Alanine analogues of [D-Trp]CJ-15,208: novel opioid activity profiles and prevention of drug- and stress-induced reinstatement of cocaine-seeking behaviour

BACKGROUND AND PURPOSE

The novel macrocyclic peptide cyclo[Phe-D-Pro-Phe-D-Trp] ([D-Trp]CJ-15,208) exhibits κ opioid (KOP) receptor antagonist activity in both in vitro and in vivo assays. The four alanine analogues of this peptide were synthesized and characterized both in vitro and in vivo to assess the contribution of different amino acid residues to the activity of [D-Trp]CJ-15,208.

EXPERIMENTAL APPROACH

The peptides were synthesized by a combination of solid phase peptide synthesis and cyclization in solution. The analogues were evaluated in vitro in receptor binding and functional assays, and in vivo with mice using a tail-withdrawal assay for antinociceptive and opioid antagonist activity. Mice demonstrating extinction of cocaine conditioned-place preference (CPP) were pretreated with selected analogues to evaluate prevention of stress or cocaine-induced reinstatement of CPP.

KEY RESULTS

The alanine analogues displayed pharmacological profiles in vivo distinctly different from [D-Trp]CJ-15,208. While the analogues exhibited varying opioid receptor affinities and κ and μ opioid receptor antagonist activity in vitro, they produced potent opioid receptor-mediated antinociception (ED50 = 0.28-4.19 nmol, i.c.v.) in vivo. Three of the analogues also displayed KOP receptor antagonist activity in vivo. Pretreatment with an analogue exhibiting both KOP receptor agonist and antagonist activity in vivo prevented both cocaine- and stress-induced reinstatement of cocaine-seeking behaviour in the CPP assay in a time-dependent manner.

CONCLUSIONS AND IMPLICATIONS

These unusual macrocyclic peptides exhibit in vivo opioid activity profiles different from the parent compound and represent novel compounds for potential development as therapeutics for drug abuse and possibly as analgesics.

Antillatoxin, a novel lipopeptide, enhances neurite outgrowth in immature cerebrocortical neurons through activation of voltage-gated sodium channels

Antillatoxin (ATX) is a structurally novel lipopeptide that activates voltage-gated sodium channels (VGSC) leading to sodium influx in cerebellar granule neurons and cerebrocortical neurons 8 to 9 days in vitro (Li et al., 2001; Cao et al., 2008). However, the precise recognition site for ATX on the VGSC remains to be defined. Inasmuch as elevation of intracellular sodium ([Na(+)](i)) may increase N-methyl-d-aspartate receptor (NMDAR)-mediated Ca(2+) influx, Na(+) may function as a signaling molecule. We hypothesized that ATX may enhance neurite outgrowth in cerebrocortical neurons by elevating [Na(+)](i) and augmenting NMDAR function. ATX (30-100 nM) robustly stimulated neurite outgrowth, and this enhancement was sensitive to the VGSC antagonist, tetrodotoxin. To unambiguously demonstrate the enhancement of NMDA receptor function by ATX, we recorded single-channel currents from cell-attached patches. ATX was found to increase the open probability of NMDA receptors. Na(+)-dependent up-regulation of NMDAR function has been shown to be regulated by Src family kinase (SFK) (Yu and Salter, 1998). The Src kinase inhibitor PP2 abrogated ATX-enhanced neurite outgrowth, suggesting a SFK involvement in this response. ATX-enhanced neurite outgrowth was also inhibited by the NMDAR antagonist, (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801), and the calmodulin-dependent kinase kinase (CaMKK) inhibitor, 1,8-naphthoylene benzimidazole-3-carboxylic acid (STO-609), demonstrating the requirement for NMDAR activation with subsequent downstream engagement of the Ca(2+)-dependent CaMKK pathway. These results with the structurally and mechanistically novel natural product, ATX, confirm and generalize our earlier results with a neurotoxin site 5 ligand. These data suggest that VGSC activators may represent a novel pharmacological strategy to regulate neuronal plasticity through NMDAR-dependent mechanisms.

Gambierol acts as a functional antagonist of neurotoxin site 5 on voltage-gated sodium channels in cerebellar granule neurons

The marine toxin gambierol, a polyether ladder toxin derived from the marine dinoflagellate Gambierdiscus toxicus, was evaluated for interaction with voltage-gated sodium channels (VGSCs) in cerebellar granule neuron (CGN) cultures. At concentrations ranging from 10 nM to 10 microM, gambierol alone had no effect on the intracellular Ca2+ concentration [Ca2+]i of exposed CGN cultures. Furthermore, there was no evidence of neurotoxicity in CGN cultures exposed for 2 h to gambierol (1 nM-10 microM). However, gambierol was a potent inhibitor (IC50 = 189 nM) of the elevation of [Ca2+]i that accompanies exposure of CGN cultures to the VGSC activator brevetoxin-2 (PbTx-2). To further explore the potential interaction of gambierol with VGSCs, the influence of gambierol on PbTx-2-induced neurotoxicity was assessed. Gambierol reduced the PbTx-2-induced efflux of lactate dehydrogenase in exposed CGN cultures in a concentration-dependent manner (IC50 = 471 nM). It is noteworthy that the potencies of gambierol as an inhibitor of both PbTx-2-induced Ca2+ influx and cytotoxicity were coincident. Finally, the inhibitory effects of gambierol on PbTx-2-induced elevation of [Ca2+]i were compared with those of brevenal, a natural inhibitor of the toxic effects of brevetoxin isolated from cultures of Karina brevis. Like gambierol, brevenal inhibited PbTx-2-induced elevation of [Ca2+]i in a concentration-dependent manner (IC50 = 108.6 nM). These results provide evidence for gambierol acting as a functional antagonist of neurotoxin site 5 on neuronal VGSCs.

Cloning and pharmacological characterization of the equine adenosine A2A receptor: a potential therapeutic target for the treatment of equine endotoxemia

The aim of the current study was to clone the equine adenosine A(2A) receptor gene and to establish a heterologous expression system to ascertain its pharmacologic profile via radioligand binding and functional assays. An eA(2A)-R expression construct was generated by ligation of the eA(2A) cDNA into the pcDNA3.1 expression vector, and stably transfected into human embryonic kidney cells (HEK). Binding assays identified those clones expressing the eA(2A)-R, and equilibrium saturation isotherm experiments were utilized to determine dissociation constants (K(D)), and receptor densities (B(max)) of selected clones. Equilibrium competition binding revealed a rank order of agonist potency of ATL > CV-1808 > NECA > 2-CADO > CGS21680, and a rank order of antagonist potency as ZM241385 > 8-phenyltheophylline > p-sulfophenyltheophylline > caffeine. Furthermore, adenylate cyclase assays using selective A(2A)-R agonists revealed that the eA(2A)-R functionally coupled to Galpha(s) as indicated by an increase in intracellular [(3)H]cAMP upon receptor activation. Finally, NF-kappaB reporter gene assays revealed a CGS21680 concentration-dependent inhibition of NF-kappaB activity. These results indicate that the heterologously expressed eA(2A)-R has a pharmacological profile similar to that of other mammalian A(2A) receptors and thus can be utilized for further characterization of the eA(2A)-R to ascertain whether it can serve as a suitable pharmacological target for equine inflammatory disease.

Cloning and pharmacological characterization of the equine adenosine A3 receptor

The aim of this study was to establish a heterologous expression system for the equine adenosine A(3) receptor (eA(3)-R) in an effort to ascertain its pharmacologic profile. Initially, radioligand binding assays identified clones expressing the eA(3)-R in human embryonic kidney cells (HEK) based on the specific binding of [(125)I]AB-MECA. Subsequently, adenylate cyclase assays were utilized to demonstrate functional coupling of the eA(3)-R to the G-protein/adenylate cyclase system. Equilibrium competition binding assays were then performed using selective and non-selective A(3) agonists and antagonists. Results from these experiments revealed a rank order of agonist potency to be IB-MECA > NECA > CGS21680, and an antagonist potency of MRS1220 > ZM241385 > 8-p-sulphophenyltheophylline; these rank orders were in agreement with that of other mammalian A(3)-R's. Lastly, NF-kappaB reporter gene assays revealed an IB-MECA concentration-dependent inhibition of TNFalpha-stimulated NF-kappaB activity. These results indicate that the heterologously expressed eA(3)-R is functional, has a pharmacological profile similar to that of other mammalian A(3) receptors, and its activation has an inhibitory effect on a key regulatory pathway in the inflammatory response. Thus, the eA(3)-R may serve as a pharmacological target in the treatment of equine inflammatory disease.

Characterization of [125I]ZM 241385 binding to adenosine A2A receptors in the pineal of sheep brain

Adenosine is a ubiquitous neuromodulator and homeostatic regulator that exerts its physiologic actions through activation of A(1), A(2A), A(2B) and A(3) adenosine receptor subtypes. In the central nervous system, adenosine's action in neurons is manifested in its modulation of tonic inhibitory control. Adenosine released in the brain during hypoxia has critical depressant effects on breathing in fetal and newborn mammals, an action suggested to be mediated by A(2A) receptors in the posteromedial thalamus. In an effort to more accurately define the spatial distribution of adenosine A(2A) receptors in fetal sheep diencephalon, we have used a receptor autoradiographic technique utilizing an iodinated radioligand [(125)I]ZM 241385, which has greater sensitivity and resolution than the tritiated compound. The distribution of ligand binding sites in the fetal sheep diencephalon indicated that the highest levels of binding were in select thalamic nuclei, including those implicated in hypoxic depression of fetal breathing, and the pineal. Given the high density of labeled A(2A) receptors in the pineal, these sites were characterized more fully in homogenate radioligand binding assays. These data indicate that [(125)I]ZM 241385 binding sites display a pharmacological signature consistent with that of adenosine A(2A) receptors and are expressed at similar levels in fetal, lamb and adult ovine brain. The adenosine A(2A) receptor pharmacologic signature of the [(125)I]ZM 241385 binding site in pineal cell membranes generalized to the site characterized in membranes derived from other portions of the lamb thalamus, including the sector involved in hypoxic inhibition of fetal breathing. These results have important implications for the functional roles of adenosine A(2A) receptors in the thalamus and pineal of sheep brain.

Structure-activity relationships of arodyn, a novel acetylated kappa opioid receptor antagonist

We previously reported that the novel dynorphin A (Dyn A, Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Lys-Leu-Lys-Trp-Asp-Asn-Gln) analog arodyn (Ac[Phe(1,2,3),Arg(4),d-Ala(8)]Dyn A-(1-11)NH(2), Bennett, M.A., Murray, T.F. & Aldrich, J.V. (2002) J. Med. Chem. vol. 45, pp. 5617-5619) is a kappa opioid receptor-selective peptide [K(i)(kappa) = 10 nm, K(i) ratio (kappa/mu/delta) = 1/174/583] which exhibits antagonist activity at kappa opioid receptors. In this study, a series of arodyn analogs was prepared and evaluated to explore the structure-activity relationships (SAR) of this peptide; this included an alanine scan of the entire arodyn sequence, sequential isomeric d-amino acid substitution in the N-terminal 'message' sequence, NMePhe substitution individually in positions 1-3, and modifications in position 1. The results for the Ala-substituted derivatives indicated that Arg(6) and Arg(7) are the most important residues for arodyn's nanomolar binding affinity for kappa opioid receptors. Ala substitution of the other basic residues (Arg(4), Arg(9) and Lys(11)) resulted in lower decreases in affinity for kappa opioid receptors (three- to fivefold compared with arodyn). Of particular interest, while [Ala(10)]arodyn exhibits similar kappa opioid receptor binding as arodyn, it displays higher kappa vs. mu opioid receptor selectivity [K(i) ratio (kappa/mu) = 1/350] than arodyn because of a twofold loss in affinity at mu opioid receptors. Surprisingly, the Tyr(1) analog exhibits a sevenfold decrease in kappa opioid receptor affinity, indicating that arodyn displays significantly different SAR than Dyn A; [Tyr(1)]arodyn also unexpectedly exhibits inverse agonist activity in the adenylyl cyclase assay using Chinese hamster ovary cells stably expressing kappa opioid receptors. Substitution of NMePhe in position 1 gave [NMePhe(1)]arodyn which exhibits high affinity [K(i)(kappa) = 4.56 nm] and exceptional selectivity for kappa opioid receptors [K(i) ratio (kappa/mu/delta) = 1/1100/>2170]. This peptide exhibits antagonistic activity in the adenylyl cyclase assay, reversing the agonism of 10 nm Dyn A-(1-13)NH(2). Thus [NMePhe(1)]arodyn is a highly kappa opioid receptor-selective antagonist that could be a useful pharmacological tool to study kappa opioid receptor-mediated activities.

The neurotoxic lipopeptide kalkitoxin interacts with voltage-sensitive sodium channels in cerebellar granule neurons

The marine neurotoxin kalkitoxin, a thiazoline-containing lipid derived from the pantropical marine cyanobacterium Lyngbya majuscula, was assayed for interaction with the tetrodotoxin-sensitive, voltage-sensitive sodium channel (TTX-VSSC) in cerebellar granule neuron cultures (CGN). The naturally occurring isomer of kalkitoxin (KTx-7) blocked veratridine-induced (30 microM) neurotoxicity in a concentration-dependent manner (EC50 22.7 nM [9.5-53.9 nM, 95% confidence interval {CI}]) in CGN. Kalkitoxin was a potent inhibitor (EC50 26.1 nM [12.3-55.0 nM, 95% CI]) of the elevation of intracellular Ca2+ concentration [Ca2+](i) that accompanies exposure of CGN to veratridine. To further explore the potential interaction of KTx-7 with TTX-VSSC, we assessed the influence of KTX-7 on the binding of [3H]batrachotoxin ([3H]BTX) to neurotoxin site 2 on the TTX-VSSC. Although kalkitoxin was without effect on the basal binding of [3H]BTX to intact cerebellar granule neurons, in the presence of the positive allosteric modulator, deltamethrin, [3H]BTX binding was inhibited by KTx-7 in a concentration-dependent manner (11.9 nM [IC50=3.8-37.2 nM, 95% CI]). These results provide both direct and functional evidence for an interaction of kalkitoxin with the neuronal TTX-VSSC.

Differential binding properties of [3H]dextrorphan and [3H]MK-801 in heterologously expressed NMDA receptors

The N-methyl-D-aspartate receptor (NMDAR) antagonists: MK-801, phencyclidine and ketamine are open-channel blockers with limited clinical value due to psychotomimetic effects. Similarly, the psychotomimetic effects of the dextrorotatory opioids, dextromethorphan and its metabolite dextrorphan, derive from their NMDAR antagonist actions. Differences in the use dependency of blockade, however, suggest that the binding sites for MK-801 and dextrorphan are distinct. In the absence of exogenous glutamate and glycine, the rate of association of [3H]MK-801 with wild-type NR1-1a/NR2A receptors was considerably slower than that for [3H]dextrorphan. Glutamate individually, and in the presence of the co-agonist glycine, had substantial effects on the specific binding of [3H]MK-801, while the binding of [3H]dextrorphan was not affected. Mutation of residues N616 and A627 in the NR1 subunit had a profound effect on [3H]MK-801 binding affinity, while that of [3H]dextrorphan was unaltered. In contrast, NR1 residues, W611 and N812, were critical for specific binding of [3H]dextrorphan to NR1-1a/NR2A complexes with no corresponding influence on that of [3H]MK-801. Thus, [3H]dextrorphan and [3H]MK-801 have distinct molecular determinants for high-affinity binding. The ability of [3H]dextrorphan to bind to a closed channel, moreover, indicates that its recognition site is shallower in the ion channel domain than that of MK-801 and may be associated with the extracellular vestibule of the NMDAR.

Characterization of the preferred stereochemistry for the neuropharmacologic actions of antillatoxin

Antillatoxin is a potent ichthyotoxin and cytotoxin previously discovered from the marine cyanobacterium Lyngbya majuscula. Ensuing studies of its mechanism of action showed it to activate the mammalian voltage-gated sodium channel at a pharmacological site that is distinct from any previously described. The structure of antillatoxin, initially formulated from spectroscopic information, was subsequently corrected at one stereocenter (C-4) as a result of synthesis of four different antillatoxin stereoisomers (all possible C-4 and C-5 diastereomers). In the current study these four stereoisomers, (4R,5R)-, (4S,5R)-, (4S,5S)-, and (4R,5S)-antillatoxin, were characterized in five different biological assay systems: ichthyotoxicity to goldfish, microphysiometry using cerebellar granule cells (CGCs), lactose dehydrogenase efflux from CGCs, monitoring of intracellular Ca(2+) concentrations in CGCs, and cytotoxicity to Neuro 2a cells. Across these various biological measures there was great consistency in that the natural antillatoxin (the 4R,5R-isomer) was greater than 25-fold more potent than any of the other stereoisomers. Detailed NMR studies provided a number of torsion and distance constraints that were modeled using the MM2 force field to yield predicted solution structures of the four antillatoxin stereoisomers. The macrocycle and side chain of natural (4R,5R)-antillatoxin present an overall "L-shaped" topology with an accumulation of polar substituents on the external surface of the macrocycle and a hydrogen bond between N(H)-7' and the C(O)-1 carbonyl. The decreased potency of the three non-naturally occurring antillatoxin stereoisomers is certainly a result of their dramatically altered overall molecular topologies.

An affinity label for δ-opioid receptors derived from [d-Ala2]deltorphin I*

A series of potential affinity label derivatives of the amphibian opioid peptide [D-Ala2]deltorphin I were prepared by incorporation at the para position of Phe3 (in the 'message' sequence) or Phe5 (in the 'address' sequence) of an electrophilic group (i.e. isothiocyanate or bromoacetamide). The introduction of the electrophile was accomplished by incorporating Fmoc-Phe(p-NHAlloc) into the peptide, followed later in the synthesis by selective deprotection of the Alloc group and modification of the resulting amine. While para substitution decreased the delta-opioid receptor affinity, selected analogs retained nanomolar affinity for delta receptors. [D-Ala2,Phe(p-NCS)3]deltorphin I exhibited moderate affinity (IC50=83 nM) and high selectivity for delta receptors, while the corresponding amine and bromoacetamide derivatives showed pronounced decreases in delta-receptor affinity (80- and >1200-fold, respectively, compared with [D-Ala2]deltorphin I). In the 'address' sequence, the Phe(p-NH2)5 derivative showed the highest delta-receptor affinity (IC50=32 nM), while the Phe(p-NHCOCH2Br)5 and Phe(p-NCS)5 peptides displayed four- and tenfold lower delta-receptor affinities, respectively. [D-Ala2,Phe(p-NCS)3]deltorphin I exhibited wash-resistant inhibition of [3H][D-Pen2,D-Pen5]enkephalin (DPDPE) binding to delta receptors at a concentration of 80 nM. [D-Ala2, Phe(p-NCS)3]deltorphin I represents the first affinity label derivative of one of the potent and selective amphibian opioid peptides, and the first electrophilic affinity label derivative of an agonist containing the reactive functionality in the 'message' sequence of the peptide.

Florida Red Tide: Inhalation Toxicity of Karenia brevis Extract in Rats

Brevetoxins are neurotoxins produced by the marine dinoflagellate Karenia brevis. Histopathologic examination of marine mammals dying following repeated exposure of brevetoxins during red tide events suggests that the respiratory tract, nervous, hematopoietic, and immune systems are potential targets for toxicity in repeatedly exposed individuals. The purpose of this experiment was to evaluate the effects of repeated inhalation of K. brevis extract on these potential target systems in rats. Male Sprague-Dawley rats were exposed four hours/day, five days/week for up to four weeks to target concentrations of 200 and 1000 μg/L K. brevis extract (approximately 50 and 200 μg/L brevetoxin-like compounds; positive neurotoxicity in a fish bioassay). Control rats were sham exposed to air. Immunohistochemical staining of pulmonary macrophages indicated deposition of brevetoxin-like compound within the lung. However, exposure resulted in no clinical signs of toxicity or behavioral changes. There were no adverse effects on hematology or serum chemistry. No histopathological changes were observed in the nose, lung, liver, kidneys, lymph nodes, spleen, or brain of exposed rats. Immune suppression was suggested by reduced responses of spleen cells in the IgM-specific antibody-forming plaque cell response assay and reduced responses of lymphocytes to mitogen stimulation in vitro. Differences between responses observed in rats in this study and those observed in manatees may be a function of dose or species differences in sensitivity.

Synthesis and evaluation of potential affinity labels derived from endomorphin-2

In an attempt to identify potential peptide-based affinity labels for opioid receptors, endomorphin-2 (Tyr-Pro-Phe-PheNH2), a potent and selective endogenous ligand for mu-opioid receptors, was chosen as the parent peptide for modification. The tetrapeptide analogs were prepared using standard Fmoc-solid phase peptide synthesis in conjunction with incorporation of Fmoc-Phe(p-NHAlloc) and modification of the p-amino group. The electrophilic groups isothiocyanate and bromoacetamide were introduced into the para position on either Phe3 or Phe4; the corresponding free amine-containing peptides were also prepared for comparison. The peptides bearing an affinity label group and their free amine analogs were evaluated in a radioligand-binding assay using Chinese hamster ovary (CHO) cells expressing mu- and delta-opioid receptors. Modification on Phe4 was better tolerated than on Phe3 for mu-receptor binding. Among the analogs tested, [Phe(p-NH2)4]endomorphin-2 showed the highest affinity (IC50 = 37 nm) for mu-receptors. The Phe(p-NHCOCH2Br)4 analog displayed the highest mu-receptor affinity (IC50 = 158 nm) among the peptides containing an affinity label group. Most of the compounds exhibited negligible binding affinity for delta-receptors, similar to the parent peptide.

Brevetoxin derivatives act as partial agonists at neurotoxin site 5 on the voltage-gated Na+ channel

Brevetoxins (PbTx-1 to PbTx-10) are potent lipid-soluble polyether neurotoxins produced by the marine dinoflagellate Karina brevis, an organism associated with 'red tide' blooms in the Gulf of Mexico. Ingestion of shellfish contaminated with K. brevis produces neurotoxic shellfish poisoning (NSP) in humans. NSP symptoms emanate from brevetoxin activation of neurotoxin site 5 on voltage-gated sodium channels (VGSC) [Toxicon 20 (1982) 457]. In primary cultures of rat cerebellar granule neurons (CGN), brevetoxins produce acute neuronal injury and death. The ability of a series of naturally occurring and synthetic brevetoxins to trigger Ca(2+) influx in CGN was explored in the present study. Intracellular Ca(2+) concentration was monitored in fluo-3-loaded CGN using a fluorescent laser imaging plate reader. The naturally occurring derivatives PbTx-1, PbTx-2 and PbTx-3 all produced a rapid and concentration-dependent increase in cytosolic [Ca(2+)]. The maximum response to PbTx-1 was approximately two-fold greater than that of either PbTx-2 or PbTx-3. Two synthetic derivatives of PbTx-3, alpha-naphthoyl-PbTx-3 and beta-naphthoyl-PbTx-3, were also tested. Both alpha- and beta-naphthoyl-PbTx-3 stimulated a rapid and concentration-dependent Ca(2+) influx that was, however, less efficacious than that of PbTx-3. These data indicate that, analogous to neurotoxin site 2 ligands, activators of neurotoxin site 5 display a range of efficacies, with PbTx-1 being a full agonist and other derivatives acting as partial agonists.

Dermorphin-based potential affinity labels for mu-opioid receptors

Dermorphin and [Lys7]dermorphin, selective micro -opioid receptor ligands originating from amphibian skin, have been modified with various electrophiles in either the 'message' or 'address' sequences as potential peptide-based affinity labels for micro -receptors. Introduction of the electrophilic isothiocyanate and bromoacetamide groups on the para position of Phe3 and Phe5 was accomplished by incorporating Fmoc-Phe(p-NHAlloc) into the peptide followed by selective deprotection and modification. The corresponding amine-containing peptides were also prepared. The pure peptides were evaluated in radioligand binding experiments using Chinese hamster ovary (CHO) cells expressing micro - and delta-opioid receptors. In dermorphin, introduction of the electrophilic groups in the 'message' domain lowered the binding affinity by > 1000-fold; only [Phe(p-NH2)3]dermorphin retained nanomolar affinity for micro -receptors. Modifications in the 'address' region of both dermorphin and [Lys7]dermorphin were relatively well tolerated. In particular, [Phe(p-NH2)5,Lys7]dermorphin showed similar affinity to dermorphin, with almost 2-fold higher selectivity for micro -receptors. [Phe(p-NHCOCH2Br)5]- and [Phe(p-NHCOCH2Br)5,Lys7]dermorphin exhibited relatively high affinity (IC50 = 27.7 and 15.1 nm, respectively) for micro -receptors. However, neither of these peptides inhibited [3H]DAMGO binding in a wash-resistant manner.

Antillatoxin is a marine cyanobacterial toxin that potently activates voltage-gated sodium channels

Antillatoxin (ATX) is a lipopeptide derived from the pantropical marine cyanobacterium Lyngbya majuscula. ATX is neurotoxic in primary cultures of rat cerebellar granule cells, and this neuronal death is prevented by either N-methyl-d-aspartate (NMDA) receptor antagonists or tetrodotoxin. To further explore the potential interaction of ATX with voltage-gated sodium channels, we assessed the influence of tetrodotoxin on ATX-induced Ca2+ influx in cerebellar granule cells. The rapid increase in intracellular Ca2+ produced by ATX (100 nM) was antagonized in a concentration-dependent manner by tetrodotoxin. Additional, more direct, evidence for an interaction with voltage-gated sodium channels was derived from the ATX-induced allosteric enhancement of [3H]batrachotoxin binding to neurotoxin site 2 of the alpha subunit of the sodium channel. ATX, moreover, produced a strong synergistic stimulation of [3H]batrachotoxin binding in combination with brevetoxin, which is a ligand for neurotoxin site 5 on the voltage-gated sodium channel. Positive allosteric interactions were not observed between ATX and either alpha-scorpion toxin or the pyrethroid deltamethrin. That ATX interaction with voltage-gated sodium channels produces a gain of function was demonstrated by the concentration-dependent and tetrodotoxin-sensitive stimulation of 22Na+ influx in cerebellar granule cells exposed to ATX. Together these results demonstrate that the lipopeptide ATX is an activator of voltage-gated sodium channels. The neurotoxic actions of ATX therefore resemble those of brevetoxins that produce neural insult through depolarization-evoked Na+ load, glutamate release, relief of Mg2+ block of NMDA receptors, and Ca2+ influx.

Dynorphin A analogs containing a conformationally constrained phenylalanine derivative in position 4: reversal of preferred stereochemistry for opioid receptor affinity and discrimination of kappa vs. delta receptors

Analogs of the opioid peptide [D-Ala8]dynorphin A-(1-11)NH2 containing optically pure (R)- and (S)-2-aminotetralin-2-carboxylic acid (Atc) in position 4 were synthesized and evaluated for opioid receptor affinity. These peptides are the first reported dynorphin A analogs containing a conformationally constrained amino acid in place of the important aromatic residue Phe4. By incorporating resolved Atc isomers, the opioid receptor affinity and the stereochemistry of the constrained residue could be unambiguously correlated. Both Dyn A analogs containing Atc in position 4 retained nanomolar affinity for kappa and mu opioid receptors. Unexpectedly the peptide containing (R)-Atc, corresponding to a conformationally constrained D-Phe analog, displaying higher affinity for both kappa and mu receptors than the peptide containing (S)-Atc. In contrast [D-Phe4,D-Ala8]Dyn A-(1-11)NH2 exhibited significantly lower affinity for kappa and mu receptors than the parent peptide, as expected. Conformational restriction of the Phe4 sidechain or incorporation of D-Phe in position 4 had the largest effect on delta receptor affinity, yielding compounds with negligible affinity for these receptors. Thus, there appear to be distinctly different structural requirements for this residue for kappa vs. delta receptors, and it is possible to completely distinguish between these two receptors by changing a single residue in Dyn A.

Synthesis and evaluation of isothiocyanate-containing derivatives of the delta-opioid receptor antagonist Tyr-Tic-Phe-Phe (TIPP) as potential affinity labels for delta-opioid receptors

Derivatives of the delta-opioid receptor-selective peptide antagonist H-Tyr-Tic-Phe-Phe-OH (TIPP) containing an isothiocyanate moiety at the para position of either Phe(3) or Phe(4) were prepared as potential affinity labels for delta-opioid receptors. The synthesis was accomplished using a general solution-phase synthetic procedure which allows for introduction of affinity labeling groups late in the synthesis of a variety of small peptide substrates. The target peptides and their corresponding amines were then evaluated in radioligand binding experiments using Chinese hamster ovary (CHO) cells expressing delta- and mu-opioid receptors. The peptides [Phe(p-NCS)(3)]TIPP (2) and [Phe(p-NCS)(4)]TIPP (4) showed affinity for delta-receptors comparable to the parent compound TIPP (IC(50) = 12 and 5 nM, respectively, vs 6 nM for TIPP). Both peptides 2 and 4 were able to inhibit radioligand binding to delta-receptors in a wash-resistant manner at a concentration of 10 nM. Therefore, the peptides [Phe(p-NCS)(3)]TIPP (2) and [Phe(p-NCS)(4)]TIPP (4) represent two affinity labels that may prove useful in the study of delta-opioid receptors.

Extended TIP(P) analogues as precursors for labeled delta-opioid receptor ligands

Tyr-Tic-Phe-Phe-OH (TIPP) and the shorter Tyr-Tic-Phe-OH (TIP) peptides are potent and highly selective antagonists at the delta-opioid receptor and, therefore, are ideal candidates for the attachment of labels to assist in the study of delta-opioid receptors. Peptides extended at the C-terminus with residues which can be used as handles for further modification and/or labeling (i.e. Asx, Glx, and Lys) were synthesized. The TIPP-D/L-Asx/Glx derivatives exhibited similar delta-receptor affinity to TIPP (K(i) = 5-10 nM vs K(i) = 6 nM), and neither the location of the carboxylic acid moiety nor the stereochemistry of the C-terminal residue significantly affected the delta-receptor affinity of these derivatives. Extension of TIPP with an additional residue did not increase mu-receptor affinity, even though the position of the acidic group, which imparts delta-receptor selectivity to TIPP, was shifted relative to the carboxylic acid moiety of TIPP. The delta-receptor affinities of the TIP-D/L-Asx/Glx derivatives were found to be influenced mainly by the position of the carboxylic acid function rather than the stereochemistry of the C-terminal residue. TIP(P)-D/L-Lys(Ac)-OH derivatives exhibited moderate delta-receptor affinity (K(i)(delta) = 16-28 nM). The most potent compounds found in the extended TIP(P) series were TIPP-D-Gln-OH and TIP-D-Gln-OH (K(i)(delta) = 5 nM) which had similar affinities to TIPP.

Synthesis and evaluation of N,N-dialkyl enkephalin-based affinity labels for delta opioid receptors

To develop affinity labels for delta opioid receptors based on peptide antagonists, the Phe(4) residues of N,N-dibenzylleucine enkephalin and N,N-diallyl[Aib(2),Aib(3)]leucine enkephalin (ICI-174, 864) were substituted with either Phe(p-NCS) or Phe(p-NHCOCH(2)Br). A general synthetic method was developed for the conversion of small peptide substrates into potential affinity labels. The target peptides were synthesized using Phe(p-NH(2)) and a Boc/Fmoc orthogonal protection strategy which allowed for late functional group conversion of a p-amine group in the peptides to the desired affinity labeling moieties. A key step in the synthesis was the selective deprotection of a Boc group in the presence of a tert-butyl ester using trimethylsilyl trifluoromethanesulfonate (TMS-OTf). The target peptides were evaluated in radioligand binding experiments in Chinese hamster ovary (CHO) cells expressing delta or mu opioid receptors. The delta receptor affinities of the N, N-dibenzylleucine enkephalin analogues were 2.5-10-fold higher than those for the corresponding ICI-174,864 analogues. In general, substitution at the para position of Phe(4) decreased binding affinity at both delta and mu receptors in standard radioligand binding assays; the one exception was N, N-dibenzyl[Phe(p-NCS)(4)]leucine enkephalin (2) which exhibited a 2-fold increase in affinity for delta receptors (IC(50) = 34.9 nM) compared to N,N-dibenzylleucine enkephalin (IC(50) = 78.2 nM). The decreases in mu receptor affinities were greater than in delta receptor affinities so that all of the analogues tested exhibited significantly greater delta receptor selectivity than the unsubstituted parent peptides. Of the target peptides tested, only N, N-dibenzyl[Phe(p-NCS)(4)]leucine enkephalin (2) exhibited wash-resistant inhibition of radioligand binding to delta receptors. To our knowledge, 2 represents the first peptide-based affinity label to utilize an isothiocyanate group as the electrophilic affinity labeling moiety. As a result of this study, enkephalin analogue 2 emerges as a potential affinity label useful for the further study of delta opioid receptors.

Behaviroal, pharmacological, and molecular characterization of an amphibian cannabinoid receptor

Investigation of cannabinoid pharmacology in a vertebrate with a phylogenetic history distinct from that of mammals may allow better understanding of the physiological significance of cannabinoid neurochemistry. Taricha granulosa, the roughskin newt, was used here to characterize an amphibian cannabinoid receptor. Behavioral experiments demonstrated that the cannabinoid agonist levonantradol inhibits both newt spontaneous locomotor activity and courtship clasping behavior. Inhibition of clasping was dose-dependent and potent (IC(50) = 1.2 microgram per animal). Radioligand binding studies using [(3)H]CP-55940 allowed identification of a specific binding site (K(D) = 6.5 nM, B(max) = 1,853 fmol/mg of protein) in brain membranes. Rank order of affinity of several ligands was consistent with that reported for mammalian species (K(D), nM) : CP-55940 (3.8) > levonantradol (13.0) > WIN55212-2 (25.7) >> anandamide (1,665) approximately anandamide 100 microM phenylmethylsulfonyl fluoride (2,398). The cDNA encoding the newt CB1 cannabinoid receptor was cloned, and the corresponding mRNA of 5.9 kb was found to be highly expressed in brain. A nonclonal Chinese hamster ovary cell line stably expressing the newt CB1 cannabinoid receptor was prepared that allowed demonstration of cannabinoid-mediated inhibition of adenylate cyclase (EC 4.6.1.1) activity. This inhibition was dose-dependent and occurred at concentrations consistent with affinities determined through radioligand binding experiments. The behavioral, pharmacological, and molecular cloning results demonstrate that a CB1 cannabinoid receptor is expressed in the CNS of the roughskin newt. This amphibian CB1 is very similar in density, ligand binding affinity, ligand binding specificity, and amino acid sequence to mammalian CB1. The high degree of evolutionary conservation of cannabinoid signaling systems implies an important physiological role in vertebrate brain function.

Effects of high-intensity resistance training on untrained older men. I. Strength, cardiovascular, and metabolic responses

Most resistance training studies of older subjects have emphasized low-intensity, short-term training programs that have concentrated on strength measurements. The purpose of this study was, in addition to the determination of strength, to assess intramuscular and transport factors that may be associated with strength increments. Eighteen untrained men ages 60-75 years volunteered for the study; 9 were randomly placed in the resistance-training group (RT), and the other half served as untrained (UT) or control subjects. RT subjects performed a 16-week high-intensity (85-90% 1 repetition maximum (RT]) resistance training program (2 x/wk) consisting of 3 sets each to failure (6-8 repetitions based on 1 RM of 3 exercises): leg press (LP), half squat (HS), and leg extension (LE) with 1-2 minutes rest between sets. Pre- and post- training strength was measured for the 3 training exercises using a 1 RM protocol. Body fat was calculated using a 3-site skinfold method. Biopsies from the vastus lateralis m. were obtained for fiber type composition, cross-sectional area, and capillarization measurements. Exercise metabolism, electrocardiography, and arterial blood pressure were observed continuously during a progressive treadmill test, and resting echocardiographic data were recorded for all subjects. Pre- and post-training venous blood samples were analyzed for serum lipids. Resistance training caused significant changes in the following comparisons: % fat decreased in the RT group by almost 3%, strength improved for all exercises: LE = + 50.4%, LP = + 72.3%, HS = + 83.5%; type IIB fibers decreased and IIA fibers increased; cross-sectional areas of all fiber types (I, IIA, IIB) increased significantly, and capillary to fiber ratio increased but not significantly. No differences were noted for ECG and echocardiographic data. The RT group significantly improved treadmill performance and VO2max. Pre- and post-training serum lipids improved but not significantly. No significant changes occurred in any pre- to post-tests for the UT group. The results show that skeletal muscle in older, untrained men will respond with significant strength gains accompanied by considerable increases in fiber size and capillary density. Maximal working capacity, VO2max, and serum lipid profiles also benefited from high-intensity resistance training, but no changes were observed for HR max, or maximal responses of arterial blood pressure. Older men may not only tolerate very high intensity work loads but will exhibit intramuscular, cardiovascular, and metabolic changes similar to younger subjects.

Fiber type composition of the vastus lateralis muscle of young men and women

This study presents data collected over the past 10 years on the muscle fiber type composition of the vastus lateralis muscle of young men and women. Biopsies were taken from the vastus lateralis muscle of 55 women (21.2+/-2.2 yr) and 95 men (21.5+/-2.4 yr) who had volunteered to participate in various research projects. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were classified using mATPase histochemistry, and cross-sectional area was measured for the major fiber types (I, IIA, and IIB). Myosin heavy chain (MHC) content was determined electrophoretically on all of the samples from the men and on 26 samples from the women. With the exception of fiber Type IC, no significant differences were found between men and women for muscle fiber type distribution. The vastus lateralis muscle of both the men and women contained approximately 41% I, 1% IC, 1% IIC, 31% IIA, 6% IIAB, and 20% IIB. However, the cross-sectional area of all three major fiber types was larger for the men compared to the women. In addition, the Type IIA fibers were the largest for the men, whereas the Type I fibers tended to be the largest for the women. Therefore, gender differences were found with regard to the area occupied by each specific fiber type: IIA>I>IIB for the men and I>IIA>IIB for the women. These data establish normative values for the mATPase-based fiber type distribution and sizes in untrained young men and women.

Fiber type composition of the vastus lateralis muscle of young men and women

This study presents data collected over the past 10 years on the muscle fiber type composition of the vastus lateralis muscle of young men and women. Biopsies were taken from the vastus lateralis muscle of 55 women (21.2+/-2.2 yr) and 95 men (21.5+/-2.4 yr) who had volunteered to participate in various research projects. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were classified using mATPase histochemistry, and cross-sectional area was measured for the major fiber types (I, IIA, and IIB). Myosin heavy chain (MHC) content was determined electrophoretically on all of the samples from the men and on 26 samples from the women. With the exception of fiber Type IC, no significant differences were found between men and women for muscle fiber type distribution. The vastus lateralis muscle of both the men and women contained approximately 41% I, 1% IC, 1% IIC, 31% IIA, 6% IIAB, and 20% IIB. However, the cross-sectional area of all three major fiber types was larger for the men compared to the women. In addition, the Type IIA fibers were the largest for the men, whereas the Type I fibers tended to be the largest for the women. Therefore, gender differences were found with regard to the area occupied by each specific fiber type: IIA>I>IIB for the men and I>IIA>IIB for the women. These data establish normative values for the mATPase-based fiber type distribution and sizes in untrained young men and women.

Partial purification and biochemical characterization of a membrane glucocorticoid receptor from an amphibian brain

A membrane receptor for corticosterone (mGR) in the brain of the roughskin newt (Taricha granulosa) has been previously identified. This manuscript reports the evaluation of several chromatographic resins for enrichment of the newt mGR solubilized from neuronal membranes. A protein with an apparent molecular weight of 63 kDa was purified to near homogeneity following sequential purification using ammonium sulfate fractionation, wheat germ agglutinin (WGA)-agarose chromatography, hydroxylapatite chromatography, and an immobilized ligand affinity resin (Corticosterone-Sepharose). Other studies employed a novel protein differential display strategy and a photoaffinity labeling strategy to visualize candidate receptor proteins following SDS-PAGE. Both of these techniques also identified a 63 kDa protein, agreeing with the estimation of molecular weight from the purification data. Furthermore, the use of 2D SDS-PAGE following the photolabeling procedure showed the candidate 63 kDa protein to have a pI of approximately 5.0. Taken together these data suggest that the newt mGR is an acidic glycoprotein with an apparent molecular weight of 63 kDa. Because these characteristics of newt mGR are inconsistent with the characteristics of intracellular glucocorticoid receptors, these two receptor proteins are apparently distinct.

Brevetoxin-induced autocrine excitotoxicity is associated with manifold routes of Ca2+ influx

Real-time alterations in intracellular Ca2+ ([Ca2+]i) were monitored in fluo-3-loaded cerebellar granule neurons (CGNs) exposed to the brevetoxin PbTx-1. [Ca2+]i was measured using a fluorescent plate reader (FLIPR), which measures simultaneously the mean intracellular Ca2+ change in a population of cultured cells in each well of a 96-well plate. PbTx-1 produced rapid and concentration-dependent increases in neuronal [Ca2+]i with a potency nearly identical to that determined previously for PbTx-1-induced neurotoxicity. The NMDA receptor antagonists MK-801, dextrorphan, and D(-)-2-amino-5-phosphonopentanoic acid, and tetanus toxin, an inhibitor of Ca2+-dependent exocytotic neurotransmitter release, effected significant reductions in both the integrated fluo-3 fluorescence response and excitatory amino acid release and protected CGNs against PbTx-1 neurotoxicity. The L-type Ca2+ channel antagonist nifedipine produced a modest reduction in the fluo-3 response but reduced substantially the plateau phase of the PbTx-1 increment in [Ca2+]i when combined with MK-801. When nifedipine and MK-801 were combined with the Na+/Ca2+ exchanger (reversed mode) inhibitor KB-R7943, the PbTx-1 increment in [Ca2+]i was nearly completely attenuated. These data show that Ca2+ entry into PbTx-1-exposed CGNs occurs through three primary routes: NMDA receptor ion channels, L-type Ca2+ channels, and reversal of the Na+/Ca2+ exchanger. There was a close correlation between reduction of the integrated fluo-3 fluorescence response and the level of neuroprotection afforded by blockers of each Ca2+ entry pathway; however, simultaneous blockade of L-type Ca2+ channels and the Na+/Ca2+ exchanger, although reducing the integrated [Ca2+]i response to a level below that provided by NMDA receptor blockade alone, failed to completely attenuate PbTx-1 neurotoxicity. This finding suggests that in addition to total [Ca2+]i load, neuronal vulnerability is governed principally by the NMDA receptor Ca2+ influx pathway.

Hydrostatic pressure alters the time course of GTP

The effects of hydrostatic pressure on the receptor-stimulated exchange of guanosine triphosphate (GTP) for guanosine diphosphate (GDP) on the a subunit of G proteins were studied in two congeneric marine teleost fishes that differ in their depths of distribution. The poorly hydrolyzable GTP analog [35S]guanosine 5'-[gamma-thio]triphosphate ([35S]GTP[S]) was used to monitor the modulation of signal transduction by the A1 adenosine receptor agonist N6-R-(phenylisopropyl)adenosine (R-PIA) in brain membranes of the scorpaenids Sebastolobus alascanus and S. altivelis. The maximal binding (Bmax) and dissociation constant (K(d)) values, determined from equilibrium binding isotherms at atmospheric pressure (5 degrees C), were similar in the two species. The Bmax values for these species are much lower than literature values for mammalian brain tissue (25 degrees C); however, the K(d) values of the teleost and mammalian G proteins are similar. The EC50 values for the A1 adenosine receptor agonist R-PIA were similar in the two species. Hydrostatic pressure of 204 atm altered the binding of [35S]GTP[S]; basal [35S]GTP[S] binding decreased 25%. The A1 adenosine receptor agonist R-PIA and the muscarinic cholinergic receptor agonist carbamyl choline stimulated [35S]GTP[S] binding at 1 and 204 atm. At atmospheric pressure the half-time (t1/2) of [35S]GTP[S] binding differed between the two species. The GTP[S] on rate (k(on)) is larger in the shallower-living S. alascanus. Increased hydrostatic pressure altered the time course, decreasing the t1/2 in both species. The pressures that elicit this change in the time course differ between the species. However, interpolating over the range of in situ pressures the species experience, the values are similar in the two species. The guanyl nucleotide binding properties of the G protein a subunits appear to be conserved at the environmental temperatures and pressures the species experience.

Antillatoxin and kalkitoxin, ichthyotoxins from the tropical cyanobacterium Lyngbya majuscula, induce distinct temporal patterns of NMDA receptor-mediated neurotoxicity

Curacin-A, antillatoxin and kalkitoxin, natural products from the marine cyanobacterium Lyngbya majuscula, were tested for neurotoxicity in primary cultures of rat cerebellar granule neurons. Curacin-A was non-toxic, whereas antillatoxin and kalkitoxin produced concentration-dependent cytotoxicity with LC50 values of 20.1+/-6.4 and 3.86+/-1.91 nM, respectively. Antillatoxin neurotoxicity was produced acutely, whereas kalkitoxin caused a delayed neurotoxic response. The cytotoxicity produced by both antillatoxin and kalkitoxin was prevented by the non-competitive NMDA receptor antagonists dextrorphan and MK-801.

Axial and lateral radiographs in evaluating patellofemoral malalignment

This is a prospective study of 431 patients (862 knees) with patellofemoral pain, patellar dislocation, or other abnormalities of the knee joint. There were 217 asymptomatic knees with no contralateral problems for comparison. All patients had a history and physical and radiographic examination of both knees. The radiographs included standard anteroposterior views, axial views at 30 degrees of knee flexion, and standing lateral views at 0 degree and 30 degrees of flexion. The presence of patellar tilt or subluxation was noted on the axial view. The lateral view of the patella, with precise overlap of the posterior femoral condyles, allowed determination of relationships between the patella's medial edge, median ridge, and lateral edge to assess patellar tilt. Sixty-two percent of patients with patellar dislocations demonstrated subluxation on the axial view, while 98% demonstrated an abnormal lateral view. Eighteen percent of the control knees revealed evidence of subluxation on the axial view while 35% demonstrated subluxation on the extended lateral view. The axial view demonstrated 62% sensitivity for dislocation, while the lateral view taken in full extension demonstrated 98% sensitivity. The specificity for previous dislocation was 82% for the axial view and 93% for the lateral flexed view. Given the high sensitivity of the lateral view for detecting prior patellar dislocation, a normal result on this view can virtually eliminate the question of previous dislocation. Also, with the high specificity of the axial view and lateral view with knee flexion, the two views combined can confirm a clinical impression of patellofemoral malalignment.

Brevetoxins cause acute excitotoxicity in primary cultures of rat cerebellar granule neurons

Brevetoxins (designated PbTx-1 to -10) are potent lipid-soluble polyether compounds that are known to bind to and modulate voltage-gated sodium channel activity. To investigate whether brevetoxins produce direct central nervous system neurotoxic effects, cultured rat cerebellar granule neurons were exposed to brevetoxins in Locke's buffer for 2 h at 22 degrees C. Neuronal injury was quantified by assaying lactate dehydrogenase activity in the exposure buffer and in conditioned growth media collected at 22 h after brevetoxin exposure. Brevetoxins produced acute neuronal injury and death in neurons with a rank order potency of PbTx-1 (EC50 = 9.31 +/- 0.45 nM) > PbTx-3 (EC50 = 53.9 +/- 2.8 nM) > PbTx-2 (EC50 = 80.5 +/- 5.9 nM) > PbTx-6 (EC50 = 1417 +/- 32 nM), which is similar to their previously determined rank order potency for brevetoxin-induced icthyotoxicity and binding to [3H]PbTx-3-labeled sodium channels on synaptosomes. The neurotoxic response could be prevented by coapplication of the sodium channel antagonist tetrodotoxin or by the competitive or noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists D-AP5 and MK-801, ketamine, dextromethorphan, and dextrorphan, respectively. NMDA receptor antagonists afforded neuroprotection with rank order potencies comparable to those measured previously for protection against glutamate-induced excitotoxic responses. Further analysis revealed that brevetoxins induced a concentration-dependent release of L-glutamate and L-aspartate into the exposure buffer. These data indicate that brevetoxin-induced injury in cultured rat cerebellar granule neurons is mediated by NMDA receptors that are activated indirectly as a consequence of PbTx-induced sodium channel activation and attendant excitatory amino acid release.

Dextrorotatory opioids induce stereotyped behavior in Sprague-Dawley and Dark Agouti rats

Dextromethorphan and dextrorphan elicited a stereotyped behavioral syndrome in rats indistinguishable from that produced by PCP and other non-competitive NMDA antagonists. The rank order of potency for the induction of stereotyped behavior in male Sprague-Dawley rats was: MK-801>PCP>(+/-)cyclazocine>dextrorphan>(+/-)ketamine>dextromethorphan. These behavioral potencies were significantly correlated (0.91; P<0.05) with their respective affinities for high affinity [3H]dextrorphan-labelled NMDA receptors in rat forebrain membranes. To address the propensity of dextromethorphan to induce stereotyped behavior, dextrorotatory-opioid induced stereotypies were investigated in female Dark Agouti and female Sprague-Dawley rats. The female Dark Agouti lacks CYP2D1, the cytochrome P450 enzyme which catalyses the oxidative O-demethylation of dextromethorphan to dextrorphan. No differences were observed in either potency or time to peak effect for dextromethorphan to induce stereotyped behavior in the rat strains, suggesting that the affinity of dextromethorphan for NMDA receptors adequately accounts for its ability to induce stereotyped behavior. Female Dark Agouti rats were, however, more sensitive to the effects of dextrorphan, which may reflect differences in the ability of this strain to metabolize dextrorphan. We find no evidence to suggest that dextromethorphan produces a behavioral syndrome in rats that is distinct from that induced by dextrorphan. The commonality between the pharmacologic profiles of these compounds suggests that the abuse potential of dextromethorphan containing antitussive preparations is related to the non-competitive NMDA antagonist activity of dextromethorphan and its metabolites.

Solubilization and pharmacological characterization of a glucocorticoid membrane receptor from an amphibian brain

Physiological functions of steroid hormones involve activation of intracellular receptors as well as poorly understood membrane receptors. We report the pharmacological characterization of a solubilized corticosterone receptor from neuronal membranes. This receptor previously was shown to localize with plasma membrane subcellular fractions and to be involved in the modulation of courtship behaviors in the roughskin newt (Taricha granulosa). We describe procedures with non-ionic detergents that solubilize the receptor and maintain high affinity [3H]corticosterone binding. The pharmacology of the solubilized corticosterone receptor resembles that of the membrane receptor with high affinity for [3H]corticosterone and an identical rank-order potency for other steroid ligands (corticosterone>cortisol>aldosterone>dexamethasone). Unlike binding in membrane preparations, [3H]corticosterone binding to the solubilized receptor is insensitive to negative modulation by guanyl nucleotides and only modestly sensitive to the presence of Mg2+. We also identified two ligands that exhibit high affinity binding to the solubilized receptor and have the potential to be used in an affinity purification scheme. They are corticosterone-3-carboxymethyloxime (CORT-3-CMO), which may be covalently attached to a Sepharose resin, and a derivitized azide form of CORT-3-CMO which can be covalently coupled to the solubilized receptor itself. The stability of the solubilized [3H]corticosterone receptor in the detergent system will facilitate further purification and molecular characterization.

Cyclopentyladenosine-induced homologous down-regulation of A1 adenosine receptors (A1AR) in intact neurons is accompanied by receptor sequestration but not a reduction in A1AR mRNA expression or G protein alpha-subunit content

We showed previously that exposure of cerebellar granule cells to the A1 adenosine receptor (A1AR)-selective agonist, cyclopentyladenosine, decreases A1AR density and G protein coupling corresponding to blunted agonist-induced adenylyl cyclase (EC 4.6.1.1) inhibition. We have now determined that A1AR-mediated adenylyl cyclase inhibition was desensitized in a homologous manner. Carbachol- and baclofen-induced inhibition of adenylyl cyclase was unaffected by 48-h exposure to 10 microM cyclopentyladenosine. Expression of G protein alpha-subunits was not affected dramatically by agonist exposure. The fraction of sequestered A1AR was increased significantly at 4, 24, and 48 h of cyclopentyladenosine exposure (35, 57, and 81% increase over control, respectively). The time course of agonist-induced A1AR sequestration was slower than that reported for other G protein-coupled receptors. Incubation with the adenosine receptor antagonist, 8-p-sulfophenyltheophylline or adenosine deaminase did not alter sequestration significantly. Neither steady-state A1AR mRNA levels nor transcript stability was affected by 48-h agonist exposure. We determined that A1AR half-life in cerebellar granule cells is 20.9 h, which is considerably longer than that reported for several other G protein-coupled receptors. The slow time course of A1AR sequestration and the stability of the corresponding mRNA may be a reflection of the tonic inhibitory tone exerted by adenosine in brain.

Catecholaminergic CATH.a cells express predominantly delta-opioid receptors

CATH.a cells are a catecholaminergic cell line of neuronal origin. The opioid receptor complement expressed by CATH.a cells was defined pharmacologically and by reverse transcription-polymerase chain reaction (RT-PCR). CATH.a cells were found to express mRNA encoding all three of the major subtypes of opioid receptors. The relative abundance of CATH.a cell opioid receptor transcripts was delta > kappa> mu. Pharmacological and functional data were in agreement with the results of RT-PCR inasmuch as delta-opioid receptor was identified as the most abundant opioid receptor subtype expressed by CATH.a cells. In addition, at least one of the opioid signalling pathways, inhibition of adenylyl cyclase activity, was found to be operant in this cell line. CATH.a cells should be of general utility for the study of opioid receptor signalling mechanisms in the context of catecholaminergic neurons.

Source of extracellular brain adenosine during hypoxia in fetal sheep

Microdialysis was performed to determine whether hypoxia increases fetal brain adenosine (ADO) concentration through dephosphorylation of extracellular 5'-adenosine monophosphate (5-AMP). Hypoxia (fetal PaO2 approximately 14 Torr) increased fetal brain ADO levels approximately two-fold when the probes were perfused with synthetic cerebrospinal fluid (CSF) containing inhibitors of the nucleoside transporter but not with this solution plus a blocker of ecto-5'-nucleotidase (AOPCP). The hypoxia-induced rise in fetal brain ADO concentrations depends critically upon the hydrolysis of extracellular 5'-AMP.

N-alkylated derivatives of [D-Pro10]dynorphin A-(1-11) are high affinity partial agonists at the cloned rat kappa-opioid receptor

As part of an effort to develop peptides with selective kappa-opioid antagonist activity, a series of N-alkylated [D-Pro10]dynorphin A-(1-11) derivatives were made through solid-phase peptide synthesis: R-Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-D-Pro-LysOH, where R = N-benzyl, N-cyclopropylmethyl, N,N-dicyclopropylmethyl, or N,N-diallyl. These derivatives and dynorphin A-(1-13)NH2 were evaluated for kappa-opioid receptor binding affinity and potency as inhibitors of adenylyl cyclase. Equilibrium competition binding experiments using [3H]diprenorphine (approximately 600 pM) were performed on membranes prepared from cultured Chinese hamster ovary (CHO) cells stably expressing the rat kappa-opioid receptor. Tissue prepared from this cell line was used to evaluate opioid peptide inhibition of forskolin-stimulated (50 microM) adenylyl cyclase activity. Displacement of [3H]diprenorphine specific binding by these peptides was observed with a rank order of affinity (Ki, nM) = [D-Pro10]dynorphin A-(1-11) (0.13) > dynorphin A-(1-13)NH2 (0.34) > N-cyclopropylmethyl- (1.4) > N,N-dicyclopropylmethyl- (12.6) approximately N-benzyl- (18.3) approximately N,N-diallyl-[D-Pro10]dynorphin A-(1-11) (26.0). A similar rank order was observed for potency of adenylyl cyclase inhibition (IC50, nM): [D-Pro10]dynorphin A-(1-11) (0.12) approximately dynorphin A-(1-13)NH2 (0.19) > N-cyclopropylmethyl- (2.7) > N,N-dicyclopropylmethyl- (13.2) approximately N,N-diallyl- (18.0) approximately N-benzyl-[D-Pro10]dynorphin A-(1-11) (36.4). The peptides differed in their percent maximal inhibition of adenylyl cyclase activity: dynorphin A-(1-13)NH2 (100%) approximately N-cyclopropylmethyl- (94.3%) approximately [D-Pro10]dynorphin A-(1-11) (87.9%) > N-benzyl- (71.4%) >> N,N-dicyclopropylmethyl- (23.6%) approximately N,N-diallyl-[D-Pro10]dynorphin A-(1-11)(18.9%). As the N,N-dicyclopropylmethyl- and N,N-diallyl-[D-Pro10]dynorphin A-(1-11) derivatives were found to have only weak partial agonist activity with respect to adenylyl cyclase inhibition, they were evaluated for their ability to reverse dynorphin A-(1-13)NH2 (10 nM) inhibition of adenylyl cyclase activity. N,N-dicyclopropylmethyl- and N,N-diallyl-[D-Pro10]dynorphin A-(1-11) reversed dynorphin A-(1-13)NH2 inhibition to levels equal to the maximal inhibition produced by N,N-dicyclopropylmethyl- and N,N-diallyl-[D-Pro10]dynorphin A-(1-11) alone. This weak partial agonism combined with nanomolar potency render the N,N-dicyclopropylmethyl- and N,N-diallyl-[D-Pro10]dynorphin A-(1-11) compounds promising leads for further attempts to synthesize peptide kappa-opioid receptor antagonists.

Orphanin FQ has an inhibitory effect on the guinea pig ileum and the mouse vas deferens

The activity of the recently isolated endogenous opioid-like peptide orphanin FQ (OFQ) was measured in two classical bioassays of opioid action. OFQ potently and concentration-dependently suppressed the electrically stimulated contractions of the guinea pig ileum (GPI) and the mouse vas deferens (MVD) with EC50 values of 1.82 +/- 0.16 and 2.97 +/- 0.01 nM, and Emax values of 56 +/- 3% and 96 +/- 4%, respectively. This effect of OFQ, in both the GPI and MVD, was insensitive to the opioid receptor antagonist naloxone. OFQ competed with [3H]diprenorphine binding to mu-, delta- or kappa-opioid receptors stably expressed in Chinese hamster ovary cell lines with IC50 values of 2.1 +/- 0.4, 2.2 +/- 0.3, 0.75 +/- 0.3 microM, respectively. Low affinity for the classical opioid receptors together with the inability of naloxone to antagonize its effect suggest that the inhibitory action of OFQ is mediated via a distinct OFQ receptor in the GPI and MVD. Consequently, the MVD could serve as a valuable bioassay of potential OFQ receptor antagonists.

Synthesis and opioid activity of [D-Pro10]dynorphin A-(1-11) analogues with N-terminal alkyl substitution

Several N-terminal di- and monoalkylated derivatives of [D-Pro10]dynorphin A-(1-11) were synthesized in order to explore the structure-activity relationships for antagonist vs agonist activity at kappa-opioid receptors. N,N-Dialkylated and N-monoalkylated (alkyl = allyl, benzyl, and cyclopropylmethyl (CPM) tyrosine derivatives were prepared from tyrosine tert-butyl ester and the corresponding alkyl halides. [D-Pro10]Dyn A-(2-11) was prepared by solid phase synthesis using Fmoc-protected amino acids, and the tyrosine derivatives were coupled to the peptide with BOP ((benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate). Both the degree of substitution and the identity of the alkyl group affected kappa-receptor affinity, selectivity, and efficacy. All of the N-monoalkylated derivatives exhibited much higher affinity (Ki < 0.05 nM) for kappa receptors in the guinea pig cerebellum and greatly enhanced kappa-receptor selectivity (Ki ratio (kappa/mu) > 200) compared to the N,N-dialkyl [D-Pro10]Dyn A-(1-11) analogues, although one disubstituted analogue, N,N-diCPM[D-Pro10]Dyn A-(1-11), retained high affinity (Ki = 0.19 nM) for kappa receptors. Thus the introduction of the second alkyl group at the N-terminus lowered kappa-receptor affinity and selectivity. The N-allyl and N-CPM analogues were moderately potent agonists in the guinea pig ileum (GPI) assay, while the N-benzyl derivative was a weak agonist in this assay. In vivo in the phenylquinone abdominal stretching assay the N-CPM analogue exhibited potent antinociceptive activity (ED50 = 1.1 micrograms/mouse), while N-allyl[D-Pro10]Dyn A-(1-11) exhibited weak antinociceptive activity (ED50 = 27 micrograms/mouse). For the N,N-dialkyl derivatives the identity of the N-terminal alkyl group affected the efficacy observed in the smooth muscle assays. The N,N-diCPM analogue exhibited negligible agonist activity, and N,N-diallyl[D-Pro10]Dyn A-(1-11) showed weak antagonist activity against Dyn A-(1-13)NH2 in the GPI. In contrast, the N,N-dibenzyl compound showed appreciable opioid agonist activity in this assay. In vivo the N,N-diallyl analogue exhibited weak antinociceptive activity (ED50 = 26 micrograms/mouse in the phenylquinone abdominal stretching assay). The N-monoalkylated peptides are among the most kappa-selective opioid peptides reported to date, showing comparable or greater selectivity and higher affinity than the kappa-selective non-peptide agonists U-50,488 and U-69,593. The N,N-diCPM and N,N-diallyl peptides are lead compounds in the development of peptide-based kappa-receptor antagonists.

Domoic acid neurotoxicity in cultured cerebellar granule neurons is mediated predominantly by NMDA receptors that are activated as a consequence of excitatory amino acid release

The participation of NMDA and non-NMDA receptors in domoic acid-induced neurotoxicity was investigated in cultured rat cerebellar granule cells (CGCs). Neurons were exposed to 300 microM L-glutamate or 10 microM domoate for 2 h in physiologic buffer at 22 degrees C followed by a 22-h incubation in 37 degrees C conditioned growth media. Excitotoxic injury was monitored as a function of time by measurement of lactate dehydrogenase (LDH) activity in both the exposure buffer and the conditioned media. Glutamate and domoate evoked, respectively, 50 and 65% of the total 24-h increment in LDH efflux after 2 h. Hyperosmolar conditions prevented this early response but did not significantly alter the extent of neuronal injury observed at 24 h. The competitive NMDA receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid and the non-NMDA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline (NBQX) reduced glutamate-induced LDH efflux totals by 73 and 27%, respectively, whereas, together, these glutamate receptor antagonists completely prevented neuronal injury. Domoate toxicity was reduced 65-77% when CGCs were treated with competitive and noncompetitive NMDA receptor antagonists. Unlike the effect on glutamate toxicity, NBQX completely prevented domoate-mediated injury. HPLC analysis of the exposure buffer revealed that domoate stimulates the release of excitatory amino acids (EAAs) and adenosine from neurons. Domoate-stimulated EAA release occurred almost exclusively through mechanisms related to cell swelling and reversal of the glutamate transporter. Thus, whereas glutamate-induced injury is mediated primarily through NMDA receptors, the full extent of neurodegeneration is produced by the coactivation of both NMDA and non-NMDA receptors. Domoate-induced neuronal injury is also mediated primarily through NMDA receptors, which are activated secondarily as a consequence of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate receptor-mediated stimulation of EAA efflux.

Synthesis and opioid activity of conformationally constrained dynorphin A analogues. 2. Conformational constraint in the "address" sequence

Several cyclic lactam analogues of Dyn A-(1-13)NH2 were prepared in order to reduce the conformational flexibility in different regions of the native linear peptide. Cyclo[D-Asp(i),Dap(i+3)]Dyn A-(1-13)NH2 (Dap = alpha,beta-diaminopropionic acid) analogues were designed on the basis of molecular modeling using AMBER, which suggested that this constraint may be compatible with an alpha-helix. The cyclic portion of these constrained analogues spanned from residues 3 to 9, a region proposed by Schwyzer (Biochemistry 1986, 25, 4281) to adopt a helical conformation at kappa receptor sites. Analogues containing Dab (alpha,gamma-diaminobutyric acid) or Orn in position i + 3 were also synthesized to examine the effects of larger ring size. The cyclic peptides exhibited marked differences in binding affinities for kappa, mu, and delta receptors and in opioid activity in the guinea pig ileum (GPI). Cyclo[D-Asp6,Dap9]Dyn A-(1-13)NH2 showed both high kappa receptor affinity and potent agonist activity in the GPI, while cyclo[D-Asp3,Dap6]Dyn A-(1-13)NH2 exhibited very weak binding affinity at all opioid receptors as well as very weak opioid activity in the GPI. Cyclo[D-Asp5,Dap8]Dyn A-(1-13)NH2 showed moderate binding affinity for kappa receptors and was the most kappa selective ligand in this study, but this peptide exhibited very weak agonist activity in the GPI assay. Compared to the corresponding linear peptides, all of the cyclic peptides exhibited decreased mu receptor affinity, while kappa receptor affinity was retained or improved. Therefore the corresponding linear peptides were generally mu selective while the cyclic constrained peptides demonstrated slight selectivity for kappa vs mu receptors or were nonselective. Increasing the ring size by incorporating Dab or Orn in positions 6, 8, or 9 did not significantly affect the binding affinity for the three opioid receptor types nor the opioid activity observed in the GPI. Circular dichroism spectra of the cyclo[D-Asp(i),Dap(i+3)] derivatives in 80% trifluoroethanol at 25 and 5 degrees C suggested differences in the stability of a helical structure when the constraint was incorporated near the N-terminus vs in the middle of the peptide.

Chronic exposure to adenosine receptor agonists and antagonists reciprocally regulates the A1 adenosine receptor-adenylyl cyclase system in cerebellar granule cells

Chronic treatment with the adenosine receptor antagonist caffeine evokes an up-regulation of A1 adenosine receptors and increased coupling of the receptor to G proteins in rat brain membranes. However, chronic agonist exposure has not been explored. Primary cultures of cerebellar granule cells were exposed chronically to A1 adenosine receptor agonists and antagonists. Exposure to the A1 adenosine receptor agonist N6-cyclopentyladenosine resulted in (1) a time- and concentration-dependent reduction in the density of receptors labeled by 1,3-[3H]dipropyl-8-cyclopentylxanthine, (2) an enhanced ability of guanyl nucleotides to decrease the fraction of A1 adenosine receptor sites displaying high affinity for 2-chloroadenosine, and (3) a functional uncoupling of receptors from adenylyl cyclase (EC 4.6.1.1). The adenosine antagonists caffeine and 8-p-sulfophenyltheophylline produced alterations in A1 adenosine receptor homeostasis that were antipodal to those associated with agonist treatment. Antagonist exposure (1) increased the density of A1 adenosine receptors in cerebellar granule cell membranes, (2) blunted the effect of guanyl nucleotides on receptor coupling to G proteins, and (3) increased the functional coupling of receptors to adenylyl cyclase inhibition. Forskolin treatment of cerebellar granule cells did not affect receptor density, suggesting that cyclic AMP is not involved in the regulation of A1 adenosine receptor expression.

Arthroscopy of the foot and ankle in the athlete

Ankle arthroscopy has evolved over the past decade to address many acute and chronic injuries in the athlete. Although similar outcomes are reported with established open procedures, arthroscopic intervention confers the advantages of decreased postoperative morbidity and earlier return to sports activity. Arthroscopic procedures for the foot are evolving; however, most are considered investigational at this time.