The Journal of Neuroscience, January 3, 2007, 27(1):75-83

Serotonin Modulates Pallidal Neuronal Activity in the Awake Monkey
 
Hitoshi Kita,¹ Satomi Chiken,^1,2 Yoshihisa Tachibana,² and Atsushi Nambu^2
 
1Department of Anatomy and Neurobiology, College of Medicine, University of Tennessee Memphis, Memphis, Tennessee 38163, and ²Division of System Neurophysiology, National Institute for Physiological Sciences, and Department of Physiological Science, The Graduate University for Advanced Studies, Okazaki 444-8585, Japan

Preparation of animals.
This study was performed in compliance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals and the National Institute of Physiological Sciences Guide for the Use and Care of Laboratory Animals in Research. The monkey preparation methods used in the present study were very similar to those reported previously (Nambu et al., 2000 ; Kita et al., 2004 , 2005a ). Each of three Japanese macaques (Macaca fuscata) was trained to sit quietly in a monkey chair. Before surgery, each monkey was anesthetized with sodium pentobarbital (25 mg/kg, i.v.) and ketamine hydrochloride (10 mg/kg, i.m.) and was placed in a homemade acrylic stereotaxic frame. Then, magnetic resonance images of the head were taken. The monkeys received surgery to install headgear for holding their heads painlessly to a metal stereotaxic frame attached to the chair. Still under the anesthesia, the skull of the monkey was widely exposed. Small stainless steel screws were attached to the skull as anchors, and the exposed skull and screws were covered with acrylic resin. Two stainless steel pipes were mounted in parallel over the frontal and occipital areas of the skull. The monkey was then removed from the chair, allowed to recover in the animal housing facility, and was cared for.

A few days after the initial surgery, a second surgery was performed to implant stimulus electrodes in the hand region of the primary motor cortex (M1) and the supplementary motor cortex (SMA). For the second surgery, the monkey was anesthetized with ketamine hydrochloride (10 mg/kg, i.m.) and xylazine hydrochloride (1–2 mg/kg, i.m.) and was seated in a monkey chair with its head fixed to a stereotaxic frame. To access the M1 and SMA, a hole was drilled in the skull. After the monkey recovered from the anesthesia, and while it was still in the chair, a glass-coated Elgiloy (Elgin, IL) alloy microelectrode (0.5–1.5 M at 1 kHz) was inserted perpendicularly to the cortical surface. Extracellular unit activity was recorded in 1–1.5 mm intervals of depth across the M1 and SMA, and the neuronal responses to somatosensory stimuli (skin touch and passive joint movement) were examined. After extracellular unit recording, intracortical microstimulation using a train of 12 cathodal pulses (200 µs duration at 333 Hz) with currents of <50 µA was delivered, and the movements evoked in the various body parts were observed.