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P A Ferchmin

Publications and source records attributed to P A Ferchmin.

At least 19 recordsLinked to original sources
PubMed2005

Tobacco cembranoids protect the function of acute hippocampal slices against NMDA by a mechanism mediated by alpha4beta2 nicotinic receptors.

Nicotine has been reported to be neuroprotective in experimental and epidemiological studies. In addition to nicotine, tobacco and cigarette smoke contain cembranoids, which are antagonists of neuronal nicotinic receptors (nAChR). Exposure of hippocampal slices to N-methyl-D-aspartate (NMDA) decreases the population spikes (PS). This parameter has been used as a measure of excitotoxicity. Surprisingly, both nicotine and tobacco cembranoids protected against NMDA and this neuroprotection was not blocked by methyllycaconitine (MLA), an antagonist of alpha7 nAChR. On the contrary, MLA had a neuroprotective effect of its own. We examined the effect of the tobacco cembranoid (1S,2E,4R,6R,7E,11E)-cembra-2,7,11-triene-4,6-diol (4R) on the neuroprotection against NMDA. DHbetaE, a selective antagonist of alpha4beta2 nAChR, inhibited the neuroprotection by nicotine, 4R, and MLA, suggesting the involvement of alpha4beta2 nAChRs in the neuroprotection. The cell-signaling pathways underlying the neuroprotection by 4R and by nicotine are different. The activity of phosphatidylinositol-3 kinase (PI3K) was required in both cases; however, 4R required the activity of L-type calcium channels and CAM kinase, whereas nicotine required the extracellular signal regulated kinase-1,2 (ERK) and protein kinase C (PKC). In addition, 4R did not enhance total phospho-ERK-1/2 but increased the amount of total Akt/PKB phosphorylated on the activation site and of glycogen synthase kinase 3-beta phosphorylated on the inhibitory site. Total levels of phosphoenzymes are presented instead of the ratio of phospho- over total enzyme because in preliminary experiments total ERK-1/2 levels were slightly increased by 4R. In conclusion, these findings demonstrate that there are two different nicotinic neuroprotective mechanisms mediated by alpha4beta2.

Animals↗
PubMed2003

Nicotinic receptors differentially regulate N-methyl-D-aspartate damage in acute hippocampal slices.

Although in neuronal cultures nicotine was reported to prevent early and delayed excitotoxic death, no studies with nicotinic drugs have been done with acute hippocampal slices. We investigated the effect of nicotine and methyllycaconitine (MLA) on the toxicity of N-methyl-d-aspartate (NMDA) in the CA1 area of hippocampal slices. The excitotoxic effect of NMDA was assessed as decreased recovery of the capability to produce synaptically evoked population spikes (PSs). Application of nicotine or MLA before NMDA application increased the recovery of PSs. This electrophysiological recovery was used as a measure of the early neuroprotective events. The neuroprotection conferred by both nicotine and MLA was inhibited by dihydro-beta-erythroidine, showing mediation of neuroprotection by alpha 4 beta 2 neuronal nicotinic receptors (nAChRs). Because nicotine activates alpha 4 beta 2 and other nAChR subtypes, whereas 10 nM MLA inhibits the alpha 7 subtype, we propose the involvement of a neuronal circuitry-dependent mechanism for nicotinic neuroprotection. The effect of nicotine downstream from the receptors was investigated using inhibitors of cell signaling. The results suggest that the effect of nicotine is mediated by tyrosine receptor kinases, 1,2-phosphatidylinositol-3 kinase, and the mitogen-activated extracellular signal-regulated kinases. Although nicotine neuroprotection is Ca2+-dependent, neither L-type Ca2+ channels nor calmodulin-dependent protein kinase is involved in the effect of nicotine. In summary, these results suggest that in acute slices nicotinic protection is initiated either by direct activation of alpha 4 beta 2 or indirectly by inhibition of alpha 7 followed by signal transduction involving tyrosine kinases, phospholipid-dependent kinases, and mitogen-activated kinases.

Animals↗
PubMed2001

Tobacco cembranoids block behavioral sensitization to nicotine and inhibit neuronal acetylcholine receptor function.

Cembranoids are cyclic diterpenoids found in tobacco and in marine invertebrates. The present study established that tobacco cembranoids inhibit behavioral sensitization to nicotine in rats and block several types of nicotine acetylcholine receptors (AChRs). 1) At the behavioral level, rat locomotor activity induced by nicotine was significantly increased after seven daily nicotine injections. This sensitization to nicotine was blocked by mecamylamine (1 mg/kg) and by the cembranoids eunicin, eupalmerin acetate (EUAC), and (4R)-2,7,11-cembratriene-4-6-diol (4R), each at 6 mg/kg. None of these compounds modified locomotor activity of nonsensitized rats. 2) In cells expressing human AChRs, cembranoids blocked carbamoylcholine-induced (86)Rb(+) flux with IC(50) in the low micromolar range. The cell lines used were the SH-EP1-halpha4beta2 cell line heterologously expressing human alpha4beta2-AChR, the SH-SY5Y neuroblastoma line naturally expressing human ganglionic alpha3beta4-AChR, and the TE671/RD cell line naturally expressing embryonic muscle alpha1beta1gammadelta-AChR. The tobacco cembranoids tested were 4R and its diastereoisomer 4S, and marine cembranoids tested were EUAC and 12,13-bisepieupalmerin. 3) At the molecular level, tobacco (4R and 4S) and marine (EUAC) cembranoids blocked binding of the noncompetitive inhibitor [(3)H]tenocyclidine to AChR from Torpedo californica electric organ. IC(50) values were in the submicromolar to low-micromolar range, with 4R displaying an order of magnitude higher potency than its diastereoisomer, 4S.

Animals↗
PubMed2000

Spermine is neuroprotective against anoxia and N-methyl-D-aspartate in hippocampal slices.

Polyamines were implicated as either neurotoxic or neuroprotective in several models of stroke. Spermine augments the excitotoxicity mediated by the N-methyl-D-aspartate (NMDA) receptor because this receptor is activated at micromolar spermine concentrations. However, at higher concentrations, spermine could be neuroprotective because it blocks the NMDA receptor and voltage-activated Ca(2+) channels. In this work, acute hippocampal slices were exposed to 1 mM spermine and either 10 min of anoxia or 0.5 mM NMDA. The percent recovery of population spikes was the measure of neuroprotection. One millimolar spermine was robustly neuroprotective; however, 0.1 mM spermine and 1 mM putrescine were not. The neuroprotective concentration of spermine was higher than the physiological concentration of free spermine. However, during an excitotoxic episode, extracellular Ca(2+) is decreased, enabling the inhibitory activity of lower spermine concentration. In addition, several noxious stimuli trigger the release of intracellular spermine and could raise local levels of spermine. Therefore, it is possible that spermine has a neuroprotective role in vivo.

Animals↗
PubMed1999

Determinants of phencyclidine potency on the nicotinic acetylcholine receptors from muscle and electric organ.

1. Phencyclidine (PCP) is an inhibitor of the nicotinic acetylcholine receptor (AChR) with characteristics of an open-channel blocker. The location of PCP binding site on the AChR molecule is unknown. 2. PCP inhibits the AChR from electric organ with a higher potency than muscle AChR. To find the molecular basis of this difference, we expressed the two native and six hybrid receptors, and two receptors containing mutated mouse gamma subunits in Xenopus laevis oocytes. The inhibition of ACh-induced current in these receptors by PCP was studied using whole-cell voltage-clamp. All hybrid receptors generated robust ACh-induced currents, while incomplete receptors (gamma-less or delta-less) did not. 3. PCP potency was higher on hybrids containing Torpedo beta and gamma subunits regardless of the alpha and delta subunit origin. A mouse gamma subunit containing the asparagine 6' to the serine mutation in the M2 segment conferred a high sensitivity to PCP. 4. These results support the conclusion that the amino acid residues at the position 6' of the M2 segments contribute to the PCP potency difference between Torpedo and mouse receptors. 5. Another noncompetitive inhibitor of the AChR, the cembranoid eupalmerin acetate (EUAC), also inhibited the electric organ receptor with a somewhat higher potency than muscle AChR. However, the IC50 values for EUAC inhibition of hybrid receptors did not follow the pattern observed for PCP. Therefore, these two inhibitors interact differently with the AChR molecule.

Acetylcholine↗
PubMed1998

Characterization of cembranoid interaction with the nicotinic acetylcholine receptor.

The class of diterpenoids with a 14-carbon cembrane ring, the cembranoids, includes both competitive and noncompetitive inhibitors of the nicotinic acetylcholine receptor (AChR). All 20 coelenterate-derived cembranoids studied in this report inhibited [piperidyl-3,4-3H]-phencyclidine ([3H]-PCP) binding to its high-affinity site on the electric organ AChR, with IC50s ranging from 0.9 microM for methylpseudoplexaurate to 372 microM for lophotoxin. Inhibition was complete with all cembranoids but lophotoxin and most Hill coefficients were close to 1. Methylpseudoplexaurate and [3H]-PCP binding was competitive. Methylpseudoplexaurate and the fourth most potent cembranoid, eunicin, competed with each other for [3H]-PCP displacement, indicating that there exist one or more cembranoid sites on the AChR. Cembranoid affinity for the AChR correlated with hydrophobicity, but was also dependent on other features. Methylpseudoplexaurate and n-octanol also competed with each other for [3H]-PCP displacement, indicating that the cembranoid site is linked to the n-octanol site on the AChR. Unlike lophotoxin, the five cembranoids tested did not inhibit [125I]Tyr54-alpha-bungarotoxin binding to the AChR agonist sites. All seven cembranoids tested on oocyte-expressed electric organ AChR reversibly blocked acetylcholine-induced currents, although the inhibitor concentration curves were shallow and the inhibition was incomplete.

Acetylcholine↗
PubMed1997

Spermine does not compete with omega-conotoxin GVIA in the striatum radiatum of the hippocampal slice.

The effect of spermine (Spm) and of omega-conotoxin GVIA (CTX) on the population excitatory postsynaptic potentials (pEPSP) in stratum radiatum of the CA1 area were compared. CTX decreased irreversibly the initial slope of pEPSP by 57%. Spm produced a maximum inhibition of 85% with an apparent dissociation constant of 0.85 mM and a maximum Hill coefficient larger than 3. The effect of Spm was mostly reversible. Preincubation with Spm did not protect the slice from the irreversible effect of CTX suggesting that they interact with different sites. Since CTX and Spm inhibited pEPSPs with very different affinities and reversibilities a kinetic model was developed to compare their effects. This model relates the inhibitors' binding to presynaptic voltage-activated Ca2+ channels (VACC) with inhibition of pEPSP. The model suggest that: all CTX and Spm effects can be explained by inhibition of VACC. Spm and CTX do not compete for the same site. CTX inhibits 20% (N-type) and Spm 40% of channels (probably the Q-type). More than three Spm molecules bind per one channel molecule, while one CTX is sufficient to inhibit channel function. The model also illustrates that the inhibitor concentration-pEPSP inhibition curves display a Hill coefficient similar to that for inhibitor binding.

Animals↗
PubMed1995

Spermine increases paired-pulse facilitation in area CA1 of hippocampus in a calcium-dependent manner.

The effect of spermine on neurotransmission was studied in area CA1 of the hippocampal slice preparation. Paired-pulse stimulation (20 ms interpulse interval) was delivered to stratum radiatum; the evoked field potential responses were recorded simultaneously from stratum radiatum and from stratum pyramidale. At mM and sub-mM concentrations, spermine decreased the slope of pEPSP in stratum radiatum and the area of the conditioning population spike in stratum pyramidale. Short-latency paired-pulse inhibition of the population spike was converted to facilitation by spermine. These effects of spermine resembled those observed at low calcium concentration. In addition, dose-response and input-output curves determined at various Ca2+ concentrations demonstrated that the depressant effects of spermine were larger at low Ca2+ levels. The results support the notion that spermine competitively blocks presynaptic voltage-sensitive Ca2+ channels, thus causing a decreased release of neurotransmitter. Since spermine is present in brain, it is likely that it is a natural modulator of Ca2+ channels.

Animals↗
PubMed1994

Spermine depresses NMDA, K/AMPA and GABAA-mediated synaptic transmission in the rat hippocampal slice preparation.

The effects of spermine, an endogenous polyamine, were examined in area CA1 of the rat hippocampal slice preparation. Spermine, at low millimolar concentrations, rapidly and potently depressed NMDA and K/AMPA-mediated population EPSPs, and GABA-mediated monosynaptic population IPSPs. These effects contrast with its well-known potentiation of NMDA currents at lower concentrations. Our results raise the possibility that the large intracellular stores of spermine that are released after various neural insults could act as an endogenous neuroprotective mechanism by limiting excessive calcium entry.

Animals↗
PubMed1994

Metabolic activation of the brain of young rats after exposure to environmental complexity.

Autoradiography with 14C-2-deoxyglucose was used to determine brain metabolic activity during the quiet period that follows after daily exploratory experiences in new complex environments. Eight 1-month-old, male Tryon rats were selected from two litters. Pairs of littermates matched by body weight were assigned to one of two conditions: rats housed individually in small home cages as the "impoverished condition," or rats exposed twice daily to changing and complex environments of two large cages with inanimate objects and conspecifics as the "enriched condition." After 4 days, rats were injected with 2-deoxyglucose, placed individually in a home cage and left undisturbed for 90 min until sacrificed. The brains of "enriched" rats were heavier than their "impoverished" littermates, and showed a global trend for metabolic enhancement. They also showed significantly greater amounts of 2-deoxyglucose in occipital cortex (27%), hippocampal subiculum (36%), and nucleus accumbens (40%).

Aging↗
PubMed1993

alpha-Difluoromethylornithine decreases inhibitory transmission in hippocampal slices independently of its inhibitory effect on ornithine decarboxylase.

We tested the effect of DL-alpha-(difluoromethyl)ornithine (DFMO), a specific inhibitor of ornithine decarboxylase (ODC), on recordings in area CA1 of rat hippocampal slices. In the concentration range in which it is used as an ODC inhibitor, DFMO increased neuronal excitability and blocked paired-pulse inhibition. The effect of DFMO was reversed by perfusing the slice with normal bathing solution. These effects were not attenuated by the simultaneous addition of putrescine; thus the activity of DFMO was not related to a decrease in putrescine caused by the inhibition of ODC. Mediation by the N-methyl-D-aspartate (NMDA) receptor was ruled out because DL-2-amino-5-phosphonovalerate (APV), an NMDA antagonist, did not block the effect of DFMO. Intracellular and extracellular recordings of pharmacologically isolated IPSPs supported the notion that DFMO depressed GABAergic transmission. DFMO has frequently been used as a tool to study the role of the ODC-polyamine system in neural preparations. This report suggests that the results from such studies must be interpreted with caution. In addition, our findings raise questions about the proposed use of DFMO as a neuroprotective agent against excitotoxicity.

2-Amino-5-phosphonovalerate↗
PubMed1993

Diterpenoids from Caribbean gorgonians act as noncompetitive inhibitors of the nicotinic acetylcholine receptor.

1. Three cyclic diterpenoids isolated from gorgonians of the Eunicea genus and characterized as eupalmerin acetate (EUAC), 12,13-bisepieupalmerin (BEEP), and eunicin (EUNI) were found to be pharmacologically active on the nicotinic acetylcholine receptor (AChR). 2. The receptor from the BC3H-1 muscle cell line was expressed in Xenopus laevis oocytes and studied with a two-electrode voltage clamp apparatus. 3. All three compounds reversibly inhibited ACh-induced currents, with IC50's from 6 to 35 microM. ACh dose-response curves suggested that his inhibition was noncompetitive. The cembranoids also increased the rate of receptor desensitization. 4. Radioligand-binding studies using AChR-rich membranes from Torpedo electric organ indicated that all three cembranoids inhibited high-affinity [3H]phencyclidine binding, with IC50's of 0.8, 11.6, and 63.8 microM for EUNI, EUAC, and BEEP, respectively. The cembranoids at a 100 microM concentration did not inhibit [alpha-125I]bungarotoxin binding to either membrane-bound or solubilized AChR. 5. It is concluded that these compounds act as noncompetitive inhibitors of peripheral AChR.

Animals↗
PubMed1993

The ion channel of muscle and electric organ acetylcholine receptors: differing affinities for noncompetitive inhibitors.

1. Muscle and electric organ acetylcholine receptors (AChR's) were expressed in Xenopus laevis oocytes and differential effects of noncompetitive blockers on each type of receptor were analyzed using a two-electrode voltage clamp. 2. The positively charged channel blockers, phencyclidine (PCP) and tetracaine, displayed a much lower potency on muscle receptor than on the electric organ receptor. The IC50 for both blockers at the electrocyte receptor was close to 1 microM at -60 mV and even lower at more hyperpolarized voltages. In contrast, with muscle receptor IC50's were 20 to 40 microM at -60 or -80 mV. 3. Eupalmerin acetate, an uncharged noncompetitive inhibitor that displaces [3H]PCP from its high-affinity binding site, inhibited both receptors with a similar potency: IC50 of 4.9 and 6.4 microM for electrocyte and muscle receptors, respectively. However, eupalmerin acetate affected the desensitization process in each receptor type differently and triggered an unusual biphasic response in the muscle receptor. 4. These results are discussed with respect to differences in the amino acid sequences of the M2 regions of the two receptors. 5. A third type of noncompetitive inhibitor, Mg2+, was also examined and it inhibited both receptors with a similar potency (IC50, 0.5-1.0 mM). However, Mg2+ appeared to act at sites other than the PCP site.

Amino Acid Sequence↗
PubMed1993

alpha-Difluoromethylornithine does not antagonize the behavioral effects of putrescine.

alpha-Difluoromethylornithine (DFMO), a specific inhibitor of putrescine synthesis, is widely used in studies of polyamine function as well as clinically. We studied the effect of DFMO on the tendency to explore in the Greek cross maze that provides the rat with the choice to enter either white or black compartments. After a single injection of 400 mg/kg DFMO, the entries into white compartments were significantly decreased. A similar decrease had been observed previously with 200 mg/kg putrescine. Simultaneous administration of DFMO (400 mg/kg) and putrescine (200 mg/kg) resulted in decreased entries into both white and black compartments. When 400 mg/kg DFMO plus 400 mg/kg putrescine were injected, the entries into both compartments were further decreased and the time spent in white compartments was also decreased. This pattern mimicked that found with anxiogenic drugs. Injection of DFMO (400 mg/kg) produced no change in either putrescine, spermidine, or spermine concentration measured in brain cortex. Putrescine (200 mg/kg) plus DFMO produced the same transient increase in cortical putrescine as putrescine alone. We conclude that DFMO is mildly anxiogenic and that this activity is independent of its inhibition of putrescine synthesis.

Animals↗
PubMed1992

Electric organ polyamines and their effects on the acetylcholine receptor.

1. The electric organ of Torpedo nobiliana contained putrescine (PUT), spermidine (SPD), spermine (SPM), and cadaverine (CAD). Traces of acetylated SPD and SPM were occasionaly seen. 2. Upon fractionation of the tissue by differential centrifugation, the polyamines (PA) were found predominantly in the soluble fraction. The postsynaptic membrane fraction, containing a high concentration of acetylcholine receptor (AChR), was proportionally enriched in SPM. The molar ratio of SPM to AChR was approximately two in these membranes. 3. The effect of exogeneous PA on AChR function was studied by two methods: carbamoylcholine (CCh)-dependent 86Rb+ influx into receptor-rich membrane vesicles and [alpha-125I]bungarotoxin (Bgt) binding to the AChR. 4. SPM inhibited both ion influx and the rate of Bgt binding at concentrations above 1 mM, and therefore it appears to act as a competitive antagonist of the AChR. 5. At submicromolar concentrations, and only after preincubation with the receptor-rich membrane, SPM and PUT increased the ion influx by about 20% over control values. 6. Preincubation with 100 nM SPM did not affect the equilibrium binding of iodinated toxin or the rate of toxin binding, and therefore SPM was not uncovering new receptors. 7. By measuring the initial rate of toxin binding after different periods of preincubation with 1 microM CCh, the rate of the slow phase of receptor desensitization was determined. This rate was not changed by 100 nM SPM. 8. Although these results suggest that at low concentrations SPM is a positive modulator of the AChR, the precise mechanism of action is not determined yet.

Animals↗
PubMed1990

Putrescine decreases exploration of a black and white maze.

The effect of putrescine and cyclohexylamine on rat cortical polyamine concentration and on behavior in a black and white maze was studied. The levels of polyamines in brain cortex were determined 15 min, 2, 4, and 6 hours after injection of putrescine (200 or 400 mg/kg) or cyclohexylamine (380 mg/kg). Putrescine concentration increased 6-fold 15 min after injection of putrescine followed by a decline during the next 6 hours. Cyclohexylamine increased putrescine concentration doubling it 4 hours after injection. Spermidine and spermine concentrations did not change after either putrescine or cyclohexylamine injection. Behavior was studied in the Greek cross maze which provides the choice to enter either white or black compartments. Putrescine 200 mg/kg decreased entries into white but not black compartments, while putrescine 400 mg/kg decreased entries into both. The effect of cyclohexylamine was similar to putrescine 400 mg/kg. The behavioral effect of each treatment was independent of the time between injection and testing for up to 6 hours, while the levels of putrescine changed during the same period. Therefore, behavior was not directly related to total cortical putrescine.

Animals↗