Injections Of Different Tracers Research Articles

Patterns of Unilateral and Bilateral Projections From Layers 5 and 6 of the Auditory Cortex to the Inferior Colliculus in Mouse.

The auditory cortex sends massive projections to the inferior colliculus, but the organization of this pathway is not yet well understood. Previous work has shown that the corticocollicular projection emanates from both layers 5 and 6 of the auditory cortex and that neurons in these layers have different morphological and physiological properties. It is not yet known in the mouse if both layer 5 and layer 6 project bilaterally, nor is it known if the projection patterns differ based on projection location. Using targeted injections of Fluorogold into either the lateral cortex or dorsal cortex of the inferior colliculus, we quantified retrogradely labeled neurons in both the left and right lemniscal regions of the auditory cortex, as delineated using parvalbumin immunostaining. After dorsal cortex injections, we observed that approximately 18–20% of labeled cells were in layer 6 and that this proportion was similar bilaterally. After lateral cortex injections, only ipsilateral cells were observed in the auditory cortex, and they were found in both layer 5 and layer 6. The ratio of layer 5:layer 6 cells after lateral cortex injection was similar to that seen after dorsal cortex injection. Finally, injections of different tracers were made into the two inferior colliculi, and an average of 15–17% of cells in the auditory cortex were double-labeled, and these proportions were similar in layers 5 and 6. These data suggest that (1) only the dorsal cortex of the inferior colliculus receives bilateral projections from the auditory cortex, (2) both the dorsal and lateral cortex of the inferior colliculus receive similar layer 5 and layer 6 auditory cortical input, and (3) a subpopulation of individual neurons in both layers 5 and 6 branch to innervate both dorsal cortices of the inferior colliculus.

С О В Р Е М Е Н Н Ы Е М Е Т О Д И Ч Е С К И Е В О З М О Ж Н О С Т И И Н Д И К А Т О Р Н О Г О ( Т Р А С С Е Р Н О Г О )

The article presents the results of modeling tracer studies of the process of flooding of an oil reservoir. As a result of the studies, the dependences on the time of the change in the volume occupied by the injected water were obtained. Formulas are given that allow us to calculate the values of the coefficient of coverage of the reservoir area by flooding as a whole and the contribution of each injection well to flooding. The technology is implemented by continuously pumping the tracer into the injection well. Continuous injection of different tracers into different injection wells allows for operational monitoring of oil field development

Cortico-Cortical Connectivity Within Ferret Auditory Cortex.

ABSTRACTDespite numerous studies of auditory cortical processing in the ferret (Mustela putorius), very little is known about the connections between the different regions of the auditory cortex that have been characterized cytoarchitectonically and physiologically. We examined the distribution of retrograde and anterograde labeling after injecting tracers into one or more regions of ferret auditory cortex. Injections of different tracers at frequency‐matched locations in the core areas, the primary auditory cortex (A1) and anterior auditory field (AAF), of the same animal revealed the presence of reciprocal connections with overlapping projections to and from discrete regions within the posterior pseudosylvian and suprasylvian fields (PPF and PSF), suggesting that these connections are frequency specific. In contrast, projections from the primary areas to the anterior dorsal field (ADF) on the anterior ectosylvian gyrus were scattered and non‐overlapping, consistent with the non‐tonotopic organization of this field. The relative strength of the projections originating in each of the primary fields differed, with A1 predominantly targeting the posterior bank fields PPF and PSF, which in turn project to the ventral posterior field, whereas AAF projects more heavily to the ADF, which then projects to the anteroventral field and the pseudosylvian sulcal cortex. These findings suggest that parallel anterior and posterior processing networks may exist, although the connections between different areas often overlap and interactions were present at all levels. J. Comp. Neurol. 523:2187–2210, 2015. © 2015 Wiley Periodicals, Inc.

Retino-retinal projection in juvenile and young adult rats and mice

Identification of retino-retinal projecting RGCs (ret-ret RGCs) has been accomplished by tracing RGCs in one retina after intravitreal injection of different tracers in the other eye. In mammals, rabbit and rat, ret-ret RGCs are scarce and more abundant in newborn than in adult animals. To our knowledge, ret-ret RGCs have not been studied in mice. Here we purpose to revisit the presence of ret-ret RGCs in juvenile and young adult rats and mice by using retrograde tracers applied to the contralateral optic nerve instead of intravitreally. In P20 (juvenile) and P60 (young adult) animals, the left optic nerve was intraorbitally transected and Fluorogold (rats) or its analogue OHSt (mice) were applied onto its distal stump. P20 animals were sacrificed 3 (mice) or 5 (rats) days later and adult animals at 5 (mice) or 7 (rats) days. Right retinas were dissected as flat-mounts and double immunodetected for Brn3a and melanopsin. Ret-ret RGCs were those with tracer accumulation in their somas. Out of them some expressed Brn3a and/or melanopsin, while other were negative for both markers. In young adult rats, we found 2 ret-ret RGCs displaced to the inner nuclear layer. In both species, ret-ret RGCs are quite scarce and found predominantly in the nasal retina. In juvenile animals there are significantly more ret-ret RGCs (9 ± 3, rats, 13 ± 3 mice) than in young adult ones (5 ± 6 rats, 7 ± 3 mice). Finally, juvenile and young adult mice have more ret-ret RGCs than rats.

Differential topography of the bilateral cortical projections to the whisker and forepaw regions in rat motor cortex

Whisker and forelimb movements in rats have distinct behavioral functions that suggest differences in the neural connections of the brain regions that control their movements. To test this hypothesis, retrograde tracing methods were used to characterize the bilateral distribution of the cortical neurons that project to the whisker and forelimb regions in primary motor (MI) cortex. Tracer injections in each MI region revealed labeled neurons in more than a dozen cortical areas, but most labeling was concentrated in the sensorimotor areas. Cortical projections to the MI forepaw region originated primarily from the primary somatosensory (SI) cortex in the ipsilateral hemisphere. In contrast, most projections to the MI whisker region originated from the MI whisker region in the contralateral hemisphere. Tracer injections in the MI whisker region also revealed a higher proportion of labeled neurons in the claustrum and in the posterior parietal cortex. Injections of different tracers into the MI whisker and forepaw regions of some rats revealed a topographic organization of neuronal labeling in several sensorimotor regions. Collectively, these findings indicate that the MI whisker and forepaw regions receive different sets of cortical inputs. Whereas the MI whisker region is most strongly influenced by callosal projections, presumably to mediate bilateral coordination of the whiskers, the MI forepaw region is influenced mainly by ipsilateral SI inputs that convey somatosensory feedback.

Contralateral corticothalamic projections from MI whisker cortex: Potential route for modulating hemispheric interactions

Rat whisking behavior is characterized by high amounts of bilateral coordination in which whisker movements on both sides of the face are linked. To elucidate the neural substrate that might mediate this bilateral coordination, neuronal tracers were used to characterize the bilateral distribution of corticothalamic projections from primary motor (MI) cortex. Some rats received tracers in the MI whisker region, whereas others received tracers in the MI forepaw region. The MI whisker region projects bilaterally to the anteromedial (AM), ventromedial (VM), and ventrolateral (VL) nuclei, and to parts of the intralaminar nuclei. By contrast, the MI forepaw region sends virtually no projections to the contralateral thalamus. Consistent with these findings, bilateral injections of different tracers into the MI whisker region of each hemisphere produced tracer overlap on both sides of the thalamus. Furthermore, MI whisker projections to the contralateral thalamus terminate in close proximity to the thalamocortical neurons that project to the MI whisker region of that contralateral hemisphere. The terminal endings of the contralateral corticothalamic projections contain small synaptic varicosities and other features that resemble the modulator pathways described for other corticothalamic projection systems. In addition, tracer injections into AM, VM, and VL revealed dense clusters of labeled neurons in layer VI of the medial agranular (Agm) zone, which corresponds to the MI whisker region. These results suggest that projections from the MI whisker region to the contralateral thalamus may modulate the callosal interactions that are presumed to play a role in coordinating bilateral whisking behavior.

Striatal projections of the vagal‐responsive region of the thalamic parafascicular nucleus in macaque monkeys

We recently reported that the thalamic parafascicular nucleus (Pf) in monkeys is strongly activated by vagus nerve afferents. The main forebrain target of Pf is the striatum, but the specific striatal regions receiving visceral input via this pathway are unknown. We examined the projections of this region by injecting anterograde tracers into the vagus evoked potential (VEP) focus in Pf of macaque monkeys. The VEP was strongest lateral and anterior to the habenulointerpeduncular tract, but it was distributed across the entire horizontal extent of the ventral half of Pf. All injections produced labeled terminals in the caudate (Cd), especially the Cd tail and the adjacent ventral posterior Pu. Terminations occurred throughout the Cd head and body but spared the most anterior and dorsolateral parts. Injections in more anterior and lateral portions of Pf produced progressively more terminations in Pu, mainly in the precommissural region and the medial aspect of posterior Pu. Dual injections of different tracers revealed overlapping projections with interdigitated strands of striatal terminations from separate regions of Pf as well as the posteromedial to anterolateral topographic gradient of increasing Pf projections to Pu. An injection in the most anteromedial portion of Pf produced strong labeling in the ventral striatum. Thus, Pf transmits viscerosensory information to the "associative" and "limbic" territories of the striatum. These findings suggest the broad involvement of homeostatic afferent activity in striatal function and perhaps a role for the striatum in autonomic function.

Unilateral and bilateral projections from cortical cells to the inferior colliculus in guinea pigs

Auditory cortex projects directly and bilaterally to the inferior colliculus (IC). We used multiple fluorescent retrograde tracers to determine whether individual cortical cells project to both the left and right IC. Injection of different tracers into each IC labeled many cells in a sheet that extended throughout much of temporal cortex in both hemispheres. Most cells contained a single tracer, with the majority of these labeled from the ipsilateral IC. Numerous double-labeled cells were observed throughout the same areas of temporal cortex. The double-labeled cells form a small percentage of the cortical cells that project to the ipsilateral IC (6.1% on average) and a much larger percentage of the cells that project to the contralateral IC (46.4% on average). Unilaterally projecting cells are well positioned to have effects limited to one IC, whereas bilaterally projecting cells are likely to have a broader influence and may coordinate activity on the two sides of the midbrain.

Separate projections from the inferior colliculus to the cochlear nucleus and thalamus in guinea pigs

We used multiple-labeling techniques with retrograde fluorescent tracers to determine whether individual cells in the inferior colliculus project to the medial geniculate body (MG) and the cochlear nucleus (CN) in guinea pigs. Four possible projection patterns were examined: (1) to ipsilateral MG and ipsilateral CN; (2) to ipsilateral MG and contralateral CN; (3) to contralateral MG and ipsilateral CN; and, (4) to contralateral MG and contralateral CN. Following injections of different tracers into two or more sites, no inferior collicular cells were double-labeled from the two contralateral targets and only a few cells were double-labeled from each of the other pairs of targets. The double-labeled cells always totaled <1% of the single-labeled populations. We conclude that collateral projections from the inferior colliculus to the MG and CN are virtually non-existent. Therefore, the ascending and descending projections to these targets arise from different cells. These cells could potentially receive different inputs and send different information to higher or lower centers of the auditory pathway.

Hypoglossal and reticular interneurons involved in oro-facial coordination in the rat.

Chewing, swallowing, breathing, and vocalization in mammals require precise coordination of tongue movements with concomitant activities of the mimetic muscles. The neuroanatomic basis for this oro-facial coordination is not yet fully understood. After the stereotaxic microinjection of retrograde and anterograde neuronal tracers (biotin-dextran, Fluoro-Ruby, Fluoro-Emerald, and Fluoro-Gold) into the facial and hypoglossal nuclei of the rat, we report here a direct bilateral projection of hypoglossal internuclear interneurons onto facial motoneurons. We also confirm the existence of a small pool of neurons in the dorsal part of the brainstem reticular formation that project ipsilaterally to both facial and hypoglossal nuclei. For precise tracer injections, both motor nuclei were located and identified by the electrical antidromic activation of their constituent motoneurons. Injections of retrograde tracers into the facial nucleus consistently labeled neurons in the hypoglossal nucleus. These neurons prevalently lay in the ipsilateral side, were small in size, and, like classic intrinsic hypoglossal local-circuit interneurons, had several thin dendrites. Reverse experiments - injections of anterograde tracers into the hypoglossal nucleus - labeled fine varicose nerve fiber terminals in the facial nucleus. These fiber terminals were concentrated in the intermediate subdivision of the facial nucleus, with a strong ipsilateral prevalence. Double injections of different tracers into the facial and the hypoglossal nuclei revealed a small, but constant, number of double-labeled neurons located predominantly ipsilateral in the caudal brainstem reticular formation. Hypoglossal internuclear interneurons projecting to the facial nucleus, as well as those neurons of the parvocellular reticular formation that project to both facial and hypoglossal nuclei, could be involved in oro-facial coordination.

Turnover of Rat Brain Perivascular Cells

Brain perivascular spaces harbor a population of cells which exhibit high phagocytic capacity. Therefore, these cells can be labeled by intraventricular injection of tracers. Such perivascular cells at the interface between blood and brain are believed to belong to the monocyte/macrophage lineage and to be involved in antigen presentation. Currently, it is unclear whether these cells undergo a continuous turnover by entering and leaving the bloodstream. Using bone-marrow-chimeric animals, migration of donor macrophages into brain perivascular spaces has been reported. On the other hand, following intracerebral injection of india ink into nontransplanted animals, ink-labeled perivascular cells were still found 2 years after injection, suggesting a high stability of this cell pool. Thus, the turnover of perivascular cells observed in chimeras might be a result of bone marrow transplantation rather than a physiological occurrence. To address this issue, we monitored de novo invasion of macrophages into perivascular spaces of apparently healthy adult rats by applying techniques other than bone marrow transplantation, (i) consecutive injections of different tracers and (ii) ex vivo isolation of macrophages from the blood, cell labeling, and reinjection into the same animal to avoid MHC mismatch. Both approaches revealed vivid de novo invasion of macrophages into perivascular spaces, but not into brain parenchyma, rendering untenable the concept of perivascular cells forming a stable population of macrophages in the brain. Thus, brain perivascular spaces are under permanent immune surveillance of blood borne macrophages in normal adult rats.

Morphological connections between the Hypoglassal and facial nerve in the brain stem of the rat

The perfect coordination and synchronization of hypoglossal and facial muscles during chewing, swallowing, breathing, and vocalization requires particular concomitant activities of the facial muscles. In contrast, no direct connection between the facial and hypoglossal nucleus on the level of the brain stem has been detected until now. Facial and hypoglossal nuclei of rats were identified on the basis of their antidromic field potential recorded after peripheral stimulation of the corresponding nerves. Stereotactically single or double fluorescence tracer injections (Biotin-Dextran, Fluorescine-Dextran, Rhodamine-Dextran, Fluoro Gold) were placed into the nuclei. Retrograde tracer injections into the facial nucleus consistently labeled small neurons in the hypoglossal nucleus. In reverse experiments the injection of anterograde tracers into the hypoglossal nucleus labeled fine caliber varicose nerve fibers, but no somata in the facial nucleus. Synchronous injections of different tracers into the facial and hypoglossal nucleus produced a small, but constant number of double-labeled cells in the parvocellular reticular formation. Both, hypoglossal interneurons projecting to the facial nucleus and neurons of the parvocellular reticular formation double-projecting to the facial and hypoglossal nucleus might play an important role in coordinated orofacial movements. Moreover, both populations of neurons might be responsible for the excellent postoperative results after hypoglossal-facial anastomosis.

Trigeminal projections to hypoglossal and facial motor nuclei in the rat.

This study was undertaken to identify the trigeminal nuclear regions connected to the hypoglossal (XII) and facial (VII) motor nuclei in rats. Anterogradely transported tracers (biotinylated dextran amine, biocytin) were injected into the various subdivisions of the sensory trigeminal complex, and labeled fibers and terminals were searched for in the XII and VII. In a second series of experiments, injections of retrogradely transported tracers (biotinylated dextran amine, gold-horseradish peroxidase complex, fluoro-red, fluoro-green) were made into the XII and the VII, and labeled cells were searched for in the principal sensory trigeminal nucleus, and in the pars oralis, interpolaris, and caudalis of the spinal trigeminal nucleus. Trigeminohypoglossal projections were distributed throughout the ventral and dorsal region of the XII. Neurons projecting to the XII were found in all subdivisions of the sensory trigeminal complex with the greatest concentration in the dorsal part of each spinal subnucleus and exclusively in the dorsal part of the principal nucleus. Trigeminofacial projections reached all subdivisions of the VII, with a gradual decreasing density from lateral to medial cell groups. They mainly originated from the ventral part of the principal nucleus. In the spinal nucleus, most of the neurons projecting to the VII were in the dorsal part of the nucleus, but some were also found in its central and ventral parts. By using retrograde double labeling after injections of different tracers in the XII and VII on the same side, we examined whether neurons in the trigeminal complex project to both motor nuclei. These experiments demonstrate that in the spinal trigeminal nucleus, neurons located in the pars caudalis and pars interpolaris project by axon collaterals to XII and VII.

Projections from the ventral cochlear nucleus to the inferior colliculus and the contralateral cochlear nucleus in guinea pigs

Multipolar cells in the ventral cochlear nucleus are the source of projections to numerous brainstem auditory nuclei, including the contralateral and ipsilateral inferior colliculi and the contralateral cochlear nucleus. Multiple fluorescent tracers were used to label the multipolar cells that project to each of these targets. Following injections of different tracers into each target, the ventral cochlear nucleus was examined for the presence of cells that contained more than one tracer. Such cells were never observed. In contrast, double-labeled cells were common in the dorsal cochlear nucleus, where cells frequently contained the two tracers that were injected into the ipsilateral and contralateral inferior colliculi. The distribution and somatic morphology of cells in the ventral cochlear nucleus that project to each of the three targets were examined. Each population contained cells with somas that ranged in shape from elongated to rounded, but there were differences in soma size. Projections to the ipsilateral and contralateral inferior colliculi arise predominantly from small to medium-sized cells, the average size being slightly less for cells with projections to the ipsilateral colliculus. Projections to the contralateral cochlear nucleus arise from cells with somas that range in size from small to large, including cells much larger than those that projected to either inferior colliculus. On the basis of these results, we conclude that projections from the ventral cochlear nucleus to the ipsilateral and contralateral inferior colliculi and to the contralateral cochlear nucleus arise in three different populations of multipolar cells.

Organization in the somatosensory sector of the cat's thalamic reticular nucleus

This study describes the organization of cells in the thalamic reticular nucleus (TRN) that project to the somatosensory part of the dorsal thalamus in the cat. Injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) and fluorescent dyes were made into the ventrobasal complex (VB) and the medial division of the posterior complex (POm) of the thalamus. The resultant retrograde labelling in TRN was analyzed. Large injections of a tracer in VB label many reticular cells that are restricted to a centroventral, or somatosensory, sector of TRN. Small injections of a tracer in VB produce narrow zones of labelled cells in this sector. In reconstructions these zones resemble thin "slabs," which lie parallel to the plane of TRN along its oblique rostrocaudal dimension and occupy only a fraction of its thickness. In comparisons of the zones of labelled cells in TRN resulting from tracer injections in different nuclei of VB, inner cells, intermediate cells, and outer cells across the thickness of TRN project to the ventral posteromedial, the medial division of the ventral posterolateral, and the lateral division of the ventral posterolateral nuclei, respectively. Furthermore, shifts in injected areas along the dorsoventral dimension of VB produce similar shifts in zones of labelled cells in TRN. Thus, reticular cells form an accurate map on the basis of their connections with VB. Large injections of a tracer in the ventral subdivision of POm label many reticular cells that are also restricted to the centroventral sector of TRN. Small injections of a tracer in ventral POm produce broad zones of labelled cells in this sector. In comparisons of the zones of labelled cells in TRN resulting from tracer injections in different regions of ventral POm, cells that project to these regions are scattered across the thickness of TRN and occupy overlapping territories. Large injections of a tracer in either VB or ventral POm also label cells in a restricted centroventral region of the perireticular nucleus. Double injections of different tracers in VB and ventral POm produce many cells in TRN that are labelled from both of these dorsal thalamic structures and fewer cells that are labelled from only one or the other of these structures. These results indicate that there is a dual organization in the projections of cells in the somatosensory sector of TRN to dorsal thalamus: Projections to VB are topographically organized whereas those to ventral POm lack a topographical organization. Furthermore, both of these mapped and nonmapped projections can arise from single reticular cells in the somatosensory sector.

Topography of serotonin neurons in the dorsal raphe nucleus that send axon collaterals to the rat prefrontal cortex and nucleus accumbens

Diverse physiological actions have been reported for 5-hydroxytryptamine (5-HT, serotonin) in the medial prefrontal cortex (MPFC) and the nucleus accumbens (Acb) suggesting that the 5-HT innervation of these forebrain areas may be derived from different populations of neurons. We examined this possibility by mapping the distribution of 5-HT-immunoreactive (ir) and non-5HT-ir neurons containing retrograde labeling following injections of different tracers into both these target regions. The analysis was focused in the dorsal raphe nucleus (DRN) of the midbrain, since 5-HT pathways to the MPFC and Acb primarily originate from this area. Volume microinjections of the fluorescent retrograde tracer, Fluoro-Gold (FG), were placed into the MPFC and microinjections of cholera toxin B subunit coupled to 15 nm gold particles (CT-Au) were placed into the Acb of the same animal. Sections through the DRN containing retrogradely labeled neurons were further processed for immunofluorescent localization of 5-HT using a rhodamine marker. Neurons retrogradely labeled from the Acb were greater in number overall than those projecting to the MPFC. In addition, Acb-projecting neurons extended into the lateral wings of the DRN, whereas MPFC-projecting neurons were more restricted to the midline. Both groups of retrogradely labeled neurons, however, were more numerous in the caudal aspect of the dorsal raphe nucleus and were scattered amongst 5-HT immunoreactive perikarya. Of783 ± 69 CT-Au labeled cells, 15% also contained the FG label and 11% contained FG and 5-HT immunoreactivity. Of613 ± 48 FG labeled cells, 24% also contained the CT-Au label and 21% were also immunoreactive to 5-HT. The results suggest a more prominent input to the Acb from both 5-HT-ir and non-5-HT-ir neurons in the caudal aspect of the DRN and further indicate that while most 5-HT-ir and non-5-HT-ir neurons project differentially to both forebrain regions, a few cells also show collateralization to the MPFC and Acb. Such collateralization of single serotonergic neurons to divergent targets mey integrate cognitive and motor activities in response to pharmacological manipulations of ascending serotonergic pathways.

Topography of cholinergic afferents from the nucleus basalis of meynert to representational areas of sensorimotor cortices in the rat

We investigated (1) the topography of projection neurons in the nucleus basalis of Meynert (NBM) with efferents to restricted regions of the primary somatosensory (SI), the second somatosensory (SII), and the primary motor (MI) cortices in the rat; (2) the percentage of these NBM projection neurons that were cholinergic; and (3) the collateralization, if any, of single NBM neurons to different subdivisions within SI, to homotopic areas of SI and SII, and to homotopic areas of SI and MI. Retrograde single- and double-labeling techniques were used to study NBM projections to electrophysiologically identified subdivisions of SI and to homotopic representational areas of SI and SII, and of SI and MI. Choline acetyltransferase immunocytochemistry was done to identify cholinergic NBM neurons. Of the retrogradely labeled NBM neurons that projected to selective subdivisions of SI, SII, and MI, 89%, 87%, and 88%, respectively, were cholinergic. We found a rostral-to-caudal progression of retrogradely labeled NBM neurons following a medial-to-lateral sequence of injections into subdivisions of SI. Overlapping groups of single-labeled NBM neurons were observed after injections of different tracers into adjacent subdivisions within SI or homotopic areas of SI and SII, and of SI and MI. We conclude that NBM innervation to SI, SII, and MI is mostly cholinergic in the rat, that each cortical area receives cholinergic afferents from neurons widely distributed within the NBM, and that each NBM neuron projects to a restricted cortical area without significant collateralization to adjacent subdivisions within SI or to homotopic areas of SI and SII, or SI and MI.

Different subsets of displaced ganglion cells in the pigeon retina exhibit cholecystokinin-like and enkephalin-like immunoreactivities

Immunohistochemical and retrograde tracing techniques were combined in order to identify chemically specific displaced ganglion cells in the pigeon retina. About 15% of the displaced ganglion cells that were retrogradely labeled following injections of different tracers into the accessory optic nucleus were shown to contain cholecystokinin 8-like immunoreactivity. These cells were medium to large (15–30 μm) and located mostly in the peripheral retina. Another population of about 9% of the retrogradely labeled displaced ganglion cells was shown to contain leucine-enkephalin-like immunoreactivity. These cells were medium-sized (11–18 μm) and distributed almost evenly throughout the retina. These two types of displaced ganglion cells represent together only about 0.1% of the total number of ganglion cells in the pigeon retina. Taken together with previous results, these data indicate that the displaced ganglion cells of the avian retina may comprise several chemically specific cell types. The present results also contribute information on the chemical heterogeneity of retinal ganglion cells.

Patterns of projections from area 2 of the sensory cortex to area 3a and to the motor cortex in cats.

Peripheral information reaches the motor cortex partly through corticocortical pathways that arise from two functional subdivisions, area 2 and area 3a, of the sensory cortex. These sensory areas are synaptically linked with one another. The patterns of connectivity and the different submodality input that each area receives suggest that they send different efferent signals to the motor cortex. The projections from area 2 to area 3a and to the motor cortex were studied with retrogradely transported fluorescent tracers. The pattern and distribution of neuronal labeling in area 2 was determined following injections of different tracers into the forelimb regions of area 3a and the motor cortex. The results showed that the projections from area 2 to the two target regions were topographically and somatotopically related. Multiple clusters of motor cortex projection neurons were found in area 2, and these clusters overlapped extensively with clusters of area 3a projection neurons. Although cells labeled with one of the dyes were often in close proximity to cells labeled with the other dye, no double-labeled cells were found. Two different laminar patterns were seen for the two populations of neurons. The projection to area 3a originated from cells located in layers II-III and layers V-VI. The projection to the motor cortex originated from cells spread throughout layers II-IV, but predominantly in layer III. Differences in laminar arrangement of the two populations of cells suggest a directional flow of information processing in the sensorimotor cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Segregated thalamocortical pathways to inferior parietal and inferotemporal cortex in macaque monkey.

Inferior parietal and inferotemporal cortex, which process different aspects of visual information through largely segregated pathways from the visual cortex, both receive thalamic afferents from the pulvinar complex. We examined the topography of pulvinar projections to these two cortical regions by placing multiple injections of different tracers (fluorescent dyes, horseradish peroxidase) in the inferotemporal and inferior parietal cortex of macaque monkeys. The patterns of label observed after injections in inferotemporal gyrus indicate that area TEO and the ventral part of area V4 receive a major input from the ventral part of the lateral pulvinar (PuLv) while area TE has strong connections with the caudal pole of the medial pulvinar (PuM) and only minor connections with PuLv. In contrast, injections in the caudal inferior parietal cortex demonstrate that area PGc, on the lateral surface of the inferior parietal gyrus, and area POa, in the ventral bank of intraparietal sulcus, receive strong projections from PuM and the adjacent fringe of the dorsal part of the lateral pulvinar (PuLd). Paired injections of two different tracers in the inferotemporal and inferior parietal cortex of the same hemisphere revealed a nearly complete segregation of the two populations of labeled neurons in the pulvinar, with only a small region of overlap in PuM, close to the PuM/PuLd border. These results demonstrate a clear separation of the thalamic afferents to the inferior parietal and inferotemporal cortex which parallels the separation of prestriate afferents to these two cortical territories (Morel & Bullier, 1990).