Árpád Párdutz

Systemic nitroglycerin increases nNOS levels in rat trigeminal nucleus caudalis.

Systemic administration of nitroglycerin, a nitric oxide donor, triggers in migraineurs a delayed attack of unknown mechanisms. Subcutaneous nitroglycerin (10 mg/kg) produced a significant increase of nitric oxide synthase (NOS)- and c-fos-immunoreactive neurons in the cervical part of trigeminal nucleus caudalis in rats after 4 h. This effect was not observed in the thoracic dorsal horn. Similar increase of NOS and c-fos was obtained in the brain stem after a somatic nociceptive stimulus, i.e. on the side of the formalin injection in the lip. Nitric oxide is thus able to increase NOS availability in second order nociceptive trigeminal neurons, which may be relevant for central sensitization and the understanding of its effect in migraine.

The role of kynurenines in disorders of the central nervous system: Possibilities for neuroprotection

The metabolism of tryptophan mostly proceeds through the kynurenine pathway. The biochemical reaction includes both an agonist (quinolinic acid) at the N-methyl-d-aspartate receptor and an antagonist (kynurenic acid). Besides the N-methyl-d-aspartate antagonism, an important feature of kynurenic acid is the blockade of the alpha7-nicotinic acetylcholine receptor and its influence on the alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid receptor. Kynurenic acid has proven to be neuroprotective in several experimental settings. On the other hand, quinolinic acid is a potent neurotoxin with an additional and marked free radical-producing property. In consequence of these various receptor activities, the possible roles of these substances in various neurological disorders have been proposed. Moreover, the possibility of influencing the kynurenine pathway to reduce quinolinic acid and increase the level of kynurenic acid in the brain offers a new target for drug action designed to change the balance, decreasing excitotoxins and enhancing neuroprotectants. This review surveys both the early and the current research in this field, focusing on the possible therapeutic effects of kynurenines.

White matter microstructural alterations in migraine: A diffusion-weighted MRI study

Summary White matter disintegration, as measured by diffusion‐weighted MRI, is reported in migraineurs, and is speculated to be either a marker of possible white matter disintegration or maladaptive plasticity. Abstract Migraine is a common and disabling neurological disease. The pathomechanism that underlies the disorder is not entirely understood, and reliable biomarkers are missing. In the current analysis we looked for microstructural alterations of the brain white matter in migraine patients by means of diffusion‐weighted magnetic resonance imaging. The measurements were carried out with a novel approach based on fine‐tuned nonlinear registration and nonparametric permutation test in an alignment‐invariant tract representation (Tract‐Based Spatial Statistics). We found reduced fractional anisotropy in the right frontal white matter cluster of migraine patients. In the same region we also found increased mean diffusivity and increased radial diffusivity. The probabilistic tractography showed connection of this cluster to other parts of the pain network (orbitofrontal cortex, insula, thalamus, dorsal midbrain). We speculate that these findings reflect maladaptive plastic changes or white matter disintegration.

L-kynurenine combined with probenecid and the novel synthetic kynurenic acid derivative attenuate nitroglycerin-induced nNOS in the rat caudal trigeminal nucleus

Systemic administration of the nitric oxide (NO) donor nitroglycerin (NTG) triggers a delayed attack without aura in many migraineurs, but not in healthy volunteers. In rats, 4 h after the systemic administration of NTG (10 mg/kg bw, s.c.), the neurons of the caudal trigeminal nucleus (TNC) are activated and the expression of neuronal NO synthase (nNOS) in the same area is increased suggesting a self-amplifying process in the trigeminal system, which seems to be crucial in migraine pathogenesis. Kynurenic acid (KYNA) and its analogues may exert modulatory effects in many neuropathological conditions, probably via N-methyl-D-aspartate (NMDA) antagonism. Since NMDA receptors play a crucial role in trigeminal pain processing, the aim of our experiments was to compare the effects of L-kynurenine (L-KYN) combined with probenecid (PROB) or with 2-(2-N,N-dimethylaminoethylamine-1-carbonyl)-1H-quinolin-4-one hydrochloride alone, a newly synthetized KYNA derivative, on the NTG-induced nNOS expression in the rat TNC. Pretreatment with L-KYN (300 mg/kg bw, i.p.) together with PROB (200 mg/kg bw, i.p.) and KYNA derivative (300 mg/kg bw, i.p.) attenuated the NTG-induced nNOS expression in the rat TNC. Our data suggest that the stimulating effect of NTG, and thus of NO, on the expression of nNOS might be modulated by increasing the KYNA level in the brain, probably through the NMDA receptors. These data could help promote a better understanding of the pathogenesis of headaches and the action of antimigraine drugs.

Lack of estrogen increases pain in the trigeminal formalin model: a behavioural and immunocytochemical study of transgenic ArKO mice

&NA; In order to examine the effect of estrogen on facial pain, we first compared the face‐rubbing evoked by a formalin injection in the lip of aromatase‐knockout (ArKO) mice, lacking endogenous estrogen production, 17β‐estradiol‐treated ArKO mice (ArKO‐E2) and wild‐type (WT) littermates. During the ‘acute’ phase of pain the time spent rubbing was similar in the three groups, whereas during the following ‘interphase’ and the second phase of pain, grooming was increased in ArKO mice. Estradiol‐treatment restored a behaviour similar to WT group. To better understand estrogens modulation on pain processes, we examined changes in 5‐HT and CGRP innervations of trigeminal nucleus caudalis (TNC) in ArKO, ArKO‐E2 and WT groups sacrified during the interphase. Whereas serotonin and CGRP immunoreactivities were comparable in WT and ArKO non‐injected control groups, our data showed that 9 min after formalin injection, the density of serotoninergic terminals increased significantly in WT, but not in ArKO mice, while that of CGRP‐immunoreactive fibers was lower in WT than in ArKO mice on the injected side. Estradiol‐treatment only partially reversed these changes in ArKO‐E2 mice. We conclude that estrogen deprivation in ArKO mice can be responsible for increased nociceptive response and that it is accompanied by transmitter changes favouring pro‐ over anti‐nociceptive mechanisms in TNC during interphase of the formalin model. That estradiol‐treatment completely reverses the behavioural abnormality suggests that estrogens absence produces chiefly functional activation‐dependent changes. However, the fact that the immunohistochemical abnormalities were not totally normalized by estradiol‐treatment suggested that some permanent developmental alterations may occur in ArKO mice.

Peripheral and central alterations of pituitary adenylate cyclase activating polypeptide-like immunoreactivity in the rat in response to activation of the trigeminovascular system

Pituitary adenylate cyclase activating polypeptide (PACAP) is present in the cranial arteries and trigeminal sensory neurons. We therefore examined the alterations in PACAP-like immunoreactivity (PACAP-LI) in a time-dependent manner in two rat models of trigeminovascular system (TS) activation. In one group chemical stimulation (CS) was performed with i.p. nitroglycerol (NTG), and in the other one the trigeminal ganglia (TRG) were subjected to electrical stimulation (ES). The two biologically active forms, PACAP-38 and PACAP-27, were determined by means of radioimmunoassay (RIA) and mass spectrometry (MS) in the plasma, the cerebrospinal fluid (CSF), the trigeminal nucleus caudalis (TNC), the spinal cord (SC) and the TRG. The tissue concentrations of PACAP-27 were 10 times lower than those of PACAP-38 in the TNC and SC, but about half in the TRG. PACAP-38, but not PACAP-27, was present in the plasma. Neither form could be identified in the CSF. PACAP-38-LI in the plasma, SC and TRG remained unchanged after CS, but it was increased significantly in the TNC 90 and 180 min after NTG injection. In response to ES of the TRG, the level of PACAP-38 in the plasma and the TNC was significantly elevated 90 and 180 min later, but not in the SC or the TRG. The alterations in the levels of PACAP-27 in the tissue homogenates in response to both forms of stimulation were identical to those of PACAP-38. The selective increases in both forms of PACAP in the TNC suggest its important role in the central sensitization involved in migraine-like headache.

Kynurenate Derivative Attenuates the Nitroglycerin-Induced CamKIIα and CGRP Expression Changes

(Headache 2010;50:834‐843)

Effect of systemic kynurenine on cortical spreading depression and its modulation by sex hormones in rat

BACKGROUND The aura symptoms in migraine are most likely due to cortical spreading depression (CSD). CSD is favored by NMDA receptor activation and increased cortical excitability. The latter probably explains why migraine with aura may appear when estrogen levels are high, like during pregnancy. Kynurenic acid, a derivative of tryptophan metabolism, is an endogenous NMDA receptor antagonist whose cerebral concentrations can be augmented by systemic administration of its precursor L-kynurenine. OBJECTIVE To determine if exogenous administration of L-kynurenine is able to influence KCl-induced CSD in rat, if the effect is sex-dependent and if it differs in females between the phases of the estrous cycle. METHODS Adult Sprague-Dawley rats (n=8/group) received intraperitoneal (i.p.) injections of L-kynurenine (L-KYN, 300 mg/kg), L-KYN combined with probenecid (L-KYN+PROB) that increases cortical concentration of KYNA by blocking its excretion from the central nervous system, probenecid alone (PROB, 200 mg/kg) or NaCl. Cortical kynurenic acid concentrations were determined by HPLC (n=7). Thirty minutes after the injections, CSDs were elicited by application of 1M KCl over the occipital cortex and recorded by DC electrocorticogram. In NaCl and L-KYN groups, supplementary females were added and CSD frequency was analyzed respective to the phases of the estrous cycle determined by vaginal smears. RESULTS In both sexes, PROB, L-KYN and L-KYN+PROB increased cortical kynurenic acid level. PROB, L-KYN and L-KYN+PROB with increasing potency decreased CSD frequency in female rats, while in males such an effect was significant only for L-KYN+PROB. The inhibitory effect of L-KYN on CSD frequency in females was most potent in diestrus. CONCLUSION L-Kynurenine administration suppresses CSD, most likely by increasing kynurenic acid levels in the cortex. Females are more sensitive to this suppressive effect of L-kynurenine than males. These results emphasize the role of sex hormones in migraine and open interesting novel perspectives for its preventive treatment.

Migraine is a neuronal disease

Migraine is a common, paroxysmal, highly disabling primary headache disorder with a genetic background. The primary cause and the origin of migraine attacks are enigmatic. Numerous clinical and experimental results suggest that activation of the trigeminal system (TS) is crucial in its pathogenesis, but the primary cause of this activation is not fully understood. Since activation of the peripheral and central arms of the TS might be related to cortical spreading depression and to the activity of distinct brainstem nuclei (e.g. the periaqueductal grey), we conclude that migraine can be explained as an altered function of the neuronal elements of the TS, the brainstem, and the cortex, the centre of this process comprising activation of the TS. In light of our findings and the literature data, therefore, we can assume that migraine is mainly a neuronal disease.

Release of PACAP-38 in episodic cluster headache patients - an exploratory study

BackgroundActivation of the trigeminal-autonomic reflex, involving the trigeminal ganglion, the superior salivatory nucleus and the sphenopalatine ganglion (SPG) is crucial in the pathophysiology of cluster headache (CH). Since pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) is present both in the SPG and the trigeminal ganglion (TG) and its role in migraine has been described, our aim was to determine the plasma PACAP-38 levels in different phases of episodic CH (ECH).Peripheral cubital fossa blood samples were taken during the ictal and inter-bout periods of male ECH patients and from age-matched healthy controls (n = 9). Plasma PACAP-38-like immunoreactivity (LI) was measured with specific and sensitive radioimmunoassay.FindingsSignificantly lower plasma PACAP-38-LI was detected in the inter-bout period of ECH patients than in healthy controls. However, PACAP-38 was significantly elevated in the plasma during CH attacks as compared to the inter-bout phase in the same subjects (n = 5).ConclusionsThis exploratory study suggests that PACAP-38 may be released during the attacks of ECH. Further patients and long-term follow-up are necessary to reveal its function.