The research team, led by Tolulope T. Arogundade of Redeemer’s University in Nigeria together with colleagues in Nigeria and Poland, chose the fruit fly Drosophila melanogaster for a reason. The insect’s antioxidant pathways are well conserved with those of mammals, its generation time allows entire life-course experiments to be completed in weeks, and its larval crawling and feeding behaviors provide quantifiable readouts of neurological function. Crucially, the fly allows researchers to isolate the developmental period with precision: larvae were reared from their first instar through pupation and eclosion on food containing the test compounds, after which the treatment ceased entirely. Any differences seen in adulthood therefore represent latent programming effects rather than ongoing toxicity.

The toxicant in question was manganese, an element with a double identity. It is essential for life, serving as a cofactor for manganese superoxide dismutase and a suite of other enzymes, yet at elevated levels it is a recognized neurotoxicant. Human epidemiological studies have linked early-life manganese exposure, whether from contaminated drinking water or occupational settings, to cognitive deficits, motor impairments, and neuropsychiatric symptoms that often emerge insidiously years later. In the experiment, larvae were exposed to manganese chloride at two concentrations, 0.5 and 3.0 millimolar, doses selected and validated through pilot survival assays to represent a sub-clinical level and a biologically active but non-lethal level. Against this, the researchers tested quercetin, a flavonoid abundant in onions and apples, at 0.25 and 1.0 millimolar.

The behavioral results painted a nuanced picture. Larvae raised on high-dose manganese crawled dramatically shorter distances than controls, covering just 1.8 centimeters in one minute compared with 2.6 centimeters for untreated animals, a dose-dependent impairment that was statistically significant. Their feeding was also disturbed, with mouth-hook contractions running roughly fifteen percent faster than controls, a hyperactive pattern that suggests the sensory-motor circuitry governing feeding had been perturbed. Yet when those same larvae eclosed into adults and were tested five days later in the rapid iterative negative geotaxis assay, which measures climbing ability, the deficits had largely vanished. Adult climbing performance was indistinguishable from controls across all treatment groups. The molecular damage, however, told a very different story.

Biochemical assays of young adult flies revealed that the manganese-exposed animals carried a persistent oxidizing burden. Hydrogen peroxide, a central reactive oxygen species, accumulated to 3.8 nanomoles per milligram of protein in the high-dose manganese group, more than double the 1.8 nanomoles measured in controls, a difference that was highly significant. This accumulation occurred despite the fact that the activities of the classic antioxidant enzymes superoxide dismutase and catalase were largely preserved, suggesting that manganese disrupts redox balance not by crippling the enzyme defenses but by overwhelming the system at its source. The authors point to manganese’s established capacity to interfere with mitochondrial electron transport, particularly at complex II, and to drive Fenton-like chemistry that generates hydroxyl radicals from hydrogen peroxide.

The genomic consequences were the study’s most dramatic finding. Using a diphenylamine colorimetric assay to quantify the DNA fragmentation index, the researchers found that high-dose manganese pushed fragmentation to approximately 54 percent, compared with 29 percent in controls, an increase of roughly 85 percent. In other words, adult flies that had never touched manganese since emerging from their pupal cases carried genomes riddled with damage seeded during their larval feeding. The mechanism is likely multipronged: hydroxyl radicals derived from elevated hydrogen peroxide attack DNA to produce lesions such as 8-oxoguanine, and manganese ions can directly inhibit OGG1, the glycosylase enzyme that initiates repair of that very lesion, by displacing the magnesium ion in its active site. Damage production and damage repair are compromised simultaneously.

A parallel story unfolded in the realm of protein damage. Advanced glycation end-products, or AGEs, irreversible protein modifications produced when lipid peroxidation byproducts such as malondialdehyde react with amino acid residues, accumulated 57 percent above control levels in the high-dose manganese group, reaching 58 nanograms per milligram of protein versus 37 in controls. AGEs are more than passive markers of wear. When they modify components of the MRE11-RAD50-NBS1 complex, the cellular machinery that senses and initiates repair of DNA double-strand breaks, they can blunt the DNA damage response itself. The correlation between elevated DNA fragmentation and elevated glycation in the manganese-exposed flies suggests a self-amplifying cycle in which oxidative and glycative stress each feed the other, degrading both genome and proteome together.

Quercetin told the opposite tale. Flies developmentally exposed to the lower dose of the flavonoid showed enhanced catalase activity, roughly 28 percent above control levels, while maintaining basal hydrogen peroxide concentrations and showing no behavioral deficits at any stage. Their DNA fragmentation index trended downward, with the 0.25 millimolar group averaging around 14 percent, roughly half the control value, although this reduction fell just short of statistical significance. AGE levels in this group were 32 percent below controls, a significant decrease. The selective boost to catalase aligns with quercetin’s known ability to activate the Keap1-Nrf2 antioxidant signaling axis, whose fly ortholog, CncC, directly regulates catalase transcription under oxidative challenge. Notably, the higher quercetin dose failed to produce further benefits, echoing the biphasic behavior of flavonoids, which at high concentrations can undergo autoxidation and paradoxically generate reactive species.

Why did the manganese-exposed adults climb normally while their larval selves had crawled poorly, and while their molecules told a story of damage? The authors propose several non-exclusive explanations. Compensatory mechanisms such as autophagy-mediated clearance of damaged proteins and synaptic homeostatic plasticity may buffer locomotor circuits against moderate developmental insults, preserving function even as molecular wear accumulates beneath the surface. Alternatively, the five-day post-eclosion assessment may simply capture a pre-symptomatic stage, with late-onset motor decline emerging in older flies as accumulated DNA damage crosses a functional threshold. This latter possibility carries obvious translational weight, given that human manganese-associated neurological deficits also tend to manifest years after the initial exposure window. The researchers suggest that monitoring biomarkers such as plasma AGEs and urinary 8-oxodG in children from manganese-endemic regions could enable early risk stratification before symptoms appear.

The study has honest limits. Quercetin was never given concurrently with manganese, so the experiment speaks to independent programming effects rather than direct rescue, and the authors explicitly call a co-treatment trial the priority next step. Sex-specific vulnerabilities were not assessed, the adult endpoint was a single time point, and mechanistic pathways were inferred rather than genetically validated. Still, the central message lands with force: hydrogen peroxide levels and DNA fragmentation indices emerge as sensitive biomarkers of latent developmental toxicant injury, and low-dose dietary antioxidants appear capable of priming antioxidant defenses during critical windows without harm. In a world where manganese exposure affects communities near industrial sites and contaminated water supplies worldwide, the idea that a common dietary flavonoid might tip the developmental balance toward resilience, rather than vulnerability, is a proposition worth serious investigation in mammalian models.

Subject of Research: Developmental programming of adult oxidative stress, DNA damage and behaviour by manganese or quercetin in Drosophila melanogaster

Article Title: Developmental exposure to manganese or quercetin differentially programs adult oxidative stress, DNA fragmentation and behaviour in Drosophila

Article References: Arogundade, T. T., Olatomide, O. D., Adeleye, D. A., Ikegulu, P. S., Akinfaye, M. O., Arogundade, O. A., Omotoso, D. R., & Gbadamosi, I. (2026). Developmental exposure to manganese or quercetin differentially programs adult oxidative stress, DNA fragmentation and behaviour in Drosophila. Discover Toxicology, 3(1), Article 9. https://doi.org/10.1007/s44339-026-00054-0

Image Credits: AI Generated

DOI: 10.1007/s44339-026-00054-0

Keywords: manganese, quercetin, Drosophila, oxidative stress, DNA fragmentation, developmental programming, neurotoxicology, advanced glycation end-products, hydrogen peroxide, catalase, Nrf2 signaling, flavonoids

The stakes of this question extend far beyond the laboratory. Spatial cognition, the capacity to acquire, store, and retrieve information about environmental geometry and object location, depends on a distributed brain network anchored by the hippocampal formation, with entorhinal grid cells and hippocampal place cells jointly constructing the cognitive maps that guide navigation. At the cellular level, the formation and consolidation of spatial memories rely on long-term potentiation at Schaffer collateral synapses connecting the CA3 and CA1 fields of the hippocampus, a process governed by NMDA and AMPA receptor-mediated glutamatergic transmission and finely tuned by dopaminergic, noradrenergic, and serotonergic inputs. Cathinone, khat’s principal psychoactive alkaloid, is a beta-keto phenethylamine structurally related to amphetamine that promotes the release of dopamine and norepinephrine and blocks their reuptake. Because dopamine and norepinephrine dynamically regulate hippocampal synaptic plasticity, cathinone’s pharmacological profile provides direct mechanistic grounds for suspecting that chronic khat exposure could disrupt the very synaptic machinery that spatial memory requires.

Human studies have long hinted at trouble. Chronic khat users perform worse than khat-free controls on working memory and cognitive flexibility tasks, on verbal learning and delayed recall, and across broader domains including attention, motor speed, decision-making, and inhibitory control, and a meta-analysis has linked khat use to measurable memory impairment. These deficits carry real functional consequences: compromised occupational performance, impaired driving safety, and reduced academic achievement among the university students and young adults among whom use is common. Yet human data are notoriously difficult to interpret. Polysubstance use, small and non-representative samples, and uncontrolled dosing histories all muddy the causal picture, leaving open the question of whether khat itself, rather than lifestyle factors correlated with its use, drives the cognitive decline. Controlled rodent experiments, which permit precise manipulation of dose, duration, and exposure route while excluding such confounds, are therefore essential for establishing a reliable dose-response relationship, and it is precisely this synthesis that the new review delivers.

To build their evidence base, the authors conducted a structured literature search across PubMed, ResearchGate, Elsevier, EMBASE, and Web of Science, screening records according to PRISMA 2020 methodology with a search end date of May 25, 2025. From an initial pool of 504 records, the investigators winnowed the field to fourteen primary studies meeting strict inclusion criteria: use of Catha edulis extract, juice, or purified cathinone; an in-vivo rodent model; validated behavioral assessment of spatial cognition; and quantifiable outcomes. The behavioral paradigms represented were dominated by the Morris Water Maze, employed in nine studies, which measures both spatial learning through escape latency and path length during acquisition trials and spatial memory retention through time spent in the target quadrant during probe trials. Three studies used the Radial Arm Maze, which tracks spatial working and reference memory through arm-entry patterns, while the T-maze, Y-maze, and Novel Object Recognition task each appeared in smaller numbers. Study quality was assessed with the SYRCLE Risk of Bias tool, validated specifically for animal intervention studies.

The pattern that emerged across the fourteen studies is strikingly duration-dependent. Acute exposure, defined as a single dose ranging from 40 to 500 milligrams per kilogram, produced bidirectional effects that initially appeared to follow an inverted-U curve. At the low end, doses of 40 to 100 milligrams per kilogram modestly improved exploratory behavior and reduced first-trial water maze latency, but the review’s authors interpret these gains as arousal-mediated motivation rather than genuine memory enhancement. At 150 to 500 milligrams per kilogram, every study reported consistent deficits across maze paradigms, including increased path length and latency and reduced working memory scores, with no graded response within this range. The reviewers argue this pattern reflects a threshold effect rather than a true inverted-U relationship: once dopaminergic stimulation exceeds a critical level, it disrupts the NMDA receptor-dependent processes required for spatial encoding. Finer dose stratification within the low-to-moderate range will be needed to settle the question formally.

Repeated exposure told a darker story. Subacute dosing, at 40 to 360 milligrams per kilogram over five to seventeen days, was consistently associated with spatial learning deficits, though with task-specific nuances: at 40 milligrams per kilogram over ten days, CBA mice showed disrupted reversal learning and impaired reference memory in the water maze, while the same dose over a shorter five-day protocol spared learning but impaired memory retention. Subchronic exposure of 29 to 90 days produced the most robust impairment profiles across multiple paradigms, with 100 milligrams per kilogram driving increased thigmotaxis, reduced spontaneous alternation, and elevated error rates in later training phases, though one study at the same dose reported no significant deficits, a discrepancy the authors attribute to methodological heterogeneity. Chronic exposure beyond 90 days, examined in a single study of 36 rats given 100, 200, or 300 milligrams per kilogram for twelve weeks, caused persistent spatial learning and memory impairment: at the highest dose, rats took significantly longer and swam significantly farther to reach the hidden platform, and spent significantly less time in the target quadrant during the probe trial. Critically, no study in the entire evidence base incorporated a washout period, so whether these deficits reverse after cessation remains entirely unknown.

Beneath the behavioral findings lie several converging mechanistic pathways that the review outlines with technical precision. As an indirect monoaminergic agonist, cathinone elevates extracellular dopamine, norepinephrine, and serotonin, and supranormal dopaminergic signaling can disrupt NMDA receptor-dependent long-term potentiation at hippocampal CA3-CA1 synapses, the cellular substrate of spatial learning. Chronic exposure has additionally been linked to reduced brain-derived neurotrophic factor signaling through its tropomyosin receptor kinase B, impaired neurogenesis, and altered dendritic spine morphology in the hippocampus, changes that would structurally erode the synaptic architecture on which memory consolidation depends. Oxidative stress and microglial activation may compound the damage by releasing pro-inflammatory cytokines such as interleukin-1 beta and tumor necrosis factor alpha, further impairing glutamatergic transmission. The authors caution, however, that direct mechanistic evidence from khat-exposed animals remains scarce, and they call for future studies combining behavioral testing with electrophysiology and molecular assays of BDNF/TrkB signaling, phosphorylated CREB, neuroinflammation, and oxidative stress markers.

The review is equally candid about the weaknesses of the evidence it synthesizes. The risk-of-bias assessment revealed that 78.6 percent of studies were at high risk of performance and detection bias because outcome assessment was not blinded, a serious concern in behavioral research where experimenter expectations can subtly inflate treatment effects. Allocation concealment was unreported in all fourteen studies, and random housing was described in only two. The evidence base is also narrow: 78.6 percent of studies used Swiss albino mice, an outbred stock with high inter-individual genetic variability, and nearly two-thirds originated from Ethiopia, with locally sourced khat of variable cathinone content that may range from 0.1 to 1.2 percent of dry weight and degrades rapidly after harvest into the weaker alkaloids cathine and norephedrine. Without standardized extract preparation and chemical fingerprinting, the nominal dose-response relationships reported across studies may not be directly comparable. All studies also relied on forced oral dosing rather than voluntary consumption models that better mirror human chewing behavior.

Translation to human exposure adds further nuance. Using body surface area scaling, the reviewers estimated that the rodent doses of 40 to 500 milligrams per kilogram correspond to human equivalent doses of roughly 6.5 to 81 milligrams per kilogram, a range whose upper end substantially exceeds realistic exposure from habitual khat chewing, estimated at approximately 7 to 28 milligrams of cathinone equivalent per session in a 70-kilogram adult. This suggests the most severe impairment profiles may reflect supraphysiological exposure scenarios, while the lower-dose studies more faithfully model everyday use. The authors argue that the cumulative message nonetheless justifies practical action: incorporating khat-use history into clinical cognitive screening, targeted public health education for youth, and epidemiological surveillance in endemic regions. Their research agenda calls for standardized cathinone-equivalent dosing, washout and recovery cohorts to test reversibility, multi-strain and both-sex comparisons, voluntary self-administration models, and longitudinal human studies integrating neuropsychological assessment with neuroimaging and biomarkers. For a plant woven into the social and economic fabric of an entire region, the emerging picture is one of meaningful cognitive risk that science is only beginning to map.

Subject of Research: Preclinical effects of the stimulant plant Catha edulis on spatial learning and memory in rodent models

Article Title: A narrative review of preclinical evidence on the effects of Catha edulis on spatial cognition and memory in rodents

Article References: Bekri, K., & Abiye, A. A. (2026). A narrative review of preclinical evidence on the effects of Catha edulis on spatial cognition and memory in rodents. Discover Toxicology, 3(1), Article 21. https://doi.org/10.1007/s44339-026-00066-w

Image Credits: AI Generated

DOI: 10.1007/s44339-026-00066-w

Keywords: Catha edulis, khat, cathinone, spatial memory, spatial cognition, Morris water maze, hippocampus, long-term potentiation, neurotoxicology, BDNF, rodent models, narrative review