Biomedical subjects
D Mitchell
Publications and source records attributed to D Mitchell.
Prevalence of rabies virus in foxes trapped in the Canadian Arctic.
Brains and salivary glands of 521 trapped arctic foxes (Alopex lagopus) submitted from four different settlement areas in the Northwest Territories were examined for rabies by the standard fluorescent antibody and mouse inoculation tests. Rabies antigen was present in 44 of 201 (21.9%) brains from foxes trapped in the Sachs Harbour area, but submissions from Cambridge Bay (127), Spence Bay (93) and Gjoa Haven (100) were negative. Virus was also present in salivary glands from 43 (97.7%) of these 44 positive foxes. The arctic fox continues to be the main wildlife reservoir of rabies in the Canadian Arctic and foxes in the prodromal stage of the disease pose a particular threat to the trapper. Preexposure vaccination should always be a consideration in this occupational group.
Fever induced in rabbits by intravenous injection of bovine serum albumin.
1. Bovine serum albumin injected into conscious rabbits produced a dose-dependent fever of short latency and duration of at least 2 1/2 hr. 2. The fever was not due to contamination by other proteins nor due to contamination by bacterial endotoxin. 3. The fever following albumin injection had characteristics similar to endogenous pyrogen fever. 4. Some traditional ways of distinguishing bacterial endotoxin fever from other types of fever need to be reassessed.
Intraventricular microinjections of a stable analogue of prostaglandin endoperoxide cause fever in rabbits.
1. Derivatives of arachidonic acid other than prostaglandin are pyrogenic, the likely candidates being the prostaglandin endoperoxides and/or the thromboxanes. 2. Intraventricular microinjections in rabbits of a stable analogue of prostaglandin endoperoxide resulted in dose-dependent increases of rectal temperature. The pyrexia was delayed in onset; no significant change in body temperature occurred for at least an hour. 3. The pyrexia was unaltered by simultaneous injection of the potent prostaglandin synthetase inhibitor indomethacin. 4. We suggest that both prostaglandins and prostaglandin endoperoxides may be implicated in fever.
Accuracy of pre- and postnatal assessment of gestational age.
The gestational age at delivery in a group of 20 neonates was estimated prenatally from measurements of the biparietal diameter made by ultrasound during pregnancy, and postnatally from the newborn infant's neurological and external physical criteria or maturity using the method of Dubowitz et al. (1970). These two assessments were compared with the gestational age at delivery calculated from the date of the last menstrual period (LMP) in mothers certain of their dates. Gestational age derived from the ultrasound data correlated well with that derived from the mother's LMP, and much better than did gestational age derived from the postnatal scoring system.
Value of measuring serum angiotensin I converting enzyme and serum lysozyme in the management of sarcoidosis.
Serum angiotensin I converting enzyme (ACE) and lysozyme have been measured in 23 controls, 115 patients with sarcoidosis, and 64 with other chest diseases. Both enzymes were significantly raised in sarcoidosis. ACE was raised above the normal range in 21 of 72 (29%) patients with definite sarcoidosis and in 17 of 38 (45%) of those who were untreated and seen within one year of presentation. The rise discriminated usefully between those with stable and progressive disease (5% and 62% respectively). Lysozyme was raised in 50 of 72 (69%) patients with sarcoidosis but also in 11 of 54 (20%) patients with other chest diseases. Discrimination between stable and progressive disease was useful only if very high levels were considered. Five patients had serial measurements after treatment with oral steroids and showed a progressive fall in levals of both enzymes, but patients with other diseases also showed a significant fall within the normal range when so treated. Measurement of these enzymes may help in the management of some cases of sarcoidosis, but results require critical interpretation.
Immune response of cattle to antigens obtained from bovine herpesvirus 1-infected tissue culture.
The ability of two antigens, termed EV and CM, derived from bovine herpesvirus 1 infected cultures to produce serum-virus neutralizing antibodies has been studied in cattle. Both EV and CM when inoculated with adjuvant induced significant increases in serum-virus neutralizing antibody titers. Control groups inoculated in a similar manner failed to induce significant increases in serum-virus neutralizing antibody. Some of the animals were vaccinated, then were bred, challenged with a virulent strain of bovine herpesvirus 1 and held until calving was completed. During this 18-month period titers declined slowly in the vaccinated animals. Proportionally there were fewer live calves born to the control cattle than to the CM vaccinated group but reduction was not large enough to conclude that this vaccine had protected the cattle against the abortigenic activity of bovine herpesvirus 1. Further challenge studies should be made to determine whether the administration of these antigens can prevent the subsequent onset of the clinical signs associated with bovine herpesvirus 1.
Descending tryptaminergic pathways and the antinociceptive effect produced by peripheral electrical stimulation in the rat [proceedings].
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Commercial heparin solution investigated in vitro after reported impaired nerve function in a patient.
Exposure to commercial heparin solution caused rapid conduction failure in frog sciatic nerve preparations. The toxic substance was not the heparin itself, but the 0,5% phenol preservative. Phenol solutions with concentrations between 0,1% and 5% caused a dose-dependent nerve failure, which manifested as a progressive decline in compound action potential amplitude. Care must be taken in the administration of any solution preserved with phenol, to prevent nerve damage.
Failure of naloxone to reverse peripheral transcutaneous electro-analgesia in patients suffering from acute trauma.
Transcutaneous electrical stimulation of the intercostal nerves innervating the site of fractured ribs in 6 patients produced subjective and clinical evidence of decrease in the pain experienced by the patients. This analgesia was not significantly modified by naloxone, a pure narcotic antagonist. The possible role of endogenous morphine-like substances in peripheral electro-analgesia in man is discussed.
Vasodilator mechanism of the intracerebral (non-sympathetic) adrenergic pathway.
Stimulation of the intracerebral noradrenergic pathway causes a vasodilatation in the hypothalamus. We have investigated whether this vasodilatation is caused by a direct vascular innervation or whether it is secondary to an activation of hypothalamic neurons. Non-specific neuronal activation using glutamate increased the mean hypothalamic blood flow. Depression of neuronal activity using barbiturate reduced hypothalamic blood flow and blocked the glutamate and the intracerebral noradrenergic pathway-induced vasodilatation. These results suggest that stimulation of the intracerebral noradrenergic pathway increases hypothalamic neuronal activity which indirectly causes a vasodilatation.
The febrile responses in rabbits and rats to leucocyte pyrogens of different species.
1. We have investigated the effects on body temperature of rats and rabbits of leucocyte pyrogen derived from the blood of rat, rabbit, ox, pig and baboon. 2. In the rabbit intravenous injections (3.5 ml.) of solutions containing leucocyte pyrogen derived from ox, pig and rabbit blood produced fevers with short latencies; no fevers resulted from injections of similar solutions derived from rat or baboon blood. 3. In the rat intraperitoneal injections (2.0 ml.) of solutions containing leucocyte pyrogen derived from ox blood caused a fever, while pig leucocyte pyrogen produced a marked hypothermia. Neither rabbit, baboon, nor rat leucocyte pyrogen had any significant effect on rectal temperature of the rats. 4. Our results show that there is a variability of response in the rat and the rabbit to injection of leucocyte pyrogen of different species; leucocyte pyrogen may be species specific.
Lack of an effect of dietary selenium on serum albumin, glucose and urea nitrogen in ewes.
The results of a study on the effect of dietary selenium administered with vitamin E on serum levels of albumin, glucose and urea nitrogen in ewes are reported. In October, at the onset of breeding, after ten months on a dystrophogenic diet, mean serum levels of albumin (g/dl), glucose (mg/dl) and urea nitrogen (mg/dl) were respectively 3.5, 52.9 and 12.8, in 65 Se-deficient ewes and 3.6, 51.7 and 14.3 in 65 Se-adequate ewes. Despite a significant difference in the serum level of urea nitrogen between Se-deficient and Se-adequate groups, no consistent effect of dietary selenium was apparent.
Naloxone-reversible peripheral electroanalgesia in intact and spinal rats.
Peripheral electrical stimulation of the rat produced a "dose-dependent" analgesia both in intact and in spinal animals. Naloxone, a narcotic antagonist, almost completely reversed this analgesia. It is felt that peripheral electroanalgesia acts via the release of endogenous narcotic-like substances, the enkephalins, at spinal and supraspinal centres.
Management of acute traumatic pain by peripheral transcutaneous electrical stimulation.
Peripheral transcutaneous electrical stimulation has been used in an attempt to relieve the pain associated with fractured ribs. Sixty-two per cent of the patients considered their pain to be greatly relieved by this electro-analgesic technique and a further 28% gained some relief. Pain was assessed by means of a visual analogue scale. In most of the patients there was a clinical improvement in their condition, the degree of which correlated well with the pain relief. This trial indicated that transcutaneous electro-analgesia is a useful technique for producing analgesia in patients suffering from acute trauma, without some of the side-effects inherent in more conventional forms of therapy.
Neuronal and behavioural responses in rats during noxious stimulation of the tail.
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Pica: a species relevant behavioral assay of motion sickness in the rat.
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