Biomedical subjects
N J Dawson
Publications and source records attributed to N J Dawson.
Intramuscular acupuncture-like electrical stimulation inhibits stretch reflexes in contralateral finger extensor muscles.
Electro-acupuncture is one of many physical measures used to relieve musculoskeletal pain and to improve the associated restricted range of motion. Experiments were designed to determine whether or not acupuncture-like stimulation inhibits stretch reflexes in an arm extensor muscle in human volunteers. Surface electromyographic recordings were made on the right extensor digitorum communis muscle and averaging techniques were used to study the reflex responses to brief deflection of the finger with a solenoid-driven probe. The ratio M1:M2 of two components of the reflex was reduced during continuous acupuncture-like stimulation of the contralateral first dorsal interosseus and extensor digitorum communis muscles near their motor points (acupuncture points LI 4 and LI 11). Concomitant changes in skin temperature were observed on the forehead and in the arm in which acupuncture-like stimulation was used. In control experiments, when the acupuncture needles were inserted subcutaneously and stimulated with the same current parameters at distinctly uncomfortable intensities, no change in the reflexes occurred. These findings show that acupuncture-like stimulation exerts physiologic effects on the central nervous system, mediated presumably by muscle afferent fibers. The effects may be relevant to relief of muscle spasm and musculoskeletal pain, and restoration of mobility.
The dynamic properties of trigeminal thermoreceptors following heat-rearing in rats.
Dynamic properties of thermoresponsive units at the caudal trigeminal nucleus are not modified by heat-rearing. The modification of the thermoregulatory system by heat-rearing is unlikely to be a consequence of altered thermoreceptive function at this level. Rats were reared at ambient temperatures of 30 degrees C (heat-reared) and 20 degrees C (controls). Extracellular recordings of thermoresponsive units at the caudal trigeminal nucleus were made while the facial receptive fields of these thermoresponsive units were stimulated with 6 different rates of temperature change (+0.5, +0.1, +0.02, -0.02, -0.1 and -0.5 degrees C/sec). All thermoresponsive units encountered were cold-sensitive. The static maxima were clustered around 13.5 degrees C and did not differ between treatment groups. Dynamic maxima occurred at temperatures around 29-30 degrees C and were not different in thermoresponsive neurones from the two treatment groups. There was no difference between the two treatment groups in the dynamic activity of trigeminal cold-responsive neurones at any of the 42 combinations of temperature and rate of temperature change examined.
Facial thermal input in the caudal trigeminal nucleus of rats reared at 30 degrees C.
1. Rats reared from birth in air at 30 degrees C showed a decreased ability to maintain colonic temperature when exposed to 10 degrees C as compared with rats reared at 20 degrees C. This difference was not due to physical factors affecting heat loss, such as surface area or fur thickness. 2. In anaesthetized rats extracellular recordings were made in trigeminal nucleus caudalis from higher order neurones with input from facial cold and warm receptors. A systematic search on a grid pattern showed there was no difference between heat-reared and control rats in facial receptive fields or in the abundance, extent and somatotopic distribution of thermal neurones in the nucleus. In both groups almost all the neurones were excited only by facial cooling. 3. When single cold neurones were tested quantitatively by the application of controlled temperature changes to their receptive fields on the face there was no difference in the static temperature/discharge rate relationship between the two groups of rats. 4. The results suggest that the observed difference in ability to regulate body temperature is not attributable to differences in skin-temperature reception at the level of the trigeminal nucleus.
Evidence for on-off control of heat dissipation from the tail of the rat.
Anterior hypothalamic temperature, tail vasoactivity, and tail heat loss were observed in unanaesthetised rats resting at an ambient temperature that was varied between 25 and 35 degrees C between experiments, but was held constant within an experiment. Vasodilation and vasoconstriction at the tail were qualitatively detectable by the appearance and disappearance of temperature differences between the tail surface overlying the ventral arterial supply, and the lateral venous drainage. Vasodilation detected this way was an abrupt singular event (being either on or off), and preceded subsequent exponential changes in tail surface temperature and heat loss. Within the ambient temperature range of 29--33 degrees C, the following sequence occurred in a 20-min cycle, despite the noncycling constant environmental and metabolic heat loads: tail vasodilation - 0.2 to 0.4 degrees C fall in hypothalamic temperature - tail vasoconstriction - 0.2 to 0.4 degrees C rise in hypothalamic temperature. This behaviour, consistent with the limit-cyclic behaviour of some nonlinear controllers, as well as the abrupt two-state nature of vasoactivity at the rat tail, provides evidence that the mechanism can be described by an on-off control model. In addition, angiography suggests that vasoconstriction rather than countercurrent heat exchange provides the major barrier to core to tail heat flow during the "off" phase.
Inhibitory controls on thermal neurones in the spinal trigeminal nucleus of cats and rats.
Although electrical stimulation of supraspinal structures and local large fibres is known to inhibit the responses of nociceptive neurones, comparable studies on thermoreceptive cells have not been made. We have studied the effects of nucleus raphe magnus (NRM) and segmental stimulation on cold and warm responsive neurones in trigeminal nucleus caudalis of both the rat and cat. All 48 neurones (46 cold and 2 warm) tested in the cat and 24 cold neurones in the rat were unaffected by the NRM at a variety of stimulation parameters. However, segmental stimulation inhibited 4/20 neurones in the cat and 11/26 cells in the rat. The results show the selectivity of the inhibition following NRM stimulation.
Cell responses evoked by tooth pulp stimulation above the marginal layer of the cat's trigeminal nucleus caudalis.
In cats anesthetized with urethane, all-or-nothing, synaptically evoked recordings were made from 80 separate units in the descending spinal tract of the trigeminal nerve above the left trigeminal nucleus caudalis, at depths not exceeding 50 micrometer from the surface of the medulla. The units were excited by the left upper (21), left lower (25), either (28), or only on simultaneous stimulation of both (six) canine tooth pulps. There was no somototopic distribution. The latency of responses ranged from 4 to 82 msec. For the group of 28 units excited by upper and lower tooth pulps, there was close matching of response latencies from the two teeth. An abrupt decrease in latency upon increasing stimulation strength ("jumping"), and a gradual increase in latency during repetitive stimulation at a frequency between 1 and 20 Hz ("drifting") was characteristic of most, but not all, responses. Units evoked by stimulation of the inferior dental or infraorbital nerves had similar characteristics. Stimulation of a tooth pulp at threshold for a particular unit was used to test the excitability of that unit after suprathreshold stimulation of the same or a different canine tooth pulp. Stimulation of the upper left canine tooth pulp was generally only facilitatory, while stimulation of the lower left canine tooth pulp was initially facilitatory and later inhibitory. Stimulation of the upper or lower right canine tooth pulps did not excite but could inhibit units excited by the left canine tooth pulps. There was a significant correlation between the frequency at which a unit would follow repetitive stimulation and the duration of the inhibition generated by the first of a pair of stimuli. Long inhibition was associated with poor frequency following.
Facilitation and suppression of antidromic invasion by orthodromic impulses in the cat [proceedings].
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Contrasting actions of cycloheximide on fever caused by arachidonic acid and by pyrogen [proceedings].
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Thermoregulation during mild exercise.
A comparison was made of the thermoregulatory effects of wearing black or white clothing during exercise under radiant heating. For subjects in black clothing the skin temperature was higher than with white but the rectal temperature and heart rate were lower.
A study of some organs and tissues in mice (Mus musculus) subjected to genetic selection for different body proportions.
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Body composition of mice subjected to genetic selection for different body proportions.
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Metabolic heat production of parents and offspring.
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Rate of passage of a non-absorbable marker through the gastrointestinal tract of the mouse (Mus musculus).
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The surface-area-body-weight relationship in mice.
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The insulative value of mouse fur.
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Physiology of heat loss from an extremity: the tail of the rat.
1. Hooded, conscious, male, laboratory rats were subjected to an ambient dry bulb temperature cycle between 12 degrees C and 35 degrees C over a period of approximately 5.5 h. The same procedure was followed using rats in which the temperature surrounding the tail was held constant, and using dead rats. 2. Temperature of the ambient air, and the rectum, flank skin, tail base and tail tip were measured during each ambient temperature cycle. 3. In both living and dead rats, a hysteresis loop was demonstrated for the relationship between all body temperatures measured and ambient temperature. 4. The hysteresis loops for tail temperature differed between living and dead rats in such a way as to indicate that tail temperature began to increase, as a result of an active process, at approximately 30 degrees C, but this response ceased at a lower temperature. 5. The results on rats in which tail ambient temperature was held constant agreed with the preceeding observations. 6. Clear evidence of a counter-current heat exchange system in the vasculature of the rat's tail was not obtained. 7. It is concluded that the tail of the rat resembles an on/off controller in its mode of operation.
Initiation and inhibition of shivering in the rat: interaction between peripheral and central factors.
1. Unanaesthetized, female white laboratory rats were subjected to almost square-wave changes in ambient temperature, from 20 degrees C to 35 degrees C, in a small climatic chamber. 2. Intracerebroventricular injections of serotonin and methysergide were made in shivering, unanaesthetized rats. 3. The integrated electromyogram of m. suprascapularis was recorded as a quantitative measure of shivering activity to monitor the effects of the above procedures. 4. Both warm transients and serotonin inhibited shivering, but methysergide blocked only the effect of serotonin.