bluuebunny/crossref_metadata_2025_split huggingface dataset:
Connections between pyramidal neurons in layer 5 of cat visual cortex (area 17)
Authors: Gabbott P. L. A. , Martin K. A. C. , Whitteridge D. 
Published: January 2005

AbstractThe structural features of two physiologically‐characterised pyramidal neurons (PC1 and PC2) closely situated in layer 5b in the visual cortex (area 17) of a single cat were studied using a combination of electrophysiological and anatomical techniques. Both PC1 and PC2 had exceptionally large somata (30–40 μm in diameter). On the basis of this and other morphological features cell PC1 was classified as a Meynert cell. PC1 possessed a very large (2.75° × 4.50°) binocularly driven standard complex receptive field. PC2 was also binocularly driven with a small, B‐type receptive field. Both cells had the same preference for the direction and orientation of visual stimuli. PC1 and PC2 could be antidromically activated from stimulating electrodes positioned above the dorsal lateral geniculate nucleus with a response latency indicating that these cells probably innervated the visual tectum or pretectum.In addition to corticoefferent axons, the two neurons possessed extensive intracortical axon arbors that ramified extensively in layers 5 and 6 of the medial and lateral banks of the lateral gyrus in area 17. Axon collaterals from both PC1 and PC2 also innervated a small common target region in area 18. A total of 313 boutons from the axonal arbors of PC1 and PC2 were examined in the electron microscope. All of the identified synaptic junctions were found to establish Gray type 1 asymmetrical contacts. The combined ultrastructural data for both neurons indicated that 80% of boutons were onto dendritic spine heads, with 14%, 6%, and 1% onto small‐, medium‐, and large‐calibre dendritic shafts, respectively. The spectrum of postsynaptic targets showed little variation with respect to lamina, distance from somata, or cortical area. Other large pyramidal neurons in layer 5 and spiny neurons in layer 6 were identified as receiving synaptic input from either PC1 or PC2.Using a computer graphics system, rotations of the bouton distributions revealed the existence of a clustered innervation of layers 5 and 6 in areas 17 and 18 derived from the two identified neurons. The bouton distributions strongly resembled the tangential pattern described previously for the functional slab‐like organisation of the cortex.The results provide a morphological basis for the clustered intrinsic connectivity of pyramidal cells in layers 5 and 6 of the cat visual cortex. Furthermore, the results indicate the widespread excitatory influence of large pyramidal neurons on other cells projecting subcortically to sites dealing with visually guided behavior.
Projections of the lateral hypothalamus and bed nucleus of the stria terminalis to the dorsal vagal complex in the pigeon
Authors: Berk Mitchell L. 
Published: January 2005

AbstractThe dorsal vagal complex is composed of the nucleus tractus solitarii (Nts) and the dorsal motor nucleus of the vagus (DMN X). In the pigeon, these nuclei are composed of cytoarchitectonically well‐defined subnuclear groups, which have connections that are partially segregated to specific organs (Katz and Karten: J. Comp. Neurol. 218:42–73, '83b, J. Comp. Neurol. 242:397–414, '85). The present study sought to determine whether forebrain afferents to Nts‐DMN X are differentially distributed to specific subnuclei and thereby modulate the functions of specific organs.Forebrain afferents to the dorsal vagal complex were determined by retrograde tracing techniques. Labeled perikarya were found in the bed nucleus of the stria terminalis (BNST), ventral paleostriatum, and stratum cellulare externum (SCE) of the lateral hypothalamus, and in the medial hypothalamus, nucleus periventricularis magnocellularis (PVM), which is the avian homologue to a portion of the mammalian paraventricular nucleus. The pattern of axonal distribution to Nts‐DMN X subnuclei from the BNST‐ventral paleostriatum and SCE were investigated by anterograde tracing techniques. These experiments revealed axonal projections distributed to specific Nts‐DMN X subnuclei. However, there is a high degree of overlap of the axonal projections to Nts‐DMN X subnuclei from BNST‐ventral paleostriatum and SCE, as well as from PVM (Berk and Finkelstein: J. Comp. Neurol. 220:127–136, '83). Labeled fibers from BNST‐ventral paleostriatum and SCE project heavily to Nts subnuclei medialis superficialis, lateralis dorsalis, and medialis ventralis and to DMN X subnucleus ventralis parvicellularis. Fewer labeled fibers were found in Nts subnucleus medialis intermedius and extremely sparse labeling was found in Nts sub‐nucleus medialis dorsalis. The Nts and DMN X subnuclei that receive forebrain projections also have peripheral connections with the aortic nerve, crop, esophagus, glandular stomach, and caudal abdominal organs. Thus, the forebrain could modulate the functions of these segments of the cardiovascular and digestive systems.
Glutamic acid decarboxylase‐like immunoreactivity in brainstem auditory nuclei of the rat
Authors: Moore Jean K. , Moore Robert Y. 
Published: January 2005

AbstractThe distribution of GABA‐producing neurons in the brainstem auditory nuclei of the rat was investigated immunohistochemically by using an antibody to glutamic acid decarboxylase (GAD). In the cochlear nuclei, GAD immunoreactive neurons are present only in the superficial granular and molecular layers, whereas terminals are found in all subdivisions of the nuclei and are particularly dense surrounding large spherical cells and one type of stellate cell. In the superior olivary complex, GAD immunoreactive neurons are located in the lateral olivary nucleus and throughout the periolivary region. Immunoreactive terminals are distributed along dendrites of principal cells of the medial and lateral olivary nuclei and are clustered around somata of globular neurons of the nucleus of the trapezoid body. An extremely dense band of immunoreactive somata and terminals is present along the ventral edge of the olivary complex. The ventral, intermediate, and dorsal nuclei of the lateral lemniscus contain small fusiform GAD‐immunoreactive neurons and a moderately dense plexus of immunoreactive terminals. The inferior colliculus contains a large population of GAD‐immunoreactive perikarya and an extremely dense accumulation of immunoreactive terminals in the central, dorsomedial, and external nuclei. These observations indicate that GABA systems are involved in function at all levels of the brainstem auditory pathway.
Nerve cell atrophy and loss in the inferior olivary complex of “Purkinje cell degeneration” mutant mice
Authors: Ghetti Bernardino , Norton James , Triarhou Lazaros C. 
Published: January 2005

AbstractThe genetically determined loss of cerebellar Purkinje cells (PCs) in “Purkinje cell degeneration” (pcd) mutant mice deprives inferior olivary (IO) neurons of their major postsynaptic target. The degeneration of PCs starts on postnatal day (P) 17 and loss of these neurons is virtually complete by P45. We examined the inferior olivary complex (IOC) of normal and pcd mutant mice by quantitative light microscopy to determine whether the degeneration of PCs is associated with atrophy and loss of their presynaptic neurons in the IOC. The number of IO neurons in 17‐day‐old mutants did not differ significantly from controls (P ≥.1). IO neurons in 23‐day‐old mutants were 23% (95% confidence limits: 12–34%) fewer than in age‐matched controls, and in 300‐day‐old mutants they were 48% (95% confidence limits: 37–58%) fewer than in their controls (P ≤.001 in both cases). The decline of the number of IO neurons in pcd mice between days 17 and 300 was 49% (P <.0001; 95% confidence limits: 38–57%). The medial accessory olive (MAO) appeared less affected than the principal (PO) and the dorsal accessory olive (DAO). The mean neuronal diameter in control mice was 11.6 μm at 23 days and 10.8 μm at 300 days of age. The respective values in pcd mutants were 11.5 μm and 8.7 μm. Diameters in old mutants were significantly smaller than those in both age‐matched controls and young mutants (P ≤.001). These findings suggest that in the mature olivocerebellar system the stability of IO neurons depends on the state of their postsynaptic PCs.
P2, P1, and P0 myelin protein expression in developing rat sixth nerve: A quantitative immunocytochemical study
Authors: Hahn A. F. , Whitaker J. N. , Kachar B. , deF. Webster H. 
Published: January 2005

AbstractMyelination and the expression of myelin proteins P2, P1, and P0 were studied quantitatively in the rat sixth cranial nerve during development. The postnatal development and growth of all myelin sheaths in this nerve have been studied morphometrically in a companion paper. Epon‐embedded blocks with closely matched topography in the transverse plane were selected from rats perfused at ages 1–4, 8, 15, and 20 days. From each block, serial semithin sections were cut, etched, and immunostained according to the peroxidase‐antiperoxidase method with well‐characterized polyclonal antisera that reacted specifically with P0 glycoprotein and the basic proteins P1 and P2. The immunoreactivities of individual myelin sheaths were measured by densitometry. Numbers of compact myelin lamellae, myelin spiral lengths, and axon diameters were determined on electronmicrographs of adjacent thin sections. At birth anti‐ P0 immunoreactivity was found on sheaths with two and more compact lamellae; neither P1 nor P2 immunoreactivity was observed. On day 2, myelin sheaths with five and eight lamellae were stained respectively by anti‐ P1 and anti‐ P2. On day 3 the percentages of myelin sheaths stained were substantially higher: P0 95%, P1 78%, P2 15%. By day 4, anti‐ P0 and anti‐ P1 immunoreactivity was present in 95% of myelin sheaths; 35% were stained by anti‐ P2. For P2, staining intensity and percentage of myelin sheaths stained continued to increase and by day 20, 85% were anti‐ P2‐positive.The density of immunoreactivity was not uniform in all myelin sheaths. At young ages staining varied with all three proteins. The variability decreased as myelin sheaths thickened; it persisted longest for anti‐ P2. We conclude that the density and distribution of immunoreactivities of P0, P1, and P2 reflect their relative concentrations during myelin sheath development and growth. We attribute lack of detectable anti‐ P2 immunoreactivity in some small sheaths at 20 days to their early stage of myelination and also to limitations of the method. We infer from our observations that all myelin‐forming Schwann cells express P2 basic protein.
Physiological evidence for branching of peripheral unmyelinated sensory afferent fibers in the rat
Authors: McMahon Stephen B. , Wall Patrick D. 
Published: January 2005

AbstractSingle unmyelinated sensory afferent nerve fibers were recorded in dorsal root filaments in urethane‐anesthetized or in decerebrate‐spinal rats. The peripheral branch of these axons ran in the sural nerve where they were stimulated by tungsten microelectrodes. All action potentials showed the characteristics of single fiber responses with a fixed all or none shape and a fixed latency at a given stimulus strength. In all units, the action potential evoked from a proximal stimulus site collided with the action potential evoked from a distal stimulus site.Of the 44 single units isolated, 17 showed the expected small progressive decrease of latency of the recorded impulse as the stimulus strength at a fixed point on the sural nerve was progressively raised above threshold. However, in 27 units there was an abrupt jump decrease of latency as the stimulus rose above the threshold. The average size of this latency shortening was 2.2 msec, which occurred as the stimulus strength rose a mean 21% above threshold. As the stimulus rose above threshold, 7 fibers showed 3 different fixed latencies and 2 fibers showed 4 fixed latencies. In order to test the possibility that the peripheral nerve contained 2 branches of the same axon with one conducting slower than the other, the peripheral nerve was stimulated at progressively longer conduction distances. As predicted, the difference between the 2 fixed latencies became larger as the conduction distance increased.We discuss 6 possible explanations for the results and conclude they are consistent with the proposals that some fibers branch distal to the dorsal root ganglion and some branches do not establish a functional sensory ending in the periphery.
Ultrastructural evidence of the formation of synapses by retinal ganglion cell axons in two nonstandard targets
Authors: Cantore William A. , Scalia Frank 
Published: January 2005

AbstractAfter unilateral ablation of the optic tectum in the frog (Rana pipiens), retinal ganglion cell axons enter the lateral thalamic neuropil in large numbers. This area is normally a target of the tectal efferent projection but is not innervated directly from the retina in normal frogs nor in frogs undergoing optic nerve regeneration in the presence of an intact tectum. The ability of retinal axons to form synaptic contacts in this nonstandard target, previously suspected only from light microscope studies, has been ultrastructurally verified in the present investigation. Retinal axon terminals were selectively labeled for light and electon microscope study by introducing horseradish peroxidase (HRP) into the optic nerve 73–413 days after unilateral ablation of the contralateral optic tectum. In some of the frogs, the optic nerve had also been crushed to test the ability of retinal axons regenerating over a long distance to form this connection. The HRP‐labeled retinal axon terminals had the same untrastructural morphology whether located in the lateral thalamic neuropil or in the correct regions of projection, e.g., the lateral geniculate complex. They contained clear, spherical synaptic vesicles and made Gray type I synapses on the unlabeled postsynaptic dendrites, The magnitude of the projection was disproportionately greater in animals having complete or nearly complete tectal ablation than in a specimen in which the lesion was significantly incomplete. An aberrant projection was also observed in the nucleus isthmi in some of the specimens.These findings have significance for chemoaffinity theories of the specification of synaptic connections in that the ability of retinal axons to synapse in nonstandard targets in this experimental context may be considered evidence for the expression of appropriate cell‐surface recognition‐molecules by the abnormally targeted postsynaptic neurons. The likelihood that the expression of these postsynaptic labels is normally repressed transynaptically by molecular signals from the intact tectal input is discussed.
Immunocytochemical distribution of met‐enkephalin‐Arg6‐Gly7‐Leu8 in the rat lower brainstem
Authors: Murakami Sadatsugu , Okamura Hitoshi , Yanaihara Chizuko , Yanaihara Noboru , Ibata Yasuhiko 
Published: January 2005

AbstractThe distribution of methionine‐enkephalin‐Arg6‐Gly7‐Leu8, a unique peptide derived from proenkephalin A in the rat brainstem, was studied immunocytochemically by using a highly specific antiserum to this octapeptide sequence.Immunoreactive perikarya with various shapes and sizes were detected in many regions of the rat brainstem. Dense accumulation of immunoreactive perikarya and fibers was seen in the nuclei associated with special sensory and visceral functions, such as the interpeduncular nucleus, the parabrachial nucleus, the nucleus of the solitary tract, and the nucleus of the spinal tract of the trigeminal nerve. Clusters of methionine‐enkephalin‐Arg6‐Gly7‐Leu8–like immunoreactive perikarya and fibers were observed in certain areas considered to play a role in nociception and analgesia, such as the central gray of the midbrain central gray and the raphe magnus nucleus. Some methionine‐enkephalin‐Arg6‐Gly7‐Leu8‐like immunoreactive perikarya were distributed in the lateral reticular nucleus, the nucleus of the solitary tract, and the raphe magnus nucleus, where monoaminergic neurons were also detected. In addition to the previously reported enkephalinergic cells, we found many methionine‐enkephalin‐Arg6‐Gly7‐Leu8 containing neurons; the rostral and caudal linear nucleus of raphe, the median raphe nucleus, entire length of the raphe magnus nucleus, the medial longitudinal fasciculus, the cuneate nucleus, the external cuneate nucleus, the gracile nucleus, and the area postrema. The wide distribution of this octapeptide‐like immunoreactivity reflected neurons expressing the preproenkephalin A gene distributed more widely than previously reported and that innervated many regions.
Hippocampus of the seizure‐sensitive gerbil is a specific site for anatomical changes in the GABAergic system
Authors: Peterson Gary M. , Ribak Charles E. 
Published: January 2005

AbstractThe brains of seizure‐sensitive (SS) and seizure‐resistant (SR) gerbils were studied with an immunocytochemical method to localize glutamic acid decarboxylase (GAD) to determine whether a defect existed in the inhibitory GABAergic system similar to that which has been reported in animal models of focal epilepsy in which GABAergic cell bodies and terminals are decreased in number. A major difference between the two strains of gerbils was found in the number of GABAergic neurons in the hippocampal formation. Specifically, a paradoxical increase occurred in the number of glutamate decarboxylase (GAD)‐immunoreactive neurons: there were approximately 65% more GABAergic cells within the dentate gyrus and the CA3 region of the hippocampus in the SS gerbils. Furthermore, the density of GAD‐immunoreactive puncta, the light microscopic correlates of synaptic boutons, was greater in the SS animals. Other histological methods were used to determine if the difference between SS and SR gerbils was specific for the GABAergic system. Nissl‐stained preparations showed that the number of granule cells in the dentate gyrus was 20% greater in SS gerbils than in SR gerbils. An examination of some hippocampal afferents, efferents, and intrinsic connections with acetylcholinesterase histochemistry and the Timm's stain for heavy metals demonstrated no differences between the two strains. In addition, Golgi‐stained preparations of the dentate gyrus indicated that the morphology of basket cells did not differ between the two strains nor between the gerbil and the rat.Several brain regions in addition to the hippocampus were studied to determine whether or not the increased number of GAD‐immunoreactive neurons was specific for the hippocampal formation. These regions included the substantia nigra, motor cortex, and nucleus reticularis thalami and were selected because they contain large populations of GABAergic neurons and have been implicated in seizure activity. No differences between the two strains were detected in any of these regions. Therefore, a major morphological difference between the brains of SS and SR gerbils exists in the hippocampal formation of SS gerbils in which an increase occurs in the number of GABAergic neurons and granule cells. If these additional inhibitory neurons act mainly to inhibit other inhibitory neurons, the net effect would be increased disinhibition of the principal excitatory neurons of the hippocampal formation. This could lead to seizure activity within the hippocampal formation and at distant sites through multiple synaptic connections.
The early development of neurons with GABA immunoreactivity in the CNS of Xenopus laevis embryos
Authors: Roberts Alan , Dale N. , Ottersen O. P. , Storm‐Mathisen J. 
Published: January 2005

AbstractWe have used an antibody to glutaraldehyde fixation complexes of γ‐amino butyric acid (GABA) to stain the developing central nervous system of Xenopus laevis embryos. Neuronal somata, growth cones, axons, and dendrites were found with GABA‐like immunoreactivity. Transmission electron microscope (TEM) observations were made of axons and synapses. By observation of the earliest stages of differentiation of neurons, seven classes of putative GABAergic interneurons were discerned. (1) Ascending neurons are first stained in the hindbrain at stage 26 and later extend caudally in the spinal cord. They have ascending ipsilateral axons. (2) Midhindbrain reticulospinal neurons are first stained at stage 25 and develop as a compact group with descending ipsilateral and contralateral axons, (3) Vestibular complex commissural neurons are first stained at stage 29/30 in a dorsal position near the entry of the seventh and eighth cranial nerves. They have ventral commissural axons that descend contralaterally and their somata form a compact mass. (4) Rostral hindbrain commissural neurons are first stained at stage 33/34 just rostral to the entry of the trigeminal nerve. They each have a decussating projection. (5). Rostral midbrain neurons are first stained in the midbrain at stage 29/30 and are later associated with prominent dorsal and ventral commissures. (6) Optic tract and (7) rostral forebrain neurons are found in the forebrain associated with strongly stained axon tracts.The direction of axonal growth from its earliest stages was distinct for each class of hindbrain and spinal cord neuron.
Divergence of single axons in afferent projections to the cat's visual cortical areas 17, 18, and 19: A parametric study
Authors: Birnbacher D. , Albus K. 
Published: January 2005

AbstractThe proportions of neurons projecting via axon collaterals to two areas in the cat's occipital cortex (diverging neurons) were determined quantitatively in subcortical and cortical afferents by making use of the retrograde axonal transport of two different tracers. The proportions of diverging neurons were determined for that part of the afferent sites in which neurons filled with tracers from both injected areas occurred (overlap zone).A number of experimental variables were tested for their role in possibly influencing the results of quantitative double‐label experiments, among them the types and the combinations of retrograde tracers, the position of the injections, the survival time, and the histological procedure. The most important variable was the position of the cortical injection, which had to be restricted clearly to the cortical grey matter and to one cortical area in order to avoid false‐positive double labeling. Other experimental variables affected the total number of retrogradely labeled neurons and/or the ratio between neurons labeled with the two different tracers rather than the proportions of double‐labeled neurons. In particular DL proportions were largely independent of the number and density of labeled neurons. They only deviated significantly from mean values in those sections in which the number of labeled neurons amounted to less than 20% of the maximal number of labeled neurons found in one section throughout the overlap zone.Our results show that divergence is common in afferents to the cat visual cortex. The amount of divergence, however, varies considerably according to the origin of the afferent projection. The proportion of diverging neurons expressed as the percentage of the total number of neurons projecting to areas 17 and 18 was 3% in the A‐laminae of the dorsal part of the lateral geniculate nucleus, about 8% in the posteromedial lateral suprasylvian area, and about 15% in the C‐laminae of the dorsal part of the lateral geniculate nucleus, in the medial interlaminar nucleus, in the lateral part of the lateral posterior nucleus, and in the claustrum. The proportions of diverging neurons in the afferent projections to areas 17 and 19, and to areas 18 and 19 were about 10%. Diverging neurons were also found in the projections of the intralaminar thalamic nuclei to the visual cortex.The findings demonstrate that the primary thalamocortical projection in the cat's central visual system, from the A‐laminae of the dorsal part of the lateral geniculate nucleus to area 17, contains a negligible proportion of diverging neurons, whereas other afferent subcortical and cortical projections may distribute up to 15% of their total information to at least two target areas in the occipital cortex.