gms | German Medical Science

Objective: With neuronal activity, metabolic demand increases. This is usually met by an increase in cerebral blood flow and upregulation facilitated by neurovascular coupling (NVC). Impairment of NVC was recently reported in the context of experimental SAH, and is thought to correlate with both disease severity and outcome. However, previous techniques required invasive procedures. In the present study, we demonstrate a protocol for non-invasive observation of retinal NVC in mice.

Methods: Mice were dark-adapted overnight; anesthesia was performed by intraperitoneal injection. Pupillary dilatation was achieved by unilateral application of a mydriaticum.A prototype of an adapted retinal vessel analyzer (RCrodent, Imedos Sytems UG) was used to assess retinal arterial and venous diameter. Dynamic vessel analysis (DVA) included application of flicker light impulses in predefined frequencies; vessel reactivity as characterized by change in vessel diameter was recorded continuously. All retinae were harvested after completion of the exams and electroretinograms (ERG) of both sides were performed.

Results: A total of 90 retinal scans was conducted in 21 male mice (12-15 weeks old, 25-31 g). Venous reaction to flicker light was observed in all animals (vasodilation in 86%, vasoconstriction in 8% of measurements). Repeated measurements resulted in a significant decrease of baseline vessel diameter (p<0.05). A trend towards attenuated reactivity was also observed with repeated measurements (p=0.106). Assessability of arteries was limited due to anatomical characteristics -mainly due to light reflection and faulty automated segmentation -, but the majority of quantitative arterial recordings showed an emphasized reaction to flicker. Transretinal signaling on ERG was significantly reduced in retinae which previously underwent repetitive DVA examination (p<0.001).

Conclusion: To the best of our knowledge, this is the first non-invasive study reporting and evaluating murine retinal vessel response to flicker light, documenting characteristic changes in response to NVC. Arterial examination may require additional contrast media (fluorescein/ICG) to overcome technicalconstraints. Venous retinal capacity is exhausted with repetitive examination, implying the need for recovery time. The imaging system can be used for basic research on vessel behavior and enables the investigation of microcirculation in control mice and genetically modified animals.