Anxiolytic potential of sulpiride, clozapine and derivatives in the open-field test

Design, synthesis, and pharmacological activity of new pyrrolo[1,2-a]pyrazine translocator protein (tspo) ligands

BACKGROUND

Translocator protein 18 kDa (TSPO) is a promising target for the creation of effective and safe neuropsychotropic drugs. The ligands of TSPO exhibit anxiolytic, antidepressant, neuroprotective and other activities without the side effects of benzodiazepines.

METHODS

New TSPO ligands in the series of N,1-diphenylpyrrolo[1,2-a]pyrazine-3-carboxamides derivatives were designed using calculated pharmacophore model and molecular docking analysis. The synthesis of new compounds was carried out by two schemes using [3+3]-cycloaddition reaction of 2-azidoacrylic acid derivatives with pyrrolphenylketone as a key stage. The anxiolytic activity of new substances has been established using open field test with flash.

RESULTS

Several synthesized N,1-diphenylpyrrolo[1,2-a]pyrazine-3-carboxamides derivatives significantly increased the total motor activity of Balb/c mice compared to the control. The structure-activity relationship was investigated. The most effective compound was found to be GML-11 (N-benzyl-N,1-diphenylpyrrolo[1,2-a]pyrazine-3-carboxamide), which had anxiolytic action in the dose range from 0.001 to 0.100 mg/kg (Balb/c, i.p.). This compound is two orders of magnitude higher in dose activity than all other pyrrolo[1,2-a]pyrazine TSPO ligands.

CONCLUSION

Molecular modelling methods allowed us to create new TSPO ligands in the series of N,1-diphenylpyrrolo[1,2-a]pyrazine-3-carboxamides with high anxiolytic activity.

Does chronic systemic injection of the DREADD agonists clozapine-N-oxide or Compound 21 change behavior relevant to locomotion, exploration, anxiety, and depression in male non-DREADD-expressing mice?

Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) are chemogenetic tools commonly-used to manipulate brain activity. The most widely-used synthetic DREADD ligand, clozapine-N-oxide (CNO), is back-metabolized to clozapine which can itself activate endogenous receptors. Studies in non-DREADD-expressing rodents suggest CNO or a DREADD agonist that lacks active metabolites, such as Compound 21 (C21), change rodent behavior (e.g. decrease locomotion), but chronic injection of CNO does not change locomotion. However, it is unknown if chronic CNO changes behaviors relevant to locomotion, exploration, anxiety, and depression, or if chronic C21 changes any aspect of mouse behavior. Here non-DREADD-expressing mice received i.p. Vehicle (Veh), CNO, or C21 (1 mg/kg) 5 days/week for 16 weeks and behaviors were assessed over time. Veh, CNO, and C21 mice had similar weight gain over the 16-week-experiment. During the 3rd injection week, CNO and C21 mice explored more than Veh mice in a novel context and had more open field center entries; however, groups were similar in other measures of locomotion and anxiety. During the 14th-16th injection weeks, Veh, CNO, and C21 mice had similar locomotion and anxiety-like behaviors. We interpret these data as showing chronic Veh, CNO, and C21 injections given to male non-DREADD-expressing mice largely lack behavioral effects. These data may be helpful for behavioral neuroscientists when study design requires repeated injection of these DREADD agonists.

An update into the medicinal chemistry of translocator protein (TSPO) ligands

The Translocator Protein 18 kDa (TSPO) has been discovered in 1977 as an alternative binding site for the benzodiazepine diazepam. It is an evolutionary well-conserved and tryptophan-rich 169-amino acids protein with five alpha helical transmembrane domains stretching the outer mitochondrial membrane, with the carboxyl-terminus in the cytosol and a short amino-terminus in the intermembrane space of mitochondrion. At this level, together with the voltage-dependent anion channel (VDAC) and the adenine nucleotide translocase (ANT), it forms the mitochondrial permeability transition pore (MPTP). TSPO expression is ubiquitary, with higher levels in steroid producing tissues; in the central nervous system, it is mainly expressed in glial cells and in neurons. TSPO is implicated in a variety of fundamental cellular processes including steroidogenesis, heme biosynthesis, mitochondrial respiration, mitochondrial membrane potential, cell proliferation and differentiation, cell life/death balance, oxidative stress. Altered TSPO expression has been found in some pathological conditions. In particular, high TSPO expression levels have been documented in cancer, neuroinflammation, and brain injury. Conversely, low TSPO expression levels have been evidenced in anxiety disorders. Therefore, TSPO is not only an interesting drug target for therapeutic purpose (anticonvulsant, anxiolytic, etc.), but also a valid diagnostic marker of related-diseases detectable by fluorescent or radiolabeled ligands. The aim of this report is to present an update of previous reviews dealing with the medicinal chemistry of TSPO and to highlight the most outstanding advances in the development of TSPO ligands as potential therapeutic or diagnostic tools, especially referring to the last five years.

Establishing an effective dose for chronic intracerebroventricular administration of clozapine in mice

OBJECTIVE

Despite its numerous side effects, clozapine is still the most effective antipsychotics making it an ideal reference substance to validate the efficacy of novel compounds for the treatment of schizophrenia. However, blood-brain barrier permeability for most new molecular entities is unknown, requiring central delivery. Thus, we performed a dose-finding study for chronic intracerebroventricular (icv) delivery of clozapine in mice.

METHODS

Specifically, we implanted wild-type C57BL/6J mice with osmotic minipumps (Alzet) delivering clozapine at a rate of 0.15 µl/h at different concentrations (0, 3.5, 7 and 14 mg/ml, i.e. 0, 12.5, 25 and 50 µg/day). Mice were tested weekly in a modified SHIRPA paradigm, for locomotor activity in the open field and for prepulse inhibition (PPI) of the acoustic startle response (ASR) for a period of 3 weeks.

RESULTS

None of the clozapine concentrations caused neurological deficits or evident gross behavioural alterations in the SHIRPA paradigm. In male mice, clozapine had no significant effect on locomotor activity or PPI of the ASR. In female mice, the 7 and 14 mg/ml dose of clozapine significantly affected both open field activity and PPI, while 3.5 mg/ml of clozapine increased PPI but had no effects on locomotor activity.

CONCLUSION

Our findings indicate that 7 mg/ml may be the optimal dose for chronic icv delivery of clozapine in mice, allowing comparison to screen for novel antipsychotic compounds.

Design, Synthesis and Anxiolytic Activity Evaluation of N-Acyltryptophanyl- Containing Dipeptides, Potential TSPO Ligands#

Background:

The 18 kDa translocator protein (TSPO), previously known as the peripheral- type benzodiazepine receptor, plays a key role for the synthesis of neurosteroids by promoting transport of cholesterol from the outer to the inner mitochondrial membrane, which is the ratelimiting step in neurosteroid biosynthesis. Neurosteroids interact with nonbenzodiazepine site of GABAa receptor causing an anxiolytic effect without the side effects.

Methods:

Using the original peptide drug-based design strategy, the first putative dipeptide ligand of the TSPO N-carbobenzoxy-L-tryptophanyl-L-isoleucine amide (GD-23) was obtained. Molecular docking of GD-23 in the active pocket of the TSPO receptor using Glide software was carried out. The lead compounds GD-23 and its analogues were synthesized using activated succinimide esters coupling method. The anxiolytic activity of GD-23 and its analogues was investigated in vivo, using two validated behavioral tests, illuminated open field and elevated plus-maze.

Results:

he in vivo studies revealed that the following parameters are necessary for the manifestation of anxiolytic activity of new compounds: the L-configuration of tryptophan, the presence of an amide group at the C-terminus, the specific size of the N-acyl substituent at the Nterminus. Compound GD-23 (N-carbobenzoxy-L-tryptophanyl-L-isoleucine amide) demonstrated a high anxiolytic-like effect in the doses of 0.05–1.0 mg/kg i.p. comparable with that of diazepam. Compound GD-23 was also active in the open field test when was administered orally in the doses of 0.1-5.0 mg/kg. The involvement of TSPO receptor in the mechanism of anxiolytic-like activity of new compounds was proved by the antagonism of compound GD-23 with TSPO selective inhibitor PK11195 as well as with inhibitors of enzymes which are involved in the biosynthesis of neurosteroids, trilostane and finasteride.

Conclusion:

A series of N-acyl-tryptophanyl-containing dipeptides were designed and synthesized as 18 kDa translocator protein (TSPO) ligands. Using a drug-based peptide design method a series of the first dipeptide TSPO ligands have been designed and synthesized and their anxiolytic activity has been evaluated. In general, some of the compounds displayed a high level of anxiolytic efficacy comparable with that of diazepam. The involvement of TSPO receptor in the mechanism of anxiolytic activity of new compounds was proved using two methods. On this basis, the N-acyl-Ltryptophanyl- isoleucine amides could potentially be a novel class of TSPO ligands with anxiolytic activity.

Prelimbic NMDA receptors stimulation mimics the attenuating effects of clozapine on the auditory electrophysiological rebound induced by ketamine withdrawal

Ketamine (KET) is a non-competitive N-Methyl-d-aspartate (NMDA) receptors antagonist that intensifies sensory experiences, prompts hallucinations and delusions, exacerbates previously installed psychosis and disrupts physiological evoked potentials (AEPs). Pharmacologically, KET stimulates glutamate efflux in the medial prefrontal cortex, mainly in the prelimbic (PrL) sub-region. Efferences from this region exert a top-down regulatory control of bottom-up sensory processes either directly or indirectly. In the midbrain, the central nucleus of the inferior colliculus (CIC) plays a fundamental role in the processing of auditory ascending information related to sound localization, sensorimotor gating, and preattentive event-related potentials. Auditory hallucinations elicited during a psychotic outbreak are accompanied by CIC neural activation. Thus, it is possible that NMDA-mediated glutamate neurotransmission in the PrL indirectly modulates CIC neuronal firing. The aim of the present study was to assess the effects of KET on the latency and amplitude of AEPs elicited in the CIC of rats tested during KET effects and following withdrawal from the chronic administration. Changes on emotionally induced by KET treatment were evaluated with the use of the elevated zero maze (EZM). Unlike typical neuroleptics, the atypical antipsychotic clozapine (CLZ) potently blocks the disruption of the sensorimotor gating induced by NMDA antagonists. Therefore, the effects of KET withdrawal on AEPs were challenged with a systemic injection of CLZ. In addition, we further investigated the role of NMDA receptors of the PrL on the AEPs expression recorded in the CIC through intra-PrL infusions of NMDA itself. Our results showed that the processing of sensory information in the CIC is under indirect control of PrL. These data suggest that the long-term KET treatment disrupts the collicular auditory field potentials, possibly through influencing PrL glutamate activity on intrinsic 5-HT mechanisms in the dorsal raphe and CIC.

Extracellular regulated protein kinaseis critical for the role of 5-HT1a receptor in modulating nNOS expression and anxiety-related behaviors

Our previous study found that serotonin 1A receptor (5-HT1aR) is an endogenous suppressor of nNOS expression in the hippocampus, which accounts for anxiolytic effect of fluoxetine. However, the precise molecular mechanism remains unknown. By using 8-OH-DPAT, a selective 5-HT1aR agonist, NAN-190, a selective 5-HT1aR antagonist, and U0126, an Extracellular Regulated Protein Kinases (ERK) phosphorylation inhibitor, we investigated the role of ERK in 5-HT1aR-nNOS pathway. Western blots analysis demonstrated that 5-HT1aR activation up-regulated the level of phosphorylated ERK (P-ERK) beginning at 5 min and down-regulated the expression of nNOS beginning at 20 min. Meanwhile, blockage of 5-HT1aR resulted in a decrease in P-ERK beginning at 20 min and caused an increase in nNOS expression beginning at 6 h. Although U0126 itself did not alter nNOS expression and activity, NO level, and anxiety-related behaviors, the treatment totally reversed 8-OH-DPAT-induced reduction in nNOS expression and function, and anxiolytic effect. Besides, our data showed that ERK phosphorylation was essential for 5-HT1aR activation-induced cAMP responsive element binding protein (CREB) phosphorylation, hippocampal neurogenesis and synaptogenesis of newborn neuron. Our study suggests a crucial role of ERK phosphorylation in the regulation of nNOS expression by 5-HT1aR, which is helpful for understanding the mechanism of 5-HT1aR-based anxiolytic treatment.

Dopaminergic mechanisms underlying catalepsy, fear and anxiety: do they interact?

Haloperidol is a dopamine D2 receptor antagonist that induces catalepsy when systemically administered to rodents. The haloperidol-induced catalepsy is a state of akinesia and rigidity very similar to that seen in Parkinson's disease. There exists great interest in knowing whether or not some degree of emotionality underlies catalepsy. If so, what kind of emotional distress would permeate such motor disturbance? This study is an attempt to shed some light on this issue through an analysis of ultrasound vocalizations (USVs) of 22 kHz, open-field test, and contextual conditioned fear in rats with some degree of catalepsy induced by haloperidol. Systemic administration of haloperidol caused catalepsy and decreased exploratory activity in the open-field. There was no difference in the emission of USVs between groups during the catalepsy or the exploratory behavior in the open-field test. In the contextual conditioned fear, when administered before training session, haloperidol did not change the emission of USVs or the freezing response. When administered before testing session, haloperidol enhanced the freezing response and decreased the emission of USVs on the test day. These findings suggest that the involvement of dopaminergic mechanisms in threatening situations depends on the nature of the aversive stimulus. Activation of D2 receptors occurs in the setting up of adaptive responses to conditioned fear stimuli so that these mechanisms seem to be important for the emission of 22 kHz USVs during the testing phase of the contextual conditioned fear, but not during the training session or the open-field test (unconditioned fear stimuli). Catalepsy, on the other hand, is the result of the blockage of D2 receptors in neural circuits associated to motor behavior that appears to be dissociated from those directly linked to dopamine-mediated neural mechanisms associated to fear.

Adolescent binge drinking increases expression of the danger signal receptor agonist HMGB1 and Toll-like receptors in the adult prefrontal cortex

Adolescence is a critical developmental stage of life during which the prefrontal cortex (PFC) matures, and binge drinking and alcohol abuse are common. Recent studies have found that ethanol increases neuroinflammation via upregulated high-mobility group box 1 (HMGB1) signaling through Toll-like receptors (TLRs). HMGB1/TLR 'danger signaling' induces multiple brain innate immune genes that could alter brain function. To determine whether adolescent binge drinking persistently increases innate immune gene expression in the PFC, rats (P25-P55) were exposed to adolescent intermittent ethanol (AIE [5.0 g/kg, 2-day on/2-day off schedule]). On P56, HMGB1/TLR danger signaling was assessed using immunohistochemistry (i.e., +immunoreactivity [+IR]). In a separate group of subjects, spatial and reversal learning on the Barnes maze was assessed in early adulthood (P64-P75), and HMGB1/TLR danger signaling was measured using immunohistochemistry for +IR and RT-PCR for mRNA in adulthood (P80). Immunohistochemical assessment at P56 and 24 days later at P80 revealed increased frontal cortical HMGB1, TLR4, and TLR3 in the AIE-treated rats. Adolescent intermittent ethanol treatment did not alter adult spatial learning on the Barnes maze, but did cause reversal learning deficits and increased perseverative behavior. Barnes maze deficits correlated with the expression of danger signal receptors in the PFC. Taken together, these findings provide evidence that adolescent binge drinking leads to persistent upregulation of innate immune danger signaling in the adult PFC that correlates with adult neurocognitive dysfunction.

Clozapine and olanzapine exhibit an intrinsic anxiolytic property in two conditioned fear paradigms: contrast with haloperidol and chlordiazepoxide

Psychotic fear and anxiety disturbances are seen at a relatively high frequency in patients with schizophrenia. Atypical anti-psychotics are believed to show superior efficacy in reducing these symptoms. However, clinical and preclinical evidence regarding their anxiolytic efficacy has been mixed. In this study, we evaluated the possible anxiolytic property of two atypicals clozapine and olanzapine and compared them with typical haloperidol and chlordiazepoxide (a prototype of sedative-anxiolytic drug) in two preclinical models of fear. In Experiment 1, we used a fear-induced passive avoidance and conditioned place aversion paradigm and examined the effects of clozapine (20 mg/kg, sc), haloperidol (0.05 mg/kg, sc) and chlordiazepoxide (10 mg/ kg, ip). In Experiments 2 and 3, we used a two-way active avoidance conditioning paradigm and further compared the effects of clozapine (20 mg/kg, sc), haloperidol (0.05 mg/kg, sc), chlordiazepoxide (10 mg/kg, ip) and three doses of olanzapine (0.5, 1.0, and 2.0 mg/kg, sc). Results show that clozapine and chlordiazepoxide, but not haloperidol, significantly attenuated the shock conditioning-induced place aversion, decreased the amount of defecations and the number of the 22-kHz vocalizations. Clozapine also reduced the shock conditioning-induced hyperthermia. Similar to clozapine, olanzapine also significantly decreased the amount of defecations and reduced the shock conditioning-induced hyperthermia, but it did not inhibit the 22-kHz vocalizations. This study demonstrates that clozapine and olanzapine possess an intrinsic anxiolytic property, which is not attributable to its superior anti-"psychotic" effect or its favorable effects on motor functions or learning and memory processes. These findings also suggest that the combined use of passive avoidance and active avoidance conditioning models can be useful in better differentiating typical and atypical anti-psychotics as well as anxiolytics.

Altered emotional behaviors in the diabetes mellitus OLETF type 1 congenic rat

GPR10 is a G-protein-coupled receptor expressed in thalamic and hypothalamic brain regions, including the reticular thalamic nucleus (RTN) and periventricular nucleus (Pev), and the endogenous ligand for this receptor, prolactin-releasing peptide (PrRP), has demonstrated regulatory effects on the stress response. We produced a congenic rat by introducing the Dmo1 allele from the OLETF rat which encodes the amino acid sequences of GPR10 with a truncated NH2-terminus, into the Brown-Norway background. Using receptor autoradiography, we determined a lack of specific [125I]PrRP binding in the RTN and Pev of these mutant rats compared to the control rats. Furthermore, intracerebroventricular injection of PrRP did not induce a significant increase of c-fos-like immunoreactivity in the paraventricular nucleus of the mutant rats compared to the control rats. The mutant rats also displayed a less anxious-like phenotype in three behavioral-based models of anxiety-like behavior (open field, elevated plus maze and defensive withdrawal test). These data show the mutant congenic rat, of which GPR10 neither binds nor responds to PrRP, expresses less anxious-like phenotypes. On the basis of these observations, the GPR10 might be a novel target for the developing new drugs against anxiety and/or other stress-related diseases.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

JL 13, an atypical antipsychotic: a preclinical review

The extensive pharmacological evaluation of JL 13 as an atypical antipsychotic drug has revealed a close similarity to clozapine, however with some major advantages. JL 13 was characterized as a weak D(2) antagonist, both in vitro and in vivo, with a strong affinity for the D(4) and the 5-HT(2A) receptors. It has no affinity for the 5-HT(2C) receptor. In vivo microdialysis experiments in rat showed that JL 13, like clozapine, preferentially increased extracellular dopamine concentrations in the prefrontal cortex compared to nucleus accumbens or striatum. Behavioral studies showed that JL 13, like clozapine, has the profile of an atypical antipsychotic. Thus, JL 13 did not antagonize apomorphine-induced stereotypy nor did it produce catalepsy, but it antagonized apomorphine-induced climbing in rodents. It was inactive against d-amphetamine-induced stereotypy but antagonized d-amphetamine-induced hyperactivity in the mouse. Likewise, in the paw test, it was more effective in prolonging hindlimb retraction time than prolonging forelimb retraction time. Like other antipsychotic drugs, JL 13 reversed the apomorphine- and amphetamine-induced disruption of prepulse inhibition. In a complex temporal regulation schedule in the dog, JL 13 showed a high resemblance with clozapine without inducing sialorrhea, palpebral ptosis or any significant motor side effects. In rats and squirrel monkeys JL 13 induced a high degree of generalization (70%) to clozapine. Regarding behavioral toxicology, JL 13 did not produce dystonia or Parkinsonian symptoms in haloperidol-sensitized monkeys. After acute administration, again like clozapine, JL 13 induced only a transient increase in circulating prolactin. Last but not the least, regarding a possible hematological toxicity, unlike clozapine, JL 13 did not present sensitivity to peroxidase-induced oxidation. Moreover, its electrooxidation potential was close to that of loxapine and far from that of clozapine. Taking all these preclinical data into account, it appears that JL 13 is a promising atypical antipsychotic drug.

Effect of low doses of clozapine on behaviour of isolated and group-housed male mice in the elevated plus-maze test

Clozapine is effective over a low and narrow dose range in the treatment of the negative symptoms of schizophrenia. Its efficacy is said to reflect an anxiolytic property of the neuroleptic. This study examined the effects of a low dose range of clozapine (0.1, 0.2 and 0.4 mg/kg) administered to isolated (7 days) and group-housed male mice on their behaviour in the elevated plus-maze. The results using this model of anxiety showed no dose-dependent effect on behaviour after treatment with low doses of clozapine. Some doses (0.1 and 0.4 mg/kg), however, reduced the duration and frequency of open arm entries compared to control-treated mice in the group-housed animals. This might indicate a slight anxiogenic effect. Support for this view is provided by some of the ethological measures, particularly head-dipping (HD). Seven days of isolation did not alter the main anxiety indices in controls. Nevertheless, some measures (e.g. closed entries and duration in the closed arm) were modified by the clozapine treatment (0.2 mg/kg) in a manner suggesting a mild anxiogenic action. The effects of the drug in individually and group-housed male mice were certainly different.

Animal models of acute drug-induced akathisia - a review

Akathisia is a complex neurobehavioural side effect of neuroleptics and some other drugs which is characterised by subjective report and objective manifestations of restlessness. Its pathophysiology is poorly understood and there are many limitations to its investigation in humans. This paper reviews the various attempts that have been made in modelling acute akathisia in animals. Homologous as well as isomorphic models have been attempted, but most models are partial as they reproduce either the subjective or the objective features of the syndrome. None of the available models has been fully validated. Neuroleptic-induced defecation in the rat, even though constrained by a lack of symptom similarity and thereby face validity, has been most studied as a model of subjective akathisia. Rat models of restlessness, in particular those involving the use of serotonergic drugs or lesions of the ventral tegmentum or medial prefrontal cortex, are interesting partial models that should be further investigated. Neuroleptic-induced akathisia is observed in primates and has been modelled in dogs, and these should be studied further for their validation. It is also necessary to consider the subtypes of akathisia in the attempts to develop these models.

A new technique for implanting a fine-wire microelectrode for chronic recording of unit activity from freely-moving mice

We report here a newly developed chronic implantation technique using an epoxy-coated fine-stainless steel wire (33 microm in diameter) to record single unit activity from the brain of freely-moving mice with as little tissue injury as possible. Since the fine-wire electrode is not capable of staying straight by itself or of penetrating into the brain, a pair of permanent neodymium magnets placed on a micromanipulator as well as below the animal's head was used for stereotaxic implantation to keep the fine-wire straight and strong by the magnetic fields. With those implanted electrodes recording of single units from the hippocampal CA1 of freely-moving mice was performed during sleep and wakefulness.

Chronical haloperidol and clozapine treatment in rats: differential RNA display analysis, behavioral studies and serum level determination

1. Adult, female rats were treated orally for 23 days with 1.6 mg/kg haloperidol or 36 mg/kg clozapine per day, to study chronic effects of the two neuroleptics. 2. At five time points during the neuroleptic treatment, animal behavior was recorded in an open field and locomotive activity was analysed. At the end of the experiment, rats were decapitated, blood samples were collected and serum concentrations of haloperidol and clozapine were determined by a radioreceptor or HPLC assay, respectively. RNA was isolated from each brain, without cerebellum, and subjected to differential RNA display. 3. Mean serum concentrations were 8 ng/ml for haloperidol and 21 ng/ml for clozapine. Analysis of open field behavior showed that haloperidol and clozapine decreased the total distance moved and the velocity as measures of the overall activity, whereas the number of rearings and the number of entries into the center, reflecting risk assessment behavior, were differentially affected. Three neuroleptic-regulated gene fragment bands were identified in differential RNA display experiments. Two gene fragments of 281 bp and 266 bp were sequenced. 4. We conclude that our study design that used behavioral, pharmacokinetic and molecular analysis increase the likelihood of finding relevant molecular events underlying the pharmacotherapeutic effects of neuroleptics in animal models.

Dissociation of impairment between spatial memory, and motor function and emotional behavior in aged rats

We investigated changes in learning and memory in aged rats, in relation to motor function and emotional behavior. Male Kbl Wistar aged rats (108-weeks-old) were divided into two groups, memory impaired and non-impaired, based on performance during six training trials in the Morris water maze task. Aged rats with a goal latency longer than the mean plus the 99% confidence limit of young rats, were regarded as memory impaired, whereas those with a goal latency within the range of the 99% confidence limit of the mean of young rats, were considered as memory non-impaired. Although the performance of the memory impaired aged rats in the standard test of the Morris water maze improved after six re-training trials to the level of the non-impaired aged rats and young rats, working memory impairment was evident. There were no differences in motor function and emotional behavior between the impaired and non-impaired aged rats. These results suggest that deficits of learning and memory in memory impaired aged rats can be dissociated from changes in motor function and emotional behavior.

Dopamine D4 receptor and anxiety: behavioural profiles of clozapine, L-745,870 and L-741,742 in the mouse plus-maze

The dopamine D4 receptor has been implicated in the therapeutic effects of the atypical antipsychotic, clozapine. As it has been proposed that anxiolytic-like activity may contribute to the efficacy of this agent in ameliorating the negative symptoms of schizophrenia, the current study employed ethological methods to fully characterize the acute behavioural profiles of clozapine and two more selective dopamine D4 receptor antagonists, L-745,870 (3-[{4-(4-chlorophenyl)piperazin-1-yl)]methyl}-1 H-pyrrolo[2,3b]pyridine) and L-741,742 (5-(4-chlorophenyl)-4-methyl-3-(1-(2-phenylethyl)piperidin-4-yl)is oxazole), in the mouse elevated plus-maze test. Results showed that while clozapine (0.3-6.0 mg/kg) dose-dependently inhibited all active behaviours (arm entries, exploration, rearing) and increased grooming and immobility, it failed to alter the major anxiety indices (percent open entries and open time). In contrast, L-745,870 (0.02-1.5 mg/kg) and L-741,742 (0.04-5.0 mg/kg) did not produce any significant behavioural changes under present test conditions. These data, which contrast markedly with the robust anxiolytic profile of the reference compound, chlordiazepoxide (10.0 mg/kg), provide little support for the suggestion that clozapine possesses anxiolytic-like properties and further indicate that selective dopamine D4 receptor antagonists are ineffective in the modulation of anxiety-related behaviours in the plus-maze.

Effects of typical and atypical antipsychotic drugs on freezing behavior induced by conditioned fear

A typical antipsychotic drugs (atypical APDs), such as clozapine, ORG5222, and olanzapine, have been suggested to possess anxiolytic activity in the conflict test and elevated plus-maze test, while several studies have suggested that typical APDs are not anxiolytic in several models of anxiety. We investigated the effects of typical and atypical APDs on the acquisition and expression of conditioned fear-induced freezing. Drugs were administered subcutaneously to male Sprague-Dawley rats 30 min before foot shock stress (the VI60s schedule, 2.5 mA for 30 min). Twenty-four hours after foot shock, freezing behavior of rats was observed in the shock chamber without shocks. The atypical APD clozapine (0.3-10 mg/kg) dose-dependently inhibited the acquisition of conditioned freezing. Candidates for atypical APDs, ORG5222 (0.1-1 mg/kg), olanzapine (1-10 mg/kg), and raclopride (3-30 mg/kg), also reduced the acquisition of conditioned freezing in a dose-dependent manner. Typical APDs, haloperidol (3 mg/kg), spiperone (0.1-1 mg/kg) and nemonapride (1 mg/kg) had significant inhibitory effects on the acquisition of conditioned freezing, but their effects were reduced at higher doses. Chlorpromazine, a typical APD, showed about 50% inhibition of the acquisition of conditioned freezing at the dose of 10 mg/kg, but did not reveal significant inhibition at any of the doses (3-30 mg/kg). The ED50S (mg/kg) for inhibiting the acquisition of conditioned freezing significantly correlated with the Ki values for D4 dopaminergic receptors, but not with the Ki values for other monoamine and acetylcholine receptors. On the other hand, clozapine or haloperidol did not change the expression of conditioned freezing. These results suggest that protective effects of clozapine and other antipsychotic drugs on the acquisition of conditioned freezing may be mediated by blockade of D4 receptors.

Dibenzoazepine analogues: the electrophysiological properties of JL3, a potential atypical antidepressant

JL3, 10-(4-methylpiperazin-1-yl)pyrido[4,3-b][1,4]benzothiazepine, has potent antidepressant-like activity in Porsolt's test in mice. Therefore, its influence on the electrical activity of central monoaminergic neurons was investigated in rats anaesthetized with chloral hydrate. JL3 induced a marked decrease of the firing rate of dorsal raphe serotonergic neurons (ID50 = 3.87 +/- 0.57 mg kg-1) and of locus coeruleus noradrenergic neurons (ID50 = 2.63 +/- 0.35 mg kg-1). The drug did not modify the electrical activity of A10 dopaminergic neurons. JL3 does not block amine uptake but it has affinity for 5-HT1A and 5-HT2 receptors. It is speculated that serotonergic mechanisms could play a role in the electrophysiological effects of JL3.

Effects of the subacute administration of nefiracetam on abnormal behavior in aged rats

We investigated the effects of nefiracetam on learning and memory by the Morris water maze task and water-finding test, and on emotional behavior by forced swimming, hole-board and open-field tests in old male Kbl Wistar rats aged 90 and 108 weeks. In the water maze task, the acquisition of the task in aged rats was slower than that in young rats. Subacute administration of nefiracetam (1 and 3 mg/kg daily) for 24 days tended to shorten the goal latency to escape onto the platform in a dose-dependent manner in the retention test, conducted 24 days after acquisition training. Nefiracetam (1 mg/kg) administration for 49 days decreased the duration of immobility in aged rats in the forced swimming test. Locomotor activity in young rats during the dark period was significantly higher than that during the light period, while there was no difference in locomotor activity between the light and dark periods in aged rats, suggesting that locomotor activity during the dark period and nocturnal habits may be impaired in aged rats. Subacute administration of nefiracetam for 14 days significantly increased the locomotor activity during the dark, but not light, period in a dose-dependent manner. In addition, nefiracetam given for 38 days, significantly shortened the increased time elapsed before animals started exploring the environment in aged rats compared with young rats in the water-finding tests. These findings suggest that nefiracetam may improve the impaired nocturnal habits and some of emotional behavior in aged rats.

Effects of prenatal ethanol exposure and early experience on home-cage and open-field activity in mice

-C57BL/6 mice were intubated from gestational day 14-18 twice daily with 1.58 g/kg ethanol, 4.2 g/kg sucrose, or remained untreated. Offspring of ethanol treated or lab chow control groups were raised either by group-housed dams and weaned on postnatal day (PND) 28 or by individually housed dams and weaned on PND 21. Offspring of the sucrose control group were raised by individually housed dams and weaned on PND 21. Groups did not differ in pup weight or litter size. Offspring were assessed for home-cage activity (PND 36-38) and open-field behavior (PND 40-42). Mice prenatally exposed to ethanol showed increased activity in their home cages, whereas open-field behavior was generally not different from that of control groups. Conversely, different preweaning rearing conditions had affected open-field behavior, but not home-cage activity. In conclusion, home-cage behavior was a sensitive paradigm for detecting hyperactivity subsequent to a relatively low dose of prenatal ethanol in mice, and communal nesting/late weaning vs. individual nesting/ standard weaning may be a useful preweaning environmental manipulation to study possible modifications of prenatal neurobehavioral effects.

Sulpiride antagonizes the biphasic locomotor effects of quinpirole in weanling rats

Low doses of dopamine (DA) agonists such as the D2 receptor subfamily agonist quinpirole are thought to stimulate DA autoreceptors selectively, thereby inhibiting locomotor activity. High doses of quinpirole initially suppress and later activate locomotion during a single test-session; the activation is presumably due to stimulation of postsynaptic receptors. The aim of this study was to investigate whether pretreatment with a selective DA D2 receptor antagonist, sulpiride, could block the putative autoreceptor-mediated inhibition at a lower dose than was required to block the postsynaptically mediated activation. Male and female 30-day-old rats were injected SC with one of eight doses of sulpiride (0.313-40 mg/kg) or the vehicle. Sixty minutes later, rats were injected SC with 0.2 mg/kg quinpirole or the vehicle. Five minutes after the second injection, rats were placed in automated activity monitors which recorded locomotor behavior for 60 min at 5-min intervals. Quinpirole at this dose first suppressed and later increased locomotor activity. Sulpiride pretreatment dose-dependently reversed both the early inhibition and later activation of quinpirole-induced locomotion. However, sulpiride did not block the quinpirole-induced early suppression at a lower dose than was required to block the later activation. Thus, there was no evidence that the locomotor suppression elicited by quinpirole is mediated by a more sensitive subset of DA receptors.

Sulpiride: an antipsychotic with selective dopaminergic antagonist properties

OBJECTIVE

To review the pharmacology, pharmacokinetics, clinical investigations, and adverse effects of sulpiride as a treatment for schizophrenia.

DATA SOURCES

Information was selected from a MEDLINE search of English-language medical literature using "sulpiride" as the search term. Manual searches of pertinent journal article bibliographies also were performed.

STUDY SELECTION

Clinical investigations with a blind, controlled, randomized design and treatment durations of at least 6 weeks were preferred. Formal assessment of a patient's schizophrenia was required. One clinical investigation using a 4-week treatment duration and 1 open investigation were included for purposes of adverse reaction assessment.

DATA EXTRACTION

Clinical investigations were evaluated for design, sample size, diagnosis, duration, and outcome. Data from all investigations were selected by 1 author and reviewed by both authors.

DATA SYNTHESIS

Sulpiride is a substituted benzamide with selective dopaminergic blocking activity. Early pharmacology reports hypothesized that sulpiride was selective for dopamine (D)2 receptors only, but sulpiride also blocks D3 and D4 receptors. Sulpiride does not block D1, adrenergic, cholinergic, gamma-aminobutyric acid-ergic, histaminergic, or serotonergic receptors to an appreciable extent. The oral bioavailability of sulpiride is poor, with estimates approximating 35%. Sulpiride does not appear to have an extensive first-pass metabolism, nor is it extensively protein-bound. There have been no identified active metabolites, and elimination appears to depend primarily on the kidneys. Clinical studies support sulpiride as being equally effective as active controls in the acute treatment of patients with schizophrenia. Daily doses permitted in these clinical investigations ranged from 100 to 3200 mg. Further investigation is required to determine the usefulness of sulpiride as a chronic treatment of schizophrenia and its effectiveness in treating the negative symptoms of schizophrenia. Sulpiride may cause extrapyramidal effects, autonomic effects, tardive dyskinesia, and the neuroleptic malignant syndrome. The incidence of these adverse reactions has not been established.

CONCLUSIONS

Sulpiride is a safe and effective pharmacotherapeutic treatment for the acute management of schizophrenia. A unique pharmacology does not appear to provide sulpiride with a greater effectiveness than the standard antipsychotics, but may provide it with minor safety advantages.

Role of dopaminergic mechanisms in the regulation of stress responses in experimental animals

The effects of some dopaminergic agents were evaluated on stress responses in normal and immunized experimental animals. Restraint stress (RS) consistently induced gastric mucosal lesions and elevated plasma corticosterone in rats. Pretreatment with alpha-methyltyrosine (alpha-MT), haloperidol, or sulpiride aggravated both responses, whereas bromocriptine attenuated them. In rats immunized with sheep red blood cells (SRBCs), RS prevented the booster-induced rise in anti-SRBC antibody titre. This response was further suppressed by alpha-MT, haloperidol, or sulpiride pretreatment, whereas bromocriptine potentiated the humoral immune response. In mice immunized with SRBCs, antigen challenge-induced increase in footpad thickness was inhibited by RS. Similar inhibitions in this response were also seen after alpha-MT or haloperidol treatment. The results are discussed in light of complex dopaminergic mechanisms in the regulation of visceral, endocrinological, and immune responses during stress.

Effects of nefiracetam on drug-induced impairment of latent learning in mice in a water finding task

We investigated the effects of nefiracetam (DM-9384), a pyrrolidone derivative, on chlordiazepoxide-, apomorphine-, and methamphetamine-induced impairment of latent learning in a water finding test in mice. Pretreatment with nefiracetam reversed the inhibitory effects of chlordiazepoxide and apomorphine, but not those of methamphetamine, on latent learning. The ameliorative effects of nefiracetam on apomorphine-induced, but not chlordiazepoxide-induced impairment of latent learning were antagonized by scopolamine. These results provide further evidence that nefiracetam has anti-amnesic effects. Further, it is suggested that the cholinergic neuronal system may be involved in the ameliorative effects exerted by nefiracetam on apomorphine-induced impairment of latent learning.

A differential dopamine receptor involvement during stress ulcer formation in rats

The involvement of dopaminergic (DA) receptors and their possible interactions were evaluated during stress ulcer formation in rats. The DA1 antagonist SCH 23390 (0.025, 0.05, or 0.1 mg/kg) produced only marginal aggravations in gastric stress pathology when compared to vehicle controls. The DA2 antagonist sulpiride (10 or 50 mg/kg) had dose-related effects. The lower dose aggravated whereas the higher dose attenuated stress ulcerogenesis. The DA2 agonist bromocriptine (2.5 or 5.0 mg/kg), however, attenuated gastric stress ulcers. Pretreatment of rats with the DA depletor alpha-methyl-para-tyrosine or the DA1-antagonist SCH23390 clearly neutralized the stress ulcer-attenuating effects of bromocriptine. These results reaffirm a gastric cytoprotective role for DA and further suggest that DA1-DA2 receptor interactions are crucial during DAergic regulation of gastric mucosal integrity during stress.

Neuroleptic-induced defecation in rats as a model for neuroleptic dysphoria

Two groups of 32 rats were challenged in a well-habituated environment with haloperidol (0.5 mg/kg), haloperidol (0.1 mg/kg), domperidone (0.1 mg/kg), or saline to study the effect of these drugs on defecation--an index of emotionality--and voluntary movements in the 2 hours after the injection. The haloperidol-treated rats in the high-dose condition had significantly more bolus counts in the 2 hours after the injection than were observed in the groups treated with domperidone (a peripheral dopamine D2 receptor antagonist) or placebo. All movements were greatly reduced in the haloperidol-treated rats and, in this group, the ones with more bolus counts did not differ in their activity levels from those with fewer bolus counts. There was a trend for the rats that were less mobile at 10 minutes after the injection to produce more boli in the 2-hour period. Our study, therefore, replicates the findings of Sanberg (1980) and Russell et al. (1987a, 1987b) that haloperidol increases "emotional" defecation in rats in well-habituated environments, but the same model does not replicate the motor component of neuroleptic-induced akathisia seen in human subjects.

Differentiation of haloperidol and clozapine using a complex operant schedule in the dog

This study aimed to differentiate chronically administered typical (haloperidol) and atypical (clozapine) neuroleptics in the dog using a complex temporal regulation schedule combining operant, voluntary, and involuntary motor parameters. Although clozapine and haloperidol showed some characteristics of neuroleptics, justifying their adherence to the same class of compounds, differences have also been highlighted and compared to the clinical observations. Haloperidol induced catalepsy, tremor, dystony, hyperkinesia, and stereotypy. Subjects produced anticipated responses before any stimulus. Incomplete and delayed responses were also produced. An interpretation in terms of akathisia and anhedonia has been suggested. Clozapine induced tremor, exploration, dystony, and hypersalivation. Subjects produced disinhibitory responses to the negative stimulus and incomplete responses but these latter were submitted to tolerance. The simultaneous presence of tranquilizing and disinhibitory effects has been reported on the clinical potential of clozapine both in cases of positive and negative schizophrenic symptomatologies.

Neuroleptic-induced changes in the anxiolytic and myorelaxant properties of diazepam in the rat

Diazepam (2.0 mg/kg) was injected (IP) into rats 30 min before chlorpromazine (2.5, 5.0, or 10.0 mg/kg) on ten occasions. All doses of chlorpromazine enhanced the capacity of diazepam to increase rats' exploration of the exposed arms of an elevated plus-maze, an animal screening test for anxiolytic and anxiogenic substances. When maze testing occurred during each of the ten diazepam----chlorpromazine trials (after diazepam but before chlorpromazine), this enhancement effect appeared on Trial 6 and persisted thereafter. Haloperidol (3.0 mg/kg, IP) changed diazepam-elicited plus-maze activity in the same manner as chlorpromazine; however, thioridazine (10.0 mg/kg) and pimozide (2.0 mg/kg) were ineffective. Additionally, haloperidol, like chlorpromazine, was found to reduce diazepam's muscle relaxation effect (inclined plane test) as a consequence of diazepam----haloperidol pairings; once again, thioridazine and pimozide proved ineffective. These results suggested that not all neuroleptics will alter diazepam activity, and also that dopamine blockade per se is not sufficient to induce such changes. While the reasons for the enhanced plus-maze effects of diazepam induced by haloperidol and chlorpromazine remain elusive, the diminished myorelaxant effect may be linked to a neuroleptic's capacity to induce muscular side effects: thioridazine and pimozide are far less likely to yield such effects than are chlorpromazine and haloperidol. Haloperidol administered chronically by itself was found to have an effect on diazepam-induced myorelaxation. Administration of this butyrophenone either orally (2.0 mg/kg daily for 22 days) or in depot form (haloperidol decanoate, 60.0 mg/kg IM once a month for four months) caused a diminished effect of diazepam in rats subjected to the inclined plane test.(ABSTRACT TRUNCATED AT 250 WORDS)

Anxiolytic activity of the progesterone metabolite 5 alpha-pregnan-3 alpha-o1-20-one

3 alpha-hydroxylated pregnane steroids have been shown to possess anesthetic, hypnotic, anticonvulsant and anxiolytic properties. In this study, metabolites of progesterone and deoxycorticosterone, 5 alpha-pregnan-3 alpha-o1-20-one (3 alpha-OH-DHP) and 5 alpha-pregnan-3 alpha,21-diol-20-one (5 alpha-THDOC), respectively, were tested for anxiolytic effects in N.I.H. Swiss-Webster mice using the light/dark transition, open-field and lick-suppression tests. Similar to the benzodiazepine (BZ) diazepam, 3 alpha-OH-DHP (5-40 mg/kg) and 5 alpha-THDOC (5-40 mg/kg) significantly increased the number of light/dark transitions. 3 alpha-OH-DHP's effects were stereospecific as its diasteriomer, 3 beta-OH-DHP was devoid of activity. The benzodiazepine antagonist CGS-8216 (10 mg/kg) blocked diazepam's (1.0 mg/kg) anxiolytic effects, but did not have any effect against 3 alpha-OH-DHP (20 mg/kg). The data indicate that the pregnane steroids produce their anxiolytic effects through a separate mechanism than the BZs. 3 alpha-OH-DHP (20 mg/kg), 5 alpha-THDOC (20 mg/kg) and diazepam (1.0 mg/kg) increased activity in a open-field test. 3 beta-OH-DHP had no effect in the open-field test. Furthermore, 3 alpha-OH-DHP produced a 235% increase in punished responding in a lick-suppression test. These results demonstrate that the endogenous pregnane steroids possess anxiolytic effects that may be clinically relevant.

Stimulant effect of the beta-carboline FG 7142 in the open-field test

The anxiogenic activity of N-methyl-beta-carboline-3-carboxamide (FG 7142) is sometimes difficult to observe in rats. As the open field has recently been applied successfully to test the anxiogenic potential of n-butyl-beta-carboline-3-carboxylate (beta-CCB) in mice, a comparable experiment was performed with FG 7142 (1, 5, 10, 30 mg/kg i.p.) in rats. In contrast to the inhibitory effects measured with beta-CCB, FG 7142 significantly increased the ambulation and rearing scores and induced aggressivity in some animals. A differential sensitivity of mice and rats to beta-carbolines, predominant analeptic properties of FG 7142, and differences in the types of anxiety induced are proposed to account for this discrepancy.

Effects of specific dopaminergic agonists and antagonists in the open-field test

It has been found that dopaminergic transmission could be involved in some aspects of anxiety. The present study aims to explore this hypothesis further, using specific DA1 (SKF 38393) and DA2 (bromocriptine) agonists or DA1 (SCH 23390), and DA2 (zetidoline) antagonists in the open-field test. The results confirm previous studies indicating that DA1 and DA2 agonists predominantly increase locomotor activity, while DA1 and DA2 antagonists predominantly decrease it. However, at low doses, the four drugs increase the peripheral ambulation score significantly and, with the exception of zetidoline, also increase the central ambulation score. The observations made with zetidoline confirm the hypothesis that a specific presynaptic DA2 antagonism could be determinant for the disinhibitory effects of low doses of neuroleptics. A collateral action on 5HT transmission is also suggested to explain an hypothetic anxiolytic action of DA agonists and SCH 23390 at lower doses.

Clozapine: an atypical neuroleptic

Since it was synthesized in 1960, much has been written about clozapine. Although a number of its properties are those of a neuroleptic, it displays marked differences from classical antipsychotics to the extent that it is currently listed as an atypical neuroleptic. A classical neuroleptic has been defined in man according to its antipsychotic properties, accompanied by extrapyramidal effects, and in animals according to its cataleptic properties, its ability to antagonize apomorphine and amphetamine stereotypies and to suppress the conditioned avoidance response. Moreover, the classical neuroleptic exerted depressive and anhedonic effects in most conditioning schedules. With clozapine, most of these properties are no longer strictly in force to the point that they call in question the validity of the tests carried out to detect the potential of neuroleptics. This article attempts to compare the characteristics of clozapine with those of classical neuroleptics from a toxicological, neuropharmacological, psychopharmacological and clinical point of view.

Anxiolytic potential of a microgram dose of chlordiazepoxide in the open-field test

Diazepam, when administered in very low doses (100 micrograms/kg), can induce a specific inhibition of coarse and ambulation activities in the rat, suggesting a novel mechanism of action occurring in the microgram dose range. This study fails to reproduce the same effects with chlordiazepoxide. On the contrary, greater stimulant and anxiolytic effects were measured with the lowest dose tested (0.1 mg/kg). These results demonstrate that the familiar effects of benzodiazepines should not be extrapolated uncritically to lower dose ranges without empirical testing.