ProtocolPreparation for the in vivo recording of neuronal responses in the visual cortex of anaesthetised marmosets (Callithrix jacchus)
Section snippets
Type of research
This paper describes a method for the preparation of a New World monkey (the common marmoset, Callithrix jacchus) for acute electrophysiological recordings, under anaesthesia and neuromuscular block. This protocol has been developed with the aim of allowing stable recordings of single-neurone activity in visual cortex, and is suited for experiments requiring many hours of data acquisition (e.g. [1], [17]).
Time required
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For premedication, induction of anaesthesia and surgical preparation up to 3 h are required.
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Electrophysiological recordings: the upper limit of the viability of this type of preparation remains to be determined, and will most likely depend on the area of the brain being targeted. Successful, stable recordings from visual cortex (including the second, middle temporal, dorsomedial and ventral extrastriate areas) have been obtained for up to 72 h and single cells are routinely held for over 3 h.
Animals
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The animals were adult male marmosets (Callithrix jacchus) with a mean body weight of 340 g. Animals were purchased from the NHMRC National Non-Human Primate Breeding Facility administered by Monash University, Melbourne, Australia.
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Once transferred from the breeding facility, the animals were held in twin caging (dimensions 1.9×0.6×0.5 m) in a temperature (27–30 °C), humidity (50–70%) and light-cycle controlled room, with access to an outside run.
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Diet consisted of a commercially available
Pre-surgical measures
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Food was withdrawn 12 h prior to the induction of anaesthesia.
Premedication, sedation, and induction of anaesthesia
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Animals were premedicated with a combined intramuscular injection of the muscarinic cholinergic receptor antagonist atropine (0.2 mg kg−1) and a long-acting benzodiazepine sedative (diazepam, 3 mg kg−1). Atropine is used to decrease salivation and bronchial secretions, and to minimise disturbances in cardiac rhythm (such as bradycardia and ventricular arrhythmia, which may be associated with the use of xylazine in the anaesthetic
Success rate
Fourteen out of 15 electrophysiological experiments conducted since the introduction of the present version of the protocol were successful, producing stable (Fig. 2) electrophysiological recordings from striate and extrastriate areas. In one animal, cellular activity could not be elicited in extrastriate cortex, and the experiment was discontinued after 6 h. The recording period under sufentanil anaesthesia varied between 12 and 72 h (28.4±8.2 h; mean±S.D.). Note, however, that in many cases
Marmosets as models for the study of visual cortical physiology
The use of marmosets for visual physiological experiments offers a number of important advantages over the macaque monkey, which is the most commonly studied diurnal primate model. The paramount advantages are related to the smaller size of the brain and the near absence of cortical sulci. These allow extensive sets of mapping data to be obtained from individuals in acute sessions [16], as well as a more reliable placement of electrode penetrations on the basis of stereotaxic coordinates [4].
Quick procedure
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Premedicate monkey with atropine and diazepam IM.
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Induce anaesthesia with ketamine/xylazine mix IM.
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Transfer to heated blanket and mask with oxygen.
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Protect eyes with Celluvisc®.
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Inject dexamethasone and procaine penicillin IM and lignocaine to incision sites.
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Shave neck, legs and head and swab with Betadine®.
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Swab penis and anus with lignocaine (5%) ointment.
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Insert rectal temperature probe and connect to homeothermic blanket.
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Perform tracheotomy and insert tracheal tube (2.0–3.0 mm I.D.) 1 cm.
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Acknowledgements
The authors wish to acknowledge the help of several colleagues who have made suggestions, which resulted in the refinement of this protocol. In particular, we would like to thank the Monash University Animal Welfare Officer and Animal Ethics Committee. We would also like to thank Rowan Tweedale for many suggestions on the manuscript. Work supported by research grants from the Australian Research Council, National Health and Medical Research Council and Monash University (Early Career Researcher
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