Multiple Tracing Research Articles

Calculation of the Impact of n = 1 Error Fields on the Divertor Heat Loading of the Tokamak Physics Experiment

Nonaxisymmetric error fields arising from departures of the coil systems from axisymmetry can pose serious problems for the tokamak divertor. The X points of the divertor are particularly sensitive to being shifted by n = 0 error fields; toroidal `bundle diverting` or bunching of heat flux coming from the core of the tokamak can produce hot spots on carefully designed divertor structures. Toroidal variation of the angle of incidence on the divertor by the n = 0 error field can also locally peak the heat flux. Multiple field line tracing of a typical diverted Tokamak Physics Experiment (TPX) configuration with nonconcentric poloidal field (PF) coils is used to predict that if the toroidal variation of the peak divertor heat flux is to be kept to within {+-}25%, the principal PF coils responsible for the diverting must be aligned to {+-}2 mm of concentricity with the toroidal field. 10 refs., 8 figs., 3 tabs.

Mapping subcortical extrarelay afferents onto primary somatosensory and visual areas in cats.

Projections from the claustrum (Cl) and the thalamic anterior intralaminar nuclei (AIN) to different representations within the primary somatosensory (S1) and visual (V1) areas were studied using the multiple retrograde fluorescent tracing technique. The injected cortical regions were identified electrophysiologically. Retrograde labeling in Cl reveals two different projection patterns. The first pattern is characterized by a clear topographic organization and is composed of two parts. The somatosensory Cl shows a dorsoventral progression of cells projecting to the hindpaw, forepaw, and face representations of S1. The visual Cl has cells projecting to the vertical meridian representation of V1 surrounded dorsally by neurons projecting to the representation of retinal periphery. A second pattern of Cl projections is composed of neurons that are distributed diffusely through the nucleus. In both somatosensory and visual sectors, these intermingle with the topographically projecting cells. Neurons retrogradely labeled from cortical injections are always present in the AIN. In the central medial nucleus, the segregation of modality is evident: The visual-projecting sector is dorsal, and the somatosensory is ventral. Projections from the central lateral nucleus display detectable somatotopic and retinotopic organization: Individual regions are preferentially connected with specific representations of S1 or V1. In the paracentral nucleus, no clear regional preferences are detectable. Also performed were comparisons of the proportions of neurons projecting to different sensory representations. Projections to V1 from both AIN and Cl are biased towards the retinal periphery representation. S1 projection preference is for the forepaw representation in Cl and for the hindpaw in the AIN. The quantitative analysis of multiply labeled cells reveals that, compared to Cl, the AIN contains a higher proportion of neurons branching between different representations of S1 or V1. The concept of topographic vs. diffuse projecting systems is reviewed and discussed, and functional implications of quantitative analysis are considered.

Independent efferent populations in the nucleus of the optic tract: an anatomical and physiological study in rat and cat.

The efferent projections of the nucleus of the optic tract (NOT) and dorsal terminal nucleus of the accessory optic system (DTN) to the contralateral NOT-DTN, ipsilateral inferior olive (IO), ipsilateral nucleus prepositus hypoglossi (NPH), and ipsilateral dorsal lateral geniculate nucleus (LGNd) were examined in pigmented rats and in cats by using anterograde and retrograde tract tracing, as well as extracellular recording and electrical stimulation. Anterograde tracing in the rat revealed a dense termination field of NOT-DTN efferents throughout the homologous contralateral territory. In both species three different cell populations, projecting to the contralateral NOT-DTN, ipsilateral IO, and ipsilateral LGNd, respectively, were distinguished by means of multiple retrograde tracing. No clear topographical segregation of the different NOT-DTN relay cell populations was observed. On the other hand, a large proportion (at least 60%) of NOT-DTN neurons projecting to the ipsilateral NPH were found to bifurcate upon the IO in the rat. Electrophysiologically, NOT-DTN neurons projecting to the IO were identified by their directionally selective responses. Such neurons were never activated by electrical stimulation of either the contralateral NOT-DTN or the ipsilateral LGNd. Neurons antidromically activated from the contralateral NOT-DTN could not be activated from the ipsilateral LGNd. Thus, in both cat and rat the NOT-DTN includes at least three independent relay cell populations. As a consequence, the NOT-DTN must serve functions additional to the generation of eye movements during optokinetic nystagnus, a function subserved by the directionally selective NOT-DTN cells.

Multiple anterograde tracing, combining Phaseolus vulgaris leucoagglutinin with rhodamine- and biotin-conjugated dextran amine

The simultaneous use of different neuroanatomical anterograde tracers provides a potentially powerful method to study the convergence of afferent systems in a particular brain area. However, a simple routine procedure to apply multiple anterograde tracers in conjunction with their simultaneous visualization is still missing. We report an easy and straightforward application of three sensitive anterograde tracers: Phaseolus vulgaris leucoagglutinin (PHA-L), rhodamine-conjugated dextran amine (RDA) and biotin-conjugated dextran amine (BDA). These tracers can be visualized simultaneously and permanently through a triple-staining procedure with nickel-enhanced diaminobenzidine (DAB-Ni), DAB and 1-naphthol/Azur B as chromogens. Our test model comprised the projections from the nucleus reuniens thalami and entorhinal cortex. Both projection systems show a high degree of overlap in their terminal fields in the hippocampus. Two tracers were injected in the left and right entorhinal cortex, respectively; a third tracer was injected in the nucleus reuniens. This combination of injections provided a good opportunity to compare the three tracers in one and the same animal. PHA-L, RDA and BDA, injected in either of the injection sites, turned out to be equally sensitive and revealed the morphology of the involved projection systems in great detail. The triple-staining protocol yielded an excellent, simultaneous detectability of the three tracers with a remarkably low background level. Thus, the combination of the anterograde tracers PHA-L, RDA and BDA, in conjunction with the triple-staining procedure, offers a very attractive approach for neuroanatomical research.

Identification and separation of water tracing dyes using pH response characteristics

Problems encountered in field applications of water tracing dyes include background fluorescence and interference between dyes, where the complexity of hydrological systems, particularly in karst areas, makes multiple dye tracing experiments desirable. The fluorescence of water tracing dyes may vary dramatically according to the pH of the water, and this property can be used to address these problems. The response of a number of commonly available water tracing dyes to pH is investigated; the distinctive curves provide a means of distinguishing between dyes, and between dyes and background fluorescence caused by algae. It is not necessary to reproduce the full pH response curve to utilize these properties. Recommendations are made in the use of pH buffering to improve sensitivity in detecting dyes, and for quantitative laboratory analysis. Buffering to a small number of predetermined pH values can be used effectively to distinguish both between dyes which fluoresce at the same wavelength, and between natural and induced fluorescence. It is particularly useful in the case of the green dyes, both for detection when there are high natural backgrounds and because it allows more than one green dye to be used simultaneously. If Rhodamine is used together with, for example, Fluorescein and Pyranine, triple dye tracing experiments can be executed.

Origins and collateralization of corticospinal, corticopontine, corticorubral and corticostriatal tracts: a multiple retrograde fluorescent tracing study

Cerebral cells of origin for the corticospinal (CST), corticopontine (CP), corticorubral (CR) and corticostriatal (CS) fibers in the rat were identified following the simultaneous retrograde transport of propidium iodide (PI), fast blue (FB), fluorogold (FG) and diamidino yellow (DY). PI was injected into the contralateral C 4 spinal cord segment while FB, FG and DY were injected into the ipsilateral medial pontine nuclei, red nucleus and striatum, respectively. Labeled pyramidal neurons projecting corticospinal axons were contralateral to injection in lamina V and ranged in size from small to large. These CST neurons occupied two distinct cortical areas. The cortical neurons of origin for the corticopontine, corticorubral and corticostriatal fibers were ipsilateral to injections. Labeled neurons were localized in cortical lamina V for the corticopontine and corticorubral fibers while corticostriate neurons were located in laminae III, V and VI. The CP, CR and CS labeled cells occupied one large cortical area which topographically included parts of the medial (AGm) and lateral (AGI) agranular cortices and the primary (SI) somatosensory cortex. Considerable overlapping of the cortical neurons of origin for the four motor fiber systems was apparent. More than 98% of the labeled cells were single labeled while less than 2% were double labeled. No triple or quadruple labeled neurons were observed. Hence, morphological evidence is presented that cortical motor neurons project mainly individual, rather than collateral, axons to each of the four motor associated nuclei investigated in this study. However, only a few cortical neurons projected axons simultaneously to a maximum of two nuclei involved in the motor pathways.

Time course of nigrostriatal system changes after tract hemisection and effects of ganglioside treatment: a multiple retrograde fluorescent tracing study

The postlesion phenomena of nigrostriatal neurons following partial tract hemisection have been studied with retrograde axonal transport of dyes in rats treated with saline or GM1 ganglioside (30 mg/kg, i.p., daily for varying times). The time course of the plastic changes in both experimental animal groups was determined by a double retrograde fluorescent tracing technique, utilizing Fast blue (FB) as prelesion tracer, and Diamidino yellow (DY) as postlesion tracer. The data show that the number of nigral cells retrogradely labeled by the prelesion intrastriatal injection of FB declined progressively to 50% of their initial number over 3 weeks. The ganglioside treatment did not significantly influence this temporal pattern of labeled cell loss. By DY-labeling, an almost complete block of the retrograde axonal transport was observed up to 1 week postlesion and only after 3 weeks a partial recovery was evident, positively influenced by the GM1 treatment. Therefore, together with the findings on nigrostriatal cell loss, these data indicate that ganglioside treatment favors and/or accelerates the recovery of axonal transport of surviving nigral neurons but does not significantly affect their degenerative rate in the first 3 weeks after the lesion.

Thalamic midline cell populations projecting to the nucleus accumbens, amygdala, and hippocampus in the rat

The organization of the thalamic midline efferents to the amygdaloid complex, hippocampal formation, and nucleus accumbens was investigated in the rat by means of multiple retrograde fluorescent tracing. The present findings indicate that these connections derive from separate cell populations of the thalamic midline, with a low degree of divergent collateralization upon more than one of the targets examined. The neural populations projecting to the amygdala, hippocampus, or accumbens are highly intermingled throughout the thalamic midline, but display some topographical prevalence. Midline thalamo-hippocampal cells are concentrated in the nucleus reuniens; thalamo-accumbens neurons prevail in the ventral portion of the paraventricular nucleus, and in the central medial nucleus. Thalamo-amygdaloid cells display a topographical prevalence in the rostral third of the thalamic midline and are concentrated in the dorsal part of the paraventricular nucleus and in the medial part of the nucleus reuniens. Both dorsally in the paraventricular nucleus and ventrally in the nucleus reuniens, thalamo-amygdaloid cells are located closer to the ependymal lining than the neurons projecting to the hippocampus or nucleus accumbens. Further, thalamo-amygdaloid cells, especially in the paraventricular nucleus, extend their dendritic processes in the vicinity of the ependymal lining, where they arborize profusely. These features indicate a close topographical relationship of neurons projecting to the amygdala with ependymal cells. The fairly discrete origin of midline outputs to the amygdala, hippocampus, and accumbens indicates that the flow of information is conveyed through separate channels from the thalamic midline to limbic and limbic-related targets. Together with the literature on the limbic afferents to the thalamus, these findings emphasize the relationships between the thalamus and the limbic system subserved by parallel input-output routes. However, because of the overlap of the projection cell populations, the thalamic midline may represent a locus of interaction among neurons connected with different parts of the limbic system. The functional implications of these findings are discussed in relation to the "nonspecific" thalamic system, as well as to the circuits involved in memory formation.

Cooperation and competition during development: neonatal lesioning of the superior cervical ganglion induces cell death of trigeminal neurons innervating the cerebral blood vessels but prevents the loss of axon collaterals from the neurons that survive

In the adult rodent trigeminal ganglion there is a period of postnatal cell death in the population of cells with axons innervating the middle cerebral artery (O'Connor and van der Kooy, 1986b). The superior cervical ganglion (SCG) also has a projection to the middle cerebral artery (MCA; Mayberg et al., 1984; Cowen et al., 1986, 1987; present report). We hypothesized that the trigeminal ganglion cells innervating the MCA may be competing with the superior cervical projection for target area or for a target factor for survival, and thus the removal of the superior cervical projection at birth (sympathectomy) may promote the survival of some of the trigeminal-artery innervating cells that normally would die. Multiple fluorescent retrograde tracing was employed to analyze the postnatal development of the trigeminal projection to the MCA in sympathectomized and sibling control rats. We found that the SCG projection to the MCA exhibits a period of postnatal cell death. The trigeminal ganglion projection exhibits axon degeneration as well as postnatal cell death. Postnatal day 0 (P0) lesioning of the SCG did not prevent cell death or axon loss in the trigeminal projection to the cerebral artery. In fact, increased cell death of the trigeminal-artery projecting neurons was observed in the lesioned animals when compared to nonlesioned sibling controls. By P55, we found that 80% of these trigeminal neurons had died in lesioned animals, compared with 50% in controls. In both control and sympathectomized rats, close to 90% of the trigeminal neurons innervating the artery in the neonate can no longer be retrogradely labeled from the MCA by tracer applications at P25-90. Thus, although the presence of an intact SCG may protect some trigeminal-artery projecting neurons from cell death, it does not prevent axon retraction and does not permit a larger absolute number of trigeminal axons to innervate the arteries in the adult. Thus, separate mechanisms are responsible for the survival of perikarya versus the retraction of their axons from the MCA. Surprisingly, in the neonatally sympathectomized rats almost 20% of those trigeminal cells that maintained a projection to the MCA at P90 also had a projection to the forehead. In contrast, less than 3% of the artery innervating trigeminal cells in the P90 control rats had an axon collateral to the forehead.(ABSTRACT TRUNCATED AT 400 WORDS)

Peripheral nerve autografts to the rat spinal cord: a study of the origin of regenerating fibres using fluorescent double labelling.

In adult Wistar rats a segment of the right sciatic nerve was grafted to the right dorsal funiculus of the spinal cord (SC). After survivals of 25-54 weeks a solution of the retrograde fluorescent cytoplasmatic tracer Fast Blue (FB) was injected into the SC and microgranules of the retrograde fluorescent nuclear tracer Diamidino Yellow (DY) were inserted into the graft. DY labelled neurones were found in the SC up to 30 mm both rostrally and caudally to the graft and were always single labelled. DY labelled cells were also found in the dorsal root ganglia (DRG) for 6-7 consecutive levels caudally to the graft. Ten to 30% of the DY labelled DRG cells were double labelled and also contained the FB tracer. The present work using the multiple retrograde fluorescent tracing method demonstrates that peripheral nerve (PN) grafts implanted in the rat SC are reinnervated by axones arising from intrinsic SC neurones and DRG cells. The axones from intrinsic SC neurones seem to result only from the regrowth of damaged neurones which have lost their intraspinal projections. The regeneration from DRG cells seem to be sustained by both the regrowth of damaged axones and the preterminal and/or collateral sprouting.

Spatial distribution of axon collaterals of single inferior olive neurons.

The aim of this study was to define the overall distribution pattern of the axon collaterals of single inferior olive (IO) neurons in relation to the multiple somatotopic maps defined by the climbing fiber (CF) input through the cerebellar cortex. In a previous study (Rosina and Provini: Brain Res. 289:45-63, '83), it was shown that the IO neurons supply interlobar collaterals to pairs of somatotopically related areas in the intermediate part of the anterior lobe (PIAL), in the paramedian lobule (PML), in crus II, and in the simple lobule, within strips C1 to D2. The residual branches then could either distribute within single folia or to adjacent folia within each somatotopically defined cerebellar area or both. We studied whether or not the IO axons branch over neighboring folia of the face-forelimb (FL) areas of PIAL and PML and how this interfolial branching relates to the interlobar collateralization by using the multiple fluorescent retrograde tracing technique. The main results of the study were as follows: the axons from neurons in IO subdivisions that are related to strips C1-C3 give off two interfolial branches in the FL area of PIAL and practically no interfolial collaterals are given in the FL area of PML; and the neurons that give off interfolial collaterals also give interlobar branches. From these data we have inferred the general branching pattern of the IO neurons that convey FL information to PIAL and PML. Each neuron gives off two interlobar collaterals: the branch directed to PIAL splits again into two interfolial collaterals, while each of these three collaterals should give off about three branches within each target folium to account for the ten collaterals estimated to be present in the cat. The distribution pattern of IO axon collaterals proposed here suggests that the same CF-relayed information may interact, at the Purkinje cell level, with different sets of mossy fiber inputs. The effect of this interaction would be to modulate the motor commands forwarded to specific muscle groups in relation to the different conditions under which a given movement is executed.

Spinal afferents and cortical efferents of the anterior intralaminar nuclei: an anterograde-retrograde tracing study

The topographical relations among the terminal field of spinothalamic fibers and the cells projecting upon areas 4 and 5 were studied in the anterior intralaminar nuclei of the cat. Terminals anterogradely labeled from the spinal cord and cell populations retrogradely labeled from the lateral pericruciate and anterior suprasylvian cortex were simultaneously observed by means of a multiple fluorescent tracing strategy. The present findings confirm that spinal afferents in the central lateral and paracentral nuclei overlap with the cells projecting to area 4. Further, the present data demonstrate that spinal terminals are largely segregated from the intralaminar cell population projecting to area 5.

Cell death organizes the postnatal development of the trigeminal innervation of the cerebral vasculature

In the adult trigeminal ganglion single cell bodies that innervate the middle cerebral artery (MCA) are different from but situated near to one or more cell bodies that innervate the forehead (O'Connor and Van der Kooy, submitted). Multiple fluorescent retrograde axonal tracing in postnatal day 3–90 rats was employed to describe the development of this adult pattern of trigeminal projections. We found that close to 90% of the cells that innervate the MCA at postnatal day 5 (PND 5) are eliminated by PND 90. Less than 20% of the ganglion cells innervating the forehead die over the same postnatal period. Subpopulations of cells in the ganglion were observed to have a maximal rate of death during different postnatal periods. First, 15–20% of the cells throughout the ophthalmic division die between PND 5 and PND 10. Second, a small population of cells that had early projections to the contralateral MCA die out completely by PND 22. Third, cells with a projection only to the MCA die primarily between PND10 and PND 54. Fourth, during the first postnatal week there are many cells that project to both the MCA and the forehead; however, 90% of this population dies by PND 90. This elimination is observed latest in the postnatal period, with these cells exhibiting their greatest rate of cell death between PND 22 and PND 90. Thus, cell death is the primary postnatal mechanism that produces this organization in the ophthalmic division of the trigeminal ganglion and retraction of axonal collaterals is a minor mechanism. We suggest that the latest period of death in cells with divergent artery and forehead projections as well as the ultimate persistence of some artery projecting cells beyond PND 90, may be due to the larger peripheral fields of innervation of these trigeminal ganglion cells.

Increased collateralization of the cerebellothalamic pathway following neonatal hemicerebellectomy

The postlesional reorganization of the cerebellothalamic cells was here studied using a multiple retrograde tracing technique. To this purpose, the cerebellothalamic cell population was investigated in 3 groups of adult rats: (a) cases hemicerebellectomized at birth; (b) cases hemicerebellectomized in adulthood; and (c) control unlesioned ones. In all of the groups the fluorescent tracers Diamidino Yellow and Fast Blue were injected bilaterally in the thalamus and the retrograde labeling obtained in the cerebellar nuclei was analyzed quantitatively. In the adult unlesioned rats the cerebellar cells projecting to the ipsilateral thalamus represented 3–4% of the cell population projecting to the contralateral thalamus. Furthermore, in agreement with previous results, it was demonstrated that the ipsilateral component was almost totally formed by axon collaterals of the main contralateral cerebellothalamic pathway. The organization of the bilateral cerebellothalamic pathway was unaffected by a hemicerebellectomy performed in adulthood. However, when the hemicerebellectomy had been performed at birth, the number of cerebellar cells that project to the ipsilateral thalamus was 3 times higher than in the controls. In these lesioned cases, as in the other ones, the ipsilateral projecting cell population was mainly represented by branched cerebellar cells which project bilaterally upon the thalamus. These results indicate that the bilaterality of the cerebellothalamic pathway is enhanced after an early hemicerebellectomy, and that this phenomenon is responsible for the reinnervation of the deafferented thalamus. Further, the present study shows that the increase in the bilaterality of the system is sustained by cerebellar cells which bifurcate bilaterally upon the thalamus, and therefore that the reinnervation of the deafferented thalamus is performed by axon collaterals of the contralateral spared cerebellothalamic pathway.

Cerebellar cortico-nucleo-cortical and commissural nuclear connections studied with the multiple fluorescent tracing method

Cerebellar cortico-nucleo-cortical and commissural nuclear connections studied with the multiple fluorescent tracing method

Evaluation of Some New Tracers for Soil Water Studies

AbstractSix anions which showed potential as tracers of soil water movement were evaluated in laboratory and field experiments. The anions included iodide (I‐), thiocyanate (SCN‐), and four fluorobenzoates: m‐(trifluoromethyl)benzoic acid (m‐TFMBA), o‐(trifluoromethyl)benzoic acid (o‐TFMBA), pentafluorobenzoic acid (PFBA) and 2,6‐difluorobenzoic acid (2,6‐DFBA). The sorption and mobility characteristics of the six potential tracers were compared to those of bromide (Br‐), which served as an index tracer in all experiments. Initial tracer concentrations ranged from 20 to 100 mg L−1. The anions were quantified simultaneously in sub‐mL samples of soil solution using a high performance liquid chromatography technique. Batch equilibrations (28 d), and breakthrough curves (7 to 10 d) in a 2.5‐m column of loamy sand, under both ponded and trickle‐irrigated conditions, indicated that all the tracers except SCN‐ were conservative and were not sorbed. SCN‐ was not retarded in the column studies but did show a negative mass balance, most likely due to chemical and/or biological transformation. Distribution of a tracer solution applied to a field soil was monitored for 69 d in soil water from suction samplers (1.0‐ and 1.8‐m depth) and in extracts from core samples. SCN‐, I‐, and m‐TFMBA showed reduced concentrations relative to Br‐ at all sampling times and depths; o‐TFMBA, PFBA, and 2,6‐DFBA had distributions similar to that of Br‐. These latter three fluorobenzoates show promise as laboratory and field tracers of soil water, particularly where multiple tracing tests or totally exotic tracers are required.

Somatotopy of climbing fiber branching to the cerebellar cortex in cat

The study was aimed at determining the distribution and incidence of the inferior olive axonal branching as related to the somatotopic organization of the climbing fiber system in cat. Multiple fluorescent tracing was used. In a first set of experiments, spectrally different fluorescent tracers were injected into somatotopically defined areas of the anterior lobe-pars intermedia and of the paramedian lobule. Retrogradely labeled cells were found to be localized in well-segregated face-forelimb or hindlimb olivary domains, within the various subdivisions. A large and consistent number of the olive cells were found to send axonal branches to face-forelimb or hindlimb regions of the anterior lobe-pars intermedia and of the paramedian lobule. It was also found that inferior olive branching is restricted to somatotopically corresponding areas of the two lobes. In a second set of experiments the same technique was used to check whether the inferior olive neurons which project to the forelimb areas of the anterior lobe-pars intermedia and the paramedian lobule also send collaterals to the face-forelimb areas of crus II (medial crus II). The data show that different sets of neurons projecting either to the face-forelimb areas of crus II and anterior lobe-pars intermedia or of crus II and paramedian lobule coexist within the face-forelimb related olivary domains with the set of neurons projecting to the face-forelimb areas of the anterior lobe-pars intermedia and paramedian lobule. Neurons branching to the 3 cerebellar regions were observed only occasionally. Therefore, at least for the face-forelimb-related cerebellar areas, the climbing fiber branching can be said to originate in sets of inferior olive neurons that connect different pairs of somatotopically homologous cerebellar cortical areas. The branching pattern is present in all the cortical zones studied, namely C1-C3, C2, D1 and D2, and appears to be a general feature of the olivocerebellar system.

Multiple isotope tracing of methanation over nickel catalyst: III. Completion of 13C and D tracing

The methanation of mixtures of carbon monoxide and hydrogen was studied by a transient superposition technique using terminal species marked by 13C and D. Further evidence is presented that the most abundant reacting intermediate is the species CH ads. It appears that the hydrogenation of this species controls the rate of methanation. Carbidic carbon consists of relatively small pool of active C ads together with a larger pool of carbon which, although not active for methanation, is also not graphitic. A mechanism is presented which summarizes the findings of this and the previous two papers in this series.

Claustroneocortical projections studied in the cat by means of multiple retrograde fluorescent tracing.

The topographical interrelations of claustroneocortical cells and their degree of divergent collateralization were investigated in cat by means of retrograde fluorescent double labeling. The tracers Fast Blue (FB) and Nuclear Yellow (NY) were injected in several combinations in two different cortical fields. FB-labeled and NY-labeled cells were found in all cases in the insular portion of the ipsilateral claustrum (CII). The distributions of labeled cells confirmed the organization reported in previous studies. In some cases the two labeled cell populations were segregated in different parts of the CII; in other cases there was more or less overlap in the two distributions. The degree of overlap was not simply related to the topographic proximity of the injected cortical territories. In all cases the vast majority of cells were single labeled. In one case both FB and NY were injected in the same cortical area in order to control that claustral axons can retrogradely transport two tracers back to the same parent cell bodies. In this control case CII cells were double labeled. All together these data indicate that widely divergent claustroneocortical projection take origin mainly from separate cells.

The cortical projections of the thalamic intralaminar nuclei, as studied in cat and rat with the multiple fluorescent retrograde tracing technique

Two retrograde fluorescent tracers were injected in two different areas of the cerebral cortex in rats and in cats. In all the experiments many single labeled cells and only some double labeled ones were seen in the thalamic intralaminar nuclei. The present results suggest that the diffusely distributed intralaminarcortical projections mainly consist of axons of separate cells, and only to a minor extent of axon collaterals of the same cells.