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We tested the hypothesis that combined use of trophic factors and caspase inhibitors increases brain resistance to ischaemia in mice. Intracerebroventricular administration of bFGF (>10 ng) 30 min after MCA occlusion decreased infarct size and neurological deficit in a dose-dependent manner following 2 h ischemia and reperfusion (20 h). Combined administration of the subthreshold doses of bFGF (3 ng) and caspase inhibitors (z-VAD.FMK, 27 ng or z-DEVD.FMK, 80 mg) reduced infarct volume by 60%, and reduced neurological deficit. Treatment with a subthreshold dose of bFGF (3 ng) extended the therapeutic window for z-DEVD.FMK (480 ng) from 1 to 3 h after reperfusion. Caspase-3 activity in the ischaemic brain was increased 30 min and 2 h after reperfusion but, was significantly reduced in bFGF-treated animals by 29 and 16%, respectively. Caspase-3 activity was not reduced by a direct bFGF effect because addition of bFGF (10 nM - 2 microM) did not decrease recombinant caspase-3 activity, in vitro. Our data show that combining caspase inhibitors and bFGF lengthens the treatment window for the second treatment, plus lowers the dosage requirements for neuroprotection. These findings are important because low doses of caspase inhibitors or bFGF reduce the possibility of side effects plus extend the short treatment window for ischaemic stroke.

1. We examined the effects of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzol[f]quinoxaline-7-sulpho namide (NBQX), the kainate receptor antagonists gamma-(R-)-glutamylaminomethanesulphonic acid (GAMS) and 6,7,8,9-tetrahydro-5-nitro-1H-benz[g]indole-2,3-dione-3-oxime (NS-102), and the group III metabotropic glutamate receptor (mGluR) agonist 2-amino-4-phosphono-S-butanoic acid (L-AP4) on c-fos-like immunoreactivity (c-fos LI) in trigeminal caudalis (Sp5C), lateral reticular (LRt), medullary reticular (Md) and solitary tract (Sol) nuclei, after intracisternal injection of capsaicin in urethane anaesthetized Sprague-Dawley rats. 2. Few c-fos labelled cells were observed within Sp5C in capsaicin-vehicle treated animals. The number of positive c-fos cells increased by 17 fold after intracisternal capsaicin (5 nmol) administration. 3. Pretreatment with CNQX (0.02, 0.1, 0.6, 3 and 15 mg kg-1) or NBQX (0.01, 0.1 and 1 mg kg-1), administered intraperitoneally 15 min before capsaicin, significantly reduced labelled cells within Sp5C by a maximum of 45 and 34%, respectively. The number of c-fox LI cells within LRt, Md and Sol was not affected. Pretreatment with L-AP4 (1, 3 and 10 mg kg-1) decreased the number of Sp5C c-fos LI cells by a maximum of 30%, whereas GAMS (1 and 10 mg kg-1) and NS-102 (1 and 5 mg kg-1) did not show any significant effect. 4. These results suggest that blockade of AMPA receptors, but not kainate receptors, or the activation of group III mGluRs, decrease the response of Sp5C neurons to trigeminovascular activation. Thus, in addition to NMDA receptors, mGluRs and AMPA receptors may modulate cephalic pain and may provide a potential therapeutic target for antimigraine drugs.

1. Excitotoxic and apoptotic mechanisms have been implicated in the pathophysiology of cerebral ischaemia. Both MK-801, an NMDA receptor antagonist, or peptide inhibitors of the caspase family (z-VAD.FMK and z-DEVD.FMK), protect mouse brain from ischaemic cell damage. In this study, we examined whether these drugs which act via distinct mechanisms, afford even greater neuroprotection when given in combination following 2 h MCA occlusion (filament model) and 18 h reperfusion. 2. Given alone as pretreatment, MK-801 (1, 3 and 5 mg kg(-1), but not 0.3 mg kg(-1), i.p.) decreased infarct size by 34-75%. When injected 1 h after occlusion and before reperfusion, 3 mg kg(-1) reduced injury but not when administered I h after reperfusion. 3. Pretreatment with a subthreshold dose of MK-801 (0.3 mg kg(-1)) plus a subthreshold dose of z-VAD.FMK (27 ng) or z-DEVD (80 ng) significantly decreased infarct size by 29 and 30%, respectively, and enhanced neurological function. 4. Administering a subthreshold dose of z-VAD.FMK (27 ng) or z-DEVD.FMK (80 ng) as pretreatment extended the time window for MK-801 (3 mg kg(-1)) by 2 h from 1 h before reperfusion to at least 1 h after reperfusion. 5. Pretreating with a subthreshold dose of MK-801 (0.3 mg kg(-1)) extended the time window for z-DEVD.FMK (480 ng) from 1 h after reperfusion to at least 3 h after reperfusion. 6. We conclude that caspase inhibitors which putatively block apoptotic cell death and inhibit cytokine production and the NMDA antagonist MK-801 act synergistically and prolong their respective therapeutic windows in cerebral ischaemia.

1. The effects of neuropeptide Y (NPY) receptor agonists (administered intravenously) were examined on plasma protein ([125I]-bovine serum albumin) leakage within dura mater evoked by unilateral trigeminal ganglion stimulation (0.6 mA, 5 ms, 5 Hz, 5 min), capsaicin (1 mumol kg-1, i.v.) or substance P (1 nmol kg-1, i.v.) in anaesthetized Sprague-Dawley rats. 2. NPY (EC50: 5.6 nmol kg-1) and NPY fragment 13-36 [NPY (13-36)] (ED50: 4.3 nmol kg-1), an NPY Y2 receptor agonist, dose-dependently attenuated [125I]-bovine serum albumin extravasation from meningeal vessels when administered 10 min prior to electrical stimulation. [Leu31, Pro34]-NPY, an NPY Y1 and Y3 receptor agonist, inhibited the response at a higher dose only (23 nmol kg-1) (P < 0.05). 3. NPY also significantly decreased plasma protein extravasation induced by capsaicin (1 mumol kg-1) but not by substance P (1 nmol kg-1). 4. Pertussis toxin (20 micrograms kg-1, administered intracisternally 48 h prior to stimulation) blocked completely the inhibitory effect of NPY and NPY (13-36) but did not inhibit extravasation alone. 5. We conclude that NPY inhibits neurogenically-mediated plasma protein extravasation acting through presynaptic pertussis toxin-sensitive NPY Y2 receptors, possibly by inhibition of neuropeptide release from perivascular trigeminovascular afferents.

1. The effects of progesterone, its A-ring-reduced metabolites, allopregnanolone, tetrahydroxydeoxycorticosterone and the synthetic neuroactive steroid alphaxalone were evaluated in a rat model of plasma extravasation within the meninges following unilateral electrical stimulation (ES) of the trigeminal ganglion (0.6 mA, 5 ms, 5 min) or substance P administration (1 nmol kg-1, i.v.). 2. When administered 55 min prior to electrical stimulation, progesterone (> or = 500 micrograms, s.c.) dose-dependently decreased plasma extravasation within the meninges (ED50: 650 micrograms) but not within conjunctiva and tongue. Promegestone (R5020), a non-metabolized progesterone agonist (1000 micrograms, i.p.) was ineffective. The administration of progestrone (> or = 500 micrograms s.c.) 55 min prior to substance P partially suppressed plasma extravasation within the meninges (ED50: 550 micrograms). 3. The GABAA-antagonist, bicuculline (ED50: 8.2 micrograms kg-1, i.p.) but not the GABAB-antagonist, phaclofen (100 micrograms kg-1, i.p.) attenuated the effects of progesterone after electrical stimulation and substance P administration. 4. The metabolites of progesterone, allopregnanolone (3 alpha-hydroxy-5 alpha- pregnan-20-one (THP); ED50: 0.58 micrograms kg-1, i.p.), tetrahydroxydeoxycorticosterone (3 alpha,21- dihydroxy-5 alpha-pregnan-20-one (THDOC); ED50: 1.2 micrograms kg-1, i.p.) as well as the synthetic steroid alphaxalone (3 alpha-hydroxy-5 alpha-pregnane-11,20-dione; ED50: 1.8 micrograms kg-1, i.p.) suppressed plasma extravasation dose-dependently following ES, whereas the epimer of allopregnanolone, 3 beta-hydroxy-5 alpha-pregnan-20-one (100 micrograms kg-1, i.p.), did not. Extravasation caused by SP administration was partially suppressed by allopregnanolone (> or = 1 microgram kg-1, i.p.) (ED50: 2.1 micrograms kg-1). 5. The effect of progesterone (1000 micrograms, s.c.) and allopregnanolone (100 micrograms kg-1, i.p.) on neurogenic plasma extravasation was reversed by bicuculline (10 micrograms kg-1, i.p.) or by a congener, bicuculline-methiodide (10 micrograms kg-1, i.p.) which does not cross the blood brain barrier. 6. Progesterone (1000 micrograms, s.c.) had no effect on mean arterial blood pressure or heart rate when measured for 60 min after administration. 7. These results indicate that neurosteroid modulation of a GABAA-receptor located outside the blood brain barrier suppresses neurogenic and substance P-induced plasma extravasation within the meninges. The findings are consistent with previously reported data showing that valproic acid and muscimol inhibit meningeal oedema by bicuculline-sensitive mechanisms. Drugs which activate GABAA-receptors and its modulatory sites might be clinically effective in the treatment of migraine and cluster headache.

1. Valproic acid, useful in the treatment of migraine, is an inhibitor of gamma aminobutyric acid (GABA) aminotransferase and activator of glutamic acid decarboxylase. Its mechanism in migraine remains obscure. The effects of valproic acid (2-propylpentanoic acid) were examined on the number of cells expressing c-fos-like immunoreactivity (c-fos-LI), a marker of neuronal activation, within the trigeminal nucleus caudalis (lamina I, IIo, TNC) 2 h after intracisternal injection of the irritant, capsaicin (0.1 ml; 15.25 micrograms ml-1), in urethane-anaesthetized Hartley guinea-pigs. Positive cells were counted in eighteen sections (50 microns) at three representative levels (rostral, middle and caudal) within lamina I, IIo of the TNC in 90 animals. 2. Numerous cells were labelled after capsaicin instillation (244 +/- 25; 1 ml; 15.25 mM) but not after capsaicin vehicle (11 +/- 1). Positive cells were also found within the medial reticular nucleus, the area postrema and the nucleus of the solitary tract. A similar distribution has been demonstrated previously after application of intracisternal irritants such as autologous blood or carrageenin. 3. Valproate (> or = 10 mg kg-1, i.p.) reduced labelled cells by 52% (P < 0.05) in lamina I, IIo but not within the area postrema, the nucleus of the solitary tract or the medial reticular nucleus. A similar finding was obtained previously after administration of sumatriptan, dihydroergotamine or the NK1 receptor antagonist RPR 100,893. 4. Pretreatment with bicuculline (30 micrograms kg-1; i.p.), a GABAA antagonist, but not phaclofen (1 mg kg-1) a GABAB antagonist, reversed the effect of valproate and increased c-fos positive cells within lamina I, IIo. Somewhat paradoxically, bicuculline by itself (30 micrograms kg-1 i.p.) decreased the number of labelled cells suggesting that more than a single GABAergic mechanism can suppress c-fos expression. 5. We conclude that the mechanism of action of valproate is mediated via GABAA receptors. Since valproate decreases both c-fos expression and as previously shown, neurogenic inflammation within the meninges, the GABAA receptor complex might provide an important target for drug development in migraine and related headaches.

1. The GABA transaminase inhibitor and activator of glutamic acid decarboxylase, valproic acid is being used for the treatment of migraine. Its mechanism of action is unknown. We tested the effects of sodium valproate and GABAA-agonist muscimol on dural plasma protein ([125I]-bovine serum albumin) extravasation evoked by either unilateral trigeminal ganglion stimulation (0.6 mA, 5 ms, 5 Hz, 5 min) or substance P (SP) administration (1 nmol kg-1,i.v.) in anaesthetized Sprague-Dawley rats. 2. Intraperitoneal (i.p.) injection of sodium valproate or muscimol, but not baclofen (< or = 10 mg kg-1, i.p.) dose-dependently reduced dural plasma protein extravasation caused either by electrical trigeminal stimulation (ED50: 6.6 +/- 1.4 mg kg-1, i.p., and 58 +/- 18 micrograms kg-1, i.p. for valproate or muscimol, respectively) or by intravenous substance P administration (ED50: 3.2 +/- 1.4 mg kg-1, i.p. and 385 +/- 190 micrograms kg-1, i.p. for valproate or muscimol, respectively). 3. Valproate (6.6 mg kg-1, i.p.) or muscimol (58 micrograms kg-1, i.p.) had no effect on mean arterial blood pressure or heart rate when measured for 30 min after i.p. administration. 4. The GABAA-antagonist bicuculline (0.01 mg kg-1, i.p.) completely reversed the effect of valproate and muscimol on plasma extravasation following electrical stimulation or substance P administration, whereas the GABAB-receptor antagonist, phaclofen (0.01-1 mg kg-1, i.p.) did not. Bicuculline or phaclofen, given alone, did not alter the plasma extravasation response after either electrical stimulation or SP administration. 5. Valproate decreased plasma extravasation following substance P administration in adult animals, neonatally treated with capsaicin by a bicuculline-reversible mechanism. This suggests that GABAA receptors are not found primarily on those afferent neurones or fibres which are sensitive to capsaicin treatment in neonatal rats.6. We conclude that sodium valproate blocks plasma extravasation in the meninges through GABAA mediated postjunctional receptors probably within the meninges. The dosages required are comparable to those used clinically. Agonists and modulators at the GABAA receptor may become useful for the development of selective therapeutic agents for migraine and cluster headache.

1. The effects of an intravenously administered sumatriptan analogue were examined on c-fos-like immunoreactivity (c-fos-LI), a marker of neuronal activation, evoked within trigeminal nucleus caudalis (TNC) and other brain stem regions 2 h after intracisternal injection of the irritant, capsaicin (0.1 ml, 0.1 mM), in pentobarbitone-anaesthetized Hartley guinea-pigs. 2. C-fos-LI was assessed in eighteen serial sections (50 microns) using a polyclonal antiserum. A weighted average, reflecting total expression within lamina I, IIo of TNC was obtained from three representative levels (i.e., at -0.225 mm, -2.475 mm and -6.975 mm.). 3. Capsaicin caused significant labelling within lamina I, IIo, a region containing axonal terminations of small unmyelinated C-fibres, as well as within the nucleus of the solitary tract, area postrema and medial reticular nucleus. A similar distribution of positive cells was reported previously after intracisternal injection of other chemical irritants such as autologous blood or carrageenin. 4. Pretreatment with a conformationally restricted sumatriptan analogue (with some selectivity for 5-HT1B and 5-HTID receptor subtypes) CP-122,288, reduced the weighted average by approximately 50-60% (P < 0.05) in lamina I, IIo at > or = 100 pmol kg-1, i.v., but did not decrease cell number within area postrema, nucleus of the solitary tract or medial reticular nucleus. A similar pattern was reported previously following sumatriptan, dihydroergotamine or CP-93,129 administration after noxious meningeal stimulation. 5. We conclude that modifications at the amino-ethyl side chain of sumatriptan dramatically enhance the suppression of c-fos expression within TNC, a finding consistent with its remarkable potency against neurogenic plasma protein extravasation within dura mater. CP-122,288 and related analogues may serve as an important prototype for drug development in migraine and related headaches.

1. The ability of an NK1 receptor antagonist, RPR 100893, and its enantiomer, RPR 103253 to block neurogenic plasma protein extravasation in guinea-pig dura mater and conjunctiva was assessed following 125I-labelled bovine serum albumin ([125I]-BSA, 50 muCi kg-1, i.v.) and unilateral electrical stimulation of the trigeminal ganglion (0.6 mA, 5 ms, 5 Hz, 5 min) or capsaicin administration (150 micrograms kg-1, i.v.). 2. When administered p.o. 60 min prior to electrical stimulation, RPR 100893 (> or = 0.1 microgram kg-1) decreased plasma protein extravasation in dura mater in a dose-dependent manner, whereas the enantiomer (10 or 100 micrograms kg-1, p.o.) was inactive. 3. When given i.v. 30 min prior to electrical stimulation, RPR 100893 (> or = 0.5 ng kg-1) significantly inhibited plasma protein extravasation in the dura mater evoked by electrical stimulation in a dose-dependent manner. 4. RPR 100893 (100 micrograms kg-1, p.o.) also reduced the leakage when given 45 min before the guinea-pigs were killed and 10, 40 and 80 min after electrical trigeminal stimulation. 5. RPR 100893 given p.o. dose-dependently inhibited capsaicin-induced plasma protein extravasation with ID50S of 7.4 micrograms kg-1 and 82 micrograms kg-1 for dura mater and conjunctiva, respectively. 6. These results are consistent with the contention that NK1 receptors mediate neurogenic plasma protein leakage following trigeminal stimulation, and suggest that NK1 receptor antagonists of the perhydroisoindolone series may be useful for treating migraine and cluster headaches.

1. The delayed effects of stimulating the trigeminal ganglion unilaterally in rats and guinea-pigs were assessed by measuring the leakage of radiolabelled albumin from blood into the dura mater at intervals for up to 120 min after a 5 min stimulation period (5 Hz, 0.6 mA, 5 ms). 2. [125I]-albumin (50 microCi kg-1) was injected i.v. as a tracer 0, 20, 50, 80 or 110 min after stimulation and the animals were killed 10 min later. Extravasation of plasma protein developed for up to 90 min poststimulation. 3. To examine the mechanism underlying delayed plasma protein extravasation, CP-93,129 (5-HT1B receptor agonist, 460 nmol.kg-1), sumatriptan (5-HT1B/D receptor agonist, 24 nmol kg-1), or neutral endopeptidase 24.11 (1 nmol kg-1) were administered 45 or 75 min after trigeminal stimulation and 5 min before radiolabelled albumin. The extravasation response was reduced at 45 min. CP-23,129 also blocked extravasation when injected 25 min after capsaicin administration (1 mumol kg-1). 4. If the tracer was injected 5 min prior to electrical trigeminal stimulation, endopeptidase 24.11 (1 nmol kg-1) given 10 min before stimulation blocked the leakage (as reported previously for CP-93,129 or sumatriptan). All three compounds blocked the leakage when administered 30 min (but not 60 min) poststimulation in this paradigm. 5. The data support the previously made contention that neuropeptide release from sensory fibres mediates the plasma extravasation response following trigeminal ganglion stimulation, and that release and plasma leakage continue many minutes beyond the stimulation period. Hence, drugs that inhibit neuropeptide release (CP-93,129, sumatriptan), or enhance breakdown of neuropeptide mediators(endopeptidase 24.11) block the delayed extravasation response. Extravasation developing later than 45 min poststimulation was not neurogenically mediated.

L-Arginine (> or = 30 mg kg-1, i.v.), but not D-arginine (300 mg kg-1) administered 5 min after unilateral common carotid/middle cerebral artery occlusion increased regional cerebral blood flow (rCBF) within the dorsolateral ischaemic cortex in spontaneously hypertensive rats. L-Arginine (300 mg kg-1) increased rCBF from 22 +/- 2.7 to 33 +/- 4% of baseline as measured by laser-Doppler flowmetry. This increase may explain the ability of L-arginine to reduce infarct size following focal cerebral ischaemia, as reported previously. The mechanism appears to be mediated by nitric oxide since topical L-NAME (1 microM), a nitric oxide synthase inhibitor, decreased pial arteriole calibre from 115 +/- 2.2 to 106 +/- 0.9% of baseline following L-arginine infusion (300 mg kg-1).

1. The effects of intravenously administered 5-HT1B receptor agonists were examined on c-fos like immunoreactivity, an indicator of neuronal activation, within the brain stem. C-fos was induced by injecting an algesic, vasoconstrictor substance (0.3 ml of autologous blood) or a pro-inflammatory molecule, carrageenin (1 mg in 0.1 ml saline) into the cisterna magna of pentobarbitone-anaesthetized Sprague-Dawley rats and was visualized in serial sections (50 micrometers) by use of a polyclonal antiserum. 2. As previously reported, the injection of blood caused significant labelling within laminae I, IIo of the trigeminal nucleus caudalis, a major nociceptive brain stem nucleus, as well as within nucleus of the solitary tract and area postrema. A similar pattern of expression with fewer cells per section was detected after carrageenin instillation. The number of expressing cells was reduced by 54% in trigeminal nucleus caudalis but not within the nucleus of the solitary tract or area postrema when blood was injected in adult rats neonatal capsaicin treatment. 3. Pretreatment with 5-HT1 agonists with some selectivity for the 5-HT1B receptor, CP-93,129 (460 nmol kg-1 x 2, i.v.), sumatriptan (720 nmol kg-1 x 2, i.v.) or dihydroergotamine (86 nmol kg-1 x 2, i.v.) reduced positive cells by 39%, 31%, and 33% respectively in trigeminal nucleus caudalis but not in nucleus of the solitary tract or area postrema after blood instillation. Pretreatment with the analgesic morphine (15 mumol kg-1, s.c.) also decreased the number of positive cells by 63% in trigeminal nucleus caudalis. 4. CP-93,129 (460 nmol kg-1 x 2, i.v.) reduced the number of c-fos labelled cells by 47% within lamina I, IIo after carrageenin instillation. 5. Drug-induced blockade appeared to be tissue-dependent. Pretreatment with sumatriptan (720 nmol kg-1 x 2, i.v.) did not block c-fos expression in trigeminal nucleus caudalis following formalin application to the nasal mucosa.6. Drug-induced blockade may be mediated by an action on primary afferent (trigeminovascular) fibres in as much as CP-93,129 (460 nmol kg-' x 2, i.v.) did not reduce the number of expressing cells within the trigeminal nucleus caudalis following blood instillation in rats treated as neonates with capsaicin.7. We infer from these results that the analgesic actions of agonists at 5-HTB receptors (the receptor subtype analogous to 5-HTID in man) need not depend upon the presence of vasodilatation and, that 5-HTID receptor-mediated blockade of neurotransmission contributes significantly to the analgesic effects of these drugs in headache.8. Based on the demonstrated effects of 5-HTB/D agonists against the actions of two chemicallyunrelated meningeal stimulants, we suggest that treatment with 5-HTID agonists may be useful for the alleviation of pain in other headache conditions associated with meningeal irritation. Bacterial, viral(including AIDS meningovascular inflammation) and other forms of chemical meningitis merit further investigation.

Pretreatment with CP-93,129 blocked plasma extravasation in rat dura mater induced by electrical trigeminal ganglion stimulation when administered at greater than or equal to 140 nmol kg-1, i.v. but did not affect plasma leakage in guinea-pig at 460 or 1400 nmol kg-1. Sumatriptan, a 5-HT1D-like receptor agonist, blocked plasma extravasation in the guinea-pig model when administered at 7 nmol kg-1. In as much as CP-93,129 binds with micromolar affinities to 5-HT1A, 5-HT1C, 5-HT1D, and 5-HT2 recognition sites, and with nanomolar affinity to the 5-HT1B receptor subtype, blockade of plasma extravasation in the rat dura mater may be mediated by 5-HT1B receptors whereas the 5-HT1D receptor may be more relevant to the guinea-pig.

1. We describe the effects of pretreatment with 5-hydroxytryptamine (5-HT) receptor agonists and antagonists on neurogenically-mediated plasma protein extravasation ([125I]-albumin) in rat dura mater and in extracranial tissues (temporalis muscle fascia, conjunctiva, eyelid and lip) induced by electrical stimulation of the right trigeminal ganglion. 2. Leakage of [125I]-bovine serum albumin from blood vessels in dura mater following high intensity stimulation (1.2 mA, 5 ms, 5 Hz for 5 min) was significantly reduced by the intravenous administration of drugs active at 5-HT receptors with some selectivity for the 5-HT1 receptor subtypes: 5-carboxamidotryptamine (5-CT) (threshold dose, 1 ng kg-1); 5-benzyloxytryptamine (5-BT) (10, 30 or 100 micrograms kg-1); 8-hydroxydipropylaminotetralin (8-OH-DPAT) (300 micrograms kg-1); and as previously reported, sumatriptan (100 micrograms kg-1), dihydroergotamine (DHE) (50 micrograms kg-1); ergotamine tartrate (100 micrograms kg-1) and chronically administered methysergide (1 mg kg-1). 3. The putative 5-HT receptor antagonist, metergoline 100 micrograms kg-1, inhibited partially the effect of sumatriptan in dura mater providing additional evidence for a 5-HT1 receptor subtype-mediated mechanism, although it was not effective against 5-CT (1 ng kg-1). Methiothepin (300 micrograms kg-1) did not affect the response to sumatriptan. When administered at high concentrations (1 mg kg-1) methiothepin and metergoline decreased plasma protein extravasation in rat dura mater. 4. Pretreatment with the 5-HT2 receptor antagonists pizotifen, 300pugkg 1, or ketanserin, 300,ugkg ', or the 5-HT3 receptor antagonists MDL 72222, 300,ugkg-1, or ICS 205-930, 300pgkg-1, did not affect plasma protein leakage following electrical trigeminal stimulation. Blockade by sumatriptan of plasma protein extravasation was not inhibited by pizotifen (300,ug kg-1) or MDL 72222 (300pg kg- '). 5. The 5-HT receptor(s) mediating this response were present only on intracranial tissues innervated by the trigeminal nerve; plasma protein extravasation in extracranial tissues was not blocked by pretreatment with the equivalent or higher concentrations of the above drugs following low intensity trigeminal stimulation (0.1 mA, 5 ms, 5 Hz). 6. The putative 5-HT receptor(s) mediating this response were not present on sympathetic fibres innervating dura mater since unilateral removal of the superior cervical ganglion did not prevent the development of plasma protein extravasation nor did it affect the blockade by sumatriptan IOOpug kg- '. 7. The above pharmacological data suggest that intracranial vessels possess 5-HT receptor(s) which are coupled to inhibition of neurogenically-mediated plasma protein extravasation. These receptors cannot be detected on extracranial cephalic blood vessels innervated by the trigeminal nerve, although available evidence strongly suggests that the 5-HT receptors reside on perivascular trigeminal nerve fibres. The rank order of effective doses (threshold concentrations; 5-CT < 5-BT < DHE < sumatriptan < 8-OHDPAT) is most consistent with a 5-HTlB- or 5-HTlD-mediated response, among the known 5-HT1 family of receptors. However, the lack of effect of methiothepin against the actions of sumatriptan, or metergoline against the effects of 5-CT suggest important differences and the possibility that a previously unrecognized 5-HT receptor(s) is involved in this response.

1. We describe the actions of GR43175, a 5-hydroxytryptamine1 (5-HT1)-like receptor agonist, on neurogenically-mediated plasma protein extravasation within an important pain-sensitive intracranial tissue, the dura mater. 2. GR43175 markedly attenuated extravasation of 125I-albumin from blood vessels within ipsilateral dura mater when administered to rats (100 micrograms kg-1) fifteen minutes before unilateral electrical trigeminal stimulation (1.2 mA, 5 Hz, 5 ms, 5 min); the ratio (stimulated/unstimulated sides) decreased from 1.81 to 1.23, P less than 0.005). 3. GR43175 (100 micrograms kg-1, i.v., rats; 30 micrograms kg-1, guinea-pigs) decreased the leakage of radiolabelled albumin from 163% to 119% (P less than 0.005, guinea-pig) or from 174 to 118% (P less than 0.05, rat) above vehicle-treated controls when injected ten minutes before systemic capsaicin treatment (0.5 or 1 mumol kg-1, i.v.). 4. GR43175 (30-300 micrograms kg-1) did not block plasma protein extravasation within extracranial tissues of rats and guinea-pigs innervated by the trigeminal nerve (conjunctiva, eyelid and lip). 5. The protein leakage which followed the i.v. administration of 5-HT (1 mumol kg-1) or neuropeptides which mediate neurogenic plasma extravasation, substance P (0.3 nmol kg-1 or 1 nmol kg-1) and neurokinin A (1 nmol kg-1), was not blocked by GR43175 (100, 300 micrograms kg-1) despite the presence of leakage in amounts equivalent to that following neurogenic stimulation. 6. GR43175 (100 micrograms kg-1) decreased bradykinin (10 mumol kg-1)-induced extravasation from 142 to 115% above vehicle-treated animals (P less than 0.05). 7. These results demonstrate an important action of GR43175 on neurogenic mechanisms in dural blood vessels. Since the ergot alkaloids possess a similar profile of drug activity, it is suggested that drugs useful in the treatment of acute vascular headaches may share a similar mechanism of action.