Elsevier

Magnetic Resonance Imaging

Volume 75, January 2021, Pages 134-140
Magnetic Resonance Imaging

Original Contribution
Effects of alfaxalone on cerebral blood flow and intrinsic neural activity of rhesus monkeys: A comparison study with ketamine

https://doi.org/10.1016/j.mri.2020.10.011Get rights and content

Highlights

  • Alfaxalone reduced CBF in the whole brain substantially.

  • The residual effects of alfaxalone on CBF were monotonous when used for induction.

  • Alfaxalone resulted in similar suppression effect on intrinsic neural activity of the monkey brain as ketamine.

Abstract

Objective

Alfaxalone has been used increasingly in biomedical research and veterinary medicine of large animals in recent years. However, its effects on the cerebral blood flow (CBF) physiology and intrinsic neuronal activity of anesthetized brains remain poorly understood.

Methods

Four healthy adult rhesus monkeys were anesthetized initially with alfaxalone (0.125 mg/kg/min) or ketamine (1.6 mg/kg/min) for 50 min, then administrated with 0.8% isoflurane for 60 min. Heart rates, breathing beats, and blood pressures were continuously monitored. CBF data were collected using pseudo-continuous arterial spin-labeling (pCASL) MRI technique and rsfMRI data were collected using single-shot EPI sequence for each anesthetic.

Results

Both the heart rates and mean arterial pressure (MAP) remained more stable during alfaxalone infusion than those during ketamine administration. Alfaxalone reduced CBF substantially compared to ketamine anesthesia (grey matter, 65 ± 22 vs. 179 ± 38 ml/100g/min, p<0.001; white matter, 14 ± 7 vs. 26 ± 6 ml/100g/min, p < 0.05); In addition, CBF increase was seen in all selected cortical and subcortical regions of alfaxalone-pretreated monkey brains during isoflurane exposure, very different from the findings in isoflurane-exposed monkeys pretreated with ketamine. Also, alfaxalone showed suppression effects on functional connectivity of the monkey brain similar to ketamine.

Conclusion

Alfaxalone showed strong suppression effects on CBF of the monkey brain.The residual effect of alfaxalone on CBF of isoflurane-exposed brains was evident and monotonous in all the examined brain regions when used as induction agent for inhalational anesthesia. In particular, alfaxalone showed similar suppression effect on intrinsic neuronal activity of the brain in comparison with ketamine. These findings suggest alfaxalone can be a good alternative to veterinary anesthesia in neuroimaging examination of large animal models. However, its effects on CBF and functional connectivity should be considered.

Introduction

Alfaxalone is a synthetic neuroactive steroid anesthetic and has been used as an induction and maintenance agent for anesthesia of large animals [1]. Alfaxalone-2-hydroxpropyl-β-cyclodextrin (Alfaxalone-HPCD) is its newest formulation and was approved by FDA for use in dogs and cats in the United States in 2012 [2]. Alfaxalone produces satisfactory induction and maintenance of anesthesia such as onset of anesthesia, fast redistribution, short elimination half-life, short duration of action [3], no cardiovascular depression at clinical doses [4,5], and a lower frequency of apnea [6]. In recent years, alfaloxone has been increasingly used in horses [7], dogs [1], pigs [8], cats [3,9], and non-human primates (NHPs) [[10], [11], [12]], suggesting alfaloxone has the potential to become an alternative anesthetic for induction and maintenance anesthesia of large animals. However, alfaxalone's effects on the cerebral blood flow (CBF) physiology and neural activity of large animals remain poorly understood.

CBF quantifies the blood supply to the brain and is highly coupled to brain metabolism and functionality [[13], [14], [15], [16]]. Several non-invasive perfusion MRI techniques can be used to perform quantitative CBF measurement in large animals like macaque monkeys non-invasively [17], and examine the effects of anesthesia on CBF and autoregulation of large animals [18,19]. In addition, resting state functional MRI (rsfMRI) can detect the intrinsic neural activity in the brain and has been widely used to examine the functional connectivity in the brain [20,21] and anesthetized subjects [12,[22], [23], [24]]. Both CBF and rsfMRI techniques are robust and non-invasive approaches to investigate the effects of anesthesia on the brain physiology and functionality in animals and human subjects [16,[25], [26], [27], [28], [29]].

Large animals (like pigs, dogs, rabbits, cats, and NHPs, et al.) are usually required to be sedated for performing invasive procedures or non-invasive imaging scans in biomedical and neuroscience research. As a popular practice in neuroimaging study, the animals are firstly knocked down with an induction agent (like ketamine) and then maintained with inhalational anesthesia (such as isoflurane) for the entire duration of scan session. The anesthesia effects of ketamine and isoflurane on the CBF and neural functionality of the brain have been explored extensively in previous studies [15,19,25,[30], [31], [32], [33], [34], [35]], demonstrating the CBF and neural functionality could be dramatically affected by applied anesthetics in a dose- and duration-related manner. We hypothesized the CBF and neural activity of the brain could be affected by alfaloxone when it is used alone or as an induction agent in veterinary anesthesia of large animals. In the present study, the anesthesia effects of alfaloxone on the CBF and intrinsic neural functionality were investigated using macaque monkeys and compared with the effects of ketamine.

Section snippets

Methods and materials

Healthy female rhesus monkeys (n = 4, 11–15 years old) were employed in the present study. Alfaxalone (Alfaxan, Jurox, MO, USA) was given initially via intramuscular injection (induction, 5 mg/kg) followed by intravenous infusion (0.125 mg/kg/min) for about 50 min during MRI scanning. Then the anesthetic was switched to isoflurane (~0.8% with 100% Oxygen) (IsoThesia, Henry Schein Animal Health, NY, USA) to keep the animal sedated continuously until the end of each scan session (for about one

Results

The temporal changes of mean arterial pressure (MAP) and HR of monkeys during the entire scanning session were examined and illustrated in Fig. 2. No significant MAP change was seen during the entire period of alfaxalone infusion. Continuous reduction of MAP was observed during ketamine and following isoflurane administration. The MAP was always reduced after the anesthetic (alfaxalone or ketamine) was switched to isoflurane. No significant changes of breathing rates were seen in any scenario

Discussion

Alfaxalone has been increasingly used as induction agent or used alone for general anesthesia of large animals in recent years. Our results indicated that alfaxalone had evident suppression effect on CBF compared to ketamine (and isoflurane) and showed comparable suppressive effects on the intrinsic neural activity with ketamine. In particular, alfaxalone resulted in more stable physiological measures when used alone or as induction agent. Also, alfaxalone's residual effect on CBF of the monkey

Conclusion

The present study revealed alfaxalone's effects on CBF physiology and intrinsic neural activities of monkeys when used alone or as induction agent for inhalational anesthesia. The findings suggest alfaxalone can be a good alternative to veterinary anesthesia in biomedical research and neuroimaging study of brain physiology and functionality. As large animals (such as pigs and non-human primates) are increasingly used for study of neurodegenerative diseases (like stroke, traumatic brain injury

Author statement

Li: Investigation, data processing and analysis, draft preparation and writing; Kempf: experimental design, investigation; Howell: conceptualization, supervision; Zhang: experimental design, conceptualization, editing, supervision.

Declaration of Competing Interest

The authors have no conflict of interest to disclose.

Acknowledgements

The authors are grateful to Sudeep Patel and Ruth Connelly for assistance in data acquisition and animal handling, and the Center for Magnetic Resonance Research (CMRR) of University of Minnesota for sharing the multiband EPI pulse sequence with us. The project is supported by the Office of Research Infrastructure Programs (OD P51OD011132).

References (77)

  • F. Zhao et al.

    BOLD study of stimulation-induced neural activity and resting-state connectivity in medetomidine-sedated rat

    Neuroimage

    (2008)
  • C.X. Li et al.

    Evaluation of prolonged administration of isoflurane on cerebral blood flow and default mode network in macaque monkeys anesthetized with different maintenance doses

    Neurosci Lett

    (2018)
  • D. Casoni et al.

    S-ketamine versus racemic ketamine in dogs: their relative potency as induction agents

    Vet Anaesth Analg

    (2015)
  • J.E. Bryant et al.

    Ketamine induced changes in regional cerebral blood flow, interregional connectivity patterns, and glutamate metabolism

    J Psychiatr Res

    (2019)
  • A.G.P. Wakeford et al.

    A review of nonhuman primate models of early life stress and adolescent drug abuse

    Neurobiol Stress

    (2018)
  • C.X. Li et al.

    Longitudinal MRI evaluation of ischemic stroke in the basal ganglia of a rhesus macaque (Macaca mulatta) with seizures

    Comp Med

    (2018)
  • J. Liu et al.

    Striatal glutamate delta-1 receptor regulates behavioral flexibility and thalamostriatal connectivity

    Neurobiol Dis

    (2020)
  • W. Muir et al.

    The cardiorespiratory and anesthetic effects of clinical and supraclinical doses of alfaxalone in cats

    Vet Anaesth Analg

    (2009)
  • A.T. Levine et al.

    Assessment of anesthesia on physiological stability and BOLD signal reliability during visual or acoustic stimulation in the cat

    J Neurosci Methods

    (2020)
  • H. Kloppel et al.

    Comparison of ketamine and alfaxalone for induction and maintenance of anaesthesia in ponies undergoing castration

    Vet Anaesth Analg

    (2011)
  • K.L. White et al.

    A clinical evaluation of the pharmacokinetics and pharmacodynamics of intravenous alfaxalone in cyclodextrin in male and female rats following a loading dose and constant rate infusion

    Vet Anaesth Analg

    (2017)
  • A. Bendtsen et al.

    Use of a continuous infusion of althesin in neuroanaesthesia. Changes in cerebral blood flow, cerebral metabolism, the EEG and plasma alphaxalone concentration

    Br J Anaesth

    (1985)
  • J.J. Lambert et al.

    Neurosteroid modulation of GABAA receptors

    Prog Neurobiol

    (2003)
  • Leon N. Warne et al.

    A review of the pharmacology and clinical application of alfaxalone in cats

    Vet J

    (2015)
  • L. Laaksonen et al.

    Comparative effects of dexmedetomidine, propofol, sevoflurane, and S-ketamine on regional cerebral glucose metabolism in humans: a positron emission tomography study

    Br J Anaesth

    (2018)
  • X. Zhang et al.

    Quantitative basal CBF and CBF fMRI of rhesus monkeys using three-coil continuous arterial spin labeling

    Neuroimage

    (2007)
  • I.S. Grant et al.

    Pharmacokinetics and analgesic effects of i.m. and oral ketamine

    Br J Anaesth

    (1981)
  • J. Tamura et al.

    The pharmacological effects of the anesthetic alfaxalone after intramuscular administration to dogs

    J Vet Med Sci

    (2015)
  • FDA

    New Animal Drugs. Approvals; Changes of Sponsor; Change of Sponsor's Name; Change of Sponsor's Address; Alfaxalone; Ivermectin and Clorsulon; Narasin; Triptorelin From the Federal Register Online via the Government Printing Office [FR Doc No: 2012-N-0002] 77

    (2012)
  • W. Bayldon et al.

    Accidental alfaxalone overdose in a mature cat undergoing anaesthesia for magnetic resonance imaging

    JFMS Open Rep

    (2016)
  • H. Nieuwendijk

    Alfaxalone (Alfaxan®)

    (2017)
  • H. Bertrand et al.

    A combination of alfaxalone, medetomidine and midazolam for the chemical immobilization of rhesus macaque (Macaca mulatta): preliminary results

    J Med Primatol

    (2017)
  • N. Konoike et al.

    Hypoxemia after single-shot anesthesia in common marmosets

    J Med Primatol

    (2017)
  • J. Bakker et al.

    Comparison of three different sedative-anaesthetic protocols (ketamine, ketamine-medetomidine and alphaxalone) in common marmosets (Callithrix jacchus)

    BMC Vet Res

    (2013)
  • A.G. Hudetz

    General anesthesia and human brain connectivity

    Brain Connect

    (2012)
  • A.C. Silva et al.

    Dynamic magnetic resonance imaging of cerebral blood flow using arterial spin labeling

    Methods Mol Biol

    (2009)
  • X. Liu et al.

    Neural origin of spontaneous hemodynamic fluctuations in rats under burst-suppression anesthesia condition

    Cereb Cortex

    (2011)
  • X. Zhang et al.

    Arterial spin labeling perfusion magnetic resonance imaging of non-human primates

    Quant Imaging Med Surg

    (2016)
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      Resting-state functional MR images (rsfMRI) were collected using a gradient echo Echo Planar Imaging (EPI) sequence (TR/TE=2190 ms/25 ms, 36 contiguous axial slices to cover the whole brain, 150 volumes, FOV = 96 mm × 96 mm, spatial resolution= 1.5 × 1.5 × 1.5 mm3). The rsfMRI data collection started ~15 min after the animal was moved into the scanner in order to minimize the dosage and duration effect of isoflurane to FC in aneathetized monkeys (Hutchison et al., 2013; Li et al., 2020; Li and Zhang, 2018). High resolution structural T1-weighed images were acquired using a 3D magnetization prepared rapid gradient echo (MPRAGE) sequence with the generalized auto calibrating partial parallel acquisition (GRAPPA) (R = 2) (TR/TE = 2500 ms/3.51 ms, FOV = 96 mm × 96 mm, spatial resolution = 0.5 × 0.5 × 0.5 mm3).

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