Role of nitric oxide in the cerebral circulation during hypotension after hemorrhage, ganglionic blockade and diazoxide in awake goats

The role of nitric oxide in cerebrovascular response to hypotension was analyzed by evaluating the changes in cerebrovascular resistance after inhibition of nitric oxide synthesis with Nw-nitro-L-arginine methyl ester (L-NAME) during three types of hypotension in conscious goats. Blood flow to one brain hemisphere was electromagnetically measured, hypotension was induced by controlled bleeding, and by i.v. administration of hexametonium (ganglionic blocker) or of diazoxide (vasodilator drug), and L-NAME was injected by i.v. route (35 mg kg-1). Under control conditions (13 goats), L-NAME increased arterial pressure from 98 +/- 3 to 123 +/- 4 mmHg and decreased cerebral blood flow from 65 +/- 3 to 40 +/- 3 ml min-1 (all P < 0.001); cerebrovascular resistance increased from 1.52 +/- 0.04 to 3.09 +/- 0.013 mmHg ml-1 min-1 (P < 0.01) (delta = 1.59 +/- 0.12 mmHg ml-1 min-1). After bleeding (five goats), mean arterial pressure decreased to 60 +/- 4 mmHg and cerebral blood flow decreased to 37 +/- 4 ml min-1 (all P < 0.01); cerebrovascular resistance did not change (1.56 +/- 0.14 vs. 1.54 +/- 0.12 mmHg ml-1 min-1, P > 0.05). During this hypotension, L-NAME increased arterial pressure to reach the normotensive values an did not affect the hypotensive values for cerebral blood flow; cerebrovascular resistance increased from the hypotensive values to 2.91 +/- 0.19 mmHg ml-1 min-1 (P < 0.01) (delta = 1.37 +/- 0.16 mmHg ml-1 min-1), and this increment is comparable to that under control conditions (P > 0.05). Ganglionic blockade (six goats) decreased arterial pressure to 67 +/- 2 mmHg) and did not affect significantly cerebral blood flow; cerebrovascular resistance decreased from 1.71 +/- 0.11 to 1.05 +/- 0.09 mmHg ml-1 min-1 (P < 0.01). During this hypotension, L-NAME increased arterial pressure to 103 +/- 6 mmHg (P < 0.001), and did not affect cerebral blood flow; cerebrovascular resistance increased from the hypotensive values to 1.68 +/- 0.18 mmHg ml-1 min-1 (P < 0.01) (delta = 0.63 +/- 0.10 mmHg ml-1 min-1), and this increment was lower than under control conditions (P < 0.01). Diazoxide (six goats) decreased arterial pressure to 69 +/- 5 mmHg (P < 0.01) without changing cerebral blood flow; cerebrovascular resistance decreased from 1.89 +/- 0.11 to 1.16 +/- 0.14 mmHg ml-1 min-1 (P < 0.01). During this hypotension, L-NAME increased arterial pressure to 87 +/- 6 mmHg (P < 0.05) and did not affect the hypotensive values for cerebral blood flow (P > 0.05); cerebrovascular resistance increased from the hypotensive values to 1.53 +/- 0.13 mmHg ml-1 min-1 (P < 0.05) (delta = 0.36 +/- 0.06 mmHg-1 ml-1 min-1), and this increment was lower than under control conditions (P < 0.01). Therefore, the role of nitric oxide in cerebrovascular response to hypotension may differ in each type of hypotension, as this role during hemorrhagic hypotension may not change and during hypotension by ganglionic blockade or diazoxide may decrease. These differences may be related to changes in nitric oxide release as stimuli on the endothelium (shear stress and sympathetic activity) may vary in each type of hypotension.     

Brain-specific protein C activation during carotid artery occlusion in humans

BACKGROUND AND PURPOSE: Activation of plasma protein C (PC) zymogen by thrombin-thrombomodulin at the endothelial surface is an important endogenous antithrombotic mechanism. It is unknown whether activated protein C (APC) is generated in vivo in the cerebrovasculature, because there is only limited thrombomodulin expression in human brain vascular endothelium. Therefore, we tested the hypothesis that carotid occlusion produces brain-specific PC activation. METHODS: Blood samples were simultaneously collected from the ipsilateral internal jugular vein and radial artery before and during carotid cross-clamping and on "de-occlusion" in 8 awake patients undergoing routine carotid endarterectomy. Plasma PC zymogen and circulating APC levels were measured using enzyme immunocapture assay and expressed as percent of pooled plasma controls. RESULTS: Internal jugular vein APC levels increased 28% exclusively during carotid occlusion and then decreased 32% with de-occlusion (F=8.1, P<0.005). PC zymogen increased only 5.9% with occlusion (F=6.3, P<0.02), consistent with hemoconcentration. There were no changes in radial artery PC or APC levels. CONCLUSIONS: These findings demonstrate brain-specific protein C activation in humans during carotid occlusion and suggest a protective role for endogenous APC generation during cerebrovascular occlusion.     

Growth factors effects on the expression of morphological and biochemical properties of avian embryonic sympathetic cells. Emphasis on NGF

Growth factors are known to be important agents in the differentiation and modulation of neuronal phenotypes. We have analyzed the effect of several growth factors on the modulation of morphological and biochemical properties of avian embryonic sympathetic neurons. The growth factors studied include: nerve growth factor (NGF), neurotrophin-3 (NT-3), brain derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), basic fibroblast growth factor (bFGF) and transforming growth factor beta-1 (TGF-beta1). Morphological properties were analyzed by immunocytochemistry to neurofilament proteins and visualization of fibers after glyoxylic acid-induced fluorescence. Biochemical modulation was determined by radioimmunoanalysis for the peptides enkephalin (ENK), somatostatin (SS) and neuropeptide Y (NPY) and by HPLC-electrochemistry quantification of catecholamines. Similar to previous results using chromaffin cell cultures [R. Ramírez-Ordó?ez, J.E. García-Arrarás, Peptidergic, catecholaminergic and morphological properties of avian chromaffin cells are modulated distinctively by growth factors, Dev. Brain Res., 87 (1995) 160-171], we found a dissociation in the modulation of biochemical and morphological properties, however, the effect of specific factors differed between the chromaffin and sympathetic cultures. We have focused on NGF to analyze its effect on the sympathetic peptide phenotypes and its lack of an effect on the chromaffin cell peptide phenotypes. The results presented here, establish interesting differences between chromaffin cells and sympathetic neurons that are of importance to studies of cell lineage and differentiation.     

Early postnatal treatment with ACTH4-9 analog ORG 2766 improves adult spatial learning but does not affect behavioural stress reactivity

Studies on adult animals and humans have shown that the ACTH4-9 analog ORG 2766 influences cognitive performance and possibly has neurotrophic effects. For this reason we studied the effect of ORG 2766 applied in early postnatal life when brain structures and neuronal pathways are still developing. Our aim was to see whether such treatment during development would result in permanent changes in adult behavioural performance. Pups received subcutaneous injections of 1 microg/g bodyweight ACTH4-9 analog ORG 2766 on day 1, 3 and 5 after birth. Control animals in the same nest received saline injections. When the animals had reached an adult age of 3 months they were subjected to a series of tests to measure their behavioural performance. In the first experiment, behavioural stress responses and anxiety were measured by subjecting the rats to the following tests: open field, defensive burying, elevated plus maze, and conditioned fear test. In a second experiment, adult cognitive function was measured in the Morris water-maze, a hippocampus-related spatial learning test, and in the active avoidance test, a more amygdala-related nonspatial test. The results showed that animals treated with ORG 2766 during early postnatal life learned faster in the spatial Morris water-maze. The treatment had a positive effect on performance during the acquisition phase of the learning task, while memory retrieval was not affected. Learning in the nonspatial active avoidance task did not change due to the postnatal ACTH4-9 treatment. In addition, there were no differences in the open field test, the defensive burying test, elevated plus maze and the conditioned fear test. The latter supports the conclusion that the differences in water-maze performance was due to a difference in learning speed, rather than a difference in anxiety or behavioural stress reactivity. Analysis of [3H]CORT binding capacity measured after the learning tests revealed no differences in the hippocampal MR and GR concentration between non-treated and treated animals.     

Neuroprotective agents

In the last decade, a huge number of drugs have been developed in order to block the different molecular reactions of the ischemic cascade. Most of neuroprotective compounds decrease infarct volume in experimental stroke models, but none of them has reduced stroke mortality and morbidity in clinical trials. This article comments those factors that justify discrepancies between the laboratory and clinical findings, and reviews the neuroprotective drugs studied in patients with acute ischemic stroke. Although the clinical investigation of many of them has been abandoned because safety concerns, preliminary observations suggest a beneficial effect of ebselen, a compound with antioxidant activity, and citicoline, a stabiliser of cell membranes. Other neuroprotective drugs like trafermin and glycine antagonists are in advanced clinical investigation, thus the neuroprotection scenario may favourably change in the near future.     

The developing profile of cerebral ischemia

Cerebral ischemia, which may be silently manifested as transitory ischemia attacks or cerebral infarction, is not a stable, but rather, a moving process. In cerebral infarctions the initial ischemic area may change or move in a high percentage of patients and may involve a significant volume (mean of 32%) of neuronal tissue. The negative changes of initial cerebral ischemia which produce a worsening of the same may be due to the progression of the thrombus, appearance of new embolisms, cerebral edema, hemorrhage, blood reperfusion and systemias causes. These changes may determine the conversion of the shaded ischemic area into a definitive, irreversible infarction. The negative changes may also be produced some distance from the initial ischemic area, either because of microthromboembolisms or diaschisis. The positive changes of initial cerebral ischemia which produce as improvement of the same, may be due to collateral circulation, lysis or fragmentation of the embolism and a decrease in cerebral edema. Clinical changes with no evident clinical manifestations may also be produced and may be diagnosed with the use of clinical scales, imaging techniques, ultrasound and hematological and biochemical markers. Acknowledgement of these cerebral ischemia changes in the acute phase may determine the salvation of a part of the brain, and thereby modify the future clinical situation of the patient.     

Partial Currarino syndrome in a non-pediatric patient. A rare cause of bacterial meningitis

Enterogenic meningitis is an infrequent cause of central nervous system infection. Among these causes the Currarino syndrome may be found presenting sacral agenesis, presacral mass and anorectal stenosis. This syndrome normally causes enterogenic meningitis in the early years of life. The case reported corresponds to a 24-year-old male presenting polymicrobial meningitis with fecal flora germs (anerobic enterococci, Bacteroides fragilis and Escherichia coli). These clinical findings led to radiologic lumbar study with the diagnosis of Currarino syndrome. The existence of neuroenteric fistulas justifies the development of fecal flora meningitis. The nosology of the syndrome as well as the therapeutic strategy are reviewed.     

Inducible genetic suppression of neuronal excitability.

Graded, reversible suppression of neuronal excitability represents a logical goal of therapy for epilepsy and intractable pain. To achieve such suppression, we have developed the means to transfer "electrical silencing" genes into neurons with sensitive control of transgene expression. An ecdysone-inducible promoter drives the expression of inwardly rectifying potassium channels in polycistronic adenoviral vectors. Infection of superior cervical ganglion neurons did not affect normal electrical activity but suppressed excitability after the induction of gene expression. These experiments demonstrate the feasibility of controlled ion channel expression after somatic gene transfer into neurons and serve as the prototype for a novel generalizable approach to modulate excitability.     

beta-amyloid deposition and neurofibrillary tangle formation in the olfactory bulb in ageing and Alzheimer's disease

Impaired olfaction, hyposmia or anosmia are part of the clinical phenotype in neurodegenerative disorders including Alzheimer's disease (AD). It has been proposed that the most severely affected areas are interconnected with the central olfactory system in contrast to the relative sparing of other sensory areas which lack olfactory connections. The pathology of the first synaptic relay in the olfactory pathway, the olfactory bulb (OB), has been studied in AD, but the results have been inconsistent. In order to define more fully the pathology of the OB, we analysed 15 AD and 15 control cases, using amyloid and tau immunohistochemistry on serial sections. This study demonstrates for the first time that all layers of the OB are severely affected in AD and in normal ageing. The principal effector cells of the OB, the mitral cells, developed neurofibrillary tangles (NFTs) both in AD and in controls. All the cases, with the exception of two of the controls, contained NFTs. Amyloid immunoreactivity was detected in diffuse, primitive, classical and compact deposits in AD, while five control cases contained mainly diffuse deposits. We did not find a correlation between amyloid deposition and NFT formation. Among the control cases, two contained neither amyloid nor NFTs, eight had NFTs but no amyloid and only five had both NFTs and amyloid. All the AD cases had NFT and amyloid deposition. Our data suggest that the earlier pathology in the OB is NFT formation and more than ten NFTs/section is compatible with 93.3% diagnostic accuracy for AD.