bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructural development of Rohon‐Beard neurons: Loss of intramitochondrial granules parallels loss of calcium action potentials
Authors: Lamborghini Janet E. , Revenaugh Marsha , Spitzer Nicholas C.
Published: January 2005

We have examined the ultrastructure of the cell body of a vertebrate spinal neuron, the Rohon‐Beard cell of Xenopus laevis, at four stages during its development (Nieuwkoop and Faber stages: 22, 29/30, 37/38 and 42). At this time it has attained its electrical excitability and the action potential mechanism in the cell body is maturing through a sequence of stages in which the inward current is carried by Ca++ (stages 20–25), later by Ca++ and Na+ (stages 25–40), and finally by Na+ (stages 40–51) (Spitzer and Baccaglini, '976; Baccaglini and Spitzer, '77). There is a change in the abundance and distribution of the organelles in the perikaryon during this period, characteristic of other developing neurons. Mitochondria and Golgi apparatus become localized progressively more in the interior of the cells, and rough endoplasmic reticulum progressively more to the periphery where it often appears in orderly tiers parallel to the plasma membrane. The mitochondria contain dense intramitochondrial granules which are known in other cells to contain concentrations of divalent cations. The number of granules declines over the course of the developmental period studied.

The presence of the intramitochondrial granules was examined quantitatively because electrophysiological data indicate that the amount of Ca++ entering the cells in early stages should raise the internal Ca++ concentration by several orders of magnitude, and that Ca++ is rapidly sequestered (Baccaglini and Spitzer, '77). A minimum of 200 mitochondrial profiles from at least four Rohon‐Beard cells were scored for the presence of dense intramitochondrial granules at each stage studied. In stage 22 Rohon‐Beard cells 75 ± 5% (mean ± SD, n = 4) of the mitochondrial profiles scored contained granules; in stage 29/30, 56 ± 10% (n = 7); in stage 37/38, 3 ± 3% (n = 5); and in stage 42, 0.5 ± 0.25% (n = 4). Therefore, dense intramitochondrial granules, an indication of calcium accumulation in mitochondria, decrease in parallel with the loss of the Ca++ component of the inward current of the action potential in Rohon‐Beard neurons.
Efferent projections from temperature sensitive recording loci within the marginal zone of the nucleus caudalis of the spinal trigeminal complex in the cat
Authors: Burton H. , Craig A. D. , Poulos D. A. , Molt J. T.
Published: January 2005

The efferent projections from nucleus caudalis of the spinal trigeminal complex in cats were studied with retrograde and anterograde axonal transport techniques combined with localization of recording sites in the thalamus and marginal zone of nucleus caudalis to innocuous skin cooling. Results showed brainstem projections from nucleus caudalis to rostral levels of the spinal trigeminal complex, to the ventral division of the principal trigeminal nucleus, the parabrachial nucleus, cranial motor nuclei 7 and 12, solitary complex, contralateral dorsal inferior olivary nucleus, portions of the lateral reticular formation, upper cervical spinal dorsal horn and, lateral cervical nucleus. Projections to the thalamus included: a dorsomedial region of VPM (bilaterally) and to the main part of VPM and PO contralaterally. Neuronal activity was recorded in the dorsomedial region of VPM to cooling the ipsilateral tongue. HRP injections in this thalamic region retrogradely labeled marginal neurons in nucleus caudalis. These results show that marginal neurons of nucleus caudalis provide a trigeminal equivalent of spinothalamic projections to the ventroposterior nucleus in cats.
Horizontal ampullary nerve fiber projections to the crista angustarum in the crista ampullaris
Authors: Dunn Robert F.
Published: January 2005

Individual nerve fibers were traced on consecutive serial 1‐μm‐thick cross‐sections to determine their position of origin within the horizontal ampullary nerve trunk (HANT) and the site at which they penetrated the basilar lamina of the horizontal crista in the guitarfish, Rhinobatos productus. Of the 132 fibers successfully traced, 87.1% followed an anatomical projection pattern consistent with the dynamic response characteristics of the nerve fibers. That projection pattern was: from the peripheral HANT region to the ipsilateral slope; from the central HANT region to the crest; and from the intermediate HANT region both to the ipsilateral slope and the crest of the horizontal crista. The 12.9% of “error” fibers not following this projection pattern were also consistent with the functional neurophysiological data. The terms crista bulbus and crista angustarum were introduced to designate specific anatomical regions of the dumb‐bell shaped crista ampullaris.
“Extra” optic fibers exclude normal fibers from tectal regions in goldfish
Authors: Meyer Ronald L.
Published: January 2005

A small group of selected optic fibers were surgically deflected from one tectum into the other, thus creating a novel additional projection originating from a small area of ipsilateral retina. The normal fibers to this “recipient” tectum were also severed so that both the deflected and the normal fibers regrew into this tectum at about the same time. The reinnervation pattern was analyzed by autoradiography and electrophysiologic mapping. Both techniques showed that the deflected fibers and the “normal” fibers failed to intermix. The deflected fibers typically formed several well‐defined patches of innervation in roughly the appropriate region of denervated recipient tectum. The normal fibers filled in the remaining uninnervated tectal areas and were completely or nearly completely excluded from the patches occupied by the deflected fibers. This segregation was often quite sharp having an apparent average overlap less than 25–50 μm. The electrophysiology indicated that the projections of both deflected and normal fibers were retinotopically organized but that the mapping by the normal fibers was compressed. This compression, an apparent consequence of being squeezed onto a smaller than normal region of tectum, was similar to that previously observed following ablations of part of the tectum. The negligible surgical damage in the present experiment, however, excludes the kind of cytochemical reorganization previously suggested to produce compression. The findings also provide evidence for a competitive type of interaction between optic fibers.
Proprioceptive reflex connections of head musculature and the mesencephalic trigeminal nucleus in the carp
Authors: Luiten P. G. M.
Published: January 2005

The location of the sensory cells concerned with the proprioception of respiratory and extraocular musculature in the carp was studied by retrograde transport of horseradish peroxidase. Sensory cell labeling after intramuscular HRP injection was exclusively found in the trigeminal‐facial‐anterior lateral line ganglion complex. The muscles innervated by the trigeminal system are represented in the more rostral ganglion areas, the muscles innervated by the facial system in the more caudal ganglion parts. Nearly all labeled cells were situated on the ipsilateral side. Sensory cells labeled after extraocular muscle injection were also found all over the V‐VII ganglion, however, to a considerable degree also on the contralateral side. All muscle injections failed to give mesencephalic trigeminal cell labeling. The results of intranerve HRP injections in peripheral trigeminal nerve branches strongly suggests a perioral mechanoreceptive function for the mes.V neurons. A bisynaptic proprioceptive reflex model is described for respiratory musculature consisting of a sensory cranial ganglion component connected to the descending trigeminal nucleus, which on its turn links the proprioceptive ganglion cells to the trigeminal and facial motorneurons. Monosynaptic proprioceptive reflex circuits are discussed on neurophysiological grounds.
The cerebellar projection of the vestibular nerve in the cat
Authors: Korte Gary E. , Mugnaini Enrico
Published: January 2005

The projection of the vestibular nerve to the cerebellum of the cat was examined with silver degeneration methods after complete lesions of the vestibular ganglion. The majority of the primary vestibular afferents were traced to the cortex of the ipsilateral nodulus and uvula, relatively fewer entering the ipsilateral flocculus. Fibers were not traced to the paraflocculus, lingula or lateral cerebellar nucleus. A sparse projection to the ipsilateral fastigial nucleus may exist, but it remains equivocal until confirmed with additional methods. Light microscopic examination of plastic sections confirmed these observations and showed further details of the organization of the primary vestibular projection to the nodulus and uvula. These results show that the region of the cerebellum densely innervated by primary vestibular afferents is smaller than previously believed.
The origin, distribution and synaptic relationships of substance P axons in rat spinal cord
Authors: Barber Robert P. , Vaughn James E. , Randall Slemmon J. , Salvaterra Paul M. , Roberts Eugene , Leeman Susan E.
Published: January 2005

Substance P positive (SP+) immunoperoxidase reaction product has been localized in light and electron microscopic preparations of rat lumbar spinal cord using an immunocytochemical method. SP+ reaction product was found to be highly concentrated in dorsal horn laminae I, II, portions of III, Lissauer's tract, s small nucleus in the dorsal part of the lateral funiculus, and in a longitudinal bundle of fibers just ventral to the central canal. Moderate accumulations of SP+ reaction product were observed in portions of laminae III‐V, lamina X and in a narrow zone bordering fasciculus gracilis which expanded in its ventral aspect to include nucleus cornucommissuralis dorsalis and nucleus dorsalis. Remaining portions of the spinal gray matter exhibited extremely sparse staining. Light microscopic observations indicated that SP+ product was concentrated in fine axons and collaterals, which displayed densely‐stained varicosities and terminal puncta. These varicosities and puncta were closely associated with neurons and blood vessels.

Dorsal rhizotomy produced a marked reduction in the number of SP+ fibers in Lissauer's tract, dorsal horn laminae I‐III and the nucleus of the dorsolateral funiculus. However, dorsal root fibers were not the only source of SP+ structures in these regions since some SP+ fibers remained following dorsal root resections. In addition, this residual population of SP+ fibers did not appear to be altered by a combination of dorsal rhizotomy and ipsilateral transverse hemisection of the spinal cord. In conjunction with the results of other investigators, this finding suggests that the SP+ fibers which remain after dorsal rhizotomy are derived from local circuit interneurons of the spinal cord.

Electron microscopic observations revealed that certain axons and axon terminals contained concentrations of SP+ product which were associated with large, granular vesicles, while lesser amounts were in the terminal cytoplasm and associated with the exterior surfaces of small, agranular synaptic vesicles. SP+ terminals formed axodendritic, axosomatic and axoaxonal synapses, but the deposition of SP+ product often was not concentrated precisely at the “active sites” of these synaptic junctions. Some SP+ axons also made rudimentary contacts with astrocytic processes including those surrounding blood vessels. Since many of the SP+ terminals are similar in several respects to neuroendocrine terminals, it is possible that substance P may be released at several different types of non‐synaptic sites as well as at conventional synaptic junctions. Thus our findings suggest that substance P could participate in a variety of neural functions ranging from those which are limited to synaptic junctions to those which are more generally distributed via an involvement of axonal plexuses as well as the glial, vascular and ventricular systems.
The organization of the second somatosensory area (SmII) of the grey squirrel
Authors: Nelson R. J. , Sur M. , Kaas J. H.
Published: January 2005

Microelectrode mapping methods were used to determine the organization of the second somatosensory representation, SmII, in grey squirrels. A systematic representation of the contralateral body surface was found in lateral parietal cortex adjoining the first somatosensory representation, SmI (Sur et al., '78a). The representation of the body in SmII was found to be much less distorted than in SmI. Under our recording conditions, almost all recording sites were activated from strictly contralateral body locations. The most important finding was that the basic orientation of the body representation in SmIi is “erect” rather than “inverted.” This orientation allows SmII and SmI to be adjoined along a common border representing the top of the head and face. This type of border has been called congruent (Allman and Kaas, '75; Kaas, '77), and it may have significance in the development of sensory representations.
The environment of axonal migration in the developing chick retina: A scanning electron microscopic (SEM) study
Authors: Suburo Angela , Carri Nestor , Adler Ruben
Published: January 2005

We have made a SEM study of the basal intercellular spaces of the retina in chick embryos of different developmental stages. Since this is the environment where optic axons grow, the structural characteristics of this region might play some role in the orientation of axonal migration towards the choroid fissure. The basal region of undifferentiated retinas is formed by the vitreal expansions of neuroepithelial cells. In pre‐axonal stages, the intercellular spaces between these expansions do not show any preferential orientation towards the fissure. The growth cones of ganglion cell axons appear in an apicobasal direction and turn towards the fissure immediately beneath the vitreal surface. Fasciculation is an early event during development and, in the more advanced stages, the vitreal expansions from retinal cells are placed in rows following the same orientation as the axon bundles. These observations are discussed in relationship to current hypotheses on axonal migration and orientation.
Electron microscopic studies of serially sectioned cat spinal α‐motoneurons. III. Motoneurons innervating fast‐twitch (type fr) units of the gastrocnemius muscle
Authors: Kellerth J‐O. , Berthold C‐H. , Conradi S.
Published: January 2005

Two intracellularly stained cat gastrocnemius α‐motoneurons of the FR‐type (Burke et al., '73) were studied ultrastructurally. The architecture and synaptology of the cell body and proximal parts of the dendrites were analyzed from a long series of consecutive sections, according to a method presented in a preceding paper (Conradi et al., '79a). Several of the dendrites had a base diameter exceeding 10 μm. The proportion of the surface covered by boutons was 40‐50% for the cell body and about 80% for the proximal dendrites. In both regions, about 20% of the boutons were of the S‐type and 70% of the F‐type. The large C‐boutons were clustered around the dendritic roots and were also present on the axon hillock. M‐boutons of dorsal root origin were located on the proximal parts of the majority of the dendrites.
The development of descending and dorsal root connections in the lumbosacral spinal cord of the postnatal rat
Authors: Gilbert Mark , Stelzner Dennis J.
Published: January 2005

Light and electron microscopy were used to study degenerating axons and synaptic endings in the lumbosacral spinal cord at different stages of postnatal development in the rat. After dorsal root section (L5‐S1) or mid‐thoracic hemisection of the spinal cord (T6‐T8), the distribution and type of degeneration argyrophilia were studied with the light microscope over varied post‐operative survival periods using a modified Fink‐Heimer method (Leonard, '74). The light microscopic results were correlated with the appearance of electron dense degeneration seen using the electron microscope.

The distribution of degeneration found in the lumbosacral spinal cord after dorsal root section was similar at the neonatal (4d), weanling (21d) and adult stages. At the neonatal stage, the type of degeneration argyrophilia appeared at an earlier postoperative survival period (12 hours), and was maximal at an earlier time (12‐18 hours) than in older animals. The appearance of electron dense degeneration using the electron microscope matched the light microscopic findings. Electron dense degenerating synaptic knobs were found at the neonatal stage making asymmetrical contact with small dendrites in areas of the dorsal horn showing degeneration argyrophilia.

No degeneration was found in the dorsal funiculus, dorsal horn or intermediate nucleus of Cajal (INC) after mid‐thoracic hemisection at the neonatal stage although degeneration was present elsewhere in the intermediate gray, in the ventral gray, and in the ventral and lateral funiculi. At this stage, the type of degeneration argyrophilia and time course of degeneration in the gray and white matter was identical to that found after dorsal root section in neonatal animals. The distribution of degeneration was not mature in the lumbosacral enlargement until 15d of age and the degeneration was still immature in the dorsal horn and INC at 21d of age.

Although degeneration argyrophilia and electron dense degeneration was found in the ventromedial gray (lamina VIII) and lateral gray (laminae VI‐VII) at the neonatal stage, electron dense degenerating synaptic knobs were not observed in these areas until 12d of age for the ventromedial and 18d of age for the lateral gray matter even using a large number of different survival periods.

Degenerating synaptic endings were first observed after mid‐thoracic hemisection during the period when behavioral maturation is nearing completion in the hindlimbs, and when response depression (spinal shock) increases and response recovery decreases after mid‐thoracic spinal transection (Weber and Stelzner, '77). Our data suggest that either the number of connections from descending sources increases markedly in the gray matter of the lumbosacral spinal cord during this period or connections, already present, reach a state of maturity where they can first be observed using the degeneration method of analysis.
Sympathetic neurons in the cat spinal cord projecting to the stellate ganglion
Authors: Chung Kyungsoon , Chung Jin Mo , Lavelle F. W. , Wurster R. D.
Published: January 2005

Horseradish peroxidase (HRP) was injected into the stellate ganglia of anesthetized cats. After a 2‐day survival time the spinal cord was processed for the HRP reaction to study the distribution of the preganglionic neurons which project to the stellate ganglia. HRP‐labeled neurons in the cord were located exclusively on the side ipsilateral to the injected stellate ganglia and were concentrated in four distinct areas: (1) intermediolateral cell column (78.2%), (2) lateral funiculus (18.5%), (3) intercalated area and (4) central autonomic area (3.3% for the latter 2 areas). Their distribution pattern in the very rostral pole of the thoracic sympathetic preganglionic cell column was different from the typical thoracic pattern in that a greater proportion of the cells were located in the lateral funiculus, and a few labeled cells were observed in the ventral horn. Longitudinally, a wide range (C8‐T8) of spinal cord levels projected to the stellate ganglia, with a peak at the T2 level. These observations infer that a large population of axonal processes of sympathetic preganglionic neurons traveled several segments of the spinal cord through an intraspinal pathway before exiting a particular ventral root.
Some telencephalic connections in the frog, Rana pipiens
Authors: Kicliter Earl
Published: January 2005

Some afferent, efferent and intrinsic connections of the telencephalon of Rana pipiens were studied using a horseradish peroxidase method. Afferents to the telencephalon from thalamic and brain stem cell groups were demonstrated. These findings, taken together with the results of previous studies, indicate that separate thalamic cell groups project visual, auditory and somatosensory information onto the striatum. A separate thalamic cell group projects to the medial telencephalic wall and probably conveys visual and somatosensory information. These telencephalic afferent systems do not appear to be directly comparable to those of birds and reptiles. Additionally, some telencephalic efferents demonstrated in previous studies using anterograde degeneration techniques were confirmed, and some intratelencephalic connections were identified.
Facial thermal input to the trigeminal spinal nucleus of rabbits and rats
Authors: Dickenson A. H. , Hellon R. F. , Taylor D. C. M.
Published: January 2005

In rabbits and rats under urethane anesthesia, a systematic survey was made of the caudal trigeminal nucleus, using glass coated tungsten microelectrodes. This revealed many neurons in the marginal layer sensitive either to warming or cooling the facial skin. The majority of these neurons were specifically temperature sensitive.

In rats, a somatotopic arrangement of cold receptive fields was evident with in the marginal layer of the trigeminal nucleus, with the ophthalmic division of the trigeminal nerve represented most laterally, the mandibular most medially and the maxillary division represented over most of the recording region. This arrangement is similar to the mediolateral distribution seen in cats. In rabbits, the distribution was less rigorous but the ophthalmic division tended to be represented caudally and the mandibular division rostrally. The maxillary division was represented over most of the recording region. All receptive fields were ipsilateral and showed spatial convergence of input. Both rabbits and rats possessed a concentration of thermal receptive‐fields around the nose, whisker pad and mouth.

At steady skin temperatures, marginal units gave bell‐shaped intensity functions which were very similar to those reported for the cold and warm receptors. With rapid changes of temperature, neurons responded with a dynamic outburst which corresponded to the equivalent receptor response.
The lateral cervical nucleus in the cat: Anatomic organization of cervicothalamic neurons
Authors: Craig A. D. , Burton H.
Published: January 2005

The morphology of the lateral cervical nucleus (LCN) and the organization of the cervicothalamic projection neurons were studied in cats which had received thalamic injections of horseradish peroxidase (HRP). The boundaries of the LCN were defined following very large thalamic HRP injections. Roughly 92–97% of LCN cells project contralaterally to thalamus; an additional 1‐5% project ipsilaterally. Computer‐assisted measurements of perikaryal areas demonstrated that there are two sizes of LCN cells, large (175–900 μm2) and small (< 175 μm2); the small cells are localized in the medial third of the LCN. LCN cells which are not labeled after large thalamic HRP injections are predominantly small, medially‐located neurons.

Small HRP injections into physiologically identified regions of ventroposterior thalamus demonstrated that cervicothalamic neurons are organized in a topography consistent with that observed physiologically in the LCN (Craig and Tapper, '78). Dorsolateral LCN cells are retrogradely labeled from nucleus ventroposterolateralis, pars lateralis (VPL1), ventromedial LCN cells are labeled from pars medialis (VPLm), and a few medial cells are labeled from nucleus ventroposteromedialis (VPM). A few cells in the medial portion of the LCN are also labeled from each part of ventroposterior thalamus. Some interspersion was observed even in the cases with the most well‐restricted labeling. We conclude that the LCN maintains a basic somatotopographic organization with an inherent variability, certain aspects of which are consistently demonstrable both physiologically and anatomically. Evidence was also obtained suggestive of a rostrocaudal inversion in the cervicothalamic projection. The cervicothalamic projection, the differentiation of the medial LCN subpopulation, and the possible redefinition of the LCN are discussed in light of these results.
Localization of neurons in the rat superior cervical ganglion that project into different postganglionic trunks
Authors: Bowers C. W. , Zigmond R. E.
Published: January 2005

Horseradish peroxidase (HRP) was used to determine whether neurons in the rat superior cervical ganglion (SCG) are localized in regions of the ganglion as a function of the postganglionic trunk they utilize. In separate experiments, each of the two major postganglionic trunks was cut 1–3 mm from the SCG and solid HRP was applied to the cut end proximal to the ganglion. The results demonstrated that the cell bodies of neurons whose axons project out the internal carotid nerve (ICN) were located primarily in the rostral part of the ganglion. Cell bodies of neurons whose axons project out the external carotid nerve (ECN) were located primarily in the caudal part. The total percentages of neurons with axons in the ICN and ECN were about 35% and 45% respectively. When HRP was applied to both these trunks, 73% of the neurons in the SCG were labeled. In the caudal portion of the ganglion, an additional group of neurons was observed whose axons project into the cervical sympathetic trunk. Control studies indicated that the neuronal labeling observed in our experiments was due to retrograde axonal transport rather than the direct uptake of HRP by neuronal cell bodies. Thus, neuronal subpopulations exist in specific regions of the rat SCG. The significance of these results to biochemical and electrophysiological studies is discussed.
The distribution of retino‐collicular axon terminals in rhesus monkey
Authors: Pollack J. G. , Hickey T. L.
Published: January 2005

The retino‐collicular projections in rhesus monkeys were studied using standard autoradiographic and degeneration techniques. A computer based technique was developed which provided a flattened visual display of the retinal projection onto the entire superior colliculus, quantified the area covered by such projections for different segments of the colliculus and showed how this morphological pattern varied with depth beneath the collicular surface.

In the anterolateral third of the colliculus (i.e., the foveal representation) the retinal projection was light, confined to a narrow region of the superficial gray and contributed primarily by the contralateral eye. In the remaining binocular segment of the superior colliculus the retinal projections showed a marked degree of local patterning, that in many instances appeared as bands of label. By combining eye removal and eye injection procedures in a single animal and comparing adjacent sections processed for autoradiography and stained for degeneration, it was possible to assess the amount of overlap between retino‐collicular projections from the two eyes. These experiments showed that total segregation of retinal afferents does occur in the monkey superior colliculus, but what occurs more often is a situation where the density of inputs from the two eyes varies reciprocally as one moves across the part of the colliculus that represents the binocular visual field.
Pikeperch horizontal cells identified by intracellular staining
Authors: Hassin Guido
Published: January 2005

Micropipettes filled with Procion yellow dye were used to record from and to stain pikeperch horizontal cells intracellularly. Three major types were found: a distal layer (H1) of relatively small cells which were luminosity or L‐type; a second and more proximal layer of larger L‐type cells (H2); and a third and yet more proximal layer of very stellate chromatic or C‐type cells (H3). A few anucleate processes which displayed slow‐potentials were found in the proximal area of the inner nuclear layer. Cells of each of the three layers were shown to be cone related by both anatomical and physiological methods.

L‐type cells were further categorized by the area over which each exhibited spatial summation and the relative sensitivity of each to red and green lights. Receptive field sizes of H2's were found to range from less than 2 mm to greater than 5 mm in diameter, whereas those of the few H1's tested were all less than 2 mm. Results from spectral screening tests indicate that most H1 and H2 cells are maximally sensitve to orange light, whereas the H3 cells hyperpolarize maximally to green and depolarize maximally to red. A small percentage of sampled C‐cells displayed an additional depolarization to violet.
Synaptic connections linking cones and horizontal cells in the retina of the pikeperch (Stizostedion vitreum)
Authors: Witkovsky Paul , Burkhardt Dwight A. , Nagy Andre R.
Published: January 2005

Cones and horizontal cells of the pikeperch retina were studied with morphological and physiological techniques. Gap junctions were observed between cone pedicles and basal processes emitted by neighboring cones. Intracellular recordings showed that the light‐evoked hyperpolarizing cone response was enhanced by light falling upon neighboring receptors within a radius of 50μm. We suggest that the network of gap junctions between cones mediates the summative lateral interaction described.

Three sub‐classes of horizontal cells (H1, H2, H3) send dendrites to cones; H1 and H2 cells appear to appear to contact twin cones, exclusively or preferntially, whereas H3 cells appear to synapse only with single cones. Horizontal cells of the same sub‐class are joined by gap junctions between dendrites or at the lateral faces of perikarya. These unions extend over several μm2 and as seen in transmission electron microscopy consist of patches of close apposition alternating with areas of membrane separation, folding and occasional zonulae adherentes. Freeze‐fracture profiles of horizontal gap junctions show localized areas of dense particle aggregation on the P‐face and pits on the E‐face flanked by regions of unspecialized membrane. These morphological findings provide support for the known spatial and color‐coding properties of pikeperch horizontal cells.
A Golgi study of the ventral tegmental area of Tsai and interfascicular nucleus in the rat
Authors: Phillipson O. T.
Published: January 2005

The ventral tegmental area of Tsai (VTA) and interfascicular nucleus of the adult rat brain has been studied with two variants of the Golgi method in three planes of section. Neurons were studied in relation to the cytoarchitectural groupings of the VTA. Dendritic organisation and dendritic fields were mapped out for each cytoarchitectural subgroup and cell types within each subgroup were classified on the basis of cell size and dendritic morphology.

In each subnucleus of VTA, neurons had distinct characteristics. In nucleus paranigralis neurons were small to medium in size and their dendritic fields organised in an approximately horizontal plane orientated in an anteromedial direction and slanting dorsally over the interpeduncular nucleus and fossa. Neurons of the parabrachial group were small to medium sized with no preferential orientation. In nucleus linearis raphe caudalis small neurons were strongly orientated in the plane of the nucleus in a dorso‐ventral direction slanting forwards. Neurons in the interfascicular group were small to very small and their maximum dendritic extents were seen in the horizontal plane. In frontal section they formed a compact ball of cells in the midline and were separated on either side from the larger neurons in the medial edge of nucleus paranigralis.

Ingeneral VTA neurons tended to fall into one of two morphological categories. Type 1 were small to medium, and had two to four primary dendrites which divided into varicose secondary dendrites. Type 2 were medium sized, with two to five primary dendrites. Both primary and secondary dendrites and the cell soma of Type 2 neurons were moderately spiny. Secondary dendrites were not varicose. Forms also occurred which were intermediate between Types 1 and 2. In the nucleus paranigralis, Type 1 was more common medially, while Type 2 was more common laterally, particularly in the ventrolateral paranigral region. Only neurons of Type 1 were seen in nucleus linearis raphe and interfascicular nuclei. Local axon circuits were observed to arise from the primary dendrites of Type 1 neurons and to ramify close to neighbouring neurons. Axon swellings from such circuits were observed to make apparent contact with primary dendrites of nearby neurons and clusters of axon swellings were observed near cell somas of neighbouring impregnated neurons of similar type.

The results are discussed and particular attention is paid to the similarities and differences between VTA and the substantia nigra pars compacts (SNC). The major difference appears to be that, whereas in SNC dendrites are organised in vertical as well as horizontal planes, in the VTA no long ventrally directed dendrites were observed. Combining these results with the known cytoarchitecture and connections of VTA and SNC, it appears that fundamental differences occur between VTA and some neurons of the SNC, both in the nature of their morphology and intrinsic organisation, and in the organisation of their efferent and afferent connections.
Endocytic activity of subependymal microglial cells in the toad brain: A cytochemical study of peroxidase uptake
Authors: McKenna Olivia C.
Published: January 2005

A population of microglial cells that rapidly incorporate extracellular material introduced into the ventricular system has been identified just beneath the ependyma of all four cerebral ventricles in the toad (Bufomarinus). In untreated tissue these cells appear to be scatterd, possess few processes and have and elongate shape with their long axes lying parallel to the ventricular surface. Their most distinctive ultrastructural features are nucleicontaining clumps of chromatin, cytoplasmic dense bodies and single strands of granular endoplasmic reticulum. When horseradish peroxidase (HRP) is perfused through the ventricular system and the tissue processed using the DAB cytochemical method, the cells change shape and incorporate HRP into cytoplasmic structures. Even after very short perfusion periods (2–5 minutes) cells become rounded, the surface is ruffled and pseudopodia develop that contain characteristic flocculent material. Reaction pruduct for HRP is contained in plain and coated vesicles, tubules, vacuoles and long structures composed of two closely apposed menranes. At these early times, relatively few multivesicular bodies and dense bodies contain reaction product, but when the cells are viewed at longer time periods after the ventricular perfusion of HRP an increasing proportion of the multivesicular bodies and dense bodies contain reaction product. By 320 minutes reaction product is found almost exclusively in these two organelles. In addition, many pseudopodia containing dense bodies with peroxidase activity are found in the neuropil; some, but not all, can be traced from the subependymal microglial cells. The cell bodies have resumed their flattened shape, When compared to the subependymal microglial cells, other brain cells‐oligodendrocytes, astrocytes, ependymal cells and neurons‐contain relatively little reaction product at short time intervals; only by 320 minutes are moderate amounts of HRP present. Because of the position of the microglial cells and their ingestive capacity, it is suggested that they function to protect the brain from foreign substances entering form the CSF.
Development of synaptic arrays in the inner plexiform layer of neonatal mouse retina
Authors: Fisher Leslie J.
Published: January 2005

Retinas from mice of the C57BL/6 strain were sampled at frequent intervals from birth to postnatal day 33 to determine the numerical density of conventional and ribbon synapses within the inner plexiform layer (IPL) as a function of time. Synaptic arrays of the IPL were formed in three phases. During Phase I, from day 3 to day 10, conventional synapses were produced at a mean rate of 0.44 synapses/1,000 μm3/hour, but no ribbons were seen. During Phase II, from day 11 to day 15, ribbons formed at a rate of 0.38 ribbons/1,000 μm3/hour and conventional synapses were produced at a rate of 1.15 synapses/1,000 μm3/hour. Phase III began at day 15, the approximate time of eye opening in these animals, and was characterized by a sharp reduction in the rate of production of both ribbons and conventional synapses. During this phase ribbons achieved a final mean density of 113 ribbons/1,000 μm3 and conventionals achieved a final mean density of 250 synapses/1,000 μm3. Serial synapses appeared in Phase II but remained at low densities.
Striate cortex and visual acuity functions in the cat
Authors: Berkley M. A. , Sprague J. M.
Published: January 2005

Using a two‐choice visual discrimination paradigm, thresholds for size (gratings), parallelness (parallel vs. non‐parallel lines), contour alignment (vernier offset), and angularity (polygon figures) were behaviorally determined in cats before and after ablations of portions of the geniculo‐cortical system.

Animals with a total loss of cortical area 17, and with a loss, in some cases, of up to 90% of area 18 (with and without infringement into area 19), showed about a 30% reduction in grating acuity, a three‐fold increase in parallelness and angularity thresholds, and a total loss of contour alignment ability. Control animals with ablations sparing area 17 showed no significant threshold changes. All animals were able to learn classic form discriminations postoperatively, but those with area 17‐18 lesions at a somewhat slower than normal rate. Control procedures indicated that all tested discrimination capabilities did not depend on luminance differences between targets, local flux cues within the targets, or on the animals' use of residual portions of area 17 representing the peripheral visual field.

Since the cat has multiple thalamo‐cortical visual pathways, the results of the present study are consistent with the hypothesis that pathways parallel to the geniculo‐striate system are capable of processing spatial information of considerable detail. The results also suggest, however, that the geniculo‐striate system is uniquely necessary for the processing of the finest attributes of spatial contours.
Regional topography within noradrenergic locus coeruleus as revealed by retrograde transport of horseradish peroxidase
Authors: Mason Stephen T. , Fibiger Hans C.
Published: January 2005

A hitherto unsuspected degree of regional topographic organization in the noradrenergic nucleus, locus coeruleus, was revealed by the use of retrograde transport of horseradish peroxidase (HRP) from terminal areas receiving noradrenergic innervation. HRP was injected into hippocampus, hypothalamus, thalamus, caudate‐putamen, septum, amygdala‐piriform cortex, cerebellum and cortex. Successful transport was obtained from all areas, including the caudate‐putamen and cerebral cortex. The pattern of HRP positive cells in the ipsilateral locus coeruleus was markedly different depending on the location of the HRP injection. Thus, hippocampal injections labeled cells i the dorsal locus coeruleus but not at all in the ventral tip. Injections of HRP into caudate‐putamen or cerebellum labeled the ventral tip along with the rest of the dorsal portion. HRP injections into the septum labeled cells only in the dorsal half of the dorsal locus coeruleus. There thus exists a three tier division of locus coeruleus into the ventral one third, dorsal one third and intermediate one third. A further division was seen in the anterior‐posterior plane with HRP injections into the thalamus labeling the posterior pole of locus very intensely but with little transport to more anterior levels; conversely HRP injection into the hypothalamus resulted in intense labeling only in the anterior pole of locus coeruleus. Amygdala‐piriform cortex HRP injections revealed a further pattern with very intensely reactive cells scattered sparsely throughout the nucleus. Cortical HRP injections yielded weaker lebeling also in occasional, scattered cells. All HRP transport to locus coeruleus was shown to be noradrenergic by degeneration with 6‐hydroxydopamine and due to terminal, rather than fiber of passage, uptake by control injection into the dorsal NA bundle. It is concluded that the locus coeruleus is not an homogenous nucleus with respect to the origin of the noradrenergic projections to sundry forebrain, spinal and cerebellar areas, but is comprised of distinct subdivisions of noradrenergic neurons.
The afferent connections and laminar distribution of cells in the cat striate cortex
Authors: Henry G. H. , Harvey A. R. , Lund J. S.
Published: January 2005

A laminar distribution of different functional cell types in the striate cortex of the cat is drawn up from the visual responses of single cells recorded in 64 electrode penetrations in 38 cats. In summary, S cells were found to be concentrated in laminae 4 and 6; SH cells in laminae 2, 3 and 4; C cells in laminae 5 and lower 3; B cells in laminae 3 and upper 5 and cells with non‐oriented receptive fields in lamina 4.

In addition, the nature of afferent innervation to striate neurons was derived from the latency of the orthodromic response to electrical stimulation in the optic chiasm and optic radiations in 19 cats. An analysis of latency values allowed the afferent innervation to a cell to be classed as belonging either to fast or slow conducting streams in the population of dLGN axons and also permitted a decision to be made on whether or not the afferent path passed directly to the cell. Direct afferent innervation from the dLGN was not found to be confined to a single class of striate neuron. Instead, examples of cells with S, SH, C, B and non‐oriented receptive fields all had orthodromic latencies that met the requirement for direct innervation. Instances of cells with orthodromic latencies suggestive of indirect innervation were also found for most receptive field classes but these cells were encontered less frequently than those with a direct afferent input. It is argud that a variety of different cell types may act as first order neurons in the striate cortex and that cells occurring at later stages in the sequence of cortical processing may have been incompletely studied because they are more difficult to stimulate either visually or electrically.
The distribution of oxytocin‐ and neurophysin‐stained fibers in the spinal cord of the rat and monkey
Authors: Swanson L. W. , McKellar S.
Published: January 2005

Immunohistochemical methods have been used to describe the distribution of neurophysin I‐ and oxytocin‐stained fibers in the spinal cord. In albino rats of either sex, such fibers descend through the dorsal part of the lateral funiculus to the caudal end of the cord. Fibers leave the lateral funiculus to innervate the marginal zone of the dorsal horn at all levels, and the intermediolateral column at thoracic, lumbar and sacral levels. Some fibers course medially through the intermediate gray to end in the central gray, which is innervated at all levels, and also appears to be innervated by fibers descending in the central gray itself. A semiquantitative analysis shows that the density of terminal fields in the intermediolateral column, marginal zone, and central gray varies significantly at different levels. The intermediolateral column is preferentially innervated between T1‐T3, T9‐T11, and T13‐L2. The nucleus intercalatus spinalis and the dorsal commissural nucleus (between T13 and L2), both of which contain preganglionic neurons, are densely innervated.

In the monkey (Macaca fascicularis), neurophysin I‐ and oxytocin‐stained fibers descend through the lateral funiculus to the filum terminale, where some of them enter the pia‐arachnoid surrounding the filum. The intermediolateral column is not innervated between T1‐T3, is sparsely innervated at sacral levels, and is moderately innervated between T4 and L3; the greatest density of fibers occurs at L3. At most levels, few if any fibers are found in the central gray and marginal zone; the central gray is sparsely innervated between T8 and L2, at S2, and between Co3‐Co6, and the marginal zone contains a small number of fibers in the region of S2 and Co6.

Neurophysin I‐ and oxytocin‐stained fibers were also found in the intermediolateral column, marginal zone, and central gray of homozygous Brattleboro, spontaneously hypertensive, and Egyptian sand rats.

The results suggest that the paraventriculo‐spinal pathway is particularly related to specific groups of sympathetic and parasympathetic preganglionic neurons, and to the marginal zone, which is involved in the relay of ascending nociceptive information through the spinothalamic tract.
Commissural columns in the sensory‐motor cortex of monkeys
Authors: Jones E. G. , Coulter J. D. , Wise S. P.
Published: January 2005

Callosally projecting cells and the terminal ramifications of their axons were identified in the monkey sensory‐motor cortex by retrograde and anterograde labeling techniques, often by double labeling cells and axons in the same animal.

Bundles of callosal fibers terminate in small column‐like zones 0.5‐1 mm wide in the motor cortex (area 4) and in the first (SI) and second (SII) somatic sensory areas. Such columns are aligned in register to form elongated strips extending mediolaterally in the long axes of the pre‐ and postcentral gyri. Significant portions of area 4, SI and SII, in regions corresponding to the representations of the hand and foot, are not callosally connected.

The cells of origin of callosal fibers in SI are largely confined to layer IIIB and form columns and strips corresponding to the above. In connected zones of SI, the callosal connection is reciprocal and precisely point‐to‐point. This and the laminar distribution of the terminal ramifications of callosal fibers (to layers I‐IV) suggest that callosal fibers may arise from and terminate upon exactly homotopic, column‐like groups of layer IIIB pyramidal cells.

Commissurally projecting cells and their terminal ramifications are not limited to particular architectonic fields or particular parts of fields in SI. All architectonic fields of SI project heterotopically to the contralateral SII.