bluuebunny/crossref_metadata_2025 huggingface dataset:
The postnatal development of neurons in the dorsal lateral geniculate nucleus of the rat: A Golgi study
Authors: Parnavelas J. G. , Mounty E. J. , Bradford R. , Lieberman A. R.
Published: December 2004

The postnatal differentiation of neurons in the dorsal lateral geniculate nucleus of the albino rat was studied using the Golgi‐Cox technique. At least four animals were used at postnatal ages 12 hours, 2, 4, 6, 8, 10, 11, 12, 13, 14, 15, 16, 18, 20, 24, 28, 35 days and adult.

Presumptive thalamo‐cortical projection cells (Class A cells of Grossman et al., '73) and non‐projection, intrinsic neurons (Class B cells), are distinguishable at 12 hours after birth. At this stage both types of neuron are immature, with prominent growth cones at their dendritic extremities. Dendritic growth and differentiation appear to be complete by 18 days.

Relay cells display two apparent “growth spurts” characterized by noticeable enlargement of the perikaryon and a marked increase in dendritic length and complexity. One occurs between days 4 and 6 and coincides with a period of enhanced synaptogenesis and gliogenesis: the second occurs between days 14 and 15, around the time of eye opening (day 14) and may be related to a further phase of increased synaptogenesis and gliogenesis (Karlsson, '67; Biesold et al., '76).

Class B cells appear to “lag” behind class A cells in their initial postnatal differentiation, but also reach their mature condition by day 18.
Ultrastructural studies of the superior cervical trunk of the mouse: Distribution, cytochemistry and stability of fibrous elements in preganglionic fibers
Authors: Lewis Jon C. , Burton Paul R.
Published: December 2004

The ultrastructure of axons in the preganglionic cervical sympathetic trunk of the mouse is described with emphasis on the number, distribution and stability of fibrous elements in the axoplasm. Neurofilaments outnumbered microtubules in myelinated and non‐myelinated axons of all sizes, and the ratio of neurofilaments to microtubules in non‐myelinated axons at each point studied was fairly consistent and independent of axonal diameter. The density of neurofilaments and microtubules, however, was greater in axons of progressively smaller dismeter. In non‐myelinated axons and small myelinated axons neurofilaments were uniformly distributed throughout the axoplams resulting in minimum and maximum interfilament distances of 300 Å and 500 Å respectively; the spacing of fibrous elements within any one axon was dependent upon its diameter and position with respect to the superior cervical ganglion in the preganglionic trunk. The maximum interfilament distance was also found in large myelinated axons where neurofilaments, occurring in fascicles, were separated by distances of approximately 500 Å. Cytochemical staining of axons with lanthanum hydroxide, ruthenium red or alkaline bismuth delineated the delicate filamentous matrix interconnecting microtubules, neurofilaments and other organelles in the axoplasm. Alkaline bismuth stain was most intense in myelinated axons where heaviest deposition of reaction product was associated with neurofilaments. Treatment in vitro of the cervical sympathetic trunk with 5 × 10−5 M vinblastine sulfate dissociated microtubules and induced formation of crystalline arrays of “tubular” elements. A uniform center to center spacing of 250–300 Å was found for crystalloids in nonmyelinated axons; however, in myelinated axons the center to center spacing was not uniform and varied in the range 300–600 Å. Neurofilaments and their surface projections were unaffected by vinblastine. Fixation in the presence of lanthanum enhanced delineation of crystalloid elements. Exposure of 0–4°C for up to three hours had no consistent effect on microtubules or neurofilaments. In contrast, cold treatment disrupted the delicate axonal matrix and resulted in the formation of aggregates of coarse flocculent material in the axoplasm.
The ultrastructure of cutaneous type I mechanoreceptors (Haarscheiben) in cats following denervation
Authors: English Kathleen B.
Published: December 2004

Denervation of specialized cutaneous mechanoreceptors (Haarscheiben or domes) in cats was followed after 20 and 25 days by the following alterations in receptor structure: (1) reduced numbers of Merkel cells, (2) Merkel cells degenerating in situ, (3) fewer dense‐core granules in the cytoplasm of Merkel cells, (4) an increased number of agranular dendritic cells and Langerhans cells in the dome, (5) the apparent phagocytosis of Merkel cells by Schwann and Langerhans cells, (6) fewer epithelial cell layers over the dome, and (7) a decrease in the number of transitional cells.

Skin excised between the domes in the denervated nerve field appeared normal when compared to innervated skin, and it was considered unlikely that the alterations in dome structure were due to generalized nutritional changes in the skin caused by transection of sympathetic axons or to some other side effect of denervation. Since domes are formed in new locations on the skin after nerves have regenerated (Burgess et al.,1974), changes in dome structure following nerve transection are probably due to loss of the “trophic” influence of the nerves supplying the dome.
The vestibular complex of the american opossum Didelphis virginiana. II. Afferent and efferent connections
Authors: Henkel C. K. , Martin G. F.
Published: December 2004

We have demonstrated the connectivity of the opossum's vestibular nuclei using degeneration, autoradiographic and horseradish peroxidase techniques and have found it to be generally comparable to that reported for the cat. Apart from the primary input described in Part I of our study, the cerebellum provides the major source of afferent connections to the vestibular complex. Axons from the cerebellar cortex distribute mainly to vestibular areas which receive no primary afferent projections, e.g., the dorsal part of the lateral vestibular nucleus, the dorsolateral margin of the inferior vestibular nucleus as well as cell groups comparable to “f” and “x” In contrast, fastigial fibers show considerable overlap with primary vestibular input, particularly in the ventral part of the lateral nucleus, the central part of the inferior nucleus and the medial nucleus. Axons of fastigial origin also distribute to the superior vestibular nucleus, to subnuclei “f” and “x” and to the parasolitary region. Although spinal fibers are diffuse within the main vestibular nuclei, they ramify quite densely within subnucleus “x”. Most of th spinovestibular projection appears to arise in the cervical spinal cord of the opossum.

Ipsilateral connections from the interstitial nucleus of Cajal and surrounding aras end predominantly, but not exclusively, in the medial vestibular nucleus. A crossed midbrain projection has been verified from the red nucleus to cell group “x” and the lateral part of the inferior nuclues, as well as to an area possibly comparable to cell group “z,” as described for the cat.

In Part I of our study we have shown that the major targets of primary vestibular fibers are the central part of the superior nuclues, a portion of parabrachial complex possibly comparabale to subnuclues “y,” the ventral part of th lateral nucleus and the medial nucleus. All of these primary zones give rise to fibers supplying extraocular nuclei and surrounding areas (present study). The ascending midbrain fibers from the superior nucleus end mainly ipsilaterally, whereas those from the putative subnucleus “y” and the medial vestibular nucleus distribute contralaterally for the most part.

Although the dorsal part of the lateral vestibular nucleus has no primary vestibular input, it does receive a major projection from the cerebellar cortex. This same region of the lateral nuclues projects to the spinal cord, but not to extraocular nuclei. The ventral part of the lateral nucleus, and perhaps the medial nucleus, also relay to the spinal cord. Additional projections from all vestibular nuclei can potentially affect multiple systems, including those innervating the spinal cord. Finally, commissural vestibular connections of the opossum are shown to arise within all four major nuclei.
Second order auditory pathways in the chimpanzee
Authors: Strominger Norman L. , Nelson Louis R. , Dougherty William J.
Published: December 2004

Substantial portions of the dorsal, and almost the entire posteroventral and anteroventral (Av) cochlear nuclei were aspirated unilaterally in a chimpanzee. Axonal degeneration was studied by the Fink‐Heimer method. The greatest amount of degeneration was followed medially from the region of Av into the lateral part of the trapezoid body. Degeneration also coursed around the superior surface of the restiform body and was traced into the dorsal and intermediate acoustic striae.

Within the superior olivary complex, degeneration was distributed to: the ipsilateral lateral superior olive; laterally and medially oriented dendrites of the ipsilateral and contralateral medial superior olivary nuclei respectively (some periosomatic degeneration also was present bilaterally); the contralateral medial trapezoid nucleus; retro‐olivary and preolivary cell groups bilaterally. Abundunt degeneration passed into the contralateral lateral lemniscus and was distributed largely to its ventral nucleus. The contralateral central nucleus of the inferior colliculus was a major site of termination of ascending second order auditory fibers. The caudal tip of the ipsilateral ventral nucleus of the lateral lemniscus received abundant degeneration, but this diminished rostrally. The ipsilateral inferior colliculus contained a moderate amount of degeneration.

A fair number of degenerated second order auditory fibers ascended in the contralateral brachium of the inferior colliculus and were distributed both to the principal and magnocellular divisions of the medial geniculate body. This pathway appears to represent a phylogenetic advance in the brain of the great ape.
The locust wing hinge stretch receptors. I. Primary sensory neurones with enormous central arborizations
Authors: Altman J. S. , Tyrer N. M.
Published: December 2004

In locusts a single‐celled stretch receptor (SR) neurone at the base of each wing monitors wing elevation and contributes to the control of the flight motor output. The central projections of these neurones are very complex but consistent in detail in the three species studied (Chortoicetes, Locusta and Schistocerca). The hindwing SR projects to the second and third thoracic ganglia, the forewing SR to the first, second and third thoracic ganglia. Both send fine axons into the abdominal connective.

Within the ganglia each SR forms an extensive arborization, entirely ipsilateral and mainly in the dorsal neuropile, divided into medial, mediolateral, and lateral branches. The projections of the two ipsilateral SR neurones overlap almost completely in the second and third ganglia. There are recurrent loops between branches of a single neurone both within and between ganglia.

Light microscope analysis shows apparent contacts between the SR neurones and flight motor neurones and other wing sensory afferents, as well as long inter‐neurones, other motor neurones and two types of multiaxonal neurones of unknown function. There are three groups of contacts between each SR and a flight motor neurone: laterally on the main branches, medially with the terminal twigs; and in the anterior dorsorriedial glomerulus, where the interganglionic recurrent branch also terminates. All contacts are ipsilateral except for those with the contralateral branches of the dorsal longitudinal muscle motor neurones.

We suggest that the SR neurones are multifunctional. Differential information transfer could result both from the spatial distribution of synaptic connections with the motor neurones from filtering caused by low safety factors at branch junctions. Information in the lateral branching could be used for general excitation and control of firing frequency of the motor neurones; that in the medial branch for wing control and coordination.
Preterminal and terminal axon arborizations in the substantia gelatinosa of cat's spinal cord
Authors: Réthelyi Miklós
Published: December 2004

Extensive terminal branchings of fine fibers in the substantia gelatinosa of Golgi‐Kopsch preparations of the adult cat spinal cord were subjected to a semi‐quantitative analysis. Transverse sections suggest that these fibers are probably unmyelinated primary afferent elements of dorsal root origin. In transverse sections these elements pass medially and ventrally and shortly disappear due to a change in orientation. Similar thin fibers in sagittal sections can be followed for several hundred microns as they give rise to side branches that also run mainly in a longitudinal direction. The side branches divide in turn to produce preterminal axon arborizations. The arborizations were distributed in 150 μ wide zones in the dorsal horn region corresponding to Rexed's lamina II. The end terminals are large bulbs, usually preceded by two to three equally large en passant enlargements. Seven to eight terminals stem from each side branch. The terminals and enlargements are arranged in narrow (16‐26μ m thick) sagittal sheets. The terminals of several side branches often converge upon a common region so that clusters of ter minals occur within the sagittal sheet. It is proposed that these observations are consistent with the substantia gelatinosa (lamina II) as the termination of unmyelinated (C) primary afferent fibers and that the latter are the only type of primary fibers ending in this portion of the spinal cord.
The substantia nigra of the rat: A golgi study
Authors: Juraska Janice M. , Wilson Charles J. , Groves Philip M.
Published: December 2004

Three variants of the Golgi method were employed to examine the cell types, their dendritic fields and organization and azonal trajectories within the substantia nigra of albino and hooded rats. In both sagittal and coronal sections, large, medium and small neurons were classified on the basis of soma size, extent of dendritic fields and dendritic caliber. In general nigral cells have three to five primary dendrites that branch relatively infrequently. Some dendrites of all cell types have thinly scattered spines or varicosities.

Small cells, found in all areas of the nucleus, have thin dendrites and small, nondirectional dendritic fields. These are considered to be interneurons. The medium cells found in pars compacta, presumed to be the dopaminergic cells of the nigroneostriatal pathway, send long dendrites into pars reticulata perpendicular to the course of pars compacta. In addition, these cells have a number of dendrites which remain in pars compacta. These cells have axons that run medio‐dorsaslly. No axon collaterals were detected. Both large and medium cells are found in pars reticulata. Cells in the dorso‐medial aspect of pars reticulata orient rostro‐caudally and roughly perpendicular to the course of pars compacta, while cells in the perpeduncular area show a strict orientation which is parallel to the crus cerebri. Some pars reticulata cells emit axon collaterals while others remain unbranched for their observable length. Both large and medium cells are also seen in pars lateralis. These cells send long dendrites ventrally into pars reticulata where they run parellel to the crus cerebri, while some shorter dendrites remain in pars lateralis.

In total, the substantia nigra appears to have a layered organization: the superior layer is the cellular pars compacta, the second is the dorso‐medial area of pars reticulata where both pars compacta and pars reticulata dendrites run rostro‐caudally and dorso‐ventrally and the third layer is the perpenduncular region where dendrites from all areas run parallel to the crus cerebri.
Formation of hemi‐desmosomes during regeneration of crayfish nerve root sheath as studied with freeze fracture
Authors: Shivers Richard R. , Brightman Milton W.
Published: December 2004

The multilamellate glial sheath of mixed nerve roots of the sixth abdominal ganglion of crayfish contains numerous hemi‐desmosomes which appear to attach glial lamellae to material in adjacent extracellular clefts. These junctions, which have been described in detail in an earlier report (Shivers and Brightman, '76), are irregular in shape, punctuate and may be as large as 1 μm in diameter. Surgical interruption of sixth ganglion nerve roots results in regeneration of motor axons and their multilamellate glial sheaths. As the glial processes grow and re‐establish a highly organized axon sheath, hemi‐desmosomes appear. These junctions are present at the advancing edge of glial processes as well as on their lateral margins. Developing hemi‐desmosomes are characterized as a diffuse aggregation of 120–130 Å intramembrane particles which are present three weeks following nerve section. As growth and reorganization of the sheath proceeds, the intramembrane particles appear to aggregate and form irregular clusters of varying dimensions. Regenerating nerves freeze‐cleaved 8 to 16 weeks following surgery exhibit junctional particle aggregates similar to those in normal unoperated nerve roots. Origin of the intramembrane particles which comprise the junctional aggre gates in unknown. Perhaps they are synthesized de novo by the regenerating glial cells or, they may be remnants of complexes which became dispersed following surgery. This is the first report of a freeze‐fracture study of hemi‐desmosome plasticity in an invertebrate nervous system.
Postnatal maturation of neurons in the rabbit superior Colliculus
Authors: Mathers Lawrence H.
Published: December 2004

The superior colliculi of Dutch‐belted rabbits aged 1 to 30 days were prepared according to Nissl and Golgi techniques and examined in comparison to the neuronal populations in the adult. It was found that the laminar dimensions of the adult are attained at 15 to 20 days, presumably due to glial and dendritic enlargement. The largest neuron in the superficial gray, the vertical cell, was found to mature earliest and to display the least evidence of dendritic development postnatally. Its dendrites do elongate from 0 to 15 days, but there are no growth cones or other unusual dendritic configurations. The intrinsic neurons of the superficial gray, the piriform and stellate cells show more evidence of postnatal dendritic development. Particularly in the case of stellate cells, there are dendritic growth cones present at birth, and early in development spines are found on the soma and large dendrites. Only at 15 to 20 days do the dendritic arbors of these cells assume normal adult shapes and sizes. These and other observations suggest that there are two phases of postnatal cellular maturation in the upper layers of the superior colliculus, one involving the smaller “interneurons.” This phased maturation is compared with the known sequence of physiological maturation as studied by the method of receptive‐field mapping.
Descending pathways from the superior colliculus: An autoradiographic analysis in the rhesus monkey (Macaca mulatta)
Authors: Harting John K.
Published: December 2004

The autoradiographic tracing method has been used to identify the various descending tectofugal pathways and their targets in the rhesus monkey (Macaca mulatta).

The present data reveal that the majority of descending tectofugal axons arise from collicular laminae which lie ventral to the stratum opticum (layer 3). Such descending axons can be grouped into two major bundles or tracts, i.e., the ipsilateral tectopontine‐tectobulbar tract and the crossed tectospinal tract (or the predorsal bundle). There is, in addition to these two major pathways, a smaller, commissural projection.

The ipsilateral pathway courses laterally and ventrocaudally to terminate within the parabigeminal nucleus, the mesencephalic reticular formation, the dorsal lateral pontine gray (in several discrete patches), the dorsal lateral wing of the nucleus reticularis tegmenti pontis, and within the nucleus reticularis pontis oralis. Other ipsilateral targets of the deep tectal layers are the cuneiform nucleus and the external nucleus of the inferior colliculus. In several experiments transported protein is also apparent within the substantia nigra.

Axons which comprise the tectospinal tract, or the predorsal bundle, cross within the dorsal tegmental decussation and descend within the brainstem in a position slightly lateral to the midline. The most rostral and quite extensive target of the predorsal bundle is the nucleus reticularis tegmenti pontis. As the predorsal bundle courses caudally within the pontine tegmentum, labeled axons enter the dorsal and medial regions of both the oral and the caudal divisions of the nucleus reticularis pontis. At caudal medullary levels, the majority of the labeled axons comprising the predorsal bundle pass ventrally to end quite profusely within the subnucleus b of the medial accessory nucleus of the inferior olivary complex. Caudal to this only a few scattered, labeled axons can be followed into the cervical spinal cord.

Labeled axons also pass to the opposite, or contralateral colliculus via the tectal commissure. Such axons appear to arise and end primarily within the deeper tectal layers.

In one experiment, the injection invaded the mesencephalic nucleus of the trigeminal nerve. Labeled axons were apparent within the motor nucleus, the chief sensory nucleus (quite profusely) and within the spinal or descending nucleus of the trigeminal nerve.
Connections of the pretectum in the cat
Authors: Berman Nancy
Published: December 2004

The connections of the pretectal complex in the cat have been examined by anatomical methods which utilize the anterograde axonal transport of tritiated proteins or the retrograde axonal transport of the enzyme horseradish peroxidase. Following injections of tritiated amino acids into the eye, label can be seen in the contralateral and ipsilateral nucleus of the optic tract and olivary nucleus where it appears as two or three finger‐like strips. Following large injections of tritiated amino acids into the pretectal complex transported label accumulates ipsilaterally in a region dorsolateral to the red nucleus, the central and pericentral divisions of the tegmental reticular nucleus, the intermediate layers of the superior colliculus, the nucleus of Darkschewitch, the thalamic reticular nucleus, zona incerta and fields of Forel, the central lateral nucleus, the pulvinar nucleus and the ventral lateral geniculate nucleus. Contralaterally label accumulates in the nucleus of the posterior commissure, the interstitial nucleus of Cajal, the anterior, posterior and medial pretectal nuclei, and the ventral lateral geniculate nucleus

From smaller injections, more or less well confined to single nuclei, the following patterns of connections are demonstrated. The nucleus of the optic tract projects to the ipsilateral ventral lateral geniculate nucleus and pulvinar nucleus and to the contralateral nucleus of the posterior commissure. The anterior pretectal nucleus projects to the ipsilateral central lateral nucleus, the reticular nucleus, zona incerta, fields of Forel, the region dorsolateral to the red nucleus and to the contralateral anterior pretectal nucleus. The posterior pretectal nucleus seems to project only to the ipsilateral reticular nucleus and zona incerta. The central tegmental fields deep to the pretectum project to the tegmental reticular nucleus of the brainstem. When the injection involves the nucleus of the posterior commissure label is seen in the ipsilateral nucleus of Darkschewitch, and in the contralateral nucleus of the posterior commissure and interstitial nucleus of Cajal but no nucleus of the pretectum could be positively identified as projecting to any of the motor nuclei of cranial nerves III, IV, and VI.

Following large injections of horseradish peroxidase into the pretectal complex, labeled cells are seen in the superficial layers of the ipsilateral superior colliculus, in the ipsilateral ventral lateral geniculate nucleus, reticular nucleus and zona incerta and in the contralateral anterior, medial and posterior pretectal nuclei, nucleus of the optic tract and ventral lateral geniculate nucleus.
The parasagittal zonation within the olivocerebellar projection. I. Climbing fiber distribution in the vermis of cat cerebellum
Authors: Groenewegen H. J. , Voogd J.
Published: December 2004

After lesions of inferior olive, survival times of 5 to 12 days and Nauta staining, degeneration is present in white matter and central cerebellar nuclei and Deiters' nucleus. Shorter survival times from 40 to 60 hours and Fink‐Heimer impregnation reveal degenerating climbing fiber terminals in the molecular layer. With 3H‐leucine autoradiography and survival times of three to seven days the entire trajectory of the climbing fibers can be traced. Olivocerebellar fibers cross in the brain stem and terminate contralaterally in cortex and central nuclei. Occasional labeling of mossy fiber terminals is explained by involvement of reticular nuclei.

Small parts of the inferior olive connect with narrow longitudinal zones in the cortex through compartments in the white matter. The corresponding distribution of olivocerebellar fibers and Purkinje cell axons over these compartments suggests that the organization of the olivocerebellar and corticonuclear projection is essentially similar. Collaterals always terminate in the central cerebellar necleus which receives a corticonuclear projection from the zone in which the parent fibers terminate.

Caudal medial accessory olive projects to medial vermal zone A and to fastigial nucleus, subnucleus beta projecting to lobule VII and caudal fastigial nucleus. Cadual dorsal accessory olive projects to lateral vermal zone B in lobules I‐VI, Deiters' nucleus and dorsomedial subnucleus of interposed nucleus. The caudal principal olive (dorsal cap, ventrolateral outgrowth receiving visual and vestibular input) projects to flocculo‐nodular lobe.
Retinogeniculate projections in the rabbit: An autoradiographic study
Authors: Takahashi Ellen S. , Hickey Terry L. , Oyster Clyde W.
Published: December 2004

As shown by autoradiographic techniques, the pattern of retinogeniculate projections in the pigmented rabbit is generally similar to that described in preious studies. Each retina projects bilaterally to the α segment of the dorsal lateral geniculate nucleus (LGd) and to the external segment of the ventral lateral geniculate nucleus (LGv). The β segment of the LGd and internal layer of the LGv receive contralateral inputs only.

The α segment of the LGd contains an irregularly shaped region which receives overlapping bilateral projections. Within this region the ipsilateral input is continuous and predominant. This pattern of ipsilateral projection can account for both the laminar arrangement perpendicular to the lines of projection and the “hidden lamination” which have been described previously for the rabbit LGd.

A separate bilateral projection is identified for a group of cells lying between the LGd and LGv rostrally. Caudally this intergeniculate leaflet extends medial and ventral to the LGv and appears to merge with the zona incerta.
Synaptic Organization of the external cuneate nucleus in the rat
Authors: Rosenstein Jeffrey M. , Leure‐Dupree Alphonse E.
Published: December 2004

The normal synaptic organization of the rat external cuneate nucleus (ECN) has been investigated. The characteristic feature of the ECN neuropil is complex synaptic arrangements termed synaptic glomeruli. These involve both axo‐dendritic and axo‐axonic synapses and usually are isolated from the surrounding neuropil by lamellar glial sheaths. Glial isolation of synaptic glomeruli is conspicuous near capillaries. Central glomerular bouton profiles vary in size (2–9 μm diam) and configuration. They form asymmetrical synapses onto dendritic shafts and spines and occasionally receive symmetrical synapses from en passant bouton profiles.

Other forms of axo‐dendritic synapses not associated with synaptic glomeruli are observed. The type frequently observed is formed by one or more boutons (0.5–4.0 μm diam) synapsing onto a dendrite or dendritic spine. “Isolated” axo‐dendritic synapses are surrounded by glial lamellae. Elongated “giant” boutons make multiple synaptic contacts along a dendritic shaft.

Serial axo‐axonic synapses are found mainly in caudal regions of the nucleus. Axo‐somatic synapses are formed by small boutons (0.3–2.0 μm diam) contacting medium (16–24 μ) and small (9–14 μm) neurons. The least frequently observed bouton type in the rat ECN contains numerous granular vesicles, 80‐100 nm in diameter. These boutons may contact dendrites, neuronal somas or other boutons.
Three types of horizontal cells in the stingray retina: Their morphology and physiology
Authors: Toyoda Jun‐Ichi , Saito Takehiko , Kondo Hiroaki
Published: December 2004

Histological and electrophysiological features of horizontal cells were studied in the stingray retina in which the ratio of rods to cones was about five to one. There were three distinct sublayers of horizontal cells; external, middle and internal. The type of horizontal cells recorded was identified by dye injection after recording. Relatively thick external horizontal cells sent their short dendrites into both rod and cone terminals to make synaptic contacts. The response recorded from them was not color‐coded but showed a Purkinje shift depending on the adaptational state. Middle horizontal cells were flat and usually two or three of them overlying each other constituted the middle sublayer. Their response, which was difficult to record in the light‐adapted retina, was characterized by a slow time course, a prolongation of the response to bright flashes and a maximum sensitivity in the green region of the spectrum without any sign of Purkinje shift. Internal horizontal cells were color‐coded. They responded with hyperpolarization at shorter wavelengths and with depolarization at longer wavelengths. It was concluded that the internal horizontal cells receive inputs from cones and the middle horizontal cells from rods, whereas the external horizontal cells receive inputs from both rods and cones.
An autoradiographic analysis of the differential ascending projections of the dorsal and median raphe nuclei in the rat
Authors: Azmitia Efrain C. , Segal Menahem
Published: December 2004

The differential projections from the dorsal raphe and median raphe nuclei of the midbrain were autoradiographically traced in the rat brain after 3H‐proline micro‐injections. Six ascending fiber tracts were identified, the dorsal raphe nucleus being the sole source of four tracts and sharing one with the median raphe nucleus. The tracts can be classified as those lying within the medial forebrain bundle (dorsal raphe forebrain tract and the median raphe forebrain tract) and those lying entirely outside (dorsal raphe arcuate tract, dorsal raphe periventricular tract, dorsal raphe cortical tract, and raphe medial tract). The dorsal raphe forebrain tract lies in the ventrolateral aspect of the medial forebrain bundle (MFB) and projects mainly to lateral forebrain areas (e.g., basal ganglion, amygdala, and the pyriform cortex). The median raphe forebrain tract lies in the ventromedial aspect of the MFB and projects to medial forebrain areas (e.g., cingulate cortex, medial septum, and hippocampus). The dorsal raphe cortical tract lies ventrolaterally to the medial longitudinal fasciculus and projects to the caudate‐putamen and the parieto‐temporal cortex. The dorsal raphe periventricular tract lies immediately below the midbrain aqueduct and projects rostrally to the periventricular region of the thalamus and hypothalamus. The dorsal raphe arcuate tract curves laterally from the dorsal raphe nucleus to reach the ventrolateral edge of the midbrain and projects to ventrolateral geniculate body nuclei and the hypothalamic suprachiasmatic nuclei. Finally, the raphe medial tract receives fibers from both the median and dorsal raphe nuclei and runs ventrally between the fasciculus retroflexus and projects to the interpeduncular nucleus and the midline mammillary body.

Further studies were done to test whether the fiber tracts travelling in the MFB contained 5‐HT. Unilateral (left) injections of 5,7‐dihydroxytryptamine (5 μgm/400 nl) 18 days before midbrain raphe microinjections of 3H‐proline produced a reduction in the grain concentrations in all the ascending fibers within the MFB. Furthermore, pharmacological and behavioural evidence was obtained to show that the 5‐HT system had been unilaterally damaged; these animals displayed preferential ipsilateral turning in a rotameter which was strongly reversed to contralateral turning after 5‐hydroxytryptophan administration.

The results show that DR and MR nuclei have numerous ascending projections whose axons contain the transmitter 5‐HT. The results agree with the neuroanatomical distribution of the 5‐HT system previously determined biochemically, histochemically, and neurophysiologically. The midbrain serotonin system seems to be organized by a series of fiber pathways. The fast transport rate in these fibers was found to be about 108 mm/day.
The morphological and physiological properties of a regenerating synapse in the C.N.S. of the leech
Authors: Muller Kenneth J. , Carbonetto Salvatore
Published: December 2004

Regeneration of an electrical synapse between particular interneurons in the medical leech was traced physiologically and morphologically using intracellular recording and horseradish peroxidase (HRP) injection. The synapse between S‐cell interneurons lies in the connective midway between segmental ganglia, so crushing near one ganglion severs only one S‐cell's axon. The severed distal stump remains connected to the adjacent uninjured S‐cell and continues for weeks to conduct impulses. The injured cell regenerates, while its uninjured “target” neuron in the next ganglion does not grow. After the sprouts of the regenerating neuron cross the crush, one or a few branches grow along the surviving distal stump toward the original synapse. After about one month when the region of original synapse has been reached, regenerating neurons from electrical junctions and stop growing. Thereafter electrical coupling improves in stages. Within two months the regenerated neuron attains full caliber, the stump degenerates and function is normal. In some instances within days or weeks of crushing, the regenerating neuron forms a basket of synapses upon its severed distal stump and then continues growing to synapse with the target. When this occurs, electrical coupling and subsequent impulse transmission between S‐cells rapidly resumes. These experiments indicate that the regenerating neuron is guided to its proper synaptic target by recognizing and following its severed distal stump. Sometimes the distal stump itself becomes an intermediate synaptic target.
Rods and cones in the mouse retina. II. Autoradiographic analysis of cell generation using tritiated thymidine
Authors: Carter‐Dawson Louvenia D. , Lavail Matthew M.
Published: December 2004

The period of cell genesis of rod and cone photoreceptor cells has been determined in the retinas of C57BL/6J mice. Embryonic mice were exposed to a single dose of 3H‐thymidine at embryonic day (E) 10‐18 by injecting pregnant mice intraperitoneally. Animals at postnatal ages were injected subcutaneously once between postnatal day (P) 0‐10. The eyes were removed at one to three months of age. After fixation, they were embedded in glyol methacrylate, sectioned at 1.5 μm and prepared for autoradiographic analysis. All of the cone cells are generated over a relatively short time interval during the fetal period. In the posterior retina, the peak of cone cell genesis occurs at E13‐E14, and no cones are generated after E16. The rods, by contrast, are generated later and over a longer time period. They first begin to be generated in the posterior retina on E13, but the peak of cell genesis in not reached until the day of birth, and some rods are generated as late as P5. For both rods and cones the peaks of cell genesis in the peripheral retina occur two to three days later than in the posterior retina. The findings demonstrate that rods and cones are developmentally distinct cell types in the mouse retina.
Postnatal development of cholinergic neurotransmitter enzymes in the mouse cerebellum. Biochemical, light microscopic and electron microscopic cytochemical investigations
Authors: Olschowka John A. , Vijayan Vijaya K.
Published: December 2004

The activity and distribution of the cholinergic neurotransmitter enzymes acetylcholinesterase (AChE) and choline acetyltransferase (ChAc) in the developing cerebellum of the mouse were investigated using biochemical assays and light microscopic histochemistry for AChE and ChAc, and electron microscopic histochemistry for AChE.

Postnatal alterations in the levels of AChE and ChAc in the cerebellum of the mouse are characterized by a divergent pattern. During the first two postnatal weeks, AChE activity increases progressively, whereas ChAc activity remains low. Beyond day 14, when AChE activity is steady or gradually decreasing, ChAc increases sharply to reach a peak on day 32. Histochemically, AChE activity is associated with the glomeruli and the Golgi cells of the internal granular layer, the medullary layer, and the deep cerebellar nuclei. Purkinje cells exhibit transient staining between days 2 and 9. At the ultrastructural level, AChE staining is first demonstrated on day 6 within the Golgi cell soma, on day 9 at the mossy fiber–granule cell synapse, and on day 11 at the Golgi terminal–granule cell synapse. The staining intensity of these structures reaches that of the adult on day 19.

The histochemical reaction for ChAc is localized to moderate number of presumed Bergmann glial cells, a few large cells of the deep cerebellar nuclei, small numbers of Golgi cells, and all immature Purkinje cells. The molecular layer, glomeruli, and the medullary layer fail to demonstrate ChAc activity. This distribution of ChAc sharply contrasts with the localization established by other methods previously and is interpreted in the light of the drawbacks of the histochemical procedure.

The biochemical fluctuations in AChE activity, correlated with the histochemical and cytochemical data, suggest that the postnatal increases in the enzyme are related to the ingrowth of the mossy fibers and to the maturation of the AChE‐positive Golgi cells. Histochemical evidence for the correlation between the ontogenetic increases in cerebellar ChAc activity and progressive mossy fiber innervation must await the application of the immunohistochemical method to the developing cerebellum.
Central gustatory paths in the crucian carp, carassius carassius
Authors: Morita Yasuhiro , Ito Hironobu , Masai Hideo
Published: December 2004

The central fiber connections of the gustatory system (VII, IX, and X nerves) in the crucian carp were examined by the Fink‐Heimer method and its modification.

The sensory and recurrence roots of the VII enter the brainstem separately and terminate in the ipsilateral half of the facial lobe (L‐VII). Afferent fibers of the IX terminate in the glossopharyngeal lobe (L‐IX). Most afferent fibers of the X terminate in the sensory layer of the vagal lobe (L‐X), in which degenerating terminals occur in some laminae. Some vagal afferents project bilaterally to the commissural nucleus of Cajal. The cutaneous component of the X projects to the nucleus of the spinal trigeminal tract (SpV) and the medial funicular nucleus (nFM).

Ascending secondary fibers from the L‐VII project bilaterally to the secondary gustatory nucleus (nGS) in the isthmus region. Descending secondary fibers from the L‐VII turn caudally in the SpV. These fibers terminate mostly in the nucleus of the SpV and sparsely in the nFM. The L‐IX and L‐X give rise to the long and short secondary paths. The long path projects as the ascending secondary tract to the ipsilateral nGS. The short path includes secondary fibers projecting to the motor layer of the L‐X and the medullary reticular formation.

Tertiary gustatory fibers arising in the nGS project ipsilaterally to two diencephalic nuclei: the nucleus glomerulosus and the nucleus diffusus lobi inferioris.
Prenatal development of the human lateral geniculate nucleus
Authors: Hitchcock Peter F. , Hickey T. L.
Published: December 2004

The development of the human lateral geniculate nucleus has been studied on Nissl‐ and silver‐stained sections from 61 fetal human brains collected during normal autopsy procedures. The age of the fetuses, which ranged from 16 to 40 (newborn) weeks was determined by comparing crown‐to‐rump lengths and body weights to the values published by Streeter (′20).

The development of the human lateral geniculate nucleus is remarkably similar to the described for the rhesus monkey (Rakic, ′77). As a result of the late growth of the pulvinar, the human lateral geniculate nucleus is displaced and rotated such that, at around week 24, the nucleus has come to lie along the ventrolateral border of the thalamus. The cellular laminae that characterize the adult nucleus are formed over a 3‐week period of time beginning around the 22nd week of gestation. More caudal parts of the nucleus laminate first. During this same period of time, the optic disc representation in laminae 4 and 6 is also formed.

Throughout most of the development of the human lateral geniculate nucleus, individual rows of cells can be seen extending across the nucleus. Although such rows of cells are best seen before the nucleus laminates, in older laminated nuclei the rows of cells are oriented either perpendicular or oblique, but never parallel, to the plane of the laminae. Previous findings in both the monkey (Rakic, ′77) and human (Hickey and Guillery, ′79) suggest it is possible that these rows of cells can be used to define the lines of projection through the nucleus. Incoming optic tract fibers run along, rather than perpendicular to, these rows of cells.
Distribution of cerebellothalamic neurons projecting to the ventral nuclei of the thalamus: An HRP study in the cat
Authors: Nakano Katsuma , Takimoto Tamotsu , Kayahara Tetsuo , Takeuchi Yoshiki , Kobayashi Yoshitaka
Published: December 2004

Distribution of cerebellothalamic neurons projecting to the ventral nuclei of the thalamus was examined in the cat, using the horseradish peroxidase (HRP) method.

After injections of HRP within the lateral or ventrolateral portions of the ventroanterior and ventrolateral nuclear complex of the thalamus (VA‐VL), neurons labeled retrogradely with HRP were seen contralaterally in the cerebellar nuclei; many of them were situated in the nucleus interpositus anterior and nucleus interpositus posterior, and a moderate number of them were located in the nucleus lateralis. Labeled neurons in the nucleus interpositus posterior were observed mainly in the medial and ventral portions of the nucleus. On the side ipsilateral to the injections, a few labeled neurons were seen in the nucleus interpositus anterior, nucleus interpositus posterior, and nucleus lateralis. Virtually no labeled neurons were found in the nucleus medialis of the cerebellum.

After HRP injections into the medial or dorsomedial portions of the VA‐VL, many labeled neurons were found contralaterally in the ventral and ventrolateral portions of the nucleus interpositus posterior, as well as in the nucleus lateralis, especially in its ventral and lateral portions. On the side ipsilateral to the injections, labeled neurons in the nucleus lateralis and nucleus interpositus posterior were small in number. In the nucleus medialis only a few labeled neurons were found bilaterally in the caudal levels of the nucleus.

After HRP injections centered on the ventromedial nucleus of the thalamus, many labeled neurons occurred bilaterally in the caudal portions of the nucleus medialis, with a slight contralateral preponderance, and contralaterally in the lateral and ventral portions of the nucleus lateralis. A few labeled neurons were also seen contralaterally in the ventrolateral and lateral portions of the nucleus interpositus posterior, and ipsilaterally in the nucleus lateralis.
Early prenatal development of substance P and enkephalin‐containing neurons in the rat
Authors: Pickel Virginia M. , Sumal Khushdev K. , Miller Richard J.
Published: December 2004

The peroxidase‐antiperoxidase (PAP) technique is used to determine the time of first detection and distribution of neuronal perikarya and processes showing substance P (SP)‐ and enkephalin (EN)‐like immunoreactivity (LI) in the central and peripheral nervous system of the fetal rat. SPLI is first detected in central perikarya at E15. By E18, SPLI is less intensely localized in certain nuclei and shows heavier accumulations of immunoreactivity in central processes in peripheral sensory neurons. ENLI is also widely distributed in perikarya and processes of the central nervous system at E18, but is not detected at E15. The distribution of SPLI and ENLI at E18 is comparable to that previously described in the adult brain with the following exceptions: (1) labeled perikarya and processes are not detected in the rostral forebrain; (2) axonal pathways are intensely labeled whereas most terminal fields are devoid of immunoreactivity.
An analysis of the axon populations in the nerves to the pelvic viscera in the rat
Authors: Hulsebosch Claire E. , Coggeshall Richard E.
Published: December 2004

The present study uses selective surgical ablations combined with electron microscopic analyses to determine the number of axons in yarious catagories in rat hypogastric, pelvic, and pudendal nerves, these being the nerves to the pelvic viscera in this animal. Unmyelinated fibers predominate in all of these nerves. One of the most significant findings is that the pelvic nerve contains almost as many postganglionic sympathetic fibers as the hypogastric nerve. Previous investigators thought that the pelvic nerve supplied the parasympathetic inflow and the hypogastric nerve the sympathetic inflow to the pelvic viscera. The finding that there is a sizable sympathetic component in the pelvic nerve negates this idea, at least for the rat, and presumably calls for a reevaluation of the syndromes that arise from pelvic as opposed to hypogastric nerve section. Other findings of interest are (1) that there are unmyelinated efferent axons in the pudendal nerve, indicating that the pudendal is not a typical somatic nerve, (2) that the hypogastric nerve has a very small sensory component, and (3) that there are fibers surviving in the distal stumps of all these nerves, particularly the pelvic and hypogastric nerves.