bluuebunny/crossref_metadata_2025 huggingface dataset:
Olfactory structures of the forebrain in the reeler mutant mouse
Authors: Caviness V. S. , Sidman R. L.
Published: December 2004

Prior studies in the reeler mutant mouse have drawn attention to cytoarchitectonic anomalies in the neocortex and hippocampus of the forebrain and in the cerebellar cortex. In the present study cresyl violet and Loyez stained serial sections were used for light microscopic analysis of the olfactory structures in the forebrain of the mutant. The olfactory bulb and accessory bulb, both targets of afferents form the peripheral nervous system, are normal. By contrast, the laminate structures to which the olfactory bulbs project — the anterior olfactory nucleus, piriform cortex, olfactory tubercle, and cortical nucleus of the amygdaloid complex — are all abnormal in their cytoarchitecture. All of these structures share in common a segregation of cell populations according to size such that the larger cells lie in a deep position close to central fiber bundles. Small, polymorphic cells occupy a superficial zone, and there is no cellsparse external plexiform layer in the mutant. We adopt the view that the relationship of pyramidal cell to complex, external plexiform layer is the cardinal geometric principle defining a normal cortex, and suggest that derangement of this relationship may be the common denominator in the reeler cortical phenotype. The developmental mechanism influenced by the reeler locus and leading to the fundamental cortical geometry in normal or mutant animals may reside in the early interaction of afferent fibers and pyramidal cells.
Afferent connections to the diencephalon in the marsupial phalanger and the question of sensory convergence in the “Posterior Group” of the thalamus
Authors: Rockel A. J. , Heath C. J. , Jones E. G.
Published: December 2004

The various afferent pathways terminating in the thalamus of the marsupial phalanger have been investigated with the Nauta techniques, with a view to determining the extent of overlap and convergence of these pathways. If this had proved to be extensive, it would have lent support to the views of some authors that, in primitive and generalized mammals, the relay nuclei are in the process of differentiating out of a single archetypical, multi‐modal nucleus.

However, the amount of overlap between the various afferent pathways in this animal is no greater than in the cat and monkey; in the case of the ventral nuclear complex, despite the presence of a common sensory and motor cortical representation, the overlap between the somatic sensory and cerebellar pathways is probaly less than in the higher mammals. The question, therefore, arises as to whether differentiation of certain thalamic nuclei may precede that of the cortical area with which they are connected.

The results furnish evidence for the homologies of the posterior group of thalamic nuclei in other mammals, but the limited amount of overlap of afferent pathways occurring in the posterior group is not necessarily indicative of its being the common precursor of all the sensory relay nuclei.
Postnatal development of the cerebellar cortex in the rat. III. Maturation of the components of the granular layer
Authors: Altman Joseph
Published: December 2004

The migration of granule cells and the maturation of the various elements of the granular layer were studied in the cerebellar cortex of rats aged 0, 3, 5, 7, 10, 12, 15, 21 and 30 days with histological, histochemical, autoradiographic and electron microscopic techniques. The bulk of the granule cells are formed during the second week, but due to the time required for their migration and the lag in the formation of dendrites, few glomerular synapses are formed with mossy fibers before the beginning of the third week and the process is still in progress at 30 days, long after the dissolution of the external germinal layer. The maturation of Golgi cells is a protracted process. Their axons synapse with granule cell dendrites as soon as the glomeruli begin to mature. Evidence was obtained that mossy fibers synapse with the dendrites of Golgi cells. Towards the end of the second week the Lugaro cells are formed and synapses appear on their somata during the third week. Among these synapses the recurrent collaterals of Purkinje cell axons were identified. The Lugaro cells may be the primary targets of the infra and supraganglionic plexuses formed by these collaterals. In conclusion it was suggested that there are three major, successive stages in the neurogenesis of the cerebellar cortex, the morphogenic, synaptogenic and gliogenic. However, in the large Purkinje cell the synaptic maturation of one region (the soma) may begin before the morphogenic and synaptogenic maturation of the entire cell (the dendrites) is completed.
Functional significance of the fibrous laminae in the ventrobasal complex of the thalamus of slow loris
Authors: Krishnamurti A. , Kanagasuntheram R. , Wong W. C.
Published: December 2004

Investigations on the thalamocortical relationships were carried out on nine slow lorises. The electrophysiological data obtained from our previous experiments on the somatotopic organization within the Sm I and Sm II cortical regions were utilized for the placement of selective cortical ablations. The thalamic regions exhibiting retrograde degenerative changes were reconstructed. The projection of fibres to the electrophysiologically defined Sm I cortex is largely confined to the ventrobasal complex of the thalamus. Moreover, this region of the thalamus in slow loris is subdivided into a lateral, an intermediate and a medial portion by two main fibrous septa. The medial septum is found between the pars medialis and pars lateralis of the ventrobasal complex separating the head representation from the forelimb representation while the lateral septum, situated within the pars lateralis delineates the forelimb representation from that of the hind limb. A correlation is found to exist between these fibrous septa and the limiting sulci found within the somatic‐sensory cortex separating functional subdivisions. Moreover, a group of cells lying ventromedial to the pars medialis showed degenerative changes in the material where Sm II cortical region was ablated indicating the projection from this group of cells of at least some fibres to the second somatic‐sensory cortex. Another interesting feature that emerged from the results of the present study is the possible connection of n. subparacentralis with the paleoclaustrum, and/or the overlying allocortex.
Spino‐bulbar, spino‐thalamic and medial lemniscal connections in the american opossum, Didelphis marsupialis virginiana
Authors: Hazlett James C. , Dom Richard , Martin George F.
Published: December 2004

Projections from the spinal cord and dorsal column nuclei to more rostral levels of the neuraxis were investigated in seventeen adult opossums by the Nauta‐Gygax and Fink‐Heimer techniques. In all cases with spinal cord lesions a greater number of degenerating fibers distributed to the medulla and pons than to the midbrain and diencephalon. Numerous degenerating fibers ended within the medial reticular formation of the medulla and caudal pons, and within the lateral reticular formation of the rostral pons and midbrain. Degenerating fibers were numerous in the reticular formation following cervical and thoracic lesions, but sparse in specimens with damage restricted to either the lumbar or sacral spinal cord. The dorsal column nuclei received afferent connections from the well known dorsal funicular pathway and, although to a much lesser extent, from the main ventrolateral spinal bundle. Although most of the latter fibers ended in the subnucleus dorsalis and spinal vestibular nucleus, some penetrated into the gracile and cuneate nuclei. Conspicuous terminal degeneration was present within the inferior olivary nucleus following cervical and thoracic lesions, but was lacking in cases of either caudal lumbar or sacral cord lesions. The location of terminal degeneration within the lateral reticular nucleus is dependent upon the level of the lesion in the spinal cord. Degenerating fibers ended within the lateral vestibular nucleus in all cases of spinal cord hemisection, and within the medial portion of the facial nucleus in cases with a lesion rostral to C‐4. After cervical and thoracic hemisections terminal fiber degeneration was present within the midbrain tegmentum, the periaqueductal gray, the intercollicular nucleus (Mehler,'69), the posterior thalamic nucleus, the ventrobasal nucleus, the parafascicular nuclei and the caudal nucleus ventralis lateralis. All thalamic nomenclature was taken from Oswaldo‐Cruz and Rocha‐Miranda, '68. In animals with more caudal lesions, no fiber degeneration was evident within the nucleus ventralis lateralis and so little within the ventrobasal nucleus that it was impossible to ascertain a somatotopic pattern of spinothalamic projections.

Lesions of the dorsal column nuclei caused terminal degeneration within the inferior olivary nucleus, the pars lateralis of the nucleus of the inferior colliculus, the zona incerta, the posterior thalamic nucleus, the caudal part of the ventral lateral thalamic nucleus and the ventrobasal nucleus of the thalamus. Diffuse connections with the reticular formation, periaqueductal gray, midbrain tegmentum and the parafascicular complex were also observed. The results from small lesions indicate that the input to the ventrobasal nucleus in the opossum is organized in the typical mammalian fashion.
Morphogenesis of the cerebellum of the frog tadpole during spontaneous metamorphosis
Authors: Gona Amos G.
Published: December 2004

The cerebellum of the frog tadpole remains in an immature state throughout the premetamorphic (growth) phase. An external granular layer is absent except for a few scattered cells. A well defined Purkinje cell zone is also lacking. Large cells, which presumably are the immature Purkinje cells, are found in the subventricular zone.

During the prometamorphic period (accelerated hind leg growth) an external granular layer, several cells thick, becomes established by a migration of cells from the base of the cerebellum. A second migration involving the movement of the external granule cells toward the ventricular region begins at this time. However, the most active period of this latter migration is at the end of the prometamorphic period and during the days following fore leg emergence, viz., metamorphic climax. Concomitantly, a well defined Purkinje cell stratum is established.
Autonomic neurons in the spinal cord of the rhesus monkey: A correlation of the findings of cytoarchitectonics and sympathectomy with fiber degeneration following dorsal rhizotomy
Authors: Petras J. M. , Cummings J. F.
Published: December 2004

Cytoarchitectonic study of cell groups in the zona intermedia of the spinal cord led to the identification of the following nuclei in the rhesus monkey: n. intermediolateralis thoracolumbalis pars principalis et funicularis (ILp, ILf); n. intercalatus spinalis (IC); n. intercalatus pars paraependymalis (ICpe); n. intermediomedialis (IM); n. intermediolateralis sacralis pars principalis et funicularis (ILSp, ILSf); n. intercalatus disseminata (ICd); and n. torsade. Unilateral thoracic or abdominal sympathectomy, or both, performed in a second group of macaques, resulted in massive numbers of chromatolytic preganglionic neurons in IC, ILp and ILf. In the third group of macaques, dorsal rhizotomy followed sympathectomy. Fiber degeneration in these cases was stained with the Nauta and Fink‐Heimer methods. Despite variations in survivaltime and staining methods, no evidence was found for dorsal root terminal connections with the somata or proximal dendritic stems of chromatolytic sympathetic or parasympathetic visceral motor neurons (IC, ILp, ILf, ILSp, ILSf) although the same cases contained terminal fibers in n. marginalis of Waldeyer, substantia gelatinosa of Rolando, n. proprius cornus dorsalis (Pd), Clarke's column, n. intermediomedialis (IM) and among axial and appendicular somatic motor neurons. The present anatomical data suggest that, within the spinal cord, visceral reflex pathways are polysynaptic. Neurons in two or more spinal cell groups, IM, Pd and Cb (central basilar area of the dorsal horn) perhaps act as intermediary cells connecting dorsal root visceral afferent fibers with visceral motor (preganglionic) neurons. The visceral reflex pathway thus described includes a four neuron chain: dorsal root cell; IM, or Pd neuron, or both; preganglionic neuron; and the postganglionic neuron of the sympathetic system in the paravertebral or collateral ganglia, or the parasympathetic postganglionic neuron lying more distally.

It was also found that many preganglionic neurons of the ILp, ILf and IC cell groups are as large as somatic motor neurons. Furthermore, the impression gained in this study is that visceral motor neurons appear in far greater numbers than somatic motor neurons.
Early neuron differentiation in the mouse olfactory bulb. II. Electron microscopy
Authors: Hinds James W.
Published: December 2004

Differentiating mitral cells were followed in serial section analysis of mouse embryos from day 12 of gestation (E12) to E14. Animals at E11 and E15 were also examined. Olfactory nerve axons reach the presumptive olfactory bulb at E12 and many penetrate deeply into the intermediate (mantle) layer at this time. The first identified young neurons (postmitotic neuroblasts) were also seen at E12. Many had a tangential orientation, and they occurred only in the region where olfactory nerve axons were present. Olfactory nerve axons (and also mitral cell axons formed later) are characterized by numerous longitudinallyoriented microtubules and an extensive system of transversely and longitudinallyorinted cisternae of smooth endoplasmic reticulum (SER). Near the growing tips of olfactory nerve axons, the microtubules disappear and the SER becomes more extensive and irregular.

The four stages of early mitral cell differentiation determined in the companion paper (Hinds, '72) were confirmed by electron microscopic analysis. In the earliest cells of the primitive radial stage few organelles occur in the perikaryon, but in later cells of this stage and in cells of the pre‐axonic tangential stage a Golgi complex and a pair of centrioles occurs on one side of the nucleus at the base of the largest tangential process, thus determining a cell polarity within the tangential plane. This initial polarity at E12 seems to be random and unrelated to the polarity attained when axon outgrowth occurs at E13 and E14, suggesting a re‐orientation prior to axon outgrowth. The growing tips of primitive tangential processes were studied and compared with those of growing primitive radial processes and growing axons.
Laminar and columnar distribution of geniculo‐cortical fibers in the macaque monkey
Authors: Hubel David H. , Wiesel Torsten N.
Published: December 2004

Single cell recordings in monkey striate cortex have shown differences in response properties from one cell layer to the next and have also shown that the IVth layer, which receives most of its input from the geniculate, is subdivided into a mosaic of regions, some connected to the left eye, others to the right. In the present study small lesions were made in single layers or pairs of layers in the lateral geniculate body, and the striate cortex was later examined with a Fink‐Heimer modification of the Nauta method. We hoped to correlate the laminar distribution of axon terminals in the cortex with functional differences between layers, and to demonstrate the IVth‐layer mosaic anatomically.

After lesions in either of the two most dorsal (parvocellular) layers, terminal degeneration was found mainly in layer IVc, with a second minor input to a narrow band in the upper part of IVa. A very few degenerating fibers ascended to layer I. In contrast, lesions in either of the two ventral (magnocellular) layers were followed by terminal degeneration confined, apparently, to IVb, or at times extending for a short distance into the upper part of IVc; no degeneration was seen in layer IVa or in layer I.

After a lesion confined to a single geniculate layer, a section through the corresponding region of striate cortex showed discrete areas or bands of degeneration in layer IV, usually 0.5–1.0 mm long, separated by interbands of about the same extent in which there was no terminal degeneration. When serial sections were reconstructed to obtain a face‐on view of the layer‐IV mosaic, it appeared as a series of regular, parallel, alternating degeneration‐rich and degeneration‐poor stripes. When a geniculate lesion involved both layer VI (the most dorsal, with input from the contralateral eye) and the part of layer V directly below (ipsilateral eye), the cortical degeneration, as expected, occupied a virtually continuous strip in layer IVc and the reconstructed face‐on view of this layer showed a large confluent region of degeneration.

In some of the reconstructions the cortical stripes seemed highly regular; in others there was a variable amount of cross connection between stripes. The stripes varied in width from 0.25 to 0.50 mm, and width did not seem to correlate with region of retinal representation.

It is concluded that the long narrow stripes of alternating left‐eye and right‐eye input to layer IV are an anatomical counterpart of the physiologically observed ocular‐dominance columns. Because of this segregation of inputs, cells of layer IV are almost invariably influenced by one eye only. A cell above or below layer IV will be dominated by the eye supplying the nearest IVth layer stripe, but will generally, though not always, receive a subsidiary input from the other eye, presumably by diagonal connections from the nearest stripes supplied by that eye.
Experimental Studies on hatching behavior in the Chick. III. The role of the midbrain and forebrain
Authors: Oppenheim Ronald W.
Published: December 2004

Various portions of the midbrain and forebrain of chick embryos were ablated by microsurgical techniques at early prefunctional stages of incubation (38–45 hours) in an attempt to assess the role of these parts of the nervous system in early embryonic motility and in later prehatching and hatching behavior.

Embryos with the entire telencephalon and anterior diencephalon removed (total FB) exhibited no behavioral defects until about 20 days of incubation, at which time they were unable to initiate the final climax stage of hatching, in which the embryo normally cracks the shell around the circumference and emerges or hatches. On the other hand, embryos with no diencephalic damage and with sparing of parts of the cerebral hemispheres, were able to initiate the final climax stage, and actually manage to hatch (partial FB).

Removal of only the dorsal part of the midbrain (primarily the primordia of the optic lobes) resulted in no behavioral deficits until after hatching. These embryos (partial MB) exhibited completely typical prehatching and hatching behavior. However, a complete gap in the midbrain region, separating the forebrain from the hindbrain, precluded all prehatching and hatching behavior. These embryos continued to exhibit behavior more characteristic of early (pre 16 day) embryonic stages and never managed to hatch.

The possibility was discussed that the basic coordinated motor pattern utilized during prehatching and hatching stages (Type III activity) is organized in the hind‐ or mid brain area, but that in order for the final climax stage of hatching to be initiated and maintained, facilitation (or a more direct influence) from either (or both) the anterior diencephalon, or the caudal and basal parts of the telencephalon is needed.
The number of Purkinje cells and inferior olivary neurones in the cat
Authors: Mlonyeni Maxwell
Published: December 2004

It is generally assumed that (i) all neurones of the inferior olive send their axons to the cerebellum; (ii) the fibers from the olive end as climbing fibers; (iii) one climbing fiber establishes extensive synaptic contact with one Purkinje cell. From this it has been inferred that there is one inferior olivary neurone per Purkinje cell. The number of neurones in both inferior olives from four cats have been counted in histologic sections. The totals obtained are 145380, 127270, 126920 and 121360, respectively. In two of the cats the Purkinje cells were counted. The ratios of inferior olivary neurones to Purkinje cells were found to be 1 : 10 and 1 : 11, respectively.
Time differences in the formation of the receptor types in the developing chick retina
Authors: Morris Valerie B.
Published: December 2004

The times at which the receptor types completed their final S phase was measured by injecting 3H‐thymidine at a series of incubation times and then rearing the embryos to hatching. Incorporation of 3H‐thymidine by the developing receptors was examined, subsequently, in EM autoradiographs of differentiated receptors whose type could be identified. The time at which each receptor type completed final S was estimated from the proportions unlabelled at each of the times at which 3H‐thymidine was injected. The incubation time at which 50% of the receptor type had completed final S was 134.2 hours for principal cones, 139.5 hours for rods, 145.6 hours for single cones and 153.5 hours for accessory cones. It is unlikely, from these estimates, that a principal cone, rod, single cone and an accessory cone, which constitute the repeating group in the retinal mosaic pattern in the periphery, are formed from one stem cell. Each receptor type in a repeating group is probably formed, in the final cell cycle, from a different precursor cell.
Postjunctional membrane specialization at cholinergic myoneural junctions in the leech
Authors: Rosenbluth Jack
Published: December 2004

Myoneural junctions are described in the body musculature of the leech. Although similar to cholinergic junctions elsewhere, these exhibit a distinctive postjunctional membrane specialization consisting of discrete, concave patches, occupying a small proportion of the total postjunctional area, at which both the inner and outer surfaces of the membrane appear to be coated. The outer coating consists of a hexagonal array of projections which arise from the outer dense lamina of the plasma membrane and extend into the junctional cleft. The projections are spaced at intervals of ∼ 150 Å and are thickened at their tips. The inner dense lamina of the membrane is coated by an amorphous cytoplasmic material. Details of this specialization show up well in specimens that have not been post‐osmicated but are stained (in sections) with permanganate and uranyl acetate. It is hypothesized that the morphologically specialized patches are composed of units containing the acetylcholine receptors.
Autoradiographic localization of hormone‐concentrating cells in the brain of the female rhesus monkey
Authors: Pfaff Donald W. , Gerlach John L. , McEwen Bruce S. , Ferin Michel , Carmel Peter , Zimmerman Earl A.
Published: December 2004

With autoradiographic procedures, cells which bind 3H‐estradiol were found in preoptic, hypothalamic and limbic structures in the brains of ovariectomized, adult female rhesus monkeys. Estrogen‐binding cells were seen in the medial preoptic area, medial anterior hypothalamus, ventromedial nucleus, and especially heavy labelling was seen throughout the extent of the arcuate (infundibular) nucleus of the hypothalamus. In limbic structures, cells in the bed nucleus of the stria terminalis and in the medial nucleus of the amygdala were well labelled. Systematic charting also revealed smaller numbers of estrogen‐concentrating cells in other specific hypothalamic and limbic locations. In the anterior pituitary, significant numbers of basophils and acidophils were found to bind estrogen. Pars intermedia and the posterior lobe were virtually unlabelled. In the uterus, heavily labelled cells were seen in the endometrial stroma and in the myometrium. These autoradiographic findings agree with results of parallel biochemical experiments.

In monkeys injected with 3H‐corticosterone, the most extensive high‐intensity binding found with autoradiography was in the hippocampus. Both pyramidal neurons and dentate gyrus granule cells were labelled. Biochemical experiments, also, showed highest cell nuclear accumulation of corticosterone in the hippocampus.

Findings with estradiol in the rhesus monkey extend to primates conclusions based on autoradiographic experiments with steroid sex hormones in a wide variety of vertebrates, including fish, amphibians, birds, and various mammalian species (Morrell et al., '75a). All of these vertebrate forms have sex hormone‐concentrating neurons, which are found in specific preoptic, hypothalamic and limbic structures. In the species studied, such hormone‐concentrating neurons appear to be involved in the hormonal control of behavioral and pituitary function.
The accessory optic system of the ferret
Authors: Thorpe Penelope A. , Herbert J.
Published: December 2004

The accessory optic system of the ferret has been studied both by silver degeneration staining and by autoradiography after intraocular 3H leucine injections. There is no anterior accessory optic tract but a posterior tract containing only crossed fibres leaves the brachium of the superior colliculus and ends in the two nuclei, the medial and lateral terminal nuclei, lying either side of the cerebral peduncle. Both suprachiasmatic nuclei receive retinal fibres visible only on autoradiographs; most fibres end in the contralateral nucleus. No other area in the hypothalamus appears to receive retinal fibres demonstrated by these methods.
A fine structural and E‐PTA study of photoreceptor synaptogenesis in the chick retina
Authors: McLaughlin Barbara J.
Published: December 2004

Photoreceptor synaptogenesis in the embryonic and hatchling chick retina was studied with conventional EM techniques and ethanolic phosphotungstic acid (E‐PTA). The photoreceptors line up between 11 and 13 embryonic days with their undifferentiated synaptic bases facing the outer plexiform layer (OPL). E‐PTA staining at 11 embryonic days does not reveal any paramembranous specializations of the receptors but numerous stained punctae adhaerentes are observed in the OPL. At 13 embryonic days neurites of presumed bipolar and horizontal neurons are aligned parallel to the bases of the receptors and cytoplasmic protrusions of the receptors project between some of these neurites to form dyad appositions. An osmiophilic undercoating, which is not E‐PTA positive at this time, is present on the cytoplasmic face of the receptor membrane in these apposition regions. Between 13 and 15 embryonic days the filopodial protrusions of the receptors continue to elongate further and become aligned with neurites in dyad and triad appositions. The osmiophilic undercoating now extends along the entire inner surface of the receptor pedicle protrusions and becomes E‐PTA positive. Between 15 and 17 embryonic days focal aggregations of osmiophilic and E‐PTA stained material appear along the membranes of the protrusions and there is some E‐PTA staining of the postsynaptic densities and intervening cleft material. Between 17 and 21 embryonic days mature ribbon synapses are observed on the surfaces of the conical‐shaped, receptor pedicles where the ribbons and their synaptic vesicles are associated with the dense aggregations (arciform densities), seen earlier as isolated focal aggregations, and the receptor undercoating is restricted to non‐synaptic regions. E‐PTA staining shows that ribbons are positively stained around their borders only and that they are contiguous with the intensely stained arciform densities. The cleft material and postsynaptic densities of some synapses first stain as V‐shaped junctions and later as Y‐shaped junctions. These observations suggest that ribbon synaptic junction formation begins with an alignment of pre‐ and postsynaptic membranes and the presence of the receptor presynaptic membrane undercoating, followed by the appearance of the presynaptic arciform densities and some staining of the cleft material and postsynaptic densities. These events are followed by the appearance of synaptic ribbons which are associated with the presynaptic arciform densities and by a further differentiation of the cleft material and postsynaptic densities.
Interhemispheric neocortical connections of the corpus callosum in the reeler mutant mouse: A study based on anterograde and retrograde methods
Authors: Caviness V. S. , Yorke C. H.
Published: December 2004

The tangential organization of the callosal system of interhemispheric connections, as judged by the distribution of axon terminals as well as by the distribution of cells of origin of callosal axons, is normal in the reeler mutant mouse. As in the normal animal connections between the two cerebral hemispheres are homotopic. In the reeler, as in the normal animal, medium‐sized pyramidal cells are, numerically speaking, the principal cells of origin of the callosal system. These lie superficially in the cortex of the normal animal but deep within the cortex of reeler. Callosal terminals are most densely concentrated at the cortical level of the small and medium‐sized pyramids in both reeler and normal animals. It is probable, therefore, that the same classes of neurons are interconnected by the callosal system in the normal and reeler mouse despite malposition of neurons in reeler. The pattern of intracortical distribution of terminals of callosal axons is evidently governed by the positions of their target cells.
Electron microscopic observations of nodes of ranvier in the external cuneate nucleus
Authors: Rosenstein Jeffrey M. , Leure‐duPree Alphonse E.
Published: December 2004

During the course of an investigation of the synaptic organization of the external cuneate nucleus (ECN) in the Sprague‐Dawley albino rat, the ultrastructural morphology of nodes of Ranvier in the neuropil has been studied.

The majority of nodes observed have the basic morphological features of conventional central nodes but there is individual variation with regard to length, surface area and cytoplasmic organelles. In addition, nodes with multiple myelinated branches are observed.

Some nodes of Ranvier were observed to form specialized synaptic boutons. Two types of nodal synaptic boutons were present; a simple type and a complex type. Simple nodal boutons were observed more frequently. These nodes usually synapse upon a single dendritic element; the portion of the node opposite the presynaptic area has a morphology similar to conventional nodes. Complex nodal boutons are of greater dimension than simple nodal boutons and are usually in contact with several neuronal elements. They may be presynaptic to dendritic shafts or spines and are occasionally observed to be postsynaptic to small axonic profiles, a synaptic relationship which, until this report, has not been demonstrated in the central nervous system (CNS).

The possible functional significance of these observations is discussed.
Effects of low‐level X‐irradiation on cat cerebella at different postnatal intervals. III. Changes in the morphology of interneurons in the molecular layer
Authors: Anderson William J. , Stromberg Melvin W.
Published: December 2004

The whole head of infant kittens was irradiated with fractionated doses of 150 R and 200 R at different postnatal intervals. Experimental age conditions consisted of a newborn, 1‐week, 2‐week, 3‐week, and a 4‐week age condition while the age of sacrifice remained constant at 70 days. Golgi analysis revealed that the interneurons found in the molecular layer of the newborn, 1‐week and 2‐week condition were basket cells. Stellate cells were found in increasing numbers in the 3‐week and 4‐week conditions. Basket cells were found to occupy the entire molecular layer in the newborn and 1‐week conditions resulting in an abnormal axonal plexus. The position of the basket cell soma was found to be in the same plane as its axonal projection. The branching point of the primary dendrite of Purkinje cells was found to correlate with the amount of molecular layer occupied by the abnormal basket cell plexus. Interneurons in the molecular layer were found to show different dendritic growth patterns dependent upon where their soma was located. Interneurons in the deep molecular layer showed only a decreased dendritic field, whereas interneurons in the middle and superficial molecular layer had an abnormal growth of dendrites into the deep molecular layer. A hypothesis is presented to account for the decreased dendritic arborization and the increased length of the primary dendrite before branching, the ectopic basket cell and their abnormally directed dendritic growth, and the difference in behavioral deficits between the newborn and the 1‐week conditions.
A quantitative study of retrograde neuronal changes in Clarke's column
Authors: Loewy Arthur D. , Schader Randolph E.
Published: December 2004

A quantitative study has been made of the retrograde neuronal changes that occur in the large neurons of Clarke's column in the L3 spinal segment, 100 days after dorsolateral column lesions at the medullary, C5, T1, T8, and L1 levels in a series of 10‐week‐old kittens. Cell counts, and nuclear and perikaryal areal measurements, have been made in thionin stained material. The results indicate that following L1 level lesions, there is about a 30% loss of Clarke neurons and the remaining neurons are reduced in size to about 75% of their normal cross‐sectional perikaryal area (as judged from the cells on the opposite side) and about 65% of their normal nuclear area. Lesions at the T8 and T1 level both cause about a 20% Clarke cell loss; but after the T8 lesions, there is about a 65% decrease in perikaryal area and a 55% decrease in nuclear area while the T1 lesions cause about a 55% decrease in perikaryal area and a 45% reduction in nuclear area. Lesions at the C5 level result in about a 15% cell loss, a 50% decrease in perikaryal area, and a 40% decrease in nuclear area. Medullary lesions produce about a 5% cell loss, a 50% decrease in perikaryal area, and a 40% decrease in nuclear area. In unoperated control preparations, the left‐right differences in the number of cells are less than 2% and the areal measurements are within 5% of each other.

The results of this study suggest that the severity of the retrograde neuronal reaction in Clarke's column is related to the proximity of the lesion to the cell body, but that this relationship is non‐linear. Several possible interpretations of these results are discussed.
Organization of auditory cortex in the owl monkey (Aotus trivirgatus)
Authors: Imig T. J. , Ruggero M. A. , Kitzes L. M. , Javel E. , Brugge J. F.
Published: December 2004

The region of cerebral cortex in the owl monkey that is responsive to acoustic stimulation is located on the dorsal and lateral surfaces of the rostral half of the superior temporal gyrus. Systematic microelectrode mapping of this area has revealed multiple frequency representations. The boundaries of these fields determined electrophysiologically correlate with the architectural bound aries apparent in Nissl stained material. On the basis of combined cytoarchitectonic and electrophysiological maps we have divided auditory cortex into five fields. Two of them, the primary field (AI) and the field rostral to it (R) are somewhat similar architectonically and constitute the central core of auditory cortex. Each of these two fields has a complete and orderly representation of the audible frequency spectrum within it. Surrounding these fields is a belt of cortex in which units are generally less responsive to acoustic stimulation and the frequency organization is more complex than in AI or R. Electrophysiological and cytoarchitectonic evidence suggest that this belt is composed of at least three and possibly four separate auditory fields.
Receptive field characteristics of neurons in a visual area of the rabbit temporal cortex
Authors: Chow Kao Liang , Douville Arthur , Mascetti Gian , Grobstein Paul
Published: December 2004

In a program of surveying the characteristics of visual receptive fields of neurons in rabbit brain, we have explored cortical sectors beyond the striate and occipital cortices and found cells in a part of the temporal lobe that were responsive to visual stimulation. Using evoked potential and unit‐cluster methods, this temporal visual areas was mapped to be roughly oval‐shaped, 3 mm × 2mm in size, and at about the level posterior to the apex region of auditory area 1. It is located ventral to and continuous with visual area 11, at about the caudal half of M. Rose's temporal cortices 1 and 2 (T1 and T2).

Only about two‐thirds of 96 units studied responded to some sort of moving light stimulation. These motion‐sensitive cells were divided into four groups. Cells in the first group (22) responded best to a large light spot or shadow sweeping quickly across the field. Cells in the second group (29) responded to slow moving, jerking spot. Nine cells responded to a narrow, dark bar thrusting into a lighted field. Four cells are “direction‐selective,” responding to light stimulus moving in one direction and showing either no response or decreased background discharges in the oppsite direction. In addition, three cells required unusual stimulus features. Of the 38 cells tested, nine of them were found to be binocularly driven. These receptive field characteristics are quite different from those described for other visual centers of the rabbit. The significance of these results together with data on the anatomical connections of this cortical area as reported in the following paper were discussed.
Neuroanatomical aspects of the gerbil inner ear: Light microscope observations
Authors: Chamberlain Steven C.
Published: December 2004

A specialization of the Mongolian gerbil inner ear allows easy access for electrophysiological recording from the auditory nerve and other structures of the internal auditory meatus. The round‐window membrane is recessed, creating a cavity connecting the bulla and the external wall of the modiolus. This cavity has been named the round‐window antrum. A small opening made in the dorsomedial wall of the round‐window antrum gives access directly to the modiolus and internal auditory meatus, with no other openings in the cranium required. This surgery is less drastic than that needed for similar access in most other mammals. The anatomy of the specialized region is presented from studied with the light microscope. Emphasis is placed on the relationship between external features of the wall of the round‐window antrum and the internal anatomy of the modiolus and internal auditory meatus. In addition, these studies reveal that cell bodies of the acoustic‐nerve nucleus are located in the auditory nerve, central to the glial dome. About 22 ± 8 cells are found in an auditory nerve. Their appearance with a Nissl stain is similar to cells found in rat, mouse, and man. The cell dendrites are preferentially oriented perpendicular to the longitudinal course of the auditorynerve fibers. The anatomy of the gerbil auditory system should allow direct electrophysiological recording from these cells.
Aging of the rat olfactory bulb: Growth and atrophy of constituent layers and changes in size and number of mitral cells
Authors: Hinds James W. , McNelly Nancy A.
Published: December 2004

A quantitative study of the rat olfactory bulb during aging was carried out by directly measuring or calculating the following parameters at 3, 12, 24, 27, and 30 months: the volume of the glomerular, external plexiform, and internal granular layers, a relative measure of the size of the olfactory nerve layer, the mean volume of mitral cell nuclei and perikarya, a relative measure of the mean volume of the mitral cell dendritic tree as well as the total length and mean crosssectional area of its constituent dendrites, and number of mitral cells. In addition, measurements of the size and number of mitral cells in the accessory olfactory bulb were performed. Data were analyzed with analysis of variance, multiple range tests for differences between means at the various ages, and simple, partial, and multiple product‐moment correlations.

From 3 to 24 months a linear increase of approximately 50% occurs in all layers of the olfactory bulb. During this time the mean perikaryal volume and dendritic volume of mitral cells increases, also in a linear fashion, approximately 100%. No significant change occurs in the number of mitral cells. From 24 to 30 months a significant decrease occurs in the volume of the layers. Although the total volume of mitral cell dendritic trees decreases slightly from 24 to 27 months, the volume of individual mitral cell dendritic treess, as well as perikaryal and nuclear size, increases sharply during this period, apparently in compensation for a sharp decrease in the number of mitral cells which occurs at this time. From 27 to 30 months no further decrease in mitral cell number occurs, but the size of mitral cell perikarya, and especially dendritic trees, decreases sharply.

The coordinated increase in olfactory bulb size from 3 to 24 months appears to be a continuation into adult life of earlier postnatal increases. The atrophy from 24 to 30 months appears not to be associated with peripheral rhinitis, since the glomerular and olfactory nerve layers do not show greater atrophy than the other layers, and atrophy also occurs in the accessory olfactory bulb, which is supplied by nerves from the vomeronasal organ, a structure not normally subject to rhinitis.
The central projections in the retina in Necturus maculosus
Authors: Caldwell John H. , Berman Nancy
Published: December 2004

The projections of the retina in Necturus maculosus were studied by injecting radioactive proline into one eye. Labeling was seen in both the contralateral and ipsilateral diencephalon and tectum. The contralateral fibers are divided into three major tracts: the marginal, axial, and basal. The ipsilateral fibers separate into a marginal and an axial optic tract.

The contralateral and ipsilateral axial optic tracts have a similar distribution. The contralateral and ipsilateral marginal optic tracts projecting to the diencephalon also have a similar distribution. However, in the tectum the ipsilateral marginal optic tract ends in the anterior third while the contralateral extends almost the entire length of the tectum. The retinotectal ipsilateral projection ends in clumps as has been described in other vertebrates. A direct ipsilateral retinotectal projection has not been described in any other amphibian.
Freeze‐fracture studies on the synapses in the organ of corti
Authors: Gulley R. L. , Reese T. S.
Published: December 2004

Receptoneural junctions and synapses in the organ of Corti of the chinchilla have been examined with the freeze‐fracture technique. The presynaptic membranes at the receptoneural junctions of inner and outer hair cells have many structural features in common with membranes found at chemical synapses outside the organ of Corti. However, the membranes of the postsynaptic afferent terminals are quite different depending on whether they are part of an inner or outer hair cell synapse. These differences in the distribution of intramembrane particles suggest that the transmitters, or transmitter actions, may be different at these two synapses. The distribution of particles in the postsynaptic membrane at efferent synapses with outer hair cell differs from that in the postsynaptic membrane at efferent synapses with afferent terminals or fibers, suggesting that transmitter actions at these locations could also differ.
Unmyelinated axons in thoracic ventral roots of the cat
Authors: Emery Dennis G. , Ito Haruhide , Coggeshall Richard E.
Published: December 2004

ABSTRACT This study shows that approximately 30% of the axons in the Tll and T12 ventral roots of the cat are unmyelinated. The unmyelinated axons fall into two categories. Slightly less than half are efferents from the spinal cord and slightly more than half arise from dorsal root ganglion cells. The efferent fibers are regarded as unmyelinated preganglionic sympathetics, the fibers of dorsal root ganglion origin are regarded as sensory. This organization of the T11‐T12 ventral roots, which are part of the sympathetic outflow, is similar to that of cat ventral roots S3 and Cal, which are part of the parasympathetic outflow, but different from cat ventral roots L7 and Sl, which are between the visceral outflows.
Bilateral ganglion cell branches in the normal rat: A demonstration with electrophysiological collision and cobalt tracing methods
Authors: Cunningham Timothy J. , Freeman John A.
Published: December 2004

The application of microelectrode recording and anatomical tracing methods to the subcortical optic projections of the normal rat shows that the uncrossed pathway from the retina of this mammal is substantially composed of branches of crossed axons. In the recording experiments, paired stimuli to the optic tracts produces an attenuated antidromic response in the optic nerve which is best explained by the collision of impulses which travel in branches of the same parent axon. Cobalt injection of one optic tract results in retrograde filling of axons in the entire contralateral optic nerve and filling of axons in restricted regions of the ipsilateral optic nerve. This procedure also results in the filling of axons in the opposite optic tract. The locations of the filled axons in the opposite tract correspond to the positions of crossed and uncrossed projections from the temporal retinae: ventrolateral and dorsomedial, respectively. The position of the temporal retinal projections in both optic tracts was determined by applying silver degeneration methods after small lesions of the retina.
The effect of superior colliculus lesions upon the visual fields of cats with cortical ablations
Authors: Sherman S. Murray
Published: December 2004

The visual fields of 18 cats were measured before and after various lesions. Preoperatively, all cats had identical fields. With both eyes open, they saw from 90° left to 90° right; with one eye, from 90° ipsilateral to 45° contralateral. Thus the field for nasal retina extends from 90° ipsilateral through to the midline; for temporal retina, from the midline through to 45° contralateral

In summary, postoperative testing led to two major conclusions. (1) Large occipito‐temporal cortical lesions produce a stable field blindness, but the blindness is alleviated by a transection of the commissure of th superior colliculus (or a unilateral collicular ablation). This transaction yields the same result whether it occurs in an operation before, during, or after the cortical lesion. These data confirm and extend the Sprague effect. (2) Cats made dependent upon retinotectal pathways due to cortical ablations responded much better to stimulatian of nasal retina than to stimulation of temporal retina. This presumably is related to the preponderance of nasal retina as a source of the retinotectal pathway. Since even smaller cortical lesions limited to areas 17, 18, and 19 produce this nasal/temporal retinal difference, it is concluded that integrity of the geniculocorticl pathways is necessary for good temporal retinal vision as determined by these methods.