Aim: 

The present study was carried out to assess the spontaneous rhythmic changes in diameter of pial arterioles in normal rats. Vasomotion was analyzed for each order of pial arterioles after their geometric characterization.

Methods: 

Male Wistar rats (250–300 g body wt; n = 15) were anesthetized with isoflurane (induction) and a-chloralose (60 mg/kg body wt., i.p.). The animals were tracheotomized and mechanically ventilated. Two catheters were placed in the left femoral artery and vein for arterial blood pressure recording and for injection of the fluorescent tracer (FITC bound to dextran 70 kDa). Pial microcirculation was observed through a cranial window utilizing a fluorescent microscopic technique. The arteriolar network was mapped by stop-frame images and pial arterioles were classified by Strahler's centripetal ordering scheme (modified according to diameter). The rhythmic diameter changes were quantified by computer-assisted method (time variant Fourier Transform).

Results: 

Pial arterioles were classified in five orders (1–5) according to diameter, length and branching. The largest arterioles, order 5 and 4, presented the lowest fundamental frequencies of activity: 0.015 0.004 Hz and 0.020 0.005 Hz, respectively. The order 3 and 2 arterioles showed an enhanced vasomotion frequency: 0.030 0.010 Hz and 0.120 0.010 Hz, respectively. The order 1 arterioles presented a frequency of 0.130 0.012 Hz. Finally, the topical application of acetylcholine and papaverine abolished the pial arteriolar diameter changes.

Conclusion: 

The rhythmic diameter changes, observed in the different pial arteriolar orders, suggest that the distribution of the cerebral blood flow supply is mainly regulated by the smallest pial arterioles.