bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental reorganization of the cerebellar cortex. III. Regeneration of the external germinal layer and granule cell ectopia
Authors: Altman Joseph
Published: January 2005

The heads of Long‐Evans hooded rats were irradiated daily from day 3, 4 or 6 onward with schedules of low‐level x‐ray which differentially delayed the regeneration of the subtotally eradicated external germinal layer or prevented its regeneration altogether. Most schedules that permitted regeneration led to the arrest of many granule cells in the molecular layer where they formed an ectopic zone. The dendrites of ectopic granule cells had synapses with mossy fibers located in their vicinity in the molecular layer. The position of the ectopic zone varied in different lobules depending on several factors: the time when regeneration began, the estimated date of descent of granule cells, regional differences in cortical maturation and in the estimated upward growth rate of mossy fibers. Within the same lobule, the longer regeneration was delayed the higher in the molecular layer the differentiating and descending granule cells were captured by the apparently autonomously ascending mossy fibers. If regeneration started early and allowed the descent of granule cells into the granular layer (early irradiation) or if regeneration of granule cells was prevented altogether (late irradiation) an ectopic zone was not formed. The technique was used for estimating the normal growth pattern of mossy fibers in the different lobules.
Pretectal region and the pupillary light reflex. An anatomical analysis in the monkey
Authors: Carpenter Malcolm B. , Pierson Roberta J.
Published: January 2005

The effects of discrete lesions in the pretectal region of the monkey upon the pupillary light reflex were studied, using infrared pupillography. Resulting degeneration was studied by silver impregnation methods.

The nucleus of the optic tract (NOT) and the sublentiform nucleus (SL) project fibers to the nuclei of the posterior commissure (NPC) and to portions of the ipsilateral inferior pulvinar, pregeniculate nucleus and dorsal lateral geniculate body. NPC gives rise to the bulk of the fibers in the posterior commissure (PC) which largely terminate upon contralateral cells of NPC. Some fibers arising from NPC enter the ipsilateral central gray and terminate bilaterally primarily upon cells of the medial visceral columns of the oculomotor complex (OMC). These fibers partially decussate ventral to the aqueduct.

Fibers from the olivary nucleus (ON) cross in the PC and project to terminations upon: (1) large cells of the opposite ON and (2) the anterior median nuclei and the contralateral lateral visceral cell column of OMC. NOT, and possibly ON, give rise to fibers crossing in PC that project to the contralateral accessory optic tract nucleus (AOTN).

Unilateral lesions that fairly selectively destroy parts of NOT, ON, SL, NPC, central fibers of PC or the nucleus of the pretectal area (NPA), produce neither miosis, mydriasis, anisocoria, nor do they impair direct or consensual pupillary light reflexes. Unilateral lesions, which impair pupillary light reflexes, involve multiple structures, such as NPC, PC and lateral regions of the central gray.
Cytoarchitecture and somatic sensory connectivity of thalamic nuclei other than the ventrobasal complex in the cat
Authors: Jones E. G. , Burton H.
Published: January 2005

This study is a re‐examination, using autoradiographic and axonal degeneration methods, of the distribution of spinal, dorsal columnlemniscal and cortico‐thalamic fibers within the thalamus of the cat. The emphasis was placed upon making an exact cytoarchitectonic delineation of regions outside the ventrobasal complex which receive spino‐thalamic fibers and corticofugal fibers arising in the sensory‐motor regions of the cerebral cortex.

It is concluded, in agreement with Boivie ('70, '71a,b) that spino‐thalamic fibers arising below the level of the lateral cervical nucleus terminate, not in the ventrobasal complex, but in a recognizable portion of the ventrolateral complex adjacent to the ventrobasal complex. This region appears to be also the thalamic relay for Group I muscle afferents. Combined experiments in which, in the same animal, the dorsal column‐lemniscal path was labeled autoradiographically and the spino‐thalamic path by the Nauta method, indicate virtually no overlap of the two systems in the ventral nuclear complex.

Spinal fibers also end in the medial division of the posterior group (Pom), which extends posteriorly as a small‐celled zone along the ventromedial aspect of the magnocellular medial geniculate nucleus. Reports of spinal terminations in the magnocellular nucleus proper may result from a failure to recognize the extent of Pom. A third part of the thalamus receiving spinal fibers consists of a posteriorly situated group of large, deeply staining cells belonging to the central lateral nucleus which lie mainly posterior to the internal medullary lamina and which, as Mehler ('69) has mentioned, have previously been confused with the centre médian and parafascicular nuclei.

Corticofugal fibers arising in the somatic sensory cortex terminate in both the ventrobasal complex and the spinal part of the ventrolateral complex as well as in the central lateral nucleus and Pom and this confirms the work of Rinvik ('68a). Those arising in the motor cortex terminate only in (a different part of) the ventrolateral complex and in the centre médian nucleus.
The connections between horizontal cells and photoreceptors in the retina of the cat: Electron microscopy of Golgi preparations
Authors: Kolb Helga
Published: January 2005

Electron microscopy of Golgi preparations reveals that the dendritic terminals of horizontal cells in the cat's retina are connected only to cones. The axon terminals of these horizontal cells connect exclusively to rods. Dendritic and axonal terminals of horizontal cells penetrate the photoreceptor endings to become lateral elements of the invaginations. In addition this study suggests that each cone is in contact with more than one horizontal cell and that each rod connects to more than one axon terminal system. The horizontal cells of the cat are similar to those of the rhesus monkey in that the rod and cone connections are segregated to different portions of these cells.
The mode of innervation of portions of the anterior and posterior pretectal nuclei of the rabbit by axons arising from the visual cortex
Authors: Giolli Roland A. , Towns Lex C. , Haste David A.
Published: January 2005

In sections processed by the Cajal method, two distinct systems of fibers can be recognized within the dorsolateral portion of the anterior pretectal nucleus and the lateral portion of the posterior pretectal nucleus of the rabbit. One is a rostrocaudal system which consists of fiber bundles oriented in parallel with the superior quadrigeminal brachium; some fibers of this system mingle with the fibers of this brachium. The other is a lateromedial system which is composed of fibers directed perpendicularly to those of the rostrocaudal system. After lesions of the visual cortex, the study of the Nauta sections reveals that there are degenerating fibers present within both systems in the portions of the anterior and the posterior pretectal nuclei studied. The degenerating rostrocaudal fibers are found to send collateral branches into the lateromedial fiber system present in these portions of the pretectal nuclei. Most, if not all, of the degenerating lateromedial fibers are the continuations of these collateral branches given off by the degenerating rostrocaudal fibers, and at the same time represent the terminal portions of corticopretectal axons. These conclusions are based upon four of the present findings: (i) the presence of degenerating rostrocaudal fibers that branch in the zones of degenerating lateromedial fibers but in no other parts of the pretectal nuclei studied; (ii) the common orientation shared by these collateral branches and the degenerating lateromedial fibers at any one location, suggesting that the two elements represent portions of the same fibers; (iii) the morphology of the degenerating lateromedial fibers with their many short side branches indicating that these fibers are the terminal segments of the corticopretectal axons (some of the degenerating rostrocaudal fibers also have short side branches along their length which would appear to represent terminal side branches); (iv) our failure to demonstrate degenerating rostrocaudal fibers which pass into the lateromedial fiber system without branching. In the Golgi‐Kopsch preparations from normal brains it has been possible to identify undegenerated lateromedial fibers with the same morphology as the degenerating lateromedial fibers seen in the Nauta sections.
DNA constancy in neurons of the human cerebellum and spinal cord as revealed by Feulgen cytophotometry and cytofluorometry
Authors: Fujita Setsuya
Published: January 2005

Neuroblasts and neurons of the human cerebellum and spinal cord from the eighth fetal week to 68 years of age were prepared as smears and the DNA content of individual cells was measured by Feulgen cytophotometry and microfluorometry. DNA constancy of large and small neurons as well as neuroblasts was confirmed by the two methods. These findings accord with autoradiographic observation that neuroblasts, once differentiated from matrix cells, do not synthesize DNA.
Morphology of afferent and efferent synapses in hearing organ of goldfish
Authors: Nakajima Yasuko , Wang D. W.
Published: January 2005

The sacculus, the hearing organ, of the goldfish was fixed with three different kinds of fixatives: osmium tetroxide, glutaraldehyde and formaldehyde. Three kinds of synapses are encountered in the sensory epithelium: the synapse between the hair cell and the afferent nerve ending, the synapse between the efferent nerve ending and the hair cell, and the synapse between the hair cell and the afferent nerve ending, there are synaptic vesicles about 370‐430 Å in average diameter in the hair cell side of the junction. The vesicles are always round in dependent of the fixative used. In the other two kinds of synapses, the efferent ending contains smaller vesicles about 310‐360 Å in average diameter. The shape of the vesicles changes according to the fixative used; round in osmium tetroxide‐fixed materials, and elongated in aldehydefixed materials. The synapse between the hair cell and the afferent nerve ending in excitatory in nature, while the other two types of synapses are thought to be inhibitory in nature.
Evolution of reptilian visual systems: Retinal projections in a nocturnal lizard, Gekko gecko (linnaeus)
Authors: Northcutt R. Glenn , Butler Ann B.
Published: January 2005

On the basis of the development of the dorsal ventricular ridge of the telencephalon, lizards can be divided into a type I group, to which Gekko and the majority of lizard families belong, and a type II group with more derived features, of which Iguana is representative. Most studies of retinal projections have utilized lizards of the type II group, which are adapted to a diurnal niche. Gekko gecko is differently adapted in that it is nocturnal. Study of the retinal projections was undertaken in Gekko gecko in order to insure that conclusions regarding the pattern of retinal pathways in saurians would be based on a sample which was more representative of the total range of variation.

Unilateral removal of the retina by suction cannula was carried out on 12 adult specimens of Gekko gecko. After survival times of 10 to 74 days, brains were processed with various silver methods. The retina projects contralaterally to the pars dorsalis and pars ventralis of the lateral geniculate nucleus and the pars ventralis of the ventrolateral nucleus in the thalamus, nuclei geniculatus pretectalis, lentiformis mesencephali, and posterodorsalis in the pretectum, layers 8–14 of the optic tectum and nucleus opticus tegmenti. Additionally, the retina projects ipsilaterally to the dorsal and ventral lateral geniculate nuclei and to the pretectal nuclei, as well as to the optic tectum, particularly layers 8 and 9.

The finding of ipsilateral retinothalamic projections in Gekko supports the idea that this pathway is generalized among saurians. However, presence of ipsilateral retinothalamic projections and the degree of binocular overlap cannot be correlated when lizards, snakes, crocodiles, and turtles are compared. The functional significance of this pathway therefore remains obscure. Ipsilateral retinotectal projections have not been previously described in land vertebrates other than mammals. Whether their presence is correlated with nocturnal visual habits or is generalized among type I lizards remains to be determined. The pattern of retinal projections has been studied in too few representatives of non‐mammalian land vertebrates to presently permit conclusions regarding the origin of non‐decussating pathways.
A stereotaxic atlas and technique for forebrain nuclei of the goldfish, Carassius auratus
Authors: Peter R. E. , Gill V. E.
Published: January 2005

A stereotaxic apparatus and technique for electrode placement in forebrain nuclei of the goldfish is described. An atlas of forebrain nuclei is given. Some new nuclear regions are described and the nomenclature of several nuclei is discussed.
The ventral spinothalamic tract and other ascending systems of the ventral funiculus of the spinal cord
Authors: Kerr Frederick W. L.
Published: January 2005

The ascending degeneration resulting from experimental lesions of the ventral funiculus of the spinal cord of Macaca mulatta has been studied using the Nauta technique and its variants.

The ventral spinothalamic tract is shown to be independent entity with respect to the lateral spinothalamic tract; its fibers are widely distributed in the ventral funiculus and it establishes connections with the brain stem and thalamus which are analogous but not identical to those of the latter. Its role in the relay of nociceptive input is discussed in view of the similarity in hodology of the two systems and it is proposed that it may be responsible for the failure of anterolateral cordotomy to control pain on a long term basis. Other ascending systems in the ventral funiculus include the spino‐olivery and spino‐reticular tracts, as well as minor connections to the N. of Edinger‐Westphal, the red nucleus and the superior colliculus. The projections from the ventral quadrant of the spinal cord to the brain stem are almost entirely ipsilateral until the rostral mesencephalon is reached, at which level the N. of Darkschewitz receives both ipsilateral and crossed input; the magnocellular nuclues of the medial geniculate body receives a small contribution which is mainly ipsilateral. In the thalamus the VPL receives predominantly ipsilateral projections while the input to the paralaminar nuclei is only slightly less pronounced contralaterally than ipsilaterally.
The efferent connections of the suprachiasmatic nucleus of the hypothalamus
Authors: Swanson L. W. , Cowan W. M.
Published: January 2005

The efferent connections of the suprachiasmatic nucleus of the hypothalamus have been studied in the rat by the injection of 3H‐proline into the nucleus and the surrounding regions of the rostral hypothalamus, and by the injection of the enzyme marker, horseradish peroxidase, into the region of the ventromedial hypothalamic nucleus. After an injection of 3H‐proline confined to the ventral portion of the suprachiasmatic nucleus, transported label can be followed, in the autoradiographs, dorsally and caudally in the periventricular area as far as the caudal end of the ventromedial nucleus, into the triangular area between this nucleus and the arcuate nucleus, and along the ventral aspect of the tuberal region, just lateral to the ventromedial nucleus. A small number of silver grains are also seen over the internal lamina of the median eminence. No label can be followed rostrally or immediately lateral to the nucleus. Comparable injections into adjoining regions of the hypothalamus (especially the anterior hypothalamic area, the medial preoptic area, and the retrochiasmatic region) show transported label over the same regions, but with a somewhat different pattern of grain distribution; in addition, the anterior hypothalamic area shows an extensive projection through the medial forebrain bundle to the mammillary and supramammillary nuclei, the midbrain tegmentum, and certain of the midline thalamic nuclei. Although it is difficult in our autoradiographs to distinguish between the course of the efferent fibers from the suprachiasmatic nucleus and the zones in which they terminate, our evidence favors a termination among the cells of the periventricular area, and upon dendrites of the cells in the ventromedial, dorsomedial and arcuate nuclei, which extend beyond the limits of the nuclei into the periventricular area and to the area beneath the ventromedial nucleus.
Atlas of estrogen‐concentrating cells in the central nervous system of the squirrel monkey
Authors: Keefer Donald A. , Stumpf Walter E.
Published: January 2005

Estrogen is concentrated within cellular nuclei in discrete regions of the monkey brain 30 and 60 minutes following intravenous injection of [3] estradiol. Chromatographic data is provided to suggest that most of the localized estrogen is in the form of estradiol with lesser amounts of estrone and estriol. Three “major” areas of estrogen accumulation include: (1) preopticostrial accumulation: n. preopticus medialis — n. interstitialis striae terminalis, (2) basal hypothalamic accumulation: n. infundibularis — n. ventromedialis — n. premammillaris ventralis, and (3) the amygdaloid accumulation. Several “minor” areas of estrogen accumulation include the tuberculum olfactorium, insulae Calleja, n. triangularis septi, a. hypothalamica anterior, n. anterior hypothalami, n. paraventricularis, n. supraopticus, n. periventricularis and the substantia grisea centralis. The neocortex, rhombencephalon and spinal cord are essentially unlabeled. The major areas of accumulation are similar in several other mammalian and avian species while these, and some minor areas of accumulation, have been shown in neuroanatomical studies to be interconnected by several pathways, especially the stria terminalis. Lesion, implant, stimulation, recording and morphometric studies, in several species, support the concept that this arrangement provides a neuroanatomical substrate which would allow the integration of the various facets of the neuroendocrine reproductive response.
Neural intersegmental connection in the spinal root and ganglion region of the rat
Authors: Jacob M. , Weddell G.
Published: January 2005

A study has been made of the macroscopic, microscopic and electron‐microscopical appearance of intersegmental neural connections in the rat. Macroscopically, spinal roots and ganglia of adjacent segments were frequently observed to be linked by discrete, slender strands, mainly in the lumbosacral region where the roots are long. When examined under the light microscope, even the smallest was found to contain as many as 72 myelinated fibres with a range of diameters between 1.5–14 μm. They were commonly accompanied by blood vessels. Connections, when present, contributed to as much as 6–28% of the total number of myelinated axons in dorsal roots.

Under the electron microscope, links between dorsal roots, or between dorsal roots and adjacent ganglia, contained unmyelinated fibres comparable in numbers to those found in the dorsal roots themselves. In links between ventral roots and ganglia the numbers of unmyelinated fibres proportionally exceeded those found in ventral roots.

The presence of these connections may account for the reported finding of undamaged nerve fibres in the dorsal roots after dorsal root sectioning or ganglionectomy and in the ventral roots after ventral root sectioning.
The distribution of the olfactory tracts in the bullhead catfish, Lctalurus nebulosus
Authors: Finger Thomas E.
Published: January 2005

Using degeneration staining methods, central projections of the olfactory tracts in the bullhead catfish, Ictalurus nebulosus were studied. Separate lesions were made of the lateral and medial olfactory tracts in an attempt to separate their zones of projection. Three major terminal fields were found: lateral, medial and central‐posterior complex. Two additional minor projections were seen: interbulbar and hypothalamic.

The lateral division of the olfactory tract terminates in lateral, central and hypothalamic terminal fields. The medial tract projects to lateral, medial, posterior and hypothalamic fields. All terminal fields were found bilaterally; the lateral tract partly crossing in both the anterior and habenular commissures and the medial tract in only the anterior commissure. A small interbulbar commissure was also found to contain medial tract fibers.

Evidence is given to show that the anterior olfactory nucleus, if present in catfish, may be located within the olfactory bulb itself. Similarities between mammalian and teleost olfactory systems are also discussed.
Visual projections to the optic tecta in Xenopus after partial extirpation of the embryonic eye
Authors: Berman Nancy , Hunt R. K.
Published: January 2005

The temporal, nasal or dorsal half (40–60%) of the eye primordium was excised in Xenopus frog embryos stage 25/26 (optic vesicle), 31/32 (optic cup) or 38 ± 1 (early larval eye). The residual nasal (NF) or temporal (TF) or ventral (VF) fragment gradually rounded‐up to form a grossly normal eye of normal or reduced size. Electrophysiologic analysis of the visuotectal projection after metamorphosis showed that (independent of stage of surgery and final eye size) most eyes of each type generated normal retinotectal maps (orderly and continuous retinotopic projection across the entire tectum). A minority of NF eyes generated double‐nasal compound maps, in which nasal and temporal halves of the adult retina projected as mirror images (of the nasal pattern) over the whole tectum. A minority of TF eyes generated double‐temporal compound maps, while a minority of VF eyes generated double‐ventral compound maps. Respectively, these compound maps simulated those generated by NN, TT or VV “compound‐eyes” prepared by fusing two nasal half eyes, or two temporal half eyes, or two ventral half eyes. The incidence of double‐maps was lowest in TF eyes at all stages, and after stage 25/26 surgery in all eye types. Lure tests and post‐synaptic recording confirmed that these eyes formed functional retinotectal synapses, and that the (presynaptic) map accurately mirrored the connectivity pattern. The results are considered in terms of (1) the patterning of locus specificities in the retinal ganglion cell population, (2) embryonic “regulation” and “reduplication” in non‐neural systems, and (3) alternative mechanisms by which partial extirpation might modify the deployment or expression of ganglion cell locus specificities to produce the retinotectal connectivity patterns we observed.
The visual connections of the adult flatfish, Achirus lineatus
Authors: Gulley R. L. , Cochran M. , Ebbesson S. O. E.
Published: January 2005

Metamorphosis in the flatfish is characterized by the migration of one eye around the dorsal surface of the head to a position adjacent to the other eye on the new top side of the animal. The visual connections of the adult flatfish, Achirus lineatus, were examined. Either the migrating or non‐migrating eye was removed and the animal allowed to survive for one to three weeks. Alternate sections of the brain were stained by a modification of the Fink‐Heimer technique, or with cresyl violet. The diencephalc visual connections of the flatfish were similar to those of other teleosts with contralateral projections to the nuclei corticalis, dorsomedialis thalmi, pretectalis, and the corpus geniculatum laterale. The distribution of the retinal efferents to the optic tectum is unique in the flatfish. In the medial one‐third of the tectum, terminal degeneration was found in three bands in the stratum opticum (SO) and the stratum griseum et fibrosum superficiale (sgfs). In the middle part of the tectum, two bands of degeneration remained over the sgfs. The lateral part of the tectum has only a very small amount of degeneration distributed randomly in scattered clusters over the deep SO and superficial sgfs. The Nissl preparations also reflected the differences between the medial and lateral parts of the tectum. Distinct layer was lacking in the medial tectum with a conspicuously absent large cell layer in the stratum griseum centrale (sgc), In contrast, the lateral tectum had a typical tectal stratification. Most notable were the large neurons of the sgc.
Developmental changes in olfactory bulb projections revealed by degeneration argyrophilia
Authors: Leonard Christiana M.
Published: January 2005

The maturation of the main and accessory olfactory bulb projections to the ventral forebrain of the golden hamster has been traced by using the Fink‐Heimer silver technique to stain degenerating axons and terminal arborizations after bulbectomy at different ages between birth and 33 days. In the youngest pups, long‐lasting degeneration argyrophilia (LLDA) is found in two regions of prepiriform cortex: at the level of the rostral tubercle and rostral amygdala. By five days of age the caudal region exhibiting a long‐lasting degeneration reaction extends from the middle of the olfactory tubercle, to the middle of the amygdala. The olfactory tubercle, medial and cortical amygdala and entorhinal cortex subsequently develop substantial LLDA at ages varying between 9 and 13 days.

In a previous study (Leonard, '74b) the onset of LLDA in optic tract terminals in the superior colliculus was found to coincide with the age of eye opening and the onset of a stage of rapid synapse formation. Since different olfactory responses appear at different times during the golden hamster pup's first two weeks of postnatal life, it seems possible that the onset of LLDA in different regions of the olfactory projection at different ages may be related to the onset of different specific olfactory functions.
The projections of cells in different layers of the cat's visual cortex
Authors: Gilbert C. D. , Kelly J. P.
Published: January 2005

The projection of cells in different layers of several cortical visual areas in the cat were studied using the method of retrograde transport of horseradish peroxidase. Injections of the enzyme were made through a recording micropipette, making it possible to localize the injection site by physiological criteria. We found that layer VI cells projected to the lateral geniculate nucleus, while a distinct population of cells in layer V projected to the superior colliculus. Cells in layers II and III were the major sources of ipsilateral cortico‐cortical connections. This pattern of projection was consistent from one visual area to another. Pyramidal cells appeared to be the source of cortico‐geniculate, cortico‐collicular and cortico‐cortical projections. The proportion of cells within a layer that terminated in a given site varied from layer to layer: apparently all of the large pyramids in layer V had terminals in the superior colliculus, about half of the pyramids in layer VI had terminals in the lateral geniculate nucleus, while only a small proportion of the pyramids in layers II and III had terminals in any single cortical area. The results indicated a remarkable specificity in the projections of the cortical layers.

The cortical connections of the different cell types in layers A and A1 of the lateral geniculate nucleus were also examined: the cells that projected to area 17 were much more numerous and were on the average smaller than those that projected to area 18. Projections to the cortex were also found from the pulvinar, the medial interlaminar nucleus and the posterior nucleus. Direct connections were observed to the lateral geniculate nucleus from several midbrain reticular nuclei. Finally, projections were found to the superior colliculus from the zona incerta, the reticular nucleus of the thalamus and the ventral lateral geniculate nucleus.
Axonal projections and connections of the principal sensory trigeminal nucleus in the monkey
Authors: Smith Ronald L.
Published: January 2005

To date, anatomical studies of ascending principal sensory trigeminal nuclear (PrV) axons in the monkey have been restricted to few incomplete investigations utilizing the Marchi method. In the present study total or partial unilateral stereotaxic lesions of PrV were made in cebus and rhesus monkeys and analyzed with the aid of a variety of Nauta silver impregnation techniques applied to frozen sections.

Analysis of the fiber degeneration emanating from PrV lesions indicates that PrV fibers from an ascending system composed of two distinct components. Most PrV axons project ventromedially from PrV through the ventral pontine tegmentum and gradually decussate across the midline in the mesencephalic tegmentum up to the level of the caudal pole of nucleus interpeduncularis. These decussated fibers form the trigeminal lemniscus, which courses dorsomedial to the medial lemniscus during its ascent into the diencephalon. A few whorls of preterminal fiber degeneration separating from the trigeminal lemniscus first appear in the magnocellular area of the thalamus medial to the medial geniculate body. The lemniscal PrV axons terminate densely throughout most, but not all, of the magnocellular part of nucleus ventralis posteromedialis (VPM) contralateral to the side of their origin. Some collateral‐like fibers from the trigeminal lemniscus also were observed ending in the ventral segment of the zona incerta. Other axons, arising chiefly from the dorsal one‐third of PrV, form a smaller ipsilateral trigeminothalamic projection. These fibers all remain on the side of their origin and terminate consistently in a discrete dorsomedial paralaminar portion of VPM that does not receive lemniscal PrV connections.

A commissural fiber system at the pontine level connects parvicellular reticular cells with their counterparts and the motor trigeminal nucleus of the opposite side. These interconnections appear to provide an anatomical link for the integration of bilateral trigeminal sensory information and motor function.
Functional role of efferents to the avian retina. II. Effects of reversible cooling of the isthmo‐optic nucleus
Authors: Pearlman Alan L. , Hughes Charles P.
Published: January 2005

Efferents to the retina in the bird arise in the isthmo‐optic nucleus of the caudal midbrain, and terminate on amacrine cells in the retina. The functional role of these efferents was studied by determining the receptive field properties of 107 optic tract fibers in the lightly anesthetized adult pigeon, and quantitating their responses to specific moving stimuli. While the recording from these fibers continued, the isthmo‐optic nucleus was cooled by a thermoelectric cooling probe, and the response properties of the cells redetermined. Recording was maintained in half of the units long enough to observe recovery from cooling, and in several units the entire procedure was repeated. In 77 of the 107 units, responsiveness to all stimuli was decreased by removing efferent influences, whereas specific receptive field properties such as motion sensitivity or directionality were not altered. All of the major receptive field types were affected in a similar fashion, irrespective of their position in the visual field. Responses to stimuli that did not involve the antagonistic surround were similarly affected by removal of the efferents, as were units with both weak and strong antagonistic surrounds.

Efferents exert their influence on retinal ganglion cells by way of the amacrine cells on which they terminate. Data available on amacrines in Necturus indicates that they are inhibitory to ganglion cells. If amacrines have a similar role in the pigeon, then it may be stated that decreased activity in the centrifugal fibers leads to enhanced inhibition throughout the receptive fields of ganglion cells, and increased activity in the efferents produces disinhibition.
Increases in collateral axonal growth rostral to a thoracic hemisection in neonatal and weanling rat
Authors: Prendergast Jocelyn , Stelzner Dennis J.
Published: January 2005

The spinal cords of newborn and weanling rats were hemisected at the mid‐thoracic level. Control studies revealed that Fink‐Heimer positive debris was absent in the gray matter at three months postoperative. The remaining animals were given a second lesion, a high cervical spinal hemisection, at five to seven months after the original thoracic hemisection. The pattern of degeneration rostral to the thoracic lesion was compared with similar regions of the spinal cord from animals receiving only a cervical hemisection at the adult stage.

In neither experimental group of doubly hemisected rats was there any degeneration observed below the thoracic lesion site, even though no glial or connective tissue scar had formed in animals originally operated at birth. Thus no regeneration had occurred. At least one segment above the initial hemisection: 1. the majority of degenerating axons were localized toward the lateral edge of the spinal cord, especially in the doubly lesioned neonatal group; 2. the area of ipsilateral white matter was reduced more in the neonatal than the weanling operates; 3. there was an upward shift in axonal diameter of ipsilateral fibers in both the region of the rubrospinal tract and the ventrolateral portion of the lateral funiculus of the doubly hemisected rats when compared with the cervically lesioned controls; 4. a significantly greater amount of degeneration was present in lamina VII of Rexed in both the neonatal and weanling experimental operates (p < 0.05 weanling; p < 0.001 neonate); 5. no mean difference in area was seen between the ipsilateral and contralateral gray matter in any group for the segments of the spinal cord in which the judgements and measurements were taken.

These data suggest that there has been sprouting of axons from descending nerve tracts rostral to the thoracic lesion in both the neonatal and weanling experimental groups. The question remains whether the sprouting of descending nerve tracts is from collaterals of axons which normally project rostral to the thoracic hemisection and are not cut by the thoracic lesion (collateral sprouting) or from collaterals of lesioned axons (regenerative sprouting). Present evidence favors collateral sprouting, especially in the neonatal operate where much retrograde cell death appears to have taken place.
Postnatal maturation of rat Purkinje cells cultivated in the absence of two afferent systems: An ultrastructural study
Authors: Privat A. , Drian M. J.
Published: January 2005

Organized cultures of newborn rat cerebellum were established in Maximow chambers in order to study the maturation of Purkinje cells in absence of afferent systems. In the first model, standard cultures were devoid of extracerebellar afferents mossy and climbing fibers. Despite this absence, somatic spines appeared upon Purkinje cells during the first week in vitro and maturation proceeded normally except for the almost absence of spiny branchlets. Large dendritic trunks were studded with numerous spines, some of which were naked, a few bearing isolated post‐synaptic densities and others occupied by boutons of parallel fibers. Stellate and basket axons made synapses upon the smooth portions of dendrites and soma.

In a second model, the cultures were fed the antimitotic drug methylazoxymethanol (MAM) to prevent multiplication of granule cell precursors. Despite the absence of climbing and parallel fibers, the elongation of Purkinje dendrites was not prevented, but again the dendritic arbor consisted of large trunks studded with spines; somatic as well as dendritic spines were contacted by large boutons identified as Purkinje recurrent collaterals (PRC). It is concluded that the Purkinje cell possesses a large autonomy from afferent systems as to the growth of soma and dendrites.

Conversely, the geometry of the dendrite and especially the spiny branchlets depend on the presence of both climbing and parallel fibers. One may conclude from the above experiments that specificity of synaptic contacts is maintained as long as postsynaptic sites are not devoid of their normal afferents. Heterologous synapses are formed when postsynaptic sites are present, their normal afferents absent and aberrant ones increasing by collateral sprouting. Such is probably the case in the second model of this study.
Glial changes in the progress of a chemical lesion. An electron microscopic study
Authors: Lemkey‐Johnston N. , Butler V. , Reynolds W. A.
Published: January 2005

The response of non‐neuronal cells in the brain to monosodium glutamate (MSG) was studied in the neonatal mouse brain. Neurons rapidly degenerate in this chemically‐induced lesion, and the glia reflect and respond to their early pyknosis and death. Astrocytic glia exhibit the most profound responses in the form of degenerative nuclear and cytoplasmic changes within 15 to 20 minutes after ingestion of MSG. After 6 to 12 hours, a large glial cell population, containing neuronal and synaptic debris, can be seen. Recovery of severely damaged astrocytes is unlikely. Further, evidence of multiplication of uninjured cells to supply this observed repopulation was found.

Microglia start to engulf debris at 6 to 12 hours and continue this process through at least 48 hours. From 3 to 48 hours, a third cell type, tentatively identified as a Gitter cell, is prominently involved in phagocytosis of neuronal elements. Nuclei of these cells enlarge and their perikarya become vastly expanded in a fashion typical of Gitter cells. These cells appear to represent the transformed microglia.

Phagocytosis following a chemical lesion induced by glutamic acid, a neurotransmitter substance, is exceedingly rapid in comparison to that elicited by other types of lesions. Further, endogenous glial cells cope with the cellular debris; no participation in this process by hematogenous cells was observed.
The basilar pontine gray in the adult monkey (Macaca mulatta): A Golgi Study
Authors: Cooper Margaret H. , Fox Clement A.
Published: January 2005

In Golgi preparations of the adult monkey(Macaca mulatta) two types of neurons are distinguished in the pontine gray: (1) larger neurons which impregnate most frequently and(2) smaller neurons which impregnate rarely. The former are judged to be projection neurons with myelinated axons because only the initial segments of their axons impregnate, while the latter are judged to be intrinsic neurons since they appear to participate only in the local circuitry of the pontine gray.

The projection neurons show a variety of sizes and shapes and are the equivalent of the large, medium and small neurons that Ramón y Cajal ('09) illustrated in the pons of the 5‐day‐old infant. Their cell bodies are rounded, polygonal, triangular, egg‐, pear‐, and spindle‐shaped. Some have somatic spines. Usually four to seven dendrites issue from the cell body and as they branch they attenuate. The dendrites have knobby, nodular protuberances which give them a gnarled appearance. Also the dendrites have a few scattered spines. In most instances the dendrites have a wavy recurring pattern. Neurons pressed against the corticospinal, corticopontine fiber bundles frequently have elongated cell bodies and the dendrites sprouting from them form tight, brush‐like arrays.

The intrinsic neurons have small ellipsoid or pear‐shaped cell bodies and two to three long dendrites, which do not taper. In some impregnations short axons issuing from the cell body were found and in other impregnations several widely separated, short axon‐like processes were found on dendrites. A striking feature of the intrinsic neurons is the presence of stalked dendritic appendages bearing one or more bulbous bodies, 1 to 3 microns in diameter. The intrinsic neurons in no way resemble the hairy or mossy cells with short axis cylinders that Ramón y Cajal ('09) described in the pons of the 5‐day‐old infant. The latter were not found in the present material.
Areal differences in the laminar distribution of thalamic afferents in cortical fields of the insular, parietal and temporal regions of primates
Authors: Jones E. G. , Burton H.
Published: January 2005

A cytoarchitectonic parcellation has been made of the cortex of the insula and of the adjoining parts of the temporal and parietal lobes in rhesus and squirrel monkeys. In conjunction with this, the intracortical distribution of the thalamo‐cortical fibers has been studied by the autoradiographic tracing technique.

There is a systematic change in the density, laminar distribution and general character of the intracortical thalamic afferent plexus which seems to follow, in particular, the progressive differentiation of cortical layering that occurs in moving from insular through granular to homotypical cortex. In the dysgranular and granular insular areas in which cortical lamination is indistinct, the thalamic plexus as demonstrated autoradiographically is sparse and extends through much of layers III and IV. In the granular cortex (areas 3b and AI), the thalamic plexus is densest and coarsest; it fills all of layers IV and IIIB and extends into layer IIIA. In the “second” and “third” sensory areas, such as the second somatic sensory and many of the auditory fields, the density of the plexus and its coarseness diminish slightly and the deeper half of layer IV becomes free of terminals. In the homotypical cortex, the plexus becomes sparser, finer and strictly confined to layer IIIB. In many areas there are additional indications of thalamic terminations in deeper layers. Where layers V and VI are not divided into sublaminae (e.g., in areas 3b and AI) there is labeling of the superficial half of layer VI. Where layers V and VI become subdivided in the homotypical cortex, the labeling is confined to layer VB. Terminations in layer I of the cortex of the auditory and adjacent fields were only observed in cases in which the magnocellular nucleus of the medial geniculate body was involved by the injection of isotope.

The boundaries of the cortical projection fields of individual thalamic nuclei, as determined autoradiographically, are remarkably sharp and invariably coincide with a sharp architectonic boundary or with a zone of maximal cytoarchitectonic change. Zones of apparent architectonic transition never showed overlap of thalamic afferents emanating from more than one nucleus.

These results raise for discussion the significance of architectonic structure in relation to cortical connectivity and have a bearing upon those studies that have attempted to relate the terminals of thalamic afferents to particular classes of cortical neuron.
The posterior thalamic region and its cortical projection in new world and old world monkeys
Authors: Burton H. , Jones E. G.
Published: January 2005

The posterior nuclear complex of the thalamus in rhesus, pigtailed and squirrel monkeys consists of the combined suprageniculate‐limitans nucleus and an ill defined region of heterogeneous cell types extending anteriorly from the dorsal lobe of the medial geniculate body towards the posterior pole of the ventral nuclear complex. This region is referred to as the posterior nucleus.

The cortical projections of each of these nuclei, together with those of the adjacent ventral, pulvinar and medial geniculate complexes, have been studied by means of the autoradiographic tracing technique. The suprageniculate‐limitans nucleus, the main input to which is the superior colliculus, projects upon the granular insular area of the cortex. The medial portion of the posterior nucleus projects to the retroinsular field lying posterior to the second somatic sensory area. There is clinical and electrophysiological evidence to suggest that the retroinsular area may form part of a central pain pathway. The lateral portion of the posterior nucleus which is closely related to certain elements of the medial geniculate complex, projects to the postaditory cortical field. The ventroposterioinferior nucleus, which may be involved in vestibular function, projects to the dysgranular insular field.

The principal medial geniculate nucleus can be subdivided into a ventral division that projects to field AI of the auditory cortex and a dorsal division that merges with the posterior nucleus; it is further subdivided into an anterodorsal component that projects to two fields on the superior temporal gyrus, together with a posterodorsal component in which separate cell populations project to areas lying anterior and medial to AI. The magnocellular medial geniculate nucleus, sometimes considered a part of the posterior complex, appears to project diffusely to layer I of all the auditory fields.

The Auditory fields are bounded on three sides by the projection field of the medial nucleus of the pulvinar which also extends into the upper end of the lateral sulcus to bound the fields receiving fibers from the posterior nucleus. The topography of the areas receiving fibers from the posterior, medial geniculate and pulvinar complexes, taken in conjunction with the rotation of the primate temporal lobe, permits all of these fields to be compared with similar, better known areas in the cat brain.
Light and electron microscopy of the ground squirrel retina: Functional considerations
Authors: West Roger W.
Published: January 2005

Light and electron microscopy of Golgi‐impregnated ground squirrel retinas have revealed a range of morphological subtypes of bipolar, amacrine, and ganglion cells. There are at least seven subtypes of bipolar cells. Those subtypes in which the somata were high (sclerad) in the inner nuclear layer (3 subtypes) had axon terminals low (vitread) in the inner plexiform layer, and those with somata low in the inner nuclear layer (4 subtypes) had axon terminals high in the inner plexiform layer. The bipolar subtypes with high axon terminals made flat contacts with receptor cells, whereas all but one of the bipolar subtypes with low axon terminals made ribbon‐related contacts with receptor cells. There are at least five subtypes of amacrine cells. The two subtypes which the Golgi method revealed most frequently were a broad‐field, unistratified neuron with a dendritic spread in excess of 1,000 m̈m and a narrow‐field, diffuse neuron with a dendritic spread of about 30 m̈m. The broad‐field, unistratified cell had the lowest proportion of amacrine vs. bipolar cell synaptic input of the amacrine subtypes (43%), whereas the narrow‐field, diffuse cell had one of the greatest proportions of amacrine cell input (96%). There are at least 15 subtypes of ganglion cells. The proportion of synaptic inputs to these cells ranged from 21% to 100% amacrine cell synapses. An attempt has been made to relate this new knowledge of retinal circuitry to the physiological output of the ganglion cells.