PubMed Health⌕ Search

Biomedical subjects

A Pertovaara

Publications and source records attributed to A Pertovaara.

At least 109 records · Page 6Linked to original sources
PubMed1988

Collateral sprouting of nociceptive C-fibers after cut or capsaicin treatment of the sciatic nerve in adult rats.

The innervation area of nociceptive C-fibers in the saphenous nerve of adult rats was detected by the Evans blue technique, in which antidromic excitation of the nociceptive C-fibers causes a visible extravasation of dye in the skin it supplied. One month after cutting the sciatic nerve, the nociceptive C-fibers of the intact saphenous nerve had sprouted to the sciatic area. When capsaicin was locally applied to the nerve trunk to destroy C-fibers of the sciatic nerve, there was no sprouting of nociceptive C-fibers from the saphenous nerve. Thus, myelinated fibers and/or the functionally impaired C-fibers of the sciatic nerve are enough to prevent collateral sprouting of nociceptive C-fibers from the saphenous nerve.

Action Potentials↗
PubMed1988

The effect of systemic cocaine on spinal nociceptive reflex activity in the rat.

In the anesthetized rat, cocaine (25 mg/kg i.p.), enhanced the frequency potentiation of nociceptively evoked polysynaptic discharges but did not affect the polysynaptic reflex discharge to single nociceptive stimuli or the habituation of this reflex to repetitive pinch stimuli. The non-nociceptive, short-latency reflex discharge was suppressed for 10-15 min after cocaine administration. The neurogenic extravasation response to antidromic cutaneous C-fiber stimulation was unaffected by cocaine. These findings suggest that systemic cocaine, in doses analgesic for the rat, does not suppress spinal nociceptive reflexes.

Action Potentials↗
PubMed1988

Effect of naloxone on tooth pulp-evoked jaw-opening reflex in the barbiturate-anaesthetized cat.

The threshold of the tooth pulp-evoked jaw-opening reflex was uninfluenced by administration of 0.5 or 5.0 mg kg-1, i.v. naloxone, a specific opioid antagonist, in the barbiturate-anaesthetized cat. Furthermore, facilitatory or inhibitory interactions between two successive tooth pulp-evoked jaw reflex responses were not influenced by naloxone. It is concluded that naloxone-sensitive opioid receptor-mediated mechanisms do not contribute to the modulation of tooth pulp-evoked reflexes by conditioning dental stimuli. Also they do not exert a tonic inhibition on the sensory or motor part of the tooth pulp-driven reflexes. Experiments performed for comparison showed that the non-nociceptive polysynaptic reflex discharge in the flexo-motor neurons of the limb was not influenced by naloxone either.

Animals↗
PubMed1987

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.

Afferent Pathways↗
PubMed1987

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.

Animals↗
PubMed1987

Late effects of early binocular visual deprivation on the function of Brodmann's area 7 of monkeys (Macaca arctoides).

It has been shown earlier that binocular visual deprivation during the early sensitive period of life reduces the representation of visual functions in the posterior parietal association cortex of monkeys, in Brodmann's area 7 (Exp. Brain Res., 42 (1981) 1-8). Moreover, the representation of somatic functions increases suggesting that competitive mechanisms between the inputs from different modalities function during the early sensitive period of life in area 7. The aim of the present study was to find out whether further reorganization of functions takes place in the posterior parietal association cortex if monkeys that have experienced binocular visual deprivation through the first year of their life, are allowed to recover from the deprivation for a longer period of time. Four monkeys were deprived of binocular vision after the birth by lid closure for 12 months. Transdural extracellular multiunit recordings were performed in Brodmann's area 7 at the end of the deprivation period after the opening of the eyes. A second set of recordings was conducted in area 7 after a recovery period of 12 months from the deprivation. The results of the recordings at the end of the deprivation period confirmed the already known deprivation effect: there was a reduction in visually responsive neurons, an increase in the representation of somatosensory and somatomotor functions as well as an increase in the amount of cell groups that were 'only spontaneously active'. The recordings performed after the recovery period showed that the representation of visual functions had remained low. However, the amount of 'only spontaneously active' neurons had decreased and the amount of cell groups responding to the monkey's own explorative movements of the hand had further increased. The results indicate that visual deprivation during the early critical period of life results in a profound and persistent reduction of visual functions in area 7. However, activity-dependent competition between inputs from different modalities continue, resulting in the domination of somatosensory and somatomotor functions over visual functions in area 7. The results also suggest that neurons which during the visual deprivation are left without active input from the visual system, gradually become integrated into other functionally active neuronal networks increasing the representation of somatic functions in this cortical area.

Action Potentials↗
PubMed1987

Human pain thresholds after the application of lypressin, a vasopressin analogue.

Recent animal studies indicate that vasopressin has analgetic properties. The aim of this study was to find out if lypressin, a vasopressin analogue, produces analgesia in man. The effect of i.n. lypressin (5 and 10 I.U.) on experimental pain was tested in healthy humans. The lower dose proved high enough to produce a significant antidiuretic effect. Lypressin did not have any marked analgetic effect at these doses either on ischaemic, cutaneous thermal, or dental pain. The results indicate that lypressin cannot be used for pain relief in man at doses low enough not to produce a hazardous water retention.

Administration, Intranasal↗
PubMed1987

The effects of stimulus area and adaptation temperature on warm and heat pain thresholds in man.

The effect of stimulus area and adaptation temperature on warm and heat pain threshold were studied in healthy human subjects using a contact thermal stimulator. The stimulus area was varied in the range of 1.3 to 11.8 cm. Both the warm and heat pain thresholds decreased with increasing stimulus surface. Heat pain and warm thresholds were equally affected by the stimulus surface. The adapting temperature was varied in the range 25-35 degrees C, and warm thresholds were elevated with increasing adaptation temperature. The change of heat pain thresholds with increasing adapting temperature was not significant. Thus, there are both differences and similarities concerning how the different stimulus conditions affect heat pain and warm thresholds.

Adaptation, Physiological↗
PubMed1987

Vibrotactile masking effects on airpuff-elicited sensations vary with skin region in the human hand.

Inhibitory interactions between two tactile signals take place predominantly within mechanoreceptive submodality channels. This finding was utilized in the present study to determine the mechanoreceptive channels contributing to tactile sensations elicited by brief airpuff stimuli applied to the hairy and glabrous skin of the human hand. A reaction time paradigm was used to estimate the sensitivity of four subjects to airpuffs without and during continuous vibration (masker) of low (30 Hz) or high (240 Hz) frequency. The sensitivity to airpuffs (test stimuli) was decreased by a low-frequency masker in the hairy skin and by low- and especially by high-frequency maskers in the glabrous skin. The masking effect was enhanced in both skin areas by increasing the intensity of the masker and by decreasing the intensity of the test stimulus. The results suggest that the mechanisms underlying airpuff-elicited sensations consist of the low-frequency channel in the hairy skin, and of both the low- and high-frequency channels in the glabrous skin.

Adult↗
PubMed1987

Attenuation of tourniquet-induced pain in man by D-phenylalanine, a putative inhibitor of enkephalin degradation.

The effect D-phenylalanine (DPA), a putative inhibitor of enkephalin degradation, on the two separate pain components produced by the submaximal effort tourniquet test was evaluated in healthy human volunteers (N = 8). DPA attenuated the increase of the intensity of the ischemic and pressure pain components with increasing ischemia duration, but only the effect on the pressure pain component was significant. The results support some earlier reports suggesting that DPA has analgetic properties.

Adult↗
PubMed1987

Pain and stress: correlation of stress hormone release to pain modulation in man.

The contribution of stress-induced and opioid-dependent mechanisms to the modulation of experimental pain was studied in man under different conditions. The contribution of these mechanisms to the possible attenuation of acute cardiac pain in human patients was also studied. According to the present series of investigations, stress-induced mechanisms might be involved in the modulation of pain caused by physical exercise but not by concurrent subacute pain or transcutaneous nerve stimulation. The lack of any negative correlation between the pain intensity and the release of stress hormones indicates that stress mechanisms do not attenuate acute ischaemic pain of the cardiac origin. The use of an opioid-antagonist, naloxone, and the measurement of plasma levels of beta-endorphin did not reveal any contribution of endogenous opinoids to pain modulation in the current study.

Coronary Disease↗
PubMed1986

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.

Adult↗
PubMed1986

Liminal and supraliminal response characteristics of mechanoreceptive neurons in the cuneate nucleus of cat.

The response characteristics of mechanoreceptive neurons (RA, SA, and PC) innervating the foot pad of cat were determined in the cuneate nucleus. The mechanical stimuli were single sinusoidal pulses of varying frequency (20, 60, 150, and 240 Hz), and vibratory trains of varying frequency (80 and 240 Hz) and duration (50, 100, and 400 ms). Thresholds and stimulus-response functions were determined with single pulses. Absolute thresholds (1 impulse/train), tuning thresholds (1 impulse/cycle), and atonal intervals (the range between absolute and tuning thresholds) were determined with vibratory stimulus trains. When tested with single pulses the thresholds resembled those of primary afferents in all unit populations. The stimulus-response function of PC units but not of all RA units were comparable to those of primary afferents. Noxious conditioning stimulation did not influence the thresholds of cuneate mechanoreceptors in the tested sample (N = 6). Mostly PC units were tested with vibratory trains. Absolute thresholds were not dependent on stimulus duration, which is a consistent finding with peripheral units. In contrast to peripheral units, the tuning thresholds in most PC units were elevated with increasing stimulus duration. The variability in the range of atonal intervals was much larger than in the periphery. Thus, it seems that both the type of the tactile signal and the type of the studied mechanoreceptive neuron are critical parameters in determining whether the response characteristics of neurons in the cuneate and in the periphery are identical or not.

Animals↗
PubMed1986

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.

Animals↗
PubMed1986

Effect of tourniquet-induced ischemia on cutaneous thermal thresholds.

The effect of tourniquet-induced ischemia on human thermal thresholds was studied. After the development of the A-fibre block (= a sharp elevation of cool threshold) the heat-pain threshold was still uninfluenced. This result supports previous evidence indicating that C-fibres mediate the liminal heat pain sensation. Thus, the quantitative determination of cutaneous heat pain thresholds provides a rather selective method for testing C-fibre mediated pain sensitivity, at least when a contact thermostimulator with a slow or moderate rise of stimulus temperature is used. The second aim of this study was to examine whether ischemia or mechanical pressure is the cause of the tourniquet-induced block of A-fibres. This was studied by varying the mechanical pressure and the amount of ischemia. With increased ischemia (with muscle work) the A-fibre block (increased cool threshold) came earlier, but this finding was not significant.

Adaptation, Physiological↗
PubMed1986

Response variability to repeated mechanical stimulation of the skin in the dorsal column system.

The response variability in the primary afferent fibers and in the post-synaptic neurons of- the cuneatus was determined using repetitive mechanical stimulation of the skin in cat. The response variability was larger in the post-synaptic neurons. Of the two studied mechanoreceptor types, the RA (rapidly adapting) units had significantly more variability at the cuneate level than the PC (Pacinian) units, but at the peripheral level no such difference was found. The results suggest that the PC units transmit signals more securely through the cuneatus than the RA units.

Action Potentials↗
PubMed1985

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.

Adrenocorticotropic Hormone↗