Stereotaxic Atlas Research Articles

PyElectrode: An open-source tool using structural MRI for electrode positioning and neuron mapping

Neurophysiologists want to place the tip of an electrode in a specific area of the brain. The coordinates of this area can be obtained from standard stereotaxic atlases. However, individual brains may not align with the atlas exactly. Additionally, for chronic recordings, electrodes are placed through a chamber attached to the animal's skull. Thus, the user wants to know where the area of interest is in chamber coordinates, not stereotaxic coordinates. After the chamber has been attached an MRI is often made. This assists in electrode placement, as the location of a target relative to the chamber can be determined based on the atlas. However, doing this in practice requires rough estimation or cumbersome calculations. pyElectrode provides a graphical display and performs calculations necessary to convert between stereotaxic and chamber coordinates, thus facilitating MR-based targeting from an implanted chamber. It also allows the experimenter to visualize recording or stimulation sites during experiments. Finally, it can display and output those sites on an MRI slice background in a format suitable for publication.

The basal ganglia and thalamus of the long-tailed macaque in stereotaxic coordinates. A template atlas based on coronal, sagittal and horizontal brain sections

A stereotaxic brain atlas of the basal ganglia and thalamus of Macaca fascicularis presented here is designed with a surgical perspective. In this regard, all coordinates have been referenced to a line linking the anterior and posterior commissures (ac–pc line) and considering the center of the ac at the midline as the origin of the bicommissural space. The atlas comprises of 43 different plates (19 coronal levels, 10 sagittal levels and 14 horizontal levels). In addition to ‘classical’ cyto- and chemoarchitectural techniques such as the Nissl method and the acetylcholinesterase stain, several immunohistochemical stains have been performed in adjacent sections, including the detection of tyrosine hydroxylase, enkephalin, neurofilaments, parvalbumin and calbindin. In comparison to other existing stereotaxic atlases for M. fasicularis, this atlas has two main advantages: firstly, brain cartography is based on a wide variety of cyto- and chemoarchitectural stains carried out on adjacent sections, therefore enabling accurate segmentation. Secondly and most importantly, sagittal and horizontal planes are included. Sagittal planes are very useful for calculating oblique trajectories, whereas, clinical researchers engaged in neuroimaging studies will be more familiar with horizontal sections, as they use horizontal (also called “axial”) brain images in their daily routine of their clinical practices.

MiRNA Expression Profile after Status Epilepticus and Hippocampal Neuroprotection by Targeting miR-132

When an otherwise harmful insult to the brain is preceded by a brief, noninjurious stimulus, the brain becomes tolerant, and the resulting damage is reduced. Epileptic tolerance develops when brief seizures precede an episode of prolonged seizures (status epilepticus). MicroRNAs (miRNAs) are small, noncoding RNAs that function as post-transcriptional regulators of gene expression. We investigated how prior seizure preconditioning affects the miRNA response to status epilepticus evoked by intra-amygdalar kainic acid in mice. The miRNA was extracted from the ipsilateral CA3 subfield 24 hours after focal-onset status epilepticus in animals that had previously received either seizure preconditioning (tolerance) or no preconditioning (injury), and mature miRNA levels were measured using TaqMan low-density arrays. Expression of 21 miRNAs was increased, relative to control, after status epilepticus alone, and expression of 12 miRNAs was decreased. Increased miR-132 levels were matched with increased binding to Argonaute-2, a constituent of the RNA-induced silencing complex. In tolerant animals, expression responses of >40% of the injury-group-detected miRNAs differed, being either unchanged relative to control or down-regulated, and this included miR-132. In vivo microinjection of locked nucleic acid-modified oligonucleotides (antagomirs) against miR-132 depleted hippocampal miR-132 levels and reduced seizure-induced neuronal death. Thus, our data strongly suggest that miRNAs are important regulators of seizure-induced neuronal death.

Switching of N-Methyl-d-aspartate (NMDA) Receptor-favorite Intracellular Signal Pathways from ERK1/2 Protein to p38 Mitogen-activated Protein Kinase Leads to Developmental Changes in NMDA Neurotoxicity

Excitotoxicity mediated by overactivation of N-methyl-D-aspartate receptors (NMDARs) has been implicated in a variety of neuropathological conditions in the central nervous system (CNS). It has been suggested that N-methyl-D-aspartate (NMDA) neurotoxicity is developmentally regulated, but the definite pattern of the regulation has been controversial, and the underlying mechanism remains largely unknown. Here, we show that NMDA treatment leads to significant cell death in mature (9 and 12 days in vitro) hippocampal neurons or hippocampi of young postnatal day 12 and adult rats but not in immature (3 and 6 days in vitro) neurons or embryonic day 18 and neonatal rat hippocampi. In contrast, NMDA promotes survival of immature neurons against tropic deprivation. Interestingly, it is found that NMDA preferentially activates p38 MAPK in mature neuron and adult rat hippocampus, but it favors ERK1/2 activation in immature neuron and postnatal day 0 rat hippocampus. Moreover, it is shown that NMDA neurotoxicity in mature neuron is mediated via p38 MAPK activation, and neuroprotection in immature neuron is mediated via ERK1/2 activation, whereas all these effects are NR2B-containing NMDAR-dependent, as well as Ca(2+)-dependent. We also revealed that mature and immature neurons showed no difference in the amplitude of NMDA-induced intracellular calcium ([Ca(2+)](i)) increase. However, the basal level of [Ca(2+)](i) is shown to elevate with the maturation of neuron, and this elevation is attributable to the changes in NMDA neurotoxicity but not to the switch of the NMDAR signaling pathway. Taken together, our results suggest that a switch of NMDA receptor-favorite intracellular signal pathways from ERK1/2 to p38 MAPK and the elevated basal level of [Ca(2+)](i) with age might be critical for the developmental changes in NMDA neurotoxicity in the hippocampal neuron.

Cut-like Homeobox 1 (CUX1) Regulates Expression of the Fat Mass and Obesity-associated and Retinitis Pigmentosa GTPase Regulator-interacting Protein-1-like (RPGRIP1L) Genes and Coordinates Leptin Receptor Signaling

The first intron of FTO contains common single nucleotide polymorphisms associated with body weight and adiposity in humans. In an effort to identify the molecular basis for this association, we discovered that FTO and RPGRIP1L (a ciliary gene located in close proximity to the transcriptional start site of FTO) are regulated by isoforms P200 and P110 of the transcription factor, CUX1. This regulation occurs via a single AATAAATA regulatory site (conserved in the mouse) within the FTO intronic region associated with adiposity in humans. Single nucleotide polymorphism rs8050136 (located in this regulatory site) affects binding affinities of P200 and P110. Promoter-probe analysis revealed that binding of P200 to this site represses FTO, whereas binding of P110 increases transcriptional activity from the FTO as well as RPGRIP1L minimal promoters. Reduced expression of Fto or Rpgrip1l affects leptin receptor isoform b trafficking and leptin signaling in N41 mouse hypothalamic or N2a neuroblastoma cells in vitro. Leptin receptor clusters in the vicinity of the cilium of arcuate hypothalamic neurons in C57BL/6J mice treated with leptin, but not in fasted mice, suggesting a potentially important role of the cilium in leptin signaling that is, in part, regulated by FTO and RPGRIP1L. Decreased Fto/Rpgrip1l expression in the arcuate hypothalamus coincides with decreased nuclear enzymatic activity of a protease (cathepsin L) that has been shown to cleave full-length CUX1 (P200) to P110. P200 disrupts (whereas P110 promotes) leptin receptor isoform b clustering in the vicinity of the cilium in vitro. Clustering of the receptor coincides with increased leptin signaling as reflected in protein levels of phosphorylated Stat3 (p-Stat3). Association of the FTO locus with adiposity in humans may reflect functional consequences of A/C alleles at rs8050136. The obesity-risk (A) allele shows reduced affinity for the FTO and RPGRIP1L transcriptional activator P110, leading to the following: 1) decreased FTO and RPGRIP1L mRNA levels; 2) reduced LEPR trafficking to the cilium; and, as a consequence, 3) a diminished cellular response to leptin.

MicroPET imaging of noxious thermal stimuli in the conscious rat brain

Small animal positron emission tomography (microPET) has been utilized in the investigation of nociception. However, a possible drawback from previous studies is the reduced activation pattern due to the application of anesthesia. The purpose of the present study was to demonstrate a potential means of avoiding anesthesia during stimulation, as well as minimizing the confounding anesthetic effect. Sodium pentobarbital and ketamine were first evaluated to determine their effect on microPET images in the current study. [18F]-Fluorodeoxyglucose (18F-FDG) was an appropriate radiotracer to reveal activated regions in rat brains. Pentobarbital anesthesia significantly reduced 18F-FDG uptake in neural tissues, blurrier to lower contrast; therefore, ketamine was used to anesthetize animals during microPET. After the rats were anesthetized and secured in a laboratory-made stereotaxic frame, a simple, noninvasive stereotaxic technique was used to position their heads in the microPET scanner and to roughly conform the images in the stereotaxic atlas. For functional imaging, conscious rats were restrained in cages with minimal ambient noise; short repetitive thermal stimuli were applied to each rat's tail subsequently. The rats were adequately anesthetized with ketamine following 30 min of scanning without stimulation. An activation index (AI) was calculated from microPET data to quantify the local metabolic activity changes according to the normalized 18F-FDG dosage. The average AI indicated a side-to-side difference for all innocuous stimulations in the thalamus. However, such side-to-side difference was only observed for noxious heat and cold stimulations in primary somatosensory cortex (SI), secondary somatosensory cortex (SII), and agranular insular cortex (AIC). The present study demonstrated the feasibility of the microPET technique to image metabolic functions of the conscious rat brain, offering better rationale and protocol designs for future pain studies.

Cytoarchitectonic and chemoarchitectonic characterization of the prefrontal cortical areas in the mouse

This study describes cytoarchitectonic criteria to define the prefrontal cortical areas in the mouse brain (C57BL/6 strain). Currently, well-illustrated mouse brain stereotaxic atlases are available, which, however, do not provide a description of the distinctive cytoarchitectonic characteristics of individual prefrontal areas. Such a description is of importance for stereological, neuronal tracing, and physiological, molecular and neuroimaging studies in which a precise parcellation of the prefrontal cortex (PFC) is required. The present study describes and illustrates: the medial prefrontal areas, i.e., the infralimbic, prelimbic, dorsal and ventral anterior cingulate and Fr2 area; areas of the lateral PFC, i.e., the dorsal agranular insular cortical areas and areas of the ventral PFC, i.e., the lateral, ventrolateral, ventral and medial orbital areas. Each cytoarchitectonically defined boundary is corroborated by one or more chemoarchitectonic stainings, i.e., acetylcholine esterase, SMI32, SMI311, dopamine, parvalbumin, calbindin and myelin staining.

The central nucleus of amygdala is involved in tolerance to the antinociceptive effect of NSAIDs

Aim: Repeated microinjections of non-opioid an-algesics into the midbrain periaqueductal gray matter and rostral ventro-medial medulla induce antinociception with development of tolerance. Antinociception following systemic administra-tion of non-steroidal anti-inflammatory drugs (N SAIDs) also exhibit tolerance. Presently our aim was to investigate the development of tolerance to the antinociceptive effects of NSAIDs analgine, ketorolac, and xefocam microinjected into cen-tral nucleus of amygdala (Ce) in rats. Methods: Under anesthesia with thiopental a stainless steel guide cannula was stereotaxically implanted uni- laterally or bilaterally into the Ce using stereo-taxic atlas coordinates, and anchored to the cra- nium by dental cement. Five days after surgery, 3 µl of these NSAIDs were injected via the injec-tion cannula while the rat was gently restrained. Twenty min post microinjection, i.e. 10-min be-fore the peak of the drugs’ effect is normally rea- ched, animals were tested with tail flick (TF) and hot plate (HP) tests. On the 5th experimental day all animals received a Ce microinjection of mor-phine. Results: Daily microinjection of NSAIDs into the Ce uni- or bilaterally, produced antino-ciception with development of complete toler-ance over a 5-day period. Following the treat-ment period, morphine microinjection into the Ce failed to elicit antinociception, indicating cro- ss-tolerance to the antinociceptive effect of N SAIDs. In other words, the “non-opioid tolerant” rats showed cross-tolerance to morphine. Con-clusions: Our data confirmed the suggestion that NSAIDs interact with endogenous opioid systems, which likely play a key role in the development of tolerance to the antinociceptive effects of NSA IDs.

Magnetic resonance imaging and micro-computed tomography combined atlas of developing and adult mouse brains for stereotaxic surgery

Stereotaxic atlases of the mouse brain are important in neuroscience research for targeting of specific internal brain structures during surgical operations. The effectiveness of stereotaxic surgery depends on accurate mapping of the brain structures relative to landmarks on the skull. During postnatal development in the mouse, rapid growth-related changes in the brain occur concurrently with growth of bony plates at the cranial sutures, therefore adult mouse brain atlases cannot be used to precisely guide stereotaxis in developing brains. In this study, three-dimensional stereotaxic atlases of C57BL/6J mouse brains at six postnatal developmental stages: postnatal day (P) 7, P14, P21, P28, P63 and in adults (P140–P160) were developed, using diffusion tensor imaging (DTI) and micro-computed tomography (CT). At present, most widely-used stereotaxic atlases of the mouse brain are based on histology, but the anatomical fidelity of ex vivo atlases to in vivo mouse brains has not been evaluated previously. To account for ex vivo tissue distortion due to fixation as well as individual variability in the brain, we developed a population-averaged in vivo magnetic resonance imaging adult mouse brain stereotaxic atlas, and a distortion-corrected DTI atlas was generated by nonlinearly warping ex vivo data to the population-averaged in vivo atlas. These atlas resources were developed and made available through a new software user-interface with the objective of improving the accuracy of targeting brain structures during stereotaxic surgery in developing and adult C57BL/6J mouse brains.

Effect of baclofen on neuronal activity in the medial vestibular nucleus after unilateral surgical labyrinthectomy in rats

Conclusions: Ipsilateral and contralateral medial vestibular nuclei (MVN) neurons respond differently to systemic injection of baclofen (4-amino-3-(4-chlorophenyl)-butanoic acid), illustrating the plastic changes of the type B γ-aminobutyric acid (GABAB) receptor during vestibular compensation. Objectives: To investigate the responsiveness of MVN neurons to baclofen during the early, partially compensated period after unilateral surgical labyrinthectomy. Materials and methods: MVN were localized using field potentials evoked by electrical stimulation, along with a stereotaxic atlas of rat brain. Neuronal activity in MVN was recorded and analyzed in rats that had undergone labyrinthectomy with and without administration of baclofen. Results: After left labyrinthectomy the mean discharge rate in ipsilesional MVN decreased, but it was nearly restored by postoperative day 8. Baclofen (3 mg/kg) reversed the mean discharge rates between bilateral MVN at days 4 and 8 after surgical labyrinthectomy. In addition, the reduction ratio of the right MVN neurons was higher than that of the left MVN neurons.

Effect of deep brain stimulation in nucleus accumbens on learning and memory ability of morphine dependence rats

Objective To explore the effect of deep brain stimulation(DBS)in nucleus accumbens on learning and memory ability of morphine dependence rats.Methods According to stereotaxic atlas of the rat brain,DBS electrodes were implanted in rats bilateral nucleus accumbens,then Morris water maze test were carried out on the tenth day of morphine injection and the first day after DBS.Results The average time of reaching platform of three groups was different significantly before DBS(F=7.49,P=0.0077);and that of morphine addiction group wag longer than saline control group(P＜0.01).While after DBS,there was also significantly different(F=7.76,P=0.0069);the time had significant difference between DBS group and fake stimulation group(P=0.014),not saline control group(P=0.43);and fake stimulation group compared with saline control group(P=0.0056).The time of crossing the platform quadrant(Ⅱ)showed significant difference between saline control group and morphine addiction group(P<0.01);and the saline control group(48.53±2.29),compared with fake stimulotion group(20.74±2.13)(P=0.001),DBS group(38.34±1.68)(P=0.062).Conclusion DBS can improve the learning and memory ability impaired by morphine in rats. Key words: Deep brain stimulation; Nucleus accumbens; Morphine; Morris water maze

Utilization of the 3-D Stereotaxic Atlas and Normal Database Analysis to Further Investigate HIV-Related Neurocognitive Impairment and Follow-up Response to Highly Active Antiretroviral Therapy

Utilization of the 3-D Stereotaxic Atlas and Normal Database Analysis to Further Investigate HIV-Related Neurocognitive Impairment and Follow-up Response to Highly Active Antiretroviral Therapy

Changes in Regional Cerebral Blood Flow After Repetitive Transcranial Magnetic Stimulation of the Left Dorsolateral Prefrontal Cortex in Treatment-Resistant Depression

Changes in Regional Cerebral Blood Flow After Repetitive Transcranial Magnetic Stimulation of the Left Dorsolateral Prefrontal Cortex in Treatment-Resistant Depression

Stereotaxic white matter atlas based on diffusion tensor imaging in an ICBM template

Brain registration to a stereotaxic atlas is an effective way to report anatomic locations of interest and to perform anatomic quantification. However, existing stereotaxic atlases lack comprehensive coordinate information about white matter structures. In this paper, white matter-specific atlases in stereotaxic coordinates are introduced. As a reference template, the widely used ICBM-152 was used. The atlas contains fiber orientation maps and hand-segmented white matter parcellation maps based on diffusion tensor imaging (DTI). Registration accuracy by linear and non-linear transformation was measured, and automated template-based white matter parcellation was tested. The results showed a high correlation between the manual ROI-based and the automated approaches for normal adult populations. The atlases are freely available and believed to be a useful resource as a target template and for automated parcellation methods.

The thalamus revisited: where do we go from here?

In my academic lifetime, two outstanding books on the thalamus have been published. Now both have been reissued as expanded, updated and improved second editions. The most massive of these, the second edition of The Thalamus by E.G. Jones, follows his 900-page, 1985 edition. While the early edition was truly remarkable, the two-volume, second edition of 1679 pages of expanded size represents an effort reminiscent of Polyak's 1390-page tome, The Vertebrate Visual System, published in 1957. Jones retains one of my favorite quotations from the first to the second volume, one attributed to the great neuroanatomist and neuroscientist, Jerzy Rose: ‘The thalamus is like the Flying Dutchman: many have heard of it, some believe in it, but few have actually seen it’ (c. 1940). Today, I am not sure how many have heard of the Flying Dutchman, a mythical sailing ship, but Jones’ first edition did much to correct uncertainties about the thalamus, as The Thalamus became one of the most referenced books in neuroscience. The basic organization and many features of the first edition are carried over to the second, but this is bigger and better in every way. Most impressive, the second edition is profusely illustrated with drawings, photographs of investigators, and especially, photomicrographs of brain sections through the thalamus. The photomicrographs are not just of a brain section here and there, but of series of sections from the same cases, and not just from the laboratory species that we can view in the many stereotaxic atlases that are now available, but also of species such as tree shrews, galagos and the egg-laying monotremes. On page 1210, for example, one can see how well differentiated the anterior nuclei of the thalamus are in rabbits compared to rats, or even most primates. No wonder rabbits played such a significant …

Patterns of fMRI Activity Dissociate Overlapping Functional Brain Areas that Respond to Biological Motion

Accurate perception of the actions and intentions of other people is essential for successful interactions in a social environment. Several cortical areas that support this process respond selectively in fMRI to static and dynamic displays of human bodies and faces. Here we apply pattern-analysis techniques to arrive at a new understanding of the neural response to biological motion. Functionally defined body-, face-, and motion-selective visual areas all responded significantly to "point-light" human motion. Strikingly, however, only body selectivity was correlated, on a voxel-by-voxel basis, with biological motion selectivity. We conclude that (1) biological motion, through the process of structure-from-motion, engages areas involved in the analysis of the static human form; (2) body-selective regions in posterior fusiform gyrus and posterior inferior temporal sulcus overlap with, but are distinct from, face- and motion-selective regions; (3) the interpretation of region-of-interest findings may be substantially altered when multiple patterns of selectivity are considered.

In vivo isotropic 3D diffusion tensor mapping of the rat brain using diffusion-weighted 3D MP-RAGE MRI

The purpose of this study was to examine the potential of diffusion-weighted (DW) three-dimensional (3D) MP-RAGE MRI for diffusion-tensor mapping of the rat brain in vivo. A DW-3D-MP-RAGE (3D-DWI) sequence was implemented at 2.0 T using six gradient orientations and a b value of 1000 s/mm2. In this sequence, the preparation sequence with a "90 degrees RF-motion proving gradient (MPG): MPG-180 degrees RF-MPG-90 degrees RF" pulse train (DW driven equilibrium Fourier transform) was used to sensitize the magnetization to diffusion. A centric k-space acquisition order was necessary to minimize saturation effects (T1 contamination) from tissues with short relaxation time. The image matrix was 128x128x128 (interpolated from 64x64x64 acquisitions), which resulted in small isotropic DW image data (voxel size: 0.273x0.273x0.273 mm3). Moreover, 3D-DWI-derived maps of the fractional anisotropy (FA), relative anisotropy (RA) and main-diffusion direction were completely free of susceptibility-induced signal losses and geometric distortions. Two well-known commissural fibers, the corpus callosum and anterior commissure, were indicated and shown to be in agreement with the locations of these known stereotaxic atlases. The experiment took 45 min, and shorter times should be possible in clinical application. The 3D-DWI sequence allows for in vivo 3D diffusion-tensor mapping of the rat brain without motion artifacts and susceptibility to distortion.

Resolution of the region of secondary somatosensory cortex that responds to stimulation of the horizontal semicircular canal in rats

AbstractTo elucidate the region within the somatosensory cortex that receives inputs from the horizontal semicircular canal (HSC) in rats, we used a multichannel recording system to measure evoked potentials in the parietal cortex in response to electrical stimulation of the HSC nerve. The recordings suggested that the HSC nerves projected bilaterally into the somatosensory cortex, with a contralateral predominance. The territory within the somatosensory cortex that responded to the stimulation of the HSC nerve was as follows: mediolateral 6.0 mm and anteroposterior –1.3 ∼ –2.3 mm from the bregma, and depth 1.4 ∼ 1.6 mm from the cortex surface horizontally by stereotaxic atlas. The evoked potential in the parietal cortex that was induced by electrical stimulation was abolished after the administration of tetrodotoxin into the oval window of the vestibular system. These results suggest that the horizontal semicircular nerve projects bilaterally into the deep layers of the secondary somatosensory cortex.

Numerical density of pyramidal neurons in the hippocampus of 4 and 20 week old male and female rats

AbstractA study designed to investigate how the cellular laterality in rosto‐caudal direction changes due to age and sex was presented. It is a well‐known fact that asymmetry is an important issue in understanding brain functions. Frontal sections of 5 µm thickness with 200 µm intervals were taken from both dorsal hippocampi of 4‐ and 20‐week‐old male and female rats. Sections were stained with hematoxylin‐eosin and the levels of sections were determined according to a stereotaxic atlas. In each level, numerical density of pyramidal cells of the right and left area CA1, CA3 and CA4 of dorsal hippocampi were estimated by means of counting pyramidal cells under 10 × 40 magnification. Numerical cell density obtained from the right and left dorsal hippocampi of male and female rats were compared. Results are as follows: 1) Numerical cell density in the left and right dorsal hippocampi of 20‐week female rats was not high than 4‐week female dorsal hippocampi (p&gt;0.05). 2) Difference between 4‐week old female and male dorsal hippocampi of right and left CA1, CA3 and CA4 areas were not raised a significant level (p&gt;0.05). Differences between 20‐week‐old group of male and female rats with the exception of female CA4 area were not also significant. 3) Right and left dorsal hippocampi CA4 areas of the 20‐week‐old group showed a higher numerical density than the same area of the 4‐week‐old group (p&lt;0.007). This difference may show a postnatal neurogenesis in area CA4. The results, which are summarized above, may be helpful in understanding the mechanisms of human brains.

Spatial organization of afferent thalamic projections to structures of the pallidum in the dog brain.

It is now generally accepted that projections of the cor-tex,basal ganglia, and thalamus are organized into a seriesof parallel, functionally segregated circuits [3], whose inter-actionsproduce a variety of behavioral acts [7]. In this sys-tem,the striatum is the main receptive component and thepallidum is its efferent part. In accordance with this model,it has been suggested that afferent information, includingthalamic information, arrives in the palladium mainly via thestriatum. This may be why thalamopallidal connections havereceived almost no study. The thalamic nuclei have signifi-cantinfluences on the functioning of the basal ganglia,including the pallidum [10, 14, 16]. The existing fragmen-tarydata on the projections of the thalamic nuclei to indi-vidualpallidal structures [4, 5, 8, 10, 16] do not give a com-pletepicture of the spatial organization of the thalamopalli-dalsystem. The aim of the present work was to study the tha-lamopallidalprojection system of the dog brain by analyzingthe distribution of labeled neurons in the thalamic nucleiafter administration of markers into pallidal structures.nucleus, and ventral pallidum using stereotaxic atlas coor-dinates[6]. Brains were perfused under anesthesia 48 hlater. This procedure and the methods used for subsequentprocessing of brains and staining of serial frontal sectionswere as described by Mesulam [12], using tetramethylben-zidinefor histochemical detection of enzyme in neurons.Luminescent markers were injected into these struc-turesin some of the dogs at doses of 0.5-1.0 ml; on days 2and 22, dogs were given 1% bisbenzimide and 5% fast blueand 2% diamidino yellow respectively and brains were per-fusedunder anesthesia. All subsequent processing of brainsand serial sections were performed as described by Kuyperset al. [11]. Parallel serial sections were stained with cresylviolet and were used to identify the cytoarchitectonicboundaries of the thalamic nuclei. Thalamic nuclei wereidentified using an atlas [1].