bluuebunny/crossref_metadata_2025 huggingface dataset:
Visual discrimination following partial telencephalic ablations in nurse sharks (Ginglymostoma cirratum)
Authors: Graeber R. Curtis , Schroeder Dolores M. , Jane John A. , Ebbesson Sven O. E.
Published: January 2005

An instrumental conditioning task was used to examine the role of the nurse shark telencephalon in black‐white (BW) and horizontal‐vertical stripes (HV) discrimination performance. In the first experiment, subjects initially received either bilateral anterior telencephalic control lesions or bilateral posterior telencephalic lesions aimed at destroying the central telencephalic nuclei (CN), which are known to receive direct input from the thalamic visual area. Postoperatively, the sharks were trained first on BW and then on HV. Those with anterior lesions learned both tasks as rapidly as unoperated subjects. Those with posterior lesions exhibited visual discrimination deficits related to the amount of damage to the CN and its connecting pathway. Severe damage resulted in an inability to learn either task but caused no impairments in motivation or general learning ability.

In the second experiment, the sharks were first trained on BW and HV and then operated. Suction ablations were used to remove various portions of the CN. Sharks with 10% or less damage to the CN retained the preoperatively acquired discriminations Almost perfectly. Those with 11‐50% damage had to be retrained on both tasks. Almost total removal of the CN produced behavioral indications of blindness along with an inability to perform above the chance level on BW despite excellent retention of both discriminations over a 28‐day period before surgery. It appears, however, that such sharks can still detect light. These results implicate the central telencephalic nuclei in the control of visually guided behavior in sharks.
Golgi studies of the neurons in layer I of the dorsal horn of the medulla (trigeminal nucleus caudalis)
Authors: Gobel Stephen
Published: January 2005

Two kinds of pyramidal neuro ns and two kinds of multipolar neurons have been identified in layer I in the adult cat on the basis of thier dendritic morphology. The spiny pyramid emits an apical dendrite which beings dividing within 50 μm of the cell body and gives rise to an extensive dendritic arbor in which some second and third order branches extend for over 100 μm. The primary branches of the basal dendrites divide into secondary branches within 20 μm of the cell body. At each of these divisions, one daughter secondary branch will turn 180° and course in the direction of the apical dendrite. It then undergoes further branching and becomes intermingled in the apical dendritic arbor. These recurrent basal dendrites and the apical dendrites are charcterized by numerous long‐necked spines. The other secondary basal branch either courses at right angles to the apical dendrite or droops basally away from it. Many of these basal dendrites are not as robust and extensive as the other dendritic branches. They may end without further branching or when they do branch they tend to be thinner and shorter with some showing signs of stunting. Smooth pyramids differ from the spiny pyramids in several respects. Their dendritic arbors contain fewer, more widely spaced spines and are more expansive than those of the spiny pyramids. While they still send branches into the apical arbors many branches run basally away from the cell body for considerable distances to give the entire dendritic field a more circular appearance. The compact multipolar neuron is found in the inner half of layer I. The long axis of its compact dendritic arbor (∼ 50 μm wide) is oriented in the rostrocaudal axis of the layer. Most of its dendritic branches lie to one side of the cell body squeezed between the axon bundles of the inner half of layer I. The loose multipolar neuron in found throughout the layer. Its loose dendritic arbor is at least 200 μm wide and, like the spiny pyramid, gives rise to several dendrites which terminate abruptly with little branching and without much change in diameter. The dendrites of all four layer I neurons are confined within layer I and its extensions into the spinal V tract. These four layer I neurons are considered to be Golgi type I projection neurons on the basis of the morphology of their initial axonal segment. Golgi type II inteneurons are not found in layer I.
Golgi studies of the neurons in layer II of the dorsal horn of the medulla (trigeminal nucleus caudalis)
Authors: Gobel Stephen
Published: January 2005

The translucent band which lies just beneath the spinal V tract at the lower end of the spinal trigeminal nucleus (nucleus caudalis) can be divided into three layers. These three layers are distinguished by textural differences in their neuropil and by the morphology and laminar distribution of the axons and dendrites of their neurons. Layer II contains four different kinds of interneurons.

Stalked cells are named after their short, stalk‐like branches. Their cell bodies are found in greatest numbers in the outer half of layer II. Their coneshaped dendritic arbors extend medially across layers II and III and sometimes extend into layer IV. Their axons form extensive, canopy‐like arborizations in layer I. Stalked cells are considered to be excitatory interneurons receiving input on their dendritic spines from primary axonal endings in the layers II and III glamour and transferring it to the dendrites of the layer I projection neurons.

Layer II contains three kinds of Golgi type II interneurons, i.e., neurons whose axons branch repeatedly within the confines of their dendrite arbors. Islet cells, similar to those found in layer III (Gobble, 1975a), are found in small clusters in layer II. Their dendrites and axons are largely confined in layer II. The dendrites of the arboreal cell burst, in tree‐like fashion, into highly focal dendrite arbors confined largely in layer II while the extensive rostral and caudal dendrite arbors of the II‐III border cell lie largely in layers II and III with a few branches extending into layer I. The axons of both of these interneurons arborist in layers II and III with a few collaterals extending into layer I. Islet cells, arboreal cells and II‐III border cells are considered to be inhibitory interneurons. They are strategically situated to interrupt transmission between primary axonal endings in layers II and III and the layer I projection neurons by altering the output of the stalked cells.
Catecholamine innervation of the basal forebrain III. Olfactory bulb, anterior olfactory nuclei, olfactory tubercle and piriform cortex
Authors: Fallon James H. , Moore Robert Y.
Published: January 2005

The catecholamine innervation of the olfactory bulb, anterior olfactory nuclei, olfactory tubercle and piriform cortex was studied in the rat using biochemical analysis and fluorescence histochemistry. Biochemical studies demonstrate a moderate norepinephrine (NE) content in all olfactory structures, a high dopamine (DA) content in the olfactory tubercle and a low DA content in the olfactory bulb, anterior olfactory nucleus and piriform cortex. Following locus coeruleus lesions NE content decreases 71% in the olfactory bulb, 82% in the anterior olfactory nucleus, 62% in olfactory tubercle and 77% in piriform cortex. Brainstem transection caudal to locus coeruleus results in a decrease of NE in the olfactory tubercle of 35% without significant changes in other olfactory structures. Following lesions of the medial substantia nigra (SN) extending into the ventral tegmental area (VTA), there is a decrease of DA content (92%) in the olfactory tubercle. VTA lesions produce smaller decreases in olfactory tubercle DA content (79%). The area included in the SN and VTA lesions overlaps, suggesting that both the VTA and SN provide DA in nervation to the olfactory tubercle. VTA lesions also produce decreases in anterior olfactory nucleus DA content (73%) whereas medial SN lesions produce decreases in piriform cortex DA content (44%). Fluorescence histochemical studies using the glyoxylic acid‐Vibratome technique demonstrate the presence of several catecholamine (CA) fiber types in the olfactory system, including large NE fibers in the olfactory tubercle which probably originate in the caudal brainstem, fine NE fibers innervating all four olfactory structures arising from the locus coeruleus, and fine DA fibers from SN‐VTA. These innervate the olfactory tubercle, the anterior olfactory nucleus, piriform cortex and olfactory bulb. The DA innervation is very dense in all layers of the olfactory tubercle, with a variable innervation of the islands of Calleja. The DA fibers enter the olfactory tubercle as fascicles from the medial forebrain bundle. Both NE and DA fibers enter the anterior olfactory nuclei to form a sparse to moderately dense innervation with some continuing in the medial olfactory tract into the olfactory bulb. A moderately dense NE innervation is evident in the inner plexiform and granule cell layer of the accessory olfactory bulb and the granule cell layer of the olfactory bulb. Additional NE fibers are distributed sparsely throughout the remaining components of the olfactory bulb, some entering the glomeruli. There is a very sparse extrinsic DA innervation to the plexiform layer of the olfactory bulb and an intrinsic DA innervation from juxtaglomerular cells.
Catecholamine innervation of the basal forebrain IV. Topography of the dopamine projection to the basal forebrain and neostriatum
Authors: Fallon James H. , Moore Robert Y.
Published: January 2005

In this study the location of dopamine (DA) neuron perikarya in the rostral mesencephalon of the rat was determined using the glyoxylic acid fluorescence histochemical technique. Subsequently the topography of the projection of these mesencephalic neurons on the basal forebrain and striatum was analyzed using the anterograde transport‐autoradiographic tracing method and the retrograde transport‐horseradish peroxidase (HRP) technique. The results of these anatomical studies were correlated with the biochemical and histochemical studies presented in previous reports (Moore, 1978; Fallon and Moore, 1978; Fallon et al., 1978) to provide the following conclusions. The topography of the DA neuron projection on the basal forebrain and neostriatum is organized in three planes, dorsal‐ventral, medial‐lateral and anterior‐posterior. DA cells are found almost exclusively in the substantia nigra (SN) and ventral tegmental area (VTA). Ventral cells of the SN and VTA project to the dorsal structures of the basal forebrain such as the septum, nucleus accumbens and neostriatum. The latter includes some DA cells located ventrally in the pars reticulata of the SN. Dorsal cells project to ventral structures. The medial‐lateral topography is organized such that the medial sectors of the SN‐VTA area project to the medial parts of nuclei in the basal forebrain and neostriatum whereas lateral sectors of the SN‐VTA area project to the lateral parts of nuclei in the basal forebrain and neostriatum. An anterior‐posterior topography also is evident such that anterior parts of the SN‐VTA project anteriorly whereas the posterior SN‐VTA projects more posteriorly in these areas. These observations are consistent with the view that the DA neurons of the SN‐VTA complex form a single nuclear group with a highly topographically organized projection innervating not only deep nuclei of the telencephalon but allocortical structures as well.
An autoradiographic study of the organization of intrahippocampal association pathways in the rat
Authors: Swanson L. W. , Wyss J. M. , Cowan W. M.
Published: January 2005

The longer associational connections of the hippocampal formation have been studied autoradiographically in a series of adult rats after small injections of 3H‐amino acids into each of its various cytoarchitectonic fields. The major findings can be summarized as follows. The dentate gyrus projects in a topographically ordered manner upon the pyramidal cells of the regio inferior by way of the supra‐ and infrapyramidal bundles of mossy fibers. Certain cells in the hilar region of the dentate gyrus (which operationally may be defined as constituting field CA4 of Ammon's horn) give rise to a hippocampodentate projection to the inner one‐quarter of the molecular layer of the dentate gyrus. Either the same or closely related cells give rise to fibers which join the Schaffer collateral system from field CA3 to the stratum radiatum and stratum oriens of the regio superior. The regio inferior is also characterized by a longitudinally directed associational bundle which runs throughout the septo‐temporal extent of the hippocampus and is centered in the region of subfield CA3a. The regio superior has no reciprocal projection to the regio inferior but sends a substantial projection back to the subiculum and to the entorhinal area. There is also a projection to the subiculum from the regio inferior, and the subiculum itself probably contributes significantly to the projection to the entorhinal and perirhinal cortices.

There is a striking parallelism between certain of these associational connections and the commissural projections to the hippocampus and dentate gyrus. Each cytoarchitectonic field that contributes a commissural projection also gives rise to an ipsilateral associational pathway which in its intrahippocampal course and its mode of termination exactly matches that of the commissural projection, although in general, the associational connections are more extensive in their distribution along the septo‐temporal extent of the hippocampus than the corresponding commissural connections. The reverse is not true; there are a number of associational projections which are not paralleled by commissural projection. All of the associational projections are topographically arranged, but those which extend across the transverse axis of the hippocampus usually show considerable divergence so that afferents from different levels overlap fairly considerably within their respective projection fields.
Spinal and medullary input to the lateral cervical nucleus
Authors: Craig A. D.
Published: January 2005

The distributions of spinal and medullary cells projecting to the lateral cervical nucleus (LCN) have been investigated in young cats and dogs using the retrograde horseradish peroxidase (HRP) technique. Labeled spinal cells, whose axons contribute to the spinocervical tract (SCT), were found at all levels of the spinal cord ipsilateral to the injection sites. No significant differences were found between cat and dog, nor between cases with single injections at different levels of the LCN. SCT cells were found predominantly, in not exclusively, within lamina IV, with some extension into medial lamina V. No apparent mediolateral or dorsoventral density gradient was observed within lamina IV; cells of all sizes were labeled. Cells in cervical laminae I and V‐VII were occasionally labeled; these, however, were considered to be propriospinal, supplying afferent fibers to the C1–2 dorsal horn. Cells of origin of spinocerebellar fibers consistently remained unlabeled in cases with restricted HRP injections and minimal fiber damage in the dorsolateral funiculus (DLF) around the injection sites. These results, therefore, corroborate and refine the findings of electrophysiological studies of the SCT and the LCN.

Labeled medullary cells were located in the caudoventral and rostral portions of the dorsal column nuclei (DCN; stellate and fusiform cells), the underlying n. medullae oblongatae centralis, subnucleus dorsalis (parvicellular medullary reticular formation), the marginal and magnocellular layers (both large and small cells) of the n. trigeminalis spinalis pars caudalis and also in pars interpolaris; a cluster of cells was also consistently labeled in the lateral reticular formation just ventral to pars caudalis. The projection from the DCN to the LCN was confirmed with the anterograde Nauta technique. Fiber degeneration was observed in the entire ipsilateral LCN, although it was less abundant than that observed in the adjacent C1–2 dorsal horn. These results indicate that neurons in the rostral portions of the DCN not only may affect the input to the LCN (at the level of the dorsal horn), but also the output of the LCN itself. These data also suggest the possibility of both noxious and non‐noxious facial input to the LCN.
Distribution of the crossed olivocochlear bundle in the chinchilla's cochlea
Authors: Iurato Salvatore , Smith Catherine A. , Eldredge Donald H. , Henderson Donald , Carr Charles , Ueno Younosuke , Cameron Susan , Richter Robert
Published: January 2005

The efferent crossed olivocochlear bundle (COCB) was transected in the brain stem of the chinchilla, and the animals sacrificed 7 to 96 days later. Electron microscopy revealed that all the large efferent nerve endings on outer hair cells in the basalmost 2 mm (round window region) of the cochlea had degenerated, 87.5% in the remainder of the first turn, 70% in the second turn and 43% in the third turn. Only a few degenerating nerve fibres were seen in the medial spiral tract (inner spiral and tunnel bundles) of the experimental animals. Nerve fibers were counted in the medial spiral tracts of the cochleas of control animals as well as in those animals whose COCB had been transected. There were considerable individual variations in the fiber numbers, and statistical analysis showed no significant difference between the numbers of nerve fibers in normal and experimental animals.

The cochlear microphonics (CM) and nerve action potentials (AP) of acute animals were assessed before and after COCB section. The CM and AP of the chronic experimental animals were compared with responses from normals. Overall, no changes in a physiological response of the anesthetized chinchilla could be attributed to complete section of the COCB.
A golgi study of goldfish optic tectum
Authors: Meek J. , Schellart N. A. M.
Published: January 2005

A study of goldfish optic tectum was performed with rapid‐Golgi, Golgi‐Kopsch and a modified Golgi‐Cox impregnation which proved quite suitable to impregnate cells in the middle tectal layers and to study more closely axonal properties. Fifteen cell types are distinguished, based upon the position of dendritic trees and axonal properties. Two cell types are found with dendrites in the marginal layer: type I with an axon terminating in the central gray layer and type II without an impregnated axon. Three cell types (III, IV, and V) have dendrites in a single, specific tectal layer and an axon terminating within the tectum. Five cell types (VI–X) have dendrites in two horizontal planes. Two of them have myelinated axons leaving the tectum, whereas the axons of the remaining three types project to different tectal layers. While these first ten cell types have dendrites almost exclusively in the superficial half of the tectum, the remaining five types have dendrites in deeper layers too. This specially holds for the most conspicuous tectal cells (types XII and XIII), which have dendritic trees branching at three or more horizontal levels and a myelinated axon leaving the tectum, with sometimes a very peculiar course (XIII1). Also type XI has three or more dendritic trees, but its axon was not found. The numerous cells with cell bodies in the deepest tectal layer (type XIV) have dendrites and axonal terminations anywhere in the tectum, except in the most superficial and the deepest layer. However, most dendrites occur in the optic layers, whereas the axons, always originating from the dendritic shaft in the superficial tectal half, generally terminate in the middle tectal layers. Type XV cells have their soma in the deepest tectal layer as well, but their dendrites do not reach the optic layers. Per tectal lobe the following numbers are estimated: type I: 5,000–20,000 neurons. Type III: 2,500–10,000; types IV – XIII: each 500–2,000 and type XIV: 1,000,000–2,000,000. The total number of myelinated tectal efferents is estimated at 2,000–8,000. Comparison with other Golgi studies in teleosts leads to the conclusion that the tecta of these species of fish are basically similar.
Laminar origins of spinothalamic projections in the cat as determined by the retrograde transport of horseradish peroxidase
Authors: Carstens Earl , Trevino Daniel L.
Published: January 2005

The method of retrograde axonal transport of horseradish peroxidase (HRP) was used to identify the locations of cells of origin of the spinothalamic tract in the cat. Injections of from 0.2–3.0 μl of 30% HRP were made unilaterally in various regions of the somatosensory thalamus. Massive injections of the caudal thalamus in several cats showed the spinothalamic cells of origin to be located mainly in laminae I, VII and VIII in the lumbar enlargement, and in laminae I, V and VII–VIII in the cervical enlargement.

Small injections of HRP were made into the three major spinothalamic terminal zones in the thalamus, to determine the laminar origin(s) of the spinal projections to each zone. Neurons in lamina I in both cervical and lumbar enlargements were found to project almost exclusively to the rostral VB‐caudal VL border zone. A small number of neurons in laminae VII and VIII also project there but a larger number project to the intralaminar region. Neurons projecting to the PO regions were located mainly in laminae IV and V. This anatomical segregation of thalamic afferents probably reflects a functional segregation of input, since the functional properties of spinal neurons vary according to their laminar location.

Comparison of these data with the differential projection spinothalamic neurons in the rat and monkey indicate that it is unlikely that the proposed “paleo‐” and “neospinothalamic” systems would arise from anatomically separate groups of spinal neurons.
The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase. VII. The projection to lobulus simplex, crus I and II
Authors: Kotchabhakdi N. , Walberg F. , Brodal A.
Published: January 2005

The olivocerebellar projection to lobulus simplex, crus I and II in the cat was investigated by means of retrograde axonal transport of horseradish peroxidase (HRP). The distribution of labeled cells in the inferior olive following HRP injections in lobulus simplex, crus I and II confirmed the findings by Brodal ('40b) that the rostral half of the principal olive projects to these areas of the cerebellar hemisphere. However, concerning details there are some differences in so far as the heaviest contribution to crus I comes from the medial parts of the ventral and dorsal lamella, that to crus II from its lateral part, especially the ventral bend. The present findings show that in addition the rostral part of the medial and the rostramedial part of the dorsal accessory olive project to these areas of the cerebellar corotex. Further details in the projection are shown in figure 8B. The findings agree fairly well with the electrophysiological results of Armstrong et al. ('74) and the experimental anatomical data of Groenewegen and Voogd ('77a, b). An attempt is made to correlate the findings with the pattern of longitudinal zonal subdivision of the cerebellum. There is evidence for a topical organization within the projection to crus I and II and parts of their projection areas in the principal olive.

The distribution of the labeled cells which project to lobulus simplex, crus I and II is discussed in relation to afferent pathways to the inferior olive.
Relative numbers of several types of synaptic connections in the substantia gelatinosa of the cat spinal cord
Authors: Duncan Donald , Morales Ricardo
Published: January 2005

The relative numbers of axo‐dendritic, axo‐axonic, dendroaxonic and dendro‐dendritic synapses were determined by classifying and recording all such specialized contacts in sample areas of the substantia gelatinosa. The samples were taken from segments L1‐L5 of the cat spinal cord. In the glomerular complexes 97% of all synapses were recorded as axon‐dendritic. In substantia gelatinosa deprived of glomerular complexes by dorsal root section, 96.5% were axo‐dendritic. The remainders were about equally divided between axo‐amonic, dendro‐dendritic and dendro‐axonic synapses.
Nerve fibers of the eighth nerve and their distribution to sensory nerves of inner ear in the bullfrog
Authors: Dunn Robert F.
Published: January 2005

The number of both myelinated and unmyelinated nerve fibers has been determined of the eighth nerve and each of its sensory branches in the bullfrog. No significant differences were found in the size distribution of the myelinated nerve fibers among the three ampullary nerves or between the saccular and lagenar nerves. Comparison of these two functional groups also showed no significant differences in the myelinated nerve fiber size distribution between the angular acceleration and otolithic receptors, collectively the equilibrium receptors. The wide variability, that was found not only among the animals but also between the right and left sides, most likely resulted in the absence of differences. Highly significant differences were noted when the myelinated nerve fiber diameter distributions to the acoustic organs were compared to those of the equilibrium organs. The most notable difference was the absence of any myelinated nerve fibers whose diameters were greater than 8 μm.
Sources and terminations of callosal axons related to binaural and frequency maps in primary auditory cortex of the cat
Authors: Imig Thomas J. , Brugge John F.
Published: January 2005

The distributions of sources and terminals of callosal fibers in the high‐frequency representation of AI were related to binaural and frequency maps in combined anatomical and electrophysiological experiments. Sources of callosal axons were retrogradely labeled with HRP. Distributions of axon terminals were determined by autoradiographic labelling with [3H]‐proline and anterograde degeneration following callosal section. Regions in which cells exhibit summation or ipsilateral dominance and suppression contain higher concentrations of sources and terminals of callosal fibers than do regions in which cells exhibit monaural contralateral responses or contralateral dominance and suppression. Callosal axon terminals aggregate into columns. In Sections cut parallel to the cortical surface callosal columns take on complex forms that exhibit certain consistent features. Two prominent elongated columns separated by a narrow zone of sparse callosal innervation run in a rostrodorsal to caudoventral direction through AI crossing several octaves of the frequency representation. Ventral to these columns, along the AI‐AII border, less densely labeled callosal columns are in evidence. Low frequency representations of AI are interconnected but details of their innervation patterns were not worked out. Outside of AI there are regions that contain complex configurations of callosal columns. Several morphologically distinct types of neurons, located in laminae III through VI, were retrogradely labeled following injections of HRP into the opposite AI. About 94% of callosal neurons are pyramidal cells of layers III and IV.
An electron microscope study of the early postnatal development of the visual cortex of the hooded rat
Authors: Juraska Janice M. , Fifková Eva
Published: January 2005

Synaptic plasticity in response to environmental events has been clearly demonstrated in the visual cortex of the rat, but no detailed data concerning the course of early synaptogenesis in this area are available. In this study, synaptogenesis in the visual cortex of hooded rats at 1, 3, 5, 7 and 10 postnatal days of age (P1‐P10) was examined with electron microscopy. The cortex was divided into the molecular layer, the superficial layers (II‐IV) and deep layers (V‐VI). In the visual cortex at P1, very few synapses are present in the molecular and deep layers and virtually none in the yet undifferentiated layers II‐IV that compose the cortical plate at this age. The synapses that are present are axodendritic and often symmetrical with little membrane thickening and few vesicles. Axosomatic synapses were seen as early as P3 but very rarely. There are marked increases in axodendritic synaptic density and maturity with increasing age. By P7 and P10, many synapses appear mature in form and the majority can be classified as asymmetrical. Axospinal synapses first appeared at P7 and were more frequent by P10. However, this classification was somewhat uncertain since no spinal apparatus was detected. Rate of synaptogenesis appeared to increase over the ages studied and showed no signs of leveling off except in the deep layers. Synaptic length was extremely variable and did not change systematically with age.
The organization of the electromotor nucleus and extraocular motor nuclei in the stargazer (Astroscopus y‐graecum)
Authors: Leonard R. B. , Willis W. D.
Published: January 2005

The organization of the oculomotor and electromotor systems was examined in the stragazer, a teleost. The electromotor system in these animals is a derivative of the oculomotor system. The extraocular motor nuclei and nerves consist of approximately equal numbers of motoneurons and axons (about 100 per muscle). In contrast, electromotor axons appear to branch several times within the intracranial portion of the IIIrd nerve. The topographical organization of the motoneurons was examined using retrograde transport of horseradish peroxidase injected into the electric organ or eye muscles. Electromotor and oculomotor neurons form distinct populations. Each electric organ receives a strong ipsilateral and a weak contralateral innervation. Individual eye muscles receive unilateral innervations with the expected laterality. Within the oculomotor nucleus there is some topographical separation of motoneurons innervating each muscle. Antidromic field potentials confirm the identity of the electromotor nucleus.
An autoradiographic study of the efferent connections of the ventromedial nucleus of the hypothalamus
Authors: Krieger Monica S. , Conrad Lily C. A. , Pfaff Donald W.
Published: January 2005

Efferent projections from the ventromedial nucleus of the hypothalamus (VMN) were traced using tritiated amino acid autoradiography in albino rats.

Ascending fibers passed through the anterior hypothalamus. Labelled fibers and terminal fields were seen in the preoptic area, bed nucleus of the stria terminalis, substantia innominata, the anterior amygdaloid area, diagonal bands of Broca and lateral septum. Fibers also projected laterally from VMN and entered the supraoptic commissures and zona incerta. These lateral projections were responsible for the fibers observed in the cerebral peduncle, the amygdala, the thalamus and the reticular formation. Fibers descending in a medial position projected through the posterior hypothalamus and then swept dorsally to terminate in the mesencephalic and pontine central grey. A projection from VMN into the median eminence was noted. The overall patterns of projection from different parts of VMN were similar; differences that existed were primarily in the relative strengths of the different projections.

The efferent projections from VMN are extensive, well organized, and would appear capable of supporting significant physiological actions on extra‐hypothalamic structures.
Conduction velocity distribution of the retinal input to the hamster's superior colliculus and a correlation with receptive field characteristics
Authors: Rhoades Robert W. , Chalupa Leo M.
Published: January 2005

Cells driven reliably by shocks delivered to the optic nerve or optic chiasm were encountered throughout the depth of the colliculus. The incidence of such cells, however, decreased markedly in the laminae ventral to the stratum opticum. The distribution of conduction velocities for the retinal afferents to the tectum was quite broad (range: 1.7‐25.5 m/sec) and clearly biomodal with peaks at about 6 and 12 m/sec. A small number of cells were innervated by rapidly (> 15 m/sec) conducting axons. No evidence of an indirect‐fast pathway from the retina to the colliculus via the lateral geniculate nucleus and visual cortex was obtained. Afferent conduction velocity was not correlated with retinal eccentricity, collicular depth or speed selectivity. It was, however, clearly related to directional selectivity. Ninety percent of the tectal neurons receiving inputs from axons having conduction velocities of less than 5 m/sec were directionally selective while only 41% of those neurons innervated by more rapidly conducting fibers (> 5 m/sec) exhibited selectivity.

One hundred and sixteen cells in the anterior portion of the colliculus were tested with shocks delivered to the ipsilateral optic nerve and photic stimulation of the ipsilateral eye. Of these, 11% exhibited some degree of binocularity and only 6% were responsive to optic nerve shocks. These electrophysiological findings were correlated with the limited nature of the retinal input to the ipsilateral superior colliculus.
Projections from the spinal and the principal sensory nuclei of the trigeminal nerve to the cerebellar cortex in the cat, as studied by retrograde transport of horseradish peroxidase
Authors: Ikeda Michiko
Published: January 2005

Projections from the spinal (Vsp) and the principal sensory (Vp) nuclei of the trigeminal nerve to the cerebellar cortex were studied by means of retrograde transport of horseradish peroxidase in the cat.

Neurons projecting to the simple lobule and the dorsal part of the paramedian lobule (PMD) were located mainly in the dorsal part of the nucleus interpolaris (Vi) and of the caudal one third of the nucleus oralis (Vo) and in the rostralmost part of the Vo. Neurons projecting to the medial part of the posterior folia of crus II (crus IIp) were located in the dorsal to ventral parts of the Vi and of the caudal one third of the Vo and in the rostralmost part of the Vo, while those projecting to the lateral part of crus IIp were confined to the ventral part of the Vi and of the caudal one third of the Vo. Neurons of the Vp also projected to all of these cortical areas. They were relatively confined to the ventral part of this nucleus. These trigeminocerebellar projections were exclusively ipsilateral to the cell origin. There were sparse projections from the Vi and Vo to lobules V to VIIIa. In addition, a small group of neurons in the subnucleus magnocellularis of the nucleus caudalis of the Vsp also projected to the above cortical areas. No projections were, however, observed to the anterior portion of the anterior lobe, crus I, the anterior folia of crus II, paraflocculus, flocculus and the ventral part of the PMD. The majority of these cerebellar pojection neurons were medium‐sized and triangular, fusiform or ovoid in shape. There were small neurons of similar types and large multipolar neurons as well.
The effect of hemidecortication on the inhibitory interactions in the superior colliculus of the cat
Authors: Buchtel H. A. , Camarda R. , Rizzolatti G. , Scandolara C.
Published: January 2005

Single neurons were recorded extracellularly from the superficial layers of the superior colliculus (SC) in 21 curarized cats. Four animals were normal unoperated cats, 17 were animals in which all cortical visual areas were ablated on one side from 7 to 69 days before the electrophysiological experiments. After cortical ablation all animals were blind in the visual field contralateral to the ablated side.

In both normal and hemianopsic cats the effect of a visual stimulus located very far from the excitatory part of the unit receptive field, on the neuron responses to visual stimuli was studied. The remote stimulus (extra‐field stimulus) was a hand moved black spot 10° in diameter.

In normal animals the introduction of the extra‐field stimulus in the hemifield contralateral or ipsilateral to the recorded SC produced a marked reduction of unit responses to visual stimuli presented in their receptive field. This effect was particularly strong when the extra‐field stimuli were introduced in the hemifield contralateral to the recorded side.

In the hemianopsic animals the neurons of the SC ipsilateral to the lesion (receptive fields in the behaviorally blind hemifield) responded well to visual stimuli, but were only weakly inhibited by the extra‐field stimuli presented in the blind hemifield. The neurons of this colliculus with the exception of those in the upper part of stratum griseum superficiale were normally inhibited by stimuli presented in the normal hemifield.

The neurons of the SC contralateral to the lesion responded well to visual stimuli and were normally inhibited by stimuli presented in the normal hemifield; they were virtually not affected by stimuli presented in the blind hemifield.

Mechanisms responsible for the abnormal inhibitory interactions between and within colliculi after cortical lesions and the possible behavioral implications of the findings are discussed.
Axonal guidance during embryogenesis and regeneration in the spinal cord of the newt: The blueprint hypothesis of neuronal pathway patterning
Authors: Singer Marcus , Nordlander Ruth H. , Egar Margaret
Published: January 2005

In our previous studies on spinal cord regeneration in the adult lizard and the newt, we observed that the radial processes of the regenerating ependyma form between them channels which are subsequently invaded by growing neurites. In the present study we compare embryogenesis of the newt spinal cord with regeneration in the adult. Except for minor differences, we observed that the germinal neuroepithelium of the embryo and larva patterns the longitudinal neural tracts in a similar manner. With these facts in mind we propose the blueprint hypothesis which asserts that inherent in the primitive germinal neuroepithelium and its derivative primitive glia is the pattern of the primary neuronal pathways which is expressed in neurogenesis as formed channels or spaces between the processes of the epithelial cells, the surfaces of which contain trace pathways which the growing neurites follow toward their destination. The trace pathways are envisioned as mechanical‐chemical itineraries which the neurites follow according to their individual affinities. The hypothesis is compared to extant theories and the limitations in central nervous regeneration of vertebrates is compared.
Topographic projections of the retina and optic tectum upon the ventral lateral geniculate nucleus in the chick
Authors: Crossland W. J. , Uchwat C. J.
Published: January 2005

The topographic projections of the retina upon the optic tectum and ventral lateral geniculate nucleus (GLv) of the chick were investigated by making small intraretinal injections of 3H‐proline. The retinotectal projection pattern was similar to that described for the pigeon. The retinal projection to the GLv was also topographic and was restricted to the outermost lamina of the nucleus. The anteroposterior retinal axis was reversed in the GLv relative to its orientation in the tectum but the superoinferior axis was oriented identically in both. Furthermore, the posterior retina had an enlarged area of projection in the GLv similar to the enlarged area of retinotectal projection for the “red field” found in pigeons. The tectogeniculate projection was topographic and was confined to the outermost geniculate lamina. The secondorder retionotopic map made by the tectogeniculate projections was in register with the retinogeniculate projection. Although the retinal and tectal projection areas were coextensive in the outermost geniculate lamina, the grain density distributions peaked at different points along a radial path through the geniculate laminae. Injections of HRP into the optic tectum led to very light retrograde labeling of a small population of GLv cells topographically corresponding to the tectogeniculate projection zone of the injection site. The data suggest that the chick GLv is comparable to the GLv of other non‐primate mammals.
The distribution and size of ganglion cells in the retina of the pigmented rabbit: A quantitative analysis
Authors: Provis Jan M.
Published: January 2005

The distribution and soma diameters of retinal ganglion cells have been examined in whole mounted retinae of pigmented rabbits. Maps of the distribution of ganglion cells confirmed several features of earlier descriptions, but generally showed lower density values and yielded lower total ganglion cell counts (250,000–270,000). The maximum ganglion cell density encountered in each retina and its retinal location both varied between rabbits. As previously reported, the dominant feature of the rabbit's retina is a strongly developed visual streak (Hughes, '71) but some evidence of an area centralis‐like specialization was found. This appears not as the area of peak ganglion cell density, but as a concentration of large (≥20 μm in diameter) ganglion cells at the temporal end of the visual streak, 2‐3 mm from the temporal margin of the retina. In one rabbit in which the optic tract was sectioned five months previously, the density distribution of large retinal ganglion cells in the retinae has been mapped. These maps indicate that the nasotemporal division for large ganglion cells in the rabbit retina is approximately centered on the area of their maximum density. It has previously been reported that in the cat the area centralis is characterized by an aggregation of smaller diameter ganglion cells of a particular functional type (Stone, '65, '78). It is possible that areas of retina which subserve area centralis‐like functions are represented not simply by localized increases in ganglion cell density, but by changes in the relative proportions of ganglion cell types, which are reflected in the changing relative proportions of ganglion cell soma diameter groups.
Golgi studies on Purkinje cell development in the frog during spontaneous metamorphosis. II. Details of dendritic development
Authors: Uray Nándor J. , Gona Amos G.
Published: January 2005

The development of Purkinje cell dendrites was studied in the bullfrog from premetamorphic tadpoles to 10‐week‐old postmetamorphic froglets by the Golgi‐Kopsch method. In this species two distinct patterns of arbor formation may be seen, which appear to be related to differences in the timing of initial dendritic development. In Purkinje cells that begin development in early tadpole stages, the dendritic tree is elaborated by continuous and concomitant growth and branching, a process by which the developing arbor expands in both height and width. Arbor formation in Purkinje cells that begin development in metamorphosing tadpoles proceeds in two separate steps. Initially, dendrites of such cells elongate, but form only a few poorly developed branches; only when the arbor reaches near‐adult height does branching become extensive. Additional differences present in Purkinje cells are reflected in the paucity of growth cones and filopodia in the tadpole, and numerous filopodia and growth cones in the metamorphic period. An interesting feature of dendritic development in this species is a tendency to alter the arboreal domain by the formation of extra‐arboreal dendrites, and possibly by the occasional resorbtion of other partially formed dendrites.

The pattern of dendritic development in the frog is different than in mammals and is difficult to interpret. Such unusual development may be due to disturbances in the timing of the formation of Purkinje cell dendrites and of the establishment of the external granular layer (EGL).
Retinal synaptic arrays: Continuing development in the adult goldfish
Authors: Fisher Leslie J. , Easter Stephen S.
Published: January 2005

We report a light‐ and electron‐microscopic examination of the inner plexiform layer of the central retina of young (c. 1 year) and old (3–4 year) goldfish. There were no new neurons added to this region during the growth period. Nonetheless, there were substantially more synapses (per cell, per mm2, or per degree2) in the older retinas. This result is discussed in the contexts of retinal function and neural development.
Retinotopic organization of areas 18 and 19 in the cat
Authors: Tusa R. J. , Rosenquist A. C. , Palmer L. A.
Published: January 2005

The location and retinotopic organization of areas 18 and 19 in cat cortex were determined using electrophysiological mapping techniques. These two areas each contain a single representation of the visual hemifield and each has a distinctive cytoarchitecture. The visual hemifield representations in these two areas are nearly mirror images of each other. Compared to area 17, areas 18 and 19 have less cortical surface area, have a lower cortical magnification factor, contain less of the visual field and contain second order instead of first order transformations of the visual hemifield. An unusual asymmetry was found between the representations of the upper and lower visual quadrants not seen before in maps of other areas of cat or other species. A considerable amount of variability in the retinotopic organization of these two areas was found among cats.
Development of neocortical circuitry: Histochemical localization of acetylcholinesterase in relation to the cell layers of rat somatosensory cortex
Authors: Kristt Donald A.
Published: January 2005

Acetylcholineserase (AchE) was istochemically localized in neocorex cerebri of newborn to 1‐week‐old rats. At birth AchE‐dependent staining is limited to scaerd somata (Cajal‐Retzius cells) in the marginal zone and a few fibers and somata in primordial layer VI. By the end of the first week, neuronal elements are relatively well sained in pzrticular cell laminae, giving th appearance of three horizontal AchE‐rich “bands” which alternate with AchE‐poor laminae. The subpial band (layer I) is a narrow tangential zone of intensel saining fibers and scatered somata. The mid‐corical band contains an AchE‐positive fiber plexus (primordial layer IV) and numerous stained somata (pyramids of primordial layer V). In layer IV of the SmI region, intermittent foci of staining are noted which overlap the barels' distribution in the barrel field. The deep cortical band (bottom of primordial layer VI) consists of numerous stained somata (Marinotti cells). It is concluded that there is a laminar patern of acetylcholinesterase‐dependent staining in postanatal rat somatosensory corex, and that the laminar pattern bears a consistent spatial relation both to the cell layers and to the depths of high synapse density in immature cortex.