EFFECT OF INTERMITTENT LONG-LASTING ELECTRICAL TOOTH STIMULATION ON PULPAL BLOOD-FLOW AND IMMUNOCOMPETENT CELLS - A HEMODYNAMIC AND IMMUNOHISTOCHEMICAL STUDY IN YOUNG-RAT MOLARS

Release of sensory neuropeptides after stimulation of afferent nerve f ibers has previously been shown to induce vasodilation and increased v ascular permeability in the dental pulp, a condition recognized as neu rogenic inflammation. In the present study a possible role for the sen sory neuropeptides in transendothelial migration of immunocompetent ce lls was investigated. The dental pulp is an isolated tissue densely in nervated with sensory fibers containing neuropeptides, and following e lectrical stimulation of the crown, the effect on pulpal blood flow an d immunocompetent cells can be studied in a noninvasive model. A laser Doppler flowmeter was used to measure relative changes in pulpal bloo d flow during long-lasting intermittent stimulation of innervated and denervated rat first molars. In the innervated teeth, stimulation prom ptly increased pulpal blood flow by on average 45% at the start of the experiment, whereas almost no blood flow increase was recorded after 4 to 5 h stimulation. Surgical sectioning of the inferior alveolar ner ve abolished blood flow increase upon stimulation. After stimulation, a quantitative analysis of CD43(+), CD4(+), CD11(+), and I-A antigen-e xpressing cells was performed, and the effect of stimulation on calcit onin gene-related peptide (CGRP)-immunoreactive and substance P (SP)-i mmunoreactive (IR) nerve fibers was studied. Immunohistochemistry was performed by the avidin-biotin peroxidase method. Stimulation resulted in an almost complete depletion of CGRP- and SP-IR nerve fibers in th e first molar pulp, whereas nerve fibers in the gingiva and neighborin g teeth were unaffected. A significant increase in the number of CD43( +) cells was found in the innervated tooth after stimulation compared to the stimulated denervated (P < 0.01) and unstimulated control (P < 0.05) first molars. For I-A antigen-expressing cells a significant inc rease (P < 0.05) was found between the innervated stimulated and unsti mulated control, but not between the innervated and denervated stimula ted first molars. Hence, from the present experiment it is concluded t hat the pulpal nerves participate in and facilitate transendothelial m igration of CD43(+) cells during acute neurogenic inflammation. (C) 19 97 Academic Press.