Impaired smell can be investigated through behavior, new-neuron formation and cellular protein handling. A 2025 methamphetamine study combined those approaches in mice and cultured neural stem cells. Its mechanistic findings are more specific than a general claim that methamphetamine simply killed smell-related neurons.
Which model and behaviors were tested?
Gu and colleagues reported a four-week mouse regimen using 5 mg/kg intraperitoneal methamphetamine. Olfactory tests, with eight mice per group, examined odor sensitivity, discrimination, social odors and buried-food retrieval. Exposed mice showed altered odor responses and took longer to find buried food.
Several behavioral tasks provide a broader assessment than one latency measure alone. Still, a food-retrieval time can reflect more than sensory detection, including motivation and task engagement. The converging odor tasks matter because an isolated delay would leave a wider range of explanations.
Was increased cell death the demonstrated explanation?
TUNEL staining did not show increased apoptotic cells in the subventricular zone under the tested conditions. Other assays indicated reduced stem-cell proliferation, a shift toward astrocytic differentiation and fewer newly generated olfactory-bulb neurons. Cellular quantification used four animals per group.
Reduced production of new neurons and death of existing neurons are different biological processes. A change in differentiation proportions can also occur without a generalized loss of every cell type. The apoptosis null limits one proposed account while leaving the measured neurogenesis changes meaningful.
Why did Notch1 protein and messenger RNA differ?
Notch1-related protein signals increased without a corresponding increase in Notch1 messenger RNA. The investigators linked this pattern to impaired autophagic degradation. Their cell experiments generally used 100 μM methamphetamine for three days.
Protein abundance reflects both production and removal. A transcription measurement alone cannot identify which side of that balance changed. The study therefore examined cellular processing rather than assuming that more protein necessarily meant more gene transcription.
Does more autophagy-related material mean better clearance?
The researchers used a fluorescent reporter to investigate autophagosome–lysosome fusion and implicated reduced syntaxin 17 in impaired flux. Manipulating this pathway and Notch1 signaling altered experimental outcomes.
Accumulation of material along a clearance pathway can reflect greater entry, slower completion or both. Measurements of intermediate structures need to be interpreted with evidence about movement through the pathway. Otherwise, a blocked process could be mislabeled as an efficiently increased one.
Did a signaling inhibitor repair established human smell loss?
No human treatment experiment was performed. The mouse Notch-pathway inhibitor was given during the first six days of methamphetamine administration, rather than first being introduced after a documented completed course of injury.
Intervention timing affects the question answered. Concurrent manipulation can test involvement in development of an experimental phenotype. It does not establish reversal of a longstanding deficit in a person. The cultured-cell concentration also cannot be equated directly with an unmeasured human brain concentration.
The study provides mechanistic evidence within its mouse and cell models. It does not validate a human smell test for methamphetamine exposure, estimate the frequency of smell impairment among users or establish a clinical therapy. This historical report is best read as a set of linked experiments with distinct behavioral, cellular and molecular endpoints.
Source
Gu C et al. Impaired olfactory bulb neurogenesis mediated by Notch1 contributes to olfactory dysfunction in mice chronically exposed to methamphetamine. Cell Biology and Toxicology. 2025;41:46. doi:10.1007/s10565-025-10004-y. Full text. Controlled mouse and neural-stem-cell experiments.