurons that set them apart from mouse neurons. Lastly, we observed certain consistent organizational patterns shared across species. This study emphasizes the existing diversity within pyramidal cell structures across different cortical areas and species, suggesting substantial species-specific variations in their computational properties.


Subject(s)
Pyramidal Cells , Humans , Pyramidal Cells/physiology , Animals , Male , Female , Mice , Adult , Dendritic Spines/physiology , Dendritic Spines/ultrastructure , Temporal Lobe/cytology , Dendrites/physiology , Middle Aged , Axons/physiology , Species Specificity
4.
Nat Commun ; 15(1): 4053, 2024 May 14.
Article in English | MEDLINE | ID: mdl-38744848

ABSTRACT

The role of the hippocampus in spatial navigation has been primarily studied in nocturnal mammals, such as rats, that lack many adaptations for daylight vision. Here we demonstrate that during 3D navigation, the common marmoset, a new world primate adapted to daylight, predominantly uses rapid head-gaze shifts for visual exploration while remaining stationary. During active locomotion marmosets stabilize the head, in contrast to rats that use low-velocity head movements to scan the environment as they locomote. Pyramidal neurons in the marmoset hippocampus CA3/CA1 regions predominantly show mixed selectivity for 3D spatial view, head direction, and place. Exclusive place selectivity is scarce. Inhibitory interneurons are predominantly mixed selective for angular head velocity and translation speed. Finally, we found theta phase resetting of local field potential oscillations triggered by head-gaze shifts. Our findings indicate that marmosets adapted to their daylight ecological niche by modifying exploration/navigation strategies and their corresponding hippocampal specializations.


Subject(s)
Callithrix , Hippocampus , Spatial Navigation , Animals , Callithrix/physiology , Spatial Navigation/physiology , Hippocampus/physiology , Male , Locomotion/physiology , Vision, Ocular/physiology , Pyramidal Cells/physiology , Head Movements/physiology , Interneurons/physiology , Female , Behavior, Animal/physiology , CA1 Region, Hippocampal/physiology , CA1 Region, Hippocampal/cytology
5.
Sci Adv ; 10(19): eadj9911, 2024 May 10.
Article in English | MEDLINE | ID: mdl-38728406

ABSTRACT

During cerebral cortex development, excitatory pyramidal neurons (PNs) establish specific projection patterns while receiving inputs from GABAergic inhibitory interneurons (INs). Whether these inhibitory inputs can shape PNs' projection patterns is, however, unknown. While layer 4 (L4) PNs of the primary somatosensory (S1) cortex are all born as long-range callosal projection neurons (CPNs), most of them acquire local connectivity upon activity-dependent elimination of their interhemispheric axons during postnatal development. Here, we demonstrate that precise developmental regulation of inhibition is key for the retraction of S1L4 PNs' callosal projections. Ablation of somatostatin INs leads to premature inhibition from parvalbumin INs onto S1L4 PNs and prevents them from acquiring their barrel-restricted local connectivity pattern. As a result, adult S1L4 PNs retain interhemispheric projections responding to tactile stimuli, and the mice lose whisker-based texture discrimination. Overall, we show that temporally ordered IN activity during development is key to shaping local ipsilateral S1L4 PNs' projection pattern, which is required for fine somatosensory processing.


Subject(s)
GABAergic Neurons , Interneurons , Somatosensory Cortex , Animals , Interneurons/metabolism , Interneurons/physiology , Interneurons/cytology , GABAergic Neurons/metabolism , GABAergic Neurons/physiology , GABAergic Neurons/cytology , Somatosensory Cortex/physiology , Somatosensory Cortex/metabolism , Somatosensory Cortex/cytology , Mice , Pyramidal Cells/metabolism , Pyramidal Cells/physiology , Parvalbumins/metabolism
6.
Curr Biol ; 34(10): 2247-2255.e5, 2024 05 20.
Article in English | MEDLINE | ID: mdl-38714199

ABSTRACT

Rapid eye movement (REM) sleep is known to facilitate fear extinction and play a protective role against fearful memories.1,2 Consequently, disruption of REM sleep after a traumatic event may increase the risk for developing PTSD.3,4 However, the underlying mechanisms by which REM sleep promotes extinction of aversive memories remain largely unknown. The infralimbic cortex (IL) is a key brain structure for the consolidation of extinction memory.5 Using calcium imaging, we found in mice that most IL pyramidal neurons are intensively activated during REM sleep. Optogenetically suppressing the IL specifically during REM sleep within a 4-h window after auditory-cued fear conditioning impaired extinction memory consolidation. In contrast, REM-specific IL inhibition after extinction learning did not affect the extinction memory. Whole-cell patch-clamp recordings demonstrated that inactivating IL neurons during REM sleep depresses their excitability. Together, our findings suggest that REM sleep after fear conditioning facilitates fear extinction by enhancing IL excitability and highlight the importance of REM sleep in the aftermath of traumatic events for protecting against traumatic memories.


Subject(s)
Extinction, Psychological , Fear , Sleep, REM , Animals , Fear/physiology , Sleep, REM/physiology , Mice , Extinction, Psychological/physiology , Male , Mice, Inbred C57BL , Memory/physiology , Memory Consolidation/physiology , Conditioning, Classical/physiology , Pyramidal Cells/physiology
7.
Neurosci Biobehav Rev ; 161: 105688, 2024 Jun.
Article in English | MEDLINE | ID: mdl-38670298

ABSTRACT

Pyramidal neurons have a pivotal role in the cognitive capabilities of neocortex. Though they have been predominantly modeled as integrate-and-fire point processors, many of them have another point of input integration in their apical dendrites that is central to mechanisms endowing them with the sensitivity to context that underlies basic cognitive capabilities. Here we review evidence implicating impairments of those mechanisms in three major neurodevelopmental disabilities, fragile X, Down syndrome, and fetal alcohol spectrum disorders. Multiple dysfunctions of the mechanisms by which pyramidal cells are sensitive to context are found to be implicated in all three syndromes. Further deciphering of these cellular mechanisms would lead to the understanding of and therapies for learning disabilities beyond any that are currently available.


Subject(s)
Learning Disabilities , Humans , Animals , Learning Disabilities/physiopathology , Learning Disabilities/etiology , Pyramidal Cells/physiology , Fetal Alcohol Spectrum Disorders/physiopathology , Neurodevelopmental Disorders/physiopathology , Down Syndrome/physiopathology , Fragile X Syndrome/physiopathology
8.
Cells ; 13(7)2024 Mar 26.
Article in English | MEDLINE | ID: mdl-38607012

ABSTRACT

Neuronal timing with millisecond precision is critical for many brain functions such as sensory perception, learning and memory formation. At the level of the chemical synapse, the synaptic delay is determined by the presynaptic release probability (Pr) and the waveform of the presynaptic action potential (AP). For instance, paired-pulse facilitation or presynaptic long-term potentiation are associated with reductions in the synaptic delay, whereas paired-pulse depression or presynaptic long-term depression are associated with an increased synaptic delay. Parallelly, the AP broadening that results from the inactivation of voltage gated potassium (Kv) channels responsible for the repolarization phase of the AP delays the synaptic response, and the inactivation of sodium (Nav) channels by voltage reduces the synaptic latency. However, whether synaptic delay is modulated during depolarization-induced analogue-digital facilitation (d-ADF), a form of context-dependent synaptic facilitation induced by prolonged depolarization of the presynaptic neuron and mediated by the voltage-inactivation of presynaptic Kv1 channels, remains unclear. We show here that despite Pr being elevated during d-ADF at pyramidal L5-L5 cell synapses, the synaptic delay is surprisingly unchanged. This finding suggests that both Pr- and AP-dependent changes in synaptic delay compensate for each other during d-ADF. We conclude that, in contrast to other short- or long-term modulations of presynaptic release, synaptic timing is not affected during d-ADF because of the opposite interaction of Pr- and AP-dependent modulations of synaptic delay.


Subject(s)
Neurons , Synapses , Synapses/physiology , Action Potentials/physiology , Pyramidal Cells/physiology , Long-Term Potentiation
9.
Mol Vis ; 30: 67-73, 2024.
Article in English | MEDLINE | ID: mdl-38586606

ABSTRACT

Purpose: Light-induced neural retinal insult leads to alterations in the visual cortex neurons. We examined light-induced neuronal alterations in the visual cortex layer 5 pyramidal neurons (V1-L5PNs) of adult male Wistar rats. Methods: A total of 24 rats were divided into the following groups (n=6 each): control (NC), blue (BL), white (WL), and yellow (YL). The exposure groups were subjected to light-emitting diodes (LED) exposure (450-500 lx) of differing wavelengths for 90 days (12:12 16 light-dark cycle). After LED exposure, the animals were sacrificed, and the brain tissues were removed and impregnated in freshly prepared Golgi-Cox stain for 21 days. Sholl's grading analysis was used to quantify the apical and basal dendritic branching points and intersections of the V1-L5PNs. Results: There was a significant difference in the number of apical branching points among all groups (p<0.001), with a particularly notable difference between the BL and WL groups (p<0.001). A post hoc test revealed that all exposure groups (BL, WL, and YL) had fewer apical branching points (p<0.001) on an average of 3.6 µm and a significant reduction in the dendritic intersections (p<0.001) compared to the number of branching points extending from layer Va (V1) neurons. Conclusions: Chronic and cumulative exposure to blue and white LEDs led to the pruning of V1-L5PNs, which might impair visual processing.


Subject(s)
Dendrites , Visual Cortex , Male , Rats , Animals , Rodentia , Rats, Wistar , Pyramidal Cells/physiology , Visual Cortex/physiology
10.
BMC Biol ; 22(1): 95, 2024 Apr 29.
Article in English | MEDLINE | ID: mdl-38679719

ABSTRACT

BACKGROUND: The medial prefrontal cortex (mPFC) is involved in complex functions containing multiple types of neurons in distinct subregions with preferential roles. The pyramidal neurons had wide-range projections to cortical and subcortical regions with subregional preferences. Using a combination of viral tracing and fluorescence micro-optical sectioning tomography (fMOST) in transgenic mice, we systematically dissected the whole-brain connectomes of intratelencephalic (IT) and pyramidal tract (PT) neurons in four mPFC subregions. RESULTS: IT and PT neurons of the same subregion projected to different target areas while receiving inputs from similar upstream regions with quantitative differences. IT and PT neurons all project to the amygdala and basal forebrain, but their axons target different subregions. Compared to subregions in the prelimbic area (PL) which have more connections with sensorimotor-related regions, the infralimbic area (ILA) has stronger connections with limbic regions. The connection pattern of the mPFC subregions along the anterior-posterior axis showed a corresponding topological pattern with the isocortex and amygdala but an opposite orientation correspondence with the thalamus. CONCLUSIONS: By using transgenic mice and fMOST imaging, we obtained the subregional preference whole-brain connectomes of IT and pyramidal tract PT neurons in the mPFC four subregions. These results provide a comprehensive resource for directing research into the complex functions of the mPFC by offering anatomical dissections of the different subregions.


Subject(s)
Connectome , Mice, Transgenic , Prefrontal Cortex , Pyramidal Cells , Animals , Prefrontal Cortex/physiology , Prefrontal Cortex/cytology , Pyramidal Cells/physiology , Mice , Male
11.
Cell Rep ; 43(4): 114115, 2024 Apr 23.
Article in English | MEDLINE | ID: mdl-38607918

ABSTRACT

In the CA1 hippocampus, vasoactive intestinal polypeptide-expressing interneurons (VIP-INs) play a prominent role in disinhibitory circuit motifs. However, the specific behavioral conditions that lead to circuit disinhibition remain uncertain. To investigate the behavioral relevance of VIP-IN activity, we employed wireless technologies allowing us to monitor and manipulate their function in freely behaving mice. Our findings reveal that, during spatial exploration in new environments, VIP-INs in the CA1 hippocampal region become highly active, facilitating the rapid encoding of novel spatial information. Remarkably, both VIP-INs and pyramidal neurons (PNs) exhibit increased activity when encountering novel changes in the environment, including context- and object-related alterations. Concurrently, somatostatin- and parvalbumin-expressing inhibitory populations show an inverse relationship with VIP-IN and PN activity, revealing circuit disinhibition that occurs on a timescale of seconds. Thus, VIP-IN-mediated disinhibition may constitute a crucial element in the rapid encoding of novelty and the acquisition of recognition memory.


Subject(s)
CA1 Region, Hippocampal , Interneurons , Recognition, Psychology , Vasoactive Intestinal Peptide , Animals , Interneurons/metabolism , Interneurons/physiology , Vasoactive Intestinal Peptide/metabolism , CA1 Region, Hippocampal/physiology , CA1 Region, Hippocampal/metabolism , CA1 Region, Hippocampal/cytology , Mice , Male , Recognition, Psychology/physiology , Pyramidal Cells/metabolism , Pyramidal Cells/physiology , Mice, Inbred C57BL , Memory/physiology , Parvalbumins/metabolism , Exploratory Behavior/physiology , Somatostatin/metabolism
12.
Cell Rep ; 43(4): 114100, 2024 Apr 23.
Article in English | MEDLINE | ID: mdl-38607921

ABSTRACT

Hippocampal pyramidal neuron activity underlies episodic memory and spatial navigation. Although extensively studied in rodents, extremely little is known about human hippocampal pyramidal neurons, even though the human hippocampus underwent strong evolutionary reorganization and shows lower theta rhythm frequencies. To test whether biophysical properties of human Cornu Amonis subfield 1 (CA1) pyramidal neurons can explain observed rhythms, we map the morpho-electric properties of individual CA1 pyramidal neurons in human, non-pathological hippocampal slices from neurosurgery. Human CA1 pyramidal neurons have much larger dendritic trees than mouse CA1 pyramidal neurons, have a large number of oblique dendrites, and resonate at 2.9 Hz, optimally tuned to human theta frequencies. Morphological and biophysical properties suggest cellular diversity along a multidimensional gradient rather than discrete clustering. Across the population, dendritic architecture and a large number of oblique dendrites consistently boost memory capacity in human CA1 pyramidal neurons by an order of magnitude compared to mouse CA1 pyramidal neurons.


Subject(s)
CA1 Region, Hippocampal , Dendrites , Pyramidal Cells , Humans , Pyramidal Cells/physiology , CA1 Region, Hippocampal/cytology , CA1 Region, Hippocampal/physiology , Animals , Male , Mice , Dendrites/physiology , Female , Middle Aged , Aged , Theta Rhythm/physiology , Adult
13.
Math Biosci ; 372: 109192, 2024 Jun.
Article in English | MEDLINE | ID: mdl-38640998

ABSTRACT

Computational models of brain regions are crucial for understanding neuronal network dynamics and the emergence of cognitive functions. However, current supercomputing limitations hinder the implementation of large networks with millions of morphological and biophysical accurate neurons. Consequently, research has focused on simplified spiking neuron models, ranging from the computationally fast Leaky Integrate and Fire (LIF) linear models to more sophisticated non-linear implementations like Adaptive Exponential (AdEX) and Izhikevic models, through Generalized Leaky Integrate and Fire (GLIF) approaches. However, in almost all cases, these models are tuned (and can be validated) only under constant current injections and they may not, in general, also reproduce experimental findings under variable currents. This study introduces an Adaptive GLIF (A-GLIF) approach that addresses this limitation by incorporating a new set of update rules. The extended A-GLIF model successfully reproduces both constant and variable current inputs, and it was validated against the results obtained using a biophysical accurate model neuron. This enhancement provides researchers with a tool to optimize spiking neuron models using classic experimental traces under constant current injections, reliably predicting responses to synaptic inputs, which can be confidently used for large-scale network implementations.


Subject(s)
CA1 Region, Hippocampal , Interneurons , Models, Neurological , Pyramidal Cells , Pyramidal Cells/physiology , Interneurons/physiology , CA1 Region, Hippocampal/physiology , CA1 Region, Hippocampal/cytology , Animals , Action Potentials/physiology , Synapses/physiology , Computer Simulation
14.
Ann N Y Acad Sci ; 1535(1): 62-75, 2024 May.
Article in English | MEDLINE | ID: mdl-38602714

ABSTRACT

Hippocampal pyramidal neuronal activity has been previously studied using conventional patch clamp in isolated cells and brain slices. We here introduce the loose patch clamping study of voltage-activated currents from in situ pyramidal neurons in murine cornus ammonis 1 hippocampal coronal slices. Depolarizing pulses of 15-ms duration elicited early transient inward, followed by transient and prolonged outward currents in the readily identifiable junctional region between the stratum pyramidalis (SP) and oriens (SO) containing pyramidal cell somas and initial segments. These resembled pyramidal cell currents previously recorded using conventional patch clamp. Shortening the depolarizing pulses to >1-2 ms continued to evoke transient currents; hyperpolarizing pulses to varying voltages evoked decays whose time constants could be shortened to <1 ms, clarifying the speed of clamping in this experimental system. The inward and outward currents had distinct pharmacological characteristics and voltage-dependent inactivation and recovery from inactivation. Comparative recordings from the SP, known to contain pyramidal cell somas, demonstrated similar current properties. Recordings from the SO and stratum radiatum demonstrated smaller inward and outward current magnitudes and reduced transient outward currents, consistent with previous conventional patch clamp results from their different interneuron types. The loose patch clamp method is thus useful for in situ studies of neurons in hippocampal brain slices.


Subject(s)
Patch-Clamp Techniques , Pyramidal Cells , Animals , Patch-Clamp Techniques/methods , Mice , Pyramidal Cells/physiology , Membrane Potentials/physiology , Hippocampus/physiology , Hippocampus/cytology , Neurons/physiology , CA1 Region, Hippocampal/physiology , CA1 Region, Hippocampal/cytology , Mice, Inbred C57BL , Male
15.
Science ; 384(6693): 338-343, 2024 Apr 19.
Article in English | MEDLINE | ID: mdl-38635709

ABSTRACT

The computational capabilities of neuronal networks are fundamentally constrained by their specific connectivity. Previous studies of cortical connectivity have mostly been carried out in rodents; whether the principles established therein also apply to the evolutionarily expanded human cortex is unclear. We studied network properties within the human temporal cortex using samples obtained from brain surgery. We analyzed multineuron patch-clamp recordings in layer 2-3 pyramidal neurons and identified substantial differences compared with rodents. Reciprocity showed random distribution, synaptic strength was independent from connection probability, and connectivity of the supragranular temporal cortex followed a directed and mostly acyclic graph topology. Application of these principles in neuronal models increased dimensionality of network dynamics, suggesting a critical role for cortical computation.


Subject(s)
Nerve Net , Pyramidal Cells , Synapses , Temporal Lobe , Animals , Humans , Nerve Net/physiology , Nerve Net/ultrastructure , Pyramidal Cells/physiology , Pyramidal Cells/ultrastructure , Rodentia , Synapses/physiology , Synapses/ultrastructure , Temporal Lobe/physiology , Patch-Clamp Techniques
16.
eNeuro ; 11(5)2024 May.
Article in English | MEDLINE | ID: mdl-38637152

ABSTRACT

Canonically, action potentials of most mammalian neurons initiate at the axon initial segment (AIS) and propagate bidirectionally: orthodromically along the distal axon and retrogradely into the soma and dendrites. Under some circumstances, action potentials may initiate ectopically, at sites distal to the AIS, and propagate antidromically along the axon. These "ectopic action potentials" (EAPs) have been observed in experimental models of seizures and chronic pain, and more rarely in nonpathological forebrain neurons. Here we report that a large majority of parvalbumin-expressing (PV+) interneurons in the upper layers of mouse neocortex, from both orbitofrontal and primary somatosensory areas, fire EAPs after sufficient activation of their somata. Somatostatin-expressing interneurons also fire EAPs, though less robustly. Ectopic firing in PV+ cells occurs in varying temporal patterns and can persist for several seconds. PV+ cells evoke strong synaptic inhibition in pyramidal neurons and interneurons and play critical roles in cortical function. Our results suggest that ectopic spiking of PV+ interneurons is common and may contribute to both normal and pathological network functions of the neocortex.


Subject(s)
Action Potentials , Interneurons , Mice, Transgenic , Neocortex , Parvalbumins , Animals , Parvalbumins/metabolism , Interneurons/physiology , Interneurons/metabolism , Neocortex/physiology , Action Potentials/physiology , Male , Mice , Female , Mice, Inbred C57BL , Pyramidal Cells/physiology , Somatostatin/metabolism
17.
Proc Natl Acad Sci U S A ; 121(18): e2322550121, 2024 Apr 30.
Article in English | MEDLINE | ID: mdl-38657053

ABSTRACT

Pronounced differences in neurotransmitter release from a given presynaptic neuron, depending on the synaptic target, are among the most intriguing features of cortical networks. Hippocampal pyramidal cells (PCs) release glutamate with low probability to somatostatin expressing oriens-lacunosum-moleculare (O-LM) interneurons (INs), and the postsynaptic responses show robust short-term facilitation, whereas the release from the same presynaptic axons onto fast-spiking INs (FSINs) is ~10-fold higher and the excitatory postsynaptic currents (EPSCs) display depression. The mechanisms underlying these vastly different synaptic behaviors have not been conclusively identified. Here, we applied a combined functional, pharmacological, and modeling approach to address whether the main difference lies in the action potential-evoked fusion or else in upstream priming processes of synaptic vesicles (SVs). A sequential two-step SV priming model was fitted to the peak amplitudes of unitary EPSCs recorded in response to complex trains of presynaptic stimuli in acute hippocampal slices of adult mice. At PC-FSIN connections, the fusion probability (Pfusion) of well-primed SVs is 0.6, and 44% of docked SVs are in a fusion-competent state. At PC-O-LM synapses, Pfusion is only 40% lower (0.36), whereas the fraction of well-primed SVs is 6.5-fold smaller. Pharmacological enhancement of fusion by 4-AP and priming by PDBU was recaptured by the model with a selective increase of Pfusion and the fraction of well-primed SVs, respectively. Our results demonstrate that the low fidelity of transmission at PC-O-LM synapses can be explained by a low occupancy of the release sites by well-primed SVs.


Subject(s)
Neurotransmitter Agents , Synaptic Vesicles , Animals , Synaptic Vesicles/metabolism , Synaptic Vesicles/physiology , Mice , Neurotransmitter Agents/metabolism , Hippocampus/metabolism , Hippocampus/physiology , Excitatory Postsynaptic Potentials/physiology , Synaptic Transmission/physiology , Interneurons/metabolism , Interneurons/physiology , Pyramidal Cells/metabolism , Pyramidal Cells/physiology , Synapses/metabolism , Synapses/physiology , Models, Neurological
18.
Anesthesiology ; 140(6): 1192-1200, 2024 Jun 01.
Article in English | MEDLINE | ID: mdl-38624275

ABSTRACT

Tonic inhibition in mouse hippocampal CA1 pyramidal neurons is mediated by α5 subunit-containing γ-aminobutyric acid type A receptors. By Caraiscos VB, Elliott EM, You-Ten KE, Cheng VY, Belelli D, Newell JG, Jackson MF, Lambert JJ, Rosahl TW, Wafford KA, MacDonald JF, Orser BA. Proc Natl Acad Sci U S A 2004; 101:3662-7. Reprinted with permission. In this Classic Paper Revisited, the author recounts the scientific journey leading to a report published in the Proceedings of the National Academy of Sciences (PNAS) and shares several personal stories from her formative years and "research truths" that she has learned along the way. Briefly, the principal inhibitory neurotransmitter in the brain, γ-aminobutyric acid (GABA), was conventionally thought to regulate cognitive processes by activating synaptic GABA type A (GABAA) receptors and generating transient inhibitory synaptic currents. However, the author's laboratory team discovered a novel nonsynaptic form of tonic inhibition in hippocampal pyramidal neurons, mediated by extrasynaptic GABAA receptors that are pharmacologically distinct from synaptic GABAA receptors. This tonic current is highly sensitive to most general anesthetics, including sevoflurane and propofol, and likely contributes to the memory-blocking properties of these drugs. Before the publication in PNAS, the subunit composition of GABAA receptors that generate the tonic current was unknown. The team's research showed that GABAA receptors containing the α5 subunit (α5GABAARs) generated the tonic inhibitory current in hippocampal neurons. α5GABAARs are highly sensitive to GABA, desensitize slowly, and are thus well suited for detecting low, persistent, ambient concentrations of GABA in the extracellular space. Interest in α5GABAARs has surged since the PNAS report, driven by their pivotal roles in cognitive processes and their potential as therapeutic targets for treating various neurologic disorders.


Subject(s)
Receptors, GABA-A , Animals , Receptors, GABA-A/drug effects , Receptors, GABA-A/metabolism , Mice , Pyramidal Cells/drug effects , Pyramidal Cells/physiology , Pyramidal Cells/metabolism , Humans , Synapses/drug effects , Hippocampus/drug effects , Hippocampus/metabolism , gamma-Aminobutyric Acid/metabolism
19.
J Physiol ; 602(10): 2343-2358, 2024 May.
Article in English | MEDLINE | ID: mdl-38654583

ABSTRACT

Training rodents in a particularly difficult olfactory-discrimination (OD) task results in the acquisition of the ability to perform the task well, termed 'rule learning'. In addition to enhanced intrinsic excitability and synaptic excitation in piriform cortex pyramidal neurons, rule learning results in increased synaptic inhibition across the whole cortical network to the point where it precisely maintains the balance between inhibition and excitation. The mechanism underlying such precise inhibitory enhancement remains to be explored. Here, we use brain slices from transgenic mice (VGAT-ChR2-EYFP), enabling optogenetic stimulation of single GABAergic neurons and recordings of unitary synaptic events in pyramidal neurons. Quantal analysis revealed that learning-induced enhanced inhibition is mediated by increased quantal size of the evoked inhibitory events. Next, we examined the plasticity of synaptic inhibition induced by long-lasting, intrinsically evoked spike firing in post-synaptic neurons. Repetitive depolarizing current pulses from depolarized (-70 mV) or hyperpolarized (-90 mV) membrane potentials induced long-term depression (LTD) and long-term potentiation (LTP) of synaptic inhibition, respectively. We found a profound bidirectional increase in the ability to induce both LTD, mediated by L-type calcium channels, and LTP, mediated by R-type calcium channels after rule learning. Blocking the GABAB receptor reversed the effect of intrinsic stimulation at -90 mV from LTP to LTD. We suggest that learning greatly enhances the ability to modify the strength of synaptic inhibition of principal neurons in both directions. Such plasticity of synaptic plasticity allows fine-tuning of inhibition on each particular neuron, thereby stabilizing the network while maintaining the memory of the rule. KEY POINTS: Olfactory discrimination rule learning results in long-lasting enhancement of synaptic inhibition on piriform cortex pyramidal neurons. Quantal analysis of unitary inhibitory synaptic events, evoked by optogenetic minimal stimulation, revealed that enhanced synaptic inhibition is mediated by increased quantal size. Surprisingly, metaplasticity of synaptic inhibition, induced by intrinsically evoked repetitive spike firing, is increased bidirectionally. The susceptibility to both long-term depression (LTD) and long-term potentiation (LTP) of inhibition is enhanced after learning. LTD of synaptic inhibition is mediated by L-type calcium channels and LTP by R-type calcium channels. LTP is also dependent on activation of GABAB receptors. We suggest that learning-induced changes in the metaplasticity of synaptic inhibition enable the fine-tuning of inhibition on each particular neuron, thereby stabilizing the network while maintaining the memory of the rule.


Subject(s)
Mice, Transgenic , Neuronal Plasticity , Pyramidal Cells , Animals , Neuronal Plasticity/physiology , Mice , Pyramidal Cells/physiology , GABAergic Neurons/physiology , Learning/physiology , Long-Term Potentiation/physiology , Male , Synapses/physiology , Optogenetics , Neural Inhibition/physiology , Piriform Cortex/physiology , Mice, Inbred C57BL , Long-Term Synaptic Depression/physiology
20.
Neuropharmacology ; 254: 109970, 2024 Aug 15.
Article in English | MEDLINE | ID: mdl-38685343

ABSTRACT

Pharmacological approaches to induce N-methyl-d-aspartate receptor (NMDAR) hypofunction have been intensively used to understand the aetiology and pathophysiology of schizophrenia. Yet, the precise cellular and molecular mechanisms that relate to brain network dysfunction remain largely unknown. Here, we used a set of complementary approaches to assess the functional network abnormalities present in male mice that underwent a 7-day subchronic phencyclidine (PCP 10 mg/kg, subcutaneously, once daily) treatment. Our data revealed that pharmacological intervention with PCP affected cognitive performance and auditory evoked gamma oscillations in the prefrontal cortex (PFC) mimicking endophenotypes of some schizophrenia patients. We further assessed PFC cellular function and identified altered neuronal intrinsic membrane properties, reduced parvalbumin (PV) immunostaining and diminished inhibition onto L5 PFC pyramidal cells. A decrease in the strength of optogenetically-evoked glutamatergic current at the ventral hippocampus to PFC synapse was also demonstrated, along with a weaker shunt of excitatory transmission by local PFC interneurons. On a macrocircuit level, functional ultrasound measurements indicated compromised functional connectivity within several brain regions particularly involving PFC and frontostriatal circuits. Herein, we reproduced a panel of schizophrenia endophenotypes induced by subchronic PCP application in mice. We further recapitulated electrophysiological signatures associated with schizophrenia and provided an anatomical reference to critical elements in the brain circuitry. Together, our findings contribute to a better understanding of the physiological underpinnings of deficits induced by subchronic NMDAR antagonist regimes and provide a test system for characterization of pharmacological compounds.


Subject(s)
Disease Models, Animal , Phencyclidine , Prefrontal Cortex , Receptors, N-Methyl-D-Aspartate , Animals , Prefrontal Cortex/drug effects , Prefrontal Cortex/metabolism , Male , Phencyclidine/pharmacology , Receptors, N-Methyl-D-Aspartate/metabolism , Mice , Schizophrenia/chemically induced , Schizophrenia/physiopathology , Schizophrenia/metabolism , Mice, Inbred C57BL , Parvalbumins/metabolism , Adaptation, Physiological/drug effects , Adaptation, Physiological/physiology , Pyramidal Cells/drug effects , Pyramidal Cells/physiology , Gamma Rhythm/drug effects , Gamma Rhythm/physiology , Hippocampus/drug effects , Hippocampus/metabolism , Excitatory Amino Acid Antagonists/pharmacology
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