Use of peroxidase substrate Vector VIP for multiple staining in light microscopy

Neuroanatomical tract-tracing techniques that did go viral

Neuroanatomical tracing methods remain fundamental for elucidating the complexity of brain circuits. During the past decades, the technical arsenal at our disposal has been greatly enriched, with a steady supply of fresh arrivals. This paper provides a landscape view of classical and modern tools for tract-tracing purposes. Focus is placed on methods that have gone viral, i.e., became most widespread used and fully reliable. To keep an historical perspective, we start by reviewing one-dimensional, standalone transport-tracing tools; these including today's two most favorite anterograde neuroanatomical tracers such as Phaseolus vulgaris-leucoagglutinin and biotinylated dextran amine. Next, emphasis is placed on several classical tools widely used for retrograde neuroanatomical tracing purposes, where Fluoro-Gold in our opinion represents the best example. Furthermore, it is worth noting that multi-dimensional paradigms can be designed by combining different tracers or by applying a given tracer together with detecting one or more neurochemical substances, as illustrated here with several examples. Finally, it is without any doubt that we are currently witnessing the unstoppable and spectacular rise of modern molecular-genetic techniques based on the use of modified viruses as delivery vehicles for genetic material, therefore, pushing the tract-tracing field forward into a new era. In summary, here, we aim to provide neuroscientists with the advice and background required when facing a choice on which neuroanatomical tracer-or combination thereof-might be best suited for addressing a given experimental design.

Chronic Infiltration of T Lymphocytes into the Brain in a Non-human Primate Model of Parkinson's Disease

Study of interactions between the nervous system and immunity offers insights into the pathogenesis of Parkinson's disease (PD) and potential therapeutic strategies for neurodegenerative diseases. Studies on rodents have revealed regulatory mechanisms of microglial activation and T lymphocyte recruitment in PD. However, the mechanisms underlying chronic T lymphocyte infiltration into the brain after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injection into a non-human primate (NHP) model of PD remain unknown. This study aimed to investigate changes in serum RANTES (regulated on activation, normal T cell expression and secretion) and analyze the chronic infiltration of T lymphocytes into the brain and microglia activation in NHPs at 48 weeks post-MPTP administration. We found selective and local chronic infiltration of CD4+ and CD8+ T lymphocytes, loss of dopaminergic neurons, dopamine transporter expression, chronic normalization of RANTES in the peripheral blood, and altered microglial morphology at 48 weeks after MPTP injection. This study confirms the involvement of CD4+ and CD8+ T lymphocyte infiltration in MPTP-induced NHP models of PD. Additionally, we corroborated previous findings regarding the mechanisms of T lymphocyte-induced neurodegeneration. The findings of chronic infiltration of T lymphocytes in our NHP model of PD provide novel insights into PD pathogenesis and the development of preventive and therapeutic agents.

High-contrast enzymatic immunohistochemistry of pigmented tissues

Historically, standard enzyme immunohistochemistry has been accomplished with brown (DAB, diaminobenzidine) substrate. This can become problematic in pigmented tissues, such as the retina, where brown pigment of retinal pigmented epithelial (RPE) cells can be easily confounded with brown substrate. Although immunofluorescence detection methods can overcome this challenge, fluorescence may fade over a period of weeks, while enzyme substrates allow for more long-lasting, archival results. In this report, we will describe a high-contrast enzyme immunohistochemistry method ideal for pigmented tissues that utilizes purple (VIP) substrate. We compared brown (DAB) and purple (VIP) substrates in enzyme immunohistochemistry experiments using human retina (paraffin sections) and monkey retinal pigmented epithelial cells (frozen sections), both containing brown pigmented cells. We compared substrates using several primary antibodies against markers that can be detected in the retina, including GFAP, VEGF, CD147 (EMMPRIN), RHO (rhodopsin) and PAX6. Methyl green was used as a counterstain for paraffin sections. A side-by-side comparison between DAB and VIP immunohistochemistry showed excellent contrast between pigmented cells and the purple VIP substrate in both human retinal tissue and monkey pigmented epithelial cells for all of the markers tested. This was a marked improvement over DAB staining in pigmented cells and tissues. For both paraffin sections and frozen sections of pigmented tissues, purple VIP substrate is an excellent alternative to brown DAB substrate and non-permanent immunofluorescence methods.

Multiplexed immunohistochemistry, imaging, and quantitation: a review, with an assessment of Tyramide signal amplification, multispectral imaging and multiplex analysis

Tissue sections offer the opportunity to understand a patient's condition, to make better prognostic evaluations and to select optimum treatments, as evidenced by the place pathology holds today in clinical practice. Yet, there is a wealth of information locked up in a tissue section that is only partially accessed, due mainly to the limitations of tools and methods. Often tissues are assessed primarily based on visual analysis of one or two proteins, or 2-3 DNA or RNA molecules. Even while analysis is still based on visual perception, image analysis is starting to address the variability of human perception. This is in contrast to measuring characteristics that are substantially out of reach of human perception, such as parameters revealed through co-expression, spatial relationships, heterogeneity, and low abundance molecules. What is not routinely accessed is the information revealed through simultaneous detection of multiple markers, the spatial relationships among cells and tissue in disease, and the heterogeneity now understood to be critical to developing effective therapeutic strategies. Our purpose here is to review and assess methods for multiplexed, quantitative, image analysis based approaches, using new multicolor immunohistochemistry methods, automated multispectral slide imaging, and advanced trainable pattern recognition software. A key aspect of our approach is presenting imagery in a workflow that engages the pathologist to utilize the strengths of human perception and judgment, while significantly expanding the range of metrics collectable from tissue sections and also provide a level of consistency and precision needed to support the complexities of personalized medicine.

Effect of hypobaric hypoxia on the P2X receptors of pyramidal cells in the immature rat hippocampus CA1 sub-field

PRIMARY OBJECTIVE

This study was designed to evaluate the effect of hypobaric hypoxia (HH) on the function and expression of P2X receptors in rat hippocampus CA1 pyramidal cells.

RESEARCH DESIGN

The functional changes of P2X receptors were investigated through the cell HH model and the expressional alterations of P2X receptors were observed through the animal HH model.

METHODS AND PROCEDURE

P2X receptors mediated currents were recorded from the freshly dissociated CA1 pyramidal cells of 7-day-old SD rats by whole cell patch clamp recording. The expression and distribution of P2X receptors were observed through immunohistochemistry and western blot at HH 3-day and 7-day.

MAIN OUTCOMES AND RESULTS

In acute HH conditions, the amplitudes of ATP evoked peak currents were decreased compared to control. The immunohistochemistry and western blot results reflected there was no change in P2X receptors expression after 3 days HH injury, while P2X receptors expression was up-regulated in response to 7 days HH injury.

CONCLUSIONS

These findings supported the possibility that the function of P2X receptors was sensitive to HH damage and long-term function decrease should result in the expression increase of P2X receptors.

A half century of experimental neuroanatomical tracing

Most of our current understanding of brain function and dysfunction has its firm base in what is so elegantly called the 'anatomical substrate', i.e. the anatomical, histological, and histochemical domains within the large knowledge envelope called 'neuroscience' that further includes physiological, pharmacological, neurochemical, behavioral, genetical and clinical domains. This review focuses mainly on the anatomical domain in neuroscience. To a large degree neuroanatomical tract-tracing methods have paved the way in this domain. Over the past few decades, a great number of neuroanatomical tracers have been added to the technical arsenal to fulfill almost any experimental demand. Despite this sophisticated arsenal, the decision which tracer is best suited for a given tracing experiment still represents a difficult choice. Although this review is obviously not intended to provide the last word in the tract-tracing field, we provide a survey of the available tracing methods including some of their roots. We further summarize our experience with neuroanatomical tracers, in an attempt to provide the novice user with some advice to help this person to select the most appropriate criteria to choose a tracer that best applies to a given experimental design.

Cholinergic innervation of pyramidal cells and parvalbumin-immunoreactive interneurons in the rat basolateral amygdala

The basolateral nucleus of the amygdala receives an extremely dense cholinergic innervation from the basal forebrain that is critical for memory consolidation. Although previous electron microscopic studies determined some of the postsynaptic targets of cholinergic afferents, the majority of postsynaptic structures were dendritic shafts whose neurons of origin were not identified. To make this determination, the present study analyzed the cholinergic innervation of the anterior subdivision of the basolateral amygdalar nucleus (BLa) of the rat using electron microscopic dual-labeling immunocytochemistry. The vesicular acetylcholine transporter (VAChT) was used as a marker for cholinergic terminals; calcium/calmodulin-dependent protein kinase II (CaMK) was used as a marker for pyramidal cells, the principal neurons of the BLa; and parvalbumin (PV) was used as a marker for the predominant interneuronal subpopulation in this nucleus. VAChT(+) terminals were visualized by using diaminobenzidine as a chromogen, whereas CAMK(+) or PV(+) neurons were visualized with Vector very intense purple (VIP) as a chromogen. Quantitative analyses revealed that the great majority of dendritic shafts receiving cholinergic inputs were CAMK(+) , indicating that they were of pyramidal cell origin. In fact, 89% of the postsynaptic targets of cholinergic terminals in the BLa were pyramidal cells, including perikarya (3%), dendritic shafts (47%), and dendritic spines (39%). PV(+) structures, including perikarya and dendrites, constituted 7% of the postsynaptic targets of cholinergic axon terminals. The cholinergic innervation of both pyramidal cells and PV(+) interneurons may constitute an anatomical substrate for the generation of oscillatory activity involved in memory consolidation by the BLa.

The amplification of polymerized diaminobenzidine with physical developers: sensitizing effects of transition metal salts and sulphide

Amplification of metal-complexed polymerized diaminobenzidine by two light-insensitive physical developers was systematically examined in a dot blot model system following either polymerizing diaminobenzidine in the presence of transition metal salts or applying the metal salts post-diaminobenzidine polymerization. The effect of sodium sulphide treatment on subsequent amplification was also investigated. Those metal-diaminobenzidine complexes that facilitated the most powerful amplification were subsequently tested in an immunohistochemical setting. The most dramatic amplification of polymerized diaminobenzidine was observed following its post-polymerization treatment with salts of platinum alone, or gold or vanadium with subsequent sulphide treatment, and allowed previously invisible quantities of polymerized diaminobenzidine to be clearly seen. Three other transition metal salts also improved the amplification of polymerized diaminobenzidine but to a lesser degree, namely nickel alone, and silver or rhodium with subsequent sulphide treatment. Sensitivity was comparable with the colloidal gold-silver amplification system.

Limited convergence of rhinal cortical and dopaminergic inputs in the rat basolateral amygdala: an ultrastructural analysis

The basolateral nuclear complex of the amygdala (BLC) receives robust sensory inputs from the rhinal cortices (RCx) that are important for the generation of emotional behavior. The BLC is also one of the main targets of the mesolimbic dopamine (DA) system. DA potentiates cortical sensory inputs to the BLC, which leads to an increase in the excitability of BLC pyramidal cells. These findings suggest that there may be convergence of RCx and DA inputs onto the dendrites of pyramidal cells in the BLC. In the present study we used dual-labeling immunohistochemistry and anterograde tract-tracing at the ultrastructural level to test this hypothesis in the rat brain. RCx axons were labeled by Phaseolus vulgaris leucoagglutinin (PHA-L) injections, whereas tyrosine hydroxylase (TH) was used as a marker for DA axons. The extent of convergence of these axons was analyzed in the posterior subdivision of the basolateral nucleus (BLp), which is densely innervated by both inputs. RCx synapses were asymmetrical and mainly contacted dendritic spines (86.4%) and dendritic shafts (12.1%). TH-positive (TH+) terminals also mainly formed synapses (symmetrical) and appositions with spines and shafts of dendrites. However, ultrastructural analysis found a very low percentage of RCx terminals converging with DA terminals onto unlabeled dendrites (9.4%) and axons (7.5 %), or exhibiting direct contacts with TH+ terminals (3.8%). These findings suggest that the association of specific behaviorally salient sensory stimuli with dopamine release in the BLC is not dependent on a point-to-point spatial relationship of cortical and DA inputs.

Multiple antigen immunostaining procedures

Detection of multiple antigens in the same tissue section can be done by combining a range of immunohisto/cytochemical techniques based either on light microscopic chromogenic precipitates or fluorochrome labeling. Light microscopic techniques preferred for this purpose use combinations of immunogold silver staining (black precipitate), immunoperoxidase, immunoalkaline phosphatase and immunogalactosidase methods using chromogens of different colors. Fluorochrome labels favored for these combinations include AMCA (blue), FITC (green), rhodamine (orange-red) and Cy5 (far red), their matching synthetic members from the Alexa series, or quantum dots. Antibodies directly labeled or those from noncross-reacting animal species (e.g., mouse, rabbit, goat, guinea pig etc.) can be applied simultaneously. When the antigens of interest are in separate cells or cell compartments (e.g., in cell membrane, cytoplasm or nucleus), and only cross-reacting antibodies are available, there have also been ways of avoiding unwanted cross-talk. These include the exploitation of the shielding effect of chromogens; inactivation of immuno-sequences of the first staining by using either acidic elution, formaldehyde fixation or microwave heating; combining unlabeled and hapten-labeled antibodies; or using labeled monovalent F(ab) secondary antibodies. In this chapter we briefly discuss the principle of multiple antigen immunolabeling and provide useful protocols for its performance.

Dopaminergic innervation of pyramidal cells in the rat basolateral amygdala

Dopaminergic (DA) inputs to the basolateral nuclear complex of the amygdala (BLC) are critical for several important functions, including reward-related learning, drug-stimulus learning, and fear conditioning. Despite the importance of the DA projection to the BLC, very little is known about which neuronal subpopulations are innervated. The present study utilized dual-labeling immunohistochemistry at the electron microscopic level to examine DA inputs to pyramidal cells in the anterior basolateral amygdalar nucleus (BLa) in the rat. DA axon terminals and BLa pyramidal cells were labeled using antibodies to tyrosine hydroxylase (TH) and calcium/calmodulin-dependent protein kinase II (CaMK), respectively. Serial section reconstructions of TH-positive (TH+) terminals were performed to determine the extent to which these axon terminals formed synapses versus non-synaptic appositions in the BLa. Our results demonstrate that at least 77% of TH+ terminals form synapses in the BLa, and that 90% of these synapses are with pyramidal cells. The distal dendritic compartment received the great majority of these synaptic contacts, with CaMK+ distal dendrites and spines receiving one-third and one-half, respectively, of all synaptic inputs to pyramidal cells. Many spines receiving innervation from TH+ terminals also received asymmetrical synaptic inputs from putative excitatory terminals. In addition, TH+ terminals often formed non-synaptic appositions with axon terminals, most of which were putatively excitatory in that they were CaMK+ and/or made asymmetrical synapses. Thus, using CaMK as a marker, the present study demonstrates that pyramidal cells, especially their distal dendritic compartments, are the primary targets of dopaminergic inputs to the basolateral amygdala.

Dopaminergic innervation of interneurons in the rat basolateral amygdala

The basolateral nuclear complex of the amygdala (BLC) receives a dense dopaminergic innervation that plays a critical role in the formation of emotional memory. Dopamine has been shown to influence the activity of BLC GABAergic interneurons, which differentially control the activity of pyramidal cells. However, little is known about how dopaminergic inputs interface with different interneuronal subpopulations in this region. To address this question, dual-labeling immunohistochemical techniques were used at the light and electron microscopic levels to examine inputs from tyrosine hydroxylase-immunoreactive (TH+) dopaminergic terminals to two different interneuronal populations in the rat basolateral nucleus labeled using antibodies to parvalbumin (PV) or calretinin (CR). The basolateral nucleus exhibited a dense innervation by TH+ axons. Partial serial section reconstruction of TH+ terminals found that at least 43-50% of these terminals formed synaptic junctions in the basolateral nucleus. All of the synapses examined were symmetrical. In both TH/PV and TH/CR preparations the main targets of TH+ terminals were spines and distal dendrites of unlabeled cells. In sections dual-labeled for TH/PV 59% of the contacts of TH+ terminals with PV+ neurons were synapses, whereas in sections dual-labeled for TH/CR only 13% of the contacts of TH+ terminals with CR+ cells were synapses. In separate preparations examined in complete serial sections for TH+ basket-like innervation of PV+ perikarya, most (76.2%) of TH+ terminal contacts with PV+ perikarya were synapses. These findings suggest that PV+ interneurons, but not CR+ interneurons, are prominent synaptic targets of dopaminergic terminals in the BLC.

Serotonin-immunoreactive axon terminals innervate pyramidal cells and interneurons in the rat basolateral amygdala

The basolateral nuclear complex of the amygdala (BLC) receives a dense serotonergic innervation that appears to play a critical role in the regulation of mood and anxiety. However, little is known about how serotonergic inputs interface with different neuronal subpopulations in this region. To address this question, dual-labeling immunohistochemical techniques were used at the light and electron microscopic levels to examine inputs from serotonin-immunoreactive (5-HT+) terminals to different neuronal subpopulations in the rat BLC. Pyramidal cells were labeled by using antibodies to calcium/calmodulin-dependent protein kinase II, whereas different interneuronal subpopulations were labeled by using antibodies to a variety of interneuronal markers including parvalbumin (PV), vasoactive intestinal peptide (VIP), calretinin, calbindin, cholecystokinin, and somatostatin. The BLC exhibited a dense innervation by thin 5-HT+ axons. Electron microscopic examination of the anterior basolateral nucleus (BLa) revealed that 5-HT+ axon terminals contained clusters of small synaptic vesicles and a smaller number of larger dense-core vesicles. Serial section reconstruction of 5-HT+ terminals demonstrated that 76% of these terminals formed synaptic junctions. The great majority of these synapses were symmetrical. The main targets of 5-HT+ terminals were spines and distal dendrites of pyramidal cells. However, in light microscopic preparations it was common to observe apparent contacts between 5-HT+ terminals and all subpopulations of BLC interneurons. Electron microscopic analysis of the BLa in sections dual-labeled for 5-HT/PV and 5-HT/VIP revealed that many of these contacts were synapses. These findings suggest that serotonergic axon terminals differentially innervate several neuronal subpopulations in the BLC.

Pyramidal cells of the rat basolateral amygdala: synaptology and innervation by parvalbumin-immunoreactive interneurons

The generation of emotional responses by the basolateral amygdala is determined largely by the balance of excitatory and inhibitory inputs to its principal neurons, the pyramidal cells. The activity of these neurons is tightly controlled by gamma-aminobutyric acid (GABA)-ergic interneurons, especially a parvalbumin-positive (PV(+)) subpopulation that constitutes almost half of all interneurons in the basolateral amygdala. In the present semiquantitative investigation, we studied the incidence of synaptic inputs of PV(+) axon terminals onto pyramidal neurons in the rat basolateral nucleus (BLa). Pyramidal cells were identified by using calcium/calmodulin-dependent protein kinase II (CaMK) immunoreactivity as a marker. To appreciate the relative abundance of PV(+) inputs compared with excitatory inputs and other non-PV(+) inhibitory inputs, we also analyzed the proportions of asymmetrical (presumed excitatory) synapses and symmetrical (presumed inhibitory) synapses formed by unlabeled axon terminals targeting pyramidal neurons. The results indicate that the perisomatic region of pyramidal cells is innervated almost entirely by symmetrical synapses, whereas the density of asymmetrical synapses increases as one proceeds from thicker proximal dendritic shafts to thinner distal dendritic shafts. The great majority of synapses with dendritic spines are asymmetrical. PV(+) axon terminals form mainly symmetrical synapses. These PV(+) synapses constitute slightly more than half of the symmetrical synapses formed with each postsynaptic compartment of BLa pyramidal cells. These data indicate that the synaptology of basolateral amygdalar pyramidal cells is remarkably similar to that of cortical pyramidal cells and that PV(+) interneurons provide a robust inhibition of both the perisomatic and the distal dendritic domains of these principal neurons.

Postsynaptic targets of somatostatin-containing interneurons in the rat basolateral amygdala

The basolateral amygdala contains several subpopulations of inhibitory interneurons that can be distinguished on the basis of their content of calcium-binding proteins or peptides. Although previous studies have shown that interneuronal subpopulations containing parvalbumin (PV) or vasoactive intestinal peptide (VIP) innervate distinct postsynaptic domains of pyramidal cells as well as other interneurons, very little is known about the synaptic outputs of the interneuronal subpopulation that expresses somatostatin (SOM). The present study utilized dual-labeling immunocytochemical techniques at the light and electron microscopic levels to analyze the innervation of pyramidal cells, PV+ interneurons, and VIP+ interneurons in the anterior basolateral amygdalar nucleus (BLa) by SOM+ axon terminals. Pyramidal cell somata and dendrites were selectively labeled with antibodies to calcium/calmodulin-dependent protein kinase II (CaMK); previous studies have shown that the vast majority of dendritic spines, whether CAMK+ or not, arise from pyramidal cells. Almost all SOM+ axon terminals formed symmetrical synapses. The main postsynaptic targets of SOM+ terminals were small-caliber CaMK+ dendrites and dendritic spines, some of which were CaMK+. These SOM+ synapses with dendrites were often in close proximity to asymmetrical (excitatory) synapses to these same structures formed by unlabeled terminals. Few SOM+ terminals formed synapses with CaMK+ pyramidal cell somata or large-caliber (proximal) dendrites. Likewise, only 15% of SOM+ terminals formed synapses with PV+, VIP+, or SOM+ interneurons. These findings suggest that inhibitory inputs from SOM+ interneurons may interact with excitatory inputs to pyramidal cell distal dendrites in the BLa. These interactions might affect synaptic plasticity related to emotional learning.

Coupled networks of parvalbumin-immunoreactive interneurons in the rat basolateral amygdala

Recent studies indicate that the basolateral amygdala exhibits fast rhythmic oscillations during emotional arousal, but the neuronal mechanisms underlying this activity are not known. Similar oscillations in the cerebral cortex are generated by a network of parvalbumin (PV)-immunoreactive interneurons interconnected by chemical synapses and dendritic gap junctions. The present immunoelectron microscopic study revealed that the basolateral amygdalar nucleus (BLa) contains a network of parvalbumin-immunoreactive (PV+) interneurons interconnected by chemical synapses, dendritic gap junctions, and axonal gap junctions. Twenty percent of synapses onto PV+ neurons were formed by PV+ axon terminals. All of these PV+ synapses were symmetrical. PV+ perikarya exhibited the greatest incidence of PV+ synapses (30%), with lower percentages associated with PV+ dendrites (15%) and spines (25%). These synapses comprised half of all symmetrical synapses formed with PV+ cells. A total of 18 dendrodendritic gap junctions between PV+ neurons were observed, mostly involving secondary and more distal dendrites (0.5-1.0 microm thick). Dendritic gap junctions were often in close proximity to PV+ chemical synapses. Six gap junctions were observed between PV+ axon terminals. In most cases, one or both of these terminals formed synapses with the perikarya of principal neurons. This is the first study to describe dendritic gap junctions interconnecting PV+ interneurons in the basolateral amygdala. It also provides the first documentation of gap junctions between interneuronal axon terminals in the mammalian forebrain. These data provide the anatomical basis for a PV+ network that may play a role in the generation of rhythmic oscillations in the BLa during emotional arousal.

Random or selective neuroanatomical connectivity. Study of the distribution of fibers over two populations of identified interneurons in cerebral cortex

We present a neuroanatomical tracing method in a stereological approach to study the proportional distribution of fibers of a particular projection over two chemically different populations of neurons. The fiber projection from the presubiculum to the medial division of the entorhinal cortex of the rat serves as a model projection. Potential target interneurons express calcium binding proteins, either parvalbumin or calretinin. The three markers were simultaneously stained in one and the same histological section. The procedure is according to a three-phase procedure, i.e., in vivo tracer injection phase, histology phase, laserscanning phase. Steps involved are: (1) Surgical application to the presubiculum (injection) of the neuroanatomical tracer, biotinylated dextran amine (BDA), with the purpose of labeling fibers innervating the entorhinal cortex. After surgery, transport of the tracer takes place during the one-week survival period; (2) Fluorescence detection of the labeled fibers through staining with fluorochromated avidin (avidin-Alexa Fluor 488 [green fluorescence]); (3) Simultaneous Immunofluorescence detection of two interneuron markers (using the appropriate primary antibodies and secondary antibodies conjugated to the fluorochromes Alexa Fluor 594 [red fluorescence] and Alexa Fluor 633 [infrared fluorescence]); (4) Acquisition of low-magnification images in a confocal laserscanning microscope and the preparation on a computer of a montage image covering the entire entorhinal cortex; (5) Overlaying this montage with a sampling grid; (6) Acquisition at high magnification of Z-series of confocal images in a statistical valid way based on this grid. Each marker was visualized in its own laser excitation/emission channel: 488, 568 and 647 nm; (7) Image processing and 3D reconstruction followed by evaluation of the results. The present approach can be used to examine whether or not a particular class of chemically identified neurons receives preferential innervation by a particular fiber projection.

Fast Fos: rapid protocols for single- and double-labeling c-Fos immunohistochemistry in fresh frozen brain sections

Immunohistochemical localization of c-Fos immunoreactivity has been used successfully for over a decade to visualize patterns of neuronal activity in the brain and spinal cord. These experiments are extremely useful in identifying physiological or pharmacological activation of specific populations of neurons. Unfortunately, conventional c-Fos immunohistochemical protocols are very time and resource intensive. We have adapted and optimized established c-Fos immunohistochemistry (IHC) methodologies for use with fresh frozen brain tissue mounted directly onto slides. The resultant rapid protocols, which we refer to as "Fast Fos", include applications for single- and double-labeling, utilizing either enzyme-substrate or fluorescent detection systems. These protocols provide increased assay throughput and reproducibility, which can be further enhanced by use of an automated slide stainer. Taken as a whole, the c-Fos IHC protocols described in this report provide a flexible system for the identification of neuronal activation that substantially reduces time and resource expenditure while increasing quality and reproducibility of data.

Calbindin D-28k positive projection neurones and calretinin positive interneurones of the rat globus pallidus

Immunohistochemistry for three calcium-binding proteins calbindin D-28k, calretinin, and parvalbumin revealed neuronal heterogeneity within the GP. Each neurone appeared to express either a single type of calcium binding protein or none at all. The co-localisation of calcium binding proteins was not observed. Combined immunohistochemistry and retrograde tract tracing using colloidal gold particles injected into the projection fields, the substantia nigra or subthalamic nucleus, revealed that projection neurones could be labelled with either calbindin or parvalbumin. These cells were of medium size (22 x 12 microm), multipolar and moderate varicose dendritic trees. In contrast, calretinin-positive neurones were never retrogradely labelled, even in regions where neuronal colloidal gold deposits were numerous. This, combined with their rarity (<1%) and small size (11 x 9 microm), suggests that calretinin may be a neurochemical marker for putative rat globus pallidus interneurones. Calcium-binding proteins are known to have unique buffering characteristics that may confer specific functional properties upon pallidal neurones. Indeed, differential calcium binding protein expression may underlie the electrophysiological heterogeneity observed in the rat globus pallidus.

Double-label confocal laser-scanning microscopy, image restoration, and real-time three-dimensional reconstruction to study axons in the central nervous system and their contacts with target neurons

The current double tracing-double confocal laser-scanning method was developed to reconstruct identified nerve fibers and their contacts with identified target neurons in the rat brain in three dimensions. It intends to fill the gap between conventional light microscopic and electron microscopic neuroanatomic tracing. The steps involved are as follows: (1) injection of two neuroanatomic tracers--Phaseolus vulgaris leucoagglutinin (PHA-L) to label fibers innervating a particular brain area and Neurobiotin to label prospective target neurons in that area; (2) immunofluorescence detection of the labeled fibers (fluorophore Cy5, infrared emission), together with fluorochromated avidin detection of the taken-up Neurobiotin (Cy2 or Alexa 488; green emission); (3) acquisition of Z-series of confocal images at high magnification with a laser-scanning microscope using the laser lines 488 nm and 647 nm; and (4) computer-processing and three-dimensional reconstruction of the labeled fibers and the presumed target dendrites. Rotation on the computer of the three-dimensional reconstructed fibers and dendrites along all three spatial axes enabled the authors to determine whether "true" or "false" contacts occur. In a true contact no space was present between the apposing structures, whereas a false contact consisted of two differently stained structures close to each other but separated by a narrow, optically empty space. One important phenomenon in the three-dimensional reconstruction of double-stained structures that needed correction was "twin image mismatch"--i.e., the observation that a three-dimensional reconstruction of a small test object (double-stained on purpose) produced two slightly shifted objects, each associated with its particular fluorochrome. To measure the actual twin image mismatch of the confocal instrument and to obtain accurate correction factors the authors took in each session in which they obtained image series of the real experiments, with both laser wavelengths Z-series of images of multifluorescent microspheres (500-nm diameter) and of thin, double-stained fibers. Given the small dimensions of the structures of interest, i.e., synaptic contacts, it is necessary in this type of research that the optical characteristics of the imaging system--e.g., the alignment errors and chromatic aberration that produce twin image mismatch--be precisely known.

A sequential protocol combining dual neuroanatomical tract-tracing with the visualization of local circuit neurons within the striatum

We describe here an experimental approach designed to aid in the identification of complex brain circuits within the rat corpus striatum. Our aim was to characterize in a single section (i) striatal thalamic afferents, (ii) striatopallidal projection neurons and (iii) striatal local circuit interneurons. To this end, we have combined anterograde tracing using biotinylated dextran amine and retrograde neuroanatomical tracing with Fluoro-Gold. This dual tracing protocol was further implemented with the visualization of different subpopulations of striatal interneurons. The subsequent use of three different peroxidase substrates enabled us to unequivocally detect structures that were labeled within a three-color paradigm.

Elucidation of neuronal circuitry: protocol(s) combining intracellular labeling, neuroanatomical tracing and immunocytochemical methodologies

We describe a protocol combining either intracellular biotinamide staining or anterograde biotinylated dextran amine (BDA) tracing with retrograde horseradish peroxidase (HRP) labeling and immunocytochemistry in order to map physiologically identified neuronal pathways. Presynaptic neurons including their boutons are labeled by either intracellular injection of biotinamide or extracellular injection of BDA while postsynaptic neurons are labeled with HRP via retrograde transport. Tissues are first processed to detect HRP using a tetramethylbenzidine and sodium-tungstate method. Biotinamide or BDA staining is then visualized using an ABC-diaminobenzidine-Ni method and finally the tissue is immunocytochemically stained using choline acetyltransferase (ChAT) or parvalbumin antibodies and a peroxidase-anti-peroxidase method. After processing, biotinamide, BDA, HRP and immunocytochemical staining can readily be distinguished by differences in the size, color and texture of their reaction products. We have utilized this methodology to explore synaptic relationships between trigeminal primary afferent neurons and brainstem projection and motoneurons at both the light and electron microscopic levels. This multiple labeling methodology could be readily adapted to characterize the physiological, morphological and neurochemical properties of other neuronal pathways.

Complex brain circuits studied via simultaneous and permanent detection of three transported neuroanatomical tracers in the same histological section

Experimental neuroanatomical tracing methods lie at the basis of the study of the nervous system. When the scientific question is relatively straightforward, it may be sufficient to derive satisfactory answers from experiments in which a single neuroanatomical tracing method is applied. In various scientific paradigms however, for instance when the degree of convergence of two different projections on a particular cortical area or subcortical nucleus is the subject of study, the application of single tracing methods can be either insufficient or uneconomical to solve the questions asked. In cases where chains of projections are the subjects of study, the simultaneous application of two tracing methods or even more may be compulsory. The present contribution focuses on combinations of several neuroanatomical tract-tracing strategies, enabling in the end the simultaneous, unambiguous and permanent detection of three transported markers according to a three-color paradigm. A number of combinations of three tracers or of two tracers plus the immunocytochemical detection of a neuroactive substance can be conceived; we describe several of these combinations implemented by us using the present multitracer protocol.

Neuroanatomical tracing at high resolution

Most techniques used for the study of the fiber connectivity in the central nervous system produce results which are visualized in the conventional light microscope or fluorescence microscope. Although in some cases this may be sufficient, often proof is necessary that fibers which enter a particular brain area indeed terminate here. Alternatively, it may be necessary to determine whether the axon terminals of traced fibers form synapses with specific processes of specific neurons. With the latter neurons all cellular elements are meant which can be labeled in some way. Evidence of synaptic connectivity necessitates visualization at a higher level of resolution, that is at the electron-microscopic level. In this contribution to the Special Issue we discuss several methods currently available to visualize individual tracers, and methods developed to visualize two different markers, that is one marker attached to a fiber or an axon terminal, and the second marker attached to a presumed pre- or postsynaptic neuronal element.

Immunocytochemical detection of two nuclear proteins within the same neuron using light microscopy

We developed a method of double immunocytochemistry (ICC) that can be used with conventional light microscopy for localizing two different nuclear proteins. The procedure involves two sequential rounds of ICC that both employ the avidin and biotin conjugated enzyme (ABC) amplification method, separated by an Avidin D and biotin blocking step to reduce non-specific avidin-biotin reactions. Round one of ICC employs the use of avidin and biotin conjugated alkaline phosphatase (ABC-AP) and the Vector Red (VR) substrate, which produces a red colorimetric reaction product. The second round of ICC makes use of avidin and biotin conjugated peroxidase (ABC-HRP) and the Vector(R) SG substrate, which produces a gray colorimetric reaction product. Neuronal nuclei that are double-labeled for both proteins appear red with a gray core. This protocol allows the simultaneous detection of two proteins within the same subcellular compartment of a single neuron, without the need for epifluorescence or scanning confocal laser microscopy.

Subtracted, unique-sequence, in situ hybridization: experimental and diagnostic applications

Nonrandom chromosomal aberrations, particularly in cancer, identify pathogenic biological pathways and, in some cases, have clinical relevance as diagnostic or prognostic markers. Fluorescence and colorimetric in situ hybridization methods facilitate identification of numerical and structural chromosome abnormalities. We report the development of robust, unique-sequence in situ hybridization probes that have several novel features: 1) they are constructed from multimegabase contigs of yeast artificial chromosome (YAC) clones; 2) they are in the form of adapter-ligated, short-fragment, DNA libraries that may be amplified by polymerase chain reaction; and 3) they have had repetitive sequences (eg, Alu and LINE elements) quantitatively removed by subtractive hybridization. These subtracted probes are labeled conveniently, and the fluorescence or colorimetric detection signals are extremely bright. Moreover, they constitute a stable resource that may be amplified through at least four rounds of polymerase chain reaction without diminishing signal intensity. We demonstrate applications of subtracted probes for the MYC and EWS oncogene regions, including 1) characterization of a novel EWS-region translocation in Ewing's sarcoma, 2) identification of chromosomal translocations in paraffin sections, and 3) identification of chromosomal translocations by conventional bright-field microscopy.

Distribution of calbindin D-28k and parvalbumin neurons and fibers in the rat basal ganglia

This review deals with the distribution of immunoreactivity for calbindin D-28k (CB) and parvalbumin (PV) in the different nuclei of the rodent basal ganglia analyzed with the data available after the use of single and double antigen procedures applied to single sections. These findings reveal that CB and PV are distributed according to a highly heterogeneous pattern in the caudate putamen complex (CPu), globus pallidus (GP), entopeduncular nucleus (EP), subthalamic nucleus (STh) and substantia nigra (SN) of the rat. In each basal ganglia structure, the two calcium-binding proteins label different neuronal subsets. Therefore, the use of CB and PV immunohistochemistry may be considered as an excellent tool to define distinct chemoarchitectonic and functional domains within the complex organization of the basal ganglia. Double immunohistochemical methods are also useful to illustrate the relationships between the different chemical subdivisions of the CPu, GP, EP, STh and SN and the chemically characterized connections with each other and with other forebrain and brainstem structures. However, specific rules should be followed when combining single and double immunostaining procedures, and the results of such studies must be evaluated with caution. When they are used properly, these methods can reveal hitherto unknown principles of organization of the basal ganglia and thus shed new light on the anatomical and functional organization of this set of subcortical structures involved in the control of motor behavior.

Multiple neuroanatomical tracing in primates

The present report deals with a multiple tract-tracing procedure in non-human primates enabling the simultaneous visualization of retrogradely transported Fluoro-Gold (FG) and cholera toxin B subunit (CTB) in combination with anterogradely transported biotinylated dextran amine (BDA). Two issues have played key roles on the achievement of this reliable procedure: first, the recent development of a commercial antiserum against FG that allows us to convert the original fluorescent signal of this dye in a permanent precipitate via standard peroxidase-anti-peroxidase methods; second, the introduction of the novel peroxidase substrate Vector(R) VIP (V-VIP), resulting in a purple precipitate. The combination of these neuroanatomical tracers in one and the same histological section opens a possibility for the permanent visualization of the convergence of inputs from a particular brain area onto identified, two different subsets of projection cells of another area. Furthermore, this combination of three tracers emerges as a powerful technical tool for obtaining broad amounts of complementary data regarding the monkey brain connectivity, thus significantly reducing the number of animals needed to complete a particular study.