S. Grunfeld

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.

Event-related slow potentials and associated catecholamine function in migraine.

Plasma norepinephrine and dopamine and event-related slow potentials were measured at menses and ovulation in migraine with and without aura relative to normal subjects. The results indicated that at menses, but not ovulation, plasma dopamine was increased and norepinephrine was decreased relative to normal. This catecholamine imbalance was greater in migraine without aura than in migraine with aura. Conversely, event-related slow potentials measured over the posterior cortex at ovulation but not at the menses was altered relative to normal. Early epoch negativity was reduced in migraine with aura, whereas late epoch negativity was reduced in migraine without aura. The results suggested that (a) migraine without aura may involve dynamic shifts in the function of both norepinephrine and dopamine responsive neurons; (b) pathophysiology of migraine with aura is less dependent on catecholamine imbalance (norepinephrine alone affected); (c) these pathophysiological mechanisms are most prevalent in or restricted to posterior cortical regions but may be modulated by brainstem mechanisms.

Ovarian steroid levels in migraine with and without aura

Radioimmunoassays were used to measure interictal levels of ovarian steroids (oestradiol, total oestrogens and progesterone) in migraine patients at the onset of menses and coincident with the luteinizing hormone surge preceding ovulation. Results of these verified bio-chemically-contrasting points of the ovarian cycle were used to compare 13 migraine patients without aura and 6 migraine patients with aura with 17 non-migraine women. No group differences were found for physiological basal levels of ovarian steroids measured at menses. Preceding ovulation elevation in oestradiol levels relative to normal was found in migraine patients with aura but not in migraine patients without aura. These results suggest that a variation in oestradiol levels is an important factor in the different clinical expressions of migraine.

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.

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.

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.

Cytosolic Ionized Calcium Homeostasis in Platelets: An Abnormal Sensitivity to PAF‐Activation in Migraine

SYNOPSIS

Platelet catecholamines in migraine

We measured platelet levels of norepinephrine (NE), epinephrine (E), and dopamine (DA) in migraine patients. Platelet NE was selectively increased in common migraine. This is attributed to platelet dense body hyposecretion.

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.

Baseline and activated platelet cytoplasmic ionized calcium in acute ischemic stroke. Effect of aspirin.

We measured cytoplasmic ionized calcium concentrations [( Cai2+]) in aequorin-loaded gel-filtered platelets from 38 patients with acute occlusive stroke (12 treated with aspirin, 26 untreated) and 25 healthy controls. Compared with controls, baseline [Cai2+] was higher in untreated patients (p less than 0.002), maximal 36-72 hours after the onset of neurologic dysfunction (p less than 0.0001), in those patients with as well as those without major stroke risk factors. The increase in [Cai2+] after stimulation with 0.5 and 1.0 unit/ml thrombin (p less than 0.05), 2 and 4 micrograms/ml collagen (p less than 0.02), and 0.5 and 1.0 mM platelet activating factor (p less than 0.05) were also greater in untreated patients, but the profiles of these changes were parallel to those in controls. Even though the platelets of stroke patients are more sensitive to activation, they are functionally similar to those of controls. Aspirin treatment reduced baseline [Cai2+] as well as thrombin- and collagen-induced [Cai2+] changes. Platelet activating factor-induced increase in [Cai2+] was not altered by aspirin treatment. Our results suggest that the usefulness of aspirin in stroke is limited because aspirin does not suppress platelet responsiveness to all in vivo thrombogenic stimuli. Specific platelet activating factor antagonists may prove to be useful therapeutic agents in stroke.