Evidence for widespread changes in the structure, composition, and fire regimes of western North American forests.

Implementation of wildfire- and climate-adaptation strategies in seasonally dry forests of western North America is impeded by numerous constraints and uncertainties. After more than a century of resource and land use change, some question the need for proactive management, particularly given novel social, ecological, and climatic conditions. To address this question, we first provide a framework for assessing changes in landscape conditions and fire regimes. Using this framework, we then evaluate evidence of change in contemporary conditions relative to those maintained by active fire regimes, i.e., those uninterrupted by a century or more of human-induced fire exclusion. The cumulative results of more than a century of research document a persistent and substantial fire deficit and widespread alterations to ecological structures and functions. These changes are not necessarily apparent at all spatial scales or in all dimensions of fire regimes and forest and nonforest conditions. Nonetheless, loss of the once abundant influence of low- and moderate-severity fires suggests that even the least fire-prone ecosystems may be affected by alteration of the surrounding landscape and, consequently, ecosystem functions. Vegetation spatial patterns in fire-excluded forested landscapes no longer reflect the heterogeneity maintained by interacting fires of active fire regimes. Live and dead vegetation (surface and canopy fuels) is generally more abundant and continuous than before European colonization. As a result, current conditions are more vulnerable to the direct and indirect effects of seasonal and episodic increases in drought and fire, especially under a rapidly warming climate. Long-term fire exclusion and contemporaneous social-ecological influences continue to extensively modify seasonally dry forested landscapes. Management that realigns or adapts fire-excluded conditions to seasonal and episodic increases in drought and fire can moderate ecosystem transitions as forests and human communities adapt to changing climatic and disturbance regimes. As adaptation strategies are developed, evaluated, and implemented, objective scientific evaluation of ongoing research and monitoring can aid differentiation of warranted and unwarranted uncertainties.

Positive interactions between leafrollers and other arthropods enhance biodiversity on hybrid cottonwoods.

We examined the potential of a common herbivore to indirectly influence other diverse community members by providing habitat. Larvae of the leafroller Anacampsis niveopulvella commonly construct shelters by rolling leaves of cottonwood trees. These leaf rolls are later colonized by other arthropods. We first documented 4 times greater species richness and 7 times greater abundance on cottonwood shoots that contained a rolled leaf compared to adjacent shoots without leaf rolls. Second, with both removal and addition experiments, we showed that leaf rolls are responsible for these differences in arthropod assemblages. Leaf roll removal caused a 5-fold decline in richness and a 7-fold decline in abundance; leaf roll addition resulted in a 2.5-fold increase in richness and a 6-fold increase in abundance. Third, to determine whether rolled leaves are colonized for food or for shelter, we compared colonization of natural and artificial leaf rolls. Both richness and abundance were approximately 2-fold greater in artificial leaf rolls, indicating that leaf rolls are colonized primarily for shelter. Fourth, in a natural hybrid zone we found that leafroller densities were 2-fold greater on backcross hybrids than on F1 hybrids. These differences are likely associated with genetically-based differences in leaf morphology and/or leaf chemistry. Ultimately, plant genotype affects positive indirect interactions that have the potential to affect community structure. This study and others demonstrate that shelter builders (i.e., leafrollers and gall formers) enhance biodiversity, while free-feeders are more likely to negatively affect biodiversity.

Treatment with carvedilol is associated with a significant reduction in microalbuminuria: a multicentre randomised study.

Patients with mild to moderate essential hypertension (n = 1570) were enrolled in a large, multicentre, randomised, open-label study designed to evaluate the safety and efficacy of different regimens of carvedilol. Reported here are the effects of carvedilol on microalbuminuria (MAU) in a subset of 876 patients who underwent MAU assessment (i.e. the Micral-Test) at baseline and at week 12. MAU was present at baseline in 245 (28%) of these patients. Despite different magnitudes of blood pressure reduction, improvements in MAU were similar in all groups (range 54-60%), with complete disappearance occurring in 48-55% of patients. The decrease in MAU did not correlate with the magnitude of blood pressure reduction, suggesting a possible renal protective effect exerted by carvedilol independent of blood pressure reduction mediated by beta-blockade and vasodilatation.

A home-made solid-phase sequencer operating at the nanomole level.

The building and functioning of a fully automated solid-phase sequencer is described. The peptide is coupled via its alpha-carboxyl end to activated glass beads and successively reacted with Chang's and Edman's reagents. All operations are electronically controlled by the automated programmer. All components necessary to build the machine are commercially available. This sequencer has been used at a nanomole level in the final phase of a protein sequence determination. The overall cost as well as the sensitivity and efficiency of the final product compare favourably to those of commercial machines.

Hypertension and acute focal cerebral ischemia. Infarction and edema after occlusion of a middle cerebral artery in cats.

Hypertension was produced in 8 cats by nephrectomy and wrapping the opposite kidney. Subsequent occlusion of one middle cerebral artery caused ischemic infarcts that were larger than those of 8 normotensive cats. The larger infarcts may have been caused by increases of ischemic cerebral edema resulting from changes in the cerebral endothelial barrier induced by hypertension. In addition to increasing the likelihood of strokes, hypertension in humans may predispose toward larger cerebral infarcts.

Influence of head position on the prognosis of experimental subarachnoid hemorrhage.

Autogenous blood was injected repeatedly into the intracranial subarachnoid space of cats, the heads of which were placed in one of four positions (prone, supine, left side down, and right side down). Epidural pressures, mean aortic blood pressures, and pulse rates were measured, and their responses to the repeated injections were analyzed. The distribution of the injected blood was different among the four groups. The cats in the sulpine position had the greatest amounts of blood in the posterior fossa and tolerated the injections least well. The position of the head at the time of a subarachnoid hemorrhage may influence the prognosis; positions that favor accumulations of blood around the brain stem carry the greatest risk.

Experimental subarachnoid hemorrhage from a middle cerebral artery. Neurologic deficits, intracranial pressures, blood pressures, and pulse rates.

Devices to produce experimental subarachnoid hemorrhage (SAH) can be implanted in animals. After SAH is produced by the puncture of a middle cerebral artery (MCA) in awake cats, neurologic deficits develop that are not as severe as those caused by MCA occlusion. Biphasic increases of epidural pressure occur and are related to the extent and distribution of the hemorrhage. Ischemic changes are more severe if the flow of blood through the MCA is interrupted.

Relationships among intracranial pressure, blood pressure, and superficial cerebral vasculature after experimental occlusion of one middle cerebral artery.

A cranial window conforming to the contours of the underlying cerebral cortical surface was implanted successfully in 18 cats. Subsequently the left middle cerebral artery (MCA) was occluded inside the sealed cranium and changes in the superficial cortical vasculature were related to measurements of intracranial pressure (ICP), measured extradurally, and to the resulting infarcts. Vascular changes early after MCA occlusion were not predictive of the outcome of the occlusion, except for aggregation of formed elements of the blood in arterioles, which was a bad prognostic sign. Secondary reactive hyperemia was not beneficial; increases of ICP suggested that hyperemia led to increased cerebral edema as well as to swelling.

Brain water alterations after unilateral nephrectomy. A study of regional circulatory factors in squirrel monkeys.

White and regional gray matter distributions of water, blood flow, and the protein tracer pertechnetate were measured in five normal squirrel monkeys. A second group of five monkeys, which had undergone unilateral nephrectomy six months previously, were found at the time of study to have blood pressures similar to those of the control animals but increased brain water and altered distribution of blood flow which was increased in white matter. No alteration of capillary permeability to the protein traces attended these changes, which appeared to be influenced by blood pressure. Nephrectomy without hypertension influences brain water content, perhaps because of an effect on cerebral resistance vessels. In hypertensive encephalopathy renal lesions, as well as intraluminal pressure changes, may be related to cerebral edema.

Report of Joint Committee for Stroke Resources. IV. Brain edema in stroke.

A classification of brain edema is provided as well as an extensive review of the animal models from which we have derived most of the basic information we have about the formation and resolution of edema. The clinical aspects of cerebral edema in stroke are discussed and also modern methods for identifying cerebral edema in the human. Attention is given to computed tomography and enhanced CT and advances in their application to this condition. Treatment of cerebral edema in the stroke patient using glycerol, dextran 40, mannitol, steroids, and other drugs is discussed and the need pointed out for controlled clinical trials of the therapeutic effectiveness of these agents.

Cortical neuronal function during ischemia. Effects of occlusion of one middle cerebral artery on single-unit activity in cats.

To assess the effects of ischemia on neuronal function, the action potentials of 261 individual cortical neurons were recorded extracellulary and related to regional cerebral blood flow (CBF) measured by hydrogen clearance in 19 cats, seven of which had the left middle cerebral artery occluded during a recording. The onset of ischemia could be associated with transient increases of activity, including "seizure discharges," as well as cessation of activity. No activity was noted at CBF less than 0.18 ml/gm/min; at higher (but ischemic) values for CBF, abnormal patterns of activity frequently were recorded. One neuron recovered function after cessation in association with an increase of CBF, indicating a potential for the restoration of function of ischemic neurons by effective therapeutic measures.

XIII. Cerebral circulation and metabolism in stroke. Cerebral circulation and metabolism in stroke study group.

An understanding of the cerebral circulation is so fundamental to comprehension of the pathogenesis of stroke that cerebral blood flow and metabolism merit review in this series of reports. The authors recognize that the research described here is very technical in nature and may appear to have little practical application to clinical medicine. Nevertheless, these matters are basic to the development of precise methods for the measurement of regional cerebral blood flow in man which could be used to monitor the therapy of stroke with greater success than is possible at present.

Pathophysiology of cerebral infarction.

Evidence available at present from animal studies indicates that the flow of blood can be restored to ischemic zones in the brain as long as 24 hours after the onset of ischemia, and that such reperfusion could result in the restoration of function of neurons that have not been functioning during the period of ischemia. However, reperfusion also can cause worsening of ischemic cerebral edema resulting in increased neurological disability or death. Adequate measures for control of cerebral edema will be necessary if surgical intervention is to become an effective therapy for acute ischemic cerebral infarcts.

Changes of epidural pressures after experimental occlusion of one middle cerebral artery in cats.

Epidural pressures (EDP) were measured in 29 cats. Twenty cats had the left middle cerebral artery (MCA) occluded; pentobarbital was used for anesthesia for 10 of these, and halothane was used for the other 10. Two cats had sham operations: the MCA was manipulated but not occluded. Seven cats were used for testing the reliability of the EDP devices. EDP was measured successfully and was directly related to the swelling of the brain and to the size of the cerebral infarct resulting from MCA occlusion. Side-to-side pressure gradients were demonstrated in 7 cats with marked increases of EDP after occlusion; in these cats, EDP may have reflected the pressure of compressed cerebral tissue rather than the pressure of cerebrospinal fluid. Cats anesthetized with pentobarbital had greater increases of EDP and died before the end of the period of observation more frequently than cats anesthetized with halothane, probably because of respiratory depression and slower recovery with pentobarbital. Measurements of EDP may be useful for studies of the treatment of cerebral edema in experimental models of acute cerebral ischemia.

Intracranial pressure, blood pressure, and pulse rate after occlusion of a middle cerebral artery in cats.

The left middle cerebral artery was occluded in 12 tranquilized but unanesthetized cats with use of a device implanted transorbitally 5 to 7 days earlier. Bilateral epidural pressures, mean aortic blood pressure, and pulse rate were measured at intervals for up to 48 hours after occlusion. The relationships of these measurements to each other and to the extent and severity of cerebral infarcts is described.

Catecholamine content of cerebral tissue after occlusion or manipulation of middle cerebral artery in cats.

The authors determined by fluorimetry the norepinephrine-epinephrine content (NE-E) of cerebral tissue from 38 cats, to ascertain whether constriction of hypersensitive arterial vessels by vasoactive agents in ischemic cerebral tissue could cause extension of cerebral infarcts and worsening of neurological deficits. Twenty-three cats had the left middle cerebral artery (MCA) occluded transorbitally, and 10 cats had sham operations. Five cats had only the surgical procedures necessary for obtaining tissue; mean NE-E content was 0.30 mug/gm (SD=0.041). For the other 33 cats, including those with sham operations, values were variable, ranging from 0.07 to 0.60 mug/gm. Low values usually were obtained for ischemic hemispheres 24 hours and 7 days after MCA occlusion, but at other times values could be high or low on either side. Many factors unrelated to tissue damage, including arterial manipulation, influence the catecholamine content of cerebral tissue.

Immediate effects of cerebral ischemia: evolution and resolution of neurological deficits after experimental occlusion of one middle cerebral artery in conscious cats.

Acute occlusion of the left middle cerebral artery (MCA) was accomplished without anesthesia and inside an intact cranium containing cerebrospinal fluid (CSF) in ten cats five to nine days after implantation of an occlusive device through the orbit. Immediate neurological deficits included forced ambuxlation, circling, and tonic deviation of the head and neck toward the side of the occluded artery; weakness of the opposite limbs; and an apathetic or akinetic state. Two cats died within 24 hours. The other eight cats improved but secondary deficits developed in two, causing death. In two of the remaining six cats no deficits were apparent seven days later. The cerbral infarcts regularly involved the basal ganglia, internal capsule, and cortical regions, and were larger and less variable than those produced by MCA occlusion through and open optic foramen or craniectomy with cranial decompression by drainage of CSF. This model of acute focal cerebral ischemia may be of value for studies of physiological and biochemical factors uninfluenced by sedatives, anesthesia, or recent surgical procedures.