Abstract Neuronal in vitro cultures are pivotal for studying brain electrophysiological function and dysfunction. Neuronal activity and communication are regulated by extracellular ion concentrations. Therefore, cell culture medium ion concentrations should ideally mimic those of cerebrospinal fluid (CSF)—considered as the milieu for brain cells in vivo. In this study, we demonstrate that commonly used cell culture media, including NeurobasalTM (+ /− A), Neurobasal PlusTM, and BrainPhysTM media, do not accurately replicate human CSF ion concentrations. Using human iPSC-derived neuronal networks on microelectrode arrays, we compare neuronal activity in standard culture media with that in physiological artificial cerebrospinal fluid (aCSF) and in human cerebrospinal fluid. We show that supraphysiological potassium levels in culture media acutely induce seizure-like neuronal network activity compared with both physiological aCSF and human CSF. Importantly, human neurons exposed to human CSF obtained from healthy individuals show fundamentally different neuronal network activity than neurons exposed to currently used cell culture media. These findings raise a critical question: How can human in vitro neuronal activity be defined as physiological and reliably distinguished from pathophysiological activity, if the routinely used ion concentrations in in vitro experiments are causing aberrant neuronal activity that is fundamentally different from that of human neurons exposed to human CSF?

Opioid abuse is a severe global health challenge, leading to rising morbidity, mortality, and increasing societal costs. The aim of this study was to investigate neuroinflammation, neuronal damage and potential changes in the orexin system or beta-amyloid metabolism in the cerebrospinal fluid (CSF) of individuals undergoing opioid substitution therapy (OST). This cross-sectional study investigates CSF biomarkers in individuals undergoing OST, compared to control subjects. Participants receiving OST were recruited from the outpatient clinic at the Department of Psychiatry, Sahlgrenska University Hospital, Gothenburg (Sweden). Each participant provided a complete medical history, including details of drug use over the past 6 months, followed by a lumbar puncture to obtain CSF samples. Molecules associated with neuroinflammation, neuronal and glial damage, beta-amyloid metabolism and orexinergic function were analysed in the participants' CSF, alongside electrolyte levels. Specifically, we analysed levels of sTREM-2, YKL-40, IL-1β, IL-6, IL-8, IL-10, TNF-α, AXL, MER, TYRO3, GAS6, NfL, GFAP, total tau (T-tau), phosphorylated tau (P-tau), neurogranin, Aβ40, Aβ42, the Aβ42/Aβ40 ratio, orexin-A, sPDGFR-β and electrolytes. The study included 15 control subjects and 17 in the opioid substitution group. Patients undergoing opioid substitution therapy exhibited elevated levels of sTREM-2, Aβ42/Aβ40 ratio and NfL in their CSF. Conversely, concentrations of Na+ and Cl- were lower compared to controls. No significant differences were found between groups for other biomarkers, including orexin-A. However, when normalized to Aβ40 levels, YKL-40, IL-8, TYRO3 and P-Tau were also elevated in individuals with opioid dependence. Elevated biomarkers of neuroimmune activation, neuronal damage and beta-amyloid metabolism in opioid dependence suggest CNS inflammation as a contributor to its pathophysiology. Reduced electrolyte levels imply disrupted CSF water regulation, possibly linked to impaired glial function. These findings highlight both neural and non-neural mechanisms in opioid dependence.

Genetic engineering of microglial cells is a promising therapeutic avenue emerging with advancements in gene delivery techniques. Using a recently developed AAV capsid for efficient in vitro transduction we report the engineering of microglia with CARs (CAR-Mic) targeting phagocytosis of amyloid beta 1‒42 (Aβ42). Functional screening of seven CAR constructs in human iPSC-derived microglia revealed up to 6-fold increases in internalized Aβ relative to viral control. CAR-driven phagocytic enhancement was selective for Aβ, dependent on intracellular domain signaling, and was confirmed in primary mouse microglia. These findings highlight the potential of using this approach to target dysfunctional microglia in Alzheimer’s disease and other CNS disorders.

Fluctuations of extracellular brain ion concentrations have been associated with transitions between brain states such as sleep and wakefulness, and disturbances have been implicated in a variety of neurological conditions, including dementia, epilepsy and migraine. This study aims to define the normal CSF ion profile and identify key factors influencing its regulation. In this cross-sectional study, we analysed samples from 42 individuals (16 men), including 28 healthy participants and 14 patients with medically unexplained neurological symptoms. Age spanned between 20 and 55 years. Using validated clinical assays, we measured paired CSF and serum concentrations of Ca²⁺, Cl⁻, K⁺, Mg²⁺ and Na⁺. We examined their interrelationships and assessed the impact of blood-brain barrier permeability (the albumin quotient), age, sampling time and sex. CSF ion concentrations were highly stable and maintained within distinct, narrow ranges, separate from serum ranges for all ions measured (P < 0.0001), with no overlapping. Cl- (+25%), Na+ (+5%) and Mg2+ (+37%) concentrations were higher, while K+ (-30%) and Ca2+ (-50%) concentrations were lower. Consistent with an independent and active CNS homeostatic control, CSF concentrations of K+, Cl- or Mg2+ showed no significant correlation with their serum counterparts, while Na+ and Ca2+ displayed moderate associations with serum levels. Moreover, blood-brain barrier permeability had no significant impact on CSF ion concentrations. Small, but significant, age-related declines were observed for Cl-, Mg2+ and Ca2+ in CSF, and circadian fluctuations affected K+, which increased slightly in the afternoon. Minor sex differences were noted, with men exhibiting slightly higher Mg2+ and Ca2+ levels. Our findings demonstrate that CSF ion concentrations are precisely regulated at the barriers of the CNS, largely independent of serum levels and with low interindividual variation, reinforcing the concept of a highly controlled CNS environment. This distinct ion composition may help modulate neuronal excitability, supporting brain state transitions such as sleep-wake cycling. Identification of hydration status as a potential confounding factor suggests that normalization to CSF-Na+ may improve the detection of pathological disruptions in CSF ion homeostasis. These insights reinforce the foundation for using CSF ion profiles as biomarkers for neurological disorders.

Slow-wave sleep has been proposed to facilitate the removal of proteins, implicated in neurodegeneration, from the brain. While mechanistic evidence from animal models is accumulating, direct human data on how slow-wave sleep shapes cerebrospinal fluid (CSF) proteostasis remain limited, constraining our understanding of physiological resilience to neurodegenerative disease. Twelve healthy adults (aged 20–40 years) underwent CSF sampling following three controlled sleep conditions in a randomized crossover design; (1) one night of sleep followed by afternoon CSF sampling, (2) one night of sleep followed by morning CSF sampling, and (3) one night of total sleep deprivation followed by morning CSF sampling. Sleep and wakefulness were verified using polysomnography and actigraphy, with > 4-week washout periods between conditions. Measured CSF biomarkers included Alzheimer’s disease-related proteins: beta-amyloid isoforms (Aβ38, Aβ40, and Aβ42), total tau, tau phosphorylated at amino acid 181 (p-tau), glial fibrillary acidic protein (GFAP), and neurofilament light chain, as well as orexin, albumin (also measured in serum), and osmolality. Differences between conditions were assessed using Friedman tests with Dunn’s post hoc correction. CSF levels of Aβ and tau tended to be consistently lower after sleep compared with both afternoon sampling and post-sleep deprivation. Concurrently, CSF albumin levels increased after sleep, while neurofilament light and GFAP remained unchanged. Orexin levels rose markedly during sleep deprivation but showed no circadian variation and did not track with biomarker levels. These findings support a model in which slow-wave sleep selectively reduces CSF concentrations of Aβ and tau, potentially through enhanced solute mobility and receptor-mediated clearance. Unchanged levels of NfL and GFAP argue against bulk clearance. Orexin may primarily function to oppose sleep pressure rather than directly regulate proteostasis. These hypotheses merit direct testing to inform strategies for delaying pathological protein accumulation in neurodegenerative disease.

The excitatory monosynaptic activation of hippocampal CA1 pyramidal cells is spatially segregated such that the proximal part of the apical dendritic tree in stratum radiatum (SR) receives input from the hippocampal CA3 region while the distal part in the stratum-lacunosum-moleculare (SLM) receives input mainly from the entorhinal cortex. The AMPA receptor-mediated (AMPA) signalling of SLM synapses in slices from neonatal rats was previously found to considerably differ from that of the SR synapses. In the present study, AMPA signalling of SLM synapses in 1-month-old rats has been examined, that is, when the hippocampus is essentially functionally mature. For the SR synapses, this time is characterized by a facilitatory shift in short-term plasticity, in the disappearance of labile postsynaptic AMPA signalling, a property thought to be important for early activity-dependent organization of neural circuits, and the expression of an adult form of long-term potentiation. We found that the SLM synapses alter their short-term plasticity similarly to that of the SR synapses. However, the labile postsynaptic AMPA signalling was not only maintained but substantially enhanced in the SLM synapses. The long-term potentiation observed was not of the adult form but like that of the neonatal SR synapses based on unsilencing of AMPA labile synapses. We propose that these features of the SLM synapses in the mature hippocampus will help to produce a flexible map of the multimodal sensory input reaching the SLM required for its conjunctive operation with the SR input to generate a proper functional output from the CA1 region.

GFRAL-expressing neurons actuate aversion and nausea, are targets for obesity treatment, and may mediate metformin effects by long-term GDF15-GFRAL agonism. Whether GFRAL+ neurons acutely regulate glucose and energy homeostasis is, however, underexplored. Here, we report that cell-specific activation of GFRAL+ neurons using a variety of techniques causes a torpor-like state, including hypothermia, the release of stress hormones, a shift from glucose to lipid oxidation, and impaired insulin sensitivity, glucose tolerance, and skeletal muscle glucose uptake but augmented glucose uptake in visceral fat. Metabolomic analysis of blood and transcriptomics of muscle and fat indicate alterations in ketogenesis, insulin signaling, adipose tissue differentiation and mitogenesis, and energy fluxes. Our findings indicate that acute GFRAL+ neuron activation induces endocrine and gluco- and thermoregulatory responses associated with nausea and torpor. While chronic activation of GFRAL signaling promotes weight loss in obesity, these results show that acute activation of GFRAL+ neurons causes hypothermia and hyperglycemia.

It is well recognized that changes in the extracellular concentration of calcium ions influence the excitability of neurons, yet what mechanism(s) mediate these effects is still a matter of debate. Using patch-clamp recordings from rat hippocampal CA1 pyramidal neurons, we examined the contribution of G-proteins and intracellular calcium-dependent signaling mechanisms to changes in intrinsic excitability evoked by altering the extracellular calcium concentration from physiological (1.2 mM) to a commonly used experimental (2 mM) level. We find that the inhibitory effect on intrinsic excitability of calcium ions is mainly expressed as an increased threshold for action potential firing (with no significant effect on resting membrane potential) that is not blocked by either the G-protein inhibitor GDP beta S or the calcium chelator BAPTA. Our results therefore argue that in the concentration range studied, G-protein coupled calcium-sensing receptors, non-selective cation conductances, and intracellular calcium signaling pathways are not involved in mediating the effect of extracellular calcium ions on intrinsic excitability. Analysis of the derivative of the action potential, dV/dt versus membrane potential, indicates a current shift towards more depolarized membrane potentials at the higher calcium concentration. Our results are thus consistent with a mechanism in which extracellular calcium ions act directly on the voltage-gated sodium channels by neutralizing negative charges on the extracellular surface of these channels to modulate the threshold for action potential activation.image

Background Disturbances in brain ion concentrations have been implicated in the regulation of brain states such as sleep and wakefulness, as well as in a variety of neurological conditions, including dementia, epilepsy, and migraine. Despite this, studies specifically characterizing normal cerebrospinal fluid (CSF) ion composition are generally lacking.Methods We quantify the normal human CSF ion composition in this non-interventional, cross-sectional, retrospective study using paired CSF and serum concentrations of Ca²⁺, Cl⁻, K⁺, Mg²⁺, and Na⁺ measured in healthy young to middle-aged volunteers (n = 28) and patients without neurological disease (n = 14). Relationships with variables such as albumin quotient, age, sampling time, and sex were analyzed. Group differences were assessed using the Kruskal-Wallis and Mann-Whitney U tests, while correlations were examined with Spearman's rank correlation coefficient.Results CSF ion concentrations were significantly different from serum for all ions measured (P < 0.0001). Cl− (+ 25%), Na+ (+ 5%) and Mg2+ (+ 37%) concentrations were higher, while K+ (-30%) and Ca2+ (-50%) concentrations were lower. These differences were consistent with no overlap between serum and CSF concentrations. There was a trend toward higher ion concentrations in samples collected later in the day and in men, but no significant correlation with the albumin quotient.Conclusions The distinct ion composition of CSF, compared to serum, may establish a low baseline neuronal excitability, allowing for controlled modulation by neuromodulators without leading to pathological hyperexcitability. This might offer new insights for targeting neurological diseases associated with disrupted ion homeostasis.

In the 2nd postnatal week hippocampus, Hebbian-induced long-term potentiation (LTP) of AMPA receptor-mediated transmission in CA3-CA1 synapses is not a genuine potentiation. Instead, it is a de-depression (unsilencing) and temporary stabilization of postsynaptically AMPA-labile synapses silenced by a prior test pulse (0.03 - 0.2 Hz) stimulation. In addition to such an LTP, Hebbian induction at these synapses also results in a labile potentiation that becomes depotentiated by test pulse stimulation, thus appearing as an Hebbian-induced short-term potentiation (STP). Although the induction of this labile potentiation was blocked in the combined presence of N-methyl-D-aspartate (NMDA) and metabotropic glutamate (mGlu) receptor antagonists, the depotentiation was not affected by these drugs. The labile potentiation was not associated with a change in paired-pulse ratio and was, after a depotentiation, fully re-established by a 20 min interruption of test pulse stimulation. These properties are shared with the silencing of previously non-stimulated (naive) AMPA-labile synapses by such test pulse stimulation. However, the depotentiation following an Hebbian induction is not a re-silencing of naive AMPA labile synapses since there is no correlation between the magnitudes of depotentiation and preceding silencing of naive synapses. The present results suggest that Hebbian induction at these neonatal CA3-CA1 synapses, in addition to unsilencing and temporary stabilization of AMPA-labile transmission, creates a labile potentiation based on the insertion/activation of an additional AMPA-labile signaling unit to a pre-existing synapse. ### Competing Interest Statement The authors have declared no competing interest.

Antisecretory Factor (AF) is an endogenous peptide known for its powerful antisecretory and anti-inflammatory properties. We have previously shown that AF also acts as a neuromodulator of GABAergic synaptic transmission in rat hippocampus in a way that results in disinhibition of CA1 pyramidal neurons. Disinhibition is expected to facilitate the induction of long-term potentiation (LTP), and LTP is known to play a crucial role in learning and memory acquisition. In the present study we investigated the effect of AF on LTP in CA3-CA1 synapses in rat hippocampus. In addition, endogenous AF plasma activity was upregulated by feeding the rats with specially processed cereals (SPC) and spatial learning and memory was studied in the Morris Water Maze (MWM). We found that LTP was significantly enhanced in the presence of AF, both when added exogenously in vitro as well as when upregulated endogenously by SPC-feeding. In the presence of the GABAA-receptor antagonist picrotoxin (PTX) there was however no significant enhancement of LTP. Moreover, rats fed with SPC demonstrated enhanced spatial learning and short-term memory, compared with control animals. These results show that the disinhibition of GABAergic transmission in the hippocampus by the endogenous peptide AF enhances LTP as well as spatial learning and memory.

SummarySleep is controlled by a circadian rhythmicity, via a reduction of arousal‐promoting neuromodulatory activity, and by accumulation of somnogenic factors in the interstitial fluid of the brain. Recent experiments in mice suggest that a reduced neuronal excitability caused by a reduced concentration of potassium in the brain, concomitant with an increased concentration of calcium and magnesium, constitutes an important mediator of sleep. In the present study, we examined whether such changes in ion concentrations could be detected in the cerebrospinal fluid of healthy humans. Each subject underwent cerebrospinal fluid collection at three occasions in a randomized order: at 15:00 hours–17:00 hours during waking, at 06:00 hours–07:00 hours immediately following 1 night of sleep, and at 06:00 hours–07:00 hours following 1 night of sleep deprivation. When compared with wakefulness, both sleep and sleep deprivation produced the same effect of a small (0.1 mm, about 3%), but robust and highly significant, reduction in potassium concentration. Calcium and magnesium concentrations were unchanged. Our results support a circadian modulation of neuronal excitability in the brain mediated via changes of the interstitial potassium concentration.

A dysfunction of the glutamatergic transmission, especially of the NMDA receptor (NMDAR), constitutes one of the main biological substrate of psychotic disorders, such as schizophrenia. The NMDAR signaling hypofunction, through genetic and/or environmental insults, would cause a neurodevelopmental myriad of molecular, cellular, and network alterations that persist throughout life. Yet, the mechanisms underpinning NMDAR dysfunctions remain elusive. Here, we compared the membrane trafficking of NMDAR in three gold-standard models of schizophrenia, i.e., patient's cerebrospinal fluids, genetic manipulations of susceptibility genes, and prenatal developmental alterations. Using a combination of single nanoparticle tracking, electrophysiological, biochemical, and behavioral approaches in rodents, we identified that the NMDAR trafficking in hippocampal neurons was consistently altered in all these different models. Artificial manipulations of the NMDAR surface dynamics with competing ligands or antibody-induced receptor cross-link in the developing rat brain were sufficient to regulate the adult acoustic startle reflex and compensate for an early pathological challenge. Collectively, we show that the NMDAR trafficking is markedly altered in all clinically relevant models of psychosis, opening new avenues of therapeutical strategies.

Huntington's disease (HD) is one of the most common, dominantly inherited neurodegenerative disorders. It affects the striatum, cerebral cortex, and other subcortical structures leading to involuntary movement abnormalities, emotional disturbances, and cognitive impairments. HD is caused by a CAG•CTG trinucleotide-repeat expansion in exon 1 of the huntingtin (HTT) gene leading to the formation of mutant HTT (mtHTT) protein aggregates. Besides the toxicity of the mutated protein, there is also evidence that mtHTT transcripts contribute to the disease. Thus, the reduction of both mutated mRNA and protein would be most beneficial as a treatment. Previously, we designed a novel anti-gene oligonucleotide (AGO)-based strategy directly targeting the HTT trinucleotide-repeats in DNA and reported downregulation of mRNA and protein in HD patient fibroblasts. In this study, we differentiate HD patient-derived induced pluripotent stem cells to investigate the efficacy of the AGO, a DNA/Locked Nucleic Acid mixmer with phosphorothioate backbone, to modulate HTT transcription during neural in vitro development. For the first time, we demonstrate downregulation of HTT mRNA following both naked and magnetofected delivery into neural stem cells (NSCs) and show that neither emergence of neural rosette structures nor self-renewal of NSCs is compromised. Furthermore, the inhibition potency of both HTT mRNA and protein without off-target effects is confirmed in neurons. These results further validate an anti-gene approach for the treatment of HD.

Lithium salts are used as mood-balancing medication prescribed to patients suffering from neuropsychiatric disorders, such as bipolar disorder and major depressive disorder. Lithium salts cross the blood-brain barrier and reach the brain parenchyma within few hours after oral application, however, how lithium influences directly human neuronal function is unknown. We applied patch–clamp and microelectrode array technology on human induced pluripotent stem cell (iPSC)-derived cortical neurons acutely exposed to therapeutic (<1 mM) and overdose concentrations (>1 mM) of lithium chloride (LiCl) to assess how therapeutically effective and overdose concentrations of LiCl directly influence human neuronal electrophysiological function at the synapse, single-cell, and neuronal network level. We describe that human iPSC-cortical neurons exposed to lithium showed an increased neuronal activity under all tested concentrations. Furthermore, we reveal a lithium-induced, concentration-dependent, transition of regular synchronous neuronal network activity using therapeutically effective concentration (<1 mM LiCl) to epileptiform-like neuronal discharges using overdose concentration (>1 mM LiCl). The overdose concentration lithium-induced epileptiform-like activity was similar to the epileptiform-like activity caused by the GABA A -receptor antagonist. Patch–clamp recordings reveal that lithium reduces action potential threshold at all concentrations, however, only overdose concentration causes increased frequency of spontaneous AMPA-receptor mediated transmission. By applying the AMPA-receptor antagonist and anti-epileptic drug Perampanel, we demonstrate that Perampanel suppresses lithium-induced epileptiform-like activity in human cortical neurons. We provide insights in how therapeutically effective and overdose concentration of lithium directly influences human neuronal function at synapse, a single neuron, and neuronal network levels. Furthermore, we provide evidence that Perampanel suppresses pathological neuronal discharges caused by overdose concentrations of lithium in human neurons.

When activated at low frequencies (0.1-1 Hz), second postnatal week synapses onto the most distal part of the apical dendritic tree (stratum lacunosum-moleculare) of rat hippocampal CA1 pyramidal cells display a frequency-dependent synaptic depression not observed for the more proximal (stratum radiatum) synapses. Depression in this frequency range is thought of as a possible contributor to behavioural habituation. In fact, in contrast to the proximal synapses, the distal synapses provide more direct sensory information from the entorhinal cortex as well as from thalamic nuclei. The use of antagonists showed that the activation of GABA(A), GABA(B), NMDA, mGlu, kainate, adenosine, or endocannabinoid receptors was not directly involved in the depression, indicating it to be intrinsic to the synapses themselves. While the depression affected paired-pulse plasticity in a manner indicating a decrease in vesicle release probability, the depression could not be explained by a stimulus-dependent decrease in calcium influx. Despite affecting the synaptic response evoked by brief high-frequency stimulation (10 impulses, 20 Hz) in a manner indicating vesicle depletion, the depression was unaffected by large variations in release probability. The depression was found not only to affect the synaptic transmission at low frequencies (0.1-1 Hz) but also to contribute to the depression evolving during brief high-frequency stimulation (10 impulses, 20 Hz). We propose that a release-independent process directly inactivating release sites with a fast onset (ms) and long duration (up to 20 s) underlies this synaptic depression.

Human induced pluripotent stem cell (hiPSC)-derived in vitro neural and organoid models resemble fetal, rather than adult brain properties, indicating that currently applied cultivation media and supplements are insufficient to achieve neural maturation beyond the fetal stage. In vivo, cerebrospinal fluid molecules are regulating the transition of the immature fetal human brain into a mature adult brain. By culturing hiPSC-3D neural aggregates in human cerebrospinal fluid (hCSF) obtained from healthy adult individuals, we demonstrate that hCSF rapidly triggers neurogenesis, gliogenesis, synapse formation, neurite outgrowth, suppresses proliferation of residing neural stem cells, and results in the formation of synchronously active neuronal circuits in vitro within 3 days. Thus, a physiologically relevant and adult brain-like milieu triggers maturation of hiPSC-3D neural aggregates into highly functional neuronal circuits in vitro. The approach presented here opens a new avenue to identify novel physiological factors for the improvement of hiPSC neural in vitro models.

Persistent neural stem cell (NSC) proliferation is, among others, a hallmark of immaturity in human induced pluripotent stem cell (hiPSC)-based neural models. TGF-β1 is known to regulate NSCs in vivo during embryonic development in rodents. Here we examined the role of TGF-β1 as a potential candidate to promote in vitro differentiation of hiPSCs-derived NSCs and maturation of neuronal progenies. We present that TGF-β1 is specifically present in early phases of human fetal brain development. We applied confocal imaging and electrophysiological assessment in hiPSC-NSC and 3D neural in vitro models and demonstrate that TGF-β1 is a signaling protein, which specifically suppresses proliferation, enhances neuronal and glial differentiation, without effecting neuronal maturation. Moreover, we demonstrate that TGF-β1 is equally efficient in enhancing neuronal differentiation of human NSCs as an artificial synthetic small molecule. The presented approach provides a proof-of-concept to replace artificial small molecules with more physiological signaling factors, which paves the way to improve the physiological relevance of human neural developmental in vitro models.

It is commonly recognized that physical exercise positively affects several CNS regions and improves cognitive abilities. For example, exercise is associated with an increase in neurogenesis and facilitation of long-term potentiation in the hippocampus. Conversely, animal models for depression are associated with a decrease in neurogenesis and a reduction of long-term potentiation in the hippocampus. Although exercise could be a viable option in the treatment of some forms of depression, the mechanisms responsible for such improvements have not been elucidated. In this study, we examine hippocampal function using electrophysiological field recordings in CA1 and dentate gyrus to study baseline synaptic transmission and long-term potentiation in adolescent and adult rats prenatally exposed to the glucocorticoid dexamethasone. One group of animals was allowed to run voluntarily for 10 or 21 days using an exercise wheel before the experiments, and the control group was prevented from running (i.e. the exercise wheel was locked). In adult saline-exposed animals, exercise was associated with increased long-term potentiation in the dentate gyrus. Unexpectedly, in dexamethasone-exposed animals, dentate gyrus long-term potentiation was facilitated, whereas long-term potentiation in CA1 was unaffected by prenatal dexamethasone or by 10 or 21 days of voluntary running. Irrespective of age, prenatal dexamethasone and running had limited effects on synaptic transmission and presynaptic release in CA1 and dentate gyrus. In summary, running facilitates dentate gyrus long-term potentiation in adult animals that resembles the effects of prenatal dexamethasone.