Ketamine, phencyclidine, and MK-801 protect against kainic acid-induced seizure-related brain damage

Recent evidence implicates the endogenous excitotoxin, glutamate (Glu), in several neurologic disorders, including seizure-related brain damage. Ketamine, phencyclidine, and MK-801, which are noncompetitive antagonists of the N-methyl-D-aspartate (NMDA) subtype of Glu receptor (but do not antagonize kainic acid receptors) were tested in the present study for their effects on behavioral and/or electrographic seizures and seizure-related brain damage induced by kainic acid. Behavioral seizure activity was reduced by these agents, as was spread of electrographic seizures to neocortex, but seizures recorded from deep brain regions such as hippocampus, piriform cortex, and amygdala were not significantly diminished. All three agents prevented seizure-related brain damage in the amygdala, piriform cortex, thalamus, and CA1 region of the hippocampus but conferred little or no protection in the lateral septum and CA3 region of the hippocampus. The regional selectivity of the neuroprotective effect suggests that NMDA receptors may play a more dominant role in seizure-related brain damage in some brain regions than in others. The ability of NMDA antagonists to prevent seizure-related damage in several brain regions without suppressing seizure activity suggests that in these brain regions persistent seizure activity can be maintained by other transmitter systems, with or without NMDA receptor participation, but that seizure-related brain damage is critically dependent on NMDA receptor participation.

Pretreatment with phencyclidine, an N-methyl-D-aspartate antagonist, attenuates long-term behavioral deficits in the rat produced by traumatic brain injury

This study examined the effects of pretreatment with phencyclidine (PCP), a selective N-methyl-D-aspartate (NMDA) antagonist, on behavioral and physiologic responses of the rat to experimental traumatic brain injury (TBI). For the behavioral experiments, rats were administered either saline or PCP (1.0, 2.0, or 4.0 mg/kg, intrapentoneally [IP] 15 min before TBI. Rats were ventilated as necessary following injury. The duration of acute suppression of several reflexes (pinna, corneal, righting, and flexion) and responses (escape, head support, and spontaneous locomotion) was recorded for up to 70 min after trauma. Longer-term behavioral assessments (beam walking, beam balance, inclined plane, ambulatory activity, and body weight) were made for up to 10 days after trauma. PCP did not significantly alter the duration of acute behavioral suppression. At a dosage of 1.0 mg/kg, PCP significantly attenuated all long-term deficits except beam walking. Maximal protection against beam walking deficits was provided by the 4.0 mg/kg dosage of PCP. Sixty-three percent of saline-treated animals died within 10 days after injury. For rats pretreated with 1.0, 2.0, and 4.0 mg/kg of PCP, 40%, 23%, and 33% died, respectively. In physiologic experiments, pretreatment with 4.0 mg/kg of PCP (IP) 15 min before injury did not significantly affect systemic cardiovascular responses, plasma glucose levels, or blood gas levels observed within 30 min after injury. While the possibility of effects mediated by other neurotransmitter systems cannot be excluded, these data suggest that NMDA agonist-receptor interactions contribute to the pathophysiology of brain injury. In addition, neural mechanisms that mediate transient unconsciousness following moderate levels of head injury may differ from mechanisms that mediate more persistent neurologic deficits.

Combined pretrauma scopolamine and phencyclidine attenuate posttraumatic increased sensitivity to delayed secondary ischemia

Fasted Wistar rats were given a mild level of traumatic brain injury (TBI) and then subjected to 6 min of transient forebrain ischemia 24 h posttrauma. One group was given simultaneous 1 mg/kg scopolamine and 4 mg/kg phencyclidine intraperitoneally (IP) 15 min before trauma and another group an equal volume of plasmalyte A solution. After 7 days of postinjury survival, placebo-treated rats demonstrated increased posttraumatic vulnerability to secondary ischemic CA1 neuronal death even 24 h after trauma. This finding confirmed that increased posttraumatic ischemic vulnerability persists for at least 24 h even following mild trauma. Combined muscarinic receptor and N-methyl-D-aspartate (NMDA) receptor coupled ion channel blockade given and present during the mild TBI statistically attenuated this enhanced secondary ischemic CA1 neuronal death and thus posttraumatic increased ischemic vulnerability. Placebo-treated rats had 335.3 +/- 93.6 CA1 neurons/10(6) microns 2 and drug-treated rats had 844.8 +/- 184.9 CA1 neurons/10(6) microns 2. This result suggests that muscarinic and/or NMDA receptor-mediated events confined to TBI and the early posttraumatic period are in part responsible for the phenomenon of increased posttraumatic ischemic vulnerability.

Neuroprotective properties of 5-HT1A receptor agonists in rodent models of focal and global cerebral ischemia

5-Hydroxytryptamine1A (5-HT1A) receptor agonists have been shown to inhibit the activity of hippocampal, cortical, and dorsal raphé neurons. We tested urapidil and a new 5-HT1A agonist, CM 57493 [4-(3-trifluoromethylphenyl)-1-(2-cyanoethyl)-1,2,3,6-tetrahydropyridine ], for their neuroprotective activity in models of focal and global cerebral ischemia in rodents. After middle cerebral artery-occlusion (MCA-0) in mice, the infarct size was reduced dose dependently by both urapidil and CM 57493. In MCA-occluded rats, CM 57493 (1 and 5 mg/kg) reduced the cortical infarct volume by 30% and application of 10 mg/kg CM 57493 led to a 40% reduction in the cortical infarct volume. The striatal damage could not be influenced by CM 57493 treatment. Furthermore, 1 and 5 mg/kg CM 57493 significantly reduced the neuronal damage within the CA1 sector of the rat hippocampus after 10 min of forebrain ischemia followed by 7 days of recovery. Measurement of cerebral and rectal temperature revealed that the neuroprotective effect of CM 57493 was not caused by a hypothermic effect. We assume that the neuroprotective activity of 5-HT1A agonists is mediated by an inhibitory action on neurons.

Phencyclidine- and diazepam-like discriminative stimulus effects of inhalants in mice

It has been shown that abused solvents, such as 1,1,1-trichloroethane (TCE) and toluene, share certain pharmacological properties with central nervous system depressants, such as alcohol and anesthetic vapors. Several vapors were tested for diazepam (DZ)- and phencyclidine (PCP)-like discriminative stimulus effects to further explore their pharmacological specificity. In DZ-trained mice, methoxyflurane fully substituted, and TCE produced partial substitution. Fluorothyl and toluene produced no appreciable DZ-lever responding at any concentration tested. On the other hand, toluene produced concentration-related partial substitution for PCP, whereas methoxyflurane, TCE, and fluorothyl did not substitute. The substitution of some these vapors for DZ or PCP suggests that, like ethanol, the discriminative stimulus effects of abused solvents partially overlap those of N-methyl-D-aspartate antagonists as well as those of gamma amino butyric acid agonists.

Phencyclidine reduces postischemic neuronal necrosis in rat hippocampus without changing blood flow

In this report the effects of phencyclidine (PCP) on physiologic variables, local cerebral blood flow (LCBF), and on hippocampal cell damage were measured in a rat model of forebrain ischemia (2-vessel occlusion and hypotension). Ischemia was induced for 10 min. LCBF was determined after 2 min of recirculation, using the [14C]iodoantipyrine technique. Hippocampal cell loss was quantified histologically 7 days postischemia as the percentage of acidic stainable neurons. Intravenous application of PCP (2 mg/kg) at 15 min prior to ischemia left postischemic LCBF unchanged, but neuronal damage was significantly reduced in hippocampal CA1 sector from 46 to 15.7%. PCP is concluded to reduce ischemic damage of neurons mainly via a direct effect on brain tissue.

Pharmacological profile of a novel neuronal calcium channel blocker includes reduced cerebral damage and neurological deficits in rat focal ischemia

Excessive calcium entry into depolarized neurons contributes significantly to cerebral tissue damage following ischemia. Therefore, blocking voltage-operated calcium channels on nerve cells should provide significant neuroprotection in ischemia. We now report on a novel neuronal calcium channel blocker, NNC 09-0026, in terms of its selective effects on neuronal calcium current and its efficacy in reducing infarct size and neurological deficits in a rat model of focal stroke. In the present studies, the effects of NNC 09-0026 on neuronal calcium influx, calcium channel binding, and cardiovascular parameters were determined. Also, phencyclidine, NNC 09-0026, or vehicle were administered i.v. to rats subjected to permanent middle cerebral and common carotid artery occlusions. Infarct volumes and contralateral forepaw and hindlimb neurological deficits were assessed at 24 and 48 h after onset of stroke. NNC 09-0026 exhibited a pharmacological profile suggesting selectivity at neuronal calcium channels. It inhibited potassium-stimulated calcium uptake into rat synaptosomes with an IC50 of 13 microM. Voltage-operated calcium currents measured from cultured rat dorsal root ganglion cells using the patch clamp technique were blocked by 43% at 10 microM (p < 0.05). The compound showed only weak effects on smooth muscle from the guinea pig taenia coli and was relatively inactive at displacing nitrendipine and omega-conotoxin in receptor-binding studies. Single, bolus injections of NNC 09-0026 as high as 10 mg/kg i.v. produced only 12% reduction in heart rate and a 28% decrease in blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Thienylphencyclidine protection for the spinal cord of adult rats against extension of lesions secondary to a photochemical injury

The purpose of this study was to evaluate treatment with the N-methyl-D-aspartate antagonist thienyl-phencyclidine (TCP) after spinal cord injury for its behavioral, electrophysiological, morphological, and immunohistochemical effects. Five minutes after a photochemical lesion was produced in rats at the T-8 level, the animals received TCP (1 mg/kg, intravenously) or TCP vehicle (saline). The animals were evaluated on Day 18 for neurological recovery by testing motor and sensory functions. The TCP-treated group showed less neurological impairment than the untreated group (p < 0.05 for inclined-plane stability and withdrawal reflex to extension). Somatosensory evoked potential testing was performed on Days 21 to 23 and the wave amplitude between the onset and P1 in the TCP-treated group was higher than in the untreated group (p < 0.05). Mean arterial blood pressure was not significantly modified after TCP injection. Morphometric studies of the lesion area in cross section revealed a significantly reduced spinal cord infarction in the TCP-treated group (p < 0.05). Immunohistochemical evaluation of the spinal cord in lumbar area showed an increased level of serotonin immunoreactivity in the dorsal horn of animals treated by TCP. These results demonstrate the efficacy of TCP in reducing secondary lesions after spinal cord injury in rats.

Depolarizing GABAA current in the prefrontal cortex is linked with cognitive impairment in a mouse model relevant for schizophrenia

Cognitive impairment in schizophrenia (CIAS) is the most critical predictor of functional outcome. Limited understanding of the cellular mechanisms of CIAS hampers development of more effective treatments. We found that in subchronic phencyclidine (scPCP)-treated mice, an animal model that mimics CIAS, the reversal potential of GABAA currents in pyramidal neurons of the infralimbic prefrontal cortex (ILC) shifts from hyperpolarizing to depolarizing, the result of increased expression of the chloride transporter NKCC1. Further, we found that in scPCP mice, the NKCC1 antagonist bumetanide normalizes GABAA current polarity ex vivo and improves performance in multiple cognitive tasks in vivo. This behavioral effect was mimicked by selective, bilateral, NKCC1 knockdown in the ILC. Thus, we show that depolarizing GABAA currents in the ILC contributes to cognitive impairments in scPCP mice and suggest that bumetanide, an FDA-approved drug, has potential to treat or prevent CIAS and other components of the schizophrenia syndrome.

Global quantitative analysis of phosphorylation underlying phencyclidine signaling and sensorimotor gating in the prefrontal cortex

Prepulse inhibition (PPI) is an example of sensorimotor gating and deficits in PPI have been demonstrated in schizophrenia patients. Phencyclidine (PCP) suppression of PPI in animals has been studied to elucidate the pathological elements of schizophrenia. However, the molecular mechanisms underlying PCP treatment or PPI in the brain are still poorly understood. In this study, quantitative phosphoproteomic analysis was performed on the prefrontal cortex from rats that were subjected to PPI after being systemically injected with PCP or saline. PCP downregulated phosphorylation events were significantly enriched in proteins associated with long-term potentiation (LTP). Importantly, this data set identifies functionally novel phosphorylation sites on known LTP-associated signaling molecules. In addition, mutagenesis of a significantly altered phosphorylation site on xCT (SLC7A11), the light chain of system xc-, the cystine/glutamate antiporter, suggests that PCP also regulates the activity of this protein. Finally, new insights were also derived on PPI signaling independent of PCP treatment. This is the first quantitative phosphorylation proteomic analysis providing new molecular insights into sensorimotor gating.

Analysis of overall gene expression induced by amphetamine and phencyclidine: novel targets for the treatment of drug psychosis and schizophrenia

Although the etiology of drug psychosis or schizophrenia is still unknown, molecular and biochemical researches have recently made significant advances in the search for the candidate genes of these disorders. Among such studies are animal models of drug psychosis or schizophrenia such as amphetamine-induced behavioral sensitization or phencyclidine-treated animals. In this review, it is suggested that amphetamine or phencyclidine change the gene expressions related to not only neurotransmitter systems such as dopamine or glutamic acid, transcription factors, cell proliferation, apoptosis, cell adhesion, but also the synapse. These alterable gene expressions may lead to the discovery of candidate genes of drug psychosis or schizophrenia and thus to novel antipsychotics.

Phencyclidine reduces inherited neocortical spindling in DBA/2J mice

The role of phencyclidine (PCP) in the control of the spike-and-wave spindling episodes (S&W) which can be spontaneously recorded in the electrocorticogram (ECoG) of DBA/2J mice was investigated. PCP (0.1-0.5-1.0-5.0 mg/kg/i.p.) dose dependently reduced both S&W number and duration of DBA/2J mice. PCP reduction is significant 30-60 min after drug administration and lasts for the whole duration of the recording period (240 min). These results suggest that PCP may play an important regulatory role on brain excitability.

[Effects of the 1987 revision of the definition for an AIDS case in Switzerland]

AIDS cases diagnosed in Switzerland after the revision of 1987 and reported to the Swiss Federal Office of Public Health until 31.12.1992 were categorised according to whether they conformed to the diagnostic criteria valid before the revision (= "pre-87"-group) or only to the new criteria introduced with the revision (= "post-87"-group). Compared to the "pre-87"-group, the proportion of injecting drug users was higher, the proportion of homosexual men was lower, the patients were younger and Pneumocystis carinii pneumonia (PCP) and Kaposi-sarcoma were diagnosed less frequently in the "post-87"-group. The revision of the AIDS case-definition affected the proportion of Aids-diagnoses with PCP over time. It improved the surveillance of AIDS morbidity in Switzerland but its effects must be distinguished from true phenomena of the AIDS-epidemic.

Neuroprotective effects of phencyclidine on acute cerebral ischemia and reperfusion injury of rabbits

Acute cerebral ischemia and reperfusion injury of rabbits was produced by permanently occluding the vertebral arteries and temporarily clamping the common carotid arteries for 30 min. Phencyclidine [1-(phenylcyclohexyl)piperidine, PCP] 40-80 micrograms.kg-1 icv 30 min before ischemia significantly attenuated the decrease of the total power of electroencephalogram (EEG) within 30 min of ischemia and improved the recovery of brain electric activity following reperfusion. PCP 20-80 micrograms.kg-1 dose-dependently suppressed the creatine kinase (CK) release during cerebral ischemia and reperfusion, and PCP 40-80 micrograms.kg-1 reduced brain ischemic damage. These improvements indicated that PCP has protective effects on acute cerebral ischemia and reperfusion injury.

Comparison of phenytoin with noncompetitive N-methyl-D-aspartate antagonists in a model of focal brain ischemia in rat

Recent in vitro and in vivo experiments have suggested that excitatory amino acid antagonists, particularly those active at the N-methyl-D-aspartate receptor subtype, are effective in ameliorating ischemic injury due to their antiexcitotoxic activity. However, these drugs are also potent and effective in vivo anticonvulsants. The present experiments compared the noncompetitive N-methyl-D-aspartate antagonists phencyclidine and MK-801 with the anticonvulsant phenytoin in a model of focal brain ischemia. Fisher F-344 rats were subjected to tandem occlusion of the middle cerebral and ipsilateral common carotid arteries under halothane anesthesia. Compounds were administered intravenously 30 minutes and 24 hours after arterial occlusion; infarct size was assessed at 48 hours after occlusion. Phencyclidine had no effect on infarct volume at 1 mg/kg, significantly reduced (by 36%) infarct volume at 3 mg/kg, and produced a nonsignificant 26% decrease at 10 mg/kg. The more potent and selective noncompetitive antagonist MK-801 reduced (by 32%) infarct volume significantly at 0.1 mg/kg, produced a nonsignificant 23% decrease at 0.3 mg/kg, and had no effect at 0.5 mg/kg. Phenytoin, which is not a glutamate antagonist, reduced the infarct volume by 45% at 28 mg/kg. A single dose of phenytoin (28 mg/kg) administered 30 minutes after occlusion was neuroprotective, but delaying drug administration for more than 2 hours was ineffective. These data suggest that blockade of the N-methyl-D-aspartate receptor is effective in reducing the infarct size after focal cerebral ischemia. The neuroprotective activity of phenytoin suggests that this may be related to the common anticonvulsant action.

The search for better noncholinergic treatment options for Alzheimer's disease

Alzheimer's disease is a biological process that involves the disruption of multiple neurochemical pathways. Current treatments for Alzheimer's disease focus on deficits in the cholinergic neurochemical pathway. While newer generation cholinergic agents have a more favorable side effect profile, only a limited, but consistent, degree of efficacy is seen. Treatments are emerging that focus on other areas of neurochemical activity such as oxidative damage, inflammation, glutamatergic neurotransmissions, and serotonergic and dopaminergic pathways. These treatments, supplemented with current cholinergic therapies, may help to ease patients' suffering and caregiver distress.

[Neuropharmacological effects of sigma receptor ligands: anxiolytic, anti-amnesic and neuroprotective effects]

There is evidence for the existence of two classes of sigma binding sites, termed "site 1" and "site 2", that are distinct from opioid and PCP receptors. Sigma receptor ligands may be useful in the treatment of schizophrenia, since they improve not only positive but also negative symptoms with little extrapyramidal side effects in animal models. In addition, recent experiments have demonstrated that sigma receptor ligands attenuate the motor suppression and colonic motor disturbances seen under mentally stressful situations, stimulate the central cholinergic function thereby ameliorating impairment of learning and memory, and protect cerebral neurons against cerebral ischemic insult. The present review describes the neuropharmacological effects of sigma receptor ligands, especially anxiolytic (anti-stress) effects, ameliorating effects on impairment of learning and memory, and neuroprotective effects.

[Sigma receptors: the key to therapeutic action or the side-effects of neuroleptics?]

The authors discuss psychotropic effects of phencyclidine (PCP) in the context of neurochemical mechanisms of schizophrenia. They concentrate on sigma receptors and PCP receptors and tie their activity with the dopaminergic system. The authors describe neuroleptic effects on sigma receptors and the therapeutic consequences. They include that the question whether the interaction of neuroleptics with sigma receptors results in therapeutic effects or rather in undesirable symptoms will decide about the future direction of treatment of schizophrenia.

Phencyclidine: pharmacologic and clinical review

Phencyclidine (PCP), discovered in Germany during the 1920s, has become over the past four decades the number one drug of abuse in the United States. While briefly showing promise as being the "ultimate" anasthetic agent during the late 1950s, it very quickly fell into disfavor because of untoward side-effects during post-anesthetic emergence (1960s). Some few years later (1970s), PCP began its ascent in the illicit drug market. PCP is a drug with a broad range of pharmacological activity. It has been implicated as a major cause of psychiatric decompensation and has a number of clinical syndromes described in the literature. In addition, PCP has been shown to cause significant medical morbidity and mortality.

[Role of magnesium ions on the regulation of NMDA receptor--a pharmacopathology of memantine]

Magnesium ion blocks the ion channel of the NMDA receptor at a stable condition. The ion channel competes with the binding site of the noncompetitive antagonists phencyclidine (PCP) and MK-801, which prevent a brain impairment due to the ischemia and so on. The binding ability of these antagonists is strong, an exchange with the magnesium ion is not easy, then the side effect of the schizophrenia-like behavior is caused. Recently, memantine can be used as a therapeutic drug of the moderate-to-severe Alzheimer's disease. Memantine is the noncompetitive antagonist, too, then those development details and a difference from MK-801 were explained.