bluuebunny/crossref_metadata_2025_split huggingface dataset:
Goldfish retinotectal system: Continuing development and synaptogenesis
Authors: Marotte L. R. 
Published: January 2005

AbstractThe development of the retina and tectum in goldfish was studied using light and electron microscopy. Soon after hatching the retina is well differentiated in that all the layers of the adult retina are present. The tectum at this time lacks the characteristic layered structure of the adult and innervation in the stratum opticum is extremely sparse, being confined mainly to the rostral region. The retina grows rapidly and retinal layers increase in thickness. This continues into adulthood. Optic innervation of the tectum increases and in fish 19 mm in body length the adult pattern of layers seen by silver staining and by electron microscopy is recognizable. At this time the optic nerve contains large number of unmyelinated axons. The thickness of tectal layers continues to increase over the entire size range of fish studied, well into adulthood. Synaptic densities in the layer of optic termination also change. Density falls in the rostral region as the fish increase in size. In the caudal region there is an initial decrease followed by a small increase. Total numbers of synapses in the main layer of optic termination increase both rostrally and caudally over the entire range of fish studied. Optic and nonoptic fibers contribute to this. The optic nerve at this stage is almost completely myelinated. The continuing growth of both the retina and tectum, including synaptogenesis, may provide a basis for the remarkable regeneration and plasticity shown by this system.
Cell responses evoked by tooth pulp stimulation above the marginal layer of the cat's trigeminal nucleus caudalis
Authors: Dawson N. J. , Hellon R. F. , Hubbard J. I. 
Published: January 2005

AbstractIn cats anesthetized with urethane, all‐or‐nothing, synaptically evoked recordings were made from 80 separate units in the descending spinal tract of the trigeminal nerve above the left trigeminal nucleus caudalis, at depths not exceeding 50 μm from the surface of the medulla. The units were excited by the left upper (21), left lower (25), either (28), or only on simultaneous stimulation of both (six) canine tooth pulps. There was no somototopic distribution.The latency of responses ranged from 4 to 82 msec. For the group of 28 units excited by upper and lower tooth pulps, there was close matching of response latencies from the two teeth.An abrupt decrease in latency upon increasing stimulation strength (“jumping”), and a gradual increase in latency during repetitive stimulation at a frequency between 1 and 20 Hz (“drifting”) was characteristic of most, but not all, responses. Units evoked by stimulation of the inferior dental or infraorbital nerves had similar characteristics.Stimulation of a tooth pulp at threshold for a particular unit was used to test the excitability of that unit after suprathreshold stimulation of the same or a different canine tooth pulp. Stimulation of the upper left canine tooth pulp was generally only facilitatory, while stimulation of the lower left canine tooth pulp was initially facilitatory and later inhibitory. Stimulation of the upper or lower right canine tooth pulps did not excite but could inhibit units excited by the left canine tooth pulps.There was a significant correlation between the frequency at which a unit would follow repetitive stimulation and the duration of the inhibition generated by the first of a pair of stimuli. Long inhibition was associated with poor frequency following.
Corticocortical neurons projecting to the medial and lateral banks of the middle suprasylvian sulcus in the cat: An experimental study with the horseradish peroxidase method
Authors: Kawamura Koki , Naito Jumpei 
Published: January 2005

AbstractCorticocortical afferents to both cortical walls of the cat middle suprasylvian sulcus (MSs area) were investigated by means of retrograde axonal transport of horseradish peroxidase (HRP).The visual cortex (V‐I and V–II) projects to the medial wall of the MSs, the projection from V–II being heavier. The auditory cortex (A‐I, A‐II, and Ep), including cortical walls of the dorsal part of the anterior and posterior ectosylvian sulci, sends fibers to the lateral wall of the MSs. Connections from the first auditory area (A‐I) are heavier than from the second (A‐II). In the rostral part of the MSs, both the medial and lateral walls receive fibers from the somatosensory (S‐I and S‐II) cortex. A larger number of association fibers appear to arise from S‐II than S‐I. Although the MSs as a whole apparently receives various kinds of sensory inputs, there seems to be a parcellation of the MSs area such that the areas receiving cortical association fibers from the visual, auditory, or somatosensory cortical areas also receive thalamic projections from those parts of the thalamus receiving sensory connections of the same modality.The cells of origin of the association fibers were mostly pyramidal, the majority located in layer III (e.g., 80% in the visual cortex and 74% in the auditory cortex), some in layer V, and a few in other layers. Most (76–79%) of the labeled cell bodies were of 15–20 μm diameter. Smaller (8–15 μm) and larger (20–26 μm) cells constituted less than 15% in each case. The mean diameters were 17.0 ± 2.8 μm (SD) in the visual cortex and 17.7 ± 3.2 μm (SD) in the auditory cortex.
Growth of a limb spinal nerve: An ultrastructural study
Authors: Prestige M. C. , Wilson Margaret A. 
Published: January 2005

AbstractA quantitative study of the delivery of nerve fibers to the developing limb has been made. Electron microscope (EM) sections of SN 9 in Xenopus were taken at close intervals between dorsal root ganglion and limb‐bud. Numbers and types of axons in each section were counted. Counts declined steadily with distance from the ganglion towards the base of the limb. This is largely due to some axons not having grown the full distance at the time of fixation. The slope corresponded with an outgrowth velocity of 0.5 mm a day, without branching. Distally, at stages 50 and 51, but not at stages 49 or 54, the decline was reversed, and a peak of axon number was found. This is strong evidence for axon branching in this region. Since this took place at least one stage before SN 9 bifurcated, and since the bifurcation was distal to the branching when it did appear, it is suggested that axon branching at a nerve bifurcation might be part of a trial‐and‐error mechanism for pathway selection. Observations were made on the sheath surrounding the nerve, and on its assembly. Initially, axons grow out naked and not parallel; Schwann cells migrate after the growing front. Processes of these cells collect individual axons, and transfer them inwards to form the primitive parallel fibre bundle, enclosed by a family of Schwann cells. Myelination later occurs in a similar manner: Schwann‐cell processes extend into a bundle of naked axons and eventually encircle a single transitional axon, with one Schwann cell eventually containing many such axons. Finally comes the stage of promyelin, in which a single Schwann cell encircles a single axon. Myelin whorls are then formed from this complex.
Transplantation of embryonic occipital cortex to the tectal region of newborn rats: A light microscopic study of organization and connectivity of the transplants
Authors: Jaeger C. B. , Lund R. D. 
Published: January 2005

AbstractOccipital cortex was taken from fetal rats and transplanted to the tectal region of newborn rats, where it developed a specific structural identity reflecting in part its cortical origin. The implants showed locally distributing intratransplant connections, and the majority formed connections with defined regions of the host cerebral cortex and the brainstem. A sparse afferent projection from the host had its origin in visual, somatosensory, and cingulate areas of the cortex, pretectum, superior colliculus, central gray, hypothalamus, pontine reticular formation, raphe nuclei, and the locus coeruleus. No input was identified from either the retina or the dorsal thalamus. Efferent fibers were observed in normal fiber preparations as compact bundles running through the host brainstem along two main routes, one group of bundles in a dorsal position and a second group more ventral. Efferent fibers traveling rostrally along the first pathway distributed in the ower part of the stratum griseum superficiale and in intermediate laminae of the superior colliculus, and in some cases they reached the pretectum and the lateral posterior thalamic nucleus. Deep efferent fibers ran rostrally and caudally in the central gray, and in some cases laterally directed fibers were seen to distribute in the midbrain tegmentum and reticular formation, in one case reaching the pontine gray.The finding that most afferent and many efferent connections of cortical transplants are uncharacteristic of normal cortex stands in marked contrast to retina and tectum, which, when transplanted to the same region, make relatively normal connections.
A comparison of thalamocortical and other synaptic inputs to dendrites of two non‐spiny neurons in a single barrel of mouse SmI cortex
Authors: White Edward L. , Rock Michael P. 
Published: January 2005

AbstractA Golgi impregnated, non‐spiny multipolar cell whose soma occurred in layer V of the region of mouse SmI cortex containing the posteromedial barrel subfield (PMBSF) (Woolsey and Van der Loos, '70) was gold‐toned and deimpregnated (Fairen et al., '77). Two of its dendrites, contained within a single PMBSF barrel, were serial thin‐sectioned and then reconstructed in three dimensions. Dendrites of an unimpregnated, non‐spiny layer IV bitufted cell, present within the same barrel, were also reconstructed in three dimensions from the series of thin sections. This approach permitted a comparison of the distribution of synapses along dendrites of the two non‐spiny neurons. Results showed dendrites of the layer IV bitufted cell formed about twice as many synapses per unit lenght as those of the multipolar cell. Particularly striking was the contrast between the large number of synapses made by degenerating thalamocortical axon terminals with the dendrites of the bitufted cell and the rarity with which such synapses occur on dendrites of the multipolar cell. Furthermore, the proportion of the total number of synapses made by thalamocortical axon terminals onto dendrites of the bitufted cell was six times greater than the proportion of the thalamocortical synapses onto the multipolar cell dendrites.
An ultrastructural and biochemical analysis of norepinephrine‐containing varicosities in the cerebral cortex of the turtle pseudemys
Authors: Ouimet Charles C. , Patrick Robert L. , Ebner Ford F. 
Published: January 2005

AbstractThe fine structure and norepinephrine content of small granular vesicle‐containing profiles were studied in normal and norepinephrine‐depleted cerebral cortex of the turtle, Pseudemys. The cortex was fixed for electron microscopy with the KMnO4 procedure of Koda and Bloom ('77), while the norepinephrine content was assayed with the radioenzymatic method of Coyle and Henry ('73). Green fluorescent fibers have been described by Parent and Poitras ('74) as located almost exclusively in the outer half of the molecular layer in turtle cortex. Small granular vesicle‐containing profiles are found down to 100 μm below the pial surface, but over 50% lie within 20 μm of the surface. Within the outer 100 μm of cortex, the frequency of labeled varicosities is 1.39/1,000 μm2. The average area of the norepinephrine‐containing varicosities is 0.61 μm2, and there is a mean of 18.4 vesicles per single section. The average number of large plus small vesicles in an entire varicosity was estimated to be 72. Synaptic membranes are not well‐preserved with KMnO4 fixation, but good examples were found of small granular vesicle‐containing profiles forming both symmetrical and asymmetrical membrane differentations. Only a small percentage of the small granular vesicle profiles were associated with a synaptic membrane differentiation in single sections. When norepinephrine‐fiber synapses are seen, they usually share a postsynaptic element with another unlabeled vesicle‐containing profile. Normal turtle cortex contains an average norepinephrine concentration of 1.95 μg/gr, which is about eight times higher than in rat cortex. The ratio of norepinephrine to dopamine is about 18 to one, suggesting that dopamine is present predominantly in a precursor pool for norepinephrine. Small granular vesicle‐containing profiles were eliminated after tratment with reserpine and 6‐hydroxydopamine in concentrations that were shown to reducenorepinephrine concentration by 94% and 86%, respectively. The labeled varicosities were partially depleted by midbrain hemisection and by an inhibitor of dopamine‐beta‐hydroxylase (FLA‐63). The norepinephrine‐containing varicosities are remarkably coextensive with the distribution of thalamic fibers, both in the total extent of cortex where they are found and in the depth of cortex where they terminate. The results support the idea that there is a close structural and functional association between locus coeruleus and thalamic fibers in cerebral cortex, and the apparent difference in frequency of synapses suggests that each fiber system exerts its influence on cortical cells in a different way.
Neurogenesis in the 3‐month‐old rat visual cortex
Authors: Kaplan Michael S. 
Published: January 2005

AbstractNewly formed neurons in the adult mammalian neocortex have been reported by several investigators using light microscopic radioautography, but these reports have not been confirmed by electron microscopy—probably because their rarity precludes any reasonable chance of observing these cells with electron microscopic radioautography. To overcome this problem I have used a recently developed method that allows serial thin sectioning and subsequent electron microscopic examination of plastic‐embedded sections previously prepared for light microscopic radioautography. Ninety‐day‐old rats were injected with 4.3 μCi per gm body weight of [H3] thymidine and allowed to survive for 30 days. In the light radioautographs, labeled cells were found in layer IV of the visual cortex, and analysis of electron micrographs of selected examples of these labeled cells clearly demonstrated their neuronal nature with synapses along their cell bodies and dendrites. In order to quantify the relative frequency of labeled neurons, the number of labeled cells seen in the light microscopic sections was expressed as a percentage of the total number of neurons found in sections through the entire thickness of the visual cortex; the percentage was 0.011%, or about 1 in 10,000. The results of this study are in agreement with evidence of neurogenesis of granular neurons in the adult rat olfactory bulb and dentate gyrus (Kaplan and Hinds, '77). Thus, it has now been confirmed that relatively small labeled neurons and their synapses are found in at least 3 brain regions (olfactory bulb, dentate gyrus, and visual cortex) in a normal adult rodent.
Central distribution of octavolateral afferents and efferents in a teleost (mormyridae)
Authors: Bell Curtis C. 
Published: January 2005

AbstractThe central distribution of afferents from individual eighth nerve branches (N VIII) and mechanical lateral line end organs in mormyrid fish are described. Afferents were labeled with horseradish peroxidase (HRP) placed on the cut ends of the different N VIII branches and the anterior and posterior lateral line nerves.Descending, tangential, and magnocellular nuclei receive input almost exclusively from the utriculus and canals. Nucleus octavius receives afferents from the lateral line nerves and all N VIII branches, with one part receiving exclusive and bilateral input from the sacculus. Afferents from both lateral line nerves and all N VIII branches, except the sacculus, end in eminentia granularis. Afferents from each of the two lateral line nerves and from each of the three otolith branches of N VIII end in different regions of the anterior lateral line lobe, with some areas of overlap.Behavioral studies in other families of fish indicate that the utriculus and canals are critical for postural control, whereas the sacculus and possibly the lagena are concerned with hearing. Such findings, together with the results of this study, suggest that mormyrids and perhaps other fish possess separate auditory and vestibular centers within the octavolateral area.The HRP method also shows the cell bodies and axons of octavolateral efferents. N VIII and lateral line efferents arise from a common nucleus, and the central course of their axons parallels that of facial motoneurons. Axons of efferent cells divide to supply two or more branches of N VIII and some axons supply both lateral line and N VIII end organs.
Abnormal axonal growth in the dorsal lateral geniculate nucleus of the cat
Authors: Robson J. A. 
Published: January 2005

AbstractRetino‐geniculate axons in the cat were induced to grow abnormally by cutting one optic nerve in kittens. Surviving optic tract axons that had grown into the denervated regions were then filled in the adults with horseradish peroxidase to reveal the terminal arbors of individual axons. Two types of abnormal axonal growth are described—translaminar growth and monocular segment growth. Translaminar growth is the most common and occurs between lamine in the binocular part to the nucleus. Axons giving rise to translaminar growth do not branch as they pass through the denervated regions of the nucleus. Instead, the abnormal branches originate from portions of the terminal arbor within the normal target lamina. These axons look like normal retino‐geniculate axons in terms of their branching patterns, cytological features, and patterns of synaptic contacts except that parts of their terminal arbors have expanded to innervate inappropriate laminae. The distribution of translaminar branches overlaps the distribution of a restricted group of surviving large neurons that have not undergone denervation atrophy.Monocular segment growth invades the lateral pole of the nucleus directly from the optic tract. These branches arise from axons passing through or near the denervated region and appear to represent the formation of new terminal arbors. The synaptic swellings arising from these branches have cytological features like the synaptic swellings arising from translaminar branches and they from similar patterns of synaptic contacts. However, monocular segment branches degenerate more rapidly when damaged and they are not associated with surviving large neurons.
Anomalous uncrossed retinal projections fail to activate superior colliculus neurons in rabbits unilaterally enucleated by fetal surgery
Authors: Chow Kao Liang , Ostrach Louis H. , Crabtree John W. , Bernegger Otto , Baumbach H. Dale , Lawson Robin 
Published: January 2005

AbstractPrevious studies have shown that unilateral enucleation of rabbit pups produces an aberrant uncrossed retinotectal projection. These fibers failed to drive collicular units when stimulated with either light or electric shock. The present study attempts to assess the possibility that enucleation at earlier stages of development would lead to a greater degree of morphological and physiological reorganization in the uncrossed retinotectal projection.Rabbit fetuses were unilaterally enucleated at day 20 or 25 of gestation. Birth is at day 31. After 3 months, the degree of reorganization of the uncrossed retinotectal projection was assessed using the following techniques: (1) autoradiographic demonstration of the projection from the remaining eye, (2) electrophysiological recording of collicular unit activity, and (3) a combination of these methods.Autoradiographic data indicated a much greater expansion of the anomalous uncrossed projection in fetally enucleated animals than in those enucleated at birth. Labelled terminals were found to occupy more than the anterior third of the ipsilateral colliculus and were distributed to the entire depth of the stratum griseum superficiale and stratum opticum.Electrode penetrations within the boundaries of the expanded projection failed to locate collicular units which could be driven by either light stimulation of the eye or electric shock of the optic nerve. Only a few cells encountered in the lateral border area, receiving the normal uncrossed retinal projection, could be driven by light stimulation.These negative findings are in contrast to the data reported for the rat and hamster where anomalous retinal projections are capable of forming functional connections. Further comparative studies of reorganization are needed.
Fate of the hippocampal mossy fiber projection after destruction of its postsynaptic targets with intraventricular kainic acid
Authors: Nadler J. Victor , Perry Bruce W. , Gentry Christine , Cotman Carl W. 
Published: January 2005

AbstractIntraventricular injections of kainic acid were used to create a model of selective cell death in order to study the fate of afferent projections that are deprived of their postsynaptic targets. This treatment rapidly destroyed hipocampal CA3 pyramidal cells, but not those neurons that give rise to their mossy fiber and entorhinal afferents. Light microscopic studies with the Timm's sulfide silver stain indicated that half or more of the mossy fiber boutons in area CA3b were lost within the first 1–3 days after kainic acid administration. This finding was confirmed by electron microscopy. Electron‐dense, usually vacuolated mossy fiber boutons accounted for about 10–20% of the total population present at a 4‐hour survival time, but were not encountered in control rats nor at survival times longer than 1 day. Other mossy fiber boutons remained electron lucent, but enlarged became more rounded in shape, and suffered and apparent loss of synaptic vesicles. It is suggested that degeneration of some mossy fiber boutons and resorption of others into the axon may have accounted for the precipitous decline in their number. The dendritic excrescences contacted by these boutons were nearly all undergoing electron‐dense degeneration 4 hours after kainic acid administration. In rats that survived 6–8 weeks mossy fiber boutons remained somewhat scarce, individual boutons appeared relatively small, and only one‐third the normal percentage were observed to be engaged in more than one synaptic contact within a single cross section. A qualitative electron microscopic study of the entorhinal projection to area CA3 suggested a response to kainic acid treatment similar to that of the mossy fiber projection, except that no entorhinal boutons were seen to become electron dense.These findings suggest that presynaptic fibers in the mature hippocampus adjust the size of their terminal arborizations and number of synaptic contacts to accommodate a reduction in the target cell population. The rapid loss of mossy fiber boutons may be attributable to an unsual fragility of these structures when they are deprived of the mechanical support normally provided by the pyramidal cell. Finally, the ability of kainic acid administration to alter the number and distribution of presynaptic elements must be taken into account whenever this toxin is used to make selective lesions of postsynaptic cells.