Dose-response analysis of the effects of buspirone on rearing in rats

Evidence for Bell-Shaped Dose-Response Emetic Effects of Temsirolimus and Analogs: The Broad-Spectrum Antiemetic Efficacy of a Large Dose of Temsirolimus Against Diverse Emetogens in the Least Shrew (Cryptotis parva)

Temsirolimus is a prodrug form of sirolimus (rapamycin). With its analogs (everolimus, ridaforolimus, and rapamycin), it forms a group of anticancer agents that block the activity of one of the two mammalian targets of rapamycin (mTOR) complexes, mTORC1. We investigated the emetic potential of varying doses (0, 0.5, 1, 2.5, 5, 10, 20, and 40 mg/kg, i.p.) of temsirolimus in the least shrew. Temsirolimus caused a bell-shaped and dose-dependent increase in both the mean vomit frequency and the number of shrews vomiting with maximal efficacy at 10 mg/kg (p < 0.05 and p < 0.02, respectively). Its larger doses (20 or 40 mg/kg) had no significant emetic effect. We also evaluated the emetic potential of its analogs (5, 10, and 20 mg/kg, i.p.), all of which exhibited a similar emetic profile. Our observational studies indicated that temsirolimus can reduce the shrew motor activity at 40 mg/kg, and subsequently, we examined the motor effects of its lower doses. At 10 and 20 mg/kg, it did not affect the spontaneous locomotor activity (distance moved) but attenuated the mean rearing frequency in a U-shaped manner at 10 mg/kg (p < 0.05). We then determined the broad-spectrum antiemetic potential of a 20 mg/kg (i.p.) dose of temsirolimus against diverse emetogens, including selective and nonselective agonists of 1) dopaminergic D2/3 receptors (apomorphine and quinpirole); 2) serotonergic 5-HT3 receptors [5-HT (serotonin) and 2-methyl-5-HT]; 3) cholinergic M1 receptors (pilocarpine and McN-A-343); 4) substance P neurokinin NK1 receptors (GR73632); 5) the L-type calcium (Ca2+) channel (LTCC) (FPL64176); 6) the sarcoplasmic endoplasmic reticulum Ca2+ ATPase inhibitor, thapsigargin; 7) the CB1 receptor inverse agonist/antagonist, SR141716A; and 8) the chemotherapeutic cisplatin. Temsirolimus prevented vomiting evoked by the aforementioned emetogens with varying degrees. The mechanisms underlying the pro- and antiemetic effects of temsirolimus evaluated by immunochemistry for c-fos expression demonstrated a c-fos induction in the AP and NTS, but not DMNX with the 10 mg/kg emetic dose of temsirolimus, whereas its larger antiemetic dose (20 mg/kg) had no significant effect. Our study is the first to provide preclinical evidence demonstrating the promising antiemetic potential of high doses of temsirolimus and possibly its analogs in least shrews.

Tests of unconditioned anxiety - pitfalls and disappointments

The plus-maze, the light-dark box and the open-field are the main current tests of unconditioned anxiety for mice and rats. Despite their disappointing achievements, they remain as popular as ever and seem to play an important role in an ever-growing demand for behavioral phenotyping and drug screening. Numerous reviews have repeatedly reported their lack of consistency and reliability but they failed to address the core question of whether these tests do provide unequivocal measures of fear-induced anxiety, that these measurements are not confused with measures of fear-induced avoidance or natural preference responses - i.e. discriminant validity. In the present report, I examined numerous issues that undermine the validity of the current tests, and I highlighted various flaws in the aspects of these tests and the methodologies pursued. This report concludes that the evidence in support of the validity of the plus-maze, the light/dark box and the open-field as anxiety tests is poor and methodologically questionable.

Cognitive dysfunction resulting from hippocampal hyperactivity--a possible cause of anxiety disorder?

Pure cognition and hence pure cognitive dysfunction might be expected to have no direct relation to any specific emotion. Changes in cognitive processing will change the assessment of stimuli and thus could change emotional responses nonspecifically. However, neurology suggests a more direct relation between at least some aspects of cognition and emotion. The limbic system in general and the hippocampus in particular have been suggested at different times to be crucial for both memory and emotion. Even recently, O'Keefe and Nadel (The hippocampus as a cognitive map, Oxford University Press, 1978) proposed that the hippocampus is a spatial, or cognitive, map, while Gray (The neuropsychology of anxiety: An enquiry into the functions of the septo-hippocampal system. Oxford University Press, 1982) proposed that it is central to anxiety. This apparent incongruity can be resolved by combining recent developments in the psychology of anxiety (which emphasise changed processing biases), recent extensions of Gray's theory (which bring it closer to cognitive views), and recent theories of the role of the hippocampus in memory (which see it as controlling rather than storing information). This paper proposes that at least some instances of clinical anxiety could result from hyperactivity of the septo-hippocampal system, which would produce cognitive dysfunction in the form of increased negative association of stimuli with a consequential increase in anxiety when the stimuli are subsequently presented.

The pituitary-adrenal axis and the different behavioral effects of buspirone and chlordiazepoxide

Benzodiazepines and the novel anxiolytic buspirone share a common capacity to relieve clinical anxiety but do not share any side effects. Anxiety releases stress hormones and, at moderate doses, anxiolytic benzodiazepines block this release. It is interesting, therefore, that buspirone and other 5-HT1A agonists release stress hormones at moderate doses. Both the U-shaped dose-response curve seen with buspirone in some animal tests of anxiety and its slow onset of clinical action could be attributed to this release of stress hormones. Metyrapone (200 mg/kg), an inhibitor of 11-beta-hydroxylase, was used in the present experiments as a form of chemical adrenalectomy and was combined with administration of corticosterone (1 mg) to produce rats with presumed approximately normal corticosterone levels but no capacity to release endogenous corticosterone. This treatment reduced the difference normally observed in the effects of chlordiazepoxide (5 mg/kg) and buspirone (0.37 mg/kg) on a fixed interval schedule particularly in the early part of the interval when release of behavioral inhibition would be expected to contribute most to the effects. These results are consistent with the previous suggestion of Johnston and File (8) that the anxiolytic action of buspirone may be counteracted by activation of the pituitary-adrenal axis. Corticosterone appears to be the most likely critical agent for this antagonist action in the present experiments, although CRF and ACTH are also possibilities. It is likely that there is a mutual functional opposition between endogenous anxiolytic factors and stress hormones.

5-Hydroxytryptamine-interacting drugs in animal models of anxiety disorders: more than 30 years of research

An overview of the behavioral data arising from the vast literature concerning the involvement of 5-hydroxytryptamine (5-HT) neurotransmission in the regulation of anxiety is presented. More than 1300 experiments were carried out in this area and they provide evidence that: (1) results obtained in ethologically based animal models of anxiety with drugs stimulating 5-HT transmission are most consistent with the classic 5-HT hypothesis of anxiety in that they show an increase in animals' emotional reactivity; (2) no category of anti-anxiety models are selectively sensitive to the anxiolytic-like effects of drugs targetting 5-HT1A, 5-HT2A or 5-HT2C receptor subtypes; (3) anxiolytic-like effects of 5-HT3 receptor antagonists, in the great part, are revealed by models based on spontaneous behaviors. Taken together, these observations lead to the conclusion that different 5-HT mechanisms, mediated by different receptor subtypes, are involved in the genesis of anxiety.

Similar effects of buspirone and chlordiazepoxide on a fixed interval schedule with long-term, low-dose administration

Buspirone is a novel anxiolytic which does not share the muscle relaxant, anticonvulsant and sedative properties of classical anxiolytics such as the benzodiazepines. Its effects on behavioural tests of anxiolytic action generally match those of classical anxiolytics provided a low dose is used. However, in a previous experiment, buspirone appeared to affect fixed interval responding in a way which differed qualitatively as well as quantitatively from the classical anxiolytic chlordiazepoxide. It takes as much as 2 weeks for the clinical effects of anxiolytics to develop, during which time the side effects of benzodiazepines undergo tolerance. We, therefore, decided to compare long-term pre-administration (60 days, three injections/day) of buspirone and chlordiazepoxide on learning of a fixed interval 60-s schedule. The doses were based on previous acute dose-response tests of hippocampal theta rhythm in freely moving animals. Buspirone (0.1 mg/ kg i.p.) and chlordiazepoxide (0.4 mg/kg i.p.) produced similar increases in responding, especially in the middle of acquisition of the fixed interval schedule. Consistent with our acute electrophysiological tests, the effects of 0.4 mg/kg chlordiazepoxide were somewhat larger than those of 0.1 mg/kg buspirone. These results suggest that the acute effects of buspirone, but probably not chlordiazepoxide, on fixed interval responding are contaminated by side effects which do not seriously affect the results with long-term administration. The effects of both novel and classical anxiolytics on control of hippocampal theta rhythm appear to predict the magnitude of their common anxiolytic effects and to be unrelated to their different side effects.

Ethological evaluation of the effects of acute and chronic buspirone treatment in the murine elevated plus-maze test: comparison with haloperidol

Buspirone is renowned for its highly inconsistent effects in animal models of anxiety. In the present study, the effects of acute (0.63-5.0 mg/kg) and chronic (1.25-5.0 mg/kg, daily, 15 days) buspirone treatment on the behaviour of mice in the elevated plus-maze test were assessed using a recently developed ethological scoring method. On acute administration, a selective reduction in risk assessment behaviours was observed at 1.25 mg/kg; these mild anxiolytic-like effects were maintained at higher doses (2.5-5.0 mg/kg) which also reduced measures of general activity. Similar, though more potent, effects were observed with chronic administration; the lowest dose tested (1.25 mg/kg) reduced open arm entries and total stretch attend postures while higher doses profoundly reduced all major indices of anxiety (traditional and novel) and, concomitantly, suppressed total entries and rearing. Acute administration of haloperidol (0.0125-0.1 mg/kg) appeared to mimic the behavioural suppressant effects of buspirone without selectively affecting anxiety-related measures at any dose. It is suggested that the anti-anxiety and behavioural suppressant profile of buspirone may reflect combined action at 5-HT1A and D2 receptors, respectively. Results are discussed in relation to the utility of risk assessment as a sensitive index of anxiety in models based upon unconditioned behaviour.

Effects of buspirone and ipsapirone on schedule induced polydipsia: comparison with 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and raclopride

In the present experiments, the effects of the azapirone anxiolytics, buspirone and ipsapirone, on excessive drinking induced by a FT-60 schedule of food delivery (schedule induced polydipsia, SIP) were investigated. Because buspirone is known to block dopamine receptors and both buspirone and ipsapirone act as agonists at the 5-HT1A receptor, their effects on polydipsia were compared to raclopride, an antagonist at D2 receptors, and 8-OH-DPAT, an agonist at the 5-HT1A receptor, thus providing information about the relative importance of the serotonergic and/or dopaminergic systems for the maintenance of polydipsia. The effects of all four drugs were investigated both acutely, and following repeated treatment. The doses employed were as follows: buspirone, 1.0, 3.0, and 10.0 mg/kg; raclopride, 0.05, 0.15, and 0.5 mg/kg; 8-OH-DPAT, 0.1, and 1.0 mg/kg and ipsapirone, 1.0, 3.0, 10.0 mg/kg. Administered acutely, the lowest doses of buspirone and raclopride did not alter drinking, whilst the low dose of 8-OH-DPAT significantly reduced polydipsia. These effects were reversed following repeated treatment over 16 successive days. Buspirone 1.0 mg/kg and 0.05 mg/kg raclopride reduced drinking, whilst tolerance developed to the effects of 0.1 mg/kg 8-OH-DPAT. Ipsapirone, at low doses, was without effect on drinking. At high doses, all four drugs reduced drinking both acutely and chronically. Repeated treatment with buspirone (3.0, and 10.0 mg/kg) reduced licking and panel entries, but induced a selective decrease in licking at the low dose (1.0 mg/kg). Similar effects were seen following raclopride treatment, although the effects were less selective. 8-OH-DPAT and ipsapirone, in contrast reduced licking only at the highest dose, and both drugs increased panel entries as testing continued. The effects of buspirone resembled those of raclopride whereas the effects of ipsapirone resembled those of 8-OH-DPAT. Buspirone appears to act as a dopamine antagonist in this test. The effects of the drugs suggest that SIP depends upon motivational and performance factors which may be more sensitive to drug manipulation than potential underlying psychological factors such as anxiety or stress.

Effects on open-field behavior of diazepam and buspirone alone and in combination with chronic caffeine

Effects of diazepam (1, 2 mg/kg) and buspirone (1.25, 2.5 mg/kg) on locomotor and rearing activity were observed in rats tested in an open field. Both doses of each drug reduced ambulation. However, for buspirone, this effect was confined to females. Walking and rearing was reduced by the higher dose of diazepam and rearing by both doses of buspirone. In rats that had ingested approximately 26 mg/kg/day of chronic caffeine for seven days prior to and immediately before testing, all effects of diazepam observed earlier failed to achieve significance except for ambulation. However, all earlier buspirone effects (including female-only decreased ambulation) were unaffected by the caffeine treatment. It was concluded that buspirone may be preferable to diazepam as an anxiolytic when in the presence of regular caffeine ingestion.

Buspirone produces a dose-related impairment in spatial navigation

Classical anxiolytic drugs and hippocampal lesions have common behavioural effects that include loss of place navigation in the water maze. The novel anxiolytic drug buspirone, unlike classical anxiolytic drugs, does not interact with GABA and is not muscle relaxant, sedative, hypnotic, anticonvulsant, or addictive. Buspirone affects hippocampal electrophysiology in a similar fashion to classical anxiolytics and so we predicted it would have similar effects on spatial navigation. Rats injected with buspirone (0.1-10.0 mg/kg, IP) showed a loss of acquisition of spatial navigation in the water maze that has a similar dose dependence to that reported for the effects of buspirone on the hippocampus. This finding demonstrates that the effects of anxiolytics on spatial navigation are not due to their side effects and supports the view that changes in hippocampal function may underlie some components of clinical anxiolytic action.