Biomedical subjects

Ole K Andersen

Publications and source records attributed to Ole K Andersen.

23 records · Page 2Linked to original sources

PubMed2003

Comparison of nociceptive withdrawal reflexes and recruitment curves between the forelimbs and hind limbs in conscious horses.

OBJECTIVE: To compare nociceptive withdrawal reflexes (NWRs) evoked from the distal aspect of the left forelimb and hind limb in conscious standing horses and to investigate NWR recruitment for graded electrical stimulation intensities. ANIMALS: 20 adult horses. PROCEDURE: Surface electromyographic (EMG) activity evoked by transcutaneous electrical stimulation of the digital palmar (or plantar) nerve was recorded from the common digital extensor and cranial tibial muscles. Stimuli consisted of 25-millisecond train-of-5 constant current pulses. Current intensity was gradually increased until NWR threshold intensity was reached. The EMG signal was analyzed for quantification of the NWR. Behavioral responses accompanying the reflex were scored (scale, 0 to 5). The NWR recruitment curves were determined at 0.9, 1.1, 1.2, and 1.3 times the NWR threshold intensity. RESULTS: The NWR threshold was significantly higher for the hind limb (median value, 6.6 mA; range, 3 to 10 mA) than the forelimb (median, 3 mA; range, 1.7 to 5.5 mA). The NWR of the hind limb had a significantly longer latency (median, 122.8 milliseconds; range, 106 to 172 milliseconds), compared with the forelimb (median, 98 milliseconds; range, 86 to 137 milliseconds), and it was associated with significantly stronger behavioral reactions. Gradual increase of NWR amplitude was evident at increasing stimulation intensities and supported by the behavioral observations. CONCLUSIONS AND CLINICAL RELEVANCE: We documented NWRs evoked from the forelimb and hind limb and their recruitment with stimuli of increasing intensity in horses. These results provide a basis for use of NWRs in studies on nociceptive modulation in horses.

Animals↗

PubMed2002

Heat hyperalgesia in humans: assessed by different stimulus temperature profiles.

The aim of the present study was to investigate the effect of the rate of temperature increase on the intensity of the evoked pain before and after hyperalgesia induced by topical capsaicin. Further, hyperalgesia to suprathreshold heat stimuli was investigated. Thirteen healthy volunteers were included in the experiment. All stimuli were applied in randomised order within the volar surface of both forearms using a computer-controlled contact stimulator. In one of the forearms, the effect of the rate of temperature change was investigated for 1.0, 5.0, and 8.0 degrees C/s reaching a peak temperature of 30.0, 33.0, 36.0, 39.0, and 42.0 degrees C in the primary hyperalgesic area and reaching a peak temperature of 33.0, 36.0, 39.0, 42.0, 45.0, 47.0, and 49.0 degrees C in the secondary hyperalgesic area before and after the induction of hyperalgesia. In the other forearm, the same procedure was repeated without capsaicin application as a control measurement. After the induction of hyperalgesia, the pain ratings were significantly higher in the arm treated with capsaicin compared with baseline for 36, 39, and 42 degrees C heating rates in the primary hyperalgesic area. The pain ratings were significantly higher with 1 degrees C/s heating rate compared with 5 and 8 degrees C/s for 36, 39, and 42 degrees C in the primary hyperalgesic area. Heat hyperalgesia was also observed within the secondary hyperalgesic area to pin-prick for stimulus temperatures of 45, 47, and 49 degrees C compared with the baseline measurements. Increased ratings were found for all three heating rates in the secondary hyperalgesic area. There were no heat hyperalgesia in the control arm. In conclusion, hyperalgesia to suprathreshold heat stimuli was observed in the secondary hyperalgesic area and C-fibres play an important role in the primary hyperalgesia to heat.

Adult↗

PubMed2002

Quantitative assessment of nociception in horses by use of the nociceptive withdrawal reflex evoked by transcutaneous electrical stimulation.

OBJECTIVES: To evoke and measure the nociceptive withdrawal reflex (NWR) by use of electromyographic recordings and to score the behavioral nociceptive responses to electrical pulses in standing nonsedated horses. ANIMALS: 10 adult horses. PROCEDURE: The lateral palmar digital nerve of the forelimb was transcutaneously stimulated, and surface electromyographic responses were recorded from the ulnaris lateralis, extensor carpi radialis, and common digital extensor muscles. Stimuli consisted of a 25-millisecond train of 5 constant-current pulses delivered by a computer-controlled stimulator. The 80- to 250-milliseconds poststimulation interval was analyzed to detect the NWR. The current intensity was increased in steps of 0.5 mA until the NWR threshold intensity (lt) was reached. The stimulus at It was repeated twice. Latency and amplitude of the NWR, together with the behavioral reaction of horses, were analyzed. The latter was scored according to a scale from 0 (no reaction) to 5 (vigorous reaction). Finally, 3 suprathreshold stimuli at 1.2 X It were analyzed. RESULTS: The median It to elicit NWR was 2.5 mA. Median onset latency of the NWR was 96.0 milliseconds at It and 89.6 milliseconds for suprathreshold stimuli. The amplitude of the reflexes was higher for suprathreshold stimulations, and behavioral reactions were slightly stronger when stimulus intensity increased. CONCLUSIONS AND CLINICAL RELEVANCE: Results of our study indicate that it is possible to record NWR in conscious standing horses, to define a reflex threshold, and to measure reflexes in response to increasing stimulus intensity.

Animals↗

PubMed2000

Interaction between cutaneous and muscle afferent activity in polysynaptic reflex pathways: a human experimental study.

Interactions between the input from cutaneous and nociceptive muscle afferents in polysynaptic reflex pathways were investigated in man. Interaction was tested by evoking reflexes before, during, and after a period of muscle pain induced by intramuscular injection of hypertonic saline. Muscle pain was induced either in the ankle flexor (tibialis anterior, TA) or in the extensor (soleus, SOL) muscles by injection of 1 ml hypertonic saline. Electrical skin stimulation (1.1 x initial reflex threshold) at the dorsum of the foot over the tarsal joint was used to elicit cutaneo-muscular polysynaptic reflexes in the knee flexor semitendinosus (ST). The injected hypertonic saline evoked a robust muscle pain (the subjects made a continuous score of the muscle pain on a 0-10 cm VAS scale, and the mean VAS area was 1229+/-251 cm x s and lasting 390+/-30 s). In five of 12 subjects, the infusion of hypertonic saline into TA evoked referred pain to the dorsal aspect of the ankle. A significant inhibition (17+/-8.2%, P<0.05) of the ST-reflex by pain in SOL was observed. Pain in TA facilitated (92+/-36%, P<0.05) the short-latency part (50-70 ms post stimulation) of the reflex. The muscle pain did not modulate the perceived sensory intensity of the electrical stimuli. The findings indicate an interaction of input from thin muscle afferents and cutaneous group A-fibre afferents in polysynaptic segmental reflex pathways, which seems to depend on the location of the muscle pain.

Adult↗

PubMed1999

Convergence of meningeal and facial afferents onto trigeminal brainstem neurons: an electrophysiological study in rat and man.

Headache is often accompanied by referred pain in the face. This phenomenon is probably due to a convergence of afferent inputs from the meninges and the face onto central trigeminal neurons within the medullary dorsal horn (MDH). The possible existence and extent of this convergence was examined in rat and man. MDH neurons activated by stimulation of the parietal meninges were tested for convergent tactile and noxious mechanical input from all three facial branches of the trigeminal nerve. All 21 units with meningeal input could also be activated by facial stimuli. Brush stimuli applied to the supraorbital nerve area activated 86%, to the infraorbital nerve area 29%, and to the mental nerve area none of the units. Pinch stimuli applied to the supraorbital nerve area activated 95%, to the infraorbital nerve area 86%, and to the mental nerve area 52% of the units. The results suggest convergence of meningeal and facial inputs concentrated on the supraorbital nerve in rat. In man convergence was examined by probing neuronal excitability of MDH applying the blink reflex (BR) during Valsalva maneuver which probably increases intracranial pressure. The BR evoked by supraorbital nerve stimulation remained unchanged, while the BR evoked by mental nerve stimulation was significantly facilitated. This facilitation may be due to convergence of meningeal and facial inputs onto trigeminal neurons in man.

Adult↗