bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification and distribution of retinocollicular terminals in the cat: An electron microscopic autoradiographic analysis
Authors: Behan Mary
Published: January 2005

The electron microscopic (EM) autoradiographic method has been used to determine the size, distribution, and ultrastructure of retinocollicular axon terminals following intraocular injection of either (3H)‐leucine or (3H)‐proline.

In the contralateral colliculus, retinal terminals are most numerous in the uppermost sublamina of the superficial grey, SGS1. The mean diameter of terminals in the contralateral SGS1 and SGS2 is 1.3 μm ± 0.33, and 1.45 μm ± 0.37, respectively. The mean diameter of terminals in the deepest contralateral sublamina, SGS3 (1.85 μm ± 0.62), is significantly larger than the mean diameter of those in the contralateral SGS1 or SGS2.

By contrast, the mean diameter of terminals in different sublayers of the ipsilateral superficial grey is relatively constant, ranging from 1.56 μm ± 0.45 to 1.63 μm ± 0.60. Most ipsilateral retinal terminals are located in the uppermost part of SGS2.

It is postulated that there are two populations of retinal terminals in the superficial grey: a population of smaller terminals present in the contralateral SGS1 and SGS2, and a population of larger terminals present in the contralateral SGS3. Both populations appear to be present in the ipsilateral sublaminae.

While all labeled retinocollicular terminals contain round vesicles and asymmetric membrane thickenings, two morphological features appear to be correlated with retinal terminal size: (1) the population of smaller retinal terminals more frequently contacts postsynaptic profiles containing scattered round vesicles; and (2) large, dense‐core vesicles are more commonly associated with the presynaptic profiles of the population of larger terminals.

A comparison of these morphological findings with available physiological data (Hoffman, 1973; Fukuda and Stone, 1974; McIlwain and Lufkin, 1976 McIlwain, 1978) suggests that the smaller terminals may be those of W‐retinal ganglion cells, and the larger terminals those of Y‐retinal ganglion cells.
Connections of the ventroposterior nucleus of the thalamus with the body surface representations in cortical areas 3b and 1 of the cynomolgus macaque, (Macaca fascicularis)
Authors: Nelson R. J. , Kaas J. H.
Published: January 2005

The somatotopic pattern of the connections of the ventroposterior nucleus of the thalamus with the representations of the body surface in somatic cortical Areas 3b and 1 were investigated in macaque monkeys using the anatomical tracers horseradish peroxidase (HRP), and 3H‐proline. These tracers, in combination or separately, were injected into one or more cortical sites, after the skin surface capable of activating neurons at each site had been defined with microelectrode mapping methods. These injection sites were later related to the overall organizations of the two cutaneous representations as determined in more extensive mapping experiments (Nelson et al., 1980). Finally, zones of anterograde and retrograde label in the thalamus were located with reference to architectonically defined subnuclei in the ventroposterior nucleus (VP). The results led to the following conclusions. (1) Zones of cells in VP projecting to a given location in either Area 3b or 1 also receive reciprocal projections from the cortical target. (2) A given cortical location typically relates to a disc‐shaped or lamellar region in VP with the disc extending rostrocaudally and dorsoventrally, being most narrow in the mediolateral dimension. (3) The representations of the same body surface in Area 1 and Area 3b relate to the same region of VP. However, since fewer cells were generally labeled after Area 1 injections, less dense terminations are suggested from VP to Area 1 than to Area 3b. (4) VP is the major or exclusive relay of somatosensory information to the two cutaneous representations from the thalamus. Labeled neurons or zones of terminations were found outside VP in other parts of the somatosensory thalamus only when injection sites extended into cortex outside Areas 3b and 1. (5) The face, hand, limbs, and foot are represented in a mediolateral sequence of subnuclei within VP. A dorsal capping subnucleus is apparently largely devoted to the axial trunk and perhaps other hairy skin surfaces such as some parts of the proximal surfaces of the limbs. (6) While anterior and posterior surfaces of the hind limb are widely separated by the glabrous foot in the cortical representations, they appear to be represented in adjacent zones in the thalamus.
White‐matter dendrites in the upper cervical spinal cord of the adult cat: A light and electron microscopic study
Authors: Rose P. K. , Richmond F. J. R.
Published: January 2005

The organization and structure of dendrites penetrating into the white matter of upper cervical spinal segments have been examined by means of Golgi staining techniques, intracellular horseradish peroxidase (HRP) injections, and ultrastructural studies. The Golgi studies established that several groups of neurons located in intermediate and ventral laminae of the upper cervical spinal cord have a substantial part of their dendritic tree extending into adjacent ventral and lateral funiculi. Most dendrites in white matter showed irregular varicosities along their length. They were devoid of spines and followed relatively direct paths. In contrast, grey matter dendrites were occasionally observed with spines and complex appendages and frequently followed tortuous paths. The size and location of some Golgi stained neurons suggested that white matter dendrites might originate from neck muscle motoneurons. This possibility was confirmed using intracellular HRP injections. These studies also showed that the distribution of white matter dendrites of neck muscle motoneurons depended on the location of the motoneuron soma. White matter dendrites of neck muscle motoneurons located deep in the ventral horn projected into all regions of white matter surrounding the ventral horn. Other neck muscle motoneurons, located in the spinal accessory nucleus, had white matter dendrites largely confined to the lateral funiculus. White matter dendrites of motoneurons in the commissural nucleus were found to project across the ventral commissure into the contralateral spinal cord.

Light microscopic studies of semi‐thin sections stained with toluidine blue and electron microscopic studies of thin sections revealed that white matter dendrites were confined to special regions of the white matter. These regions resembled the grey matter neuropil and contained dendrites and unmyelinated and small diameter myelinated axons. Axon terminals were also found in white matter. These terminals contained either flattened or spherical vesicles and formed synaptic contacts on white matter dendrites.

White matter dendrites, by virtue of their frequency of occurrence, distribution, and type of synaptic contacts may represent a means by which descending or ascending spinal systems can influence spinal neurons without recourse to axon collaterals which terminate in grey matter.
Effect of peripheral nerve injury on receptive fields of cells in the cat spinal cord
Authors: Devor Marshall , Wall Patrick D.
Published: January 2005

When the sciatic and saphenous nerves are cut and ligated in adult cats, the immediate effect is the production of a completely anesthetic foot and a region in medial lumbar dorsal horn where almost all cells have lost their natural receptive fields (RFs). Beginning at about 1 week and maturing by 4 weeks, some 40% of cells in the medial dorsal horn gain a novel RF on proximal skin, that is, upper and lower leg, thigh, lower back, or perineum. This new RF is supplied by intact proximal nerves and not by sciatic and saphenous nerve fibers that sprouted in the periphery. During the period of switching of RFs from distal to proximal skin there was no gross atrophy of dorsal horn grey matter and no Fink‐Heimer stainable degeneration of central arbors and terminals of peripherally axotomized afferents. In intact animals medial dorsal horn cells showed no sing of response to mechanical stimulation of proximal skin. RFs of some of the cells had spontaneous variations in size and sensitivity, but these were not nearly sufficient to explain the large shifts observed after chronic nerve section. Tetanic electrical stimulation of skin or peripheral nerves often caused RFs to shrink, but never to expand. Although natural stimuli of proximal skin would not excite medial dorsal horn cells in intact or acutely deafferented animals, it was found that electrical stimulation of proximal nerves did excite many of these cells, often at short latencies. In the discussion we justify our working hypothesis that the appearance of novel RFs is due to the strengthening or unmasking of normally present but ineffective afferent terminals, rather than to long‐distance sprouting of new afferent arbors within the spinal cord.
Corneal and periocular representation within the trigeminal sensory complex in the cat studied with transganglionic transport of horseradish peroxidase
Authors: Panneton W. M. , Burton H.
Published: January 2005

The central projections of afferent fibers from the cornea, and the infraorbital, infratrochlear, frontal, lacrimal and auriculotemporal nerves were investigated by means of the transganglionic transport of horseradish peroxidase. Afferent projections to the dorsal horn of the medulla are organized along both the rostrocaudal axis and the ventrolateral to dorsomedial margin of the medullary dorsal horn. An inverted but discontinuous facial representation exists through the rostrocaudal axis of the dorsal horn of the medulla with perioral and nasal receptive fields innervated by the infraorbital and infratrochlear nerves represented rostral to the progressively more posterior receptive fields innervated by the frontal, lacrimal and auriculotemporal nerves, respectively. The organization of the primary afferents is not uniform over the laminae of the dorsal horn of the medulla; the projections from the different nerves show the least overlap in lamina II, while overlap is most extensive in laminae I and V. The sensory projection from the cornea to the medullary dorsal horn is most dense in laminae I and II.

All nerves, including those innervating the cornea, project to the interpolar, oral and principal trigeminal nuclei and are somatotopically organized. Projections to the reticular formation and the contralateral trigeminal sensory complex were not found in this study.

These results support the organization of the dorsal horn of the medulla proposed by Déjerine (1914) and show that this organization is most evident for the primary afferent projections to lamina II.
An autoradiographic study of the efferent connections of the entorhinal cortex in the rat
Authors: Michael Wyss J.
Published: January 2005

The longer connections of the entorhinal cortex have been studied autoradiographically in a series of rats, each of which received a small injection of 3H‐amino acids in one of the various cytoarchitectonic subfields of the entorhinal cortex. The major findings can be summarized as follows. Whereas the projection of the lateral entorhinal area (LEA) to the dentate gyrus is broad in its longitudinal extent, the medial entorhinal area (MEA), and especially the ventral portion of this zone, projects in a more lamellar fashion. In the transverse plane the LEA preferentially projects to the inner (dorsal) blade of the dentate gyrus, while the MEA innervates both blades equally. Within the radial dimension, the entorhinal cortex projects to the dentate gyrus according to a medial to lateral gradient, with lateral portions of the LEA projecting along the pial surface and successively more medial portions of the entorhinal projecting closer to the granule cells. The commissural entorhinal to dentate projections are similar to the ipsilateral projections in location; however, they are considerably reduced in septotemporal extent and do not arise from cells in the ventral half of either LEA or the intermediate entorhinal area (IEA). The projection of the entorhinal cortex to Ammon's horn reflects the same longitudinal characteristics as the denate projections. An alvear input which extends only to the pyramidal cells at the CA1‐subicular junction was most noticeable at ventral hippocampal levels. Finally the extrahippocampal projections have been analyzed. These arise predominantly from cells in the LEA and project forward along the angular bundle to the piriform and periamygdaloid cortices, as well as the endopiriform nucleus, the lateral, basolateral, and cortical amygdaloid nuclei, the nucleus of the lateral olfactory tract, the olfactory tubercle, the anterior olfactory nucleus, the taenia tecta, and the indusium griseum. These extrinsic projections are to a large extent reciprocal to the major extrinsic inputs to the LEA.
Organization of corticothalamic projections from parietal cortex in cat
Authors: Robertson Richard T. , Cunningham Timothy J.
Published: January 2005

Corticothalamic projections from areas 5a, 5b, and 7 of cat parietal cortex were studied with autoradiographic techniques. Each cortical area was identified by its cytoarchitectural characteristics and the patterns of termination were related to the thalamic nuclear groups. Injections of 3H‐leucine in cortical area 5a were associated with terminal labeling primarily in the spinal recipient zone of the ventral lateral nucleus (VLsp) and the medial division of the posterior group (POm). The corticothalamic projections of area 5a are loosely topographically organized; medial parts of 5a project heavily to rostral and lateral parts of VLsp and sparsely to POm, while lateral parts of 5a project to more medial and caudal parts of VLsp and heavily to POm. Cortical area 5b projects primarily to the rostral portions of the lateral posterior nucleus (LP). These projections also appear to be topographically organized. The part of area 5b on the marginal gyrus projects to more ventral parts of rostral LP, while area 5b on the middle suprasylvian gyrus projects to more dorsal and lateral parts of rostral LP. Cortical area 7 projects to LP and the pulvinar (Pul). Rostral parts of area 7 project heavily to dorsal and lateral parts of LP and lightly to Pul; more caudal portions of area 7 project relatively more heavily to Pul. The reticular, central lateral, and paracentral nuclei also receive projections, especially from the suprasylvian gyrus. The results are discussed with regard to putative sensory response characteristics of these cortical areas and to general thalamocortical organization.
Giant neural systems in the inner retina and optic nerve of small whales
Authors: Dawson William W. , Hawthorne Minnie N. , Jenkins Robert L. , Goldston Richard T.
Published: January 2005

Giant neural cell systems (dendrites, cell bodies, and axons) are present among more usual structures in the retina and optic nerve of the small whale (dolphin) Tursiops truncatus retina. Giant cell body dimensions range up to 75 μm in diameter. Nuclei of the cells are frequently larger (>20 μm) than nearby ganglion, bipolar, and receptor cell bodies. The presence of the giant cell system and giant elements in the nerve fiber layer agree with the unusually broad fiber spectrum of the dolphin optic nerve where more than 6% of the axons are >15 μm in diameter. Smaller axons in the size distribution are typical of dimensions found in terrestrial mammals. The axon estimate totaled 157,000 per optic nerve. The giant cell‐axon systems of the whale retina may be a unique expression of the large ganglion cell‐axon (transient or “Y” functional unit) systems recently identified in terrestrial mammals.
An enzyme tracer study of the organization of the somatic motor center for the innervation of different muscles of the tongue: Evidence for two sources
Authors: Chibuzo Gregory A. , Cummings John F.
Published: January 2005

The hypoglossal nucleus has been described as the sole ipsilateral source of somatic motor innervation of the lingual and geniohyoideus muscles (Streeter, 1940; Barnard, 1940; Crosby et al., 1962; Watkins, 1978; Jenkins, 1978). In this study microliter amounts of 30% solution of horseradish peroxidase (HRP) were injected into intact but surgically isolated canine genioglossus, hyoglossus, styloglossus, geniohyoideus, and intrinsic lingual muscles. All injections were confined to the left half of the tongue, and the right half served as control. The HRP injections resulted in ipsilateral labeling of hypoglossal neurons with the exception of the injections into the genioglossus muscle, which labeled this nucleus bilaterally. Surprisingly, a few neurons associated with the ventromedial aspect of the caudal pole of the ipsilateral facial motor nucleus also labeled after injections of lingual muscles. The somatotopic representation of the geniohyoideus and lingual muscles within the hypoglossal nucleus suggested that those muscles known to originate from the same or related primodia labeled in the same or closely related hypoglossal subnuclei. The presence of labeled neurons associated with facial motor nucleus supported the hypothesis (Langman, 1975) of a possible dual origin of lingual muscles.
Afferent and efferent connections of the rat tail flick reflex (a model used to analyze pain control mechanisms)
Authors: Grossman M. L. , Basbaum A. I. , Fields H. L.
Published: January 2005

Although the rat tail flick reflex (TFR) is widely used to study neural mechanisms of analgesia, its underlying anatomy has not been systematically studied. In the present study axonal transport of horseradish peroxidase (HRP) was used to trace the efferent and afferent connections of the TFR. The extensor caudae medialis (ECM), extensor caudae lateralis (ECL), and abductor caudae dorsalis (ACD) were identified as tail flick muscles and injected with HRP. Labeled motor neurons were found in lumbar segments L4–L6, sacral segments S1–S4, and coccygeal segments Co1–Co2; ECL injections also labeled cells in Co3. Motor neurons were concentrated at levels L5‐S2 for ECM, at levels S2‐Co2 for ECL, and at levels L5‐Co1 for ACD.

To label the terminals of tail flick afferents, the dorsolateral tail nerve (DLTN) and the ventrolateral tail nerve (VLTN) which innervate the skin of the tail were cut and exposed to HRP. Application of HRP to either DLTN or VLTN labeled afferent terminals in S4, Co1, Co2, and Co3. For DLTN, the greatest density of afferent label was observed in the lateral half of laminae I and II of the dorsal horn. In contrast, labeled afferents from VLTN were concentrated in the medial half of laminae I–II. With longer survival times afferent terminals were also labeled in S3, and in the ventral horn of segments L6‐S2. Bilateral dorsal rhizotomies at levels S3‐Co3 were necessary and sufficient to abolish the tail flick. This corroborated the results from the anatomical studies.

Although tail flick motor neurons were present in ten spinal segments, L4‐Co3, tail flick afferents were concentrated caudally in segments S3‐Co3. Thus, in addition to segmental connections, the TFR requires an ascending propriospinal connection from coccygeal and caudal sacral dorsal horn to S1, S2, and to the lumbar enlargement. The intense labeling from tail afferents found in the substantia gelatinosa (SG) is consistent with pharmacological, anatomical, and physiological studies implicating the SG as an important site for inhibition of the tail flick reflex by opiates and by brainstem stimulation.
Two types of GABA‐accumulating neurons in the superficial gray layer of the cat superior colliculus
Authors: Mize R. Ranney , Spencer Robert F. , Sterling Peter
Published: January 2005

Two types of neuron in the upper superficial gray layer of the cat superior colliculus accumulated exogenous 3H‐gamma‐aminobutyric acid intensely. The first type was a horizontal cell with a fusiform cell body, horizontal dendrites, a low synaptic density, but a high percentage of cortical synaptic contacts. This cell had presynaptic dendrites. The second type was a granule cell (type A) with a small round cell body, thin and obliquely oriented dendrites, a moderate synaptic density, and few cortical synaptic contacts. These two types differed in size, shape, dendritic morphology, and patterns of synaptic input. They likely participate in different inhibitory mechanisms.

Four types of unlabeled neurons were also identified. Type B granule cells were found only within the upper subdivision of the superficial gray layer. They had moderate‐sized cell bodies, a high synaptic density, and numerous somatic spines. A third type of granule cell (type C) was found only in the deep subdivision of the superficial gray. This type had a low synaptic density and spines that contained synaptic vesicles. Vertical fusiform and stellate forms were also found. We conclude that at least six types of neurons populate the upper superficial gray layer of the cat superior colliculus.
Ultrastructural identification of labeled neurons in the dorsal motor nucleus of the vagus nerve following injections of horseradish peroxidase into the vagus nerve and brainstem
Authors: McLean John H. , Hopkins David A.
Published: January 2005

The efferent connections of two types of neurons in the dorsal motor nucleus of the vagus nerve (DMV) were studied in the cat by light and electron microscopy following horseradish peroxidase (HRP) injections into the cervical vagus nerve or brainstem. After injections of HRP into the vagus nerve, up to 80% of medium‐sized neruons averaging 26 × 20 μm in 1‐μm‐thick sections were retrogradely labeled while no small neurons were labeled in the DMV. Incubation with either diaminobenzidene (DAB) or p‐phenylenediamine‐pyrocatechol (PPD‐PC) chromogens yielded electron‐dense reaction products localized mainly in lysosomes. Identification of label at the ultrastructural level was facilitated by omitting lead citrate staining and by counting numbers of lysosomes, which were higher in labeled neurons. Quantitative comparisons of the dimensions of labeled and unlabeled somata demonstrated that retrograde transport and incorporation of HRP had no effect on cell size within the 2–3‐day survival times used in this study.

In order to determine whether neurons in the DMV project to higher levels of the brain stem, large injections of HRP (1–3 μl) were made into the pons, mesencephalon, hypothalamus, and amygdala. After injections of HRP into the brainstem, only small neurons, measuring 17 × 10 μm, were retrogradely labeled. Approximately 90% of the small neurons remained unlabeled following the HRP injections. The ultrastructrual features of the labeled small neurons included an invaginated nucleus, low cytoplasmic/nuclear ratio, and relatively fewer organelles than the medium‐sized neurons. A quantitative analysis of labeled and unlabeled small neurons demonstrated that the labeled neurons were significantly larger than the unlabeled small neurons. Thus, two populations of small neurons may exist in the DMV. One population appears to have ascending projections to higher levels of the brainstem while the other more numerous population may be interneurons or project for only short distances.
The morphology and connections of the posterior hypothalamus in the cynomolgus monkey (Macaca fascicularis). II. Efferent connections
Authors: Veazey R. B. , Amaral D. G. , Cowan W. M.
Published: January 2005

The efferent connections of the posterior hypothalamus have been analyzed autoradiographically in a series of eight cynomolgus monkey (Macaca fascicularis) brains with injections of 3H‐amino acids in different regions of the mamillary complex and the surrounding areas.

The medial mamillary nucleus was found to project through the mamillothalamic tract to the ipsilateral anteroventral, anteromedial, and interanteromedial nuclei, and by way of the mamillotegmental tract principally to the deep tegmental nucleus (of Gudden). It also appears to contribute fibers to the medial forebrain bundle, some of which reach as far rostrally as the medial septal nucleus. The lateral mamillary nucleus projects through the mamillothalamic tract bilaterally upon the anterodorsal nuclei of the thalamus, and through the mamillotegmental system to the dorsal tegmental nucleus; it also appears to contribute fibers to the medial forebrain bundle. The supramamillary area has extensive ascending and descending connections that are distributed with the medial forebrain bundle to the hypothalamus and rostral midbrain; in addition, it gives rise to an unusually well‐defined projection to field CA2 of the hippocampus and to a narrow zone overlying the outer part of the granule cell layer and the adjoining part of the molecular layer of the dentate gyrus. We have not been able to distinguish the connections of the posterior hypothalamic nucleus from those of the caudal part of the lateral hypothalamic area: they both appear to contribute substantially to the ascending components of the medial forebrain bundle, and through its descending projection to the tegmental fields of the midbrain, the nucleus centralis superior of the raphe complex, the locus coeruleus, and the central gray as far caudally as the facial nerve. Their further projections to the spinal cord were not examined.

Viewed broadly, and in the light of previous work, our observations confirm, once again, the constancy of the connections of the hypothalamus in the mammalian brain, and the pivotal position that the posterior hypothalamus occupies in the elaborate system of connections that links the limbic areas of the forebrain with the complex of structures that Nauta has aptly designated the “midbrain limbic region”.
Amygdalopetal projections in the cat. II. Subcortical afferent connections. A study with retrograde tracing techniques
Authors: Russchen Fokje T.
Published: January 2005

The subcortical afferent connections of the amygdaloid complex of the cat were studied by means of retrograde tracing of horseradish peroxidase and the fluorescent substances bisbenzimid and nuclear yellow. The results of the present study indicate that structures in the basal forebrain, hypothalamus, brainstem, and thalamus project in a topographical manner to the various amygdaloid nuclei.

Within the basal forebrain “ventral pallidal” structures project to the lateral and basolateral amygdaloid nuclei. The nucleus of the horizontal limb of the diagonal band and the medial part of the bed nucleus of the stria terminalis project predominantly to the medial and the medial central amygdaloid nuclei. Fibers from the substantia innominata distribute to nearly the entire expanse of the amygdaloid complex.

The medial preoptic area and medial hypothalamic nuclei, including the paraventricular, ventromedial, arcuate, premammillary, and supramammillary nuclei, project most heavily to a region of the amygdala which includes the medial and the medial central nuclei. The caudal part of the lateral hypothalamic area sends strong projections to the medial central amygdaloid nucleus and more weakly projects to the basolateral nucleus.

Brainstem neurons located in the cell groups A8 and A10, the dorsal raphe nucleus, the locus coeruleus, and the parabrachial nucleus project mainly to the medial central amygdaloid nucleus. Fibers originating in the medial part of the parabrachial nucleus in addition have a dense termination in the anteror amygdaloid area.

Of the various midline nuclei of the thalamus which project to the amygdaloid complex, the paraventricular and ventral reuniens nuclei distribute fibers to the medial central and basolateral nuclei. The parataenial and the interventral nuclei project only to the medial central amygdaloid nucleus. Fibers from the interanteromedial nucleus exclusively reach the basolateral nucleus of the amygdala. Caudally in the ventral thalamus the subparafascicular and peripeduncular nuclei have been found to project to the medial, central, lateral, and cortical nuclei. In the posterior thalamus the medial part of the medial geniculate nucleus and the nucleus mediolateralis‐suprageniculate complex give rise to fibers which reach the lateral central amygdaloid nucleus.
The generation and migration of the chick's isthmic complex
Authors: Clarke Peter G. H.
Published: January 2005

By thymidine autoradiography it is shown that the entire isthmic complex is arranged according to a single and very finely grained gradient of proliferation that manifests itself in each of the component cell groups individually. Ventral neurons are generated first, dorsal last. The neurons in the various isthmic cell groups complete their final phase of DNA synthesis mainly between the following stages (of Hamburger and Hamilton, ′51): N. semilunaris, HH‐22 to HH‐24; N. lemnisci lateralis pars ventralis, HH‐23 to HH‐25; N. lemnisci lateralis pars dorsalis, HH‐24 to HH‐27; N. isthmi partes principales magnocellularis and parvocellularis, HH‐24 to HH‐29; N. isthmo‐opticus, HH‐27 to HH‐31. By thymidine autoradiography combined with the peroxidase retrograde transport technique, it is shown that the retinopetal neurons ventral to N. isthmo‐opticus are generated over the same period as the isthmo‐optic neurons and substantially later than the nonretinopetal neurons amongst which they are scattered.

Using similar autoradiographic methods but in embryos fixed at various ages, it is then shown that the isthmic alar plate gives rise to all the cell groups of the isthmic complex except possibly N. isthmi pars principalis magnocellularis. In confirmation of Vaage's (′73) account, it is shown that two main migrations, “dorsal” and “dorsolateral”, originate from the dorsal and dorsolateral parts of the germinal epithelium, traveling first laterally and then ventrally, and that some cells from the former subsequently join the latter to create the mixed migration. The dorsal migration gives rise to N. semilunaris, N. isthmi pars principalis parvocellularis and N. isthmo‐opticus, whereas the mixed gives rise to N. lemnisci lateralis partes dorsalis and ventralis and to much of the adjacent reticular formation. The migration is extremely rapid (15–30 μm per hour for the dorsal migration), but much of this speed may be due topassive bulk displacement, since there seems to be little relative movementbetween adjacent cells.
Quantitative analyses of neuronal development in the lateral motor column of mouse spinal cord. III. Generation and settling patterns of large and small neurons
Authors: Holley John A. , Wimer Cynthia C. , Vaughn James E.
Published: January 2005

The generation and settling patterns of large and small lateral motor column (LMC) neurons were compared in the spinal cords of three inbred strains of mice by means of tritiated thymidine autoradiography. No significant strain differences were observed for the number of large LMC cells (presumptive alpha motor neurons) that were heavily labeled on each injection day, although there were significant strain variations for this measure with regard to small LMC neurons (presumed gamma motor neurons and interneurons). The generation of both large and small LMC neurons began at the same time, but peak production of large cells preceded that of the small neurons. There were no strain differences observed for this relationship between the large and small cells. These findings indicate that the LMC, from the time of its initial formation contains cells destined to become large and small neurons. The positions of large and small neurons within the adult LMC relative to their times of origin (settling patterns) were analzyed statistically. A significant ventrodorsal sequence for early‐to‐late generated cells was observed for both large and small LMC neurons. No significant strain difference were found in the analysis of settling patterns. A ventrodorsal settling pattern also has been described for amphibia (Prestige, ′73) and, in conjunction with the proximodistal sequence of limb development describedby other investigators, the ventrodorsal sequence could play a key role in the development of motor neuronal somatotopic organization.
A Golgi study of rat neostriatal neurons: Light microscopic analysis
Authors: Chang H. T. , Wilson C. J. , Kitai S. T.
Published: January 2005

At least two types of large neurons (somatic cross‐sectional areas, SA > 300 μm2) and five types of medium neurons (SA between 100 and 300 μm2) were distinguished in Golgi preparations of the adult rat neostriatum. Type I large cells had aspinous somata with long, radiating, sparsely spined dendrites which were sometimes varicose distally, whereas type II large cells had spines on both somatic and dendritic surfaces. Type I medium cells had aspinous somata and proximal dendrites, but their distal dendrites were densely covered with spines. Type II medium cells had somatic spines, and their radiating dendrites were sparsely spined. Other medium cells had no somatic spines: Type III cells had poorly branched and sparsely spined dendrites. Type IV cells had profusely branched, sparsely spined dendrites. Type V cells had radiating and varicose dendrites which could also be sparsely spined.

Several small neurons (SA mostly less than 100 μm2) were also found in the rat neostriatum: Some had aspinous soma with sparsely spined dendrites; others had somatic spines.

Except for the type II large cells, intrinsic axon collaterals were observed for every type of neuron, indicating that they all had local integrating functions.
Subcortical structures projecting to visual cortical areas in squirrel monkey
Authors: Tigges Johannes , Tigges M. , Cross N. A. , McBride R. L. , Letbetter W. D. , Anschel S.
Published: January 2005

In 17 adult squirrel monkeys (Saimiri), horseradish peroxidase was used as a retrograde tracer substance to reveal the subcortical structures (other than the lateral geniculate nucleus and pulvinar) which project to the occipital lobe, and, in particular, to the central visual field representation in areas 17, 18, 19, and MT. Evidence is provided that each of areas 17, 18, and MT receives a projection from locus coeruleus, nucleus dorsalis raphae, nucleus annularis, nucleus centralis superior, formatio reticularis pontis oralis, nucleus basalis of Meynert, lateral hypothalamus, claustrum, and nuclei paracentralis and centralis medialis thalami. Area 19 receives a projection from all these structures except from the nucleus annularis. Only area MT was determined to be a target of a projection from the nucleus linearis. For technical reasons, only area MT was determined to receive afferent fibers from the nucleus basalis lateralis amygdalae. The results indicate that there is no topographical organization of subcortical inputs to the central visual field representation in individual cortical areas.
Structure of the synaptic membranes in the inner plexiform layer of the retina: A freeze‐fracture study in monkeys and rabbits
Authors: Raviola Elio , Raviola Giuseppina
Published: January 2005

The internal structure of the synaptic membranes in the inner plexiform layer (IPL) of the retina of monkeys and rabbits was studied with the freeze‐fracturing technique. In ribbon synapses, the presynaptic active zone is characterized by an aggregate of P‐face particles, images of synaptic vesicle exocytosis, and forming coated vesicles which occupy distinct, contiguous membrane domains from apex to base of the synaptic ridge. The postsynaptic membrane contains a prominent aggregate of homogeneous particles which remain associated with the E‐face. In the presynaptic membrane of conventional synapses, images of synaptic vesicle exocytosis are intermingled with large P‐face particles, whereas forming coated vesicles surround the active zone. Three types of internal organization characterize the postsynaptic membrane of conventional synapses. Usually, the postsynaptic membrane exhibits the same internal structure as the surrounding nonjunctional plasmalemma. A second, less common type of conventional synapse contains a loose aggregate of heterogeneous particles which remain associated with the P‐face. Finally, synapses were exceptionally found which are macular in shape and contain an aggregate of E‐face particles within the postsynaptic membrane. The freeze‐fracture evidence suggests that the axonal endings of bipolar cells—or at least some of them—make excitatory synapses, whereas the vast majority of amacrine cell dendrites make inhibitory synapses. Additional specializations of the cell surface in the IPL include gap junctions, puncta adhaerentia, subsurface cisterns, and cell corner aggregates.
The distribution of axon collaterals from the olfactory bulb and the nucleus of the horizontal limb of the diagonal band to the olfactory cortex, demonstrated by double retrograde labeling techniques
Authors: Luskin Marla B. , Price Joseph L.
Published: January 2005

Three different pairs of double retrograde axonal tracers have been used to study the distribution of axon collaterals from individual cells in the olfactory bulb and the nucleus of the horizontal limb of the diagonal band: (1) horseradish peroxidase (HRP) and tritiated apo‐HRP (3H‐HRP), (2) HRP and 125I‐wheat germ agglutinin (I‐WGA), and (3) the flurochromes true blue (TB) and bisbenzimide (BB) or nuclear yellow (NY). With each combination of tracers, paired injections were made into different parts of the olfactory system, and the olfactory bulb and the nucleus of the diagonal band were examined for the presence and arrangement of cells labeled with one or both retrograde tracers.

In the olfactory bulb both single and double retrogradely labeled mitral cells were found following injections in disparate parts of the olfactory cortex. Furthermore, no consistent pattern was found in the distribution of single‐ or double‐labeled cells in the olfactory bulb; that is, the distribution of cells labeled from one area of the cortex was not consistently different from the distribution of cells labeled from other parts of the cortex. Therefore, it was concluded that individual mitral cells project to widely spaced parts of the olfactory cortex, and that there is no apparent correspondence between the location of a given cell in the olfactory bulb and the distribution of its axon in the cortex.

In contrast to this, cells in the nucleus of the horizontal limb of the diagonal band were only rarely double‐labeled from nonoverlapping injections into the olfactory cortex or olfactory bulb, although overlapping injections produced a high proportion of double‐labeled cells. Cells which were single‐labeled from different injection sites were extensively intermixed within the nucleus. Therefore, in this case it was concluded that individual cells project to relatively restricted areas, although there was again no apparent correspondence between the position of a cell in the nucleus and the terminal field of its axon.
Afferents to the trigeminal and facial motor nuclei in pigeon (Columba livia L.): Central connections of jaw motoneurons
Authors: Berkhoudt Herman , Klein Bradley G. , Zeigler H. Philip
Published: January 2005

Trigeminal and facial motor nuclei innervating the pigeon's jaw muscles were identified using a combination of microstimulation and EMG recording and HRP injections were made iontophoretically. The trigeminal motor nucleus receives an ipsilateral projection from sensory neurons in the trigeminal mesencephalic nucleus which forms the afferent limb of the monosynaptic stretch reflex of the jaw‐closers. Both the trigeminal and facial motor nuclei receive bilateral projections from interneurons in the intertrigeminal area and the lateral (parvocellular) reticular formation of the pons and medulla. These neurons serve as premotor elements in the control of jaw movements, mediating ascending, descending and internuclear connections. The similarity of inputs to the trigeminal and facial nuclei may reflect their common function as jaw motoneurons in this species.
Parasagittal organization of the olivocerebellar projection in the mouse
Authors: Beyerl Brian D. , Borges Lawrence F. , Swearingen Brooke , Sidman Richard L.
Published: January 2005

The inferior olivocerebellar projection of the normal inbred C57BL/6J mouse was visualized after anterograde transport of horseradish peroxidase conjugated to the lectin wheat germ agglutinin (HRP‐WGA conjugate). Following injections of HRP‐WGA conjugate which filled the entire inferior olivary nucleus on one side, olivocerebellar fibers were followed across the midline of the medulla and into the contralateral cerebellar cortex via the inferior cerebellar peduncle. The molecular layer was heavily but nonuniformly labeled in all cortical lobules. Labeled olivocerebellar fibers within the contralateral cerebellar molecular layer were grouped into distinct bands separated by regions of molecular layer containing no labeled fibers. The bands of olivocerebellar terminals in the molecular layer were in turn organized into distinct sets of bands oriented in parasagittal planes. The organizational basis for this banding pattern, previously recognized by other workers in other mammalian and avian species, remains unknown.
Failure of host axons to regenerate through a once successful but later rejected long nerve allograft
Authors: Zalewski Andrew A. , Silvers Willys K. , Gulati Adarsh K.
Published: January 2005

Host axons will regenerate through a long nerve allograft in an immunologically tolerant rat. However, if tolerance is abolished, rejection occurs and allogeneic cells (e.g., Schwann, vascular, perineurial, etc.) as well as regenerated host axons disappear from the allograft. Because following tolerance abolition host axons begin to regenerate into the connective tissue remnants of the rejected nerve allografts, the extent of this renewed axonal growth was investigated. It was found that in a tolerance‐abolished rat, host axons only regrew into the proximal 1 cm of a 4‐cm allograft which in a fully tolerant recipient would have had numerous allogeneic Schwann cell‐myelinated axons throughout its length. It is concluded that viable allogeneic cells (i.e., Schwann, fibroblast, and vascular) together with their connective tissue matrix provide the best way to aid host nerve fiber regeneration through a long nerve allograft.
Spinal cord development in anuran larvae: II. Ascending and descending pathways
Authors: Forehand Cynthia J. , Farel Paul B.
Published: January 2005

The ontogeny of ascending and descending spinal pathways was examined in bullfrog (Rana catesbeiana) tadpoles using the transported histochemical marker, horseradish peroxidase (HRP). The adult pattern of brainstem projections to lumbar spinal cord is evident as early as larval stage I (Taylor and Kollros, Anat. Rec., 94:7–24, 1946), although the number and size of projecting cells increases as the animal matures. These projections arise from presumptive hypothalamic neurons at the diencephalicmesencephalic border as well as from neurons of the vestibular nucleus, oculomotor nucleus, and reticular formation. In contrast to the stability of the pattern of descending projections, the sources of fibers ascending to the brainstem change during larval life. In early larval stages, brainstem projections from lumbar spinal cord arise primarily from Rohon‐Beard cells and neurons of the superficial dorsal horn. In later stages, neurons in the intermediate and ventral areas of the spinal gray can also be retrogradely labeled by HRP application to the brainstem at the level of the VIIIth nerve. Evidence of the existence of dorsal column and lateral cervical nuclei in adult frog and tadpoles older than stage VIII is presented.

The ascending projections of embryonically born primary neurons were also investigated. Rohon‐Beard cells, which are sensory neurons with their cell bodies in the spinal cord, were found to send ascending processes as least as far rostral as the level of the VIIIth nerve entry zone. Anterolateral and dorsal marginal cells, probable homologs, respectively, of mammalian spinal border cells and cells of Waldeyer (1888), were also found to project rostrally at least to the rhombencephalon. These marginal cells persisted through metamorphosis into adulthood.
Gap junctions among the perikarya, dendrites, and axon terminals of the luminosity‐type horizontal cell of the turtle retina
Authors: Witkovsky P. , Owen W. G. , Woodworth M.
Published: January 2005

Gap junctions of the H1 horizontal cell of the turtle retina (Leeper, 1978) were studied in thin‐sectioned material and in freeze‐fracture replicas. Peri‐karyal gap junctions were extremely restricted, 0.02–0.07 μm2 in area, whereas those of axon terminals were much larger, most being 0.1–1.0 μm2. Both varieties, however, had the usual seven‐layered appearance in thin sec‐tion and measured 15 ± 1 nm in overall width between cytoplasmic faces. Freeze‐fractured views of the perikaryal junctions revealed roughly circular patches of P‐face 9‐nm particles and E‐face pits. The axon terminal gap junctions were seen as large areas of P‐face particles and E‐face pits containing occasional islands of unsnecialized membrane. Particle densities varied from 1, 455to 2, 448 μm−2 serial reconstruction was made or a portion of the axon terminal network in order to measure the surface areas of the axons con‐tained therein and the fraction occupied by gap junctions. These data demonstrated that the fractional area occupied by gap junctions was roughly in inverse proportion to the area of the axon region (tuberous core vs. terminal process). It is argued that this constitutes an impedance matching device to ensure adequate current flow through the axon processes. Assuming that each P‐face particle represents a connexon having a conductance of 10−10 and given the P‐face particle density and gap junctional areas determined in this report, we calculated that the gap junction distribution is adequate to account for the spatial properties of the horizontal cell axon network (Lamb, 1976).
Neural correlates of flight loss in a mexican grasshopper, Barytettix psolus. II. DCMD and TCG interneurons
Authors: Arbas Edmund A.
Published: January 2005

Comparison of the nervous systems of a flightless grasshopper (Barytettix psolus), and locusts (Schistocerca) is extended to include two large interneurons, the descending contralateral movement detector (DCMD) and the tritocerebral commissure giant (TCG). These interneurons are thought to play a role in locu st flight. Both were visualized in Barytettix with cobalt staining techniques.

Most features of the two neurons are similar in both locusts and Barytettix. Yet, several differences were noted. In locusts, the dorsal DCMD branch in its metathoracic projection terminates in dorsolateral neuropile and synapses with flight motorneurons (Pearson and Goodman, 1979). In Barytettix, no branch terminates in the corresponding region. Of the animals examined, 52% lacked branches corresponding to locust dorsal branches. When present, they all had abnormal projections by comparison to their counterparts in locusts.

The maintenance of the TCG in Barytettix with so similar a form to that of locusts suggests that the role of the cell in behavior other than flight should be examined. The differences in DCMD projection suggest that a discrete set of output connections may have been modified in Barytettix by the alteration of a single first‐order axonal branch.