bluuebunny/crossref_metadata_2025_split huggingface dataset:
The structure of the diencephalic prepacemaker nucleus revisited: Light microscopic and ultrastructural studies
Authors: Zupanc Günther K. H. , Heiligenberg Walter 
Published: May 2005

AbstractThe prepacemaker nucleus (PPn), a bilateral cluster of neurons at the boundary of diencephalon and mesencephalon, controls frequency modulations of the electric organ discharge in weakly electric knifefish (Eigenmannia sp.). Previous light microscopic studies employing retrograde labelling with horseradish peroxidase suggested that the PPn is restricted to a small area, located approximately 400 μm laterally from the third ventricle and fusing at its medial edge with the thalamic central posterior nucleus (CP). In the present investigation we used Phaseolus vulgaris‐leucoagglutinin and cholera toxin as highly sensitive markers. In contrast to the previous studies, these experiments yielded a large number of labelled cells not only in the region of the traditionally defined PPn but also in an area reaching far into the CP. Since the PPn has been defined by retrograde labelling rather than by topographic criteria, this result questions the traditional separation between PPn and CP. Such a notion is in agreement with observations of Nissl‐stained sections at the light microscopic level and with a quantitative analysis of several morphological characteristics of the cell bodies in the PPn and CP at the ultrastructural level. Both sets of experiments failed to find differences between the two nuclei. Furthermore, autoradiographic studies have shown that, even in adulthood, cells are continuously born within the ventricular zone of the CP, and at least some of these newborn cells differentiate into CP cells and migrate laterally towards the PPn. Therefore, we postulate that CP and PPn form one large complex, with the medial CP providing precursors of neurons in the lateral CP and PPn. © 1992 Wiley‐Liss, Inc.
Fine structure and blood‐brain barrier properties of the central nervous system of a dipteran larva
Authors: Juang Jyh‐Lyh , Carlson Stanley D. 
Published: May 2005

AbstractUsing scanning and transmission electron microscopy, we studied basic ultrastructure, membrane specializations, and blood‐brain barrier properties of the ventral ganglion and abdominal nerves of the last (third) instar larva of a dipteran fly, Delia platura. Both ganglion and nerves are covered with a non‐cellular neural lamella. A monolayer of flattened perineurial cells lies beneath the neural lamella. Perineurial cells contain stores of metabolites and nutrients and these cells extensively interdigitate with one another. An extensive extracellular series of channels pervades perineurial cells. Glial cells beneath the perineurium envelope but do not entwine axons. In a minority of cases, adjacent axons in nerve and neuropil appear to be contiguous without glial intervention. Extensive (pleated) septate junctions with triangular septa are present between perineurial cells. Hemidesmosomes, half desmosomes (a first report for invertebrates), and desmosomes were also observed. Although no tight junctions were discovered, an effective blood‐brain barrier exists, and tracer (ionic lanthanum) in no case reached neuronal surfaces. Extracellular tracer halted within the extensive septate junctions between perineurial cells. We postulate that in the absence of tight junctions the functional blood‐brain barrier is effected by the septate junctions in the central nervous system of the Delia larva.
Projections from the laterodorsal nucleus of the thalamus to the limbic and visual cortices in the rat
Authors: Van Groen Thomas , Wyss J. Michael 
Published: May 2005

AbstractThe laterodorsal nucleus (LD) of the thalamus is an important source of thalamic afferents to the limbic cortex, but the topography and lamination of these projections has not been investigated in detail. Using the anterograde transport of Phaseolus vulgaris leucoagglutinin and Fluoro‐Ruby, the present study demonstrates that in the rat, LD projects to infraradiata, precentral agranular, retrosplenial, visual (area 18b), subicular, and entorhinal cortices. Each subregion of LD has a distinct pattern of terminals within these cortical areas. The rostral part and the dorsalmost part of LD project densely to retrosplenial granular a (Rga) cortex, presubiculum and parasubiculum. Slightly more caudal parts of dorsal LD project primarily to the postsubiculum. More ventral parts of LD project primarily to retrosplenial dysgranular (Rdg) and retrosplenial granular b (Rgb) cortices. The projection of LD to area 18b originates from cells in the caudalmost part of LD. In each cortical region, LD terminals display distinct laminar patterns. In area 18b and the adjacent Rdg cortex, the LD terminal field is in layers I, III, and IV, but in both the Rgb and Rga cortices the terminal field is located predominantly in layer I. In the postsubiculum the LD terminals are distributed to layers I and III/IV and extend into superficial layer V; in the presubiculum and the parasubiculum the LD terminals are only in the deep layers (i.e., layers IV–VI). A small number of LD axons terminate in the deep layers (i.e., layers IV–VI) of the medial entorhinal cortex. These results indicate that each area of LD has a distinct projection to limbic and adjacent neocortex.
The superficial plexiform layer: A third retinal association area
Authors: Wieniawa‐Narkiewicz Elzbieta , Hughes A. 
Published: May 2005

AbstractElectron microscopy enables the identification of a new association area in the mammalian retina. It is a region whose processes and synaptic junctions form a diffuse and intermittent layer bridging the boundary between the optic nerve fibre layer and ganglion cell layer. It involves displaced amacrine cells, retinal ganglion cells and probably interplexiform cell processes. Because it is close to the vitreal surface of the retina and has several properties of a plexiform layer, it has been named the superficial plexiform layer. It is much more sparse than the outer or inner plexiform layers in the rabbit, but contains a significant and substantial density of 6,100 synapses/mm2 near the visual streak.Morphological criteria distinguish two classes of synapses in the new association area. One has features of Colonnier's symmetric type and is formed by amacrine‐like processes or their terminals, onto other amacrine‐like processes or the cell bodies, dendrites and axon hillocks of some large ganglion cells. It makes up 79% of the population at a density of 4,800 synapses/mm2 in the examined sample.The second class arises from large processes of the fibre layer, which resemble axons rather than amacrine cell branches, has Colonnier's asymmetric form, and synapses onto a variety of other neuronal processes and cells. At a local density of 1,300/mm2 this type forms 21% of the population.A series of experiments including Wallerian degeneration, retrograde degeneration, electron microscopy and horseradish peroxidase (HRP) transport was employed to determine the nature of the large synapse‐forming processes of the fibre layer that were the most amenable to investigation. It is concluded that the processes project into the optic nerve because they can be filled with HRP by retrograde transport from the end of the transected optic nerve. Although this result is based on limited evidence, it is complemented by the observation that the majority of the fibres undergo retrograde degeneration within 25 days of optic nerve section. It is concluded that the processes are either centrifugal fibres or the axons of retinal ganglion cells. The persistence of a relatively normal density of synapse‐forming large fibres for seven days after optic nerve section, without Wallerian degeneration, argues that they are not the terminals of centrifugal axons. This conclusion is complemented by a separate class of profiles that did degenerate in this short period and are concluded to represent the centrifugal fibres.The large synapsing processes of the fibre layer are concluded to be the axons of some large ganglion cells. Their connections indicate the presence of feedback loops onto other large retinal ganglion cells both directly and indirectly through amacrine pathways. The superficial plexiform layer thus contains a rich variety of organised synaptic connections whose functional significance remains to be established.
A multiterminal stretch receptor, chordotonal organ, and hair plate at the wing‐hinge of Manduca sexta: Unravelling the mystery of the noctuid moth ear B cell
Authors: Yack Jayne E. 
Published: May 2005

AbstractThe present study aims to shed light on the evolutionary origin of the B cell, a sensory element of unknown function in the noctuid moth ear.Peripheral projections of the metathoracic nerve IIIN1b1, homologue of the noctuid moth tympanic nerve, are described in the atympanate moth Manduca sexta on the basis of dissections with the aid of Janus Green B, and intracellular tracer dyes Lucifer yellow and cobalt lysine. A large multiterminal (Type II) neurone, attaching to membranous cuticle ventral to the hind wing axillary cord, was discovered. This cell appears to be homologous to the B cell in the noctuid moth ear. Recordings from the IIIN1b1 nerve in M. sexta reveal a continuous train of large, uniform spikes, presumed to originate From the multiterminal cell. This unit increases its rate of firing in response to hind wing elevation, suggesting that it functions as a stretch receptor monitoring wing movements during flight. Also identified in the tympanic nerve homologue, and closely associated with the multiterminal cell, were a chordotonal organ and hair plate. The chordotonal organ consists of a proximal scolopidial region and a distal strand that attaches to the sclerotized epimeron slightly medial to the multiterminal cell. This simple chordotonal organ, having three uniterminal (Type I) sensory cells, is homologous to the auditory cells of the noctuid moth ear.The significance of these receptors as proprioceptors in M. sexta, and as evolutionary precursors to the noctuid moth ear, is discussed.
Ultrastructural development of the medial superior olive (MSO) in the ferret
Authors: Brunso‐Bechtold J. K. , Henkel C. K. , Linville C. 
Published: May 2005

AbstractWhen ferrets are born, four weeks before the onset of hearing, few synapses are evident in the medial superior olive (MSO). The synapses present are immature and almost exclusively found in the neuropil. The MSO somata are virtually devoid of synaptic contacts but are contacted by fine glial processes that increasingly ensheathe the somata during the first postnatal week. By P12, somatic synaptogenesis in the MSO is evident. Initially the terminals contain vesicles of irregular shape, size, and distribution. The glial lamellae appear to withdraw as the synaptic contacts form but continue to cover the asynaptic portions of the cell surface. The lamellae frequently extend from an sheathing the soma to encapsulate the immature terminals. During the next two weeks, synaptic density and terminal encapsulation proceed until the somata is surrounded by encapsulated synaptic terminals as in the adult ferret MSO. While most immature terminals contain round vesicles, during the first postnatal week some terminals with nonround vesicles can be distinguished. The first distinction between types of nonround vesicle‐containing terminals, i.e., pleiomorphic and ovoid, is in the second postnatal week. This distinction becomes increasingly clear and by the end of the first postnatal month, terminal types can be reliably categorized. These observations indicate that: (1) synapses are present in the MSO neuropil one month prior to the onset of hearing, (2) the major period of synaptogenesis begins approximately two weeks prior to the onset of hearing, and (3) glial lamellae ensheathe MSO somata prior to the onset of somatic synaptogenesis, withdraw as synapses form, and subsequently re‐extend to encapsulate newly formed synapses.
Redeployment of trigeminal motor axons during metamorphosis
Authors: Omerza Frank F. , Alley Keith E. 
Published: May 2005

AbstractAs a consequence of the degeneration and replacement of the jaw muscle fibers in the leopard frog, Rana pipiens, trigeminal motoneurons innervate different targets before and after metamorphosis. This investigation examined the morphological correlates of the reassignment of trigeminal motoneurons during the initial phases of myofiber turnover. Specifically, silver‐cholinesterase histochemistry and electron microscopy were used to 1) identify the fate of motor axons within the neuromuscular junctions (NMJs) applied to degenerating larval myofibers and 2) to determine the origin(s) of the motor axons that innervate the postmetamorphic muscle fibers of the jaw.The results demonstrate that the NMJs are retained on larval myofibers throughout their degeneration and are readily identifiable on the residual larval basal laminae that remain after involution of the sarcoplasm. Light and electron microscopic observations provide evidence that both pre‐ and post‐synaptic elements are present on the degenerating fibers. Furthermore, morphometric analyses indicate that the preponderance (86%) of motor axons supplying adult muscle fibers originates from the larval NMJs. This condition suggests that metamorphic redeployment of trigeminal motoneurons occurs through the resumption of growth at the axon terminal supplying larval muscle rather than through the proximal collateralization of these axons and resorption of larval terminals. © 1992 Wiley‐Liss, Inc.
Independent efferent populations in the nucleus of the optic tract: An anatomical and physiological study in rat and cat
Authors: Schmidt Matthias , Schiff Daniel , Bentivoglio Marina 
Published: May 2005

AbstractThe efferent projections of the nucleus of the optic tract (NOT) and dorsal terminal nucleus of the accessory optic system (DTN) to the contralateral NOT‐DTN, ipsilateral inferior olive (IO), ipsilateral nucleus prepositus hypoglossi (NPH), and ipsilateral dorsal lateral geniculate. nucleus (LGNd) were examined in pigmented rats and in cats by using anterograde and retrograde tract tracing, as well as extracellular recording and electrical stimulation.Anterograde tracing in the rat revealed a dense termination field of NOT‐DTN efferents throughout the homologous contralateral territory.In both species three different cell populations, projecting to the contralateral NOT‐DTN, ipsilateral IO, and ipsilateral LGNd, respectively, were distinguished by means of multiple retrograde tracing. No clear topographical segregation of the different NOT‐DTN relay cell populations was observed. On the other hand, a large proportion (at least 60%) of NOT‐DTN neurons projecting to the ipsilateral NPH were found to bifurcate upon the IO in the rat.Electrophysiologically, NOT‐DTN neurons projecting to the IO were identified by their directionally selective responses. Such neurons were never activated by electrical stimulation of either the contralateral NOT‐DTN or the ipsilateral LGNd. Neurons antidromically activated from the contralateral NOT‐DTN could not be activated from the ipsilateral LGNd.Thus, in both cat and rat the NOT‐DTN includes at least three independent relay cell populations. As a consequence, the NOT‐DTN must serve functions additional to the generation of eye movements during optokinetic nystagnus, a function subserved by the directionally selective NOT‐DTN cells. © 1995 Wiley‐Liss, Inc.
Ultrastructure of the synaptic terminals of the dorsal giant serotonin‐IR neuron and deutocerebral commissure interneurons in the accessory and olfactory lobes of the crayfish
Authors: Sandeman R. E. , Watson A. H. D. , Sandeman D. C. 
Published: May 2005

AbstractThe olfactory and accessory lobes in the crayfish are large spherical neuropils found on each side of its brain. The olfactory lobes receive the afferent axons of chemoreceptors that are located along the outer branches of the biramous first antennae. The accessory lobes receive a large input from interneurons whose axons lie in the deutocerebral commissure. A pair of large serotonergic neurons (the dorsal giant neurons) branch unilaterally in the accessory and olfactory lobes of each side. From physiological recordings, it has been proposed that the deutocerebral commissure interneurons synapse with elements in the accessory lobes that in turn connect to the dorsal giant neuron. It has also been proposed that the dorsal giant neuron is activated by inputs in the accessory lobe and that its output is in the olfactory lobe. This ultrastructural study tests this hypotheses by examining the polarity of synaptic terminals on dorsal giant neurons and deutocerebral interneurons that have been filled with neurobiotin. In double‐labelled preparations, we found the deutocerebral interneurons to be presynaptic to elements in the accessory lobes, but none of these postsynaptic elements was identifiable as the dorsal giant neuron. The dorsal giant neurons receive many more synaptic inputs in the accessory lobes than in the olfactory lobe. Very few giant serotonin neuron output synapses were found in either lobe. © 1995 Wiley‐Liss, Inc.
Modulation of neurotransmitter receptors following unilateral L1–S2 deafferentation: NK1, NK3, NMDA, and 5HT1a receptor binding autoradiography
Authors: Croul S. , Sverstiuk A. , Radzievsky A. , Murray M. 
Published: May 2005

AbstractFollowing surgical deafferentation of the spinal cord, cut dorsal roots degenerate, and spared projections compensate for this loss by collateral sprouting (reactive reinnervation). Light microscopic immunocytochemistry has shown sprouting by selected undamaged intraspinal projections, including those that express the transmitters substance P and serotonin. Quantitative immunoelectron microscopy supports these results by demonstrating loss and subsequent recovery of substance P‐containing terminals and an increase in serotonin‐containing terminals. To test the hypothesis that changes in afferent innervation modulate neurotransmitter receptors on second‐order neurons, we used receptor binding autoradiography in this model. Adult rats were subjected to L1–S2 unilateral dorsal rhizotomy and killed at 1, 2, 6, or > 20 weeks after surgery. Receptor binding densities of tachykinin (neurokinins‐1 and ‐3), glutamate (N‐methyl‐D‐aspartate), and serotonin (serotonin‐1a) receptors were assayed in the lumbar dorsal horn. Neurokinin‐1 binding density was increased in lamina II of the deafferented side by 1 week after surgery, remained elevated at 2 weeks, and returned to control values by 6 weeks. Neurokinin 3 binding density was elevated at 2 weeks and then returned to control levels. N‐methyl‐D‐aspartate receptor binding showed slight but not statistically significant increased binding density at 6 and at > 20 weeks. No significant changes were found in serotonin‐1a receptor binding density. The elevations in tachykinin receptor binding density occur when afferents in the dorsal horn are degenerating and suggest reactive up‐regulation of the receptor. The return to normal levels coincides with reactive reinnervation in the spinal cord, which restores synaptic numbers. Changes in N‐methyl‐D‐aspartate binding occur much later than the restitution of synaptic numbers but may indicate a role for this receptor in synaptic stabilization following reactive reinnervation. © 1995 Wiley‐Liss, Inc.
Projections of ankle joint afferents to the spinal cord and brainstem of the chicken (Gallus G. domesticus)
Authors: Gentle Michael J. , Hunter Louise N. , Sterling Robert J. 
Published: May 2005

AbstractThe projections of the ankle joint capsule afferents were studied by transganglionic transport of horseradish peroxidase injected directly into the ankle joint. The number and size of the labelled dorsal root ganglion cells were measured from synsacral nerves 2–9. In the dorsal root ganglia, all sizes of sensory neurones were labelled, and the largest number of labelled cells was in ganglia 5–7. The extensive sympathetic innervation of the ankle joint was identified by the large number of cell bodies labelled in the sympathetic ganglia of the paravertebral chain. Labelled afferent fibres projected to the spinal cord from the 2nd to the 8th synsacral nerves, with the rostral projection mainly via Lissauer's tract and the dorsal funiculus. Terminal labelling in the dorsal horn was identified in laminae I–III and VI, with a slight projection to V. Two areas of dense labelling, which did not correspond with the largest number of labelled dorsal root ganglion cells, were identified. A rostral area with the highest density of label was observed at the level of synsacral nerves 3–4 and a second slightly less dense area between synsacral nerves 7–8. In the caudal medulla, diffuse terminal labelling was observed in the nucleus gracilis et cuneatus, nucleus of the tractus solitarius, and the nucleus cuneatus externus.These results are discussed in a comparative context to identify similarities and differences between different primary afferent projections in birds and mammals and to highlight the possible functional significance of the avian articular afferent projection. © 1995 Wiley‐Liss, Inc.
Comparative ultrastructural localization of the NMDAR1 glutamate receptor in the rat basolateral amygdala and bed nucleus of the stria terminalis
Authors: Gracy K. Noelle , Pickel Virginia M. 
Published: May 2005

AbstractThe N‐methyl‐D‐aspartate (NMDA)‐type glutamate receptor in the basolateral amygdala (BLA) has been implicated in activity‐dependent plasticity important for cortically evoked acquisition of fear‐potentiated startle response. We examined the ultrastructural immunoperoxidase labeling of the R1 subunit of the NMDA receptor in the BLA of adult rats to determine the potential cellular and subcellular sites mediating the effects generated by NMDA activation. The localization was compared with that seen in the bed nucleus of the stria terminalis (BNST), the major efferent pathway from the central nucleus of the amygdala, which has a more pronounced involvement in autonomic function. Electron microscopy established that in the BLA, 68. 4% (n=177) of the profiles showing NMDAR1–like immunoreactivity (NMDAR1–LI) were dendrites, and 19. 8% were distal tips of astrocytic processes. In contrast, profiles containing NMDAR1–LI (n=262) in the BNST were more equally distributed between dendrites (37. 4%) and axons (38. 2%). The subcellular localization of NMDAR1 immunoreactivity was, however, similar in both regions. Our findings provide the first ultrastructural evidence that glutamate may prominently act through NMDAR1 receptors to elicit postsynaptic actions on intrinsic neurons in the BLA and BNST. The results also indicate that, in the BLA, the NMDAR1 receptor plays an important role in astrocytic function, whereas the receptor is more preferentially a presynaptic modulator in axons which terminate in or pass through the BNST. © Wiley‐Liss, Inc.