bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the selectivity of the impregnation of neurons by the Golgi method
Authors: Shimono Masatake , Tsuji Nobuyuki
Published: January 2005

The selectivity of the impregnation of neurons by the Golgi method was examined by comparing Nissl‐stained specimens with Golgi‐stained specimens in terms of the somatic orientation, cross‐sectional area, and long and short axes of the soma in the ventromedial hypothalamic nucleus (VMH) and lateral hypothalamic area (LHA) of 5‐week‐old rats. With regard to somatic orientation, we made comparisons directly between the Nissl distribution pattern and the Golgi pattern. The two distribution patterns did not differ significantly in either VMH or LHA (Smirnov test, P > 0.05). For somatic cross‐sectional area and diameter (long and short), a mean value of every 10% of the total frequency was estimated for each histogram; the histogram was segmented into 10 percentile frequency domains, and a mean value for each domain was estimated. A linear regression was calculated between Golgi mean values and Nissl's at the same place. By use of the linear regression, all of the observed values on Nissl sections for somatic cross‐sectional area and diameter were transformed into their corresponding Golgi values. The frequency distribution of these transformed Nissl values was compared with that of the actually observed Golgi values. There was a high degree of similarity between the two distribution patterns in all regions examined for long and short diameters as well as cross‐sectional area of the soma (Smirnov test, P > 0.05). These findings suggest that the sampling of VMH and LHA neurons in the Golgi method used in the present study is similar to the corresponding sampling in Nissl preparation. The result thus provides evidence that the Golgi method impregnates neurons nonselectively, at least hypothalamic neurons. We have also demonstrated, through direct comparisons between Nissl and Golgi specimens, that somatic orientation serves as a useful parameter in the evaluation of the selectivity/nonselectivity of the Golgi method.
Synaptic circuits involving an individual retinogeniculate axon in the cat
Authors: Hamos James E. , Van Horn Susan C. , Raczkowski Denis , Sherman S. Murray
Published: January 2005

In order to describe the circuitry of a single retinal X‐cell axon in the lateral geniculate nucleus, we physiologically characterized such an axon in the optic tract and injected it intra‐axonally with horseradish peroxidase. Subsequently, we recovered the axon and employed electron microscopic techniques to examine the distribution of synapses from 18% of its labeled terminals by reconstructing the unlabeled postsynaptic neurons through a series of 1,200 consecutive thin sections. We found remarkable selectivity for the axon's output, since only four of the 43 available neurons in a limited portion of the terminal arbor receive synapses from labeled terminals. Moreover, the distribution of these synapses on the four neurons, which we term cells 1 through 4, varies with respect to synapses from other classes of terminals that contact the same cells, including synapses from unlabeled retinal terminals. For cells 1 and 3, the labeled terminals provide 49% and 33%, respectively, of their retinal synapses, and these are located on both dendritic shafts and appendages. Synapses from the injected axon to these cells are thus integrated with those from other retinal axons. For cell 2, the labeled terminals provide 100% of its retinal synapses, but these synapses converge on clusters of dendritic appendages where they are integrated with convergent inhibitory inputs. Finally, for cell 4, the labeled terminals provide less than 2% of its retinal inputs, and these are distally located; we suggest that these synapses are remnants of physiologically inappropriate miswiring that occurs during development. The findings from this study support a concept of selectivity in neuronal circuitry in the mammalian central nervous system and also reveal some of the diverse integrative properties of neurons in the lateral geniculate nucleus.
Growth of axons into developing muscles of the chick forelimb is preceded by cells that stain with Schwann cell antibodies
Authors: Noakes Peter G. , Bennett Max R.
Published: January 2005

A study has been made of the development of limb and muscle nerves in relation to the first appearance of Schwann cells in the flexor digitorum profundus (fdp) and flexor carpi ulnaris (fcu) muscles of the avian forelimb. Schwann cells were identified by immunofluorescent techniques with antibodies to the glycoprotein HNK‐1. Myotubes and nerves were identified by using antibodies to myosin and to neurofilament, respectively. At stage 24/25 The brachialis longus inferior (Bli n) and superior (Bls n) nerve trunks within proximal regions of the forelimb were surrounded by Schwann cells. These cells extended in a column for a distance of approximately 100 μm beyond the growing ends of nerves. At stage 26 both interosseus nerve (in n) and the medial‐ulnar nerve (m‐u n) had formed from the Bli n; each of these branches was surrounded by Schwann cells, which again extended approximately 100 μm beyond the growing ends of the nerves. By stage 26/27 the fdp and fcu muscles were clearly delineated by groups of myotubes. No nerves were detected within these groups; however, Schwann cells were observed between the myotubes. At stage 27 axons had left the in n and m‐u n and grown into the fdp and fcu muscles, respectively. These axons were surrounded by Schwann cells.

The present observations show that Schwann cells are located ahead of the main limb and muscle nerves as they grow into the fdp and fcu muscles of the limb. It is possible that these Schwann cells play a role in guiding nerves to their correct muscles in the developing chick forelimb.
Connections between pyramidal neurons in layer 5 of cat visual cortex (area 17)
Authors: Gabbott P. L. A. , Martin K. A. C. , Whitteridge D.
Published: January 2005

The structural features of two physiologically‐characterised pyramidal neurons (PC1 and PC2) closely situated in layer 5b in the visual cortex (area 17) of a single cat were studied using a combination of electrophysiological and anatomical techniques. Both PC1 and PC2 had exceptionally large somata (30–40 μm in diameter). On the basis of this and other morphological features cell PC1 was classified as a Meynert cell. PC1 possessed a very large (2.75° × 4.50°) binocularly driven standard complex receptive field. PC2 was also binocularly driven with a small, B‐type receptive field. Both cells had the same preference for the direction and orientation of visual stimuli. PC1 and PC2 could be antidromically activated from stimulating electrodes positioned above the dorsal lateral geniculate nucleus with a response latency indicating that these cells probably innervated the visual tectum or pretectum.

In addition to corticoefferent axons, the two neurons possessed extensive intracortical axon arbors that ramified extensively in layers 5 and 6 of the medial and lateral banks of the lateral gyrus in area 17. Axon collaterals from both PC1 and PC2 also innervated a small common target region in area 18. A total of 313 boutons from the axonal arbors of PC1 and PC2 were examined in the electron microscope. All of the identified synaptic junctions were found to establish Gray type 1 asymmetrical contacts. The combined ultrastructural data for both neurons indicated that 80% of boutons were onto dendritic spine heads, with 14%, 6%, and 1% onto small‐, medium‐, and large‐calibre dendritic shafts, respectively. The spectrum of postsynaptic targets showed little variation with respect to lamina, distance from somata, or cortical area. Other large pyramidal neurons in layer 5 and spiny neurons in layer 6 were identified as receiving synaptic input from either PC1 or PC2.

Using a computer graphics system, rotations of the bouton distributions revealed the existence of a clustered innervation of layers 5 and 6 in areas 17 and 18 derived from the two identified neurons. The bouton distributions strongly resembled the tangential pattern described previously for the functional slab‐like organisation of the cortex.

The results provide a morphological basis for the clustered intrinsic connectivity of pyramidal cells in layers 5 and 6 of the cat visual cortex. Furthermore, the results indicate the widespread excitatory influence of large pyramidal neurons on other cells projecting subcortically to sites dealing with visually guided behavior.
Projections of the lateral hypothalamus and bed nucleus of the stria terminalis to the dorsal vagal complex in the pigeon
Authors: Berk Mitchell L.
Published: January 2005

The dorsal vagal complex is composed of the nucleus tractus solitarii (Nts) and the dorsal motor nucleus of the vagus (DMN X). In the pigeon, these nuclei are composed of cytoarchitectonically well‐defined subnuclear groups, which have connections that are partially segregated to specific organs (Katz and Karten: J. Comp. Neurol. 218:42–73, '83b, J. Comp. Neurol. 242:397–414, '85). The present study sought to determine whether forebrain afferents to Nts‐DMN X are differentially distributed to specific subnuclei and thereby modulate the functions of specific organs.

Forebrain afferents to the dorsal vagal complex were determined by retrograde tracing techniques. Labeled perikarya were found in the bed nucleus of the stria terminalis (BNST), ventral paleostriatum, and stratum cellulare externum (SCE) of the lateral hypothalamus, and in the medial hypothalamus, nucleus periventricularis magnocellularis (PVM), which is the avian homologue to a portion of the mammalian paraventricular nucleus. The pattern of axonal distribution to Nts‐DMN X subnuclei from the BNST‐ventral paleostriatum and SCE were investigated by anterograde tracing techniques. These experiments revealed axonal projections distributed to specific Nts‐DMN X subnuclei. However, there is a high degree of overlap of the axonal projections to Nts‐DMN X subnuclei from BNST‐ventral paleostriatum and SCE, as well as from PVM (Berk and Finkelstein: J. Comp. Neurol. 220:127–136, '83). Labeled fibers from BNST‐ventral paleostriatum and SCE project heavily to Nts subnuclei medialis superficialis, lateralis dorsalis, and medialis ventralis and to DMN X subnucleus ventralis parvicellularis. Fewer labeled fibers were found in Nts subnucleus medialis intermedius and extremely sparse labeling was found in Nts sub‐nucleus medialis dorsalis. The Nts and DMN X subnuclei that receive forebrain projections also have peripheral connections with the aortic nerve, crop, esophagus, glandular stomach, and caudal abdominal organs. Thus, the forebrain could modulate the functions of these segments of the cardiovascular and digestive systems.
Glutamic acid decarboxylase‐like immunoreactivity in brainstem auditory nuclei of the rat
Authors: Moore Jean K. , Moore Robert Y.
Published: January 2005

The distribution of GABA‐producing neurons in the brainstem auditory nuclei of the rat was investigated immunohistochemically by using an antibody to glutamic acid decarboxylase (GAD). In the cochlear nuclei, GAD immunoreactive neurons are present only in the superficial granular and molecular layers, whereas terminals are found in all subdivisions of the nuclei and are particularly dense surrounding large spherical cells and one type of stellate cell. In the superior olivary complex, GAD immunoreactive neurons are located in the lateral olivary nucleus and throughout the periolivary region. Immunoreactive terminals are distributed along dendrites of principal cells of the medial and lateral olivary nuclei and are clustered around somata of globular neurons of the nucleus of the trapezoid body. An extremely dense band of immunoreactive somata and terminals is present along the ventral edge of the olivary complex. The ventral, intermediate, and dorsal nuclei of the lateral lemniscus contain small fusiform GAD‐immunoreactive neurons and a moderately dense plexus of immunoreactive terminals. The inferior colliculus contains a large population of GAD‐immunoreactive perikarya and an extremely dense accumulation of immunoreactive terminals in the central, dorsomedial, and external nuclei. These observations indicate that GABA systems are involved in function at all levels of the brainstem auditory pathway.
Nerve cell atrophy and loss in the inferior olivary complex of “Purkinje cell degeneration” mutant mice
Authors: Ghetti Bernardino , Norton James , Triarhou Lazaros C.
Published: January 2005

The genetically determined loss of cerebellar Purkinje cells (PCs) in “Purkinje cell degeneration” (pcd) mutant mice deprives inferior olivary (IO) neurons of their major postsynaptic target. The degeneration of PCs starts on postnatal day (P) 17 and loss of these neurons is virtually complete by P45. We examined the inferior olivary complex (IOC) of normal and pcd mutant mice by quantitative light microscopy to determine whether the degeneration of PCs is associated with atrophy and loss of their presynaptic neurons in the IOC. The number of IO neurons in 17‐day‐old mutants did not differ significantly from controls (P ≥.1). IO neurons in 23‐day‐old mutants were 23% (95% confidence limits: 12–34%) fewer than in age‐matched controls, and in 300‐day‐old mutants they were 48% (95% confidence limits: 37–58%) fewer than in their controls (P ≤.001 in both cases). The decline of the number of IO neurons in pcd mice between days 17 and 300 was 49% (P <.0001; 95% confidence limits: 38–57%). The medial accessory olive (MAO) appeared less affected than the principal (PO) and the dorsal accessory olive (DAO). The mean neuronal diameter in control mice was 11.6 μm at 23 days and 10.8 μm at 300 days of age. The respective values in pcd mutants were 11.5 μm and 8.7 μm. Diameters in old mutants were significantly smaller than those in both age‐matched controls and young mutants (P ≤.001). These findings suggest that in the mature olivocerebellar system the stability of IO neurons depends on the state of their postsynaptic PCs.
P2, P1, and P0 myelin protein expression in developing rat sixth nerve: A quantitative immunocytochemical study
Authors: Hahn A. F. , Whitaker J. N. , Kachar B. , deF. Webster H.
Published: January 2005

Myelination and the expression of myelin proteins P2, P1, and P0 were studied quantitatively in the rat sixth cranial nerve during development. The postnatal development and growth of all myelin sheaths in this nerve have been studied morphometrically in a companion paper. Epon‐embedded blocks with closely matched topography in the transverse plane were selected from rats perfused at ages 1–4, 8, 15, and 20 days. From each block, serial semithin sections were cut, etched, and immunostained according to the peroxidase‐antiperoxidase method with well‐characterized polyclonal antisera that reacted specifically with P0 glycoprotein and the basic proteins P1 and P2. The immunoreactivities of individual myelin sheaths were measured by densitometry. Numbers of compact myelin lamellae, myelin spiral lengths, and axon diameters were determined on electronmicrographs of adjacent thin sections. At birth anti‐ P0 immunoreactivity was found on sheaths with two and more compact lamellae; neither P1 nor P2 immunoreactivity was observed. On day 2, myelin sheaths with five and eight lamellae were stained respectively by anti‐ P1 and anti‐ P2. On day 3 the percentages of myelin sheaths stained were substantially higher: P0 95%, P1 78%, P2 15%. By day 4, anti‐ P0 and anti‐ P1 immunoreactivity was present in 95% of myelin sheaths; 35% were stained by anti‐ P2. For P2, staining intensity and percentage of myelin sheaths stained continued to increase and by day 20, 85% were anti‐ P2‐positive.

The density of immunoreactivity was not uniform in all myelin sheaths. At young ages staining varied with all three proteins. The variability decreased as myelin sheaths thickened; it persisted longest for anti‐ P2. We conclude that the density and distribution of immunoreactivities of P0, P1, and P2 reflect their relative concentrations during myelin sheath development and growth. We attribute lack of detectable anti‐ P2 immunoreactivity in some small sheaths at 20 days to their early stage of myelination and also to limitations of the method. We infer from our observations that all myelin‐forming Schwann cells express P2 basic protein.
Physiological evidence for branching of peripheral unmyelinated sensory afferent fibers in the rat
Authors: McMahon Stephen B. , Wall Patrick D.
Published: January 2005

Single unmyelinated sensory afferent nerve fibers were recorded in dorsal root filaments in urethane‐anesthetized or in decerebrate‐spinal rats. The peripheral branch of these axons ran in the sural nerve where they were stimulated by tungsten microelectrodes. All action potentials showed the characteristics of single fiber responses with a fixed all or none shape and a fixed latency at a given stimulus strength. In all units, the action potential evoked from a proximal stimulus site collided with the action potential evoked from a distal stimulus site.

Of the 44 single units isolated, 17 showed the expected small progressive decrease of latency of the recorded impulse as the stimulus strength at a fixed point on the sural nerve was progressively raised above threshold. However, in 27 units there was an abrupt jump decrease of latency as the stimulus rose above the threshold. The average size of this latency shortening was 2.2 msec, which occurred as the stimulus strength rose a mean 21% above threshold. As the stimulus rose above threshold, 7 fibers showed 3 different fixed latencies and 2 fibers showed 4 fixed latencies. In order to test the possibility that the peripheral nerve contained 2 branches of the same axon with one conducting slower than the other, the peripheral nerve was stimulated at progressively longer conduction distances. As predicted, the difference between the 2 fixed latencies became larger as the conduction distance increased.

We discuss 6 possible explanations for the results and conclude they are consistent with the proposals that some fibers branch distal to the dorsal root ganglion and some branches do not establish a functional sensory ending in the periphery.
Ultrastructural evidence of the formation of synapses by retinal ganglion cell axons in two nonstandard targets
Authors: Cantore William A. , Scalia Frank
Published: January 2005

After unilateral ablation of the optic tectum in the frog (Rana pipiens), retinal ganglion cell axons enter the lateral thalamic neuropil in large numbers. This area is normally a target of the tectal efferent projection but is not innervated directly from the retina in normal frogs nor in frogs undergoing optic nerve regeneration in the presence of an intact tectum. The ability of retinal axons to form synaptic contacts in this nonstandard target, previously suspected only from light microscope studies, has been ultrastructurally verified in the present investigation. Retinal axon terminals were selectively labeled for light and electon microscope study by introducing horseradish peroxidase (HRP) into the optic nerve 73–413 days after unilateral ablation of the contralateral optic tectum. In some of the frogs, the optic nerve had also been crushed to test the ability of retinal axons regenerating over a long distance to form this connection. The HRP‐labeled retinal axon terminals had the same untrastructural morphology whether located in the lateral thalamic neuropil or in the correct regions of projection, e.g., the lateral geniculate complex. They contained clear, spherical synaptic vesicles and made Gray type I synapses on the unlabeled postsynaptic dendrites, The magnitude of the projection was disproportionately greater in animals having complete or nearly complete tectal ablation than in a specimen in which the lesion was significantly incomplete. An aberrant projection was also observed in the nucleus isthmi in some of the specimens.

These findings have significance for chemoaffinity theories of the specification of synaptic connections in that the ability of retinal axons to synapse in nonstandard targets in this experimental context may be considered evidence for the expression of appropriate cell‐surface recognition‐molecules by the abnormally targeted postsynaptic neurons. The likelihood that the expression of these postsynaptic labels is normally repressed transynaptically by molecular signals from the intact tectal input is discussed.
Immunocytochemical distribution of met‐enkephalin‐Arg6‐Gly7‐Leu8 in the rat lower brainstem
Authors: Murakami Sadatsugu , Okamura Hitoshi , Yanaihara Chizuko , Yanaihara Noboru , Ibata Yasuhiko
Published: January 2005

The distribution of methionine‐enkephalin‐Arg6‐Gly7‐Leu8, a unique peptide derived from proenkephalin A in the rat brainstem, was studied immunocytochemically by using a highly specific antiserum to this octapeptide sequence.

Immunoreactive perikarya with various shapes and sizes were detected in many regions of the rat brainstem. Dense accumulation of immunoreactive perikarya and fibers was seen in the nuclei associated with special sensory and visceral functions, such as the interpeduncular nucleus, the parabrachial nucleus, the nucleus of the solitary tract, and the nucleus of the spinal tract of the trigeminal nerve. Clusters of methionine‐enkephalin‐Arg6‐Gly7‐Leu8–like immunoreactive perikarya and fibers were observed in certain areas considered to play a role in nociception and analgesia, such as the central gray of the midbrain central gray and the raphe magnus nucleus. Some methionine‐enkephalin‐Arg6‐Gly7‐Leu8‐like immunoreactive perikarya were distributed in the lateral reticular nucleus, the nucleus of the solitary tract, and the raphe magnus nucleus, where monoaminergic neurons were also detected. In addition to the previously reported enkephalinergic cells, we found many methionine‐enkephalin‐Arg6‐Gly7‐Leu8 containing neurons; the rostral and caudal linear nucleus of raphe, the median raphe nucleus, entire length of the raphe magnus nucleus, the medial longitudinal fasciculus, the cuneate nucleus, the external cuneate nucleus, the gracile nucleus, and the area postrema. The wide distribution of this octapeptide‐like immunoreactivity reflected neurons expressing the preproenkephalin A gene distributed more widely than previously reported and that innervated many regions.
Hippocampus of the seizure‐sensitive gerbil is a specific site for anatomical changes in the GABAergic system
Authors: Peterson Gary M. , Ribak Charles E.
Published: January 2005

The brains of seizure‐sensitive (SS) and seizure‐resistant (SR) gerbils were studied with an immunocytochemical method to localize glutamic acid decarboxylase (GAD) to determine whether a defect existed in the inhibitory GABAergic system similar to that which has been reported in animal models of focal epilepsy in which GABAergic cell bodies and terminals are decreased in number. A major difference between the two strains of gerbils was found in the number of GABAergic neurons in the hippocampal formation. Specifically, a paradoxical increase occurred in the number of glutamate decarboxylase (GAD)‐immunoreactive neurons: there were approximately 65% more GABAergic cells within the dentate gyrus and the CA3 region of the hippocampus in the SS gerbils. Furthermore, the density of GAD‐immunoreactive puncta, the light microscopic correlates of synaptic boutons, was greater in the SS animals. Other histological methods were used to determine if the difference between SS and SR gerbils was specific for the GABAergic system. Nissl‐stained preparations showed that the number of granule cells in the dentate gyrus was 20% greater in SS gerbils than in SR gerbils. An examination of some hippocampal afferents, efferents, and intrinsic connections with acetylcholinesterase histochemistry and the Timm's stain for heavy metals demonstrated no differences between the two strains. In addition, Golgi‐stained preparations of the dentate gyrus indicated that the morphology of basket cells did not differ between the two strains nor between the gerbil and the rat.

Several brain regions in addition to the hippocampus were studied to determine whether or not the increased number of GAD‐immunoreactive neurons was specific for the hippocampal formation. These regions included the substantia nigra, motor cortex, and nucleus reticularis thalami and were selected because they contain large populations of GABAergic neurons and have been implicated in seizure activity. No differences between the two strains were detected in any of these regions. Therefore, a major morphological difference between the brains of SS and SR gerbils exists in the hippocampal formation of SS gerbils in which an increase occurs in the number of GABAergic neurons and granule cells. If these additional inhibitory neurons act mainly to inhibit other inhibitory neurons, the net effect would be increased disinhibition of the principal excitatory neurons of the hippocampal formation. This could lead to seizure activity within the hippocampal formation and at distant sites through multiple synaptic connections.
The early development of neurons with GABA immunoreactivity in the CNS of Xenopus laevis embryos
Authors: Roberts Alan , Dale N. , Ottersen O. P. , Storm‐Mathisen J.
Published: January 2005

We have used an antibody to glutaraldehyde fixation complexes of γ‐amino butyric acid (GABA) to stain the developing central nervous system of Xenopus laevis embryos. Neuronal somata, growth cones, axons, and dendrites were found with GABA‐like immunoreactivity. Transmission electron microscope (TEM) observations were made of axons and synapses. By observation of the earliest stages of differentiation of neurons, seven classes of putative GABAergic interneurons were discerned. (1) Ascending neurons are first stained in the hindbrain at stage 26 and later extend caudally in the spinal cord. They have ascending ipsilateral axons. (2) Midhindbrain reticulospinal neurons are first stained at stage 25 and develop as a compact group with descending ipsilateral and contralateral axons, (3) Vestibular complex commissural neurons are first stained at stage 29/30 in a dorsal position near the entry of the seventh and eighth cranial nerves. They have ventral commissural axons that descend contralaterally and their somata form a compact mass. (4) Rostral hindbrain commissural neurons are first stained at stage 33/34 just rostral to the entry of the trigeminal nerve. They each have a decussating projection. (5). Rostral midbrain neurons are first stained in the midbrain at stage 29/30 and are later associated with prominent dorsal and ventral commissures. (6) Optic tract and (7) rostral forebrain neurons are found in the forebrain associated with strongly stained axon tracts.

The direction of axonal growth from its earliest stages was distinct for each class of hindbrain and spinal cord neuron.
Divergence of single axons in afferent projections to the cat's visual cortical areas 17, 18, and 19: A parametric study
Authors: Birnbacher D. , Albus K.
Published: January 2005

The proportions of neurons projecting via axon collaterals to two areas in the cat's occipital cortex (diverging neurons) were determined quantitatively in subcortical and cortical afferents by making use of the retrograde axonal transport of two different tracers. The proportions of diverging neurons were determined for that part of the afferent sites in which neurons filled with tracers from both injected areas occurred (overlap zone).

A number of experimental variables were tested for their role in possibly influencing the results of quantitative double‐label experiments, among them the types and the combinations of retrograde tracers, the position of the injections, the survival time, and the histological procedure. The most important variable was the position of the cortical injection, which had to be restricted clearly to the cortical grey matter and to one cortical area in order to avoid false‐positive double labeling. Other experimental variables affected the total number of retrogradely labeled neurons and/or the ratio between neurons labeled with the two different tracers rather than the proportions of double‐labeled neurons. In particular DL proportions were largely independent of the number and density of labeled neurons. They only deviated significantly from mean values in those sections in which the number of labeled neurons amounted to less than 20% of the maximal number of labeled neurons found in one section throughout the overlap zone.

Our results show that divergence is common in afferents to the cat visual cortex. The amount of divergence, however, varies considerably according to the origin of the afferent projection. The proportion of diverging neurons expressed as the percentage of the total number of neurons projecting to areas 17 and 18 was 3% in the A‐laminae of the dorsal part of the lateral geniculate nucleus, about 8% in the posteromedial lateral suprasylvian area, and about 15% in the C‐laminae of the dorsal part of the lateral geniculate nucleus, in the medial interlaminar nucleus, in the lateral part of the lateral posterior nucleus, and in the claustrum. The proportions of diverging neurons in the afferent projections to areas 17 and 19, and to areas 18 and 19 were about 10%. Diverging neurons were also found in the projections of the intralaminar thalamic nuclei to the visual cortex.

The findings demonstrate that the primary thalamocortical projection in the cat's central visual system, from the A‐laminae of the dorsal part of the lateral geniculate nucleus to area 17, contains a negligible proportion of diverging neurons, whereas other afferent subcortical and cortical projections may distribute up to 15% of their total information to at least two target areas in the occipital cortex.
Synaptic organization of GABAergic neurons in the mouse SmI cortex
Authors: Keller Asaf , White Edward L.
Published: January 2005

Immunocytochemical methods were used to examine GABAergic neurons in the barrel region of the mouse primary somatosensory cortex. GABAergic neurons occur in all layers of the barrel cortex but are more concentrated in the upper portion of layers II/III and in layers IV and VI. Nine cells in layer IV were examined with the electron microscope, and portions of their dendrites were reconstructed from serial thin sections. These cells are of the nonspiny, multipolar or bitufted varieties, and some of them have beaded dendrites. The labeled cell bodies and their reconstructed dendrites were postsynaptic at asymmetrical synapses with thalamocortical axon terminals labeled by lesion‐induced degeneration and with unlabeled axon terminals. Each cell also received symmetrical synapses from GABAergic axon terminals and from unlabeled axon terminals. Our results indicate that GABAergic cell bodies and processes receive synapses from thalamocortical axon terminals but that different cells display marked differences in the proportion of thalamocortical and other synapses they receive. These results indicate that GABAergic cells form a heterogeneous population with respect to their morphologies and patterns of synaptic inputs. The synaptic sequences revealed here for GABAergic neurons represent an anatomical substrate for various inhibitory processes known to occur within the cerebral cortex.
Dependence of cytochrome oxidase activity in the rat lateral geniculate nucleus on retinal innervation
Authors: Land Peter W.
Published: January 2005

Patterns of cytochrome oxidase (CO) activity were examined histochemically in the dorsal lateral geniculate nucleus (LGNd) and retina of pigmented rats. CO staining was not uniform and was distributed in a pattern similar to that of retinal afferents. Portions of the LGNd receiving an exclusively crossed projection were moderately reactive whereas regions receiving an uncrossed or overlapping crossed and uncrossed projection were darkly reactive. The dependence of oxidative metabolic activity in the LGNd on retinal innervation was verified in animals with unilateral enucleation. In adults, chronic monocular enucleation led to a decrease in CO staining in portions of the LGNd deprived of retinal input; in animals enucleated at birth, normal patterns of CO reactivity failed to develop and both LGNd had a more uniform pattern of moderate CO staining.

Most neurons in the ganglion cell layer of the retina were moderately reactive for CO. However, there were approximately 3,000 darkly reactive cells, most of which appear to be ganglion cells. The darkly reactive cells were more numerous in the peripheral temporal retina. The laminar pattern of CO staining in the retina was similar to that described previously for carnivores and primates. The most reactive laminae were the inner and outer plexiform layers and the photoreceptor inner segments. Within the inner plexiform layer, sublamina a was more darkly stained than sublamina b. These results suggest that the physiological properties of crossed and uncrossed visual pathways in rats are functionally dissimilar at the level of both the retina and the LGNd.
Distribution of acetylcholinesterase in the hippocampal region of the rabbit: III. The dentate area
Authors: Geneser Finn A.
Published: January 2005

The distribution of acetylcholinesterase (AChE) in the dentate area, a part of the hippocampal region, of the adult rabbit was described. A modification of the Koelle copper thiocholine method was used for the histochemical demonstration of AChE. The dentate area contained high amounts of this enzyme, distributed in a well‐defined stratified pattern. Thus, in the molecular layer seven distinct and differently stained layers were observed at most septotemporal levels. The granular cell bodies were entirely devoid of AChE, but stained precipitate occurred between the cell bodies, in particular in the superficial half of the granular cell layer. In the hilus, five layers of alternating stronger and weaker activity were recognizable. In the molecular layer and the granular cell layer, almost all activity was restricted to the neuropil, whereas a great number of intensely stained cell bodies were observed in the hilus.

Criteria for the delimitation of the dentate area, as defined by Blackstad, are discussed in view of the concepts of Cajal and Lorente de Nó and in relation to more recent hodological and histochemical data. The results obtained in the present report compare well with the concept of a layered rabbit hilus, the cytoarchitecture of this being representative of one group of animals including the guinea pig, monkey, and humans and differing from the nonlayered hilus found in, for example, the rat and mouse.

The distribution of AChE in the rabbit was compared with that in the rat and guinea pig, described previously. Very striking differences in the staining pattern of the molecular layer were observed, whereas the granular cell layer had a virtually identical appearance. The stratified pattern observed in the rabbit hilus corresponds to the distribution profile of the enzyme in the guinea pig, but contrasts with the rather diffuse distribution in the rat. This variation in the staining pattern of the hilus, however, mainly reflects the differences in cytomorphology between the rabbit and guinea pig on the one hand and the rat on the other, rather than being representative of a true species difference.

The possible correlation of the AChE observed in the rabbit dentate area with cyto‐ and fibroarchitecture, in particular the terminal fields of fiber systems known from experimental investigations, is discussed in detail.

The possibility that some of the AChE observed in the hippocampal region could be involved in the hydrolysis of a number of neuropeptides, in particular substance P and enkephalin, is considered.
The GABAergic neurons and axon terminals in the lateralis medialis‐suprageniculate nuclear complex of the cat: GABA‐immunocytochemical and WGA‐HRP studies by light and electron microscopy
Authors: Norita Masao , Katoh Yoshimitsu
Published: January 2005

In order to get more detailed information on the neural circuit of the lateralis medialis‐suprageniculate nuclear (LM‐Sg) complex of the cat, the GABAergic innervation of this complex was studied by GABA immunohistochemical techniques. Small immunoreactive cells were found throughout the LM‐Sg complex. On the basis of their ultrastructural features, these GABAergic cells were identified as Golgi type II interneurons. The neuropil of this nucleus displayed a conspicuous granular immunoreactivity. Ultra‐structurally, the immunoreactive neural profiles in the neuropil were identified as the presynaptic dendrites of interneurons, myelinated axons, or axon terminals. The GABAergic‐dendritic profiles, containing pleomorphic synaptic vesicles, were involved in synaptic glomeruli. Additionally, GABAergic axon terminals containing pleomorphic synaptic vesicles formed symmetric axodendritic synaptic contacts mainly in the extraglomerular neuropil. They appeared to correspond to either axon terminals from the thalamic reticular nucleus (TRN) or the axon terminals of interneurons.

The projections from the TRN to the LM‐Sg complex were studied by using wheat germ agglutinin‐conjugated horseradish peroxidase (WGA‐HRP). Following injection of WGA‐HRP into the LM‐Sg complex, a number of retrogradely labeled cells were observed in the TRN. The connections between the TEN and the LM‐Sg complex appeared to be topographically organized, the dorsal TRN being connected mainly with the dorsomedial portion of the LM‐Sg complex, and the ventral TRN being connected chiefly with the ventrolateral portion of the LM‐Sg complex. Following injection of the tracer into the TRN. ultrastructural examination of anterograde labeling in the LM‐Sg complex revealed that labeled terminals contain pleomorphic vesicles and make symmetric synaptic contacts mainly with small to medium‐sized dendrites. The labeled terminals were not involved in synaptic glomeruli.

The present results provide anatomic support for the contention that the projection cells of the LM‐Sg complex may be inhibited by both the TRN axons and interneurons, probably through the mediation of GABA.
Fetal tectal or cortical tissue transplanted into brachial lesion cavities in rats: Influence on the regrowth of host retinal axons
Authors: Harvey Alan R. , Gan Seng Khee , Pauken Janice M.
Published: January 2005

Fetal neural tissue was transplanted into suction lesions of the left brachium and pretectal region in young rats. Tectal tissue was grafted into 6–18‐day‐old rats and cortical tissue was transplanted into 17–20‐day‐old animals. The aim was to determine whether grafts could potentiate the regrowth of damaged retinal axons and, as a consequence, stimulate the axons to reenter their host target, the superior colliculus (SC).

Fifteen to 581 days after transplantation, host retinal projections were traced by injecting the right eye with horseradish peroxidase (HRP). Parallel series of frozen brain sections were stained for HRP histochemistry, acetylcholinesterase, Nissl, or neurofibrils. At all ages studied, grafts survived and grew within the wound cavity; survival was better in the older animals. Most cortical grafts and a small number of tectal grafts filled the wound cavity and formed complete tissue bridges across the lesion. The majority of tectal grafts were attached to one or the other side of the lesion and were connected to the opposite lesion face by glial and connective tissue membranes that formed over the lesion site.

In many animals that received tectal transplants, host retinal axons were traced growing into the grafts. Regenerating axons innervated specific, localized areas within the grafts, and it appeared that the axons retained the ability to recognize their appropriate target cells within the graft neuropil. Comparable ingrowth into cortical grafts was not observed. Optic axons were occasionally seen reentering the superficial layers of the host SC; however; compared to fetal tectal grafts, the density of host SC innervation was sparse. The implications of these data are discussed with regard to the possible use of fetal neural tissue grafts as reconstructive tissue bridges in the mammalian central nervous system.
Central projections of the mesencephalic nucleus of the fifth nerve: An autoradiographic study
Authors: Luschei Erich S.
Published: January 2005

Projections of cells of the mesencephalic nucleus of the fifth nerve (Mes V) to brainstem structures in the cat were studied by labelling Mes V cells with tritiated leucine. Before the leucine injections were made, however, large kainic acid lesions were produced in the vicinity of Mes V cells because these neurons are resistant to being killed or injured by this neurotoxin. Thus Mes V cells were selectively labelled by the leucine even though they are scattered among many other neurons.

Leucine injections near Mes V cells located in the mesencephalon, which are primarily the somata of jaw muscle spindle afferent fibers, produced essentially the same pattern of terminal labelling as injections near a caudally located group of Mew V cells that includes the somata of many tooth mechanoreceptive afferents. Labelling was dense above the trigeminal motor nucleus in the nucleus supratrigeminalis and in the most medial portion of the principal trigeminal sensory nucleus. A scattering of labelled axons and diffuse label was seen along the length of the tract of Probst, which follows the medial border of the descending trigeminal sensory nucleus as far caudally as the dorsal motor nucleus of the vagus.

Labelling within most of the trigeminal motor nucleus, which is known to receive direct synaptic input from Mes V cells, was very light. The only reasonably dense region of label was confined to a small dorsolateral portion of the motor nucleus.

Although Mes V has generally been supposed to be involved with jaw control in a direct, reflexive manner, the extensive projections to nucleus supratrigeminalis and parts of the trigeminal sensory system draw attention to the potential proprioceptive sensory contribution of Mes V.
Subcortical connections of the superior colliculus in the mustache bat, Pteronotus parnellii
Authors: Covey E. , Hall W. C. , Kobler J. B.
Published: January 2005

The mustache bat, Pteronotus parnellii, depends on echolocation to navigate and capture prey. This adaptation is reflected in the large size and elaboration of brainstem auditory structures and in the minimal development of visual structures. The superior colliculus, usually associated with orienting the eyes, is nevertheless large and well developed in Pteronotus. This observation raises the question of whether the superior colliculus in the echolocating bat has evolved to play a major role in auditory rather than visual orientation. The connections of the superior colliculus in Pteronotus were studied with the aid of anterograde and retrograde transport of wheat germ agglutinin conjugated to HRP. These results indicate that the superior colliculus of Pteronotus is composed almost entirely of the layers beneath stratum opticum. The retinal projection is restricted to a very thin zone just beneath the pial surface. Prominent afferent pathways originate in motor structures, particularly the substantia nigra and the deep nuclei of the cerebellum. Sensory input from the auditory system originates in three brainstem nuclei: the inferior colliculus, the anterolateral periolivary nucleus, and the dorsal nuclei of the lateral lemniscus. The projections from these auditory structures terminate mainly in the central tier of the deep layer. The most prominent efferent pathways are those to medial motor structures of the contralateral brainstem via the predorsal bundle and to the ipsilateral midbrain and pontine tegmentum via the lateral efferent bundle. Ascending projections to the diencephalon are mainly to the medial dorsal nucleus and zona incerta. Thus, the superior colliculus in Pteronotus possesses well‐developed anatomical connections that could mediate reflexes for orienting its ears, head, or body toward objects detected by echolocation.
Regional distribution of cholecystokinin receptors in primate cerebral cortex determined by in vitro receptor autoradiography
Authors: Kritzer M. F. , Innis R. B. , Goldman‐Rakic P. S.
Published: January 2005

Cholecystokinin (CCK) is a putative peptide neurotransmitter present in high concentration in the cerebral cortex. By using techniques of in vitro receptor autoradiography, CCK binding sites in primate cortex were labeled with 125I‐Bolton‐Hunter‐labeled CCK‐33 (the 33‐amino‐acid C‐terminal peptide) and 3H‐CCK‐8 (the C‐terminal octapeptide). Biochemical studies performed on homogenized and slide‐mounted tissue sections showed that the two ligands labeled a high‐affinity, apparently single, saturable site.

Autoradiography revealed that binding sites labeled by both ligands were anatomically indistinguishable and were distributed in two basic patterns. A faint and diffuse label characterized portions of medial prefrontal cortex, premotor and motor cortices, the superior parietal lobule, and the temporal pole. In other cortical areas the pattern of binding was layer‐specific i.e., binding sites were concentrated within particular cortical layers and were superimposed upon the background of diffuse label. Layer‐specific label was found in the prefrontal cortex, anterior and posterior cingulate gyrus, somatosensory cortex, inferior parietal lobule, retrosplenial cortex, insula, temporal lobe cortices, and in the primary visual and adjacent visual association cortices.

The areal and laminar localization of layer‐specific CCK binding sites consistently coincided with the cortical projections of thalamic nuclei. In prefrontal cortex, CCK binding sites were present in layers III and IV, precisely paralleling the terminal fields of thalamocortical projections from the mediodorsal and medial pulvinar nucleus of the thalamus. In somatosensory cortex, the pattern of CCK binding in layer IV coincided with thalamic inputs arising from the ventrobasal complex, while in the posterior cingulate gyrus, insular cortex, and retrosplenial cortex, layer IV and lower III binding mirrored the laminar distribution of cortical afferents of the medial pulvinar. CCK binding in layers IVa, IVc alpha, IVc beta, and VI of primary visual cortex corresponded to the terminal field disposition of lateral geniculate neurons, whereas in adjacent visual association cortex, binding in layers III, IV, and VI faithfully followed the cortical distribution of projections from the inferior and lateral divisions of the pulvinar nucleus of the thalamus.

We interpret the diffusely labeled binding sites in primate cortex as being associated with the intrinsic system of CCK‐containing interneurons that are distributed throughout all layers and areas of the cortex. The stratified binding sites, however, appear to be associated with specific extrinsic peptidergic projections. The anatomical coincidence of layer‐specific CCK binding sited and thalamocortical terminal fields suggests that certain thalamocortical projection fibres either contain CCK or interact with CCK. containing systems.