Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SENSATION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMed1984

Sensation of respiratory force following low cervical spinal cord transection.

The psychophysical technique of magnitude scaling was used to assess the sensation of respiratory muscle force in patients with low cervical spinal cord transection. The exponents of the power function relationship between load magnitude and sensation intensity during graded elastic and resistive ventilatory loading in the quadriplegic patients were 0.51 and 0.54, respectively. These values were significantly lower than those in normal subjects (P less than 0.05). This impairment in load sensation could not be attributed to differences in either the duration or magnitude of the forces generated by muscles of inspiration during loading, since the power function relationships between airway pressure and sensation intensity corrected for inspiratory duration were also significantly lower in the quadriplegic patients compared with the normal subjects. In contrast the perception of respiratory force during inspiratory maneuvers against a closed airway, as determined by both magnitude estimation and production tests, was the same in normal subjects and quadriplegics. These results suggest that afferent signals from rib cage receptors are important in shaping the intensity of the sensation during submaximal ventilatory loading. During maximal loading, i.e., airway occlusion, when respiratory muscle tension changes proportionally with the motor command, centrally generated efferent command signals may be employed to subserve the sensation of respiratory muscle force when inputs from rib cage muscle receptors are not available.

Adult↗
PubMed1997

Characteristics of temporal summation of second pain sensations elicited by brief contact of glabrous skin by a preheated thermode.

Temporal summation of sensory intensity was investigated in normal subjects using novel methods of thermal stimulation. A Peltier thermode was heated and then applied in a series of brief (700 ms) contacts to different sites on the glabrous skin of either hand. Repetitive contacts on the thenar or hypothenar eminence, at interstimulus intervals (ISIs) of 3 s, progressively increased the perceived intensity of a thermal sensation that followed each contact at an onset latency > 2 s. Temporal summation of these delayed (late) sensations was proportional to thermode temperature over a range of 45-53 degrees C, progressing from a nonpainful level (warmth) to painful sensations that could be rated as very strong after 10 contacts. Short-latency pain sensations rarely were evoked by such stimuli and never attained levels substantially above pain threshold for the sequences and temperatures presented. Temporal summation produced by brief contacts was greater in rate and amount than increases in sensory intensity resulting from repetitive ramping to the same temperature by a thermode in constant contact with the skin. Variation of the interval between contacts revealed a dependence of sensory intensity on interstimulus interval that is similar to physiological demonstrations of windup, where increasing frequencies of spike train activity are evoked from spinal neurons by repetitive activation of unmyelinated nociceptors. However, substantial summation at repetition rates of > or = 0.33 Hz was observed for temperatures that produced only late sensations of warmth when presented at frequencies < 0.16 Hz. Measurements of subepidermal skin temperature from anesthetized monkeys revealed different time courses for storage and dissipation of heat by the skin than for temporal summation and decay of sensory intensity for the human subjects. For example, negligible heat loss occurred during a 6-s interval between two trials of 10 contacts at 0.33 Hz, but ratings of sensory magnitude decreased from very strong levels of pain to sensations of warmth during the same interval. Evidence that temporal summation of sensory intensity during series of brief contacts relies on central integration, rather than a sensitization of peripheral receptors, was obtained using two approaches. In the first, a moderate degree of temporal summation was observed during alternating stimulation of adjacent but nonoverlapping skin sites at 0.33 Hz. Second, temporal summation was significantly attenuated by prior administration of dextromethorphan, a N-methyl-D-aspartate receptor antagonist.

Adult↗
PubMed1996

Respiratory sensation related to resistive loads in lung transplant recipients.

In order to assess the contribution of pulmonary afferent nerves to the processing of respiratory sensation, we compared sensation related to inspiratory resistive loaded breathing in 14 lung transplant recipients with normal lung function with that in 14 matched healthy control subjects. Respiratory sensation was characterized for each subject by the correlation coefficient and slope of the linear relationship between the intensity of sensation (expressed as Borg scores [BSc]) and peak inspiratory mouth pressure (peak Pm), which was considered the main physical stimulus of the sensation. Individual correlation coefficients were very high and did not differ between lung transplant recipients and controls. In contrast, individual slopes of BSc as a function of peak Pm (BSc/peak Pm slopes) were significantly lower in lung transplant recipients than in controls (0.63 versus 1.26; p < 0.01). Furthermore, ventilatory responses to external loads differed significantly between lung transplant recipients and controls in terms of higher values and ranges of generated peak Pm and peak inspiratory flow in lung transplant recipients than in controls (all p < 0.05). These results suggest that pulmonary afferent nerves may contribute to ventilatory and sensory responses to external loads. However, as suggested by the inverse relation between BSc/peak Pm slopes and peak Pm ranges, higher stimulus ranges in lung transplant recipients may also have contributed to intergroup differences in respiratory sensation related to loaded breathing.

Adult↗
PubMed2003

Nociceptive sensation and sensitivity evoked from human cornea and conjunctiva stimulated by CO2.

PURPOSE: To compare sensation and sensitivity evoked from human cornea and conjunctiva stimulated by CO2. METHODS: Twenty healthy participants were recruited for the study. Central corneal and temporal conjunctival chemical sensation and sensitivity of only one eye of each subject were evaluated. Air mixed with different concentrations of CO(2) was delivered by a modified Belmonte pneumatic esthesiometer. The ascending method of limits was used to determine the sensitivity and subjects were required to characterize the sensation at threshold. RESULTS: The sensations evoked by CO(2) in the cornea and conjunctiva were stinging or burning. The sensation evoked by mechanical stimulation was that of irritation. The corneal and conjunctival chemical thresholds were 31% +/- 2% and 54% +/- 5% CO(2) (mean +/- SE), respectively. The corneal and conjunctival mechanical thresholds were 80 +/- 6 and 140 +/- 10 mL/min (mean +/- SE), respectively. The corneal sensitivity was significantly higher for both mechanical and chemical stimuli (P < 0.05). CONCLUSIONS: The results suggest that CO(2) stimulates similar corneal and conjunctival nociceptors in that the interpretations were the same (i.e., nociceptive). The central cornea had a higher sensitivity to CO(2) than the temporal conjunctiva, which may reflect a different peripheral innervation, such as different nerve density or different receptor characteristics. Sensations evoked by mechanical and chemical stimulation were different, which suggests that at the peripheral level, the two modalities stimulate two different kinds of molecular receptors or channels and that this information is somehow retained within the nociceptive system.

Adult↗
PubMed2005

Effects of naloxone on respiratory sensation before and after a removal of severe respiratory stress.

Severe respiratory stress causes dyspnea, and a sudden release of this stress frequently accompanies a euphoric sensation. We hypothesized that acute severe respiratory stress may result in an elaboration of endogenous opioids within the central nervous system, and that these opioids may play significant roles in relieving dyspnea and generating euphoric sensation after a sudden removal of the stress. To test this hypothesis, we examined the effects of naloxone (0.04 mg/kg, I.V.) and the placebo (normal saline) on changes in respiratory sensation before and after the release of severe respiratory stress in a double-blind, randomized, crossover study in 14 healthy adults. Acute severe respiratory stress was induced by loaded breathing with a combination of resistive loading and hypercapnia. The subjects rated their changes in sensation by using a bidirectional visual analogue scale. Naloxone pretreatment affected neither the ventilation nor the development of dyspneic sensation during loaded breathing. Naloxone pretreatment only slightly attentuated the euphoric sensation developed after the release of severe respiratory stress. These findings suggest a small role of opioids in relieving dyspnea and in generating euphoria before and after a sudden removal of stress.

Adult↗
PubMed2004

'Objective' assessment of rectal sensation: a novel approach.

Rectal sensation is used as an investigative tool in the diagnosis of anorectal pathology. However, the data obtained are subjective depending on the patient's perception of the sensation. We investigated the hypothesis that sympathetic skin response (SSR) can be used as a tool for objective assessment of the rectal sensation. The SSR was recorded in 24 healthy volunteers (age 37.2 years, 14 men) using a surface electrode applied to the skin of the palmar surface of the subject's hand and a reference electrode to the dorsum of the same hand. The EMG activity of the pelvic floor muscles was registered by a surface electrode fixed to the perineal skin. The subject was asked before and after individual anesthetization of the rectum and palm to report the first rectal and urge sensations during balloon filling of the rectum in increments of 10 ml of saline. Low volume rectal distension effected no sympathetic skin or pelvic floor responses, while larger volumes produced the response. The skin and pelvic floor responses occurred with every rectal sensation and corresponded with the volunteers' subjective perception. Urge suppression was associated with synchronous decrease of skin and pelvic floor responses which disappeared on balloon expulsion. Rectal balloon distension, 20 minutes after individual anesthetization of the rectum or palm produced no palm skin response, which returned however 3 hours later. A novel approach which can objectively define subjective perceptions arising from the rectum has been identified. Rectal sensations produce coordinated sympathetic skin response and pelvic floor activity which seem to be mediated through a reflex which we term the "recto-palmar reflex". Further studies are required to investigate the role of this reflex in defection and sympathetic disorders.

Anal Canal↗
PubMedDate not supplied

Effects of topical ketorolac and diclofenac on normal corneal sensation.

BACKGROUND: A randomized, double-masked study was conducted to investigate the effects of 0.5% ketorolac tromethamine (Acular) and 0.1% diclofenac sodium (Voltaren) on normal human corneal sensation. METHODS: Thirty normal volunteers were divided into two groups, (1) two-drop group, and (2) multiple-drop group. In the two-drop group, 15 volunteers randomly received two drops of 0.5% ketorolac tromethamine on one eye and two drops of 0.1% diclofenac sodium on the fellow eye. A masked investigator measured corneal sensation with the Cochet-Bonnet esthesiometer before applying the drops, and at 15, 30, and 60 minutes after using the eye drops. In the multiple-drop group, another 15 volunteers were randomly administered one drop of 0.5% ketorolac tromethamine or 0.1% diclofenac sodium in each eye, and the procedure was repeated every 5 minutes for 20 minutes. Corneal sensation was measured before, and 0, 15, 30 and 60 minutes after applying the drops. RESULTS: In the two-drop group, neither of the eye drops had any effect on corneal sensation when only two drops were applied. In the multiple-drop group, corneal sensation was significantly reduced after multiple drops (p < 0.05) and was subsequently effective for at least 1 hour. CONCLUSION: Both 0.5% ketorolac and 0.1% diclofenac can significantly decrease corneal sensation in normal eyes when multiple drops are used.

Administration, Topical↗
PubMed1994

The predictive value of sensation testing in the development of neuropathic ulceration on the hands of leprosy patients.

The early detection of the loss of protective sensation in leprosy patients is vital if neuropathic ulceration and subsequent disabilities are to be avoided. The aim of this study was to find protective value of sensory thresholds in the hands of leprosy patients. Thresholds for touch-pressure, vibration and temperature were assessed in areas on leprosy-affected hands near ulcers or ulcer scars (LU-group), in areas without lesions (LN-group), and in controls (N-group). Semmes-Weinstein monofilaments were used for testing the touch-pressure threshold (PST), a biothesiometer for the vibration threshold (VST) and a Thermo Sensation Tester for the temperature threshold (TST). The distribution of ulcers was about equal on palmar and dorsal aspects of the hands. In the LU-group there was a negative response to SWF of 2.0 g in all patients, while 74% could feel the 2.0 g in LN-areas and in N-areas 100% could detect the 2.0 g SWF. In the LU-group about 11% felt 8 V VST, in the LN-group about 60% and in the N-group 89%. Testing temperature sensation was given up prematurely because the results in controls were unsatisfactory. Both palmar and dorsal sides of the hands should be tested for sensation. The thresholds for protective sensation are 2.0 g SWF and 8 V for vibration sense. It is recommended that Semmes-Weinstein monofilaments should always be used for early detection of loss of protective sensation.

Adolescent↗
PubMed2000

[Neurosarcoidosis with girdle sensation and polyradiculoneuropathy masquerading as Guillain-Barré syndrome].

We herein report two patients with neurosarcoidosis presenting girdle sensation in the trunk and polyradiculoneuritis. The first patient, a 53-year-old woman, manifested subacute progressive paresthesia in all four limbs and below the Th 3 level with girdle sensation from the thorax to lower abdomen and mild weakness in the left upper limb and the bilateral lower limbs. The patient was diagnosed to have sarcoidosis based on a biopsy of the scalenus anticus lymph nodes. The second patient, a 63-year-old woman, showed an acute onset of weakness and paresthesia in all four limbs and girdle sensation from the Th 5 to Th 8 level. On examination, she demonstrated diminished tendon reflexes in all four limbs, mild to severe weakness in all four limbs, paresthesia in all four limbs and below the Th 5 level. Although Guillain-Barré syndrome was initially suspected in this patient, the presence of girdle sensation led us to examine the possibility of neurosarcoidosis. Her examination demonstrated an abnormal accumulation of gallium in the bilateral hilar lymph nodes and mediastinum on scintigraphy, an elevated CD 4/CD 8 ratio in the bronchoalveolar lavage fluid, a negative tuberculin reaction, and elevated serum lysozyme level. These findings thus fulfilled the clinical criteria for sarcoidosis. None of the two patients showed any abnormalities in the thoracic cord MRI. In the first patient F wave was not evoked in either upper or lower limbs, while in the second patient temporal dispersion on M wave was observed in the right median and both ulnar nerves. We therefore consider the girdle sensation to have not been caused by myelopathy but instead by polyradiculopathy. When sarcoid peripheral neuropathy masquerades as Guillain-Barré syndrome, then the presence of girdle sensation may help diagnosis of neurosarcoidosis.

Diagnosis, Differential↗
PubMed1997

Effects of artificial tear temperature on corneal sensation and subjective comfort.

PURPOSE: Cooling reduces acute inflammation and local nerve sensation. We investigated the relationship between artificial tear temperature, ocular surface sensation, and patient comfort. METHODS: We placed preservative-free artificial tears and eye mask stored at four temperatures (36 degrees C, 25.2 degrees C, 4 degrees C, and -10 degrees C) in the right eyes of 24 normal subjects, whose left eyes served as controls. Corneal and conjunctival sensations were measured and corneal temperature was recorded. Comfort was reported on a 7-point scale. RESULTS: Corneal temperature was significantly lowered with all temperature artificial tears and frozen eye mask (p < 0.001 for each temperature relative to the previous one). Aesthesiometer readings were inversely correlated with corneal temperature (r = -0.45, p = 0.0005), decreasing with lower temperatures, reaching 2.0 +/- 1.3 g/mm2 (p = 0.001) for the mask. Conjunctival sensation reacted similarly and was well correlated with both corneal temperature (r = 0.43, p = 0.0009) and corneal sensation (r = 0.39, p = 0.006). Treatments provided relief, with the 4 degrees C tears being the most comfortable (p = 0.0001). CONCLUSION: Although there may still be some biases, cooled artificial tears provide relief to the eye by the mechanism of reduced corneal and conjunctival sensation.

Administration, Topical↗
PubMed1984

Optokinetic sensations evoked by local stimulation of the peripheral retina.

Optokinetic sensations of movement have been investigated by means of a moving pattern of stripes presented in the periphery of the visual field. Linear sensations of movement occur. The more peripheral in the visual field the pattern is presented, the more sensitive the retina becomes. Stimuli perpendicular to the horizontal meridian evoke stronger reactions than stimuli presented perpendicular to the vertical meridian. Vertically directed stimuli in the temporal field of vision give rise to more intense sensations than the same stimuli applied to the nasal field. An upward movement of stimulus pattern causes a more pronounced sensation of 'lift' than a downward movement. As for horizontal stimulation, sensations are more pronounced when stripes move from temporal to nasal than in the opposite direction. Only stimulation perpendicular to the meridian, either horizontal or vertical, induces sensations of movement. Stimulation in the same direction as these meridians, whether upward or downward for the vertical axis or to the left or the right for the horizontal axis, do not induce linear or circular vection. The results may be of importance in working with monitor screens. The differences between the method routinely used in optokinetic examination and the present stimulus method, are discussed.

Evoked Potentials, Visual↗
PubMed1992

Temporary threshold shift of temperature sensation caused by vibration exposure.

The temporary threshold shift of temperature sensation due to vibration exposure was studied to clarify the significance of frequency and acceleration on it. The discrete frequencies of the vibrations tested were 32, 63, 125, 250 and 500 Hz, and the accelerations were at the level of 2, 4, 8 and 16 g. The threshold shift of warm sensation (TTSw) was markedly, but that of cool sensation was small and not significantly different from the control value. TTSw increased with a rise in the level of acceleration and was largest at 125 Hz among the frequencies examined. The most effective frequency among the vibrations tested for warm sensation was inferred to be lower than that for vibratory sensation. After exposure, TTSw or the increment of the neutral zone decayed exponentially but bounced slightly in the later period. These patterns of TTSw are similar to those of the vibration-induced TTS of vibratory sensation.

Adult↗
PubMed1989

Upper esophageal sphincter tone and reactivity to stress in patients with a history of globus sensation.

Anxiety and abnormal upper esophageal sphincter function have been ascribed ill-defined roles in the etiology of globus sensation. In this study, we examined the psychological profile and effect of acute mental stress (dichotic listening task) on UES tone in seven patients reporting to the clinic with globus sensation and 13 healthy controls. Alterations in heart rate, blood pressure, frontalis EMG, and skin conductance confirmed the effectiveness of the stress test in patients and controls. During resting conditions, UES pressure (mean +/- SE) in patients (40.4 +/- 4.6 mm Hg) did not differ significantly from controls (46.5 +/- 4.7 mm Hg). In response to stress, UES pressure rose by 31% in patients (P = 0.04) and by 25% in controls (P = 0.002). The stress-induced rise in UES pressure in patients (9.5 +/- 3.8 mm Hg) was not significantly different to that observed in controls (11.8 +/- 3.0 mm Hg). Psychological profiles of globus patients presenting to the clinic revealed them to be more introverted, anxious, neurotic, and depressed than normal controls. We conclude that in patients with a history of globus sensation, resting UES pressure and its response to stress is normal. Although individuals presenting to the clinic with globus sensation showed increased levels of psychoneurosis, acute, predictable stress is not a factor in the genesis of globus sensation. UES hyperresponsiveness to other stimuli or subjective intolerance to changes in UES pressure could account for symptoms of globus sensation.

Adult↗
PubMed1995

A multivariate genetic analysis of sensation seeking.

The genetic architecture of sensation seeking was analyzed in 1591 adolescent twin pairs. Individual differences in sensation seeking were best explained by a simple additive genetic model. Between 48 and 63% of the total variance in sensation seeking subscales was attributable to genetic factors. There were no sex differences in the magnitude of the genetic and environmental effects. The different dimensions of sensation seeking were moderately correlated. The strongest correlations were between the subscales Thrill and Adventure Seeking and Experience Seeking (r = 0.4) and between Boredom Susceptibility and Disinhibition (r = 0.4 in males, r = 0.5 in females). A triangular decomposition showed that the correlations between the sensation seeking subscales were induced mainly by correlated genetic factors and, to a smaller extent, by correlated unique environmental factors. The genetic and environmental correlation structures differed between males and females. For females, higher genetic correlations for Experience Seeking with Boredom Susceptibility and Disinhibition and higher correlations among the unique environmental factors were found. There was no evidence that sex-specific genes influenced sensation seeking behavior in males and females.

Adolescent↗
PubMed1996

Effect of topically applied menthol on thermal, pain and itch sensations and biophysical properties of the skin.

The effect of menthol and alcohol as its vehicle on thermal sensations, pain, experimental itch and irritation were studied in 18 subjects, using a computerized thermal sensory analyzer, laser Doppler flowmetry and an evaporimeter for transepidermal water loss (TEWL). Menthol had a subjective cooling effect lasting up to 70 min in 12/18 subjects; however, it did not affect cold and heat threshold, nor did it affect cold and heat pain threshold. Alcohol produced an immediate cold sensation lasting up to 5 min in 4/18 subjects and lowered the sensitivity of cold sensation threshold (P < 0.05). Histamine injection did not change thermal and pain thresholds. Menthol did not alleviate histamine-induced itch magnitude, nor its duration. Following histamine injection, cold sensation median threshold decreased by 1.2 degrees C from (29.9 degrees C to 28.7 degrees C) on the site treated with menthol (P < 0.01) with similar changes in thresholds at the alcohol-treated site (P < 0.05). Warm sensation and pain threshold in subjects receiving histamine injections, measured after menthol and alcohol application, did not differ from their baseline values with histamine alone. TEWL at the site treated with menthol was significantly higher (P < 0.05) than at the alcohol-treated and the control site (P < 0.01), suggesting that menthol has a higher skin irritating effect, or at least alters the stratum corneum water permeability. Our results suggest that menthol fulfills the definition of a counterirritant, but does not affect histamine-induced itch, nor does it affect pain sensation.

Administration, Topical↗
PubMed2003

Remote activation of referred phantom sensation and cortical reorganization in human upper extremity amputees.

Phantom limb sensation, whether painful or not, frequently occurs after peripheral nerve lesions. It can be elicited by stimulating body parts adjacent to the amputation site (referred to as phantom sensation) and it is often similar in quality to the stimulation at the remote site. The present study induced referred phantom sensations in two upper limb amputees. Neuroelectric source imaging (ESI) as well as functional magnetic resonance imaging (fMRI) was used to assess reorganization in primary somatosensory cortex (SI). Whereas recent studies found mislocalization of sensation related to stimulation mainly in regions adjacent and ipsilateral to the amputation site, we report here the elicitation of phantom sensation in the arm by stimulation in the lower body part both ipsi- and contralateral to the amputation in two arm amputees. The fMRI evaluation of one patient showed no shift in the location of the foot whereas ESI revealed major reorganization of the mouth region in primary somatosensory cortex in both patients. These data suggest that cortical structures other than SI might be contributing to the phenomenon of referred sensation. Candidate structures are the thalamus, secondary somatosensory cortex, posterior parietal cortex and prefrontal cortex.

Adult↗
PubMed1998

Cutaneous reactions and sensations after intracutaneous injection of vasoactive intestinal polypeptide and acetylcholine in atopic eczema patients and healthy controls.

We analysed vasoreactions and sensations of atopic eczema (AE) patients and healthy controls after intracutaneous (i.c.) injection of vasoactive intestinal polypeptide (VIP) and acetylcholine (ACh). Blood flow was measured by laser Doppler flowmetry (LDF). Plasma extravasation and flare size were evaluated planimetrically, and sensations were recorded using visual analog scales. Three groups of subjects (controls, AE patients suffering from acute eczema and AE patients during a symptom-free period) were investigated. We administered VIP separately at concentrations of 1.5 x 10(-7), 1.5 x 10(-6) and 1.5 x 10(-5) M and in combination with ACh (5.5 x 10(-6) M) into the volar forearm of the subjects. Both substances led to an increase in LDF measurements and induced a wheal and flare reaction. Blood flow was elevated as a function of dose after a single VIP application in all groups. Compared with healthy controls, a significant increase in blood flow was measured after combined VIP and ACh administration in AE patients suffering from acute AE, whereas flare area and plasma extravasation were significantly reduced after single VIP and combined VIP and ACh injections, respectively. In all groups, VIP induced dose-dependent pruritus. Compared with a control stimulus (0.9% sodium chloride and ACh), combined injections of VIP and ACh had no additional effect on the magnitude of the sensation. In AE patients, the intensity was similar to that experienced by the control subjects, but the quality of sensation was different: ACh induced pain in the control subjects, pruritus in AE patients, and a mixture of pain and itching in AE patients showing no symptoms. Our results suggest that VIP- and ACh-induced skin reactions and the quality of the sensations depend on the activity of the atopic eczema. Confirming our former studies, AE patients develop a different quality of sensation after ACh administration and also after administration of VIP combined with ACh. Therefore, we suggest that ACh might be involved in the pathomechanisms of pruritus in AE.

Acetylcholine↗
PubMed1986

Selective reduction of second pain sensations by systemic morphine in humans.

A variety of forms of painful stimulation were delivered to human subjects in order to determine whether therapeutic dosages of systemic morphine might produce significant attenuation of some forms of phasic pain that are tolerable for experimental usage. Consistent with previous reports, simple application of thermal or electrical energy to the skin (for 3 sec) produced sensations of pain that were not significantly reduced by prior administration of morphine. Similarly, subjects that were trained to focus their attention on the magnitude of the immediate (first) pain sensation evoked by brief electrical or mechanical stimulation did not report reduction by morphine of pain attributed to conduction in myelinated peripheral nociceptors. In contrast, the magnitude of late (second) pain sensations produced by brief pulses of electrical, thermal or mechanical stimuli to the same subjects was consistently reduced significantly by doses of 5 or 10 mg of morphine. The simplest interpretation of the effect on second pain intensity is that morphine preferentially attenuates input from unmyelinated nociceptors. This conclusion was reinforced by an experiment in which chemicals were applied to the skin. Morphine reduced pain produced by capsaicin (presumed to selectively excite unmyelinated peripheral afferents) but did not diminish pain elicited by bradykinin (presumed to excite A delta and C nociceptors). Comparing long duration pains from chemical stimulation (lasting in excess of 5 min) with briefer pains elicited by 50 msec to 3 sec of stimulation did not support the notion that morphine acts selectively on tonic pain. Also, after-sensations that could be discerned following second pain were not eliminated by morphine, and paired pulse facilitation of first pain sensations remained after administration of morphine, indicating that temporal summation is not preferentially reduced. Regardless of duration, frequency or latency, pain arising exclusively from unmyelinated nociceptors was attenuated substantially, but other elicited sensations were not reliably affected. For example, detection thresholds for warmth were unaffected by morphine, demonstrating that input from all unmyelinated afferents is not reduced.

Adult↗