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Biomedical subjects

A E Jacobson

Publications and source records attributed to A E Jacobson.

At least 145 records · Page 8Linked to original sources
PubMed1986

Antagonism of phencyclidine action by metaphit in rat cerebellar Purkinje neurons: an electrophysiological study.

Metaphit (1-[1-(3-isothiocyanatophenyl)-cyclohexyl]piperidine), a derivative of the psychotomimetic drug phencyclidine (PCP), is postulated to bind irreversibly to PCP receptors. We examined here the electrophysiological interactions of metaphit with PCP in rat cerebellar cortex, since a specific effect of PCP on cerebellar neuronal circuitry has been shown. Metaphit, applied locally to Purkinje neurons by micropressure ejection through multibarreled micropipettes, has a reversible depressant action lasting for 5-20 min. Following this, PCP-induced inhibition is blocked with no recovery despite repeated applications of PCP for over an hour. This blockade was not seen unless the dose of metaphit was sufficient to transiently depress Purkinje neuron discharge. Metaphit does not antagonize inhibitory effects of locally applied norepinephrine or gamma-aminobutyric acid. This electrophysiological data suggests that metaphit is an irreversible antagonist of PCP in the cerebellum.

Action Potentials↗
PubMed1986

Upregulation of the mu-noncompetitive delta binding site by chronic morphine administration: effect of preincubating membranes in 400 nM sodium chloride.

Rats treated chronically with morphine were found to have an increased number of mu-noncompetitive delta binding sites. The increase in the Bmax was 39% and the enhancement was blocked by pre-incubation in 50 mM Tris, pH 7.4 with 400 mM NaCl for one hour at 25 degrees C. These findings are consistent with the removal of newly manifested binding sites being a specific property of sodium, by analogy with previous studies where sodium has been shown to extract extrinsic proteins from red cell ghosts.

Animals↗
PubMed1986

Metaphit, a proposed phencyclidine receptor acylator: phencyclidine-like behavioral effects and evidence of absence of antagonist activity in pigeons and in rhesus monkeys.

Metaphit, a derivative of phencyclidine (PCP), binds irreversibly to PCP sites and appears to act as an antagonist of PCP under some conditions and as a PCP-like agonist under other conditions. To describe further these conditions, the authors investigated the behavioral effects of metaphit by using different routes of administration, behavioral procedures and species. In pigeons, metaphit induced PCP-like catalepsy after i.c.v. administration and, after i.m. administration, produced PCP-like discriminative stimulus effects and stereotyped operant responding. In rhesus monkeys, metaphit produced ataxia and convulsions but did not induce catalepsy, anesthesia or PCP-like discriminative stimulus effects. None of the effects of PCP-type drugs [i.e., PCP, ketamine or (+/-)-SKF 10,047] in pigeons or rhesus monkeys was antagonized by metaphit. Metaphit potentiated the discriminative stimulus effects of PCP and of SKF 10,047 in pigeons. These results suggest that metaphit acts not as an antagonist of PCP but as a PCP-like agonist under these conditions. Metaphit's potentiation of behavioral effects of PCP may be related to the presumed ability of metaphit to acylate PCP receptors. The extent to which metaphit produces PCP-like behavioral effects in part may be species dependent.

Acylation↗
PubMed1986

Metaphit, an acylating ligand for phencyclidine receptors: characterization of in vivo actions in the rat.

Metaphit, which acylates phencyclidine (PCP) receptors in vitro, was shown to acylate PCP receptors and antagonize the behavioral and electrophysiological effects of PCP in vivo. Metaphit (2 mumol/rat) administered i.c.v. produced PCP-like stereotyped behavior and ataxia in 10 to 20% of rats. At a lower dose, Metaphit (1 mumol/rat) antagonized the ability of PCP to induce stereotyped behavior and ataxia for 3 and 4 days, respectively. The Metaphit-induced antagonism of PCP induction of stereotyped behavior and ataxia was dose-dependent and specific as Metaphit did not antagonize induction of stereotyped behavior by amphetamine. Further evidence for a specific PCP receptor mechanism was the finding that PCP pretreatment blocked the effects of subsequent Metaphit administration. Metaphit also antagonized PCP-induction of stereotyped behavior, but not ataxia, after i.v. administration. Doses of Metaphit that produced long-term antagonism of the behavioral effects of PCP also produced a significant decrease in the maximum binding, but not Kd, of the binding of the PCP analog, [3H]-1-(2-thienyl)cyclohexyl]piperidine, in Metaphit-pretreated rats. The binding of [3H]etorphine and [3H]spiroperidol was not altered significantly by pretreating rats with Metaphit. (-)-Cyclazocine and (+)-SKF 10,047 induced stereotyped behavior and ataxia that was not antagonized by Metaphit-pretreatment. In electrophysiological experiments, Metaphit, like PCP, initially depressed the firing of caudate neurons as does PCP, but then irreversibly inhibited PCP-induced depression of caudate neurons. These results suggest that metaphit antagonized the effects of PCP by selectively acylating PCP receptors and that (-)-cyclazocine- and (+)-SKF 10,047-induced behavioral effects are not mediated primarily by PCP receptors.

Acylation↗
PubMed1986

Electrophysiological interactions of isomers of cyclazocine with the phencyclidine antagonist metaphit in rat cerebellar Purkinje neurons.

Metaphit, 1-(1-(3-isothiocyanatophenyl) cyclohexyl) piperidine, an analog of phencyclidine (PCP) has been shown previously to selectively block PCP receptors and to irreversibly antagonize the depressant effect of PCP in cerebellum. In this study, we examined the electrophysiological interactions of metaphit and naloxone with stereoisomers of cyclazocine, an agent known to have analgesic and psychotomimetic activity in behavioral studies, effects that have been ascribed to opiate and PCP receptor activity. A dose-dependent and reversible slowing of Purkinje neuron discharge was seen with local application of (+)- or (-)-cyclazocine. We found that the blockade of (-)-cyclazocine effects required both high doses of naloxone and the presence of metaphit, whereas the responses to (+)-cyclazocine were blocked by metaphit alone on most cerebellar Purkinje neurons. These findings suggest that the depressant reaction of (+)-cyclazocine in cerebellar Purkinje neurons is primarily mediated through PCP receptors. (-)-Cyclazocine responses, on the other hand, appear to be due to activity at both PCP and kappa opioid receptors.

Animals↗
PubMed1985

Differentiation of [3H]phencyclidine and (+)-[3H]SKF-10,047 binding sites in rat cerebral cortex.

The potency of a series of opioid and non-opioid psychotomimetic drugs to inhibit the specific binding of [3H]PCP and (+)-[3H]SKF-10,047 to rat cerebral cortical membranes was examined. (+)-PCMP, the 3-methylpiperidino analog of PCP, was a potent inhibitor of the specific binding of both ligands. All of the other 12 compounds examined, however, displayed a 3-277-fold selectivity for either [3H]PCP or (+)-[3H]SKF-10,047 binding. These results suggest that although these opioid and non-opioid psychotomimetics bind to both sites, most have significantly different affinities. The binding sites for [3H]PCP appear to be distinct from the 'sigma' binding sites labeled with (+)-[3H]SKF-10,047.

Animals↗
PubMed1985

A specific acylating agent for the [3H]phencyclidine receptors in rat brain.

A derivative of phencyclidine (PCP, 1 in fig. 1) bearing an isothiocyanate moiety on the meta position of the aromatic ring (Metaphit, 3 in fig. 1) has been synthesized and identified as a rapid and specific site-directed acylating agent of the [3H]phencyclidine binding site in rat brain homogenates. The percentage of sites irreversibly inactivated by Metaphit was found to be the same in the hippocampus and striatum and the remaining sites were unaffected by Metaphit treatment under any conditions, suggesting that at least two distinct binding sites are present. An isomeric isothiocyanate derivative did not irreversibly inhibit [3H]phencyclidine receptors, indicating structural specificity for Metaphit in the inhibition of these receptors. The availability of Metaphit should greatly facilitate study of the structure and function of the phencyclidine receptors.

Acylation↗
PubMed1985

Leucine enkephalin noncompetitively inhibits the binding of [3H]naloxone to the opiate mu-recognition site: evidence for delta----mu binding site interactions in vitro.

Using quantitative methods, this study examined the hypothesis that delta-ligands are noncompetitive inhibitors at a population of mu-binding sites. Evidence is presented that with the defined set of in vitro assay conditions utilized, [3H]naloxone labels two binding sites: the mu binding site and a second site tentatively identified as a kappa binding site, and that leucine enkephalin is a noncompetitive inhibitor at the mu recognition site.

Animals↗
PubMed1985

Local anesthetic properties of opioids and phencyclidines: interaction with the voltage-dependent, batrachotoxin binding site in sodium channels.

[3H]Batrachotoxinin-A 20-alpha-benzoate ([3H]BTX-B) binds specifically and with high affinity (Kd = 30 nM) to a site on voltage-dependent Na+ channels. Compounds with local anesthetic activity inhibit the binding of [3H]BTX-B by a mutually exclusive, allosteric mechanism. The potential local anesthetic potency of a series of 23 opioids and phencyclidine-like compounds has been estimated by their inhibition of [3H]BTX-B binding to Na+ channels in a preparation of synaptoneurosomes from guinea pig cerebral cortex. The potency of these compounds were also tested as inhibitors of the specific binding of [3H]phencyclidine ([3H]PCP) to a high affinity site on rat brain membranes. Opioids such as morphine and codeine show little affinity for the [3H]BTX-B binding site or for the [3H]PCP binding site. Other analgesics, many of the PCP-like compounds and dioxadrol derivatives are potent versus [3H]BTX-B binding and display both stereospecificity and high affinity towards the PCP-binding site. However, there was no correlation between local anesthetic potency assessed as antagonism of [3H]BTX-B binding and affinity towards the PCP site. Five classical local anesthetics had no affinity for the PCP-site, but did displace [3H]BTX-B from its binding site.

Anesthetics, Local↗
PubMed1985

Evidence that the delta-selective alkylating agent, fit, alters the mu-noncompetitive opiate delta binding site.

Considerable evidence supports the notion that the prototypic delta agonist [3H]D-ala2-D-leu5-enkephalin labels two binding sites on brain membranes in vitro. Recent studies have demonstrated that treatment of brain membranes with the delta-selective, site-directed, alkylating agent, FIT (Rice et al., Science 220, 314-316, 1983) results in a membrane preparation devoid of detectable higher affinity [3H]D-ala2-D-leu5-enkephalin binding sites, but contain residual lower affinity binding sites at which mu-ligands are apparent noncompetitive inhibitors (Rothman et al., Neuropeptides 4:210-215, 1984). In this paper we extend these data by showing that although FIT eliminates the higher affinity binding site, it also alters the properties of the residual lower affinity binding sites.

Affinity Labels↗
PubMed1985

Increased affinity of dimeric enkephalins is not dependent on receptor density.

The equilibrium binding and dissociation kinetics of the enkephalin dimer bis-(D-Ala2-D-Leu5-enkephalin)-ethylenediamide (designated DPE2) to neuroblastoma glioma NG108-15 cells were investigated and compared with the monomers D-Ala2-D-Leu5-enkephalin (DADL) and D-Ala2-Leu5-enkephalinamide (DALEA). Binding was studied after exposure of the membrane to increasing concentrations of the irreversible delta receptor selective ligand FIT in order to decrease the density of binding sites on the cell membrane. The increased affinity of DPE2 did not revert to that of the monomer DADL by this reduction of binding sites. Similarly, the dissociation of DPE2 did not approach that of the monomer DALEA in the presence of 1 microM DALEA. These data strongly suggest that crosslinking does not occur, and fail to confirm the hypothesis that dimers with short spanning chain length aid the clustering of receptors. We postulate: 1) If the dimer binds to a bivalent binding site, the monovalent binding state of our bivalent ligand may not exist to an appreciable extent, and 2) the bivalent ligand cannot bind when the binding site is irreversibly blocked by a monovalent ligand.

Animals↗
PubMed1985

Preparation of rat brain membranes highly enriched with opiate kappa binding sites using site-directed acylating agents: optimization of assay conditions.

The goal of this study was to determine optimal conditions with which to measure opiate kappa binding sites in rat brain. Membranes were pretreated with mu-selective (BIT) and delta-selective (FIT) site-directed acylating agents (Rice et al., Science 220, 314-316), and the binding of [3H]bremazocine to the residual binding sites was defined as the kappa binding site. The binding of [3H]bremazocine to BIT/FIT-treated membranes was greatly increased by conducting the assay at 0 degrees C in the presence of 0.4 M NaCl. Using this 0 degrees C/NaCl assay condition, the binding of [3H]bremazocine was best described by a one-site binding model with a KD of 0.45 nM and a Bmax of 378 fmol/mg protein. Autoradiographic studies demonstrated that, using this assay condition, [3H]bremazocine densely labeled the deep layers of guinea pig cortex, an area known to be enriched with kappa binding sites. These and additional data suggest that the binding of [3H]bremazocine to the kappa binding site of rat brain is optimally assayed at 0 degrees C in the presence of 0.4 M NaCl using BIT/FIT-treated membranes and that rat brain is endowed with a high level of kappa binding sites.

Alkylating Agents↗
PubMed1985

Purification of the opiate receptor of NG108-15 neuroblastoma-glioma hybrid cells.

Opiate receptors from NG108-15 neuroblastoma-glioma hybrid cell membranes were purified to apparent homogeneity in a form covalently labeled with the opiate affinity ligand 3-methylfentanylisothiocyanate (super-FIT). The purification procedure consists of five steps: quantitative labeling of opiate receptors in membranes with super-FIT; solubilization in a lubrol/3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate mixture; adsorption to and elution from a wheat germ agglutinin-Sepharose column; immunoaffinity chromatography on columns of immobilized anti-fentanyl; preparative gel electrophoresis in the presence of NaDodSO4. The protein was purified approximately 30,000-fold in 3% overall yield to a state in which there is 1 mol of super-FIT bound per mol of protein, corresponding to 21,000 pmol per mg of protein, the theoretically expected specific activity. The protein is glycosylated and migrates on NaDodSO4 gel electrophoresis with a Mr near 58,000. It has a strong tendency to dimerize, even in the presence of denaturing detergents, and it exists primarily as an oligomer in nondenaturing detergents.

Affinity Labels↗
PubMed1985

Pharmacological actions of the racemic and the enantiomeric 1,4-dimethyl-10-hydroxy-2,3,4,5,6,7-hexahydro-1,6-methano-1H-4-benz azo nines (C-homobenzomorphans).

The racemate and optical isomers of the C-homobenzomorphans, 1,4-dimethyl-10-hydroxy-2,3,4,5,6,7-hexahydro-1,6-methano-1H-4-benzaz onine, were evaluated in a number of assays sensitive to narcotics of different types. All three C-homobenzomorphans were active in vitro in guinea pig ileum, mouse vas deferens, and rat brain membrane binding assays, but were of low potency. These C-homobenzomorphans showed different profiles of in vivo activity. The (+)-isomer and racemate were active as agonists in the tail-flick assay, whereas the (-)-isomer was inactive. At higher doses, the (-)-isomer and the racemate behaved as antagonists of morphine in the tail-flick assay. All three compounds were active in the phenylquinone test, but naloxone did not block this effect. In addition, all three were potent in the hot-plate test. Neither of the isomers substituted for morphine in dependent rats or monkeys. However, the (+)-isomer precipitated withdrawal in these monkeys. The (-)-isomer produced opioid-like physical dependence in both rats and monkeys. Some of the implications regarding the results with these remarkable homobenzomorphans are discussed.

Analgesics↗
PubMed1985

A quantitative study of [3H]D-Ala2-D-Leu5-enkephalin binding to rat brain membranes. Evidence that oxymorphone is a noncompetitive inhibitor of the lower affinity delta-binding site.

The mechanism by which mu ligands inhibit the binding of prototypic delta agonists to preparations of brain membranes is controversial. Most investigators assume competitive inhibition. In this study, we examine the interaction of the mu agonist oxymorphone and delta agonist DSTLE (D-Ser2-Thr6-Leu-enkephalin) with [3H]D-Ala2-D-Leu5-enkephalin (DADL) binding to membranes of rat brain. According to the two-site competitive model, mu ligands are competitive inhibitors at both sites. The two-site allosteric model supposes that mu ligands are competitive inhibitors at one binding site, and noncompetitive inhibitors at the other binding site. Quantitative analysis of DSTLE and oxymorphone binding demonstrated that the two-site allosteric model fit the data significantly better than did the two-site competitive model, and that oxymorphone is a noncompetitive inhibitor of the lower affinity [3H]DADL-binding site. Autoradiographic studies demonstrated that the lower affinity [3H]DADL-binding site (mu-noncompetitive binding site) had an anatomical distribution apparently indistinguishable from that obtained with [3H]oxymorphone (type I pattern), supporting the hypothesis that the lower affinity delta-binding site is the delta-binding site of an opiate receptor complex consisting of interacting mu- and delta-binding sites.

Animals↗