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Numerous in vitro studies suggest that inflammation is associated with enhanced release of substance P (SP) in the dorsal horn. To test the hypothesis that inflammation increases the evoked concentration of SP in the intact animal, we used in vivo microdialysis with a highly sensitive radioimmunoassay to monitor SP-like immunoreactivity (SP-LI) in the dorsal horn. Seven days after the induction of persistent unilateral inflammation with hindpaw injection of complete Freund's adjuvant, perfusion of the microdialysis probe with 10 microM capsaicin (a concentration which failed to induce SP-LI release in rats without inflammation) induced a significant increase of microdialysate SP-LI. Inclusion of an NMDA antagonist in the perfusion fluid completely blocked this capsaicin-evoked SP release. Administration of a five-fold higher dose of capsaicin did not further increase SP release. These results in a rat model of chronic arthritis suggest that persistent inflammatory signaling facilitates capsaicin-evoked SP release in the dorsal horn in vivo.

The aim of the present in vivo microdialysis study was to determine the possible contribution of N -methyl- d -aspartate (NMDA) or α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate (KA) receptors to capsaicin-induced release of substance P-like immunoreactivity (SP-LI) in the dorsal horn of the rat. Perfusion of a microdialysis probe with capsaicin (50 or 100 μM) induced a significant eight-fold increase of the extracellular SP-LI level. The capsaicin (50 μM)-evoked release of SP-LI was blocked by spinal administration of the NMDA antagonist 2-amino-5-phosphonopentanoic acid (D-APV; 5 mM), but not by the AMPA/KA antagonist 6-nitro-7-sulphamoylbenzo[ f ]quinoxaline-2,3-dione disodium (NBQX; 0.5 mM). In contrast, the SP-LI release induced by 100 μM capsaicin could not be prevented by D-APV (10 mM) or NBQX (0.5 mM). The data suggest that the spinal SP-LI release induced by a moderate concentration of capsaicin is in part dependent on the release of glutamate acting on NMDA receptors.

The gene expression of cholecystokinin (CCK), a neuropeptide with anti-opioid properties, has been reported to be up-regulated in some primary sensory neurons after a peripheral nerve lesion. We have recently demonstrated that the up-regulation of CCK mRNA is not accompanied by an increased potassium-evoked release of CCK-like immunoreactivity (CCK-LI) 2-4 weeks after a complete transection of the sciatic nerve. The potassium-evoked release of CCK-LI at earlier and later time points has, however, not been studied. The aim of the present in vivo microdialysis study was to monitor how the basal and stimulated extracellular level of CCK in the dorsal horn of the spinal cord is affected at various time points after a complete transection of the sciatic nerve (axotomy). During the first week after transection of the sciatic nerve a tendency towards an elevation of the potassium-induced (100 mM in the perfusion fluid) release of spinal CCK-LI was observed. In contrast, no potassium-induced release of CCK-LI could be detected 2-3 weeks and 2 months after axotomy. No significant effect was observed on the basal extracellular levels of CCK-LI in the dorsal horn. The present study provides further support for the notion that the adaptive changes in the dorsal horn 2 weeks and later after a deafferentiation injury do not include an increased release of CCK.

Local actions of acetylcholine on vasomotor regulation in rat incisor pulp were investigated in anaesthetized animals. Pulpal blood flow was measured with laser Doppler flowmetry. lontophoresis (40 or 60 muA for 20 s) with acetylcholine or carbachol on an exposed dentin surface caused a biphasic response: an initial vasoconstriction was followed by an atropinesensitive vasodilation. The vasoconstrictor response was enhanced by 171% in the presence of atropine, whereas in control experiments, using isotonic saline as a medium for the direct current, similar vasoconstriction was unaffected by atropine. Carbachol-induced vasodilation was significantly reduced by 30% after intravenous injection of the nitric oxide synthesis blocker N omega-nitro-L-arginine methyl ester (10 mg kg-1), and the remaining vasodilation was abolished by atropine. The present results support the concept of a cholinergic modulation of sympathetic vasoconstrictor function and of a partial contribution of nitric oxide in carbachol-induced vasodilation in rat incisor pulp.

Blood flow of mammalian dental pulp is under both remote and local control. There is evidence for the existence of parasympathetic nerves in the pulp, but functionally the cholinergic influence is weak, and the physiological significance of this autonomic system seems to be low. The evidence for sympathetic vasoconstrictor nerves in the pulp is robust, and there is convincing support for the contention that these nerves play a physiological role, operating via release of noradrenaline and neuropeptide Y. However, there is no significant functional evidence in support of sympathetic beta-adrenoceptor-mediated vasodilation in the pulp. The local control of blood flow involves a subset of intradental sensory nerves. By virtue of their neuropeptide content, these afferent fibers cause vasodilation and inhibit sympathetic vasoconstriction in response to painful stimulation of the tooth. Such locally governed control may serve to meet immediate demands of the pulp tissue. A locally triggered reflex activation of sympathetic nerves in the pulp may modulate this control and limit its magnitude. Thus, there are competitive interactions between local and remote vascular controls which may be put out of balance in the injured and inflamed dental pulp.

The possible involvement of the neuropeptides substance P and calcitonin gene-related peptide (CGRP) in the development of neurogenic plasma extravasation in the lower lip, gingiva and incisor pulp was examined in anaesthetized rats by means of the Evans blue method and by using newly developed blockers of substance P (CP-96,345) and CGRP (CGRP8-37). Electrical stimulation of the inferior alveolar nerve (15 V, 2 ms, 10 Hz) for 5 min significantly increased the Evans blue content of the ipsilateral lip, gingiva and pulp by 60 (p < 0.01), 62 (p < 0.01) and 92% (p < 0.05), respectively (n = 8). Pretreatment with CP-96,345 (total dose: 1.5 mg/kg, intravenously) counteracted the dye leakage in the lip and pulp but not in the gingiva (n = 6). The inactive enantiomer (CP-96,344, 1.5 mg/kg, n = 8) or the nitric oxide synthesis inhibitor (N omega-nitro-L-arginine methyl ester hydrochloride, 10 mg/kg, n = 7) did not reduce the stimulation-induced dye extravasation in any of the tissues. Pretreatment with CGRP8-37 (0.3 mg/kg, n = 7) did not significantly influence the development of neurogenic extravasation in the lip and incisor pulp, but it slightly attenuated extravasation in the gingiva. The results indicate that the afferent nerve-induced dye extravasation in the lip and pulp, but not in the gingiva, is to a large extent mediated by substance P acting via neurokinin-1 receptors. There was no evidence for an involvement of nitric oxide or CGRP in neurogenic extravasation in rat incisor and lip.

The effects of unilateral extramandibular inferior alveolar nerve injury on pulpal blood-flow responses to electrical stimulation and i.v. injections of substance P (SP) in cat mandibular canine teeth with a dentinal lesion were investigated with laser Doppler flowmetry. After blood-flow recordings, the teeth were fixed and the pulps were examined with light and electron microscopy. The distribution of pulpal SP, neurokinin A (NKA), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), growth-associated protein (GAP-43) and low-affinity neurotrophin receptor (LANR)-like immunoreactivity was examined with immunohistochemical fluorescence microscopy. Blood-flow recordings, performed at 10 days and 1 month postoperatively, showed that vasodilation, occurring in control teeth after bipolar electrical stimulation of the tooth crown, was absent in the denervated pulps, whereas at 3 months, five of six teeth had regained responsiveness, although at a low level. There was enhanced vasodilation (by 370%) to SP injections (400 fmol i.v.) at 10 days in denervated pulps. 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 demonstrated that surgery had resulted in total pulpal denervation. At 3 and 6 months, a large number of regenerated pulpal axons reappeared, in accordance with previous findings. At 10 days and 1 month after nerve transection immunohistochemistry showed a complete loss of pulpal immunoreactivity to all the neuropeptides that were studied. At 3 and 6 months, neuropeptide immunoreactivity reappeared but far fewer number of pulpal nerve fibers were SP-, NKA- and CGRP-immunoreactive than under normal conditions, as demonstrated by double-labeling experiments with GAP-43- or LANR-antiserum. The results indicate that pulpal hemoregulatory functions, which are lost after denervation, do not return to normal 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.

The role of nitric oxide in the mediation of (a) antidromic and (b) substance P-induced vasodilation in the pulp, lip, oral mucosa and submandibular gland was investigated in anaesthetized rats by means of laser Doppler flowmetry. Bolus or continuous infusion of Nω-nitro-L-arginine methyl ester (L-NAME) increased mean arterial blood pressure and reduced basal blood flow in the pulp but not in the lip. Electrical stimulation of the inferior alveolar nerve, in the presence of phenoxybenzamine, resulted in a long lasting vasodilation in lower lip and incisor pulp. Infusion of L-NAME enhanced the antidromic vasodilation in both lip and pulp. Pretreatment with L-arginine prevented these effects. Administration of the enantiomer (D-NAME) did not exert any effect on basal blood flow and on antidromic vasodilation. Infusion of substance P resulted in a transient vasodilation in all of the oral tissues studies. L-NAME reduced this vasodilation in the submandibular gland (only the lower doses) but it potentiated the responses in the pulp and oral mucosa. Pretreatment with L-arginine prevented the potentiated responses in the pulp and those induced by the lower doses of substance P in the oral mucosa. Thus, nitric oxide appears to differentially regulate the basal blood flow and the antidromic or substance P-induced vasodilation in the microvasculature of the lip and dental pulp.

Previous studies have shown that sympathetic nerve stimulation reduces afferent nerve-induced vasodilation by mechanisms unrelated to vasoconstriction in the rat incisor pulp. The present investigation concerned whether similar modulatory mechanisms might also influence neurogenic plasma extravasation in dental pulp. Rat mandibular incisors were electrically stimulated and blood flow reactions in the pulp were recorded by laser Doppler flowmetry. Plasma extravasation in the incisor pulp, gingiva and lip were indirectly assessed by the Evans-blue method. Stimulation of teeth with 50 microA (5 min) did not cause increased dye accumulation in the stimulated pulps whereas stimulation with 100 microA significantly increased the dye content in ipsilateral pulps by 32% as compared to controls; 100 microA stimulation was without effect in unilaterally denervated animals. Tooth stimulation with 50 microA (5 min), in the presence of either the alpha-adrenergic blocker phenoxybenzamine (3 mg/kg), or the alpha 1-adrenergic antagonist prazosin (50 micrograms/kg), as well as in chronically sympathectomized animals, significantly increased the Evans-blue content in the stimulated pulps by 47, 83 and 86%, respectively. Application of short trains of impulses (same number of impulses as for the continuous stimulation but producing minimal vasoconstriction) resulted in some dye accumulation, which was enhanced in the ipsilateral pulps in the presence of prazosin (100 micrograms/kg) or after acute resection of the superior cervical sympathetic ganglion by 70 and 64%, respectively. The Evans-blue content in the lip and gingiva was uninfluenced by the tooth stimulation. The results indicate that activation of sympathetic nerves inhibits the afferent nerve-induced plasma extravasation in rat incisor pulp and this effect is mediated by alpha-adrenoceptors not associated with vasoconstriction.

Previous studies of the sympathetic nerve supply of the rat mandibular incisor pulp have shown conflicting results. Here, the neurovascular control of the rat lower incisor pulp was investigated by stimulating the tooth crown and the cervical sympathetic trunk electrically and monitoring blood-flow changes in the pulp by laser Doppler flowmetry. In addition the presence of noradrenaline (NA) in the pulp and gingiva was examined biochemically in untreated and sympathectomized animals by high-performance liquid chromatography. The tissue concentrations of NA in the pulp were 11-fold greater than those of gingiva. Surgical sympathectomy significantly reduced the NA content in the pulp by 76%. Monopolar electrical stimulation of teeth (25-50 microA) for 1 min resulted in a frequency-dependent reduction followed by an increase in pulpal blood flow. At 16 Hz the reduction in blood flow was 65% and the subsequent increase was 9%. After intravenous administration of the alpha-adrenoceptor antagonist phentolamine, the stimulation-induced reduction in pulpal blood flow was diminished by 94% while the increase was significantly enhanced (from 9 to 40%). Infusion of the beta-adrenoceptor antagonists propranolol and timolol significantly reduced this increase in blood flow by 53 and 55%, respectively. Preganglionic sympathetic nerve stimulation also induced a frequency-dependent reduction followed by a slight increase in pulpal blood flow. This reduction in blood flow was almost abolished after alpha-adrenergic blockade and there was no subsequent increase. These findings suggest that there are sympathetic nerve fibres in rat incisor pulp and that they are activated upon monopolar electrical stimulation of teeth resulting in alpha- and beta-adrenoceptor mediated blood-flow responses.

In 15 subjects, laser-Doppler flowmetry (LDF) was used to investigate whether the nervous control of pulpal blood flow (PBF) is affected by three tests known to excite the sympathetic nervous system. For comparison, skin blood flow was similarly recorded. Dynamic exercise (bicycle ergometer, 5 min, 90–100 W) in eight subjects was accompanied by a rise in PBF. PBF was increased by the cold pressor test (2 min) in eight subjects, while in five the flow decreased or remained unaffected. The isometric hand grip (2 min, 30% MVC) and the subsequent muscle ischaemia (2 min) led to a rise in PBF in two subjects and a fall in four. Following unilateral anaesthesia of the mandibular nerve, PBF in five subjects became unresponsive to dynamic exercise or the cold pressor test, indicating pressure autoregulation. All three tests triggered increases in mean arterial pressure (MAP) and heart rate (HR). Skin blood flow usually increased in response to the tests, but could also decrease, and often changed in a direction opposite to that of PBF. It is concluded that the circulation of blood in the human tooth is affected by evoked changes in autonomic nerve activity, involving activation of both vasodilator and vasoconstrictor nerves to vessels serving the tooth.

The distribution of laminin-like immunoreactivity in adult normal and denervated cat mandibular tooth pulps was studied by the use of fluorescence microscopy and pre-embedding immunogold electron microscopy. Immunoreactivity to collagen IV was also assessed in order to distinguish basement membranes. In normal pulps, light-microscope laminin-like immunoreactivity was strong along blood vessels and Schwann cell sheaths, and a faint immunoreactivity was seen also in the odontoblast layer. Electron microscopy confirmed the laminin-like immunoreactivity of endothelial and Schwann cell basement membranes at all pulpal levels. In the odontoblast layer and the predentine, nerve-like structures lacking basement membranes but possessing strong membrane laminin-like immunoreactivity were encountered. In addition, a clear-cut laminin-like immunoreactivity of plasma membranes of the somata and processes of odontoblasts was seen. Observations on denervated pulps as well as pulps in which nerve regeneration had taken place did not reveal any changes in the pattern of laminin-immunoreactivity in basement membranes or odontoblasts. Distribution of collagen IV-like immunoreactivity was very similar to laminin-like immunoreactivity in basement membranes of blood vessels and Schwann cells, and appeared unaffected by denervation. The odontoblasts and nerve-like profiles in the odontoblast layer were devoid of collagen IV-like immunoreactivity. We propose that odontoblast-associated laminin could be of significance as guidance for regenerating terminal pulpal nerve fibers to appropriate targets.

The effect of angiotensin II (Ang II) was studied on blood flow in the submandibular gland and tongue in male rats. Blood flow changes were determined with laser Doppler flowmetry and Ang II was infused into the common carotid artery before and after i.v. doses (18 nmol kg-1) of the angiotensin II antagonist saralasin. Angiotensin II (10-60 pmol min-1) dose-dependently increased blood pressure and tongue blood flow, whereas glandular blood flow decreased at all of the doses used. After saralasin administration the angiotensin II effects on blood pressure, tongue and glandular blood flow were significantly diminished (glandular blood flow reduction was diminished from 29%-3%, P less than 0.005, n = 9). However, the responsiveness of these 3 parameters to local infusions with noradrenaline (0.75-3.0 pmol min-1) was unaffected by saralasin. The dose of saralasin used in the present study did not affect any of the parameters on it's own. Our results show that vascular receptors sensitive to angiotensin II operate in the submandibular gland but not in the tongue.

The anticonvulsant drug gabapentin has been demonstrated to alleviate symptoms of painful diabetic neuropathy as well as other types of neuropathic pain. The aim of the present study was to investigate the effect of gabapentin in a recently developed mouse model of peripheral neuropathy. This model is based on a photochemical ischemic lesion of the sciatic nerve generated by laser-induced activation of the photosensitizing dye erythrosin B. Following laser irradiation of the sciatic nerve for 2, 5, or 10 min, tactile allodynia was observed during at least 3 weeks. The degree of allodynia was most marked following 10 min of irradiation. Subcutaneous administration of gabapentin [175-300 micromol/kg ( approximately 30-51 mg/kg), cumulative doses, at 1-h intervals] significantly reversed tactile allodynia induced by 10-min laser irradiation. The maximal dose of gabapentin increased the withdrawal threshold from approximately 0.55 to approximately 1.85 g (i.e., about 77% of the threshold in normal animals, approximately 2.4 g). Gabapentin did not affect the tactile withdrawal threshold in intact animals. A dose of gabapentin (100 micromol/kg, sc) that had no effect on allodynia was found to significantly reduce the pain behavior during phase 2 of the formalin test. The present study demonstrates that systemic administration of gabapentin suppresses both allodynia induced by an ischemic lesion of the sciatic nerve and pain behavior in the formalin test.

Long-term potentiation (LTP) in wide dynamic range (WDR) neurons in the dorsal horn has been suggested to contribute to central sensitization and the development of chronic pain. Indirect experimental evidence indicates an involvement of substance P (SP), in this respect. The aim of the present study was to monitor the extracellular level of substance P-like immunoreactivity (SP-LI) in the dorsal horn of the rat during and after induction of LTP in WDR neurons in vivo. Electrophysiological recordings of single (WDR) neurons were performed in parallel with microdialysis in the dorsal horn under urethane-anaesthesia. The amount of SP-LI in the microdialysate was determined by radioimmunoassay. As previously shown, high frequency conditioning stimulation of the sciatic nerve induced an increased firing response of WDR neurons. An increased response to C-fibre stimulation, but not A-fibre stimulation, could be determined. A significant increase of the extracellular level of SP-LI in the dorsal horn was detected during, but not after, induction of LTP. These data suggest that SP may be involved in the induction of LTP by high frequency stimulation. However, the maintenance of spinal LTP following high frequency peripheral nerve stimulation does not seem to depend on an increased release of SP.

The blocking effect of lidocaine on nerve-induced vascular reactions was investigated in lower incisor teeth of anaesthetized rats. Pulpal blood flow was measured with laser Doppler flowmetry. Monopolar electrical stimulation of the rat incisor evoked a biphasic vascular response: an initial vasoconstriction was followed by a long-lasting vasodilation. Iontophoresis of lidocaine on a superficially exposed dentin surface with 60 microA of anodal direct current for 20 min blocked almost completely the stimulus-induced blood flow increase for about 25 min without any systemic effects. Iontophoresis of lidocaine with 40 microA for 20 min was almost without effect. Topical application of a mixture of lidocaine and prilocaine (25 + 25 mg/ml) in deep dentinal cavities was also without effect on the neurogenic reactions. Intravenous administration of lidocaine at 5 and 10 mg/kg in rats pretreated with phenoxybenzamine reduced the stimulus-induced increase in blood flow by an average of 29% and 54%, respectively, whereas the remaining alpha-adrenoceptor resistant vasoconstriction was not influenced. The present results show that iontophoresis of lidocaine on exposed dentin blocks nerve-induced vascular responses without causing systemic effects.

The effects of injury to the inferior alveolar nerve on the distribution of neuropeptides and neurogenic blood-flow reactions were studied in rat mandibular dental pulp. In normal incisor pulps, calcitonin gene-related peptide (CGRP)-like immunoreactivity was common, while substance P- and neurokinin (NKA)-positive nerve fibres were much less abundant. There were no signs of vasoactive intestinal peptide-like, neuropeptide Y-like or 5-hydroxytryptamine-like immunoreactivity. In normal pulps, electrical stimulation (100 μA, 5 ms, 15 Hz for 30 s) of the tooth crown resulted in transient vasoconstriction followed by vasodilation, which was enhanced after α-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 in response to tooth stimulation. The vasoconstrictor response was also absent during this period but at 4 weeks postoperatively a weak response was obtained and after 7 weeks the vasoconstrictor response had regained normal amplitude. At 7 weeks postoperatively, a large number of CGRP-positive fibres had reappeared and at 11 weeks the pattern of CGRP-immunoreactivity was normal. However, substance P- and NKA-immunoreactivity were not found at 7 or 11 weeks after surgery. Vasodilator responses appeared at 7 weeks, and showed normal amplitude at 11 weeks after the creation of the nerve lesion. The results show that during nerve regeneration, sympathetic vasoconstriction was regained earlier than neurogenic vasodilation in rat incisor teeth. The reappearance of neurogenic vasodilation after nerve injury was temporarily associated with the presence of CGRP-immunoreactivity in regenerating trigeminal afferent nerves.

This investigation was designed to study the formation of secondary dentin in permanent teeth of young cats after denervation. In eight animals, cervical dentin was exposed bilaterally in the mandibular canines, 7-10 d after unilateral resection of the inferior alveolar nerve. The observation intervals were 30 d, 90 d and 180 d, after which histological examination of dentin was performed. In order to verify the loss and regeneration of pulpal innervation and an intact blood supply, blood flow responses to electrical stimulation of the tooth and to i.v. injections of substance P (SP) were recorded by laser Doppler flowmetry before and at 7-10 d after denervation, at the end of the experiments, and at predetermined intermediate intervals. SP-induced vasodilation was significantly enhanced at 1 wk and 30 d postoperatively and was normalized to control values at 90 and 180 d. Vasodilation in response to electrical tooth stimulation, which was absent after denervation, reappeared after 90 d in two of four cats. There was no irregular dentin formation under the exposed dentin at any time in denervated or control teeth. Formation of regular secondary dentin appeared to be enhanced on the denervated side at 30 d and 90 d postoperatively, whereas at 180 d there was no difference between sides. The results indicate that intradental nerves influence secondary dentin formation in feline permanent teeth.

In this study we examined whether the indoleamine, serotonin (5-hydroxytryptamine, 5-HT), is contained in the rat incisor pulp and gingiva as well as its possible role in regulation of blood flow in these tissues. Tissue biochemical analysis, by means of high performance liquid chromatography coupled to electrochemical detection, revealed the presence of 5-HT and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), as well as the catecholamine, dopamine, in both pulp and gingiva. Unilateral surgical sympathectomy or resection of the inferior alveolar nerve failed to affect 5-HT levels in either tissue while dopamine contents in the pulp and gingiva were diminished following sympathectomy. Electrical stimulation of the sympathetic trunk induced a frequency-dependent vasoconstriction in the pulp and gingiva as measured by laser Doppler flowmetry. This vasoconstriction was unaffected by infusion of 5-HT2 or 5-HT3 receptor antagonists or dopamine receptor antagonists but it was significantly reduced in both tissues after alpha 1-adrenoceptor blockade. During this blockade the remaining vasoconstriction induced by high frequency stimulation (16 Hz) was reduced in gingiva by the 5-HT1 receptor blocker, methiothepin. The results indicate an involvement of 5-HT1 receptors and alpha 1-adrenoceptors in the sympathetic vascular control in the gingiva.

In this study the newly developed blockers of substance P (CP-96,345) and calcitonin gene-related peptide (CGRP8-37) were used to examine whether substance P and CGRP are involved in the afferent nerve induced vasodilation in the rat lower incisor pulp and lip. Electrical stimulation of the inferior alveolar nerve (10 V, 2 ms, 10 Hz, 30 s) in the presence of phenoxybenzamine (3 mg kg-1) induced an immediate vasodilation in the pulp and lip (52 and 186% increase in blood flow respectively, n = 12) with a long duration. Infusion of 2 mg kg-1 CP-96,345, a dose that inhibited the vasodilator effects of substance P (5-25 ng kg-1) in oral tissues, did not have any effect on antidromic vasodilation in either tissue. After infusion of CGRP8-37 (0.3 mg kg-1) the duration of the antidromic vasodilation in the pulp and lip was significantly reduced by 72 and 67% respectively (P < 0.05, n = 4), whereas the maximal increase of the response was unaffected. The blocking effect of the drug was short-lasting. When combined infusions of CP-96,345 and CGRP8-37 were given, a similar reduction in the duration of antidromic vasodilation in the pulp and lip occurred but in this case the amplitude of vasodilation in the pulp was reduced (from 35 +/- 9 to 12 +/- 3%, P < 0.05, n = 4). However, in the lip, the amplitude of vasodilation was not significantly reduced. The present findings indicate an involvement of CGRP in the mediation of the late phase of antidromic vasodilation in rat oral tissues and a role of substance P in the initiation of antidromic vasodilation in the incisor pulp.

Pulpal haemodynamics are naturally intermeshed with inflammatory responses. Cellular and humoral factors may be the vehicles that aid in physiological regulation, but when these systems are overly activated, they may lead to pathological changes. Sensory nerves may initiate inflammatory reactions when activated, and interestingly, recent findings show that vasoconstrictor nerves in the pulp can inhibit the release of neurally stored vasoactive and inflammatory mediators. Thus, there are options for endogenous control of inflammation. Perhaps a variation in the effectiveness of such control can explain why symptoms of hypersensitivity and pain are so unpredictable and individual. What naturally occurring agents are involved in early tissue changes and how do they act? Some agents exert their effects both on vessels and nerves. Thus, there is an intriguing mutual interplay between nerves and tissue reactions. A prolonged, painful stimulation may generate increased blood flow and inflammation, and vice versa, inflammation may lead to pain. This complexity of mechanisms generates many questions that need answers.

Whether increased extravasation of plasma protein may occur in the rat incisor pulp as a result of antidromic stimulation of afferent nerves was investigated, and this preinflammatory reaction compared with that in adjacent soft tissues. In anaesthetized rats, the inferior alveolar nerve was exposed and stimulated electrically (10-15 V, 2 ms, 10 Hz for 30 s or 5 min). Blood flow changes in the lower lip and incisor pulp were recorded by laser Doppler flowmetry. Increased vascular permeability in the lip, gingiva and pulp was indirectly determined by means of the Evans blue dye method and spectrophotometric analysis. Stimulation of the inferior alveolar nerve for 30 s, in the presence of the alpha-adrenergic blocker phenoxybenzamine (3 mg/kg), increased blood flow in the lip by 172 +/- 16% and in the pulp by 38 +/- 5% as compared to basal blood flow. Intravenous (i.v.) administration of atropine (1 mg/kg), chlorisondamine (3 mg/kg), timolol (150 micrograms/kg), cimetidine plus mepyramine (3 mg/kg of each), methysergide (1 mg/kg) and diclofenac sodium (3 mg/kg) was without effect on this response. Acute pretreatment with capsaicin (1-3 mg/kg, i.v.), however, abolished the vasodilation in the pulp and reduced that in the lip by 58% (p0.05). In untreated animals, stimulation of the inferior alveolar nerve for 5 min increased the Evans blue content in the ipsilateral lip by 164% (p0.001), gingiva by 55% (p0.01) and pulp by 67% (p0.01). Pretreatment (i.v.) with a combination of cimetidine and mepyramine counteracted the dye extravasation only in the gingiva.(ABSTRACT TRUNCATED AT 250 WORDS)

In this study we examined the presence and localization of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity in the dental pulp, periodontal tissues and alveolar bone of the rat. The presence of NADPH-d activity was also examined in cat pulp. The rat histochemical analysis revealed the presence of prominent NADPH-d activity both in cells of the sub-odontoblastic cell layer and in the odontoblasts, in the root as well as in the coronal pulp regions. In the pulpal horns, odontoblasts often had long processes with a high level of labelling indicating NADPH-d activity extending through the predentin and dentin. Moreover, endothelial cells of pulpal blood vessels were positive for NADPH-d in both species. However, no clearcut examples were found of pulpal nerve fibres positive for NADPH-d in the rat or cat and denervation performed in rats did not alter the enzyme staining patterns. In the periodontal tissue, NADPH-d activity was localized to cells on the alveolar bone surface of the periodontal ligament and, in addition, alveolar bone marrow crypts were filled with intensely labelled cells. In the gingival papillae, NADPH-d activity was observed in the basal cell layer of the epithelium. Endothelial cells of periodontal and gingival blood vessels showing positive staining for NADPH-d were occasionally noted.

In order to elucidate a possible influence of the sympathetic nervous system on afferent nerve function, rat mandibular incisors were electrically stimulated and blood flow changes monitored in the incisor pulp of untreated and sympathectomized animals by a laser Doppler flowmeter. Monopolar electrical stimulation of the tooth (200 microA, 5 ms, 40 Hz, 1 s) in normal animals resulted in a transient reduction in pulpal blood flow (PBF) (16% reduction, n = 10) followed by a small but long-lasting increase (11% increase). After administration of phenoxybenzamine or phentolamine (3 mg kg-1, i.v.) the initial dip in PBF was reduced by 59% (P < 0.001) while the subsequent increase was enhanced by 185% (P < 0.001). Similarly, infusion of prazosin (50 micrograms kg-1, i.v.) and idazoxan (0.5 mg kg-1, i.v.) significantly enhanced the increase in PBF by 118 and by 79%, respectively. In chronically sympathectomized animals the increase in PBF was 250% larger than that seen in untreated animals (P < 0.001). This increase in PBF was not further enhanced after alpha-adrenergic blockade. Acute resection of the superior cervical sympathetic ganglion, also resulted in some enhancement (by 56%) of the stimulation-induced increase in PBF (P < 0.01, n = 6). The increase in PBF was unaffected by infusion of timolol (150 micrograms kg-1) and atropine (1 mg kg-1) but was totally abolished by intravenous pre-treatment with capsaicin (1-3 mg kg-1). The present results suggest that activation of sympathetic nerves exerts inhibitory effects on the afferent nerve-induced vasodilation in the rat incisor pulp unrelated to sympathetic vasoconstriction.

A unilateral resection of the mandibular nerve ( n = 20) was made 10–14 days before investigation of the contribution of afferent nerves in vasodilator reactions in the dental pulp. Lower canine teeth were subjected to various stimuli and pulp blood-flow responses monitored by laser Doppler flowmetry. An absence of response to bipolar electrical (5 impulses, 50 μA, 5 ms, 2 Hz) stimulation on the tooth surface was used to demonstrate a successful chronic nerve lesion. Local application of capsaicin (10 −4 M) in a deep dentinal cavity induced a long-lasting increase in pulpal blood flow in control teeth only. Bradykinin (10 −3 M) induced significantly larger responses in control than in denervated teeth (58.3 ± 9.8% and 24.5 ± 4.9%, respectively, p n = 8); in addition, the onset was slower and the duration of the response significantly (60%) shorter than in control teeth. Intermittent grinding of surface dentine instantly increased flow in control teeth by 53.0 ± 12.5% ( n = 12) whereas in denervated teeth the response was delayed and significantly (70%) smaller. Deeper preparation produced responses of similar magnitude in control and denervated teeth (69 and 50%, respectively) but the onset was delayed in denervated teeth. Low-intensity ultrasonic stimulation caused vasodilation in intact teeth (38% increase) but had no effect in denervated teeth. This effect was abolished after local anaesthetic (mepivacaine) injection. Sympathectomy ( n = 3) did not influence stimulation-induced blood-flow responses in the dental pulp. The results show that afferent nerves make an important contribution to haemodynamic reactions in the pulp in response to experimental and clinical procedures directed at the tooth.

In order to test the hypothesis that ACh mediates the transmission of pain stimuli from dentin to sensory intradental nerve endings the following experiments were performed. Intradental nerve impulses were recorded by means of low impedance electrodes inserted in dentinal cavities in the tooth of the cat. An air blast proved to be an efficient physical stimulus to excite the intradental nerves. Local application of acetylcholine caused a similar response. This response to acetylcholine was followed by a transient blockage to repeated application. The response to acetylcholine could be blocked by d-tubocurarine, atropine, succinylcholine and hexamethonium administered locally. In contrast, the response to physical stimuli (air blasts) could not be blocked by these drugs. Moreover, during the period of depression following acetylcholine the preparation responded to physical stimuli. These findings suggest that acetylcholine is not a mediator in the intradental pain transmission provoked by physical stimuli.

Blood flow changes in the dental pulp of lower canine teeth of mature cats and incisors of mature rats were investigated with simultaneous laser Doppler flowmetry and local 125I-clearance (wash-out) during electrical sympathetic stimulation, efferent stimulation of n. alveolaris inferior (IAN) (cats) and i.a. infusions of substance P (SP) (cats). Stimulation (1-4 Hz, 4 V., 1.5 ms) of the cervical sympathetic trunk produced frequency-dependent decreases in both laser Doppler output and disappearance rate of iodine tracer from the dental pulp. For the effects of sympathetic stimulation, the correlation (r2) between the results obtained by the two methods was 0.89 (12 observations, six animals). Blood flow measurements by both methods were increased following i.a. infusions of SP (r2 = 0.64, six observations, three animals). However, upon stimulation of IAN (10 Hz 10 V, 5 ms) the laser Doppler flow values showed an increase while the local 125I clearance rate was unaffected or even decreased. The discrepancy between the results obtained following IAN stimulation indicates that the two methods reflect blood flow changes in different parts of the pulpal vascular bed and that the flow is unevenly distributed to these parts during antidromic IAN stimulation. The laser Doppler flowmetry seems to reflect the total blood flow in the coronal pulp and therefore this non-invasive method may be useful for monitoring blood flow changes in the tooth.

Mechanical stress was applied to canine teeth in anaesthetized cats to excite intradental A-fibres and to produce digastric muscle EMG responses. Activity in the intradental sensory units was recorded by two electrodes,- one inserted in a dentinal cavity, the other in contact with the gingival sulcus. A pneumatically driven piston was used to cause a mechanical stress (10–150 N) on the stabilized tooth crown for 30 s, with instantaneous onset and release. Application of a load of 30 N produced a momentary burst of impulses in 2 of 12 teeth; 8 out of 10 teeth responded when 150 N was used. Digastric EMG responses were obtained at and above 60 N. Removal of the coronal pulp or cooling of the tooth crown with ethyl chloride abolished this reflex, whereas percussion of the tooth still produced a digastric response. Our results suggest that load-induced deformation of teeth activates intradental sensory mechanisms and a reflex withdrawal reaction unrelated to periodontal stimulation.

Substance P (SP)- and calcitonin gene-related peptide (CGRP)-immunoreactivity (-IR) were localized by immunohistochemistry in the same nerve cell bodies in the trigeminal ganglia as well as in nerve terminals of the dental pulp. The distribution of SP- and CGRP-IR nerves were identical in the dental pulp and mainly associated with blood vessels. The level of CGRP-IR in the dental pulp, as measured by radio-immunoassay (RIA), was 1.4 +/- 0.2 pmol g-1 wet wt, which is in the same range as that found for substance P. Local intra-arterial infusion of synthetic CGRP and substance P produced vasodilatation in the dental pulp as measured by both laser Doppler flowmetry and an 125I clearance technique. The CGRP was effective as a vasodilator when infused in the femtomole per minute range, and SP in the picomole range. The effect of CGRP (50 fmol min-1) was 10 times larger when given after SP (15 pmol min-1) than before it. Since the two peptides coexist in the same neurons, it is suggested that they both contribute to the vasodilation seen upon antidromic stimulation of sensory nerves.

Olgart, L. and B. Gazelius, Inhibition of compound 48/80-induced intradental sensory nerve activity by disodium cromoglycate and serotonin antagonists. Acta physiol. scand. 1978. 104. 415–421. Local application of compound 48/80 induced long lasting nerve activity in intradental sensory nerves in the teeth of cats and dogs. This effect was inhibited by pretreatment with disodium cromoglycate (DSCG) given locally (2 × 10-2 M) or i.a. (20 mg/min). DSCG did not have any effect on the nerve excitability per se, as judged from the responses to hypertonic NaCl and air blasts applied to exposed dentin before and after administration of DSCG. Local treatment with lysergic acid diethylamide (0.1-1 mg/ml) and methysergide (0.05-0.5 mg/ml) selectively reduced or inhibited the compound 48/80 induced nerve activity. Systemic administration of methysergide (12.5 μglkg) prevented the excitatory effects of compound 48/80 but was without effect when administrated during a state of established activity. The present findings support the hypothesis that compound 48/80 has an indirect effect on intradental sensory nerves and indicate that vascular reactions take part in intradental sensory nerve excitation.

Blood flow and tissue volume were recorded in the isolated canine subcutaneous adipose tissue, enclosed in a plethysmography. Adrenaline and felypressin (octapressin) were infused intra-arterially at doses producing a blood flow reduction of approximately 60%. Adrenaline (4.6-23 ng/min) caused an initial reduction in tissue volume, indicating a constriction of capacitance vessels. Octapressin (0.46-9.2 ng/min) had no effect on tissue volume. Neither adrenaline or octapressin caused appreciable filtration or absorption, suggesting that the pre- to postcapillary resistance ration remained unchanged. In contrast to sympathetic stimulation and noradrenaline, adrenaline significantly reduced the capillary filtration coefficient (CFC) by 34%, the change in CFC being related to the flow reductions, while octapressin did not reduce CFC sffect of adrenaline on precapillary sphincter sections and on capacitance vessels is greater than that of octapressin in doses producing similar flow reductions.

In fractured dentin in fifteen teeth, the mean flow produced by a hydrostatic pulpal pressure of 30 mm. Hg exceeded 0.6 μl/mm. 2 d; this implies that a patent tubule can be emptied about ten times a day. The histologic examination of twelve teeth suggests that the reduction in the odontoblast layer by aspiration of the cells into the dentinal tubules under exposed dentin, caries, or leaky fillings is a result of the outward flow in the tubules produced by a physiologic pressure gradient.

The objective of the study was to determine the response in the pulpal blood flow to vasodilator substances at different levels of vasomotor tone.Simultaneous determinations of iodide disappearance rate (k-value) from dentinal cavities and, as control, from the adjacent alveolar submucosa were performed on anesthetized cats. Changes in k-value reflected changes in blood flow. Close i.a. infusion of acetylcholine, histamine and bradykinin did not influence pulpal microcirculation when the sympathetic nervous tone was low. At a higher level of nervous vascular tone, obtained by direct electrical stimulation of the cut sympathetic cervical trunk, the substances were shown to increase the pulpal blood flow. Papaverine and warming had a more pronounced vasodilator influence on pulpal blood flow, suggesting the presence of a local myogenic vascular tone regulating the exchange function, which was unaffected by acetylcholine, histamine and bradykinin. These substances were thus shown to act as inhibitors of symp...

In order to investigate the origin of intradentinal nerve-like structures, unilateral transection of the sensory (inferior alveolar nerve) and/or the autonomic (cranial cervical sympathetic ganglion) supply was performed in 6 cats. After 2—4 weeks, when degenerative change was expected in the cut nerves, electrophysiological recordings from the dentin showed total absence of impulse activity in teeth subjected to sensory denervation regardless of whether or not the autonomic innervation was intact. Control teeth, on the other hand, responded to different local pain stimuli. Electron microscopic study of predentin and inner dentin in control teeth showed intratubular nerve-like structures similar to «associate cells» earlier described in human teeth. In teeth subjected to sensory nerve resection, however, the intradentinal «associate cells» showed advanced degenerative change or were absent. Resection of the sympathetic nerve supply did not influence the appearance of these intratubular structures.The pres...

The effects of nerve stimulation on blood flow were studied in the dental pulp of anesthetized cats. Changes in iodide disappearance rate (k-value) from dentinal cavities were used to determine changes in pulpal blood flow. Electrical stimulation of the distal end of the cut inferior alveolar nerve after alpha-adrenoceptor blockade (phentolamine, 3 mg/kg) consistently resulted in a rapid increase in disappearance rate. The first stimulation produced the greatest response (an average increase in k-values of 60%) and repeated stimulations showed a successive attenuation in response, the fourth stimulation usually having no effect. A progressive decrease in resting k-values was observed after the first stimulation, indicating an impaired exchange function of the capillary vessels. Systemic pretreatment with propranolol (0.5--1 mg/kg), atropine (3 mg/kg), mepyramine (3 mg/kg) and cimetidine (3 mg/kg) did not influence the rapid increase in k-values produced by the nerve stimulation. The experiments show that vasodilatation in the cat dental pulp produced by stimulation of the inferior alveolar nerve is not mediated by common efferent vasodilatory mechanisms and strengthen the hypothesis that the sensory nerve axon reflex mechanism is involved.

Tissue levels of substance P (SP) were determined by radioimmunoassay in cat dental pulps after unilateral electrical stimulation of the inferior alveolar nerve. Nerve stimulation (10 V, 10 Hz, 5 ms for 3 min) reduced the SP level at the stimulated side by approximately 40%, indicating a release of SP. Stimulation performed after infusion of morphine (0.3 mg/kg/min, i.v.) for 10 min did not reduce the pulpal SP-level. Naloxone (3 mg/kg, i.v.) administered immediately before the morphine infusion in three experiments, did not influence the effect of morphine on pulpal SP levels after nerve stimulation. This may indicate an action of morphine on a naloxone-insensitive receptor type. Morphine in the dosage used did not influence the intradental sensory nerve conductivity. The results indicate that morphine is able to inhibit stimulus evoked release of SP from peripheral endings of primary afferent neurons.

Tissue levels of substance P-like immunoreactivity (SPLI) were determined by radioimmunoassay in incubated cat dental pulps with and without previous electrical stimulation of the inferior alveolar nerve (I.A.N.). The ability of the dental pulp to degrade substance P (SP) was also studied. The pulpal SPLI levels in teeth incubated at 37 degrees C for up to 240 min immediately after removal from the jaws did not differ from those in contralateral unincubated teeth. Following I.A.N. stimulation (3-45 min at 10 V, 15 Hz and 5 ms) and subsequent incubation (30 min at 37 degrees C) of the teeth the SPLI levels in ipsilateral pulps were significantly lower (45% reduction) than those in contralateral unstimulated controls. Incubation of homogenized pulp tissue at 37 degrees C with synthetic bovine SP or 125I-Tyr8-SP led to rapid inactivation of SP, whereas similar incubation of whole blood with 125I-Tyr8-SP had little effect. Endogenous SPLI levels were also rapidly reduced (50% reduction within 3 min) in incubated pulp homogenates. Incubation at a lower temperature (22 degrees C) resulted in a somewhat reduced rate of degradation and incubation with boiled homogenates failed to inactivate SP. The results indicate that the pulp contains enzymes capable of destroying SP and that within the nerve terminals SP is stored in such a way that it is protected against degradation. The data obtained also provide further evidence for a nerve evoked release of SP.

The present investigations in cats were designed to study the effects of local anaesthetics containing adrenaline and felypressin (octapressin) on dental pulp function. Intradental sensory nerve excitability was measured using electrodes placed in dentinal cavities in canine teeth. Changes in pulp blood flow were measured using the disappearance rate of a radioactive tracer placed in the same cavities. Injections (0.5 ml) of lidocaine (20 mg/ml) - adrenaline (12.5 microng/ml) or prilocaine (30 mg/ml) - octapressin (0.54 microng/ml) were given supraperiosteally in the apical area of the tooth. Adrenaline either alone or with lidocaine caused almost complete inhibition of pulp blood flow within a few minutes. This effect was followed by a total inhibition of the sensory nerve activity. In most cases there was a recovery of both functions after 3 hours. Octapressin, on the other hand, had no inhibitory effects on pulp blood flow or sensory nerve activity. Lidocaine and prilocaine were also without effect. These findings indicate a different mode of action of the two vasoconstrictors and suggest that octapressin may be preferred in infiltration anaesthesia during treatment of the vital tooth.

The concentration of substance P-like immunoreactivity (SPLI) was determined in dental pulps from cat, dog and man by radioimmunoassay. Pulps from mature cats showed the highest SPLI-levels (mean 32 pmol/g); these are comparable to or higher than those found in any other organ outside the central nervous system. The SPLI concentrations were lower in pulp from immature teeth. The immunological and chromatographic behav behaviour of the pulpal SPLI from cat and man resembled that of synthetic substance P (SP), indicating that the assayed substance is closely related to or identical with SP. Release of pulpal SPLI in canine teeth ws evoked by stimulation of the inferior alveolar nerve in anaesthetized cats. In 9 of 16 experiments the amounts of SPLI found in pulp suprafusates following stimulation (4–31 fmol) were larger than those in unstimulated controls (0–7 fmol). Stimulation also reduced the pulpat tissue concentration of SPLI to 60% of that in homologous control pulps. The high concentration of SPLI found in the dental pulp and the demonstration of nerve-induced release strengthen the hypothesis that SP serves some function in the dental pulp.

Intradental sensory nerve impulse activity was measured from dentinal cavities in canine teeth of anesthetized cats. No spontaneous activity was usually recorded in cavities filled with isotonic saline. Heat stimulation of 15–20oC failed to give any impulse activity, while other stimuli, such as air blasts produced bursts of impulses. Lowering extracellular calcium ion concentration. by local application of sodium citrate, sodium oxalate or EDTA, induced impulse activity. Under these conditions, heat produced a rapid increase in discharge activity. which lasted as long as the stimulus was applied. Increased extracellular calcium concentration abolished this response to heat. The present findings show that a change in the extracellular calcium ion concentration modulates the excitability of intradental sensory units, and may thus also modulate the resulting experience of pain.

Laser Doppler flowmetry was applied to human teeth to study whether blood How in the pulp can be recorded. In sensitive, intact incisors the level of the output signal Ironi the flowmeter was clearly distinguishable from that obtained in adjacent nonsensitive or pulpeetomized teeth. Heart beat synchronous oscillations, which were present in the recording signal from normal teeth, were absent in nonvital teeth. Local injection of lidocaine (20 mg/ml) with adrenaline (12.5 μg/ml) caused a pronounced and long-lasting reduction of the flowmetric values in healthy teeth. The oscillations were also reduced in amplitude. Repeated recordings showed good reproducibility. Thus, changes in blood (low may be assessed in a tooth by tin's non-invasive method. The instrument is a promising tool in the clinical evaluation of pulp vitality following traumatic injuries.

The responses of intradental sensory nerves to hyperosmotic solutions of sucrose (4M) and calcium chloride (6M) applied in dentinal cavities were studied in anesthetized cats. Nerve impulse activity was recorded from canine teeth after application of the test solutions in shallow and deep cavities. In shallow cavities (thickness of remaining dentin, about 500 micron) sucrose and calcium chloride caused an immediate and transient excitation of the nerves in 3 out of 15 teeth and in 8 of 12 teeth, respectively. Treatment of such cavities with lactic acid (1M) increased the frequency of nerve responses to 100%. When applied in deep cavities (thickness of remaining dentin, 0-50 micron), sucrose induced a burst of impulses followed by continuous nerve activity, whereas calcium chloride decreased the nerve excitability. Our results support the hypothesis that solutions exerting an effective osmotic pressure excite the intradental nerves by an indirect mechanism when applied on the dentin and that they exert a direct effect on nerves when in contact with the pulp. In addition, it is suggested that acids produced in carious dentin may facilitate the induction of pain by hyperosmotic stimuli.

The occurrence of substance P (SP)-like immunoreactivity was studied in dental pulps of the cat. In untreated animals SP-positive fibres were found in all areas of the pulp. Most fibres were seen in central parts of the pulp but they were also observed in relation to the odontoblasts. Single, possibly unmyelinated, or fine caliber fibres or small bundles of them were seen running close to large non-fluorescent myelinated nerves, to blood vessels or without any obvious association with either of these structures. Fourteen days after transection of the inferior alveolar nerve no SP-positive fibres were observed in pulps on the denervated side. Transection of the cervical sympathetic ganglion did not change the occurrence of SP-positive fibres. The results indicate the existence of at least two types of afferent fibres in the dental pulp of the cat. Since the tooth pulp has been demonstrated to give rise only to pain sensation when stimulated, the results give morphological support for a role of SP neurones in pain transmission.

Augmentation of the rat parotid salivary secretion to intravenous injections of substance P (SP) occurred when SP was combined with vasoactive intestinal peptide (VIP), or stimulation of the auriculo-temporal nerve in the presence of atropine and the adrenergic blockers, dihydroergotamine and propranolol. The largest increase was obtained when SP (0.5 micrograms kg-1) was used together with subthreshold doses of VIP (84% at 0.05 micrograms kg-1 and 105% at 0.5 micrograms kg-1) and low frequency stimulation (92% at 2 Hz and 97% at 5 Hz), which did not produce any salivary secretion by itself. There was no facilitated secretion when VIP and nerve stimulation were combined. Amylase output was much larger (250-500%) when SP was combined with nerve stimulation (0.5-5 Hz) or VIP (0.005-5 micrograms kg-1) than when SP was used alone. Similar results were obtained in rats where the auriculo-temporal nerve was stimulated during the early phase (24-90 h) of Wallerian degeneration, when the nerve-induced responses were seemingly completely blocked. Our results are consistent with the hypothesis that both VIP and SP contribute to the atropine-resistant parotid secretion, and that they have a complementary role in the rat parotid exocrine function.

The effect of somatostatin on nerve-induced vasodilatation and the release of substance P (SP) was studied in the dental pulp of anesthetized cats. Changes in pulpal blood flow were determined by measuring the rate of disappearance of a local depot of radioactive tracer. The release of SP was studied indirectly by determining the residual amounts of substance P-like immunoreactivity (SPLI) in the pulps by radioimmunoassay. Electrical stimulation (3 min at 10 V, 15 Hz and 5 ms) of the distal end of the cut inferior alveolar nerve (IAN) increased pulpal blood flow. After pretreatment (10 min) with somatostatin (30 pmol/min) similar nerve stimulation was without effect on pulpal blood flow. Intra-arterial infusion of somatostatin (30 pmol/min) had no effect on pulpal blood flow and did not influence the vasodilator response to SP. Following IAN stimulation (3--45 min) and subsequent incubation (30 min, 37 degrees C) of the lower canine teeth, the SPLI levels in ipsilateral pulps were significantly lower (47.5% reduction) than those in contralateral, unstimulated controls. In cats pretreated with somatostatin (30 pmol/min for 10 min, i.a.) similar nerve stimulation (3 min) did not reduce the pulpal SPLI levels as compared to controls. The results show that nerve-induced vasodilatation and release of SPLI are inhibited by somatostatin. They are consistent with the hypothesis that vasodilatation in the cat dental pulp produced by stimulation of the IAN is mediated by substance P.