PHNO, a selective dopamine D2 receptor agonist, does not reduce prepulse inhibition of the startle reflex in rats

RATIONALE: Dopamine agonists nonselective for dopamine receptor subtypes, such as apomorphine, reduce prepulse inhibition of the startle reflex. It has been suggested that either D2 or D3 dopamine receptors mediate this action of apomorphine. OBJECTIVE: The present study investigated whether a selective D2 agonist with relatively low affinity for D3 receptors can reduce prepulse inhibition. METHODS: Rats (n=48) were treated with vehicle or one of three doses ( 15, 30 or 60 microg/kg, s.c.) of the specific dopamine D2 receptor agonist (+)-4-propyl-9-hydroxynaphthoxazine (PHNO) for 11 days. On days 1, 6 and 11 of treatment, the rats (n=12 in each group) were tested for their acoustic startle reflexes (105-dB, 40-ms white noise) and for prepulse inhibition (5-kHz tone, 5 dB above a 65 dB background white noise). Prepulses were presented with a range of stimulus onset asynchronies (SOAs: 5-160 ms) or lead times between the onset of the prepulse and the onset of the startle stimulus. In a second experiment, two groups of rats (n=10 in each group) were tested in a similar manner after vehicle or apomorphine (0.8 mg/kg, s.c.) to verify the sensitivity of the present procedure to agonist-induced reductions in prepulse inhibition. RESULTS: At doses that increased motor activity, PHNO increased prepulse inhibition at SOAs less than 80 ms and had no effect on prepulse inhibition at SOAs of 80 ms or above. However, all doses decreased startle amplitudes on trials in which only the startle-eliciting stimulus was presented. Apomorphine reduced prepulse inhibition under the same conditions. CONCLUSIONS: These findings with PHNO are in contrast to the less-specific D2 agonist, quinpirole, which has been reported to decrease prepulse inhibition. It is concluded that activation of D2 dopamine receptors alone is not sufficient to attenuate prepulse inhibition of the startle reflex.     

Quinelorane, a dopamine D3/D2 receptor agonist, reduces prepulse inhibition of startle and ventral pallidal GABA efflux: time course studies

Startle is inhibited when the startling stimulus is preceded 30–300 ms by a weak prepulse. Prepulse inhibition (PPI), an operational measure of sensorimotor gating, is deficient in schizophrenia patients, and reduced in rats and humans by dopamine agonists. The neural basis for the PPI-disruptive effects of dopamine agonists in rats is studied to understand neural circuitry regulating PPI and its deficits in schizophrenia. Existing data suggest that ventral pallidal (VP) GABAergic transmission regulates PPI and its disruption by dopamine agonists. We measured changes in VP GABA efflux and PPI in rats in response to the D2/D3 agonist, quinelorane. Wistar rats were administered quinelorane (vehicle, 0.003 or 0.01 mg/kg). In some rats, VP dialysate was analyzed for GABA content. In others, PPI was assessed using 120 dB(A) startle pulses and prepulses 10 dB over a 70 dB(A) background. Quinelorane reduced GABA efflux, with significant effects for 0.01 but not 0.003 mg/kg, persisting for at least 100 min. Quinelorane reduced PPI for 50 min, an effect significant for both the 0.003 (p < 0.05) and 0.01 mg/kg doses (p < 0.015). Differences in time course and dose sensitivity of quinelorane effects on VP GABA efflux and PPI are discussed.     

Using prepulse inhibition to detect functional D3 receptor antagonism: Effects of WC10 and WC44

Prepulse inhibition of startle (PPI) is an operational measure of sensorimotor gating that is impaired in schizophrenia. Treatment with mixed dopamine D2/D3 antagonists diminishes schizophrenia symptoms, and opposes dopamine agonist-induced PPI deficits in rats. There are reasons to believe that functional D3 receptor antagonists might offer more favorable therapeutic profiles compared to current antipsychotics. However, D3-related drug discovery is hampered by the absence of assays sensitive to D3-mediated (antipsychotic) properties in vivo. Here, we characterized two putative D3-active compounds - WC10 and WC44 - in a PPI-based screening assay, comparing the sensitivity of test compounds to oppose PPI deficits induced by the mixed D1/D2-like agonist apomorphine vs. the preferential D3 agonist pramipexole in rats. WC10, WC44 (0, 1, 3, 10 mg/kg, each), and the preferential D2 antagonist L741,626 (0, 1 mg/kg) were studied, in combination with apomorphine (0, 0.5 mg/kg), or pramipexole (0, 1 mg/kg). L741,626 prevented apomorphine-, but not pramipexole-induced PPI deficits. WC10, but not WC44, prevented apomorphine-induced PPI deficits; both compounds opposed pramipexole-induced PPI deficits, suggesting functional D3 and D1/D2 antagonist profiles for WC10, and functional D3 receptor antagonism for WC44. This assay may be valuable for detecting predominantly D3 vs. D2 receptor-linked mechanisms of action in vivo.     

Parametric approaches towards understanding the effects of the preferential D3 receptor agonist pramipexole on prepulse inhibition in rats

The preferential dopamine D3 receptor agonist pramipexole (PRA) disrupts prepulse inhibition (PPI) of acoustic startle, an operational measure of sensorimotor gating, in rats. Drug effects on PPI are sensitive to numerous experimental variables; proceeding with in-depth analyses of drug effects without a clear understanding of these variables is inefficient. The present studies characterized the impact on PRA-induced PPI deficits by a range of experimental parameters. As shown previously, PRA reduced both PPI and startle magnitude beginning 5-15 min post-injection; PRA effects on PPI were statistically significant through 35 min post-injection, while those on startle magnitude were still significant 65 min post-injection. PRA-induced PPI deficits were evident under conditions that matched startle magnitude in vehicle and PRA conditions and were independent of PRA-induced changes in prepulse-elicited motor activity. Additionally, PRA-induced PPI deficits did not differ significantly between uni- vs. cross-modal stimuli or between male vs. female rats, with no robust effect of estrous phase in females. These findings demonstrate that PRA effects on PPI are observed across several different experimental conditions and are dissociable from changes in startle magnitude or prepulse-elicited responses. Recommendations are made regarding “optimal” experimental conditions for studying the neurobiology of PRA-induced changes in PPI in rats.     

Functional behavioral homology between rat 5-HT1B and guinea pig 5-HT1D receptors in the modulation of prepulse inhibition of startle

The serotonin (5-HT) 1B receptor in rats and mice appears to be homologous to the 5-HT_1D receptor found in other mammals, such as guinea pigs and humans. The present series of experiments explored the functional similarity between the rat 5-HT_1B receptor and the guinea pig 5-HT_1D receptor on two behavioral measures known to be influenced by 5-HT_1B receptor manipulations in rats: prepulse inhibition of the startle response (PPI) and locomotor activity. Because the 5-HT_1B agonist RU 24969 disrupts PPI and stimulates locomotor behavior in rats, it was predicted that the 5-HT_1D agonist, SDZ 219–964, would demonstrate a similar behavioral profile in guinea pigs. In support of this hypothesis, SDZ 219–964 was found to disrupt PPI dose-dependently (1.0 and 2.0 mg/kg) without significantly affecting startle amplitude and to increase locomotor activity (0.5–2.0 mg/kg) in guinea pigs. In guinea pigs, RU 24969 failed to affect PPI, although it did increase locomotor activity, indicating that RU 24969 may have activity at the 5-HT_1D receptor. As expected, RU 24969 in rats disrupted PPI (2.5 and 5.0 mg/kg) and significantly increased locomotor activity (1.25–5.0 mg/kg). In rats, however, SDZ 219–964 had generalized, stimulatory effects on startle reactivity, without independent effects on PPI or locomotor activity. The spatial patterns of locomotion exhibited by guinea pigs treated with SDZ 219–964 versus those of rats treated with RU 24969 demonstrate important qualitative differences in structure, indicating that the neural substrates subserving these effects may be different. It is concluded that a functional similarity exists between 5-HT_1D and 5-HT_1B receptors with regard to the modulation of sensorimotor inhibition and, to a lesser extent, locomotor activity.     

Effects of dopamine D1-like and D2-like agonists on cocaine self-administration in rhesus monkeys: rapid assessment of cocaine dose-effect functions

Rationale: The reinforcing effects of cocaine have been most compellingly related to its action as an indirect dopamine agonist. Although it is generally believed that both D_1-like and D_2-like receptor mechanisms may be involved, recent studies suggest that D_1-like and D_2-like agonists have differing profiles of cocaine-related actions. Objective: To develop a procedure for rapid assessment of complete dose–effect functions for cocaine self-administration in rhesus monkeys and to compare the effects of D_1-like and D_2-like agonists on cocaine self-administration using this procedure. Methods: Responding was maintained by various doses of cocaine or by food under a multiple-component schedule [fixed ratio (FR) 30; time out period (TO) 10 s] in 2-h sessions. After responding stabilized, the effects of pretreatment with D_1-like and D_2-like agonists (administered i.m., 10 min or 30 min prior to the session) were assessed. Results: Complete inverted U-shaped dose–effect functions for cocaine self-administration were obtained in all five rhesus monkeys trained with the rapid assessment procedure. Both the position and shape of the cocaine dose– effect function remained stable in repeated assessments, and levels of responding were controlled by the unit dose of cocaine rather than by other variables (e.g., infusion duration and volume) that were used to vary the cocaine dose. Pretreatment with the D_1-like agonists SKF 82958 (0.32–1.8 mg/kg) and R-6-Br-APB (0.1–1.0 mg/kg) produced downward shifts in the cocaine dose–effect function at doses that also markedly decreased food-maintained responding. In contrast, pretreatment with the D_2-like agonists quinelorane (0.001–0.01 mg/kg) and 7-OH-DPAT (0.01–0.10 mg/kg) shifted the cocaine dose–effect function to the left. D_2-like agonists also increased responding maintained by the cocaine-associated cue lights alone, and moderately decreased food-maintained responding. Conclusions: The results suggest that D_1-like and D_2-like agonists produce qualitatively different effects on cocaine self-administration that may influence their usefulness for the treatment of cocaine abuse and dependence. Received: 20 March 1999 / Final version: 10 August 1999     

Serotonin1B receptor modulation of startle reactivity, habituation, and prepulse inhibition in wild-type and serotonin1B knockout mice

 Two operational measures of central information processing mechanisms are habituation and prepulse inhibition (PPI) of the startle response. Both measures can be assessed reliably in humans and other animals, and have been shown to be deficient in patients with schizophrenia. The three present experiments assessed the involvement of the serotonin_1B (5-HT_1B) receptor in modulating startle reactivity, habituation, and PPI by comparing 5-HT_1B receptor gene knockout (5-HT_1B knockout) with wild-type 129/Sv mice. In experiment 1, female mice received saline, 2.0 mg/kg 5-methoxy-3(1,2,3,6)tetrahydropyridin-4-yl-1H-indole (RU24969), a 5-HT_1A/1B agonist, and 1.0 mg/kg 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT), a selective 5-HT_1A agonist. Female mice received saline, 10.0 mg/kg RU24969, and 5.0 mg/kg 8-OH-DPAT in experiment 2, and male mice received saline, 10.0 mg/kg RU24969, and 5.0 mg/kg 8-OH-DPAT in experiment 3. All three studies used identical within-subjects designs. Two phenotypic differences were observed following saline treatment: 5-HT_1B knockout mice consistently exhibited a small increase in PPI that achieved significance in experiment 1; and 5-HT_1B knockout male mice exhibited robust decreases in startle reactivity. Habituation was disrupted consistently by RU24969 in wild-type but not in 5-HT_1B knockout mice, while 8-OH-DPAT had no effect on habituation. Consistent with the phenotypic difference in PPI, the high dose of RU24969 significantly and consistently reduced PPI in wild-type but not in 5-HT_1B knockout mice. 8-OH-DPAT increased PPI in both wild-type and 5-HT_1B knockout mice in every experiment. These findings suggest that 5-HT_1B receptors modulate startle reactivity, habituation, and PPI in mice. Additionally, a potential species difference may exist in the behavioral effects of 5-HT_1A receptor activation on PPI. Received: 24 December 1996 / Final version: 10 March 1997     

Blockage of histamine H1 receptor attenuates social isolation-induced disruption of prepulse inhibition: a study in H1 receptor gene knockout mice

Rationale Histaminergic neurotransmission has been implicated in the pathophysiology of stress-related psychiatric diseases. Although several atypical antipsychotics are potent H1 anagonists, the clinical significance of interaction between atypical antipsychotics and H1 receptors is still unknown.Objective In this study, we investigated the effects of H1 receptors blockage on social isolation-induced behavioral changes in H1 receptor gene knockout (H1KO) mice and their wild-type (WT) mice.Methods Both H1KO and their WT mice were subjected to 4-week social isolation rearing after weaning (21 postnatal days). After the 4-week isolation period, mice behavioral changes were evaluated using behavioral tests.Results Locomotor activity in home cages was significantly lower in isolation-reared WT mice than in socially reared WT mice. However, no change in locomotor activity was observed between socially and isolation-reared H1KO mice. Social isolation significantly impaired prepulse inhibition (PPI) of startle response in WT mice but not in H1KO mice. In addition, social isolation significantly impaired spatial learning and memory in WT mice but not in H1KO mice. Furthermore, H1KO mice treated with methamphetamine (METH) showed no enhancement in isolation-induced disruption of PPI. A neurochemical study revealed that isolation-reared WT mice had significantly lower dopamine (DA) levels and slightly increased DA turnover in the cortex than socially reared WT mice. Conversely, isolation-reared H1KO mice showed significantly higher DA contents as compared with socially reared H1KO mice. Conclusion: The results of our study indicate that blockage of H1 receptor-mediated neurotransmission attenuates social isolation-induced behavioral changes and that the therapeutic effects of atypical antipsychotics are mediated, at least in part, by interaction with H1 receptors in the brain.     

Effects of selective dopamine D1- and D2-type receptor antagonists on the development of behavioral sensitization to 7-OH-DPAT

The primary objective of this study was to determine whether the development of behavioral sensitization to the putative dopamine D₃ receptor agonist 7-OH-DPAT could be prevented by either selective D₁-type or D₂-type dopamine receptor antagonists. In three experiments, male Wistar rats (250–350 g) were given seven to nine injections (at 48-h intervals) of 7-OH-DPAT (1.0 mg/kg, SC) or vehicle in combination with the D₂-type dopamine antagonist eticlopride (0.3 mg/kg, SC), the D₁-type dopamine antagonist SCH 23390 (0.1 or 0.2 mg/kg, SC), or vehicle. After the injections, the rats were tested for locomotor activity in photocell arenas for 2 h. In the first two experiments, after seven injections, all rats were tested for activity following vehicle injections to test for possible conditioning effects. In each experiment, after the last pre-exposure session, all rats were given a challenge injection of 7-OH-DPAT (1.0 mg/kg, SC) and tested for activity. Major findings were as follows: a) 7-OH-DPAT treatments produced a progressively greater increase in locomotor activity with repeated treatment; b) concurrent treatment with eticlopride or SCH 23390 (0.1 and 0.2 mg/kg) blocked the acute locomotor-activating effects of 7-OH-DPAT across days; c) eticlopride, but not SCH 23390, completely blocked the development of behavioral sensitization to 7-OH-DPAT. Although the low dose of SCH 23390 (0.1 mg/kg) produced a partial attenuation of sensitization, the higher dose (0.2 mg/kg) of SCH 23390 appeared to augment, rather than block, sensitization to 7-OH-DPAT; d) rats previously treated with SCH 23390 (0.2 mg/kg, but not 0.1 mg/kg) without 7-OH-DPAT displayed a hyperactive response to the 7-OH-DPAT challenge injection; and e) after vehicle injections, rats previously given 7-OH-DPAT, SCH 23390, or eticlopride either alone or in combination were more active than vehicle control rats. These findings suggest that the neurochemical mechanisms mediating the development of behavioral sensitization to 7-OH-DPAT may differ from those of other dopamine D₂-type agonists such as quinpirole or bromocriptine. Moreover, these results demonstrate that hyperactivity responses following vehicle injections in drug-pretreated animals do not necessarily reflect conditioning mechanisms. Received: 28 May 1997/Final version: 2 April 1998     

The "selective" dopamine D1 receptor antagonist, SCH23390, is a potent and high efficacy agonist at cloned human serotonin2C receptors

RATIONALE: The benzazepine and "selective" dopamine D1 receptor antagonist, SCH23390 [(R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-benzazepine-7-ol], shows significant affinity at native serotonin (5-HT)2C receptors. OBJECTIVES: We examined its functional actions at cloned human (h)5-HT2C receptors (VSV isoform) stably expressed in CHO cells. METHODS: Since 5-HT2C receptors are positively coupled to phospholipase C (PLC), their activation was determined by depletion of membrane-bound pools of pre-labelled [3H]phosphotidylinositol ([3H]PI). RESULTS: SCH23390 showed high affinity (Ki, 9.3 nM) at h5-HT2C sites and depleted [3H]PI with an EC50 of 2.6 nM. Its efficacy was equivalent to that of 5-HT. [3H]PI depletion elicited by SCH23390 was concentration-dependently abolished by the selective 5-HT2C antagonist, SB242,084, with a K(B) of 0.55 nM. Further, in the presence of a fixed concentration of SB242,084 (10 nM), the concentration-response curve for SCH23390 was shifted to the right without loss of maximal effect, yielding a K(B) of 0.57 nM. CONCLUSIONS: SCH23390 is a potent and high efficacy agonist at h5-HT2C receptors. Activation of 5-HT2C receptors by SCH23390 may contribute to its functional properties both in animals and in humans.     

TLR4对MHV-3诱导的C3H／He小鼠病毒性肝炎转归的影响

目的探讨TLR4对3型鼠肝炎病毒（MHV-3）诱导的C3H／He小鼠肝炎转归的影响。方法观察C3H／HeJ及C3H／HeN小鼠感染MHV-3后的临床症状（皮毛异常、呼吸加快及身体颤抖）并进行评分。记录两亚系小鼠的存活情况并进行比较。所有小鼠观察至感染后40d。结果小鼠品系对临床症状评分不起作用（P=0．718）。临床评分有随时间变化的趋势（P〈0．001）,且时间因素的作用随小鼠品系而不同（P=0．004）。C3H／HeJ及C3H／HeN小鼠临床症状评分仅在感染后第5、6、13天出现差异：（13．071±1．184）和（10．933±4．608）（P〈0．001）,（8．321±5．048）和（11．304±3．901）（P〈0．001）,（13．091±1．578）和（10．846±3．671）（P=0．015）。C3H／HeJ及C3H／HeN小鼠存活率分别为26．7％和23．3％,平均存活时间分别为16．267d和16．433d,无显著差异（P=0．922）。结论MHV-3诱导的C3H／He小鼠病毒性肝炎转归不依赖于TLR4。     

Effects of 4-nonylphenol on adipogenesis in 3T3-L1 preadipocytes and C3H/10T1/2 mesenchymal stem cells

Obesogens are a subset of endocrine disruptor chemicals (EDCs) that cause obesity. The typical EDC 4-nonylphenol (4-NP) has been identified as an obesogen. However, the in vitro effects of 4-NP on adipogenesis remain unclear. In this study, 3T3-L1 preadipocytes and C3H/10T1/2 mesenchymal stem cells (MSCs) were used to investigate the influence of 4-NP on adipogenesis. The differentiation protocols for 3T3-L1 preadipocytes and C3H/10T1/2 MSCs took 8 and 12 days, respectively, beginning at Day 0. In differentiated 3T3-L1 preadipocytes, 20 μM 4-NP decreased cell viability on Days 4 and 8. Exposure to 4-NP inhibited triglyceride (TG) accumulation and adipogenic marker expression on Days 0–8, but the inhibitory effects were weaker on Days 2–8. The protein expression of pSTAT3 or STAT3 decreased on Days 0–8 and 2–8. Conversely, 4-NP promoted TG accumulation and the adipogenic marker expression in C3H/10T1/2 adipocytes. The opposing effects were attributed to physiological differences between the two cell lines. The 3T3-L1 preadipocytes are dependent on mitotic clonal expansion (MCE) to drive differentiation, while C3H/10T1/2MSCs and human preadipocytes are not. Additionally, 4-NP downregulated β-catenin expression in C3H/10T1/2 adipocytes. Accordingly, we hypothesized that 4-NP promotes adipogenesis. The role of the canonical Wnt pathway in the promotion of adipogenesis by 4-NP requires further validation. This study provides new insights into the mechanisms and appropriate risk management of 4-NP.     

Effect of a dopamine D1/5 receptor antagonist on haloperidol-induced inhibition of the acquisition of conditioned fear

This study examined the effects of combined treatment with the typical antipsychotic drug haloperidol and dopamine D1/5 receptor antagonist SCH 23390 on the acquisition of contextual conditioned fear (re-exposure to an environment paired previously with inescapable electric footshocks), compared with those of various antipsychotic adjuvants, which may increase the effects of antipsychotic drugs. Rats were treated subcutaneously with haloperidol (3 mg/kg) combined with SCH 23390 (0.03 mg/kg) and were given fear conditioning by 5 min footshocks in shock chambers 30 min after the injection. One week after the footshocks, the rats were tested in the same shock chamber without shocks and freezing behavior was observed as an index of fear and anxiety. Haloperidol significantly inhibited the acquisition of conditioned freezing. SCH 23390 combined with haloperidol inhibited the acquisition of conditioned freezing more than either drug alone did. These results suggest that combined dopamine D2-like receptor antagonism and dopamine D1-like receptor antagonism is a promising and effective strategy to increase antipsychotic effects.     

Long-term effects of postnatal amphetamine treatment on striatal protein kinase A activity, dopamine D(1)-like and D(2)-like binding sites, and dopamine content

The purpose of the present study was to determine whether exposure to amphetamine during the preweanling period would alter dopaminergic functioning in the dorsal striatum of adult rats. In three experiments, we assessed the effects of repeated amphetamine treatment on striatal protein kinase A (PKA) activity, dopamine (DA) D₁-like and D₂-like binding sites, and DA content. Rats were pretreated with saline or amphetamine (2.5 mg/kg, ip) for 7 consecutive days starting on postnatal day (PD) 11. At PD 90, rats were killed and their dorsal striata (i.e., caudate–putamen) were removed and frozen until time of assay. Amphetamine pretreatment produced long-term reductions in both striatal PKA activity and DA content. Early amphetamine exposure also resulted in an upregulation of D₂-like binding sites, while leaving D₁-like binding sites unaffected. It is likely that the upregulation of D₂-like binding sites was stimulated by the persistent decline in striatal DA levels. Although speculative, it is possible that excess striatal D₂-like receptors were responsible for inhibiting PKA activity through actions on the cAMP signal transduction pathway. The behavioral relevance of these amphetamine-induced neurochemical changes has not yet be determined.     

The discriminative stimulus effects of dopamine D2- and D3-preferring agonists in rats

Rationale  Previous research has found the stimulus effects of dopamine D2- and D3-preferring agonists difficult to distinguish in drug discrimination studies. Antagonism studies suggest that the stimulus effects of both types of agonists may be mediated primarily through D2 receptors. Objectives  The current study was designed to further assess the receptors mediating the stimulus effects of these agonists and to attempt to train rats to discriminate directly between D2- and D3-preferring dopamine agonists. Materials and methods  Four groups of eight rats were trained to discriminate either 0.1 mg/kg of the D3-preferring agonist pramipexole from saline, 1.0 mg/kg of the D2-preferring agonist sumanirole from saline, 0.1 mg/kg pramipexole from either saline or 1.0 mg/kg sumanirole, or 1.0 mg/kg sumanirole from either saline or 0.1 mg/kg pramipexole. Results  Three of eight rats in the 0.1 mg/kg pramipexole vs. 1.0 mg/kg sumanirole or saline failed to meet the training criteria, and the discrimination in this group was tenuous. The D2-preferring antagonist L-741,626 at 1.0 mg/kg was more effective at shifting to the right the pramipexole dose-response curve in pramipexole-trained rats, while 32 mg/kg of the selective D3 antagonist PG01037 had little effect. Quinpirole and 7-OH-DPAT fully or partially substituted for both pramipexole and sumanirole in each group tested, while cocaine did not substitute in any group. Conclusions  Antagonist data along with the pattern of training and substitution data suggested that D2 receptor activation is primarily responsible for the stimulus effects of both sumanirole and pramipexole with D3 receptor activation playing little or no role.     

Evidence that the enhancement of dopamine function by repeated electroconvulsive shock requires concomitant activation of D1-like and D2-like dopamine receptors

In this study, the behavioural response to dopamine D₁-like receptor agonists (SKF 38393, SKF 81297 and SKF 77434) and D₂-like receptor agonists (quinpirole and RU 24213), administered alone and in combination to rats treated repeatedly with electroconvulsive shock (five ECS over 10 days) or sham, was tested. Agonist-induced behaviour was monitored by automated activity meters and direct observation using a checklist scoring method. Repeated ECS (compared to sham controls) had no significant effect on the behavioural response to SKF 38393 (7.5 mg/kg SC), SKF 81297 (0.2 mg/kg SC), SKF 77434 (0.1 mg/kg SC), quinpirole (0.1 and 0.25 mg/kg SC) or RU 24213 (0.3 mg/kg SC), when administered alone. In contrast, repeated ECS markedly increased locomotion (activity counts and scores) induced by the non-selective dopamine agonist apomorphine (0.5 mg/kg SC) and by co-administration of a D₁-like agonist plus a D₂-like agonist [SKF 38393 (7.5 mg/kg SC) plus quinpirole (0.25 mg/kg SC), SKF 81297 (0.2 mg/kg SC) plus quinpirole (0.1 mg/kg SC), and SKF 77434 (0.1 mg/ kg SC) plus RU 24213 (0.3 mg/kg SC)]. This ECS-induced enhancement of dopamine-mediated behaviour was observed for up to 3 weeks after cessation of ECS treatment. In addition, ECS also enhanced the locomotor response to intra-accumbens SKF 38393 plus quinpirole (0.4 and 1.0 μg/side, respectively). These results provide evidence that the enhancement of dopamine function by repeated ECS requires concomitant stimulation of both D₁-like and D₂-like receptors, and that this effect is long-lasting. Received: 24 January 1997 /Final version: 5 March 1997     

Variables affecting prepulse inhibition of the startle reflex and the response to antipsychotics in DBA/2NCrl mice

Rationale DBA/2 mice demonstrate poor prepulse inhibition (PPI) as is also observed in schizophrenic patients, and their PPI is improved by antipsychotics. Thus, the DBA/2 mouse is increasingly used for testing of novel antipsychotics in PPI; however, the strain has not been fully characterized for relevant variables affecting compound testing. Objectives The objectives of this study were to compare four DBA/2 substrains, evaluate light- and dark-phase testing on startle, PPI, and drug-induced improvement in PPI in DBA/2NCrl mice, test chamber lighting on startle and PPI in DBA/2NCrl mice and to evaluate vehicles on baseline PPI in DBA/2NCrl mice. Results DBA/2NCrl and DBA/2J mice were acceptable for PPI testing, while DBA/2NHsd mice had diminished startle reflexes. Startle responses to the prepulses alone were observed in 46% of the DBA/2NTac mice. PPI and startle did not show diurnal variations or variations due to chamber lighting. Olanzapine and aripiprazole showed better drug-induced improvements in PPI during the light phase. The vehicle 25% (2-hydroxypropyl)-β-cyclodextrin variably improved PPI, an effect not observed with other vehicles. Conclusions DBA/2NHsd and DBA/2NTac mice were unacceptable for PPI experiments. The finding of responses to the prepulses alone by DBA/2NTac mice further indicates the advisability of routinely monitoring responses to prepulses alone. Unlike rats, DBA/2NCrl mice did not have greater startle amplitudes during the dark phase. Compound efficacy was better during the light phase because of poorer PPI in the vehicle group. Some vehicles may have unacceptable effects on PPI in DBA/2NCrl mice and may not be appropriate for studies evaluating novel compounds.     

Dose-dependent inhibition of CYP1A2, CYP2C19 and CYP2D6 by citalopram,fluoxetine, fluvoxamine and paroxetine

Objectives: The purpose of this pharmacokinetic study was to investigate the dose-dependent inhibition of model substrates for CYP2D6, CYP2C19 and CYP1A2 by four marketed selective serotonin reuptake inhibitors (SSRIs): citalopram, fluoxetine, fluvoxamine and paroxetine. Methods: The study was carried out as an in vivo single-dose study including 24 young, healthy men. All volunteers had been identified as sparteine- and mephenytoin-extensive metabolisers. The volunteers received in randomised order, at weekly intervals, increasing single oral doses of one of the four SSRIs, followed 3 h later by sparteine (CYP2D6), mephenytoin (CYP2C19) and caffeine (CYP1A2) tests. Fluoxetine was given at 3-week intervals because of the long half-life of fluoxetine and its metabolite norfluoxetine. Citalopram, fluoxetine and paroxetine were given in doses of 10, 20, 40 and 80 mg and fluvoxamine was given in doses of 25, 50, 100 and 200 mg. Results: With increasing doses, there was a statistically significant increase in the sparteine metabolic ratio (MR) (P < 0.01, Page’s test for trend) for all four SSRIs. The increase was modest after intake of citalopram and fluvoxamine, while the increase was more pronounced after fluoxetine intake, although no volunteers changed phenotype from extensive metabolisers to poor metabolisers. Three of the six volunteers changed phenotype from extensive metabolisers to poor metabolisers after intake of 40 or 80 mg paroxetine. There was a statistically significant increase in the mephenytoin S/R ratio (P < 0.01, Page’s test for trend) with increasing doses of fluoxetine and fluvoxamine, but not after citalopram and paroxetine. However, no volunteers changed phenotype from extensive to poor metabolisers of S-mephenytoin. After intake of fluvoxamine, the urinary excretion of the metabolites related to N3 demethylation of caffeine were below the limit of quantification, whereas there were no significant changes in the urinary caffeine metabolic ratios after intake of the other three SSRIs. Conclusion: This investigation confirms that paroxetine and fluoxetine are potent inhibitors of CYP2D6, that fluvoxamine and fluoxetine are moderate inhibitors of CYP2C19 and that fluvoxamine is a potent inhibitor of CYP1A2 in humans in vivo. The clinical prediction of interaction from single-dose experiments may have to take the degree of accumulation during steady-state after multiple doses into account. Received: 11 December 1995/Accepted in revised form: 29 February 1996