bluuebunny/crossref_metadata_2025 huggingface dataset:
Corticofugal projections from the visual cortices to the thalamus, pretectum and superior colliculus in the cat
Authors: Kawamura S. , Sprague J. M. , Niimi K.
Published: May 2005

Small lesions were placed in visual cortical areas 17, 18, 19, 20, 21, 7, and Clare‐Bishop in the cat, and the sites of terminal degeneration seen with Fink‐Heimer technique were plotted in thalamus, pretectum and superior colliculus. No degeneration was found in these sites after area 20 lesions; lesions in the other cortical areas gave different patterns of degeneration. Two major patterns were present, one from lesions in 17–18, one from lesions in 21, 7 and C‐B, with degeneration from 19 forming a transition between the two groups.

Areas 17, 18 and 19 project to the dorsolateral geniculate nuclear complex (LGNd); areas 21, C‐B and 7 do not. Area 17 projects to the laminar part, area 18 to both laminar and interlaminar (NIM) parts, and 19 only to NIM. The corticogeniculate projections from all three areas are topically organized anteroposteriorly, and at least that from area 17 is topically organized mediolaterally.

Areas 17 and 18 project topically to a columnar locus of the medial pulvinar (=lateral posterior) nucleus which ventrally includes that area known as the posterior nucleus. Area 19 has a double columnar projection to this part of the thalamus, one in the medial and one in the lateral pulvinar area. The medial column lies medial to that from 17–18, and appears to overlap the termination of the ascending projection from the superior colliculus. Cortical areas 21, C‐B and 7 also have a double projection to the pulvinar.

These findings indicate that the corticorecipient neurons in both medial and lateral sectors of the pulvinar are organized so that dorsal neurons are activated by stimuli in upper visual fields (lower retina) and ventral neurons by stimuli in lower fields (upper retina).

Areas 17 and 18 project to the external layer of the ventrolateral geniculate (LGNv) nucleus, 19 to both external and internal layers, and 21, C‐B and 7 to internal layer only.

The pretectal projection from 17–18 is limited to its caudal pole chiefly in the posterior pretectal nucleus (NPP), and also in the nucleus of the optic tract (NOT). Area 19 fibers terminate in NPP, NOT and also in the reticular part of the anterior pretectal nucleus (NPAr). Those from 21 and C‐B end primarily in NPAr, and from area 7 in both reticular and compact parts of NPA. These corticopretectal systems all appear to be organized topically.

Areas 17, 18 and 19 have a double termination in the superior colliculus, a focal pattern in the superficial layers (chiefly lamina II), and a diffuse pattern in deeper layers (laminae IV, V, VI). The superficial pattern only provides the retinotopical matching with the optic afferents. All other cortical areas project diffusely to the deep layers. After lesions in 21 and C‐B, the superficial foci are larger and centered in lamina III; after area 7 lesions this focal degeneration is centered in laminae III and IV and spread over much of the width of the colliculus. Degeneration to pontine nuclei and inferior olive was not examined.
The organization of the retinal projection to the dorsal lateral geniculate nucleus in pigmented and albino rats
Authors: Lund R. D. , Lund Jennifer S. , Wise Renée P.
Published: May 2005

The retina maps over the dorsolateral and posterior surfaces of the contralateral dorsal lateral geniculate nucleus of albino and pigmented rats, such that the upper retina projects posteriorly and the lower retina projects over the dorsolateral surface. Nasal retina projects ventrolaterally and temporal retina dorsomedially. From the surface, lines of projection (demonstrated after either localised retinal or visual cortical lesions) tend to run deep and anteriorly within the nucleus.

The area covered by the uncrossed optic pathway differs between pigmented and albino rats. In the pigmented animals it extends no more than 60° from the edge of the visual field represented in the crossed projection, while in albino animals it extends as far as 100° or more. The uncrossed projection in the albino strains tends to be deficient posteriorly (upper retinal representation) and dorsomedially, and the overall density is less than that found in the pigmented animals.

Small lesions localised in the extreme peripheral temporal retina of both albino and pigmented rats have always produced degeneration in the contralateral as well as ipsilateral geniculate, even though some of the lesions map only as far as, or within the peripheral 20° on the contralateral colliculus. Most of these lesions in the albino rats give two patches of uncrossed degeneration in the geniculate with at least one focus of degeneration in the contralateral geniculate. Those made in the lower temporal retina of the albino rat give in addition to the uncrossed patches, two areas of crossed degeneration in the geniculate separated by about 50° in terms of visual field projection. These double projection aberrations do not occur in pigmented animals.

The suggestion is offered that in albino rats the retina of each eye maps totally on the contralateral lateral geniculate nucleus. However, the vertical midline of the visual field is represented at about 40–50° from the medial edge of the nucleus. A normal (but sparse) uncrossed pathway maps lateral to this position, but also maps in duplicate medial to it. In addition, it appears that some crossed axons may also be abnormal in their termination, and project to both sides of the vertical meridian. If the above interpretation is correct, the anomalies of the albino rat may derive from a confusion of attempting both field and retinotopic maps on the same nucleus. The possibility exists that a comparable total crossed retinogeniculate projection exists in pigmented animals but that the retina temporal to the vertical midline projection is restricted in its connection to a small band on the medial border of the contralateral nucleus.
The upper layers of the superior colliculus of the rat: A Golgi study
Authors: Langer T. P. , Lund R. D.
Published: May 2005

A number of questions deriving from a previous electron microscopic study of the superficial layers of the rat superior colliculus pointed out the need for a comprehensive study of the cell types of the superior colliculus and their detailed morphology. In the present Golgi study the cells of the superficial layers of the superior colliculus were found to be of five major types; marginal cells, horizontal cells, narrow field vertical cells, wide field vertical cells, and stellate cells. Some of these categories were further subdivided. Each cell type has a distinctive set of dendritic field characteristics, a regional distribution, and consistent axon characteristics. The horizontal cells were found to have a preference in the orientation of their dendrites along the vertical and horizontal axes of the visual field projection upon the superior colliculus. It is argued that the horizontal cells are the presynaptic elements in the majority of the dendrodendritic synapses.
Structure of layer IV in the somatosensory neocortex of the rat: Description and comparison with the mouse
Authors: Welker Carol , Woolsey Thomas A.
Published: May 2005

The cytoarchitecture of layer IV of SmI neocortex of the rat has been studied in sections parallel and perpendicular to layer IV. The neurons of layer IV are arranged into discrete multicellular units, called barrels, which we have previously described in both mouse and rat. Using the barrels as markers, it is possible to outline precisely a cytoarchitectonic field—the barrel field—which (1) is confined to SmI. (2) has a consistent appearance from hemisphere to hemisphere, and (3) contains at least 220 barrels. A special region of the barrel field has been identified—the posteromedial barrel subfield (PMBSF)—in which the barrels are arranged in five rows and are larger than elsewhere. However, in contrast to other barrels in the rat barrel field and to the barrels that make up the PMBSF in the mouse, the PMBSF barrels in the rat are filled with small neurons nearly throughout the thickness of layer IV.

From experimental evidence, it has been possible for the first time to establish consistent homologies between small groups of neocortical neurons in layer IV. The most surprising finding is that homologous barrels in the PMBSF of two closely related species, the rat and the mouse, have such a different cytoarchitectonic appearance. On the basis of this observation, we suggest that a careful study of these PMBSF barrels in the mouse, the rat and other species may provide a clue to understanding how neocortical neuronal circuits of varying complexity are assembled.
The rubro‐olivary projection in the macaque: An experimental study with silver impregnation methods
Authors: Courville J. , Otabe S.
Published: May 2005

The rubro‐olivary projection in the macaque has been studied by making lesions in the red nucleus and mapping terminal degeneration with the method of Nauta‐Laidlaw. Lesions restricted to the parvocelluar region have been obtained and confirm that the tract originates from that portion of the red nucleus. The distribution is mainly in the principal olive and in this sub‐nucleus, more extensive than in the cat. Small projections to the medial accessory olive and dorsomedial cell column of the olive are also reported. A topographical arrangement of the rubro‐olivary fibers was found. The projection is made of fibers of fine caliber which degenerate slowly. Optimal survival time was around 16 days. A correlation of the rubro‐olivary projection with the distribution of the olivo‐cerebellar projection indicates that the rubro‐olivary fibers represent one of the links in reciprocal connections between the cerebellum and red nucleus.
Area specific reflexes from normal and supernumerary hindlimbs of Xenopus laevis
Authors: Hollyday Margaret , Mendell Lorne
Published: May 2005

Two area specific reflexes elicited by natural stimulation of different regions of the hindlimbs of Xenopus laevis have been identified. Light or intense mechanical stimulation of the foot evokes reflex activity in the ipsilateral knee flexor nerve; moderate pressure applied to the calf evokes reflex activity predominantly in the ipsilateral knee extensor nerve. The reflex responses have been recorded electrophysiologically to overcome the limitations of behavioral observations for determining the presence of activity in particular muscles. Normal area specific reflexes are elicited in the normal ipsilateral hindlimb by stimulation of grafted supernumerary hindlimbs innervated either by hindlimb (lumbar) or by non‐limb (thoracic) spinal cord segments. The area specific reflexes can be elicited only if the limb is grafted to a host younger than stage 54–55 of Nieuwkoop and Faber ('56), the stage at which reflex movements are first observed behaviorally. Abnormal reflex responses are evoked by stimulation of supernumerary limbs innervated by either thoracic or lumbar segments when the limb buds are grafted to older larvae. Supernumerary forelimbs grafted at early stages and innervated by either thoracic or lumbar spinal cord segments generally fail to elicit area specific reflex responses in the normal hindlimb. Single‐unit recordings of afferent fibers supplying the normal and supernumerary hindlimbs show that each limb receives a separate nerve supply. No evidence for branched afferent fibers has been found. The implications of these results for theories of neuronal specification are discussed, particularly the hypothesis that peripheral tissues are able to specify the central actions of afferent fibers that innervate them.
A block model of the cat cochlear nucleus
Authors: Kiang Nelson Y. S. , Godfrey Donald A. , Norris Barbara E. , Moxon Susan E.
Published: May 2005

A three‐dimensional block model of the cochlear nucleus of the cat was constructed from histologic sections. Boundaries of various subdivisions, based on cytoarchitectonic criteria, were included in the model. Usage of the block model in correlating physiological and anatomical data is illustrated by localizing characteristic waveforms of gross evoked responses and characteristic frequencies of single units.
Dopaminergic neurons in the nematode Caenorhabditis elegans
Authors: Sulston J. , Dew M. , Brenner S.
Published: May 2005

Dopamine is the putative transmitter of eight neurons in the hermaphrodite form of the nematode Caenorhabditis elegans. These include the cephalic and deirid neurons, which are believed to be mechanosensory. The male has an additional six dopaminergic neurons in the tail. Mutants have been selected which have defects in the formaldehyde induced fluorescence and lack dopamine to varying degrees, but they are not insensitive to touch. The dopaminergic neurons of C. elegans are compared with the homologous neurons in Ascaris lumbricoides.
Postnatal development of the cerebellar cortex in the rat. IV. Spatial organization of bipolar cells, parallel fibers and glial palisades
Authors: Altman Joseph
Published: May 2005

The ontogeny of the spatial organization of some components of the molecular layer was investigated in cerebella sectioned systematically in the sagittal, coronal and horizontal planes.

There is no discernible organization in the distribution of cells of the proliferative zone of the external germinal layer (EGL) but from birth the differentiating bipolar cells of the subproliferative zone are aligned parallel to the surface and to the long axis of the folium. While they are still in or at the base of the EGL, the bipolar cells emit long processes, the future parallel fibers. The next step is the outgrowth of a vertical process which may reach the base of the molecular layer before the granule cell nucleus becomes translocated. The idea that the cell body truly migrates through the molecular layer is not supported by the observations.

Bergmann glia cells are frequently seen in Golgi material in neonates but they are probably less numerous than in older infants and their processes are not as well as aligned. It is only gradually that the EGL is perforated by glial endfeet which in older infants are occasionally organized into longitudinal rows. In mature cerebella the parallel fibers are separated by thin and relatively narrow, unstained spaces which are oriented in the longitudinal plane and can be traced from the pial surface to a zone just above the layer of Purkinje cells. It is postulated that these spaces are occupied by glial palisades formed by apposed thin vertical processes to which many Bergmann glia cells contribute. The alignment of these palisades is dependent on the orientation of parallel fibers. When the parallel fibers are reoriented by X‐irradiation the glial palisades become correspondingly realigned.

These observations indicate that the orieted growth of parallel fibers, which follows the polarization of bipolar cells, determines the spatial organization of the glial framework of the molecular layer. They also suggest that the glial palisades mediate functions that are not primarily developmental in nature.
Comparative anatomical studies of the Sml face cortex with special reference to the occurrence of “barrels” in layer IV
Authors: Woolsey Thomas A. , Welker Carol , Schwartz Richard H.
Published: May 2005

In the SmI cortex of mice and rats there are cytoarchitectonically identificable groups of cells — called barrels — some of which have been shown to be directly related to whiskers and other sensory hairs on the contralateral face. In this study we have used a comparative approach to determine the incidence and variation of the barrels.

The brains of 27 mammalian species have been examined histologically to determine whether barrels exist in layer IV of what is known or likely to be the face area of SmI. Thick sections (50–100 μm) were taken tangential to the pia overlying SmI and stained with thionin. The patterns of facial whiskers were also mapped by dissection of the facial skin. Barrels were seen only in brains of species belonging to three of the seven mammalian orders examined. We have confirmed Weller's ('72) observation of barrels in the Australian brush‐tailed possum but have not found barrels in two marsupials from the western hemisphere. Barrels were demonstrable in representatives of four of five rodent suborders examined and in the rabbit.

From the study of the rodent brains, a number of trends emerge. (1) The organization of the barrel fields is “dictated” by the organization of the sensory periphery. Animals with five rows of large mystacial (moustache‐like) vibrissae have five rows of PMBSF (Posterom edial barrel sub‐field) barrels. (2) The barrels are confined to layer IV of (what is known or likely to be) the SmI face area. The pattern and cortical location of the barrel field is consistent among different specimens of the same species. (3) Certain behavioral patterns do not preclude the existence of the barrels. Species which possess well developed visual systems and behaviors (e.g., grey squirrel) and forms which do not actively explore the environment by whisking their vibrissae (e.g., guinea pig) have barrels. (4) Within a given rodent suborder, the barrels become more difficult to identify, as the brains become larger. We have not yet been able to demonstrate barrels in the largest rodent, the capybara.
Interhemispheric neocortical connections of the corpus callosum in the normal mouse: A study based on anterograde and retrograde methods
Authors: Yorke C. H. , Caviness V. S.
Published: May 2005

Interhemispheric neocortical connections are widely distributed through the corpus callosum in the mouse. Callosal connections are present in all cytoarchitectonic fields except field 25. The distal extremity representations of SmI, and MsI the representation of the mystacial vibrissae in SmI, and the more peripheral field representation of VI are relatively acallosal. Dense projections lie in the midline or truncal representations of SmI, MsI, SmII, at the vertical meridian representations bordering field 17, and medial to the AI representation. The radial distribution of terminals is bimodal in most cytoarchitectonic fields. It is unimodal in the supracallosal segment of field 29b and fields 49 and 27, trimodal in fields 13 and 35.

The cells of origin of callosal fibers appear to have the same topographic pattern of distribution as the callosal terminals, observing the same steep and gradual density gradients. No cells giving rise to callosal axons are identified in the acallosal regions of fields 2 and 17. Further, superficial focal lesions in cortical areas which receive callosal connections give rise only to homotopic contralateral degeneration. Acallosal areas of 17 and 2 give rise to no callosal connections. The cells of origin of callosal connections are located at all laminar levels of the cortex and include pyramidal and polymorphic cells but not the granule cells of layer IV.
Anatomical identification of a telencephalic visual area in crocodiles: Ascending connections of nucleus rotundus in Caiman crocodilus
Authors: Pritz Michael B.
Published: May 2005

Nucleus rotundus receives a major input from the optic tectum in crocodiles, Caiman crocodilus. Telencephalic projections of nucleus rotundu were studied in Caiman by means of the Fink‐Heimer procedure after anodal, stereotaxic lesions. Efferent axons of nucleus rotundus assemble on the ventrmedial aspect of this nucleus and swing ventrolaterally to enter the dorsal peduncle of the lateral forebrain bundle. These ascending fibers continue rostrally in the dorsal peduncle of the lateral forebrain bundle to enter the telencephalon where they remain restricted to a lateral portion of the lateral forebrain bundle. At more anterior levels, these fascicles turn dorsally, pass through the ventrolateral area, and terminate massively in a lateral part of the rostral dorsolateral area.

The results of this experiment are compared with similar studies on thalamotelencephalic connections of diencephalic visual areas in other amniotes. Parallels in fiber connections of thalamic auditory and visual areas and the segregation these modalities in the telencephalon of Caiman are discussed. These similarities in neural circuitry and synaptic elements of auditory and visual systems that synapse in the midbrain of Caiman form the basis for a different interpretation of sensory system organization in amniotes.
Organization and development of brain stem auditory nuclei of the chicken: Organization of projections from N. magnocellularis to N. laminaris
Authors: Parks Thomas N. , Rubel Edwin W.
Published: May 2005

The tonotopic and topographic organization of the bilateral projection from second‐order auditory neurons of nucleus magnocellularis (NM) to nucleus laminaris (NL) was examined in young chickens. In one group of birds, the NM axons which innervate the contralateral NL were severed by cutting the crossed dorsal cochlear tract at the midline. Heavy terminal degeineration in NL was confined to the neuropil area immediately ventral to the perikaryl lamina. Very little degeneration was seen in the dorsal neuropil region. In a second series of animals, the characteristic frequency (CF) of cells in an area of NM was first determined by microelectrode recording techniques and then a small electrolytic lesion was made through the recording electrode. Following survival periods of 24–48 hours, the distribution of projections from the lesioned area to the ipsilateral and contralateral NL was examined usinig the Fink‐Heimer method.

As previously described in the pigeon, projections from NM terminate densely in the neuropil region immediately dorsal to the ipsilateral NL cell bodies and ventral to the perikaryl layer on the contralateral side, providing each NL neuron with segregated binaural innervation. Lesions in any area of NM produced degeneration confined to a limited caudo‐rostral and medio‐lateral portion of both laminar nuclei. To investigate this topographic relationship, the caudorostral extents of the lesion in NM and of the resulting degeneration in both NL were determined. Linear regression and correlation analyses then related these positional values to each other and to the CF found at the center of each lesion. All correlations were highly significant and ranged from 0.78 between the position of the lesion in NM and CF to 0.91 between the caudo‐rostral position of degeneration in the NL ipsilateral and contralateral to the lesion.

It is concluded that neurons in NM project in a very discrete topographic, tonotopic and symmetrical fashion to NL on both sides of the brain, contributing to the binaural response properties and tonotopic organization of neurons in NL. The results also suggest that the organization of projections from NM to NL could provide a mechanism for the differential transmission delay required by a “place” model of low‐frequency sound localization.
Autoradiographic studies of cerebellar histogenesis in the bullfrog tadpole during metamorphosis: The external granular layer
Authors: Gona Amos G.
Published: May 2005

Spontaneously metamorphosing bullfrog tadpoles and those induced to metamorphose by injections of thyroid stimulating hormone (TSH) were given a single intraperitoneal injection of thymidine‐3H (10 μCi/g body weight). The brains were dissected out at various periods 3 hours to 14 days later, and processed for autoradiography. At the 3‐hour interval after thymidine‐3H injection, ependymal cells were labelled, but not the external granular layer (EGL) cells. Furthermore, in all the metamorphosing tadpoles intense labelling was restricted to the ependyma of the marginal region of the cerebellar plate. At 48 hours, labelled cells were seen in the EGL of the marginal region. At the 4‐day interval, most of the EGL was labelled, and labelled cells were also seen migrating from the EGL into the internal granular layer (IGL). By 14 days, several labelled cells were seen in the IGL. Although the sequence of cerebellar histogenesis in the frog is similar to the general pattern described in other vertebrate groups, the results indicate that the EGL of the frog cerebellum does not serve the function of a secondary proliferating zone.
Projections of the optic tectum in two teleost species
Authors: Ebbesson Sven O. E. , Vanegas Horacio
Published: May 2005

The efferent pathways of the optic tectum have been investigated in the percomorph Eugerres and the berycomorph Holocentrus. A portion of the dorsal‐dorsolateral region of the optic tectum was unilaterally resected by suction. The animals were perfused 6–30 days thereafter, and the brains were processed according to a modification (Method 7 in Ebbesson, '70) of the Fink‐Heimer ('67) technique for the selective silver impregnation of degenerating axons and terminals.

Three groups of fibers emerge from the lesioned region: (a) a medial group, which runs towards the midline and terminates in the ipsilateral torus longitudinalis and the contralateral tectum; (b) an ascending group, which enters the dorsocaudal region of the diencephalon and terminates in pretectal cell groups, in the dorsomedial optic thalamic nucleus, and in the nucleus rotundus or prethalamicus; and (c) a descending group, which funnels down into the midbrain tegmentum. Here abundant terminals are given to dorsolateral cell groups and to the nucleus isthmi. A recurrent fascicle leaves the mainstream and ascends to terminate in scattered diencephalic cell groups, in the nucleus geniculatus posterior pars ventralis, and in the nucleus rotundus or prethalamicus. The bulk of descending fibers then forms an ipsilateral bundle, which gives terminals to the lateral reticular formation of mesencephalon and rhombencephalon, and a contralateral (i.e., the predorsal) bundle, which terminates in the medial reticular formation of mesencephalon and rhombencephalon.
Scotopic and photopic vision in the california ground squirrel: Physiological and anatomical evidence
Authors: Jacobs Gerald H. , Fisher Steven K. , Anderson Don H. , Silverman Martin S.
Published: May 2005

The California ground squirrel is a highly diurnal species previously thought to have an all‐cone retina. This issue was re‐examined in physiological and anatomical experiments. The electroretinogram (ERG) was used to measure the spectral sensitivity of the eye under different conditions of adaptation. The occurrence of a Purkinje shift could be demonstrated, although there was some indication that not all members of this species show such a shift. Spectral sensitivity of the dark‐adapted eye of this squirrel is close to that predicted by a typical mammalian rhodopsin. Light adaptation produces a shift in spectral sensitivity to a peak location of about 525 nm. It was shown that two mechanisms having different spectral sensitivities contribute to the photopically recorded ERG. The degree to which these two mechanisms contribute to the ERG was found to be strikingly different from the degree to which the two contribute to visual behavior.

Our anatomical results indicate that the retina of the California ground squirrel has two structurally distinct photoreceptors which, on the basis of various criteria, can be classified as cone and rod‐like. The rod‐like receptors comprise about 6–7% of the total. The two photoreceptor types differ in placement of their inner segments, size of their outer segments, outer segment ultrastructure, and terminal structure and organization.
Nigrothalamic projections in the monkey demonstrated by autoradiographic technics
Authors: Carpenter Malcolm B. , Nakano Katsuma , Kim Ronald
Published: May 2005

In spite of repeated demonstrations by degeneration technics, nigrothalamic fibers have been regarded with some skepticism. Attempts were made to trace‐ nigral efferent projections in the monkey by autoradiographic technics. Tritiated amino acids (L‐leucine, L‐lysine and L‐proline), injected into portions of the substantia nigra (SN), labeled cells in four regions, designated as, (1) rostrolateral, (2) caudolateral, (3) rostromedial and (4) central.

Rostrolateral nigral neurons transported radioactive label preferentially and abundantly to thalamic nuclei; localized isotope was found in parts of three thalamic nuclei, the medial part of the ventral lateral nucleus (VLm), the magnocellular part of the ventral anterior nucleus (VAmc), and the paralaminar part of the dorsomedial nucleus (DMpl).

Lateral neurons in the caudal half of the SN transmitted radioactive label to the same thalamic nuclei as rostrolateral nigral neurons. Isotope transported to portions of the striatum was modest and localized. Radioactive label taken up by large cells in the caudal third of the SN was transported to portions of the striatum, but not to thalamic nuclei.

Labeled nigral neurons in the medial two‐thirds of the rostral half of the SN, and in the middle third of the central part of the SN, transported the label mainly to parts of the caudate nucleus and putamen. In these animals modest radioactive label was seen in VLm and VAmc, but not in other thalamic nucleus.

There was no evidence that nigral neurons project to the subthalamic nucleus. No radioactive transport from nigral neurons was detected in the superior colliculus, the midbrain tegmentum, or the red nucleus, and none was transported to more caudal brain stem nuclei.

Nigrothalamic fibers arise particularly from cells in rostral and lateral parts of the substantia nigra. While some cells in other parts of the nigra project to thalamic nuclei, these appear scattered and less numerous. Large cells in caudal parts of the SN do not project to thalamic nuclei. These observations confirm nigrothalamic projections to VLm and VAmc, and identify a new nigral projection to part of the dorsomedial nucleus of the thalamus (DMp1). No nigral efferent fibers project to any of the intralaminar thalamic nuclei.
Central control of song in the canary, Serinus canarius
Authors: Nottebohm Fernando , Stokes Tegner M. , Leonard Christiana M.
Published: May 2005

We have traced central nervous pathways controlling bird son in the canary using a combination of behavioral and anatomical techniques. Unilateral electrolytic brain lesions were made in adult male canaries whose son had been previously recorded and analysed on a sound spectrograph. After severral days of postoperative recording, the birds were sacrificed and their brains processed histologically for degeneration staining with the Fink‐Heimer technique. Although large lesions in the neostriatum and rostral hyperstriatum had no effect on song, severe song deficits followed damage to a discrete large‐celled area in the caudal hyperstriatum ventrale (HVc). Degenerating fibers were traced from this region to two other discrete nuclei in the forebrain: one in the parolfactory lobe (area X, a teardrop‐shaped small‐celled nucleus) and a round large‐celled nucleus in the archistriatum (RA). Unilateral lesions of X had no effect on song; lesions of RA, however, caused severe song deficits. Degenerating fibers from RA joined the occipitomesencephalic tract and had widespread ipsilateral projections to the thalamus, nucleus intercollicularis of the midbrain, reticular formation, and medulla. It is of particular interest that direct connections were found onto the cells of the motor nucleus innervating the syrinx, the organ of song production. Unilateral lesions of n. intercollicularis (previously implicated in the control of vocal behavior) had little effect on song.

One bilateral lesion of HVc resulted in permanent (9 months) and complete elimination of the audible components of song, although the bird assumed the posture and movements typical of song. Preliminary data suggest that lesions of the left hemisphere result in greater deficits than lesions of the right one. This finding is consistent with earlier reports that the left syrinx controls the majority of song components. Results reported here suggest a localization of vocal control in the canary brain with an overlying left hemispheric dominance.
Amygdaloid projections to subcortical structures within the basal forebrain and brainstem in the rat and cat
Authors: Krettek J. E. , Price J. L.
Published: May 2005

The efferent fiber connections of the nuclei of the amygdaloid complex with subcortical structures in the basal telencephalon, hypothalamus, midbrain, and pons have been studied in the rat and cat, using the autoradiographic method for tracing axonal connections. The cortical and thalamic projections of these nuclei have been described in previous papers (Krettek and Price, ′77b,c). Although the subcortical connections of the amygdaloid nuclei are widespread within the basal forebrain and brain stem, the projections of each nucleus have been found to be well defined, and distinct from those of the other amygdaloid nuclei.

The basolateral amygdaloid nucleus projects heavily to the lateral division of the bed nucleus of the stria terminalis (BNST), to the caudal part of the substantia innominata, and to the ventral part of the corpus striatum (nucleus accumbens and ventral putamen) and the olfactory tubercle; it projects more lightly to the lateral hypothalamus. The central nucleus also projects to the lateral division of the BNST and the lateral hypothalamus, but in addition it sends fibers to the lateral part of the substantia nigra and the marginal nucleus of the brachium conjunctivum. The basomedial nucleus has projections to the ventral striatum and olfactory tubercle which are similar to those of the basolateral nucleus, but it also projects to the core of the ventromedial hypothalamic nucleus and the premammillary nucleus, and to a central zone of the BNST which overlaps the medial and lateral divisions. The medial nucleus also projects to the core of the ventromedial nucleus and the premammillary nucleus, but sends fibers to the medial division of the BNST and does not project to the ventral striatum. The posterior cortical nucleus projects to the premammillary nucleus and to the medial division of the BNST, but a projection from this nucleus to the ventromedial nucleus has not been demonstrated. Projections to the “shell” of the ventromedial nucleus have been found only from the ventral part of the subiculum and from a structure at the junction of the amygdala and the hippocampal formation, which has been termed the amygdalo‐hippocampal area (AHA). The AHA also sends fibers to the medial part of the BNST and the premammillary nucleus.

Virtually no subcortical projections outside the amygdala itself have been demonstrated from the lateral nucleus, or from the olfactory cortical areas around the amygdala (the anterior cortical nucleus, the periamygdaloid cortex, and the posterior prepiriform cortex). However, portions of the endopiriform nucleus deep to the prepiriform cortex project to the ventral putamen, and to the lateral hypothalamus.
Intratrigeminal and thalamic projections of nucleus caudalis in the squirrel monkey (Saimiri sciureus): A degeneration and autoradiographic study,
Authors: Ganchrow Donald
Published: May 2005

In order to test the hypothesis that thalamic efferents of trigeminal nucleus caudalis (NC) are the cranial analogue of the spinothalamic system, lesion and autoradiographic studies were carried out in the squirrel monkey, and the terminal projection fields in thalamus were noted. Results showed that NC, including lateral reticular formation (LRF), projects to contralateral VPM, the VPM‐VPL border and medial VPL, and a region dorsal to ventroposterior nucleus (VP) proper which contains cells larger than those in VPM yet which stain as darkly as VPL neurons; this latter zone of termination may be homologous with VPLo (Vim) in other species, which is that area receiving lemniscal and cerebellar afferents (Mehler, '71; Walsh and Ebner, '73; Boivie, '74). In addition, a small projection is noted in an area intercalated between dorsomedial MG, limitans nucleus and posterior VP which closely agrees with the medial division of Posterior nucleus (Po) described in rhesus and squirrel monkey (Burton and Jones, '76). No terminations were observed in the gustatory nucleus medial to VPM.

Bilateral, terminal projection fields were observed in posterior mediodorsal nucleus (MD), and a paralaminar area (PL) which lies in the ventrolateral strip of MD and is particularly prominent in primates; other bilateral fields were noted in CL, particularly the more medial segment of the nucleus. A sparse projection was noted in contralateral CM. Ipsilateral, intratrigeminal connections between NC and main sensory nucleus (MSV) also were observed.

We conclude that, in the squirrel monkey, NC efferents, probably including LRF, may be considered analagous to the spinothalamic system by virtue of terminations in older medial and newer ventroposterior thalamus. Terminations in posterior MD may be specific to Primates. Moreover, projections to an area just dorsal to VP proper in squirrel monkey may be included within the broader definition of a neo‐spinothalamic area as reflected in spinothalamic tract projections to the ventrolateral complex in cat (Boivie, '71b; Jones and Burton, '74). The small NC projection to a part of Po is consistent with spinothalamic terminations to a “posterior” thalamic area in other primates (Mehler, '69), and with the suggestion that medial Po transmits pain information (Burton and Jones, '76).
Role of visual experience in postcritical‐period reversal of effects of monocular deprivation in cat striate cortex
Authors: Smith Douglas C. , Spear Peter D. , Kratz Kenneth E.
Published: May 2005

We reported previously that the effects of monocular deprivation on cat striate cortex cells can be partially reversed after the critical period by enucleation of the experienced eye (Kratz et al., '76). The enucleation resulted in a rapid (less than 12 hours) increase in the percent of cells which responded to the deprived eye; however, the receptive field properties of the responsive cells were abnormal. There was no change in this result if the animals were allowed to survive 3 to 16 months after the enucleation, during which the deprived eye remained closed. The present study investigated whether enucleation of the experienced eye extends the period of sensitivity during which connections from the deprived eye can be modified by visual experience. That is, we asked whether opening the deprived eye and allowing it normal visual experience after enucleation of the experienced eye would lead to a further increase in the percentage of responsive cells or produce a modification of receptive field properties.

Using single‐cell recording in striate cortex, comparisons were made between monocularly deprived control kittens (MD), kittens which had the experienced eye enucleated at four months of age while the deprived eye remained closed (MD‐DE) or was opened (MD‐DE‐O) for an additional three to four months, and kittens which received reverse‐suture at the same age and for the same duration (MD‐RS). Kittens in both the MD‐DE and MD‐DE‐O groups showed an increase in the percent of cells responsive to the deprived eye compared to MD control kittens, replicating our previous findings. However, there were no differences between the MD‐DE and MD‐DE‐O groups either in terms of percent responsive cells or in the receptive field properties of those which responded. Reverse‐suture also produced a significant, although variable, increase in the percent of cells responding to the initially deprived eye. However, this increase was significantly less than that produced by enucleation of the experienced eye in MD‐DE and MD‐DE‐O animals. Among the cells responsive to the initially deprived eye in the reverse‐suture animals, the receptive field properties remained abnormal.

These results suggest that binocular interactions continue to play an active role in the effects of monocular deprivation after the previously defined critical period. However, reversal procedures such as suture or enucleation of the experienced eye do not extend the period in development during which cells in striate cortex can be modified by visual experience. Rather, they may simply release those cells already receiving anatomical connections from the deprived eye from a tonic inhibition mediated by the experienced eye.
Organization of anterior dorsal ventricular ridge in snakes
Authors: Ulinski Philip S.
Published: May 2005

Anterior dorsal ventricular ridge (ADVR) is a major telencephalic structure in reptiles. The intrinsic, efferent, and afferent connections of ADVR were studied in water snakes (Natrix sipedon) and garter snakes (Thamnophis sirtalis) using orthograde degeneration and Golgi techniques.

ADVR in these snakes contains four zones oriented concentric with the ventricular surface and named zones A, B, C, and D, with zone A being the most peripheral. Each zone contains a characteristic population of neurons. Zone A neurons have dendrites which extend obliquely through zone A and into zone B. Zone B neurons have dendrites with a high density of dendritic spines and axons which ramify in zone A concentric with the ventricle, typically bearing large varicosities about 5 μ in length. Zone C neurons have dendrites with a low density of dendritic spines and axons which ramify within about 300 μ of the soma, typically bearing small varicosities about 3 μ in length. Zone D neurons resemble those in zone C, except that their axons may course ventrally out of ADVR into the subjacent striatum.

Lesions placed superficially in ADVR produce terminal degeneration which is restricted to ADVR in Fink‐Heimer preparations. Lesions which damage the ventral part of ADVR produce degeneration in striatal nuclei (medial striatal nucleus, intrapeduncular nucleus, and perifascicular complex) as well as in the ventral two‐thirds of the posterior dorsal ventricular ridge. Unilateral transections of the midbrain produce degeneration in a system of thick caliber axons, with thin collaterals, which enters ADVR caudally behind the anterior commissure and rostrally through the lateral forebrain bundle. These fibers are oriented primarily along the radii of ADVR and confined predominantly to zones B, C, and D. Lesions of the dorsal thalamus produce degeneration in a system of thin caliber axons which enters ADVR rostrally through the lateral forebrain bundle. These fibers course radially through zones C and D and then turn to run concentric with the ventricle in zone B.

These observations suggest that snake ADVR consists of two fundamentally different parts. Neurons in zones A and B interact strongly with neighboring neurons through somatosomatic and axodendritic contacts and participate in connections which run concentric with the ventricle. Neurons in zones C and D participate in connections which run radially. Some of the neurons in zone D, and possibly some in zone C, project to the striatum. Neurons situated near the ventral border of ADVR are the only source of ADVR efferents. Neurons in each zone interact with those in neighboring zones.
Dark rearing in the cat: Effects on visuomotor behavior and cell growth in the dorsal lateral geniculate nucleus
Authors: Kalil Ronald
Published: May 2005

The morphological and behavioral effects of complete binocular deprivation were studied by rearing cats from birth in total darkness. Nineteen animals were sacrificed immediately upon removal from the dark at intervals that ranged from 3 to 16 weeks. Measurements of cell sizes in the dorsal lateral geniculate nucleus revealed that dark rearing affects cell growth in two stages. During the first three months of dark rearing the growth rate of geniculate cells is reduced, and a maximum size difference between cells from light reared control animals and dark reared cats is seen at 12 weeks. However, during the fourth month of deprivation, geniculate cells recover from the effects of dark rearing, and grow to essentially normal size by 16 weeks.

In a separate set of experiments, cats were removed from the dark at 8, 12 and 16 weeks, and given normal visual experience for as long as one and one‐half years. Lateral geniculate neurons in these animals were also normal in size.

These results indicate that the effects of dark rearing on cell growth in the lateral geniculate nucleus are significant, but transitory, since they can be reversed either by long term deprivation, alone, or by exposure to normal levels of illumination.

Behavioral experiments were performed to study the influence of dark rearing upon visually guided avoidance, jumping, placing, and following. After 8, 12 and 16 weeks of dark rearing, cats appear blind when first examined, and fail each of the behavioral tests. Within four weeks, however, visuomotor behavior recovers almost completely.

Visual field perimetry testing was also carried out, and the results indicate that orientation is not reliably affected by periods of dark rearing less than 12 weeks in duration. However, 16 week dark reared animals show visual field defects, which persist for several months, and suggest that only the nasal hemiretina is used for orientation. Since the dark reared cats which showed deficits in orientation also demonstrated a pronounced convergent strabismus, it is proposed that misalignment of the visual axes may be directly responsible for the behavioral impairment.
Cytoplasmic laminated bodies in the lateral geniculate nucleus of normal and dark reared cats
Authors: Kalil Ronald , Worden Ian
Published: May 2005

The postnatal development of cytoplasmic laminated bodies in lamina A cells of the lateral geniculate nucleus in normal and dark reared cats has been studied quantitatively with light microscopy. In the normal cat laminated bodies develop between the sixth and eighth postnatal week and increase steadily in number thereafter. These inclusion bodies are found chiefly in medium size cells and are distributed more densely in the medial part of lamina A than laterally. Laminated bodies appear not to be a general feature of the visual pathways since they are not found in cells of the visual cortex, superior colliculus, or ventral lateral geniculate. In the dark reared cat laminated bodies develop at about the same time as in the normal animal, but approximately twice as many of them are seen at all ages investigated.

Our experiments indicate that dark rearing does not cause a proliferation of multiple laminated bodies within single neurons, but rather induces the formation of a laminated body in cells that normally would not acquire one. This effect appears to be permanent since it is not reversed by long term dark rearing nor by periods of normal visual experience following deprivation.

Physiological experiments (Sherman et al., '72) have shown that fewer Y‐cells are recorded in binocularly deprived cats than in normally reared animals. On the basis of the present results, it is suggested that dark rearing influences the functional specificity of developing lateral geniculate neurons. In this view, deprivation prevents normal numbers of Y‐cells from developing. Neurons which would have become Y‐cells develop instead as X‐cells; a change in functional organization which is associated structurally with an increase in the number of cells that contain cytoplasmic laminated bodies.