Use of pneumoencephalography to increase stereotaxic accuracy in rhesus monkeys

A method for localizing microelectrode trajectories in the macaque brain using MRI

Magnetic resonance imaging (MRI) is often used by electrophysiologists to target specific brain regions for placement of microelectrodes. However, the effectiveness of this technique has been limited by few methods to quantify in three dimensions the relative locations of brain structures, recording chambers and microelectrode trajectories. Here we present such a method. After surgical implantation, recording chambers are fitted with a plastic cylinder that is filled with a high-contrast agent to aid in the segmentation of the cylinder from brain matter in an MRI volume. The resulting images of the filled cylinder correspond to a virtual cylinder that is projected along its long axis - parallel to the trajectories of microelectrodes advanced through the recording chamber - through the three-dimensional image of the brain. This technique, which does not require a stereotaxic coordinate system, can be used to quantify the coverage of an implanted recording chamber relative to anatomical landmarks at any depth or orientation. We have used this technique in conjunction with Caret [Van Essen DC, Drury HA, Dickson J, Harwell J, Hanlon D, Anderson CH. An integrated software suite for surface-based analyses of cerebral cortex. J Am Med Inform Assoc 2001;8:443-59] and AFNI [Cox RW. AFNI: software for analysis and visualization of functional magnetic resonance neuroimages. Comput Biomed Res 1996;29:162-73] brain-mapping software to successfully localize several regions of macaque cortex, including the middle temporal area, the lateral intraparietal area and the frontal eye field, and one subcortical structure, the locus coeruleus, for electrophysiological recordings.

A method for accurate determination of stereotaxic coordinates in single-unit recording studies in monkeys by high-resolution three-dimensional magnetic resonance imaging

For single-unit recording from the brain in monkeys, the precise determination of recording targets is essential. Although magnetic resonance imaging (MRI) has been used recently in several laboratories, it has been difficult to obtain three-dimensional information on a target from two-dimensional pictures, and, therefore, it has also been difficult to determine precise coordinates. We developed a new method for precisely determining target-area coordinates based on reconstructed rendering pictures made from three-dimensional MRI data. We also combined this method with magnetic resonance angiography to avoid severe vessel complications in recording experiments.

Use of 6-hydroxydopamine to deplete brain catecholamines in the rhesus monkey: effects on urinary catecholamine metabolites and behavior

The purpose of this study was to determine: 1) whether 6-hydroxydopamine (6-OHDA), previously shown to deplete brain catecholamines (CA) in rodents, depletes brain CA in rhesus monkeys; 2) whether depletion of brain CA produces changes in behavior; and, 3) whether urinary output of 3-methoxy-4-hydroxyphenylglycol (MHPG) reflects brain norepinephrine (NE) depletions. Repeated intracerebroventricular (ICV) injection of 6-OHDA (N = 20; 15.5-73.3 mg/subject) produced chronic changes in social behavior and, at higher dosages, reduced output of urinary MHPG. However, 4 weeks after the last ICV 6-OHDA injection, urinary MHPG excretion returned to baseline values and whole brain CA content was not reliably different from control. A single treatment with 6-OHDA microinjected into the substantia nigra (SN) (N = 12; 120-240 microgram/subject) produced chronic whole brain depletions of brain CA without depleting serotonin. Reductions in brain CA were associated with a specific set of motor behaviors, aphagia, and adipsia. SN 6-OHDA produced greater brain NE depletions than ICV 6-OHDA, but urinary MHPG output was not reduced. SN 6-OHDA treated subjects showed chronic changes in social behavior and were more sensitive to the operant response rate decreasing effects of alpha-methyl-para-tyrosine (AMPT) than control subjects. Subjects with the largest depletions of brain dopamine (DA) (greater than 90%) were hypokinetic, rigid, and had a distal limb tremor. These results show that SN but not ICV injection of 6-OHDA can deplete brain CA in the rhesus monkey. The most prominent behavioral changes were characterized by disturbances in motor function. Urinary MPHG output does not reflect depletions of brain NE in this species.

Magnetic resonance imaging of the rhesus monkey brain: use for stereotactic neurosurgery

Standard stereotactic procedures rely upon external cranial landmarks and standardized atlases for localization of subcortical neural regions. Magnetic resonance imaging permits the visualization of the neural structure of the brain in vivo. A stereotactic instrument compatible with a magnetic resonance unit was constructed and together with magnetic resonance imaging a procedure was developed that overcomes the limitations and inaccuracies of the traditional stereotactic methods and allows accurate and reliable localization of subcortical targets in the rhesus monkey brain.

Techniques for improving stereotaxic accuracy in Macaca fascicularis

Sources of stereotaxic variability in long-tailed macaques (Macaca fascicularis) were examined by X-ray techniques. Accuracy in the vertical dimension can be improved significantly by measuring from the top of the brain rather than from the Frankfurt plane established by external bony landmarks. Even greater accuracy in both the vertical and anterior-posterior dimensions can be attained by rotating the cranium in the stereotaxic instrument to bring the intercommissural line, as defined by ventriculography, into a plane parallel to the horizontal stereotaxic plane, thus approximating the orientation of the brain as represented in both of the brain atlases currently available for this species. An adjustable eyebar spacer, which allows the cranium to be rotated in the stereotaxic instrument, is described.

Corticotropin-releasing factor administered intraventricularly to rhesus monkeys

Synthetic ovine corticotropin-releasing factor (CRF) administered intraventricularly (ICV) to rhesus monkeys resulted in endocrine and behavioral changes. At doses of 20 and 180 micrograms, CRF stimulated the pituitary-adrenal axis in four chair-restrained monkeys. These monkeys showed concomitant increases in arousal. To study these animals in a less restrictive setting, three of the monkeys later received CRF ICV (20 and 180 micrograms) in their home cages. At the 180-micrograms dose the monkeys exhibited a combination of huddling and lying down behavior. These behavioral effects did not seem to be due to alterations in blood pressure.

A chronic stereotaxic guide-tube platform for intracranial infections in macaques

Intracranial injection is a valuable method for testing the effects of pharmacologic agents on the central nervous system or specific areas of the brain with minimal peripheral effects. Improved apparatus and techniques have made it possible to treat the same site repeatedly over extended periods of time in unrestrained subjects. Methods are described for the construction and implantation of a durable platform that assures stereotaxic accuracy of intracranial injections for up to two years. The design and use of two kinds of injection cannula for intracerebroventricular and intracerebral injections of one or a few microliters are described in detail. The apparatus and methods have been used in studies of large number of rhesus, longtailed, and pigtailed macaques over a period of several years. The influence of species characteristics and skull growth on the effectiveness of the techniques is discussed.

Reduced forebrain norepinephrine in rhesus monkeys made obese by hypothalamic lesions

Young adult male rhesus monkeys received bilateral lesions in the anteromedial lateral hypothalamus. During the year of observation following surgery the animals were hyperphagic and became markedly obese. The mean increase in body weight averaged 66% more for the experimental animals than for the controls. Analyses of catecholamine concentrations in 12 brain regions at the time of sacrifice revealed consistently lower concentrations of norepinephrine (averaging 51% of control) in the frontal cortex of the obese animals as well as a more variable decrease in norepinephrine in the caudate and striatum. There was no consistent effect of the lesions on dopamine in any of the regions studied. There was no obvious relationship between regional catecholamine levels and weight gain within the experimental group.

X-ray controlled implantation of the brain stem

Using X-rays to improve accuracy of stereotaxic implantation of the brain stem of Macaca irus monkeys overcomes the problems of moveable brain stem and inaccurate fixation in the stereotaxic frame. The method is independent of standard atlases and correct ear bar fixation. The key to the method is the establishment of a nomogram which relates the implantation target to bony landmarks. The nomogram is established by X-ray contrast studies which outline the brain stem, the implantation target in the brain stem being decided by superimposed histology. This target is nomographically related to bony landmarks seen both on the contrast X-ray and on a plain X-ray taken later at implantation with the monkey in the stereotaxic frame. Being able to locate the target on this plain X-ray, and having included on the X-ray a metal marker, the stereotaxic coordinates of which are known, the distance can be measured (allowing for X-ray magnification) between target and stereotaxic marker and thus one computes the target coordinates. Accuracy of implantation according to these coordinates is monitored with further plain X-rays.