Abstract
Decerebration permits neurophysiological experimentation absent the confounding effects of anesthesia. Use of the unanesthetized decerebrate preparation in vivo offers several advantages compared with recordings performed in reduced slice preparations, providing the capacity to perform extracellular and intracellular neuronal recordings in the presence of an intact brainstem network. The decerebration procedure typically generates variable degrees of blood loss, which often compromises the hemodynamic stability of the preparation. We describe our microsurgical techniques and discuss microsurgical pearls utilized in order to consistently generate normotensive supracollicularly decerebrate preparations of the rat, exhibiting an augmenting pattern of phrenic nerve discharge. In brief, we perform bilateral ligation of the internal carotid arteries, biparietal craniectomies, securing of the superior sagittal sinus to the overlying strip of bone, removal of the median strip of bone overlying the superior sagittal sinus, supracollicular decerebrative encephalotomy, removal of the cerebral hemispheres, and packing of the anterior and middle cranial fossae with thrombin soaked gelfoam sponges. Hypothermia and potent inhalational anesthesia ensure neuroprotection during postdecerebrative neurogenic shock. Advantages of our approach include a bloodless and fast operation with a nil percent rate of operative mortality. We allow animal arterial pressure to recover gradually in parallel with gentle weaning of anesthesia following decerebration, performed contemporaneously with the provision of the neuromuscular antagonist vecuronium. Anesthetic weaning and institution of vecuronium should be contemporaneous, coordinate, gentle, gradual, and guided by the spontaneous recovery of the arterial blood pressure. We describe our microsurgical techniques and perioperative management strategy designed to achieve decerebration and accordingly survey the literature on techniques used across several studies in achieving these goals.
Highlights
The use of anesthesia significantly attenuates neuronal firing rate and neural network oscillatory synchrony, confounding the study of a variety of neurophysiological processes, especially those evaluating brainstem and spinal cord modulation of respiratory rhythm generation and pattern formation, sympathetic tone, cardiovagal premotoneuronal outflow, locomotor activity, nociception, and hippocampal theta oscillations (Sapru and Krieger, 1979)
We typically reduce the level of isoflurane anesthesia in quantal decrements of approximately 0.5% every 15 to 20 minutes, though we encourage the custom design and individualization of perioperative management of anesthetics fitting the instinct of the investigator
We extensively discuss and detail critical and nuanced microsurgical techniques and perioperative strategies through which to optimize the generation of stable decerebrate animal preparations and present several methodological modifications annihilating or minimizing perioperative blood loss, hastening recovery of the neural elements comprising the brainstem oscillators generating the breathing rhythm and sympathetic tone driving the arterial blood pressure, and generating consistently stable decerebrate animal preparations (Ghali and Marchenko, 2015, 2016a,b; Ghali, 2015, 2019c; Marchenko et al, 2012; Marchenko and Rogers, 2009, 2007, 2006a,b)
Summary
The use of anesthesia significantly attenuates neuronal firing rate and neural network oscillatory synchrony, confounding the study of a variety of neurophysiological processes, especially those evaluating brainstem and spinal cord modulation of respiratory rhythm generation and pattern formation, sympathetic tone, cardiovagal premotoneuronal outflow, locomotor activity, nociception, and hippocampal theta oscillations (Sapru and Krieger, 1979). Massive intraoperative blood loss and a general paucity of studies detailing the steps of the decerebration approach and preemptive strategies to prevent intraoperative hemorrhage represent the principal impediments to the effective and faithful use of the decerebrative procedure in rats and other small animals, yielding hypotensive preparations (Woolf, 1984) and significantly compromising the brainstem neural networks generating the breathing rhythm and sympathetic oscillations. We will evaluate the physiological and microsurgical variables governing successful decerebration in order to encourage and facilitate the widespread use of this experimental animal model in an economical, efficient, and systematically-reproducible manner
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