Discrete Projection Research Articles

Organization of visual cortex in the mouse revealed by correlating callosal and striate-extrastriate connections

In this study, we have investigated the organization of mouse visual cortex by correlating in detail the distribution of striate-extrastriate projections with the pattern of callosal connections revealed by the transport of horseradish peroxidase from the contralateral hemisphere. Single injections of 3H-proline into striate cortex produce 8-9 discrete projection fields in the belt of cortex surrounding area 17. The number and arrangement of these fields closely resemble the pattern of extrastriate visual areas in the rat. The callosal pattern is also very similar to that in the rat, and provides a set of landmarks for the location of the striate-recipient zones. Thus, cortical regions containing dense aggregations of callosal cells and terminations surround totally or partially the sparsely callosal striate-recipient zones. By comparing our results with previous accounts of the rat visual plan, we were able to identify in lateral extrastriate cortex of the mouse areas anterolateral (AL), lateromedial (LM), laterointermediate (LI), laterolateral (LL), posterolateral (PL), and posterior (P). We also observed 1-2 projections fields into anteromedial (AM) extrastriate cortex, and one field (S) into the posteromedial border of the head representation in primary somatosensory cortex. Our results support the notions that the visual cortex in the mouse is subdivided into multiple visual areas, and that these areas are arranged according to a plan that is common in rodents.

Proton chemical-shift mapping using PREP

We report the first demonstration of spatial mapping of proton chemical shifts using a modified projection reconstruction/echo-planar hybrid technique (PREP) ( 1, 2). PREP is a fast chemical-shift imaging technique which allows the generation of a full three-dimensional data set (x-y-6) with Npoints in each of the spatial dimensions and L points in the chemical-shift dimension, from data gathered in Nseparate experiments. The technique uses a single rapidly switched magnetic field gradient and this imposes hardware requirements similar to those of standard echo-planar imaging (EPI) (3). It therefore offers a compromise between the rapid echo-planar shift mapping technique (EPSM) ( I, 4) which can produce a three-dimensional data set in a single experiment and the standard 3DFT technique (5). 3DFT imposes lesser hardware requirements but requires the execution of N X N or N X L experiments for the generation of an N X N X L data array. The timing sequence of the PREP technique is shown in Fig. 1. This was slightly altered by the addition of a nonselective 180” pulse and an r-gradient prepulse of duration 7p in order to ensure that all spins regardless of spatial position or chemicalshift value are in phase when sampling begins at time 7 T/ 2. After slice selection a rapidly switched field gradient G,, with period 47, is applied in the direction r . This produces a signal S(t) comprising a series of echoes with peaks occurring at times 27, 47, etc., after slice selection. These are progressively affected by dephasing due to chemical-shift differences in the sample. As in standard double EPI (3), data processing requires the formation of a set of echoes which evolve in a purely positive (S+(t)) or purely negative gradient (S-(t)). This is accomplished by appropriately splicing together the signals from two experiments each with opposite starting phases of G,, as shown in Fig. 1. Fourier transformation of this spliced signal yields a discrete stick spectrum projection profile of the object which, for a common chemical-shift species, has equally spaced sticks. However, when other chemical species are present, the sticks in appro-

Topographic organization of the central projections of the spiral ganglion in cats

The morphological organization of inputs from restricted sectors of the cat cochlear spiral ganglion into the cochlear nucleus was studied by making focal extracellular injections of horseradish peroxidase (HRP) into the spiral ganglion. Injections resulted in Golgi-like labeling of a small cluster of spiral ganglion cells and their peripheral and central axons. Large injections involved most of the cells within Rosenthal's canal in sectors of the spiral ganglion innervating greater than or equal to 1 mm of the basilar membrane and resulted in narrow, complete laminae of labeled axons and preterminal fields within each cochlear nucleus subdivision. The positions of these bands were consistent with the "isofrequency laminae" appropriate for the frequencies represented at the injection sites, with high frequency laminae situated more dorsally, and lower frequencies progressively more ventral. A discrete projection to the small cell cap area was observed that was discontinuous with the main projection laminae in the ventral cochlear nuclei (VCN). In the dorsal cochlear nucleus, projecting fibers and terminals were excluded from the molecular cell layer. No labeled fibers entered the granule cell areas. In contrast to larger injections, very small HRP deposits labeled only part of an isofrequency lamina. Specifically, injections restricted to the scala tympani aspect of the spiral ganglion labeled only the lateral part of VCN isofrequency laminae, whereas injections limited to the scala vestibuli aspect of the ganglion labeled the medial aspect of the isofrequency planes. Thus these data indicate a previously unrecognized topographic representation of the vertical dimension of the spiral ganglion across VCN isofrequency laminae. Some possible functional implications of this projection organization are discussed.

Descending projections from the superior olivary complex to the cochlear nucleus of the cat.

Subdivisions of the cochlear nuclear complex give rise to a number of discrete projections to certain cell groups of the superior olivary complex and also received substantial descending projections from the periolivary nuclei. In the present study, we sought to determine by means of retrograde transport of horseradish peroxidase (HRP), and anterograde transport of radiolabeled protein, if the periolivary nuclei give rise to discrete projections to the various subdivisions of the cochlear nuclear complex. Following medium to large injections of HRP into the cochlear nucleus, irrespective of location, labeled cells were found in all periolivary nuclei bilaterally. In every case more than 40% of the labeled cells were found in the lateral nucleus of the trapezoid body on the same side and the ventral nucleus of the trapezoid body of both sides. Other periolivary nuclei contributing more than 5% of the total number of cells in individual cases were the contralateral lateral nucleus of the trapezoid body and the ipsilateral anterolateral and dorsal periolivary nuclei. Injections of tritiated leucine into periolivary nuclei gave rise to axonal labeling to the trapezoid body and the dorsal acoustic stria, usually bilaterally, and to terminal labeling that was widely distributed within the cochlear nuclear complex. In several cases with small injections, particularly in the lateral nucleus of the trapezoid body, the projections from the periolivary nuclei to the anteroventral and dorsal cochlear nuclei connected areas described as having similar best-frequency representation. The autoradiographic data corroborated the main results from the HRP experiments and provided additional information permitting these conclusions: the projections from the periolivary nuclei to the cochlear nuclear complex are organized tonotopically, at least in part; each periolivary nucleus (and perhaps individual cells), projects widely throughout the cochlear nuclear complex; the pattern of termination of projections from different periolivary nuclei to a given region of the cochlear nuclear complex are similar, as seen in autoradiograms, and the lateral and dorsal periolivary nuclei project mainly ipsilaterally, while the medial periolivary nuclei project bilaterally with a contralateral bias. The magnitude of these projections and their widespread distribution within the cochlear nuclear complex would suggest an important role for the descending projections in the normal functioning of the cochlear nucleus.

Functional interdependence of discrete vagal projections to SA and AV nodes.

Dynamic modulation of chronotropic and dromotropic function was evaluated in anesthetized dogs before and after selective parasympathectomy of the atrioventricular (AV) node. Vagal and cardiac sympathetic efferent nerves were decentralized, and the distal cut ends of the cervical vagi were stimulated at frequencies from 1 to 25 Hz with step-wise voltage changes. To investigate parasympathetic modulation of AV conduction, stimulations were performed with and without atrial pacing. After determination of chronotropic and dromotropic responses, in the intact state, selective AV node parasympathectomy was performed as previously described [Am. J. Physiol. 248 (Heart Circ. Physiol. 17): H61-H68, 1985]. Stimulation protocols were then repeated. Control results in intact animals reveal a parallel and finely balanced vagal regulation of chronotropic and dromotropic responses over a wide range of frequency stimulations. Conversely, selective parasympathectomy of the AV node interrupts extrinsic vagal modulation of AV conduction without affecting parasympathetic control of chronotropic function. The dynamic balance of chronotropic and dromotropic function, modulated by extrinsic vagal input, reflects the parallel activation of functionally and anatomically distinct parasympathetic projections to the sinoatrial (SA) and AV nodal tissue. Thus present experiments allow a more detailed examination of vagal innervation of the SA and AV nodes, the importance of their balance through neuroregulation, and progress toward understanding the pathophysiology of disturbances to this balance.

Oral and facial representation in the trigeminal principal and rostral spinal nuclei of the cat.

Transganglionic transport of horseradish peroxidase (HRP) was used to study the patterns of termination of somatic afferent fibers innervating oral and facial structures within the principal nucleus (Vp), nucleus oralis (Vo), and nucleus interpolaris (Vi). The primary trigeminal afferent fibers that innervate the oral cavity supplied by the pterygopalatine, superior alveolar, lingual, buccal, and inferior alveolar branches, as well as the facial skin supplied by the frontal, corneal, zygomatic, infraorbital, auriculotemporal, mylohyoid, and mental branches, were traced in this experiment. The results show that trigeminal afferent nerves that innervate the oral cavity project mainly to the principal nucleus, the rostrodorsomedial part (Vo.r) and dorsomedial division (Vo.dm) of pars oralis, and the dorsomedial region of pars interpolaris, while an extensive overlap of projections is found in the Vo.r, Vo.dm, and rostral Vi. The central processes of fibers innervating the anterior face (i.e., mental, infraorbital, and frontal nerves) terminate in the ventral division of principalis (Vpv), caudal region pars oralis (Vo.c), and ventrolateral Vi, with the largest numbers of terminals being found in the Vpv and Vi. In contrast, the central projection patterns of the corneal, zygomatic, mylohyoid, and auriculotemporal afferents are different from those of other afferent nerves examined, and present a discrete projection to the trigeminal sensory nuclear complex (TSNC). The corneal, mylohyoid, and auriculotemporal afferents mainly project to the restricted regions of principalis and caudal Vi, while zygomatic afferent nerve fibers project to the caudal third of pars interpolaris. The typical somatotopic organization with the face of the mouth open inverted is represented in the rostrocaudal midlevels of the Vpv and caudal pars interpolaris. The Vpd receives topographical projection from primary afferent nerves that innervate the oral structure only, while this projection was organized in a complicated manner. The relationship between the functional segregation and the cytoarchitectonic differentiation of the TSNC is discussed, particularly with respect to this somatotopic organization, combined with the characteristics of projecting cells in the TSNC.

Positron emission tomography: Use of short-lived radionuclides for neurological research

Positron emission tomography (PET) measures the temporal and spatial distributions of short-lived positron emitting nuclides within the human body. Positron annihilation radiation is detected by rings of discrete scintillators surrounding the body. Images (128 × 128 pixels) of the radioactivity distributions are reconstructed from the discrete ray projections of the detected coincident photons. Each pixel is fit to a mathematical model that represents a physiological process such as blood flow or metabolism to create a new three parameter functional or parametric image.

Forebrain origins and terminations of the medial forebrain bundle metabolically activated by rewarding stimulation or by reward-blocking doses of pimozide

Using [14C]-2-deoxyglucose autoradiography, we determined which forebrain and diencephalic areas showed metabolic alterations in response to unilateral electrical stimulation of the posterior medial forebrain bundle at parameters chosen to produce a just-submaximal rewarding effect. At these parameters, only a few areas were activated. There was no detectable activation anterior or dorsal to the genu of the corpus callosum. Just anterior to the anterior commissure, there was strong activation of the vertical limb of the diagonal band of Broca, with a focus in the nucleus of the diagonal band. Just posterior to the anterior commissure, there was strong activation of compartment "c" of the medial forebrain bundle (MFB), with weaker activation of the bed nucleus of the stria terminalis and the medial preoptic area. At midhypothalamic levels, the dorsolateral, dorsomedial, and ventral MFB all showed activation. There was bilateral suppression of activity in the lateral habenula. Activation appeared to end in the anterior ventral tegmental area of Tsai. Reward-blocking doses of the neuroleptic pimozide activated the caudate and the lateral habenula but did not alter any of the unilateral effects of stimulation. Using longer pulse durations and/or shifting the site of stimulation to the substantia nigra activated many of the systems not activated in the first experiment, including all of the major dopaminergic projection systems, proving the capacity of the technique to reveal activation of these systems. The results permit one to define a discrete projection system that merits electrophysiological investigation as a likely substrate for the rewarding effect of MFB stimulation. They also suggest that dopaminergic projection systems may not form part of the reward pathway itself.

Descending projections to the cervical spinal cord in the developing kitten

The distribution of neurons filled by retrograde axonal transport of horseradish peroxidase from the cervical enlargement is described in kittens prior to and following the time of appearance of mature α-motoneuron responses to motor cortical stimulation (at 107–111 days gestational age; about 41 days postnatally). Cortex and brainstem reconstructions of the distributions of filled neurons demonstrate a well-defined, discrete projection from cortical area 4 to spinal cord segments C3 to C8, both in mature and immature (20 and 24 days postnatal) animals. In addition, appropriate rubrospinal, reticulospinal and vestibulospinal projections were present at all ages studied.

Compact Derivations on Von Neumann Algebras

AbstractIf is a von Neumann algebra that thas no nonzero finite discrete central projection, then there is no nontrivial compact derivation of into itself.

Brain stem nuclei giving fibers to lobules VI and VII of the cerebellar vermis

The HRP method has been used to identify all the brain stem nuclei, which may project to lobule VI and/or VII of the posterior cerebellar vermis. Three tentative degrees of labeling of the different structures have been assigned: 'massive', 'clear' and 'discrete'. (1) Massive projections have been found to reach lobule VI and VII from the inferior olive and lobule VII only from the nucleus reticularis tegmenti pontis. (2) Clear projections have been found to reach lobule VI only from the pontine nuclei, the nucleus reticularis tegmenti pontis, the nucleus reticularis lateralis and the reticularis paramedianus; lobule VII only from the raphe nuclei, and both VI and VII from the perihypoglossal and vestibular nuclei. (3) Discrete projections have been found to reach lobule VI and VII from the deep cerebellar nuclei; lobule VI only from the nucleus tracti solitarii and nucleus cuneatus externus; lobule VII only from the nucleus lemnisci lateralis pars ventralis, the nuclei parabrachiales and the nucleus subcoeruleus.

Two types of presynaptic configurations in insect central synapses: An ultrastructural analysis

Two structurally distinct types of synapses have been identified in the cockroach metathoracic ganglion. The two synaptic types are distinguished on the basis of (a) the shape and position of the presynaptic density seen by serial thin sectioning and (b) the arrangement and location of vesicle attachment sites (VAS) on the presynaptic membrane obtained from replicas of aldehyde-fixed, freeze-fractured neuropile. Bar-type synapses in thin sections possess a long presynaptic density located in a trough or groove opposite the extracellular space between two contiguous postsynaptic processes. In freeze-fracture, this trough is flanked by two rows of vesicle attachment sites. The second synaptic conformation consists of rows of discrete dense projections located on the convexities of the presynaptic membrane, i.e., directly opposite a single postsynaptic process. This conformation has been correlated with groups of VAS linearly arranged also on the convexities of the presynaptic membrane. These structurally different synapses may represent functionally different contacts within the insect ganglion.

Tomosynthesis-3-D X-ray Imaging by Means of Holography or Electronics

Tomography is a well-established X-ray technique for imaging a medical object in its three dimensions by generating images of certain layers. This process, however, suffers from the disadvantage that only a single tomogram is produced at each exposure run. Tomosynthesis overcomes this restriction by using a set of discrete projection images to synthesize layers of arbitrary depth and of arbitrary number. This means that the object can be completely displayed with only one tomographic exposure run, thus saving time and dosage. After a brief description of the basic principle much attention will be devoted to the implementation of tomosynthesis. The reconstruction process has been experimentally realized by holography as well as by analogue video electronics. Implementation by digital electronics is also discussed. The strengths and weaknesses of the various techniques will be examined.

Tonotopic organization in the avian telencephalon

The mammalian and avian auditory pathways have distinctly homologous cell groupings. Tonotopic organization has been demonstrated by means of single unit recordings in the cochlear nuclei of both birds and mammals. The avian thalamic nucleus ovoidalis, the homolog of the mammalian medial geniculate body, has a discrete projection to an area of the telencephalic neostriatum caudale, field L (see ref. 6, 17). Although the primary projection of the ascending auditory pathway to the telencephalon of mammals has been shown to have a tonotopic organization, single unit recordings from neither field L of the ring dove nor that of the starling have produced evidence for a tonotopic organization of individual neurons of the avian telencephalon. The absence of tonotopic organization in field L of birds would appear to underscore the dissimilarities between the gross characteristics of field Land primary auditory cortex. We wish to report, however, an initial set of experiments using single unit recordings in a song bird, the zebra finch, which define a point-by-point projection from the avian cochlea to the auditory area of the telencephalon, the first such demonstration in a sensory pathway of an infra-mammalian vertebrate.

The morphological categorization of developing synaptic junctions.

The molecular layer of rat occipital cortex was studied at a number of ages throughout postnatal development in an attempt to a formulate a quantitative morphogenetic scheme of synaptic development. As previous work had pointed to the potential usefulness of E-PTA stained material in synaptogenic studies, this technique was employed. Synaptic junctions were assigned to five categories, A-E, on the basis of variations in the organization of their presynaptic densities. Of these categories, Type A represented a mature junctional form with well-defined and discrete dense projections. Type E, by contrast, represented the immature end of the spectrum, its presynaptic apposition generally lacking recognizable densities. Types B-D represented intermediate forms. As development proceeded, the percentage of A type junctions increased from 0.3% at 7 days to 25% in the adult. Type E junctions showed the opposite trend falling from 42% at 7 days to 5% in the adult. On the basis of these results, and those relating to types B-D, possible morphogenetic schemes involving the five synaptic categories are put forward. These schemes incorporate and extend those previously suggested by other workers. By placing observations on a quantitative footing, the schemes proposed here lend themselves to use in experimental investigations.

The fine structure of the microconidium of Blastomyces dermatitidis.

Aspects of the fine structure of the microconidium of the mycelial phase of the dimorphic fungal pathogenBlastomyces dermatitidis as seen by techniques of scanning and transmission electron microscopy are described and illustrated by electron micrographs. The conidia ofB. dermatitidis undergo changes in the ultrastructural appearance of the cell wall as the spore matures. The cell wall becomes irregular in its thickness and possesses two distinct layers. No discrete or unique surface spines or projections were evident when the conidium ofB. dermatitidis was viewed by scanning electron microscopy. Upon maturity there is a marked deposition of lipid material in large, multiple storage bodies which occupy much of the cytoplasmic area. However, the cytoplasmic organelles appear to retain their structural integrity.

Projections to the cat's cerebral cortex from low threshold joint afferents.

AbstractThe projections to the cerebral cortex from the contralateral low threshold afferents of the musculocutaneous branch to the elbow joint (Ejt) and the posterior knee joint nerve (Kjt) were investigated in cats anesthetized with chloralose. Graded electrical stimulation of the nerves was used to evoke the cortical potentials. Three discrete joint projection areas were found in the cytoarchitectonic area 3 of the posterior sigmoid gyrus, i.e. one Ejt and two Kjt loci. These loci overlapped with the projections from group I muscle afferents. One Ejt and one or two Kjt loci were observed in positions corresponding to cytoarchitectonic areas 1 and 2. They did not receive input from group I muscle afferents. A separate locus with overlap between forelimb joint and muscle afferents was located in area 4 y. Components 1 and II of the joint nerve volley evoked short latency potentials in all cortical loci. Low threshold cutaneous afferents evoked responses in all joint loci. The spinal course of the ascending Ejt path was mainly located in the dorsal column. Kjt component I afferents travelled mainly in the dorsal columns and component I and II afferents in the dorsolateral fascicle. The Kjt path in the dorsolateral fascicle ascended uncrossed to the level of Ci.

Anatomical evidence for cortical subdivisions based on vertically discrete thalamic projections from the ventral posterior nucleus to cortical barrels in the rat

Anatomical evidence for cortical subdivisions based on vertically discrete thalamic projections from the ventral posterior nucleus to cortical barrels in the rat

Efferent projections of the superior colliculus in the opossum.

AbstractThe Fink and Heimer technique was used to study the ascending and descending fiber degenerations resulting from unilateral electrolytic lesions in the superior colliculus of sixteen adult opossums. The ascending fiber degeneration left the colliculus by way of a small parabrachial bundle or with the brachium of the superior colliculus. The former bundle contributed degenerating terminals to the suprageniculate, parabrachial, and magnocellular medial geniculate nuclei and appeared to terminate in the lateral terminal nucleus of Hayhow (Hayhow, '66). The latter bundle contributed fibers to the pretectal and posterolateral nuclei as well as discrete projections to the ventral lateral geniculate nucleus and ventral thalamus.Descending degenerating fibers in the brainstem were destributed along three tracts: (1) a medial predorsal bundle, (2) an intermediate tectoreticular, and (3) a lateral tectopontine. These tracts were seen to terminate mainly in tegmental and reticular centers as well as in the lateral basilar nucleus of the pons. Degenerating fibers of the predorsal bundle were followed to lower medullary levels but could not be traced to spinal levels.The present findings are descussed in relation to data reported for more developed mammalian species.

Projections from the medial geniculate body to the cerebral cortex in the cat

Stereotaxic lesions made in the MGB lead to the finding of Nauta-stained degeneration in the anterior, middle and posterior ectosylvian gyri, i.e., areas AI, AII, Ea, Ep, SF and I-T. Degeneration was not found in SII except in 2 brains in which the ventrobasal complex was probably involved in the lesion. There was no significant projection from the MGB to the marginal gyrus, suprasylvian gyrus or precuciate gyrus. Small lesions in MGB produced continous distributions of cortical degeneration, and no evidence was found for multiple discrete projections. There was some indication that the more rostral parts of MGB project more rostrally on the ectosylvian gyrus. The more medial lesions in the MGB affecting the magnocellular nucleus caused a spread of degeneration further towards the temporal pole and insulotemporal area than the more lateral lesions.