Further studies on platelet-mediated neurotoxicity

The mechanism of ischemic neuronal injury is not fully resolved. The present view is that vascular occlusion per se does not fully account for the extent of neurological dysfunction. We hypothesized that platelet secretory products might contribute to ischemic neuronal injury in the central nervous system (CNS) (Joseph et al., Stroke, 20 (1989) 38-44 and 1316-1319). Our preliminary studies using organotypic rat spinal cord cultures exposed to human platelet and its secretory products, revealed that platelet product(s) had neurotoxicity. Further studies, using the same methods, were conducted here, with the addition of several refinements such as use of gel-filtered platelets (as opposed to washed platelets), adding additional relevant controls including platelet membranes, red blood cells and washed rat platelets. The results confirmed our initial finding that an agent(s) in platelet secretion is neurotoxic. Subsequently, we identified serotonin (5HT), a major platelet product, as having toxic effects on neurons. This toxicity of 5HT appeared to be blocked by ketanserin, a 5HT2 receptor antagonist. Judging by the concentrations of 5HT that demonstrated neurotoxicity in these in vitro studies, it appears that products secreted from activated platelets could have pathological significance in vivo.

Neurologic evaluation and its relation to acupuncture. Acupuncture for neurologic disorders

Acupuncture provides companion animal veterinarians a valid therapeutic alternative to medicine and surgery in a variety of neurologic disorders. The veterinarian must arrive at a lesion localization in the nervous system and determine a presumptive diagnosis before instituting acutherapy. Signalment, type of neurologic disorder, efficacy of conventional treatments versus acupuncture, financial constraints, and ethical issues are useful patient selection criteria. In general, animals experiencing pain respond faster and more completely to acupuncture than those demonstrating neurologic deficits consistent with loss of function. Acupuncture offers clients a noninvasive alternative when medications are contraindicated or surgery is not an option. This chapter serves as an introduction to acupuncture for neurologic disorders in pets. It is hoped that the information here will inspire clinical investigations to evaluate more completely patient selection, patient response, and long-term outcome.

Study of platelet-mediated neurotoxicity in rat brain

BACKGROUND AND PURPOSE

The mechanism of ischemic neuronal injury is not fully resolved. The present view is that vascular occlusion per se does not fully account for the extent of neurological dysfunction. We previously hypothesized that platelet secretory products might contribute to neuronal injury in the central nervous system. Our preliminary studies using organotypic rat spinal cord cultures exposed to human platelet and its secretory products revealed that platelet products had neurotoxic properties.

METHODS

Further studies, using the same methods, were conducted, with the addition of several refinements such as use of gel-filtered platelets (as opposed to washed platelets) and adding additional relevant controls including platelet membranes, red blood cells, and washed rat platelets.

RESULTS

Exposure of spinal cord explant cultures to platelet secretory products resulted in reduced number of neurons per ventral horn compared with control.

CONCLUSIONS

Our findings suggest that platelet secretory products have neurotoxic properties. This effect was seen with platelet secretion obtained from physiological platelet concentrations. It appears possible that more abundant release of platelet products at the site of thrombus formation could have pathological significance in vivo.

Platelet activity and stroke severity

Although platelets constitute the major component of a thrombus, its role in determining the clinical severity of thrombotic stroke is unknown. Therefore, we investigated the relationship between platelet ionized calcium ([Ca2+i]), a measure of platelet activity and presumably proneness to thrombosis, and clinical stroke severity in 45 consecutively studied acute ischemic stroke patients. Even though there was no correlation between the clinical neurological scores and the levels of baseline and activated platelet [Ca2+i], stroke was less severe in patients who had been taking aspirin at the time of stroke onset. These results raise several important questions: (a) is the extent of platelet activation a reflection of thrombus volume, (b) does the clinical severity of neurological deficit reflect the causative thrombus volume, and (c) whether the beneficial effect of aspirin in stroke prophylaxis is through its inhibition of platelets alone.

Serotonin may have neurotoxic properties

Serotonin (5HT), a major platelet secretory product, has been shown to suppress CNS function in vivo. As part of an ongoing project to study interactions between neuron and platelet, we used organotypic explant cultures of rat spinal cord to study if 5HT had a morphologically demonstrable neurotoxic effect. The results suggest that serotonin may be neurotoxic, and that this effect may be prevented by ketanserin, a specific 5HT2 antagonist. Related experiments, using acetylcholinesterase (AChE) enzyme activity as a biochemical parameter, indicate that 5HT hastens the decline of enzyme activity. The concentrations of 5HT at which neurotoxicity was demonstrated were comparable to the calculated 5HT concentration potentially present in the vicinity of an acute cerebral thrombus. These findings could provide new insight into the mechanism of ischemic neuronal injury.

Platelet secretory products have a damaging effect on neurons

We studied the direct effect of platelet secretory products on rat spinal cord explants. Morphological changes in the ventral horn neurons were assessed after staining for acetylcholinesterase (AChE). Compared to control, exposure to platelet secretory products was associated with a significant decrease in the number of AChE-positive neurons per ventral horn. Aspirin appeared to partially prevent this neurotoxicity. These results suggest that platelet secretory products may contribute to neuronal injury.

Molecular characterization and in-vitro hormonal requirements for expression of two casein genes from a marsupial

Two marsupial casein genes have been isolated from a tammar wallaby (Macropus eugenii) mammary gland cDNA library. Comparisons of the tammar alpha- and beta-casein genes with their eutherian homologous reveal extensive divergence at the levels of nucleotide and amino acid sequences. Regions of similarity between the tammar and eutherian Ca(2+)-sensitive caseins are restricted to the major phosphorylation sites and the signal peptides. Quantification of casein mRNA levels in hormone-stimulated mammary gland explants from tammars in late pregnancy suggests that maximal induction of the beta-casein gene is dependent upon prolactin and insulin, while maximal induction of the alpha-casein gene is dependent upon prolactin, insulin and cortisol. These results are in contrast to earlier studies which show that the maximal induction of a putative 19 kDa casein, alpha-lactalbumin and beta-lactoglobulin in the tammar mammary gland is dependent upon prolactin alone. The expression of the latter three genes is not modulated by other hormones known to play a role in the in-vitro initiation of lactation in eutherians.

Cancer control and the older person. Psychosocial issues

Three major areas related to psychosocial issues pertinent to the provision of cancer control services to older people have been delineated. These are values and medical decision making, psychosocial barriers to screening and access to care and services, and quality of life, including rehabilitation. These areas are explored, salient issues are defined, and specific questions and areas for consideration in future research are identified at the macro and micro levels.

Platelet secretory products may contribute to neuronal injury

BACKGROUND

We do not fully understand the mechanisms for neuronal damage following cerebral arterial occlusion by a thrombus that consists mainly of platelets. The view that certain endogenous substances, such as glutamate, may also contribute to neuronal injury is now reasonably well established. Blood platelets are known to contain and secrete a number of substances that have been associated with neuronal dysfunction. Therefore, we hypothesize that a high concentration (approximately several thousand-fold higher than in plasma, in our estimation) of locally released platelet secretory products derived from the causative thrombus may contribute to neuronal injury and promote reactive gliosis.

SUMMARY OF COMMENT

We have recently been able to report some direct support for this concept. When organotypic spinal cord cultures were exposed to platelet and platelet products, a significant reduction in the number and the size of the surviving neurons occurred in comparison with those in controls. We further observed that serotonin, a major platelet product, has neurotoxic properties. There may be other platelet components with similar effect.

CONCLUSIONS

The hypothesis of platelet-mediated neurotoxicity gains some support from these recent in vitro findings. The concept could provide a new area of research in stroke, both at the clinical and basic levels.

Platelet glycine, glutamate and aspartate in primary headache

Platelet levels of glutamic and aspartic acid and glycine were measured in patients with migraine with aura, migraine without aura, tension headache and cluster headache. High levels of these amino acids were found in patients with migraine with aura compared to normal subjects and other headache groups. During headache, glutamate levels further increased in migraine with aura patients. These findings may have relevance to the neurological symptoms of migraine with aura.

De novo biosynthesis and localization of inhibin in marmoset (Callithrix jacchus) and rat epididymis

Using specific polyclonal antibodies generated against a 13 Kd human testicular inhibin, immunocytochemical localization was carried out in epididymis of intact and castrated marmoset monkey and rat epididymis. Inhibin was found to be present in the cytoplasm of epithelial cells of caput, corpus and cauda epididymis. The intensity of staining and pattern of distribution did not change following castration. Further, the in vitro biosynthesis of inhibin studied by incorporating 3H-leucine and precipitating it with specific antibody indicated maximum biosynthesis in the corpus epididymis in case of marmosets and cauda in case of rats. Following castration in rats, the epididymal tissue still retained the capacity to biosynthesize inhibin. These studies indicate that marmoset and rat epididymis are capable of biosynthesizing/absorbing inhibin and whose synthesis does not depend on androgens.

The latest theories and treatment for diabetic foot complications

Most diabetic patients will encounter ulcerations ranging from grade 0 to grade 5 during the course of their lifetime. These ulcerations, with prompt diagnosis and rapid care using a team approach, will be converted to grade 0 ulcerations with the exception of the grade 5 foot. The use of padding and shoe gear aid in healing these ulcerations once the infection is eradicated and sufficient debridement has been performed.

Endothelin-1 and human platelet activity

Endothelin-1, a peptide produced by endothelium, causes vascular smooth muscle contraction possibly by mobilizing intracellular calcium. Shifts in ionized calcium may also play a role in platelet activation. Accordingly, the effects of endothelin on platelet ionized calcium and aggregation were studied. The measurements were made in aequorin-loaded gel-filtered human platelets derived from healthy donors. Endothelin even in a final concentration of 10(-6) M did not cause a measurable change in platelet ionized calcium or aggregation. When tested in combination with collagen, thrombin and platelet activating factor, endothelin showed no synergistic effect. These observations raise the possibility that endothelin may not interact with platelets in a physiologically significant way.

Animal illness and human emotion. Neurologic problems

Clients' decisions are based on the veterinarian's ability to familiarize them with nervous system disease. Unfortunately, the nervous system does not lend itself to complete examination without advanced neurodiagnostic tests. These tests usually require general anesthesia, may be invasive, and often require advanced training. Therefore, a logical and orderly approach to animals with neurologic disease should be mastered. Problems can be avoided by educating the client about the extent of neurologic disease, the working diagnosis, pros and cons of diagnostic and therapeutic options, and a plan of action should unanticipated problems arise.

[Effect of chronic antiplatelet treatment on platelet activating factor-induced platelet activity in stroke]

The effect of chronic antiplatelet treatment on PAF--induced platelet aggregation, ATP--release, and cytoplasmic ionized calcium was studied in 20 acute ischemic stroke patients. Chronic antiplatelet treatment failed to suppress these PAF--induced platelet responses. We speculate that selective PAF antagonists may be useful in suppressing PAF--induced platelet activation, and thereby possibly improve the treatment of stroke.

A marsupial beta-lactoglobulin gene: characterization and prolactin-dependent expression

Analysis of the tammar wallaby beta-lactoglobulin cDNA and inferred amino acid sequences reveal extensive sequence divergence from the eutherian beta-lactoglobulins. Conserved residues include the cysteines and a number of individual amino acids involved in structure and ligand-binding. The only region of extended similarity is a heptapeptide sequence which may impart specificity to its interaction with a receptor protein. Northern analysis of total mammary RNA revealed two transcripts which result from differential utilization of polyadenylation signals. The concentration of beta-lactoglobulin mRNA increased in late lactation and correlates with increases in milk production and levels of milk fat. Quantification of beta-lactoglobulin mRNA levels in hormone-stimulated mammary gland explants from tammars in late pregnancy suggests that maximal induction of the gene is dependent on prolactin alone and that expression is not modulated by other hormones known to play a role in the initiation of lactation in eutherians.

Hormone-responsive survival of mammary gland explants from the pregnant tammar wallaby (Macropus eugenii) in the absence of exogenous hormones and growth factors

1. The level of beta-lactoglobulin mRNA increased maximally in mammary explants from late pregnant tammars cultured for 3 days in media containing either prolactin or insulin, cortisol and prolactin. 2. The same level of accumulation occurred when explants were first cultured for 4 days in a chemically defined medium with no exogenous hormones, serum or growth factors, suggesting that the tissue remains viable and hormone-responsive during the initial incubation. 3. Mammary explants cultured for 4 days in medium with no hormones demonstrated a progressive increase in the rate of RNA and DNA synthesis suggesting that the tissue is under a positive autocrine/paracrine stimulus.

Resuscitation at birth

Birth asphyxia is frequent and often severe, occurring in about 10% and 1% respectively of all births; in a third it is unexpected. Delivery rooms must be organised and equipped and trained staff readily available so as to provide appropriate and timely resuscitation of the newborn. Simple procedures designed to prevent hypothermia, maintain a patent airway, improve oxygenation and ventilation are sufficient for the majority of babies. Circulatory support and biochemical resuscitation will be needed in a few. In the absence of other abnormalities, the long term prognosis for newborns who respond promptly to resuscitation is good. Every baby, no matter how severely asphyxiated must therefore be promptly and vigorously resuscitated. Only those with a Apgar score of less than 4 at 10 minutes, prolonged hypotonia or seizures have a poor prognosis. With the needs in cardio-pulmonary resuscitation understood and met, research is now being directed at neuroresuscitation.

ATP:citrate lyase of Rhodotorula gracilis: purification and properties

ATP:citrate lyase was purified from the oleaginous yeast Rhodotorula gracilis to homogeneity as judged by polyacrylamide gel electrophoresis, using a novel citrate-Sepharose procedure. The enzyme was found to have a molecular weight of 520,000 and consisted of four identical subunits (Mr = 120,000). Two minor low molecular weight bands were observed on SDS-PAGE (Mr 51,000 and 49,000). Trypsin digestion experiments indicated that these could have been the result of limited proteolysis by an endogenous trypsin-like proteinase. In this respect, it resembles the mammalian ATP:citrate lyase. The enzyme was stimulated by NH+4 ions and inhibited by palmitoyl, lauroyl, oleoyl, myristoyl and stearoyl-CoA esters, glutamate and glucose 6-phosphate but not by acetyl-CoA or shorter chain fatty acyl-CoA esters. The enzyme exhibited normal Michaelis-Menten kinetics for citrate; however there was a 3-fold increase in Km with a high concentration of Cl- ions (0.25 M). The possible regulatory roles of ATP:citrate lyase in R. gracilis are discussed in the light of these findings.

Modulation of lipid peroxidation in human spermatozoa and human prostate by prostatic inhibin

Loss of sperm motility as a result of the production of hydrogen peroxide by lipid peroxidation is regulated by as yet unidentified prostatic factor(s). Inhibinlike peptide of prostatic origin isolated from human seminal plasma, with a molecular size of about 10,400 daltons, was studied for its effect on ascorbate-induced lipid peroxidation in human spermatozoa. Dose-related suppression of lipid peroxidation was observed at dose levels of 0.25, 0.5, and 1.0 micrograms. The data suggest that inhibinlike peptide could be one of the factors involved in the regulation of lipid peroxidation and thereby of sperm motility. Inhibinlike peptide also exhibited local action in both normal and benign hyperplastic human prostate tissue by enhancing the rate of lipid peroxidation. These findings have implications in the pathophysiology of the prostate.

Cloning, cDNA analysis and prolactin-dependent expression of a marsupial alpha-lactalbumin

The gene for alpha-lactalbumin has been cloned from a tammar wallaby (Macropus eugenii) mammary gland cDNA library. Tammar alpha-lactalbumin has approximately 50 and 30% homology to the alpha-lactalbumins of eutherians at the levels of nucleotide and protein sequence respectively. Comparison of the inferred tammar polypeptide sequence with the sequence of the eutherian proteins reveals extensive divergence at almost all of the non-essential amino acid residues. However, the hydropathy plots of the tammar protein are almost identical to those of eutherian alpha-lactalbumins, suggesting that protein conformation is conserved. The tammar gene encodes a transcript of approximately 975 bases. Northern blot analysis of hormone-stimulated mammary gland explants shows that maximal induction of alpha-lactalbumin mRNA is dependent on prolactin and that expression is not modulated by other hormones that play a role in the initiation of lactation in eutherians.