Effects of pan- and subtype-selective N-methyl-D-aspartate receptor antagonists on cortical spreading depression in the rat: therapeutic potential for migraine.

Spreading depression (SD) has long been associated with the underlying pathophysiology of migraine. Evidence that the N-methyl-D-aspartate (NMDA) glutamate receptor (NMDA-R) is implicated in the generation and propagation of SD has itself been available for more than 15 years. However, to date, there are no reports of NMDA-R antagonists being developed for migraine therapy. In this study, an uncompetitive, pan-NMDA-R blocker, memantine, approved for clinical use, and two antagonists with selectivity for NMDA-R containing the NR2B subunit, (1S,2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol (CP-101,606) and (+/-)-(R*,S*)-alpha-(4-hydroxyphenyl)-beta-methyl-4-(phenylmethyl)-1-piperidine propanol (Ro 25-6981), were investigated to assess their protective effects against SD in the rat. Under isoflurane anesthesia, d.c. potential and the related cortical blood flow and partial pressure of O2 (pO2) were recorded simultaneously at separate cortical sites. Drugs (1, 3, and 10 mg/kg i.p.) were given 1 h or 30 min before KCl application to the brain surface. Core temperature and arterial pCO2,pO2, and pH measurements confirmed physiological stability. KCl induced 7.7+/-1.8 (mean+/-S.D.) SD events with d.c. amplitude of 14.9+/-2.8 mV. Memantine and CP-101,606 dose-dependently decreased SD event number (to 2.0+/-1.8 and 2.3+/-2.9, respectively) and SD amplitude at doses relevant for therapeutic use. Ro 25-6981 also decreased SD events significantly, but less effectively (to 4.5+/-1.6), without affecting amplitude. These results indicate that NR2B-containing NMDA receptors are key mediators of SD, and as such, memantine- and NR2B-selective antagonists may be useful new therapeutic agents for the treatment of migraine and other SD-related disorders (e.g., stroke and brain injury). Whether chronic, rather than acute, treatment may improve their efficacy remains to be determined.

Characterization of the human HCN1 channel and its inhibition by capsazepine.

The human hyperpolarization-activated cyclic nucleotide-gated 1 (hHCN1) subunit was heterologously expressed in mammalian cell lines (CV-1 and CHO) and its properties investigated using whole-cell patch-clamp recordings. Activation of this recombinant channel, by membrane hyperpolarization, generated a slowly activating, noninactivating inward current. The pharmacological properties of hHCN1-mediated currents resembled those of native hyperpolarization-activated currents (I(h)), that is, blockade by Cs(+) (99% at 5 mm), ZD 7288 (98% at 100 microm) and zatebradine (92% at 10 microm). Inhibition of the hHCN1-mediated current by ZD 7288 was apparently independent of prior channel activation (i.e. non-use-dependent), whereas that induced by zatebradine was use-dependent. The VR1 receptor antagonist capsazepine inhibited hHCN1-mediated currents in a concentration-dependent (IC(50)=8 microm), reversible and apparently non-use-dependent manner. This inhibitory effect of capsazepine was voltage-independent and associated with a leftward shift in the hHCN1 activation curve as well as a dramatic slowing of the kinetics of current activation. Elevation of intracellular cAMP or extracellular K(+) significantly enhanced aspects of hHCN1 currents. However, these manipulations did not significantly affect the capsazepine-induced inhibition of hHCN1. The development of structural analogues of capsazepine may yield compounds that could selectively inhibit HCN channels and prove useful for the treatment of neurological disorders where a role for HCN channels has been described.

Mitogen and stress response kinase-1 (MSK1) mediates excitotoxic induced death of hippocampal neurones.

Activation of the mitogen-activated protein kinase (MAPK/ERK) signal transduction pathway may mediate excitotoxic neuronal cell death in vitro and during ischemic brain injury in vivo. However, little is known, of the upstream regulation or downstream consequences of ERK activation under these conditions. Magnesium removal has been described to induce hyperexcitability and degeneration in cultured hippocampal neurones. Here, we show that neurotoxicity evoked by Mg2+ removal in primary hippocampal neurones stimulates ERK, but not p38, phosphorylation. Removal of Mg2+ also resulted in induction of the MAPK/ERK substrate mitogen- and stress-response kinase 1 (MSK1) and induced phosphorylation of the MSK1 substrate, the transcription factor cAMP response element binding protein (CREB). Neuronal death and phosphorylation of components in this cascade were inhibited by the Raf inhibitor SB-386023, by the MEK inhibitor U0126, or by the MSK1 inhibitors H89 and Ro318220. Importantly, this form of cell death was inhibited in hippocampal neurones cultured from MSK1-/- mice and inhibitors of Raf or MEK had no additive neuroprotective effect. Together, these data indicate that MSK1 is a physiological kinase for CREB and that this activity is an essential component of activity-dependent neuronal cell death.

The neuronal versus vascular hypothesis of migraine and cortical spreading depression.

Our understanding of the pathophysiological mechanisms of migraine remains poor despite the availability of clinically effective drugs and many years of research. Historically, two independent theories regarding the aetiology of headache were suggested: vascular and neuronal. However, recent data demonstrate that neuronal excitation modulates both the pial and meningeal circulation through a critical interaction with the trigeminal nerve, supporting the concept that the integration of neuronal and vascular information in the trigeminovascular network represents a key event in the aetiology of migraine.

Eletriptan Pfizer.

Pfizer has developed and launched eletriptan, a 5-HT1B/1D agonist, for the potential treatment of migraine with and without aura. Eletriptan has 6-fold greater affinity for the 5-HT1D receptor than sumatriptan, and a 3-fold greater affinity for the 5-HT1B receptor [249570]. Eletriptan pharmacology has also been evaluated in vitro in comparison with zolmitriptan (AstraZeneca plc) and naratriptan (GlaxoSmithKline plc) [290116].

The selective p38 inhibitor SB-239063 protects primary neurons from mild to moderate excitotoxic injury.

Inhibition of the p38 mitogen-activated protein kinase (MAP Kinase) pathway reduces acute ischemic injury in vivo, suggesting a direct role for this signaling pathway in a number of neurodegenerative processes. The present study was designed to evaluate further the role of p38 MAP Kinase in acute excitotoxic neuronal injury using the selective p38 inhibitor SB-239063 (trans-1-(4hydroxycyclohexyl)-4-(fluorophenyl)-5-(2-methoxy-pyrimidin-4-yl) imidazole). Unlike the widely used p38 inhibitor, SB-203580 (4-(4-Fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole), this second generation p38 inhibitor more selectively inhibits p38 MAP Kinase without affecting the activity of other MAP Kinase signaling pathways and provides a more accurate means to selectively assess the role of p38 in excitotoxicity that has not been previously possible. SB-239063 provided substantial protection against cell death induced by either oxygen glucose deprivation (OGD) or magnesium deprivation in cultured neurons. The ability of this compound to block excitotoxicity was not due to direct inhibition of N-methyl-D-aspartate (NMDA) receptor-mediated currents as SB-239063 did not alter NMDA electrophysiological responses. SB-239063 did not protect against a severe excitotoxic insult induced by 60-min exposure to NMDA. However, when tested against a less severe, brief (5 min) NMDA exposure, p38 inhibition provided substantial protection. These data demonstrate that inhibition of p38 MAP Kinase can confer neuroprotection in vitro against mild but not severe excitotoxic exposure, and suggests that other additional pathways/mechanism(s) may be involved in severe excitotoxic cell death.