Timo Huopaniemi

Modification of dental pain and cutaneous thermal sensitivity by physical exercise in man

The effect of physical exercise on dental pain thresholds, the release of pituitary stress hormones and thermal sensitivity of skin was tested in healthy human subjects. Different levels of exercise (100-300 W) at different pedal frequencies were produced by a cycle ergometer. Thermal limen (the interval between warm and cool thresholds) determined from glabrous hand, hairy forearm and leg was used as a parameter of thermal sensitivity. In all subjects the heart rate and blood pressure were increased with increasing work load. Dental pain thresholds were elevated at high work loads with a concomitant activation of pituitary stress hormone (especially growth hormone) release. Thermal limens at all 3 sites were increased work load, too, independent of the pedal frequency. The increase of thermal limen was most marked in the leg and least in the glabrous hand. The results indicate that physical exercise produces a non-segmental, load-dependent decrease of pain and thermal sensitivity with a concomitant activation of pituitary stress mechanisms. The magnitude of modification varies with skin region. Activation of inhibitory mechanisms at spinal levels via muscle and proprioceptive afferents, in a way suggested by the gate control theory of pain mechanisms, seems to have only a minor, if any, contribution to the present findings, since a higher pedal frequency did not produce a more marked decrease of sensitivity.

The influence of exercise on dental pain thresholds and the release of stress hormones

Different levels of exercise (50-200 W) were produced by a bicycle ergometer. In all six subjects the heart rate and blood pressure were increased with increasing work load. Dental pain thresholds tended to increase with increasing work load, too. Plasma ACTH levels were above the normal range during the whole experiment in all subjects, whereas plasma cortisol and prolactin levels were elevated only in one subject. Growth hormone levels had a tendency to elevation at 200 W. There was no correlation between the release of cortisol, prolactin or ACTH and the dental pain threshold elevation. However, there was significant correlation between the release of growth hormone and the dental pain threshold elevation. The results indicate that physical exercise at submaximal work loads is enough to produce a pain threshold elevation in some subjects, with a minor coactivation of stress mechanisms.

The effect of temporal parameters on subjective sensations evoked by electrical tooth stimulation

&NA; The effect of stimulus duration and frequency on subjective sensations evoked by electrical tooth stimulation was studied in 12 subjects. The sensory responses were classified using 5 equi‐sensation categories (perception threshold, prepain, pain threshold, moderate pain, intense pain). Both continuously increasing and randomised stimuli were applied. A comparison was made with the activation thresholds of intradental A‐ and C‐fibres in the cat. The mean threshold of intradental A‐fibres was lower than the perception threshold at all pulse durations. Perception threshold decreased with increasing stimulus frequency. Current intensities which evoked prepain at a stimulus frequency of 1 Hz were rated as pain at 20 Hz. At supraliminal pain levels the effects of summation were more marked. High‐frequency stimulation produced intense pain sensations at intensities well below the activation thresholds of pulpal C‐fibres in the cat. We conclude that both perception and pain thresholds and supraliminal pain are modified by temporal summation, and that activation of different pulpal fibre populations is not responsible for production of prepain and pain sensations.

Activation of heat-sensitive nerve fibres in the dental pulp of the cat.

Abstract We have recorded responses of inferior alveolar nerve fibres to heating of the intact enamel of the canine tooth crown in anaesthetized cats. After identification of intradental nerve units by monopolar electrical stimulation, the tooth was heated with an electrothermal stimulator (Peltier element). The rate of temperature change in the tooth was considerably slow (< l°C/sec). Responses of 37 heat‐sensitive units were recorded. They were all quite slowly conducting (CV = 1.7 ± 0.7 (S.D.) m/sec). Only 8 fibre units with conduction velocity below 3.5 m/sec did not respond to heating. The mean threshold temperature was 43.8 ± 3.4 (S.D.)°C. Nerve activity appeared as irregular bursts of action potentials. When heating was repeated at short intervals (2–3 min), an elevation in the thresholds was noticed. After cooling or a recovery period of about 10 min the thresholds for heating returned towards the initial ones, but they still remained somewhat elevated. This change in thresholds might have been due to heat induced injury in pulp tissue. When heating was stopped the activity ceased with declining temperature regardless of the temperature reached during the stimulation. Spontaneous firing never occurred. Not one of the units with a conduction velocity above 3.5 m/sec (n = 28,CV = 13.2 ± 7.1 (S.D.) m/sec) were activated by heating. Cooling of the tooth did not induce responses in any of the recorded units. Only 3 of 10 slowly conducting units fired, when pulp was mechanically irritated. On the other hand 11 of 14 fast conducting units were mechanosensitive. It is concluded that there exist differences in heat sensitivity of fast and slowly conducting pulp nerve units in the cat. The possible activation of slowly conducting intradental nerve fibres also in man might be significant in mediation of pain sensations induced by heating of the tooth crown.

A laminin graft replaces neurorrhaphy in the restorative surgery of the rat sciatic nerve

We investigated the role of laminin in functional recovery of a peripheral nerve injury using electrophysiological and behavioral approaches on the rat sciatic nerve in vivo. These studies were complemented by neurofilament protein immunocytochemistry on the sciatic nerve 20 days after an operation, in which an 8-mm piece of the nerve was removed and replaced by a graft of laminin, its neurite outgrowth-promoting peptide, a control peptide, collagen, or by resuturing of the removed piece of the nerve. Electrophysiological measurements of muscle strength 4 months after the sciatic nerve transection showed that a laminin graft was as effective as neurorrhaphy in supporting functional recovery of an injured peripheral nerve. A laminin graft also significantly reduced autotomy in the operated animals. Immunocytochemistry confirmed that both a laminin graft and resuturing supported growth of the 200-kDa neurofilament-positive axons into the distal stump of the nerve within 20 days of operation. A graft with a neurite outgrowth-promoting peptide of the B2 chain of laminin supported similar axon growth, whereas another peptide graft also derived from laminin or a collagen graft did not support axon growth. All grafts allowed Schwann cell growth into the distal stumps of the nerves, but neurites accompanied them only in the regeneration-supporting grafts and in the resutured nerves. The Schwann cells of the regenerating nerves expressed high levels of the neurite outgrowth-promoting domain of the B2 chain of laminin, whereas the Schwann cells of the degenerating nerves failed to express this domain in the distal stumps of the degenerating nerves. These results provide the first in vivo evidence for the functional role of laminin in peripheral nerve regeneration. As the neurite outgrowth-promoting domain of the B2 chain of laminin is as efficient as laminin or resuturing in supporting a short-term recovery of an injured sciatic nerve, this area may be a regeneration-promoting domain of this glycoprotein. More importantly, as grafting significantly reduces post-traumatic pain behavior in the operated animals, the laminin graft surgery may provide a useful method for clinical restoration of the injured peripheral nerves.

Elevation of dental pain threshold induced in man by physical exercise is not reversed by cyproheptadine-mediated suppression of growth hormone release.

The effect of cyproheptadine on growth hormone (GH) secretion and dental pain threshold elevation during physical exercise was studied in healthy human subjects. Different levels of exercise (200-300 W) were produced by a cycle-ergometer. Dental pain thresholds were tested with a constant current pulp tester. In all 6 subjects dental pain thresholds and the heart rate were increased with increasing work load. Cyproheptadine did not have any significant effect on dental pain threshold elevations, although it suppressed the exercise-induced GH release. The results indicate that the exercise-induced dental pain threshold elevation is not based on GH-related stress mechanisms, since cyproheptadine did not reverse the pain threshold elevation.

Tooth pulp-evoked activity in the spinal trigeminal nucleus caudalis of cat: Comparison to primary afferent fiber, reflex, and sensory responses

Tooth pulp-evoked single-neuron responses were recorded in the spinal trigeminal nucleus caudalis of the cat. The thresholds to monopolar electric pulses of various durations (0.2 to 20 ms) were determined using a constant current stimulator. With stimulus pulse durations of 10 to 20 ms, the thresholds were comparable with those of primary afferent A-fibers, although the most sensitive primary afferent fibers had lower thresholds. Primary afferent C-fibers had higher thresholds than the postsynaptic neurons studied. The threshold for the tooth pulp-elicited jaw-opening response was obtained at a lower stimulus intensity than the liminal response in most postsynaptic neurons of this study. The threshold rise of the postsynaptic trigeminal neurons with decreasing stimulus pulse duration (from 5 to 0.2 ms) was much steeper than that of primary afferent A-fibers or jaw-opening response. The strength-duration curves for tooth pulp-elicited pain sensations in man resemble those of spinal trigeminal neurons. Sixty-two percent of the units had a threshold elevation during a noxious pinch of the tail. The results indicate that the activation of postsynaptic trigeminal neurons requires a considerable temporal summation of primary afferent impulses. The jaw reflex thresholds cannot be explained by the properties of the neurons in the subnucleus caudalis of the trigeminal tract. The results support the concept that dental pain is based on the activation of spinal trigeminal nucleus caudalis neurons receiving their input from intradental A-fibers.

Response characteristics of tooth pulp-driven postsynaptic neurons in the spinal trigeminal subnucleus interpolaris of the cat: comparison with primary afferent fiber, subnucleus caudalis, reflex, and sensory responses

Tooth pulp-evoked single neuron responses were recorded in the spinal trigeminal subnucleus interpolaris of the cat. The thresholds to monopolar electric pulses of varying duration (0.2-20 ms) were determined using a constant current stimulator. The thresholds were comparable with those of primary afferent A-fibers, although the most sensitive primary afferent fibers have lower thresholds. The thresholds and latencies showed that none of the interpolaris neurons received their input solely from intradental C-fibers. The most sensitive subnucleus interpolaris neurons had lower thresholds than the respective subnucleus caudalis neurons studied in our previous work. The thresholds and strength-duration curves of the most sensitive interpolaris neurons and of the tooth pulp-elicited jaw-opening reflex are nearly similar, although the jaw reflex can be elicited at an intensity which is slightly lower than that needed to activate the most sensitive interpolaris neurons of the present sample. The most sensitive interpolaris neurons were activated at current intensities that were below the intensity needed to produce liminal dental pain in man, and the strength-duration curves of these neurons were flatter than the curve depicting liminal dental pain sensation in man. The relationship between stimulus intensity and response magnitude could be well described by power functions, the median exponent of which was 1.251. A conditioning stimulation of the tooth pulp at low intensity produced a short (less than 25 ms) enhancement of the response to the following test stimulus, whereas a high intensity conditioning stimulus produced a longer (greater than 40 ms) suppression of the response to the following stimulus. The threshold of 33% of the neurons was elevated during a noxious tail pinch, and this elevation was not reversed by naloxone, an opioid antagonist. The results indicate that in the trigeminal subnucleus interpolaris there are tooth pulp-driven neurons with an input from intradental A-fibers and that a considerable temporal summation of impulses from primary afferent fibers is needed to activate most of them. Human dental pain thresholds cannot be explained by the liminal response properties of the most sensitive interpolaris neurons, but they may be important in the mediation of near-threshold reflex events. It is possible, however, that the high-threshold interpolaris neurons may have a role in the mediation of sensory responses.

Tooth pulp-evoked jaw-opening reflex in the cat: Evidence for central facilitation induced by noxious discharge in the intradental nerve fibers

The tooth pulp-evoked jaw-opening reflex was studied in the barbiturate-anesthetized cat. At liminal intensity of the stimulus, a stable short-latency response was obtained in the digastricus and in the tongue. At a higher stimulus intensity, there occasionally appeared to be a prolonged discharge of variable duration in the digastricus, and a second period of activity in the tongue after a silent period. The threshold intensity for these late discharges was supraliminal for the intradental A-fibers and subliminal for intradental C-fibers. Noxious conditioning stimulation of a tooth led to a temporary decrease of the threshold for the jaw-opening reflex elicited from a contralateral or adjacent tooth; only conditioning stimulation at an intensity producing a marked arousal reaction was effective in this respect. Infiltration of the tooth apex with epinephrine produced a local elevation of the threshold for the tooth pulp-evoked jaw-opening reflex. Distant noxious conditioning stimulation (tail pinch) did not influence the jaw-opening threshold. The results indicated that based on some central mechanisms, conditioning noxious stimulation of a tooth can produce a facilitation of the jaw-opening reflex.

Alcohol detoxification accelerated by oxygenated drinking water

Abstract The liver eliminates ethanol through several oxygen dependent processes. Since the liver receives most of its blood flow through the portal vein, it should be possible to increase its oxygen tension by augmenting the oxygen saturation of the portal vein. We therefore studied elimination of ethanol administered intravenously to three monkeys who received strongly oxygenated drinks at 20 to 30 minute intervals during the whole experiment. From these drinks dissolved oxygen was presumably released in the stomach and upper intestine and arrived to the liver along the portal vein. As a consequence of this treatment the elimination rate of ethanol increased 60 % on the average. The increase was significant on the level of p