HEMODYNAMIC AND IMMUNOHISTOCHEMICAL STUDIES OF RAT INCISOR PULP AFTERDENERVATION AND SUBSEQUENT RE-INNERVATION

The effects of injury to the inferior alveolar nerve on the distributi on of neuropeptides and neurogenic blood-flow reactions were studied i n rat mandibular dental pulp. In normal incisor pulps, calcitonin gene -related peptide (CGRP)-like immunoreactivity was common, while substa nce P- and neurokinin (NKA)-positive nerve fibres were much less abund ant. There were no signs of vasoactive intestinal peptide-like, neurop eptide Y-like or 5-hydroxytryptamine-like immunoreactivity. In normal pulps, electrical stimulation (100 mu A, 5 ms, 15 Hz for 30 s) of the tooth crown resulted in transient vasoconstriction followed by vasodil ation, which was enhanced after alpha-adrenoceptor blockade. At 3 days -4 weeks after unilateral nerve section there were no signs of CGRP-, substance P- and NKA-immunoreactivity, and there was no vasodilation i n response to tooth stimulation. The vasoconstrictor response was also absent during this period but at 4 weeks postoperatively a weak respo nse was obtained and after 7 weeks the vasoconstrictor response had re gained normal amplitude. At 7 weeks postoperatively, a large number of CGRP-positive fibres had reappeared and at 11 weeks the pattern of CG RP-immunoreactivity was normal. However, substance P- and NKA-immunore activity were not found at 7 or 11 weeks after surgery. Vasodilator re sponses appeared at 7 weeks, and showed normal amplitude at 11 weeks a fter the creation of the nerve lesion. The results show that during ne rve regeneration, sympathetic vasoconstriction was regained earlier th an neurogenic vasodilation in rat incisor teeth. The reappearance of n eurogenic vasodilation after nerve injury was temporarily associated w ith the presence of CGRP-immunoreactivity in regenerating trigeminal a fferent nerves.