bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytoarchitectonic analysis of the SDN‐POA of the intact and gonadectomized rat
Authors: Bloch G. J. , Gorski R. A.
Published: January 2005

The densely staining group of cells referred to as the sexually dimorphic nucleus of the preoptic area (SDN‐POA) is greater in volume in the male than in the female rat. Because we and others have reported absolute volumes that have been consistent within individual studies but that vary considerably, we characterized the SDN‐POA by describing its morphology with respect to the cytoarchitectonic divisions of the medial preoptic nucleus (MPN) in intact and gonadectomized rats. We report three major findings: the SDN‐POA is heterogeneous and is composed of cells belonging to three distinct cytoarchitectonic divisions; the cytoarchitecture of the MPN and its medial and lateral divisions (MPNm and MPNl, respectively) in male rats appear to be influenced by the hormonal status in adulthood; and a small anteroventral division of the MPN (MPNav) is present in males but virtually absent in females. Specifically, the SDN‐POA is located within the MPNm, but consists of subcomponents located within the central division of the MPN (MPNc), the MPNav, and part of the MPNm‐exclusive of the MPNc and MPNav. The percentage of the total SDN‐POA located within the MPNc and MPNav was greater in males, and that in the MPNm‐exclusive of the MPNc and MPNav was greater in females, indicating that the SDN‐POA has a different cytoarchitectonic composition in the two sexes. Gonadectomy produced no significant differences in SDN‐POA volume, but the MPN, MPNl, and MPNm were significantly reduced in gonadectomized versus intact males, suggesting an activational effect of testicular hormones on these structures.
Organization of retinogeniculate projections in turtles of the genera Pseudemys and Chrysemys
Authors: Ulinski Philip S. , Nautiyal Jaishanker
Published: January 2005

Organization of retinal projections to the dorsal lateral geniculate complex in turtles has been studied by means of light and electron microscopic axon tracing techniques.

Orthograde degeneration studies with Fink‐Heimer methods following restricted retinal lesions show the entire retina has a topologically organized projection to the contralateral dorsal lateral geniculate complex. The nasotemporal axis of the retina projects along the rostrocaudal axis of the geniculate complex; the dorsoventral axis of the retina projects along the dorsoventral axis of the geniculate complex. The projection to the ipsilateral dorsal lateral geniculate complex originates from the ventral, temporal and nasal edges of the retina. The nasotemporal axis of the ipsilateral retina projects along the rostrocaudal axis of the geniculate complex. It was not possible to determine the orientation of the dorsoventral axis of the ipsilateral retina on the geniculate complex.

Light microscopic autoradiographic tracing experiments and electron microscopic degeneration experiments show the retinogeniculate projection has a laminar organization. Retinogeniculate terminals are found in both the neuropile and cell plate throughout all three subnuclei of the dorsal lateral geniculate complex but have a distinctive distribution in each sub‐nucleus. In the subnucleus ovalis, they are frequent in both the neuropile and cell plate which forms the rostra1 pole of the complex. In the dorsal subnucleus, they are most prevalent in the outer part of the neuropile layer, less frequent in the inner part of the neuropile, and rare in the cell plate. In the ventral subnucleus, they are frequent in the outer part of the neuropile but are also common in the inner part of the neuropile and cell plate.

These observations point to several principles of geniculate organization in turtles. First, the complex receives projections from the entire contralateral retina and a segment of the ipsilateral retina. It thus has monocular and binocular segments that together receive a topologically organized representation of the binocular visual space and the contralateral monocular visual space. Second, the three geniculate subnuclei receive information from different, specialized regions of the retina and visual space. Subnucleus ovalis receives information from the frontal binocular visual field. The ventral subnucleus receives information from the caudal binocular field. The dorsal subnucleus receives input from the contralateral monocular field. Third, there is a lamination of retinal inputs in the geniculate complex which differs in character within the three subnuclei. It apparently results in particular distributions of retinal and cortical inputs along the receptive surfaces of geniculate neurons.
Connections of area 8 with area 6 in the brain of the macaque monkey
Authors: Arikuni Tomio , Watanabe Kyoko , Kubota Kisou
Published: January 2005

The corticocortical connections between the arcuate area (Walker's areas 8A and 45 or Brodmann's area 8) and the premotor and supplementary motor areas (Vogts' area 6) in the brain of the macaque monkey were studied microscopically with wheat germ agglutinin‐conjugated horseradish peroxidase (WGA‐HRP), which was injected into Brodmann's area 8 primarily to elucidate the projections of area 8 into area 6. In addition, in the same material, the pattern of connections between the arcuate area and area 46 of the prefrontal cortex was studied. On the basis of the findings of the present study, an anatomical cortical hierarchy for areas 8, 6, and 46 is discussed.

Anterogradely labeled axon terminals and retrogradely labeled cells appeared in the premotor area, in the supplementary motor area, and in area 46 on the side of injection; sites containing labeled axon terminals also contained labeled cells. In other words, the examined connections were reciprocal. In the labeled areas, labeled terminals and cells coexisted, and most formed radial columns. However, no labeling of cells and terminals was seen in the motor area (Brodmann's area 4).

After injection of WGA‐HRP into area 8A, labeled terminals and cells appeared predominantly in the superior premotor area (a region of the premotor area above the arcuate spur, Vogt and Vogt's upper areas 6aα and 6aß), forming one, two, or three bands of label in the anteroposterior direction, whereas labeling occurred to a lesser extent in the inferior premotor area (a region of the premotor area below the arcuate spur, Vogt and Vogt's areas 4c, lower 6aα and 6b). In contrast, injection of WGA‐HRP into area 45 resulted in the predominant labeling of the inferior premotor area with scant labeling in the superior premotor area.

In the premotor area, labeled terminals were distributed over the entire cortical depth, although few were found in the lower half of layer III, and labeled cells were distributed mainly in layer III. In area 46 of the banks of the principal sulcus in the prefrontal cortex, labeled terminals were distributed in all cortical layers or over the entire cortical depth with a lower concentration in layer IV; labeled cells were found mostly in layers III and V, with a relatively high density in layer V.
Neural associations of the substantia innominata in the rat: Afferent connections
Authors: Grove Elizabeth A.
Published: January 2005

The afferent connections of the substantia innominata (SI) in the rat were determined employing the anterograde axonal transport of Phaseolus vulgaris leucoagglutinin (PHA‐L) and the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP), in combination with histochemical procedures to characterize the neuropil of the SI and identify cholinergic cells. Both neurochemical and connectional data establish that the SI is organized into a dorsal and a ventral division. Each of these divisions is strongly affiliated with a different region of the amygdala, and, together with its amygdalar affiliate, forms part of one of two largely distinct constellations of interconnected forebrain and brainstem cell groups.

The dorsal SI receives selective innervation from the lateral part of the bed nucleus of the stria terminalis, the central and basolateral nuclei of the amygdala, the fundus of the striatum, distinctive perifornical and caudolateral zones of the lateral hypothalamus, and caudal brainstem structures including the dorsal raphe nucleus, parabrachial nucleus, and nucleus of the solitary tract. Projections preferentially directed to the ventral SI arise from the medial part of the bed nucleus of the stria terminalis, the rostral two‐thirds of the medial nucleus of the amygdala, a large region of the rat amygdala that lies ventral to the central nucleus, the medial preoptic area, anterior hypothalamus, medialmost lateral hypothalamus, and the ventromedial hypothalamus. Both SI divisions appear to receive afferents from the dorsomedial and posterior hypothalamus, supramammillary region, ventral tegmental area, and the peripeduncular area of the midbrain. Projections to the SI whose selectivity was not determined originate from medial prefrontal, insular, perirhinal, and entorhinal cortex and from midline thalamic nuclei. Findings from both PHA‐L and WGA‐HRP experiments additionally indicate that cell groups preferentially innervating a single SI division maintain numerous projections to one another, thus forming a tightly linked assembly of structures.

In the rat, cholinergic neurons that are scattered throughout the SI and in parts of the globus pallidus make up a cell population equivalent to the primate basal nucleus of Meynert (Mesulam et al.: Neuroscience 10:1185–1201, '83). PHA‐L‐filled axons, labelled from lectin deposits in the dorsal raphe nucleus, peripeduncular area, ventral tegmental area, or caudomedial hypothalamus were occasionally seen to approach individual cholinergic neurons in the SI, and to contact the surface of such cells with axonal varicosities (putative synaptic boutons). Pending confirmation in an electron microscopic study, such findings suggest that several sources of innervation of the SI may provide afferents to the cholinergic cells in the region.
The ventral lateral geniculate nucleus in the cat: Thalamic and commissural connections revealed by the use of WGA‐HRP transport
Authors: Nakamura Hiroyuki , Kawamura Syosuke
Published: January 2005

The present investigation was carried out to clarify the topographical details of both the origin and terminal site of the thalamic projections and the commissural connections of the ventral lateral geniculate nucleus (LGNv) in the cat by using bidirectional transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP).

Thalamic projections: Unilateral injections of WGA‐HRP into the LGNv produced orthograde labeling in the intralaminar nuclei bilaterally and in the lateralis posterior (LP) and the pulvinar (Pul) nucleus ipsilaterally. In the intralaminar nuclei the rostral part of the nucleus centralis lateralis (CL) was most densely labeled by orthogradely transported material, particularly in its dorsal and lateral large‐celled portion. Other intralaminar nuclei—such as the nucleus paracentralis, centralis medialis, and centralis dorsalis—also were labeled bilaterally with ipsilateral predominance, but no labeling was detected in the caudal portion of the CL and the centromedian and parafascicular nuclei. In the Pul, labeling of terminal ramifications was found to be concentrated in a region just medial to th so‐called retinorecipient zone of the Pul as a slim band of labeling inclining dorsoventrally. In the LP, fine labeled fibers were located in the lateral portion of the LP.

Commissural connections: Commissural fibers crossed in the dorsal part of the posterior commissure and reached the most caudal part of the contralateral LGNv. Labeling in the contralateral LGNv was concentrated in the dorsomedial part of the medial zone that extends medially to the middle portion of the cerebral peduncle. Origins of the commissural connections arose mostly from the medial zone that roughly corresponds to the commissural terminal zone and partly from aberrant cells dispersed among optic tract fibers.

From these results, together with the previous studies, it is concluded that although the cat's LGNv has connections with diverse structures in the central nervous system, the origin and terminal site of the connections are partially segregated within the nucleus, which suggests that the LGNv may contain functional subsystems.
Projections of digit afferents to the cuneate nucleus in the raccoon before and after partial deafferentation
Authors: Rasmusson Douglas D.
Published: January 2005

Within the cuneate nucleus of the raccoon, the representations of individual forepaw digits are anatomically separated by densely myelinated laminae. This unique arrangement was utilized to determine whether the terminations of cutaneous afferents from individual digits are precisely restricted to the appropriate region of the cuneate nucleus or overlap with afferents from adjacent digits. By using the transganglionic transport of horseradish peroxidase (HRP), it was found that, for each digit, the terminal labeling was restricted to the appropriate 150–250‐μm‐wide column that extended rostrocaudally throughout the nucleus. The topographical arrangement of digit input corresponded to the known electrophysiology, with the terminal column for the fifth digit located most medially within the nucleus and those for digits 4 to 1 successively more laterally. Within a column, the density of labeling was greater over cell clusters than between clusters. These results indicate that afferents from adjacent digits do not overlap in the cuneate nucleus. In six animals, the fifth digit was amputated, and 2–4 months later, HRP was injected into the nerves of the fourth digit to determine whether its afferents had sprouted into the denervated fifth‐digit column. The projection pattern from the fourth digit in each of these animals was the same as in normal animals and the same as in the intact contralateral side. These results indicate that the reorganization seen in the cerebral cortex following peripheral deafferentation cannot be attributed to changes in the afferent fiber projections to the cuneate nucleus.
Laminar distribution and morphology of gamma‐aminobutyric acid (GABA)‐immunoreactive neurons in the medial and dorsomedial areas of the cerebral cortex of the lizard Podarcis hispanica
Authors: Schwerdtfeger Walter K. , Lorente Maria‐José
Published: January 2005

The morphology and laminar distribution of immunolabeled neurons in the medial and dorsomedial telencephalic cortices of the lizard Podarcis hispanica were examined in vibratome sections after preembedding γ‐aminobutyric acid (GABA)‐immunocytochemistry. In both cortical areas and at all rostrocaudal levels, GABA‐immunoreactive neurons were found in all cortical layers, with the largest number (74%) of GABA‐positive cells in layer 3. GABA‐positive neurons were classified into pyramidlike, vertical‐fusiform, multipolar, and horizontal neurons. Cells that could be so classified were counted in each cortical lamina.

In the medial cortex, multipolar and horizontal‐bipolar cells dominated layer 1. Layer 2 displayed mainly horizontal and pyramidlike cells at its outer margin and pyramidlike cells at its inner margin. In layer 3, horizontal cells were the prevalent group. In the dorsomedial cortex, layer 1 mainly contained small multipolar neurons (35% of layer‐1 cells) in its outer third and vertical‐fusiform neurons (37% of layer‐1 cells) in its inner two thirds. In layer 2, 47% of the few GABA‐positive perikarya were pyramidlike. The largest population of neurons in layer 3 was that formed by multipolar cells (45% of layer‐3 cells).

Ultrastructural examination revealed that GABA‐immunoreactive neurons possessed indented euchromatic nuclei with a central nucleolus. Their cytoplasm contained numerous mitochondria and a very well‐developed granular endoplasmic reticulum. Their somata were contacted by numerous unstained boutons making asymmetric contacts and by a few symmetric synapses of GABA‐positive terminals. Dendrites of GABA‐immunoreactive cells were thin, with irregular outlines, and generally aspinous. Like the somata, dendrites were contacted by many unstained asymmetric synapses. Some dendritic profiles also received symmetric contacts from GABA‐positive boutons.

GABA‐positive terminal‐like puncta were found throughout the layers, with a maximal concentration in layer 2. Electron microscopy confirmed that nearly all of the puncta represent GABA‐positive terminal boutons.

Comparison of GABA‐immunoreactive cells in Podarcis with those found in the mammalian hippocampus suggests that these cells may be inhibitory neurons, as in the hippocampus of mammals.
Intrinsic connections of rat primary visual cortex: Laminar organization of axonal projections
Authors: Burkhalter Andreas
Published: January 2005

The organization of local projections within the rat primary visual cortex (area 17) was investigated by tracing fibers with HRP in in vitro brain slices. The projections from different layers showed distinct laminar patterns. Layer 4 made a strong, topographically precise, projection to lower layer 2/3; weaker projections extended laterally and terminated diffusely in layer 2/3 but also ran vertically to layers 5 and 6. The connections of lower and upper layer 2/3 were reciprocal and point‐to‐point. Within layer 2/3, a large number of fibers ran horizontally and terminated at variable distances from the injection site without making terminal clusters. The main output from layer 2/3 was to layer 5. The most prominent projections from the upper half of layer 5 were to layers 2/3 and 6; lower layer 5, in contrast, made wide‐ranging, clustered projections to layer 1, the bottom of layer 2/3, and the top of layers 4 and 5. The patches were 130–160 μm wide and spaced apart by 230–260 μm. The main projection that arose from the superficial layer 6 terminated in layer 4 above the injection site. In contrast, lower layer 6 made clustered projections to the layer 3/4 border, extending up to 2 mm in the coronal plane. The patches were 190–220 μm wide and spaced apart by 320–390 μm. Additional projections went to the layer 5/6 border and layers 1 and 2.

These results indicate that geniculocortical input is processed through interlaminar connections that are topographically precise, widespread, or patchy. These connectivity patterns suggest a role for these connections in the transformation of functional maps between layers; focused projections preserve the architecture of the layers of origin, and diverging or patchy projections rearrange this organization and form new maps in the target layers (Lund: Annu. Rev. Neurosci. 11:253–288, '88). However, only a few interlaminar connections show one of these patterns in isolation, making it difficult to assign a single function to a particular connection. We, therefore, tentatively conclude that projections terminating in layers 1–4, with the possible exception of the connection between upper layer 6 and layer 4, transform functional maps. In contrast, the topographically precise projections from upper to lower layers preserve functional maps. The specific role of these connections in the construction of receptive field properties, however, is not known. But it is interesting that some of these local connections are clustered and show an organization which is a common feature of intracortical connections in species with a columnar organization of visual cortex.
Developmental plasticity of the rubrospinal tract in the North American opossum
Authors: Xu Xiao Ming , Martin George F.
Published: January 2005

We have shown previously that rubral axons can grow caudal to a lesion of their pathway at thoracic levels of the spinal cord in the developing opossum, Didelphis virginiana. In the present report we expand on that observation and present evidence which suggests that the critical period for plasticity of the rubrospinal tract ends earlier at cervical than at thoracic levels. In addition, we show that most rubrospinal neurons die as a result of axotomy during early stages of the critical period. The opossum was chosen for study because the development of its rubrospinal tract occurs after birth.

In one set of experiments the area containing the rubrospinal tract was lesioned at cervical or thoracic levels and after 30 days or more, retrograde transport techniques were used to determine if rubral axons had grown caudal to the lesion. When the lesions were made at rostral cervical levels between estimated postnatal day 26 and maturity, neurons could not be labeled in the contralateral red nucleus by injections of retrograde markers ipsilateral to the lesion and caudal to it. We were not able to obtain adequate survival after cervical lesions made prior to estimated postnatal day 26. When the lesions were made at mid to caudal thoracic levels between estimated postnatal days 19 and 26, neurons could be labeled in the contralateral red nucleus. When comparable lesions were made at estimated postnatal day 40, there was usually a decrease in the number of labeled neurons, and when they were made at estimated postnatal day 54, none was labeled. In selected cases, operated at estimated postnatal day 19, cell counts provided evidence for loss of neurons in the red nucleus contralateral to the lesion.

In orthograde transport experiments performed on animals with thoracic lesions of the rubrospinal tract made between estimated postnatal days 18 and 33, rubral axons could be labeled caudal to the lesion, and they seemed to take the most direct route around it. Although they sometimes assumed abnormal positions caudal to the lesion, rubral axons appeared to reach areas of the gray matter appropriate to them. When lesions were made at estimated postnatal day 54 or in older animals, labeled axons could be traced to the lesion site but not caudal to it.

In still other experiments rubrospinal neurons were labeled by caudal thoracic or rostral lumbar injections of Fast Blue at estimated postnatal day 26 and 3–4 days later the injected animals were subjected to a lesion of the rubrospinal tract three segments rostral to the injection and ipsilateral to it. They were killed 30–34 days after the lesion so that the red nucleus contralateral to it could be examined for labeled neurons. The results showed that only a few rubrospinal neurons survived axotomy, suggesting that the growth of new axons around the lesion is a major factor in plasticity.
Evidence for an alteration of the tonotopic map in the gerbil cochlea during development
Authors: Sanes Dan H. , Merickel Michael , Rubel Edwin W
Published: January 2005

We have investigated developmental alterations in the tonotopic projection of the gerbil lateral superior olive. Single neurons were characterized in the frequency domain and the recording site marked with fast green. Transverse tissue sections from the auditory brainstem of each animal were visualized with a video‐equipped microscope, and the image was digitized for subsequent alignment. The three‐dimensional display indicated little variation in the rostrocaudal axis, allowing us to collapse the data into a two‐dimensional tonotopic map. The tonotopic map was found to change with age such that the characterstic frequency of neurons in a given anatomical location became successively higher during development. These results are consistent with the hypothesis that the place code gradually shifts in the developing cochlea.
Target dependence of hypoglossal motor neurons during development and in maturity
Authors: Snider W. D. , Thanedar S.
Published: January 2005

We have investigated the target dependence of hypoglossal motor neurons in postnatal rats by transecting the hypoglossal nerve and preventing reinnervation of the tongue. After transection in early postnatal life, approximately 60% of hypoglossal motor neurons die and surviving neurons are markedly atrophic compared to contralateral controls. In maturity, there is also substantial neuronal atrophy and about 30% of motor neurons appear to die after the procedure. However, most hypoglossal neurons in adults survive transection for periods up to 1 year. The adult response is present by 3 weeks of age.

The time course of neuronal atrophy and death after permanent target deprivation was investigated in adult animals. One month after the hypoglossal nerve was deflected, there was marked axonal atrophy, although somatic atrophy was minimal. By 3 months after the procedure substantial neuronal atrophy and apparent cell loss (about 30%) had occurred. There was little change between 3 and 6 months.

We conclude that hypoglossal motor neurons are influenced by connections with their targets in postnatal life. Even in maturity, neurons require target connections for maintenance of axonal and somatic morphology. However, the majority of motor neurons in adult animals can survive target deprivation for prolonged periods.
Immunocytochemical localization of GABAA receptors in goldfish and chicken retinas
Authors: Yazulla Stephen , Studholme Keith M. , Vitorica Javier , De Blas Angel L.
Published: January 2005

A monoclonal antibody (mAb 62–3G1) to the GABAA receptor/benzodiazepine receptor/Cl− channel complex from bovine brain was used with light and electron microscopy in goldfish retina and light microscopy in chicken retina to localize GABAA receptor immunoreactivity (GABAr‐IR). GABAr‐IR was found in the outer plexiform layer (OPL) in both species, in three broad bands in the inner plexiform layer (IPL) of goldfish, and in seven major bands of the chicken IPL. A small percentage of amacrine cell bodies (composing at least three types) were stained in chicken. In goldfish OPL, GABAr‐IR was localized intracellularly and along the plasma membrane of cone pedicles, whereas rod spherules were lightly stained, but always only intracellularly. In chicken, all three sublayers of the OPL were GABAr‐IR. The presence of GABAr‐IR on photoreceptor terminals is consistent with data indicating feedback from GABAergic horizontal cells to cones. In the goldfish IPL, GABAr‐IR was localized to postsynaptic sites of amacrine cell synapses; intracellular staining of processes in the IPL also was observed in presumed “GABAergic” targets. A comparison of GABAr‐IR with the distributions of 3H‐muscimol uptake/binding, glutamate decarboxylase‐IR, GABA‐IR, and 3H‐GABA uptake in the IPL showed either a reasonable correspondence or mismatch, depending on the marker, species, and lamina within the IPL. The distribution of GABAr‐IR in the retina corresponded better with the 3H‐muscimol than with 3H‐benzodiazepine binding patterns yet overall was in excellent agreement with many other physiological and anatomical indicators of GABAergic function. We suggest that intracellular GABAr‐IR represents the biosynthetic and/or degradative pathway of the receptor and we conclude that mAb 62–3G1 is a valid marker of GABAA receptors in these retinas and will serve as a useful probe with which to address the issue of mismatches between the localization of GABAA receptors and indicators of presynaptic GABAergic terminals.
Descending projections from auditory brainstem nuclei to the cochlea and cochlear nucleus of the guinea pig
Authors: Winter Ian M. , Robertson Donald , Cole K. Stewart
Published: January 2005

Projections from auditory brainstem nuclei to the cochlear nuclei in the guinea pig were studied by injection of two retrograde fluorescent neuronal tracers. For seven experiments fast blue was injected into the scala tympani of one cochlea and diamidino yellow was injected into dorsal or anteroventral cochlear nucleus of the same side. The results show that the efferent projections to the cochlea and cochlear nucleus generally form two separate neuronal systems even though they share many common nuclei of origin. The largest projections to the cochlear nucleus come bilaterally from the lateral and ventral nuclei of the trapezoid body. Other nuclei, the lateral superior olive, the ventral nucleus of the lateral lemniscus, the dorsomedial periolivary nuclei, and the medial nucleus of the trapezoid body showed an ipsilateral bias in their projections to the cochlear nucleus.

An upper limit of 3.5% of the medial system olivocochlear efferent neurones projecting to the cochlea were labelled with both diamidino yellow and fast blue, suggesting that few efferent neurones projecting to the cochlea send collaterals to the cochlear nucleus in this species. However, the site of medial system olivocochlear efferent collateral terminations is the granule cell area for the cat, mouse, and gerbil. When diamidino yellow was injected in the superficial layers of the cochlear nucleus, including the superficial granule cell layer of the ventral cochlear nucleus, approximately 3.6% of medial system olivocochlear efferents projecting to the cochlea sent collaterals to the cochlear nucleus.

In three animals fast blue was injected into the cochlear nucleus and diamidino yellow into the cochlea. These experiments revealed a greater proportion of the medial system olivocochlear efferents projecting to the cochlea sending collaterals to the cochlear nucleus, but this proportion was still less than 10%. These results were confirmed by the extracellular injection of horseradish peroxidase into the intraganglionic spiral bundle. Only three medial system olivocochlear efferents were observed to send collaterals to the cochlear nucleus. This number was less than 10% of all labelled medial system fibres.

Although these experiments suggest that in the guinea pig the number of olivocochlear efferents sending collaterals to the cochlear nucleus is considerably smaller than is found for the cat, mouse, and gerbil, it is not possible with the current experimental procedures to conclude whether the results are due to species or methodological differences.
Multiple types of neuropeptide Y‐containing neurons in primate neocortex
Authors: Kuljis Rodrigo O. , Rakic Pasko
Published: January 2005

The avidin‐biotin‐peroxidase method was used at the light and electron microscopic levels to analyze neuropeptide Y (NPY)‐containing neurons in the neocortex of six adult macaque monkeys. Regions studied included various sensory, motor, limbic, and association areas, designated as 17, 18, 7, 22, 3, 4, 6, 24, and 9 by Brodmann (Beiträge zur Histologischen Lokalisation der Grosshirnrinde. Leipzig: Barth, '06). Several types of NPY‐containing neurons can be distinguished by their laminar location, by the size of their perikarya, and by the size, shape, and pattern of ramification of their processes: (1) layer I small local circuit neurons; (2) layer II granule cells; (3) aspiny stellate cells located in layers II–III and V–VI, with long, slender dendrites; (4) sparsely spiny stellate cells; (5) aspiny stellate cells with long, horizontally oriented dendrites, whose cell body is situated in layer VI; (6) Martinotti cells in areas 9, 7, and 24; and (7) multipolar neurons situated in the white matter subjacent to the cortical gray. The possibility of additional neuronal types containing NPY is suggested by labeled densely spinous dendrites in area 6 and recurving axons and axonal loops in the supragranular layers in areas 7 and 9. No NPY‐containing neurons were found in layer IV of any area, except layers IVA and B of the visual cortex. Likewise, nonneuronal elements were not labeled. The regional differences in the distribution of some NPY‐containing neuron types may reflect adaptations of local neuronal circuits for specialized functions.
Fluorescent histochemical localization of neutral endopeptidase‐24.11 (enkephalinase) in the rat spinal cord
Authors: Back Stephen A. , Gorenstein Charles
Published: January 2005

The localization of neutral endopeptidase‐24.11 (E.C. 3.4.24.11; enkephalinase) in rat spinal cord was investigated by a novel fluorescent histochemical method. Enkephalinase was localized by using a coupled enzyme assay based upon the sequential cleavage of the synthetic peptide substrate glutaryl‐ala‐ala‐phe‐4‐methoxy‐2‐naphthylamide by enkephalinase and exogenous aminopeptidase M. Enzyme distribution was examined in segments from cervical, thoracic, lumbar, and sacral cord.

At all spinal cord levels, enkephalinase was localized to discrete regions of the gray matter. The substantia gelatinosa displayed rich enkephalinase staining which overlapped the inner and outer zones of lamina II. A staining pattern similar to that observed in lamina II was observed in the spinal trigeminal nucleus in the medulla. In lamina III the enzyme was associated with small and medium‐sized cells. Lamina IV showed staining associated with medium‐sized and large cell bodies. The medial boundary of the dorsal gray of laminae IV and V had medium‐sized fusiform cells which stained for enkephalinase. In the lateral reticulated areas of lamina V, enkephalinase reaction product was localized to scattered medium‐sized and large cells compressed against the white matter of axon bundles. Staining in lamina VI was similar in appearance to lamina V. Enkephalinase reaction product was widely distributed in the ventral horn. Numerous ventral horn motor neurons of varied size and morphology in laminae VIII and XI stained richly for the enzyme. The enzyme was also localized to medium‐sized and large cells in lamina X and to cells of the central cervical nucleus.

The size and morphology of the cell types associated with the enzyme supported a neuronal association for enkephalinase. The regional distribution of the enzyme overlapped that of enkephalin‐ and substance‐P rich regions of the spinal cord. These findings support a role for enkephalinase in the metabolic regulation of centrally acting neuropeptides.
Neural organization of the masseter muscle in the pig
Authors: Herring Susan W. , Anapol Fred C. , Wineski Lawrence E.
Published: January 2005

The neural organization of the pig masseter, an architecturally and functionally compartmentalized muscle, was investigated by using dissection, glycogen depletion, evoked electromyography, and counts of axon numbers at various levels along the masseteric nerve. The masseteric nerve enters the muscle as two rostral branches, which also supply the zygomatico‐mandibularis, and a more caudal main branch, which soon divides into four terminal nerves with variable distributions. Stimulation of filaments containing roughly 50 extrafusal motor axons resulted in glycogen depletion of 5–20% of the muscle fibers in very small subvolumes of the masseter; the affected subvolumes were delimited by perimysium. Electromyography after stimulation of various branches of the nerve confirmed the distributions deduced from anatomy and further indicated that axons do not branch between the rostral and main nerve branches but may occasionally do so among the more distal terminal branches of the main branch. The proximal trunk of the masseteric nerve contains about 3,500 myelinated fibers with a bimodal size distribution. Approximately 1,000 of the larger fibers were estimated to be extrafusal motor axons. Along the proximal trunk of the nerve, fibers were constantly rearranged; coupled with the observation that the locations of motor unit territories were usually not related to the position of the stimulated axons within the nerve, this suggests that the nerve trunk is not strictly ordered somatotopically.
Hormonal control of neuron number in sexually dimorphic spinal nuclei of the rat: III. Differential effects of the androgen dihydrotestosterone
Authors: Sengelaub D. R. , Nordeen E. J. , Nordeen K. W. , Arnold A. P.
Published: January 2005

The spinal cord of the rat contains two sexually dimorphic nuclei: the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN). These nuclei and the perineal muscles they innervate are present in males but reduced or absent in females. The sex difference in motoneuron number in these nuclei is due to an androgen‐regulated motoneuron death. Developing females treated with the androgen testosterone propionate (TP) have a fully masculine number of SNB and DLN motoneurons and retain the perineal muscles they would normally have lost. Paradoxically, females treated prenatally with the androgen dihydrotestosterone propionate (DHTP) also retain the perineal musculature but as adults lack the SNB motoneurons which would normally innervate them. The SNB target muscles retained by DHTP females are anomalously innervated by motoneurons in the DLN.

Counts of motoneurons and degenerating cells in the developing SNB of DHTP‐treated females showed that their feminine number is the result of a failure of DHTP to prevent the death of SNB motoneurons. Furthermore, the peak number of SNB motoneurons was below that of normal females, suggesting that DHTP treatment may also have inhibited motoneuronal migration. However, DHTP treatment fully masculinized both motoneuron number and degenerating cell counts in the DLN of these females, and it is this masculinized DLN that gives rise to the anomalous projection. Taken together, these results suggest that the effects of different androgens during development are specific and complex, involving the regulation of motoneuron death, migration, and specification of peripheral projections.
Origins of the descending spinal projections in petromyzontid and myxinoid agnathans
Authors: Ronan Mark
Published: January 2005

The origins of the descending spinal pathways in sea lampreys (Petromyzon marinus), silver lampreys (Ichthyomyzon unicuspis), and Pacific hagfish (Eptatretus stouti) were identified by the retrograde transport of horseradish peroxidase (HRP) placed in the rostral spinal cord. In lampreys, the majority of HRP‐labeled cells were located along the length of the brainstem reticular formation in the inferior, middle, and superior reticular nuclei of the medulla, mesencephalic tegmentum, and nucleus of the medial longitudinal fasciculus. Labeled reticular cells included the Mauthner and Müller cells. Horseradishperoxidase‐filled cells were also present in the descending trigeminal tract, intermediate and posterior octavomotor nuclei, and a diencephalic cell group, the nucleus of the posterior tubercle. As in lampreys, the reticular formation of the Pacific hagfish was the largest source of descending afferents to the spinal cord. Labeled cells were found in the dorsolateral and ventromedial reticular nuclei, the dorsal tegmentum at the juncture of the medulla and midbrain, and the nucleus of the medial longitudinal fasciculus. Additional medullary cells projecting to the cord were located in the perivagal nucleus, the central gray, and the anterior and posterior magnocellular octavolateralis nuclei. The existence of reticulospinal and possible vestibulo‐, trigemino‐, and solitary spinal projections in lampreys and hagfishes and the wide distribution of these pathways in jawed vertebrates suggest that they evolved in the common ancestor of gnathostomes and both groups of jawless fishes. However, descending spinal pathways from the cerebellum, red nucleus, and telencephalon appear to be gnathostome characters.
Morphology of peptide‐immunoreactive neurons in the rat central nucleus of the amygdala
Authors: Cassell M. D. , Gray T. S.
Published: January 2005

The morphological characteristics of peptide‐immunoreactive neurons in the rat central nucleus of the amygdala were examined. Observations were compared with details of neuron morphology available from Golgi‐stained tissue to determine whether peptide immunoreactivity was associated with specific cell types in the central nucleus. The lateral subdivision (CL) of the central nucleus contained mainly medium‐sized, densely spiny neurons. Larger, pyramiform spiny neurons; medium‐sized, sparsely spinous neurons; and small, aspinous cells were also present in CL. Somatostatin−, neurotensin−, corticotropin‐releasing factor (CRF)‐, and enkephalin‐immunoreactive neurons in CL were characterized as the medium spiny and larger, pyramiform types. No obvious morphological differences were evident among medium spiny neurons containing different peptides. In the medial subdivision, substance P, neurotensin, somatostatin, and CRF were present within pyramiform, sparsely spinous neurons with long dendrites. Galanin immunoreactivity in the medial subdivision was associated with moderately spiny, pyramiform neurons and a larger, aspinous, polygonal neuron. The ventral subdivision of the central nucleus contained neurons similar to those found in the adjacent medial and lateral subdivisions. In addition, this subdivision contained a characteristic ovoid neuron with long, sparsely spinous dendrites. Vasoactive intestinal polypeptide (VIP) and neurotensin appeared to be present within this cell type. In the lateral capsular subdivision, neurotensin and enkephalin were present in cells resembling the medium spiny neurons characteristic of this part of the central nucleus. Numbers of spindle‐shaped, bipolar somatostatin, and VIP neurons were identified in the medial, lateral, and ventral subdivisions.

The present results provide evidence for a heterogeneous morphology of peptide‐immunoreactive neurons in the rat central nucleus that are distributed across cytoarchitectonic boundaries. Except for substance P, neuropeptides in the central nucleus appear to be expressed by a variety of neurons rather than morphologically characteristic types of cell.
Nigrotectal projection to the inferior colliculus: Horseradish peroxidase transport and tyrosine hydroxylase immunohistochemical studies in rats, cats, and bats
Authors: Olaźbal U. E. , Moore J. K.
Published: January 2005

The present study investigated descending projections from the substantia nigra to the auditory tectum. Small (0.02–0.05 μl) injections of a 30–60% aqueous solution of horseradish peroxidase (HRP) were made unilaterally into the inferior colliculus in rats, cats, and bats (Eptesicus fuscus). Tissue blocks including the substantia nigra, superior colliculus, and inferior colliculus were removed, sectioned, and processed for visualization of HRP. Results show that the substantia nigra, pars lateralis, projects to the inferior colliculus ipsilaterally. In addition, retrogradely labeled cells are found dorsal to the pars lateralis, in a column within the lateral tegmental area of the midbrain. Analysis of injection sites suggests that the principal target of this nigral projection is the dorsal and rostral pericentral region of the inferior colliculus. Immunohistochemical studies with an antibody to tyrosine hydroxylase demonstrate catecholaminergic neurons within the pars lateralis and lateral tegmentum that are similar in location and morphology to one class of HRP retrogradely labeled cells within these structures. These immunohistochemical studies also demonstrate a plexus of fine, varicose tyrosine hydroxylase‐positive axons in the rostral pericentral region of the colliculus. The presence of this nigrotectal projection to the inferior colliculus is discussed in relation to its possible role in the control of acousticomotor behavior.
Tyrosine phosphorylation in the postnatal rat brain: A developmental, immunohistochemical study
Authors: Tillotson Meryl Lee , Wood John G.
Published: January 2005

We have used antibodies against phosphotyrosine to probe 50‐μm cerebellar sections from rats of various ages as well as sections of adult brainstem, cerebrum, and olfactory bulb to investigate the developmental appearance of this phosphorylation system as revealed by light microscopy. While the overall intensity of staining in the cerebellum was highest at 7 days, the pattern of staining in the adult is quite disparate from that seen in younger animals. From 10 to 21 days postnatal, staining is associated primarily with the white matter and/or the lower premigratory zone of the external granular layer and adjacent formative molecular layer. While the temporal and spatial appearance of phosphotyrosine immunoreactivity corresponds well to the established patterns of axonal growth in these areas, we cannot at the light level ascertain whether the immunoreactivity is intrinsic or extrinsic to the growing fibers. In animals 28 days and older, however, staining is restricted to a subpopulation of multipolar cells distributed throughout the cerebellum, as well as the olfactory bulb, cerebrum, and brainstem. The phosphotyrosine‐positive cells in the adult cerebellum are not comparable to glial‐fibrillary‐acidic‐protein‐immunoreactive elements with regard to morphology or distribution, and they fail to colocalize with neuronal somata stained with anti‐microtubule‐protein‐2 antibodies. While it appears that the radial fibers of the Bergmann glia in the external granular layer stain at 7 days, there is no staining detected in the mitotically active neuroblasts of this layer at any age. We conclude that in the immature cerebellum, the majority of tyrosine phosphorylation detectable by this method may be involved in the formation and growth of axonal processes. In the adult rat cerebellum, however, it is most likely that detectable tyrosine phosphorylation occurs in the somata and processes of a neuroglial subpopulation.
Morphology of jaw‐muscle spindle afferents in the rat
Authors: Dessem Dean , Taylor Anthony
Published: January 2005

The morphology of jaw‐muscle spindle afferents in the rat has been studied by intra‐axonal injection of horseradish peroxidase. All stained axons were located in the motor root of the trigeminal nerve and could be traced dorsomedially to the vicinity of the trigeminal motor nucleus, where they divided into an ascending branch in the tract of the mesencephalic nucleus and a descending branch in the tract of Probst. Axon collaterals and swellings on fine collateral branches presumed to be synaptic boutons were located in the following regions: the trigeminal motor nucleus, the region dorsal to the trigeminal motor nucleus including the supratrigeminal nucleus, the parvicellular reticular formation immediately caudal to the trigeminal motor nucleus, the reticular formation at the level of the facial nucleus, and the caudal portion of the mesencephalic nucleus. No evidence of a projection to the cerebellum was observed. Boutons were most numerous in the region surrounding the trigeminal motor nucleus, especially dorsally. Here they were not demonstrated in close proximity to counterstained cells, and therefore it was not possible to determine how many of these contacts are located on cells in this region and how many are on the distal dendrites of trigeminal motorneurons. Boutons located within the trigeminal motor nucleus were always confined to a small portion of the nucleus and were significantly larger than those located dorsally. Some boutons were found in close apposition to trigeminal motor‐neurons and presumably make somatic contacts. These results suggest that jaw‐muscle spindle afferents make somatic and proximal dendritic contacts with only a limited number of trigeminal motorneurons and also project to masticatory interneuronal regions dorsal and caudal to the motor nucleus.