A comparison of motor behaviours in groups of rats distinguished by their climbing response to apomorphine

Assessing NH300094, a novel dopamine and serotonin receptor modulator with cognitive enhancement property for treating schizophrenia

Background: Schizophrenia is a serious psychiatric disorder that significantly affects the quality of life of patients. The objective of this study is to discover a novel antipsychotic candidate with highly antagonistic activity against both serotonin and dopamine receptors, demonstrating robust efficacy in animal models of positive, negative, and cognitive symptoms of schizophrenia. Methods: In the present study, we examined the activity of antipsychotic drug (NH300094) on 5-HT2A, 5-HT2C, 5-HT1A, 5-HT1B, 5-HT7, H1, M1, Alpha1A, D2L, D2S, Alpha2A, D3 receptor functional assay in vitro. In addition, multiple animal models, including dizocilpine (MK-801) induced hyper-locomotion; APO induced climbing; Conditioned Avoidance Response (CAR); DOI-Induced Head Twitch; Forced swimming test; Scopolamine induced cognitive impairment model, were used to verify the antipsychotic activity of NH300094 in preclinical. Results: In vitro functional assays have indicated that NH300094 is a potent antagonist of 5-HT receptors and dopamine receptors, with higher relative antagonistic activity against 5-HT2A receptor (5-HT2A IC50 = 0.47 nM) than dopamine receptors (D2L IC50 = 1.04 nM; D2S IC50 = 11.71 nM; D3 IC50 = 31.55 nM). Preclinical in vivo pharmacological study results showed that NH300094 was effective in multiple models, which is more extensive than the clinic drug Risperidone. Furthermore, the safety window for extrapyramidal side effects of NH300094 is significantly wider than that of Risperidone (For NH300094, mice catalepsy model ED50/ Mice MK-801 model ED50 = 104.6-fold; for Risperidone, mice catalepsy model ED50/ Mice MK-801 model ED50 = 12.9-fold), which suggests a potentially better clinical safety profile for NH300094. Conclusion: NH300094 is a novel potent serotonin and dopamine receptors modulator, which has good safety profile and therapeutic potential for the treatment of schizophrenia with cognition disorders.

An ethanolic extract of Desmodium adscendens exhibits antipsychotic-like activity in mice

BACKGROUND

Desmodium adscendens extract (DAE) is used traditionally in Ghana for the management of psychosis. The present study aimed at providing pharmacological evidence for its ethnomedical use by testing the hypothesis that an ethanolic extract of Desmodium adscendens may possess antipsychotic properties.

METHODS

The primary behavioral effects of DAE on the central nervous system of mice were investigated using Irwin's test paradigm. Novelty-induced and apomorphine-induced locomotor and rearing behaviors in mice were explored in an open-field observational test system. Apomorphine-induced cage climbing test in mice was used as the antipsychotic animal model. The ability of DAE to induce catalepsy and enhance haloperidol-induced catalepsy was also investigated in mice.

RESULTS

The DAE produced sedation, cholinergic-, and serotonergic-like effects in mice when evaluated using the Irwin's test. No lethality was observed after 24 h post-treatment. The LD50 in mice was estimated to be greater than 3000 mg/kg. The DAE significantly decreased the frequency of novelty- and apomorphine-induced rearing and locomotor activities in mice. It also significantly lowered the frequency and duration of apomorphine-induced climbing activities in mice. It did not induce any cataleptic event in naïve mice but only significantly enhanced haloperidol-induced catalepsy at a dose of 1000 mg/kg.

CONCLUSIONS

The ethanolic extract of Desmodium adscendens exhibited antipsychotic-like activities in mice. Motor side effects are only likely to develop at higher doses of the extract.

Psychotropic Effects of an Alcoholic Extract from the Leaves of Albizia zygia (Leguminosae-Mimosoideae)

Background

Albizia zygia is used in Ghanaian traditional medicine for the management of mental disorders. The present study tested the hypothesis that an extract of the leaves of Albizia zygia (AZE) may possess antipsychotic and antidepressant properties.

Method

The novelty- and apomorphine-induced locomotor and rearing behaviours of AZE in mice were explored in an open-field observational test system. The effects of AZE in apomorphine-induced cage climbing test, extract-induced catalepsy, and haloperidol-induced catalepsy on mice were also investigated. Lastly, the forced swimming and tail suspension tests in mice were employed to screen the possible antidepressant effects of AZE.

Results

AZE (100-3000 mg/kg) showed signs of central nervous system (CNS) depression under observation, with no lethality, 24 h after treatment in mice. AZE (100-1000 mg/kg) produced a significant decrease in the frequency of novelty- and apomorphine-induced locomotor activities in mice. The extract also significantly decreased the frequency and duration of apomorphine-induced climbing activities in mice. AZE, while failing to produce any cataleptic event in naïve mice, significantly enhanced haloperidol-induced catalepsy at a dose of 1000 mg/kg. However, AZE did not produce any significant antidepressant effects in the test models employed.

Conclusion

The extract of Albizia zygia exhibited an antipsychotic-like activity in mice.

Extract of Synedrella nodiflora (L) Gaertn exhibits antipsychotic properties in murine models of psychosis

BACKGROUND

The hydro-ethanolic whole plant extract of Synedrella nodiflora (SNE) has demonstrated anticonvulsant, sedative and analgesic effects. Preliminary studies conducted in animals, SNE significantly decreased stereotypic behaviours suggesting antipsychotic potential. Coupled with the central nervous system depressant effects of SNE, we hypothesized that it may have utility in the management of psychosis. The present study therefore investigated the antipsychotic potential of the SNE in several murine models of psychosis.

METHOD

The primary central nervous system activities of SNE (30-3000 mg/kg, p.o) were investigated using the Irwin's test. The novelty-induced rearing, locomotion and stereotypy counts provoked by SNE (100-1000 mg/kg, p.o) were conducted using the open-field paradigm. The antipsychotic test models used in the screening of SNE (100-1000 mg/kg, p.o) included apomorphine-induced stereotypy, rearing, locomotion and cage climbing activities. The combined effects of a low dose of SNE (100 mg/kg) with various doses of haloperidol and chlorpromazine were analysed using the apomorphine-induced cage climbing and stereotypy, respectively. The ability of SNE to cause catalepsy in naïve mice as well as its effect on haloperidol-induced catalepsy was assessed.

RESULTS

SNE showed acetylcholine-like and serotonin-like activities in the Irwin test, with sedation occurring at high doses. SNE significantly reduced the frequencies of novelty- and apomorphine-induced rearing and locomotion; stereotypy behaviour and the frequency and duration of apomorphine-induced cage climbing in mice. In all the tests performed, SNE was less potent than the reference drugs used (chlorpromazine and haloperidol). In addition, SNE potentiated the effects of haloperidol and chlorpromazine on apomorphine-induced cage climbing and stereotypy activities in mice.

CONCLUSION

SNE, while exhibiting antipsychotic properties itself, can also potentiate the antipsychotic effects of chlorpromazine and haloperidol.

Psychoneuropharmacological activities and chemical composition of essential oil of fresh fruits of Piper guineense (Piperaceae) in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Piper guineense Schum & Thonn (Piperaceae) is a medicinal plant used in the Southern States of Nigeria to treat fever, mental disorders and febrile convulsions.

AIMS OF THE STUDY

This study aims at determining the chemical composition and the central nervous system (CNS) activities of the essential oil obtained from the plant׳s fresh fruits in order to rationalize its folkloric use.

MATERIALS AND METHODS

Essential oil of P. guineense (EOPG) obtained by hydrodistillation was analysed by GC/MS. EOPG (50-200mg/kg, i.p.) was evaluated for behavioural, hypothermic, sedative, muscle relaxant, anti-psychotic and anticonvulsant activities using standard procedures.

RESULTS AND DISCUSSION

Analysis of the oil reveals 44 compounds of which 30 compounds constituting 84.7% were identified. The oil was characterized by sesquiterpenoids (64.4%) while only four monoterpeneoids (21.3%) were found present in the oil. Major compounds identified were β-sesquiphellandrene (20.9%), linalool (6.1%), limonene (5.8%), Z-β-bisabolene (5.4%) and α-pinene (5.3%). The EOPG (50-200mg/kg, i.p.) caused significant (p<0.01) inhibition on rearing {F(4,20)=43}, locomotor {F(4,20)=22} activity and decreased head dips in hole board {F(4,20)=7} indicating CNS depressant effect; decreased rectal temperature {F(4,20)=7-16}, signifying hypothermic activity; decreased ketamine-induced sleep latency {F(4,20)=7.8} and prolonged total sleeping time {F(4,20)=8.8}, indicating sedative effect; reduced muscular tone on the hind-limb grip test {F(4,20)=22}, inclined board {F(4,20)=4-49} and rota rod {F(4,20)=13-106}, implying muscle relaxant activity; induced catalepsy {F(4,20)=47-136}, inhibited apomorphine-induced climbing behaviour {F(4,20)=9} and inhibited apomorphine-induced locomotor {F(4,20)=16}, suggesting anti-psychotic effect; and protected mice against pentylenetetrazole-induced convulsions, indicating anticonvulsant potential.

CONCLUSION

The most abundant component of the fresh fruits essential oil of P. guineense was β-sesquiphellandrene (20.9%); and the oil possesses CNS depressant, hypothermic, sedative, muscle relaxant, antipsychotic and anticonvulsant activities, thus providing scientific basis for its ethnomedicinal applications.

New hybrids of quipazine and trazodone as selective inhibitors of uptake of 5-hydroxytryptamine

Two new congeners, 4-(chloropropyl)-1-(2-quinolyl)piperazine- and 2-[3-[4-[2-(quinolyl)]-1-piperazinyl]propyl]-1,2,4-triazolo] 4,3-a]pyridin-3(2H)-one, of trazodone were synthesized and found to be potent and selective inhibitors of synaptosomal uptake of 5-hydroxytryptamine [5-HT, serotonin; IC50 = norepinephrine greater than 5 microM, 5-HT = 210-890 nM], with minimal effects in antagonizing (-)-apomorphine-induced climbing behavior and suppression of spontaneous locomotor activity in mice (ED50 greater than 50 mg/kg). The two compounds behaved like atypical antidepressants, since they weakly antagonized reserpine-induced hypothermia. The acute toxicity studies have shown that these compounds were less lethal when compared with imipramine or quipazine. Furthermore, chronic treatments (20 mg/kg, daily for 10 and 21 days) significantly decreased the isoprenaline-induced increase in cyclic AMP in the rat brain cortex, suggesting desensitization of beta-adrenoceptors. These findings point to the effects of these compounds as potential antidepressants dealing with specific serotonergic mechanisms.

Neurotensin selectively antagonizes apomorphine-induced stereotyped climbing

In order to better characterize the neuroleptic properties of neurotensin, the dose-related effects of the peptide on stereotyped climbing, sniffing and licking induced by 0.6 mg/kg apomorphine were examined. The following doses of the peptide were injected intraventricularly 30 min prior to apomorphine administration: 0.9, 3.75, 30.0 and 60 micrograms. Results indicate that, whereas oro-facial stereotypies remained unaffected by the peptide, stereotyped climbing was significantly decreased with the two largest doses of neurotensin. These findings indicate that the profile of neurotensin's neurobehavioral effects is more akin to that of atypical than typical neuroleptics.

Search after neurobiological profile of individual-specific features of Wistar rats

The first part of this study demonstrates that the bimodal shape of variation in "fleeing" and "nonfleeing" or "freezing" rats of an outbred strain of Wistar rats forms part of an overall biomodal variation in behavioural responses to injections of agents, which selectively alter, or reflect, the noradrenergic or dopaminergic activity in the ventral striatum, and dopaminergic activity in the dorsal striatum, the GABA-ergic activity in the substantia nigra, pars reticulata, and the GABA-ergic activity in the deeper layers of the superior colliculus. It is concluded that the "fleeing" and "nonfleeing" rats, each of them marked by their own trans-situational consistency in pharmacological and behavioural responses, represent the two fundamentally different types of individuals which normally exist in unselected populations of rodents. The second part of this study demonstrates that the pharmacogenetic selection of apomorphine-susceptible (APO-SUS) and apomorphine-unsusceptible (APO-UNSUS) rats, i.e., one individual-specific feature of the overall bimodal variation for pharmacological responses in our outbred strain of rats, is a valid tool to disperse the above-mentioned individual-specific features as far as possible. First, these lines allowed us to prove that the overall bimodal shape of variation in pharmacological and behavioral responses of individual outbred rats is in part genetically determined. Second, these lines allowed us to prove that a bimodal variation in neurochemical features of the circuitry, in which the ventral striatum is embedded, underlies the overall bimodal variation in pharmacological and behavioural responses. Third, these lines allowed us to demonstrate that a fundamental difference in organizing behaviour with the help of external and internal information has to be considered as a common factor giving rise to the individual differentiation found in the present study. Given the notion that this individual differentiation appears to be valid across lines, substrains and strains of rats, the present study lays the foundation for understanding at least a part of the physiological basis underlying differences between the two fundamentally different types of individuals existing in normal populations of rodents.

Differential ability of selective and non-selective dopamine agonists to induce climbing in the rat indicates the involvement of both D-1 and D-2 receptors in this behaviour

Approximately 50% of female Wistar rats examined exhibited a continuous climbing response to a screening dose of apomorphine. In animals identified as climbing, the mixed D-1/D-2 agonists apomorphine, pergolide and L-dopa, and the indirectly acting agonists nomifensine and (+)-amphetamine, induced a dose-related climbing response. The selective D-1 agonist SKF 38393 caused only minimal climbing, and the selective D-2 agonists bromocriptine, lisuride and LY 141865 induced a weak climbing response. All agonists examined, except SKF 38393, caused a dose-related stereotypy response. The selective D-1 antagonist SCH 23390, and the selective D-2 antagonist sulpiride, both produced maximum inhibition of apomorphine-induced climbing. SCH 23390 also inhibited stereotyped behaviour, but sulpiride was less effective. In animals identified as "non-climbers" using the screening dose of apomorphine, only L-dopa induced a marked climbing response. Nomifensine and bromocriptine produced weak or discontinuous climbing in this group, while the other agonists examined had little or no effect. In contrast all drugs examined, except SKF 38393, induced stereotyped behaviour of the same intensity observed in the "climbers". It is concluded that stimulation of both D-1 and D-2 receptors is necessary to induce a continuous climbing behaviour in rats. D-2, but not D-1 stimulation, alone can induce a weak or discontinuous climbing response, but concomitant stimulation of D-1 receptors potentiates this effect. Failure of some rats to climb does not appear to be related to relative degrees of D-1 and D-2 stimulation.

Antipsychotic properties of new N-(4-substituted-1-piperazinylethyl)- and N-(4-substituted-1-piperidinylethyl)-phthalimides

A series of N-(4-phenyl- and 4-pyridyl-1-piperazinylethyl)- and N-(4-phenyl-1-piperidinylethyl)-phthalmides were synthesized and tested for antipsychotic activity. All compounds suppressed the spontaneous motor activity and the apomorphine-induced climbing in mice and pergolide-induced locomotor activity in rats, demonstrating psychotropic properties equal to the corresponding properties of sulpiride. Although the compounds, like sulpiride, were less potent than haloperidol in blocking the locomotor activities, they caused no catalepsy, a major side effect following treatment with conventional antipsychotic agents. It is likely that the new compounds produce their neuroleptic activities through inhibition of limbic dopamine receptors.

The pharmacological characterisation of pilocarpine-induced purposeless chewing behaviour in the rat

Purposeless chewing in rats was induced by the acute administration of the cholinergic agonist pilocarpine or by physostigmine. Pilocarpine-induced chewing was antagonised by the centrally acting anticholinergic drugs scopolamine, benzhexol and secoverine, but not by the peripherally acting anticholinergic drug methylscopolamine. Both benzhexol and secoverine caused dose-dependent inhibition of pilocarpine-induced chewing. The D-2 antagonist sulpiride and the D-1 antagonist SCH 23390 did not inhibit pilocarpine-induced chewing. The non-selective neuroleptics pimozide, trifluoperazine and thioridazine also were inactive. In contrast, clozapine caused a dose-related inhibition of pilocarpine-induced chewing. The alpha-1 antagonist prazosin, the alpha-2 antagonist idazoxan, the beta-antagonists propranolol and metoprolol and the H-1 antagonist mepyramine did not reduce pilocarpine-induced chewing. Purposeless chewing behaviour induced by pilocarpine was reduced in a dose-related manner by the administration of the 5-HT antagonists methiothepin and mianserin, but not by spiperone or ketanserin. These data confirm that pilocarpine-induced chewing behaviour in the rat is a model of central cholinergic activity, but suggest that a serotonergic component may be involved in the mediation of this behaviour.

Heterogeneous 3H-rauwolscine binding sites in rat cortex: two alpha 2-adrenoceptor subtypes or an additional non-adrenergic interaction?

Ligand binding and isolated tissue data have provided evidence for the existence of two, tissue-specific, alpha 2-adrenoceptor subtypes in various rodent and non-rodent species. Thus it has been proposed that the complex binding of alpha 2-antagonists to rat cortical membranes is due to the presence of both subtypes in this tissue. We have previously shown that the alpha 2-antagonist 3H-rauwolscine binds to two sites on rat cortical membranes: a high affinity component characterised pharmacologically as an alpha 2-binding site, and a low affinity, spiperone-sensitive, serotonergic-like component. By the use of computerised non-linear curve-fitting, and the inclusion of (in the incubation buffer of displacement experiments) a concentration of spiperone previously shown to selectively occlude the low affinity component of the 3H-rauwolscine saturation isotherm, we have determined the rank order of affinity at each of the two sites. Whereas the rank order of affinity at the high affinity site retains the pharmacological profile of a single, monophasic alpha 2-binding site, that at the low affinity component is markedly different and is similar to that at the putative 5HT1A subtype. These data, together with the additional, functional serotonergic interactions of rauwolscine and yohimbine, indicate that there is no evidence to support the existence of heterogeneous alpha 2-binding sites, as measured by 3H-rauwolscine binding, on rat cortical membranes. Furthermore, we present evidence that the specific, low affinity serotonergic interaction of 3H-rauwolscine could be avoided by a more judicial estimation of specific binding.

Differential effects of chronic ethanol on apomorphine-induced locomotion, climbing and aggression in rats

Male Wistar rats were tested for apomorphine-induced locomotion, climbing and aggression after 3 week's intragastric ethanol (EtOH) treatment, 5 g/kg as 20% solution daily. The ability of apomorphine (APO) to elicit rearing (1 mg/kg i.p.) and climbing (0.5 mg/kg i.p.) was significantly suppressed in EtOH withdrawn animals. General locomotor activity in response to 1 mg/kg of APO i.p. did not differ between control and EtOH-treated groups. Affective aggression was checked in pairs of low-aggressive rats, i.e. resistant to the aggression inducing action of 10 mg/kg APO. No symptoms of aggression appeared in control animals whereas EtOH administered rats responded with marked aggression to APO. The different effect of chronic EtOH on responsiveness to APO in three behavioral models is discussed in terms of varying involvement of dopaminergic systems and receptors in behavioral phenomena as well as their susceptibility to prolonged EtOH.

The paw test: a behavioural paradigm for differentiating between classical and atypical neuroleptic drugs

An often used animal model based on the effects of neuroleptics on spontaneous behaviour is the catalepsy test. However, this test seems to be particularly insensitive to the atypical neuroleptics thioridazine and, especially, clozapine. We have therefore developed an alternative test, the paw test, which measures the ability of drugs to prevent the spontaneous withdrawal of fore- and hindlimbs in rats, and have compared this with the classical catalepsy test. The results show that: 1) the classical neuroleptic drugs haloperidol and chlorpromazine, the atypical neuroleptic drugs clozapine and thioridazine, the potential atypical neuroleptic drugs molindone and SCH 23390, and the potential classical neuroleptic drug metoclopramide are potent in increasing the hindlimb retraction time; 2) the paw test discriminates between classical neuroleptics which are equipotent in prolonging both the forelimb (FRT) and hindlimb retraction time (HRT) an atypical neuroleptics which are much more potent in prolonging HRT than in prolonging FRT; 3) the non-neuroleptic drugs desipramine, diazepam and morphine do not influence the variables measured in the paw test, although morphine does produce catalepsy; 4) Molindone as well as SCH 23390 behave like atypical neuroleptic drugs in the paw test. In comparison with the classical wood block catalepsy test, the paw test is shown to be superior for predicting the profile of the neuroleptics tested. Although more neuroleptics and non-neuroleptics have to be tested to determine whether false positives and false negatives do occur, we feel that the paw test might be an interesting animal model, because the increase in hindlimb retraction time was associated with the antipsychotic potential, whereas the increase in forelimb retraction time was associated with the potential to induce so-called extrapyramidal side effects.