bluuebunny/crossref_metadata_2025 huggingface dataset:
Organization of the visual system in larval lampreys: An HRP study
Authors: De xsMiguel Encarnación , Rodicio María Celina , Anadon Ramón
Published: January 2005

The organization of the visual system of larval lampreys was studied by anterograde and retrograde transport of HRP injected into the eye. The retinofugal system has two different patterns of organization during the larval period. In small larvae (less than 60–70 mm in length) only a single contralateral tract, the axial optic tract, is differentiated. This tract projects to regions in the diencephalon, pretectum, and mesencephalic tegmentum. In larvae longer than 70–80 mm, there is an additional contralateral tract, the lateral optic tract, which extends to the whole tectal surface. In addition, ipsilateral retinal fibers are found in both small and large larvae. Initially, the ipsilateral projection is restricted to the thalamus‐pretectum, but it reaches the optic tectum in late larvae. Changes in the organization of the optic tracts coincide with the formation of the late‐developing retina and consequently, the origin of the optic tracts can be related to specific retinal regions.

The retinopetal system is well developed in all larvae. Most retinopetal neurons are labeled contralaterally and are located in the M2‐M5 nucleus of the mesencephalic tegmentum, in the caudolateral mesencephalic reticular area and adjacent ventrolateral portions of the optic tectum. Dendrites of these cells are apparent, especially those directed dorsally, which in large larvae extend to the optic tectum overlapping with the retino‐tectal projection.

These results indicate that in lampreys, visual projections organize mainly during the blind larval period before the metamorphosis, their development being largely independent of visual function.
Specificity of initial axonal projections to embryonic chick wing
Authors: Hollyday Margaret
Published: January 2005

Anterograde transport of HRP was used to map initial segmental projection patterns of motor and sensory axons to the chick embryo wing. At the earliest stages of innervation, before the peripheral nerves had formed, motor axons were distributed as two loosely organized sheets, one directed towards the dorsal muscle mass and the other to the ventral. Labeled axons emerging from a given spinal cord segment were distributed within the sheets in a pattern that reflected the origin of the axons along the rostro‐caudal axis of the lateral motor column. The segmental specificity of the motor projections was analyzed again after the axonal sheets had formed recognizable nerve trunks and muscle nerves. As was observed at the younger stages, axons were distributed in a pattern that was correlated with both the relative antero‐posterior (A/P) and proximo‐distal (P/D) position of the forming nerve, with cranial spinal nerves projecting to anterior and proximal limb regions. Whereas most axons emerging from a given ventral root projected in accord with what would be expected from the known adult motor pool maps, segmentally unexpected projections were frequently observed. The proportion of aberrantly projecting axons appears to be quite small, and in most embryos, it was impossible to determine whether the erroneous projections originated from unbranched axons or were collateral branches of others. The findings indicate that the initial projections of motor axons to the developing wing are patterned along the A/P axis of the wing and are largely accurate; however, the guidance processes are not sufficiently precise to exclude fibers entirely from inappropriate nerves. It is likely that later developmental processes act to fine‐tune the initial projection pattern.
Dendritic morphologies of retinal ganglion cells projecting to the nucleus of the optic tract in the rabbit
Authors: Pu Mingliang , Amthor Franklin R.
Published: January 2005

Focal injections of Rhodamine‐latex microspheres or Fast Blue were made in the nucleus of the optic tract (NOT) of four rabbits. After survival times of 8–10 days, both dyes were retrogradely transported to medium to large sized ganglion cell somas in the retinas contralateral, but not ipsilateral, to the injected NOT. Most labelled cells were located in or near the visual streak, but a significant percentage were also found in the midperiphery of both the inferior and superior retina. One hundred fifteen labelled cells in four living supervised retinas were impaled under visual control and successfully injected with Lucifer Yellow. The dendritic arborizations of 60 of these were drawn from photographic montages for morphological identification and analysis. Nearly all the injected ganglion cells had large, relatively dense dendritic trees that stratified narrowly in the proximal inner plexiform layer. The dendritic field size and dendritic density of these cells varied with eccentricity, but at all eccentricities their anatomical characteristics closely resembled those of intracellularly stained On directionally selective ganglion cells. In three of the four experiments, a small percentage of ganglion cells were also labelled in the visual streak that had bistratified morphologies resembling those of On‐Off directionally selective ganglion cells.
GABA‐like immunoreactivity in a population of locust intersegmental interneurones and their inputs
Authors: Watson Alan H. D. , Laurent Gilles
Published: January 2005

Intracellular labelling of locust intersegmental interneurones with lucifer yellow or horseradish peroxidase was carried out in combination with light and electron microscope immunocytochemistry by using an antibody raised against gamma amino butyric acid (GABA). Fifteen percent (four out of 27) of intracellularly stained interneurones showed GABA‐like immunoreactivity. This is in agreement with previous physiological observations that 20% of the interneurones in this population make inhibitory output conceptions in the metathoracic ganglion. GABA‐like immunoreactivity was also found in processes presynaptic to the interneurones in the mesothoracic ganglion. The presence of such immunoreactive inputs onto the intersegmental interneurones correlates well with physiological evidence that their receptive fields are in part shaped by direct input from GABA‐ergic spiking local interneurones.
Microglial cell responses in the rabbit retina following transection of the optic nerve
Authors: Schnitzer Jutta , Scherer Jürgen
Published: January 2005

The response of retinal microglial cells, which accompanies retrograde degeneration of ganglion cell axons and perikarya (induced by transection of the optic nerve), was studied in whole‐mounted rabbit retinae labeled enzyme‐histochemically for nucleoside diphosphatase (NDPase), which is a microglial cell marker.

A few days after transection, the number of microglial cells/mm2, as well as their staining intensity, began to increase in the inner plexiform layer. The mosaic‐like distribution of the star‐shaped microglial cells present in the inner plexiform layer of a normal rabbit retina was preserved during ganglion cell degeneration. As in the normal retina, processes of individual cells never overlapped with those of neighboring cells in the inner plexiform layer because individual cells in the “degenerating” retina acquired shorter processes, i.e., the cells occupied a smaller territory compared to the normal retina.

In the nerve fiber layer the number and staining intensity of NDPase‐labeled microglial cell processes (most of which are aligned in parallel with degenerating ganglion cell axons) transiently increased and returned to normal values by 5 months post‐transection.

Microglial cells that are not detectably NDPase labeled in the outer plexiform layer of a normal rabbit retina acquire intense staining a few days after the nerve is cut. The functional significance of the increased NDPase activity in the plasma membrane of microglial cells during degeneration remains to be determined.
Immunoreactive GAP‐43 in the neuropil of adult rat neostriatum: Localization in unmyelinated fibers, axon terminals, and dendritic spines
Authors: DiFiglia Marian , Roberts Rosalinda C. , Benowitz Larry I.
Published: January 2005

GAP‐43 is a neuron‐specific phosphoprotein that has been implicated in neuronal development, axonal regeneration, and synaptic plasticity. Although in mammals the caudate‐putamen is among those brain areas that retain a high content of GAP‐43 throughout life, the role of the phosphoprotein in the neostriatum is unknown. In order to understand better the possible function(s) of GAP‐43 in the adult striatum, its cellular localization was examined with immunohistochemistry at the light and electron microscopic levels by using a sheep polyclonal antibody. At the light microscopic level immunoreactive GAP‐43 was abundant throughout the neostriatal neuropil but was absent from neuronal somata. At the ultrastructural level, labeling was most prevalent in small unmyelinated axons (0.12–0.15 μm diameter). Reaction product was distributed along fibers in discrete patches about 1 μm apart and in preterminal sites from which vesicle‐filled boutons arose. Staining was also present in small (0.35 μm) axon terminals that contained round vesicles and formed asymmetric synapses, mostly with thin spines. Following unilateral cortical lesions, some degenerating cortical axons in the neostriatum exhibited GAP‐43 labeling. Unexpectedly, in normal striatum, GAP‐43 was also occasionally found in the heads of dendritic protrusions and in thin spines that received asymmetric contacts. We speculate that in the adult neostriatum, the protein may be important in the remodeling of synapses onto medium spiny neurons that involve, in part, the corticostriatal pathway.
Peptide‐immunocytochemistry of neurosecretory cells in the brain and retrocerebral complex of the sphinx moth Manduca sexta
Authors: Homberg U. , Davis N. T. , Hildebrand J. G.
Published: January 2005

Antisera against a variety of vertebrate and invertebrate neuropeptides were used to map cerebral neurosecretory cells in the sphinx moth Manduca sexta. Intense immunoreactive staining of distinct populations of neurosecretory cells was obtained with antisera against locust adipokinetic hormone, bovine pancreatic polypeptide, FMRFamide, molluscan small cardioactive peptide (SCPB), leucine‐enkephalin, gastrin/cholecystokinin, and crustacean β‐pigment dispersing hormone (βPDH). Other antisera revealed moderate to weak staining. Each type of neurosecretory cell is immunoreactive with at least one of the antisera tested, and most of these neurons can be identified anatomically. The staining patterns provide additional information on the organization of cerebral neurosecretory cells in M. sexta. Based upon anatomical and immunocytochemical characteristics, 11 types of neurosecretory cells have been recognized in the brain, one type in the suboesophageal ganglion, and one in the corpus cardiacum. Extensive colocalization experiments show that many neurosecretory cells are immunoreactive with several different antisera. This raises the possibility that these cells may release mixtures of neuropeptides into the hemolymph, as has been demonstrated in certain other systems. The immunocytochemical data should be helpful in efforts to identify additional peptide neurohormones released from the brain of this and other insects.
Distributions of choline acetyltransferase and acetylcholinesterase activities in the retinal layers of the red‐tailed hawk and road runner
Authors: White Leonard E. , Ross C. David , Godfrey Donald A.
Published: January 2005

The activities of choline acetyltransferase and acetylcholinesterase were assayed in submicrogram samples from layers of red‐tailed hawk and road runner retina. Both enzyme activities were concentrated in and near the inner plexiform layer. Within the inner plexiform layers of both species, activities of each enzyme were concentrated in two bands, one in each half of this layer. Little choline acetyltransferase activity was found superficial to the middle third of the inner nuclear layer. The distributions of acetylcholinesterase activities corresponded well to those of choline acetyltransferase, except in the outer plexiform layer and the outer margin of the inner nuclear layer of the hawk. These distributions of enzyme activities indicate that populations of amacrine cells in the retinae of these species are cholinergic. In addition to these same cells and presumably cholinoceptive amacrine and ganglion cells, acetylcholinesterase activity in the hawk was associated with a population of horizontal cells that may be unrelated to synaptic cholinergic neurotransmission. Choline acetyltransferase activities associated with amacrine somata and processes were about four times greater in the hawk than in the road runner suggesting important differences in the density and function of cholinergic elements between species. Possible synaptic relationships in the inner plexiform layer consistent with the interspecies differences in enzyme activities are considered.
Fine structure of synapses and retinal innervation of substance P and adenosin deaminase containing neurons in the superior colliculus of the rat
Authors: Miguel‐Hidalgo J. Javier , Senba Emiko , Takatsuji Koichi , Tohyama Masaya
Published: January 2005

The fine structure of substance P (SP) and adenosine deaminase (ADA) immunoreactive structures in synaptic contacts localized to the superficial layers of the superior colliculus of the rat was investigated by means of immunoelectron microscopy. We also examined the possibility of retinal innervation of SP‐ and ADA‐ containing neurons by immunohistochemistry after degeneration of retinal terminals caused by enucleation.

SP‐like immunoreactive presynaptic terminals of the stratum griseum superficial (SGS) formed both asymmetric and symmetric synaptic contacts, Presynaptic dendrite like structures were also observed. SP immunoreactive postsynaptic elements made contacts with terminals showing diverse features. ADA‐like immunoreactive structures were seen only as postsynaptic elements to different kinds of nonimmunoreactive terminals and were mostly localized in the ventral third of the SGS and the dorsalmost stratum opticum (SO).

After enucleation, degenerating retinal terminals were found to form synaptic contacts with SP and ADA immunoreactive structures. The highest number of such degenerating terminals on ADA immunoreactive structures was observed 2 days after retinal denervation, very few being seen after 5 days. These degenerating terminals were restricted to the ventral SGS and dorsal SO. SP immunoreactive structures postsynaptic to degenerating retinal terminals were most numerous 5 days after enucleation and mainly localized in the dorsal SGS. Occasionally, SP immunoreactive dendrite like processes forming synapses with degenerating retinal terminals were simultaneously presynaptic to other nonimmunoreactive profiles, defining, therefore, serial synapses. The present results suggest that SP‐I and ADA‐I collicular neurons may be part of distinct channels carrying visual information to the lateral posterior and lateral geniculate nuclei of the thalamus, respectively.
Dendritic and axonal morphology of HRP‐injected neurons in the inferior colliculus of the cat
Authors: Oliver Douglas L. , Kuwada Shigeyuki , Yin Tom C. T. , Haberly Lewis B. , Henkel Craig K.
Published: January 2005

The dendritic and axonal morphology of neurons in the inferior colliculus of the cat was investigated after intracellular injection of HRP, in vivo. All injected axons gave off local collaterals, and most showed a widespread distribution and lacked a specific orientation. In contrast, the dendrites of injected neurons were distinguished by their degree of orientation and the direction of the longest axis of orientation. Dendrites showed a high, moderate, or low degree of orientation. Most highly oriented cells had their longest axis in the rostrocaudal direction with fewer in the mediolateral direction. In the central nucleus, only the rostrocaudally oriented cells correspond to the disc‐shaped cells identified in Golgi preparations. Unlike most cells in our sample, the two cells that were disc‐shaped had axons that were parallel to the orientation of the dendritic tree. In the dorsal cortex, rostrocaudally oriented cells also were found, but they had unoriented axons. In both the central nucleus and dorsal cortex, cells with a mediolateral axis of orientation or no specific orientation correspond to stellate cells and had axons with widespread local collaterals.

These results suggest that an extensive network of local axon collaterals may contribute to neural processing within the inferior colliculus. In the central nucleus, local axons may establish connections within or across the fibrodendritic laminae. In the dorsal cortex, the local and afferent axons may form a complex reticular network. Finally, some injected cells had axons terminating locally and also entering the brachium of the inferior colliculus. This suggests that cells in the inferior colliculus may function as both interneurons and projection neurons.
Posteroventral cochlear nucleus projections to olivocochlear neurons
Authors: Thompson Ann M. , Thompson Glenn C.
Published: January 2005

The presence of ascending auditory inputs from the posteroventral cochlear nucleus (PVCN) to olivocochlear neurons was examined in guinea pig by using the combination Phaseolus vulgaris‐leucoagglutinin (PHA‐L) anterograde and horseradish peroxidase (HRP) retrograde tract‐tracing technique. By labeling the somata of olivocochlear neurons after injection of HRP into the cochlea and simultaneously labeling terminal endings of PVCN efferent neurons after injection of PHA‐L into PVCN, we observed neuronal connections between these two elements within all regions of the superior olivary Complex known to contain olivocochlear neurons. These regions include the superior paraolivary nucleus, medial nucleus of the trapezoid body, lateral superior olive, and periolivary regions. All possible projection patterns regarding side of input and output of both large (four combinations) and small (two combinations) olivocochlear neurons were observed. However, the most frequently observed pattern was the PVCN projection to a contralaterally located and contralaterally projecting, large olivocochlear neuron. Thus the most prevalent pattern demonstrated a feedback pathway that crossed the brainstem twice. Additional patterns demonstrated pathways that fed back to the same cochlea as well as pathways that fed forward to the opposite cochlea.
Autonomic responses and efferent pathways from the insular cortex in the rat
Authors: Yasui Yukihiko , Breder Christopher D. , Safer Clifford B. , Cechetto David F.
Published: January 2005

The anatomical distribution of autonomic, particularly cardiovascular, responses originating in the insular cortex was examined by using systematic electrical microstimulation. The localization of these responses to cell bodies in the insular cortex was demonstrated by using microinjection of the excitatory amino acid, D, L‐homocysteic acid. The efferents from the cardiovascular responsive sites were traced by iontophoretic injection of the anterograde axonal tracer Phaseoleus vulgaris leucoagglutinin (PHA‐L).

Two distinct patterns of cardiovascular response were elicited from the insular cortex: an increase in arterial pressure accompanied by tachycardia or a decrease in arterial pressure with bradycardia. The pressor responses were obtained by stimulation of the rostral half of the posterior insular cortex while depressor sites were located in the caudal part of the posterior insular area. Both types of site were primarily located in the dysgranular and agranular insular cortex. Gastric motility, changes originated from a separate but adjacent region immediately rostral to the cardiovascular responsive sites in the anterior insular cortex.

Tracing of efferents with PHA‐L indicated a number of differences in connectivity between the pressor and depressor sites. Pressor sites had substantially more intense connections with other limbic regions including the infralimbic cortex, the amygdala, the bed nucleus of the stria terminalis and the medial dorsal and intralaminar nuclei of the thalamus. Alternatively, the depressor region of the insular cortex more heavily innervated sensory areas of the brain including layer I of the primary somatosensory cortex, a peripheral region of the sensory relay nuclei of the thalamus and the caudal spinal trigeminal nucleus. In addition, there were topographical differences in the projection to the lateral hypothalamic area, the primary site of autonomic outflow for these responses from the insular cortex. These differences in connectivity may provide the anatomic substrate for the specific cardiovascular responses and behaviors integrated in the insular cortex.
Factors determining the morphology and distribution of astrocytes in the cat retina: A ‘contact‐spacing’ model of astrocyte interaction
Authors: Chan‐Ling Tailoi , Stone Jonathan
Published: January 2005

The retina provides a valuable opportunity to examine the interaction of astrocytes with neurones and vasculature, in adult tissue and in vivo. We have studied astrocytes in cat retina to delineate the interactions that determine their morphology and distribution. Their morphology varied with their interaction with surrounding cells, from a classic stellate shape to an elongated bipolar form associated with axon bundles. Evidence is presented that the distribution of astrocytes across the retina is determined by their morphology and by a previously unrecognised interaction between astrocytes, which we term ‘contact‐spacing’ in which astrocytes maintain contact with their neighbours through their processes, but keep their somas apart. Evidence is also presented that astrocytes are not influenced in their distribution by surrounding neurones, and the influence of developmental mechanisms is identified. These observations are summarised in a contact‐spacing model of astrocyte distribution, and four predictions of the model are tested. The concentration of astrocytes along axon bundles dispersed when the axons degenerate but not when vessels were prevented from forming. Further, when both axons and vessels were eliminated, the concentrations of astrocytes dispersed and they became stellate in form. Finally, in the retina of the rat, in which astrocytes show no affinity for axons, the distribution of astrocytes is essentially uniform. We suggest that the contact‐spacing interaction among astrocytes provides the anatomical basis of a functional glial network extending across the retina and throughout the central nervous system.
Region‐specific expression of the mRNAs encoding β subunits (β1, β2, and β3) of GABAA receptor in the rat brain
Authors: Zhang Jian‐Hua , Sato Makoto , Tohyama Masaya
Published: January 2005

The expression of mRNAs encoding different β subunits (β1, β2 and β3) of the gamma‐aminobutyric acidA (GABAA) receptor in the rat brain was investigated by in situ hybridization histochemistry. Transcripts of each subunit showed region‐specific localization. Some areas contained all three β subunit mRNAs, while other areas showed marked differences in the location and level of expression of each subunit mRNA. The regions with strong to very strong labeling by the β3 probe were as follows: the olfactory bulb, the cortex, the caudate‐putamen, the accumbens nucleus, the hypothalamus, the amygdala, the hippocampal formation, and some areas of the brainstem and spinal cord. Weak to moderate labeling was detected in the thalamus, superior and inferior colliculus, and many areas of the brainstem. The regions with strong to very strong labeling by the β 2 probe were as follows: the olfactory bulb, the ventral pallidum, the globus pallidus, the nucleus of the diagonal band, the preoptic magnocellular nucleus, the thalamus, the subthalamic nucleus, the substantia nigra, and the cerebellum. Weak to moderate labeling was detected in the regions that showed strong expression of β3 subunit mRNA. Expression of β1 subunit mRNA was only weak to moderate compared to that of the β2 and β3 subunit mRNAs. The regions with moderate labeling by the β1 probe were the following: the cortex, the claustrum, the bed nucleus of the stria terminale, some nuclei of thalamus and amygdala, the hypothalamus, the hippocampal formation, the subiculum, the cerebellum, and several areas of the brainstem and spinal cord. Thus, our findings showed that the β subunit mRNAs of the GABAA receptor were differentially expressed in the rat brain, perhaps indicating the existence of different subtypes of the GABAA receptor in different brain regions.
Influence of grafting a smaller target muscle on the magnitude of naturally occurring trochlear motor neuron death during development
Authors: Sohal G. S. , Stoney S. D. , Campbell L. R. , Arumugam T. , Kumaresan K. , Hirano S.
Published: January 2005

About half of the motor neurons produced by some neural centers die during the course of normal development. It is thought that the size of the target muscle determines the number of surviving motor neurons. Previously, we tested the role of target size in limiting the number of survivors by forcing neurons to innervate a larger target (Sohal et al., '86). Results did not support the size‐matching hypothesis because quail trochlear motor neurons innervating duck superior oblique muscle were not rescued. We have now performed the opposite experiment, i.e., forcing neurons to innervate a smaller target. By substituting the embryonic forebrain region of the duck with the same region of the quail before cell death begins, chimera embryos were produced that had a smaller quail superior oblique muscle successfully innervated by the trochlear motor neurons of the duck. The number of surviving trochlear motor neurons in chimeras was significantly higher than in the normal quail but less than in the normal duck. The smaller target resulted in some additional loss of neurons, suggesting that the target size may regulate neuron survival to a limited extent. Failure to achieve neuron loss corresponding to the reduction in target size suggests that there must be other factors that regulate neuron numbers during development.
Crossed and uncrossed projections to cat sacrocaudal spinal cord: II. Axons from muscle spindle primary endings
Authors: Ritz Louis A. , Bailey Steven M. , Carter Richard L. , Sparkes Mary L. , Masson Robert L. , Rhoton Eric L.
Published: January 2005

The terminal fields of primary afferent fibers from tail muscle spindle primary endings were mapped within cat sacrocaudal spinal cord (S3‐Ca7), using intra‐axonal recording and horseradish peroxidase staining techniques. We sought to determine the ipsilateral and contralateral projection patterns and to relate these to the fibers' muscles of origin.

Fifty‐three group Ia fibers were successfully stained. Segmental collaterals originated from either the ascending or descending branch within the dorsal columns. Collaterals coursed rostromedially within the dorsal columns and traversed the medial aspect of the dorsal horn. Ipsilateral terminations were similar for all fibers. Within the ventral horn, boutons were consistently observed in the medial or central portions of lamina VII. In lamina VIII, a variable number of boutons was seen on fine branches emerging from larger fibers coursing ventrally. Clusters of terminals were plentiful in the regions of motoneurons, i.e., lamina IX and the nucleus commissuralis. Terminals were found in the adjacent white matter.

In addition to ipsilateral terminations, some group Ia fibers (20 of 53) had collateral branches that crossed ventrally to the central canal, terminating within the midline ventral gray commissure and/or the contralateral ventral horn. Crossed projections always originated in medial (dorsal or ventral), but not lateral, muscles of the tail.

These data suggest that ipsilateral projections of group Ia fibers make connections on sacrocaudal motoneurons, on neurons mediating segmental reflex functions and on neurons conveying ascending information. It is speculated that crossed and uncrossed connections between group Ia fibers from medial muscles and bilateral dendritic trees of motoneurons subserve synchronized co‐contraction of synergistic muscles located on the two sides of the body, such as with dorsal or ventral flexion of the tail. Group Ia projections from lateral muscles, that are entirely ipsilateral, would be involved with lateral movements of the tail.
Immunocytochemical localization and development of multiple kinds of neuropeptides and neuroendocrine proteins in the chick ultimobranchial gland
Authors: Kameda Yoko
Published: January 2005

The ultimobranchial gland is an endocrine organ consisting of C cell groups. In chickens, the glands are richly supplied by nerve fibers immunoreactive for neurofilaments. It was found by immunocytochemical staining that C cells of chick ultimobranchial glands showed immunoreactivities for multiple kinds of neuropeptides and neuroendocrine proteins in addition to calcitonin, i.e., calcitonin gene‐related peptide (CGRP), somatostatin, neurotensin, chromogranin A, and tyrosine hydroxylase. Furthermore, enkephalin‐immunoreactive cells that showed long cytoplasmic processes and large cell bodies, being distinct from the C cell feature, were detected. The densities of these cells per unit area of ultimobranchial gland were assessed using computer‐assisted image analysis system; calcitonin cells were 42.9 ± 10.0%; CGRP cells 26.9 ± 5.6%; neurotensin cells 8.6 ± 6.9%; somatostatin cells 3.1 ± 1.4%, chromogranin A cells 11.8 ± 1.8%; tyrosine hydroxylase cells 10.0 ± 5.2%; enkephalin cells 2.9 ± 1.3%. Dense distributions of peptidergic nerve fibers were also detected in chick ultimobranchial glands. Numerous varicose fibers immunoreactive for substance P were distributed in the close vicinity to C cell clusters and blood vessels. Enkephalin‐immunoreactive fibers were also prominent around C cell clusters. Galanin‐, vasoactive intestinal peptide (VIP)‐, and tyrosine hydroxylase‐immunoreactive fibers were distributed around blood vessels only. Subsequently, the ontogeny of these neuropeptides, neuroendocrine proteins, and peptidergic innervations was examined in chickens at various developmental stages. In 10‐day‐old embryos, weak to moderately intense immunoreactivity for calcitonin was already present in almost all C cells. Immunoreactivities for somatostatin, CGRP, and tyrosine hydroxylase began to appear at this age. At 12 days of incubation, substance P‐immunoreactive fibers were first detected in the parenchyma of ultimobranchial glands. Considerable numbers of enkephalin‐immunoreactive fibers and cells were also observed. At 14 days of incubation, the largest populations of somatostatin‐ and enkephalin‐immunoreactive cells were attained; the densities of somatostatin‐ and enkephalin‐immunoreactive cells per unit area were 21.2 ± 3.2% and 12.9 ± 3.1%, respectively. Substance P‐immunoreactive fibers became numerous throughout the gland at this age. Thereafter, calcitonin‐, CGRP‐, tyrosine hydroxylase‐immunoreactive cells progressively increased in number with embryonic age, whereas somatostatin‐ and enkephalin‐immunoreactive cells started to decrease. Chromogranin A‐ and neurotensin‐immurioreactive cells began to appear at 16 days and 18 days of incubation, respectively. Galanin‐, VIP‐, and tyrosine hydroxylase‐immunoreactive fibers were inconspicuous during embryonic life.
Topographical organization in the origin of serotoninergic projections to different regions of the cat cerebellar cortex
Authors: Kerr Christopher W. H. , Bishop Georgia A.
Published: January 2005

The distribution of serotonin immunoreactivity in the cat cerebellum was studied by using the indirect antibody peroxidase‐antiperoxidase (PAP) technique. Furthermore, the origin of these chemically defined afferents was determined by combining the retrograde transport of horseradish peroxidase (HRP) with the PAP technique. In the cerebellar cortex, serotonin immunoreactivity is present in a plexus of beaded fibers that is confined almost exclusively to the granule and Purkinje cell layers; a few fibers are present in the molecular layer. Serotoninergic axons and varicosities have a dense and uniform distribution throughout all lobules of the cerebellum with the exception of lobule X where the fiber density is sparse. Serotonin cell bodies were not found within the cerebellar cortex. However, following pretreatment with pargyline and L‐tryptophan, serotonin positive cell bodies were found in all deep cerebellar nuclei as well as the raphe and reticular nuclei in the brainstem.

The present study demonstrates that the serotoninergic projection to the cat's cerebellum has some degree of topographical organization. Serotoninergic fibers in the anterior vermis (lobules I–V) were shown to arise from neurons located within the paramedian reticular nucleus, the lateral reticular nucleus, and the lateral tegmental field. Injections of HRP into either the posterior vermis (lobule VI–IX) or the paramedian lobule, labeled serotoninergic neurons exclusively in the lateral reticular nucleus. Lobus simplex, crus I and crus II (the hemisphere) receive a serotoninergic input from cells located in the lateral tegmental field, the peri‐olivary reticular formation and the paramedian reticular nucleus. In no cases were neurons in the raphe double‐labeled, although there were cells positive for HRP or serotonin alone.

The data indicate that there is a topographical organization in the serotoninergic projection from the caudal brainstem to specific regions of the cat's cerebellar cortex. In addition to climbing and mossy fibers, this projection represents a third major source of cerebellar afferents based on its dense and widespread distribution as well as its morphological and chemical characteristics.
Axonal projections and synaptogenesis by supraspinal descending neurons in the spinal cord of the chick embryo
Authors: Shiga Takashi , Künzi Ralf , Oppenheim Ronald W.
Published: January 2005

Following the injection of horseradish peroxidase (HRP) into the brachial spinal cord of the chick on embryonic day (E)4.5, retrogradely labeled neurons can be found in the brainstem (Okado and Oppenheim: Journal of Comparative Neurology 232:143–161, 1985). By contrast, following high cervical spinal transection, functional (behavioral) deficits are not observed until E10 (Oppenheim: Journal of Comparative Neurology 160:37–50, 1975). To determine whether this temporal difference between projections and function reflects a delay in synaptogenesis, we looked for the presence of anterogradely HRP‐labeled pre‐synaptic terminals in brachial cord following injection of HRP into the boundary between brainstem and spinal cord at ages between E3.5 and E7. HRP‐labeled fibers were observed in the brachial cord by E4.5 and were diffusely distributed in the ventral and lateral marginal zones (presumptive ventral and lateral funiculi, respectively). Although some axo‐dendritic and axo‐somatic synapses were observed in the brachial cord prior to E6, the presynaptic profiles were always unlabeled by HRP and thus must originate from propriospinal sources. The first HRP‐labeled supraspinal synapses were found in the ventral and lateral funiculi on E6. They contained several clear spherical synaptic vesicles and were axo‐dendritic in nature. The cells of origin of the postsynaptic dendrites were determined by injecting HRP into the wing‐bud to label the brachial motoneurons retrogradely and the presynaptic component was identified as supraspinal by HRP injections into the brainstem/spinal cord boundary to orthogradely label the descending fibers. Several double‐labeled axo‐dendritic synapses were found in the ventral and lateral funiculi of E6 brachial cord. Therefore, at least some descending supraspinal fibers make synapses directly onto motoneuron dendrites. We conclude that (1) there is a delay of about 1.5 days between the arrival of supraspinal fibers and synapse formation in, the brachial cord, (2) the earliest synapses are axo‐dendritic in nature, (3) at least some supraspinal fibers make direct contact with motoneuron dendrites as early as E6, and 4) synaptogenesis from propriospinal sources precedes that from supraspinal descending axons. These observations provide evidence indicating that the temporal difference between the onset of projections of supraspinal descending fibers and the onset of their function may be partly owing to delayed synaptogenesis.
Serially homologous development of the peripheral nervous system in the mouthparts of the grasshopper
Authors: Meier Thomas , Reichert Heinrich
Published: January 2005

Segmentally homologous neurogenesis and neuronal differentiation processes characterize the formation of the peripheral nervous system in the developing mouthparts of the grasshopper embryo. The peripherally located neurons derive from the ectoderm in each of the embryonic mouthparts. The major nerve branches serving the mandibles, maxillae, and labium are established by peripheral pioneer neurons, which project their axons into the central nervous system via a set of guidepost cells. The two secondary nerve branches in each appendage are established by fasciculation of peripheral afferent pioneers and central efferent pioneers or by efferent pioneers alone. Sensory cells differentiate and connect with the peripheral nerve branches after a basic peripheral nerve scaffold has been established. The serial homology of these developmental processes in the mouthparts and in the thoracic legs is striking and can be documented at the level of individual identified cells. Thus despite the enormous differences in gross structure and function among cephalic mouthparts and true thoracic legs, many aspects of neurogenesis and early neuronal differentiation are remarkably conserved in all of these appendages.
Origin of spinal projections to the anterior and posterior lobes of the rat cerebellum
Authors: Berretta Sabina , Perciavalle Vincenzo , Poppele Richard E.
Published: January 2005

The present study was carried out to analyze the topography of spinal projections to the anterior and posterior lobes of the cerebellum and to investigate whether projections to the two lobes come from different spinocerebellar neurons or from branching axons of the same cells. We used orthograde transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA‐HRP) to identify the cerebellar areas where spinocerebellar axons terminate and retrograde double‐labeling techniques to estimate the incidence of spinocerebellar neurons projecting to both anterior and posterior lobes via axon collaterals. Orthograde labeling confirmed that the rat, like other mammalian species, has spinocerebellar projections to two different regions of cerebellar cortex, i.e., lobules I–V of the anterior lobe and lobule VIII of the posterior lobe, with the highest incidence in lobules II, III, and VIII. We did not observe a clear difference in the distribution of afferents coming from different spinal segments to either of the two lobes. The double‐labeled cells were located primarily in the lower thoracic and upper lumbar segments, almost exclusively in Clarke's column and in the dorso‐lateral part of lamina 7 (in the region of the spinal border cells). It is likely that most or all of the spinocerebellar neurons in these structures project to both anterior and posterior lobes. Therefore, the two lobes of the cerebellum are likely to receive common information from these cells, but different information from the separate populations of spinocerebellar neurons that project only to one lobe or the other.
Vasoactive intestinal polypeptide‐containing cells in the rabbit retina: Immunohistochemical localization and quantitative analysis
Authors: Casini Giovanni , Brecha Nicholas C.
Published: January 2005

Vasoactive intestinal polypeptide (VIP) possesses neuroactive properties in the nervous system. In this study we characterized VIP immunoreactive neurons in the rabbit retina to provide a basis for a better understanding of the role of this peptide in retinal functions and to further define the morphology of wide‐field amacrine cells. VIP immunoreactivity was demonstrated in colchicine‐treated retinas. Immunolabeling was observed in amacrine cells located in the proximal inner nuclear layer and, occasionally, in the ganglion cell layer and inner plexiform layer (IPL). Varicose fibers were distributed in laminae 1, 3, and 5 of the IPL. The distribution of VIP immunoreactive cells showed a peak of ∼ 50 cells/mm2 in the visual streak and minimum values of ∼ 12 cells/mm2 in the peripheral retina. The total number of VIP immunopositive neurons was estimated to be about 11,000. Cell body diameters in the visual streak (8–9 μm) were slightly smaller than those measured in the dorsal or in the ventral retina (9–10 μm). The distribution of nearest neighbor distances (∼ 109 μm in the visual streak and ∼ 99 μm in the peripheral retina) showed that VIP immunoreactive neurons were nonrandomly spaced. Labeled neurons emitted one to three thick primary processes, arborizing in secondary processes and collaterals rich in varicosities; these processes often crossed among different IPL laminae. Arborization fields of individual cells overlapped extensively. In the dorsal retina, estimated areas of single arborization fields were larger and processes had lower branching frequency than in the visual streak and in the ventral retina. On the whole, VIP immunoreactive amacrine cells gave rise to a loose meshwork of fibers in the IPL. These characteristics indicate VIP is contained in a class of wide‐field amacrine cells and is likely to be involved in widespread regulatory or modulatory functions rather than in the direct transmission of visual information through the retina.
HVEM serial‐section analysis of rabbit foliate taste buds: I. Type III cells and their synapses
Authors: Royer Suzanne M. , Kinnamon John C.
Published: January 2005

Serially sectioned rabbit foliate taste buds were examined with high voltage electron microscopy (HVEM) and computer‐assisted, three‐dimensional reconstruction. This report focuses on the ultrastructure of the type III cells and their synapses with sensory nerve fibers. Type III cells have previously been proposed to be the primary gustatory receptor cells in taste buds of rabbits and other mammals.

Within rabbit foliate taste buds, type III cells constitute a well‐defined, easily recognizable class and are the only taste bud cells observed to form synapses with intragemmal nerve fibers. Among 18 type III cells reconstructed from serial sections, 11 formed from 1 to 6 synapses each with nerve fibers; 7 reconstructed type III cells formed no synapses. Examples of both convergence and divergence of synaptic input from type III cells onto nerve fibers were observed. The sizes of the active zones of the synapses and numbers of vesicles associated with the presynaptic membrane specializations were highly variable. Dense‐cored vesicles 80–140 nm in diameter were often found among the 40–60 nm clear vesicles clustered at presynaptic sites. At some synapses, these large dense‐cored vesicles appeared to be the predominant vesicle type. This observation suggests that there may be functionally different types of synapses in taste buds, distinguished by the prevalence of either clear or dense‐cored vesicles. Previous investigations have indicated that the dense‐cored vesicles in type III cells may be storage sites for biogenic amines.
Organization of the cerebellum in the pigeon (Columba livia): I. Corticonuclear and corticovestibular connections
Authors: Arends J. J. A. , Zeigler H. Philip
Published: January 2005

The projections of the cerebellar cortex upon the cerebellar nuclei and the vestibular complex of the pigeon have been delineated using WGA‐HRP as an anterograde and retrograde tracer. Injections into individual cortical lobules (II–IXa) produce a pattern of ipsilateral terminal labeling of both the cerebellar and vestibular nuclei. The pattern of corticonuclear projections indicates both a rostrocaudal and a mediolateral organization with respect to the lobules and is consistent with a division of the cerebellar nuclei into a medial (CbM) and a lateral (CbL) nucleus. The retrograde experiments indicate that these nuclei receive projections, respectively, from Purkinje cells within medial (A) and lateral (C) longitudinal zones, which alternate with longitudinal zones (B, E) projecting upon the vestibular complex.

Purkinje cells in (vestibulocerebellar) lobules IXb–X show only limited projections upon the cerebellar nuclei, but do project extensively upon the cerebellovestibular process (PCV), as well as upon the medial, superior, and descending vestibular nuclei. As the injection site shifts from medial to lateral, there is a corresponding shift in focus of the. projection within PCV from areas bordering CbM to those abutting CbL.

The topographic organization of corticovestibular projections is less clear‐cut than those of the corticonuclear projections. Lobules II–X project upon the lateral vestibular nucleus (anterior lobe) or the dorsolateral vestibular nucleus (posterior lobe). These projections originate from either side of the lateral (C) zone. Projections originating from the medialmost (B) zone are interrupted in lobules VI and VII. The anterior and posterior portions of the lateralmost (E) zone overlap along lobules VI and VII. In addition, the E zone of the anterior lobe is the source of projections upon the medial, the descending, and the superior vestibular nuclei. Projections from the auricle and adjacent lateral unfoliated cortex (F zone) focus upon the infracerebellar nucleus, the medial tangential nucleus, and the medial division of the superior vestibular nucleus.

The data suggest that the cerebellar cortex of the pigeon, like that of mammals, may be subdivided into a mediolaterally oriented series of longitudinal zones, with Purkinje cells in each zone projecting ipsilaterally to specific cerebellar nuclei or vestibular regions. For cortical regions exclusive of the auricle and lateral unfoliated cortex, three such zones (A, B, and C) are defined that are comparable in their efferent targets with the A, B, and C zones of mammals. There does not appear to be a D zone in the pigeon. The results are discussed in relation to comparative data on amphibians, reptiles, and mammals.
SCPB‐ and FMRFamide‐like immunoreactivities in lobster neurons: Colocalization of distinct peptides or colabeling of the same peptide(s)?
Authors: Arbiser Zoya K. , Beltz Barbara S.
Published: January 2005

Virtually all of the SCPB‐like immunoreactive neurons (ca. 60 cells) in the lobster Homarus americanus also contain FMRFamide‐like immunoreactivity. Control experiments reveal that SCPB‐and FMRFamide‐like immunoreactivities are successfully preadsorbed with their specific antigens, while the normal staining pattern is retained following preadsorption of each antibody with the alternate peptide. These experiments potentially lead to the conclusion that the anti‐SCPB and anti‐FMRFamide antibodies are labeling distinct compounds that are colocalized in lobster neurons.

The lobster nervous system does not, however, contain authentic FMRFamide, but rather several FMRFamide‐like compounds (Trimmer et al., J. Comp. Neurol. 266:16–26, 1987). The most abundant of these is the octapeptide TNRNFLRFamide. Experiments demonstrate that SCPB‐like immunoreactivity is completely preadsorbed with synthetic TNRNFLRFamide, while there is a significant or complete loss of staining after preadsorption of the FMRFamide antibody with this molecule. Met‐enkephalin‐Arg‐Phe‐amide (YGGFMRFamide), an extended opioid peptide containing the FMRFamide sequence, also preadsorbs SCPB‐and FMRFamide‐like immunoreactivities, while Met‐enkephalin‐Arg‐Phe (YGGFMRF) has no effect on the staining properties of these antibodies. These results suggest that the SCPB antibody can bind to extended forms of FMRFamide‐like molecules, and that anti‐SCPB. and anti‐FMRFamide antibodies may be colabeling one or more FMRFamide‐like molecules in lobster neurons.