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Effects of nicotinic agonists and antagonists on N-methyl-D-aspartate-induced 3H-norepinephrine release and 3H-(1-[1-(2-thienyl)cyclohexyl]-piperidine) binding in rat hippocampus.

The nicotinic agonists dimethylphenylpiperazinium iodide (DMPP) and carbachol (CARB) as well as (-)nicotine [-)NIC) were tested alone and in combination with N-methyl-D-aspartate (NMDA) for their abilities to enhance the efflux of 3H-norepinephrine (NE) from slices of rat hippocampus. CARB and (-)NIC produced small, transient increases in NE efflux, while DMPP produced larger, longlasting increases. Inasmuch as the nicotinic antagonists mecamylamine (MECA) and hexamethonium (C6) did not consistently inhibit the increases in NE efflux produced by these agonists, the role of a nicotinic receptor in mediating these responses is uncertain. CARB and DMPP enhanced the ability of NMDA to stimulate NE release, while (-)NIC did not. MECA, but not C6, was found to selectively antagonize NMDA-stimulated NE release that did not appear to involve a nicotinic receptor. Binding studies indicated that MECA and the related nicotinic antagonist pempidine produced an inhibition of NMDA-stimulated NE release by an action at the PCP receptor that is known to be linked to the NMDA receptor-ionophore complex. These data suggest that the actions of these ganglionic blocking agents on excitatory responses in the hippocampus involve inhibition of excitatory amino acid as well as nicotinic receptors.

Animals↗

RTI-4793-14, a new ligand with high affinity and selectivity for the (+)-MK801-insensitive [3H]1-]1-(2-thienyl)cyclohexyl]piperidine binding site (PCP site 2) of guinea pig brain.

[3H]TCP, an analog of the dissociative anesthetic phencyclidine (PCP), binds with high affinity to two sites in guinea pig brain membranes, one that is MK-801 sensitive and one that is not. The MK-801-sensitive site (PCP site 1) is associated with NMDA receptors, whereas the MK-801-insensitive site (PCP site 2) may be associated with biogenic amine transporters (BAT). Although several "BAT ligands" are known that bind selectively to PCP site 2 and not to PCP site 1 (such as indatraline), these compounds have low affinity for site 2 (Ki values > 1 microM). Here we demonstrate that the novel pyrrole RTI-4793-14 is a selective, high affinity ligand for PCP site 2. We determined the IC50 values of RTI-4793-14 and several reference compounds [PCP, (+)-MK801 and indatraline] for PCP site 1 (assayed with [3H](+)-MK801), PCP site 2 (assayed with [3H]TCP in the presence of 500 nM (+)-MK801) and a variety of BAT-related measures ([3H]CFT binding to the DA transporter, [3H]nisoxetine binding to the norepinephrine transporter, [3H]dopamine uptake, [3H]serotonin uptake). In addition, we determined the ability of RTI-4793-14 to block NMDA responses in cultured hippocampal neurons under voltage clamp. (+)-MK801 had high affinity for PCP site 1 (4.6 nM) and potently inhibited NMDA-induced responses, but was much less potent in the BAT-related measures (IC50 s > 10 microM). PCP had high affinity at PCP site 1 (IC50 = 92 nM) and PCP site 2 (IC50 = 117 nM), and was moderately potent in all BAT-related measures except [3H]nisoxetine binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Pharmacological characterization of the discriminative stimulus properties of the phencyclidine analog, N-[1-(2-benzo(b)thiophenyl)-cyclohexyl]piperidine.

RATIONALE: Although both cocaine and the phencyclidine analog, BTCP, have dopamine (DA) re-uptake blocking properties, under some conditions their behavioral effects can be differentiated. Therefore, we examined whether the discriminative stimulus (DS) effects of BTCP are different from those of cocaine. OBJECTIVES: To compare the effects of monoamine re-uptake blockers, varying in their in vitro potencies as inhibitors of DA, norepinephrine (NE), or serotonin re-uptake, in different groups of rats trained to discriminate either BTCP or cocaine from saline. Additionally, drugs from other pharmacological classes were tested in both groups. METHODS: Rats were trained to discriminate either BTCP (5 mg/kg, i.p.) or cocaine (10 mg/kg, i.p.) from saline under a two-lever FR10 drug discrimination procedure. RESULTS: BTCP and cocaine cross-substituted in BTCP- and cocaine-trained rats. The DA re-uptake blockers, mazindol, indatraline, methylphenidate, GBR12909, and GBR12935, occasioned dose-related drug-lever (DL) selection both in cocaine- and in BTCP-trained rats, with potencies that were significantly correlated. In contrast, the NE re-uptake blockers, nisoxetine, desipramine, and nortriptyline, produced higher levels of DL selection in BTCP-trained rats than in cocaine-trained rats, a profile like that reported in low-dose cocaine-trained rats. Drugs from other classes acted similarly in both discriminations. Further, the alpha1-adrenergic antagonist prazosin dose dependently blocked the DS effects of the training dose of BTCP, but not of cocaine. CONCLUSIONS: The results suggest that the DS effects of BTCP are similar to cocaine, and resemble those of a low training dose of cocaine.

Animals↗

Comparison of [3H] phencyclidine ([3H] PCP) and [3H] N-[1-(2-thienyl) cyclohexyl] piperidine ([3H] TCP) binding properties to rat and human brain membranes.

The investigation of [3H] PCP and [3H] TCP binding properties to rat cerebrum and cerebellum resulted in the demonstration of multiple binding sites for the two drugs. In the two tissue preparations PCP had a lower affinity than TCP. In membranes from the cerebrum an equal number of high affinity binding sites were present for [3H] PCP and [3H] TCP. However, low affinity binding sites were two times more numerous for [3H] PCP than for [3H] TCP. In the cerebellum, the number of high and low affinity sites labeled by the two radioligands was identical, but the number of high affinity sites was about 7 fold lower than in the cerebrum. Taken together these results may indicate that in the cerebrum [3H] PCP labels other sites than NMDA/PCP receptor(s), maybe sigma receptors and/or the dopamine uptake complex. In human cerebral cortex samples [3H] TCP also bound to two different sites. The number of high and low affinity sites were 12 and 3 times, respectively, less abundant than in the rat cerebrum. Low affinity sites were of higher affinity (5 times) than corresponding sites in the rat brain. In the human cerebellum [3H] TCP binding parameters were identical to those measured in the same region in the rat.

Animals↗

Modulation by dopamine of [3H]N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine ([3H]BTCP, a phencyclidine derivative) binding to the dopamine uptake complex.

The modulation by dopamine of the binding of [3H]BTCP to the dopamine (DA) uptake complex was investigated in vivo (in control, reserpine- and L-DOPA-treated mice) and in vitro (on membrane preparations of the striatum of the rat). In both cases increasing doses of DA exerted a non-competitive inhibition of binding of [3H]BTCP, with a Ki value close to its K0.5, determined in competition experiments. Amphetamine and cocaine were also non-competitive inhibitors of the binding of [3H]BTCP, while GBR 12783 was competitive. In the presence of DA, the amount of cocaine required to inhibit the binding of [3H]BTCP was increased both in vitro and in vivo. These results suggest that inhibitors of the uptake of DA, such as BTCP or GBR 12783, modulate allosterically the uptake of DA, by binding to a site different from the DA recognition site. Cocaine, however, seems to share the same recognition site as DA.

Animals↗

OHM3295: a fentanyl-related 4-heteroanilido piperidine with analgesic effects but not suppressive effects on splenic NK activity in mice.

The immunoregulatory effects of fentanyl and a fentanyl-related compound, OHM3295, were studied in mice. Male CD1 mice treated with a range of fentanyl doses (0.1-1.0 mg/kg, subcutaneously) showed suppression of splenic natural killer (NK) activity following 0.25-0.50 mg/kg fentanyl dose but not higher (0.75-1.0 mg/kg) or lower (0.1 mg/kg) doses. Fentanyl (0.01-32.0 mg/kg) also induced dose-related analgesia as measured by an increase in tail flick latency; these analgesic effects were antagonized by naltrexone (1.0-10.0 mg/kg). Pretreatment with naltrexone (1.0-3.2 mg/kg) resulted in significant suppression of splenic NK activity following fentanyl (10.0-32.0 mg/kg) administration. In comparison to fentanyl, OHM3295 (3.2-25.0 mg/kg) augmented splenic NK activity in a naltrexone-reversible manner. Similar to fentanyl, OHM3295 (1.0-32.0 mg/kg) also induced a naltrexone-sensitive, dose-related analgesia as measured by an increase in tail flick latency. These results with OHM3295 demonstrate a novel profile of effects which includes naltrexone-sensitive analgesic effects in the absence of immunosuppressive effects. In addition, this is the first reported case in which a compound with opioid analgesic effects has been shown to potentiate natural killer cytolytic activity following in vivo administration.

Analgesics↗

Novel acetylcholinesterase inhibitor as increasing agent on rhythmic bladder contractions: SAR of 8-{3-[1-(3-fluorobenzyl)piperidin-4-yl]propanoyl}-1,2,5,6-tetrahydro-4H-pyrrolo[3,2,1-ij]quinolin-4-one (TAK-802) and related compounds.

As part of an on-going investigation to develop an increasing agent on rhythmic bladder contractions, 1-aryl-3-(1-benzylpiperidin-4-yl)propanones were synthesized and examined as noncarbamate acetylcholinesterase (AChE) inhibitors. Among compounds with various aryl groups, 1,2,5,6-tetrahydro-4H-pyrrolo[3,2,1-ij]quinolin-4-one derivative 9c was found to possess a potent AChE inhibition activity with an IC(50) value of 1.3nM. The compound 9c increased rhythmic bladder contractions in Guinea pigs and rats without affecting the basal intravesical pressure, which suggests that 9c may be useful for the treatment of voiding dysfunction caused by detrusor underactivity.

Acetylcholinesterase↗

Antiproliferative effect of the piperidine nitroxide TEMPOL on neoplastic and nonneoplastic mammalian cell lines.

The stable nitroxide 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL) is widely used as a probe in biophysical studies and as an antioxidant in several experimental models. The potential cytotoxic effects of TEMPOL were tested on a panel of human and rodent cell lines, and the nitroxide proved to be significantly more effective in inhibiting the growth of neoplastic than nonneoplastic cell lines after a 96-h exposure. More detailed studies on MCF-7/WT cells indicate that at least 24 h are necessary for TEMPOL to induce irreversible cell damage, which seems to be related to the reactivity of the nitroxyl group. This observation, together with the antagonistic effect of N-acetylcysteine, suggests an involvement of free radical-mediated processes. Cell cycle studies indicate a biphasic effect of TEMPOL, with a short-term accumulation of the cells in the G1 phase and a later increase in G2/M phase; the pattern of DNA fragmentation observed in TEMPOL-treated cells points to an apoptotic mode of cell death. In conclusion, our data suggest that, while the possible cytotoxic effects of TEMPOL should not be overlooked when using this compound as a biophysical probe or antioxidant, these same properties could be exploited as a novel approach to cancer chemotherapy, especially in tumor cells exhibiting unfavorable characteristics, such as a multidrug-resistant phenotype or loss of hormone receptors.

Acetylcysteine↗

Study of in vitro and in vivo effects of the piperidine nitroxide Tempol--a potential new therapeutic agent for gliomas.

The identification of novel therapeutic agents for the management of malignant gliomas represents an area of active research. Here, we show that Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl; TPL), a stable nitroxide free radical, inhibits the growth of C6 glioma cells both in vitro and in vivo. Morphological features of apoptosis were apparent in C6 cells following in vitro treatment with TPL. Cell death was preceded by dose-dependent increase in p21(WAF1/CIP1) expression, without apparent stabilisation of the TP53 gene product. When C6 cells were grown as xenografts in nude mice, treatment with TPL induced a significant dose-dependent decrease in tumour growth, without signs of general or organ toxicity. Tumours from treated mice showed an increase in the number of apoptotic cells and a decrease in the rate of neo-vascularisation compared with tumours from control mice. Our findings suggest a potential use for TPL as a novel antiproliferative agent for the treatment of malignant gliomas.

Animals↗

Phenoxypyrimidine inhibitors of p38alpha kinase: synthesis and statistical evaluation of the p38 inhibitory potencies of a series of 1-(piperidin-4-yl)-4-(4-fluorophenyl)-5-(2-phenoxypyrimidin-4-yl) imidazoles.

As a continuation of our work with 1,4,5 substituted imidazole inhibitors of p38alpha, we report a series of 1-(4-piperidinyl)-4-(4-fluorophenyl)-5-(2-phenoxy-4-pyrimidinyl) imidazoles related to 7. The compounds have IC50's for inhibition of p38alpha ranging from 6.0 to 650nM. Statistical analysis of the p38beta inhibitor potencies shows a correlation of IC50's with the electron donating strength of low molecular weight substituents.

Enzyme Inhibitors↗

Two non-racemic preparations of a piperidine-based NMDA antagonist with analgesic activity.

(2R,3S,1'R)-3-(1-Hydroxy-2-phosphonoethyl)-2-piperidinecarboxyl ic acid 1 has been synthesized by two different methods. The NMDA receptor binding affinities (Ki values) are 74 nM for compound 1, and 64 nM for the corresponding ketone 2. The analgesic effects were evaluated using the mouse hot-plate test and the mouse formalin model. The ED50 values for the racemates of compounds 1 and 2, using the mouse hotplate and intrathecal injection, were 0.53 and 0.51 nmol, respectively.

Analgesics↗

Viscosity of the aqueous liquid/vapor interfacial region: 2D electrochemical measurements with a piperidine nitroxy radical probe.

Surface partitioning of 2,2,6,6-tetramethyl-1-piperidynyloxy radical (Tempo) to the air/water interface follows a Langmuir isotherm. The partition constant was obtained by the surface tension measurements in the concentration range of 1.0 x 10(-4)-2.4 x 10(-3) M yielding K = 640 +/- 99 M(-1). The lateral mobility of Tempo at the air/water interface was measured electrochemically in the surface concentration range of 2.0 x 10(-11)-1.4 x 10(-10) mol/cm2, corresponding to ca. 7.3-50% full monolayer coverage. The measurements employed cyclic voltammetry with line microelectrodes touching the air/water interface. The Tempo lateral diffusion constant of (1.5 +/- 0.7) x 10(-4) cm2/s is independent of surface concentration below 4.0 x 10(-11) mol/cm2. The extent of Tempo water interactions was assessed by the electronic structure calculations. These calculations showed that, at most, two water molecules can hydrogen bond with the oxygen atom of the nitroxyl group of Tempo, and that a single water molecule forms a hydrogen bond that is ca. 30% stronger than the H2O-H2O hydrogen bond. These calculations led to a postulate that Tempo diffuses along the interface largely unimmersed, and that it is coupled to the interfacial water via hydrogen bonding with H2O. In view of this postulate, the viscosity of the aqueous liquid/vapor interfacial region obtained by interpreting the Tempo diffusion constant in the low concentration region is as much as 4 times smaller than that of bulk liquid water.

Journal Article↗

New 4-(heteroanilido)piperidines, structurally related to the pure opioid agonist fentanyl, with agonist and/or antagonist properties.

A research program based on certain heterocyclic modifications (12-50) of the fentanyl (1) molecule has generated a novel class of opioids. In the mouse hot-plate test, these compounds were weaker analgesics than 1. Two types of antagonists were observed in morphine-treated rabbits: those (e.g., 28) that reversed both respiratory depression and analgesia and those (e.g. 32) that selectively reversed respiratory depression. Evaluation of in vitro binding affinities to rat brain opioid receptors was inconclusive for a common locus of action for the agonist as well as the antagonist component. Further pharmacological evaluation of 32, N-(2-pyrazinyl)-N-(1-phenethyl-4-piperidinyl)-2-furamide, in the rat showed it to be a potent analgesic (ED50 = 0.07 mg/kg, tail-flick test) with little cardiovascular and respiratory depression when compared to fentanyl.

Analgesics, Opioid↗