INTERACTIONS BETWEEN SENSORY PERIVASCULAR NERVES AND THE ENDOTHELIUM BRAIN MICROVESSELS

The purpose of our study was to see if selective denervation of sensory perivascular nerves leads to changes in release of vasoactive substances of endothelial origin from brain microvessels during increased flow. Male rats pups were treated with the neurotoxin, capsaicin, to destroy primary afferent sensory nerves. Three months later, brain microvessels were isolated, placed on a micropore filter and perfused with Krebs buffer. During the course of a 30-min experiment, the flow rate was increased from 0.5 to 3.0 ml/min for two 3-min periods. The levels of ATP, substance P, vasopressin and endothelin in the effluent were measured. Microvessels from 5 rats were pooled for each perfusion experiment. Data from 5 perfusion experiments showed that the release of substance P was significantly higher in the capsaicin-treated rats during the second period of increased flow (3.02 +/- 1.04 pmol/min/mg protein) compared to the vehicle-treated controls (0.30 +/- 0.21 pmol/min/mg protein; p < 0.02). In contrast, the release of ATP at low flow and during the second period of increased flow was significantly lower in the capsaicin-treated rats(0.21 +/- 0.04 compared to 0.50 +/- 0.03 pmol/min/mg protein for controls at low flow, p < 0.001; and 1.19 +/- 0.15 compared to 2.11 +/- 0.26 pmol/min/mg protein for controls during the second period of increased flow, p < 0.01). The release patterns of endothelin and vasopressin were similar in capsaicin-treated and vehicle-treated controls. In conclusion, chronic depletion of sensory innervation leads to altered release of two endothelium-dependent vasodilators, ATP and substance P from the brain microvasculature. These changes may be compensatory and suggest that there is an ongoing interaction between sensory perivascular nerves and the endothelium in brain microvessels.