Fluorescent retrograde double labeling: axonal branching in the ascending raphe and nigral projections

An algebraic approach to the detection of multiple markers in complex neuronal systems

An important class of neuroanatomical problems requires identification of neurons that contain two or more substances. Based on the additivity of neuronal elements that are independently labeled, a simple numerical approach may be applied to these problems. This approach provides a sensitive and viable alternative to direct multiple labeling of endogenous or transported neuronal markers.

The subcortical afferents to caudate nucleus and putamen in primate: a fluorescence retrograde double labeling study

The cellular origin and degree of collateralization of the subcortical afferents to the caudate nucleus and the putamen in squirrel monkeys (Saimiri sciureus) were studied using the following combinations of fluorescent retrograde tracers: Evans blue and DAPI-Primuline, Fast blue and Nuclear yellow, True blue and Nuclear yellow. After the injections, cells containing the tracer delivered in caudate nucleus (caudate-labeled cells) and others labeled with the complementary tracer injected in putamen (putamen-labeled cells) occur in large number in intralaminar nuclei, substantia nigra pars compacta, midbrain raphe nuclei and central midbrain tegmentum. In addition, a small to moderate number of putamen-labeled cells is found in external pallidum, pulvinar and laterodorsal thalamic nuclei, and basolateral amygdaloid nucleus, whereas some caudate and putamen-labeled cells are scattered in ventral tegmental area and locus coeruleus. However, ver few double-labeled cells are present in all these structures. In rostral intralaminar nuclei, the labeled cells are not confined to the know cytoarchitectonic boundaries of the nuclei but impinge slightly upon ventrolateral and mediodorsal nuclei. At this level, the caudate-labeled cells lie more dorsally and medially relative to putamen-labeled cells, but a high degree of intermingling exists and some double-labeled cells occur particularly in nucleus centralis lateralis. In caudal intralaminar nuclei, caudate-labeled cells are strictly confined to parafascicular nucleus and putamen-labeled cells present only in centre median, without any overlap between the two neuronal populations. In substantia nigra pars compacta, clusters of caudate-labeled cells are closely intermingled with clusters of putamen-labeled cells according to a complex mosaic-like pattern that varies along the rostrocaudal extent of the structure. Overall, however, caudate-labeled cells predominate rostrodorsally and putamen-labeled cells are more abundant caudoventrally in substantia nigra pars compacta, with only a few double-labeled cells. Some caudate and putamen-labeled cells are also scattered in contralateral substantia nigra pars compacta. In dorsal raphe nucleus, putamen labeled cells tend to occupy a more lateral position relative to caudate-labeled cells, with again very few double-labeled neurons. The caudate and putamen-labeled cells are less numerous and more closely intermingled in nucleus centralis superior. Numerous striatal afferent cells are also found bilaterally in the peribrachial region of midbrain tegmentum, comprising the pedunculopontine nucleus area.(ABSTRACT TRUNCATED AT 400 WORDS)

The cytology of dopaminergic and nondopaminergic neurons in the substantia nigra and ventral tegmental area of the rat: a light- and electron-microscopic study

The results of this study support the conclusion that dopaminergic cells can be distinguished from non-dopaminergic cells, at both the light- and electron-microscopic level, by cytological features, and particularly by the pattern of Nissl substance. In both the substantia nigra and the ventral tegmental area, two main categories of cell type can be identified in Nissl preparations: (1) dark-staining, basophilic cells with large masses of Nissl substance and (2) light-staining cells with more translucent cytoplasm. The following findings provide evidence that the basophilic cells of both substantia nigra and ventral tegmental area are the dopaminergic cells. (1) There is a good correlation between the topographic distribution of basophilic cells and that of dopaminergic cells mapped by both histofluorescence and immunohistochemical methods. (2) After unilateral destruction of the dopaminergic neurons by intracerebral injection of 6-hydroxydopamine in the dopaminergic pathway, the basophilic cells in the substantia nigra and ventral tegmental area disappeared on the lesion side, while the lighter-staining cells appeared unaffected. (3) In normal rats, and in rats with unilateral 6-hydroxydopamine lesions, intraventricular injection of [3H]norepinephrine was used for specific labeling of dopaminergic neurons. In autoradiograms of semithin sections, such labeling was observed only in dark-staining and not in light-staining cells, and in cases of unilateral 6-hydroxydopamine lesion was totally absent on the lesion side. Electron-microscopy showed much of the cytoplasm of the basophilic dopaminergic cells to be densely filled with free ribosomes associated with large, well organized complexes of rough endoplasmic reticulum. The cytoplasm of the light, non-dopaminergic cells contains only sparse free ribosomes and small, widely spaced aggregates of rough endoplasmic reticulum. Both cell types occur in a similar variety of size and shape.

DAPI staining improved for quantitative cytofluorometry

DNA-DAPI complexes emit strong bluish white fluorescence when excited by ultraviolet light so that even very small amounts of DNA such as those in mitochondria, chloroplasts, and virus particles can be visualized. Moreover, the staining procedure with DAPI is very simple and requires no hydrolysis. However, DAPI staining was considered unsuitable for quantitative purpose; nonspecific cytoplasmic fluorescence, scattering of strong emission light, and fading of the fluorescence under UV excitation were major problems of DAPI staining in quantitative cytofluorometry. We found that (1) nonspecific cytoplasmic fluorescence could be eliminated by reducing the DAPI concentration to 50 ng/ml, (2) fluorescence decay was markedly decreased by adding electron donors and molecules containing SH radicals in the mounting media, and (3) light scattering became negligible after reducing the intensity of the excitation light. Thus satisfactory precision could be obtained in DNA quantification by epifluorescent cytophotometry on DAPI stained specimens.

Characterization of estrogen-concentrating hypothalamic neurons by their axonal projections

A method combining steroid autoradiography and fluorescent dye retrograde neuroanatomical tracing has been devised. This method makes it possible to demonstrate that some estrogen-concentrating cells in the ventrolateral subdivision of the ventromedial nucleus of the rat hypothalamus are neurons that send axons to the dorsal midbrain. Other cells only concentrate estrogen or only project to the midbrain. Estrogen-concentrating neurons in the ventromedial hypothalamus that project to the dorsal midbrain are likely to transmit hormone-influenced signals that regulate circuits for reproductive or other behaviors or autonomic functions.

The distribution and origin of serotonin-containing fibers in the septal area: a combined immunohistochemical and fluorescent retrograde tracing study in the rat

The distribution of 5-hydroxytryptamine (serotonin, 5-HT)-containing nerve fibers and terminals in the septal area of the rat was studied by using immunohistochemistry with specific antibodies to 5-HT in combination with fluorescent retrograde tracing methods. The 5-HT innervation of the septum is heterogeneous with regard to both the morphology of individual processes and the density of distribution in different parts of the septum. Three major classes of 5-HT like immunoreactive processes can be distinguished: 1) thin, convoluted fibers with small, round or elongated varicosities; 2) thick and relatively straight fibers with few varicosities; and 3) pericellular plexuses with large varicosities in close association with perikarya in the lateral septum. Three areas of the septum receive a prominent innervation by 5-HT processes: the diagonal band of Broca, the ventral part of the lateral septum, and an area bordering the medial edge of the islands of Calleja (insula magna). Whereas the two latter areas contain dense terminal networks, the diagonal band of Broca is occupied primarily by 5-HT fibers en route to other parts of the septum. Intraseptal injections of HRP or fluorescent dyes (granular blue, propidium iodide) resulted in retrograde labeling of neuronal cell bodies in several nuclei of the brainstem which are known to contain 5-HT neurons: the dorsal raphe, the median raphe, the nucleus reticularis tegmenti pontis, the raphe pontis, and the raphe magnus. Where fluorescent retrograde tracing was performed with 5-HT immunohistochemistry on the same tissue section, a prominent 5-HT containing pathway and a non-5-HT-containing pathway from the raphe nuclei to the septum were revealed. Finally, double retrograde fluorescent labeling after injections of granular blue or propidium iodide into the septum and entorhinal area respectively of the same rat revealed extensive branching of the raphe efferents. Thus, individual raphe neurons may simultaneously connect with septum and the entorhinal area, two structures essential for normal hippocampal function.

Monoamine innervation of the forebrain: collateralization

The forebrain is characterized by a dense, localized dopamine (DA) innervation pattern, a diffuse, widespread norepinephrine (NE) innervation pattern, and a serotonin (5-HT) innervation intermediate between the DA and NE patterns. These innervation patterns have implied that basic differences exist in the way DA, NE and 5-HT axons collateralize to different brain structures; that is, DA axons are thought to be poorly collateralized and NE and 5-HT axons are presumed to be more highly collateralized. In the present study, we used injections of retrograde labeling fluorescent dyes into various forebrain regions in order to determine axonal branching patterns from nuclei that contain DA, NE and 5-HT neurons, namely the substantia nigra-ventral tegmental area (SN-VTA), locus coeruleus (LC) and raphe nuclei (DR-MR). The results suggest that at least two subpopulations of neurons can be defined in each monoamine nucleus with respect to the way their axons collateralize. Each area contains a centrally located nuclear area with highly collateralized neurons, and more peripherally situated areas with less highly collateralized neurons. Thus, previous suppositions of the branching of monoamine axons must be revised to account for the existence of cells exhibiting totally different collateralization patterns within each monoamine nucleus.

The projections of the ventral tegmental area and adjacent regions: a combined fluorescent retrograde tracer and immunofluorescence study in the rat

The organization of projection neurons in the ventral tegmental area (VTA), and in adjacent parts of the raphe nuclei medial to it (the central and rostral linear, and interfascicular nuclei), the mammillary body (the supramammillary region and the tuberomammillary nucleus), and the substantia nigra have been examined in the rat with Kuypers' retrograde double labeling method, and with a combined retrograde labeling (with true blue)-immunohistochemical method for the demonstration of dopaminergic neurons. First, the distribution, within the VTA and adjacent regions, of dopaminergic and non-dopaminergic cells that project to terminal fields in the telencephalon (nucleus accumbens, lateral septum, pre- and supragenual fields of the anterior limbic cortex, amygdala, dorsal hippocampus, and entorhinal area), in the diencephalon (lateral habenula), and in the brainstem (locus coeruleus, and parabrachial nucleus) was determined. Then, 15 different combinations of injections of the tracers bisbenzimide and true blue into different terminal fields were made to determine whether individual cells in the region of the VTA send collaterals to more than one site. Taken together, the results indicate that essentially separate groups of cells in the VTA and adjacent regions of the raphe project to each terminal field. In addition, each group can be further divided into dopaminergic and non-dopaminergic components, although the proportion of dopaminergic cells in each group can vary from over 80% (e.g., to the nucleus accumbens) to less than 1% (to the lateral habenula and to the locus coeruleus). In addition, it was found that the supramammillary region, which contains a dense extension of the A10 cell group in its medial part, and the tuberomammillary nucleus, project to, or through, most of the regions injected with retrograde tracers. Virtually all of the projections from the VTA and adjacent regions are partially crossed, the percentage of cells on the uninjected side ranging from over 40% (e.g., for locus coeruleus injections) to only about 2% (e.g., for amygdalar injections). Most of the groups of projection neurons in the region of the VTA are considerably intermixed with the exception of those that project to the lateral septum, to the lateral habenula, and to the hippocampal formation, which are concentrated in ventral and medial parts of the VTA, and in the raphe nuclei medial to the VTA. It was concluded that in the ventral part of the midbrain, essentially separate groups of aminergic and non-aminergic neurons in both the reticular formation (VTA) and in the adjacent nuclei of the raphe project bilaterally to a variety of similar terminal fields in the telencephalon, diencephalon, and brainstem. Further work at the single cell level is needed to determine whether these cell groups are differentially innervated by known inputs to the VTA and adjacent regions, most of which appear to descend through the medial forebrain bundle from sites in the limbic system and hypothalamus.

Identification of serotonin and non-serotonin-containing neurons of the mid-brain raphe projecting to the entorhinal area and the hippocampal formation. A combined immunohistochemical and fluorescent retrograde tracing study in the rat brain

We have studied the localization of serotonin- and non-serotonin-containing cell bodies in the midbrain raphe nuclei that project to the entorhinal area and the hippocampal formation in the rat brain, using the technique of combined retrograde fluorescent tracing and immunohistochemistry on the same tissue section. The branching properties of these neurons were studied by retrograde double labelling using two fluorochromes which emit fluorescence with different spectral characteristics. After injections of granular blue or propidium iodide into the medial entorhinal area, retrogradely-labelled cells were found situated bilaterally in the caudal half of the dorsal raphe nucleus, the medial part of the median raphe and throughout the rostrocaudal extension of the nucleus reticularis tegmentipontis. Injections placed successively more laterally in the entorhinal area labelled progressively less cells contralaterally in the dorsal raphe and the reticular tegmental nucleus of the pons. After fluorochrome injections into the dorsal part of the hippocampal formation, retrogradely-labelled cells were found in the caudal part of the dorsal raphe, in the peripheral part of the median raphe and to a minor extent in the medial part of this nucleus, but not in the nucleus reticularis tegmentipontis. The experiments with double retrograde fluorescent tracing showed that the raphe nuclei do not send bilateral projections to the entorhinal area in spite of the fact that many of these cells are located contralateral to the injected hemisphere in single labelling experiments. Injections of the fluorochromes into the entorhinal area and hippocampal formation showed that at least 10% of the raphe cells project to both areas simultaneously. Analysis of sections incubated with antiserum to serotonin showed that a majority of the retrogradely-labelled versus serotonin-immunoreactive cells was found to vary within different parts of the individual raphe nuclei: the ventromedial part of the dorsal, the medial part of the median and the nucleus reticularis tegmentipontis being the highest. The findings indicate that both serotonin- and non-serotonin-containing neurons in the raphe innervate the hippocampal region, that these projections may be crossed but not bilateral, and that the same neuron in the raphe may influence the neural activity in the entorhinal area and the hippocampus simultaneously.

The localization of the motor neurons innervating the cricothyroid muscle in the adult dog by the fluorescent retrograde axonal labeling technique

Injection of 4'6-diamidino-2-phenylindol 2 HCl (DAPI) into the cricothyroid muscle of the adult dog resulted in blue fluorescence of cells found exclusively in the rostral part of the ipsilateral nucleus ambiguus. These labeled neurons on the average extended 1.8 mm from the level just caudal the facial nucleus to the caudal extension. In the rostral tip of the nucleus, labeled cells were located in a scattered ventral group of larger neurons of the nucleus.

Immunocytochemical evidence for the existence of GABAergic neurons in the nucleus raphe dorsalis. Possible existence of neurons containing serotonin and GABA

It has been established that nerve cell bodies of the nucleus raphe dorsalis (NRD) belong to ascending 5-hydroxytryptamine systems. These neurons could be modulated by GABAergic interneurons or interposed GABA neurons. A high glutamate decarboxylase (GAD) activity in the NRD and a specific high-affinity uptake mechanism for GABA suggest the presence of GABA synthesizing elements in the NRD. Anti-GAD antibodies were used by an immunocytochemical procedure to demonstrate the presence of GABAergic elements. Anti-GAD antibodies were previously tested in the cerebellum and substantia nigra. Large amounts of GAD-positive reaction product were observed in the cytoplasm of some neurons (fusiform, ovoid or multipolar) or appeared as punctate deposits apposed to dendrites, soma and dispersed in the neuropil of the NRD. At the electron microscopic level, GAD-positive reaction product was observed within the cytoplasm of numerous somata in sections from colchicine-treated rats. GAD-positive staining was observed in numerous fibers or axonal terminals and two types of morphologically different fibers could be distinguished. The first displays small clear vesicles and few large granular vesicles (LGV) (80-100 nm), the second displays only clear round vesicles (40-60 nm). After 5,7-dihydroxytryptamine treatment (a neurotoxic for 5-HT terminals), the immunocytochemical labeling is much decreased. Some reactive neurons are still dispersed in the nucleus but the fibers containing LGV are no longer observed. These results strongly suggest that some neuronal elements in the NRD are morphologically, pharmacologically and anatomically similar to 5-HT neurons described at this level. Such cell elements could possess a double GABA and 5-HT potentiality. If this is not the case, a population of GABA neurons could be sensitive to 5,7-DHT and so have the capacity to take up 5-HT. The other reactive elements, insensitive to 5,7-DHT, could represent the GABAergic interneurons postulated at this level. Numerous GAD positive fibers or axon terminals were observed in synaptic contact with dendrites, axons or soma of other neurons. The chemical nature of the neuronal postsynaptic elements remains unknown. These findings strongly support the hypothesis for GABA-mediated inhibition in the NRD.

Bilateral serotonergic projections to the dorsal hippocampus of the rat: simultaneous localization of 3H-5HT and HRP after retrograde transport

Horseradish peroxidase (HRP, Sigma VI, 30-70 nl of a 10-15% solution in saline) or 3H-5HT (30 Ci/mmole, 2.5 X 10 -3 M containing 3.3 X 10(-3) M norepinephrine in saline, 50-100 nl) was injected unilaterally into the dorsal hippocampus in separate groups of rats. HRP-labeled cells were seen in the hippocampus, medial septal nucleus, nucleus of the diagonal band, supramammilary nucleus, median raphe nucleus, interfascicular portion of the dorsal raphe nucleus, and the locus coeruleus. In contrast, 3H-5HT-labeled cells were largely restricted to the raphe nuclei. In this nucleus an equal number of ipsilateral and bilateral cells were found. Occasionally, these labeled cells stretched across the midline (bridge pattern). In another series, the 3H-5HT and HRP were injected into the same hippocampus either as a mixture or sequentially. This resulted in double labeling of the median and dorsal raphe neurons. A final group of rats received injections of 3H-5HT and HRP into opposing hippocampi. Double-labeled cells accounted for 10% of the neurons labeled. In addition, closely paired neurons composed of an HRP- and 3H-5HT-containing cell were found. In summary, the serotonergic fibers may play a key role in harmonizing the electrical activity of the hippocampi by use of bilateral projections, paired neurons with differential projections, and bridging neurons stretching across the midline but with unilateral projections.

The organization of the efferent projections of the parabrachial nucleus of the forebrain in the rat: a retrograde fluorescent double-labeling study

The organization of the efferent projections of the parabrachial nucleus (PBN) to the forebrain has been investigated in the rat by means of combined injections of two fluorescent retrograde tracers: red fluorescent Evans Blue and a blue fluorescent mixture of 4',6'-diamidino-2-phenylindol 2 HCl and primuline. First, the distributions of retrogradely labeled neurons in the PBN after bilateral injections of tracers in the central nucleus of the amygdala (CNA) was examined. The CNA on one side of the brain was injected with one of the tracers and the CNA on the opposite side of the brain was injected with the other tracer. Next, the distributions of labeled neurons were examined after bilateral ventral medial thalamus (VMT) injections. Finally, the retrograde labeling of the PBN was studied after combined ipsilateral injections of one tracer in the CNa and the other tracer in the VMT. After the various injections, characteristic distributions of populations of labeled neurons within the PBN were seen. Double-labeled neurons were present only after bilateral VMT injections. From this it was concluded that the PBN projections to the VMT in the rat are bilateral. Based on the relative distributions of populations primarily taste information to the VMT and mainly visceral information to the CNA. This transfer of information to the forebrain is discussed.

Laminar connections of the cat's auditory cortex

The retrograde and the anterograde transport of horseradish peroxidase were used to study the connections established by cells in different layers of the cat's primary auditory cortex (AI). Injections of peroxidase into the medial geniculate body show that pyramidal cells in layers V and VI of AI are the sources of the corticothalamic projections. Large pyramidal cells in the outer rim of layer V also send their axons to the inferior colliculus, and it is possible that some of these cells have axons that branch to innervate both the inferior colliculus and the medial geniculate body. Cells in AI that give rise to callosal axons lie principally in layers III and VI. The callosal neurons are found in irregular clusters as wide as 1100 microgram separated by spaces that contain relatively few callosal neurons. Experiments utilizing the anterograde transport of peroxidase show that callosal terminals are found in bands running from layers VI through I. These bands are about 500 microgram in width, and the terminals seem most densely packed in layers II and III. Since the dimensions of the cell clusters and bands of callosal terminals are not the same, it is likely that not all zones which give rise to callosal axons also receive them. The bands of callosal terminals labeled by orthograde transport may be seen in the same section along with the cell bodies labeled by retrograde transport, and the two zones of label are clearly not coextensive. Complete reciprocity, therefore, seems to be absent in the callosal auditory pathway.

The organization of the efferent projections and striatal afferents of the entopeduncular nucleus and adjacent areas in the rat

Multiple retrograde fluorescent tracing was employed to investigate the organization of the rat entopeduncular nucleus projections to the lateral habenula, ventral anterior-ventral lateral thalamus, parafasicular-centre median complex, and tegmenti pedunculopontis area of the brain stem. The results indicate that neurons in the rostral 2/3 of the entopeduncular nucleus project to the lateral habenula. In contrast, neurons in the caudal 1/3 of the entopeduncular nucleus project to the ventral anterior-ventral lateral thalamus, parafasicular-centre median complex, and tegmenti pedunculopontis area of the brain stem. The majority of neurons in the caudal 1/3 of the entopeduncular nucleus are retrogradely double-labeled from various combinations of tracer injections into the 3 termination areas to which they projected. Little or no retrograde labeling in the entopeduncular nucleus was produced by tracer injections in the substantia nigra or subthalamic nucleus. Only large injections of tracers in the tegmenti pedunculopontis are and the surrounding brain stem produced retrograde labeling in the entopeduncular nucleus. These brain stem injections also labeled a band of cells surrounding the entopeduncular nucleus in the zona incerta, lateral hypothalamus, of the ansa lenticularis and central nucleus of the amygdala. [3H]Leucine injections in the head of the caudate-putamen complex (but not in the cortex or globus pallidus) produced dense accumulations of silver grains over both the rostral and caudal portions of the entopeduncular nucleus. [3H]Leucine injections in the caudal body of the caudate-putamen complex produced accumulations of silver grains over a "ventral entopeduncular nucleus area' in the nucleus of the ansa peduncularis. It was suggested that the head of the striatum projects both to the neurons of the rostral "limbic' portion of the entopeduncular nucleus, which project to the lateral habenula, and to the neurons of the caudal "motor' portion of the entopeduncular nucleus, which project primarily by way of axon collaterals to the ventral anterior-ventral lateral thalamus, parafascicular-centre median complex, and tegmenti pedunculopontis area of the brain stem.

Two visual pathways to the telencephalon in the nurse shark (Ginglymostoma cirratum). II. Ascending thalamo-telencephalic connections

As part of a study on retino-telencephalic pathways the ascending connections to the telencephalic central nucleus were investigated by retrograde transport of horseradish peroxidase. The central nucleus of the telencephalon, which is the main recipient for input from the brainstem, grossly can be divided into three rostrocaudal parts according to their afferent connections. The rostral third receives input mainly from the contralateral central thalamic nucleus and to a lesser degree from the lateral geniculate nucleus, periventricular gray, and a nucleus called the ventral mesencephalic tegmentum. The middle third of the central nucleus maintains an afferent connection with contralateral lateral geniculate, ventrolateral optic, and central thalamic nucleus, with the ventral mesencephalic tegmentum and periventricular gray bilaterally, and with a group of cells in the superior raphé nucleus. Caudal central nucleus injections of HRP resulted in labeling of cells in the contralateral lateral geniculate nucleus, ventral mesencephalic tegmentum, and central thalamic bilaterally, and in the superior raphé nucleus preoptic area and periventricular gray. From these results it can be concluded that visual information may reach the central telencephalic nucleus by two separate pathways: one pathway from retina via ventrolateral optic nucleus to the middle third of the central nucleus, and a second pathway from retina to optic tectum, which reportedly projects to the lateral geniculate nucleus, which in turn provides afferents to the caudal two-thirds of the central nucleus. As such the nurse shark's visual system possesses structural features that are homologous to the two visual systems of higher vertebrate groups.

Target neuron-specific process formation by embryonic mesencephalic dopamine neurons in vitro

Mesencephalic dopamine neurons from the embryonic mouse brain were dissociated, aggregated in vitro in the presence of dissociated cells from appropriate or inappropriate target neuron areas, and visualized by the Falck-Hillarp histofluorescence technique after exposure to 1 microM exogenous dopamine. When aggregated with the surrounding rostral mesencephalic tegmentum cells only or with the addition of rostral tectum cells, the dopamine neurons formed a dense dendritic arborization, but no axons were observed. In the presence of dopamine-neuron target cells from the corpus striatum, a dense axonal plexus characteristic of that formed in this area in vivo was observed. In contrast, in aggregates formed with target cells from the frontal cortex, branching fluorescent axons bearing irregularly spaced and shaped varicosities were found coursing through the neuropil, as is characteristic of the dopaminergic innervation to the frontal cortex in vivo. Only proximal dendrites were observed in the presence of these axonal target cells. Dopamine neurons cultured with inappropriate target cells from the occipital cortex did not form either extensive axonal or dendritic processes. Thus, the presence, type, and distribution of dopamine neuronal processes are dependent on the presence of appropriate target cells. The formation of unique patterns of neuronal processes by dissociated neurons in vitro suggests that the information necessary for this differentiation is intrinsic to the dopamine neurons and their target cells. This system provides a useful model with which to study basic mechanisms underlying neuronal recognition.

Double retrograde neuronal labeling through divergent axon collaterals, using two fluorescent tracers with the same excitation wavelength which label different features of the cell

Recent studies show that several fluorescent substances are transported retrogradely through axons to their parent cell bodies and label in different colors different features of the cell at the same 360 nm excitation wavelength. Thus, Bisbenzimide (Bb) and "Nuclear Yellow" (NY; Hoechst S 769121) produce green and golden-yellow retrograde labeling of the neuronal nucleus. "True Blue" (TB) and "Fast Blue" (FB) produce blue retrograde labeling of the neuronal cytoplasm. In the present study the possibility of retrograde double labeling of neurons by way of divergent axon collaterals using combinations of Bb or NY with TB or FB has been explored in rat and cat. The findings show that in these animals these tracer combinations are transported retrogradely through two axon collaterals to one and the same cell. Neurons which are retrogradely double-labeled with these tracer combinations display a blue fluorescent cytoplasm and a white or golden-yellow fluorescent nucleus at the same 360 nm excitation wavelength. Therefore, these tracer combinations can be successfully used to demonstrate the existence of divergent axon collaterals in the brain.

Single subthalamic nucleus neurons project to both the globus pallidus and substantia nigra in rat

The organization of the major efferents of the rat subthalamic nucleus (STN) was investigated using a fluorescent retrograde double-labeling technique. Red fluorescent Evans Blue was injected into the globus pallidus and blue fluorescent DAPI-Primuline was injected into the substantia nigra. After retrograde axonal transport many double-labeled neurons were seen throughout the STN. Occasionaly double-labeled cells were seen in the lateral hypothalamus just medial to the STN and in a thin lateral strip of neurons extending laterally from the STN. Evidence for a mediolateral topography in both the STN-pallidal and STN-nigral pathways was obtained. The STN contains few, if any, local interneurons. Cell counts revealed that at least 94% of, and possibly all, STN neurons send axon collaterals to both the globus pallidus and substantia nigra.

Marking tip positions of fine capillary microelectrodes in teleost nervous tissue

A method is decribed for marking the tip position of fine (1-4 microns) capillary electrodes following recording. Evans blue dissolved in teleost Ringer, which at the same time serves as recording electrolyte, is deposited by iontophoresis. In frozen sections the spots appear as blue labelled neurones with a light microscope, or as a brilliant red neurones surrounded by reddish tissue with a fluorescence microscope. Counterstaining with cresyl fast violet (nissl stain) is possible.

Double and triple labeling of neurons with fluorescent substances; the study of collateral pathways in the ascending raphe system

A retrograde labeling procedure utilizing fluorescent substances (Granular Blue, Nuclear Yellow and propidium iodide) was used to establish the presence of branching axons in the ascending raphe system of young rats. After injections in septum, medial thalamus and olfactory cortex, the number of double-labeled cells in various combinations was found to be relatively large in the dorsal raphe nucleus, whereas triple-labeled cells occurred more rarely. Each class of neurons, i.e. single-, double- and triple-labeled, were shown to have a predominant distribution within specific parts of the nucleus.

Dorsal raphe cells with collateral projections to the caudate-putamen and substantia nigra: a fluorescent retrograde double labeling study in the rat

The relationship between the dorsal raphe neurons projecting to the caudate-putamen and those projecting to the substantia nigra was investigated using a fluorescent retrograde double labeling technique in the rat. The majority of the dorsal raphe neurons projecting to the substantia nigra were found to project also to the caudate-putamen. In addition, a large population of dorsal raphe neurons innervating the caudate-putamen but not the substantia nigra was seen. The cells projecting to the substantia nigra were situated primarily in the dorsal part of the dorsal raphe, whereas those projecting to the caudate-putamen were located throughout the dorsal raphe.

Circling behavior in rats with partial, unilateral nigro-striatal lesions: effect of amphetamine, apomorphine, and DOPA

Partial, unilateral lesions of the nigro-striatal tract were produced in rats by injecting various quantities of 6-hydroxydopamine into the substantia nigra. The extent of each animal's lesion was estimated by comparing tyrosine hydroxylase activities in its lesioned and control striata. L-DOPA and apomorphine induced contralateral (i.e., away from the lesion) circling behavior only in rats in which more than 90% of the nigro-striatal system had been destroyed. In contrast, d-amphetamine caused turning in the ipsilateral direction when as few as 50% of the nigro-striatal neurons had been destroyed.

Simultaneous fluorescent retrograde axonal tracing and immunofluorescent characterization of neurons

A simple method is described for simultaneously double labeling single neurons with fluorescent retrograde axonal tracers and immunofluorescence using an antibody to serotonin. Caudata-putamen injection of orange fluorescent propidium iodide, in particular, proved effective in retrogradely labeling dorsal raphe cell bodies. These same perikarya could be stained green with the indirect immunofluorescent method, using green fluorescent fluorescein isothiocynate (FITC) as the second antibody.