Temporal dynamics of degenerative and regenerative events associated with cerebral ischemia in aged rats

BACKGROUND AND PURPOSE: The age-related decline in plasticity of the brain may be one factor underlying the poor functional recovery after stroke. In the present work we tested the hypothesis that the attenuation of neural plasticity could be the result of an age-related REDUCTION in the upregulation of factors promoting brain plasticity (microtubule-associated protein 1B [MAP1B], beta-amyloid precursor protein [betaAPP]), and an age-related INCREASE in glial reactivity and the accumulation of Abeta, a proteolytic cleavage product of betaAPP with neurotoxic properties. METHODS: Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 3- and 20-month-old male Sprague-Dawley rats. The functional outcome was assessed in neurobehavioral tests 3, 7, 14 and 28 days after surgery. At the indicated time points, brains were removed and immunostained for glial cells. Abeta, as well as the markers of brain plasticity, betaAPP and MAP1B. RESULTS: Histologically, in young rats there was a gradual activation of both microglia and astrocytes that peaked by days 14-28 with the formation of a glial scar. In contrast, aged rats showed an accelerated astrocytic and microglial reaction that peaked in the first week after stroke. The expression patterns of a growth-associated phenotype of betaAPP as well as with MAP1B accumulation in varicosities along axons in cortical areas affected by stroke peaked between days 14 and 28 in young animals. In aged rats their expression was both delayed (28 days) and reduced. In addition the carboxy terminal fragment of betaAPP steadily accumulated over time and reached a maximum by day 14 in aged rats as compared to 28 days in young rats. CONCLUSIONS: These results suggest that a temporally anomalous gliotic reaction to cerebral ischemia in aged rats in conjunction with a late and limited upregulation of neuronal plasticity proteins as well as a diminished neurogenesis potential lead to the prevalence of scar tissue that impedes functional recovery from stroke.     

Temporal arteritis.

Temporal arteritis, like tuberculosis and syphilis, is a disease of protean manifestations. No single clinical symptom, sign or laboratory test can be relied upon for establishing the diagnosis. Hamilton [1] emphasizes the importance of a detailed analysis of each case—“More often than not the latter (physical findings indicative of active arteritis) are absent and a history indicating the likelihood of an arteritis is obtained only when probing questions are asked by one who is fully cognizant of the varied symptoms and signs this disorder may induce.” In dealing with geriatric patients, the clinician should maintain a high index of suspicion for temporal arteritis. Unexplained fever, malaise, depression, anemia or even carpal tunnel syndrome may be the initial presentation of the disease.The erythrocyte sedimentation rate is usually an accurate aid to diagnosis and clinical monitor of disease suppression during treatment. Realizing that active arteritis can exist without an abnormality in the erythrocyte sedimentation rate in some instances, the clinician must not ignore symptoms or signs consistent with the disease when the erythrocyte sedimentation rate is normal.Palpatory abnormalities need not be present before arterial biopsy reveals active arteritis. Pathologic abnormalities may be confined to short segments thereby making unilateral arterial biopsies inconclusive in eliminating the diagnosis. Contralateral biopsies have been positive in 53 per cent of one series. With appropriate corticosteroid intervention, the clinician can prevent the major threat from temporal arteritis—blindness.     

Evaluation of vision in slow-stream wards.

Two hundred and twenty-one patients in slow-stream geriatric wards in the Portsmouth district were questioned about their vision; 159 of these were examined. It was possible to give help with vision to 21 per cent of patients and to give a further 6 percent help with other eye problems. Eighteen months later, when half the patients examined had died, 14 per cent of those still alive were continuing to enjoy their improved vision, and 6 per cent were benefitting from the help they had received with other eye problems. As a result, we recommend that all admissions should be assessed with regard to their visual ability and that all those with adequate mental faculties should be examined by an ophthalmologist or an optician on admission and when necessary therafter.     

Temporal comparisons in bacterial chemotaxis.

Responses of tethered cells of Escherichia coli to impulse, step, exponential-ramp or exponentiated sine-wave stimuli are internally consistent, provided that allowance is made for the nonlinear effect of thresholds. This result confirms that wild-type cells exposed to stimuli in the physiological range make short-term temporal comparisons extending 4 sec into the past: the past second is given a positive weighting, the previous 3 sec are given a negative weighting, and the cells respond to the difference. cheRcheB mutants (defective in methylation and demethylation) weight the past second in a manner similar to the wild type, but they do not make short-term temporal comparisons. When exposed to small steps delivered iontophoretically, they fail to adapt over periods of up to 12 sec; when exposed to longer steps in a flow cell, they partially adapt, but with a decay time of greater than 30 sec. cheZ mutants use a weighting that extends at least 40 sec into the past. The gain of the chemotactic system is large: the change in occupancy of one receptor molecule produces a significant response.     

How photons start vision.

Recent studies have elucidated how the absorption of a photon in a rod or cone cell leads to the generation of the amplified neural signal that is transmitted to higher-order visual neurons. Photoexcited visual pigment activates the GTP-binding protein transducin, which in turn stimulates cGMP phosphodiesterase. This enzyme hydrolyzes cGMP, allowing cGMP-gated cationic channels in the surface membrane to close, hyperpolarize the cell, and modulate transmitter release at the synaptic terminal. The kinetics of reactions in the cGMP cascade limit the temporal resolution of the visual system as a whole, while statistical fluctuations in the reactions limit the reliability of detection of dim light. Much interest now focuses on the processes that terminate the light response and dynamically regulate amplification in the cascade, causing the single photon response to be reproducible and allowing the cell to adapt in background light. A light-induced fall in the internal free Ca2+ concentration coordinates negative feedback control of amplification. The fall in Ca2+ stimulates resynthesis of cGMP, antagonizes rhodopsin's catalytic activity, and increases the affinity of the light-regulated cationic channel for cGMP. We are using physiological methods to study the molecular mechanisms that terminate the flash response and mediate adaptation. One approach is to observe transduction in truncated, dialyzed photoreceptor cells whose internal Ca2+ and nucleotide concentrations are under experimental control and to which exogenous proteins can be added. Another approach is to observe transduction in transgenic mouse rods in which specific proteins within the cascade are altered or deleted.     

Submillisecond events in protein folding.

The pathway of protein folding is now being analyzed at the resolution of individual residues by kinetic measurements on suitably engineered mutants. The kinetic methods generally employed for studying folding are typically limited to the time range of > or = 1 ms because the folding of denatured proteins is usually initiated by mixing them with buffers that favor folding, and the dead time of rapid mixing experiments is about a millisecond. We now show that the study of protein folding may be extended to the microsecond time region by using temperature-jump measurements on the cold-unfolded state of a suitable protein. We are able to detect early events in the folding of mutants of barstar, the polypeptide inhibitor of barnase. A preliminary characterization of the fast phase from spectroscopic and phi-value analysis indicates that it is a transition between two relatively solvent-exposed states with little consolidation of structure.     

Early events in acute pancreatitis.

Studies using experimental models indicate that the earliest changes in acute pancreatitis involve intra-acinar cell events including the co-localization of lysosomal hydrolases with digestive enzyme zymogens. This co-localization phenomenon leads to trypsinogen activation and subsequent cell injury. Following acinar cell injury, a series of extra-acinar cell changes determine the severity of pancreatitis by promoting or reducing the inflammatory response and by influencing cell death events. Most patients with pancreatitis are diagnosed when acinar cell injury has already occurred. Therapies designed to modify the subsequent extra-acinar cell inflammatory process may prove useful in the management of clinical pancreatitis.     

Possible cellular events in leukemia.

An immunologically unresponsive state induced in experimental animals can be modulated by a number of procedures. Such modulation can result in the termination of the unresponsive state if there exists a normal complement of immunocompetent B cells in the presence of unresponsive T cells. It is possible to bypass the T cells and activate the B cells to respond to otherwise tolerated antigens. The bypass results from supplying a second (nonspecific) signal to the B cells, which, in the presence of antigen (specific signal), permits the B cell to differentiate. The role of the T and B cells and their activation and/or inactivation in the fate of both leukemic cells and oncogenic viruses is discussed.     

Peripheral vision suppression of melatonin.

The suppression of melatonin by bright light is probably mediated by the suprachiasmatic nucleus (SCN) in humans. In animals, SCN cells have broad visual receptive fields, suggesting that peripheral bright light could be effective for melatonin suppression. Twelve healthy subjects were subjected to 1000 lux illumination for 2 hr from 0100 to 0300 on two occasions: once lighting the central visual field 5 degrees from the center of gaze and once lighting the peripheral visual field 60 degrees lateral to the direction of gaze. Six subjects were observed on a third occasion in dim light. The three conditions differed significantly, with less melatonin secreted in 1000 lux, but melatonin levels with central and peripheral illumination did not differ. This suggests that phototherapy using bright light in the visual periphery may be effective.     

Temporal sequence of major biochemical events during Blood Bank storage of packed red blood cells

Background.

We used sensitive spectroscopic techniques to measure changes in Band 3 oligomeric state during storage of packed red blood cells (RBC); these changes were compared to metabolic changes, RBC morphology, cholesterol and membrane protein loss, phospholipid reorganisation of the RBC membrane, and peroxidation of membrane lipid. The aim of the study was to temporally sequence major biochemical events occurring during cold storage, in order to determine which changes may underlie the structural defects in stored RBC.

Materials and methods.

Fifteen RBC units were collected from normal volunteers and stored under standard blood bank conditions; both metabolic changes and lipid parameters were measured by multiple novel assays including a new mass spectrometric measurement of isoprostane (lipid peroxidation) and flow cytometric assessment of CD47 expression. Band 3 oligomeric state was assessed by time-resolved phosphorescence anisotropy, and RBC morphology by microscopy of glutaraldehyde-fixed RBC.

Results.

Extracellular pH decreased and extracellular potassium increased rapidly during cold storage. Band 3 on the RBC membrane aggregated into large oligomers early in the storage period and coincident with changes in RBC morphology. Membrane lipid changes, including loss of unesterified cholesterol, lipid peroxidation and expression of CD47, also changed early during the storage period. In contrast loss of acetylcholinesterase activity and haemolysis of RBC occurred late during storage.

Discussion.

Our results demonstrate that changes in the macromolecular organisation of membrane proteins on the RBC occur early in storage and suggest that lipid peroxidation and/or oxidative damage to the membrane are responsible for irreversible morphological changes and loss of function during red cell storage.     

Salient life events in three-generation families.

A short, simple procedure for eliciting salient life events is reported in this article. Respondents from three-generation families were asked to list events that had had an impact on them and their families. Responses were examined for content, criterion, and construct validity. The 10 events listed by 10% of at least one generation were major life cycle markers: Six (marriage, childbirth, divorce, retirement, widowhood, and ill health) pertained to the individuals, and four (marriage, birth, divorce, and ill health) pertained to their extended family networks. The expected relationship between events and depression (CES-D) was observed: The importance of low frequency events was reflected in their relationship to depression in the middle-aged and youngest generations. The importance of network events was reflected both in their presence on the lists of all age groups, and in their relationship to depression in the youngest generation.     

Motile events in pancreatic endocrine cells.

Monolayer cultures of neonatal rat endocrine pancreatic cells were examined by time lapse cinematography. Motion analysis revealed two major types of motile events. On one hand, particles (0.3 micrometers in diameter) tentatively identified as secretory granules were found to undergo back and forth saltatory movements along oriented pathways. The existence of such pathways was statistically validated by the large prevalence of angles close to either 0 degrees of 180 degrees between successive movements of the same particle. The movements occurred at a mean speed of 0.8 micrometers/sec. Glucose (16.7 mM) increased the frequency of such movements. Vincristine (10 microM) caused a progressive inhibition of saltatory movements, which may depend, therefore, on the integrity of the microtubular apparatus. On the other hand, areas of the cell boundary displayed contractile-like movements, which were stimulated by insulinotropic agents, such as glucose and the ionophore A23187. Cytochalasin B also affected this second type of motile event, which is thought to reflect the activity of actin-like microfilaments. These findings suggest that the microtubular apparatus serves as a guiding cytoskeleton for the oriented translocation of secretory granules, whereas the microfilamentous cell web may control the eventual access of the granules to exocytotic sites.     

Cerebral disorders of vision in systemic lupus erythematosus.

Sensory neuroophthalmic abnormalities due to cerebral lupus erythematosus, with involvement of visual pathways posterior to the optic chiasm, occurred in 12 patients with systemic lupus erhthematosus. Five underwent detailed evaluation because of an hallucination, 4 for visual loss, and 3 for both. Hallucinations were either unformed (for example, bright lights, straight lines) or highly formed (for example, faces), in which case they were invariably recognized by the patient as inappropriate. In no instance did they occur in association with delirium, confusion, or use of hallucinogenic drugs. Patients with loss of vision had scotomas, homonymous field defects, and cortical blindness. These features indicate disease in the posterior cerebral artery circulation, a localization often supported by ancillary neurologic findings, for example, vocal cord paralysis, diminished gag reflex. Thus, various visual dysfunctions may occur in systemic lupus erythematosus due to cerebral vasculitis. At times they may be the most prominent and disabling feature of the disorder.     

Primary photochemical event in vision: proton translocation.

Picosecond studies of rhodopsin in low-temperature glasses have been carried out in order to observe directly the risetime of prelumirhodopsin, the first intermediate in the visual pathway. Only at 20 K or below can the risetime of this intermediate be resolved and even at 4 K it is astoundingly rapid, about 36 psec. An examination of the Arrhenius dependence on temperature of the rate of formation of prelumirhodopsin shows a strong deviation from linearity at low temperatures, i.e., non-Arrhenius behavior. This marked non-linear behavior is characteristic of a quantum mechanical tunneling event such as the translocation of hydrogen. An excellent candidate for the tunnelling process is the hydrogen of the protonated Schiff base formed between opsin and its retinal chromophore. Deuterium-exchanged rhodopsin, in which the Schiff base hydrogen is replaced by a deuterium, also shows a marked non-Arrhenius temperature dependence at low temperatures, consistent with tunneling. The rate of formation of prelumirhodopsin in deuterium-exchanged samples is much slower and a deuterium isotope effect kH/kD approximately or equal to 7 is observed. The data support a model in which the formation of prelumirhodopsin involves translocation of a proton toward the Schiff base nitrogen of the retinal chromophore.