bluuebunny/crossref_metadata_2025 huggingface dataset:
Embryonic development of the rat cerebellum. I. Delineation of the cerebellar primordium and early cell movements
Authors: Altman Joseph , Bayer Shirley A.
Published: May 2005

Short‐survival and long‐survival thymidine radiograms, and methacrylate‐embedded tissue from normal and X‐irradiated rat embryos were used to delineate the neuroepithelial source of the cerebellum and trace the earliest cell movements. The cerebellar anlage, crescent shaped, is demarcated by two ventricular landmarks, the anterior extension of the tela choroidea of the fourth ventricle and the embryonic cerebellar fissure. The cerebellar tela choroidea extends from the medullary fourth ventricle posteromedially to the lateral recess of the pontine fourth ventricle anterolaterally. The embryonic cerebellar fissure begins caudally as a single midline incision beneath the fused posterior cerebellar primordium, then splits to follow the unfused cerebellar halves, first separating each from the isthmus then from the pons.

The cerebellar primordium is divided into three parts. The lateral cerebellar primordium caps the lateral recess of the fourth ventricle; it is contiguous with the pons medially and separated ventrally from the anlage of the cochlear nuclei by the tela choroidea. The subisthmal cerebellar primordium is situated beneath the isthmus, medially lining the isthmus canal. Laterally and posteriorly, it is continuous with the lateral and postisthmal primordia. The postisthmal cerebellar primordium caps the postisthmal recess of the fourth ventricle and extends to the medullary fourth ventricle. As we shall describe later, each of these primordia is a source of different components of the developing cerebellum.

Most cells of the superficially located nuclear transitory zone are labeled with 3H‐thymidine administered on day E14 but not thereafter. A high proportion of the cells of the deeper cortical transitory zone could still be labeled on day E15. This supports the assumption made earlier that the first is composed of differentiating deep neurons, the second of Purkinje cells. The cells of the nuclear transitory zone originate in the lateral cerebellar primordium near the junction with the tela choroidea prior to the formation of the germinal trigone and migrate in a superficial position medially. Beginning on day E16, the nuclear transitory zone splits into two components. One has transversely oriented cells that seem to be the source of a decussating fiber tract, presumably the hook bundle of Russell. The other is composed of longitudinally oriented cells that apparently contribute fibers to the ipsilateral superior cerebellar peduncle. The translocation of the cells of the nuclear transitory zone from the cerebellar surface to its depth, to form the deep nuclei, and the radial migration of the cells of the cortical transitory zone to the surface, to form the Purkinje cell layer, will be described in the succeeding paper.
Embryonic development of the rat cerebellum. II. Translocation and regional distribution of the deep neurons
Authors: Altman Joseph , Bayer Shirley A.
Published: May 2005

In thymidine radiograms and plastic‐embedded sections, the migration of cerebellar deep neurons was traced from their germinal source to their final settling sites. The route proved to be roundabout and three developmental events could be distinguished during the process. First, between days E14 and E16, transversely oriented cells of the nuclear transitory zone move in an arc from the ventrolateral neuroepithelium of the lateral cerebellar primordium in a medial direction. Second, between days E16 and E18, the cells of the rostral component of the nuclear transitory zone assume a longitudinal orientation. We postulated that this is the period of axonogenesis, the longitudinally oriented cells issuing efferents that join the superior cerebellar peduncle ipsilaterally and the transversely oriented cells (representing the neurons of the caudal fastigial nucleus) sending decussating fibers to the uncinate fasciculus (the hook bundle of Russell). Third, between days E18 and E21, the earlier‐produced superficial cells of the nuclear transitory zone and the later‐produced deep cells of the cortical transitory zone (the young Purkinje cells) exchange positions. The descent of the deep neurons is in the direction of the fibers of the inferior cerebellar peduncle, which becomes distributed throughout the cerebellum on day E17. The ascent of the Purkinje cells is in the direction of the external germinal layer, which begins to spread from caudal to rostral on day E17. The three deep nuclei, the lateral (dentate), interpositus, and medial (fastigial), can be distinguished before their descent into the depth of the cerebellum, and by day E22 a small‐celled and a large‐celled subdivision is identifiable in each nucleus.
Embryonic development of the rat cerebellum. III. Regional differences in the time of origin, migration, and settling of Purkinje cells
Authors: Altman Joseph , Bayer Shirley A.
Published: May 2005

The time of origin, site of origin, migratory path and settling pattern of the Purkinje cells of the cerebellar hemispheres, anterior vermis, and posterior vermis were investigated in thymidine radiograms and plastic‐embedded materials from rat embryos ranging in age from 15 to 22 days. In the hemispheres there is a rostral‐to‐caudal cytogenetic gradient: the Purkinje cells of lobulus simplex, crus I, and crus II are produced earlier than the Purkinje cells of the paramedian lobule and paraflocculus, followed by the Purkinje cells of the flocculus. The Purkinje cells of the vermis, in general, are generated later than those of the hemispheres, and with a reverse gradient from caudal to rostral: the Purkinje cells of the posterior vermis (lobules X–VI) being produced ahead of the Purkinje cells of the anterior posteriorly directed wedge of early‐produced Purkinje cells through the vermis.

Evidence was obtained that the Purkinje cells of the hemispheres derive from the lateral cerebellar primordium capping the lateral recess of the fourth ventricle anteriorly. The Purkinje cells of the anterior vermis originate from the subisthmal cerebellar primordium medially lining the isthmal canal. The Purkinje cells of the posterior vermis originate in the postisthmal cerebellar primordium overlying the tela choroidea caudally. The young Purkinje cells migrate from the neuroepithelium to the surface of the cerebellum in a strictly caudal‐to‐rostral order, paralleling the spread of the EGL superficially from posteroventral to anterodorsal. This pattern is independent of the time of origin of Purkinje cells. In the posterior vermis the earliest‐settling Purkinje cells of the uvula follow a short radial course, and a discrete Purkinje layer is formed 3 days after they are generated. In the anterior vermis the Purkinje cells of lobulus centralis, which follow an anterodorsal migratory course, are still settling on day E22, 7 days after their production, presumably awaiting the fusion of the cerebellar base anteriorly. The fissura prima forms medially at the interface region of Purkinje cells derived from the postisthmal and subisthmal cerebellar primordia. For 1–2 days after their settling, the Purkinje cells of the newly forming lobules can be distinguished by certain cytological criteria from the cells in the more caudally‐situated, earlier‐settled lobules.
Projections of the entorhinal area to the striatum, nucleus accumbens, and cerebral cortex in the guinea pig
Authors: Sørensen K. E.
Published: May 2005

A study of the efferent projections of the entorhinal area in the guinea pig, by using anterograde (autoradiographic tracing of tritiated amino acids) and retrograde(fluorochrome tracing) methods, revealed the following projections: (1) to nonhippocampal cortices: retrosplenial cortex (area 29), cingulate cortex (areas 23, 24), prelimbic cortex (area 32), infralimbic cortex (area 25), perirhinal cortex (areas 35, 36), prepyriform cortex (area 51B), and insular cortex (areas 13–16). All received direct projection; (2) to subcortical targets', distinct terminations were observed in the lateral thalamic nucleus, the striatum, and the accumbens nucleus.

In retrograde experiments, the cells giving rise to the projections to the hippocampus were found to He in layers II and III, those projecting to the nonhippocampal cortical regions to originate in layer IV, and those projecting to the striatum and the accumbens to lie in layers V and VI.

Many of the efferent projections to the cerebral cortical regions are associated with reciprocal projections from these regions to the superficial layers (I–III) of the entorhinal cortex. The entorhinal efferent projections generally terminate ipsilaterally. A weak termination is, however, present at the contralateral side. The efferent projections of the entorhinal area represent a route for important caudally directed, nonfornical hippocampal output.
Ontogenesis of neurons producing luteinizing hormone‐releasing hormone (LHRH) in the nervus terminalis of the rat
Authors: Schwanzel‐Fukuda Marlene , Morrell Joan I. , Pfaff Donald W.
Published: May 2005

Immunoreactive luteinizing hormone‐releasing hormone (LHRH) was first detected at 15 days of gestation in ganglion cells associated with the peripheral, intracranial, and central parts of the nervus terminalis of the rat. LHRH was not detected in any other structure of the central nervous system at this age.

In the 17‐day‐old fetal rat, 62% of the total LHRH‐reactive neuronal population was found in ganglion cells of the nervus terminalis. At this same age, immunoreactive beta‐luteinizing hormone (β‐LH) was first seen in gonadotropes of the anterior pituitary gland.

At 19 days of gestation, 31% of the total number of LHRH‐reactive neurons observed in the rat brain was found in the nervus terminalis, and immunoreactive processes were first seen in the organum vasculosum of the lamina terminalis and in the median eminence.

Our data indicate that from 15 to 19 days of gestation the nervus terminalis is a principal source of LHRH in the fetal rat. Presence of the decapeptide in the nervus terminalis prior to appearance of β‐LH in the anterior pituitary suggests a possible role for LHRH in this system on maturation of the gonadotropes and differentiation of the brain‐pituitary‐gonadal axis.
II. Cortical neurons immunoreactive with antisera against neuropeptide Y are altered in Alzheimer's‐type dementia
Authors: Chan‐Palay V. , Lang W. , Allen Y. S. , Haesler U. , Polak J. M.
Published: May 2005

Neurons identified by their immunoreactivity with antisera against neuropeptide Y (NPY) were studied in three selected areas of the cerebral cortex in brains from controls and in senile dementia of the Alzheimer type (ATD). Changes were more profound in temporal cortex than in parietal cortex, and more severe in parietal cortex than in frontal cortex, paralleling the severity of neuritic plaque formation and incidence of neurofibrillary tangles in these regions. NPY‐i neurons became distorted, with enlarged misshapen cell somata and reduced, thickened, and gnarled dendrites. There was a sharp reduction in the extensiveness and delicacy of the axonal plexus; the reorganized axons were haphazard compared to the normal symmetry of these fibers. Besides the alteration in form and sizes, there were also appreciably fewer cells. Nevertheless, the NPY population is not eliminated. Double‐label studies of NPY‐i and thioflavin indicate that NPY‐i fibers can participate in neuritic plaque formation although not all neuritic plaques contained NPY‐i axons and not all NPY‐i axons were associated with plaques. The surviving NPY cells were evident in all cortices examined, thus giving rise to the speculation that these peptide neurons may have unusual survival and reorganization potential even in terminal neurological disease.
Morphological features of lamina V neurons receiving nociceptive input in cat sacrocaudal spinal cord
Authors: Ritz Louis A. , Greenspan Joel D.
Published: May 2005

Thirty‐six neurons from laminae III‐VII in cat sacrocaudal spinal cord were labeled by intracellular injection of horseradish peroxidase, following physiological characterization. Of these 36 neurons, 24 had cell bodies within lamina V. Twelve lamina V neurons were multireceptive; i.e., they responded differentially to innocuous and noxious mechanical stimuli. Most multireceptive neurons had the following morphological features: (1) large cell bodies; (2) extensive dendritic spreads in all directions; and (3) axons which ascended in the contralateral ventral white matter.

Three labeled lamina V neurons were activated only by noxious stimuli. Compared to the multireceptive neurons, these nociceptive‐specific (NS) units had smaller cell bodies but a similar dendritic spread. Seven lamina V neurons were excited by innocuous mechanical stimuli with no evidence of nociceptive input. These seven neurons had less extensive dendritic trees than the multireceptive and the NS neurons. Six neurons labeled in lamina VII (three multireceptive and three NS) contrasted to most lamina V cells by having smaller cell bodies and short, sparsely branched dendrites. Among the lamina VII neurons, there was no obvious morphological feature that distinguished the multireceptive group from the NS group.

Fifteen fully stained neurons from laminae III–VII had late discharges which were correlated with C fiber input. The dendrites of three of these neurons extended into laminae II and I; the dendrites of two neurons reached into the inner portion of lamina II; and the dorsal dendrites of the remaining ten neurons extended no further than the nucleus proprius (laminae III and IV). Thus, deeper dorsal horn neurons evincing reliable, excitatory influences from C fibers do not necessarily have superficially situated dendrites.

Tests for correlations between size of cutaneous, excitatory receptive field (RF) and dendritic spread revealed a significant positive correlation between the mediolateral extent of dendritic spread and the size of the low‐threshold component of the RF for lamina V neurons.
Topography of regenerating optic fibers in goldfish traced with local wheat germ injections into retina: Evidence for discontinuous microtopography in the retinotectal projection
Authors: Meyer Ronald L. , Sakurai Kari , Schauwecker Elyse
Published: May 2005

A small injection of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) was injected into dorsal or ventral peripheral retina in normal goldfish and in goldfish with prior optic nerve crush. Serial sections of tectum were subsequently taken for horseradish peroxidase (HRP) histochemistry 18 hours after injection and studied with light microscopy and densitometric reconstructions. In normals, a small, sharply delineated patch of product 200–300 μm wide was observed at the appropriate medial or lateral periphery of tectum. This product filled the entire SFGS, the main optic termination layer, and fell off abruptly at its edges. No labelling was detected in the optic pathways.

In regenerates at about 20 days after nerve crush, these retinal injections yielded product that was dispersed across 1,000 μm or more of tectum but not in a uniform fashion. The densest product was biased toward the appropriate tectal position while product of intermediate density was mainly distributed along a path from the anterior end of tectum to this region. Product in the inappropriate half of tectum was much lighter and typically fiberlike in appearance. By about 40 days, product had condensed considerably at roughly the correct region of tectum but it was not as sharply delimited as in normals. Dense label occupied a single area about twice that of normals and exhibited flanking regions of light label extending for several hundred micrometers. At 59–148 days, a further condensation was observed but into more than one patch of product. The patches were of variable size and consisted of sharply delimited dense product which filled the entire SFGS at each position. Morphologically, these patches bore a remarkable resemblance to the ocular dominance columns previously seen in this system.
The effects of monocular deprivation on the size of GAD + neurons in the cat's dorsal lateral geniculate nucleus
Authors: Robson J. A. , Martin‐Elkins C. L.
Published: May 2005

Previous studies have shown that suturing one eyelid closed in a newborn kitten results in profound changes in the development of the visual system. Among these is a retardation in the growth of neurons in the layers of the dorsal lateral geniculate nucleus receiving retinal input from the closed eye. Moreover, the greatest effect appears to be in the largest neurons. The present study examines the effects of monocular deprivation en the perikaryal size of select group of small lateral geniculate neurons, GABAergic neurons, that may be interneurons. These cells were selectively labeled by an antiserum to glutamic acid decarboxylase (GAD) and immunocytochemical methods. The results demonstrate that GAD+ neurons are among the smallest in the lateral geniculate nucleus and that they are insensitive to the effects of monocular deprivation. That is, GAD+ neurons in deprived laminae A and A1 are similar in size to those in the corresponding, nondeprived laminae. These findings are consistent with the hypothesis that GAD+ neurons are interneurons and therefore not subject to binocular competition in the visual cortex. This interpretation, however, is complicated by additional studies of the postnatal development of GAD+ neurons which reveal that GAD+ neurons grow to their adult size relatively early, before the onset of the critical period. Thus the insensitivity of the perikarya of GAD+ neurons to monocular deprivation may be attributable to their precocious growth.
Glial fibrillary acidic (GFA) protein in vertebrates: Immunofluorescence and immunoblotting study with monoclonal and polyclonal antibodies
Authors: Dahl D. , Crosby C. J. , Sethi J. S. , Bignami A.
Published: May 2005

We report a comparative immunofluorescence and immunoblotting study of GFA protein, the subunit of glial filaments, in nonmammalian vertebrates. The study was conducted with polyclonal antibodies raised to human and shark antigen and with monoclonal antibodies isolated from mice immunized with chicken and bovine antigen. With the exception of cyclostomes, glial filaments appeared remarkably conserved in vertebrate phylogeny, both with respect to the molecular weight and immunoreactivity of their protein subunit. In most species, the antibodies decorated a single band in brain, spinal cord, and optic nerve extracts by the immunoblotting procedure. This band had the same molecular weight in the different CNS regions. With the exception of the turtle, species differences in the molecular weight of the band were not greater than those observed among mammalian vertebrates (human, bovine, and rat). However, there were some exceptional findings in fish. In goldfish and trout brain and spinal cord extracts, the antibodies decorated with the same intensity two bands. In accordance with previous immunofluorescence findings, goldfish optic nerve extracts were negative by the immunoblotting procedure. In four fishes (sea bass, tautog, trout, and scup), optic nerves reacted with the antibodies. However, the band decorated by the antibodies was higher in molecular weight than that obtained from brain and spinal cord extracts. Glial fibers were demonstrated by immunofluorescence in the brain, spinal cord, optic nerve, and retina of most species studied. In amphibia immunofluorescent structures were comparatively few, probably accounting for the negative results by immunoblotting. A comparative immunohistological study of the cerebellum showed the presence of perpendicular glial fibers in the molecular layer of most species examined. Birds and amphibia were different in this respect. Bergmann glia in chicken were GFA negative. In the frog and the toad, immunofluorescent fibers in the molecular layer of the cerebellum were haphazardly oriented. Ependymal radial glia was GFA‐negative in the cerebellum of subavian vertebrates. Antisera raised in rabbit to shark GFA protein reacted with the same bovine GFA fragments recognized by polyclonal and monoclonal antibodies raised to human and bovine antigens, respectively, i.e., 30‐kDa N‐bromosuccinimide fragment (tryptophan cleavage); 35‐kDa 2‐nitro‐5‐thiocyanobenzoic acid fragment (cysteine cleavage); 18‐kDa cyanogen bromide fragment (methionine cleavage). Conversely, the chicken GFA monoclonal antibodies selected for this study only reacted with noncleaved protein.
A quantitative analysis of the geometry of cat motoneurons innervating neck and shoulder muscles
Authors: Rose P. K. , Keirstead S. A. , Vanner S. J.
Published: May 2005

The geometry of the somata and dendritic trees of motoneurons innervating neck and shoulder muscles was investigated by using intracellular injections of HRP. In general, these motoneurons did not belong to a homogeneous population of motoneurons. Differences in average primary dendritic diameter, number of primary dendrites, and other measures of dendritic tree size were found between different neck and shoulder motoneuron groups. Several indices of proximal dendritic tree size (number of primary dendrites, sum of dendritic diameters, Rall's dendritic trunk parameter, and the sum of dendritic holes) were weakly correlated with the diameter or surface area of the soma. Some of these correlations depended on the muscle supplied by the motoneuron.

The total combined dendritic length ranged from 66,660 to 95,390 μm. There was a weak, but positive, correlation between the diameter of primary dendrites and combined dendritic length. This relationship varied from motoneuron to motoneuron.

The diameters of all dendrites of three trapezius motoneurons were examined in detail. The total dendritic surface area examined ranged from 415,000 to 488,100 μm2 and represented approximately 99% of the total neuronal surface area. Last‐order dendrites showed a high degree (39.9%) of taper. Dendritic tapering, by itself, was a major factor in the decrease of the (sum of dendritic diameters)3/2 measured at progressively distal sites from the soma. Although few parent and daughter dendrites obeyed the “three‐halves law,” the average exponent was 1.57. The diameters of primary dendrites and dendritic surface area were weakly correlated. The correlation between dendritic diameter and combined dendritic length or surface area improved if the weighted average of the diameter of second‐order dendrites was used as a measure of dendrite size. Second‐order dendrites, whose branches terminated in different regions of the spinal cord, showed different relationships between dendritic diameter and combined dendritic length or surface area.

Comparisons between the motoneurons examined in the present study and motoneurons innervating other muscles indicate that, although all spinal motoneurons share several common features (e.g., long dendrites, dendritic tapering), each motoneuron group has a set of unique features (e.g., soma shape, relationship between primary dendrite diameter and dendritic surface area). Thus, the rules governing motoneuron dendritic geometry are not fixed but depend on the species of the motoneuron.
Topography of the goldfish optic tracts: Implications for the chronological clustering model
Authors: Springer Alan D. , Mednick Adam S.
Published: May 2005

Both the dorsal and ventral optic tracts of goldfish have similar shapes when they are sectioned perpendicularly to their longitudinal axes. Each tract is pear‐shaped, consisting of a narrow and a deep apex, a wide mid‐span, and a progressively curved and tapered superficial base. The tracts differ in that the apex of the dorsal optic tract points caudally, while the apex of the ventral optic tract points medially. In addition, upon segregating from the main optic tract, the dorsal optic tract courses dorsally while the ventral optic tract courses caudally. Thus, the two optic tracts have similar shapes and are orthogonal to one another.

The topography of the retinal fibers within the optic tracts was determined either by ablating part of the retina and subsequently filling the axons from the intact hemiretina with cobaltous‐lysine or by applying cobaltous‐lysine to a slit in the retina. Both optic tracts contain a similar arrangement of optic fibers. Axons of central retinal ganglion cells (RGCs) are in the apex of each tract and optic fibers of peripheral RGCs are located along the base of each tract. Axons of temporal RGCs are located dorsally in the ventral optic tract and laterally in the dorsal optic tract, while axons of nasal RGCs are located ventrally in the ventral optic tract and medially in the dorsal optic tract. These findings indicate that the optic axons are organised as laminae. Deeper laminae contain the axons of older annuli of RGCs and superficial laminae contain the axons of younger annuli of RGCs. This type of chronological organization appears to be consistent across vertebrates. Furthermore, the organization of the optic axons across laminae is constant. Temporal RGC axons are at one end, and nasal RGC axons are at the other end of each lamina. These results are consistent with those found in other nonmammalian vertebrates. Moreover, these findings preclude the possibility that the axons of a half‐annulus of RGCs in goldfish travel together as a fascicle in the optic tracts that is continuous with a fascicle in the stratum opticum of the tectum.

The general position of the fibers from different retinal quadrants in the optic tracts may lead to a probabilistic determination as to which part of the tectum they innervate. Namely, temporal RGC axons, destined for the rostral tectum, are situated in the optic tracts so that they are close to the rostral tectum. Nasal RGC axons, destined for caudal tectum, are situated in the optic tracts so thay they are farthest from the rostral tectum. Thus, axons of nasal, RGCs have a lower probability of innervating the rostral tectum.
Observations on the afferent and efferent organization of the vagus nerve and the innervation of the stomach in the squirrel monkey
Authors: Gwyn D. G. , Leslie R. A. , Hopkins D. A.
Published: May 2005

Horseradish peroxidase was injected into the cervical vagus nerve or stomach wall of adult squirrel monkeys. Following cervical vagus nerve injections, labelled afferent fibres were present in the tractus solitarius and labelled fibres and terminals were present in medial and lateral parts of the nucleus of the tractus solitarius (NTS) ipsilaterally. Afferent labelling was also seen in the ipsilateral commissural nucleus and in the area postrema. Labelling was present contralaterally in caudal levels of the medial parts of the NTS, in the commissural nucleus, and in the area postrema. Afferent projections to the ipsilateral pars interpolaris of the spinal trigeminal nucleus and to the substantia gelatinosa of the C1 segment of the spinal cord were also labelled. Following injections of HRP into the anterior and posterior stomach walls, the tractus solitarius was labelled bilaterally. Afferent labelling was concentrated bilaterally in the dorsal parts of the medial division of the NTS, i.e., in the subnucleus gelatinosus, and in the commissural nucleus. The regions of NTS immediately adjacent to the tractus solitarius were largely unlabelled.

Injections of HRP into the cervical vagus nerve resulted in heavy retrograde labelling of neurons in the ipsilateral dorsal nucleus of the vagus (DMX) and in the nucleus ambiguus (NA). In addition a few neurons were labelled in the intermediate zone between these two nuclei. Retrogradely labelled neurons were also present in the nucleus dorsomedialis in the rostral cervical spinal cord and in the spinal nucleus of the accessory nerve. Injections of HRP into the left cricothyroid muscle in two cases resulted in heavy retrograde labelling of large neurons in the left NA. Following stomach wall injections of HRP retrograde labelling of neurons was seen throughout the rostrocaudal and mediolateral extent of the DMX; there was no apparent topographical organization of the projection. In these cases, a group of labelled smaller neurons was found lying ventrolateral to the main part of the NA through its rostral levels.

This study in a primate indicates that a large vagal afferent projection originates in the stomach wall and terminates primarily in the subnucleus gelatinosus of the NTS and in the commissural nucleus with a distribution similar to that described previously in studies in several subprimate mammalian species. The present results and those of other studies suggest some degree of segregation of visceral input within different subnuclei of the NTS. In addition, the investigation shows that while the majority of neurons which supply the stomach are located in the DMX, a small number are found in the ambiguus complex.
Development of the trochlear nucleus in quail and comparative study of the trochlear nucleus, nerve, and innervation of the superior oblique muscle in quail, chick, and duck
Authors: Sohal G. S. , Knox T. S. , Allen J. C. , Arumugam T. , Campbell L. R. , Yamashita T.
Published: May 2005

The present study was undertaken to examine the development of the trochlear nucleus in quail and to compare the mature trochlear nucleus, nerve, and their sole target of innervation, the superior oblique muscle, in quail, chick, and duck. Study of the trochlear nucleus in quail from embryonic day 5 through hatching shows a maximum of 1,248 neurons on embryonic day 10 followed by spontaneous degeneration of 40% of the neurons between days 10 and 16. Previous studies have shown that although the initial and final number of neurons is different in chick and duck, the magnitude of trochlear cell loss in both species is about 40%. This study shows the average number of neurons in the nucleus of quail, chick, and duck, 2 weeks post‐hatching, to be 658, 743 and 1,459, respectively. Fiber counts in the trochlear nerve from electron micrograph montages at the same period indicated a ratio of about 1:1 between neurons and axons. While a majority of the fibers in these nerves are myelinated, an average of 3–6% of the fibers are unmyelinated. The nucleus in the quail not only contains the smallest number of neurons but it also innervates the smallest muscle in terms of total number of muscle cells and endplates. However, the opposite relationship does not hold true. The nucleus in duck contains the largest number of neurons, yet the largest number of muscle cells and endplates were found in the chick. The ratios between the neurons and muscle cells as well as between neurons and endplates are about the same in quail and duck. These ratios are much higher in the chick, reflecting the relatively small neuron pool destined for a relatively large target. In spite of variations in the number of neurons, muscle fibers, and endplates the average number of endplates per muscle fiber is relatively constant among the three species.
Early estrogen‐induced nuclear changes in rat hypothalamic ventromedial neurons: An ultrastructural and morphometric analysis
Authors: Jones Kathryn J. , Pfaff Donald W. , McEwen Bruce S.
Published: May 2005

Alterations in the fine structure of nuclei of ventromedial hypothalamic neurons in ovariectomized (OVX) rats after either a 2‐hour exposure to estradiol (E2) or a discontinuous exposure (2 hours E2/7 hours off/2 hours E2), previously shown sufficient for female rat sexual behavior (Parsons et al., 1982a), were examined with the electron microscope. Morphometric measurements of nucleolar, nuclear, and somal areas, and nuclear shape and perimeter were accomplished at the light microscope level.

After 2 hours of E2, the appearance of the nucleoplasm was altered, with a decrease in the small, scattered clumps of heterochromatin. Nuclear shape appeared dramatically altered from nonspherical, invaginated profiles toward spherical, smooth profiles. Nucleolar, nuclear, and somal hypertrophy were evident. In addition, stacked rough endoplasmic reticulum was present more frequently in E2‐treated than control OVX neurons. After the discontinuous (2 hours/7 hours/2 hours) E2 treatment, progressive loss of small clumps of heterochromatin along the nuclear envelope as well as in the nucleoplasm had occurred. Decrease in a large heterochromatin clump along the nuclear envelope was correlated with an increase in nucleolus‐associated chromatin. As determined by a distribution analysis, these estrogen‐induced nuclear changes co‐occurred more frequently than predicted from mutual independence.

These findings, the marked co‐occurrence of E2‐induced changes in 30% or more of the cells, and the differences between the 2‐hour E2 and the 2‐hour/7‐hour/2‐hour group are consistent with a cascade of cell nuclear changes in the first few hours after estrogen onset.
Organization of motoneuronal pools in the rostral spinal cord of the sea robin, Prionotus carolinus
Authors: Finger Thomas E. , Kalil Katherine
Published: May 2005

The functional organization of the motoneurons in the spinal cord of the sea robin, Prionotus carolinus, was studied by means of retrograde transport of horseradish peroxidase (HRP). This species has a complex pectoral apparatus which includes not only a webbed fin, but also three independently mobile fin rays.

The motoneurons in the rostral spinal cord fall into two longitudinal columns: dorsal and ventral. The motoneurons of the ventral column innervate the appendicular musculature of the pectoral apparatus.

Within the ventral motor column of the rostral spinal cord, four distinct motoneuronal pools were found. The largest pool is situated at the rostral‐most end of the spinal cord and contains the motoneurons that innervate the musculature of the webbed pectoral fin. The motoneurons that innervate the fin rays are located in sequentially more posterior pools so that the antero‐ventral fin ray is controlled by motoneurons situated farthest caudally. The somatotopic arrangement exactly corresponds to the sensory somatotopy determined previously. Furthermore, each fin ray has its sensory representation in a unique accessory spinal lobe which is connected in a reflex fashion to the motoneuronal pool that provides motor output to the same fin ray.
Peripheral and central oculomotor organization in the goldfish, Carassius auratus
Authors: Graf Werner , McGurk James F.
Published: May 2005

Peripheral and central oculomotor organization was studied in the goldfish. The sizes of the extraocular muscles were quantified by counting the fibers contained in a given muscle and by area measurements of the cross‐sectional surfaces. All the muscles were of approximately similar size. Kinematics were determined by electrical stimulation of a given muscle. The macroscopic appearance and kinematics of the muscles had the characteristics of other lateral‐eyed animals (e.g., rabbit). Locations of extraocular motor neurons wert found by retrograde transport of horseradish peroxidase (HRP) following injections into individual extraocular muscles. The eye muscles were innervated by four ipsilateral (lateral rectus, medial rectus, inferior oblique, inferior rectus) and two contralateral (superior rectus, superior oblique) motor neuron pools. The oculomotor nucleus was found in the midbrain, at the level of the caudal zone of the inferior lobe of the hypothalamus. Inferior rectus motor neurons were located drosally in the oculomotor nucleus, whereas medial rectus, superior rectus, and inferior oblique motor neurons were intermingled in its more caudal portions. All labelled cells were located dorsally and medially to the medial longitudinal fasciculus (MLF) in close proximity to either the floor of the ventricle or the midline region. Occasionally, motor neurons were interspersed within the fiber bundles of the MLF or the exiting fibers of the oculomotor nerve. The trochlear nucleus, containing superior oblique motor neurons, was found in the immediate lateral and caudal neighborhood of the oculomotor nucleus, where its rostral border overlapped with the caudal border of the latter. The abducens nucleus, containing lateral rectus motor neurons, was located in the posterior brainstem in the neighborhood of the vestibular nuclear complex. This nucleus was divided into a rostral and a caudal portion. The axons of ipsilaterally projecting motor neurons headed toward their respective nerve roots via the shortest possible route, as did the axons of superior rectus motor neurons, which crossed the midline without detour to enter the contralateral oculomotor nerve. In contrast, trochlear motor neuron axons arched around the dorsal aspect of the ventricle through the cerebellar commissure to reach the contralateral trochlear nerve. The morphology of individual motor neurons was visualized by intrasomatic injection of HRP. Cell somata had oblong shapes, and their large dendrites were oriented laterally and ventrally. The axons did not collateralize within the midbrain region or the oculomotor nerve as far as they could be traced. The oculomotor system of the goldfish is similar to that found in other teleosts and higher vertebrates, displaying characteristics of an animal whose eye movements cover all regions of its external environment.
Transient tectogeniculate projections in neonatal kittens: An autoradiographic study
Authors: Stein Barry E. , McHaffie John G. , Harting John K. , Huerta Michael F. , Hashikawa Tsutomu
Published: May 2005

By using anterograde transport autoradiography, the present experiments demonstrated that the pattern of tectogeniculate projections in young (birth–14 postnatal days) kittens is strikingly different from that present in adult cats. Rather than being confined to the ventral C laminae, the neonatal projection extended across all layers of the lateral geniculate nucleus. This projection, like that in the adult cat, originates from cells in superficial laminae and is visuotopically organized. Thus, labeling only a portion of the superior colliculus with tritiated leucine produced a topographically appropriate strip of labeling in the ipsilateral lateral geniculate nucleus that encompassed all laminae and was especially dense in all interlaminar zones. Transported label also invaded the medial interlaminar nucleus (MIN).

The loss of tectogeniculate projections in the neonate from MIN and the dorsal laminae and interlaminar zones of the lateral geniculate nucleus does not appear to begin until 1–2 weeks postnatal. Once initiated, however, the process is nearly completed by 21 days postnatal. It is not yet known whether the loss of these “anomalous” projections is due to the pruning of axonal collaterals, cell death, or a combination of the two processes. However, by comparing these data with those from other laboratories, it does appear that the loss of tectogeniculate projections depends on the presence of the two eyes and may reflect the differential laminar distribution of W‐, X‐, and Y‐cell types. The protracted postnatal anatomical maturation of tectogeniculate projections differs substantially from the earlier maturing patterns apparent in all other tectofugal pathways.
An HRP‐TMB ultrastructural study of rubral afferents in the rat
Authors: Naus C. G. , Flumerfelt B. A. , Hrycyshyn A. W.
Published: May 2005

The projections from the deep cerebellar nuclei and the sensorimotor cortex to the red nucleus were studied in the rat using anterograde transport of horseradish peroxidase conjugated with wheat germ agglutinin (HRP‐WGA). The anterogradely transported HRP‐WGA was visualized ultrastructurally by using a modification of the tetramethylbenzidine (TMB) histochemical technique of Carson and Mesulam ('82). Following injection of HRP‐WGA into the sensorimotor cortex, ultrastructural examination of anterograde labeling in the ipsilateral red nucleus revealed labeled synaptic terminals located on small‐diameter dendrites of the parvocellular region. These terminals made asymmetrical contacts and contained round vesicles. HRP‐WGA placement in the nucleus lateralis resulted in anterograde labeling of synaptic terminals which made asymmetrical contacts with small‐ to medium‐sized dendrites of the parvocellular red nucleus. Similar placements in the nucleus interpositus gave rise to anterograde labeling of synaptic terminals which made asymmetrical contacts with somata and proximal dendrites of magnocellular neurons. In addition, retrograde labeling of magnocellular neurons was also observed following HRP‐WGA placements in the nucleus interpositus. Anterogradely labeled interpositorubral synaptic terminals were located on retrogradely labeled rubrocerebellar neurons. The rat red nucleus thus receives topographically organized afferents which are characterized by their specificity in location at the cellular level.
An analysis of the origins of the cholinergic and noncholinergic septal projections to the hippocampal formation of the rat
Authors: Amaral D. G. , Kurz J.
Published: May 2005

These experiments were directed at determining the proportion and distribution of cholinergic septal cells which project to the rat hippocampal formation. Injections of WGA‐HRP were placed into different regions of the hippocampal formation and sections through the septal complex were processed for the simultaneous demonstration of the retrogradely transported marker and for choline acetyltransferase (ChAT) immunoreactivity. Preliminary analysis of adjacent normal series prepared either for the demonstration of ChAT or stained by the Nissl method demonstrated several distinct cell groups in the classically defined medial septal nucleus and vertical limb of the nucleus of the diagonal band. The groups of cells ranged from almost entirely ChAT‐positive to entirely noncholinergic. On the basis of shape and size of the constituent cells, the ChAT‐positive cells of the septal complex were divided into dorsal, intermediate, and ventral subdivisions.

The proportion of retrogradely labeled cells that were also ChAT positive ranged from 22.8% to 77.4% in different experiments. When only the hippocampus and dentate gyrus are considered, this variation can largely be accounted for by the topographic organization of the septohippocampal projection. The medial, noncholinergic half of the medial septal nucleus projects primarily to the rostral or septal portions of the dentate gyrus and hippocampus, whereas the lateral half, in which the dorsal ChAT group is located, projects heavily to more temporal levels. Rostral portions of the hippocampus and dentate gyrus receive most of their cholinergic input from the ventral ChAT cell group which forms a major component of the vertical limb of the nucleus of the diagonal band. While some ChAT‐positive cells in the intermediate group project to the hippocampal formation, they are generally less numerous than those from the dorsal and ventral groups. However, in a control experiment in which the WGA‐HRP injection was placed into the cingulate cortex overlying the rostral hippocampal formation, the intermediate ChAT group accounted for 71.2% of the double‐labeled cells.
Ultrastructural characterization of synaptic terminals formed on newly generated neurons in a song control nucleus of the adult canary forebrain
Authors: Burd Gail D. , Nottebohm Fernando
Published: May 2005

The fine structure of synaptic terminals contacting neurons generated in the forebrain of adult male canaries was investigated by autoradiography and electron microscopy. The procedure for labeling the new neurons included pretreating adult canaries with 3H‐thymidine and sacrificing them 23–45 days later. Neurons were identified as newly generated by the presence of 3H‐thymidine in the cell nucleus. The new neurons in the nucleus hyperstriatum ventralis, pars caudalis (HVc) were identified by autoradiography and light microscopy and examined with electron microscopy.

Several types of synaptic terminals contacted the cell body and proximal dendrites of the newly formed neurons. Synaptic junctions were formed by terminals that contained (1) spherical, agranular vesicles, (2) large densecore vesicles and spherical, agranular vesicles, and (3) pleomorphic or flattened synaptic vesicles. Terminals that contained spherical vesicles were most often associated with asymmetric synaptic densities, and terminals that contained pleomorphic or flattened vesicles formed symmetric junctions. New neurons were also contacted by small terminals that contained few vesicles and had little pre‐ or postsynaptic density associated with the junction; these terminals may be a special type or may be in the process of developing their synaptic contact with the new neuron. In addition, rare terminals that appeared to be degenerating or to contain debris from other degenerating neural elements contacted new neurons. In summary, these data indicate that the new neurons, which are known to be inserted into existing neural networks, receive synaptic input from at least three different sources.
The distribution of synapses on the two fields of neurites of spiking local interneurones in the locust
Authors: Watson A. H. D. , Burrows M.
Published: May 2005

Spiking local interneurones in the metathoracic ganglion of the locust have two fields of neuropilar branches linked by a single process. One, with numerous fine neurites of relatively uniform diameter, is in a ventral area of neuropile where the afferents from hairs on a hind leg also terminate. The other, with sparser and varicose neurites, is in a more dorsal area of neuropile where the motor neurones of the leg muscles have many neurites. Physiological studies have shown that these interneurones receive direct inputs from some hair afferents and in turn synapse directly upon some leg motor neurones (Burrows and Siegler, '82; Siegler and Burrows, '83). The distribution of synapses in these two fields was revealed by injecting HRP intracellularly into an interneurone following its physiological characterization. In the ventral field, the majority of synapses are input synapses. Many are from profiles with round agranular vesicles of similar diameter to those of known afferents. Other presynaptic profiles contain pleomorphic agranular, or large round granular, vesicles. There are also some output synapses, each with only a small population of vesicles. Most input synapses are made onto small‐diameter neurites, whereas the majority of outputs are made from the larger‐diameter neurites. In the dorsal field, the majority of synapses are output synapses. They are made from vesicle‐filled varicosities onto postsynaptic profiles of small diameter. A single varicosity can be the site of many output synapses. Input synapses are few in number, but occur close to the output synapses. The absence of varicosities in the ventral field cannot therefore be correlated with a lack of output synapses and while the dorsal varicosities can be the sites of output, they can also receive input synapses.