bluuebunny/crossref_metadata_2025 huggingface dataset:
Pattern formation in the striatum: Neurons with early projections to the substantia nigra survive the cell death period
Authors: Fishell Gord , Van Der Kooy Derek
Published: January 2005

During the early postnatal period the striatum undergoes significant cell death. The specificity and regulation of this regressive event may be particularly interesting in the light of recent findings demonstrating that a developmentally organized compartmental architecture exists in the striatum. The striatum can be divided into two complementary and phenotypically distinct compartments, the patches and the matrix. In the adult, these two striatal compartments can be distinguished on the basis of their anatomy and a series of compartment‐specific biochemical and hodological markers. We have previously demonstrated that the neurons within the patch and matrix compartments become postmitotic and make connections with the substantia nigra at distinct and sequential developmental times. The majority of patch neurons become postmitotic between embryonic days 12 and 15 and make a striatonigral connection prenatally. In contrast, a majority of matrix neurons become postmitotic between embryonic days 17 and 20 and do not form an efferent connection to the substantia nigra until the first postnatal week. Here we investigated whether either neuronal birthdate or time of making an efferent projection correlates with a neuron's probability of surviving the cell death period. We found that both the patch and matrix compartments undergo their entire cell death period by the end of the first postnatal week. During this period approximately 30% of striatal neurons are subject to cell death, regardless of striatal compartment. Neuronal counts within the striatal patch compartment suggest that both early born neurons (embryonic day 13) and early projecting neurons (to the substantia nigra) are preferentially spared. However, their considerable overlap (i.e., most early born neurons also have a nigral projection) prevents assessment of which feature is critical for survival. In contrast, there are small, but mostly separate, populations of early born and early projecting neurons within the matrix compartment. Quantitative analysis of these two distinct populations suggests that while early projection neurons within the matrix are spared, the early born matrix neurons lacking an early nigral projection undergo significant cell death. This proposal is further supported by the observation that the percentage of early born neurons in both the patch and matrix compartments that also have an early nigral projection increases from postnatal day 2 to 17. This finding suggests that among the early born striatal neurons in both compartments, those that do not project to the nigra selectively die during the cell death period. Together these results support the hypothesis that completion of an early projection to the substantia nigra gives neurons an advantage for surviving the cell death period.
Patterns of connectivity in the cat sensory‐motor cortex: A light and electron microscope analysis of the projection arising from area 3a
Authors: Porter Linda L.
Published: January 2005

Through its complex network of interconnections, each of the functionally specialized subdivisions in the cat primary somatosensory cortex may provide the motor cortex with different input and thus play a unique role in motor behavior. Areas 2 and 3a receive separate peripheral information. Cells in both regions project directly to the cat motor cortex but are thought to target different populations of neurons. In this study the morphology and distribution patterns of the area 3a projection to the motor cortex were compared to previous findings on the projection from area 2. Also, details of the projection from area 3a to area 2 were studied. Injections of Phaseolus vulgaris leucoagglutinin were made into area 3a and fixed brain tissue was processed for immunohistochemical staining of this anterograde tracer. Tissue was examined with the light microscope to determine the patterns of the 3a projections to area 2 and motor cortex, area 4. Axons arising from cells in area 3a terminated in multiple column‐like clusters in both motor cortex and area 2. The small number of cells labeled at the injection sites suggested that multiple foci of the 3a fibers are formed by collateral axonal branches of the same neurons. The topography of the projection from area 3a to the motor cortex was more clearly denned than that from area 3a to area 2. Electron microscope analysis determined the laminar distribution and types of synapses formed between area 3a efferents and their target neurons. A high proportion of synapses was found in layer III in both target regions. However, unlike in area 4, labeled terminals were sparse in laminae I and II of area 2. Axospinous synapses were slightly more numerous than axodendritic synapses, but both were distributed similarly throughout the thickness of the cortex. In area 2 the axospinous synapses accounted for 63% of synapses and in area 4 for 57% of synapses. No axosomatic synapses were detected.
Developmental alterations in nociceptive threshold, immunoreactive calcitonin gene‐related peptide and substance P, and fluoride‐resistant acid phosphatase in neonatally capsaicin‐treated rats
Authors: Hammond Donna L. , Ruda M. A.
Published: January 2005

This study examined the effect of neonatal administration of capsaicin on nociceptive threshold and the distribution of calcitonin gene‐related peptide (CGRP), substance P (SP), and fluoride‐resistant acid phosphatase (FRAP) in the dorsal horn of the spinal cord during the course of development (10 days to 12 weeks of age) in the rat. As early as 10 days of age, CGRP‐like immunoreactivity was reduced in laminae I, II, and V, as well as in the bundles of fibers situated dorsal and ventral to the central canal. However, beginning on or about 6 weeks of age, the density of CGRP‐like immunoreactivity in the superficial laminae and in the bundles dorsal and ventral to the central canal increased. Moreover, thick, nonvaricose CGRP‐like immunoreactive fibers appeared in laminae III and IV. These recurring fibers were of primary afferent origin as demonstrated by their disappearance after multiple, unilateral rhizotomies. A similar age‐dependent alteration in the density of FRAP activity was also observed. Although virtually absent at 10 days of age after neonatal administration of capsaicin, the density of FRAP activity increased in lamina II by 8 weeks of age. This activity disappeared after multiple, unilateral rhizotomies, indicating that the FRAP activity that reappeared was of primary afferent origin. Neonatal administration of capsaicin also reduced the density of SP‐like immunoreactivity in the dorsal horn as early as 10 days of age, although the density of SP‐like immunoreactivity showed some recovery after 6 weeks of age. However, unlike CGRP‐like immunoreactivity or FRAP activity, the density of SP‐like immunoreactivity in capsaicin‐treated rats was not detectably altered by multiple, unilateral rhizotomies, indicating that it originated principally from intrinsic dorsal horn neurons. Age‐dependent alterations in both thermal and mechanical, but not chemical, nociceptive thresholds were also observed in these same animals. Thus, tail flick latency, hot plate latency, and paw withdrawal threshold were maximally increased at 6 weeks of age, after which time thresholds declined to vehicle‐treated values. In contrast, capsaicin‐treated animals were uniformly insensitive to ophthalmic administration of capsaicin. The correspondence between developmental alterations in CGRP‐like immunoreactivity or FRAP activity and in thermal and mechanical nociceptive thresholds is suggestive of a role of CGRP‐ or FRAP‐containing primary afferents in thermal and mechanical nociception.
Organization of callosal connections in the visual cortex of the rabbit following neonatal enucleation, dark rearing, and strobe rearing
Authors: Grigonis Antony M. , Murphy E. Hazel
Published: January 2005

The organization of visual callosal projections was studied in (1) normal adult rabbits; (2) adult rabbits which had undergone monocular enucleation (ME) or binocular enucleation (BE) at birth; and (3) adult rabbits which had been deprived of normal visual experience during development by dark rearing (DR) or strobe rearing (SR). Previously published observations (Murphy and Grigonis, Behav Brain Res 30:151, 1988) on callosal organization in adult rabbits in which retinal ganglion cell activity was eliminated during development by intraocular tetrodotoxin (TTX) injections, are also summarized for comparison with these data.

The tangential extent of the callosal cell zone was significantly larger than normal in DR, TTX, and ME rabbits, was unchanged in BE rabbits, and was significantly reduced in SR rabbits. An analysis of the laminar distribution of the callosal cells revealed a significant increase in the percentage of callosal cells in lamina IV in ME, DR, and TTX animals. Measurements of density of callosal cells showed a significant increase in the density of the callosal projection in ME and SR rabbits and a decrease in density in BE rabbits compared with normal.

The data suggest that the mechanisms involved in the development of the tangential and laminar organization of the callosal cell zone are different. In addition, the data suggest that the mechanisms involved in the maintenance of callosal projections are different from the mechanisms involved in the elimination of callosal projections during development.

The effects of these developmental manipulations on callosal organization in other mammals are reviewed and compared with the effects in rabbits. The data suggest that species differences in the degree of maturity of the visual system at birth and in the extent of callosal development at the time of eye opening, may underlie species differences in the effects of these manipulations on the organization of visual callosal projections during development.
A light and electron microscopic study of the development of the mauthner cell and vestibular nerve in the axolotl
Authors: Leber Steven M. , Model Pat G.
Published: January 2005

Vestibular axons form synapses on a restricted area of the lateral dendrite of the Mauthner cell, a large, identified brainstem neuron found in fish land amphibians. The differentiation of the vestibular nerve, medullary neuropil, and Mauthner cell of the axolotl (Ambystoma mexicanum) was studied to understand better the means by which this synaptic specificity arises. The Mauthner cell first extends a medial process and then a lateral dendrite. The latter initially elongates as a simple process and later sends out branches. As the lateral dendrite grows, vestibular axons enter the brainstem to form one of the earliest of several discrete axon fascicles that course longitudinally through the neuropil. The fascicles, many of which are identifiable on the basis of their location and axonal morphology, are the precursors of the longitudinal tracts of the mature salamander. The lateral dendrite grows dorsally over the orthogonally oriented fascicles, making contact with each at a characteristic time and place. The first afferents to form synapses do so on the soma and proximal lateral dendrite; subsequent afferent groups terminate more distally. Axons within a given fascicle form synapses with the Mauthner cell in a discrete and initially homogeneous domain. As dendritic branches form and the organization of the longitudinal fascicles becomes more complex, the homogeneity of axons terminating on a given region of the Mauthner cell surface is lost, but no major rearrangement or migration of terminals is apparent. These observations are consistent with both active recognition and passive spatiotemporal models of synaptic site specificity.
Effect of precocious and delayed afferent arrival on synapse localization on the amphibian mauthner cell
Authors: Leber Steven M. , Model Pat G.
Published: January 2005

Afferents often form synapses on restricted regions of their target cells. The connections between vestibular axons and the Mauthner cell are an example of this sort of specificity. The Mauthner cells are a pair of identifiable central neurons in certain fish and amphibians. In the axolotl (Ambystoma mexicanum), the large vestibular axons form club endings on only one portion of one dendrite of the Mauthner cell. During development, this specific distribution might result from nothing more than when and where the growing axons and dendrite meet (spatiotemporal model). Alternatively, the distribution might reflect constraints on where the developing axons may grow (axon segregation model) or form synapses (active recognition model). As a test of the spatiotemporal model, ears and vestibular ganglia from older embryos (Harrison stage 33/34–) were unilaterally grafted in place of prospective ear/ganglion placodes of younger embryos (stage 23). Light and electron microscopic examination revealed that the axons precociously entered the brain and formed synapses on the Mauthner cell. Similarly, grafts from younger to older embryos resulted in a delay. In both situations, mapping the club endings on the mature Mauthner cells of 21–mm larvae revealed a distribution similar to that of the contralateral control cells. Thus precocious and delayed afferent arrival did not alter the eventual localization of the synapses. These results conflict with the spatiotemporal model and imply that the vestibular axons are either restricted to a certain region of the neuropil or capable of recognizing a specific region of the Mauthner cell surface.
Dendritic morphology and development in the ferret lateral superior olivary nucleus
Authors: Henkel Craig K. , Brunso‐Bechtold Judy K.
Published: January 2005

The dendritic morphology of cells in the lateral superior olivary nucleus was studied with the Golgi method in adult and postnatal ferrets. The lateral superior olivary nucleus in the adult ferret is a convoluted structure with an M‐shape in frontal sections. The major cell type appears to have disk‐shaped dendritic trees. Most dendritic trees appear to be approximately orthogonal to the curved medial‐lateral axis of the nucleus. Depending on their position in the limb and on the plane of section with respect to the dendritic tree, the disk‐shaped cells are either bipolar or radiate in orientation. One subclass of disk‐shaped cells has secondary dendritic branches that end as tufts of tendril‐like processes. In a second subclass of cells, the dendrites exhibit several orders of dichotomous branching and lack obvious tufts of terminal processes. Marginal cells are observed at the border of the nucleus and have dendrites restricted to the margins of the cell plate.

The bipolar orientation of disk‐shaped cells orthogonal to the axis of the limbs is already apparent by the time of birth. Transient spines and other appendages are abundant on somata and dendrites during the first postnatal week. By the end of the first postnatal month only distal appendages are found. Tufts of fine tendril‐like processes appear at the ends of dendrites between postnatal days 28 and 56.
GABA‐like immunoreactive cells containing nicotinic acetylcholine receptors in the chick retina
Authors: Hamassaki‐Britto D. E. , Brzozowska‐Prechtl A. , Karten H. J. , Lindstrom J. M. , Keyser K. T.
Published: January 2005

The possibility that GABA‐like immunoreactive cells of the chick retina also contain neuronal nicotinic acetylcholine receptors was investigated by means of immunohistochemical techniques. Double‐labeled cell bodies containing GABA‐like immunoreactivity and nicotinic receptor‐like immunoreactivity were seen in the inner third of the inner nuclear layer and were presumably amacrine cells. Approximately 29–36% of the GABA‐positive cells in the inner nuclear layer contained nicotinic receptor immunoreactivity. Their soma sizes ranged from 5–12 μm. Some double‐labeled cells ranging from 7–21 μm were observed in the ganglion cell layer as well. Between 9–37% of the GABA‐positive cells in this layer contained nicotinic receptor‐like immunoreactivity. Following injection of a retrograde tracer into the optic tectum, some of the retrogradely labeled cells were also double labeled with antibodies against GABA and nicotinic receptors. This indicates that at least some of the GABA‐positive cells containing nicotinic acetylcholine receptors in the ganglion cell layer are indeed ganglion cells. The present data appear to represent the first demonstration of the presence of acetylcholine receptors in GABA‐containing cells in the retina, thus providing a basis for a possible influence of acetylcholine upon those presumptive GABAergic cells.
Ontogeny of steroid accumulation in spinal lumbar motoneurons of the rat: Implications for androgen's site of action during synapse elimination
Authors: Jordan Cynthia L. , Breedlove S. Marc , Arnold Arthur P.
Published: January 2005

Androgens influence the postnatal development of motoneurons in the spinal nucleus ofthe bulbocavernosus (SNB) by regulating neuromuscular synapse elimination, the process through which multiple axonal inputs are retracted from each muscle fiber until single innervation is established. In the rat levator ani (LA), one of the target muscles for SNB motoneurons, much of this loss of multiple innervation can be prevented by prepubertal androgen treatment. We used steroid autoradiography to measure the ontogeny of steroid accumulation in the SNB and the retrodorsolateral nucleus (RDLN), two motoneuronal groups thought to differ in their sensitivity to androgens. Spinal cord tissue was analyzed from castrated male rats at 7, 14,21, and 60 days of age after injection of radiolabelled testosterone. SNB and RDLN motoneurons differ in the ontogeny of androgen accumulation. Over 80% of SNB motoneurons develop the capacity to accumulate androgen during the second week after birth, during the period when androgen regulates synapse elimination in the LA. In contrast, androgen accumulation in RDLN motoneurons develops much later (after 21 days). These data suggest that androgen may act directly on SNB motoneurons to influence synapse elimination.
Comparison of dorsal and ventral spinal root regeneration through semipermeable guidance channels
Authors: McCormack M. L. , Goddard M. , Guéanard V. , Aebischer P.
Published: January 2005

Semipermeable guidance channels have been shown to support nerve regeneration in the peripheral nervous system (PNS) possibly through interactions with the wound healing environment. This study quantitatively assesses the ability of such channels to support regeneration in the PNS segment of the spinal roots across a 4 mm gap and compares the resultant dorsal and ventral root regeneration. Acrylic copolymer guidance channels with a molecular weight (Mw) cutoff of 50,000 Da were used in a transected rat spinal root model. Cohorts of 23 animals (11 ventral, 12 dorsal) were examined at four weeks; 6 animals (3 ventral, 3 dorsal) at ten weeks; and 10 animals (5 ventral, 5 dorsal) at twenty‐four weeks post‐implantation. Both the dorsal and ventral roots were able to regenerate across the gap within the semipermeable channel. At all time periods, the regenerated dorsal roots contained fewer myelinated axons than found in the contralateral control root and consisted of an abundance of collagenous tissue. In contrast, by ten weeks the regenerated ventral roots contained twice the contralateral control number of myelinated axons and were composed predominantly of large, myelinated axons. At twenty‐four weeks the number of unmyelinated axons was also quantified, with the regenerated dorsal root containing only one‐fifth of the control number and the regenerated ventral root containing more than four times the control. Due to the proximity of the dorsal root lesion to the axonal cell bodies, the dorsal root ganglion (DRG) neuronal cell loss was investigated at four weeks post‐implantation. A comparison of the cell numbers on the experimental side to those on the contralateral control side yielded a mean E/C ratio of 1.07, suggesting that a significant cell loss is an unlikely causative factor in the impairment of regeneration in the dorsal root. This study reports a difference in the regenerative capacities of dorsal and ventral roots using semipermeable guidance channels. Future studies involving variations in the regenerative environment may help determine the factors responsible for the different regenerative capabilities of the spinal roots.
Central projections of Limulus photoreceptor cells revealed by a photoreceptor‐specific monoclonal antibody
Authors: Calman B. G. , Lauerman M. A. , Andrews A. W. , Schmidt M. , Battelle B.‐A.
Published: January 2005

Studies of lateral, median, and ventral eyes of the chelicerate arthropod Limulus polyphemus (the common American horseshoe crab) are providing important basic information about mechanisms for information processing in the peripheral visual system and for the modulation of visual responses by light and circadian rhythms. The processing of visual information in Limulus brain is less well understood in part because the specific central projections of the various classes of visual neurons are not known.

This study describes a mouse monoclonal antibody, 3C6A3, which binds to Limulus photoreceptor cell bodies, their axons, and terminals, but not to any other cell type in the central nervous system. This antibody, and intracellular injection of biocytin, are used to demonstrate the central projections of each type of photoreceptor.

Our main conclusions are that: (1) the photoreceptors (retinular cells) of the lateral eye project only to the lamina; (2) the photoreceptors of the lateral rudimentary eye project to both the lamina and medulla; (3) the photoreceptors of the median ocellus project only to the ocellar ganglion; and (4) the photoreceptors of the rudimentary median (endoparietal) eye project to the ocellar ganglion and also into the optic tract.

These results, along with previous studies, allow us to infer the projections of the secondary cells. The eccentric cells of the lateral eye project to the lamina, medulla, optic tract, and ocellar ganglion. The arhabdomeral cells of the median ocellus project through the ocellar ganglion and the optic tract to the medulla.
Reinnervation of developing rat muscle by non‐axotomized motoneurons
Authors: Ziskind‐Conhaim Lea , Presley Scarlett
Published: January 2005

To study the ability of developing motoneurons to reinnervate their denervated muscle, axotomized motoneurons in rat neonates and pups were retrogradely labeled with two fluorescent tracers. Fluorogold (FG), a long‐lasting fluorescent dye, was injected into intercostal muscle T9 to retrogradely label the motoneurons that innervated it. Two days later intercostal nerves T7–T9 were cut. The intercostal muscle denervated at birth was reinnervated within 10–20 days, as evidenced by nerve‐evoked muscle contraction. Three weeks following axotomy, tetramethylrhodamine isothiocyanate (TRITC) was injected into the same muscle to label the motoneurons that reinnervated it. The motoneurons double‐labeled with FG and TRITC were, therefore, axotomized motoneurons that regenerated to reinnervate T8.

In neonates, axotomy resulted in a significant reduction in the number of FG‐labeled motoneurons, which suggests that axon transection at early postnatal days causes a massive motoneuron death. The percentage of double‐labeled motoneurons was significantly smaller than that in non‐axotomized rats. TRITC‐labeled motoneurons constituted the majority of stained motoneurons; these were located in different nuclei than the intercostal motoneurons. These findings suggest that muscle reinnervation is, at least in part, by motoneurons which originally did not innervate intercostal muscle T8.

Unlike axotomy at birth, axotomy performed 2–3 weeks after birth did not result in a significant motoneuron loss. The number of stained motoneurons labeled with both FG and TRITC was significantly smaller, however, than in non‐axotomized spinal cords. Our data indicate that in pups only a small percentage of axotomized motoneurons reinnervated the denervated muscle.
The contributors to volume 1 (1891) of The Journal of Comparative Neurology: C.L. Herrick, C.H. Turner, H.R. Pemberton, B.G. Wilder, F.W. Langdon, C.J. Herrick, C. von Kupffer, O.S. Strong, T.B. Stowell
Authors: Haines D. E.
Published: January 2005

The concept of a truly innovative “neurology” journal germinated in the mind of Clarence Luther Herrick and then flowered, in March of 1891, as the first issue of Volume 1 of The Journal of Comparative Neurology. The other parts appeared in June, October, and December of the same year. The contributors to this volume, and their affiliations, were: C.L. Herrick (University of Cincinnati‐UC), C.H. Turner (UC), B.G. Wilder (Cornell), F.W. Langdon (Miami Medical College, Cincinnati), C.J. Herrick (UC) H.R. Pemberton (Princeton), T.B. Stowell (State Normal and Training School, Potsdam), and O.S. Strong of Columbia who translated a large paper by Carl von Kupffer, the famous German anatomist. In 1890–91 some of these scientists (e.g., Wilder, Langdon, Stowell, von Kupffer) were well known and had already made notable contributions in their chosen fields. However, several were students (e.g., Turner, C.J. Herrick, Pemberton, Strong), most of whom would make important contributions in later years. The founder of JCN, Clarence Luther Herrick, by 1891 had an excellent reputation in geology and natural science and had already established a successful scientific journal.

Based on the totality of their contributions, the authors of the papers that made up Volume 1 of JCN were a unique group. Textbooks that went through several editions came from Wilder, C.J. Herrick, and Strong; the latter is currently going into its 9th edition. Structures were named in recognition of the original descriptions by von Kupffer and C.L. Herrick, a type of insect behavior recognized Turner's discovery, and after their deaths several had university buildings, one a scientific club, and one a research award, named in their honor.

There were also interesting and important links between these nine men. Turner and C.J. Herrick were students of C.L. Herrick, and Stowell served as a member of the Association of American Anatomists nomenclature committee which was chaired by Wilder, C.J. Herrick became a student (for his Ph.D.) of Strong's, and Strong became an associate editor of JCN under C.J. Herrick. Of the nine, two practiced medicine; Langdon in an academic setting, Pemberton in private practice.

The lives of the nine scientists whose work made up Volume 1 of JCN are reviewed. Many of these individuals were notable, not only for their work in the first volume of JCN, but for their larger and enduring contributions in the biomedical sciences.
Postlarval growth of the peripheral gustatory system in the channel catfish, Ictalurus punctatus
Authors: Finger Thomas E. , Drake Susan K. , Kotrschal Kurt , Womble Mary , Dockstader Karen C.
Published: January 2005

The phenomenon of postlarval cell addition to the peripheral nervous system offish has been reported for some sensory systems, but has yet to be characterized for the gustatory system. Many fishes, such as catfish, possess taste buds scattered across their body surface, and presumably, the number of taste buds increases during growth of the animal. The present study was undertaken in order to examine the process of growth in the peripheral gustatory system and to determine whether the degree of convergence of receptors onto primary sensory afferents changes during growth.

The recurrent facial nerve of channel catfish was used for these studies since this nerve contains no general cutaneous components and innervates taste buds along the fish's body surface. Electron micrographs were made of cross sections of this nerve taken from individuals ranging in size from 5.1 to 39.5 cm standard length. In addition, estimates were made of the number of taste buds innervated by this nerve by determining taste bud density along selected regions of the flank and fins in large and small fish.

As catfish get larger, the number of both myelinated and unmyelinated axon profiles in the recurrent facial nerve increases, but at a slower rate than the number of taste buds innervated by this nerve. Thus, on average, the number of taste buds innervated by each fiber increases as the fish enlarges; on average there are 2 taste buds per axon profile in small fish and nearly 14 taste buds per axon profile in large fish. The rate of addition of new axon profiles to the nerve is estimated at roughly 70 per day over the range of sizes studied. Although generation of new ganglion cells and axons may contribute to this increase, several lines of evidence indicate that axonal branching occurs.

In addition, the mean axon diameter for both myelinated and unmyelinated axons increases during postlarval growth. The finest myelinated fibers (0.2 μm) in small animals are significantly smaller than the finest myelinated fibers (0.7 μm) in larger animals.
Cytoskeletal components and calibers in developing fish Mauthner axon (Salmo gairdneri Rich)
Authors: Alfei L. , Albani L. Medolago , Mosetti A. R. , Scarfo C. , Stefanelli A.
Published: January 2005

In developing axons of many vertebrates, microtubular density is inversely correlated with fiber caliber. It is suggested that microtubules are causally related to axonal caliber. For this reason, cytoskeletal analysis during development of the fish Mauthner axon, which displays a giant caliber, is of particular interest. The Mauthner axon originates from the Mauthner cell in the medulla and runs in the fasciculus longitudinalis medialis in the spinal cord.

At embryonic, larval and postlarval stages in trout (Salmo gairdneri Rich.), the following parameters were measured on conventional electron micrographs of Mauthner axon cross sections: axonal caliber, number of microtubules per axons, and microtubular and neurofilament densities. Results at each stage point to an inverse correlation between axonal caliber (x) and microtubular density (y) expressed by the equation y = axb (R = 0.932).

Furthermore, three periods of Mauthner axon development are identified on the basis of the cytoskeletal content: (1) embryonic; the Mauthner axon has small caliber with a high microtubule density, (2) elongation period (larval stages); the axon enlarges and a transient peak of microtubules, corresponding to the caliber increment, is observed, and (3) postlarval; the axon enlarges still further (<500 μm2) but has the lowest microtubular content. During this period neurofilaments are the main axonal component.
Spatio‐temporal patterns of retinal ganglion cell death during Xenopus development
Authors: Gaze R. M. , Grant P.
Published: January 2005

During development of the retina in mammals and birds, most retinal ganglion cells (RGC) that are produced are eliminated later in development by cell death. In lower vertebrates, however, such massive cell death has not been observed; total ganglion cell number increases linearly during most of development. Using 3H‐thymidine or 5‐bromodeoxyuridine labeling of retinal cell nuclei, we have been able to identify postmitotic RGC populations in Xenopus central retina at different developmental stages and follow their fate during development to postmetamorphic stages. RGC populations that become postmitotic between embryonic stages 32 and 49, during the initial stages of retinal growth, lose 40–77% of their cells during metamorphosis (approximately 4,000–5,000 cells). Twenty percent of the RGC present at stage 54, which later disappear, represent the same population of dying RGC that were present at stage 49. This suggests that the ganglion cells that became postmitotic between stage 49 and 53/54 show no apparent decline in numbers during metamorphosis. Since thyroxine is known to stimulate an increase in RGC number as well as the extent of fiber projection on the tectum, we suggest that this reduction in RGC numbers is not due to thyroxine‐induced neuronal cell death. After stage 54, however, binocular vision develops in Xenopus (Keating, '74) and ipsilateral fibers begin to grow into thalamic visual neuropils (Hoskins and Grobstein, '85). We suggest, therefore, that as in mammals, in which RGC elimination correlates with binocular segregation of contralateral and ipsilateral retinal axons in visual centers, a similar process may occur in the frog among those RGC projecting to thalamic visual neuropils.
Immunohistochemical evidence for transient expression of fibronectin in the developing dorsal lateral geniculate nucleus of the ferret
Authors: Brunso‐Bechtold J. K. , Agee D. , Sweatt A. J.
Published: January 2005

In recent years, the important role of the extracellular matrix in neural development has been increasingly recognized. In order to begin to examine what role might be played by the extracellular matrix in the developing dorsal lateral geniculate nucleus (dLGN), the present study used immunocytochemistry to assess the distribution of a recognized extracellular matrix molecule, fibronectin (FN), during postnatal development of the ferret dLGN. Prior to the segregation of cell layers, no clear pattern of FN distribution can be distinguished within the dLGN. By P16, when layers A and A1 are separated by an interlaminar space, FN is localized in that space. By P24, FN is present not only between layers A and A1, but also within layers A and A1 as bands parallel to the laminar borders. These bands appear to correspond spatially and temporally to the development of sublaminar boundaries in the ferret (Hahm and Sur, Neurosci Abstr 14:460, 1988). By the end of the first postnatal month, immunoreactivity is diminished but still present. FN is no longer present at P44 or in the adult. Adjacent sections were incubated with antiserum to glial fibrillary acid protein (GFAP). When a laminar pattern of GFAP can be distinguished, it coincides with the interlaminar distribution of FN. The findings described here are consistent with a role for FN in the development of a laminar organization in the dLGN.
Substance P innervation of the rat and cat thalamus. II. Cells of origin in the spinal cord
Authors: Battaglia Giorgio , Rustioni Aldo
Published: January 2005

Evidence in the preceding paper suggests that fibers and terminals immunopositive for substance P (SP) in somatosensory thalamic nuclei are part of the spinothalamic tract (STT). In this paper, more direct evidence on this point is provided by immunocytochemistry for SP on the cervical spinal cord, alone or combined with the retrograde transport of colloidal gold‐labeled wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase (WGAapoHRP‐Au). In cats and rats pretreated with colchicine and/or anterolateral chordotomy (to increase SP content in cell bodies), many small to large cell bodies are SP‐immunopositive especially in laminae I and V, but also in more ventral laminae of the upper cervical cord. SP neurons are also present in the dorsolateral funiculus (in the lateral spinal nucleus, LSN, in rats) but not in the lateral cervical nucleus or in the internal basilar nucleus. In both species there is a considerable degree of overlap in the distribution of SP‐positive neurons and that of STT neurons.

SP immunocytochemistry in rats after WGAapoHRP‐Au injection in the somatosensory thalamus reveals SP‐positive STT neurons in LSN, in lamina I and in lamina V, and, to a lesser extent, in more ventral laminae. These results demonstrate that SP is a marker and/or neuromediator for some STT neurons. Together with the evidence discussed in the preceding paper, the results also suggest that SP‐positive neurons may be involved in the transmission of nociceptive input.
Neuropeptide Y‐like immunoreactivity in the diencephalon of the little brown bat (Myotis lucifugus): Localized variations with physiological state
Authors: Laemle Lois K. , Cotter John R.
Published: January 2005

The current study used light microscopic immunocytochemistry to demonstrate and compare neuropeptide Y‐like immunoreactivity (NPY‐IR) in the diencephalon of the little brown bat (Myotis lucifugus) at different stages in its annual cycle of activity and hibernation. Animals were sacrificed in each of three discrete physiological states: euthermic, hypothermic, and hibernating.

In general, NPY‐IR was abundant in the hypothalamus and sparse in other diencephalic areas. Immunoreactivity was present in a number of pathways which project to or originate from diencephalic nuclei; these include the ansa peduncularis, medial forebrain bundle, inferior thalamic peduncle, stria terminalis, stria medullaris, mammillary peduncle, and dorsal longitudinal fasiculus. Dense fiber plexuses were present throughout the hypothalamus; however, NPY‐IR was conspicuously absent from the suprachiasmatic nucleus. Immunoreactive perikarya were located in the supraoptic, dorsomedial, ventromedial, and arcuate nuclei, in the external division of the ventral lateral geniculate nucleus, and in the pineal gland. Localized changes in density and/or distribution of NPY‐IR were correlated with changes in physiological state.
Expression of GABA and GABAa receptors by neurons of the subplate zone in developing primate occipital cortex: Evidence for transient local circuits
Authors: Meinecke Douglas L. , Rakic Pasko
Published: January 2005

Several lines of evidence suggest that the transient subplate zone of the embryonic mammalian telencephalon could influence cortical development through synaptic or trophic interactions with growing cortical afferents and migrating neurons. Since such interactions may involve neurotransmitters and their receptor molecules, we have examined the expression of GABA and subunits of the GABAA/benzodiazepine receptor complex in the occipital lobe of embryonic rhesus monkeys by immunochemistry and in situ hybridization. We found that during the second half of gestation, when the subplate zone reaches peak maturity in this species, many neurons can be immunolabeled with both GABA antisera and monoclonal antibodies against GABAA receptor subunits. The most robust labeling occurs at approximately embryonic day (E)125 (birth is at E165). Electron microscopic observations of receptor subunit‐immunolabeled material confirmed that subunits of the GABAA receptor are localized in the subplate neurons and their dendritic processes. In many instances the reaction product is associated with the plasma membranes of labeled processes, some of which form symmetrical synapses with small unlabeled axon terminals. The results of in situ hybridization are in accord with the results of receptor subunit immunochemistry. From E80 to E141, hybridization signal for GABAA receptor subunit mRNA occurs in the subplate zone and increases steadily to peak levels between E125 and E141. The present results reveal that all the elements necessary for the formation of functional GABAergic synaptic circuitry are present in the subplate zone. Further, the ages showing the most pronounced receptor and transmitter expression in this primate coincide with the ingrowth of major cortical afferent systems. Taken together, these findings suggest that GABAergic local neuronal circuits in the subplate may be involved in the development of long tract connections stationed in this zone prior to their transfer to the overlying cortical plate.
The mosaic of alpha cells in the cat retina is not dependent on axon terminal interactions during development
Authors: Jeffery Glen , Whitmore Alan , Grant Simon
Published: January 2005

Alpha ganglion cells in the cat retina are distributed in a regular array. It has been proposed that the development of this mosaic pattern is achieved by class‐specific interactions between the dendrites and/or axon terminals of neighbouring alpha cells, but the relative contributions that are made by each of these factors to the regularity of the mosaic remain unclear. An opportunity to address this question is provided by a comparative study of the distribution of alpha cells across the nasotemporal division of normally pigmented and Siamese cat retinae. In this strip of retina the alpha cell population divides its axon terminals between the two sides of the brain. Hence, the potential for interactions between axon terminals of alpha cells whose somata are adjacent within this region of the retina is undermined. This situation is exacerbated in Siamese cats because they have a congenital abnormality in this region, which results in an abnormally wide nasotemporal division.

In this study the regularity of the alpha cell mosaic has been analysed at a wide range of eccentricities, including the nasotemporal division. In normally pigmented cats the nasotemporal division was visualised directly following unilateral horseradish peroxidase injections into the thalamus. In Siamese cats, the location of the abnormally wide nasotemporal division was inferred from electrophysiological recordings undertaken in their striate cortices. In both strains of cat the regularity of the alpha cell mosaic was shown to be largely independent of their density or retinal location. Furthermore, in the normals, the separate mosaics for ipsilaterally or contralaterally projecting alpha cells within the nasotemporal division were found to be no more or less regular than that for the combined population. This finding implies that there is no disturbance in their order across the discontinuity formed by their separate chiasmatic routes. Similar results were obtained from within the abnormal nasotemporal division of the Siamese cat. It is concluded that terminal interactions play an insignificant role in the formation of the adult alpha cell mosaic, the regularity of which is probably established by class‐specific intraretinal Interactions.
Projections from rabbit caudal medulla to C1 and A5 sympathetic premotor neurons, demonstrated with phaseolus leucoagglutinin and herpes simplex virus
Authors: Li Yu‐Wen , Wesselingh S. L. , Blessing W. W.
Published: January 2005

We combined Phaseolus vulgaris leucoagglutinin anterograde tracing and Herpes simplex virus transneuronal retrograde tracing to determine whether neurons in the vasodepressor region of the rabbit caudal ventrolateral medulla project to brainstem neurons containing the virus after its transneuronal transport from the adrenal medulla. Five days after adrenal injection of virus, 764 ± 159 virus‐positive neurons were found bilaterally in the brainstem: 61% in the C1 sympathoexcitatory region of the rostral ventrolateral medulla, 30% in the A5 region, 5% in the parapyramidal region, and 3% in the paraventricular nucleus of the hypothalamus. Many of the virus‐positive neurons in the C1 and A5 areas also contained tyrosine hydroxylase and, in the parapyramidal area, many contained 5‐hydroxytryptamine. After iontophoretic deposit of leucoagglutinin into the vasodepressor region of the caudal ventrolateral medulla, brain regions containing varicose processes labeled with leucoagglutinin included the regions containing virus‐positive neurons. We examined the C1 and A5 regions following injections of both tracers in the same rabbits, leucoagglutinin into the caudal ventrolateral medulla and virus into the adrenal gland. Varicosities containing leucoagglutinin were seen in contiguity with perikarya and dendritic branches of neurons containing HSV1, in both the C1 and A5 regions. Studies also revealed labeled varicosities in contiguity with TH‐containing C1 and A5 neurons. The projection from the caudal medulla to presumed sympathetic premotor neurons in the C1 area, including some C1 cells, represents a potential pathway whereby activity of neurons in the caudal medulla could reduce blood pressure by inhibiting sympathoexcitatory neurons in the rostral medulla.
Synaptic innervation of the giant cerebral neuron in sated and hungry snails
Authors: Chase Ronald , Tolloczko Barbara
Published: January 2005

The giant cerebral neuron (GCN) is a serotoninergic cell that facilitates feeding behaviour in gastropod molluscs. We have examined the morphology of its cerebral arborizations after labelling them by intracelhilar injection of hexamminecobalt. Observations in the light microscope reveal extensive arborizations, with similar overall distributions, in the terrestrial snails Achatina fulica and Rumina decollata. All the major peripheral nerves terminate within the zone covered by the GCN arbor. In a sample of 370 synapses in which the GCN participated, the GCN was identified as the postsynaptic element in every case, thereby establishing the dendritic nature of the cerebral arborizations. A total of approximately 1,000 synapses contacts the GCN, with no evident regional differences in innervation density. The synaptic membrane of the presynaptic profile is characterized by an agglomeration of small clear vesicles and small dense vesicles. At nonsynaptic membranes there are agglomerations of larger dense and dense core vesicles, suggestive of nonsynaptic release. The dendrites of the GCN also contain vesicles. Starvation for five days (Rumina decollata) caused a significant increase in the proportion of curved synapses relative to flat synapses. This might be a plastic change allowing for a greater efficiency of transmission between sensory afferents and the GCN.
Ultrastructure of the horseshoe bat's organ of corti. I. Scanning electron microscopy
Authors: Vater Marianne , Lenoir Marc
Published: January 2005

The organ of Corti of the echolocating horseshoe bat (Rhinolophus rouxi) was investigated with scanning electron microscopy in order to provide a comparison with non‐echolocating mammals.

Throughout the cochlea of horseshoe bats, each outer hair cell (OHC) possesses three rows of stereocilia and there are no morphological distinctions among the different rows of OHCs. However, there are morphological differences between different regions along the cochlea. In the lower and upper basal turn, the receptor surfaces of OHCs are characterized by extremely wide W‐shaped stereocilia bundles and wingshaped cuticular plates. The cuticular plates of OHCs of the middle and outermost rows are arranged parallel to each other. Stereocilia length is only 0.8 μm and there is an exaggerated angle of inclination of the shortest row of stereocilia towards the next taller one. Stereocilia arrangements in the apex of the horseshoe bat's cochlea closely resembles those observed in the midbasal region of the rat cochlea.

Inner hair cells (IHC) in the lower basal turn appear specialized. They possess only two rows of stereocilia and only 7–8 stereocilia per row. Their cuticular plates are small and oval and widely separated from one another in the longitudinal direction. IHCs at all other locations possess three and up to four rows of stereocilia and 17–20 stereocilia per row. Their cuticular plates are elongated and closely spaced. The transition from specialized to typical mammalian morphology occurs abruptly (over a distance of about 100–150 μm) at the border between the lower and the upper basal turn. This transition is not accompanied by a change in OHC morphology.

In the subsurface of the tectorial membrane, throughout the cochlea, there are distinct imprints of the tallest row of stereocilia of all three rows of OHCs and of the IHCs.

Data are discussed in relation to specialized aspects of the cochlear frequency map in horseshoe bats and as possible micromechanical adaptations to ultra‐high frequency hearing.