Scopolamine impairs the ability of parturient ewes to learn to recognise their lambs

Within a 4-h period after parturition, the ewe learns the odor of her lamb that will later allow recognition of her offspring from an alien lamb. This study investigated the involvement of the cholinergic system in this olfactory learning. At parturition and 2 h later, ewes received IM injections of saline (C group, n = 21), scopolamine methylbromide (METSCOP group, 100 μg/kg, n = 14) a peripherally acting muscarinic antagonist, a low dose of scopolamine hydrobromide (SCOP32 group, 32 μg/kg, n = 15) or a higher dose of scopolamine hydrobromide (SCOP100 group, 100 μg/kg, n = 18). Maternal behavior was observed at parturition and selective behavior was tested after 4 h of mother-young contact. No differences in maternal behavior at parturition were found between groups. By contrast, the proportion of ewes showing selectivity was significantly lower in the SCOP100 group (7/18) than in the METSCOP group (12/14, P = 0.01), SCOP32 group (12/15, P = 0.03), or C group (17/21, P = 0.01). In addition, saline-treated ewes, after having established their selective bond, received 100 μg/kg scopolamine and were again tested for selectivity 20 min later. Only one out of the 17 tested ewes failed to recognize their lambs after this treatment. These results indicate that intact central muscarinic transmission of the brain is required for the learning of individual lamb odor at parturition but not for the recall of this information. Received: 1 July 1996/Final version: 12 September 1996     

Training-dependent biphasic effects of corticosterone in memory formation for a passive avoidance task in chicks

This study investigates the functional role of corticosterone in memory formation for a passive avoidance task in the day-old chick. Whereas training chicks with a strong aversant results in an enduring memory, memory for a weak aversant which is only retained for a few hours (< 9 h) is facilitated by intracerebral corticosterone administration. We now report that only chicks trained on the strong task, a learning situation that results in a high percentage of chicks (around 80%) forming a long-term memory, showed increased post-training plasma corticosterone levels, whereas chicks trained on the weak task showed corticosterone values comparable to untrained chicks. We also questioned whether the effects of corticosterone on retention might be concentration dependent. In the weak task, intracerebral administration of 1 μg corticosterone facilitated retention, but a higher dose failed to induce this effect. However, in the strong task, corticosterone administration at doses of 1 and 5 μg produced an impairment in long-term retention for the avoidance response. These results support a crucial role of corticosterone release following training on the physiological mechanisms ensuring the transition from short- to long-term memory, and provide an animal learning model for the study of the mechanisms of action of a biphasic modulation of memory formation by acute corticosterone administration. Received: 24 October 1996 /Final version: 3 April 1997     

Non-response to citalopram in depressive patients: pharmacokinetic and clinical consequences of a fluvoxamine augmentation

The effect of comedication with fluvoxamine on the plasma concentrations of the enantiomers of citalopram and its metabolites in dextromethorphan/mephenytoin phenotyped patients pretreated with citalopram (CIT) was studied: seven female patients (45.1 ± 13.9 years) suffering from a major depressive episode [ICD-10: F _32.2 (n = 3 patients), F _33.2 (n = 2), F _32.10 (n = 1) or F _32.11 (n = 1)] , who were non-responders to a 3-week treatment with 40 mg/day CIT (From day-21 to day 0) (day 0: MADRS score ≥12), were comedicated for another 3 weeks with fluvoxamine (50 mg/day from day 1–7, 100 mg/day from day 14–21). All patients were extensive metabolizers of mephenytoin (CYP2C19) and dextromethorphan (CYP2D6), except one patient, who had a genetic deficiency of CYP2D6. There was a significant increase of the plasma concentrations of S- and R-citalopram from day 0 (27 ± 14 μg/l and 55 ± 23 μg/l, respectively) to day 21 (83 ± 38 μg/l and 98 ± 44 μg/l, respectively), after addition of fluvoxamine (P < 0.02, for each comparison), and the mean ratio S/R-citalopram increased from 0.48 to 0.84. S-Citalopram inhibits more potently 5-HT uptake than R-citalopram: therefore, fluvoxamine increases the pharmacologically more active S-citalopram with some stereoselectivity. According to a previous in vitro study, this pharmacokinetic interaction occurs on the level of CYP2C19, but also of CYP2D6 and CYP3A4 which, in contrast to CYP1A2, contribute to the N-demethylation of citalopram and which are stereoselectively inhibited by fluvoxamine. All but one patient showed clinical improvement by a decrease of the MADRS score by at least 50% and a final score ≤13 (mean ± SD: day 0:30.6 ± 9.2; day 21:11.0 ± 6.5). Some patients showed minor symptoms, such as nausea and tremor, but the combined treatment was generally well tolerated. Received: 29 May 1996 /Final version: 2 September 1996     

Relative efficacy of three different inhalers containing salbutamol in patients with asthma

Objective: To investigate the relative efficacy of three inhalers containing salbutamol: Turbuhaler (TBH), Rotahaler (RH) and Diskhaler (DH). Methods: A randomized, open, three-way crossover, cumulative dose response study was performed in 20 patients with asthma with mean forced expiratory volume in 1s (FEV₁) values of 60% of predicted (range 41–90%) and a 27% reversibility in FEV₁ (range 15–61%). Four doses of salbutamol were inhaled at 30-min intervals: 50 μg, 50 μg, 100 μg and 200 μg by TBH and 200 μg, 200 μg, 400 μg and 800 μg by both RH and DH. FEV₁ was measured at baseline and 25 min after each dose. Results: The increases in FEV₁ after the first doses (50 μg by TBH, 200 μg by RH and by DH) were not statistically significantly different (23.6%, 25.1% and 28%, respectively). Based on the parallel shift in the dose response curves, salbutamol TBH was calculated to be 2.4 times as potent as salbutamol RH (95% confidence interval 1.4–3.3) and 2.2 times as potent as salbutamol DH (90% CI 1.3–3.3). Additionally, during dosing with TBH, fewer patients experienced adverse events than during dosing with RH or DH. Conclusion: Turbuhaler is a twofold more efficient inhaler for salbutamol than Rotahaler or Diskhaler as measured by its bronchodilating effect. Received: 15 February 1996/Accepted in revised form: 16 February 1996     

Human cytochromes mediating N-demethylation of fluoxetine in vitro

Biotransformation of the selective serotonin reuptake inhibitor antidepressant, fluoxetine, to its principal metabolite, norfluoxetine, was evaluated in human liver microsomes and in microsomes from transfected cell lines expressing pure human cytochromes. In human liver microsomes, formation of norfluoxetine from R,S-fluoxetine was consistent with Michaelis-Menten kinetics (mean K_m = 33 μM), with evidence of substrate inhibition at high substrate concentrations in a number of cases. The reaction was minimally inhibited by coincubation with chemical probes inhibitory for P450-2D6 (quinidine), -1A2 (furafylline, α-naphthoflavone), and -2E1 (diethyldithiocarbamate). Substantial inhibition was produced by coincubation with sulfaphenazole (K_i = 2.8 μM), an inhibitory probe for P450-2C9, and by ketoconazole (K_i = 2.5 μM) and fluvoxamine (K_i = 5.2 μM). However, ketoconazole, relatively specific for P450-3A isoforms only at low concentrations, reduced norfluoxetine formation by only 20% at 1 μM, and triacetyloleandomycin (≥ 5 μM) reduced the velocity by only 20–25%. Microsomes from cDNA-transfected human lymphoblastoid cells containing human P450-2C9 produced substantial quantities of norfluoxetine when incubated with 100 μM fluoxetine. Smaller amounts of product were produced by P450-2C19 and -2D6, but no product was produced by P450-1A2, -2E1, or 3A4. Cytochrome P450-2C9 appears to be the principal human cytochrome mediating fluoxetine N-demethylation. P450-2C19 and -3A may make a further small contribution, but P450-2D6 is unlikely to make an important contribution. Received: 23 December 1996 / Final version: 4 March 1997     

Phenacetin O-deethylation by human liver microsomes in vitro: inhibition by chemical probes,SSRI antidepressants,nefazodone and venlafaxine

Biotransformation of phenacetin via O-deethylation to acetaminophen, an index reaction reflecting activity of Cytochrome P450-1A2, was studied in microsomal preparations from a series of human livers. Acetaminophen formation was consistent with a double Michaelis-Menten system, with low-K_m (mean K_m1 = 68 μM) and high-K_m (mean K_m2 = 7691 μM) components. The low-K_m enzyme accounted for an average of 96% of estimated intrinsic clearance, and was predicted to contribute more than 50% of net reaction velocity at phenacetin concentrations less than 2000 μM. Among index inhibitor probes, α-naphthoflavone was a highly potent inhibitor of the low-K_m enzyme (K_i1 = 0.013 μM); furafylline also was a moderately active inhibitor (K_i1 = 4.4 μM), but its inhibiting potency was increased by preincubation with microsomes. Ketoconazole was a relatively weak inhibitor (K_i1 = 32 μM); quinidine and cimetidine showed minimal inhibiting activity. Among six selective serotonin reuptake inhibitor (SSRI) antidepressants, fluvoxamine was a potent inhibitor of 1A2 (mean K_i1 = 0.24 μM). The other SSRIs were more than tenfold less potent. Mean K_i1 values were: fluoxetine, 4.4 μM; norfluoxetine, 15.9 μM; sertraline, 8.8 μM; desmethylsertraline, 9.5μM; paroxetine, 5.5 μM. The antidepressant nefazodone and four of its metabolites (meta-chloro-phenylpiperazine, two hydroxylated derivatives, and a triazoledione) were very weak inhibitors of P450-1A2. Venlafaxine and its O- and N-desmethyl metabolites showed minimal inhibitory activity. Received: 18 March 1996/Final version: 10 July 1996     

Comparison of the effects of venlafaxine, paroxetine and desipramine on the pupillary light reflex in man

Rationale: The time-course of the pupillary light reflex response is determined by the successive activation of the parasympathetic and sympathetic innervations of the iris, the latency and the amplitude reflecting parasympathetic and the recovery time mainly sympathetic activity. Objective: To compare the effects of single doses of three antidepressants (venlafaxine: serotonin/noradrenaline reuptake inhibitor, paroxetine: selective serotonin reuptake inhibitor, and desipramine: tricyclic antidepressant) on resting pupil diameter and the pupillary light reflex response. Methods: Fifteen healthy male volunteers participated in five weekly sessions, each of which was associated with one treatment (venlafaxine 75 mg or 150 mg, paroxetine 20 mg, desipramine 100 mg, or placebo) according to a double-blind, double-dummy, balanced, cross-over design. An infrared binocular television pupillometer was used for the recording of the resting pupil diameter and the pupillary light reflex in darkness, in previously dark-adapted eyes. Resting pupil diameter in darkness was recorded before and after treatment. The pupillary light reflex was elicited after treatment, with six light flashes (green, 565 nm peak wavelength) of 200 ms duration and of incremental illuminance (measured in the plane of the cornea): 3.0 × 10^–3, 8.5 × 10^–3, 2.5 × 10^–2, 7.0 × 10^–2, 0.18, 0.43 mW cm⁻². The parameters studied were: latency, amplitude and 75% recovery time. Results: Analyses of variance followed by post hoc tests (least significant difference test or Dunnett’s test; P < 0.05) revealed that both doses of venlafaxine produced a significant increase in resting pupil diameter, decrease in amplitude and shortening of the 75% recovery time of the light reflex response; venlafaxine 150 mg prolonged the latency, while the other treatments had no significant effects. Conclusions: The increase in resting pupil diameter could be indicative of parasympathetic inhibition and/or sympathetic activation. The shortening of the recovery time of the light reflex response is consistent with sympathetic potentiation resulting from noradrenaline uptake blockade in the iris. The prolongation of the latency and decrease of the amplitude of the light reflex response are indicative of a parasympatholytic effect of venlafaxine. However, as venlafaxine has negligible affinity for muscarinic cholinoceptors, this effect cannot be attributed to the blockade of cholinoceptors in the iris. A possible explanation for this finding is that it reflects a central rather than a peripheral effect of the drug: the blockade of noradrenaline uptake in the brain could lead to the potentiation of the noradrenergic inhibition of central parasympathetic (Edinger-Westphal) neurones. These results demonstrate the ability of therapeutically relevant single doses of venlafaxine to potentiate noradrenergic responses in man, consistent with the blockade of noradrenaline uptake. Received: 29 July 1998/Final version: 17 November 1998     

Benzo(a)pyrenediolepoxide-hemoglobin adducts and 3-hydroxy-benzo(a)pyrene urinary excretion profiles in rats subchronically exposed to benzo(a)pyrene

 The time profiles of benzo(a)pyrenediolepoxide (BaPDE)-hemoglobin (Hb) adduct formation and 3-hydroxybenzo(a)pyrene (3-OHBaP) urinary excretion were studied in male Sprague-Dawley rats exposed to daily benzo(a)pyrene (BaP) intraperitoneal doses of 1.25, 6.25, and 31.25 μmol/kg administered Tuesday to Friday for 4 consecutive weeks. Blood was withdrawn weekly, on Tuesdays, prior to dosing. Twenty four hour urine samples were collected on Mondays (following 72 h without treatment) and Thursdays. Analytes were quantified by high performance liquid chromatography (HPLC)/fluorescence. Exposure to BaP resulted in the accumulation of BaPDE-Hb adducts, reaching an average of 1.2±0.3, 8.3±1.9, and 38.2±6.1 pmol/g Hb for the 1.25, 6.25, and 31.25 μmol/kg per day doses after 4 weeks of treatment. The expected saw tooth excretion profile of 3-OHBaP was observed, with peaks on Thursdays and troughs on Mondays, and showed a progressive rise on both Mondays and Thursdays. Increase in Monday values with time suggested a possible increase in BaP body burden during exposure. To verify this aspect further, the urinary excretion kinetic of 3-OHBaP following acute intraperitoneal dosing (31.25 μmol/kg) was determined. Urine samples were collected at frequent timed intervals for up to 164 h post-dosing. Two-step elimination was observed, the second step having a half-life of 25 h, presumably linked to the slow release of BaP accumulated in fatty tissues upon repeated treatment. Therefore, it seems that 1) BaPDE-Hb adducts are good indicators of repeated exposure, 2) the difference between pre- and post-exposure 3-OHBaP urinary excretion gives a measure of recent exposure, and 3) excretion levels of this latter metabolite after a non-exposure period of sufficient duration, to allow elimination of the bulk BaP from the last dose, could reflect BaP body burden. Received: 3 November 1994/Accepted: 11 January 1995     

Discriminative stimulus effects of S(−)–methcathinone (CAT): a potent stimulant drug of abuse

Methcathinone (“CAT”) is a CNS stimulant that is a very significant drug of abuse in the former Soviet Union. It has also appeared on the clandestine market in the United States and has been recently classified as a Schedule I substance. In the present study, S(−)-methcathinone [S(−)-CAT, 0.50 mg/kg, IP] was employed as the training drug in a two-lever drug discrimination task in rats. Once established, the S(−)-CAT stimulus was shown to have a rapid onset to action (within 5 min) and a duration of effect of approximately 60–90 min. In tests of stimulus generalization (substitution), the S(−)-CAT (ED₅₀ = 0.11 mg/kg) stimulus generalized to S(+)-methamphetamine (ED₅₀ = 0.17 mg/kg), S(−)-cathinone (ED₅₀ =  0.19 mg/kg), S(+)-amphetamine (ED₅₀ = 0.23 mg/kg), aminorex (ED₅₀ = 0.27 mg/kg), (±)-CAT (ED₅₀ = 0.25 mg/kg), (±)-cathinone (ED₅₀ = 0.41 mg/kg), R(+)-CAT (ED₅₀ = 0.43 mg/kg), cis-4-methylaminorex (ED₅₀ = 0.49 mg/kg), methylphenidate (ED₅₀ = 0.83 mg/kg), and cocaine (ED₅₀ = 1.47 mg/kg). S(−)-CAT-stimulus generalization did not occur to fenfluramine, a structurally related nonstimulant anorectic. Lastly, haloperidol (AD₅₀ = 0.18 mg/kg), a dopamine receptor antagonist, potently antagonized the S(−)-CAT stimulus. It is concluded that S(−)-methcathinone is a very potent CNS stimulant, which appears to produce its stimulus effect, at least in part, via a dopaminergic mechanism. Received: 4 August 1997/Final version: 27 March 1998     

The cholecystokinin-B receptor antagonist CI-988 failed to affect CCK-4 induced symptoms in panic disorder patients

The effects of the cholecystokinin-B (CCK-B) receptor antagonist CI-988 on symptoms elicited by the cholecystokinin tetrapeptide (CCK₄) were studied in DSM-IIIR patients with panic disorder. The study employed a double-blind, two-period incomplete block design. Patients (n = 14) received two different dosages of CI-988 (50 mg or 100 mg) or placebo 2 h prior to an IV bolus injection of CCK₄ (20 μg) on two separate occasions. The primary efficacy parameter was the total intensity score on the Panic Symptoms Scale (PSS). Secondary parameters were the number of panic symptoms, time to and occurrence of the first panic symptoms, duration of symptoms, intensity of apprehension and the percentage of patients who did not have a panic attack. The PSS failed to show a statistically significant treatment effect on any of these outcome measures. The average panic rate was 50%, 14.3% and 37.5% after placebo, 50 and 100 mg CI-988, respectively. The differences in panic rate were not statistically significant. The results of this study suggest that CI-988 in doses up to 100 mg is not effective in reducing symptoms of panic anxiety induced by CCK₄. Received: 13 May 1996/Final version: 27 September 1996     

Dichloromethane as an inhibitor of cytochrome c oxidase in different tissues of rats

 Based on the metabolism of dichloromethane (DCM) to carbon monoxide (CO), a process mediated by cytochrome P-4502E1 (CYP2E1), cytochrome c oxidase activity was determined in different tissues of rats after DCM exposure. It is likely that binding of CO to cytochrome c oxidase is significant at low carboxyhemoglobin levels, because intracellular effects of CO depend on CO partial pressures in the tissues. Two methods of exposure were used: (1) administration of DCM, 3.1, 6.2, and 12.4 mmol/kg p.o. in Oleum pedum tauri, 10% (v/v), producing a maximum of 10% COHb 6 h after gavage, and (2) accidental scenario, i.e. rats were exposed nose-only to DCM, 250 000 ppm for 20 s, producing 3–4% COHb after 2 h. Cytochrome c oxidase activity was reduced 6 h after the high oral DCM dose in brain, lung, and skeletal muscle by 28–42% and 20 min after inhalative uptake of DCM in the brain, liver, kidney, and skeletal muscle by 42–51%. COHb formation due to DCM, 6.2 mmol/kg p.o., was completely prevented after treatment of rats with the mechanism-based inhibitor of CYP2E1, diethyldithiocarbamate (DDTC), using an oral dose of 32 μmol/kg. The decrease in cytochrome c oxidase activity after exposure to DCM was not evident in rats treated with this dose of DDTC. Therefore, it seems that the effect of DCM is produced by the DCM metabolite CO. Received: 12 July 1994/Accepted: 5 September 1994     

Activation of acetylcholine receptors and 5-HT2 receptors have additive effects in the suppression of neocortical high-voltage spindles in aged rats

We investigated if activation of the muscarinic or nicotinic acetylcholine receptors and serotonin (5-hydroxytryptamine; 5-HT) subtype 2 receptors would have additive or synergistic effects on the suppression of thalamocortically generated rhythmic neocortical high-voltage spindles (HVSs) in aged rats. The 5-HT₂ receptor antagonist, ketanserin, at a moderate dose (5 mg/kg) prevented the ability of a muscarinic acetylcholine receptor agonist, (oxotremorine 0.1 mg/kg), and a nicotinic acetylcholine receptor agonist (nicotine 0.1 mg/kg), to decrease HVSs. At a higher dose (20 mg/kg), ketanserin completely blocked the decrease in HVSs produced by moderate doses of muscarinic acetylcholine receptor agonists (pilocarpine 1 mg/kg and oxotremorine 0.1 mg/kg), and by a high dose of nicotine (0.3 mg/kg), though not that produced by high doses of pilocarpine (3 mg/kg) and oxotremorine (0.9 mg/kg). The ability of a 5-HT₂ receptor agonist, (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (0.1–1.0 mg/kg), to suppress HVSs was non-significantly modulated by the nicotinic acetylcholine receptor antagonist, mecamylamine (1–15 mg/kg), and the muscarinic acetylcholine receptor antagonist, scopolamine (0.03–0.3 mg/kg). The effects of the drugs on behavioral activity could be separated from their effects on HVSs. The results suggest that activation of the muscarinic or nicotinic acetylcholine receptors plus 5-HT₂ receptors has additive effects in the suppression of thalamocortical oscillations in aged rats. Received: 2 November 1996 /Final version: 7 February 1997     

The behavioural effects of corticotropin-releasing factor-related peptides in rats

The present study determined the behavioural effects of the corticotropin releasing factor (CRF)-related peptides, human/rat CRF (h/rCRF), ovine CRF (oCRF), sauvagine (SAUV), urotensin I (UT) and the recently discovered neuropeptide, rat urocortin (rUCN). All of the peptides dose-dependently increased motor activity in a familiar environment and reduced feeding in hungry rats. There was no apparent relationship between potency/affinity at CRF₂ receptors and effects in these two tests. In a comparison of h/rCRF and rUCN upon discrete spontaneous behaviours, both peptides (3.0 μg ICV) increased activity and grooming, induced a fore-paw tremor and reduced the incidence of motionlessness. However, h/rCRF reduced motionlessness to a greater extent and was a more potent inducer of defaecation, weight loss, oral movements and fore-paw tremor than rUCN. In the elevated X maze, both h/rCRF and rUCN (1.0 μg ICV) had anxiogenic-like effects upon behaviour. In contrast, h/rCRF (1.0 μg ICV), but not rUCN (1.0–10 μg ICV) increased the startle response to an acoustic stimulus. In summary, all the CRF-related peptides increased motor activity and reduced feeding in rats in a similar manner and both rUCN and h/rCRF induced anxiogenesis. However, there were some behavioural differences between rUCN and h/rCRF which require further study. Further pharmacological investigation of the role of CRF receptor subtypes requires the use of subtype selective antagonists. Received: 8 January 1997/Final version: 24 January 1998     

Effects of ketoprofen and ibuprofen on platelet aggregation and prostanoid formation in man

Objective: In the present randomized, four-way crossover study we determined the effects of two oral doses each of ketoprofen and ibuprofen on platelet aggregation and prostanoid formation in man. Methods: Twelve healthy female volunteers received for 2 consecutive days, followed by a 5-day drug-free interval, one of the following: ketoprofen 3 × 25 mg per day, or ketoprofen 3 × 50 mg per day, or ibuprofen 3 × 200 mg per day, or ibuprofen 3 × 400 mg per day. The response criteria, determined before and on the 2nd day of each treatment period, were: maximal platelet aggregation in response to 1.0 mmol ⋅ l^–1 arachidonic acid measured by the method of Born and Cross, thromboxane B₂ (TXB₂) concentration in platelet-rich plasma after aggregation measured by radioimmunoassay, and PGE-M, the index metabolite of total body prostaglandin E₂ (PGE₂) production, assessed by gas chromatography/tandem mass spectrometry using ¹⁸O₂-PGE-M as internal standard. Results: Platelet aggregation was significantly reduced by ketoprofen 3 × 25 mg per day (−57%) and ketoprofen 3 × 50 mg per day (−85%) as compared to control, whereas ibuprofen 3 × 200 mg per day (−3%) and ibuprofen 3 × 400 mg per day (−22%) had no significant effects. TXB₂ synthesis was significantly decreased by ketoprofen 3 × 25 mg per day (−72%), ketoprofen 3 × 50 mg per day (−97%) and ibuprofen 3 × 400 mg per day (−48%) as compared to control; ibuprofen 3 × 200 mg per day did not reduce TXB₂ formation significantly (−23%). All four treatments reduced 24-h urinary excretion of PGE-M significantly in the range of−39% (ketoprofen 3 × 25 mg per day) to −53% (ibuprofen 3 × 400 mg per day) without significant differences between treatments. Conclusion: Our data show that both ketoprofen dosages were more effective in inhibition of platelet aggregation and platelet thromboxane synthesis than ibuprofen in low or high dosage. Total body synthesis of the E-prostaglandins was inhibited by all drug schedules without significant differences between treatments. Received: 26 January 1996;/Accepted in revised form: 11 June 1996     

The discriminative stimulus properties of cocaine: effects of microinfusion of cocaine, a 5-HT1A agonist or antagonist, into the ventral tegmental area

 Serotonin (5-HT) afferents may modulate the dopamine mesoaccumbens circuit, which has been shown to be critically involved in the locomotor stimulatory, discriminative stimulus, and rewarding properties of cocaine. In the present study, we investigated the role of 5-HT_1A receptors in the ventral tegmental area (VTA) in mediating the discriminative stimulus effects of cocaine. Male Sprague-Dawley rats were trained to discriminate cocaine (10 mg/kg) from saline in a two-lever, water-reinforced FR 20 task. After acquiring the cocaine-saline discrimination, rats were stereotaxically implanted with bilateral guide cannulae into the VTA or adjacent substantia nigra reticulata (SNR). Intraperitoneal administration of cocaine (0.625–10 mg/kg) produced a dose-related increase in drug-lever responding. Both intra-VTA and intra-SNR infusion of cocaine (12.5–50 μg/0.5 μl/side) engendered primarily saline-like responding. Microinjection of the 5-HT_1A agonist 8-hydroxy-2-(di-N-propylamino) tetralin (DPAT; 0.1–10 μg/0.5 μl/side) or the 5-HT_1A antagonist WAY 100635 (0.01–1.0 μg/0.5 μl/side) into the VTA or SNR did not substitute for the systemic cocaine cue. Further, intra-VTA or intra-SNR DPAT or WAY 100635 in combination with systemic doses of cocaine did not alter (i.e., attenuate or potentiate) the systemic cocaine cue. Overall, these data indicate that 5-HT_1A receptors in the VTA do not mediate or modulate the discriminative stimulus effects of cocaine in the rat. Received: 15 April 1997 / Final version: 21 October 1997     

Comparison of the pharmacodynamic effects of deflazacort and prednisolone in healthy subjects

  Objective: Deflazacort, a synthetic oxazoline derivative of prednisolone, has been suggested as having major advantages over other glucocorticoids, as it is claimed to cause fewer adverse effects at equivalent antiinflammatory potency. The assumed equipotency ratio of deflazacort versus other glucocorticoids is critical for this assumption. Methods: In a randomized cross-over study we compared the acute effects of deflazacort and prednisolone on serum cortisol, osteocalcin, insulin and blood cells (eosinophils and lymphocytes) in normal subjects. On seven occasions separated by a wash out period ≥ 1 week all participants received placebo, prednisolone (8 mg, 20 mg, 40 mg) and deflazacort (12 mg, 30 mg, 60 mg). The medication was given orally at 20.00 h as a single dose. Blood was collected at 8.00 h before and after each medication. Log (dose) response relationships were calculated and were used to compare the drugs. Results: The following equipotent dose ratios (mg deflazacort: mg prednisolone) were found: osteocalcin suppression 1.54, cortisol suppression 2.27, suppression of eosinophils 1.14 and lymphocytes 2.77. As parallelism between regression curves was rejected, equipotency could not be calculated for insulin. In 3 subjects even the highest dose of deflazacort failed to suppress serum cortisol. Conclusion: Our study highlights the difficulties of establishing equipotency ratios for glucocorticoids. It casts doubts on the generally assumed equipotency dose ratio of deflazacort vs prednisolone, as both for cortisol and lymphocytes the 95% CI was > 1.2. Thus, reduced adverse effects during deflazacort therapy may be a consequence of lower effective glucocorticoid dosage. Received: 11 December 1995 /Accepted in revised form: 16 March 1996     

A comparison of bd and tid dose regimens of quetiapine (Seroquel) in the treatment of schizophrenia

Quetiapine (Seroquel, ICI 204,636) is an atypical antipsychotic that is effective in the treatment of both positive and negative symptoms of schizophrenia, and has a low propensity to cause extrapyramidal symptoms. The compound has a relatively short plasma elimination half-life (approximately 7 h). However, since dopamine D₂ receptor occupancies correlate poorly with plasma concentrations of antipsychotics, plasma elimination half-life may not predict either duration of clinical effect or dosing frequency. Accordingly, the efficacy and tolerability of three dosing regimens (450 mg/day given in two or three divided doses daily, and 50 mg/day given twice daily) were compared in a 6-week, double-blind, randomized, multicentre, parallel-group study. The study recruited hospitalized men and women aged 18–65 years meeting DSM-IIIR criteria for acute exacerbation of chronic or subchronic schizophrenia. Six hundred and eighteen patients were randomly assigned to treatment with quetiapine 150 mg tid (n = 209), 225 mg bd (n = 200), or a comparator dose of 25 mg bd (n = 209). At day 42, the last day of randomized treatment and the primary timepoint for efficacy, quetiapine 450 mg/day was more effective than 50 mg/day: 225 mg bd was consistently superior to 25 mg bd in all measures of efficacy (total BPRS, P = 0.006; CGI severity, CGI improvement and SANS, P < 0.03), and 150 mg tid was statistically significantly superior to 25 mg bd with respect to BPRS total score (P = 0.05). The 225 mg bd and 150 mg tid groups were not significantly different from each other with respect to any efficacy measure. Quetiapine was generally well tolerated. Extrapyramidal symptom (EPS) adverse events were generally rare, and occurred with similar frequencies in the two 450 mg/day groups. Quetiapine was not associated with sustained increases in plasma prolactin at any dose. These data support the atypical profile developed from preclinical studies and show that quetiapine is an effective, well tolerated antipsychotic that can be given twice daily. Received: 16 May 1997/Final version: 13 October 1997     

Antidepressant treatment in helpless rats: effect on the electrophysiological activity of raphe dorsalis serotonergic neurons

Chronic treatment with antidepressants renders serotonergic neuronal firing less sensitive to the inhibitory effect of serotonin (5-HT) reuptake blockers in the rat, and this has been considered as a major correlate of the therapeutic action of these drugs. We investigated whether the same mechanisms could be evidenced in an experimental model of depression, the learned helplessness paradigm. Rats rendered helpless by a single session of inescapable electrical footshocks exhibit, for several days, depression-like behavioural deficits which can be reversed by sub-chronic, but not acute, treatment with antidepressants. Recording of serotonergic neurons in the dorsal raphe nucleus revealed that, under baseline conditions, the spontaneous firing was similar in helpless rats and in non-helpless controls. However, neurons in the former group exhibited an enhanced sensitivity to the inhibitory action of the 5-HT reuptake blocker, citalopram (ED₅₀ = 0.18 ± 0.02 mg/kg IV in helpless rats versus 0.27 ± 0.03 mg/kg IV in controls, P < 0.05). Treatment with zimeldine during 3 consecutive days induced in both helpless and control rats, a decrease in the inhibitory response of serotonergic neurons to the citalopram challenge, which resulted in a normalization of the neuronal reactivity in the helpless group (ED₅₀ = 0.31 ± 0.03 mg/kg IV). Since this adaptive phenomenon parallels the behavioural improvement induced by the repeated administration of zimeldine and other antidepressants in helpless rats, it might be considered as a crucial event in the mechanism of therapeutic action of these drugs. Received: 14 August 1996 / Final version: 4 November 1996     

Effects of acute and chronic administration of olanzapine in comparison to clozapine and haloperidol on extracellular recordings of substantia nigra reticulata neurons in the rat brain

Rationale: Previously, we have shown that the atypical antipsychotics clozapine and risperidone, unlike haloperidol, decreased the firing rate of substantia nigra reticulata (SNR) neurons. As the SNR receives substantial input from the striatum, an area where motoric side-effects of antipsychotics are thought to be mediated, the SNR might be an interesting brain structure with regard to motor side-effects. Objective: The newly developed atypical antipsychotic olanzapine was studied for its effects on the firing rate of SNR cells. In addition, to gain insight in the implications of our experimental setup for clinical use, responses upon clozapine, olanzapine and haloperidol were studied after chronic treatment. Methods: In chloralhydrate-anaesthetized male Wistar rats, extracellular recordings were made from SNR neurons upon intravenously (IV) administered cumulative doses of the antipsychotics. Naive rats and rats that were subcutaneously (SC) injected for 21 days with an antipsychotic were used. Results: Olanzapine (50–1600 mg/kg; IV), significantly inhibited the firing rate of the SNR neurons. Upon 21 days of treatment with a daily SC injection of 20 mg/kg clozapine, the challenge on day 22 with cumulative injections of clozapine (200–6400 mg/kg; IV) significantly inhibited the firing rate of the SNR neurons. Olanzapine (50–1600 mg/kg; IV) also significantly inhibited the SNR activity when pretreated with olanzapine in an SC administered dose of 1 mg/kg, but not 5 mg/kg. Haloperidol (12.5–800 μg/kg; IV) did not significantly affect the SNR activity in rats pretreated with SC administered 0.5 mg/kg haloperidol. Conclusions: Upon acute and chronic administration of clozapine and olanzapine versus haloperidol, differential effects on SNR neuronal firing could be obtained. The experimental setup seem to be valid for further studies into the mechanism of action of typical versus (relatively low doses of) atypical antipsychotics. The implications of the inhibitory effect of atypical antipsychotics on the SNR firing rate are presently unknown, but could be associated with the lower propensity to induced motoric side-effects. On the other hand, the SNR activity might also reflect non-motoric activity possibly related to negative symptoms. Received: 11 December 1998/Final version: 20 January 1999     

Assessment of primary neuronal culture as a model for soman-induced neurotoxicity and effectiveness of memantine as a neuroprotective drug

 An in vitro mammalian model neuronal system to evaluate the intrinsic toxicity of soman and other neurotoxicants as well as the efficacy of potential countermeasures was investigated. The link between soman toxicity, glutamate hyperactivity and neuronal death in the central nervous system was investigated in primary dissociated cell cultures from rat hippocampus and cerebral neocortex. Exposure of cortical or hippocampal neurons to glutamate for 30 min produced neuronal death in almost 80% of the cells examined at 24 h. Hippocampal neurons exposed to soman for 15–120 min at 0.1 μM concentration caused almost complete inhibition (≥90%) of acetylcholinesterase but failed to show any evidence of effects on cell viability, indicating a lack of direct cytotoxicity by this agent. Acetylcholine (ACh, 0.1 mM), alone or in combination with soman, did not potentiate glutamate toxicity in hippocampal neurons. Memantine, a drug used for the therapy of Parkinson’s disease, spasticity and other brain disorders, significantly protected hippocampal and cortical neurons in culture against glutamate and N-methyl-D-aspartate (NMDA) excitotoxicity. In rats a single dose of memantine (18 mg/kg) administered 1 h prior to a s.c. injection of a 0.9 LD₅₀ dose of soman reduced the severity of convulsions and increased survival. Survival, however, was accompanied by neuronal loss in the frontal cortex, piriform cortex and hippocampus. Received: 2 May 1994 / Accepted: 9 November 1994