Preclinical pharmacology of buspirone hydrochloride

Challenges of Delirium Management in Patients with Traumatic Brain Injury: From Pathophysiology to Clinical Practice

Traumatic brain injury (TBI) can initiate a very complex disease of the central nervous system (CNS), starting with the primary pathology of the inciting trauma and subsequent inflammatory and CNS tissue response. Delirium has long been regarded as an almost inevitable consequence of moderate to severe TBI, but more recently has been recognized as an organ dysfunction syndrome with potentially mitigating interventions. The diagnosis of delirium is independently associated with prolonged hospitalization, increased mortality and worse cognitive outcome across critically ill populations. Investigation of the unique problems and management challenges of TBI patients is needed to reduce the burden of delirium in this population. In this narrative review, possible etiologic mechanisms behind post-traumatic delirium are discussed, including primary injury to structures mediating arousal and attention and secondary injury due to progressive inflammatory destruction of the brain parenchyma. Other potential etiologic contributors include dysregulation of neurotransmission due to intravenous sedatives, seizures, organ failure, sleep cycle disruption or other delirium risk factors. Delirium screening can be accomplished in TBI patients and the presence of delirium portends worse outcomes. There is evidence that multi-component care bundles including an analgesia-prioritized sedation algorithm, regular spontaneous awakening and breathing trials, protocolized delirium assessment, early mobility and family engagement can reduce the burden of ICU delirium. The aim of this review is to summarize the approach to delirium in TBI patients with an emphasis on pathogenesis and management. Emerging CNS-active drug therapies that show promise in preclinical studies are highlighted.

Acute buspirone dosing enhances abuse-related subjective effects of oral methamphetamine

There is not an approved pharmacotherapy for treating methamphetamine use disorder. This study sought to determine the effects of acute buspirone treatment on the subjective and cardiovascular effects of oral methamphetamine in order to provide an initial assessment of the utility, safety, and tolerability of buspirone for managing methamphetamine use disorder. We predicted that acute buspirone administration would reduce the subjective effects of methamphetamine. We also predicted that the combination of buspirone and methamphetamine would be safe and well tolerated. Ten subjects completed the protocol, which tested three methamphetamine doses (0, 15, and 30mg) in combination with two buspirone doses (0 and 30mg) across 6 experimental sessions. Subjective effects and physiological measures were collected at regular intervals prior to and after dose administration. Methamphetamine produced prototypical subjective and cardiovascular effects. Acute buspirone administration increased some of the abuse-related subjective effects of methamphetamine and also attenuated some cardiovascular effects. The combination of oral methamphetamine and buspirone was safe and well tolerated. Acute buspirone administration may increase the abuse liability of oral methamphetamine. Chronic buspirone dosing studies remain to be conducted, but given preclinical findings and the outcomes of this work, the utility of buspirone for treating methamphetamine use disorder appears limited.

Effects of buspirone and the dopamine D3 receptor compound PG619 on cocaine and methamphetamine self-administration in rhesus monkeys using a food-drug choice paradigm

RATIONALE

The dopamine (DA) D2 and D3 receptors have been associated with cocaine abuse. A recent study with the D3 receptor (D3R) partial agonist PG619 found that it attenuated cocaine-induced reinstatement and the D2-like receptor antagonist buspirone has shown positive outcomes in two studies of cocaine abuse in monkeys. However, a recent clinical trial indicated that buspirone did not improve abstinence in treatment-seeking cocaine abusers.

OBJECTIVE

The objective of the study was to examine PG619 and buspirone under a food-drug choice paradigm in order to better model the clinical findings. In addition, we extended the characterization of both compounds to include methamphetamine (MA) self-administration (SA).

METHODS

Six adult male rhesus monkeys were trained to respond under a concurrent food (1.0-g pellets) and drug (0.01-0.3 mg/kg/injection cocaine or MA) choice paradigm in which complete SA dose-response curves were determined each session (N = 3/group). Monkeys received 5 days of treatment with either PG619 (0.1-3.0 mg/kg, i.v.) or buspirone (0.01-1.0 mg/kg, i.m.). In a follow-up study, the SA doses were reduced (0.003-0.1 mg/kg/injection) to increase reinforcement frequency and buspirone was retested.

RESULTS

PG619 did not affect cocaine or MA choice, while buspirone increased low-dose cocaine choice. Changing the SA doses increased the number of reinforcers received each session, but buspirone did not decrease drug choice.

CONCLUSIONS

Consistent with clinical findings, these results do not support the use of buspirone for psychostimulant abuse and suggest that food-drug choice paradigms may have greater predictive validity than the use of other schedules of reinforcement.

Effects of aging on 5-HT(1A) receptors and their functional response to 5-HT(1a) agonist in the living brain: PET study with [carbonyl-(11)C]WAY-100635 in conscious monkeys

Age-related changes in the serotonin 5-HT(1A) receptors in the living brains of conscious young (5.9 +/- 1.8 years old) and aged (19.0 +/- 3.3 years old) monkeys (Macaca mulatta) were evaluated by [carbonyl-(11)C]WAY-100635 and high-resolution positron emission tomography (PET). The regional distribution pattern of [carbonyl-(11)C]WAY-100635 at 60-91 min postinjection was the highest in the cingulate gyrus and hippocampus, high in the frontal and temporal cortices, lower in the occipital cortex, striatum, thalamus, and raphe nuclei, and lowest in the cerebellum in both young and aged monkeys. Graphical Logan plot analysis with metabolite-corrected plasma radioactivity as an input function into the brain was applied to evaluate 5-HT(1A) receptor binding in vivo. Significant age-related decreases in 5-HT(1A) receptor binding were observed only in the frontal and temporal cortices. In the hippocampus, although 5-HT(1A) receptor binding indicated no significant age-related changes, it showed an inverse correlation with individual cortisol levels in plasma. When the 5-HT(1A) receptor agonist 8-OH-DPAT was administered intravenously at a dose of 0.1, 0.3, or 1 mg/kg 30 min after tracer injection, binding of [carbonyl-(11)C]WAY-100635 was displaced in both age groups in a dose-dependent manner. However, the degree of displacement was more marked in young than in aged monkeys. These observations demonstrated the usefulness of [carbonyl-(11)C]WAY-100635 as an indicator of the age-related changes in cortical 5-HT(1A) receptors measured noninvasively by PET. In addition, these observations suggested that the age-related impairment of 5-HT(1A) receptor responses to 8-OH-DPAT might be related to the reduced efficacy of antidepressant therapy in elderly patients with depression.

Autoradiographic localization of 5-HT1A receptors in the post-mortem human brain using [3H]WAY-100635 and [11C]way-100635

The distribution of 5-HT1A receptors was examined in the post-mortem human brain using whole hemisphere autoradiography and the selective 5-HT1A receptor antagonist [3H]WAY-100635 ([O-methyl-3H]-N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2- pyridinyl)cyclohexanecarboxamide trihydrochloride). The autoradiograms showed very dense binding to hippocampus, raphe nuclei and neocortex. The labeling in neocortex was slightly lower than in the hippocampus and was mainly at superficial layers, although a faintly labeled band could be seen in deeper neocortical layers. Other regions, such as the amygdala, septum and claustrum, showed low densities caudatus and putamen, in cerebellum or in structures of the brain stem except in the raphe nuclei. The labeling of human 5-HT1A receptors with [3H]WAY-100635 was antagonised by the addition of 5-HT1A receptor ligands, 5-HT, buspirone, pindolol or 8-OH-DPAT (10 microM), leaving a very low background of non-specific binding. Saturation analysis of semiquantitative data from several human regions indicated that [3H]WAY-100635 has a Kd of approximately 2.5 nM. The selective labeling of 5-HT1A receptors with [3H]WAY-100635 clearly show that this compound is useful for further studies of the human 5-HT1a receptor subtype in vitro [11C]WAY-100635 is used for the characterization of 5-HT1A receptors with positron emission tomography (PET). WAY-100635 was also radiolabeled with the short-lived positron-emitting radionuclide carbon-11 (t1/2 = 20 min) and used for in vitro autoradiography on human whole hemisphere cryosections. [11C]WAY-100635 gave images qualitatively similar to those of [3H]WAY-100635, although with a lower resolution. Thus, the hippocampal formation was densely labeled, with lower density in the neocortex. Buspirone, pindolol or 8-OH-DPAT (10 microM), blocked all binding of [11C]WAY-100635. The in vitro autoradiography of the distribution of 5-HT1A receptors obtained with radiolabeled WAY-100635 provide detailed qualitative and quantitative information on the distribution of 5-HT1A-receptors in the human brain. Moreover, the studies give reference information for the interpretation of previous initial results at much lower resolution in humans with PET and [11C]Way-100635. These data provide a strong basis for expecting [11C]WAY-100635 to behave as a highly selective radioligand in vivo.

Involvement of alpha 1- but not alpha 2-adrenergic systems in the antagonizing effect of paeoniflorin on scopolamine-induced deficit in radial maze performance in rats

Paeoniflorin, a major constituent of peony root (1 mg/kg, p.o.), attenuated scopolamine-induced deficit in radial maze performance. Both prazosin (0.5 mg/kg, i.p.) and yohimbine (0.3 mg/kg, i.p.) neither impaired radial maze performance by itself nor augmented the scopolamine-induced performance deficit. Prazosin significantly blocked the antagonizing effect of paeoniflorin on the scopolamine deficit, whereas yohimbine did not affect the paeoniflorin effect. These data suggest that the alpha 1-adrenergic but not alpha 2-adrenergic systems are involved in the antagonizing effect of paeoniflorin on the scopolamine deficit in radial maze performance in rats.

The long-term effects of diazepam, lorazepam, and buspirone on behavioral suppression by a shock signal

1. Two experiments examined the long-term effects of treatment with buspirone (a nonbenzodiazepine anxiolytic), diazepam, or Lorazepam (two pharmacokinetically distinct benzodiazepines) on the capacity of a shock cue to disrupt appetitively conditioned behavior. 2. In Experiment 1, rats were injected with diazepam (5 mg/kg), buspirone (1.5 mg/kg or .75 mg/kg), or saline shortly before each of 12 bar press training sessions. Injections were suspended and three days later the rats received five days of Pavlovian fear conditioning (bars removed) in which a tone signaled shock. The capacity of the tone to disrupt bar pressing was then assessed. 3. Bar pressing of rats previously injected with diazepam was more suppressed by the shock cue than that of rats previously injected with buspirone or saline. The long-term effects of buspirone and saline did not differ. 4. In Experiment 2, Lorazepam had effects different from diazepam during bar press training. Nonetheless, rats previously injected with Lorazepam were also more disrupted by a shock cue than were controls. 5. The results suggest that one long-term consequence of treatment with benzodiazepines may be hypersensitivity to behavioral disruption by stimuli that presumably elicit fear or anxiety.

Alpha 2-adrenoceptor antagonist activity may account for the effects of buspirone in an anticonflict test in the rat

The anxiolytic effects of buspirone, its metabolite, 1-(2-pyrimidyl)piperazine (1-PP) and several alpha 2-adrenoceptor antagonists have been compared in an anticonflict (shock-induced suppression of drinking) paradigm in rats. Idazoxan, WY 26392 and yohimbine had anticonflict effects comparable to those of buspirone and 1-PP, and enhanced the release of suppressed responding induced by buspirone. The response to buspirone was antagonised by the alpha 2-adrenoceptor agonist clonidine. In tests of clonidine-induced mydriasis, the antagonist potencies of buspirone, 1-PP, idazoxan, WY 26392 and yohimbine corresponded closely to the doses of the compounds active in the anticonflict test. Clonidine-induced hypolocomotion was also antagonised by 1-PP, although this response was potentiated by buspirone. The results suggest that the anticonflict effects of buspirone involve an alpha 2-adrenoceptor mechanism.

The effects of buspirone, a selective anxiolytic, on stress ulcer formation in rats

The effects of buspirone hydrochloride were investigated on the formation of cold-immobilization gastric stress ulcers. Low doses significantly attenuated, while higher doses greatly potentiated gastric stress pathology. The dopamine antagonist haloperidol, and the agonist apomorphine respectively, reversed the buspirone effects. The role of dopamine in the expression of buspirone's effects is discussed, although other transmitter systems may mediate some of the actions of buspirone.

Buspirone: an update on a unique anxiolytic agent

Buspirone (Buspar) is a azaspirodecanedione anxiolytic agent. Its mechanism of action is extremely complex, but current investigations indicate that its main neuropharmacologic effects are mediated by the 5-HT1A receptors. Other neuroreceptor systems could be involved, as buspirone displays some affinity for DA2 autoreceptors and 5-HT2 receptors. It has been proposed that inhibition of synthesis and release of serotonin result through the combined interactions of neuroreceptors and secondary messenger systems. This action leads to inhibition of the firing rate of 5-HT-containing neurons in the dorsal raphe. From this novel profile, that differs from that of the benzodiazepines, buspirone lacks anticonvulsant and muscle-relaxant properties, and causes only minimal sedation. The drug is rapidly absorbed after oral administration, with a mean bioavailability of 3.9%. After a single oral dose, the mean elimination half-life is 2.1 hours. Buspirone is mainly bound to albumin and alpha 1-acid glycoprotein. It is metabolized to an active metabolite 1-(2-pyrimidinyl) piperazine (1-PP). The mean elimination half-life of 1-PP is 6.1 hours. Buspirone is indicated in the treatment of generalized anxiety disorders. Its efficacy is comparable to the benzodiazepines. Its use in depression and panic disorders requires further investigation. When combined with alcohol or given alone, psychomotor impairment was not detected. Abuse, dependence, and withdrawal symptoms have not been reported. The frequency of adverse effects is low, and the most common effects are headaches, dizziness, nervousness, and lightheadness. Buspirone should be added to drug formularies and could represent a significant addition in psychopharmacology.

The effect of anxiolytic drugs on memory in anxious subjects

The benzodiazepines (BZs), represented by diazepam, are the class of drugs used most frequently to treat clinical anxiety disorders. Since it is known that acute BZ intake impairs memory function, the effects of BZs on memory were evaluated in chronic users of BZ medications. In addition, the acute effects of diazepam were compared with those of the non-BZ anxiolytic buspirone on memory function in anxious subjects. Memory function was evaluated by a free verbal recall procedure where subjects recalled a list of 16 noncategorized nouns immediately after the word list was read (immediate recall) and again 20 min later (delayed recall). When the chronic BZ users were tested for free verbal recall during their first visit, 4-14 h after their last dose, they did not differ in immediate or delayed recall from an age- and sex-matched group of unmedicated anxious subjects. At a subsequent visit, the acute effects of BZ medications were studied 60-90 min after the subjects took their usual dose. Although acute BZ administration did not alter immediate recall, delayed recall was significantly impaired in the chronic BZ users. Thus, complete tolerance does not develop to the acute memory-impairing effects of BZs after long-term use. Acute administration of the anxiolytic drugs diazepam (5 mg) or buspirone (5 or 10 mg) did not alter immediate recall in another group of unmedicated anxious subjects. Diazepam selectively impaired delayed recall of the word list when compared with placebo. In contrast, neither dose of buspirone altered delayed recall. To the extent that such effects on verbal recall tests are reflected in a patient's daily activities, the failure of buspirone to adversely affect memory function could contribute to its usefulness as an alternative antianxiety therapy.

Azaspirodecanediones in generalized anxiety disorder: buspirone

Buspirone is a new anxiolytic that is structurally unrelated to other psychotropic drugs. The drug is as effective as benzodiazepines for the treatment of generalized anxiety, and superior to placebo. The effect of buspirone on other anxiety disorders, such as panic disorder or post-traumatic stress disorder, remains untested. Although buspirone's mechanism of action is unknown, it clearly does not act on the same receptor systems that are affected by benzodiazepines. Buspirone appears to lack dependence and abuse potential and has little or no sedative effect. In addition, the drug does not potentiate sedative-hypnotic drugs and does not potentiate functional impairment produced by alcohol. Like benzodiazepines, buspirone appears to be safe even when given in very high doses.

Differential effects of the anxiolytic drugs, diazepam and buspirone, on memory function

The effects of the anxiolytic drugs diazepam (5 mg) or buspirone (5 or 10 mg) were studied in comparison with placebo on memory function in 39 subjects diagnosed with generalized anxiety disorder. Neither drug altered the immediate recall of a list of 16 nouns or impaired digit span, a second test of immediate memory. Diazepam selectively impaired the recall of nouns after a 20 min delay when compared with placebo. In contrast, neither dose of buspirone altered the delayed recall of the word list. The implications of such different effects of anxiolytic drugs on memory function for the clinical treatment of anxiety are discussed.

Buspirone. A preliminary review of its pharmacological properties and therapeutic efficacy as an anxiolytic

Buspirone hydrochloride (HCl)1 is a new anxiolytic with a unique chemical structure. Its mechanism of action remains to be elucidated. Unlike the benzodiazepines, buspirone lacks hypnotic, anticonvulsant and muscle relaxant properties, and hence has been termed 'anxioselective'. As evidenced by a few double-blind clinical trials, buspirone 15 to 30 mg/day improves symptoms of anxiety assessed by standard rating scales similarly to diazepam, clorazepate, alprazolam and lorazepam. Like diazepam, buspirone is effective in patients with mixed anxiety/depression, although the number of patients studied to date is small. In several studies, a 'lagtime' of 1 to 2 weeks to the onset of anxiolytic effect has been noted; hence motivation of patient compliance may be necessary. Sedation occurs much less often after buspirone than after the benzodiazepines; other side effects are minor and infrequent. In healthy volunteers, buspirone does not impair psychomotor or cognitive function, and appears to have no additive effect with alcohol. Early evidence suggests that buspirone has limited potential for abuse and dependence. Thus, although only wider clinical use for longer periods of time will more clearly define some elements of its pharmacological profile, with its low incidence of sedation buspirone is a useful addition to the treatments available for generalised anxiety. It may well become the preferred therapy in patients in whom daytime alertness is particularly important.

Monoaminergic involvement in the pharmacological actions of buspirone

Buspirone, MJ-13805 and MJ-13653 did not produce a '5-hydroxytryptamine (5-HT) syndrome' in rats at doses up to 20 mg kg-1. These drugs were very weak 5-HT uptake blockers (IC50 much greater than 10 microM) compared to drugs such as chlorimipramine. These drugs did not inhibit either monoamine oxidase (MAO)-A or MAO-B. The Ki values for these agents as inhibitors of [3H]-5-HT and [3H]-ketanserin binding to rat frontal cortex or hippocampal membranes were in the microM range, well above the brain concentrations achieved after an oral dose of 25 mg kg-1. Parenterally administered buspirone blocked apomorphine-induced stereotypy, inhibited the 5-HT syndrome elicited by 5-methoxy-N,N-dimethyltryptamine, and delayed the onset of p-chloroamphetamine induced behaviours.

Buspirone: a new type of anxiolytic

Buspirone is a member of a new class of agents known as azaspirodecanediones, and represents the first nonbenzodiazepine anxiolytic to be introduced in the U.S. in recent years. It does not resemble the benzodiazepines or older anxiolytics such as meprobamate and the barbiturates in pharmacologic profile. Buspirone lacks anticonvulsant activity, interacts minimally with central nervous system depressants such as alcohol, and does not cause muscle relaxation. The drug is reported to have minimal sedating effect, to cause no impairment of driving-related skills, and to have no euphoriant effect or addictive potential. With this low side-effect profile, buspirone should not require Drug Enforcement Agency scheduling controls. Clinical trials indicate buspirone is efficacious in the treatment of mild to moderate anxiety disorders. Answers to questions of possible side effects related to dopaminergic intractions must await post-marketing experience. Buspirone is a suitable addition to drug formularies as its pre-marketing data suggest several advantages compared with anxiolytics currently available.

Buspirone: an anxiolytic without sedative effect

Twelve volunteers with a complaint of chronic insomnia participated in a placebo-controlled, double-blind, crossover study of the effects of buspirone t.i.d. on sleep pattern and daytime function. The drug was tested alone and in combination with flurazepam or triazolam. Buspirone alone did not impair objective measures of daytime wakefulness or performance. Impaired alertness was seen the day after bedtime administration of flurazepam but not after triazolam; buspirone did not alter these effects. Buspirone did not affect the Multiple Sleep Latency Test, a sensitive measure of changes in daytime alertness.