bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemosensory anterior dorsal fin in rocklings (GaidropsarusandCiliata, teleostei, Gadidae): Somatotopic representation of the ramus recurrens facialis a revealed by transganglionic transport of HRP
Authors: Kotrschal Kurt , Whitear Mary
Published: January 2005

The anterior dorsal fin in rocklings consists of a fringe of 50–80 delicate, vibratile rays, which are densely beset with epidermal chemosensory cells. The innervation of these cells is from the dorsal branch of the recurrent facial nerve, which also innervates all other fins and the skin of the trunk. This nerve carries at least three classes of fibres: small (0.5–1.5 μm in diameter), medium (1.5–4 μm), and large (>4 μm). Approximately 12,000 small and weakly myelinated nerve fibres from the recurrent facial nerve innervate the anterior dorsal fin organ. Application of HRP at different locations of the recurrent facial nerve labelled three different sizes of sensory perikarya within the geniculate ganglion–small (6–15 μm in diameter), medium (18–24 μm), and large (>25 μ)–which corresponds to the different size classes of fibres present within the nerve. Retrograde transganglionic transport of HRP revealed somatotopy within the brainstem facial lobe: the delicate nerve fibres innervating the chemosensory anterior dorsal fin terminate exclusively in a distinct, dorsal portion of the facial lobe. Fibres innervating the posterior dorsal fin, the anal and caudal fins, as well as the skin of the trunk terminate within caudal and dorsal areas of the ventral facial lobe; pectoral and pelvic fins are represented in the ventral and caudal portions of the ventral facial lobe. Innervation by a distinct type of fibre and exclusive representation within a distinct, dorsal part of the facial lobe may indicate a peculiar biological role in the anterior dorsal fin chemosensory organ in the rocklings.
Aberrant optic axons in the retinal pigment epithelium during chick and quail visual pathway development
Authors: Halfter Willi
Published: January 2005

Examination of a large number of retinal pigment epithelia revealed that, in a small proportion, optic axons in chick and quail eyes aberrantly entered the pigment cell layer between embryonic day (E) 7 to E14. The aberrant retinal axons originated from the main stream of retinal fibers in the optic nerve and invaded the pigment layer from various positions of the optic nerve head or fissure by growing along the basal side of the pigment epithelium. The axon bundles grew several millimeters into the epithelial sheet and arborized at the margin of the eye. As shown by electron microscopy the nerve fibers occurred as bundles of three to several hundred axons. They always were located at the basal side of the epithelium, and were enveloped by processes of epithelial cells. Very large bundles of axons, however, displaced the epithelial cells from the basal matrix. These retinal axons contacted the pigment epithelial basal lamina. The basal extracellular matrix from the retinal pigment epithelium was isolated and used as substratum for in vitro cultures of various types of neural explants. The matrix preparations consisted of a sheet of a 50 nm thick basal lamina with a central lamina densa, two laminae rarae, and a 15 μm thick stroma. Axons from avian retina explants, as well as sensory ganglia, grew on the basal lamina side of the pigment cell matrix with the same growth rate and with the same fiber density as on similarly prepared basal laminae from the neural retina. These experiments show that the matrix from the pigment epithelium of the avian eye does not have negative effects on axonal growth and indicate that a basal lamina from a normally non‐innervated tissue can provide a favorable matrix for axonal growth.
Immunohistochemical localization of neuropeptides in the vocal control regions of two songbird species
Authors: Ball Gregory F. , Faris Patricia L. , Hartman Boyd K. , Wingfield John C.
Published: January 2005

Immunohistochemistry was used to map the distribution of four neuropeptides in song control regions of two songbird species, the European starling (Sturnus vulgaris) and the song sparrow (Melospiza melodia). We searched for positively stained cell bodies or apparent terminals containing vasoactive intestinal peptide (VIP), methionine‐enkephalin (MET), cholecystokinin (CCK), and substance P (SUB P). Intraventricular colchicine pretreatment was administered to enhance the visualization of peptide‐containing cell bodies. Four areas implicated in the central control of song were examined. Three of these areas are sexually dimorphic telencephalic nuclei characteristic of songbirds: the caudal nucleus of the ventral hyperstriatum (HVc), the robust nucleus of the archistriatum (RA), and the magnocellular nucleus of the anterior neostriatum (MAN). The fourth region is the mesencephalic nucleus intercollicullaris (ICo), common to all birds, which contains the dorsomedial nucleus (DM) that appears to be specifically involved in the motor control of song.

The pattern of neuropeptide localization was similar between the two species. However, the neuropeptides were heterogeneously dispersed among the four areas. VIP and MET were the most widely distributed, whereas CCK and SUB P were seen only in DM. MAN and HVc revealed remarkably similar patterns of staining for both MET and VIP. Fine varicosities immunolabeled for both these peptides appear to encircle nonreactive somata. In both these nuclei positively stained somata were observed for MET but not for VIP. In RA there was a dense accumulation of MET‐positive multipolar cell bodies. VIP‐containing neurons were seen in the surrounding archistriatum and caudal neostriatum but not in RA itself. Cell bodies and fibers for all four peptides were observed in DM; in no case were they limited to this subregion, but rather seemed to encompass the surrounding intercollicular area as well. The widespread distribution of VIP and MET strongly suggests a role for these peptides in the acquisition or production of passerine song.
Cortical connections of electrophysiologically and architectonically defined subdivisions of auditory cortex in squirrels
Authors: Luethke L. E. , Krubitzer L. A. , Kaas J. H.
Published: January 2005

Multiunit recordings with microelectrodes were used to identify and delimit subdivisions of auditory cortex in squirrels. In the same animals, cortical connections of subdivisions of auditory cortex were determined by placing injections of the tracer wheat germ agglutinin conjugated with horseradish peroxidase (WGA‐HRP) into electrophysiologically defined locations. The electrophysiological results and patterns of connections were later related to myeloarchitectonic distinctions in brain sections cut parallel to the surface of the artificially flattened cortex. As previously described (Merzenich et al.: J. Comp. Neurol 166:387–402, '76), a primary auditory field, A‐I, was characterized by (1) neurons narrowly tuned to tone frequency; (2) a tonotopic map with high frequencies, which represented caudal to low frequencies; and (3) dense myelination. A‐I was reciprocally connected with a rostral field, R, a parietal ventral somatosensory representation, PV, cortex ventral to A‐I, and other nearby regions of cortex of the same hemisphere. Callosal connections of A‐I were with A‐I, R, and two or more other regions of temporal cortex. The less densely myelinated rostral field, R, also had neurons that were frequency tuned, but the neurons were often less securely driven. R appeared to have a tonotopic organization that roughly mirrored that of A‐I. Ipsilateral connections of R included A‐I, PV, and cortex ventral and caudal to R. Callosal connections were with R, A‐I, PV, and other locations in temporal cortex. Cortex in caudal PV, ventral to A‐I, and ventral to R was responsive to auditory stimuli, but responses to pure tones were weak and inconsistent, and habituation to a repeated stimulus was rapid. The cortex responsive to auditory stimuli included some but not all of the cortex connected with A‐I and R. The results lead to the conclusion that auditory cortex of squirrels contains at least two tonotopically organized fields, possibly as many as five or more auditory fields, and at least two auditory‐somatosensory fields.
Catecholamine‐synthesizing neuronal projections to the nucleus tractus solitarii of the rat
Authors: Thor Karl B. , Helke Cinda J.
Published: January 2005

The objective of the present study was to determine the location of the neurons that give rise to catecholamine‐containing terminals in the nucleus tractus solitarii. This was done by injecting rhodamine‐filled latex microspheres into the nucleus tractus solitarii of rats to retrogradely label neuronal cell bodies and by processing sections from the brains of these animals to determine if the labelled neurons were immunoreactive for the catecholamine‐synthesizing enzymes, dopamine‐beta‐hydroxylase (DBH) and phenyl‐ethanolamine‐N‐methyl transferase (PNMT).

Approximately 60% of the DBH‐immunoreactive neurons that projected to the nucleus tractus solitarii belonged to the A1/C1 cell group, while an additional 20% belonged to the A5 cell group. Thus, these two ventrolateral rhombencephalic cell groups accounted for nearly 80% of the total number of rhodamine‐bead‐labelled DBH‐immunoreactive neurons in this series of experiments. Only a small number of DBH‐immunoreactive neurons of the A2/C2 cell group contained rhodamine‐filled latex microspheres. Rarely, DBH‐immunoreactive neurons in the locus coeruleus and the nucleus subcoeruleus were found to project to the nucleus tractus solitarii.

The majority of the PNMT‐immunoreactive neurons that projected to the nucleus tractus solitarii belonged to the C1 cell group. Only small numbers of PNMT‐immunoreactive neurons of the C2 and C3 groups were found to contain rhodamine‐filled latex microspheres.

It is concluded that neurons in the ventrolateral medulla and pons, some of which presumably utilize norepinephrine and/or epinephrine as a transmitter, could regulate autonomic function via direct projections to the nucleus tractus solitarii.
Calcitonin gene‐related peptide (CGRP) in the human spinal cord: A light and electron microscopic analysis
Authors: Harmann P. A. , Chung K. , Briner R. P. , Westlund K. N. , Carlton S. M.
Published: January 2005

The distribution of CGRP immunoreactivity in the cervical, thoracic, lumbar, and sacral levels of the human spinal cord was mapped at the light microscopic level with the aid of a rabbit‐generated antiserum against human calcitonin gene‐related peptide (CGRP). CGRP‐positive fibers formed a dense plexus in lamina I, II, the reticulated region of lamina V, and the tract of Lissauer at all spinal cord levels. The distribution of fibers showed some variations dependent on the cord level analyzed. At the light microscopic level, intervaricose fiber diameters consistantly measured 1.0 μm or less, and two types of CGRP varicosities were observed: a small (1 to 2 μm in diameter), relatively round profile and a larger, (3 to 4 μm in diameter) oval or oblong profile. At the electron microscopic level, immunostained varicosities contained a mixture of round clear vesicles and vesicles that contained dense cores. The CGRP immunoreaction product was often associated with vesicles containing dense cores. The reaction product was also seen associated with clear round vesicles or in the cytoplasmic matrix. Postsynaptic elements included dendritic spines, small and large diameter dendritic shafts and vesicle containing profiles. The presence of CGRP in the superficial dorsal horn of human spinal cord is highly suggestive of a role in primary afferent transmission as postulated in lower vertebrates. This study establishes the distribution of CGRP at four different spinal levels in human cord and will serve as a basis for future studies related to the pathologic conditions affecting sensory systems.
Medial gastrocnemius motor nucleus in the rat: Age‐related changes in the number and size of motoneurons
Authors: Hashizume Ken , Kanda Kenro , Burke Robert E.
Published: January 2005

The age‐related alterations in the number and size of alpha‐ and gamma‐motoneurons were studied in the medial gastrocnemius (MG) motor nuclei in rats at four ages: young (5 months), middle aged (10–13 months), old (26 months), and very old (31 months). Small volumes (0.1–0.5 μl) of 40% horseradish peroxidase (HRP) solution were injected into the cut MG nerve bilaterally by using glass micropipettes and a pressure injection system. The number, position, and soma size (average soma diameter) of MG motoneurons were determined by using photographic maps of each TMB‐stained section. The total number of myelinated axons was counted in seven MG nerves from the same animals.

The average soma diameters in each MG nucleus were distributed bimodally; cells with average diameter greater than 21.0–24.0 μm were presumed to be alpha‐motoneurons and those with smaller diameters were presumed to be gamma. The mean number of presumed alpha‐motoneurons was significantly less in the old and very old groups as compared with the young and middle‐aged. In contrast, the number of presumed gamma‐motoneurons was the same across age groups. The mean average soma diameter of both alpha‐ and gamma‐motoneurons was smaller in the old animals. The apparent decrease in the total number of labeled motoneurons in old animals was also reflected in a decrease in myelinated axon counts. We conclude that there is a significant decrease in the absolute numbers of motoneurons in rats aged 26 months and older, with most of the decrease occurring among the larger alpha‐motoneurons.
Immunohistochemical and in situ hybridization analysis of the development of the rat somatostatin‐containing neocortical neuronal system
Authors: Naus C. C. G. , Miller F. D. , Morrison J. H. , Bloom F. E.
Published: January 2005

The chemical differentiation of somatostatin (SS) neurons in rat neocortex was characterized by molecular biochemical and morphological methods. Northern (RNA) blotting indicates that regional distribution of SS mRNA correlates with the known distribution patterns of SS‐containing neurons in the adult, while similar analysis of poly (A)+ RNA isolated from telencephalon at various times postnatally shows an increase between P9 and P15, with a slight decrease in the adult. In situ hybridization with a probe specific to SS mRNA, and immunohistochemistry using antisera specific for the N‐terminally extended form of SS, SS28, and SS28(1–12), were used to detect neocortical neurons containing this mRNA or its translation product. The appearance of SS mRNA is coincident with detectable immunoreactivity for SS peptides. The expression of the SS gene by cortical neurons occurs in two waves. From P1 to P11, hybridizing neurons are predominant below the cortical plate in the developing infragranular layers. Immunohistochemical analysis of immunoreactivity to SS28 reveals a significant development of this neocortical system by late gestation (E20). At this point SS28(1–12), the predominant SS form detected, is mainly in neurons of the subplate, with less detectable immunoreactivity in the intermediate zone and cortical plate. By P2, neurons in the subplate exhibit detectable SS28 and SS28(1–12). Although immunoreactive perikarya are no longer detectable at P2 in the cortical plate or marginal zone, a very dense plexus of SS28(1–12) fibers is seen in the subplate, marginal zone, and intermediate zone; relatively few immunoreactive fibers are found in the cortical plate. By P12, a dramatic shift occurs; a large supragranular population of these SS neurons is observed by both mRNA and antibody methods, as is a subsequent decrease in number in the adult. The shift in immunoreactivity occurs with supragranular SS28‐containing neurons now prominent, and SS28(1–12)‐containing neurons and fibers greatly diminished. The number of neurons containing SS mRNA or SS28 immunoreactivity decreases from P12 to adult, when these neurons exhibit a bilaminar distribution. Neurons immunoreactive for SS28(1–12) are now sparsely distributed throughout the cortex, while SS28(1–12) fibers densely innervate layers I and V/VI.
Afferent innervation of outer hair cells in adult cats: II. Electron microscopic analysis of fibers labeled with horseradish peroxidase
Authors: Simmons D. D. , Liberman M. C.
Published: January 2005

Outer spiral fibers (OSFs) were retrogradely labeled with injections of horseradish peroxidase. After the peripheral arborization patterns were reconstructed at the light microscopic level (Simmons and Liberman, '88), restricted regions of selected fibers were analyzed via electron‐microscopic reconstruction of serial sections. The ultrastructural data in the present study suggested that the contact between the outer hair cell (OHC) and the terminal swellings of OSFs corresponds to the afferent synapse described in numerous other ultrastructural studies. The en passant swellings that contacted OHCs also appeared to be points of synaptic contact. However, en passant synapses were not always associated with a swelling of the OSF at the point of contact: thus, the light‐microscopic reconstructions probably underestimate the numbers of synapses. OSF branches terminating well below the OHCs were seen to end most commonly in intimate contact with the Deiters' cells. Membrane specialization was occasionally seen at this point of contact; however, the specialization was sufficiently undifferentiated to preclude identification.
GABAergic elements in the neuronal circuits of the monkey neostriatum: A light and electron microscopic immunocytochemical study
Authors: Pasik Pedro , Pasik Tauba , Holstein Gay R. , Hámori Jozsef
Published: January 2005

An antibody raised in rabbits against a GABA‐BSA conjugate was used together with the PAP technique to label elements in the neostriatum of three Old World monkeys. Light microscopy revealed numerous immunoreactive medium‐size neurons of various staining intensities, some of which had indented nuclei, as well as an occasional large cell. The neuropil showed a plexus of fine processes with frequent puncta, Ultrastructurally, the medium‐size GABA‐positive neurons were of two types: one with smooth nuclei and scanty cytoplasm, similar to spiny I cells, the other with invaginated nuclear envelopes and more abundant perikaryon, resembling the aspiny type. Correspondingly, labeled dendrites were either spiny or varicose. Some stained axons were myelinated, and the boutons had either large and ovoid, or small and pleomorphic vesicles. All of these boutons formed symmetric synapses, the former type with GABA‐positive dendritic shafts but also with unlabeled dendrites; the latter type usually with GABA‐negative elements, either dendrites, dendritic spines, or somata. Synapses were also observed between unreactive boutons and immunostained dendrites. Terminals with densely packed, small round vesicles that established asymmetric synapses with spines were always GABA‐negative. Glial elements were consistently unlabeled, save, for some astroglial endfeet. These findings provide positive evidence for the existence of two classes of GABAergic striatal neurons corresponding to a long‐axoned spiny I type and an aspiny interneuron. Furthermore, the simultaneous labeling of GABA‐immunoreactive presynaptic and postsynaptic profiles offers possible morphologic bases for the various kinds of intrastriatal inhibitory processes, including the feedforward, feedback, and “autaptic” types.
Ultrastructural study on the meninx of the goldfish brain
Authors: Momose Yoshiaki , Kohno Kunio , Ito Ryuzo
Published: January 2005

The cranial meninges of the goldfish were studied by means of transmission electron microscopy combined with the freeze‐fracturing technique. The goldfish has three cranial meninges. The outer layer consists of flattened cells, which are stratified in 3 to 7 layers and are packed densely with many interdigitations of cell processes. The constituent cells in the outer layer have copious smooth endoplasmic reticulum and are joined by gap junctions but have no desmosomes. The intermediate layer is thin, continuous, and single cell. In the replicas, both the upper and the lower surfaces of the intermediate layer cells have numerous openings of pinocytotic vesicles, but the upper surface is characterized by round gap junctions, whereas the lower surface is identified by a linear continuation of a combination of tight junctions and gap junctions and by desmosomes. The lateral surface has a hexagonal network of tight junctions and gap junctions with internally located desmosomes, which functions as a barrier to intercellular movement of lanthanum. The inner layer consists of a meshwork of reticular cells and large intercellular spaces, in which fine granular material, capillaries, and different types of blood‐derived free cells can be found. Cells in the inner layer contain rough endoplasmic reticulum stacked in lamellae and have irregular processes joined by desmosomes. The goldfish meninges are compared with the meninges of mammals.
Immunohistochemistry of aromatic L‐amino acid decarboxylase in the cat forebrain
Authors: Kitahama Kunio , Denoyer Michel , Raynaud Brigitte , Borri‐Voltattorni Carla , Weber Michel , Jouvet Michel
Published: January 2005

The topographic distribution of aromatic L‐amino acid decarboxylase (AADC)‐immunoreactive (IR) neurons was investigated in the cat hypothalamus, limbic areas, and thalamus by using specific antiserum raised against porcine kidney AADC. The perikarya and main axons were mapped on an atlas in ten cross‐sectional drawings from A8 to A16 of the Horsley Clarke stereotaxic plane. AADC‐IR neurons were widely distributed in the anterior brain. They were identified in the posterior hypothalamic area, rostral arcuate nucleus of the hypothalamus, dorsal hypothalamic area, and periventricular complex of the hypothalamus, which contain tyrosine hydroxylase (TH)‐IR cells and are known as All to A14 dopaminergic cell groups. AADC‐IR perikarya were also found in the other hypothalamic areas where few or no TH‐IR cells have been reported: the supramamillary nucleus, tuberomamillary nucleus, pre‐ and anterior mamillary nuclei, caudal arcuate nucleus, dorsal hypothalamic area immediately ventral to the mamil‐lothalamic tract, anterior hypothalamic area, area of the tuber cinereum, retrochiasmatic area, preoptic area, suprachiasmatic and dorsal chiasmatic nuclei. We also identified them in the anterior commissure nucleus, bed nucleus of the stria terminalis, stria terminalis, medial and central amygdaloid nuclei, lateral septal nucleus, and nucleus of the diagonal band of Broca. AADC‐IR neurons were localized in the ventromedial part of the thalamus, lateral posterior complex, paracentral nucleus and lateral dorsal nucleus of the thalamus, medial habenula, parafascicular nucleus, subparafascicular nucleus, and periaqueductal gray. Conversely, we detected only a few AADC‐IR cells in the supraoptic nucleus whose rostral portion contains TH‐IR perikarya. Comments are made on the relative Idealizations of the AADCvIR and THvIR neurons, on species differences between the cat and rat, as well as on the possible physiological functions of the enzyme AADC.
Ultrastructural characterization of substance P‐like immunoreactive neurons in the rostral ventrolateral medulla in relation to neurons containing catecholamine‐synthesizing enzymes
Authors: Milner Teresa A. , Pickel Virginia M. , Abate Cory , Joh Tong H. , Reis Donald J.
Published: January 2005

Substance P (SP) and catecholamines, particularly adrenaline, have been implicated in cardiovascular responses mediated by neurons in the rostral ventrolateral medulla (RVL). Immunoperoxidase labeling of an antiserum against SP and/or immunoautoradiographic localization of catecholamine (tyrosine hydroxylase—TH)‐ or adrenaline (phenylethanolamine N‐methyltransferase—PNMT)‐synthesizing enzymes were examined histologically to determine the cellular basis for a functional interaction involving either synaptic or intracellular relations between these putative transmitters in the adult rat RVL. Peroxidase labeling for SP was localized in perikarya, dendrites, and axon terminals. Most of these perikarya were located medial and ventral to those labeled with TH or PNMT within the same section. However, as others have previously demonstrated by light microscopy, colocalization of SP‐like immunoreactivity (SPLI) and PNMT was seen in a few perikarya of colchicine treated animals. Both single‐ and dual‐labeled perikarya contained abundant dense core vesicles.

The terminals with SPLI were 0.4–1.4 μm in diameter and contained a few mitochondria, a large population of small, clear vesicles, and from three to 11 large dense core vesicles. In some cases the terminals were seen in continuity with more proximal processes of neurons in the RVL. These terminals formed synapses with a few perikarya and many dendrites, some of which also contained SPLI. In the material dually labeled for TH and SP, terminals with SPLI (n = 32) formed synaptic junctions primarily with TH‐labeled dendrites (69%); the remainder were with TH‐labeledperikarya (6%) or with unlabeled dendrites (25%). The axosomatic junctions were exclusively symmetric, whereas the majority of axodendritic junctions were primarily asymmetric on small dendrites (0.8–1.0 μm in diameter) or dendritic spines. In sections dually labeled for PNMT and SP, the terminals containing SPLI (n = 37) formed synaptic associations with PNMT‐labeled perikarya (11%), PNMT‐immunoreactive dendrites (59%), or with perikarya and dendrites lacking PNMT immunoreactivity (30%). The axosomatic junctions were all symmetric and most often associated with the spinous portion of the soma. The axodendritic junctions were primarily asymmetric and were found both on the shaft and spinous portion of the PNMT‐labeled dendrites. In addition, both TH‐ and PNMT‐labeled somata and dendrites received symmetric and asymmetric contacts from terminals lacking SPLI.

These findings provide ultrastructural evidence that in the rat RVL, SP or a closely related neurokinin located in intrinsic neurons or other afferents provides a major direct input to adrenergic neurons. Additionally, the peptide may modulate the activity of adrenergic neurons through synapses with neurons containing SP or other transmitters or through intracellular interactions.
In situ hybridization analysis of osmotic stimulus‐induced changes in ribosomal RNA in rat supraoptic nucleus
Authors: Kawata M. , McCabe J. T. , Harrington C. , Chikaraishi D. , Pfaff D. W.
Published: January 2005

A quantitative in situ hybridization analysis was used to investigate changes in levels of ribosomal RNA (rRNA) in neurons of the supraoptic nucleus (SON) of rats stimulated osmotically by giving 2% NaCl as drinking solution for 0 (control rats), 1, 4, and 14 days. The quantitation was autoradiographically accomplished by in situ hybridization with a nick‐translated tritiated ribosomal DNA probe and with the use of computer‐based image analysis system. The mean number of grains per neuron in the ventral SON was significantly increased: 1.8‐fold for 1 day, 2.9‐fold for 4 days, and 1.7‐fold for 14 days of salt loading, whereas the mean number of grains per neuron in the dorsal SON was increased 1, 3‐fold for 1 day, 2.5‐fold for 4 days, and 1.7‐fold for 14 days. Kolmogorov‐Smirnov analysis of frequency histograms of grains per neuron indicated that the amount of rRNA in neurons in the ventral and dorsal SON was significantly increased by osmotic stimulation. These increases were accompanied by increases in cell size. The subcellular location of hybridizable rRNA in magnocellular neurons was altered by osmotic stimulation. Following 1–14 days of salt‐drinking, rRNAs appeared to be more unevenly distributed throughout the cytoplasm. These findings are consistent with the notion that hyperosmotic stimulation has a substantial effect on the expression of rRNA genes in neurons of both the ventral and dorsal SON.
Quantitative relationships between motoneuron and muscle development in Xenopus laevis: Implications for motoneuron cell death and motor unit formation
Authors: McLennan Ian S.
Published: January 2005

A common approach to the study of neural regression has been to correlate the timing of cell loss with other events such as target development. Most of these studies have areas of uncertainty. First, the analysis is normally carried out on groups of neurons that innervate a variety of targets. Second, there are some doubts about the reliability of light microscopic quantitation of muscle development. In this study, the period of cell death in the semimembranosus motor pool of Xenopus laevis has been estimated and correlated with an electron microscopic study of the development of the semimembranosus.

The period of cell death of semimembranosus motoneurons was estimated on the basis of their position in the spinal cord and from the number of myelinated axons in the semimembranosus motor nerve. The semimembranosus motor pool contained approximately 70 motoneurons and was located 17–37% along the rostrocaudal axis of the lumbar cord. Cell loss from this motor pool occurred between stages 53–54 and 56, whereas cell death in the entire lumbar cord extended beyond stage 58. Primary myogenesis occurred between stages 53 and 54 in the semimembranosus. There was then a hiatus in myotube production until secondary myogenesis began around stage 56.

It is concluded that secondary myotubes are not involved in regulating motoneuron cell death and that the number of primary myotube clusters is similar in magnitude to the number of motoneurons that will ultimately survive the period of cell death. The implications of these observations for theories of cell death and motor unit formation are discussed.
Capsaicin‐induced neuronal degeneration: Silver impregnation of cell bodies, axons, and terminals in the central nervous system of the adult rat
Authors: Ritter Sue , Dinh Thu T.
Published: January 2005

Capsaicin is a neurotoxic substance valued in neurobiological research because of its ability to selectively damage small unmyelinated primary sensory neurons. Previous work has indicated that systemic capsaicin administration causes permanent neuronal degeneration in neonatal rats, but evidence that capsaicin has a similar effect in adults is equivocal and incomplete. Therefore, we used silver impregnation, a method that labels degenerating neurons, to examine the central nervous system of adult rats after systemic capsaicin treatment. Adult rats were injected with a single intraperitoneal dose of capsaicin (50 or 90 mg/kg) or vehicle solution and killed 6, 12, 18, 24, 48, 96, or 240 hours later. Sections of brain and spinal cord were stained with the Carlsen–de Olmos cupric silver method. As reported previously, stained sections revealed degeneration in areas known to be innervated by small‐diameter primary sensory fibers: the substantia gelatinosa of the spinal cord dorsal horn and spinal trigeminal nucleus, the solitary nucleus and tract, and the lateral borders of the area postrema. In addition, axon and terminal degeneration was observed in several discrete forebrain and hindbrain areas not previously associated with capsaicin‐induced degeneration in either adult or neonatal rats: the inferior olive, the olivary pretectal nucleus, the interpeduncular nucleus, the suprachiasmatic nucleus, and the lateral septum/medial accumbens region. Furthermore, degenerating cell bodies were observed in the intrafascicular nucleus of the ventromedial midbrain tegmentum, in the supramammillary nucleus, and in the posterior hypothalamic area. Unilateral nodose ganglionectomy produced terminal staining on the denervated side very similar to that induced bilaterally by capsaicin. In addition, unilateral nodose ganglionectomy 1 month prior to capsaicin injection greatly attenuated staining in the ipsilateral nucleus of the solitary tract, confirming the hypothesis that capsaicin damages vagal sensory neurons innervating this nucleus. Capsaicin‐induced damage in adult rats was long‐lasting, since the second of two capsaicin treatments spaced 4.5 months apart produced no additional degeneration.
Induction of aberrant functional afferents to the chick cochlear nucleus
Authors: Jackson Hunter , Parks Thomas N.
Published: January 2005

Surgical extirpation of the otocyst on embryonic day (E) 3 in chick embryos prevents formation of the cochlear nerve and results in development of an aberrant axonal projection from the contralateral cochlear nucleus (nucleus magnocellularis, NM) to the deafferented NM. We have studied the morphology of this projection using horseradish peroxidase injections in NM axons and light and electron microscopy. The ability of the projection to activate its target neurons synaptically was assessed by means of extracellular microelectrode recording from in vitro preparations of the chick brainstem. The aberrant projection arises as a vertically directed branch from the contralaterally traveling NM axon at the medial border of nucleus laminaris (NL). This axonal branch forms boutonal endings that may terminate anywhere in NM but are most common in its ventral and medial regions. In our experiments, this projection is not seen on the unoperated side of experimental animals or in normal controls from E11 onward but is found on the operated sides of all experimental animals, including those with bilateral removal of the otocysts. The aberrant projection persists at least from E11 through hatching and has essentially identical features in unilaterally and bilaterally lesioned animals. The endings of the aberrant projection are boutonal in form and, in the electron microscope, exhibit all of the elements associated with normal synapses. Electrophysiological studies confirm that stimulation of the aberrant axons can elicit postsynaptic responses in NM and suggest that these synapses use an excitatory amino acid neurotransmitter.
A comparison of the efferents of the amygdala and the hippocampal formation in the rhesus monkey: I. Convergence in the entorhinal, prorhinal, and perirhinal cortices
Authors: Saunders Richard C. , Rosene Douglas L.
Published: January 2005

This is the first in a series of papers investigating the neuroanatomical basis for the interaction of the amygdala and the hippocampal formation in the rhesus monkey. The present report focuses on the complementary and convergent projections of the amygdala and hippocampal formation to the entorhinal and perirhinal cortices. These results were obtained from complementary experiments using injections of radioactively labeled amino acids to identify the anterograde projection patterns and injections of horseradish peroxidase and fluorescent retrograde tracers to confirm the cytoarchitectonic location of the neurons of origin for each projection.

The results of this investigation demonstrate that both the hippocampal formation and the amygdala project to the entorhinal and perirhinal cortices where, with a few exceptions, the major projections of each structure generally are found in different layers of the same cytoarchitecture subdivisions of the entorhinal cortex but overlap in the same layers of the perirhinal cortex. Thus, the lateral and accessory basal nuclei of the amygdala project to layer 3 of areas Pr1, 28I, 28L, and 28S, and the accessory basal nucleus projects strongly to layer 1 of these same areas. In contrast, the subiculum, prosubiculum, and subfield CA1 of the of the hippocampal formation all have a projection to layer 5 of these same areas. In area 28M, the accessory basal nucleus of the amygdala projects to layer 1, while the subiculum, prosubiculum, and subfield CA1 of the hippocampal formation all project to layer 5, and the presubiculum projects to layer 3.

In addition to these complementary laminar projectios, there are a few areas of laminar overlap. Thus in area 28S, both the presubiculum and the CA1 subfield project to layer 3, where the lateral and accessory basal amygdaloid nuclei also project. Similarly, in 28I there is a major projection from the presubiculum and a lighter projection from the subiculum and CA1 to layer 3, where the lateral and accessory basal nuclei also project. There is also extensive laminar overlap in the perirhinal cortex. From the amygdala, the accessory basal nucleus projects to layers 1 and 3 and the lateral basal nucleus to layers 3, 5, and 6, while from the hippocampal formation, the prosubiculum projects to layers 3, 5, and 6, and the CA1 subfield projects to layer 5. This pattern of hippocampal and amygdaloid projections to the entorhinal and perirhinal cortices indicates that these cortices constitute a region of potentially extensive interaction between the amygdala and the hippocampus.
Comparison of the efferents of the amygdala and the hippocampal formation in the rhesus monkey: II. Reciprocal and non‐reciprocal connections
Authors: Saunders Richard C. , Rosene Douglas L. , Van Hoesen Gary W.
Published: January 2005

The pattern of direct connections between the amygdala and the hippocampal formation in the rhesus monkey (Macaca mulatta) was delineated by using both anterograde and retrograde tract‐tracing techniques.

From the amygdala the accessory basal, medial basal, and the cortical nuclei and the cortical amygdaloid transition area send projections to the hippocampal formation. The efferents from the magnocellular part of the accessory basal nucleus and the cortical nuclei terminate in the molecular layer of subfields CA3, CA2, and CA1′, and to a lesser extent in the molecular layer and the superficial part of the pyramidal cell layers of the prosubiculum. In contrast, the projections from the medial basal nucleus and the cortical amygdaloid transition area terminate in the molecular layer and the superficial part of the pyramidal cell layers of the prosubiculum only.

From the hippocampal formation, subfield CA1′ and the prosubiculum send efferents that terminate in the medial basal nucleus, the cortical transition area, and the ventral part of the cortical nuclei. In addition, the CA1′ subfield projects to the ventral, parvicellular part of the accessory basal nucleus.

The present data emphasize an important role for the prosubiculum and the CA1′ subfield in medial temporal lobe area connections. Both regions, in addition to supporting direct connections between the amygdala and the hippocampal formation, also have extensive connections with the entorhinal cortex. As for the amygdala, the accessory basal nucleus sends efferents to both the hippocampal formation and the entorhinal cortex. The data demonstrate an anatomical means by which the amygdala, hippocampal formation, and the entorhinal cortex may interact. It is proposed that these connections may be important in the limbic memory system.
Analysis of the rat interpeduncular subnuclei by immunocytochemical double‐staining for enkephalin and substance P, with some reference to the coexistence of both peptides
Authors: Shinoda Koh , Michigami Toshimi , Awano Kikuo , Shiotani Yahe
Published: January 2005

The rat interpeduncular nucleus (IPN) was immunocytochemically double‐stained for enkephalin (ENK) and substance P (SP) on the same sections. On the basis of both peptidergic distribution patterns and topographic relationship, the IPN was divided into nine subnuclei and one cap: the rostral subnucleus (IP‐R), the central subnucleus (IP‐C), the rostral‐lateral subnucleus (IP‐RL), the main lateral subnucleus (IP‐L), the caudal‐lateral subnucleus (IP‐CL), the dorsal‐lateral subnucleus (IP‐DL), the dorsal‐medial subnucleus (IP‐DM), the apical subnucleus (IP‐A), the intermediate subnucleus (IP‐I), and the dorsal cap (IP‐Cap). As the descriptions of the IP‐RL, IP‐L, and IP‐CL were inconsistent with previous reports, they were reevaluated; the IP‐RL was proposed as the region situated in the lateral portion at rostral levels and characterized by the lack of ENK and SP immunoreactive structures, the IP‐L as the region situated throughout the rostrocaudal extent in the lateral portion of the IPN and containing the highest density of SP immunoreactive fibers but no ENK immunoreactive fibers, and the IP‐CL as the region situated just laterocaudal to the IP‐L in the caudal pole of the IPN and containing ENK immunoreactive cells and fibers but no SP immunoreactive structures.

Our results also showed that some cells in the IP‐R have both ENK and SP immunoreactivity. This coexistence was observed in some small spherical cells of the IP‐R, but rarely in larger oval‐shaped cells, which occasionally showed only ENK immunoreactivity. In addition, paired ENK immunoreactive fiber bundles entering the IP‐R were found to run just rostral to the paired SP immunoreactive columns, both of which composed parts of the interpedunculotegmental tract.

A three‐dimensional model representing the subnuclear organization of the IPN was proposed on the basis of the present results.
Anatomical specificity of noradrenergic inputs to the paraventricular and supraoptic nuclei of the rat hypothalamus
Authors: Cunningham E. T. , Sawchenko P. E.
Published: January 2005

The distribution of neural inputs to the paraventricular (PVH) and supraoptic (SO) nuclei from the regions of the A1, the A2, and the A6 (locus coeruleus) noradrenergic cell groups was investigated by using a plant lectin, Phaseolus vulgaris leucoagglutinin (PHA‐L), as an anterogradely transported tracer. An immunofluorescence double‐labeling procedure was used to determine the extent to which individual anterogradely labeled fibers and terminals in the PVH and the SO also displayed immunoreactive dopamine‐β‐hydroxylase (DBH), a marker for catecholaminergic neurons. The results may be summarized as follows: (1) Projections from the A1 region were found primarily, and in some experiments almost exclusively, in those parts of the magnocellular division of the PVH and the SO known to contain vasopressinergic neurons. (2) Projections from the A2 region were distributed primarily throughout the parvicellular division of the PVH and were most dense in the dorsal medial part, a region known to contain a prominent population of corticotropin‐releasing factor (CRF)‐immunoreactive neurons. In addition, a less‐dense projection to the magnocellular division of the PVH and to the SO was consistently found. (3) Fibers originating from the locus coeruleus were distributed almost exclusively to the parvicellular division of the PVH, with the most prominent input localized to the periventricular zone, a part of the PVH known to contain dopamine‐, somatostatin‐, and thyrotropin‐releasing‐hormone‐containing neurons. We found no evidence for a projection from A6 to the SO. (4) The majority of fibers originating from the A1, the A2 or the A6 regions contained DBH immunoreactivity, although an appreciable number did not. These results suggest that each of the three brainstem noradrenergic cell groups that contribute to the innervation of the PVH and/or the SO is in a position to modulate the activity of anatomically and chemically distinct groups of neurosecretory neurons.
Cell birthdays and rate of differentiation of ganglion and horizontal cells of the developing cat's retina
Authors: Zimmerman Roger P. , Polley Edward H. , Fortney Richard L.
Published: January 2005

Tritiated thymidine autoradiography experiments demonstrated that three cell classes are produced by ventricular cells during the first phase of neurogenesis: retinal ganglion cells, A‐type horizontal cells, and cone photoreceptors. Light microscopy and scanning electron microscopy were used to study the migration and morphological differentiation of these three cell classes.

The patterns of postmitotic migration are of interest because these three classes of cells are found in three different layers of the adult retina. Cones retain their position at the outer limiting membrane (OLM) throughout life and do not migrate. Ganglion cells migrate immediately to the proximal (vitread) layer of the retina and begin to differentiate. In contrast, A‐type horizontal cells migrated away from the OLM within 10–14 days after their final mitosis but were morphologically relatively undifferentiated at that time. Subsequent differentiation of the A‐type horizontal cell is also protracted; dendrites are not observed until approximately 3 weeks after the final mitosis.

These observations suggest that there are several interacting mechanisms involved in neurogenesis: a sequence that produces a specific cohort of committed cells at a specific time, the subsequent migration of postmitotic neuroblasts to an appropriate position in the retina, and a spatial gradient of differentiation increasing from distal to proximal layers. While this distribution of differentiated cells early in fetal development is striking, the existence of underlying time‐dependent processes that might cause this apparent spatial phenomenon cannot be eliminated.
Corticothalamic and corticotectal somatosensory projections from the anterior ectosylvian sulcus (SIV cortex) in neonatal cats: An anatomical demonstration with HRP and 3H‐leucine
Authors: McHaffie John G. , Kruger Lawrence , Clemo H. Ruth , Stein Barry E.
Published: January 2005

Corticothalamic and corticotectal projections from the anterior ectosylvian sulcus (AES) in neonatal cats were studied with anterograde and retrograde neuroanatomical techniques. When the injection site was relatively restricted to the sulcal walls and fundus of the rostral AES (i.e., the SIV cortex), heavy ipsilateral thalamic label was observed in the medial subdivision of the posterior group, in the suprageniculate nucleus, and in the external medullary lamina. No terminal label was seen in the contralateral thalamus although the contralateral homotopic cortex was heavily labeled. Within the ventrobasal complex (VB), dense axonal label was observed in fascicles that traversed VB, but only light terminal label was observed within VB itself. However, in cases where the tracer spread into adjacent SII, terminal label in VB was pronounced. Similarly, when the injection site extended into auditory cortex, terminal label was observed in the lateral and intermediate subdivisions of the posterior group.

Rostral AES injections produced distinct, predominantly ipsilateral, terminal label in the superior colliculus that was distributed in two tiers: a discontinuous band in the stratum griseum intermedium and a more diffuse band in stratum griseum profundum. Caudally, dense terminal label was seen in the intercollicular zone and dorsolateral periaqueductal gray. When the injection site did not include rostral AES, no label was observed in the superior colliculus. Horseradish peroxidase injections into the superior colliculus of neonates produced retrogradely labeled neurons throughout the AES, but none was found on the crown of the gyrus where SII is located. Thus, the neonatal corticotectal somatosensory projection arises exclusively from AES and parallels that found in adults.

These data indicate that the elaboration of a major descending somatosensory pathway from AES to the thalamus and midbrain is largely a prenatal event. The in utero anatomical maturation of the corticofugal projections from SIV cortex to the superior colliculus contrasts with the protracted postnatal development of the corticotrigeminal projections from SI cortex but is consistent with the mature anatomical state of ascending trigeminotectal projections.