Painful heat reveals hyperexcitability of the temporal pole in interictal and ictal migraine States.

During migraine attacks, alterations in sensation accompanying headache may manifest as allodynia and enhanced sensitivity to light, sound, and odors. Our objective was to identify physiological changes in cortical regions in migraine patients using painful heat and functional magnetic resonance imaging (fMRI) and the structural basis for such changes using diffusion tensor imaging (DTI). In 11 interictal patients, painful heat threshold + 1°C was applied unilaterally to the forehead during fMRI scanning. Significantly greater activation was identified in the medial temporal lobe in patients relative to healthy subjects, specifically in the anterior temporal pole (TP). In patients, TP showed significantly increased functional connectivity in several brain regions relative to controls, suggesting that TP hyperexcitability may contribute to functional abnormalities in migraine. In 9 healthy subjects, DTI identified white matter connectivity between TP and pulvinar nucleus, which has been related to migraine. In 8 patients, fMRI activation in TP with painful heat was exacerbated during migraine, suggesting that repeated migraines may sensitize TP. This article investigates a nonclassical role of TP in migraineurs. Observed temporal lobe abnormalities may provide a basis for many of the perceptual changes in migraineurs and may serve as a potential interictal biomarker for drug efficacy.

Major histocompatibility complex class II-expressing endothelial cells induce allospecific nonresponsiveness in naive T cells.

The role of endothelial cells (EC) in initiating a primary T cell response is of importance in clinical transplantation and autoimmunity since EC are the first allogeneic target encountered by the recipient's immune system and may display tissue-specific autoantigens in the context of an inflammatory response. In this study, we have investigated the antigen-presenting cell function of human umbilical vein-derived EC (HUVEC), depleted of constitutively major histocompatibility complex class II+ cells and induced to express class II molecules by interferon-gamma. The results show that HUVEC do not express B7 but can support proliferation by antigen-specific T cell clones. In contrast, they were unable to initiate a primary alloresponse using three independent HUVEC cultures and MHC class II-mismatched CD4+ T cells from eight donors. The response to HUVEC was reconstituted by trans-costimulation provided by DAP.3 transfectants expressing human B7.1. Coculture of peripheral blood T cells with EC expressing allogeneic DR molecules had markedly different effects on CD45RO+ and RA+ subsets. Subsequent reactivity of the RO+ T cells was unaffected by exposure to EC, indicating a neutral encounter. In contrast, culture with DR+ EC induced allospecific nonresponsiveness in RA+ T cells.

Characterization of the calcitonin gene-related peptide receptor antagonist telcagepant (MK-0974) in human isolated coronary arteries.

The sensory neuropeptide calcitonin gene-related peptide (CGRP) plays a role in primary headaches, and CGRP receptor antagonists are effective in migraine treatment. CGRP is a potent vasodilator, raising the possibility that antagonism of its receptor could have cardiovascular effects. We therefore investigated the effects of the antimigraine CGRP receptor antagonist telcagepant (MK-0974) [N-[(3R,6S)-6-(2,3-difluorophenyl)-2-oxo-1-(2,2,2-trifluoroethyl)azepan-3-yl]-4-(2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridine-1-yl)piperidine-1-carboxamide] on human isolated coronary arteries. Arteries with different internal diameters were studied to assess the potential for differential effects across the coronary vascular bed. The concentration-dependent relaxation responses to human alphaCGRP were greater in distal coronary arteries (i.d. 600-1000 microm; E(max) = 83 +/- 7%) than proximal coronary arteries (i.d. 2-3 mm; E(max) = 23 +/- 9%), coronary arteries from explanted hearts (i.d. 3-5 mm; E(max) = 11 +/- 3%), and coronary arterioles (i.d. 200-300 microm; E(max) = 15 +/- 7%). Telcagepant alone did not induce contraction or relaxation of these coronary blood vessels. Pretreatment with telcagepant (10 nM to 1 microM) antagonized alphaCGRP-induced relaxation competitively in distal coronary arteries (pA(2) = 8.43 +/- 0.24) and proximal coronary arteries and coronary arterioles (1 microM telcagepant, giving pK(B) = 7.89 +/- 0.13 and 7.78 +/- 0.16, respectively). alphaCGRP significantly increased cAMP levels in distal, but not proximal, coronary arteries, and this was abolished by pretreatment with telcagepant. Immunohistochemistry revealed the expression and colocalization of the CGRP receptor elements calcitonin-like receptor and receptor activity-modifying protein 1 in the smooth muscle cells in the media layer of human coronary arteries. These findings in vitro support the cardiovascular safety of CGRP receptor antagonists and suggest that telcagepant is unlikely to induce coronary side effects under normal cardiovascular conditions.

Distinct mechanism for antidepressant activity by blockade of central substance P receptors.

The localization of substance P in brain regions that coordinate stress responses and receive convergent monoaminergic innervation suggested that substance P antagonists might have psychotherapeutic properties. Like clinically used antidepressant and anxiolytic drugs, substance P antagonists suppressed isolation-induced vocalizations in guinea pigs. In a placebo-controlled trial in patients with moderate to severe major depression, robust antidepressant effects of the substance P antagonist MK-869 were consistently observed. In preclinical studies, substance P antagonists did not interact with monoamine systems in the manner seen with established antidepressant drugs. These findings suggest that substance P may play an important role in psychiatric disorders.

Structure-based development of anticancer drugs: complexes of NAD(P)H:quinone oxidoreductase 1 with chemotherapeutic quinones.

BACKGROUND: NAD(P)H:quinone acceptor oxidoreductase (QR1) protects animal cells from the deleterious and carcinogenic effects of quinones and other electrophiles. Remarkably, the same enzyme activates cancer prodrugs that become cytotoxic only after two-electron reduction. QR1's ability to bioactivate quinones and its elevated expression in many human solid tumors makes this protein an excellent target for enzyme-directed drug development. Until now, structural analysis of the mode of binding of chemotherapeutic compounds to QR1 was based on model building using the structures of complexes with simple substrates; no structure of complexes of QR1 with chemotherapeutic prodrugs had been reported. RESULTS: Here we report the high-resolution crystal structures of complexes of QR1 with three chemotherapeutic prodrugs: RH1, a water-soluble homolog of dimethylaziridinylbenzoquinone; EO9, an aziridinylindolequinone; and ARH019, another aziridinylindolequinone. The structures, determined to resolutions of 2.0 A, 2.5 A, and 1.86 A, respectively, were refined to R values below 21% with excellent geometry. CONCLUSIONS: The structures show that compounds can bind to QR1 in more than one orientation. Surprisingly, the two aziridinylindolequinones bind to the enzyme in different orientations. The results presented here reveal two new factors that must be taken into account in the design of prodrugs targeted for activation by QR1: the enzyme binding site is highly plastic and changes to accommodate binding of different substrates, and homologous drugs with different substituents may bind to QR1 in different orientations. These structural insights provide important clues for the optimization of chemotherapeutic compounds that utilize this reductive bioactivation pathway.

When to harvest peripheral-blood stem cells after mobilization therapy: prediction of CD34-positive cell yield by preceding day CD34-positive concentration in peripheral blood.

PURPOSE: To evaluate whether the CD34+ yield from a single peripheral-blood stem-cell (PBSC) harvest could be predicted by measurement of the patient's circulating WBC and CD34+ cell concentrations on the day before harvest. PATIENTS AND METHODS: Thirty-nine patients with hematologic or nonhematologic malignancy underwent 41 stem-cell mobilization episodes with cytotoxic chemotherapy and/or granulocyte colony-stimulating factor (G-CSF), and a total of 63 leukapheresis procedures were performed. Peripheral-blood samples were analyzed for WBC and CD34+ cell concentration both on the day before and the day of leukapheresis. RESULTS: The median WBC and CD34+ concentrations on the day preceding leukapheresis were 10.0 x 10(9)/L (range, 0.4 to 44.4) and 24.9 x 10(6)/L (range, 0.1 to 349.4), respectively. On the day of harvest, the corresponding figures were 15.1 x 10(9)/L (range, 1.5 to 52.6) and 29.3 x 10(6)/L (range, 0.1 to 543.1), respectively. The median CD34+ cell number collected in a single leukapheresis was 2.6 x 10(6)/kg body weight (range, 0.1 to 26.1). Both the preceding day (r = .84, P < .001) and harvest day (r = .95, P < .001) CD34+ circulating concentrations correlated significantly with the number of CD34+ cells per kilogram collected at leukapheresis. The correlation between CD34+ cells per kilogram collected and harvest day WBC count was also significant (r = .43, P <.001), but with the preceding day WBC count was nonsignificant. CONCLUSION: The number of CD34+ cells harvested in a single leukapheresis can be predicted by measurement of the preceding day peripheral-blood circulating CD34+ concentration, and on the basis of these data a table of probable CD34+ cell yield has been constructed. This correlation may facilitate the efficient organization of leukapheresis procedures.

Screening cascade and development of potential Positron Emission Tomography radiotracers for mGluR5: in vitro and in vivo characterization.

PURPOSE: Use of mGluR5 receptor radiotracers to determine whether an in vitro binding assay is able to predict how good a radiotracer is likely to be in imaging receptor in the central nervous system (CNS) via positron emission tomography (PET). PROCEDURES: Saturation and equilibrium competition studies in rat and rhesus membranes were used to determine receptor concentrations and tracer affinities. In addition, specific binding of metabotropic receptor subtype 5 (mGluR5) radioligands in rhesus and rat brain sections was determined using a "no-wash protocol," and the in vivo binding signal in rats was determined using micro-PET. RESULTS: Affinity values were determined for a series of mGluR5 antagonists (1-5) and ranged from 0.1 to 11 nM in rat. A previously reported "no-wash protocol" was then employed to determine specific binding in tissue sections following a 20-min incubation, and the regional distribution of these mGluR5 radiotracers determined in rat brain via autoradiography. The analogs 1b, 2b, 3b, and 4b, but not 5b, displayed good signal-to-noise ratios under these conditions with high density of binding in caudate, cortex, and hippocampus and lower density in cerebellum. With this information it was predicted that 1c, 2c, 3b, and 4b would display measurable signal-to-noise ratios in vivo, and that the larger in vitro signals for 3b and 4b would translate to 3b and 4b yielding the best in vivo signals. These predictions were investigated using micro-PET imaging in rat. Compound 1c showed a rapid wash-in and rapid wash-out profile in rat brain. Compound 2c showed similar signal-to-noise ratio as 1b, but slower washout. Compounds 3b and 4b showed the best signal-to-noise ratio in vivo, while 5b did not provide a significant signal, as predicted. In vivo occupancy estimates for 2-methyl-6-(phenylethynyl)-pyridine (MPEP) following intravenous administration were determined using radiolabeled compounds 1c, 2c, and 3b; they were essentially the same and were on the order of 1 mg kg(-1) (ID(50)). CONCLUSIONS: An in vitro screen of several mGluR5 tracers was used to rapidly predict whether radiolabeled mGluR5 analogs would be useful as PET radiotracers. Results provided an extension to previously reported data. Two of the four radiotracers with the best in vitro "no-wash" results also showed the best potential as measured noninvasively using micro-PET.

A new screening system for NAD(P)H:quinone oxidoreductase (NQO1)-directed antitumor quinones: identification of a new aziridinylbenzoquinone, RH1, as a NQO1-directed antitumor agent.

NAD(P)H:quinone oxidoreductase (NQO1; DT-diaphorase) is elevated in certain tumors, such as non-small cell lung cancer (NSCLC). Compounds such as mitomycin C and streptonigrin are efficiently bioactivated by NQO1 and have been used in an enzyme-directed approach to chemotherapy. Previously, 2,5-diaziridinyl-3,6-dimethyl-1,4-benzoquinone (MeDZQ) was identified as a potential antitumor agent based on its high rate of bioactivation by human NQO1 and its selective cytotoxicity to cells containing elevated NQO1. RH1, a water-soluble analogue of MeDZQ synthesized in this work, was a better substrate for recombinant human NQO1 than the parent compound. RH1 was, correspondingly, more cytotoxic to human tumor cells expressing elevated NQO1 activity (H460 NSCLC and HT29 human colon carcinoma), as measured by 3-(4,5-dimethylthiazol-2,5-diphenyl)tetrazolium assay, than it was to cells deficient in NQO1 activity (H596 NSCLC and BE human colon carcinoma). RH1 exhibited a greater selective toxicity (ratio of IC50s in H596:H460 and BE:HT29) to cells with elevated NQO1 activity relative to MeDZQ. Additionally, we report the establishment of a stable line of BE human colon carcinoma cells transfected with wild-type human NQO1 (BE-NQ7). BE cells are devoid of NQO1 activity due to a homozygous point mutation in the NQO1 gene. In comparison to the parental cell line, RH1, MeDZQ, and mitomycin C were significantly more cytotoxic to BE-NQ7 cells (17-, 7-, and 3-fold, respectively), confirming that the presence of NQO1 is sufficient to increase cytotoxicity of these antitumor quinones. These data suggest that RH1 may be an effective NQO1-directed antitumor agent for the therapy of tumors with elevated NQO1 activity, such as NSCLC.

Optimizing Central Nervous System Drug Development Using Molecular Imaging.

Advances in multimodality fusion imaging technologies promise to accelerate the understanding of the systems biology of disease and help in the development of new therapeutics. The use of molecular imaging biomarkers has been proven to shorten cycle times for central nervous system (CNS) drug development and thereby increase the efficiency and return on investment from research. Imaging biomarkers can be used to help select the molecules, doses, and patients most likely to test therapeutic hypotheses by stopping those that have little chance of success and accelerating those with potential to achieve beneficial clinical outcomes. CNS imaging biomarkers have the potential to drive new medical care practices for patients in the latent phases of progressive neurodegenerative disorders by enabling the detection, preventative treatment, and tracking of disease in a paradigm shift from today's approaches that have to see the overt symptoms of disease before treating it.

The neuroprotective effect of the glycine site antagonist 3R-(+)-cis-4-methyl-HA966 (L-687,414) in a rat model of focal ischaemia.

3R-(+)-cis-4-Methyl-HA966 (L-687,414) is a novel and selective, low intrinsic activity, partial agonist at the glycine site of the N-methyl-D-aspartate (NMDA) receptor. Thus, while it acts primarily to block NMDA receptor function in the presence of glycine, it fails to produce a complete block of NMDA receptor activation. In this study, we have investigated its neuroprotective effects in a rat model of focal ischaemia, involving permanent occlusion of the left middle cerebral artery. L-687,414 was administered as a bolus dose of 17.6 mg/kg i.v. straight after the occlusion or as a bolus dose + infusion for 4 h. The doses of L-687,414 used for the infusion studies were 7 mg/kg i.v. + 7 mg/kg/h, 14 mg/kg + 14 mg/kg/h, or 30 mg/kg + 30 mg/kg/h. The 17.6-mg/kg dose gave an estimated peak plasma level of 24 micrograms/ml, which decayed with a t1/2 of 56 min. The three infusion dosing regimens gave mean plasma levels over the 4 h of 11, 25 and 61 micrograms/ml plasma, respectively. The 17.6-mg/kg dose of L-687,414 gave no significant protection against the volume of hemispheric, cortical, or caudate damage when compared with the control group of animals. The lowest infusion dosing regimen of L-687,414 which gave a plasma level of 11 micrograms/ml over the 4 h was also ineffective against the volume of infarction measured in the different brain regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional blood-brain glucose transfer in the rat: a novel double-membrane kinetic analysis.

Regional blood-brain glucose transfer was studied in pentobarbitone-anaesthetized rats using a programmed intravenous infusion technique that maintained steady levels of unlabeled (up to 55 mM) and tracer D-glucose in the circulating plasma. Regional cerebral blood flow, glucose phosphorylation rate, and tissue glucose content were also measured under comparable conditions. Data were analysed in terms of irreversible Michaelis-Menten kinetics assuming independent influx and efflux (Type I) and reversible Michaelis-Menten kinetics (Type II) across both the luminal and the abluminal membranes of the endothelial cell. The latter analysis corresponds to simple stereospecific membrane pores. The mathematical model allowed for changes in tissue glucose content and back-diffusion of tracer during the experiments. Type I analyses gave Kt values of approximately 6.6 mM, whereas those by Type II were consistently lower. Interregional differences were not significant using either scheme. Comparison of Type II with Type I analyses revealed a possible explanation for discrepancies in the estimates of nonsaturable glucose transfer by different methods and highlighted the importance of tissue glucose measurements in studies of unidirectional glucose influx. Since the experimental data may be described equally well by either scheme and some interaction between influx and efflux across the endothelial cell might be expected, consideration of this alternative approach is suggested.

Studies on the relationship between cerebral glucose transport and phosphorylation using 2-deoxyglucose.

Regional rates of blood-brain glucose transfer and phosphorylation have been measured in anaesthetized fasted and conscious fed and fasted rats using a dual-label 2-deoxyglucose technique that exploits differences in the early-time distribution of analogue and native glucose between blood and brain. Regional cerebral blood flow was also measured in comparable groups of rats. Estimates of glucose influx in the anaesthetized group were compared with those calculated from previously published kinetic constants obtained using [14C]D-glucose as tracer. The close agreement of these two sets of results served to validate estimates of influx obtained using the glucose analogue. Comparisons between all three groups showed that regional rates of glucose influx were maintained at levels appropriate to the rate of cerebral glucose phosphorylation. This occurred despite wide variations in plasma glucose concentration. The results indicate that at least two factors are involved in the adaptation of glucose supply to meet metabolic demand. One is related to blood flow, and probably reflects changes in the surface area of the capillary endothelium perfused. The second involves changes in the blood-brain barrier permeability to glucose and could reflect changes in the density of functioning glucose transporters within capillary endothelial cell membranes.

Mechanisms of action of serotonin 5-HT1B/D agonists: insights into migraine pathophysiology using rizatriptan.

Current theories on the etiology of migraine headache suggest that it is a neurovascular disorder (i.e., vascular change secondary to neural activation), with a primary CNS dysfunction giving rise to headache pain as a result of local intracranial vasodilatation and release of sensory neuropeptides from nerve endings in an activated trigeminal system. The serotonin 5-HT1B/1D agonists, known as the triptans, represent a major advance in the treatment of acute migraine. This article describes their mechanisms of action. The development of 5-HT1B/1D agonist drugs, such as rizatriptan, and the study of their pharmacology have enhanced our understanding of the mechanisms involved in the pathophysiology of migraine.

Differential involvement of neurotransmitters through the time course of cisplatin-induced emesis as revealed by therapy with specific receptor antagonists.

Advances in antiemetic therapy for chemotherapy-induced emesis have resulted in improved protection against symptoms occurring within 24 h of chemotherapy. However, the vomiting which tends to occur beyond 24 h after chemotherapy (delayed-phase vomiting) is still relatively poorly controlled by the currently available drugs, suggesting that more than one mechanism may mediate these symptoms. The standard antiemetic regimen currently recommended for prevention of chemotherapy-induced emesis includes a serotonin (5-HT(3)) antagonist and a corticosteroid. The neurokinin-1 (NK(1)) antagonist aprepitant represents a new class of antiemetic currently in clinical development. Using data obtained in 2 Phase II clinical trials of aprepitant in patients receiving chemotherapy based on the highly emetogenic chemotherapeutic agent cisplatin, we compared the time course of antiemetic effect of aprepitant, a 5-HT(3) antagonist, or a combination of both. Over the entire observation period (up to 7 days post-cisplatin), patients who received the NK(1) antagonist had a superior prevention of emesis. However, in the first 24 h after cisplatin, emesis occurred in fewer patients who received the 5-HT(3) antagonist than in patients who did not receive this class of drug. Furthermore, the majority of treatment failures in patients who received the NK(1) antagonist occurred within the first 8-12 h of chemotherapy, whereas the treatment failures in patients who received a 5-HT(3) antagonist were more evenly distributed over time. Patients who received both drugs had superior control of symptoms compared with patients who received one or the other. The difference in the time course of emesis blockade observed with two different classes of receptor antagonists provides substantial evidence for involvement of separate pathophysiological mechanisms in chemotherapy-induced vomiting. Serotonin mediates the early vomiting process that occurs within 8-12 h following cisplatin-based chemotherapy, after which time substance P acting at NK(1) receptors becomes the dominant mediator of vomiting

Mechanisms of action of quinone-containing alkylating agents: DNA alkylation by aziridinylquinones.

Aziridinyl quinones can be activated by cellular reductases eg. DT-diaphorase and cytochrome P450 reductase to form highly reactive DNA alkylating agents. The mechanisms by which this activation and alkylation take place are many and varied. Using clinically relevant and experimental agents this review will describe many of these mechanisms. The agents discussed are Mitomycin C, EO9 and analogues, diaziridinylbenzoquinones and the pyrrolo[1, 2-alpha]benzimidazolequinones.

Enantioselective inhibition of apomorphine-induced emesis in the ferret by the neurokinin1 receptor antagonist CP-99,994.

These studies have examined the effects of the selective neurokinin1 (NK1) receptor antagonist CP-99,994 on the retching and vomiting response to apomorphine. CP-99,994 (1-3 mg/kg i.p.) attenuated retching and vomiting induced by apomorphine (0.25 mg/kg s.c.) with complete inhibition of retching and vomiting at the 3 mg/kg dose. In contrast CP-100,263 (3 mg/kg i.p.), the enantiomer of CP-99,994 with 1000-fold lower affinity for the NK1 receptor, was without effect.

Differential effects of 5-HT1B/1D receptor agonists on neurogenic dural plasma extravasation and vasodilation in anaesthetized rats.

These studies compared the effects of the 5-HT1B/1D receptor agonists sumatriptan, CP-122 288 ((R)-N-methyl-[3-(1-methyl-2-pyrrolidinylmethyl)-1H-indol-5-yl] methanesulphonamide succinate) and CP-93 129 (3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one dihydrochloride) on neurogenic dural extra-vasation and vasodilation in anaesthetized rats. Dural extravasation, evoked by high intensity (1.2 mA) stimulation of the trigeminal ganglion, was measured using the radioactive plasma marker 125I-labelled bovine serum albumin. Dural vasodilation produced by lower intensity (50-300 microA) stimulation of trigeminal fibres, was measured through a closed cranial window using intravital microscopy. All compounds inhibited dural extravasation (rank order of potency: CP-122 288 > > sumatriptan > CP-93 129) and dural vasodilation (rank order of potency: CP-93 129 > > sumatriptan = CP-122 288). Comparison of the potency of these compounds with their potencies in an in vitro functional model, agonist-induced [35S]GTP gamma S binding, suggests that blockade of dural extravasation was consistent with an action at rat 5-HT1D receptors, but activity at another, unknown, "extravasation receptor" could also be involved. In contrast, inhibition of dural vasodilation was consistent with an action at rat 5-HT1B receptors. We suggest that in our preparations, production of dural vasodilation involves activation of trigeminal A delta-fibres whereas production of dural extravasation involves activation of trigeminal C-fibres. The differential effects of compounds on dural extravasation and vasodilation may therefore be due to the different receptor subtypes involved and to the selective localization of these subtypes on different populations of trigeminal sensory fibre.

Enantiospecific inhibition of emesis induced by nicotine in the house musk shrew (Suncus murinus) by the neurokinin1 (NK1) receptor antagonist CP-99,994.

Effects of the NK1 receptor antagonist CP-99,994 on nicotine-induced emesis were examined in Suncus murinus. CP-99,994 (3 and 10 mg/kg i.p.) attenuated emesis to (-)nicotine (4 mg/kg s.c.). CP-100,263 (3 and 10 mg/kg i.p.), the enantiomer of CP-99,994 with 1000 fold lower affinity for the NK1 receptor was without effect and RP67580 reduced emesis only at a dose of 30 mg/kg i.p. Responses to NK1 antagonists were ranked according to their affinities for the Suncus murinus NK1 receptor.

Comparison of the effects of sumatriptan and the NK1 antagonist CP-99,994 on plasma extravasation in Dura mater and c-fos mRNA expression in trigeminal nucleus caudalis of rats.

Dural plasma extravasation produced by electrical stimulation of the trigeminal ganglion was measured in rats and the concomitant expression of c-fos mRNA produced in the trigeminal nucleus caudalis (NtV) was measured using in situ hybridization techniques. The non-peptide NK1 receptor selective antagonist CP-99,994 (1-3000 micrograms kg-1) and the 5HT1D receptor agonist sumatriptan (1-1000 micrograms kg-1) reduced dural plasma extravasation dose-dependently with ID50S of 52 micrograms kg-1 and 30 micrograms kg-1 respectively. CP-99,994 (1000 micrograms kg-1). a compound known to have good brain penetration, decreased c-fos mRNA expression in the NtV by 37 +/- 7% without disruption of the blood brain barrier (BBB). Sumatriptan (1000 micrograms kg-1), known to be poorly brain penetrant, had no significant effect on c-fos mRNA expression in the NtV unless the BBB was disrupted by infusion of a hyperosmolar mannitol solution after which sumatriptan decreased c-fos mRNA expression by 65 +/- 11%. The results suggest that brain penetrant NK1 receptor antagonists may have anti-migraine effects peripherally through blockade of dural extravasation and centrally by inhibition of nociceptive pathways. Furthermore the data indicates that the anti-migraine action of sumatriptan must be predominantly peripherally mediated, be it via inhibition of plasma extravasation or direct vasoconstriction, since it had little effect on the activation of neurones in the NtV unless the BBB was disrupted.

Tachykinin NK1 receptor antagonists act centrally to inhibit emesis induced by the chemotherapeutic agent cisplatin in ferrets.

These studies have compared the pharmacological profile of two non-peptide human type neurokinin1 (hNK1) receptor selective antagonists, L-741,671 and a quaternised compound L-743,310. In radioligand binding studies L-741,671 and L-743,310 had high affinity for ferret and cloned hNK1 receptors [Ki (nM) ferret 0.7 and 0.1; human 0.03 and 0.06, respectively] but low affinity for rodent NK1 receptors [Ki (nM) 64 and 17, respectively] suggesting that ferret receptors have hNK1-like binding pharmacology. Studies in vivo showed that L-741,671 and L-743,310 had equivalent functional activity in the periphery (ID50s of 1.6 and 2 micrograms/kg i.v., respectively) as measured by inhibition of plasma protein extravasation evoked in the oesophagus of guinea pigs by resiniferatoxin (7 nmol/kg i.v.). Using an in situ brain perfusion technique in anaesthetised rats, L-741,671 was shown to be much more brain penetrant than the quaternary compound L-743,310 which had an entry rate similar to the poorly brain penetrant plasma marker inulin. These compounds thus provided an opportunity to compare the anti-emetic effects of equi-active hNK1 receptor antagonists with and without brain penetration to central NK1 receptor sites. When tested against cisplatin-induced emesis in ferrets, L-741,671 (0.3, 1 and 3 mg/kg i.v.) produced marked dose-dependent inhibition of retching and vomiting but L-743,310 was inactive at 3 and 10 micrograms/kg i.v. In contrast, direct central injection of L-741,671 and L-743,310 (30 micrograms) into the vicinity of the nucleus tractus solitarius or L-743,310 (200 micrograms) intracisternally was shown to inhibit retching and vomiting induced by i.v. cisplatin. L-741,671 and L-743,310 had equivalent functional activity, at the same dose, against cisplatin-induced emesis when injected centrally. These observations indicated that had L-743,310 penetrated into the brain after systemic administration it would have been active in the cisplatin-induced emesis assay and so show that brain penetration is essential for the anti-emetic action of systemically administered NK1 receptor antagonists.