bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aging in the rat olfactory system: Relative stability of piriform cortex contrasts with changes in olfactory bulb and olfactory epithelium
Authors: Curcio Christine A. , McNelly Nancy A. , Hinds James W. 
Published: January 2005

AbstractPrevious studies have quantified growth and atrophy of the olfactory bulb and olfactory epithelium of the Sprague‐Dawley rat from maturity to senescence. Major events occurring in these structures include changes in the volume of mitral cells and changes in the number of septal olfactory receptors. These effects are large, consist of a growth phase followed by atrophy, and are temporally related in that events in the olfactory epithelium precede those in the mitral cells. A hypothesis of aging based on transneuronal effects would predict that these changes would be similarly transmitted to the next synaptic station in the olfactory pathway. Therefore, cells and synapses of the piriform cortex were studied in rats 3, 12, 18, 24, 27, 30, and 33 months of age. Alternate Vibratome sections through brains perfused with mixed aldehydes were processed for light and electron microscopy.No significant age effects were found for the volumes of cortical laminae Ia and Ib. Both numerical and surface density of synaptic apposition zones in layer Ia, formed primarily by mitral cell axons, were stable with age. A modest (18%) but significant decline in the proportion of layer Ia occupied by dendrites and spines was mirrored by an increase in the proportion of glial processes; no change in the proportion of axons and terminals was observed. Neither nuclear volume, nor soma volume, nor numerical density of layer II neurons changed with age.Thus, contacts made in the piriform cortex by mitral cell axons remain relatively stable in senescence, despite the marked volumetric changes in the mitral cell somata, changes which were confirmed again in this study. Age‐related dendritic regression in layer II neurons may be attributable to functional deafferentation subsequent to reduced receptor input to mitral cells.
Immunocytochemical localization of serotonin in the rat periaqueductal gray: A quantitative light and electron microscopic study
Authors: Clements Jane R. , Beitz Alvin J. , Fletcher Tom F. , Mullett Mary A. 
Published: January 2005

AbstractThe distribution of serotonin‐like immunoreactivity in five regions of the rodent midbrain periaqueductal gray (PAG) was studied by using light and electron microscopic immunohistochemistry in combination with quantitative analysis. Light microscopic analysis revealed the presence of serotonin‐like immunoreactive cell bodies located in the ventrolateral and ventromedial regions of the caudal PAG and serotonin‐like immunoreactive processes throughout the PAG. Ultrastructural analysis showed dendritic profiles that stained positively for serotonin primarily in ventral regions, although an occasional profile was seen dorsally. Numerous synaptic contacts between unstained axon terminals and ventral dendritic profiles were seen. Axonal profiles that contained reaction product were identified throughout the PAG, but were rarely observed to make any type of specialized contact. Ultrastructural quantification of serotonin‐like immunoreactive processes indicated that the highest volume fraction of serotonin immunoreactivity occurred caudoventrally where stained processes constituted 2.6% of the neuropil volume. Rostroventrally stained processes constituted only 0.14% of the neuropil volume at the level of the posterior commissure. By contrast the amount of serotonin‐like immunoreactivity found dorsally remained relatively constant at all rostrocaudal levels. Analysis of serotonin staining among PAG regions demonstrated the lowest overall volume friction in the dorsal region and the highest overall volume fraction in the ventromedial region. No significant differences were observed between medial and lateral regions. A comparison of the results of light microscopic quantitative analysis of serotoninergic processes with electron microscopic quantitative analysis indicated that both techniques produce comparable results.
Compensatory climbing fiber innervation after unilateral pedunculotomy in the newborn rat: Origin and topographic organization
Authors: Angaut P. , Alvarado‐Mallart R. M. , Sotelo C. 
Published: January 2005

AbstractIn neonatal rats the unilateral transaction of the cerebellar peduncles causes a fast and complete degeneration of the contralateral inferior olive. Axons from the remaining olive recross the cerebellar midline and partially innervate the deprived hemicortex. Analysis of the topographic organization of this compensatory projection studied with the axonal tracing method provided the following results.Retrograde tracing experiments revealed that the bulk of compensatory afferents originates from neurons in the ipsilateral medial accessory olive, especially from its medial region, whereas afferents from the principal olive and the dorsal accessory olive contribute to a much lesser degree. In case of incomplete neonatal pedunculotomy, neurons with a similar location in the ipsilateral intact olive still contribute to the innervation of the partially deprived hemicortex, along with the atrophic contralateral olive. Moreover, these experiments revealed important information about the organization of the compensation. Although its specificity was not totally maintained, the mediolateral distribution of sprouted afferents in the cerebellum matched the caudorostral disposition of parent neurons in the olive, as in the case in normal olivocerebellar projection.Anterograde studies showed that compensatory fibers recrossing the cerebellar midline spread throughout the whole extent of the deprived cortex and terminate solely in the molecular layer as typical climbing fibers. The latter were not homogeneously distributed, their density being markedly reduced according to a mediolateral gradient. Compensatory projection followed a sagittal striped pattern, as does the normal climbing fiber projection. Moreover, if the cortex is divided broadly into vermal, intermediate, and hemispheral regions, an apparent reciprocity seems to exist concerning the relative involvement of the various cortical subdivision in both hemicerebella.Our present results indicate that the immature olivocerebellar system is capable of anatomical plasticity, although to a limited extent. More important, they suggest that a certain degree of specificity is maintained during the process of sprouting, resulting in a topographical arrangement of the transcommissural climbing fiber projection. This indicates, in turn, that cues which guide the growth of olivocerebellar fibers during normal development could also direct the compensatory innervation.
Retinofugal and retinopetal projections in the cichlid fish astronotus ocellatus
Authors: Springer Alan D. , Mednick Adam S. 
Published: January 2005

AbstractThe retinofugal and retinopetal projections of the cichlid fish Astronotus ocellatus were studied by applying cobaltous‐lysine to the optic nerve. Retinal axons terminate bilaterally in a preoptic‐suprachiasmatic region between the base of the third ventricle and the anterior genu of the horizontal commissure and among periventricular cells along the sides of the ventricle. Other retinal axons innervate the tuberal region of the hypothalamus anterior to the infundibulum. Targets innervated in the pretectum include nucleus lateralis geniculatus and dorsal, medial, and ventral pretectal nuclei. Three other targets (nucleus opticus dorsolateralis, nucleus opticus commissurae posterior, nucleus opticus ventrolateralis) are innervated by fibers that leave the medial edge of the dorsal optic tract. Two other targets (basal optic nucleus and accessory optic nucleus) are innervated by fibers from the ventral optic tract. These retinal projections are similar to those previously reported for goldfish in an experiment that used the cobaltous‐lysine method (Springer and Gaffney, J. Comp. Neurol. 203:401–424, 1981). Retinotectal optic axons were found in a superficial lamina just above the stratum opticum, in the stratum opticum, in three layers of the stratum fibrosum et griseum superficiale, in a lamina just beneath the stratum fibrosum et griseum superficiale, and in the stratum album centrale just above the stratum periventriculare. This result is similar to that previously reported for goldfish; however, the spatial relationships between the various retinorecipient laminae differ for goldfish and Astronotus ocellatus.Efferents to the retina originate in two nuclei and both project contralaterally. The first is the nucleus olfactoretinalis, which is located ventrally between the olfactory lobe and telencephalon. It consists of about 400 cells, of which, approximately 200 cells project to the retina. The second retinopetal nucleus, nucleus thalamoretinalis, is a diffuse group of about 200 cells that project to the retina.
Microtubules and caliber of central and peripheral processes of sensory axons
Authors: Fadić R. , Vergara J. , Alvarez J. 
Published: January 2005

AbstractThe microtubular content and caliber of sensory axons were studied in the L7 dorsal root, at the distal pole of the L7 spinal ganglion, and in the sural nerve of cats. Calibers of myelinated axons were symmetrical about the ganglion. In contrast, nonmedullated axons were strikingly different; 80% of the population at the root were smaller than 0.4 μm2, whilst just across the ganglion the same group was less than 20%. The microtubule densities of myelinated axons of the root were 11.8 and 6.1 microtubules/μm2 for 3‐ and 10/μm diameter axons, respectively. Across the ganglion the densities of myelinated axons of equal sizes were 24.2 and 14.4 microtubules/μm2, respectively. These values represent an approximate ratio of 1:2 between central and peripheral microtubule densities. Microtubule densities for nonmedullated axons also decreased with the increase in the cross‐sectional area. The densities of root nonmedullated axons ranged between 90 and 10 microtubules/μm2; these were smaller, usually by a factor of three, than the densities of peripheral axons of a similar size (range: 367–44). Contrasting with the differences observed across the ganglion, the microtubular content and caliber of sensory axons seems to be quite uniform along their peripheral course. This is supported by the similar values found in the juxtaganglionic and sural nerves.It is estimated that an axon that contains 90 microtubules/μm2 has 26.7 mg of tubulin per ml of axoplasm in its assembled form, and 3.0 mg/ml if it contains 10 microtubules/μm2; these values are the practical limits of assembled tubulin in axoplasms.We conclude that the microtubule density of an axon is related to axonal size and location (central or peripheral), but is independent of axonal length, axoplasmic mass, distance to soma, and neuronal class. We propose that local exogenous factors contribute to the specification of the microtubular content of axons.
RNA content of normal and axotomized retinal ganglion cells of rat and goldfish
Authors: Barron Kevin D. , McGuinness Charlotte M. , Misantone Louis J. , Zanakis M. F. , Grafstein Bernice , Murray Marion 
Published: January 2005

AbstractThe responses of rat and goldfish retinal ganglion cells to axotomy were examined by a quantitative cytochemical method for RNA and by morphometric measurement 1–60 (rat) and 3–90 (goldfish) days after interruption of one optic nerve or tract intracranially. Unoperated control animals were studied also.The RNA content of axotomized neurons of rat fell 7–60 days postoperatively. Additionally, atrophy of the axotomized somas occurred. Over time, neuronal atrophy approximately paralleled the loss of RNA, and mean cell area and RNA content were reduced by about 25% 60 days after axotomy. Incorporation of 3H‐uridine by axotomized neurons declined also.Axotomized retinal ganglion cells of goldfish behaved differently from those of the rat and showed increases in RNA content, most conspicuously 14–60 days postoperatively. Enlargement of axotomized fish neurons occurred but was less proportionately than concomitant increases in RNA content.The nonaxotomized ganglion cells of goldfish displayed statistically significant increases in size and RNA content 14–49 days after unilateral optic nerve or tract lesions. In contrast, alterations in rat retinal ganglion cells contralateral to interruption of one optic nerve were of limited and questionable significance.The contrasting reactions to axotomy by the retinal ganglion cells of these two vertebrates, one of which regenerates optic axons and one of which does not, may support the proposition that the somal response to axon injury has an important bearing upon the success or failure of CNS regeneration.Although mammalian intrinsic neurons commonly undergo regressive changes after axotomy, they may remain viable for long periods during which they may yet prove to be stimulable by pharmacologic or other means to the mounting of a restitutive response to axon injury.
Convergence of intra‐ and interhemispheric cortical afferents: Lack of collateralization and evidence for a subrhinal cell group projecting heterotopically
Authors: Sarter Martin , Markowitsch Hans J. 
Published: January 2005

AbstractThe distribution of corticocortical projecting neurons in the rat's brain was investigated with fluorescent dyes and the retrograde transport of horseradish peroxidase. Although the fluorescent techniques especially revealed the existence of a considerable number of neurons interconnecting the limbic areas (sub‐ and perirhinal cortex, prefrontal, cingulate, and retrosplenial cortex) both intra‐ and interhemispherically, only a negligibly small number of neurons with collateralized axons could be detected. In the rat's anterior dorsolateral cortex an area is described whose neurons are organized in a columnlike fashion and project intra‐ and interhemispherically to the limbic areas examined. The density of efferent connections differed between areas, with an especially high density found in a small region of the subrhinal cortex.Injections of horseradish peroxidase into different regions of the cingulate and retrosplenial cortex confirmed the existence of widespread heterotopic interhemispheric connections originating from this defined subrhinal area, though the number of retrogradely labeled cells remained consistently smaller than that obtained following the injection of fluorescent dyes. Among the regions studied with horseradish peroxidase injections, those into the retrosplenial cortex showed the highest density of labeled cells within this subrhinal area.A more detailed examination of the subrhinal region containing the densely labeled neurons (projecting to the contralateral hemisphere) made use of Nissl stains and revealed a morphologically separable area which was characterized by medium‐sized, dark‐staining neurons whose long axons were oriented mediolaterally. The region includes portions of the insular‐perirhinal, entorhinal, and piriform cortex.It is suggested that the corticocortical projections are basically noncollateralized in the rat. However, there apparently is a dense interhemispheric interconnectivity between the limbic areas. Functional evidence for the defined subrhinal area suggests a prominent role of its neurons in cognitive information processing.The present evidence for considerable interhemispheric cortical projections may provide a new impetus for studying the intercommunication of the two sides of the brain with both anatomical and behavioral methods.
AComparative analysis of the development of the primary somatosensory cortex: Interspecies similarities during barrel and laminar development
Authors: Rice Frank Lambert , Gomez Caroline , Barstow Chris , Burnet Ann , Sands Peter 
Published: January 2005

AbstractThe development of the barrels and layers II‐V was examined in Nissl‐stained preparations of the primary somatosensory cortex in six species‐ hamster, mouse, rat, gerbil, rabbit, and guinea pig–that have increasingly longer gestation periods. The barrels and layers II‐V begin to differentiate postnatally during the first week postpartum in the hamster, mouse, rat, and gerbil; perinatally in the rabbit; and ∼4 weeks prenatally in the guinea pig.The structure of the barrels and layers II‐V is similar at the onset of their differentiation in each species, even though there are interspecies differences in the mature structure of the barrels and layer V. The rate of the initial differentiation of the barrels and layers II‐V is also similar in each species, even though there are considerable interspecies differences in the duration of the preceding period of development. In each species, layer V begins to differentiate first from the cortical plate and, within 1 or 2 days, contains sublayers that eventually disappear in the rabbit and guinea pig. About 3 days after the initial differentiation of layer V, layers II‐IV begin to differentiate, seemingly simultaneously, causing the cortical plate to have a trilaminar appearance.Barrels are first evident just before the appearance of the trilaminar plate in hamsters; concomitant with the trilaminar plate in mice, rats, and guinea pigs; and just after the trilaminar plate in gerbils and rabbits. Septa appear 1 or 2 days after the barrels except in rabbits, which never have septa. Barrel maturation proceeds rapidly after the initial appearance in all species except the hamster, in which continued maturation seems to be delayed until the appearance of the trilaminar plate. The barrels in immature rats and rabbits become more prominent than they will eventually be in the adults.Our results indicate a close and rapid developmental affilation between layers II‐V, especially layers II‐IV, that seems quite separate from the development of layers I and VI. However, barrel development and differentiation of layers II‐IV seem to be closely, but independently initiated. Secondary remodeling occurs in layer V and the barrels of some species.
Gradual changes in the structure of the barrels during maturation of the primary somatosensory cortex in the rat
Authors: Rice Frank Lambert 
Published: January 2005

AbstractThe maturation of the barrel field in the primary somatosensory cortex was observed in Nissl‐stained preparations from rats ranging in age from 12 days to 1.5 years postpartum. Prior to the 20th day, the barrels in the rat resemble those of the mouse and have distinct cell‐sparse hollows that are surrounded by cell‐dense sides. They span the full thickness of layer IV. Between the 20th and 34th days, the barrels in only the posteromedial part of the barrel field gradually change and the distinction between the hollows and sides is lost throughout all but the deepest part of layer IV. The resulting mature barrels are relatively indistinct and have a uniformly high cell density that extends well into the supragranular layers. In contrast, the barrels in the anterolateral part of the barrel field remain essentially unchanged. The remodeling apparently is not due passively to cortical growth because, by P20, the thicknesses of the cortical layers and the dimensions of the barrels are virtually the same as in the adult. Several mechanisms are considered that may account for the changes. These include a redistribution of the neurons that originally were in barrel sides; a reduction in the neuropil between the neurons that originally were within hollows; and differential growth of layer IV dendrites. The changes in the barrel structure may be related to the differentiation and quantity of innervation in the hairy skin between the vibrissae.
Time of origin of opioid peptide‐containing neurons in the rat hypothalamus
Authors: Khachaturian Henry , Lewis Michael E. , Alessi Norman E. , Watson Stanley J. 
Published: January 2005

AbstractBy using a combined technique of immunocytochemistry and [3H]thymidine autoradiography, we have determined the “birth date” of opioid pep‐tide‐containing neurons in several hypothalamic nuclei and regions. These include proopiomelanocortin (POMC) neurons (represented by ACTH immunoreactivity) in the arcuate nucleus; dynorphin A neurons in the supraoptic and paraventricular nuclei and the lateral hypothalamic area; and leuenkephalin neurons in the periventricular, ventromedial, and medial mammillary nuclei, as well as in preoptic and perifornical areas. Arcuate POMC neurons were born very early in embryonic development, with peak heavy [3H]thymidine nuclear labelling occurring on embryonic day E12. Supraoptic and paraventricular dynorphin A neurons were also labelled relatively early (peak at E13). The lateral hypothalamic dynorphin A neurons showed peak heavy labelling also on day E12, By contrast, leu‐enkephalin neurons in the periventricular nucleus and medial preoptic area exhibited peak heavy nuclear labelling on day E14. Furthermore, perifornical and ventromedial leu‐enkephalin neurons were also born relatively early (peak on days E12 and E13, respectively). However, the leu‐enkephalin neurons in the medial mammillary nucleus were born the latest of all cell groups studied (i.e., peak at E15). The results indicate a differential genesis of these opioid peptide‐containing neuronal groups in different hypothalamic nuclei and regions.
Adrenergic beta receptors are not uniformly distributed in the cerebellar cortex
Authors: Sutin Jerome , Minneman Kenneth P. 
Published: January 2005

AbstractThe noradrenergic (NE) innervation of the cerebellar cortex is sparse, forming a broad plexus of radially oriented axons distributing throughout the granular and molecular layers. Autoradiographic studies of beta‐adrenergic receptor distribution in the rat show the greatest density of silver grains in the molecular layer (Palacios and Kuhar, 1982). In the course of studies of NE hyperinnervated structures, we found that beta receptors are nonhomogeneously distributed in the Purkinje cell layer, where they occur in “patches” overlying small groups of Purkinje cell somata. Tissue sections were incubated in 10 pM 125iodocyanopindolol (ICYP), which binds equally to beta1 and beta2 adrenergic receptors. Nonspecific binding was determined in sections incubated in 125 ICYP and 1 μM dl‐propranolol. Beta‐adrenergic receptor patches are of irregular size and are most prominent in the vermis of lobules I‐IX, although the medial cerebellar hemispheres also show areas of increased silver grains over Purkinje cells. In order to determine the subtype of beta receptors, adjacent sections were incubated with either 125ICYP and the beta2‐selective antagonist IPS‐339, or 125ICYP and the beta1‐selective antagonist practolol. Patches were observed after each incubation procedure, indicating that they are composed of both beta1 and beta2 receptors. Patches are observed in normal animals and also in rats in which cerebellar NE content was increased 165% by neonatal treatment with 6‐hydroxydopamine. This treatment does not alter the density of beta receptors. The cerebellar elements in which the beta receptors are located is not known. While silver grains accumulate over small groups of Purkinje cell somata, they are not coextensive with these cell bodies. The distribution of beta‐adrenergic receptors does not parallel the arrangement of noradrenergic varicosities in the rat cerebellar cortex.