CAT DENTAL-PULP AFTER DENERVATION AND SUBSEQUENT RE-INNERVATION - CHANGES IN BLOOD-FLOW REGULATION AND DISTRIBUTION OF NEUROPEPTIDE-AFFINITY, GAP-43-AFFINITY AND LOW-AFFINITY NEUROTROPHIN RECEPTOR-LIKE IMMUNOREACTIVITY

The effects of unilateral extramandibular inferior alveolar nerve inju ry on pulpal blood-flow responses to electrical stimulation and i.v. i njections of substance P (SP) in cat mandibular canine teeth with a de ntinal lesion were investigated with laser Doppler flowmetry. After bl ood-flow recordings, the teeth were fixed and the pulps were examined with light and electron microscopy. The distribution of pulpal SP, neu rokinin A (NKA), calcitonin gene-related peptide (CGRP), vasoactive in testinal polypeptide (VIP), neuropeptide Y (NPY), growth-associated pr otein (GAP-43) and low-affinity neurotrophin receptor (LANR)-like immu noreactivity was examined with immunohistochemical fluorescence micros copy. Blood-flow recordings, performed at 10 days and 1 month postoper atively, showed that vasodilation, occurring in control teeth after bi polar electrical stimulation of the tooth crown, was absent in the den ervated pulps, whereas at 3 months, five of six teeth had regained res ponsiveness, although at a low level. There was enhanced vasodilation (by 370%) to SP injections (400 fmol i.v.) at 10 days in denervated pu lps. Such supersensitivity was reduced at 1 month despite the apparent lack of nerve fibers, and the response fell further towards the level in control teeth at 3 months when pulpal axons reappeared. At 10 days and 1 month postoperatively, light and electron microscopy demonstrat ed that surgery had resulted in total pulpal denervation. At 3 and 6 m onths, a large number of regenerated pulpal axons reappeared, in accor dance with previous findings. At 10 days and 1 month after nerve trans ection immunohistochemistry showed a complete loss of pulpal immunorea ctivity to all of the neuropeptides that were studied. At 3 and 6 mont hs, neuropeptide immunoreactivity reappeared but far fewer number of p ulpal nerve fibers were SP-, NKA- and CGRP-immunoreactive than under n ormal conditions, as demonstrated by double-labeling experiments with GAP-43- or LANR-antiserum. The results indicate that pulpal hemoregula tory functions, which are lost after denervation, do not return to nor mal levels after nerve regeneration. This malfunction may be caused by inadequate target re-innervation and/or a deficiency of neuropeptides in the re-innervated pulp.