Robert Chicheportiche

Role of the aromatic group in the inhibition of phencyclidine binding and dopamine uptake by PCP analogs

Thirty-seven arylcyclohexylamines including phencyclidine (PCP) and derivatives, N[1-(2-thienyl)cyclohexyl]piperidine (TCP) and derivatives and N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP) were assessed for their ability to inhibit [3H]PCP binding and [3H]dopamine ([3H]DA) synaptosomal uptake. Their pharmacological property (ataxia) was measured by means of the rotarod test. A very good correlation was observed between the inhibition of [3H]PCP binding and the [3H]DA uptake only for arylcyclohexylamines bearing an unmodified phenyl group. Conversely the comparison between the inhibition of [3H]PCP binding and the activity in the rotarod test shows a good correlation with arylcyclohexylamines having any aromatic group (phenyl, substituted phenyl and thienyl rings). This study outlined a new compound (BTCP) without ataxic effect, which is one of the more potent inhibitors of the [3H]DA uptake (IC50 = 8 nM) and which seems very specific since it has a low affinity for [3H]PCP receptors (IC50 = 6 microM). These data show that the aromatic group of the compounds leads to molecules that bind differently to the PCP receptor and to the DA uptake complex. They also suggest that the behavioral properties of arylcyclohexylamines revealed by the rotarod test occur essentially as a result of an interaction with the sites labeled with [3H]PCP and that TCP is more selective than PCP itself in this recognition.

Differential interaction of phencyclidine-like drugs with the dopamine uptake complex in vivo

Abstract: The phencyclidine (PCP) derivative, [3H]N‐[1‐(2‐benzo[b]thiophenyl)cyclohexyl]piperidine ([3H]BTCP), was used to label in vivo the dopamine uptake complex in mouse brain. The striatum accumulated the highest level of total and specific binding. Drugs which bind to the dopamine uptake site inhibited [3H]BTCP binding on an order similar to their in vitro affinities for the high‐affinity [3H]BTCP site. Drugs which label selectively other monoamine uptake complexes, PCP, or σ recognition sites were ineffective at doses up to 40 mg/kg. PCP bound to and dissociated from the dopamine uptake complex very rapidly. N‐[1‐(2‐Thienyl)cyclohexyl]piperidine (TCP) and (+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo[a,d]cyclohepten‐5,10‐imine maleate (MK‐801) had no effect at any time or at any dose. These results imply that the pharmacological effects of PCP are due to its simultaneous interaction with the dopamine uptake complex and the PCP receptor. Conversely, TCP and MK‐801, which have the same behavioral properties as PCP, exert their action only through the interaction with the PCP receptor.

Anaesthetic properties of phencyclidine (PCP) and analogues may be related to their interaction with Na+ channels

Among other properties, phencyclidine (PCP) and analogues display anaesthetic and anticonvulsant properties. Interaction of PCP and some analogues with the voltage-sensitive Na+ channels have been investigated and compared with their interaction with the PCP receptor. PCP and TCP inhibit apparently in a competitive manner the veratridine stimulated 22Na+ synaptosomal uptake with Ki values of 8.6 and 12.7 microM, respectively, close to those obtained in the inhibition of [3H]BTX-B binding (IC50 = 4.1 and 3.8 microM, respectively). The specific [3H]TCP binding to synaptosomes in ionic near physiological conditions is inhibited by PCP and TCP with IC50 values of 1.25 and 0.29 microM, respectively. Other PCP derivatives (GK3 and GK4) and PCP-like drugs (ketamine and MK801) inhibit 22Na+ uptake in an order of potency (GK3 greater than GK4 greater than PCP greater than TCP greater than MK801 greater than ketamine) which is different from that obtained in the inhibition of [3H]TCP binding (MK801 greater than TCP greater than PCP greater than ketamine greater than GK4 greater than GK3). Ketamine inhibits the veratridine-stimulated Na+ uptake at a concentration where its anesthetic effect occurs. It was concluded that the interaction of these drugs with the Na+ channel may reflect their anaesthetic properties while the interaction with the PCP receptors may be mainly related to their anticonvulsant and ataxic properties.

Kindling and electrode effects on the benzodiazepine receptors density of olfactory bulb and hippocampus after olfactory bulb kindling.

The olfactory bulb (OB) kindling is a model of limbic secondary generalized epilepsy. Ten days after the completion of OB kindling, we have studied the long term effects of both electrode insertion and kindling on the binding of [3H]diazepam to crude mitochondrial fractions. On the one hand, we have shown that electrode implantation in sham-operated controls induced an obvious increase in benzodiazepine (BZD) receptor density (Bmax) only at the site of the electrode in comparison to sham-unoperated rats. These results might indicate an additional mechanism extending earlier observations reported by others, who have shown that prolonged electrode implantation induced changes in sham-operated and kindled rats. On the other hand, the long lasting effect of OB kindling on the binding parameters of [3H]diazepam was examined in the focus and in the hippocampus. The results indicate a bilateral increase of BZD receptors in the OB and an ipsilateral increase in the hippocampus. These changes might be a regulation phenomenon in response to a hyperexcitability state and to focal stimulations.

Use of ATP bioluminescence measurements for the estimation of biomass during biological humification

SummaryThe development of the microflora during the humification of grape pulp has been investigated by the determination of ATP using the bioluminescence technique. Several extraction methods were tested including the use of dimethylsulphoxide, trichloroacetic acid, grinding and ultrasonification. Dimethylsulphoxide and ultrasonification for 15 sec appeared to be the most effective. The ATP extract was stabilized when it was mixed with 0.75 mM glycine, 4.4 mM Mg-EDTA, pH 7.5 and frozen. The relative error of the ATP assay by bioluminescence did not exceed 6.5%. This method allowed us to show that at least five distinct reproducible microbial phases exist during grape pulp humification. These results show that the microbial biomass changes noticeably and at distinct times during composting.

Effect of amygdaloid kindling on the high- and low-affinity [3H]TCP binding sites of the rat CNS

The regulation of the binding sites of [3H]TCP, a non-competitive ligand of the N-methyl-D-aspartate (NMDA) receptor, was studied on membranes prepared from different CNS regions of amygdaloid-kindled rats. The high-affinity binding sites (KdH = 4.2-7.4 nM), identified as the NMDA-gated ion channels, were not affected by kindling or by a daily injection of TCP (5 mg/kg before each electrical stimulation) which prevented kindling. These results suggest that the NMDA receptors participate to the establishment and not to the permanence of kindling. Kindling increases the number of low affinity [3H]TCP binding sites in the hippocampus (+21%, P less than 0.01) without change of the affinity (KdL = 340 nM). In the striatum both KdL and BmaxL were increased (3.3-4.4 fold, P less than 0.001) in animals pretreated with TCP before each electrical stimulation for 20 days. These last results argue in favour of a function of the low-affinity [3H]TCP binding sites, the nature of which remains to be determined.

Binding Properties of 3‐[125I]Iodophencyclidine, a New Radioligand for N‐Methyl‐D‐Aspartate‐Gated Ionic Channels

Abstract: The binding properties of the 125l‐labeled phencyclidine derivative N‐[1‐(3‐[125I] iodophenyl)cyclohexyl] piperidine (3‐[125I]iodo‐PCP), a new ligand of the N‐methyl‐D‐aspartate (NMDA)‐gated ionic channel, were investigated. Association and dissociation kinetic curves of 3‐[125I]iodo‐PCP with rat brain homogenates were well described by two components. About 32% of the binding was of fast association and fast dissociation, and the remaining binding was of slow association and slow dissociation. Saturation curves of 3‐[125I] iodo‐PCP also were well described using two binding sites: one of a high affinity (KDH= 15.8 ± 2.3 nM) and the other of a low affinity (KDL= 250 ± 40 nM). 3‐Iodo‐PCP inhibited the binding of 3‐[125I]iodo‐PCP with inhibition curves that were well fitted by a two‐site model. The binding constants (KiH, BmaxH; KiL, BmaxL) so obtained were close to those obtained in saturation experiments. Ligands of NMDA‐gated ionic channels also inhibited the binding of 3‐ [125I]iodo‐PCP with two constants, KiH and KiL. There was a very good correlation (r = 0.987) between the affinities of these ligands to bind to NMDA‐gated ionic channels and their potencies to inhibit the binding of 3‐[125I]iodo‐PCP with a high affinity. Moreover, the regional distribution of the high‐affinity binding of 3‐[125I]‐iodo‐PCP paralleled that of tritiated N‐[1‐(2‐thienyl)cyclohexyl]piperidine ([3H]TCP). In contrast to that of [3H]TCP, the binding of 3‐[125I]iodo‐PCP to well‐washed rat brain membranes was fast and insensitive to glutamate and glycine. We conclude that 3‐[125I]iodo‐PCP, at low concentrations, is suited for future rapid autoradio‐graphical studies of both open and closed forms of NMDA‐gated ionic channels and that 3‐[123I]iodo‐PCP could be used successfully for in vivo studies by single‐photon emission computed tomography analysis.

TCP shortens the latency of onset of isoelectricity in hypoglycaemia and fails to protect striatal neurones and dentate gyrus granule cells from hypoglycaemic injury in rats

Competitive N-methyl-D-aspartate (NMDA) receptor antagonists are known to protect neurones against hypoglycaemic damage. We tested N-[1-(2-thienyl)cyclohexyl]piperidine (TCP), a non-competitive NMDA antagonist, in a recovery model of hypoglycaemic coma in the rat. Administered concomitantly with insulin, TCP shortened the latency of onset of electrocerebral silence, and failed to prevent striatal and dentate gyrus hypoglycaemia-induced injury. This effect is probably related to an increase in glucose consumption of neurones: TCP enhances energy metabolism in several brain structures, which could facilitate, at low blood glucose levels, the onset of isoelectricity, and hamper a putative neuro-protective effect of the drug.