bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of serotonin in the brain of the mormyrid teleost Gnathonemus petersii
Authors: Meek J. , Joosten H. W. J.
Published: January 2005

The distribution of serotonin‐immunoreactive neurons and fibers was studied in the highly developed brain of the weakly electric fish Gnathonemus petersii with the aid of specific antibodies against serotonin. Serotoninergic cell bodies occur in three regions: the raphe region of the brainstem, the hypothalamus, and the transition zone between the dorsal thalamus and the pretectum. Serotoninergic raphe neurons are clustered in three groups: nucleus raphes superior, intermedius, and inferior. The latter has not been described in other teleosts and thus might be the source of the serotoninergic innervation of specific mormyrid electrosensory brain regions. Most hypothalamic serotoninergic neurons have cerebrospinal‐fluid (CSF)‐contacting processes and thus belong to the paraventricular organ (PVO), which in Gnathonemus is located around a number of small infundibular recesses. The distribution of serotonin in the PVO precisely matches the distribution of dopamine, as described previously. Serotoninergic cells in the thalamopretectal transition zone also have been described in other teleosts, but not in other vertebrate groups, and thus seem to represent a teleostean specialization.

Serotoninergic fiber density is especially high in the medial forebrain bundle and surrounding preoptic and hypothalamic regions as well as in several telencephalic and preoptic subependymal plexus. Serotoninergic fibers appear to be almost completely absent in the large and differentiated corpus and valvula cerebelli. Comparison with the literature on teleostean serotoninergic innervation patterns reveals several mormyrid specializations, including the absence of serotonin in large parts of the mormyrid telencephalic lobes, a differentiated innervation pattern of distinct electrosensory and mechanosensory subnuclei of the torus semicircularis, a refined serotoninergic lamination pattern in the midbrain tectum, and a prominent innervation of the electrosensory lateral line lobe, the associated caudal cerebellar lobe, and the electromotor medullary relay nucleus. A distinct innervation of several types of (pre)motor neurons, such as the Mauthner cells and facial motor neurons, has not been reported previously for other teleosts. Consequently, the distribution of serotoninergic fibers as well as neurons in the mormyrid brain is substantially adapted to the high degree of differentiation of its electrosensory and telencephalic brain regions, but serotoninergic innervation is not involved in the circuitry of the most impressive part of the mormyrid brain; i.e., its large corpus and valvula cerebelli.
Regeneration of axons from the adult rat optic nerve: Influence of fetal brain grafts, laminin, and artificial basement membrane
Authors: Hausmann Beate , Sievers Jobst , Hermanns Joachim , Berry Martin
Published: January 2005

After transection of the optic nerve of adult rats, most of the axons in the proximal stump die and the surviving ones are unable to regenerate into the distal optic nerve. Since the fetal brain has an inherent capacity to regenerate axons, we investigated whether fetal (E16) target regions of optic axons (thalamus and tectum) transplanted to the completely transected optic nerve of adult rats would promote axon regeneration. In control operated rats, axon growth beyond the site of transection was restricted to a few fibers that grew irregularly within the connective tissue scar. By contrast, in grafted animals directed outgrowth of optic axons toward the transplant started at 6 days postoperation (p.o.) and reached its maximum 15 days p.o. and later, when numerous single optic fibers and small axon fascicles had grown toward and into the graft, where they formed arborizations and terminal varicosities. Regenerating optic axons were further advanced than GFAP‐positive strands of astroglia that emanated from the proximal optic nerve stump. Laminin immunoreactivity appeared at 6 days p.o. in the zone of reactive astroglia in the terminal part of the optic nerve stump. Later it showed a distribution complementary to the pattern of GFAP immunoreactivity, which it seemed to circumscribe. There was no unequivocal codistribution of laminin immunoreactivity with regenerating axons.

In further experiments, target regions from different ontogenetic stages (E14 to neonate and adult) and nontarget regions (E16, cerebral cortex or spinal cord) were grafted to the optic nerve stump. With the exception of the adult grafts, all transplants had effects on axon regeneration comparable to those of E16 target regions. In order to test the effects of extracellular matrix molecules on axon regeneration, a basement membrane gel reconstituted from individual components of the Engelbreth‐Holm‐Sarcoma (EHS) sarcoma was implanted between proximal and distal optic nerve stumps. No axons were induced to regenerate by this matrix. Likewise, laminin adsorbed to nitrocellulose paper and implanted at the lesion site did not stimulate axon growth from the proximal optic nerve stump.

These results indicate that fetal brain is able to induce and direct regrowth of axons from the optic nerve toward the graft across a substrate that is not composed of astroglia or basement membrane components like laminin. The directed growth of axons in the absence of a preformed substrate implies a chemotactic growth response along a concentration gradient mediated by neurotropic molecules released from the graft.
Fetal brain grafts rescue adult retinal ganglion cells from axotomy‐induced cell death
Authors: Sievers Jobst , Hausmann Beate , Berry Martin
Published: January 2005

After intraorbital transection of the optic nerve of adult rats, 90% of the retinal ganglion cells die within 30 days. Since fetal brain extracts and cocultured fetal target regions support the survival of retinal ganglion cells in vitro (Nurcombe and Bennett: Exp. Brain Res. 44: 249–258, '81; McCaffery et al.: Exp. Brain Res. 48: 377–386, '82; Armson and Bennett: Neurosci. Lett. 38: 181–186, '83) we investigated whether cell death in the adult retina could be prevented by transplanting fetal (E16) thalamus and tectum to the proximal stump of the optic nerve of adult rats that was completely transected 2–3 mm behind the optic disc. Unoperated eyes contained 119,973 (±939, SEM) retinal ganglion cells, estimated from axon counts of the intact optic nerve. Of these, 11,601 (±1,857) remained in control operated eyes at 30 days postoperation while in the eyes of grafted rats, 35,086 (±2,278) retinal ganglion cells were counted. Thus, 23,485 (=22% of those normally dying after transection of the optic nerve) ganglion cells were rescued by the fetal grafts from cell death normally following axotomy.

These results indicate that fetal target regions of retinal ganglion cells contain and/or produce neurotrophic molecules that promote the survival of adult axotomized retinal ganglion cells.
Morphological characterization of substance P‐like immunoreactive glomeruli in the superficial dorsal horn of the rat spinal cord and trigeminal subnucleus caudalis: A quantitative study
Authors: Ribeiro‐da‐silva A. , Tagari P. , Cuello A. C.
Published: January 2005

The aim of this work was to study the ultrastructural distribution of substance P–like immunoreactivity in laminae I and II of rat spinal cord and trigeminal subnucleus caudalis in relation to synaptic glomeruli. A bispecific monoclonal antibody directed against substance P and horseradish peroxidase was used, combining sensitive immunocytochemistry with preservation of fine ultrastructural detail. Some of the quantitative observations were carried out with an automated image analysis system.

The study revealed that in lamina I of the spinal cord, almost all immunoreactive profiles counted were nonglomerular, and a considerable number of them contacted medium‐size or large dendrites or were in direct contact with other vesicle‐containing profiles. In ventral lamina II, 9.4% of the labeled axonal varicosities were central boutons of type I glomeruli (CI). They could be identified by their scalloped contour, number and types of peripheral profiles, reduced density of mitochondria, and localization in the dorsal horn. However, these immunoreactive glomerular CI boutons (14.1% of the total number of CI) differed statistically from the prevailing population of nonimmunoreactive CI, by being surrounded by less peripheral neuronal profiles, which established fewer synapses. In addition, they contained more than three dense‐core vesicles per central profile.

In the trigeminal subnucleus caudalis laminae I and II, the substance P fibers and varicosities had a plexiform orientation at the light microscopic level, which contrasted with the mainly rostrocaudal orientation of the spinal cord's lamina II plexus. However, the main ultrastructural findings were similar.

These results demonstrate that substance P–like immunoreactivity occurs in a large number of type I synaptic glomeruli with specific morphological features and reinforce the current concept that the substantia gelatinosa of the spinal cord and trigeminal subnucleus caudalis are homologous structures.
Role of commissural projections in the representation of bilateral auditory space in the barn owl's inferior colliculus
Authors: Takahashi Terry T. , Wagner Hermann , Konishi Masakazu
Published: January 2005

The central nucleus of the barn owl's inferior colliculus (ICc) contains a representation of both the ipsilateral and contralateral auditory hemifields. The representation of ipsilateral space is found in the “core” of the ICc, a subdivision defined by the terminal field of nucleus laminaris, the avian analogue of the medial superior olivary nucleus. The representation of contralateral space is found in the lateral portion of the “shell” of the ICc. The shell surrounds the core and is defined by the terminal field of the nucleus angularis, one of the cochlear nuclei. The representation of ipsilateral space in the core of the ICc may be accounted for by the crossed projection from the nucleus laminaris because most of the nucleus laminaris is devoted to a representation of contralateral space.

We present evidence to suggest that the representation of contralateral space is due to a commissural projection from the core of one side to the lateral shell of the opposite side. Injection of horseradish peroxidase (HRP) into the lateral portion of the ICc shell produced retrogradely labeled somata in the core of the opposite side. Injection of tritiated proline into the core produced anterograde label confined to the lateral shell, thus confirming the observations made with HRP. Thus, for example, the left ICc core, which contains predominantly a representation of the left hemifield, innervates the right lateral shell, endowing it with a representation of the left, or contralateral hemifield. The representation of contralateral space in the lateral shell is ultimately conveyed to the external nucleus of the inferior colliculus where it contributes the horizontal axis to a two‐dimensional map of space.
Ultrastructural analysis of axosomatic contacts on functionally identified primate spinothalamic tract neurons
Authors: Carlton S. M. , Lamotte C. C. , Honda C. N. , Surmeier D. J. , Delanerolle N. , Willis W. D.
Published: January 2005

The morphology and frequency of axosomatic contacts on three functionally identified primate spinothalamic tract (STT) cells were analyzed at the electron microscopic level. The STT cells analyzed were wide‐dynamic‐range neurons responsive to activation of low‐ and high‐threshold cutaneous afferents innervating the foot. The somas were located in the lateral border of lamina V; the dendritic trees were oriented dorsally and were very extensive. Numerous spinelike appendages were observed emanating from two of the cell bodies. Terminal types contacting the cell bodies were categorized at several different layers through each neuron. Six morphologically different terminal types were established following analysis of serial sections. Profiles classified as round (R) terminals containing round clear vesicles and zero or one densecore vesicle made up over 50% of the total population in contact with the STT somas. Profiles containing round clear vesicles and two to four small‐diameter dense‐core vesicles (D1 category) made up approximately 10% of the population in contact with each soma. Flat (F) terminals with oblong or flattened clear vesicles made up approximately 8% of the population. The remaining three categories (D2, L1, and L2) distinguished by the number and size of the dense‐core vesicles made up a small percentage of the total population in contact with the cell bodies. The distribution of terminal types on the soma proper versus somatic spines was also determined for one cell. The proportions of the six terminal types contacting the soma of these cells were very similar, although the physiological characteristics of each cell were different. However, the relative proportions of terminal types on these three lamina V STT cell bodies were different from those previously reported contacting somata in lamina V, suggesting that there may be a unique innervation of STT cells that differentiates them from other cell types in lamina V.
Connectional analysis of the ipsilateral and contralateral afferent neurons of the superior temporal region in the rhesus monkey
Authors: Cipolloni P. B. , Pandya D. N.
Published: January 2005

The interhemispheric and ipsilateral afferents of the superior temporal region (STR) were investigated with the aid of fluorescent retrograde tracers (Diamidino Yellow and Fast Blue). Different tracers were injected in selected cortical areas of the STR of each hemisphere of four rhesus monkeys. The results show that the interhemispheric afferents originate not only from the homotopic but also from heterotopic areas. The heterotopic areas giving rise to interhemispheric projections correspond to cortical areas of the origin of the ipsilateral projections. Although there is considerable overlap of labeled neurons of both afferent systems, only occasional double‐labeled neurons are found. Whereas the laminar patterns of ipsilateral neurons of origin vary considerably, the interhemispheric projection neurons are located mainly in cortical layer III.

This study provides additional information about the ipsilateral connectional organization of the superior temporal region. That is, the primary auditory area receives projections not only from adjacent lateral and medial cortical regions but also from adjoining rostral and caudal cortical regions. Thus, the highly differentiated primary auditory cortical area receives strong projections from the surrounding less‐differentiated cortical regions. This connectional pattern is discussed from the perspective of the growth ring concept of cortical development.
Developing retinotectal projection in larval goldfish
Authors: Stuermer Claudia A. O. , Raymond Pamela A.
Published: January 2005

The retinotectal projection in larval goldfish was studied with the aid of anterograde filling of optic fibers with HRP applied to the retina. The results show that optic fibers have already reached the tectum and begun to form terminal arbors in newly hatched fish. The projection is topographic in that fibers from local regions of the retina project to discrete patches of tectum, with the smallest patch covering 3.5% of the total surface area of tectal neuropil. Many fibers in young larvae have numerous short side branches along their length and only some of them show evidence of terminal sprouting. The arbors are approximately elliptical in shape and average about 1,500 μ;m2. Growth cones are seen frequently. In older Iarvae, terminal arbors are larger and more highly branched, and they have begun to resemble those in adult fish. Fibers terminate in two strata; those in the upper layer are smaller (1,800 μ;m2 on average) than those in the deeper stratum (4,000 μ;m2 on average). The fraction of tectal surface area covered by individual arbors (the “tectal coverage”) ranges from 1.5% to 3% of the total surface area of the tectal neuropil. In contrast, the tectal coverage of individual arbors in young adult goldfish is much smaller, ranging from 0.02% to 0.42% of tectal surface area (Stuermer, '84, and unpublished). This apparent increase in precision of the map in older animals is not due to retraction of arbors, which are slightly larger in adults, but is accounted for by overall tectal growth: the tectal neuropil in goldfish increases in area by about 250‐fold during this period (Raymond, '86).
Structure‐function relationships in rat brainstem subnucleus interpolaris: IV. Projection neurons
Authors: Jacquin Mark F. , Barcia Michele , Rhoades Robert W.
Published: January 2005

In a companion paper (Jacquin et al., '89), the structure and function of local circuit (LC) neurons in spinal trigeminal (V) subnucleus interpolaris (Sp Vi) were described. The present report provides similar data for 44 projection neurons in Sp Vi. Of these, 25 thalamic, 16 cerebellar, 2 superior collicular, and 1 inferior olivary projecting neurons were studied. The majority responded to vibrissa(e) deflection, and all except 4 of these had multivibrissae receptive fields. The remainder were responsive to either guard hair deflection or indentation of glabrous skin. Latencies to V ganglion shocks were suggestive of monosynaptic activation from the periphery.

SpVi projection neurons were topographically organized in a manner consistent with that of their primary afferent inputs. Nonvibrissa sensitive cells had diverse morphologies. Morphometric analyses of the more heavily sampled thalamic and cerebellar projecting, vibrissa(e)‐sensitive cells indicated the following. (1) As compared to LC neurons, projection neurons had bigger receptive fields, cell bodies, dendritic trees, and axons; less circular dendritic trees; a greater preponderance of spiny dendrites and fewer axon collaterals in Sp Vi. (2) Dendritic tree extent correlated significantly with receptive field size, thus suggesting that dendritic tree size is one mechanism contributing to receptive field size in vibrissae‐sensitive projection neurons. (3) V thalamic cells had significantly bigger receptive fields and dendritic trees, and also give off more local axon collaterals, than V cerebellar neurons. Collicular and inferior olivary projecting neurons shared structural and functional attributes with other Sp Vi long‐range projecting cells.

Structure‐function relationships exist for vibrissa‐sensitive projection neurons in Sp Vi. The relevant parameters correlating with projection neuron morphology are receptive field size and projection status, whereas for Sp Vi LC neurons the relevant correlative parameter is peripheral receptor association.
Morphology of augmenting inspiratory neurons of the ventral respiratory group in the cat
Authors: Sasaki Hiroshi , Otake Kazuyoshi , Mannen Hajime , Ezure Kazuhisa , Manabe Motomu
Published: January 2005

The present study examined, in Nembutal‐anesthetized and artificially ventilated cats, the morphologic properties of the inspiratory neurons of the ventral respiratory group (VRG). Horseradish peroxidase (HRP) was injected into 21 augmenting inspiratory or late inspiratory neurons with peak firing rates in the late inspiratory phase. The majority of the stained neurons were antidromically activated by stimulation of the cervical cord. Thirteen somata, located within or around the nucleus ambiguus (AMB), between 100 μm caudally and 2,000 μm rostrally to the obex, were stained. In ten cases, the stem axons issuing from the cells of origin coursed medially to cross the midline without giving off any axonal collaterals. Three neurons gave rise to axonal collaterals on the ipsilateral side, distributing boutons in the medullary reticular formation, in the vicinity of the AMB, hypoglossal nucleus, solitary tract, and dorsal motor nucleus of the vagus. In eight neurons, only the axons were labeled; in four of these, which were antidromically activated from the spinal cord, the stem axons crossed the midline 2,000‐3,000 μm rostral to the obex and descended in the reticular formation around the AMB down to the cervical cord. They issued several axonal collaterals, distributing terminal boutons at the level of the caudal end of the retrofacial nucleus and about 1,000 μm rostral and caudal from the obex. Terminals were found mainly in and around the AMB, and a few were found in the vicinity of the dorsal motor nucleus of the vagus. The remaining four nonactivated axons distributed their terminal boutons widely in the reticular formation around the AMB. Thus, the augmenting inspiratory neurons of the VRG were shown to project not only to the spinal cord, but also to the VRG, hypoglossal nucleus, and dorsal motor nucleus of the vagus.
Afferent connections of the oculomotor nucleus in the chick
Authors: Labandeira‐garcia J. U. , Guerra‐seijas M. U. , Labandeira‐garcia J. U. , Jorge‐barreiro F. J.
Published: January 2005

Horseradish peroxidase was injected into the oculomotor nucleus of the chick in order to locate and characterize the neurons projecting to this nucleus. In the rostral mesencephalon, 120‐180 neurons were labelled in the medial area of the ipsilateral nucleus campi Foreli; 190‐220 in the interstitial nucleus of Cajal (most of them contralateral); and smaller numbers bilaterally in the medial mesencephalic reticular formation, the nucleus of the basal optic root complex, and the central grey matter. More caudally, numerous neurons were labelled in the contralateral abducens nucleus and the vestibular complex and a few in the nucleus reticularis pontis caudalis. Labelled neurons appeared ipsilaterally in the caudal region of the nucleus vestibularis superior and in the rostral tip of the nucleus descendens just lateral to the tractus lamino‐olivaris. In the contralateral vestibular complex, a group of labelled cells observed in the dorsolateral area may be homologous to the mammalian cell group Y. At the level of the contralateral abducens nucleus, the most numerous group of cells (625‐700) projecting to the oculomotor nucleus formed a lateromedial fringe that affected the nucleus tangentialis, the rostral tip of the nucleus descendens and the ventrolateral region of the nucleus medialis. Only a few labelled neurons were seen in the contralateral nucleus vestibularis superior, the ipsilateral cell group A, and the ipsilateral nucleus vestibularis medialis.
Extracellular matrix components of the peripheral pathway of chick trigeminal axons
Authors: Moody Sally A. , Quigg Marks S. , Little Charles D.
Published: January 2005

The directed growth of axons to their peripheral targets during development may be influenced by a variety of intrinsic and environmental factors, the latter including the pattern of extracellular matrix components in the region through which they grow. We investigated the localization within the chick trigeminal mesenchyme of a variety of extracellular matrix molecules (laminin, heparan sulfate proteoglycan, entactin, collagen type IV) by using indirect immunofluorescence techniques. The trigeminal mesenchyme contained several of these molecules, but only laminin was specifically localized to trigeminal axon pathways. Double immunofluorescence localization of affinity‐purified laminin antibodies and monoclonal antibodies directed against a neuron‐specific β‐tubulin (to visualize growing axons and postmitotic V ganglion neurons) demonstrated that the V motor and sensory peripheral nerves confine their growth to two patches of laminin‐rich mesenchyme—a ganglionic laminin patch colocalized with V ganglion neurons and their axons, and a mandibular laminin patch colocalized with the V motor axons. Thus, laminin pathways in the mesenchyme may help guide V axons along their appropriate routes in the periphery. Double immunofluorescence localization of these laminin antibodies and monoclonal antibodies that recognize neural crest cells (to visualize precursors of V ganglion neurons and glia) demonstrated that the majority of cells within the ganglionic laminin patch were neural crest and differentiating neurons derived from the trigeminal epidermal placode. Since these cells often were laminin‐immunopositive, they might be a source of the ganglionic laminin matrix. The mandibular laminin patch contains nearly no neural crest cells, and probably contains the somitomeric precursors to the mandibular muscle mass. These results suggest that laminin, a matrix molecule implicated in the guidance of trigeminal peripheral axons, might be produced in localized patches by peripheral nervous system components and by muscle targets.
Identification and distribution of a proctolin‐like neuropeptide in the nervous system of the gypsy moth, Lymantria dispar, and in other lepidoptera
Authors: Davis Norman T. , Velleman S. G. , Kingan T. G. , Keshishian H.
Published: January 2005

Although the neuropeptide proctolin has important functions in many arthropods, it is reported to be absent in Lepidoptera. Its possible occurrence in these insects was reinvestigated by bioassays of HPLC fractions and immunocytochemistry.

A proctolin‐like substance was recovered from the frontal and subesophageal ganglia of Lymantria dispar. This substance has the same chromatographic retention time as proctolin; enzymatic degradation indicates that it is a peptide; it is bound by proctolin antisera; and thus it is indistinguishable from authentic proctolin.

A small subpopulation of proctolin‐like immunoreactive (PLI) neurons was stained in the larval CNS of L. dispar, Manduca sexta, Trichoplusia ni, Galleria mellonella, and Vanessa cardui. Most prominent of these cells are median neurosecretory neurons in the brain, paired neurons in the frontal ganglion, two clusters of neurons in the subesophageal ganglion, paired lateral neurons in the thoracic ganglia, and dorsomedial neurons in the abdominal ganglia. Also, varicose PLI axons are found in the corpora cardiaca and perivisceral organs. In L. dispar, PLI cells also were found in the corpora cardiaca.

The results of this study indicate that proctolin is of general occurrence in the Lepidoptera, that it has an important role in the stomatogastric nervous system, and that it may be released as a local neurohormone from various neurohemal organs.
Numerical matching in the mammalian CNS: Lack of a competitive advantage of early over late‐generated cerebellar granule cells
Authors: Vogel Michael W. , Herrup Karl
Published: January 2005

In this report we use postnatal 3H‐thymidine injections to test whether granule cells that are generated early in postnatal cerebellar development and whose axons have access to their Purkinje cell target beginning in the first postnatal week have an advantage over granule cells generated 9 days later in the competition for target‐related stabilization. In the wild‐type mouse, 3–5% of the adult granule cell population is labeled by injection of 3H‐thymidine at either postnatal day 4 (P4) or P13. In the lurcher mutant, however, over 40% of the surviving granule cells are labeled by P4 injection while less than 1% are labeled after a P13 injection. Together, these results suggest that time of target contact is a critical factor in the competition for neuronal survival. The results from the lurcher chimeras, however, reveal that the situation is likely to be more complicated. In all chimeras examined, with target sizes ranging from 3 to 108% of wild type, equivalent numbers of granule cells were labeled at P4 and P13. These data lead to the contradictory conclusion that, in this experimental situation, early generated granule cells do not have a competitive advantage over later‐generated granule cells. The results are discussed in terms of various models of target stabilization. We propose that, of the various hypotheses, our results are best explained by postulating two distinct mechanisms for developmental cell death. Supporting evidence for this hypothesis from other neuronal systems is also briefly reviewed.
Morphology of a new population of spiking local interneurones in the locust metathoracic ganglion
Authors: Nagayama Toshiki
Published: January 2005

A new population of spiking local interneurones is described in the metathoracic ganglion of the locust. All have their cell bodies in a cluster at the ventral, anteromedial portion of the ganglion close to the inner edge of an anterior connective. Their branches are restricted to the same half of the ganglion as their cell bodies.

Fifteen types of these unilateral interneurones have been characterized by their morphology, as revealed by intracellular injection of dye, and by their physiology, as revealed by intracellular recording. Each interneurone has a characteristic shape and physiological action, but they form three distinct subgroups according to their gross morphology and their mode of operation. Interneurones of the first subgroup have ventral branches that extend over most of one‐half of the metathoracic neuropil and receive inputs mainly from exteroceptors on the ipsilateral hind leg. Typically, they have extensive and reciprocal receptive fields along the dorsoventral axis of the hind leg. Interneurones of the second subgroup have two main ventral branches which extend either medially or laterally and receive inputs mainly from proprioceptors of the hind leg. Interneurones of the third subgroup have few ventral branches and are inhibited by inputs anywhere on the hind leg.
Effects of unilateral cochlea removal on anteroventral cochlear nucleus neurons in developing gerbils
Authors: Hashisaki George T. , Rubel Edwin W.
Published: January 2005

Afferent regulation of neurons in the cochlear nucleus as a function of age was investigated at the light microscope level. Unilateral cochlea removal was performed on Mongolian gerbils of three age groups: 1, 8, and 20 weeks postnatal. Animals survived for either 2 days or 2 weeks. An additional group of neonatally operated animals had a prolonged survival of 9 weeks. The number of neurons in anteroventral cochlear nucleus (AVCN) was counted, and cross‐sectional area measurements of large spherical cells in AVCN were made.

In animals 1 week old at the time of surgery, there was a 35% reduction in neuron number in AVCN after 2 days, a 58% reduction after 2 weeks, and a 59% reduction 9 weeks after inner ear destruction. However, in animals 20 weeks old at the time of surgery, there was no cell loss in AVCN either 2 days or 2 weeks after surgery. Animals in each age group showed a reduction in cross‐sectional area of large spherical cells in AVCN after cochlea ablation. The gerbils that underwent cochlea removal at 8 and 20 weeks showed an average decrease of 14–18%. This effect was seen as early as 2 days after cochlea removal. Animals that underwent cochlea removal at 1 week exhibited the greatest change; a 25% decrease at 2 days progressed to 38% at 2 weeks following cochlea removal. No appreciable further changes were seen at 9 weeks after neonatal cochlea removal.

The results indicate greater susceptibility of 1‐week‐old gerbil cochlear nucleus neurons to peripheral loss than found in older animals. In all groups the changes in cell size and neuron number occurred considerably sooner after cochlea ablation than previously has been reported. Interestingly, these changes were seen before the onset of hearing and before the onset of measurable cochlear microphonic responses to sound.
Ultrastructural study of the GABAergic, cerebellar, and mesodiencephalic innervation of the cat medial accessory olive: Anterograde tracing combined with immunocytochemistry
Authors: de Zeeuw C. I. , Holstege J. C. , Ruigrok T. J. H. , Voogd J.
Published: January 2005

The rostral medial accessory olive (MAO) of the cat was studied by using an ultrastructural technique combining wheat germ agglutinin–coupled horseradish peroxidase (WGA‐HRP) anterograde tracing and postembedding GABA immunocytochemistry. One group of cats received a WGA‐HRP injection in the posterior interposed nucleus of the cerebellum and another group received an injection in the nucleus of Darkschewitsch.

Based on differences in their morphology three types of GABAergic and three types of nonGABAergic terminals were observed. One type of GABAergic terminal was often GABA/WGA‐HRP double‐labeled in the cerebellar experiments, and one type of nonGABAergic terminal was often WGA‐HRP‐labeled in the mesodiencephalic experiments.

Following injections of WGA‐HRP in the cerebellar nuclei virtually all WGA‐HRP‐labeled terminals were GABA positive. Quantification of these GABA/WGA‐HRP‐double‐labeled terminals showed that (1) 30% of the GABAergic terminals randomly selected from the entire neuropil were double‐labeled, (2) 13% of the GABAergic terminals adjacent to perikarya were double‐labeled, and (3) 34% of the GABAergic terminals strategically located next to both of the dendritic elements linked by a gap junction were doublelabeled. Statistical analysis of the above data showed that significantly fewer GABAergic terminals adjacent to perikarya were double‐labeled (P < .001) than would be expected from the double‐labeled proportion of the randomly selected GABAergic terminals.

Following injection of WGA‐HRP in the nucleus of Darkschewitsch, all WGA‐HRP‐labeled terminals were GABA‐negative. Quantification of these terminals showed that (1) 26% of the randomly selected nonGABAergic terminals were WGA‐HRP labeled, (2) 20% of the nonGABAergic terminals adjacent to perikarya were WGA‐HRP labeled, and (3) 23% of the nonGABAergic terminals strategically located next to a gap junction were WGA‐HRP labeled. No significant differences were found among these populations.

Quantification of terminals of both groups of experiments mentioned above showed that GABAergic terminals composed (1) 38% of the randomly selected terminals, (2) 64% of the terminals apposed to perikarya, and (3) 53% of the terminals strategically located next to gap junctions. Statistical analysis of the above data showed that significantly more GABAergic terminals were located adjacent to perikarya (P < .001) and strategically next to a gap junction (P < .05) than would be expected from the random GABAergic innervation.

The above findings of the GABAergic, cerebellar, and mesodiencephalic input are discussed with regard to their functional role in the neuronal cir‐ cuitry of the rostral MAO. In addition, the possible noncerebellar origins of the GABAergic inputs to the inferior olive are discussed.
Functional organization of mustached bat inferior colliculus: II. Connections of the FM2 region
Authors: Frisina Robert D. , O'Neill William E. , Zettel Martha L.
Published: January 2005

Echolocating bats estimate target distance by analyzing the time delay between frequency‐modulated portions of their emitted ultrasonic vocalizations and the resultant echoes. In the companion paper we investigated, in the central nucleus of the inferior colliculus, the representation of the predominant second‐harmonic frequency‐modulated component (FM2) of the mustached bat biosonar signal (O'Neill et al.: J. Comp. Neurol. 283:000–000, '89). In the present paper we report the connections of this part of the colliculus, as determined by focal, iontophoretic injections of HRP following single‐unit mapping of the FM2 representation. It was found that the major inputs to the FM2 region of the inferior colliculus come from the contralateral cochlear nucleus; ipsilaterally from the medial superior olive, periolivary nuclei, and ventral and intermediate nuclei of the lateral lemniscus; and bilaterally from the lateral superior olive and dorsal nucleus of the lateral lemniscus. This study identifies for the first time those specific regions of brainstem nuclei providing input to the central nucleus of the inferior colliculus that process FM2 information in the mustached bat. The primary outputs of the FM2 region project to the medial and dorsal divisions of the medial geniculate body. In sharp contrast to other mammals, we found little evidence of connections to the ventral division of the medial geniculate. Other regions receiving significant inputs from the FM2 area include the deep superior colliculus ipsilaterally and the ipsilateral lateral pontine nuclei. Some fibers also terminated near the midline in the dorsal midbrain periaqueductal gray. Sparse intrinsic connections were also seen to the ipsilateral dorsoposterior division of the central nucleus and to the contralateral inferior colliculus at a location homologous to the injection site in the anterolateral division. The finding that FM2 projections to the medial geniculate heavily favor the medial and dorsal divisions is consistent with the location of “FM‐FM” delay‐dependent facilitation neurons found by Olsen (Processing of Biosonar Information by the Medial Geniculate Body of the Mustached Bat, Pteronotus parnellii. Dissertation, Washington Univ., St. Louis, '86) in these divisions, and with thalamocortical projection patterns in this species. These findings demonstrate that for the FM portions of the biosonar signal, a transformation from a tonotopic form of processing to a more specialized, convergent pattern of organization occurs at the level of the inferior colliculus outputs.
Retinogeniculate projection fibers in the monkey optic nerve: A demonstration of the fiber pathways by retrograde axonal transport of WGA‐HRP
Authors: Naito Jumpei
Published: January 2005

Seven Japanese monkeys (Macaca fuscata) were used to investigate the fiber pathways of the optic nerve. Optic nerve fibers and retinal ganglion cells were retrogradely labeled by iontophoretic injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) into electrophysiologically defined positions of the lateral geniculate nucleus (LGN). By gross anatomical observation, the optic nerve usually had one distinct bend, which flexed dorsally 3‐4 mm from the eyeball, and occasionally another ventrally directed bend was found just behind the eyeball. In the optic nerve head, fibers from the various retinal areas were arranged in a wedge according to the fiber trajectory on the retinal surface. For about a 3 mm distance from the disc, fibers rapidly spread out radially. Subsequently, rather than scattering dorsoventrally, they progressed to the chiasm with a gradual increase in the degree of mediolateral (nasotemporal) scatter. The degree of the scatter was different depending on the retinal site from which the axons originated. Fibers from the peripheral retina spread out widely for a few millimeters behind the eyeball. Thereafter the scatter was rather limited until the chiasm. On the other hand, the scatter of fibers from the foveal and parafoveal areas progressed gradually through the nerve. The present study also suggests that the difference in scatter depends on the types of cells of origin. Fibers from large ganglion cells displayed more extensive scatter than fibers from medium‐sized cells. In spite of the extensive scatter of fibers, two clear segregations were found; one was a dorsoventral segregation, which was displayed by both central and peripheral retinal fibers, and the other was a center‐peripheral segregation in which the fibers from the nasal central (papillomacular) retina were located almost exclusively in the central part of the optic nerve surrounded by peripheral retinal fibers. However, the temporal central retinal fibers were located in the lateral periphery of the nerve, and they overlapped significantly with fibers from the temporal peripheral retina. Furthermore, a broad intermingling was found between nasal and temporal peripheral retinal fibers owing to their mediolateral scatter. Thus, the present findings based on more precise anatomical techniques indicate that the classical notion of the retinal quadrant topography in the monkey optic nerve probably is suspect. In addition, the “rotation” of the fiber arrangement was not demonstrated.
Olivocerebellar and cerebelloolivary connections of the oculomotor region of the fastigial nucleus in the macaque monkey
Authors: Ikeda Yoichi , Noda Hiroharu , Sugita Shoei
Published: January 2005

Anatomical connections of the caudal portion of the fastigial nucleus (FN) with the inferior olive (IO) were studied in macaque monkeys with wheat‐germ‐agglutinin‐conjugated horseradish peroxidase (WGA/HRP) and HRP. When injected HRP was confined to a caudal portion of the FN, retrogradely labeled Purkinje cells (P cells) appeared in the oculomotor vermis. We defined the area that receives the projection from vermal lobule VII as the fastigial oculomotor region. The same HRP injection resulted in retrograde labeling of IO neurons in an area of group b (of Bowman and Sladek: J. Comp. Neurol. 152:299‐316, '73) of the contralateral medial accessory olive (MAO). This area was designated as the Z‐portion because in the coronal section it appears like the letter “Z.” Retrogradely labeled IO neurons were also found in the Z‐portion when HRP was injected into the oculomotor vermis, indicating that neurons in this portion project to both the fastigial and vermal oculomotor regions. Anterogradely labeled axons from the contralateral fastigial oculomotor region also terminated in the Z‐portion.

When the effective site included a region anterior to the fastigial oculomotor region, labeled P cells appeared in lobule V and labeled IO neurons appeared in group a. Labeled terminals of fastigial fibers were also found in group a. When the effective site included a region ventral to the oculomotor region, labeled P cells appeared in vermal lobules VIII and IX and labeled IO neurons appeared in caudal parts of a and b, in addition to group c. HRP injection into the posterior interposed nucleus (PIN) resulted in labeling of P cells in the paravermal zone and of IO neurons in the rostral two‐thirds of the MAO and the dorsal accessory olive (DAO). The location of the labeled terminals coincided with the region where the densest labeling of IO neurons was found. Thus, the olivary projections to both the cerebellar cortex and deep cerebellar nuclei and the nucleoolivary projection exhibited a closely related topographical organization.
Sex‐specific neuronal respecification during the metamorphosis of the genital segments of the tobacco hornworm moth Manduca sexta
Authors: Thorn Robert S. , Truman James W.
Published: January 2005

At metamorphosis, the terminal abdominal segments of larvae of the moth Manduca sexta transform into either male or female genitalia. At the start of this transformation, the larval muscles degenerate but their remains may persist to form the scaffolding on which the new adult muscles differentiate. The survival and subsequent orientation of larval muscle remnants is determined by the sex of the individual and is independent of motor innervation at the start of metamorphosis. Many of the larval motoneurons persist through metamorphosis and innervate the skeletal muscle of the adult. The survival of particular motoneurons is also sex‐dependent and correlated with the survival of its respective muscle remnant. No new skeletal motoneurons arise postembryonically, so all of the adult skeletal muscle motoneurons are derived from preexisting larval skeletal muscle motoneurons.

The fates during metamorphosis are more complex for the visceral muscle motoneurons. Those innervating the adult hindgut of both sexes are identical and are derived from the larval hindgut motoneurons. Other hindgut motoneurons in the larva switch targets during metamorphosis and come to innervate the oviduct in adult females or perish in adult males. Other regions of the reproductive tract become innervated by adult‐specific cells that differentiate during metamorphosis. These cells come from distinct lineages in males and females.
Development of vasoactive‐intestinal‐polypeptide‐immunoreactive neurons in the rat occipital cortex: A combined immunohistochemical‐autoradiographic study
Authors: Cavanagh Marion E. , Parnavelas John G.
Published: January 2005

The postnatal development of vasoactive intestinal polypeptide (VIP)‐immunoreactive neurons, previously labeled with [3H]thymidine on embryonic days E14‐E22, has been studied in the rat occipital cortex. Immunohistochemistry combined with autoradiography showed very little evidence of an “inside‐out” pattern of maturation. Most VIP neurons are generated between E17 and E21 and are found in layers II‐IV of the cortex, but their position within these layers is not dictated by their date of birth. There is evidence of a temporal maturation since E17 VIP neurons were seen first (at day 7) and E21 last. Peak numbers of VIP neurons were generated on E19. The numbers of VIP‐immunoreactive neuronal somata detected in the cortex increased from the first week after birth to the third week and declined thereafter. However VIP‐immunoreactive dendrites were still visible, suggesting that VIP levels in the cell bodies were very low, and not that there was a loss of neurons.
Enkephalin‐like immunoreactivity in the cat superior colliculus: Distribution, ultrastructure, and colocalization with GABA
Authors: Mize R. Ranney
Published: January 2005

The distribution of enkephalin (ENK) immunoreactivity has been examined in the cat superior colliculus (SC) by means of light and electron microscope immunocytochemistry. The antisera were directed against leucine enkephalin but also recognized methionine enkephalin. Colocalization of ENK with gamma aminobutyric acid (GABA) was studied with a two‐chromagen double‐labeling technique. Enkephalin antiserum labeling was highly specific. Dense neuropil labeling was found only in a thin band 75–100 μm wide within the upper superficial gray layer of SC. Negligible neuropil labeling was seen deeper, except for patches of label within the intermediate gray layer. Intensely labeled neurons also had a specific distribution. Forty‐seven percent were located within the upper 200 μm of SC, 40% within the deep superficial gray layer, 11% in the optic layer, and only 2% below that layer. Almost all ENK‐labeled cells were small (mean area of 117 μm2). Some of these had horizontal fusiform cell bodies and horizontally oriented dendrites. Others had small round somata and thin, obliquely oriented dendrites. In double‐labeling experiments, 18% of anti‐ENK‐labeled cells were also immunoreactive for GABA.

Four distinct types of ENK‐labeled profile were identified with the electron microscope. Presynaptic dendrites (PSD) with loose accumulations of synaptic vesicles were densely labeled with the antiserum. Conventional dendrites were also labeled. Both types of labeled profile received input from unlabeled synaptic terminals, including those from the retina that contained pale mitochondria and round synaptic vesicles and formed asymmetric synaptic contacts. Retinal terminals were never labeled with the antisera. However, some axon terminals with round synaptic vesicles, dark mitochondria, and symmetric synaptic densities were labeled by the antisera, as were some thinly myelinated axons. These results show that there is a small population of enkephalinergic neurons in the cat SC, some of which also contain GABA. Because not all cells with identical morphologies were double labeled, it appears that neurons of like morphology are chemically heterogeneous.