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Biomedical subjects

B Lynn

Publications and source records attributed to B Lynn.

At least 55 records · Page 3Linked to original sources
PubMed1986

Effects of sympathetic stimulation on mechanoreceptive and nociceptive afferent units from the rabbit pinna.

Single afferent units from the rabbit great auricular nerve were examined using cutaneous stimuli before, during and after tetanic stimulation of the cervical sympathetic trunk for 1-4 min. G-hair units showed a depression of responses during and for 1-2 min after sympathetic stimulation; D-hair units showed a similar pattern but the average depression was less. These changes are not likely to be due to a reduction in blood flow since no comparable effect was produced by arterial occlusion. Sensitive C-mechanoreceptor units were excited transiently by sympathetic stimulation and by arterial occlusion. Responses of nociceptors, both A-fibre high threshold mechanoreceptors and C-fibre polymodal nociceptors were unaffected by sympathetic stimulation.

Animals↗
PubMed1986

The effects of locally applied capsaicin on conduction in cutaneous nerves in four mammalian species.

By examination of compound action potentials in the saphenous nerve of the anaesthetized rat it has been shown that capsaicin causes a rapid, dose-dependent, failure of conduction in many C-fibres when applied directly to the nerve. A large reduction in C-fibre conduction occurs with concentrations as low as 110 microM. After a 15-30 min exposure to capsaicin, only partial recovery occurs in 1 h. Similar block of C-fibre conduction occurs in the ferret. However, only smaller, reversible, reductions in C-fibre conduction were seen in the guinea-pig and rabbit, even at the highest concentration of capsaicin used (33 mM). A small reduction in the A delta component of the compound action potential occurred in all four species. In the rat and ferret the effects were much less than those on C-fibres. At high doses, small reversible effects were also seen on the fastest conducting A alpha beta component of the compound action potential in the rat, rabbit and guinea-pig; no effects were seen on the A alpha beta fibres in the ferret. Decreases in amplitude of the compound action potential were accompanied by some slowing of conduction in most cases. The slowing was less than 5% except for the rat A alpha beta and C-fibres and the ferret C-fibres where 9-15% changes occurred at the highest doses of capsaicin. Opening the connective tissue sheath of the nerve did not significantly increase the effectiveness of capsaicin.

Action Potentials↗
PubMed1985

Receptive field size of hair follicle afferents in rats treated neonatally with capsaicin.

Receptive field parameters of G- and D-hair units were investigated in adult rats given capsaicin as neonates. An air jet stimulator mounted on a two-way micromanipulator was used for accurate mapping of receptive fields. Diameters of G- and D-hair unit receptive fields were similar in both control and treated groups averaging 2.14 and 2.44 mm respectively with a 1.5 X threshold stimulus. It is concluded that the reported expansion of rat spinal cord cutaneous receptive fields following capsaicin treatment does not have any significant peripheral component.

Animals↗
PubMed1984

Effect of neonatal treatment with capsaicin on the numbers and properties of cutaneous afferent units from the hairy skin of the rat.

Neonatal treatment with capsaicin caused a 40% reduction in the number of C-fibres in the rat saphenous nerve. Within the reduced total the proportion of nociceptive C fibres was similar in both capsaicin-treated and untreated rats. No change was found in the conduction velocities or firing thresholds (to pressure and to heat) in A-fibre and C-fibre nociceptors. The perimeters of axons were also unchanged by capsaicin. From a comparison of the morphometric and conduction velocity (v) data it is suggested that in the rat saphenous nerve v (m/s) = 1.9 X axon perimeter (micron) for A fibres and v = 0.44 X square root of the axon perimeter for C fibres.

Action Potentials↗
PubMed1984

Organization and sensory properties of small myelinated fibres in the dorsal cervical rami of the cat.

A study using both anatomical dissection and electrophysiological recording has been made to analyse sensory components of the cervical dorsal rami in the cat. Particular attention has been paid to the physiological properties of Group III muscle afferents. The dorsal rami from C2 to C4 are composed of many nerve bundles that contain afferents from both muscle and skin. Bundles containing only cutaneous and only muscle afferents were identified and found to follow a relatively consistent pattern of organization within the ramus. In nerve bundles serving the biventer cervicis muscle, a population of Group III afferent fibres was identified that responded to strong localized pressure or localized stretch. Their receptive fields were generally small and situated on the muscle borders or in tendinous inscriptions. Such units comprised 73% of those with conduction velocities less than 20 m/s. Group III afferent fibres from neck muscles fired readily to intramuscular 6% sodium chloride, but were mostly not sensitive to bradykinin injected locally or intra-arterially.

Action Potentials↗
PubMed1982

Primary afferent units from the hairy skin of the rat hind limb.

The properties of cutaneous units in the saphenous nerve of the rat have been surveyed. We studied 137 units with myelinated (A-fibre) axons conducting at 4-44 m/s. Of the A-fibre units 66% gave a rapidly adapting discharge following hair movement and could be classified into categories similar to those described previously in cat and rabbit. Two categories predominated: (1) D-hair units with slowly conducting axons and relatively large receptive fields that responded to slow movement of hairs, including down hairs when these were present and (2) G-hair units with larger axons and relatively small fields that were only excited by fast movement of guard hairs. Of the A-fibre units 20% were high threshold mechanoreceptors. As in other species, these had a wide range of conduction velocities and multi-point receptive fields. Other types of A-fibre units found were (a) sensitive, RA units not excited by hair movement, (b) relatively insensitive RA units with diffuse receptive fields and (c) slowly adapting mechanoreceptor units. We studied 149 units with unmyelinated (C-fibre) axons conducting at 0.49-0.89 m/s. Of the C-fibre units 73% were of the polymodal nociceptor type. They had small receptive fields and responded to pressure and heating. The average heat threshold was 47 degrees C (+/- 6 degrees C, S.D.). Units were often not sensitized by suprathreshold heating unlike similar units in cat and rabbit. Other C-fibre units found were sensitive mechanoreceptors (12%), cold thermoreceptors (4%) or were very insensitive or inexcitable (11%). The pattern of innervation of rat limb hairy skin resembles previously studied mammalian species. A notable feature is the large proportion of C-polymodal nociceptor units. In this respect the rat resembles the primate and differs from the cat.

Afferent Pathways↗
PubMed1982

The stability of amoxycillin sodium in intravenous infusion fluids.

The stability of amoxycillin sodium has been determined at 25 degrees C in water and in ten intravenous infusion fluids at concentrations of 1, 2 and 5% w/v. Little difference in stability was found between 1% and 2% amoxycillin solutions in the various vehicles, but the antibiotic was significantly less stable at 5%. Stabilities in sodium and potassium chloride solutions were similar to those in water and were markedly superior to those in dextrose or dextran fluids. Solutions in lactate or bicarbonate had intermediate stability. The antibiotic was, for practical purposes, unstable in 30% sorbitol solution. Guidelines are provided for intravenous infusion of amoxycillin in the solutions studied.

Amoxicillin↗
PubMed1981

Vascular and sensory responses of human skin to mild injury after topical treatment with capsaicin.

1 Immediately after several topical applications of capsaicin at 2-hourly intervals, human forearm skin would no longer develop flare (vasodilation) around a small injury. At the same time heat pain thresholds were reduced on average by 3.5 degrees C. These results are consistent with block by capsaicin of the effector side of the axon reflex, perhaps by depleting nerve terminals of substance P. 2 Over a period from several days to several weeks after treatment, flare was diminished and heat pain thresholds were slightly elevated. These changes may be due to long-lasting damage of cutaneous nerve terminals by capsaicin.

Administration, Topical↗
PubMed1979

Are audiotapes cheaper than lectures?

First year pre-clinical medical students were taught about blood grouping and haemostasis using four audiotapes and associated booklets as the sole method of formal instruction. The audiotapes were readily accepted by the great majority of students as a replacement for lectures and those who listened to the tapes scored significantly higher in a multiple choice test 10 months later than did a previous years's student who had covered the same topics by means of lectures. If booklets are provided for each student, tapes are more expensive than lectures in terms of the time and running costs involved. By contrast, if booklets are sold or made available on loan with the audiotapes, then costs become equivalent when tapes are distributed to four to six average-sized medical schools and become increasingly cheaper as the number distributed increases. Other less readily quantifiable benefits of audiotape learning are discussed and it is concluded that in terms of both costs and effectiveness of learning, audiotapes can usefully replace a proportion of lectures in a conventional course. Consideration should be given to the provision of more space for audiotape tuition and less for formal lectures.

Audiovisual Aids↗
PubMed1979

The heat sensitization of polymodal nociceptors in the rabbit and its independence of the local blood flow.

1. The firing frequency of polymodal nociceptor units with C-fibre axons was found to increase exponentially with skin temperature as the latter was raised linearly at 1 degree C/sec. Q10 values ranged from 3.6 to 120. 2. Following skin heating to 54--64 degrees C, average firing thresholds fell substantially. This sensitization was accompanied by a 46% increase in interval by interval variability of firing during heat stimulation. 3. Stopping the blood flow to the saphenous area by ligaturing the femoral or saphenous arteries had no significant effect on heat thresholds, on firing patterns during heat stimulation or on variability of firing in sensitized units. There were no changes in continuous, background firing during periods of arterial ligation. 4. It is concluded that if the maintenance of nociceptor heat sensitization depends on the continuous local production of chemical substances, these substances must either be rapidly broken down locally or able to move only slowly into blood vessels.

Action Potentials↗
PubMed1977

Failure of acupuncture to produce localized analgesia.

The pain sensitivity of 49 healthy volunteers has been tested both before and during electro-acupuncture at two or three widely separated places on the body surface. Test areas fell into two categories. The "target" areas were within the part of the body that experienced acupuncturists predicted would be most affected by acupuncture of specified traditional points. "Non-target" control areas fell outside this zone of predicted maximal effect. The subjects and the observers who administered the tests knew that acupuncture anesthesia was being studied, but they did not know which areas were the "targets". Each subject was tested using at least two sensory testing methods. Altogether 4 different tests of pain sensitivity (pinprick discrimination, cold pain ratings, heat pain thresholds and pinch pain thresholds) were used. Small, but statistically highly significant, decreases in pain sensitivity occurred with all 4 tests during acupuncture. However, pain sensitivity fell by the same amount at "target" and "non-target" areas. The variability of the data was sufficiently low that moderate differences between areas would have been detected. The mechanism of "acupuncture anesthesia" is discussed in the light of these negative findings.

Acupuncture Therapy↗
PubMed1977

The sensitization of high threshold mechanoreceptors with myelinated axons by repeated heating.

1. Seventy high threshold mechanoreceptor units (HTMs) with myelinated axons were isolated from the sural nerves of cats and rabbits. Thirteen cat and forty-two rabbit HTMs were testec by controlled, repeated heating of the skin of the foot or lower leg to noxious levels. 2. Many of the units (77% in the cat and 40% in the rabbit) fired to heating. Only six (11%) of these fired to the first brief heating to 50-55 degrees C. The rest required 2-6 heat trials before responding. 3. Heat responding units always became more sensitive with repeated heat stimulation but their mechanical sensitivity showed no comparable changes when heat sensitization occurred. 4. If these results are applicable to man, they suggest that HTMs play little role in generating the first pain that follows skin heating but that they may be involved in the increased sensitivity to heat pain (hyperalgesia) shown by skin previously injured by heating.

Action Potentials↗