J.C. de la Torre

Can disturbed brain microcirculation cause Alzheimer's disease?

Recent ultrastructural studies demonstrate characteristic and extensive angioarchitectural distortions of cerebral capillaries in Alzheimer’s brains. Alzheimer’s disease subjects additionally show ...

Chronic cerebrovascular insufficiency induces dementia-like deficits in aged rats

Young and aged rats were subjected to cerebrovascular insufficiency (CVI) for 3 and 9 weeks. At the end of each time period, local cerebral blood flow (lCBF), spatial memory function, 31P- and 1H-NMR spectroscopy and imaging of the brains were evaluated in vivo. Morphometric counts of CA1 hippocampal neuron damage and staining for glial fibrillary acidic protein (GFAP) were done post-mortem. Results show that after 3 weeks of CVI, cortical and hippocampal lCBF was significantly reduced in young and aged animals respectively. In addition, young and aged rats at 3 weeks following CVI showed spatial memory deficits in the Morris water maze and elevation of 31P-phosphomonoester as measured by non-invasive NMR spectroscopy. At the same time period, in vivo 1H-microimaging (MRI) of brains showed areas of high signal intensity (suggesting local edema) localized asymmetrically to the right hippocampal region in young and aged CVI rats. Morphometry of the hippocampal CA1 sector at post-mortem confirmed the in vivo MRI changes and demonstrated that a significant percentage of the CA1 pyramidal cells were damaged after CVI. Nine weeks after CVI, hippocampal CBF reductions, spatial memory impairment, spectroscopic-microimaging changes and CA1 sector cell damage continued to be observed in the aged animals but were resolved in the young rat brains. In addition, GFAP immunoreaction progressively increased in the hippocampus of aged rats subjected to CVI for 9 weeks. It is concluded that cognitive, metabolic and morphologic damage was significantly more severe and longer lasting in aged than young rat brain after chronic CVI. The deficits observed in this rat model appear to mimic the early pathology reported in Alzheimers disease and suggest that the present model could provide fundamental clues relative to the etiology and possible management of this dementia.

Cerebral hypoperfusion yields capillary damage in the hippocampal CA1 area that correlates with spatial memory impairment

The impact of chronic cerebral hypoperfusion on cognitive function and cerebral capillary morphology in the hippocampus was examined. Young adult Wistar rats were subjected to permanent ligation of both common carotid arteries (two-vessel occlusion). One month after vascular occlusion, a small but non-significant impairment in the acquisition of spatial information was registered compared with sham-operated controls. Two months after surgery, the occluded animals displayed an impaired performance throughout the training period. One year after surgery, the acquisition curves demonstrated a significant attenuation of the learning rate in the occluded rats group, whereas no significant differences in long-term retention were observed. Thus, chronic hypoperfusion induced by two-vessel occlusion gave rise to impairment of spatial memory. Following behavioural testing, the rats were killed at the age of 17 months, and capillaries in the CA1 and dentate gyrus were examined using transmission electron microscopy. Typical age-related capillary abnormalities such as degenerative pericytes and thickened basement membranes (with or without fibrosis) were detected in the hippocampus of sham animals. In occluded rats, the occurrence of capillaries displaying such abnormalities almost doubled in the CA1 region, but was similar in the dentate gyrus, compared with sham controls. A highly significant correlation was found between the last Morris maze performance and the percentage of capillaries with deposits in the basement membrane in the hippocampal CA1 area of occluded rats, which was not present in the sham animals. We conclude that a long-term hypoperfusion accelerated the development of age-related ultrastructural aberrations of capillaries in the hippocampal CA1 area, but not in the dentate gyrus. Thus, not only neurons, but also capillaries in the hippocampal CA1 area are sensitive to an impaired microcirculation. Moreover, the cognitive performance of hypoperfused rats correlated closely with the condition of the capillaries in the CA1 area, suggesting that capillary integrity is one of the important determinants of brain function in conditions that compromise cerebral microcirculation.

Hemodynamic Consequences of Deformed Microvessels in the Brain in Alzheimer's Disease

ABSTRACT: The cause of sporadic Alzheimers disease (AD) remains a mystery. Mounting clinical and experimental data, however, suggest that a cerebral hemodynamic role may affect neuronoglial metabolism. Light and electron microscopy have consistently revealed that the microvasculature in AD brains contains structurally deformed capillaries which create a distorted intraluminal conduit for blood flow. The cerebral capillary distortions can create “disturbed” rather than “laminar” blood flow. Chronically disturbed capillary blood flow will impair normal delivery of essential nutrients to brain neurons as well as impede catabolic outflow of CNS waste products. This condition will negatively affect cerebral metabolism, primarily because of impaired glucose delivery to neurons. Impaired glucose delivery to AD brain results in a patho‐chemical cascade that will impair the Na+, K+‐ATPase ion pump and affect the syntheses of ATP, acetylcholine, and other neurotransmitters. The outcome of this metabolic dysfunction can promote neurofibrillary tangle and senile plaque formation in AD brain.

Reduced cytochrome oxidase and memory dysfunction after chronic brain ischemia in aged rats

The effects of chronic cerebrovascular ischemia on memory function and cytochrome oxidase (CO) activity were investigated. Cerebrovascular insufficiency was induced by permanent bilateral carotid artery ligation (2-VO) in 19 month old rats. Sham surgery in no-vessel occlusion (no-VO) rats were used for controls. Memory function was tested 1 week prior to surgery and then weekly for 21 days using the Morris water maze. Regional brain activity of CO was measured 4 weeks after surgery by quantitative histochemistry. Histologic examination of brain slices was used to evaluate any neuropathology present. Results showed that 2-VO rats were significantly impaired in the water maze task at each testing period with respect to no-VO controls. In addition, CO activity in 2-VO rats was markedly reduced only in the dorsal CA1 region of the hippocampus and in the posterior parietal cortex. These brain regions are involved in visuo-spatial memory mechanisms. Analysis of other brain regions in 2-VO rats did not reveal further CO activity changes. There were no damaged or loss of neurons in 2-VO or no-VO groups in any region examined, including CA1 and posterior parietal cortex. The CA1 region however, is known to undergo neuronal loss 25 weeks after chronic 2-VO suggesting that this vascular insult can induce a slowly-evolving cascade consisting of neuronal damage, atrophy and death. The present findings indicate that reduced CO activity in CA1 and posterior parietal regions can predict neural damage and atrophy prior to structural perikaryal pathology following chronic brain ischemia. In addition, the data shows that neuronal energy metabolic deficiency may initiate visuo-spatial memory impairment in this aging rat model.

Hippocampal nitric oxide upregulation precedes memory loss and Aβ 1-40 accumulation after chronic brain hypoperfusion in rats

Abstract Chronic brain hypoperfusion (CBH) using permanent occlusion of both common carotid arteries in an aging rat model, has been shown to mimic human mild cognitive impairment (MCI), an acknowledged high risk condition that often converts to Alzheimers disease. An aging rat model was used to determine whether hippocampal nitric oxide (NO) is abnormally expressed following CBH for two or eight weeks. At each time point, spatial memory was measured with the Morris water maze and hippocampal Aβ 1-40/1-42 concentrations were obtained using sandwich ELISA. Real-time amperometric measures of NO representing the constitutive isoforms of neuronal nitric oxide synthase (nNOS) and endothelial (e)NOS were also taken at each time point to ascertain whether NO levels changed as a result of CBH, and if so, whether such NO changes preceded or followed any memory or amyloid-beta pathology. We found that two weeks after CBH, NO hippocampal levels were upregulated nearly four-fold when compared to nonoccluded rats but no alteration in spatial memory of Aβ products were observed at this time point. By contrast, NO concentration had declined to control levels by eight weeks but spatial memory was found significantly impaired and Aβ 1-40 (but not Aβ 1-42) had increased in the CBH group when compared to control rats. Since changes in shear stress are known to upregulate eNOS but generally not nNOS, these results suggest that shear stress induced by CBH hyperactivated vascular NO derived from eNOS in the first two weeks as a reaction by the capillary endothelium to maintain homeostasis of local cerebral blood flow. The return of vascular NO to basal levels after eight weeks of CBH may have triggered metabolic changes within hippocampal cells resulting in hippocampal dysfunction as reflected by spatial memory impairment and by accumulation of Aβ 1-40 peptide. In conclusion, our study shows that CBH initiates spatial memory loss in aging rats thus mimicking human MCI and also increases Aβ 1-40 in the hippocampus. The memory and amyloid changes are preceded by NO upregulation in the hippocampus. These preliminary findings may be important in understanding, at least in part, the molecular mechanisms that precede memory impairment during chronic brain ischemia and as such, the pre-clinical stage leading to Alzheimers disease.

A chronic physiological rat model of dementia

We have developed an aging rat model that mimics specific pathology reported in dementia, particularly Alzheimers disease (AD). The model involves subjecting rats to chronic cerebrovascular insufficiency (CVI) for 1-9 weeks. Gross and sensory-motor function remains normal but spatial memory acquisition and retention are impaired after 1 week and worsens progressively with time. In vivo [31P]NMR spectroscopy evaluation in CVI animals showed membrane phospholipid synthesis increase in the hippocampal-cortex region of affected animals which increases with time. Post-mortem examination revealed that CA1 neurons can express selective damage 1 week after CVI and the number of CA1 neurons thus affected increases in proportion with time. MOreover, there is progressive increase in GFAP hypertrophy and hyperplasia in the hippocampal region during the 9-week observation period. Reduction of microtubule-associated protein 2 and pre-terminal noradrenergic varicosities in the hippocampus-cortex is seen after 9 weeks but not 1 week of CVI. All the above changes have been reported in AD-affected brains. The present CVI model appears as a useful screen in investigating potential therapy for AD as well as increasing understanding of this disorder.

Axonal regeneration after spinal cord transection and reconstruction

Following complete transection of the spinal cord, cats were separated into 2 groups to undergo: (i) surgical reconstruction of the disconnected cord using a neuroactive agent mixed into a collagen matrix bridge and omental transposition and (ii) cord transection-only. After 90 days, animals were killed and the brain and spinal cord were removed for immunohistochemistry. Two weeks prior to sacrifice, spinal cord blood flows were measured and the retrograde axonal tracer Fluoro-Gold was injected below the transection site. Gross inspection of the spinal cords at autopsy showed excellent integration and continuity of the collagen matrix bridge with the proximal-distal stumps in the surgical reconstruction group. In the transection-only group, the proximal-distal stumps were connected by a fibrotic, often tapered in the middle, tissue bridge. Results show that omental transposition in the surgical reconstruction group increased spinal cord blood flow by 58% when compared to transection-only animals. Fluoro-Gold was found in mesencephalic and brainstem catecholaminergic and cholinergic neurons known to send axons to the spinal cord. Immunohistochemical staining with antibodies against catecholamine synthesizing enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) showed that surgical reconstruction treated cat cords but not transection-only, developed dense bundles of dopaminergic and noradrenergic fibers which were present in the collagen matrix bridge and in the distal spinal cord. Extension of these catecholaminergic fibers in surgical reconstruction treated cats showed maximal outgrowth of 90 mm below the transection site when the neuroactive agent 4-aminopyridine was mixed into the collagen matrix. In addition, the synaptogenic marker synaptophysin (SYN) was observed on preganglionic sympathetic neurons in association with dopaminergic- and noradrenergic-containing varicosities distal to the collagen matrix bridge, an indication that neo-synaptic contacts may have been made on these previously denervated neurons. No TH, DBH or SYN was observed below the transection site in transection-only cats. These findings indicate that surgical reconstruction treated cords can develop dense supraspinal fiber outgrowth across a treated collagen matrix bridge fed by an omental blood supply and that these fibers may have made neo-synaptic contacts with appropriate distal spinal cord target tissue.

Collagen-omental graft in experimental spinal cord transection

SummarySpinal cord transection was induced in 3 groups of cats. The gap was surgically reconstructed using a collagen matrix bridge (Group COL), collagen matrix + pedicled omentum graft (Group COM), or gelfoam (Group GEF). After a variable observation period, animals underwent distal cord horse-radish peroxidase (HRP) injections, somatosensory evoked potentials recordings and polarographic measurement of local spinal cord blood flow (lSCBF) using the hydrogen clearance technique. The cord tissue was removed for histologic and immunohistochemical analysis.Results showed retrograde HRP labelling of proximal segmental cord neurons and somatosensory evoked potentials were present in group COM but not in COL or GEF treated animals. Local SCBF was 66% and 87% higher in COM than COL or GEF animals respectively but this increase could be reversed if flow from the pedicled omentum was clamped-off. Histologic examination of cord tissue after 45 days revealed the presence of catecholaminergic axons distal to the transection site in COM but not COL or GEF groups. Moreover, after 90 days, the rate and density of tyrosine hydroxylase immunoreactive (TH-IR) axons was 10-fold higher in COM than COL group and this was accompanied by a proportionate increase in the vascular density between the two groups. GEF treated animals showed no regeneration of transected fibers and poor blood flow pattern. These findings indicate that the placement of a pedicled omentum on a collagen matrix bridge results in near restoration of normal SCBF to the reconstructed cord region and is associated with marked regeneration of axons below the lesion site.

Dimethly sulphoxide lowers ICP after closed head trauma

SummaryTen patients with closed head trauma and elevated intracranial pressure (ICP) ranging from 40–127 mm Hg were treated with intravenous dimethyl sulphoxide (DMSO) every 6 h for 1–10 days. Four patients received DMSO and intermittent oxygen.All patients showed a reduction of ICP after 24 h and 7 had normal ICP after 6 days of treatment. Two patients died of their injuries.Neurological assessment at the time of discharge showed 2 patients with severe neurological deficits and 6 patients with mild to no deficit. After a 3 month follow-up, 1 patient remained severely impaired and 7 patients showed mild to no deficit.It appears that intravenous DMSO can rapidly reduce elevated ICP in severe closed-head injury and that it improves neurological outcome.