Layer 6b controls brain state via apical dendrites and the higher-order thalamocortical system.

The deepest layer of the cortex (layer 6b [L6b]) contains relatively few neurons, but it is the only cortical layer responsive to the potent wake-promoting neuropeptide orexin/hypocretin. Can these few neurons significantly influence brain state? Here, we show that L6b-photoactivation causes a surprisingly robust enhancement of attention-associated high-gamma oscillations and population spiking while abolishing slow waves in sleep-deprived mice. To explain this powerful impact on brain state, we investigated L6b's synaptic output using optogenetics, electrophysiology, and monoCaTChR ex vivo. We found powerful output in the higher-order thalamus and apical dendrites of L5 pyramidal neurons, via L1a and L5a, as well as in superior colliculus and L6 interneurons. L6b subpopulations with distinct morphologies and short- and long-term plasticities project to these diverse targets. The L1a-targeting subpopulation triggered powerful NMDA-receptor-dependent spikes that elicited burst firing in L5. We conclude that orexin/hypocretin-activated cortical neurons form a multifaceted, fine-tuned circuit for the sustained control of the higher-order thalamocortical system.

Multi-layered maps of neuropil with segmentation-guided contrastive learning.

Maps of the nervous system that identify individual cells along with their type, subcellular components and connectivity have the potential to elucidate fundamental organizational principles of neural circuits. Nanometer-resolution imaging of brain tissue provides the necessary raw data, but inferring cellular and subcellular annotation layers is challenging. We present segmentation-guided contrastive learning of representations (SegCLR), a self-supervised machine learning technique that produces representations of cells directly from 3D imagery and segmentations. When applied to volumes of human and mouse cortex, SegCLR enables accurate classification of cellular subcompartments and achieves performance equivalent to a supervised approach while requiring 400-fold fewer labeled examples. SegCLR also enables inference of cell types from fragments as small as 10 µm, which enhances the utility of volumes in which many neurites are truncated at boundaries. Finally, SegCLR enables exploration of layer 5 pyramidal cell subtypes and automated large-scale analysis of synaptic partners in mouse visual cortex.

A thalamocortical substrate for integrated information via critical synchronous bursting.

Understanding the neurobiological mechanisms underlying consciousness remains a significant challenge. Recent evidence suggests that the coupling between distal-apical and basal-somatic dendrites in thick-tufted layer 5 pyramidal neurons (L5PN), regulated by the nonspecific-projecting thalamus, is crucial for consciousness. Yet, it is uncertain whether this thalamocortical mechanism can support emergent signatures of consciousness, such as integrated information. To address this question, we constructed a biophysical network of dual-compartment thick-tufted L5PN, with dendrosomatic coupling controlled by thalamic inputs. Our findings demonstrate that integrated information is maximized when nonspecific thalamic inputs drive the system into a regime of time-varying synchronous bursting. Here, the system exhibits variable spiking dynamics with broad pairwise correlations, supporting the enhanced integrated information. Further, the observed peak in integrated information aligns with criticality signatures and empirically observed layer 5 pyramidal bursting rates. These results suggest that the thalamocortical core of the mammalian brain may be evolutionarily configured to optimize effective information processing, providing a potential neuronal mechanism that integrates microscale theories with macroscale signatures of consciousness.

Thalamocortical control of cell-type specificity drives circuits for processing whisker-related information in mouse barrel cortex.

Excitatory spiny stellate neurons are prominently featured in the cortical circuits of sensory modalities that provide high salience and high acuity representations of the environment. These specialized neurons are considered developmentally linked to bottom-up inputs from the thalamus, however, the molecular mechanisms underlying their diversification and function are unknown. Here, we investigated this in mouse somatosensory cortex, where spiny stellate neurons and pyramidal neurons have distinct roles in processing whisker-evoked signals. Utilizing spatial transcriptomics, we identified reciprocal patterns of gene expression which correlated with these cell-types and were linked to innervation by specific thalamic inputs during development. Genetic manipulation that prevents the acquisition of spiny stellate fate highlighted an important role for these neurons in processing distinct whisker signals within functional cortical columns, and as a key driver in the formation of specific whisker-related circuits in the cortex.

Gegen-Qinlian decoction-A traditional Chinese medicine formula-Alleviates methamphetamine withdrawal induced anxiety by targeting GABAergic interneuron-pyramidal neuron pathway in mPFC.

Methamphetamine (Meth) withdrawal elicits anxiety, which is a public health concern with limited therapeutic options. Previous studies implied a strong correlation between mPFC and Meth withdrawal. Here, we examined the role of Gegen-Qinlian decoction (GQD) in Meth withdrawal anxiety and explored potential therapeutic targets in mPFC. We found that intra-gastric administration of GQD during the withdrawal period efficiently alleviated anxiety-like behaviours in Meth-withdrawn mice. Further, GQD could restore Meth withdrawal-triggered pathway of GABAergic interneurons (GABA IN)-pyramidal neurons (PN) in the mPFC of Meth-withdrawn mice, especially the prelimbic cortex (PrL) sub-region and PV-positive GABA IN. While, GQD had no obvious effects on the glial cells in the mPFC of Meth-withdrawn mice. By transcriptomic analysis and validation of several gene candidates, we found that genes in the MAPK signalling pathway, especially those related to heat shock proteins, including Hspa1a, Hspa1b and Hspb1, might be GQD-targeting genes in mPFC to treat Meth withdrawal anxiety, as indicated that these genes were up-regulated by Meth withdrawal but rescued by GQD in mPFC. Collectively, our findings identified for the first time that GQD could efficiently alleviate Meth withdrawal anxiety, partially through regulating the local GABA IN-PN pathway and transcriptomic profile of mPFC. The present study confirms that TCM, such as GQD, will be a desirable therapeutic approach in the treatment of drug addiction and related emotional deficits.

Anti-Hebbian plasticity in the motor cortex promotes defensive freezing.

Regional brain activity often decreases from baseline levels in response to external events, but how neurons develop such negative responses is unclear. To study this, we leveraged the negative response that develops in the primary motor cortex (M1) after classical fear learning. We trained mice with a fear conditioning paradigm while imaging their brains with standard two-photon microscopy. This enabled monitoring changes in neuronal responses to the tone with synaptic resolution through learning. We found that M1 layer 5 pyramidal neurons (L5 PNs) developed negative tone responses within an hour after conditioning, which depended on the weakening of their dendritic spines that were active during training. Blocking this form of anti-Hebbian plasticity using an optogenetic manipulation of CaMKII activity disrupted negative tone responses and freezing. Therefore, reducing the strength of spines active at the time of memory encoding leads to negative responses of L5 PNs. In turn, these negative responses curb M1's capacity for promoting movement, thereby aiding freezing. Collectively, this work provides a mechanistic understanding of how area-specific negative responses to behaviorally relevant cues can be achieved.

Structural and functional changes of deep layer pyramidal neurons surrounding microelectrode arrays implanted in rat motor cortex.

Devices capable of recording or stimulating neuronal signals have created new opportunities to understand normal physiology and treat sources of pathology in the brain. However, it is possible that the tissue response to implanted electrodes may influence the nature of the signals detected or stimulated. In this study, we characterized structural and functional changes in deep layer pyramidal neurons surrounding silicon or polyimide-based electrodes implanted in the motor cortex of rats. Devices were captured in 300 µm-thick tissue slices collected at the 1 or 6 week time point post-implantation, and individual neurons were assessed using a combination of whole-cell electrophysiology and 2-photon imaging. We observed disrupted dendritic arbors and a significant reduction in spine densities in neurons surrounding devices. These effects were accompanied by a decrease in the frequency of spontaneous excitatory post-synaptic currents, a reduction in sag amplitude, an increase in spike frequency adaptation, and an increase in filopodia density. We hypothesize that the effects observed in this study may contribute to the signal loss and instability that often accompany chronically implanted electrodes. STATEMENT OF SIGNIFICANCE: Implanted electrodes in the brain can be used to treat sources of pathology and understand normal physiology by recording or stimulating electrical signals generated by local neurons. However, a foreign body response following implantation undermines the performance of these devices. While several studies have investigated the biological mechanisms of device-tissue interactions through histology, transcriptomics, and imaging, our study is the first to directly interrogate effects on the function of neurons surrounding electrodes using single-cell electrophysiology. Additionally, we provide new, detailed assessments of the impacts of electrodes on the dendritic structure and spine morphology of neurons, and we assess effects for both traditional (silicon) and newer polymer electrode materials. These results reveal new potential mechanisms of electrode-tissue interactions.

Motor cortex projections to red and pontine nuclei have distinct roles during movement in the mouse.

Motor control largely depends on the deep layer 5 (L5) pyramidal neurons that project to subcortical structures. However, it is largely unknown if these neurons are functionally segregated with distinct roles in movement performance. Here, we analyzed mouse motor cortex L5 pyramidal neurons projecting to the red and pontine nuclei during movement preparation and execution. Using photometry to analyze the calcium activity of L5 pyramidal neurons projecting to the red nucleus and pons, we reveal that both types of neurons activate with different temporal dynamics. Optogenetic inhibition of either kind of projection differentially affects forelimb movement onset and execution in a lever press task, but only the activity of corticopontine neurons is significantly correlated with trial-by-trial variations in reaction time. The results indicate that cortical neurons projecting to the red and pontine nuclei contribute differently to sensorimotor integration, suggesting that L5 output neurons are functionally compartmentalized generating, in parallel, different downstream information.

Mapping thalamic innervation to individual L2/3 pyramidal neurons and modeling their 'readout' of visual input.

The thalamus is the main gateway for sensory information from the periphery to the mammalian cerebral cortex. A major conundrum has been the discrepancy between the thalamus's central role as the primary feedforward projection system into the neocortex and the sparseness of thalamocortical synapses. Here we use new methods, combining genetic tools and scalable tissue expansion microscopy for whole-cell synaptic mapping, revealing the number, density and size of thalamic versus cortical excitatory synapses onto individual layer 2/3 (L2/3) pyramidal cells (PCs) of the mouse primary visual cortex. We find that thalamic inputs are not only sparse, but remarkably heterogeneous in number and density across individual dendrites and neurons. Most surprising, despite their sparseness, thalamic synapses onto L2/3 PCs are smaller than their cortical counterparts. Incorporating these findings into fine-scale, anatomically faithful biophysical models of L2/3 PCs reveals how individual neurons with sparse and weak thalamocortical synapses, embedded in small heterogeneous neuronal ensembles, may reliably 'read out' visually driven thalamic input.

Quantitative Fluorescence Analysis Reveals Dendrite-Specific Thalamocortical Plasticity in L5 Pyramidal Neurons during Learning.

High-throughput anatomic data can stimulate and constrain new hypotheses about how neural circuits change in response to experience. Here, we use fluorescence-based reagents for presynaptic and postsynaptic labeling to monitor changes in thalamocortical synapses onto different compartments of layer 5 (L5) pyramidal (Pyr) neurons in somatosensory (barrel) cortex from mixed-sex mice during whisker-dependent learning (Audette et al., 2019). Using axonal fills and molecular-genetic tags for synapse identification in fixed tissue from Rbp4-Cre transgenic mice, we found that thalamocortical synapses from the higher-order posterior medial thalamic nucleus showed rapid morphologic changes in both presynaptic and postsynaptic structures at the earliest stages of sensory association training. Detected increases in thalamocortical synaptic size were compartment specific, occurring selectively in the proximal dendrites onto L5 Pyr and not at inputs onto their apical tufts in L1. Both axonal and dendritic changes were transient, normalizing back to baseline as animals became expert in the task. Anatomical measurements were corroborated by electrophysiological recordings at different stages of training. Thus, fluorescence-based analysis of input- and target-specific synapses can reveal compartment-specific changes in synapse properties during learning.SIGNIFICANCE STATEMENT Synaptic changes underlie the cellular basis of learning, experience, and neurologic diseases. Neuroanatomical methods to assess synaptic plasticity can provide critical spatial information necessary for building models of neuronal computations during learning and experience but are technically and fiscally intensive. Here, we describe a confocal fluorescence microscopy-based analytical method to assess input, cell type, and dendritic location-specific synaptic plasticity in a sensory learning assay. Our method not only confirms prior electrophysiological measurements but allows us to predict functional strength of synapses in a pathway-specific manner. Our findings also indicate that changes in primary sensory cortices are transient, occurring during early learning. Fluorescence-based synapse identification can be an efficient and easily adopted approach to study synaptic changes in a variety of experimental paradigms.

Motor training promotes both synaptic and intrinsic plasticity of layer V pyramidal neurons in the primary motor cortex.

Layer V neurons in the primary motor cortex (M1) are important for motor skill learning. Since pretreatment of either CNQX or APV in rat M1 layer V impaired rotor rod learning, we analysed training-induced synaptic plasticity by whole-cell patch-clamp technique in acute brain slices. Rats trained for 1 day showed a decrease in small inhibitory postsynaptic current (mIPSC) frequency and an increase in the paired-pulse ratio of evoked IPSCs, suggesting a transient decrease in presynaptic GABA release in the early phase. Rats trained for 2 days showed an increase in miniature excitatory postsynaptic current (mEPSC) amplitudes/frequency and elevated AMPA/NMDA ratios, suggesting a long-term strengthening of AMPA receptor-mediated excitatory synapses. Importantly, rotor rod performance in trained rats was correlated with the mean mEPSC amplitude and the frequency obtained from that animal. In current-clamp analysis, 1-day-trained rats transiently decreased the current-induced firing rate, while 2-day-trained rats returned to pre-training levels, suggesting dynamic changes in intrinsic properties. Furthermore, western blot analysis of layer V detected decreased phosphorylation of Ser408-409 in GABAA receptor ß3 subunits in 1-day-trained rats, and increased phosphorylation of Ser831 in AMPA receptor GluA1 subunits in 2-day-trained rats. Finally, live-imaging analysis of Thy1-YFP transgenic mice showed that the training rapidly recruited a substantial number of spines for long-term plasticity in M1 layer V neurons. Taken together, these results indicate that motor training induces complex and diverse plasticity in M1 layer V pyramidal neurons. KEY POINTS: Here we examined motor training-induced synaptic and intrinsic plasticity of layer V pyramidal neurons in the primary motor cortex. The training reduced presynaptic GABA release in the early phase, but strengthened AMPA receptor-mediated excitatory synapses in the later phase: acquired motor performance after training correlated with the strength of excitatory synapses rather than inhibitory synapses. As to the intrinsic property, the training transiently decreased the firing rate in the early phase, but returned to pre-training levels in the later phase. Western blot analysis detected decreased phosphorylation of Ser408-409 in GABAA receptor ß3 subunits in the acute phase, and increased phosphorylation of Ser831 in AMPA receptor GluA1 subunits in the later phase. Live-imaging analysis of Thy1-YFP transgenic mice showed rapid and long-term spine plasticity in M1 layer V neurons, suggesting training-induced increases in self-entropy per spine.

Region-selective control of the thalamic reticular nucleus via cortical layer 5 pyramidal cells.

Corticothalamic pathways, responsible for the top-down control of the thalamus, have a canonical organization such that every cortical region sends output from both layer 6 (L6) and layer 5 (L5) to the thalamus. Here we demonstrate a qualitative, region-specific difference in the organization of mouse corticothalamic pathways. Specifically, L5 pyramidal cells of the frontal cortex, but not other cortical regions, establish monosynaptic connections with the inhibitory thalamic reticular nucleus (TRN). The frontal L5-TRN pathway parallels the L6-TRN projection but has distinct morphological and physiological features. The exact spike output of the L5-contacted TRN cells correlated with the level of cortical synchrony. Optogenetic perturbation of the L5-TRN connection disrupted the tight link between cortical and TRN activity. L5-driven TRN cells innervated thalamic nuclei involved in the control of frontal cortex activity. Our data show that frontal cortex functions require a highly specialized cortical control over intrathalamic inhibitory processes.

Connectomic analysis of thalamus-driven disinhibition in cortical layer 4.

Sensory signals are transmitted via the thalamus primarily to layer 4 (L4) of the primary sensory cortices. While information about average neuronal connectivity in L4 is available, its detailed higher-order circuit structure is not known. Here, we used three-dimensional electron microscopy for a connectomic analysis of the thalamus-driven inhibitory network in L4. We find that thalamic input drives a subset of interneurons with high specificity, which in turn target excitatory neurons with subtype specificity. These interneurons create a directed disinhibitory network directly driven by the thalamic input. Neuronal activity recordings show that strong synchronous sensory activation yields about 1.5-fold stronger activation of star pyramidal cells than spiny stellates, in line with differential windows of opportunity for activation of excitatory neurons in the thalamus-driven disinhibitory circuit model. With this, we have identified a high degree of specialization of the microcircuitry in L4 of the primary sensory cortex.

Layers 3 and 4 Neurons of the Bilateral Whisker-Barrel Cortex.

In Robo3R3-5cKO mouse brain, rhombomere 3-derived trigeminal principal nucleus (PrV) neurons project bilaterally to the somatosensory thalamus. As a consequence, whisker-specific neural modules (barreloids and barrels) representing whiskers on both sides of the face develop in the sensory thalamus and the primary somatosensory cortex. We examined the morphological complexity of layer 4 barrel cells, their postsynaptic partners in layer 3, and functional specificity of layer 3 pyramidal cells. Layer 4 spiny stellate cells form much smaller barrels and their dendritic fields are more focalized and less complex compared to controls, while layer 3 pyramidal cells did not show notable differences. Using in vivo 2-photon imaging of a genetically encoded fluorescent [Ca2+] sensor, we visualized neural activity in the normal and Robo3R3-5cKO barrel cortex in response to ipsi- and contralateral single whisker stimulation. Layer 3 neurons in control animals responded only to their contralateral whiskers, while in the mutant cortex layer 3 pyramidal neurons showed both ipsi- and contralateral whisker responses. These results indicate that bilateral whisker map inputs stimulate different but neighboring groups of layer 3 neurons which normally relay contralateral whisker-specific information to other cortical areas.

A stereological study reveals nanoscale-alumina induces cognitive dysfunction in mice related to hippocampal structural changes.

Aluminum (Al) is known to induce neurotoxicity in both humans and rodents. Recent evidence has indicated that the toxicity of Al Oxide (Al2O3) nanoparticles (Al-NP), one of the most abundantly used engineered nanoparticles, is far greater than that of Al itself. To date, however, no information is available regarding the effect of Al-NP on the stereological parameters of hippocampus. In particular, no stereological studies have evaluated the effect of Al-NP on hippocampal CA1, dentate gyrus volume, and number of pyramidal and granular cells. Thus, the present study aimed to take a multidimensional approach to assess the concomitant cognitive, stereological, and apoptotic changes induced by a five-day Al-NP ingestion (10 mg/kg/day) in mice. The results demonstrated that the five-day Al-NP ingestion elicited a reduced preference to explore a novel object in the novel object recognition test (a hippocampal-dependent task). Perhaps contributing to this memory deficit, Al-NP induced additional alterations in the hippocampus of male NMRI mice in terms of (1) hippocampal volume (decreased the volume of the whole hippocampus, CA1, and dentate gyrus regions), (2) cell number (decreased the number of CA1 pyramidal neurons and dentate gyrus granular cells), and (3) increased cleaved caspase-3 in the whole hippocampus. These results provided new mechanistic insight to understand the impairing effect of AL-NP on the hippocampal function and structure.

Paradoxical somatodendritic decoupling supports cortical plasticity during REM sleep.

Rapid eye movement (REM) sleep is associated with the consolidation of emotional memories. Yet, the underlying neocortical circuits and synaptic mechanisms remain unclear. We found that REM sleep is associated with a somatodendritic decoupling in pyramidal neurons of the prefrontal cortex. This decoupling reflects a shift of inhibitory balance between parvalbumin neuron-mediated somatic inhibition and vasoactive intestinal peptide-mediated dendritic disinhibition, mostly driven by neurons from the central medial thalamus. REM-specific optogenetic suppression of dendritic activity led to a loss of danger-versus-safety discrimination during associative learning and a lack of synaptic plasticity, whereas optogenetic release of somatic inhibition resulted in enhanced discrimination and synaptic potentiation. Somatodendritic decoupling during REM sleep promotes opposite synaptic plasticity mechanisms that optimize emotional responses to future behavioral stressors.

Dynamic interplay between thalamic activity and Cajal-Retzius cells regulates the wiring of cortical layer 1.

Cortical wiring relies on guidepost cells and activity-dependent processes that are thought to act sequentially. Here, we show that the construction of layer 1 (L1), a main site of top-down integration, is regulated by crosstalk between transient Cajal-Retzius cells (CRc) and spontaneous activity of the thalamus, a main driver of bottom-up information. While activity was known to regulate CRc migration and elimination, we found that prenatal spontaneous thalamic activity and NMDA receptors selectively control CRc early density, without affecting their demise. CRc density, in turn, regulates the distribution of upper layer interneurons and excitatory synapses, thereby drastically impairing the apical dendrite activity of output pyramidal neurons. In contrast, postnatal sensory-evoked activity had a limited impact on L1 and selectively perturbed basal dendrites synaptogenesis. Collectively, our study highlights a remarkable interplay between thalamic activity and CRc in L1 functional wiring, with major implications for our understanding of cortical development.

Hyperthermia accelerates neuronal loss differently between the hippocampal CA1 and CA2/3 through different HIF­1α expression after transient ischemia in gerbils.

The hippocampus has a different vulnerability to ischemia according to the subfields CA1 to CA3 (initials of cornu ammonis). It has been reported that body temperature changes during ischemia affect the degree of neuronal death following transient ischemia. Hypoxia­inducible factor 1α (HIF­1α) plays a key role in regulating cellular adaptation to low oxygen conditions. In the present study, we investigated the pattern of neuronal death (loss) in CA1 and CA2/3 following 5 min transient forebrain ischemia (TFI) under hyperthermia (39.5±0.2˚C) and the relationship between neuronal death and changes in HIF­1α expression using western blot analysis and immunohistochemistry in gerbils. Normothermia or hyperthermia was induced for 30 min before and during the TFI, and neuronal death and HIF­1α expression were observed at 0, 3, 6 and 12 h, 1, 2 and 5 days after TFI. Under normothermia, TFI­induced neuronal death of CA1 pyramidal neurons occurred on day 5 after TFI, but CA2/3 pyramidal neurons did not die. In contrast, under hyperthermia, the death of CA1 and CA2/3 pyramidal neurons was observed on day 2 after TFI. Under normothermia, HIF­1α expression was significantly elevated in both CA1 and CA2/3 pyramidal neurons at 12 h and 1 day after TFI, and the increased HIF­1α immunoreactivity in CA1 was dramatically reduced from 2 days after TFI, but not in CA2/3 pyramidal neurons. Under hyperthermia, the basal expression of HIF­1α in the sham group was significantly higher in both CA1 and CA2/3 pyramidal neurons at 0 h after TFI than in the normothermia group. HIF­1 expression was continuously higher, peaked at 12 h after TFI, and then significantly decreased from 1 day after TFI. Overall, the present results indicate that resistance to ischemia in CA2/3 pyramidal neurons is closely associated with the persistence of increased expression of HIF­1α after ischemic insults and that hyperthermia­induced exacerbation of death of pyramidal neurons is closely related to decreased HIF­1α expression after ischemic insults.

Neural Substrates and Models of Omission Responses and Predictive Processes.

Predictive coding theories argue that deviance detection phenomena, such as mismatch responses and omission responses, are generated by predictive processes with possibly overlapping neural substrates. Molecular imaging and electrophysiology studies of mismatch responses and corollary discharge in the rodent model allowed the development of mechanistic and computational models of these phenomena. These models enable translation between human and non-human animal research and help to uncover fundamental features of change-processing microcircuitry in the neocortex. This microcircuitry is characterized by stimulus-specific adaptation and feedforward inhibition of stimulus-selective populations of pyramidal neurons and interneurons, with specific contributions from different interneuron types. The overlap of the substrates of different types of responses to deviant stimuli remains to be understood. Omission responses, which are observed both in corollary discharge and mismatch response protocols in humans, are underutilized in animal research and may be pivotal in uncovering the substrates of predictive processes. Omission studies comprise a range of methods centered on the withholding of an expected stimulus. This review aims to provide an overview of omission protocols and showcase their potential to integrate and complement the different models and procedures employed to study prediction and deviance detection.This approach may reveal the biological foundations of core concepts of predictive coding, and allow an empirical test of the framework's promise to unify theoretical models of attention and perception.

Lead acetate induces hippocampal pyramidal neuron degeneration in mice via up-regulation of executioner caspase-3, oxido-inflammatory stress expression and decreased BDNF and cholinergic activity: Reversal effects of Gingko biloba supplement.

PURPOSE: It has been hypothesized that compounds with strong anti-oxidant activity might mitigate lead-induced neurotoxicity that resulted to neuronal degeneration.Ginkgo biloba supplement (GB-S) is a neuroactive supplement which has been reported to demonstrate neuroprotective effects. In this study, we investigated the reversal effect and the underlying mechanism of GB-S following lead-induced neurotoxicity in mice. METHODS: Male Swiss mice (n = 8) were pre-treated with lead acetate (100 mg/kg) for 30 min before GB-S (10 mg/kg and 20 mg/kg) or Ethylenediaminetetraacetic acid (EDTA) (50 mg/kg) intraperitoneally for 14 consecutive days. Memory impairment symptoms were evaluated on day 13 and 14 using Y-maze and Novel object recognition test (NORT) respectively. Thereafter, spectrophotometry, ELISA, immunohistochemistry and histomorphormetry were used to estimate the degree and expression of biomarkers of neuronal inflammation: oxido-inflammatory stress, apoptosis and degeneration in the hippocampus (HC). RESULTS: Lead acetate treatment significantly (p < 0.05) induced neurobehavioral impairment which was reversed by GB-S as evident in increased percentage alternation and discrimination index. GB-S significantly (p < 0.05) reduced lipid peroxidation and nitrite level, inhibited TNF-α and acetylcholinesterase activity and improved glutathione, catalase and superoxide dismutase activity in the HC. Moreover, GB-S inhibited hippocampal apoptosis via elevated expression of caspase-3 with marked increase level of brain derived neurotrophic factor (BDNF). Also, the histomorphormetric study showed that GB-S rescued death of pyramidal neurons (CA3) in the HC. CONCLUSION: Our findings however suggest that GB-S decreased memory impairment progression induced by lead acetate via mechanisms connected to inhibition of oxido-inflammatory stress mediators, restrained acetylcholinesterase activity, up-regulated BDNF/Caspase-3 expression and suppression of hippocampal pyramidal neuron degeneration in mice.