Buspirone-induced hypothermia in normal male volunteers

Hypothermia in acute ischemic stroke therapy

Therapeutic hypothermia (TH) is a potent neuroprotective therapy in experimental cerebral ischemia, with multiple effects at several stages of the ischemic cascade. In animals, TH is so powerful that all preclinical stroke studies require strict temperature control. In humans, multiple clinical studies documented powerful protection with TH after accidental neonatal hypoxic-ischemic injury and global cerebral ischemia with return of spontaneous circulation after cardiac arrest. National and international guidelines recommend TH for selected survivors of global ischemia, with profound benefits seen. Recently, a study comparing target temperature 33-36°C failed to demonstrate significant effects in cardiac arrest patients. Additionally, clinical trials of TH for head trauma and stroke have so far failed to confirm benefit in humans despite a vast preclinical literature. Therefore, it is now critical to understand the fundamental explanation for the success of TH in some, but famously not all, clinical trials. TH in animals appears to work when used soon after ischemia onset; for a short duration; and at a deep target temperature.

Therapeutic Potential of Non-Psychotropic Cannabidiol in Ischemic Stroke

Cannabis contains the psychoactive component delta⁹-tetrahydrocannabinol (delta⁹-THC), and the non-psychoactive components cannabidiol (CBD), cannabinol, and cannabigerol. It is well-known that delta⁹-THC and other cannabinoid CB₁ receptor agonists are neuroprotective during global and focal ischemic injury. Additionally, delta⁹-THC also mediates psychological effects through the activation of the CB₁ receptor in the central nervous system. In addition to the CB₁ receptor agonists, cannabis also contains therapeutically active components which are CB₁ receptor independent. Of the CB₁ receptor-independent cannabis, the most important is CBD. In the past five years, an increasing number of publications have focused on the discovery of the anti-inflammatory, anti-oxidant, and neuroprotective effects of CBD. In particular, CBD exerts positive pharmacological effects in ischemic stroke and other chronic diseases, including Parkinson’s disease, Alzheimer’s disease, and rheumatoid arthritis. The cerebroprotective action of CBD is CB₁ receptor-independent, long-lasting, and has potent anti-oxidant activity. Importantly, CBD use does not lead to tolerance. In this review, we will discuss the therapeutic possibility of CBD as a cerebroprotective agent, highlighting recent pharmacological advances, novel mechanisms, and therapeutic time window of CBD in ischemic stroke.

Allometric Scaling of Pharmacodynamic Responses: Application to 5-Ht1A Receptor Mediated Responses from Rat to Man

PURPOSE

The aim of the present study was to assess whether two widely used biomarkers for 5-HT(1A)-receptor mediated responses in the rat (hypothermia and corticosterone increase) could be scaled to man using allometric principles.

MATERIALS AND METHODS

Mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) models were developed and characterized in rats for the standard 5-HT(1A)-receptor agonists, buspirone and flesinoxan. Allometric scaling was investigated on the basis of simulation taking into account the inter-individual variability and clinical study design. The model-predicted effects of both flesinoxan and buspirone were compared to those published in the literature.

RESULTS

The main finding of this analysis was that for both hypothermia and cortisol increase, the model could predict the extent of the pharmacological response in man adequately. For the hypothermic response, the time course of the response was also predicted with a high degree of accuracy. In contrast, in the case of the cortisol response, the observed time lag was, despite the fact that it fell within the model uncertainty, not predicted.

CONCLUSIONS

Based on these analyses, it is concluded that allometrically scaled mechanism based PK-PD models are promising as a means of predicting the pharmacodynamic responses in man. This approach provides for a novel way of interpreting and scaling pre-clinical pharmacological responses and ultimately facilitates the understanding and prediction of pharmacological responses in man.

Repeated treatment with cannabidiol but not Δ9-tetrahydrocannabinol has a neuroprotective effect without the development of tolerance

Both Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and cannabidiol are known to have a neuroprotective effect against cerebral ischemia. We examined whether repeated treatment with both drugs led to tolerance of their neuroprotective effects in mice subjected to 4h-middle cerebral artery (MCA) occlusion. The neuroprotective effect of Delta(9)-THC but not cannabidiol was inhibited by SR141716, cannabinoid CB(1) receptor antagonist. Fourteen-day repeated treatment with Delta(9)-THC, but not cannabidiol, led to tolerance of the neuroprotective and hypothermic effects. In addition, repeated treatment with Delta(9)-THC reversed the increase in cerebral blood flow (CBF), while cannabidiol did not reverse that effect. Repeated treatment with Delta(9)-THC caused CB(1) receptor desensitization and down-regulation in MCA occluded mice. On the contrary, cannabidiol did not influence these effects. Moreover, the neuroprotective effect and an increase in CBF induced by repeated treatment with cannabidiol were in part inhibited by WAY100135, serotonin 5-HT(1A) receptor antagonist. Cannabidiol exhibited stronger antioxidative power than Delta(9)-THC in an in vitro study using the 1,1-diphenyl-2-picryhydrazyl (DPPH) radical. Thus, cannabidiol is a potent antioxidant agent without developing tolerance to its neuroprotective effect, acting through a CB(1) receptor-independent mechanism. It is to be hoped that cannabidiol will have a palliative action and open new therapeutic possibilities for treating cerebrovascular disorders.

A trial of therapeutic hypothermia via endovascular approach in awake patients with acute ischemic stroke: methodology

BACKGROUND

Therapeutic hypothermia has been shown to be of benefit in improving neurological outcome in cardiac arrest. It now is being investigated in acute stroke and myocardial infarction. The majority of the literature describes its use in intubated, pharmacologically paralyzed patients, using surface cooling techniques that are susceptible to patient shivering, imprecise temperature control, time lag to target-temperature acquisition, and rebound hyperthermia.

OBJECTIVES

To develop a method of inducing therapeutic hypothermia in a rapid, precise, and tolerable fashion in awake, nonintubated patients.

METHODS

This method was developed for an ongoing clinical trial investigating a combination of therapeutic hypothermia and intravenous thrombolysis for acute ischemic stroke. In the protocol, an endovascular cooling device is placed in the inferior vena cava of a patient, and a combination of buspirone, meperidine, and cutaneous warming with a heating blanket is used to suppress shivering as the patient is cooled to a target temperature of 33 degrees C, kept there for a total of 24 hours from hypothermia initiation, and then rewarmed in a controlled fashion during the next 12 hours.

RESULTS

Ten patients underwent the therapeutic hypothermia protocol. The median pretreatment core temperature was 36.1 degrees C (interquartile range [IQR]: 35.8 degrees C-36.4 degrees C). On initiation of cooling, the core temperatures dropped rapidly and then leveled off, approaching a median plateau value of 33.4 degrees C (IQR: 33.2 degrees C-33.9 degrees C) in a mean time of 1.7 (+/- 0.7) hours from cooling initiation, with a median average postplateau temperature during the cooling phase of 33.8 degrees C (IQR: 33.3 degrees C-34.6 degrees C), and a median lowest temperature of 33.1 degrees C (IQR: 33.0 degrees C-33.3 degrees C). The procedure was well tolerated, with minimal shivering and no rebound hyperthermia.

CONCLUSIONS

This is a method by which a rapid and precise therapeutic decrease in core temperature can be achieved without the necessity for intubation or neuromuscular blockade and with minimal patient discomfort or shivering.

Clozapine increases cutaneous blood flow and reduces sympathetic cutaneous vasomotor alerting responses (SCVARs) in rats: comparison with effects of haloperidol

RATIONALE

Clozapine inhibits sympathetic outflow to the cutaneous vascular bed. Clozapine reverses hyperthermia and cutaneous vasoconstriction induced by 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) or by lipopolysaccharide (LPS). Clozapine also reverses cutaneous vasoconstriction elicited by exposure to cold. These actions distinguish clozapine from haloperidol. Clozapine could also inhibit sympathetic cutaneous vasomotor alerting responses (SCVARs), vasoconstrictor episodes that reflect emotional/psychological function, and this property might also distinguish clozapine from haloperidol.

OBJECTIVES

Experiments in rats determined whether clozapine and haloperidol inhibit SCVARs, and whether SR46349B (a 5HT2A receptor antagonist), 8-OH-DPAT (a 5-HT1A agonist), L741,626 (a dopamine D2 antagonist) or SCH23390 (a dopamine D1 antagonist) have clozapine-like effects on SCVARs.

METHODS

Mean level and pulse amplitude of the tail artery Doppler flow signal were recorded in conscious freely moving rats before and after alerting stimuli (e.g. tapping the cage), and expressed as a SCVAR index (fall to zero flow implies SCVAR index of 100%, no fall implies 0%).

RESULTS

Clozapine (0.0625-1.0 mg/kg, s.c.) dose-dependently increased resting tail blood flow. After 1 mg/kg, the SCVAR index was 18+/-1%, compared with 83+/-2% after vehicle. SR46349B (0.01-1.0 mg/kg) and 8-OH-DPAT (0.25 mg/kg) had similar but less potent effects on cutaneous blood flow and on SCVARs. Haloperidol (0.005-0.5 mg/kg) and L741,626 (1 mg/kg) had no or little effect on these variables. SCH23390 mildly inhibited SCVARs.

CONCLUSIONS

Clozapine, but not haloperidol, increases resting cutaneous blood flow and decreases SCVARs. Antagonism at 5-HT2A receptors and agonism at 5-HT1A receptors could contribute to these actions.

5-Hydroxytryptamine 1A receptors inhibit cold-induced sympathetically mediated cutaneous vasoconstriction in rabbits

5-HT1A receptor agonists lower body temperature. We have investigated whether activation of 5-HT1A receptors inhibits cutaneous sympathetic discharge so that dilatation of the cutaneous vascular bed lowers body temperature by increasing heat transfer to the environment. We measured ear pinna blood flow in conscious rabbits (with chronically implanted Doppler ultrasound flow probes), and postganglionic sympathetic vasomotor nerve activity in anaesthetized rabbits. Recordings from conscious rabbits were made in a cage at 26 degrees C and the rabbit was then transferred to a cage at 10 degrees C. The ear pinna Doppler signal fell from 56 +/- 4 cm s-1 in the 26 degrees C cage to 4 +/- 1 cm s-1 (P < 0.0001, n = 24) after 30 min in the 10 degrees C cage, and body temperature increased from 38.8 +/- 0.2 to 39.0 +/- 0.2 degrees C (P < 0.01, n = 24). The 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.1 mg kg-1 I.V.) reversed the cold-induced fall in ear pinna blood flow (Doppler signal increased from 5 +/- 1 to 55 +/- 8 cm s-1, P < 0.001, n = 7) within 5 min when administered 30 min after transfer to the 10 degrees C cage, and prevented the fall in ear pinna blood flow when administered before the rabbit was transferred to the 10 degrees C cage. Body temperature decreased after administration of 8-OH-DPAT. These changes were abolished by the specific 5-HT1A antagonist WAY-100635 (0.1 mg kg-1 I.V.). In anaesthetized rabbits, 8-OH-DPAT (0.1 mg kg-1 I.V.) reduced resting postganglionic cutaneous sympathetic vasomotor discharge, and prevented the increase normally elicited by cooling the trunk. Our experiments constitute the first demonstration that activation of 5-HT1A receptors powerfully inhibits cold-induced increases in cutaneous sympathetic vasomotor discharge, thereby dilating the cutaneous vascular bed and increasing transfer of heat to the environment.

Pharmacokinetic-pharmacodynamic modeling of buspirone and its metabolite 1-(2-pyrimidinyl)-piperazine in rats

The objective of this investigation was to compare the in vivo potency and intrinsic activity of buspirone and its metabolite 1-(2-pyrimidinyl)-piperazine (1-PP) in rats by pharmacokinetic-pharmacodynamic modeling. Following intravenous administration of buspirone (5 or 15 mg/kg in 15 min) or 1-PP (10 mg/kg in 15 min), the time course of the concentrations in blood were determined in conjunction with the effect on body temperature. The pharmacokinetics of buspirone and 1-PP were analyzed based on a two-compartment model with metabolite formation. Differences in the pharmacokinetics of buspirone and 1-PP were observed with values for clearance of 13.1 and 8.2 ml/min and for terminal elimination half-life of 25 and 79 min, respectively. At least 26% of the administered dose of buspirone was converted into 1-PP. Complex hypothermic effects versus time profiles were observed, which were successfully analyzed on the basis of a physiological indirect response model with set-point control. Both buspirone and 1-PP behaved as partial agonists relative to R-(+)-8-hydroxy-2-(di-n-propylamino)tetralin (R-8-OH-DPAT) with values of the intrinsic activity of 0.465 and 0.312, respectively. Differences in the potency were observed with values of 17.6 and 304 ng/ml for buspirone and 1-PP, respectively. The results of this analysis show that buspirone and 1-PP behave as partial 5-hydroxytryptamine(1A) agonists in vivo and that following intravenous administration the amount of 1-PP formed is too small to contribute to the hypothermic effect.

Buspirone and meperidine synergistically reduce the shivering threshold

Mild hypothermia (i.e., 34 degrees C) may prove therapeutic for patients with stroke, but it usually provokes shivering. We tested the hypothesis that the combination of buspirone (a serotonin 1A partial agonist) and meperidine synergistically reduces the shivering threshold (triggering tympanic membrane temperature) to at least 34 degrees C while producing little sedation or respiratory depression. Eight volunteers each participated on four randomly-assigned days: 1) large-dose oral buspirone (60 mg); 2) large-dose IV meperidine (target plasma concentration of 0.8 microg/mL); 3) the combination of buspirone (30 mg) and meperidine (0.4 microg/mL); and 4) a control day without drugs. Core hypothermia was induced by infusion of lactated Ringer's solution at 4 degrees C. The control shivering threshold was 35.7 degrees C +/- 0.2 degrees C. The threshold was 35.0 degrees C +/- 0.8 degrees C during large-dose buspirone and 33.4 degrees C +/- 0.3 degrees C during large-dose meperidine. The threshold during the combination of the two drugs was 33.4 degrees C +/- 0.7 degrees C. There was minimal sedation on the buspirone and combination days and mild sedation on the large-dose meperidine day. End-tidal PCO2 increased approximately 10 mm Hg with meperidine alone. Buspirone alone slightly reduced the shivering threshold. The combination of small-dose buspirone and small-dose meperidine acted synergistically to reduce the shivering threshold while causing little sedation or respiratory toxicity.

IMPLICATIONS

Mild hypothermia may be an effective treatment for acute stroke, but it usually triggers shivering, which could be harmful. Our results indicate that the combination of small-dose buspirone and small-dose meperidine acts synergistically to reduce the shivering threshold while causing little sedation or respiratory toxicity. This combination may facilitate the induction of therapeutic hypothermia in stroke victims.

The effects of the novel anxiolytic drug lesopitron, a full and selective 5-HT1A receptor agonist, on pupil diameter and oral temperature in man: comparison with buspirone

We investigated the effects of two 5-HT1A receptor agonists, buspirone and lesopitron, upon pupil size in human volunteers at an ambient luminance level of 32 Cd m(-2) and in darkness. Pupil diameter was monitored with a binocular infrared television pupillometer, before and after the administration of treatments for 4 h at 20-min intervals. Two experiments were conducted. In Experiment 1, 14 healthy male volunteers participated in seven weekly sessions, each associated with the ingestion of one capsule (buspirone 5, 10 and 20 mg, lesopitron 10, 20 and 40 mg and placebo), according to a double-blind balanced, cross-over design. Both buspirone and lesopitron tended to decrease pupil diameter. In darkness, only the highest dose of buspirone (20 mg) caused a miosis that was statistically significant. However, at the luminance level of 32 Cd m(-2) buspirone 10 and 20 mg evoked statistically significant miotic effects, as did the highest dose of lesopitron (40 mg). The miotic effect was significantly greater at 32 Cd m(-2) than in darkness after each dose of buspirone and the highest dose (40 mg) of lesopitron. In Experiment 2, pupil diameter and oral temperature were monitored with an electronic thermometer at 40-min intervals. Twenty healthy male volunteers participated in two weekly sessions, each associated with the sublingual application of 100 microl hydroalcoholic solution (lesopitron 20 mg, placebo), according to a double-blind balanced cross-over design. Lesopitron caused a significant miosis both in darkness and at the luminance level of 32 Cd m(-2); the miosis was greater at 32 Cd m(-2) than in darkness. Lesopitron tended to decrease oral temperature; this effect however, was not statistically significant. The greater effectiveness on the pupil of lesopitron administered sublingually in a solution indicates the importance of first-pass metabolism in reducing the effectiveness of the drug when administered by the mouth. The miosis observed in both experiments may be due to either a sympatholytic or a parasympathomimetic effect of the drugs, or both. The light-dependence of the miosis indicates that the 5-HT1A receptor agonists can modulate the light reflex, possibly via the noradrenergic control of central cholinergic neurones in the Edinger-Westphal nucleus.

Prolactin response to buspirone challenge in the presence of dopaminergic blockade

Buspirone-stimulated prolactin release has been employed as an indirect measure of central serotonin activity; however, it is not clear whether serotonergic or dopaminergic systems are responsible for this response. In an attempt to further elucidate the mechanism, we studied the prolactin response to buspirone in eight subjects in the presence of maximal dopaminergic receptor blockade with metoclopramide under placebo-controlled, double-blind conditions. The prolactin response to buspirone in the presence of metoclopramide was not statistically different from that to placebo under the same conditions. The demonstration of further prolactin release by a bolus of thyrotropin-releasing hormone under maximal dopaminergic receptor blockade provided evidence against potential pituitary prolactin depletion by metoclopramide. These results lend further support to a dopaminergic mechanism in buspirone-induced prolactin secretion; therefore, further caution is warranted in interpreting the results of this challenge test as a measure of serotonergic activity in the brain.

Effects of hydrocortisone on brain 5-HT function and sleep

The effects of hydrocortisone administration (20 mg, orally, twice daily) on the sensitivity of brain 5-HT1A receptors in healthy volunteers were studied using a buspirone challenge paradigm. The effects of hydrocortisone administration on sleep architecture were also studied. Hydrocortisone treatment significantly attenuated the hypothermic and cortisol responses to buspirone; however, the prolactin and growth hormone responses were unchanged. Hydrocortisone also decreased the amount of rapid eye movement sleep (REM). The ability of hydrocortisone to attenuate 5-HT1A receptor mediated hypothermia and decrease REM sleep is shared by certain antidepressant treatments and may be related to the effects of corticosteroids on mood.