Electroencephalographic (EEG), EEG power spectra, and behavioral correlates in rats given phencyclidine.

The electroencephalogram (EEG), electromyogram (EMG) and behavior were monitored in rats with chronic cerebrocortical and temporalis muscle electrodes. They were injected acutely with 0, 2, 4 and 8 mg/kg of phencyclidine (i.p.). The EEG power spectra correlated in a dose-related manner, with the direct EEG and behavioral effects of phencyclidine. At 2 mg/kg, the EEG consisted primarily of low amplitude theta activity from 6 to 8 Hz, accompanied by behavioral arousal and hyperactivity. At 4 mg/kg, the EEG theta activity persisted and was superimposed on a background of high amplitude slow waves which were associated with the emergence of ataxia. Locomotion and stereotypy intensified at this dose. The power spectra of these changes in the EEG were characterized by two distinct spectral peaks lying between 0-5 and 5-10 Hz. After 8 mg/kg, EEG activity shifted predominantly to lower frequencies between 2 and 3 Hz. This shift produced a large increase in spectral power in the 0-5 Hz band which was accompanied behaviorally by severe ataxia, limited locomotion, and stereotypy of head and forepaw movements. Similarities and differences between these EEG changes induced by phencyclidine and the EEG effects of ketamine and SKF 10047 were obtained.

Cortical EEG changes during the self-administration of phencyclinoids.

Female rats, implanted with cerebrocortical EEG recording electrodes, were trained to self-administer cocaine and then ketamine under a fixed ratio 10 schedule of reinforcement, during limited access sessions. Periodically, a single unit dose of either phencyclidine (0.5 mg/kg), ketamine (4 mg/kg) or 1-(1-phenylcyclohexyl)morpholine (PCM 4 mg/kg) was substituted for ketamine, while the cortical EEG was recorded. Spectrum quantities of samples of EEG, taken immediately before and after each injection, were subjected to a discriminant analysis. For each drug, the preinjection state of the EEG could be classified separately from the postinjection state, using specific EEG spectrum quantities from the global frequency range (0.1-20 Hz). Furthermore, the relevant EEG parameters, which described the change from pre- to postinjection states, were unique for each drug (phencyclidine: total power and complexity; ketamine: peak frequency, relative power and mobility; PCM: all parameters except peak frequency), indicating potential differences in the EEG, occurring with a level of intake of drug which was controlled by the subject. Overall, these data serve to model the changes in the EEG that occur during the self-administration of three phencyclinoids. Furthermore, the combination of EEG spectrum analysis with discriminant analysis is useful in detecting subtle differences in the effects of these three drugs on the EEG.

Effects of self-administered phencyclidine on regional uptake of 2-deoxy-D-[1-14C]glucose in brain.

Phencyclidine profoundly alters cerebral metabolism in the rat. This study explored whether cerebral metabolic effects of phencyclidine differed when the drug was self-administered by trained rats, compared with when it was given acutely to naive rats. The regional cerebral uptake of 2-deoxy-D-[1-(D14C] glucose (DG) was examined following two injections of phencyclidine (0.5 mg/kg/injection, i.v.) or saline in freely-moving, drug-experienced rats. Naive controls received phencyclidine or saline according to an identical dose regimen. In self-administering and naive rats, phencyclidine produced many of the same effects on uptake of DG, including the following: decreases in the habenula, inferior colliculus, sensory cortical areas and corresponding thalamic relay nuclei; and increases in limbic areas (entorhinal and retrosplenial cortices, subicular areas). Some regions (auditory and motor cortices, medial geniculate body, globus pallidus) showed different effects in self-administering and naive rats. Another study, in which rats were not self-administering phencyclidine, but had histories of treatment with drugs similar to those of the self-administering rats, indicated that chronic exposure to drug accounted for some of the differences. Furthermore, differences between the effects of phencyclidine in self-administering, versus non-self-administering rats with similar histories suggested that activity in some regions of the brain may relate to training in drug self-administration and/or behavior.

Synthesis and preliminary biological studies of 4- and 5-[2-hydroxy-3-(isopropylamino)propoxy]benzimidazoles: selective beta2 adrenergic blocking agents.

Benzimidazoles carrying the 2-hydroxy-3-(isopropylamino)propoxy side chain at either the C-4 or C-5 ring positions were synthesized and investigated for beta-adrenergic blocking activity. Both compounds demonstrated beta2 selectivity when evaluated in guinea pig atrial and tracheal preparations. The C-4 isomer was 17 times more selective toward tracheal tissue, and its overall potency was roughly comparable to that of propranolol. beta2 selectivity of the C-5 isomer was minimal, with a potency about one-hundredth that of propranolol.

Effects of selective D1 and D2 dopamine antagonists on cocaine self-administration in the rat.

The effect of the selective D1 antagonist, SCH 23390, and the selective D2 antagonist, spiperone, was investigated in rats trained to self-administer intravenous cocaine on a fixed-ratio (FR) 5 schedule of reinforcement. Both SCH 23390 and spiperone pretreatment increased responding up to doses of 10.0 micrograms/kg, and decreased responding at higher doses. Since rate of responding maintained by a drug can be influenced by factors other than its reinforcing efficacy, behavior maintained by cocaine was also investigated under a progressive-ratio schedule. The breaking point obtained under this schedule is used as a measure of the efficacy of the reinforcer and this value is not exclusively determined by response rate. With the progressive-ratio schedule, both SCH 23390 and spiperone produced dose-dependent decreases in the highest ratio completed in rats self-administering cocaine. The results obtained using the FR 5 and progressive-ratio schedules suggest that both D1 and D2 receptors are involved in mediating the reinforcing effects of cocaine.

D-ala2-methionine-enkephalinamide self-administration in the morphine-dependent rat.

The self-administration of D-enkephalin was studied in the dependent rat self-administering morphine. The rats were prepared with chronic IV and bilateral intraventricular (IVT) injection cannulae. They were made physically dependent on morphine and trained to lever press for IV morphine self-injections (inj) (10 mg/kg) on a fixed ratio (20) (FR20) schedule of reinforcement. Substitution of D-enkephalin either IVT (40 microgram/inj) or IV (10 mg/kg/inj) in the morphine-dependent rat maintained consistent lever pressing and self-administration behavior similar to morphine self-administration. No signs of abstinence were observed during the D-enkephalin substitution. However, saline substitution (0.05 ml/inj IV) for morphine in the self-administering rat produced an abstinence syndrome characterized by extinction of responding, wet-dog shakes, writhes, and diarrhea, which were reversed for 1 h by a single IVT injection of D-enkephalin (40 or 80 microgram). These results indicate that D-enkephalin will serve as a reinforcer to maintain opiate-seeking behavior and support physical dependence in the rat.

Effects of levo-alpha-acetylmethadol (LAAM) on morphine self-administration in the rat.

Rats bearing cerebrocortical electrodes for recording the electroencephalogram (EEG) were rendered tolerant to and physically dependent on morphine and subsequently trained to self-administer morphine (10 mg/kg injection) through a chronic intravenous cannula. Morphine was available for self-administration 24 h/day. Once morphine intake had stabilized (10-12 injections/day), levo-alpha-acetylmethadol (LAAM) was administered noncontingently via a chronic intragastric (IG) cannula as a single daily dose of either 1 or 4 mg/kg. These morphine self-administering rats were maintained on daily LAAM treatment for 12 consecutive days. Analysis of the patterns of lever pressing, morphine self-injections, and sleep-awake behavior revealed that daily IG administration of LAAM effectively suppressed morphine self-administration. The 1 mg/kg dose of LAAM reduced morphine intake by 30%-50%, while 4 mg/kg produced an 80%-90% decrease. The reduction in morphine self-administration occurred in the absence of overt signs of narcotic withdrawal, behavioral toxicity, or disruption of sleep-awake behavior in these rats. Termination of LAAM maintenance resulted in a gradual return of level pressing and morphine intake to pre-LAAM levels.

Drug self-administration and sleep-awake activity in rats dependent on morphine, methadone, or l-alpha-acetylmethadol.

Morphine post-dependent rats were prepared with chronic cortical EEG and temporalis muscle EMG electrodes and i.v. jugular cannulae and permitted to self-administer morphine (10 mg/kg/injection) on a fixed-ratio schedule of reinforcement to reestablish and maintain dependence. Morphine was then replaced by methadone or 1-alpha-acetyl-methadol (LAAM) at a dose of 2 and 1 mg/kg, respectively. The rats developed stable patterns of self-administration of each narcotic and maintained the dependent state. The mean (+/- S.E.) interinjection interval was 2.5 +/- 0.1 h for morphine, 1.4 +/- 0.1 h for methadone and 8.8 +- 0.8 H FOR LAAM. The distribution of sleep, REM sleep, and awake within the interinjection interval for the three narcotics was similar. A short phase of behavioral stupor concomitant with EEG slow bursts emerged following the self-injections. This phase was followed by arousal with EEG activation. Sleep and REM sleep then reappeared and predominated before the next injection. LAAM manifested a relatively slow onset of action in comparison with morphine and methadone.

Head-shake distributions during self-maintained dependence on morphine, methadone, and l-alpha-acetylmethadol (LAAM) in the rat.

Adult female Sprague-Dawley rats were prepared with chronic cortical and muscle electrodes and i.v. cannulas, made tolerant to and physically dependent on morphine, and trained to level press for i.v. morphine self-injections to maintain dependence. Methadone or l-alpha-acetylmethadol (LAAM) was then substituted for morphine in some of these rats. During self-maintained dependence on either morphine or methadone, head shakes appeared and increased in frequency before lever pressing for self-injections. In contrast, there were fewer head shakes during LAAM dependence, which were evenly distributed over the entire duration of the interinjection interval. These findings suggest a relationship between head-shake distributions, drug-seeking behavior and the pharmacodynamics of these three narcotics.

Effects of fixed ratio size and dose on phencyclidine self-administration by rats.

Female Sprague-Dawley rats were trained to self-administer phencyclidine (PCP; 0.125, 0.25, or 0.5 mg/kg/injection) on a fixed ratio (FR) schedule of reinforcement under limited access conditions (3 h). Initial training began with cocaine, which was later replaced with ketamine and then one of the three unit doses of PCP. Baseline rates of injection were determined at FR 10. The size of the ratio was then incremented geometrically every fifth daily session. Increasing the ratio resulted in a decrease in the number of injections per session. Furthermore, this decrease was greater for the 0.25 mg/kg dose than for the 0.5 mg/kg unit dose. The self-administration of the 0.125 mg/kg dose was variable and rapidly extinguished upon the increase in fixed ratio. The results indicate that PCP is self-administered by rats under the conditions imposed in this study. Furthermore, the relative reinforcing efficacy of the different unit doses of PCP could be discriminated using this type of response cost procedure.

The anticonvulsant and behavioral effects of phencyclidine and ketamine following chronic treatment in rats.

The effects of chronic phencyclidine (PCP) or ketamine (KET) on their respective acute behavioral and anticonvulsant actions were investigated. Female rats were treated for 15 days with twice daily i.p. injections of saline, 20 mg/kg PCP or 40 mg/kg KET. Subjects treated chronically with PCP were challenged with either 10 mg/kg or 20 mg/kg i.p. PCP, while subjects treated chronically with KET were challenged with 40 mg/kg i.p. KET only. Neither chronic drug treatment induced tolerance to the acute anticonvulsant effect, nor to hyperlocomotion and stereotypy as measured by automated activity monitors. However, evidence of tolerance to the stereotypy induced by acute KET was obtained when an observer-based rating scale was employed. In addition, tolerance occurred to the ataxia induced by KET and the 10 mg/kg, but not 20 mg/kg, dose of PCP. Thus, tolerance occurs to some of the acute behavioral effects of PCP and KET while the anticonvulsant action of these compounds remains unaffected.

The convulsant and anticonvulsant effects of phencyclidine (PCP) and PCP analogues in the rat.

The pro- and anticonvulsant effects of phencyclidine (1-[1-phenylcyclohexyl]piperidine HCl, PCP), a number of its analogues, and SKF 10047 were investigated in rats. The PCP analogues were compounds produced by substitutions for the phenyl and piperidine rings of PCP and were selected to elucidate the structure-activity relationships existing between PCP and its pro- and/or anticonvulsant effects. All of the compounds, except ketamine, induced convulsions at high (12.8-25.6 mg/kg, i.v.), yet almost always sublethal doses. Ketamine failed to induce convulsions, even at lethal doses (51.2 mg/kg, i.v.). The acute pro- or anticonvulsant actions of PCP were then investigated. Rats were subjected to transorbital electroconvulsive shock subsequent to i.p. injections of saline or 0.625, 2.5, 5.0, 10.0 or 20.0 mg/kg PCP. It was found that PCP induced an acute, dose-dependent anticonvulsant effect. The acute pro- and/or anticonvulsant actions of the remaining compounds were then investigated by administration of electroconvulsive shock subsequent to i.p. injections of saline or one of two doses of each compound. The low and high doses of each compound were selected to be behaviorally equivalent to 2.5 and 10.0 mg/kg PCP i.p., respectively. With one exception, each dose of each drug induced an acute anticonvulsant action, with no difference in efficacy between the compounds tested. However, PCA (produced by substitution of an amine for the piperidine ring of PCP) induced a statistically greater anticonvulsant action at the higher, compared to the lower, dose. In addition, PCA was the only compound to eliminate all motor signs of the electrically induced seizure.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of calcium in sigma-mediated neuroprotection in rat primary cortical neurons.

Since unique calcium dynamics have been reported for toxic (40-80 M) and non-toxic (5-10 microM) concentrations of glutamate, we evaluated the effect of neuroprotective sigma ligands on glutamate and potassium chloride (KCl)-stimulated changes in [Ca2+]i using 12-15 day old primary rat neuronal cortical cultures. In approximately 80% of the neurons tested, 80 microM glutamate caused a sustained calcium flux previously shown to be associated with neurotoxicity. The majority of sigma ligands that were evaluated altered glutamate-induced calcium flux. For example, the primary effect of maximally neuroprotective concentrations of the sigma ligands dextromethorphan, (+)-pentazocine, (+)-cyclazocine, (+)-SKF 10047, carbetapentane and haloperidol was a shift from a sustained, to either a biphasic or a monophasic transient calcium response indicative of neuroprotection. (+)-3-PPP, previously shown not to be neuroprotective in this model system, failed to alter glutamate-induced calcium flux. In contrast to glutamate, KCl (50 mM) produced changes in [Ca2+]i which were not neurotoxic to the neurons as measured by LDH release. The primary response observed in 59% of the neurons treated with 50 mM KCl alone was an initial spike in [Ca2+]i which abruptly declined then plateaued above basal levels throughout the 12 min of analysis (modified sustained response). The highly selective sigma ligands produced a shift from the modified sustained response to a monophasic transient calcium response. Again, (+)-3-PPP had no effect on KCl-induced calcium dynamics. Of the PCP-related sigma ligands only (+)-SKF-10047 consistently attenuated the KCl-induced calcium flux. Collectively, these results indicate that modulation of [Ca2+]i through receptor and voltage-gated calcium channels contributes significantly to sigma mediated neuroprotection.

Neuroprotective sigma ligands attenuate NMDA and trans-ACPD-induced calcium signaling in rat primary neurons.

The effect of neuroprotective sigma ligands possessing a range of relative selectivity for sigma and phencyclidine (PCP) binding sites on N-methyl-D-aspartate (NMDA) and (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD)-stimulated calcium flux was studied in 12-15-day-old primary cultures of rat cortical neurons. In approximately 80% of the neurons tested, NMDA (80 microM) caused a sustained increase in intracellular calcium ([Ca2+]i). With the exception of R-(+)-3-(3-hydroxyphenyl)-N-propylpiperidine hydrochloride ((+)-3-PPP) (previously shown not to be neuroprotective) all of the sigma ligands studied significantly altered NMDA-induced calcium dynamics. The primary effect of dextromethorphan, (+)-pentazocine, (+)-cyclazocine, (+)-SKF10047, carbetapentane, 1,3-di(2-tolyl) guanidine (DTG), and haloperidol was to shift the NMDA response from a sustained, to either a biphasic or a transient, calcium event. In contrast to NMDA, the primary response observed in 62% of the neurons treated with trans-ACPD (100 microM) was a transient elevation in [Ca2+]i. Here, however, only the highly selective neuroprotective sigma ligands (i.e., those lacking substantial PCP binding affinity) significantly decreased the number of transient responses elicited by trans-ACPD whereas the PCP-related sigma ligands such as dextromethorphan, (+)-SKF10047 and (+)-cyclazocine were ineffective. Unexpectedly, (+)-3-PPP potentiated trans-ACPD activity. These results demonstrating attenuating effects of sigma ligands on NMDA-stimulated neuronal calcium responses agree with earlier studies using glutamate and KCl and identify a sigma receptor modulation of functional NMDA responsiveness. Furthermore, the ability of sigma ligands to attenuate NMDA-, trans-ACPD- and KCl-evoked neuronal calcium dynamics indicates that the receptor mechanisms mediating sigma neuroprotection comprise complex interactions involving ionotropic, metabotropic, and even voltage-gated calcium signaling processes.

1-alpha-acetylmethadol (LAAM), methadone and morphine abstinence in dependent rats: EEG and behavioral correlates.

Adult female Sprague-Dawley rats were prepared with chronic intravenous cannulas and cortical and muscle electrodes for recording electroencephalograms and electromyograms, respectively. They were made physically dependent on morphine by automatic intravenous injections and then trained to lever press in order to self-administer morphine on a FR-20 schedule of reinforcement. Upon stabilization of morphine self-administration, one group continued to self-administer morphine, while two other groups were switched to methadone or 1-alpha-acetylmethadol (LAAM) self-administration for an additional five to ten days. Continuous EEG and EMG recordings were collected. Initially, automatic injections of morphine suppressed rapid eye movement (REM) sleep time, then tolerance developed to this effect. REM sleep time in rats self-administering LAAM, methadone or morphine was within the lower limit of the normal range. Following withdrawal, REM sleep was severely suppressed during the first 24 h with morphine and methadone, but only moderately suppressed with LAAM. Increases in lever pressing during withdrawal from morphine and methadone occurred earlier and were more intense and prolonged than for LAAM. The incidence of head shakes peaked earlier and was higher for morphine and methadone during withdrawal than for LAAM. Irritability scores increased for morphine and methadone during the first day of withdrawal, but did not show any increase until the third day for LAAM. These findings suggest that in dependent rats withdrawal from LAAM is less severe than withdrawal from morphine or methadone.

Evaluation of neuroprotection and behavioral recovery by the kappa-opioid, PD117302 following transient forebrain ischemia.

The effects of the selective kappa-opioid, PD117302 ((+/-)-trans-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]benzo[b]thiophene-4-acetamide), on transient (15 min) global forebrain ischemia, induced by four-vessel occlusion, was evaluated using a multiple fixed-ratio, fixed-interval schedule of food presentation in rats. The schedule produced distinctive patterns of responding in the fixed-ratio and fixed-interval components. Ischemia produced CA1 hippocampal necrosis and prolonged suppression of responding under both schedule components. When responding resumed, the pattern of responding rapidly returned. Response disruption and CA1 hippocampal necrosis were minimal or nonexistent in sham-occluded rats. Behavioral recovery time under both components of the schedule of reinforcement correlated with CA1 necrosis. On average, CA1 necrosis was less, and behavioral recovery time was shorter, in rats treated with PD117302 postocclusion as compared with vehicle-treated rats. The difference, however, did not reach statistical significance. These results demonstrate the utility of schedule-controlled responding for evaluating potentially therapeutic compounds for the treatment of ischemic injury. These results also further characterize the neuroprotective actions of kappa opioids.

Behavioral and receptor binding studies of phencyclidine (PCP) and lithium interaction in the rat.

Three groups of female Sprague-Dawley rats (n = 4) were conditioned to drink water during a daily 2 hr session. The water was then changed to a solution of 1.0 mg/ml lithium chloride producing average doses between 62.9 and 72.1 mg/kg/day for Groups I and II. These rats were challenged with 4 mg/kg PCP i.p. before and during lithium treatment. Group I was tested for spontaneous locomotor activity in the open field apparatus. Lithium alone did not affect activity. After 1, 2, and 3 weeks of chronic lithium, PCP-induced activity increased 2.1, 1.7, and 2.8 fold, respectively, relative to PCP-induced activity during limited access to water only. Whole brain homogenates from Group II, after one week of chronic lithium, were used for receptor binding experiments using [3H] PCP; Group III served as water controls. The Kd (nM +/- S.E.M.) was not different in untreated (146.39 +/- 18.95) and lithium-treated (181.22 +/- 14.35) rats. The Bmax (pmole/mg protein +/- S.E.M.), however, was increased 48% (p less than 0.01) from 1.50 +/- 0.08 to 2.22 +/- 0.10 after lithium. These preliminary results suggest that chronic administration of lithium modifies the behavioral effects of PCP possibly via alterations at the receptor level.

Evaluating a possible pharmacokinetic interaction between remifentanil and esmolol in the rat.

Remifentanil (Ultiva) is a novel, ultra-short-acting opioid which has recently been approved for use as an analgesic during induction and maintenance of general anesthesia. Esmolol is a short-acting beta-blocker used during surgical procedures to reduce heart rate and blood pressure. Both drugs are metabolized by nonspecific esterases in the blood and other tissues and may be administered concomitantly during surgery. The goal of this study was to determine if coadministration of esmolol significantly alters the pharmacokinetics of remifentanil in the rat. Two groups of rats were dosed with remifentanil [25 micrograms/kg/min (n = 8)] and remifentanil plus esmolol [25 and 200 mg/kg/min (n = 7)] for 20 min. Cardiovascular measurements were collected continuously over the course of the study. Serial blood samples (12) were collected over 25 min into test tubes containing 0.5 mL of acetonitrile. Blood samples were extracted (liquid-liquid) with methylene chloride and then analyzed by a validated GC-MS assay. Compartmental data analysis was performed using PCNONLIN. The mean(+/- SD) for Cl and t1/2 observed in treatment I were 390(+/- 98) mL/min/kg and 0.69(+/- 0.27) min and in treatment II were 421(+/- 164) mL/min/kg and 0.56(+/- 0.22) min, respectively. Comparison of clearance, volume of distribution, and terminal half-life between the two groups showed that coadministration of esmolol had no significant (p < 0.05) effect on the pharmacokinetics of remifentanil in the rat.

Animal models of intravenous phencyclinoid self-administration.

Phencyclidine (1-(1-phenylcyclohexyl)piperidine, PCP) self-administration has been demonstrated in rhesus monkeys, baboons, dogs and rats. Generally, an orderly inverted U-shaped dose-response curve for rates of self-injection has been observed. Total drug intake appears to increase slightly with increases in unit dose; however, this increase is much less than might be expected with other CNS depressants such as barbiturates or morphine. Additionally, several arylcyclohexylamine analogues of PCP and some members of the benzomorphan and dioxolane classes referred to collectively as "phencyclinoids" are self-administered by primates and dogs. New data are presented in this review profiling the self-administration of some of these drugs in rats, as well as a characterization of the self-administration of higher unit doses of PCP than previously reported. Also, preliminary results of the assessment of the reinforcing efficacy of some PCP analogues measured by the progressive ratio procedure are presented.