How can you tell if a rat has had a stroke? - briefly
Key indicators include abrupt unilateral weakness, impaired balance, abnormal gait, and facial drooping. Additional signs are reduced limb use, altered reflexes, and sudden changes in motor coordination.
How can you tell if a rat has had a stroke? - in detail
Identifying a cerebrovascular incident in a laboratory rat requires a combination of behavioral observation, functional testing, and, when possible, imaging or post‑mortem analysis.
Observable signs develop within minutes to hours after the event. Typical manifestations include:
- Unilateral weakness or paralysis of the forelimb or hindlimb, often evident as reduced ability to grasp or push against a wall.
- Asymmetrical whisker movement or facial droop on the affected side.
- Circling behavior toward the impaired side, or persistent leaning.
- Loss of balance, frequent falls, or abnormal gait such as dragging of one hindlimb.
- Decreased spontaneous locomotion in open‑field arenas, reflected by reduced total distance traveled.
- Altered posture, including a hunched back or head tilt.
Standardized functional assays quantify these deficits:
- Neurological Severity Score (NSS) – a composite rating of motor, sensory, reflex, and balance functions, yielding a numeric value that correlates with infarct size.
- Cylinder test – counts forelimb contacts with the cylinder wall during rearing; a disproportionate use of one forelimb indicates unilateral impairment.
- Adhesive removal test – places a small adhesive patch on each forepaw; prolonged latency to detect or remove the patch on one side signals sensory loss.
- Rotarod performance – measures latency to fall from a rotating rod; reduced endurance reflects motor coordination deficits.
- Grip strength meter – records maximal pulling force of each forelimb; a significant inter‑limb difference confirms weakness.
When resources allow, imaging provides direct evidence of vascular occlusion or tissue injury:
- Magnetic resonance imaging (MRI) with diffusion‑weighted sequences detects acute ischemic lesions within minutes.
- Computed tomography (CT), especially with contrast, visualizes hemorrhagic events and large infarcts.
- Laser Doppler flowmetry or laser speckle contrast imaging quantifies cerebral blood flow reductions in real time.
Post‑mortem verification employs histological techniques:
- 2,3,5‑Triphenyltetrazolium chloride (TTC) staining distinguishes viable tissue (red) from infarcted tissue (pale) on brain slices.
- Immunohistochemistry for NeuN, GFAP, and Iba‑1 assesses neuronal loss, astrocyte activation, and microglial response.
- Hematoxylin‑eosin (H&E) staining identifies hemorrhage, edema, and necrosis.
Physiological parameters may also shift. Elevated plasma lactate, altered blood gas values, and changes in heart rate variability often accompany severe cerebral events, offering supplementary diagnostic clues.
A comprehensive assessment integrates these observations: initial behavioral screening, quantitative functional tests, optional imaging for confirmation, and histopathological analysis for definitive diagnosis. This multilayered approach ensures accurate detection and characterization of stroke‑like events in rats.