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PubMed1995

Nucleus medialis-nucleus interpositus interface: its olivary and cerebellocortical projections in the rat.

The nuclear target of the X zone of the cerebellar cortex was identified in rats as clusters of neurons scattered at the interface between the nuclei medialis (NM) and interpositus (NI). In a previous study, we had outlined these target neurons and termed them "interstitial cell groups" (icg). In order to determine whether the icg should be considered as part of either the NM or the medial NI, we analyzed two efferent pathways from the icg: their nucleocortical and nucleoolivary projections. These were compared to their homologues from the NM and the NI. This analysis is based on mapping retrograde cell labeling and anterograde terminal labeling following microinjections of tracers in either the cerebellar cortex, the cerebellar nuclei, or the inferior olive. Nucleocortical projections originating from the icg are of the three types described previously: a "reciprocal" projection to the ipsilateral X zone, a "nonreciprocal" projection to the ipsilateral A zone, and a "symmetrical" projection to the contralateral X zone. These features can be considered as the summed characteristics of the nucleocortical projections from the NM and from the medial NI. Nucleoolivary projections from the icg target the lateral-rostral portion of the dorsal accessory olive as well as the centrocaudal part of the medial accessory olive. These pathways converge with the nucleoolivary projections from the medial NI and from the NM, respectively. The icg receives olivary afferents from both the regions of the dorsal and medial accessory olives to which it projects. On the basis of similarities shown here between the two types of efferents originating from the icg and those from the NM as well as the medial NI, the icg may be regarded as a "mosaic" of neuron clusters alternately belonging to the NM and the medial NI. Therefore, the icg would be reciprocally connected with the inferior olive.

Animals↗

PubMed2003

The entorhinal cortex of the mouse: organization of the projection to the hippocampal formation.

The origin and the terminations of the projections from the entorhinal cortex to the hippocampal formation of the mouse (C57BL/6J strain) have been studied using anterogradely and retrogradely transported tracers. The entorhinal cortex is principally divided into two areas, the lateral entorhinal area (LEA) and the medial entorhinal area (MEA). LEA is the origin of the lateral perforant path that terminates in the outer one-third of the molecular layer of the dentate gyrus, and MEA is the origin of the medial perforant path that ends in the middle one-third of the molecular layer of the dentate gyrus. This projection is mostly to the ispsilateral dentate gyrus; only a few labeled axons and terminals are found in the contralateral dentate gyrus. The projection to the dentate gyrus originates predominantly from neurons in layer II of the entorhinal cortex. The entorhinal cortex also projects to CA3 and CA1 and to subiculum; in both CA3 and CA1, the terminals are present in stratum lacunosum-moleculare, whereas in the subiculum the terminals are in the outer part of the molecular layer. The projection from the entorhinal cortex to CA3, CA1, and subiculum is bilateral, and it originates predominantly from neurons in layer III, but a small number of neurons in the deeper layers of the entorhinal cortex contributes to this projection. The projection of entorhinal cortex to the hippocampus is topographically organized, neurons in the lateral part of both LEA and MEA project to the dorsal part (i.e., septal pole) of the hippocampus, whereas the projection to the ventral (i.e., temporal pole) hippocampus originates from neurons in medial parts of the entorhinal cortex.

Animals↗

PubMed2001

Reciprocal connections between the entorhinal cortex and hippocampal fields CA1 and the subiculum are in register with the projections from CA1 to the subiculum.

The topology of the connections between the entorhinal cortex (EC), area CA1, and the subiculum is characterized by selective and restricted origin and termination along the transverse or proximodistal axis of CA1 and the subiculum. In the present study, we analyzed whether neurons in CA1 and the subiculum that receive EC projections are interconnected and give rise to return projections to EC, such that they terminate deep in the area of origin of the EC-to-CA1/subiculum projections. Both for the lateral and medial subdivision of EC, the projections to CA1/subiculum, as well as the projections from CA1 to the subiculum and back to EC, are rather divergent. Interestingly, we only rarely observed evidence for the presence of "reentry loops," i.e., cells in layer III of EC giving rise to projections to interconnected neurons in CA1 and the subiculum, while the targeted CA1 neurons also projected back to the deep layers of the area of origin of the pathway in EC. We conclude that although fibers originating from a restricted part of EC distribute extensively in a divergent way along the longitudinal axis of CA1 and the subiculum, only restricted portions of the latter two areas, receiving inputs from the same entorhinal area, are interconnected. Moreover, only a small percentage of the CA1 neurons that project to the correspondingly innervated subicular neurons give rise to projections that return to the deep layers of the originating part of EC. The present findings are taken to indicate that the EC-hippocampal circuitry functionally comprises many parallel-organized specific "reentry loops."

Animals↗

PubMed1995

Projection pattern of sensory neurons in the central nervous system of a homeotic mutation of the moth Manduca sexta.

Octopod (Octo) is a mutation of the moth Manduca sexta, which transforms the first abdominal segment (A1) in the anterior direction. Mutant animals are characterized by the appearance of homeotic thoracic-like legs on A1. We exploited this mutation to determine what rules might be used in specifying the fates of sensory neurons located on the body surface of larval Manduca. Mechanical stimulation of homeotic leg sensilla did not cause reflexive movements of the homeotic legs, but elicited responses similar to those observed following stimulation of ventral A1 body wall hairs. Intracellular recordings demonstrated that several of the motoneurons in the A1 ganglion received inputs from the homeotic sensory hairs. The responses of these motoneurons to stimulation of homeotic sensilla resembled their responses to stimulation of ventral body wall sensilla. Cobalt fills revealed that the mutation transformed the segmental projection pattern of only the sensory neurons located on the ventral surface of A1, resulting in a greater number with intersegmental projection patterns typical of sensory neurons found on the thoracic body wall. Many of the sensory neurons on the homeotic legs had intersegmental projection patterns typical of abdominal sensory neurons: an anteriorly directed projection terminating in the third thoracic ganglion (T3). Once this projection reached T3, however, it mimicked the projections of the thoracic leg sensory neurons. These results demonstrate that the same rules are not used in the establishment of the intersegmental and leg-specific projection patterns. Segmental identity influences the intersegmental projection pattern of the sensory neurons of Manduca, whereas the leg-specific projections are consistent with a role for positional information in determining their pattern.

Animals↗

PubMed1996

Connectional specification of regenerating entorhinal projection neuron classes cannot be overridden by altered target availability in postnatal organotypic slice co-culture.

Layer II neurons of the entorhinal cortex project to the dentate gyrus and field CA3 and also send collaterals to the subiculum; layer III neurons project to the subiculum and field CA1, but not to the dentate gyrus; and layer IV neurons project to the perirhinal cortex. We have previously shown that these specific differences between the projections of the layer II and III neurons are maintained and can regenerate in organotypic slice culture. In the present experiments we have confronted Postnatal Day 7 (P7) rat entorhinal cortex with P7 tissue selected from restricted parts of the overall entorhinal projection field. (1) When entorhinal slices were co-cultured with target slices containing only dentate gyrus, extracellular uptake of biotin dextran from crystals placed on the dentate gyrus retrogradely labeled neurons in layer II, and those of layer III were not labeled. (2) When entorhinal slices were co-cultured with target slices that contained only the subiculum and the hippocampal field CA1 (but not dentate gyrus), neurons in both layers II and III of the entorhinal area were labeled. (3) When entorhinal slices were co-cultured with target slices containing the perirhinal area and no hippocampal or dentate tissue, the neurons of entorhinal layer IV were labeled, but (4) when co-cultured with control target slices taken from the rostral parietal neocortex, no entorhinal neurons were labeled. Thus the exclusive relationship of layer II entorhinal neurons to the dentate gyrus has already been established by 1 week of age and is maintained by the regenerating entorhinal axons. Layer III entorhinal neurons cannot be induced to project to the dentate gyrus even when deprived of their own target, and layer IV neurons are specified to project to the perirhinal area and will not project to any part of the hippocampal complex or to the rostral parietal cortex. Thus, deprivation of the normal target tissue and presentation of an incorrect target tissue (even when it is the correct target for one of the other classes of entorhinal neurons) are not sufficient to override the specificity of the entorhinal projection neurons.

Age Factors↗

PubMed1996

Axotomy affects the retrograde labeling of cervical and lumbar-cord-projecting rubrospinal neurons differently.

The effect of axotomy at cervical and lumbar spinal levels upon the ability of rubrospinal neurons to retrogradely transport tracer was compared. Unilateral rubrospinal tractotomy was performed first at C5 and, after a few days, at C2 vertebral levels. Different retrograde tracers were applied at the lesioned sites right after tractotomy. Tracer applied at C5 labeled both cervical and lumbar-cord-projecting neurons. Tracer applied at C2 also labeled both groups of neurons if performed 2 days after that at C5; however, only cervical-cord-projecting neurons were labeled when it was performed 3 or 5 days after that at C5. In another set of experiments, a T10 tractotomy without tracer application was performed 2 or 5 days prior to the C5/C2, series of tract lesions. When preceded by a T10 lesion 2 days in advance, tracer applied at C5 labeled both cervical and lumbar-cord-projecting neurons. However, a T10 lesion 5 days in advance resulted in the labeling of only cervical-cord-projecting neurons by the tracer applied at C5. In either case, tracer applied at C2 consistently labeled only cervical-cord-projecting neurons, irrespective of the intervals-2, 3, or 5 days-allowed between C5 and C2 lesions. Most neurons labeled from C2 were also double-labeled by the tracer applied at C5. Thus, unlike lumbar-cord-projecting counterparts, cervical-cord-projecting rubrospinal neurons retain the ability to uptake and/or transport retrograde tracer several days following axotomy. This implies that cervical-cord-projecting rubrospinal neurons survive in a different functional state from their lumbar-cord-projecting counterparts following axonal injury.

Animals↗

PubMed1982

Location and vestibular responses of interstitial and midbrain reticular neurons that project to the vestibular nuclei in the cat.

Experiments were performed on cats anesthetized with alpha chloralose to locate neurons in and around the interstitial nucleus of Cajal (INC) that project to the vestibular nuclei, and to study labyrinthine inputs to these neurons. Neurons that project to the vestibular nuclei were identified by microstimulation confined to the vestibular nuclei on both sides. All neurons thus identified were activated antidromically from the ipsilateral (but not contralateral) vestibular nuclei. Vestibular projecting neurons were found in the INC and the reticular formation rostral, dorsal and caudal to the INC. About 23% of these neurons were vestibular branching spinal projecting neurons. The median conduction velocity of vestibular projecting neurons was estimated to be in the neighborhood of 12-16 m/s. Stimulation of the contralateral vestibular nerve evoked firing in 29% of neurons projecting to the vestibular nuclei, but not to the spinal cord. Interstitial neurons responded more frequently than reticular neurons (45% vs 11% chi 2 test, p less than 0.001). By stimulation of individual semicircular canal nerves, it was shown that vestibular projecting neurons receive excitation from the contralateral vertical canals, but do not receive substantial inputs from the horizontal canal. Stimulation of the ipsilateral vestibular nerve excited 10% of neurons; suppression of activity was observed for six cells and four of the six were excited by stimulation of the contralateral vestibular nerve. Stimulation of ipsilateral individual semicircular canal nerve did not excite any cells tested; the activity of a few cells was suppressed by stimulation of the vertical canal nerves. One neuron received excitation from the contralateral anterior canal and suppression from the ipsilateral posterior canal. Vestibular branching spinal projecting neurons rarely received labyrinthine inputs as already reported (Fukushima et al. 1980a). These results suggested that vestibular projecting neurons may be involved in vertical vestibular reflexes.U

Action Potentials↗

PubMed1986

Cholinergic and non-cholinergic projections from the canine pontomesencephalic tegmentum (Ch5 area) to the caudal intralaminar thalamic nuclei.

The distribution and morphology of cholinergic and non-cholinergic neurons projecting to the caudal intralaminar thalamic nuclei from the Ch5 area in the dog were examined using a technique combining horseradish peroxidase (HRP) retrograde labeling with choline acetyltransferase (ChAT) immunocytochemistry. After processing for ChAT, cholinergic neurons were found primarily within the nucleus tegmenti pedunculopontinus (PPN) and the central tegmental tract (ctt). ChAT positive neurons were also located in the nucleus cuneiformis and among the fibers of the lateral lemniscus and medial longitudinal fasciculus. On the basis of immunocytochemical and cytoarchitectonic data, PPN was divided into two distinct cell groups - a compact cell group located dorsolateral to the brachium conjunctivum and a diffuse cell group intermingled among the fibers of the brachium conjunctivum. Tissue processed for WGA-HRP and ChAT following injections of lectin-conjugated horseradish peroxidase into either the centrum medianum (CM) or parafascicular (Pf) nucleus resulted in double labeled cholinergic projection neurons in both PPN and ctt. Injections which involved CM and the caudal part of the central lateral thalamic nucleus (CL) resulted in more retrogradely labeled neurons than did those injections involving Pf. Injections of CM and CL also resulted in more double labeled cells in the dorsolateral compact portion of PPN than did injections confined to Pf. In all cases a small number of cholinergic neurons located in the contralateral PPN were retrogradely labeled as well. A substantial number of retrogradely labeled neurons were not ChAT positive, and in some cases, comprised up to 27% of the total population of projection neurons. Measurements of cell soma areas indicated that cells comprising the general cholinergic population were mostly medium (300-600 micrograms2) or large (greater than 600 micrograms2) in size. The majority of cholinergic projection neurons fell within the medium size category while the noncholinergic projection neurons were significantly smaller than their cholinergic counterparts. The results of this study suggest that in the dog, Ch5 cholinergic neurons which project to the caudal intralaminar thalamic nuclei are medium in size and are located primarily within PPN and ctt. In addition, a parallel projection to the caudal intralaminar nuclei exists which originates from smaller, non-cholinergic neurons in these same regions. Based on the results of this study, it appears that cholinergic projections to intralaminar thalamic nuclei which in turn project to the neostriatum may be one of the pathways over which PPN can affect basal ganglia activity.

Animals↗

PubMed1980

Low threshold afferent projections from the oral cavity and the face to the cerebral cortex of the cat.

The projections of low threshold afferents from the oral cavity and the face to the cerebral cortex of cats anaesthetized with chloralose were investigated. The projection fields of the ipsi- and contralateral lingual, inferior alveolar, mental, superior alveolar, infraorbital, (separate branches from whiskers and nose), ophthalmic, great auricular and the contralateral superficial radial nerves were localized. Surface potentials of short latency and maximal amplitude were recorded and their location traced on photographs of the rostral part of the right cerebral hemisphere. Reference points were indicated with india ink punctures. The extent of the cytoarchitectonic areas was determined on histological serial sections and the borders transferred to the photographs of the hemisphere. The features of the projections were related to the cytoarchitecture and to the pattern of the gyri and sulci. It was observed that the low threshold afferents from the oral cavity and the face projected via fast conducting, presumably three synaptic paths, to separate locations in areas 3a, 3b, 5a and 6a beta. The projections to area 3b were somatotopically organized starting with the auricular and the ophthalmic nerve projections lateral to the 3b projection of the forelimb in the posterior sigmoid gyrus and continuing with the maxillary nose, maxillary whiskers, mental nerve, superior alveolar, inferior alveolar and lingual nerve fields along the coronal gyrus towards the presylvian sulcus. The somatotopy was, however, not isomorphic with the body surface but displayed consecutive, overlapping bands across area 3b. The projections to area 3a were similarly organized. The somatotopy was less obvious in area 5a and 6a beta. Convergent projections with responses of slightly longer latency were observed in area 43 (gyrus orbitalis).

Afferent Pathways↗

PubMed1982

Spino-olivary projections from the upper cervical spinal cord: an experimental study using autoradiography and horseradish peroxidase.

Spino-olivary projections from segments C1 and C2 were examined in 17 cats using autoradiographic methods and in nine cats using the method of retrograde horseradish peroxidase (HRP) transport. Injections of 3H-leucine at the junction of the C1-C2 segments produced anterograde terminal labelling in two regions of the contralateral inferior olive, one in the rostromedial half of the dorsal accessory olive (DAO), the other in the caudal half of the medial accessory olive (MAO). Projections to the rostromedial DAO were best demonstrated when tracer labelled the ventromedial part of the dorsal horn, while projections to the caudal MAO were strongly labelled by injections in both the lateral and medial parts of the intermediate grey matter. Injections of HRP into the region of the inferior olive led to retrograde marking of cells in both regions of the contralateral spinal cord implicated by autoradiographic studies to have spino-olivary projections. Dense groupings of small rounded or fusiform cells were labelled contralaterally on the medial aspect of the dorsal horn in C1 and C2, while medium-sized multipolar cells were more sparsely distributed throughout intermediate laminae of C1-C5. Olivary projections from dorsal column nuclei were also examined and compared to those of spino-olivary projections. Injections of 3H-leucine into n. gracilis and cuneatus led to terminal labelling in three olivary regions, including the rostral DAO, the caudo-lateral DAO and the caudal MAO. Projections from the DCN to the rostral DAO and the caudal MAO overlapped with regions of projection from upper cervical segments although the territories occupied by DCN and upper cervical projections were not identical. Amino acid injections which were confined to n. cuneatus gave rise to terminal labelling in only the rostromedial DAO.

Afferent Pathways↗

PubMed1988

Organization of feedback and feedforward projections of the barrel cortex: a PHA-L study in the mouse.

In order to analyze the organization of the efferent projections of single barrel columns (BC, i.e. a barrel in layer IV of parietal cortex plus the cortical tissue above and below it), we made small iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin in the barrel cortex of 20 adult mice. On the basis of reconstructions of the sites of terminal labelling, the brain regions receiving projections from the barrel cortex could be identified and classified in five groups. Each group is characterized by the topography of the distribution of efferents arising from a single BC. The projections to the trigeminal sensory complex are point to point: i.e. one BC projects only to the site of termination of the primary sensory neurons innervating the corresponding whisker follicle. In the ventrobasal thalamic nucleus BC projections are not restricted to the corresponding barreloid; instead they contract parts of barreloids belonging to one arc. In the reticular and posterior thalamic nuclei the projections from a row of BC's converge to a collective termination site, whereas in the superior colliculus the projections from an arc of BC's converge to a common termination site. There is a complete overlap of BC projections in restricted zones within SII, motor cortex, perirhinal cortex, contralateral barrelfield, caudoputamen and pons. The organization of the efferents from the barrel cortex demonstrates a contrast between feedback and feedforward projections from this important area of neocortex.

Animals↗

PubMed1988

The projection from superior colliculus to cuneiform area in the rat. I. Anatomical studies.

Although the ipsilateral descending pathway is a major output projection of the superior colliculus, little is known of its functions. We therefore carried out two studies to investigate in rats the part of the ipsilateral projection that terminates in an area ventral to the inferior colliculus, referred to as the cuneiform nucleus. The first study, described here, used orthograde and retrograde tract-tracing techniques to locate the cells of origin and precise region of termination of the tectocuneiform pathway. The main findings were as follows. Injections of WGA-HRP into the superior colliculus gave terminal label in the cuneiform nucleus and also in surrounding structures which included central grey, the midbrain tegmentum bordering the parabigeminal nucleus, and the external nucleus of the inferior colliculus. As well as the strong ipsilateral projection, there was a much weaker contralateral one which crossed the midline in the tectal commissure. Label in the cuneiform nucleus was heaviest after injections into the medial deep layers. However, no clear evidence was found for topography within the tectocuneiform projection: cuneiform label varied in intensity rather than pattern of distribution with variation in the collicular location of the injection site. Injections of retrograde tracers into the cuneiform are a labelled large numbers of collicular cells, which were distributed mainly in the deep and intermediate grey layers. In agreement with the data from orthograde tracing, the heaviest concentration of labelled cells was found in the medial deep layers. This concentration extended into the adjacent dorsolateral part of central grey. A similar distribution of labelled cells was seen after injections into the structures next to the cuneiform nucleus that also receive a tectal projection. Comparison of this distribution with that obtained from injections into other parts of the ipsilateral projection, including dorsolateral basilar pons, suggested that the projection to the cuneiform area may arise from a distinct set of collicular output cells. The projection from the superior colliculus to the cuneiform nucleus and immediately adjacent areas may therefore be also functionally distinct, mediating a particular kind of tectally-elicited response. The lack of clear topography in the projection suggests that this response may not have precise spatial direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1998

Zonal organization of cortico-nuclear and nucleo-cortical projections of the paramedian lobule of the cat cerebellum. 1. the C1 zone.

The cortico-nuclear (C-N) and nucleo-cortical (N-C) projections of the C1 cortical zone in pars anterior (pa) and pars copularis (pc) of the paramedian lobule (PML) in the posterior lobe of the cat cerebellum were investigated with a combined electrophysiological and neuroanatomical technique. In each experiment the mediolateral boundaries of the zone were located on the cortical surface by recording field potentials mediated via climbing fibres and evoked in the zone by activity elicited in spino-olivocerebellar paths through percutaneous stimulation of fore- and hindlimbs; a small (15-30 nl) injection of WGA-HRP was then made into the zone. The distributions in the deep cerebellar nuclei were determined (with light microscopy) both for terminal labelling due to anterograde axonal transport by Purkinje cells and for cell bodies labelled due to retrograde transport in N-C axons. The extent to which injection sites were confined to the C1 zone was assessed both by comparing injection site and zone widths and by determining the distributions of retrogradely labelled neurones within the contralateral inferior olive. The C-N projection from the part of the zone in PML pa (a forelimb part) terminates almost exclusively (perhaps exclusively) in nucleus interpositus anterior (NIA), primarily in caudal and dorsal parts, where it overlaps heavily with the C-N projections from the lobule V parts (also forelimb parts) of the C1 and C3 zones as previously defined. The C-N projection from the part of the zone in PML pc (a hindlimb part) also terminates virtually exclusively in NIA but primarily in almost all parts of the medial third of the nucleus. There is, nevertheless, sufficient overlap between the PML pa and PML pc projections that approximately one third of the termination territory of each projection overlaps that of the other. The PML pc part of the zone is almost entirely lacking in a N-C projection, as previously found for the lobule V part of the C1 zone (and C3 zone). However, the PML pa part of the zone receives N-C projections that arise, in descending order of size, from nucleus interpositus posterior (NIP), from NIA, from the NIA/nucleus lateralis (NL) fusion area and (perhaps) NL. The projection from NIP is similar in size to that provided by the nucleus to the C2 zone in lobule V of the anterior lobe. The findings are discussed, with particular emphasis on their implications for the hypothesis that the cerebellum is divisible into a number of olivo-cortico-nuclear complexes or compartments.

Animals↗

PubMed1997

Perikaryal projections of developing spinal ganglion neurons in the chick demonstrated by scanning electron microscopy.

The perikaryal projections of sensory ganglion neurons in chick embryos were observed by scanning electron microscopy after removal of the connective tissues and satellite cells by enzymatic digestion treatment. The perikaryal projections were seen not only on the surface of the perikarya but also on the surface of the stem processes. The projections were up to 3 microm in length, and their transverse diameters ranged between 0.12 and 0.24 microm from incubation (embryonic) day 10 to posthatching day 2. On days 6 and 8 of incubation, thicker projections with transverse diameters of 0.24-0.9 microm were observed transiently in addition to those described above, and some of them looked like vestiges of neuronal processes during development. The thin projections emerging mainly in the later developmental stages increased in number as spindle-shaped bipolar neurons differentiated into (pseudo)unipolar cells. Morphometric analysis revealed that the density of perikaryal projections correlated well with the shape and size of each neuron; thin perikaryal projections were more numerous on those of mature pseudounipolar neurons than on the surface of premature ganglion neurons, and they increased in number as the individual ganglion cell bodies grew larger. The neuronal shape- and size-dependent increase in perikaryal projections during development may support the hypothesis that perikaryal projections are structural devices for increasing neuronal surface areas and possibly the efficiency of metabolic activities.

Animals↗

PubMed2002

The pore of the leaf cavity of Azolla species: teat cell differentiation and cell wall projections.

The differentiation of the specialized secretory teat cells of the leaf cavity pore of Azolla species was investigated at the ultrastructural level with emphasis on their peculiar cell wall projections. The results indicated that the projections are formed as soon as the teat cells complete their differentiation and that their production is principally associated with changes in endoplasmic reticulum profiles. The number of projections increases with the teat cell age and is stimulated under salt and P deficiency stresses. Salt stress also promotes their emergence on Azolla species that under normal conditions do not produce projections. Cytochemical tests on different Azolla species showed that the projection composition is almost identical: proteins, acidic polysaccharides, and pectin are always detected. This study revealed that Azolla teat cell projections differ fundamentally from other types of hitherto described cell wall projections that are considered as remnant structures from cell separation. In contrast, in Azolla teat cells projections are actively produced and compounds are excreted by an exocytotic mechanism. The possible role of the projections in the symbiosis of Azolla spp. with Anabaena azollae is discussed.

Cell Differentiation↗

PubMed1976

The cortical projections of the inferior pulvinar and adjacent lateral pulvinar in the rhesus monkey (Macaca mulatta): an autoradiographic study.

An autoradiographic technique was used to determine superior colliculus (SC) and pulvinar projections in the rhesus monkey. SC projects bilaterally to the inferior pulvinar (PI) while occipital cortex projects to PI and the lateral pulvinar (PL). PI has sustaining, topographical projections to layers IV, III and I of areas 18 and 19 (and VI and I of 17) which agrees with the central representation of the visual hemifield and suggests that there is more than one hemifield representation in prestriate cortex. PL adjacent to PI also projects to the same cortical areas and layers, while the portion of PL extending into the caudal pole of the pulvinar projects to layers IV, III and I of areas 20 and 21. Thus, occipital cortices are associated by cortico-thalamocortical connections and also receive direct lemniscal input via SC-PI and the dorsal lateral geniculate nucleus (DLG), while inferotemporal areas 20 and 21 receive only cortico-thalamocortical connections. It is concluded that Stoffels' principle of lamellation holds and, that one pulvinar subdivision projects to several cortical areas, that adjacent pulvinar subdivisions have overlapping projections to these cortical areas and their layers and that the pulvinar also projects to the same cortical area as DLG but to different layers. These connections are similar to those in lower mammals but not to those in the squirrel monkey and bushbaby.

Animals↗

PubMed1978

Cortical projections of the thalamic mediodorsal nucleus in the rabbit.

The cortical projection of the thalamic mediodorsal nuclear complex (MD) in the rabbit was mapped retrograde horseradish peroxidase and anterograde tritiated proline techniques. The projection field occupied the entire medial wall rostral to a mid corpus callosal level, wrapped around the frontal pole onto the lateral convexity and tailed off caudally on the dorsal bank of the rhinal sulcus. The projection of the lateral approximately one-half of MD, the half which does not receive olfactory input, was confined to medial cortex supply all but the most rostral region. This projection field of lateral MD was precisely organized in two dimensions with the most lateral part projecting most caudally and the most dorsal part projecting most ventrally. A representation for the third, anterior-posterior (A-P), dimension was not evident since any cortical point within the field was supplied by a cylinder of cells extending the entire A-P extent of lateral MD. The medial half of MD, which does receive olfactory input, projected to the remaining rostral medical cortex, the lateral convexity and rhinal sulcal region. The inverse dorsoventral relationship was partially preserved and on overlapping A-P gradient was present with sulcal projections originating more caudally in medial MD and the rostral medial projection originating more rostrally.

Animals↗

PubMed1980

Brain stem projections of the aortic nerve in the cat: a study using tetramethyl benzidine as the substrate for horseradish peroxidase.

The intra-axonal transport of horseradish peroxidase (HRP) has been used to trace the nodose ganglion and brain stem projections of a physiologically distinct nerve - the aortic depressor nerve - following electrophysiological identification. Tetramethyl benzidine (TMB) has been used as the substrate for demonstrating the centrally transported HRP15, 16. This sensitive method for horseradish peroxidase histochemistry has permitted the visualization of the central projections of aortic nerve afferents and has also provided information regarding the anatomical localization of cell bodies of these sensory nerve fibers within the nodose ganglion. This study demonstrates the usefulness of using TMB as a substrate for HRP histochemistry in anatomical studies where the detection of anterogradely transported HRP is an essential prerequisite. The uptake of HRP from the cut central ends of sensory nerve fibers and the transport of this enzyme to the sensory ganglion and subsequently into the central processes of these sensory neurons have made possible this study of the central projections of a functionally distinct peripheral nerve. Information has been provided by this study that cell bodies of aortic nerve afferent fibers are localized in the rostrolateral pole of the nodose ganglion. Dense central projections of sensory terminals of aortic afferents have been found in the dorsolateral and medial subdivisions of the nucleus of the tractus solitarius. These central projections of aortic afferents extend for 6 mm rostrocaudally in the medulla with the densest projection being found at the level of the obex. These projections are bilateral at all rostrocaudal levels. This anatomical demonstration of the dorsolateral and medial subdivisions of the nucleus of the tractus solitarius confirms earlier reports based on electrophysiological studies. Of particular interest in this study is the new observation that there exists a dense projection of aortic nerve afferents to the area postrema. The possible physiological implications of a direct input of peripheral chemoreceptor afferents to a region of central chemosensitivity are discussed. The complete absence of any retrogradely labeled cell body in the brain stem from exposure of the aortic nerve to horseradish peroxidase is noteworthy. This indicates that the aortic nerve is purely afferent in function and that reflex control of afferent activity in the aortic nerve is not mediated by brain stem neurons projecting down the same nerve.

Animals↗