Biphasic effects of melatonin on the propagation of excitation waves in the chicken retina

Effect of neonatal melatonin administration on behavioral and brain electrophysiological and redox imbalance in rats

Introduction

Melatonin (MLT) reportedly has beneficial effects in neurological disorders involving brain excitability (e.g., Epilepsy and Migraine) and behavioral patterns (e.g., Anxiety and Depression). This study was performed to investigate, in the developing rat brain, the effect of early-in-life administration of two different doses of exogenous MLT on behavioral (anxiety and memory) and electrophysiological (CSD analysis) aspects of brain function. Additionally, brain levels of malondialdehyde (MDA) and superoxide dismutase (SOD), both cellular indicators of redox balance status, were evaluated. We hypothesize that MLT differentially affects the behavioral and CSD parameters as a function of the MLT dose.

Materials and methods

Male Wistar rats received, from the 7th to the 27th postnatal day (PND), on alternate days, vehicle solution, or 10 mg/kg/or 40 mg/kg MLT (MLT-10 and MLT-40 groups), or no treatment (intact group). To perform behavioral and cognition analysis, from PND30 to PND32, they were tested in the open field apparatus, first for anxiety (PND30) and then for object recognition memory tasks: spatial position recognition (PND31) and shape recognition (PND32). On PND34, they were tested in the elevated plus maze. From PND36 to 42, the excitability-related phenomenon known as cortical spreading depression (CSD) was recorded, and its features were analyzed.

Results

Treatment with MLT did not change the animals' body weight or blood glucose levels. The MLT-10 treatment, but not the MLT-40 treatment, was associated with behaviors that suggest less anxiety and improved memory. MLT-10 and MLT-40 treatments, respectively, decelerated and accelerated CSD propagation (speed of 2.86 ± 0.14 mm/min and 3.96 ± 0.16 mm/min), compared with the control groups (3.3 ± 0.10 mm/min and 3.25 ± 0.11 mm/min, for the intact and vehicle groups, respectively; p < 0.01). Cerebral cortex levels of malondialdehyde and superoxide dismutase were, respectively, lower and higher in the MLT-10 group but not in the MLT40 group.

Conclusion

Our findings suggest that MLT intraperitoneal administration during brain development may differentially act as an antioxidant agent when administered at a low dose but not at a high dose, according to behavioral, electrophysiological, and biochemical parameters.

Aura in trigeminal autonomic cephalalgia is probably mediated by comorbid migraine with aura

OBJECTIVE

The presence of aura is rare in cluster headache, and even rarer in other trigeminal autonomic cephalalgias. We hypothesized that the presence of aura in patients with trigeminal autonomic cephalalgias is frequently an epiphenomenon and mediated by comorbid migraine with aura.

METHODS

The study retrospectively reviewed 480 patients with trigeminal autonomic cephalalgia in a tertiary medical center for 10 years. Phenotypes and temporal correlation of aura with headache were analyzed. Trigeminal autonomic cephalalgia patients with aura were further followed up in a structured telephone interview.

RESULTS

Seventeen patients with aura (3.5%) were identified from 480 patients with trigeminal autonomic cephalalgia, including nine with cluster headache, one with paroxysmal hemicrania, three with hemicrania continua, and four with probable trigeminal autonomic cephalalgia. Compared to trigeminal autonomic cephalalgia patients without aura, trigeminal autonomic cephalalgia patients with aura were more likely to have a concomitant diagnosis of migraine with aura (odds ratio [OR] = 109.0, 95% CI 30.9-383.0, p < 0.001); whereas the risk of migraine without aura remains similar between both groups (OR = 1.10, 95% CI = 0.14-8.59, p = 0.931). Aura was more frequently accompanied with migraine-like attacks, but not trigeminal autonomic cephalalgia attacks.

INTERPRETATION

In most patients with trigeminal autonomic cephalalgia, the presence of aura is mediated by the comorbidity of migraine with aura. Aura directly related to trigeminal autonomic cephalalgia attack may exist but remains rare. Our results suggest that aura may not be involved in the pathophysiology of trigeminal autonomic cephalalgia.

Acute sleep deprivation enhances susceptibility to the migraine substrate cortical spreading depolarization

BACKGROUND

Migraine is a common headache disorder, with cortical spreading depolarization (CSD) considered as the underlying electrophysiological event. CSD is a slowly propagating wave of neuronal and glial depolarization. Sleep disorders are well known risk factors for migraine chronification, and changes in wake-sleep pattern such as sleep deprivation are common migraine triggers. The underlying mechanisms are unknown. As a step towards developing an animal model to study this, we test whether sleep deprivation, a modifiable migraine trigger, enhances CSD susceptibility in rodent models.

METHODS

Acute sleep deprivation was achieved using the "gentle handling method", chosen to minimize stress and avoid confounding bias. Sleep deprivation was started with onset of light (diurnal lighting conditions), and assessment of CSD was performed at the end of a 6 h or 12 h sleep deprivation period. The effect of chronic sleep deprivation on CSD was assessed 6 weeks or 12 weeks after lesioning of the hypothalamic ventrolateral preoptic nucleus. All experiments were done in a blinded fashion with respect to sleep status. During 60 min of continuous topical KCl application, we assessed the total number of CSDs, the direct current shift amplitude and duration of the first CSD, the average and cumulative duration of all CSDs, propagation speed, and electrical CSD threshold.

RESULTS

Acute sleep deprivation of 6 h (n = 17) or 12 h (n = 11) duration significantly increased CSD frequency compared to controls (17 ± 4 and 18 ± 2, respectively, vs. 14 ± 2 CSDs/hour in controls; p = 0.003 for both), whereas other electrophysiological properties of CSD were unchanged. Acute total sleep deprivation over 12 h but not over 6 h reduced the electrical threshold of CSD compared to controls (p = 0.037 and p = 0.095, respectively). Chronic partial sleep deprivation in contrast did not affect CSD susceptibility in rats.

CONCLUSIONS

Acute but not chronic sleep deprivation enhances CSD susceptibility in rodents, possibly underlying its negative impact as a migraine trigger and exacerbating factor. Our findings underscore the importance of CSD as a therapeutic target in migraine and suggest that headache management should identify and treat associated sleep disorders.

Melatonin inhibits cortical spreading depression-evoked trigeminal nociception

This study was conducted to determine the effect of melatonin on cortical spreading depression-evoked trigeminovascular nociception. Melatonin (20 or 40 mg/kg) or saline was given to Wistar rats. KCl was placed on the cortical surface to elicit the cortical spreading depression. Cortical blood flow was monitored and ultrastructure of cerebral microvessels was studied. The medulla and cervical cord were removed for Fos and nitric oxide synthase immunohistochemical study. The results showed that melatonin pretreatment significantly minimized the cortical spreading depression-evoked cerebral hyperaemia and attenuated the cortical spreading depression-induced microvascular changes. Pretreatment with melatonin also reduced the number of Fos and nitric oxide synthase immunoreactive cells in the trigeminal nucleus caudalis. The results of this study suggest that melatonin can attenuate the process of trigeminovascular nociception induced by cortical spreading depression.

Propagation velocity and triggering threshold of retinal spreading depression are not correlated

Spreading depression (SD) is a pronounced but transient disturbance of cellular homeostasis in the neuropil of the central nervous system which spreads in a wave-like manner across the tissue. At the wavefront the cells depolarize and a distinct ion redistribution between intra- and extracellular space is observed. In the aftermath of SD the recovering tissue is refractory: during an early absolute refractory period no further SD can be triggered, during the subsequent relative refractory period SD waves spread at lower velocity than usual. In this paper we shall examine the influence of temperature on SD triggering and on SD propagation in the chicken retina (retinal spreading depression, rSD) and we shall examine rSD triggering and rSD propagation in the refractory period. It will be shown that cooling decreases the threshold of rSD triggering, i.e. it becomes easier to trigger rSD when the temperature is reduced. At the same time cooling slows rSD propagation. In contrast, during the relative refractory period triggering rSD is more difficult than usual while rSD propagation is also slowed. These results demonstrate that the propagation velocity of rSD is not correlated with the triggering threshold. In particular, the propagation velocity of rSD must not be used to predict the influence of experimental conditions on the triggering threshold.

Safety of the magnetic field generated by a neuronal magnetic stimulator: evaluation of possible mutagenic effects

OBJECTIVE

The possible mutagenicity of a magnetic stimulus was checked using the Ames test with Salmonella typhimurium TA98 and TA100 as tester strains.

METHODS

Samples of these bacteria were exposed to a pulsed magnetic field, on the order of 1 T. The magnetic pulses were generated by a neuronal magnetic stimulator with a flat coil. The magnetic stimulus was a continuous sequence of slightly damped half sinusoids at a rate of 5 pulses/s. Exposure times were 2-5 and 15 min. Exposure position was such as to maximise the magnetic field and minimise the induced electric field. Room temperature was maintained at 28.5 +/- 0.5 degrees C and the temperature was measured inside the samples.

RESULTS

None of the exposure conditions showed any increase in mutation in either of the two bacterial strains.

CONCLUSIONS

These results are discussed in comparison with effects found in the literature. The magnetic stimulation used under the conditions of this study does not appear to have mutagenic effects. This does not apply to cases where both strong electric and magnetic fields are present.