Serotonin Depletion Increases Nociception‐Evoked Trigeminal NMDA Receptor Phosphorylation

Objective.— To investigate the effect of serotonin depletion on phosphorylation and expression of NR1 subunit of N‐methyl‐D‐aspartate (NMDA) receptor in trigeminal nucleus caudalis (TNC), and on trigeminal nociception evoked by dural inflammation. Background.— Migraine is associated with low serotonin condition and an increased neuronal excitability. NMDA receptor is implicated in central plasticity change that leads to neural sensitization. Alteration in NMDA receptor phosphorylation or expression in TNC may be responsible for increased trigeminal nociception in serotonin‐depleted state. Methods.— Adult male Wistar rats were separated into normal and low serotonin groups. Serotonin was depleted by intraperitoneal injection with para‐chlorophenylalanine 3 days before the experiment. Trigeminal nociception was induced by applying inflammatory soup on exposed dura. Two hours after induction, phosphorylated NR1, NR1, and Fos expressions were studied in TNC by immunohistochemistry. Results.— Dural application of inflammatory soup led to the activation of trigeminal nociceptive system as well as the phosphorylation of NR1, which were further enhanced in the low serotonin condition. There was a strong relationship between NR1 phosphorylation and trigeminal nociception. However, neither meningeal inflammation nor serotonin depletion altered NR1 expression. Conclusions.— Low serotonin condition facilitates dural inflammation‐induced NR1 phosphorylation and trigeminal nociception. It is suggested that the mechanism of nociceptive facilitation in serotonin‐depleted state may involve the increase in NR1 phosphorylation rather than the upregulation of NR1 subunit of NMDA receptor.     

Pathophysiology of Medication Overuse Headache—An Update

The pathogenesis of medication overuse headache is unclear. Clinical and preclinical studies have consistently demonstrated increased excitability of neurons in the cerebral cortex and trigeminal system after medication overuse. Cortical hyperexcitability may facilitate the development of cortical spreading depression, while increased excitability of trigeminal neurons may facilitate the process of peripheral and central sensitization. These changes may be secondary to the derangement of central, probably serotonin (5‐HT)‐, and perhaps endocannabinoid‐dependent or other, modulating systems. Increased expression of excitatory cortical 5‐HT_2A receptors may increase the susceptibility to developing cortical spreading depression, an analog of migraine aura. A reduction of diffuse noxious inhibitory controls may facilitate the process of central sensitization, activate the nociceptive facilitating system, or promote similar molecular mechanisms to those involved in kindling. Low 5‐HT levels also increase the expression and release of calcitonin gene‐related peptide from the trigeminal ganglion and sensitize trigeminal nociceptors. Thus, derangement of central modulation of the trigeminal system as a result of chronic medication use may increase sensitivity to pain perception and foster or reinforce medication overuse headache.     

Serotonin depletion, cortical spreading depression, and trigeminal nociception

BACKGROUND: The attack of migraine has been observed to be associated with low level of serotonin (5-HT). Although the mechanism underlying this relationship is still unclear, change in cortical excitability or susceptibility of trigeminal system is a possible explanation. Objectives: The aim was to study the effect of 5-HT depletion on the development of cortical spreading depression (CSD) and CSD-evoked trigeminal nociception. METHODS: Wistar rats were separated into low 5-HT and control groups (eight rats each). 5-HT was depleted by administration of para-chlorophenylalanine, a tryptophan hydroxylase inhibitor. CSD was induced by applying 3 mg of potassium chloride on parietal cortex. Cortical activity was monitored for 1 hour. Trigeminal nociception was determined using number of Fos-immunoreactive (Fos-IR) neurons in trigeminal nucleus caudalis as the indicator. RESULTS: Application of KCl led to the development of series of depolarization shift characteristics for CSD. The development of these CSD waves was enhanced in low 5-HT state. The area under curve of each CSD wave and the number of CSD waves occurring within 1 hour were greater in low 5-HT group. No significant change in peak amplitude and duration of CSD wave was observed. The numbers of Fos-IR cells on ipsilateral and contralateral trigeminal nucleus caudalis were significantly greater in the low 5-HT group than those of the controls. CONCLUSION: Our findings indicate that 5-HT depletion enhances CSD-induced trigeminal nociception by increasing the cortical excitability and sensitivity of trigeminal nociceptive system. These findings may provide a better understanding regarding the relationship between low 5-HT and clinical headaches.     

Ultrastructural changes in endothelial cells of cerebral microvessels after exposure to nitric oxide donor

It has been largely accepted that nitric oxide (NO) plays an important role in cerebral vasomotor control. NO has also been proposed to be a significant chemical in the process of endothelial cell injuries in various pathological conditions. Although the toxic effect of high concentrations of NO has been shown, only a few ultrastructural studies have been reported. The purpose of this study is to demonstrate physiological and pathological changes in cerebral microvessels after exposure to a high dose of NO donor. Glyceryl trinitrate, a NO donating chemical, was administered intravenously (10 mg/kg) to experimental rats. The vasomotor response was monitored by in vivo fluorescein videomicroscopy and ultrastructural changes were studied using transmission electron microscopy. The result showed long-lasting vasodilatation of pial microvessels. The greatest response was observed in microvessels with baseline diameter of less than 10 μm compared with microvessels of a larger diameter (P = 0.003). Exposure to NO donor produced considerable changes in the ultrastructure of cerebral microvessels. Such morphological changes were characterized by increased pinocytosis, increased microvillous formation, mitochondrial swelling, doming of the endothelial surface, swelling of the perivascular astrocytic foot plate and partial separation of endothelial cells from the adjacent brain tissue. These results confirm the cytotoxic effect of NO on cerebral endothelial cell and further elaborate the role of this substance in endothelial cell injury observed in various conditions.     

A Rapid Stability Indicating HPLC Method for Determination of Quetiapine Fumarate in Tablets and Extemporaneous Formulations

Pharmaceutical Chemistry Journal - Quetiapine fumarate is an atypical antipsychotic drug, which is clinically used for the treatment of depression and bipolar disorders. A stability indicating...     

Serotonin depletion leads to cortical hyperexcitability and trigeminal nociceptive facilitation via the nitric oxide pathway

(Headache 2011;51:1152‐1160) Objective.— To investigate the role of nitric oxide (NO) in the development of cortical hyperexcitability and trigeminal nociceptive facilitation induced by serotonin (5‐HT) depletion. Background.— Nitric oxide and 5‐HT are important in the pathogenesis of primary headaches. An increase in cortical excitability and trigeminal nociception has been demonstrated in animals with low 5‐HT levels. Although the mechanism underlying this increase is unclear, an alteration of the NO system is one possible explanation. Methods.— Male Wistar rats were divided into control and 5‐HT‐depleted groups. 5‐HT was depleted by i.p. injection of parachlorophenylalanine (100 mg/kg). Three days after injection, a microelectrode was inserted into the cerebral cortex for electrocorticograph recording and waves of cortical spreading depression (CSD) were triggered with KCl application. N‐nitro‐L‐arginine methyl ester (L‐NAME; 10 mg/kg by i.v. injection) or saline was given after the second CSD wave. Following the experiment, the cerebral cortex and brain stem were removed for anti‐neuronal nitric oxide synthase (nNOS) and anti‐Fos immunohistochemistry. Results.— Relative to the control group, the 5‐HT‐depleted group exhibited a higher frequency of CSD waves, more nNOS‐immunoreactive cells in both the cerebral cortex and brainstem and more Fos‐immunoreactive cells in the trigeminal nucleus caudalis (TNC). In the control group, L‐NAME application led to fewer nNOS‐immunoreactive cells in the cerebral cortex and TNC, and fewer Fos‐immunoreactive cells in the TNC; however, L‐NAME was without effect on the CSD pattern. By contrast, in addition to decreased nNOS and Fos expression, L‐NAME significantly reduced the frequency of CSD events in the 5‐HT‐depleted group. Conclusions.— Inhibition of NO production can counter both the cortical hyperexcitability and facilitation of trigeminal nociception that develop in the depleted 5‐HT state. Therefore, NO is likely involved in the increase in both CSD events and CSD‐evoked trigeminal nociception under decreased 5‐HT conditions.     

Upregulation of Pro-inflammatory Cytokine Expression Following Chronic Paracetamol Treatment in Astrocyte

The present study aimed to investigate the effect of APAP treatment on the expression of pro-inflammatory cytokines in the astrocytes. The mouse astrocyte cells (C8-D1A) were treated with APAP at the concentration of 100 μM for 24 h, 16 and 28 days. The expressions of pro-inflammatory cytokines and NF-kB were determined using western blot analysis. Furthermore, the expression and localization of phosphorylation of NF-kB were detected by immunohistochemical and immunofluorescent analysis. The ultrastructure of C8-D1A cells was as well monitored. The results revealed that acute APAP treatment (24 h) had no effect on the expression of pro-inflammatory cytokines and pNF-kB. This treatment did not alter the ultrastructure of C8-D1A cells when compared with those in the control cells. However, the results obtained from the study on chronic APAP-treated cells (16 and 28 days) showed the different effect of APAP treatment. The results obtained from western blot analysis showed the increment of pro-inflammatory cytokine (IL-1β and TNF-α) expressions and the activation of NF-kB signaling pathway. Nuclear translocation of pNF-kB and alteration of several cell structures were well observed in the C8-D1A cells with chronic APAP treatment. The results obtained from this study suggest that chronic APAP treatment can induce an upregulation of pro-inflammatory cytokines (IL-1β and TNFα) in astrocytes. This alteration implies the involvement of the activation of NF-kB signaling pathway.