bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of tyrosine‐hydroxylase (TH)‐immunoreactive neurons in the diencephalon of the pigeon (Columba livia domestica)
Authors: Kiss József Zoltán , Péaczely Péter
Published: January 2005

The distribution of tyrosine‐hydroxylase (TH)immunoreactive cell bodies and fibers in the diencephalon has been investigated with immunohistological techniques in the pigeon. The results suggest that TH is present in a number of morphologically distinct neuronal systems. Preoptic and hypothalamic TH neurons were subdivided into a medial periventricular and a lateral group. The medial group starts with a rostral collection of small cells in the preoptic region. A significantly larger collection of TH neurons occupies the paraventricular nucleus (PVN)(stratum cellulare internum) and mainly consists of large multipolar cells. Further caudally, the main concentration of cells is in the hypothalamic posteromedial and the periventricular regions of the tuberoinfundibular (arcuate) nucleus. No TH neuron was found in the ventral and lateral parts of the tuberoinfundibular region, suggesting that the prominent tuberoinfundibular dopaminergic system described in mammals is absent in the pigeon. This is further substantiated by the relative scarcity of TH immunoreactive fibers and varicosities in the neurohemal zone of the median eminence (ME). The caudalmost components of the medial group appear to be continuous with the large population of TH neurons distributed in the midline of the mesencephalon. Tyrosine‐hydroxylase‐immunopositive cells have not been found in the paraventricular organ. The lateral group consists of TH neurons loosely arranged in the lateral hypothalamus, including regions of the supraoptic nucleus and hypothalamic posterolateral nucleus. Tyrosine‐hydroxylase containing neurons vary widely in size, shape, and dendritic arborization in each diencephalic region. However, it is possible to distinguish two main cell types. Small bipolar neurons with two simple arborizing dendrites were concentrated in the medial periventricular system. The second type of cell is large, multipolar with four to five branching dendrites. This latter cell type occurs mainly in the lateral system and in the PVN. Major fiber bundles containing TH immunoreactivity were identified in the lateral and periventricular hypothalamus. The paraventricular organ and the organum vasculosum laminae terminalis contained the densest arborization of fibers and varicosities. In the ME, dense innervation was found in the subependymal layer. Dense arborizations of TH positive fibers and varicosities were located in the septal nuclei and the paleostriatum augmentation.
Single‐unit study of lateral line cells in the optic tectum of Xenopus laevis: Evidence for bimodal lateral line/optic units
Authors: Lowe D. A.
Published: January 2005

Responses of single units in the Xenopus tectum to stimulation of the contralateral anterior lateral line nerve (cALLN) and optic nerve were studied. Cells responded to cALLN stimulation with a phasic burst of spikes that was repeatable between trials; latencies ranged from 4 to 23 msec. The most excitable cells were located in layer 6 of the ventrolateral tectum. Cells responding to stimulation of the ipsilateral ALLN were far less numerous and robust, and showed latencies 3–10 msec greater than those of contralateral responses. Tectal cell responses to cALLN nerve stimulation grew progressively to saturation with stimulus voltage and paralleled the growth of the ALLN compound action potential; cells responded to stimulation of either supra‐ or infraorbital branches of cALLN. These observations indicate convergence of primary lateral line afferents in the medulla and/or tectum. Lateral line tectal cells showed strong habituation at interstimulus times less than 8–20 seconds. Experiments on bimodal cells revealed facilitatory and inhibitory interactions between optic and lateral line inputs. Some cells responded to stimulation of either lateral line or optic nerves, with combined stimulation producing responses exceeding the sum of responses to separate nerve stimulation. In other cells the response to optic nerve stimulation was markedly increased by lateral line nerve stimulation, despite the absence of response to lateral line nerve stimulation alone. Facilitation was also evident in cells that responded only to combined stimulation of lateral line and optic nerves. Some cells exhibited an early (5–10 msec) and late (20–40 msec) response to optic nerve stimulation; lateral line nerve stimulation, despite eliciting no response itself, produced strong facilitation of the early but almost complete suppression of the late optic nerve response.
Functional organization of primary visual cortex in the mink (Mustela vison) and a comparison with the cat
Authors: LeVay Simon , McConnell Susan K. , Luskin Marla B.
Published: January 2005

The functional organization of geniculocortical afferents and the visual responses of neurons in primary visual cortex (area 17) were studied in barbiturate‐anesthetized, paralyzed minks and cats.

Responses of the afferents were studied after silencing intrinsic cortical activity with injections of kainic acid. In both species, afferents were segregated into patches on the basis of eye of origin. In the mink, but not in the cat, there was a further segregation on the basis of center type, with on‐ and off‐center afferents terminating in alternating, partially overlapping patches.

The visual responses of cortical neurons in the mink showed many similarities to those in the cat. Nearly all units were orientation‐selective, and there was a columnar organization for preferred orientation. Many units were selective for one direction of movement. Within the binocular segment of cortex, although many units could be driven from either eye, there was a marked bias toward the contralateral eye compared to the cat. There was a columnar system for ocular dominance, but contralateral eye columns were wider than ipsilateral.

In both species, a quantitative study was made of the responses of cortical neurons to stationary, flashing slits as a function of position in the receptive field. In the mink, and less clearly in the cat, units could be identified as simple or complex on the basis of the spatial separation or overlap of “on” and “off” discharge zones. In both species, simple cells were found most commonly in layers IV and VI, while layer V contained the greatest proportion of complex cells.

The relative strengths of the on and off discharges of single cells were also measured. In the mink, many units gave better overall responses to the on or off phase of the stimulus, and 15% showed a strong (>9:1) preference for one or the other, compared to 4% in the cat.

In the mink, units with a common preference for the on or off phase of stationary stimuli were arranged in columnar aggregates, a feature of cortical organization that was not found in the cat. These columns probably result from the partial segregation of on‐center and off‐center geniculate afferents within layers IV and VI of the mink's cortex. On‐dominated columns were, however, wider or more numerous than off‐dominated columns.
Development of the precerebellar nuclei in the rat: II. The intramural olivary migratory stream and the neurogenetic organization of the inferior olive
Authors: Altman Joseph , Bayer Shirley A.
Published: January 2005

Sequential thymidine radiograms from rats labeled on days E13 and E14, and killed at daily intervals thereafter, were analyzed to trace the migratory route and settling pattern of neurons of the inferior olive. Long‐survival thymidine radiograms from perinatal rats injected on day E14 were used to subdivide the inferior olivary complex on the basis of neurogentic criteria.

The inferior olivary neurons originate on days E13 and E14 in the primary precerebellar neuroepithelium. The olivary neurons labeled on day E14 (the late generated components) translocate into the inferior olivary premigratory zone on day E15. On day E16 these cells join the olivary migratory stream, which follows an intramural circumferential path between the gray and white matters of the medulla. By day E17 the olivary migratory stream is reduced to a small band near the corpus of the inferior olive, which has been settled by this time by neurons generated on day E13. As a result, the unlabeled cells are situated on day E17 dorsomedially and the labeled cells ventrolaterally. The regional segregation of neurons forming subdivisions of the inferior olive begins on day E18, and by day E19 the major subdivisions are all recognizable.

In thymidine radiograms from perinatal rats injected on day E14, four neurogenetic components can be distinguished in the inferior olive, those composed: (1) of unlabeled cells (generated on day E13), (2) of predominantly unlabeled cells, (3) of predominantly labeled cells (generated on day E14), and (4) of labeled cells. By combining these neurogenetic differences with the morphological features of the inferior olivary complex, we propose a modification of the currently accepted classification. The four major divisions of the inferior olive are the successively produced posterodorsal olive, anterolateral (principal) olive, posteroventral olive, and anteroventral olive. The location and configuration of these divisions are illustrated in relation to the traditional classification both in the coronal and the sagittal plane.
An extensive intrinsic association fiber system within cat area 7 revealed by anterograde and retrograde axon tracing methods
Authors: Callahan Eileen C. , Haberly Lewis B.
Published: January 2005

The associational connections within area 7 on the crown of the middle suprasylvian gyrus in adult cats were investigated with extracellular axon tracing techniques. Injections of wheat germ agglutinin conjugated to horseradish peroxidase or of 3H‐proline into area 7 revealed the presence of widespread intrinsic connections that extend over the rostral to caudal extent of the middle suprasylvian gyrus (up to 10 mm in one direction from injection sites). The connections have a complex organization with cell bodies and particulate label concentrated in patches. The patches are irregular in shape and do not form any obvious pattern. Although the transported label is concentrated in patches, large numbers of retrogradely labeled cells and significant quantities of anterogradely transported label are found in the spaces between patches. The long associational connections originate from cells in layers 2–6 and project to all cortical layers. Pyramidal cells are the primary source of the projections.
Localization of hydroxyindole‐O‐methyltransferase‐like immunoreactivity in photoreceptors and cone bipolar cells in the human retina: A light and electron microscope study
Authors: Wiechmann Allan F. , Hollyfield Joe G.
Published: January 2005

The localization of the melatonin‐synthesizing enzyme hydroxyindole‐O‐methyltransferase (HIOMT) was examined by light and electron microscopic immunocytochemistry in the human retina. HIOMT‐like immunoreactivity was observed in the photoreceptor layers and the inner nuclear layer (INL). The immunoreactive cells in the INL were more numerous in the central retina than in the peripheral retina and sent processes to both the outer plexiform and inner plexiform layers. The HIOMT immunoreactivity in the inner plexiform layer (IPL) appeared as punctate terminals in the proximal and distal one‐thirds of that layer.

At the ultrastructural level, HIOMT‐like immunoreactivity was localized to the cytoplasm of rod and cone photoreceptors and to a population of cone bipolar cells. HIOMT‐immunoreactive bipolar cell dendrites were observed to make both invaginating and flat synaptic contacts with cone pedicles. No immunoreactive invaginating contacts in rod spherules were observed. HIOMT immunoreactivity was observed in the bipolar cell cytoplasm in the INL, and in the bipolar synaptic terminals in the IPL. These terminals contained synaptic ribbons, which formed synaptic contacts with unlabeled cells in the IPL. HIOMT radioenzymatic assays confirmed the presence of HIOMT in the human retina. Average HIOMT activity of eight donors was determined to be 15.0 pmol/mg protein/hour ± 7.2 S.D. The ultrastructural localization of HIOMT observed in this study, combined with reports from other laboratories, suggests that the cytoplasm of the photoreceptors and a population of cone bipolar cells may be the sites of melatonin synthesis in the human retina.
Sources of presumptive glutamergic/aspartergic afferents to the rat ventral striatopallidal region
Authors: Fuller T. A. , Russchen F. T. , Price J. L.
Published: January 2005

The distribution of presumptive glutamergic and/or aspartergic neurons retrogradely labeled following injections of 3H‐D‐aspartate (3H‐D‐Asp) into the ventral Striatopallidal region was compared with the distribution of neurons labeled by comparable injections of wheat germ agglutunin‐horseradish peroxidase (WGA‐HRP). The afferents labeled by 3H‐D‐Asp were a subset of those labeled by WGA‐HRP. The major sources of afferents to the nucleus accumbens and olfactory tubercle that could be labeled by 3H‐D‐Asp were in the medial frontal and insular cortices; the olfactory cortex; the lateral, basolateral, and basomedial amygdaloid nuclei; and the midline nuclear complex of the thalamus. The corresponding afferents to the ventral pallidum arose in the central, medial, and basomedial amygdaloid nuclei and the midline thalamic nuclei. In addition, the nucleus of the lateral olfactory tract was moderately or heavily labeled by 3H‐D‐Asp injections into all three areas, and cells were labeled in the subiculum following injection in the anteromedial part of the nucleus accumbens. Conversely the ventral Striatopallidal structures themselves were, at best, sparsely labeled by any of the 3H‐D‐Asp injections. Neurons in the substantia nigra, ventral tegmental area, dorsal raphe, and locus coeruleus were labeled by WGA‐HRP but not by 3H‐D‐Asp, except for an occasional cell in the raphe. The results indicate that 3H‐D‐Asp is a specific retrograde tracer and suggest that there are widespread, presumably excitatory, glutamergic and/or aspartergic inputs to the ventral striatum and pallidum.
Axon collaterals in the thalamic reticular nucleus from thalamocortical neurons of the rat ventrobasal thalamus
Authors: Harris Roger M.
Published: January 2005

Thalamocortical relay neurons from the rat ventrobasal nucleus were identified physiologically and injected intracellularly with horseradish peroxidase. The axons of those cells were followed through serial sections in order to determine if collaterals were given off within the ventrobasal nucleus or the thalamic reticular nucleus. No local collaterals were seen in the ventrobasal nucleus, thus indicating that interactions between relay cells in this nucleus are minimal. Of axons that could be followed into the internal capsule, 76% gave off visible collaterals in the thalamic reticular nucleus. Half of these axons had collaterals showing extensive branching with the potential of innervating a large number of thalamic reticular neurons. The other half had short, simple branches of restricted extent. No correlations were found between the physiological properties of a cell and the existence or extent of axon collaterals. These results describe the anatomical basis for the initial part of a feedback loop through the thalamic reticular nucleus that provides the major inhibitory influence on rat ventrobasal neurons.
Evidence for parallel processing in the frog's auditory thalamus
Authors: Hall Jim C. , Feng Albert S.
Published: January 2005

We have conducted anatomical and physiological experiments to investigate the functional organization of the dorsal thalamus in the northern leopard frog (Rana pipiens pipiens). Our studies provide evidence for parallel auditory processing at this level of the frog's brain. Acoustically evoked potentials were recorded from the posterior and central thalamic nuclei and several differences in sound‐evoked activity were noted between them: (1) the amplitude of acoustically evoked potentials (AEPs), in response to a standard search stimulus, was always greater in the central, as opposed to the posterior, nucleus; (2) the posterior, but not central, nucleus exhibited the phenomenon of nonlinear summation when 350‐Hz and 1,700‐Hz tones were presented simultaneously rather than individually; and (3) the central, but not posterior, nucleus showed selectivity for the repetition rate of pulsed sound signals. The posterior and central thalamic nuclei also possessed distinct innervation patterns as revealed by the HRP transport patterns arising from these structures. The central nucleus was reciprocally connected with the major auditory relay stations along the frog's central auditory pathway including the superior dive, nucleus of the lateral lemniscus, and the torus semicircularis. Major projections to the lateral thalamic nucleus, ventral hypothalamus, and the telencephalic striatal complex were also observed. The posterior nucleus, on the other hand, established reciprocal connections primarily with the medial reticular nucleus, ventral mid‐brain tegmentum, and structures constituting of the ventral thalamic nuclei, particularly the nucleus of Bellonci. Thus, time and frequency cues contained within the species mating call, and conveying information concerning species identity, appear to be processed independently within the frog's thalamus with separate neural channels for each.
Morphology of expiratory neurons of the Bötzinger complex: An HRP study in the cat
Authors: Otake Kazuyoshi , Sasaki Hiroshi , Mannen Hajime , Ezure Kazuhisa
Published: January 2005

In anesthetized and artificially ventilated cats, the physiological and morphological properties of expiratory neurons or their axons of the Bötzinger complex (BOT) were studied using intracellular recording and intracellular HRP labeling techniques. Thirteen expiratory neurons (nine cell somata and four axons) were successfully stained. Four of them were motoneurons, having relatively large cell somata in the retrofacial nucleus (RFN) and axons without any collaterals inside the brainstem. All the motoneurons showed a plateau shape of depolarization potentials during the expiratory phase. Any of the other nine expiratory neurons exhibited augmenting type firing or membrane potential changes during the expiratory phase. In five out of nine augmenting neurons, cell somata were stained and located ventral to the RFN. In four, only axons were stained. The majority of the augmenting neurons had two major axonal branches: one traveling toward the contralateral side and the other descending ipsilaterally in the brainstem. The most striking feature of the axonal trajectory was that all of the stained augmenting expiratory neurons, including the axons, had collateral branches with synaptic boutons in the BOT area, thus indicating that BOT expiratory neurons interact with some respiratory neurons in the BOT area and its vicinity.
Distribution of GABA‐immunoreactive neurons in the basal ganglia of the squirrel monkey (Saimiri sciureus)
Authors: Smith Y. , Parent A. , Seguela P. , Descarries L.
Published: January 2005

The distribution of GABA‐immunoreactive neurons was visualized in the basal ganglia of the squirrel monkey (Saimiri sciureus), by using a highly specific antiserum raised against GABA‐glutaraldehyde‐lysyl‐protein conjugate and revealed by the indirect peroxidase‐antiperoxidase immuno‐histochemical method. In the dorsal striatum, GABA‐immunoreactive nerve cell bodies were small to medium in size (sectional area ranging from 90 to 125 μm2), but some larger ones (500‐600 μm2) were also found. These cells displayed no obvious clustering but were significantly more numerous in the caudate nucleus than in the putamen; their number was also markedly greater at caudal than at rostra1 striatal levels. A moderate number of evenly distributed positive axon terminals were visible in both the caudate nucleus and the putamen. In the ventral striatum, GABA‐immunoreactive nerve cell bodies and axon terminals were seen in fair number within the nucleus accumbens and in the deep layers of the olfactory tubercle. Many positive terminals but no somata were found in the islands of Calleja. In the globus pallidus, virtually all nerve cell bodies were GABA‐immunoreactive and the neuropil exhibited a multitude of positive terminals. In the Substantia innominata, clusters of small, globular GABA‐immunoreactive somata were scattered among aggregates of larger, nonimmunoreactive neurons belonging to the nucleus basalis, and the whole region showed a low to moderate number of evenly spread GABA‐positive terminals. In the subtha‐lamic nucleus, nerve cell bodies were generally surrounded by several GABA‐positive terminals but were not themselves immunoreactive. The substantianigra showed many GABA‐immunoreactive somata, which predominated in the pars lateralis and diminished progressively in number along the latero‐medial axis of the pars reticulata. These cells formed a rather pleomorphic group comprising round, fusiform, or polygonal elements of relatively large size (sectional area ranging from 200 to 800 μm2). In the pars compacta and ventral tegmental area, a few GABA‐immunoreactive neurons of small size were dispersed among larger, unreactive neurons. In both pars lateralis and pars reticulata of the substantia nigra, the number of GABA‐positive termi‐nals was high and their distribution was rather uniform; a smaller number were visible in the pars compacta of the substantia nigra and in the ventral tegmental area.

The present results demonstrate that GABA‐containing neurons are widely and heterogeneously distributed in the various components of the squirrel monkey's basal ganglia. Such normative data should be useful as a basis for further investigations of the functional role of GABA in the brain of primates.
Evidence for the inhibitory neurotransmitter γ‐aminobutyric acid in aspiny and sparsely spiny nonpyramidal neurons of the turtle dorsal cortex
Authors: Blanton Mark G. , Shen Janet M. , Kriegstein Arnold R.
Published: January 2005

In order to learn more about the anatomical substrate for γ‐aminobutyric acid (GABA)‐mediated inhibition in cortical structures, the intrinsic neuronal organization of turtle dorsal cortex was studied by using Golgi impregnation, immunohistochemical localization of GABA and its synthetic enzyme glutamic acid decarboxylase (GAD), and histochemical localization of the presynaptic GABA‐degrading enzyme GABA‐transaminase (GABA‐T). GABAergic markers are found in neurons identical in morphology and distribution to Golgi‐impregnated aspiny and sparsely spiny nonpyramidal neurons with locally arborizing axons and appear to label most if not all of the nonpyramidal neurons. In addition, the GABAergic markers are found in punctate structures in a distribution characteristic of presumed inhibitory terminals. The spine‐laden pyramidal neurons, the principal projecting cell type in the dorsal cortex, are devoid of labelling for GABAergic markers but are surrounded by presumed GABAergic terminals. The data complement previous physiological and ultrastructural studies that implicate aspiny and sparsely spiny nonpyramidal neurons as mediators of intrinsic inhibition of pyramidal neurons in turtle cortex. The results also suggest similarities in the functional organization of intrinsic inhibitory elements in turtle and mammalian cortex.
Somatostatin‐like immunoreactivity in the midbrain of the cat
Authors: Spangler Kevin M. , Morley Barbara J.
Published: January 2005

Somatostatin (SS) immunoreactivity was localized in cat brain sections with an immunoperoxidase technique. Cell bodies in the midbrain containing SS immunoreactivity were found in the superficial and intermediate gray layers of the superior colliculus, the interpeduncular nucleus, the raphe, the inferior colliculus and nucleus of its brachium, the nucleus of the optic tract, and the lateral tegmental field. Additional positive neurons were seen in the parabigeminal nucleus and in the dorsal periaqueductal gray in kitten material. Immunoreactive fibers were observed in the periaqueductal gray and in the midbrain tegmentum, with particularly dense labeling just dorsal to the substantia nigra and in the parabrachial nuclei. This is the first report of the distribution of SS immunoreactivity in the midbrain of the cat. It is concluded that somatostatin has a distribution compatible with a role as a major neurotransmitter/neuromodulator within oertain midbrain nuclei, especially the interpeduncular nucleus and the superior colliculus.
Experience‐independent development of dendritic organization in the avian nucleus laminaris
Authors: Parks Thomas N. , Gill Sarvjit S. , Jackson Hunter
Published: January 2005

The third‐order auditory neurons of the avian nucleus laminaris (NL) have distinct dorsal and ventral dendritic tufts that receive their predominant synaptic input from, respectively, the ipsilateral and contralateral cochlear nucleus. Beginning about embryonic day (E) 14 in the chick and continuing for some weeks after hatching, NL neurons undergo a complex series of morphological transformations that result in the formation of a steep anteromedial‐to‐posterolateral gradient of increasing total dendritic length across the nucleus. This gradient perfectly parallels the tonotopic axis of NL. It has been proposed that acoustically evoked activity in the auditory pathway contributes importantly to formation of the gradient of dendritic length in NL and to several other features of dendritic development. The present experiment tested this hypothesis by surgically removing both otocysts (embryonic precursors of the inner ear) and studying the developing NL in the absence of peripheral input. The results of a quantitative study of Golgi‐impregnated material show that at E17 both the steepness and predictability of the spatial gradient of dendritic length in operated animals are indistinguishable from normal. Similarly, the correlation of dorsal and ventral dendritic lengths on individual cells in operated animals is not significantly different from normal. The absolute length of both dendritic fields is reduced below normal, although only dorsal dendrites show a statistically reliable (14%) decrease. This is a significantly smaller effect than the 44% length reduction seen previously in animals with unilateral otocyst removal (T.N. Parks: J. Comp. Neurol. 202:47–57, '81); symmetrical afferent input appears more important to the regulation of NL dendritic length than the absolute level of this input. The only other significant effect of otocyst removal is to retard or prevent the alignment of the gradients of dorsal and ventral dendritic length that occurs normally between E15 and E17; the immature dorsal gradient has a much less prominent lateral‐to‐medial component than the ventral gradient at the same age. Thus, whereas the absolute size of NL dendrites depends upon a normal inner ear, most of the highly specialized dendritic organization of NL can develop normally in the complete absence of peripheral influences. The results suggest that each brainstem auditory nucleus is organized along an intrinsically determined axis that specifies how incoming auditory afferent axons will be organized into tonotopic arrays.
Initial junctions between developing parallel fibers and Purkinje cells are different from mature synaptic junctions
Authors: Landis Dennis M. D.
Published: January 2005

During postnatal development of cerebellar cortex, junctions are formed between parallel fiber axons and the shafts of Purkinje cell dendrites. These shaft junctions resemble synaptic junctions on spines in thin sections, in that the axon contains a cluster of synaptic vesicles, and the pre‐ and postjunctional membranes are lined by electron‐dense material. The shaft junctions do not have the aggregate of particles arrayed on the extracellular half of the postjunctional membrane that is characteristic of mature spine synaptic junctions in freeze‐fractured preparations, however, and so presumably have a different protein composition. Shaft junctions are transient specializations, present only in developing tissue, but do not appear simply to be intermediates in the formation of mature spine synaptic junctions. In normal development, spines are formed by the Purkinje cell dendrite at sites not occupied by shaft junctions. Moreover, in certain neurological mutant mice, shaft junctions form in the absence of spine synapses, and in other systems spines develop in the absence of shaft junctions. We suggest that shaft junctions are a class of synapse formed during development which is distinguished by its capacity to dissociate, and that only some fraction of the parallel fibers forming shaft synapses with a developing Purkinje cell will have established spine synapses in the adult.
Several morphological types of terminal arborizations of primary afferents in laminae I‐II of the rat spinal cord, as shown after HRP labeling and golgi impregnation
Authors: Cruz F. , Lima D. , Coimbra A.
Published: January 2005

The morphology of the terminal arborizations in laminae I‐II of primary afferent fibers was studied in sections stained by the heavy metal (nickel and cobalt) intensification of diaminobenzidine (DAB) after crushing one dorsal root with horseradish peroxidase (HRP) crystals, and with the mixed Golgi method which duplicated the staining provided by the first method. Besides the flame‐shaped arbors located in deep lamina IIi as an extension of the arbors of lamina III, which were derived from 1.7‐μm thick stem fibers (probably Aαβ fibers), six types of terminal arbors, all rostrocaudally oriented, arising from fine stem fibers and having preferential locations, were disclosed. The lateral third of laminae I‐II contained a longitudinal plexus of parallel 0.8‐μm thick stem fibers (C fibers) with longitudinal side branches generating many boutons en passant. Laminae I and IIo, in their middle third, contained dichotomizing longitudinal fibers with elongated boutons, arising from 1‐μm thick stem fibers (C or Aδ), and, in the medial third, a dense plexus with terminal networks carrying large boutons, which arose from 1.3‐μm thick stem fibers (Aδ). Fibers ending in terminal bouquets and issuing from 1‐μm thick stem fibers (C or Aδ) occupied the dorsal part of middle and medial lamina IIi, while the intermediate part contained clusters (swarms) of ultrafine boutons arising from extremely fine fibers. The whole medial lamina Hi also contained fine undulating fibers arising from 0.3 μm‐thick stem fibers (C fibers) with large boutons near their ends. The functional meaning of this multiplicity of morphological types and locations is still unclear. It may be clarified when single unit analysis of HRP‐injected fine fibers is made possible, or immunocytochemical stainings disclose the neurotransmitters utilized by each fiber type.
Wheat germ agglutinin‐apoHRP gold: A new retrograde tracer for light‐ and electron‐microscopic single‐ and double‐label studies
Authors: Basbaum A. I. , Menetrey D.
Published: January 2005

In this report, we describe a new colloidal‐gold‐labelled retrograde tracer, wheat germ agglutinin (WGA) conjugated to enzymatically inactive horseradish peroxidase (apoHRP). This protein gold complex (WGAapoHRP‐Au) is a sensitive marker for retrograde tracing of the projections of CNS neurons at the light‐microscopic (LM) level when a silver‐enhancement procedure is used to detect the gold in the tracer. For electron‐microscopic (EM) analysis, the silver‐enhanced sections undergo a further gold‐toning step. This protects against rapid oxidation and dissolution of the silver precipitate during the osmication procedure.

A major advantage of WGAapoHRP‐Au is that it can be used in a variety of multiple‐labelling studies. When the retrograde transport of the new tracer is combined with that of the fluorescent dye, True Blue, neurons that have bifurcating axons can be readily demonstrated. Simultaneous immunofluorescent detection of the cytochemistry of the double‐retrogradely labelled neurons is also possible. In contrast to a WGA‐HRP gold complex, the new complex has no enzymatic activity. Thus HRP‐based techniques (e.g., anterograde transport of WGA‐HRP or peroxidase‐antiperoxidase immunocytochemistry) can be performed on tissue that contains retrogradely labelled neurons marked with WGAapoHRP‐Au without having to pretreat tissue so as to destroy endogenous HRP enzyme activity. At the EM level, the gold is readily distinguished from DAB immunoreaction product. This makes both LM and EM double‐labelling studies possible.

The great sensitivity of the new tracer, its compatibility with a variety of aldehyde fixatives, its ease of detection, and the fact that it can be simultaneously used with several fluorescent and HRP‐based immunocytochemical and tracing techniques make WGAapoHRP‐Au a valuable tool for LM and EM characterization of CNS cytochemistry and connectivity.
Development of the brachial lateral motor column in the wingless mutant chick embryo: Motoneuron survival under varying degrees of peripheral load
Authors: Lanser Mark E. , Fallon John F.
Published: January 2005

Survival of motoneurons in the lateral motor column (LMC) of the chick embryo is known to depend on the periphery. How this dependence relates to the normally occurring death of motoneurons is unknown. Analysis of the time course of LMC cell loss in the absence of varying amounts of limb musculature could help bring about an understanding of this relationship. We undertook this analysis by studying LMC development in wingless chick embryos. Grossly these embryos lack wings, but we have reported that some of them possess more than 40% of the normal volume of wing bud‐derived muscles (M.E. Lanser and J.F. Fallon, Anat. Rec. 217:61–78, 1987). In the present work we compared the time course of LMC development in wingless embryos that possessed varying amounts of wing bud‐derived musculature with that in normal embryos. In normal embryos little cell loss occurs from the brachial LMC prior to day 8 (15% of the: total cell loss). Most of the normal cell loss occurs between 8 and 10 days (62% of the total cell loss). In the wingless LMC, anywhere from 55% to 70% of the total cell loss occurs before day 8. The death of motoneurons prior to day 8 is proportional to the amount of wing bud musculature eliminated by the mutation. Cell loss after day Bis proportional to the amount of wing bud musculature spared by the mutation. Therefore, when the limb is missing, most motoneurons die before the major period of cell loss even begins in the normal LMC. Counts of dead cells in the LMC also support this conclusion. In addition, curves plotting the rates at which cells are lost from the brachial LMC provide a suggestion that normal cell loss is biphasic and that limb removal enhances primarily the first phase of cell loss. These data suggest that the majority of motoneurons may die for different reasons in the normal and the limb‐deprived LMCs. Overall, the number of motoneurons surviving in the brachial LMC is proportional to the volume of wing bud‐derived muscle present. However, as the muscle volume approaches zero, motoneuron number does not. This suggests that most, but not all, motoneurons depend on limb bud‐derived muscles for survival. Finally, the decreased motoneuron number in the wingless LMC, when compared to normal after the cell death period, cannot be totally accounted for by the additional loss of cells that occurred during the cell death period in the wingless LMC. This raises the possibility that limb absence influences the initial formation of the LMC, a possibility that deserves further investigation.
Corneal sensory pathway in the rat: A horseradish peroxidase tracing study
Authors: Marfurt Carl F. , Del Toro David R.
Published: January 2005

The methods of transganglionic transport of horseradish peroxidase (HRP) and horseradish peroxidase–wheat germ agglutinin (HRP‐WGA) were used to determine the location within the trigeminal ganglion of the primary afferent neurons that innervate the rat central cornea, and the brainstem and spinal cord termination sites of these cells. In each of 18 animals, solutions of HRP or HRP‐WGA were applied to the scarified corneal surface and allowed to infiltrate into the corneal epithelium and stroma for 15 minutes. Postmortem examination of the corneal whole mounts from the experimental animals, and of corneas and neural tissues from several control animals, showed that the HRP/HRP‐WGA remained confined to the central cornea with no spread into adjacent intra‐ or extraorbital tissues.

HRP‐labeled corneal afferent somata were located in the dorsal part of the ophthalmic region of the ipsilateral trigeminal ganglion. The central fibers of the corneal afferent neurons projected very heavily to interstitial nuclei of Cajal in the spinal tract of V at the level of caudal pars interpolaris and rostral pars caudalis, lightly to the pars caudalis/C1 transition zone, and sparsely to the dorsal horn of spinal cord segments C1‐C3. The trigeminal main sensory nucleus, pars oralis, the rostral three‐fourths of pars interpolaris, and an extensive midregion of pars caudalis were totally devoid of reaction product. Terminal fields in Caudal pars caudalis and in the spinal cord dorsal horn were concentrated largely in the outer half of lamina II, with lesser accumulations in lamina I, the deeper half of lamina II, and in lamina III.

The present study demonstrates for the first time by means of an anatomical tracing procedure the brainstem termination sites of corneal afferent neurons in the rat. The patchy, discontinuous nature of the corneal afferent projection to the caudal trigeminal brainstem nuclear complex (TBNC), and the total lack of corneal projections to rostral subdivisions of the TBNC, provide an exception to the general rule of trigeminal organization in which most areas of the head and face are represented as continuous columns throughout the rostrocaudal extent of the ipsilateral TBNC.
Transneuronally transported wheat germ agglutinin labels glia as well as neurons in the rat visual system
Authors: Rhodes C. Harker , Stieber Anna , Gonatas Nicholas K.
Published: January 2005

Following intraocular injection in adult rats of 125I‐labeled wheat germ agglutinin (I‐WGA), the ultrastructural distribution of label in the superior colliculus and lateral geniculate was examined by electron microscope auto‐radiography. Three days after injection, 5.4% of the label in the lateral geniculate was associated with neuronal perikarya, and 3.6% was associated with glial perikarya. The corresponding figures for the superior colliculus were 5.1% and 0.8%. When the data were expressed as number of grains per μm2 cytoplasm, there was no statistically significant difference between the grain density over neuronal or glial cytoplasm in either the lateral geniculate or the superior colliculus, A statistical analysis of the distance between the silver grains and the cell membranes showed that in both neurons and glia, the observed labeling was the product of internalized I‐WGA and not the result of scatter from the neuropil or from label bound to the surface of the cells. These results indicate that much of the WGA released from axons and axon terminals is not confined to a specific “transsynaptic” pathway, but produces a generalized labeling of nearby cells, much like a microinjection of WGA into the region.
Distribution of external cuneate nucleus afferents to the cerebellum: I. Notes on the projections from the main cuneate and other adjacent nuclei. An experimental study with radioactive tracers in the cat
Authors: Jasmin L. , Courville J.
Published: January 2005

Transport of radioactive leucine was used to demonstrate cerebellar projections from the external cuneate nucleus (NCE) and from adjacent portions of the main cuneate nucleus (NC), of the spinal trigemmal nucleus (N.tr.sp.V) and of the vestibular nuclei. Projections from NCE and NC in part terminate over exclusive regions and in part overlap. After injections limited to NCE, labeling is found in all regions of the anterior lobe and lobule VI, in vermal lobules VII, VIII, and IX, and in medial regions of central folia of the paramedian lobule. Afferents from NC are observed in intermediate and lateral regions of lobules IV‐VI, in lobules VIII and IX, in medial portions of crura I and II, and in lateral parts of central folia of the paramedian lobule as well as in its rostral folia. Afferents from N.tr.sp.V are distributed in lateral regions of lobules II‐VI, in the rostral folium of lobule IX, in medial parts of crura I and II, and in rostral folia of the paramedian lobule. Afferents from the vestibular nuclei are present in vermal lobules VII, IX, and X and in the paramedian lobule. Projections from NCE are bilateral with ipsilateral predominance, whereas those from NC and N.tr.sp.V are ipsilateral. Projections from NCE are generally much denser than those from the other nuclei. Throughout the projection area, afferents from NCE are distributed in greater amounts in folia close to the medullary core and are much less dense near the surface. Afferents from the other nuclei do not show surface‐to‐depth density differences.
Organization of amygdaloid projections to the mediodorsal thalamus and prefrontal cortex: A fluorescence retrograde transport study in the rat
Authors: McDonald Alexander J.
Published: January 2005

Previous studies have shown that the amygdala projects to both the mediodorsal thalamic nucleus (MD) and its cortical projection area, the prefrontal cortex (PFC). In this investigation rats received injections of different fluorescent retrograde tracers (true blue and diamidino yellow) into MD and either the lateral, polar, or medial PFC in order to examine the relationship of amygdaloid neurons with cortical and/or thalamic projections. PFC injections labeled neurons in the basolateral (BL), basomedial (BM), ventral endopiriform (Env), and rostral lateral nuclei as well as the periamygdaloid cortex (PAC) and the medial part of the amygdalohippocampal area (AHA). In BL, which contained the great majority of neurons projecting to PFC, most labeled cells were concentrated in particular parts of the nucleus and were topographically organized. The overwhelming majority of labeled neurons in BL were large pyramidal or piriform cells that correspond to class I neurons described in Golgi studies. Occasional small neurons with thin dendrites were also observed; these cells may be class II neurons.

MD injections labeled numerous cells in the anterior division of the cortical nucleus, medial nucleus, and caudomedial part of the central nucleus. Moderate numbers of labeled cells were found in caudal portions of BM and PAC, whereas scattered cells were observed throughout the rest of the amygdala with the exception of the lateral nucleus. In BL and AHA many MD‐projecting neurons were observed along nuclear boundaries and in the adjacent white matter. Neurons in BL, BM, and AHA usually had large elongated or irregular somata and two to four primary dendrites that branched sparingly. Other cells had smaller ovoid somata. The morphology and distribution of MD‐projection cells in the basolateral amygdala indicate that they are primarily large class II neurons.

Double‐labeled amygdaloid neurons, labeled by both cortical and thalamic injections, were observed only in a small number of animals. Control experiments suggest that most of the double‐labeled cells in these cases were artifacts caused by spread of the thalamic injectate into the third ventricle with subsequent uptake by fibers in the anterior commissure. Thus the findings of this study suggest that different neuronal populations in the amygdala project to the two poles of the MD‐PFC system. In the basolateral amygdala class I neurons are the predominant cell type involved in PFC projections, whereas a subpopulation of class II neurons, hitherto thought to be primarily local‐circuit neurons, project to MD.
Development of the rhesus monkey retina: II. A three‐dimensional analysis of the sequences o synaptic combinations in the inner plexiform layer
Authors: Nishimura Yozo , Rakic Pasko
Published: January 2005

The inner plexiform layer (IPL) of the retina provides a useful model for ultrastructural analysis of synaptic development. In primates, the IPL consists of numerous combinations of neuronal contacts that assume the morphological configuration of either conventional or ribbon synapses. We have determined the sequential development of these combinations by analyzing serial electron microscopic sections from fetal rhesus monkeys. Our analysis reveals an orderly emergence of various pre‐ and postsynaptic elements: (1) patches of dense filamentous membrane first appear on the dendrites of ganglion (G) cells; (2) membrane densities on ganglion cell dendrites then become apposed to amacrine (A) cell processes still lacking their own membrane densities and synaptic vesicles; (3) amacrine cell processes acquire membrane specializations associated with vesicles at the sites apposing ganglion cell dendrites, thereby establishing the first morphologically complete, A → G subtype of conventional synapse; (4) pairs of amacrine cell processes form A → A subtypes of conventional synapses; (5) next, monad ribbon synapses are established between bipolar (B) and ganglion or amacrine cell processes (B → G; B → A); (6) the three subclasses of dyad ribbon synapses (B → GG; B → GA; B → AA) are subsequently formed by the introduction of additional amacrine or ganglion cell processes in the dyad synapse; (7) concurrently, processes of some amacrine and interplexiform (I) cells form a feedback circuit with bipolar cell axons (A → B; I → B), thereby completing the synaptic microcircuitry of the IPL.

Present findings provide evidence that the sequence of synaptic differentiation in the IPL proceeds from the postsynaptic to the presynaptic site. Furthermore, lateral interactions (A → G and A → A) are established prior to the formation of the “straight signal” pathway from photoreceptors (P) via bipolar cells to ganglion cells (P → B → G). Observed developmental events provide new insight into the order of establishment of local neuronal circuits in the primate retina.