Pharmacological studies on Y-8894. (VIII). Effects on learning and memory in the radial maze task in mice

Effects of Y-8894 on learning and memory were studied using a radial maze task in intact and scopolamine-induced amnesic mice. The following results were obtained: 1) Repeated administration of Y-8894 (1, 2.5 and 5 mg/kg, i.p.) significantly increased the number of initial correct responses (ICR) in the training session in intact mice, facilitating the learning of the maze task. Dihydroergotoxine (5 mg/kg, i.p.) significantly facilitated the learning of this task in the initial stage of the training session, but non-specifically inhibited the performance in the late stage of training. Ca-hopantenate did not modify the learning of this task. 2) A single administration of Y-8894 (2.5 or 5 mg/kg, i.p.) showed an antagonistic effect on scopolamine (1 mg/kg, s.c.)-induced amnesic mice. Dihydroergotoxine (5 mg/kg, i.p.) and Ca-hopantenate (500 mg/kg, i.p.) also significantly antagonized the ICR-decreasing effect of scopolamine. These results suggest that Y-8894 has an ameliorative and/or facilitative effect on learning and memory in the radial maze task, and Y-8894 is more potent than dihydroergotoxine and Ca-hopantenate.     

Pharmacological studies on Y-8894. (V) Effect on learning and memory in intact and experimentally amnesic rats

The effects of Y-8894 on learning and memory were studied using the pole climbing avoidance (PCA) response in intact and experimentally induced amnesic rats. The following results were obtained: A single administration of Y-8894 (2.5 mg/kg, i.p.) to experimentally induced amnesic rats significantly antagonized the decrease in the mean number of PCA responses induced by an electroconvulsive shock (ECS). At a higher dose (10 mg/kg, i.p.), however, this effect was reduced. Repeated administration of Y-8894 (5 mg/kg, i.p.) significantly antagonized the facilitation of the extinction of the PCA response induced by exposure to CO2. Repeated administration of Y-8894 (2.5 mg/kg, i.p.) significantly facilitated the learning of the PCA response in intact rats. At a higher dose (5 mg/kg, i.p.), however, this effect was reduced. A single administration of Y-8894 (5 mg/kg, i.p. and 25 mg/kg, p.o.) significantly delayed the extinction of the PCA response in intact rats. These results suggest that Y-8894 has an ameliorative and facilitative effect on learning and memory in experimentally induced amnesic and intact rats.     

Pharmacological studies on Y-8894. (VII). Effects on transient cerebral ischemia-induced amnesia in rats

The effects of Y-8894 on experimental amnesia in rats induced by transient cerebral ischemia (600 sec) according to the method of Pulsinelli and Brierley were studied using the one trial passive avoidance response and the pole climbing discrete avoidance response. All drugs were administered to the rats immediately after recirculation. The following results were obtained: 1) In the one trial passive avoidance response test, Y-8894 (2.5, 5 and 10 mg/kg, i.p.) improved significantly the decreased latency induced by the ischemia, and it was most effective at 5 mg/kg. Calcium-hopantenate (100, 250 and 500 mg/kg, i.p.) and dihydroergotoxine (5 and 10 mg/kg, i.p.) tended to increase the latency. On the other hand, physostigmine (0.025, 0.05 and 0.1 mg/kg, i.p.), a cholinesterase inhibitor, increased the latency significantly, and it was most effective at 0.05 mg/kg. 2) The pole climbing discrete avoidance response was significantly decreased by the ischemia compared with the sham operated group, and Y-8894 (5 mg/kg, i.p.) tended to improve this decreased avoidance response. 3) Y-8894 (5 mg/kg, i.p.) facilitated recovery from the changes in glycolytic metabolism, and inhibited the accumulation of choline due to the dysfunction of the neuronal membranes induced by the ischemia. These results show that Y-8894 has beneficial effects on experimental amnesia induced by transient cerebral ischemia.     

Characteristics of the cortical and hippocampal EEG power spectra of rabbits during normal behavioral states and after administration of CNS acting drugs

The EEG power spectra of the motor cortex (MC) and hippocampus (HPC) in rabbits were characterized, and the effects of CNS acting drugs on the spectra were investigated. The EEGs of rabbits with chronically implanted electrodes were recorded with bipolar leads and simultaneously analyzed for 15 min with a computer to obtain their power spectra. MC spectra had one peak of delta wave, and HPC spectra had two peaks of delta and theta waves, whose peak powers and frequencies were changed in correspondence to the level of consciousness. Pentobarbital (20 mg/kg, i.v.) produced the peaks at 11 and 4 Hz in MC and HPC spectra, respectively. Morphine (5 mg/kg, i.v.) produced the peak at 7 Hz in MC spectra and shifted the theta wave peak of HPC to lower frequencies. Diazepam (4 mg/kg, i.v.) produced the peak at 14 Hz in MC spectra and decreased the two peak powers in HPC spectra. Chlorpromazine (4 mg/kg, i.v.) shifted the theta wave peak of HPC to lower frequencies. Amitriptyline (5 mg/kg, i.v.) increased the peak powers of the delta waves in MC and HPC spectra. These results suggest that each of the five CNS acting drugs produces the characteristic spectra, and they are different from the spectra obtained during normal behavioral states.     

Rheoencephalographic and electroencephalographic studies on nicergoline

The effect of nicergoline on the rheoencephalogram (REG) and on spontaneous electroencephalographic activity (EEG) was studied in acute experiments in cats. The following REG parameters were assayed: amplitude, anacrotic section of the curve and its relative part and dicrotic index. EEG spectra were derived from 10-sec samples of ECoG and the relative amplitude was estimated at 2 Hz-intervals from 0-44 Hz. The REG study showed that nicergoline (0.05 mg/kg i.v.) caused an increase of the amplitude, and a decrease of the anacrote, of the relative part of the anacrote and the dicrotic index - changes indicating a lowering of cerebrovascular resistance. EEG study showed a decrease of the slow activities (theta and delta), and an increase of the fast activities (alpha and beta-1).     

Effect of propranolol on cortical electrical activity in conscious and anesthetized rats

The effect of propranolol on electrocorticographic (ECoG) activity was studied in conscious and anesthetized rats. Cortical electrodes and femoral venous cannulae were implanted 5 days before the experiments. The ECoG was recorded continuously and analyzed to different frequency bands, 2 hr before and 4 hr after the administration of propranolol. After a single infusion of 2 and 5 mg/kg or 5 consecutive daily doses of 2 mg/kg propranolol, frequent bursts of large amplitude 6-7 c/sec wave in the ECoG were observed. This ECoG phenomenon lasted between 60-100 min after the infusion of propranolol and was entirely abolished by pentobarbital anesthesia. Frequency analysis of the ECoG showed an immediate shift from predominantly delta (delta 0.5-4 c/sec) activity to overwhelmingly theta (theta 4-8 c/sec) activity following the infusion of propranolol. It is suggested that these changes in ECoG induced by propranolol are related to the sleep-enhancing and tranquilizing effects of propranolol.     

Comparison of changes in the EEG of freely moving rats induced by enciprazine, buspirone and diazepam

The effect of enciprazine, buspirone and diazepam was investigated on the cortical electrical activity in freely-moving rats. Enciprazine (5 mg/kg, i.p.) and buspirone (5 mg/kg, i.p.) induced comparable changes, consisting in decreases of mean power values in delta and theta and increases in alpha and beta EEG frequency bands. Regarding only a particular area of the brain or particular frequency bands, these two compounds could not be clearly separated from each other. Changes in frequency bands induced by O-methoxy-phenyl-piperazine (5 mg/kg i.p.) (D 15157), the presumed main metabolite of enciprazine, were dose-related to that caused by the parent compound. The second metabolite (R,S)-1-4-(1-methoxy-4-hydroxy-phenyl)piperazin-1-yl-3-(3,4,5- trimethoxyphenoxy)propan-2-ol-dihydrochloride (D 20092) (5 mg/kg i.p.) evoked only minimal changes in the different frequency bands of the rats. The power spectra did not significantly differ from those seen in animals treated with saline. The action of diazepam (2 mg/kg i.p.) was characterized by decreases in alpha and delta frequency bands, accompanied by marked increases in fast beta waves. The marked frequency shifts caused by buspirone and enciprazine could clearly be differentiated from the EEG changes evoked by the minor tranquilizer, diazepam.     

Effect of enantiomers of deprenyl (selegiline) and amphetamine on physical abuse liability and cortical electrical activity in rats

In the present study, whether the repeated administration of (-)deprenyl to rats resulted in physical dependency was investigated. In a second experiment, the effect of (-)-deprenyl was investigated on the cortical electrical activity of freely moving rats and last, the influence of (-)-deprenyl on the behaviour of the animals was studied. In all experiments, different stereospecific configurations of amphetamine and deprenyl were also employed in order to establish differences and similarities. During and after the chronic oral administration of (-)-deprenyl (4 mg/kg) over 6 weeks, no signs of physical dependency were observed in rats after withdrawal of the drug. By contrast, (+)-deprenyl (5 mg/kg, p.o.) and (+)-amphetamine (5 mg/kg, p.o.) induced typical symptoms of amphetamine-dependency: during withdrawal of drug, the body weight of the rats was increased. A similar phenomenon was observed after oral administration of (+/-)-amphetamine (6 mg/kg, p.o.). After a single oral administration of (-)-deprenyl (1 and 5 mg/kg) and (-)-amphetamine (10 mg/kg, p.o.), decreases in delta and increases in theta frequency bands in the EEG were observed. In contrast, (+)-amphetamine (1 mg/kg, p.o.), (+/-)-amphetamine (5 mg/kg, p.o.) and (+)-deprenyl (1 and 5 mg/kg, p.o.) evoked increases in the mean power values in delta and decreases in theta frequency bands. In agreement with the EEG studies, the (-) and (+)-isomers of amphetamine and deprenyl caused differences in the behaviour of the animals. Based on these findings, it can be concluded that (-)-deprenyl undergoes a stereospecific metabolism in the organism and the amounts of its metabolites with (+) configuration might be negligible, even at the larger doses which are necessary to inhibit monoamine oxidase-B (MAOB) in brain.     

Effects of phencyclidine (PCP) and MK 801 on the EEGq in the prefrontal cortex of conscious rats; antagonism by clozapine, and antagonists of AMPA-, alpha(1)- and 5-HT(2A)-receptors.

1. The electroencephalographic (EEG) effects of the propsychotic agent phencyclidine (PCP), were studied in conscious rats using power spectra (0 - 30 Hz), from the prefrontal cortex or sensorimotor cortex. PCP (0.1 - 3 mg kg(-1) s.c.) caused a marked dose-dependent increase in EEG power in the frontal cortex at 1 - 3 Hz with decreases in power at higher frequencies (9 - 30 Hz). At high doses (3 mg kg(-1) s.c.) the entire spectrum shifted to more positive values, indicating an increase in cortical synchronization. MK 801 (0.05 - 0.1 mg kg(-1) i.p.) caused similar effects but with lesser changes in power. 2. In contrast, the non-competitive AMPA antagonists GYKI 52466 and GYKI 53655 increased EEG power over the whole power spectrum (1 - 10 mg kg(-1) i.p.). The atypical antipsychotic clozapine (0.2 mg kg(-1) s.c.) synchronized the EEG (peak 8 Hz). The 5-HT(2A)-antagonist, M100907, specifically increased EEG power at 2 - 3 Hz at low doses (10 and 50 microg kg(-1) s.c.), whereas at higher doses (0.1 mg kg(-1) s.c.) the profile resembled that of clozapine. 3. Clozapine (0.2 mg kg(-1) s.c. ), GYKI 53655 (5 mg kg(-1) i.p.), prazosin (0.05 and 0.1 mg kg(-1) i.p.), and M100907 (0.01 and 0.05 mg kg(-1) s.c.) antagonized the decrease in power between 5 and 30 Hz caused by PCP (1 mg kg(-1) s.c.), but not the increase in power at 1 - 3 Hz in prefrontal cortex.     

Effects of antitussive drugs on the central respiratory mechanisms during the cough reflex

Effects of antitussive drugs on the phrenic nerve activities during the cough reflex were investigated by means of a power spectrum analysis as a quantitative evaluation of each of the frequency band components of the phrenic nerve activities in anesthetized dogs. The efferent activities of the phrenic nerve were recorded from the central cut end of the phrenic nerve. Each fraction of the phrenic nerve activity was fractionated into bands spanning a range of 100 Hz each by a variable filter and analyzed using a program for the power spectrum analysis. The increase in power of each of the frequency band components was observed during the cough reflex induced by mechanical stimulation of the tracheal mucosa. Particularly, the power of the 2 approximately 100 Hz band components increased significantly as compared with the other frequency band components. An i.v. administration of codeine (3 mg/kg) significantly inhibited the increase in power of all frequency band components during the cough reflex. After administration of dextromethorphan (10 mg/kg, i.v.) or fominoben (8 mg/kg, i.v.), the increase in power of the 2 approximately 100 Hz band components of the phrenic nerve activity during the cough reflex was decreased significantly for 5 approximately 10 min; however, the other frequency band components were not affected. These results provide some evidence for a difference between these three antitussive drugs with respect to the mechanisms of action in the process of the central integration for the cough reflex.     

The benzodiazepine (+)-tifluadom (KC-6128), but not its optical isomer (KC-5911) induces opioid kappa receptor-related EEG power spectra and evoked potential changes

Tifluadom, a benzodiazepine with purported opioid receptor-related analgesic properties, was studied in regard to its acute effects on power spectra of the EEG to demonstrate vigilance changes. Additionally, somatosensory-evoked potentials (SEP) were derived to evaluate its effect on the propagation of impulses in sensory nerve fibers. In order to demonstrate stereospecificity, the two enantiomers of tifluadom (KC-5911 and KC-6128) were given in graded doses (20, 40, 80, 160 micrograms/kg i.v.) to awake, unrestrained and trained dogs at 10-min intervals. KC-6128, but not its optical counterpart KC-5911, induced synchronization of the EEG at 20 micrograms/kg with an increase of power (pW) in the delta (1-4 Hz; +300%), theta (4-8 Hz; +450%), and alpha (8-13 Hz +90%) bands. This was accompanied by a reduction of power in the fast beta domain (13-30 Hz; -95%). Vigilance changes were reflected in the beta/delta quotient which dropped from 3.7 (control) to 0.8 (20 micrograms/kg) and to 0.3 (40 micrograms/kg). A further increase in the dose resulted in saturation. At the highest dose (160 micrograms/kg) there was an additional reduction of the beta/delta quotient to 0.1. In order to unmask the receptor population, possibly mediating the observed changes, a benzodiazepine antagonist and opioid antagonists were given. Ro 15-1788 (240 micrograms/kg) had no effect and naloxone (20 micrograms/kg) induced a short term (5 min) arousal. Only the kappa antagonist Mr 2266 (20 micrograms/kg) induced a reversal of the beta/delta quotient back to 5.5. KC-5911 induced an insignificant drop in the beta/delta quotient which was reversed by Ro 15-1788.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of Y-20811, a specific thromboxane A2 synthetase inhibitor, on chemical mediator-induced bronchoconstriction in guinea pigs

We investigated the effects of Y-20811 on chemical mediator-induced bronchoconstriction and the release of chemical mediators into lung perfusion fluid during arachidonic acid (AA)-induced bronchoconstriction in guinea pigs. Y-20811 (0.01-1 mg/kg, i.v.), like acetylsalicylic acid or indomethacin, dose-dependently suppressed arachidonic acid- and LTD4-induced bronchoconstriction, and it (1 mg/kg, i.v.) also inhibited PAF-induced bronchoconstriction in guinea pigs. However, at a dose of 1 mg/kg, i.v., it was inactive against the bronchoconstriction induced by histamine, serotonin and acetylcholine in guinea pigs. Y-20811 (0.3-10 mg/kg) administered orally also prevented the LTD4-induced bronchoconstriction in a dose-dependent manner. This protective effect of Y-20811 (10 mg/kg, p.o.) persisted for at least 24 hr. Y-20811 (10 mg/kg, p.o.) also inhibited antigen-induced bronchoconstriction in guinea pigs passively sensitized with anti-ovalbumin guinea pig serum and pretreated with mepyramine. In the perfused and ventilated guinea pig lungs, Y-20811 inhibited AA-induced bronchoconstriction, decreased the release of TXA2 (estimated as TXB2) and increased the release of PGE2 into the perfused lung fluid, significantly (TXB2 and PGE2 were measured by HPLC). Therefore, Y-20811 suppressed various stimulant-induced bronchoconstrictions through the decrease of TXA2 production and the increase of PGE2 production. Thus, Y-20811 should prove useful as an anti-asthmatic drug.     

Combination benefit of a pyrimidylpiperazine derivative (Y-40138) and methotrexate in arthritic rats

Anti-tumor necrosis factor-alpha (TNFalpha) antibody in combination with methotrexate dramatically decreases joint destruction in rheumatoid arthritis. The aim of this study was to examine combined treatment with N-[1-(4-([4-(pyrimidin-2-yl)piperazin-1-yl]methyl)phenyl)cyclopropyl] acetamide HCl (Y-40138) and methotrexate in rat adjuvant-induced arthritis. The increase in hindpaw volume and joint destruction was suppressed by single therapeutic administration (days 15-20) of Y-40138 (30 mg/kg, p.o.), but not by prophylactic administration (days 1-9). However, arthritic progression was suppressed by single prophylactic administration of methotrexate (0.3 mg/kg, p.o.), but not by therapeutic administration. Combined administration (days 10-20) of Y-40138 (0.3-1 mg/kg) and methotrexate (0.03 mg/kg) synergistically suppressed the increase in hindpaw volume and joint destruction. We concluded that Y-40138 in combination with methotrexate synergistically suppressed arthritic progression. These data suggest that combined treatment with Y-40138 and methotrexate may increase efficacy of therapy for rheumatoid arthritis.     

Pharmacological studies on Y-8894 (VI). The effect on monoamine uptake and turnover in mouse brain

The effect of Y-8894 (+/-) 2-[[o-(2-thenyl)phenoxy]methyl] morpholine maleate, which has been shown to improve experimentally induced learning and memory deficits, on cerebral monoamine uptake and turnover was studied in the mouse. The following results were obtained: 1) It inhibited in vitro norepinephrine (NE) uptake to the mouse cerebral synaptosomal fractions about 800 and 1250 times more potently than it did those of dopamine (DA) and serotonin (5-HT), respectively. 2) It dose-dependently inhibited in vivo NE uptake, but not DA or 5-HT uptake. 3) It reduced the accumulation of the NE metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), increased that of the 5-HT metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and had no effect on that of the DA metabolite, homovanillic acid (HVA). These effects were compared with those of imipramine, calcium hopantenate (Ca-hopantenate) and dihydroergotoxine. Y-8894 appeared to act by stimulating the noradrenergic receptor, and it acts to a lesser extent by blocking the serotonergic receptor in the brain.     

Effects of metoprolol, alone and in combination with lidocaine, on ventricular fibrillation threshold: comparison with atenolol, propranolol, and pindolol

Metoprolol and other beta-adrenergic blocking drugs are known to exert cardioprotective effects that include significant reduction in occurrence of ventricular fibrillation (VF) following myocardial ischemia and infarction. To help determine the mechanism of these cardioprotective effects, this study evaluated the effect of equipotent beta-blocking doses of metoprolol and three other beta-blockers with differing ancillary properties on ventricular fibrillation threshold (VFT) in the normal canine heart. Metoprolol tartrate (1.0 mg/kg i.v.), atenolol (0.3 mg/kg i.v.), propranolol hydrochloride (0.3 mg/kg i.v.), pindolol (0.03 mg/kg i.v.), or saline control (0.9% NaCl solution; vehicle) was given, alone and in combination with lidocaine (L), to groups of six pentobarbital (32.5 mg/kg i.v.) anesthetized mongrel dogs after control VFT and control isoproterenol-induced (ISO) positive chronotropic effects had been determined. The D- (membrane stabilizing, non-beta blocking) and L- (beta blocking) isomers of propranolol also were administered to separate groups of six anesthetized dogs in a dose of 0.3 mg/kg i.v. Blood samples (venous) were taken before drug or vehicle administration, 10 min after drug/vehicle administration and at half-hour intervals thereafter during experimentation. ISO responses and VFT were determined 5 and 15 min, respectively, after drug/vehicle administration and at half-hour intervals for a total experimental period of 165 min. VF was induced with a train of pulses (5 s, 100 Hz, 3-ms duration, 250-omega resistance) applied by bipolar platinum electrodes to a paced heart (200 beats/min). Voltage (V) was increased every 60 sec (0.25-V increments between 0-3.5 V and 0.5-V increments greater than 3.5 V) until VF occurred. Metoprolol increased VFT significantly (p less than 0.05) and maximally (max delta V = 2.3 +/- 0.7 V) at 135 min postdrug when the ISO-induced increase in heart rate was inhibited (%I ISO) by less than 53%. Max delta V was not significantly increased following i.v. administration of atenolol (0.8 +/- 0.6 V), pindolol (0.1 +/- 0.1 V), or saline (0.1 +/- 0.1 V). Max delta V was 0.5 +/- 0.2 in the D-propranolol-treated group and 0.5 +/- 0.3 in the L-propranolol-treated group. These values did not differ from max delta V obtained in the propranolol-treated group (0.6 +/- 0.4 V). Changes in VFT for all groups were, over time, negatively correlated with %I ISO and were not dependent on membrane stabilizing effect (metoprolol, propranolol (D,DL), pindolol), intrinsic sympathomimetic activity (pindolol), or cardioselectivity (metoprolol, atenolol).(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of S-adenosyl-L-methionine sulfate tosylate (FO-1561) on functional recovery after transient cerebral ischemia in rats

The present investigation was undertaken to examine the recovery of functions, spontaneous EEG activity and cerebral ATP content during blood recirculation following cerebral ischemia in rats. The ischemia was induced by bilateral carotid artery 30 min-occlusion 24 hr after the permanent electrocauterization of bilateral vertebral arteries. EEG spectral analysis was performed by the Berg transform. The recovery of EEG activity was assessed by the time elapsing from the onset of blood recirculation until the delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-13 Hz) or beta (13-32 32 Hz) band reappeared and the relative proportion of the four bands at 45 and 60 min after recirculation. Following the 20 min recirculation, the brains were frozen in situ with liquid nitrogen and then stored at -80 degrees C for later extraction for analysis. Concentrations of ATP in the cerebral cortex were determined with enzymatic methods. In animals administered FO-1561 (10 approximately 100 mg/kg, i.v.) simultaneously with blood recirculation, the reduction of time elapsing until reappearance of the theta, alpha and beta bands, the decrease in proportion of the delta band and the increase in that of the theta, alpha and beta bands which indicated the facilitation of transition to the normal state were observed. In animals administered FO-1561 (100 mg/kg), the improvement of ATP content was detected. These results demonstrate that FO-1561 may have a beneficial effect on the recovery from dysfunctions due to cerebrovascular disorder.     

Clinical pharmacology of a new antidepressant, Y-8894 in healthy young and elderly volunteers.

In the first experiment the influences of a single oral administration of a new antidepressant, Y-8894 50 mg, nortriptyline 50 mg, and placebo on physiological and psychological parameters were evaluated by a double-blind, crossover method in 10 healthy male volunteers. As the second experiment eight elderly healthy men were also recruited to examine the clinical pharmacology of Y-8894. Y-8894 50 mg showed no significant anticholinergic, sedative, or cardiovascular effect on any of the measures used in young subjects. In the elderly Y-8894 50 mg increased pulse rate (P less than 0.05-0.01), lowered systolic blood pressure (P less than 0.05-0.005), and decreased salivary flow (P less than 0.05) compared with those of pre-drug baseline. C.f.f. was improved after Y-8894 50 mg, but not significantly. Neither psychomotor performance nor immediate memory was influenced after either treatment in young subjects. Furthermore, in the elderly Y-8894 50 mg did not affect these parameters. In the elderly both k21 and ke were smaller, t1/2,z was longer, and AUC was larger compared with young subjects (P less than 0.01). In conclusion, Y-8894 50 mg seemed to lack the anticholinergic, sedative and cardiovascular effects which were observed after nortriptyline 50 mg in young subjects. In the elderly some affects were recognized, in part, due to pharmacokinetic alteration.     

Quantitative electroencephalographic profile of 3-(4-hydroxy-1-piperidinyl)-6-(2,4-dichlorophenyl)-pyridazine (SR 41378) in the rat

Summary Quantitative electroencephalographic (QEEG) analysis was performed in rats following the oral administration of SR 41378 [3-(4-hydroxy-1-piperidinyl)-6-(2,4-dichlorophenyl)-pyridazine], a novel aminopyridazine derivative, which has been shown to possess anticonvulsant, antianxiety and hypnotic activities in mice and rats. The EEG effects of SR 41378 (10, 30 and 100 mg/kg) were compared to those of secobarbital (30 and 60 mg/kg) and diazepam (1, 3 and 10 mg/kg). SR 41378 and secobarbital increased the power of the middle-frequencies (8–16 Hz) of the EEG, reduced that of 4–8 Hz (theta) activities and did not affect 1–4 Hz (delta) activities. Diazepam also increased the power of middle-frequency activities and decreased that of both delta and theta activities. Quantitative EEG profiles were calculated from the mean integrated power (MIP) of selected frequency bands. The QEEG profile of SR 41378 was found to share common characteristics with those of secobarbital and diazepam: dose-dependent decrease of theta band MIP and increase of 8–20 Hz (middle beta bands) MIP. However, both SR 41378 and secobarbital induced a reduction of the 28–32 Hz (fast beta bands) MIP, whereas diazepam diminished the delta band. These results suggest that SR 41378, a novel chemical structure, shares common psychotropic properties with barbiturates and benzodiazepines.Part of this work has been presented at the 15th Annual Meeting of the Society for Neuroscience, October 20–25, 1985, Dallas, Texas, USA     

Histamine H3 receptor-mediated inhibition of sympathetically evoked mydriasis in rats

This study was designed to determine if the histamine H3 receptor agonist R-alpha-methylhistamine would play a role in modulation of sympathetically evoked mydriasis in anesthetized rats, and if so, to ascertain the specific receptor subtype(s) involved. Reproducible frequency-response curves of pupillary dilation were generated by stimulation of the cervical preganglionic sympathetic nerve (1-32 Hz). Systemic administration of R-alpha-methylhistamine (0.3-3.0 mg kg(-1)) produced a dose-related inhibition of the evoked mydriasis. The greatest inhibition was seen at lower frequency levels, with about 43% depression observed at 2 Hz. The specific histamine H3 receptor antagonist, clobenpropit (3.0 mg kg(-1), i.v.), blocked the inhibitory effect of R-alpha-methylhistamine, whereas neither the histamine H2 receptor antagonist, cimetidine (5.0 mg kg(-1), i.v.), nor the histamine H1 receptor antagonist, chlorpheniramine (0.5 mg kg(-1), i.v.), was effective. The histamine H2 receptor agonist, dimaprit (10 mg kg(-1), i.v.), was also without effect on the evoked mydriasis. R-alpha-methylhistamine (3.0 mg kg(-1)) did not inhibit phenylephrine-induced mydriasis. These results support the conclusion that R-alpha-methylhistamine produces inhibition of sympathetically evoked mydriasis via histamine H3 receptor stimulation, presumably by an action on presynaptic histamine H3 receptors.     

RELATIONSHIP BETWEEN THE DOSE-RESPONSE EFFECTS OF DIAZEPAM AND CLOBAZAM ON ELECTROENCEPHALOGRAPHIC PARAMETERS AND ON KINDLED AMYGDALOID SEIZURE ACTIVITY IN RATS

1. The possibility that the anticonvulsant activity of the benzodiazepines, diazepam and clobazam, is related to changes in EEG parameters, particularly beta activity, was investigated in amygdaloid kindled rats. 2. The effects of diazepam (1, 2, 4, 8 and 16 mumols/kg), administered intraperitoneally (i.p.), clobazam (1, 2, 4, 8, 16 and 32 mumols/kg, i.p.) or vehicle (dimethyl sulfoxide) on the cortical EEG of amygdaloid kindled rats were quantitated for 15 min using computerized period amplitude analysis. Immediately afterwards, the amygdala was stimulated and the after-discharge duration (AD) and the seizures stage (SS) were determined. 3. The equivalent percentage time (EPT) of the diazepam-treated group was decreased in the theta band (4-8 Hz) and increased in the alpha (8-12 Hz) and first six beta (12-36 Hz) bands. The mean peak amplitude (MPA) was increased in the alpha (8-12 Hz) and all seven beta bands (12-40 Hz). Clobazam increased the EPT and MPA in the alpha (8-12 Hz) and all seven beta (12-40 Hz) bands. The MPA was also increased by clobazam in the theta (4-8 Hz) band. 4. Diazepam reduced both the AD and SS of the kindled seizures at doses of 4, 8 and 16 mumols/kg, whereas clobazam was anticonvulsant at doses of 16 and 32 mumols/kg. The reduction in both AD and SS correlated with increases in the EPT and MPA in the first beta (12-16 Hz) band in the diazepam-treated group and in the first four beta (12-28 Hz) bands in the clobazam-treated group.