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Biomedical subjects

R F Hellon

Publications and source records attributed to R F Hellon.

At least 37 records · Page 2Linked to original sources
PubMed1980

Suppression of fever in rabbits by a protein synthesis inhibitor, anisomycin.

1. The protein synthesis inhibitor, anisomycin, was given into the cerebral ventricles of rabbits as a priming dose followed by a continuous infusion. Doses of 100, 200 and 300 microgram followed by infusions at 100, 200 and 300 microgram/hr inhibited the incorporation of [14C] leucine into hypothalamic protein by over 90%. 2. Injection and infusion of anisomycin (300 microgram) suppressed the febrile response to leucocyte (endogenous) pyrogen given into the ventricles (I.C.V.) or I.V. 3. Dialysis experiments showed that anisomycin did not combine irreversibly with leucocyte pyrogen. 4. Anisomycin did not interfere with thermoregulation in a cold environment. 5. It is concluded that pyrogenesis may involve a step which is dependent on synthesis of hypothalamic protein with a rapid turnover.

Animals↗
PubMed1979

Facial thermal input to the trigeminal spinal nucleus of rabbits and rats.

In rabbits and rats under urethane anesthesia, a systematic survey was made of the caudal trigeminal nucleus, using glass coated tungsten microelectrodes. This revealed many neurons in the marginal layer sensitive either to warming or cooling the facial skin. The majority of these neurons were specifically temperature sensitive. In rats, a somatotopic arrangement of cold receptive fields was evident within the marginal layer of the trigeminal nucleus, with the ophthalmic division of the trigeminal nerve represented most laterally, the mandibular most medially and the maxillary division represented over most of the recording region. This arrangement is similar to the mediolateral distribution seen in cats. In rabbits, the distribution was less rigorous but the ophthalmic division tended to be represented caudally and the mandibular division rostrally. The maxillary division was represented over most of the recording region. All receptive fields were ipsilateral and showed spatial convergence of input. Both rabbits and rats possessed a concentration of thermal receptive-fields around the nose, whisker pad and mouth. At steady skin temperatures, marginal units gave bell-shaped intensity functions which were very similar to those reported for the cold and warm receptors. With rapid changes of temperature, neurons responded with a dynamic outburst which corresponded to the equivalent receptor response.

Animals↗
PubMed1978

Noxious thermal input from the rat tail: modulation by descending inhibitory influences.

In anaesthetized rats, single fibres have been dissected from the tail nerves. Fibres were found which became excited when the temperature of water surrounding the tail was raised above 40 degrees C. Firing rate increased with stepwise increases in temperature, showing first a transient outburst followed by adaptation to a static level. Corresponding neurones were also found in the dorsal horn at the entry zone of the roots coming from the tail. The cord neurones had a higher threshold temperature of 42.5--45 degrees C. When the spinal cord was reversibly blocked by cooling in the thoracic region, then the threshold of the dorsal horn neurones was reduced to that of the afferent fibres. In addition, at suprathreshold temperatures dorsal horn activity was greater during cord blockade. We conclude that dorsal horn neurones responding to noxious heating are subject to a tonic descending inhibitory control.

Action Potentials↗
PubMed1978

The representation of facial temperature in the caudal trigeminal nucleus of the cat.

1. In cats anaesthetized with urethane, extracellular micro-electrode recordings were made in the marginal layer of the trigeminal nucleus caudalis between the level of the obex and the Cl rootlets. 2. Nearly 300 neurones were found whose discharge rate increased with a reduction of facial temperature and a few which were excited by an increase in temperature. Over half of the neurons in each group were specifically sensitive to temperature and the remainder had a weak input from mechanical stimulation of the face. 3. Thermal receptive fields were all ipsilateral and found most frequently on the nose, lips, lower eyelid and pinna. There was a somatotopic organization of the receptive fields according to the three divisions of the trigeminal nerve. 4. On quantitative thermal testing, the neurones showed responses which were similar to those of the skin temperature sensors. 5. The thermal neurones could be antidromically fired by a stimulating electrode in the thalamus.

Animals↗
PubMed1978

Thermal stimulation of intra-abdominal veins in conscious rabbits.

1. Infusions of hot and cold Hartmann's solution were given into the hepatic portal vein and inferior vena cava of conscious rabbits. Similar infusions were given into an ear vein as controls. The time integral of the displacement of brain temperature was measured. 2. There was no evidence for the presence of warm sensors in the inferior vena cava, portal vein, liver or hepatic vein, and no evidence for a concentration of cold sensors in the inferior vena cava. 3. There may be cold-sensitive elements in the portal vein or the tissue perfused by blood passing through it.

Abdomen↗
PubMed1977

Are there functionally important temperature sensors in the right heart or lungs?

1. In conscious rabbits, paired hot or cold infusions were given into the left atrium or jugular vein. For each pair of infusions the volume and temperature of the fluid was identical. The time course of the displacement of brain temperature was measured. 2. The magnitude of the displacement of brain temperature was not influenced to any major extent by the route of infusion. 3. This evidence suggests that there are no temperature sensors of any importance in the right heart or lungs.

Animals↗
PubMed1976

Thermoregulation in rabbits during fever.

1. We have studied the effect of fever on the efficacy of the thermoregulatory control system in conscious rabbits. 2. The control system was challenged by a series of systemic thermal loads produced by the intravenous infusion of hot or cold isotonic solutions. The time integral of the consequent upward or downward displacement of brain temperature was used as an index of the response of the control system. Steady-state fever was induced by intravenous infusion of plasma containing leucocyte pyrogen. 3. With cold loads there was a linear relation between load and response. The regression coefficients were not significantly changed by fever in any of the six rabbits. Wth hot loads given to afebrile rabbits the regression of response on load was generally not statistically significant, but the responses were not demonstrably greater in the febrile state. 4. We were not able to demonstrate impairment in the capacity of the febrile animal to compensate for systemic thermal loads.

Animals↗
PubMed1976

Evidence that brain prostaglandin synthesis is not essential in fever.

1. We have tested the hypothesis that a fever caused by pyrogen depends upon the synthesis of prostaglandin E in the brain and that the prostaglandin in turn acts on the hypothalamus to produce fever. 2. In rabbits, fever was produced by the injection of leucocyte pyrogen in a lateral cerebral ventricle. The latency, rate of rise and magnitude of the fever was unaffected by the simultaneous intraventricular injection of two prostaglandin antagonists, SC 19220 and HR 546. 3. Both antagonists effectively attenuated the fever caused by the intraventricular injection of prostaglandin E2. 4. This evidence is not consistent with the hypothesis that prostaglandin E is the principal mediator of fever.

Animals↗
PubMed1975

Thermal receptors in the scrotum of the rat.

1. The technique of single fibre dissection has been used to study the warm and cold thermoreceptors in the rat scrotum. 2. The warm receptors showed dynamic activity during increases of scrotal temperature and static activity when temperature was constant. The static activity/temperature curve was bell-shaped, with minima at 31 and 45 degrees C and a peak at 42 degrees C. 3. The cold receptors also showed dynamic and static responses to reductions of temperature. At steady temperatures the impulses from some receptors were grouped in bursts. The number of impulses in each burst increased from zero at 30 degrees C to four at 20 degrees C.

Action Potentials↗
PubMed1975

Convergence in a thermal afferent pathway in the rat.

1. In anaesthetized rats, unit activity was recorded in the afferent somatosensory pathway leading from the scrotum. Recording sites were in the dorsal horn near the entry zone of the scrotal nerve, in the ventrobasal complex of the thalamus and in the somatosensory (SI) cortex. During recording, the temperatures of the left and right sides of the scrotum were varied independently. 2. Almost all (64/67) the units in dorsal horn, thalamus and cortex responding specifically to scrotal temperature were equally affected by temperature changes on either side of the scrotum. The receptive fields of these units were bilateral and large, implying a massive convergence of fibres from thermoreceptors on to each central unit. In contrast, mechanosensitive units responded only to unilateral stimulation. 3. As a consequence of the convergence in the thermal pathway, the firing rate of each central unit was a function of an additive combination, often simply the sum, of the temperatures of the two sides of the scrotum. 4. The relationship between firing rate and the temperature of one side of the scrotum was sigmoid, the position, but not the shape, of the curve depending on the temperature at which the opposite side was maintained. An increase in the maintained temperature shifted the sigmoid response curve towards lower temperatures and vice versa. 5. The convergence which this pathway exhibits would be well suited to integration of the temperature of the scrotal skin, but not to spatial discrimination.

Action Potentials↗
PubMed1975

Is brain prostaglandin synthesis involved in responses to cold?

1. Experiments with rats have suggested that prostaglandin synthesis in the C.N.S. may mediate thermoregulatory reactions to cold. This possibility was investigated in cats using two types of experiment. 2. In one series of experiments, c.s.f. collected from the cisterna magna of conscious cats exposed to a cold and a hot environment was assayed for prostaglandin-like activity. During cold exposure there was a slight increase in activity which persisted after return to neutral ambient temperature. There was no correlation between prostaglandin-like activity and rectal temperature. During the heat exposure there was no demonstrable change in activity. 3. In the second series, conscious cats were exposed to cold conditions and given intravenous injections of salicylate, paracetamol, or indomethacin, all of which inhibit prostaglandin synthesis. Indomethacin salicylate nor paracetamol caused any significant change in rectal temperature. 4. The results do not support a role for C.N.S. prostaglandin synthesis in thermoregulatory reactions to cold in cats.

Acetaminophen↗