Bertil Gazelius

In vivo release of substance P in cat dorsal horn studied with microdialysis

Variations in the extracellular concentration of substance P (SP) were measured in cat dorsal horn in vivo by microdialysis and radioimmunoassay. Electrical unilateral stimulation of the sciatic nerve was used to evoke release of SP. At high-intensity stimulation, activating slowly conducting (approx. 0.9 m/s) fibres, there was an increase in substance P-like immunoreactivity (SP-LI) to 338% of the preceding control value (P less than 0.05, n = 5) in the dialysates collected at levels L6-L7 at the stimulated side. A less pronounced increase, to 164% of the basal level, was found at the contralateral side. More cranially (L1-L5) in the dorsal horn at the stimulated side, only a moderate or no increase in SP-LI was seen. Stimulation with low intensity, sufficient to activate fast (greater than 20 m/s), but not slowly conducting fibres, evoked no increase in SP-LI. The results indicate that unilateral peripheral C-fibre activation induces a local SP release in the dorsal horn present also on the side not stimulated.

Abnormal afferent nerve endings in the soft palatal mucosa of sleep apnoics and habitual snorers

Habitual snoring precedes obstructive sleep apnea (OSA), but the pathophysiological mechanisms behind progression are still unclear. The patency of upper airways depends on a reflexogen mechanism reacting on negative intrapharyngeal pressure at inspiration, probably mediated by mucosal receptors, i.e., via afferent nerve endings. Such nerves contain a specific nerve protein, protein-gene product 9.5 (PGP 9.5) and in some cases substance P (SP) and calcitonin gene-related (CGRP). Biopsies of the soft palatial mucosa were obtained from non-smoking men ten OSA patients, 11 habitual snorers and 11 non-snoring controls. The specimens were immunohistochemically analyzed for PGP 9.5, SP and CGRP. As compared to controls, an increased number of PGP-, SP- and CGRP-immunoreactive nerves were demonstrated in the mucosa in 9/10 OSA patients and 4/11 snorers, in addition to varicose nerve endings in the papillae and epithelium. Using double staining methodology, it could be shown that SP- and CGRP-like immunoreactivities (LIs) often coexisted in these fibres, as did CGRP- and PGP 9.5-LIs. The increased density in sensory nerve terminals are interpreted to indicate an afferent nerve lesion. Our results support the hypothesis of a progressive neurogenic lesion as a contributory factor to the collapse of upper airways during sleep in OSA patients.

Involvement of afferent nerves in pulpal blood-flow reactions in response to clinical and experimental procedures in the cat

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 microA, 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 less than 0.005, 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Photochemically induced ischaemic lesion of the rat sciatic nerve. A novel method providing high incidence of mononeuropathy

The incidence of behavioural signs of mononeuropathy in rats subjected to chronic constriction injury (CCI) of the sciatic nerve is unpredictable and often low. In the present study, an ischaemic lesion of the rat sciatic nerve was induced photochemically using a low power laser. In these rats tactile allodynia developed with a considerably greater incidence (95%) than in control rats subjected to CCI (45%). The allodynia lasted longer and was more prominent. Responses to thermal stimulation did not markedly differ between the two groups. The ischaemic lesions displayed marked degeneration, particularly of large myelinated fibres. The results suggest that laser irradiation of a peripheral nerve inducing a local photochemical reaction followed by Wallerian degeneration may be a convenient and reproducible experimental method of producing signs of peripheral mononeuropathy.

Habitual Snorers and Sleep Apnoics Have Abnormal Vascular Reactions of the Soft Palatal Mucosa on Afferent Nerve Stimulation

A local disturbance in the afferent nerves involved in the reflexogenic dilation of the upper airways (UAs) could contribute to the increased collapsibility seen in patients with obstructive sleep apnea (OSA). Laser Doppler perfusion monitoring, combined with electrical stimulation, is a method for investigating the afferent nerve regulation of the microcirculation. It was used in the mucosa of the soft palate in 35 patients with various degrees of UA obstruction and in 13 control subjects, all nonsmoking men. In a majority of snorers and patients with mild OSA, stimulation induced an exaggerated vasodilation, compared with controls. In contrast, in patients with severe OSA, the vasodilation was significantly reduced, compared with controls. These signs of disturbances in the microcirculation support the hypothesis of a local progressive afferent nerve lesion in heavy snorers with or without OSA.

Effects of adrenaline and felypressin (octapressin) on blood flow and sensory nerve activity in the tooth.

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.

Neurogenic Mediators in Control of Pulpal Blood Flow

In view of recent findings, classical nerve-released transmitters that modulate pulpal blood flow share their roles with novel vasoactive peptides. Noradrenaline coexists with neuropeptide Y in sympathetic nerves in the pulp and both substances contribute to a vasoconstriction. Vasoactive intestinal peptide has vasodilator effects and its presence in nerves in the pulp may represent a parasympathetic influence on pulpal vessels. Sensory nerves in the pulp contain a number of peptides which have vasodilatory effects. They are released and cause rapid increase in blood flow when the tooth is reached by an intense stimulus. A population of sensory nerves may thus play a role in instant defense reactions in the pulp.

IN VIVO RELEASE OF SEROTONIN IN CAT DORSAL VAGAL COMPLEX AND CERVICAL VENTRAL HORN INDUCED BY ELECTRICAL STIMULATION OF THE MEDULLARY RAPHE NUCLEI

Extracellular levels of serotonin (5-hydroxytryptamine; 5-HT) were monitored by microdialysis in the dorsal vagal complex (DVC) and the ventral horn of the spinal cord at the level of the phrenic motor nucleus in decerebrated cats. A selective serotonin uptake inhibitor, alaproclate (10(-4) M) was included in the dialysis probe perfusion fluid to increase basal and stimulated levels of 5-HT. Electrical stimulation (30 Hz, 10 V, 0.5 ms) in the nucleus raphe obscurus, containing neurons projecting to the DVC and to the ventral horn, induced a 2-3-fold increase of the 5-HT release in both these regions. After termination of the stimulation, the release gradually decreased during the following 60 min. Substance P, which coexists with 5-HT in descending neurons, did not significantly affect the 5-HT release when it was added (100 microM) to the probe perfusion fluid. The present findings are in accordance with the hypothesis that prolonged release of 5-HT is responsible for the previously demonstrated long-lasting facilitation of phrenic activity following raphe obscurus stimulation.

Bedside monitoring of regional cortical blood flow in comatose patients using laser Doppler flowmetry

Continuous beside monitoring of regional cerebrocortical blood flow was carried out using laser Doppler flowmetry (LDF) in four comatose patients. Newly designed thin and flexible optical probes that were easily implanted into the cortex were employed. When the patients were in a deep comatose state, the recordings revealed a conspicuous relationship to intracranial pressure. As the patients improved, the flux values gradually increased, and the recordings showed characteristic changes in the wave pattern, presumably related to the restoration of an impaired cerebral autoregulation. Changes in regional cerebrocortical blood flow were also observed during routine nursing procedures, the use of medications, and voluntary activities, as demonstrated by one patient after a complete recovery. Although the volume of tissue scanned with LDF was limited, and the flux values did not directly express regional cerebrocortical blood flow in terms of milliliters per unit volume, changes in cerebral circulation were portrayed clearly in the flow recordings. Thus, LDF, which is simple to use, permits continuous bedside monitoring of the cerebral microcirculation. Its use should improve the management of comatose patients and also open avenues for a better understanding of the cerebral circulation in pathological states.

Activation of sympathetic fibres in the pulp by electrical stimulation of rat incisor teeth

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.