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Apoptosis, also called programmed cell death, is generally characterized by distinct morphological characteristics.

TUNEL staining detects DNA strand breaks by using terminal deoxynucleotidyl transferase to add labeled nucleotides to exposed 3′-OH DNA termini, generating either microscopic staining in fixed cells or tissue sections, or fluorescence/cytometric signal in cell suspensions. TUNEL positivity reflects DNA fragmentation but should not be interpreted alone as definitive apoptosis, because TUNEL can also label necrotic, autolytic, mechanically damaged, or DNA-repair-associated DNA breaks.

Annexin V-based apoptosis assays rely on the detection of phosphatidylserine (PS) externalization from the inner leaflet of the plasma membrane to the outer leaflet, an early biochemical hallmark of apoptosis. Fluorescently labeled Annexin V binds PS in a calcium-dependent manner, enabling identification of early apoptotic cells by flow cytometry or fluorescence microscopy. When combined with a membrane-impermeant DNA-binding dye (e. g. , propidium iodide), this approach allows discrimination between viable (Annexin V−/dye−), early apoptotic (Annexin V+/dye−), and late apoptotic or necrotic (Annexin V+/dye+) cell populations by assessing membrane integrity and PS exposure.

The Morris Water Maze is a rodent spatial learning and memory assay in which a mouse or rat swims in opaque water to find an escape platform; in the hidden-platform version, the animal cannot see the platform and must use distal extra-maze cues to learn its fixed spatial location. The assay primarily measures hippocampus-dependent spatial learning during acquisition trials and spatial reference memory during probe trials after platform removal; readouts include escape latency, swim path length, swim speed, quadrant occupancy, platform-site crossings, and proximity to the former platform location.

Apoptosis is a regulated, generally non-lytic cell-death pathway that removes unwanted, damaged, infected, or abnormal cells through coordinated morphological changes, caspase activation, DNA fragmentation, and membrane remodeling. The intrinsic apoptosis pathway is controlled mainly by mitochondrial outer membrane permeabilization, BCL-2 family proteins, cytochrome c release, apoptosome formation, caspase-9 activation, and downstream executioner caspase-3/7 activation. The extrinsic apoptosis pathway is initiated by death receptors such as Fas, TNFR, and TRAIL receptors, which recruit adaptor proteins and activate caspase-8 before engaging executioner caspases or mitochondrial amplification through BID cleavage. Apoptosis is linked to many phenotypes, including cancer cell killing, tissue homeostasis, immune regulation, neurodegeneration, infection response, and treatment-induced cytotoxicity; unresolved questions include how apoptosis interacts with necroptosis, pyroptosis, ferroptos

Hematoxylin-eosin staining is a routine histological method that stains nuclei mainly blue-purple with hemalum and stains cytoplasm, extracellular matrix, and many stromal components pink with eosin, allowing tissue architecture, cell morphology, necrosis, inflammation, fibrosis, tumor growth pattern, and treatment-associated injury to be evaluated by light microscopy. In cancer cells, primary neurons, mouse tumor models, intestinal organoids, inflammatory macrophage preparations, and drug-screening tissues, H&E is a morphology assay rather than a molecular assay; it should be interpreted with complementary molecular or immunostaining assays when the biological question concerns specific proteins, RNA levels, ferroptosis, mitophagy, or immune phenotypes.

Congo red amyloid staining is a histochemical method used to detect extracellular amyloid deposits in tissue sections based on the affinity of Congo red dye for β-pleated sheet-rich protein aggregates. When bound to amyloid, Congo red produces characteristic apple-green birefringence under polarized light microscopy, which is widely regarded as a diagnostic feature of amyloid deposition in histopathology. The diagnostic principle relies on the combination of dye binding (congophilia) and optical anisotropy under polarized illumination, which distinguishes amyloid from most non-amyloid eosinophilic extracellular deposits in routine histological evaluation. Amyloid identification by Congo red staining remains a cornerstone in diagnostic pathology despite the availability of adjunct methods such as immunohistochemistry and mass spectrometry, particularly because of its ability to localize deposits directly within tissue architecture. The specificity of Congo red-positive deposits is incre

Alzheimer’s Disease (AD) is a neurodegenerative disorder characterized by a progressive decline in cognitive functions and loss of specific types of neurons and synapses. Alzheimer's symptoms can be simulated in mice by injecting drugs (such as Aβ) or genetically modified.