bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytoarchitecture of cerebral cortex in snakes
Authors: Ulinski Philip S.
Published: May 2005

Cerebral cortex in snakes consists of three neuronal layers. Layer 1 contains primarily axons and dendrites ascending from lower layers, but does contain a few neurons. Layer 2 is characterized by the presence of many densely packed somas. Layer 3 usually contains many loosely packed somas. A layer of columnar ependymal cells lies beneath layer 3. Ependymal cells have processes which extend through layer 3 and into layer 2. Four cortical areas are defined by regional variations in the three neuronal layers. They form rostrocaudally aligned strips in the hemisphere and are named according to their position.

Medial cortex contains small, densely packed neurons in layer 2 whose dendrites ramify primarily in layer 1 in a candelabra pattern.

Dorsomedial cortex contains large, loosely packed neurons in layer 2 whose dendrites ramify in both layers 1 and 3 in a double pyramidal configuration.

Dorsal cortex contains a moderate number of circular and fusiform neurons in layers 2 and 3 which have double pyramidal or stellate dendritic fields.

Lateral cortex contains many loosely packed circular somas in layers 2 and 3 which have stellate or double pyramidal dendritic fields.
Caliber spectra of fibers in the fasciculus gracilis of the cat cervical spinal cord: A quantitative electron microscopic study
Authors: Hwang Yann‐Ching , Hinsman Edward J. , Roesel O. F.
Published: May 2005

In order to obtain a better understanding of the microscopic structure of the cat fasciculus gracilis, entire cross‐sections of the fasciculus were examined with the electron microscope. Twenty‐five thousand, two hundred and eighty‐four fibers were encountered in one fasciculus. The fiber caliber spectra obtained from the study show that the fasciculus gracilis at cervical level has a unique fiber distribution pattern. The fiber diameters range from less than 1 μ to 15 μ, however, 97% of fibers have diameters less than 8 μ; and the majority of the fibers are in the 2–5 μ range.
Single unit activity in the posteroventral cochlear nucleus of the cat
Authors: Godfrey Donald A. , Kiang Nelson Y. S. , Norris Barbara E.
Published: May 2005

Single unit activity in the posteroventral cochlear nucleus (PVCN) was recorded for a variety of stimulus conditions. The units were classified according to their response characteristics. The locations of units were plotted onto a three‐dimensional block model of the cochlear nucleus. Certain types of units that responded best to the onsets of stimuli were located predominantly in the octopus cell region of the PVCN. The remainder of the PVCN, which contains a rather heterogeneous collection of small and multipolar cells, was found to contain several types of units with the dominant type being “chopper” units.
Single unit activity in the dorsal cochlear nucleus of the cat
Authors: Godfrey Donald A. , Kiang Nelson Y. S. , Norris Barbara E.
Published: May 2005

Single unit activity was examined in three component layers of the dorsal cochlear nucleus (DCN): the molecular layer, the fusiform cell layer, and the polymorphic layer (deep DCN). Electrophysiological units were classified into types on the basis of their activity under a variety of stimulus conditions. In the molecular layer spike activity was small and difficult to isolate. Almost all units in the fusiform cell layer could be classified as either “pauser” or “buildup” units. Classification of units in the deep DCN was sometimes difficult, but “pauser,” “chopper,” and some “on” units were found. The “on” types of units tended to be located in the more superficial part of the deep DCN. Unit locations were referred to a three‐dimensional block model of the cochlear nucleus.
A study of cochlear innervation patterns in cats and rats with the Golgi method and Nomarski optics
Authors: Perkins R. E. , Morest D. K.
Published: May 2005

Cochlear innervation patterns were studied in infant cats and rats with the rapid Golgi method. Examination of thick serial sections and surface preparations with the differential interference contrast microscope (Nomarski optics) allowed direct visualization of individually impregnated spiral ganglion cells, complete with their peripheral processes and endings in the organ of Corti. Individually impregnated efferent fibers could be recognized as heavily varicose axons that project radially to endings beneath inner and outer hair cells after taking a tangential course in the intraganglionic spiral bundle. It was often possible to visualize unimpregnated hair cells in contact with the impregnated endings of both types of fibers. There are at least two types of spiral ganglion cells in the cochlea of the infant cat and rat. One type innervates only inner hair cells by means of radial fibers. These ganglion cells constitute the overwhelming majority of ganglion cells impregnated in our preparations, and each cell typically innervates two inner hair cells. Hence, these ganglion cells establish nearly “point‐to‐point” connections between the auditory nerve and the organ of Corti. The other type of ganglion cell innervates outer hair cells by means of long spiral fibers; each cell typically innervates many outer hair cells through the numerous angular enlargements and short end branches of its spiral fiber. In addition, a few of these spiral fibers also send branches to inner hair cells by means of short collaterals; it remains to be seen if such fibers also occur in mature cochleas. Efferent fibers have been traced to inner and outer hair cell regions. The simplest pattern is formed by fine beaded axons with only a few branches ending mainly beneath inner hair cells. More complex patterns are formed by larger axons with many branches ending beneath inner or outer hair cells. Many efferent fibers send branches to both inner and outer hair cells. Electrophysiological studies so far have not demonstrated different populations of units that clearly correspond to the spiral and radial fibers. Therefore, the physiological differences between inner and outer hair cell innervation remain undefined.
A cytoarchitectonic analysis of the spinal cord of the pigeon (Columba livia)
Authors: Leonard Robert B. , Cohen David H.
Published: May 2005

The spinal gray of the pigeon is described cytoarchitectonically to establish a foundation for anatomical and physiological studies of the pigeon spinal cord. The material includes segments from the high cervical cord through the lumbosacral enlargement, and nine cellular layers are described. In addition to this laminar organization, various distinct cell groups such as the dorsal magnocellular column, column of Terni, marginal cells and lobes of Lachi are described.

Layers I–IV occupy the head of the dorsal horn, are apparent at all spinal levels examined, and represent the clearest case of laminar organization of the spinal gray of the pigeon. Layer V occupies the full extent of the neck of the dorsal horn at all segmental levels investigated. Also, the dorsal magnocellular column is situated in the central region of this layer from the rostral pole of the cervical enlargement through the lumbosacral enlargement, and arguments are advanced that this cell column is homologous to the column of Clarke. In the intermediate zone a Layer VI is defined, but it is apparent only at the enlargements. Layers VII–IX constitute the ventral horn, Layer IX being the motoneuronal cell groups. With the exception of the motoneuronal groups, the boundaries of the ventral horn layers are considerably less distinct than those of the dorsal horn, and no attempt is made to distinguish Layers VII and VIII at lumbosacral levels. At the enlargements there is a prominent lateral motoneuronal cell group consisting of large cells.

It is generally concluded that the cytoarchitectonic organization of the spinal gray of the pigeon bears a rather close resemblance to that described for various mammalian species, particularly with respect to the dorsal horn.
The receptor mosaic of Aotes trivirgatus: Distribution of rods and cones
Authors: Ogden Thomas E.
Published: May 2005

The distribution and density of rods and cones have been determined in the temporal retina of the owl monkey Aotes trivirgatus. Rod density varied from 175,000/mm2 in the far periphery to 387,000/mm2 in the area centralis. Cone density was 4000/mm2 in the periphery and 7300/mm2 within the central retinal area. Variation of densities across the retina was continuous but the ratio of rods to cones remained about 50:1 at all locations. The cones are not randomly scattered, but are separated by distances of about 10 μ in central retina and 13 μ in peripheral retina.
The distribution of catecholamines within the inferior olivary complex of the cat and rhesus monkey
Authors: Sladek John R. , Bowman James P.
Published: May 2005

Catecholamine histofluorescence was examined in the inferior olivary complex of the cat and rhesus monkey. Species‐specific patterns of catecholamine‐containing varicosities were observed. In the rat, the highest concentration of catecholamine varicosities was seen within the dorsal lamella of the principal nucleus. In contrast, this same portion of the inferior olivary complex appeared void of catecholamine varicosities in the cat and rhesus monkey. In the cat, the highest concentration of varicosities occurred within the medial one‐half of the dorsal accessory nucleus while few, if any, varicosities were seen in this portion of the complex in the rat and monkey. The lateral lamella of the principal nucleus contained the highest concentration seen in the rhesus monkey, a finding which contrasts to the minimal number of varicosities seen in this area in the rat and cat. Catecholamine‐containing cell bodies, reported to exist in the rat, were not observed in cat and monkey. These data extend the previous observation of species‐specific distribution in rodents to include members of the more phylogenetically advanced orders; Carnivora and Primata. Catecholamines were found primarily within those portions of the olivary complex reported to be involved in harmaline‐induced tremor activity in the cat.
Some cortical projections of the dorsomedial visual area (DM) of association cortex in the owl monkey, Aotus trivirgatus
Authors: Wagor E. , Lin C. S. , Kaas J. H.
Published: May 2005

Efferent projections from the dorsomedial visual area (DM) in the owl monkey to other portions of visually responsive cortex were determined by degeneration and autoradiographic methods of demonstrating axon pathways. The most prominent ipsilateral pathway was to posterior parietal cortex (PP) just medial to the terminal portion of the Sylvian fissure. Other ipsilateral projections were to subdivisions of the temporal lobe, the middle temporal visual area (MT) and the surrounding dorsolateral crescent (DL), to regions just rostral to area 18 on the medial wall of the cerebral hemisphere, and to the upper bank of the Sylvian fissure. The callosal projections of DM were to DM, PP, and MT of the opposite cerebral hemisphere. The results support the notion that visual association cortex consists of a number of separate, but complexly interrelated, subdivisions. The efferents to posterior parietal cortex suggest the possibility of an area for the integration of somatosensory and visual information.
Retrograde changes in the nerve fibers of the dorsal spinocerebellar and spinocervical tracts in the cat
Authors: Loewy Arthur D.
Published: May 2005

The potential retrograde changes that occur in the proximal segment of transected nerve fibers found in the region of the spinocervical tract (SCT) and in the region of the dorsal spinocerebellar tract (DSCT) after unilateral dorsolateral column (DLC) lesions were studied in kittens and adult cats. Nerve fibers in the region of the SCT and DSCT in the spinal segments caudal to the lesion were studied in transverse sections of Epon embedded material that had been fixed by vascular perfusion with a 4% buffered paraformaldehyde solution, post‐fixed in osmium tetroxide, and stained with Azur II‐methylene blue.

T8 level DLC lesions in the 10‐week old kitten resulted in a 14 to 25% decrease in mean fiber diameter in the SCT fibers (≥ 5 μ) of the T13 level. Retrograde fiber degeneration occurred in the small and large caliber fibers of the DSCT. A 15 to 30% decrease in mean fiber diameter occurred in the DSCT fibers (≥ 5 μ). The fiber density of the DSCT decreased by 20 to 30% and this could be correlated with a 20% loss of class C neurons (Loewy, '70) and a severe atrophy affecting the remaining 80% of the surviving class C neurons in the L3 segment.

Mid‐cervical DLC lesions in the 10‐week old kitten resulted in a 10% decrease in mean fiber diameter in the SCT fibers (≥ 5 μ), a 15% decrease in mean fiber diameter in the DSCT fibers (≥ 5 μ), and no change in fiber density could be determined despite the finding that these lesions produced about a 10% loss of class C neurons.

A T1 level lesion in a 20‐week old kitten produced no change in the SCT fibers suggesting that the changes seen in the 10‐week old kitten after midcervical lesions were probably age‐dependent changes. A 20% decrease in mean fiber diameter (≥ 5 μ) and a 6% decrease in fiber density was detected in the DSCT.

T13‐L1 level DLC lesions in the adult cats resulted in degeneration of some of the large and medium size fibers in the DSCT which was most noticeable at 20 to 25 days after surgery. DLC lesions did not cause degenerative changes in the SCT fibers 5 to 25 days after surgery.
Proliferation gradients in the inner ear of the monkey (Macaca mulatta) embryo
Authors: Wilson Doris B. , Sawyer Roger H. , Hendrickx Andrew G.
Published: May 2005

Radioautographic studies were conducted on early developmental stages of the inner ear in monkey (Macaca mulatta) embryos ranging in age from stage 11 to stage 20 (25 to 39 days' gestation) and labeled for one hour with [3H] thymidine. The most active period of proliferation occurred at stage 13, at which time all regions of the otocyst, including the endolymphatic duct, were heavily labeled. In subsequent stages the dorsal portion of the endolymphatic duct failed to incorporate label, whereas proliferation continued in the ventral portion of the duct near its communication with the medial wall of the otocyst. The duct thus appeared to grow upward as a result of cell division from below. Mitotic activity continued in the remainder of the otocyst although there was a progressive temporal decrease in the labeling index. Spatial gradients also occurred, with dorsal and lateral regions less active than ventral and medial ones. As the otocyst differentiated, the cells in various areas became attenuated. These flattened cells were still capable of undergoing cell division, as indicated by the presence of labeled nuclei in all regions of the utricle, saccule, semicircular ducts, and cochlear duct.
Dorsal column nuclei projections to the cerebellar cortex in cats as revealed by the use of the retrograde transport of horseradish peroxidase
Authors: Cheek M. D. , Rustioni A. , Trevino D. L.
Published: May 2005

The existence of a cerebellar projection from the dorsal column nuclei (gracile and cuneate nuclei, DCN) has been proposed on electrophysiological grounds but questioned when studied with neuroanatomical techniques. The retrograde transport of horseradish peroxidase (HRP) has been used for the present study and provides anatomical evidence of a DCN‐cerebellar pathway. In adult cats, 1 to 6 μl of 30% HRP were injected in pars intermedia of the anterior lobe (lobules IV–V), in paramedial lobule and in vermis of the anterior (lobules IV–V) and of the posterior lobe (lobule VII). After survival of 24 to 48 hours, all animals were perfused with a double aldehyde mixture and serial 40 μ sections through the medulla oblongata were incubated for visualization of HRP. In all cases, medullary nuclei known to project to the injected cortical regions of the cerebellum contained HRP‐positive neurons mainly ipsilateral to the injection (e.g., external cuneate nucleus) or mainly contralateral to it (e.g., inferior olivary complex).

Following ipsilateral injections in either the paramedian lobule or the pars intermedia, HRP‐positive neurons in the cuneate nucleus were concentrated in its rostral portion where multipolar cells with radiating dendrites predominate. In contrast, none of the cells of the clusters region, in the caudal part of the cuneate nucleus, displayed HRP‐positive granules. In cases in which the anterior vermis was injected a few labelled cells were present in the rostral part of the gracile nucleus but not in the clusters region of this nucleus. No labelling of DCN neurons was evident after posterior vermis injection.

To compare the distribution of cells contributing to the DCN‐cerebellar pathway with that of thalamic relay cells in the DCN, 0.5 to 3 μl of 30% HRP were injected in the nucleus ventralis posterolateralis of the thalamus in another series of cats. Contralateral to the thalamic injection, labelled cells were concentrated in the clusters region of the gracile and cuneate but rostrally in these nuclei they were scattered among unlabelled neurons.

The preferential location in the DCN of cells which project to the cerebellum and of cells which project to the thalamus stresses the heterogeneous organization of these nuclei along the rostrocaudal axis. Further, the results indicate that regions of the DCN which have been distinguished on the basis of cytoarchitectonics (Kuypers and Tuerk, '64) and of afferents (Rustioni, '73, '74) differ also in their efferent projections.
Autoradiographic localization of hormone‐concentrating cells in the brain of an amphibian, Xenopus laevis. I. Testosterone
Authors: Kelley Darcy B. , Morrell Joan I. , Pfaff Donald W.
Published: May 2005

Autoradiographic methods were used to investigate locations of hormone concentrating cells in the CNS of Xenopus laevis. Both male and female frog brains contained labelled cells. Four major hormone uptake sites were identified: the anterior preoptic area, the ventral infundibular nucleus, a dorsal tegmental area of the medulla and a presumptive motor nucleus of cranial nerves IX–X. The distribution of labelled cells was very similar for male and female brains. Available information on these testosterone uptake sites in anurans indicates possible roles in gonadotropin regulation and reproductive behavior.
Autoradiographic localization of hormone‐concentrating cells in the brain of an amphibian, Xenopus laevis. II. Estradiol
Authors: Morrell Joan I. , Kelley Darcy B. , Pfaff Donald W.
Published: May 2005

Autoradiographic techniques for light microscopic examination of sex steroid retention were applied to the brains of male and female Xenopus laevis, an anuran amphibian, after 3H‐estradiol administration. Estrogen was concentrated by cells in three telencephalic areas (the ventral striatum, the ventral‐lateral septum and the amygdala), the anterior preoptic area, the ventral thalamus, the ventral infundibular nucleus, and in the torus semicircularis. The anterior preoptic area and the ventral infundibular nucleus contained the greatest number of labelled cells.

The topography of estrogen‐concentrating cells was the same in male and female brains. This fact and comparisons of 3H‐estradiol with 3H‐testosterone retention in Xenopus suggest that the sex steroid itself, and not the genetic sex of Xenopus determines the pattern of uptake by cells in the brain.

The distribution of hormone‐concentrating cells in Xenopus has many similarities to that found in birds and mammals. Preoptic, hypothalamic (tuberal), limbic forebrain and specific mesencephalic sites in all these forms contain labelled cells following radioactive sex steroid administration. Findings in Xenopus add to the argument for a phylogenetically stable system of hormone‐concentrating nerve cells in limbic, hypothalamic and mesencephalic structures.
Junctions in the meninges and marginal glia
Authors: Nabeshima Sachio , Reese T. S. , Landis Dennis M. D. , Brightman M. W.
Published: May 2005

The meninges of various mammals were prepared for examination with the electronmicroscope by thin sectioning or freeze‐fracturing. Particular attention was given to the distribution of tight junctions in order to determine the basis for the meningeal barrier between the blood circulating in dural vessels and the cerebrospinal fluid in the subarachnoid space. While some dural blood vessels are fenestrated, those in the subarachnoid space are not and their component endothelial cells are joined by an extensive system of tight junctions. An extensive and continuous system of tight junctions was also found in a layer of specialized cells at the border of the arachnoid with the dura. This arachnoid barrier layer is apparently the only basis of the meningeal barrier because often cellular layers in the dura and arachnoid lack tight junctions although they are linked by gap junctions and desmosomes. In particular, tight junctions are lacking at the border of the “subdural space” which is actually a fascial plane within the dura. Tight junctions are also lacking between astrocytes at the surface of the brain but these cells are linked by gap junctions and a new type of intercellular junction. The distribution of these junctions, as well as assemblies of intramembranous particles at the astrocytic border, raises the question whether this layer might have a role in the exchange of certain substances between the brain and cerebrospinal fluid.
Distribution and properties of commissural and other neurons in cat sensorimotor cortex
Authors: Miller Robert
Published: May 2005

Commissural, cortico‐cortical and cortico‐caudate neurons have been investigated in the primary sensorimotor cortex of the cat, using antidromic stimulation techniques, and histological identification of recording sites. These neurons are to be found in all cortical laminae except the first; commissural and cortico‐cortical neurons were found to be commonest in laminae III and VI, whilst cortico‐caudate neurons were most abundant on the border between laminae III and V, in motor areas. In sensory areas topographically identified as representing distal parts of limbs, commissural neurons are very rare, confirming neuroanatomical studies on the origin and termination of callosal fibres.

The intracerebral neuronal projections investigated in this study had slow conduction velocities (less than 1 m/sec, up to about 10 m/sec). It was found that projections from area 6, whether commissural, cortico‐caudate, or corticopeduncular have slower conduction velocities than their counterparts from area 4. It is suggested that this is related to the type of motor control in which these two areas are involved (slowly‐responding postural movements, as opposed to more rapid distal limb movements). No neurons were found which had both commissural (or cortico‐cortical), and cortico‐fugal projections.
Tectal efferents in the blind cave fish Astyanax Hubbsi
Authors: Sligar Catherine M. , Voneida Theodore J.
Published: May 2005

Suction lesions were placed in the optic tecta of 36 blind cave fish. Three main bundles of tectal efferents were observed. A large, caudally directed fascicle distributes to the ipsilateral torus semicircularis, nucleus isthmi, and lateral tegmental areas of the mesencephalon and pons via the ipsilateral tectobulbar tract. Contralaterally, this fascicle descends to pontine levels as the contralateral tectobulbar tract.

A second, rostrally directed bundle exits from the tectum at two levels. A small fascicle leaves from the caudal tectum and ascends rostrally as the commissura transversa. This bundle then joins with more rostrally exiting fibers and the combined fascicles collect in the area of the medial optic tract. They remain in this position until the level of the postoptic commissure where they decussate. Subsequently, this bundle moves caudally and enters the contralateral tectum at its most rostral extreme.

The third bundle of tectofugal efferents leaves the tectum medially, at the level of the lesion, and enters the tectal commissure, through which it is distributed to the ipsilateral torus longitudinalis and contralateral optic tectum.
Early formation of synapses in the molecular layer of the fetal rat cerebellum
Authors: West Mark J. , Del Cerro Manuel
Published: May 2005

The initial phase of synaptogenesis in the molecular layer of the albino rat cerebellum has been studied quantitatively and qualitatively with the electron microscope. Using both aldehyde‐osmium (AL‐OS) and ethanolic phosphotungstic acid (E‐PTA) preparations, synapses were observed as early as embryonic day 19 throughout the entire rostro‐caudal extent of the vermal molecular layer. The undeveloped nature of the elements participating in the formation of these synapses precluded their identification, for at this stage of cerebellar development, the Purkinje cells have not developed characteristic dendrites and both the massive production of cells within the external granule layer and the migration of neuroblasts through the molecular layer are in their initial phases. Evidence of synapse formation at this early stage of molecular layer development indicates that the rudiments of neuronal systems are present before the bulk of the molecular layer has come into existence and before most of the constituent elements of the cerebellum have differentiated. From embryonic day 19 to embryonic day 22, the number of E‐PTA synaptic contacts was always less than the number of AL‐OS synapses. This discrepancy and the variations observed in the morphology of the presynaptic components of E‐PTA stained synaptic contacts, indicate that E‐PTA morphology, and particularly the development of presynaptic dense projections, represents a late stage of synapse formation.
The topographical distribution of S‐100 and GFA proteins in the adult rat brain: An immunohistochemical study using horseradish peroxidase‐labelled antibodies
Authors: Ludwin S. K. , Kosek J. C. , Eng L. F.
Published: May 2005

The cytological and topographical distribution of S‐100 and glial fibrillary acidic (GFA) proteins in the adult rat brain has been compared using the horseradish peroxidase‐labelled antibody technique. Both proteins are present in astrocytes and structures composed of astrocytic processes, namely the glial limitans and the perivascular membranes, but the cytological localization varies between the two proteins. S‐100 is found in the nucleus and cytoplasm whereas GFA protein is confined to the cytoplasm. Neither is found in neurons, but S‐100 is present in some oligodendroglia, suggesting a general regulatory role in glia. Although GFA protein is present in both protoplasmic and fibrous astrocytes, it is more prominent in the latter, confirming its association with astrocytic filaments.
Topological analysis of the brain stem of the axolotl Ambystoma mexicanum
Authors: Opdam Paul , Nieuwenhuys Rudolf
Published: May 2005

The ventricular sulcal pattern and the cellular structure of the brain stem of the axolotl Ambystoma mexicanum have been studied in transversely cut Nissl and Bodian stained serial sections. Six longitudinal sulci, the sulcus medianus inferior, the sulcus intermedius ventralis, the sulcus limitans, the sulcus intermedius dorsalis, the sulcus medianus superior and the sulcus lateralis mesencephali could be distinguished. A seventh groove, the sulcus isthmi, clearly deviates from the overall longitudinal pattern of the other sulci. Although most neuronal perikarya are contained within a diffuse periventricular gray, 19 cell masses could be delineated: seven of these are primary efferent or motor nuclei, four are primary afferent or sensory centers, four nuclei are considered as components of the reticular formation, and the remaining four cell masses can be interpreted as “relay” nuclei.

In order to study the zonal pattern of the brain stem, this structure was subjected to a topological analysis )cf. Nieuwenhuys, '74 and fig. 13(. This analysis yielded the following results. In the rhombencephalon the grisea are arranged in four longitudinal zones which, following Kuhlenbeck, have been termed: area ventralis, area Intermedioventralis, area intermediodorsalis and area dorsalis. Where present the sulcus intermedius ventralis, the sulcus limitans and the sulcus intermedius dorsalis mark the boundaries between these four morphological entities. The zonal areas in question coincide largely, but not sntirely, with the so‐called functional columns of Herrick and Johnston. The most obvious incongruity is that the area intermediodorsalis contains, in addition to the nucleus fasciculi solitarii and the nucleus visceralis secundarius, two non‐visceral sensory cell masses, namely the nucleus vestibularis magnocellularis and the nucleus cerebelli. The four morphological zones delineated in the rhombencephalon cannot be distinguished in the mesencephalon and it is of particular importance that the sulcus limitans does not extend into this part of the brain. Functionally, however, the medial part of the tegmentum mesencephali may be considered the rostral extreme of the somatic motor column, whereas the tectum primarily represents a somatic sensory correlation area.
The synaptic cluster )glomerulus( in the inferior olivary nucleus
Authors: King James S.
Published: May 2005

This report describes the fine structural features and distribution of the synaptic cluster )glomerulus( within the inferior olivary nucleus of the opossum. The postsynaptic elements typically include spiny appendages and small diameter dendrites which exhibit attachment plaques and gap junctions. Profiles presynaptic to the central core of postsynaptic elements were differentiated on the basis of vesicle shape, vesicle size, as measured by a computer system, and junctional characteristics. Three categories of terminals with clear vesicles are present within the synaptic clusters in all nuclear divisions of the olive, whereas a fourth with large dense core vesicles is restricted primarily to the principal nucleus. The groups of pre and postsynaptic elements are surrounded by astrocytic lamellae and are most frequently encountered in the principal and rostral portions of the medial accessory nuclei. Possible identification of the sources of the synaptic components is discussed in relation to data available from Golgi impregnations, physiological reports and hodological evidence.
Autoradiographic studies of the projections of the midbrain reticular formation: Ascending projections of nucleus cuneiformis
Authors: Edwards Stephen B. , de Olmos José S.
Published: May 2005

The ascending projections of the cuneiform nucleus in the cat were traced by autoradiography in the transverse and sagittal planes following stereotaxically placed injections of 3H‐leucine. The ascending fibers are almost exclusively ipsilateral and enter the diencephalon as a wide radiation. At the mesodiencephalic junction fibers enter the nucleus of the posterior commissure and pretectal nuclei, and others cross in the posterior commissure to distribute to these structures on the contralateral side. More ventrally directed fibers distribute to the fields of Forel and then spread into the posterior hypothalamus and zona incerta. At the caudal level of the ventral thalamic group, the ascending fibers diverge and follow two separate courses. One division of fibers continues forward beneath the ventral thalamic group and distributes to the zona incerta and dorsal hypothalamic area. It rapidly diminishes in size as it attains more rostral levels where it is found in the bed nuclei of the stria terminalis and the anterior commissure. Other fibers of this division spread laterally to innervate the ventral lateral geniculate nucleus, the lateral hypothalamus, and preoptic area, and still others follow the entire conformation of the thalamic reticular nucleus. The second division of fibers ascends through midline and intralaminar nuclei, completely encircling the mediodorsal nucleus, which is uninnervated except for a small ventral region. The distribution of this division is heaviest to the paraventricular, parafascicular, and central dorsal nuclei. Neither division is conspicuous rostral to the anterior commissure. No projections to neostriatum or specific thalamic nuclei were evident.
Gustatory pathways in the bullhead catfish. I. Connections of the anterior ganglion
Authors: Finger Thomas E.
Published: May 2005

The central projections of the external gustatory system in bullhead catfish were examined using orthograde degeneration and retrograde transport of horseradish peroxidase (HRP) techniques.

Both large and small cells were observed in the anterior ganglion which contains a mixture of elements from the trigeminal, facial and anterior lateral line nerves. Some of the large cells on the lateral margin of the ganglion were found to belong to the lateral line system. No separation of trigeminal and facial nerve connections could be made.

Using HRP, the relation between the barbels and specific ganglion regions was determined. The dorsalmost portion of the ganglion received recurrens nerve inputs (from taste buds on the trunk); the rostromedial portion of the ganglion, from the nasal barbel nerve; and the ventral portion of the ganglion, from the maxillary and mandibular barbel nerves.

The facial lobe (similar to part of the n. solitarius) was found to be divided into lobules by fascicles of nerve fibers. The lateral lobule received input only from the dorsal‐most part of the ganglion (recurrens nerve: trunk receptors); the intermediate lobule from the rostro‐lateral part of the ganglion (nasal barbel); and the medial lobule from the ventral areas of the ganglion (maxillary and mandibular barbels).

Thus a topographical relationship exists between the different taste receptor groups and their locus of representation in the facial lobe. The trunk receptors connect to the lateral lobule; the nasal barbel receptors to the intermediate lobule, and the maxillo‐mandibular receptors to the medial lobule.
The rabbit optic nerve: Fibre diameter spectrum, fibre count, and comparison with a retinal ganglion cell count
Authors: Vaney D. I. , Hughes A.
Published: May 2005

This electron microscopic study indicates that the rabbit optic nerve contains 394,000 ± 20,000 (p < 0.05) nerve fibres, of which at least 98% are myelinated. The fibre diameter spectrum of the nerve is unimodal and ranges from 0.25–7 μm with its peak at 0.75 μm. The projection of the visual streak fibres is not apparent in local diameter spectra near the optic nerve head. Integration of a ganglion cell density map of the retina from another rabbit indicates a total ganglion cell count lying between 455,000 and 547,000. The optic nerve fibre and ganglion cell counts are both substantially greater than the maximum fibre count previously reported.
Structural and functional changes in an identified cricket neuron after separation from the soma. I. Structural changes
Authors: Clark Richard D.
Published: May 2005

The morphological effects of separation from the soma were examined in isolated arborization and isolated axon segments of an identified motor neuron in the Polynesian field cricket, Teleogryllus oceanicus. The identified neuron, the contralateral dorsal longitudinal motor neuron of the metathoracic ganglion (CDLM), possesses an arborization most of which lies contralateral to its soma within the metathoracic ganglion. Midline surgical lesions in the metathoracic ganglion separated CDLM into a distal segment composed of the axon and most of the arborization, and a proximal segment comprised of the remaining arborization, neurite, and soma. Isolated axonal segments were produced by cutting the nerve root containing the axon of CDLM close to the ganglion.

The normal anatomy of CDLM was determined by axonal dye‐fills using cobaltous chloride. Morphological changes in the isolated arborization of CDLM were examined by axonal dye‐fills at successive time intervals. Changes in the isolated CDLM axon were examined via dissection and histological cross‐sections of the distal nerve at graded time intervals.

In one example, a remnant of the isolated CDLM arborization survived to 168 days postoperative, a time comparable to the longest previously‐reported physiological and morphological survival times of distal axonal segments of invertebrates. In general the isolated arborization does not survive this long. Normally occurring branches of the arborization can be preserved about 0 to 50 days. After this period branches of the arborization seem to be lost in progressive fashion from smaller to larger, leading to complete loss of the arborization and axon in most cases at 100 or more postoperative days. There is evidence for the presence of supernumerary fibers in the isolated CDLM arborization between 0 to 63 days postoperative. Such supernumerary fibers indicate an independent capacity for outgrowth of the isolated arborization without connection to the nucleus.

The distal axonal segment of CDLM degenerates physiologically and morphologically within 4 to 15 days after peripheral nerve section. This time course is close to that of Wallerian degeneration of vertebrate peripheral nerve axons.
Three bulbospinal pathways from the rostral medulla of the cat: An autoradiographic study of pain modulating systems
Authors: Basbaum Allan I. , Clanton Charles H. , Fields Howard L.
Published: May 2005

Small amounts of 3H‐leucine were injected into discrete regions in the rostral medulla of the cat. Descending projections from these sites were studied with autoradiographic methods. On the basis of differential projections to the medulla and spinal cord, three distinct regions were delineated. Nucleus reticularis gigantocellularis (Rgc), located dorsally in the medullary reticular formation, projects primarily to “motor” related sites, including cranial motor nuclei VI, VII, XII, nucleus intercalatus, and a part of the ipsilateral medial accessory olive. The projection to the spinal cord is primarily via the ipsilateral ventrolateral and contralateral ventral funiculi. The Rgc terminal field is in lamina VII and VIII ipsilateral and lamina VIII contralateral to the injection site. In contrast, nucleus raphe magnus, (NRM) located ventrally, in the midline of the rostral medulla projects primarily to structures with known nociceptive and/or visceral afferent input. These sites include the solitary nucleus, the dorsal motor nucleus (X) and the marginal and gelatinous layers of the spinal trigeminal nucleus caudalis. The projection to the spinal cord is bilateral, via the dorsolateral funiculus. Terminal fields are found in the marginal zone and the substantia gelatinosa of the dorsal horn, and more deeply in lamina V, medial VI and VII. Nucleus reticularis magnocellularis (Rmc), located lateral to NRM and ventral to Rgc, has an overlapping projection with NRM, but the projection is ipsilateral. This difference between Rmc and Rgc is correlated with cytoarchitectural features of the two regions. The possibility that the raphe‐spinal pathway in the DLF mediates opiate and brain stimulation‐produced analgesia is discussed.
A description of the amygdaloid complex in the rat and cat with observations on intra‐amygdaloid axonal connections
Authors: Krettek J. E. , Price J. L.
Published: May 2005

The cytoarchitectonic structure and divisions of the amygdaloid complex are described in the rat and cat, with special reference to the axonal connections of each of the amygdaloid nuclei, and to interspecies variations and similarities. Several intra‐amygdaloid connections are also described, based on autoradiographic experiments with small injections of 3H‐amino acids into the individual nuclei. Although it has probably not been possible to determine all of the intra‐amygdaloid projections from these experiments, the connections which have been shown are very specific. The lateral nucleus projects to the basomedial nucleus, the lateral part of the central nucleus, and the periamygdaloid cortex, while the basolateral nucleus projects only to itself, the medial part of the central nucleus, and the nucleus of the lateral olfactory tract. The basomedial nucleus projects to the cellular layer of the medial nucleus and the amygdalo‐hippocampal area, while the molecular layer of these structures and of the posterior cortical nucleus, receives projections from the periamygdaloid cortex or from the endopiriform cortex. There are also interconnections between the medial and posterior cortical nuclei, and commissural connections between the posterior cortical nuclei of the two sides.
Spinal projections from the midbrain in monkey
Authors: Castiglioi A. J. , Gallaway M. C. , Coulter J. D.
Published: May 2005

Neurons descending from the midbrain to the spinal cord in the monkey were identified with the retrograde horseradish peroxidase technique. Beginning in the caudal midbrain and extending anteriorly beneath the superior colliculus, large numbers of neurons of the nucleus cuneiformis and lateral central gray were found to project ipsilaterally to the spinal cord. In the posterolateral superior colliculus, neurons of the intermediate and deep layers, stratum griseum intermediale and stratum griseum profundum, were found to give rise to contralateral projections to the upper cervical spinal segments. An ipsilateral tectospinal projection from the anteromedial part of the collicus may also exist. In the red nucleus, neurons of the magnocellular division were shown to give rise to a somatotopically organized projection to the upper cervical cord and spinal enlargements. No neurons of the parvocellular red nucleus were labeled from the spinal cord. In the anterior midbrain, neurons of the interstitial nucleus of Cajal, nucleus of Darkschewitsch, and the adjacent dorsomedial and ventromedial midbrain tegmentum were found to give rise to an extensive ipsilateral descending spinal projection. Neurons located in various midline nuclei including the supratrochlear nucleus, oculomotor nucleus, Edinger‐Westphal nucleus, and the ventral part of the central gray were also labeled from the spinal cord. These findings indicate that the primate midbrain is the origin of an extensive system of descending spinal pathways, some of which are likely to be involved in mediating descending influences involved in complex motor and sensory behavior.
Thalamic projections to S‐I in macaque monkey
Authors: Whitsel B. L. , Rustioni A. , Dreyer D. A. , Loe P. R. , Allen E. E. , Metz C. B.
Published: May 2005

The organization of thalamic input to functionally characterized zones in primary somatosensory cerebral cortex (S‐I) of macaque monkeys (Macaca mulatta) was investigated using the method of labelling by retrograde transport of horseradish peroxidase (HRP). It was found that the cell columns positioned at the posterior margin of the band of cortex representing a given body region receive thalamic input from a posterior level of the ventroposterior thalamic nucleus (VP), and that cell columns at successively more anterior positions within that band receive input from successively more anterior levels of VP. The extreme posterior and anterior margins of the S‐I hand, foot and face areas receive input from neuron populations which are not as widely separated in the anteroposterior dimension of VP as the neurons projecting to the extreme anterior and posterior margins of the proximal limb and trunk representations in S‐I. These characteristics of the organization of the projections from VP to S‐I are consistent with the view that the body representations in VP and S‐I have the same connectivity and differential submodality distribution; and with the idea that thalamocortical connections only exist between functionally equivalent neuron populations in VP and S‐I.
Acute whisker removal reduces neuronal activity in barrels of mouse sml cortex
Authors: Durham Dianne , Woolsey Thomas A.
Published: May 2005

The autoradiographic 2‐deoxy‐D‐glucose (2‐DG) method has been used to map relative changes in metabolic activity in the CNS during various functional states (Plum et al., '76). Here we describe the application of the 2‐DG method to assay regional activity in the posteromedial barrel subfield (PMBSF) region of the mouse SmI cortex after acute removal of mystacial vibrissae.

One day prior to isotope injection, various combinations of vibrissae (e.g., all vibrissae, row‐C only, rows‐B and ‐D only) were plucked from adult male Swiss Webster mice under anesthetic. The next day, 5 μCi of 14C‐2‐DG were injected into a tail vein, and the mice were allowed to actively explore an empty cage for 45 minutes. The animals were then sacrificed, the brains quickly removed, frozen, and sectioned either parallel or perpendicular to the pia at 80 μm in a cryostat. The sections were mounted, dried on coverslips, and were used to expose X‐ray film, after which the sections were stained with thionin and the X‐ray film developed. The tissue sections and matching autoradiograms were compared directly from photomicrographs of each.

The autoradiograms showed areas of higher activity in barrels for which corresponding vibrissae were present and lower activity in barrels for which appropriate vibrissae were missing. In tangential sections from animals with all vibrissae intact, the PMBSF was uniformly and consistently higher in activity than in cases with all vibrissae missing. The removal of row‐C or rows‐B and ‐D resulted in strips of decreased activity in the corresponding PMBSF rows. The same patterns of increased or decreased activity were also seen in sections normal to the pia, but the changes in activity, while greatest in layer IV, extended through all layers of the cortex. Finally, in a number of the autoradiograms, density patterns could be recognized which later were shown to relate directly to sides of individual barrels.

The results indicate: (1) Acute removal of the peripheral vibrissal hairs is sufficient to deprive the related contralateral cortical barrel neurons of normal activity. Thus in the mouse somatosensory system it may be possible to determine the relative importance of sensory deprivation and neonatal peripheral lesions in normal cortical development. (2) The barrels are part of a functional cortical columnar organization similar to that in other sensory systems. And, (3) the 14C‐2‐DG‐X‐ray technique is sufficiently sensitive to reveal parts of individual barrels in autoradiograms and thus, with some modification, may be suitable for the study of small populations of neurons.
Temporal and spatial sequence of anterograde degeneration in the cochlear nerve fibers of the cat. A light microscopic study
Authors: Arnesen Atle Rønning , Osen Kirsten Kjelsberg , Mugnaini Enrico
Published: May 2005

This study deals with anterograde degeneration in the cochlear nerve fibers following cochlear lesions. The observations are based on 2‐μm thick sections of material embedded in resin according to procedures used in electron microscopy and stained with toluidine blue. Among the various operative approaches used in this study, sparing of the modiolus afforded the least local reaction and furnished the material best suited for anterograde degeneration studies in this nerve only 2 mm long. The anterograde degeneration of the cochlear nerve is characterized by segmental swelling of myelinated nerve fibers followed by shrinkage of the axoplasm and collapse of the distended myelin sheaths. The swelling, which begins at the nodal‐paranodal region of the axon, is preceded by accumulation in the cytoplasm of granular organelles, presumably mitochondria and lysosomes. The portions of the cochlear fibers situated in the nerve root, i.e., within the cochlear nuclei and including the axon terminals, follow essentially the same pattern of degeneration as those in the peripheral portion of the nerve. Both peripherally and centrally degenerative changes occur first in the basal, high frequency fibers and progress to the apical, low frequency fibers. The difference between the two extremes in the onset of degeneration is, approximately, 24 hours. Once initiated, however, the pace of degeneration is the same along the whole fiber spectrum.