Richard Scherschlicht

Electrophysiological studies on the specific benzodiazepine antagonist Ro 15-1788.

SummaryThis is an electrophysiological study in cats and rats of the imidazobenzodiazepinone derivative, Ro 15-1788, the first representative of specific benzodiazepine antagonists.(1)In unanaesthetized spinal cats, 1–10 mg kg−1 Ro 15-1788 i.v. did not affect segmental dorsal root potentials (DRPs), polysynaptic ventral root reflexes (VRRs), Renshaw cell responses to antidromic ventral root volleys and spontaneous γ-motoneurone activity. However, at 1 mg kg−1 i.v., it antagonized the enhancement of DRPs as well as the depression of polysynaptic VRRs, Renshaw cell discharges and γ-motoneurone activity induced by meclonazepam (0.1 mg kg−1 i.v.), diazepam (0.3 mg kg−1 i.v.) or zopiclone (1 mg kg−1 i.v.). The same dose of Ro 15-1788 failed to reduce similar effects of phenobarbital (10 mg kg−1 i.v.) on spinal cord activities.(2)In unanaesthetized “encéphale isolé” rats, 3 mg kg−1 Ro 15-1788 i.v. abolished the decrease induced by 5 mg kg−1 midazolam i.v. of spontaneous multiunit activity (MUA) in the substantia nigra pars compacta, nucleus raphé dorsalis, nucleus locus coeruleus and the CAl area of the hippocampus dorsalis, but not the decrease produced by 10 mg kg−1 pentobarbital i.v. Ro 15-1788 (12 mg kg−1 i.v.) by itself did not affect MUA in the substantia nigra, but slightly depressed MUA in the other 3 areas.(3)In intact immobilized rats, the increase of power induced by 1 mg kg−1 flunitrazepam i.v. in the 0.5–48 Hz range of the electrocorticogram as well as in the 0.5–8 Hz, 8–32 Hz and 32–48 Hz frequency bands was transiently abolished by 5 mg kg−1 Ro 15-1788 i.v.(4)In unrestrained cats, 5 mg kg−1 Ro 15-1788 i.p. had no effect on the electrical threshold for eliciting a rage reaction evoked by electric hypothalamic stimulation, but abolished the threshold increase caused by 1 mg kg−1 diazepam i.p. These results are in line with biochemical and behavioural findings and support the selective antagonism by Ro 15-1788 of central effects of benzodiazepines through an interaction at benzodiazepine receptors.

Ro 15-4513: Partial inverse agonism at the BZR and interaction with ethanol☆

The imidazobenzodiazepinone derivative Ro 15-4513 has the activity profile of a partial inverse (low efficacy) agonist at the benzodiazepine receptor (BZR). It reverses central nervous depressant effects of diazepam, and, in part, of phenobarbitone and ethanol in mice, rats and cats in behavioural, electrophysiological, and neurochemical paradigms. The interaction of Ro 15-4513 with barbiturates and ethanol is due to its inverse agonistic (negative allosteric modulatory) property at the BZR, as it was reversed by the selective BZR blocker flumazenil (Ro 15-1788). In the present experiment situations, other BZR partial inverse agonists in subconvulsant or overt convulsant doses were less effective against ethanol effects than Ro 15-4513. Possible mechanisms for this differential activity of BZR inverse agonists are discussed.

Sleep and EEG slow-wave activity in the domestic cat : effect of sleep deprivation

The 24-h sleep-wake distribution, the vigilance states and the time course of EEG slow-wave activity was investigated in 8 adult domestic cats individually maintained in isolation under 14-h light (06.00-20.00 h)/10-h dim conditions. The frontal EEG and motor activity were continuously recorded for 22 h (during the daily cleaning and food-replenishing period between 07.00 and 09.00 h the cats were only observed). Sleep was prevented for 14 h (07.00-21.00 h) by playing with the animals. Recovery from sleep deprivation was recorded for the remaining 10 h of the dim period. Non-rapid eye movement (non-REM) sleep, REM sleep and waking were uniformly distributed over the light and dim period, with the exception of the 2-h feeding period where the cats were always awake. EEG power density in the delta band (0.75-4.5 Hz; slow-wave activity) was computed in non-REM sleep. The values in the light period were higher than in the dim period. In neither of the lighting periods was a trend observed. After sleep deprivation a small increase of non-REM sleep and REM sleep was present. EEG slow-wave activity was initially enhanced and then declined progressively. We conclude that despite the small circadian difference in the sleep-wake pattern observed in our cats, sleep homeostasis is similar to that observed in other mammalian species.

Sleep and EEG spectra in the rabbit under baseline conditions and following sleep deprivation

The 24-hr sleep-wake distribution and power spectra of the electroencephalogram were determined in rabbits that had been implanted with cortical and hippocampal electrodes. A diurnal preference for sleep was observed. The spectral power density in nonrapid eye movement sleep (NREM sleep) of the cortex showed a decreasing trend in most frequencies within the 12-hr light period. In the 12-hr dim period no clear trend was present. Most hippocampal EEG frequencies decreased in NREM sleep in the first two hours of the light period, and thereafter stayed on a constant level. Sleep deprivation elicited the following changes: a prolonged increase of NREM sleep and a short increase of REM sleep; in the cortex, an increase of slow-wave activity (SWA; power density in the 0.25-2.0 Hz frequency band) in NREM sleep, which declined in the course of recovery; an enhancement of slow-wave (1.25-3 Hz) and theta (6.25-7 Hz) activity in REM sleep. The hippocampus showed an increase in NREM sleep power density in almost all frequencies. In REM sleep the hippocampus exhibited an increase in power density in the 6.25-7 Hz and 12.25-13 Hz bands, whereas in the 7.25-8 Hz band the values were below baseline. The results show that SWA in NREM sleep and theta activity in REM sleep are enhanced by sleep deprivation, as has been observed in other mammalian species. The EEG changes in the hippocampus resembled those in the cortex.

Benzodiazepines promote the intermediate stage at the expense of paradoxical sleep in the rat

The effects of diazepam, a long half-life benzodiazepine, midazolam and triazolam, two with short half-life, on the transitional stage between deep slow wave sleep and paradoxical sleep were studied in Wistar and WAG/Rij rats. This intermediate stage is characterized by the unusual association of cortical spindles and low frequency hippocampal theta rhythm. The main result was extension of the intermediate stage at the expense of paradoxical sleep by diazepam and triazolam by influencing only the duration of the intermediate stage and both the onset and maintenance of paradoxical sleep. Midazolam increased both intermediate stage and paradoxical sleep. Several differences in the qualitative modulation of the stage characteristics and between rat strains were found. In regard to the possible peculiar physiological significance of the intermediate stage, we conclude that benzodiazepines promote a transient pharmacological cerveau isolé-like stage during sleep in rats.

Some Pharmacological Effects of Delta-Sleep-Inducing Peptide (DSIP)

The synthetic nonapeptide DSIP was studied in rabbits and cats under normal conditions and under conditions of disturbed sleep. In other experiments, the effect of the oligopeptide on withdrawal jumping provoked by naloxone in morphine-dependent mice was studied. In rabbits, DSIP at 25 micrograms X kg-1 i.v. and 1 mg X kg-1 s.c. augmented spindle-dominated, light nonREM sleep and prevented hyposomnia after a stressful situation. In cats, 25 micrograms X kg-1 i.v. and 100 micrograms X kg-1 s.c. preferentially augmented REM sleep and abolished the sleep suppressant effect of morphine. In morphine-dependent mice, 25.5 micrograms X kg-1 i.v. as well as doses beyond 85 micrograms X kg-1 s.c. attenuated naloxone-induced withdrawal jumping. In most experimental situations, indications for bell-shaped dose-response curves of DSIP were found.

L-Cycloserine: behavioural and biochemical effects after single and repeated administration to mice, rats and cats

L-Cycloserine dose-dependently inhibited the activity of gamma-aminobutyric acid (GABA)-transaminase (GABA-T) and elevated the level of GABA in whole mouse brain with a peak effect 3-4 hr after a single intraperitoneal injection. At a dose (30 mg/kg) which elevated the level of GABA almost 4-fold, L-cycloserine moderately increased the content of alanine and slightly reduced that of aspartate, glutamate and glycine in the brain. L-Cycloserine (10-30 mg/kg, p.o. or i.p.) prevented tonic seizures induced by 3-mercaptopropionic acid (3-MPA) and audiogenic seizures in DBA/2 mice, without affecting those evoked by pentylenetetrazol, bicuculline and electroshock. Similarly small doses of L-cycloserine reduced the level of cGMP in the cerebellum of rats, prevented its elevation by 3-MPA and attenuated the hypothalamically-elicited rage reaction in cats. Larger doses of L-cycloserine (greater than 30-100 mg/kg) impaired the performance of mice in the rotarod, chimney and horizontal wire tests, and reduced spontaneous locomotor activity of rats. Upon repeated administration the inhibitory effect of L-cycloserine on the activity of GABA-T and on seizures elicited by 3-MPA in mice increased. In contrast, the depressant action of L-cycloserine on motor performance and locomotion declined in subchronically-treated mice and rats. The levels of amino acids in brain after repeated administration did not differ markedly from those in acutely-treated mice. It is suggested that small doses of L-cycloserine, probably by increasing GABAergic inhibition, reduce hyperexcitability in the brain in acute- and subchronically-treated animals. Larger doses of L-cycloserine, possibly by inducing multiple neurochemical changes, evoke central depressant effects which diminish during subchronic treatment.