Relative vulnerability of the brain and spinal cord to ischemia

In this experiment CER and SER were monitored as blood flow was progressively lowered by lowering the systemic arterial pressure below the lower limits of autoregulation (bleeding). Blood flow in the brain and dorsal column of the spinal cord was monitored and recorded with the hydrogen clearance method. Long tract neural conduction in the spinal cord appeared quite refractory to the effects of ischemia and disappeared only after 8--18 min of essentially absolute ischemia. The CER was more sensitive to the effects of ischemia, disappearing first in one animal and returning later in all of the animals. The SER returned in all animals after re-infusion of the blood and re-establishment of the blood flow even after a 13--23 min period of absolute ischemia and a 5 min period of electrical silence.

Cardiac arrhythmias accompanying acute compression of the spinal cord

This study was undertaken to determine the cardiovascular response to compression of the spinal cord and to determine the autonomic mechanisms involved. The electrocardiogram and arterial blood pressure were recorded in anesthetized monkeys during inflation of a balloon catheter in the epidural space of the mid-thoracic region. Acute spinal cord compression resulted in a wide variety of severe cardiac arrhythmias and acute hypertension. The arrhythmias were found to result from hyperactivity of both the sympathetic and parasympathetic divisions of the autonomic nervous system.

Experimental acute balloon compression of the spinal cord. Factors affecting disappearance and return of the spinal evoked response

Acute balloon compression of the thoracic spinal cord for 15, 7, 5, 3, and 1 minute in monkeys caused immediate disappearance of the spinal evoked response and complete focal ischemia of the compressed segment in all animals. Only the animals in the 1-minute group, however, demonstrated return of the evoked response. These data, coupled with data from previous experiments of slow balloon compression of the spinal cord and spinal cord ischemia, suggest that the major pathological substrate for neural dysfunction after balloon compression of the spinal cord, be it acute or slow, is physical injury of the neural membrane, irrespective of blood flow changes. These findings also suggest that the ability of that membrane to recover is related to rapidity and length of time of compression. Focal changes in blood flow do not appear to be significant in this mechanism.

The effects of ischemia on long-tract neural conduction in the spinal cord

In this experiment, the effects of ischemia on neural conduction in the monkey spinal cord were studied. In six monkeys generalized ischemia of the spinal cord was created by bleeding the animals to a hypotensive level below the lower limits of autoregulation in the spinal cord. The progressive development of spinal cord ischemia was documented by blood-flow measurement using the hydrogen clearance method. Physiological integrity of the spinal cord was monitored and recorded by the spinal evoked response. The spinal evoked response did not disappear until at least 10 minutes of profound ischemia. At levels of ischemia 20% to 25% of normal blood flow, the spinal evoked response was unchanged. It is concluded that long-tract neural conduction in the spinal cord is relatively resistant to the effects of ischemia.

The effect of sciatic nerve stimulation on spinal cord blood flow

Focal spinal cord blood flow was measured in the left dorsal column during left sciatic nerve stimulation, and compared to blood flow in the same area during sciatic nerve inactivity. Blood flow was found to be significantly increased during stimulation. It is suggested that this increased blood flow is a reflection of increased metabolic demands of the neurons and synaptic systems within the internuncial neural pools, activated by stimulation of all components of the sciatic nerve, rather than a reflection of increased non-synaptic axonal conduction in the dorsal column.

Etiology of the negative chronotropic responses to transient coronary artery occlusion in the anesthetized rhesus monkey

Etiology of the negative chronotropic response to coronary artery occlusion was studied in chloralose-anesthetized monkeys. One-minute occlusion of the circumflex (CIRC) coronary artery resulted in marked negative chronotropic responses and consistent alterations in atrial electrograms. These responses were dependent on interruption of flow to a small proximal CIRC branch, and postmortem examination revealed that it perfused the sinus node region. The negative chronotropic response was not dependent on any apparent neural reflexes because it was not affected by autonomic blockade. Coronary artery occlusion in anesthetized monkeys can result in significant decreases in heart rate and changes in atrial electrical activity when flow to the pacemaker region is interrupted. We suggest that (1) rhesus monkeys may be suitable for study of the sick sinus syndrome, and (2) atropine-resistant bradycardia and atrial arrhythmias observed in postinfarction patients may be due to sinus node artery blockade.

Reflux mechanisms involved in cardiac arrhythmias induced by hypothalamic stimulation

Electrical stimulation of widespread areas in the CNS has been shown to cause cardiac arrhythmias, which occur most frequently after cessation of stimulation. To determine the reflex and autonomic mechanism responsible for the poststimulation arrhythmias, we anesthetized cats with chloralose, and recorded arterial pressure, ECG, and cardiac vagal nerve activity. Stimulation of the hypothalamus consistently caused increases in blood pressure and heart rate during stimulation and caused arrhythmias, accompanied by vagal hyperactivity, immediately following stimulation. The arrhythmias were mediated solely by the vagus nerves because vagotomy or propantheline administration prevented them, whereas propranolol did not. Administration of either phentolamine or spinal cord transection prevented both the rise in blood pressure during stimulation and the poststimulation arrhythmias, but sectioning the carotid sinus and aortic depressor nerves had no preventative effect. However, when this denervation was combined with sectioning of vagal afferents, bursts of vagal activity (used as an index of cardiac rhythm disturbances) were prevented in three of six animals. Subsequent administration of phentolamine prevented the bursts in the remaining animals. It is concluded that poststimulation arrhythmias are elicited by the rise in blood pressure occurring during stimulation causing a sudden surge in parasympathetic outflow to the heart. The reflexogenic areas involved appear to be stretch receptors innervated by afferent vagal fibers.

The effects of beta adrenergic blockade on spinal cord autoregulation in the monkey

Blood flow in the spinal cord was measured in a group of monkeys over a wide range of artificially varied blood pressures after the administration of propranolol, a beta adrenergic blocker. Spinal cord blood flow was found to be constant and in the normal range between a mean system arterial blood pressure of 50 to 150 mm Hg. From 150 to 180 mm Hg spinal cord blood flow decreased. There was no breakthrough of autoregulation, previously seen in the untreated animal. It is suggested, therefore, that the previously observed breakthrough of autoregulation is a beta adrenergic-mediated phenomenon.

Humoral immune response to the heat-labile enterotoxin of Escherichia coli in naturally acquired diarrhea and antitoxin determination by passive immune hemolysis

Acute- and convalescent-phase sera from 132 students attending a university in rural Mexico were assayed for antibody against the heat-labile enterotoxin (LT) of Escherichia coli by neutralization of LT activity in the Y-1 adrenal cell assay and by passive immune hemolysis of LT-sensitized sheep erythrocytes. The two titration methods produced comparable results with respect to antitoxin responses detected. An inverse relationship was found between acute geometric mean antitoxin titer and the occurrence of diarrhea associated with LT-producing E. coli, especially in newly arrived students from the U.S.A. A significant correlation (P less than 0.00 5) was found between a rise in antitoxin titer detectable by the passive immune hemolysis technique and diarrhea with LT-producing E. coli isolated. Thus, humoral antitoxin titers appear to be a useful indicator of immune status with respect to enterotoxigenic (LT) E. coli diarrhea.

The effect of alpha adrenergic blockade on spinal cord autoregulation in the monkey

Spinal cord blood flow (SCBF) was measured over a wide range of artificially varied mean systemic arterial blood pressures (MAP) in a group of monkeys with alpha adrenergic receptors blocked by the intravenous administration of phenoxybenzamine (Dibenzyline). The SCBF was found to vary linearly with changes in MAP. Autoregulation appeared to have been abolished. These data are cited as evidence for a dominant role of the sympathetic nervous system in control of the spinal circulation.

Cardiac arrhythmias resulting from experimental head injury

The cardiovascular events resulting from experimental head injury were studied to determine the incidence of cardiac arrhythmias and to define the autonomic mechanisms responsible for these changes. Electrocardiograms and arterial blood pressure were recorded in anesthetized monkeys before and after the animals were subjected to temporoparietal head impact. Cardiac arrhythmias and hypotension occurred immediately following impact in every animal studied. Various atrioventricular nodal and ventricular arrhythmias were seen. Cholinergic blockage was found to prevent arrhythmias induced by head injury whereas adrenergic blockage was found to be ineffective.

The Ornithodoros (Alectorobius) capensis group (Acarina: Ixodoidea: Argasidae) of the palearctic and oriental regions. O. (A.) maritimus: identity, marine bird hosts, virus infections, and distribution in western Europe and northwestern Africa

In 1967, Vermeil and Marguet described Ornithodoros coniceps maritimus from larvae reared from larvae taken from marine birds on Dumet Island (Atlantic Ocean), Basse Bretagne, France. We collected O. (A.) coniceps Canestrini, 1890, from the type locality (Venice, Italy) and determined that the taxons coniceps and maritimus each require full species status. We selected a lectotype and paralectotypes for the taxon maritimus from the original Dumet Island material. The larva of maritimus is redescribed and the nymph, male, and female are described for the first time. Collection data are recorded from Dumet and other islands off France, Aegimures Islands off Tunisia, Puffin Island off northern Wales, and Great Saltee Island off Ireland. This tick infests nesting colonies of the common tern, roseate tern, sandwich tern, herring gull (northern and Mediterranean races), common cormorant, shag, razorbill, common murre, black-legged kittiwake, and probably other marine birds nesting nearby. Adults and nymphs (tentatively identified as maritimus but lacking associated larvae for full confirmation) were taken near nests of the little egret in Lake Tunis, Tunisia. Soldado virus was isolated from Puffin Island tick samples and a Soldado-like virus from Great Saltee Island tick samples. An experimental study of West Nile virus in the Tunisian tick population is reviewed. The birds species associated with maritimus in each collecting locality, and their nesting and resting habits and migration patterns in relation to tick and arbovirus survival and distribution, will be reported in the following paper in this series.

Soldado virus from Ornithodoros (Alectorobius) maritimus (Ixodoidea: Argasidae) infesting herring gull nests on Puffin Island, Northern Wales

Three strains of Soldado (SOL) virus (Hughes serogroup) were isolated from nymphal and adult Ornithodoros (Alectorobius) maritimus Vermeil et Marguet collected in and near nests of the Herring Gull, Larus a. argentatus Pontoppidan, on Puffin Island, northern Wales. Reciprocal complement fixation (CF) titration results demonstrated recovered virus strains to be SOL virus and antigenically distinct from other Hughes serogroup members. All isolates killed mice and guinea pigs, and 1-2 day old domestic chicks when inoculated intracerebrally.

Role of the nervous system in experimentally induced arrhythmias

The purpose of our studies was to examine the role of the nervous system in arrhythmias produced by digitalis overdose and coronary artery occlusion in the cat. This was done by observing the effect of these arrhythmogenic procedures on cardiac efferent neural activity and then determining whether any observed alteration in neural activity contributed to the cardiac rhythm disturbances evoked by digitalis and coronary artery occlusion. Our data indicate that both procedures used to evoke arrhythmias activate each division of the autonomic nervous system. Activation of the sympathetic nervous system resulted in a deleterious effect on cardiac rhythm whereas activation of the parasympathetic nervous system, in general, resulted in a beneficial effect on cardiac rhythm. With coronary occlusion, the role exerted by the nervous system depended on the anatomic location of the involved myocardium. Studies directed at elucidating the mechanisms whereby the nervous system caused cardiac rhythm disturbances indicated that there may be an important difference between the antiarrhythmic efficacy of beta-adrenergic blockade and bilateral stellate ganglionectomy. The latter procedure proved to be a more effective way of removing deleterious sympathetic neural effects on the heart. In conclusion, our findings suggest that the development of new drugs for treating arrhythmias resulting from digitalis and coronary occlusion should be aimed at finding drugs that act to either depress central sympathetic outflow or enhance parasympathetic effects on the ventricle.

Effect of ouabain and its interaction with diphenylhydantoin on cardiac arrhythmias induced by hypothalamic stimulation

Cardiac arrhythmias induced by central nervous system stimulation in the cat were used to evaluate the possible central nervous system effects of ouabain and diphenylhydantoin. Electrical stimulation of the posterior portion of the hypothalamus resulted in alterations of cardiac rhythm, and recordings from cardiac-bound sympathetic nerves revealed continuous activity during the time of arrhythmia. Intravenous administration of small doses of ouabain (i.e., 10-30 mug/kg) prevented both the arrhythmias and the associated hyperactivity on the sympathetic nerves. The antiarrhythmic effect was not present in animals with denervated baroreceptors indicating that the ouabain effects were due to sensitization of baroreceptor reflexes. Intravenous administration of large but subarrhythmic doses of ouabain (i.e., 60-80 mug/kg) converted a subarrhythmogenic hypothalamic electrical stimulus to a threshold stimulus for arrhythmias. The increased response of the heart to brain stimulation in the presence of these doses of ouabain was associated with an increased discharge of cardiac sympathetic nerves, indicating that ouabain was exerting its arrhythmogenic enhancing effect on the central nervous system rather than on the heart. Pretreatment with diphenylhydantoin prevented the arrhythmias produced by the combination of ouabain and hypothalamic stimulation. Prevention of the arrhythmia was associated with prevention of the associated sympathetic hyperactivity responsible for the arrhythmia, thus indicating a central nervous system site of action of diphenylhydantoin. These data suggest that central nervous effects of ouabain and diphenylhydantoin are important in the ability of these drugs to alter cardiac rhythm.

Neural mechanisms involved in acetylstrophanthidin-induced bradycardia

The role of neural sites in the bradycardia produced by acetylstrophanthidin (14.1, 22.5 and 35.5 mug/kg) was studied in chloralose-anesthetized cats with efferent vagal tone blocked by atropine. The sites were: carotid sinus baroreceptors, aortic arch baroreceptors, cardiac sensory receptors, nodose ganglion receptors and central nervous system structures. The role of each site was determined by selective ablation of all sites except the one under study. Significant slowing in heart rate occurred when: 1) only carotid sinus baroreceptors were intact; 2) only aortic arch baroreceptors were intact and 3) only cardiac sensory receptors were intact. No cardiac slowing was observed when only nodose ganglion receptors, central sympathoinhibitory sites and beta adrenergic receptors were intact. These results indicate that in atropine-treated cats, the further slowing in heart rate produced by acetylstrophanthidin arises from activation of reflex sites located in the carotid sinus, aortic arch and myocardium.

Anaesthesia and the epileptic pateint. A review

A review is presented of some of the problems that may arise in association with anaesthesia for epileptic patients. There is the possibility of precipitating anticonvulsant drug toxicity. Numerous drug interactions are possible with some anticonvulsant agents, such as phenobarbitone and phenytoin, which affect hepatic microsomal enzyme systems. There is the risk of convulsions occurring in susceptible patients following the use of the new anaesthetic agents which are capable of inducing CNS excitability.

High-speed angiography of experimental head injury

✓ Cineangiograms were performed at 1000 frames/sec in anesthetized rhesus monkeys during 4 meters/sec impact head injuries. Impacts that did not fracture the skull resulted in rapid transient movements of intracranial arteries. Lateral blows distorted the ipsilateral middle cerebral artery and reversibly displaced the anterior cerebral artery across the midline. Occipital blows distorted the peripheral branches of the middle and posterior cerebral arteries, and produced marked stretching of extracranial vessels. These data indicate that most of the intracranial movements hypothesized as etiological in brain injury occur in the first milliseconds following trauma. This technique makes possible quantitative measurement of these intracranial events and so may aid in the understanding of brain injury.