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Biomedical subjects

R F Hellon

Publications and source records attributed to R F Hellon.

At least 55 records · Page 3Linked to original sources
PubMed1975

A dissociation between fever and prostaglandin concentration in cerebrospinal fluid.

1. Sustained fever has been induced in conscious rabbits by I.V. injection and infusion of endogenous pyrogen. 2. Cerebrospinal fluid (e.s.f.) was sampled from the cisterna magna at hourly intervals. The concentration of prostaglandin increased in parallel with rectal temperature. The prostaglandin was identified as one of the E series. 3. When sodium salicylate (1-5 m-mole followed by a continuous infusion of 9 mumole/min) was started 1 hr before endogenous pyrogen, the febrile response to the pyrogen was not significantly diminished but no rise of prostaglandin concentration was detected in c.s.f. 4. This dissociation between fever and prostaglandin concentration means that changes in cisternal prostaglandin concentration cannot be accepted as evidence that prostaglandin mediates the febrile response.

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PubMed1973

Neurones in the dorsal horn of the rat responding to scrotal skin temperature changes.

1. Micro-electrode recordings have been made from single neurones in the dorsal horn of male rats anaesthetized with urethane. Scrotal temperature was altered within the range 13-43 degrees C by means of a thermode. The mean firing rate of neurones was correlated with step and ramp changes of temperature.2. In the region where the scrotal nerve enters the cord, 47% of the neurones were responsive to scrotal temperature: half were excited by warming and half by cooling. Most of these thermally responding units were not affected when the scrotal skin was touched and only one-fifth responded to both modalities.3. Both the ;warm' and ;cold' groups of neurones showed responses to step changes of temperature which were classified as dynamic plus static, dynamic only or static only. Comparison of these responses with those published for the scrotal thermoreceptors showed that the incoming thermal information was being processed in the dorsal horn.4. Histological examination of the cord showed that recording sites were in laminae I to V of the dorsal horn.

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PubMed1973

Neurones in the ventrobasal complex of the rat thalamus responding to scrotal skin temperature changes.

1. In rats the scrotal temperature was raised or lowered with a water-perfused thermode while micro-electrode recordings were made of unit activity in the ventrobasal complex of the thalamus. The electrodes were aimed at the region where evoked responses had been found by electrical stimulation of the scrotum. Recording sites were marked by iontophoresis of dye from the micro-electrode.2. Changes in firing rate of thalamic neurones were only found in the scrotal temperature range of 31-40 degrees C. Within this range, 72% of the 123 cells tested were excited or suppressed by skin warming. At temperatures above or below this range, activity was not affected. Most of the cells responded just to temperature and only 7% were also excited by touch.3. Raising temperature in the range 31-40 degrees C caused 82% of the thermally responding cells to increase their firing rate and 18% to decrease their rate. Individual neurones showed a sudden and maintained change in their activity for scrotal temperature increases of only 2, 1 or even 0.5 degrees C. Mean firing rates changed by factors of about 8 or more with these temperature increases and further warming did not change the rate. These step-like changes in firing rate were found at different points over the whole skin temperature range of 31-40 degrees C, but most were between 33 and 38 degrees C.4. For a given neurone the step-like change in activity occurred once its critical temperature was reached, irrespective of whether this was achieved by a step increase of skin temperature over 1-2 sec or by a slow ramp increase lasting several minutes.5. It is not possible to say whether the skin warm receptors, cold receptors or both were responsible for these thalamic responses, but the results do show that incoming thermal information is considerably processed when it reaches the thalamic level.

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PubMed1973

Neurones in the somatosensory cortex of the rat responding to scrotal skin temperature changes.

1. In rats the scrotal temperature was raised or lowered with a water-perfused thermode while micro-electrode recordings were made of unit activity in the somatosensory (SI) cortex. The electrodes were inserted in the area where the largest evoked potentials had been found from electrical stimulation of the scrotum.2. Changes in firing rate of cortical neurones were found only in the scrotal temperature range of 32-41 degrees C. Within this range 40% of all the cells tested were excited or suppressed by skin warming. At temperatures above or below this range, activity was not affected. Most of the cells responded just to temperature and only 14% were also excited by touch.3. Raising temperature in the range 33-41 degrees C caused 83% of the thermally responding cells to decrease their firing rate and 17% to increase their rate. Individual neurones showed a sudden and maintained change in their activity for scrotal temperature increases of only 2, 1 or even 0.5 degrees C. Mean firing rates changed several-fold with these temperature increases and further warming did not change the rate. These step-like changes in firing rate were found at different points over the whole skin temperature range of 33-41 degrees C but most were between 35 and 39 degrees C.4. For a given neurone the step-like change in activity occurred once its critical temperature was reached, irrespective of whether this was achieved by a step increase of skin temperature over 1-2 sec, or by a slow ramp increase lasting several minutes.5. The results are very similar to those found in the thalamus (preceding paper), but the proportions of cortical cells which were excited or suppressed on skin warming were the reverse of the proportions seen in the thalamus.

Animals↗
PubMed1972

Hypothalamic endogenous noradrenaline and thermoregulation in the cat and rabbit.

1. The imino-dibenzyl drugs, imipramine and desipramine, which inhibit the uptake by neurones of noradrenaline, were injected into the lateral cerebral ventricles of cats and rabbits: changes in body temperature resulted which were different for the two species, but nevertheless closely resembled those following intraventricular injection of relatively large quantities of exogenous noradrenaline.2. The endogenous noradrenaline content of the hypothalamus in both species was reduced by repeated injections into the lateral ventricle of the methyl ester of DL-alpha-methyl-p-tyrosine: in animals so treated the hypothalamic content of 5-hydroxytryptamine was not significantly changed.3. Noradrenaline-depleted animals showed significantly reduced responses to intraventricular imipramine and desipramine. The diminished responses were primarily due to reduction in endogenous noradrenaline.4. These observations indicate that endogenous noradrenaline, present in the hypothalamus, can influence body temperature in cats and rabbits.

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