bluuebunny/crossref_metadata_2025 huggingface dataset:
Accelerated rates of synaptogenesis by “sprouting” afferents in the immature hippocampal formation
Authors: Gall Christine , McWilliams Randall , Lynch Gary
Published: January 2005

Light and electron microscopic methods were used to study the rate with which undamaged afferents sprout into and form synapses within denervated dendritic zones in the immature rat brain. The middle and outer molecular layers of the dentate gyrus were deafferented by ablation of the ipsilateral entorhinal cortex in 14‐day‐old rats, and the extension of the commissural projections, which are normally restricted to the inner molecular layer, into the denervated territory was studied by light microscopic autoradiographic tracing methods. Collateral growth was noted as early as 13 hours after the lesion and was found to reach throughout the middle and outer molecular layers by 48 hours postlesion. Quantitative analyses (grain counts) revealed that the addition of commissural fibers and terminals to the denervated zones proceeded extremely rapidly up to 72 hours after the removal of the entorhinal cortex, but slowed markedly thereafter. Electron microscopic procedures were used to assess the rate at which synapses formed during this period and yielded the following information: 1) The density of intact synapses fell to below 20% of normal values within 20 hours of the lesion, 2) reinnervation began before 30 hours postlesion, and 3) the rate at which synapses were added to deafferented middle molecular layer was much more rapid from 20–96 hours postlesion than is observed in this zone during normal development. Furthermore, the sprouting of the inner molecular layer afferents into the middle molecular layer did not retard the pace of synaptogenesis in their normal target region. These results suggest that intrinsic limitations in the capacity of axons and dendrites are not responsible for determining the rate of synaptogenesis in the developing hippocampus. It is proposed instead that existing synapses (or terminals and spines) tend to suppress the formation of new contacts such that the local density of connections regulates the speed with which further innervation occurs.
2‐deoxyglucose uptake in the cat spinal cord during sustained and habituated activity in the plantar cushion reflex pathway
Authors: Proshansky Eric , Kauer John S. , Stewart William B. , David Egger M.
Published: January 2005

[14C]2‐deoxy‐D‐glucose (2‐DG) was administered intravenously to anesthetized cats during electrical stimulation of the plantar cushion (central foot pad). Afferent volleys and the efferent reflex were monitored by recording from the tibial nerve at the ankle. Plantar cushion stimulation at 3 HZ, 5 × threshold for 45 minutes led to a discrete region of increased 2‐DG uptake dorsomedially in the dorsal horn, predominantly in Rexed's laminae III and IV, ipsilateral to the stimulation. A less marked increase in labeling was also sometimes observed in the medial portion of lamina V. No labeling specific to stimulation was observed in the ventral horns. A control preparation, to determine the effects of surgical manipulations alone, confirmed that the labeling was indeed specific to the plantar cushion stimulation.

A pattern of labeling identical to that seen during 3 Hz, 5 × threshold stimulation occurred when 2‐DG was administered during 10 Hz, 5 × threshold stimulation, after the reflex elicited by plantar cushion stimulation had completely habituated.

The most straightforward interpretation of our results suggests that the increases in 2‐DG labeling produced by stimulation of the plantar cushion probably occurred in regions with heavy concentrations of axon collaterals of the primary afferent Aαβ fibers from the plantar cushion, at or near their sites of termination in the dorsal horn.
Early development of the inferior olivary complex in pouch young opossums. II. An electron microscopic study
Authors: Maley Bruce E. , King James S.
Published: January 2005

At birth the inferior olivary complex (IOC) is not present in the caudal ventro‐medial brainstem of the opossum. In the 3‐‐7‐day‐old animal (15–19 days post‐conception), this same region does contain neurons of the developing IOC. The immature neurons are characterized by large, centrally numerous small‐diameter profiles which contain bundles of filaments and scattered microtubules. Occasional synaptic endings, containing round clear vesicles, contact large, flocculent profiles which contain bundles of filaments and scattered microtubules. Occasional synaptic endings, containing round clear vesicles, contact large, flocculent profiles. By 10–14 days of age, the olivary cell bodies and the surrounding neuropil exhibit many of the same features as in the 3–7 day‐old opossums. In opossums 21–25 days old, there is an increase in varicosities and irregular contours along many of the dendritic shafts. Furthermore, synaptic terminals, possessing round clear vesicles, now contact the soma, dendritic shafts, dendritic varicosities, spines, and large, flocculent profiles. Terminals containing pleomorphic vesicles or a mixture of clear and large granular vesicles are presynaptic only to dendritic spines or large, flocculent profiles. Neuroglial cell bodies have been identified at all ages examined.

It is not until days 65–68 that pre‐ and postsynaptic elements are organized into synaptic clusters (glomeruli), which are typical of the adult. Spiny appendages and small‐diameter dendrites comprise the central core of the clusters which are surrounded by synaptic endings containing a variety of vesicle types. Thus it would appear that subsequent to their initial arrival (day 16–17), the synaptic relationships of cerebellar and midbrain afferents are modified to reflect their adult configuration by days 65–68. This extended period of development (postnatal days 3–68) for the olivary complex provides a good model for assessing the effects of experimental manipulations.
The ontogeny of the distribution of callosal projection neurons in the rat parietal cortex
Authors: Ivy Gwen O. , Killackey Herbert P.
Published: January 2005

The ontogeny of callosal projection neurons in the rat parietal cortex was examined using the retrograde and anterograde transport of horseradish peroxidase (HRP), as well as Golgi and Nissl stains. From postnatal day 0 (PND 0) to early PND 4, the callosal projection neurons are distributed as two continuous horizontal bands of cells which extend throughout the subplate in layers Va and Vc‐upper VIa. Neurons within the cortical plate (CP), however, do not transport HRP from a contralateral injection site until PND 3 to early PND 4, when a few cells at the lower CP border are generally labeled. However, by late on PND 4, and more consistently by PND 5, several changes in the distribution of callosal projection neurons take place. First, cells at all levels of the CP become labeled in a sequential fashion, from the lower border upward. Second, gaps, or areas devoid of HRP, become apparent in layer IV of the barrel field area. Third, in the cortical areas containing the gaps, as well as in other areas which are destined not to be callosally connected in the adult, there is a noticeable decrease in the number of cells labeled with HRP. This decrease continues through PND 15 and possibly into adulthood. The foregoing developmental events are compared to cortical maturation as seen in both Golgi‐ and Nissl‐stained material. By PND 15, the basic adult pattern of callosal projection neurons is established. The neurons reside mainly in layers III and Va, with fewer in layers II and Vc‐upper VIa, and fewer still in the other cortical layers. They are aligned in vertical arrays in discrete areas of the cortex.
The emergence, localization, and maturation of neurotransmitter systems during development of the retina in xenopus laevis: II. Glycine
Authors: Rayborn Mary E. , Sarthy P. Vijay , Lam Dominic M. K. , Hollyfield Joe G.
Published: January 2005

The high‐affinity uptake and release of glycine was studied in retinas of Xenopus laevis. In the toad and tadpole retina, 3H‐glycine was accumulated by a population of cells located predominantly in the inner nuclear layer. When retinas preloaded with 3H‐glycine were subjected to high K+‐concentrations, these retinas released large amounts of 3H‐glycine by a Ca++‐dependent mechanism. The appearance and maturation of these putative glycinergic properties was followed during retinal development. Our results indicate that the high‐affinity uptake of glycine first appears around stage 33/34 whereas K+‐stimulated glycine release cannot be detected until stage 42.
Efferent vestibular neurons: A study employing retrograde tracer methods in the pigeon (Columba livia)
Authors: Schwarz Irmgard E. , Schwarz Dietrich W. F. , Fredrickson John M. , Landolt Jack P.
Published: January 2005

Efferent neurons innervating the vestibular labyrinth and cochlea of the pigeon have been identified by means of a variety of retrograde tracers: [3H]‐adenosine (Ad), horseradish peroxidase (HRP), Evan's Blue (EB) and Bisbenzimide (Bb). Discrete injections into individual cristae ampullares of the semicircular canals, into the macula utriculi, or into several of these end organs resulted in similar patterns of neuronal labelling. Efferent vestibular neurons were always found within a small portion of the nucleus reticularis pontis caudalis (RP), ventrolateral to the abducens nucleus on both sides. No systemic difference in the locations of labelled cells was found following injection into different sensory epithelia. Cell counts following injections into individual cristae did not differ significantly from those following injections into all three cristae. The injections into all cristae in both labyrinths yielded cell counts that were much lower than twice the number of cells labelled by injections into the three cristae on one side only. When HRP was injected into the right lateral canal crista and Ad into the right posterior canal crista, a high proportion of neurons was labelled with both compounds (61% of the HRP‐labelled cells and 67% of the Ad‐labelled cells). Injection of EB into all three cristae on the right side and Bb into all three cristae on the left side produced a smaller percentage of doubly labelled cells (10% of the EB‐labelled cells and 6% of the Bb‐labelled cells). It is concluded, therefore, that there is a considerable degree of collateralization within one labyrinth. Fewer collaterals of efferent neurons are directed to both labyrinths. Since each semicircular canal represents head rotation in one direction and one plane, it is unlikely that efferents which contact several different movement sensors can provide sensory motor control that is specific for directions and planes of head movements.

Control injections of these tracers into the cochlea yielded labelled cells in a different reticular structure, the nucleus reticularis paragigantocellularis lateralis (Pgc), on both sides, as well as in the RP. It is proposed that the Pgc cells represent cochlear efferents, while the RP neurons are related to the macula lagenae, an otolithic organ of balance in the pigeon.
Regional specialization in retinal ganglion cell projection to optic tectum of Dipsosaurus dorsalis (lguanidae)
Authors: Peterson Ellengene H.
Published: January 2005

Regional variation in the composition of the ganglion cell layer is a characteristic feature of vertebrate retinas. This suggests that corresponding patterns of regional variation might be expected in CNS structures which receive a direct, topographic projection from the retina. To investigate this possibility, I studied the retinotectal projection in an iguanid lizard (Dipsosaurus dorsalis), which shows a marked degree of regional variation in its retinal ganglion cell layer. Results of these experiments indicate that in D. dorsalis the optic tectum is differentiated horizontally into five regions which can be distinguished on the basis of cytoarchitecture and the patterning of retinal afferents, as visualized with silver degeneration and autoradiographic tracing techniques. These five areas are named according to their location: (1) Ventral Rim, (2) Lateral Wall, (3) Dorsolateral Area, (4) Dorsal Wall and (5) Medial Rim.

Following enucleation, the Medial and Ventral Rim are characterized by fascicles of coarse degenerated fibers in layers 13, 12, and 9, by a relative absence of fine particulate debris in reduced silver material, and by the absence of silver grains in autoradiographs following intraocular injections of tritiated proline. They differ in the density of large calibre fibers and in the temporal course of degeneration. In the Lateral Wall the cellular layers are best differentiated, and nine retino‐recipient layers can be distinguished below the stratum opticum. Degeneration is particularly heavy over the plexiform layers 9, 11, and 13. There is a superficial to deep gradient of degeneration density and of silver grains within layers 13 and 11. In the lower half of layer 11, argyrophilic debris and silver grains are aligned in vertical columns. The Dorsolateral Area is a circular region which covers the dorsolateral convexity of the tectum just caudal to mid tectal levels. It is characterized by a relatively low density of degenerated fibers in layers 13, 12, and especially in layer 9. Finally, the Dorsal Wall is similar to the Lateral Wall in the laminar distribution of degeneration and silver grains, except that there is an additional band of fine debris over layers 12 and 13 which is not visible in the Lateral Wall. Rostrally, the Dorsal Wall is greatly expanded (the Dorsal Expansion) and in this region a well developed plate of neurons lies immediately subjacent to the stratum opticum. This is the only tectal area which shows substantial degeneration at short survival times.

These data suggest that in D. dorsalis there is horizontal variation in the morphology and patterning of retinal ganglion cell axons to the superficial tectal layers. Since Dipsosaurus retina exhibits a substantial degree of regional variation in the ganglion cell layer, and since the retina projects topographically onto the tectum, it is suggested that regional variation in the optic tectum may reflect regional variation in the ganglion cell layer of the retina.
An analysis of the sympathetic preganglionic neurons projecting from the upper thoracic spinal roots of the cat
Authors: Oldfield B. J. , McLachlan Elspeth M.
Published: January 2005

The distribution of sympathetic preganglionic neurons that project via the right stellate ganglion has been studied quantitatively in adult cats. Retrograde transport of horseradish peroxidase (HRP) injected into the ganglion or applied to transected axons of the cervical sympathetic trunk (CST) resulted in labelling of neurons in the ipsilateral spinal cord over T1–T9 and T1–T7, respectively. Their distribution and morphology in the subnuclei of the intermediate zone were determined. Neurons within the principal part of the intermediolateral column (ILp) comprised the majority of labelled cells at all levels, irrespective of the site of HRP application, while more medially located neurons projected differentially. A combination of the application procedures labelled what appeared to be a sum of the individual projections, and few ILp cells remained unlabelled in the most rostral segments. From reconstructions of different segmental levels, most of the cells in the ILp were found to lie in a column ∼200 μm in diameter composed of a series of cell aggregations of 20–150 neurons at intervals of ∼300 μm. Less frequently, mediolaterally aligned cells extended toward the central canal, near which small cell clusters were also detected. After selective HRP application to individual rami of T1–T3, labelled cells were restricted to one segment's length, so that neurons located more caudally must project extraspinally to the stellate ganglion. Consideration of the maximum cell numbers labelled by each procedure suggests that preganglionic collaterals (probably unmyelinated) diverging from the pathway to the preferred target of their parent neuron were not labelled by this technique.
An electron microscopic analysis of the dorsal root in the frog
Authors: Wilhelm Gary B. , Coggeshall Richard E.
Published: January 2005

It is generally accepted that each dorsal root ganglion cell gives rise to a single central axon that enters the spinal cord via the dorsal root. This concept arose, in large part, from the reports that the numbers of dorsal root ganglion cells and dorsal root axons in mammals are equal. By contrast, in the frog a considerable excess of ganglion cells over axons was reported. None of these reports can be accepted, however, because the unmyelinated dorsal root axons could not be counted accurately with the light microscope. In the present study the counts in the frog are repeated, except that the axons are counted in the electron microscope, which has the necessary resolution for unmyelinated axons, and surgical controls are done to make certain that there are no extraneous axons in the root. When this is done, we show a considerable excess of axons to ganglion cells for all spinal segments in the frog, and there are no extraneous axons in the root. These data are interpreted as indicating that dorsal root axons branch either in the ganglion or in the root itself. Thus the concept that each frog dorsal root ganglion cell sends a single central process to the spinal cord needs to be modified.

One of our control procedures was to make certain that no fibers survive in the proximal stump of a dorsal rhizotomy. This shows that there are no dorsal root efferents in frog dorsal roots, an important consideration in the interpretation of certain physiological phenomena that result from dorsal root stimulation.

Finally, the study shows that there is a total of 43,000 dorsal root ganglion cells and 72,000 dorsal root axons in the bullfrog. These figures are considerably lower than similar figures from mammals and make an interesting comparison with some useful invertebrate preparations.
The aberrant retino‐retinal projection during optic nerve regeneration in the frog. III. Effects of crushing both nerves
Authors: Bohn Ronald C. , Stelzner Dennis J.
Published: January 2005

Previous reports from this laboratory have shown that a substantial number of optic axons are misrouted after optic nerve regeneration in the adult frog, Rana pipiens. Regenerating axons from a crushed optic nerve are distributed throughout the opposite nerve. In this study, we report the effect of crushing both optic nerves (double crush) on the pattern and degree of axonal misrouting. In 28 frogs both optic nerves were crushed at the same time (simultaneous double crush) and animals survived for varying periods before the right eye was injected with 3H‐proline and the brain processed for autoradiography 24 hours later. In every frog with postoperative survivals longer than 2 weeks, labeled axons from the right eye were found in the left optic nerve. However, when compared to the amount of label seen in frogs in which only the right optic nerve was crushed (single crush) there was substantially less label within the left nerve of frogs after crushing both nerves. Label was also found only at the edge of the left nerve in material from double crush frogs, unlike that found after single crush. In four of six frogs where the left nerve was crushed 1 week after the right nerve (delayed double crush), the proximal end of the left nerve was completely filled with label, but more distally, label was found only along the edge of this nerve. Although fewer optic axons were labeled in the opposite optic nerve of double crush frogs, label did extend to the optic disc of that eye. However, label was not apparent in the ganglion cell fiber layer of the opposite eye. Instead, it was confined to the edge of the optic disc in a space apparently associated with papilledema resulting from crushing the optic nerve of that eye. In six frogs the retina of the left eye was removed at the same time the right optic nerve was crushed. Labeled axons of the right eye filled the left optic nerve to the retina‐less shell of the left eye. Thus, these data show that the amount and distribution of axonal misrouting into the opposite optic nerve during optic nerve regeneration is affected by intact or regenerating optic axons from the other eye.
Topographic and morphometric effects of bilateral embryonic eye removal on the optic tectum and nucleus isthmus of the leopard frog
Authors: Constantine‐Paton Martha , Ferrari‐Eastman Patricia
Published: January 2005

Rana pipiens were raised through metamorphosis after extirpation of both eye primordia at Shumway embryonic stage 17 (Shumway '40). The visual connections between the isthmic nuclei and the optic tectum were examined in these animals using horseradish peroxidase (HRP) histochemistry. Isthmo‐tectal projections are normally aligned with the primary retinotectal map. We asked whether these connections would develop normal topographic organization in the absence of normal retinal input.

HRP was formed into a solid pellet (≃ 200–500 μm diameter) and inserted into one tectal lobe on the tip of a fine metal probe. The procedure produced relatively restricted retrograde label in somas and dendrites in both isthmi nuclei. In the nucleus isthmus ipsilateral to the tectal lobe receiving the HRP pellet, processes of tecto‐isthmi neurons were labeled by anterograde transport.

The topography of the isthmo‐tectal and tecto‐isthmic projections were identical in the developmentally enucleated animals and in normal frogs, even though eye removal severely reduced the volume of the optic tecta and the isthmi nuclei. Thus our analyses indicate that retinal contacts do not play an active role in the development of the positional or polarity cues that are involved in “mapping” projections between central visual nuclei. These results are discussed in the context of peripheral specification of central connections and in terms of models that have recently been proposed to explain the development of the retinotectal system.
Spinal projections from the medullary reticular formation of the North American opossum: Evidence for connectional heterogeneity
Authors: Martin G. F. , Cabana T. , Humbertson A. O. , Laxson L. C. , Panneton W. M.
Published: January 2005

Retrograde and orthograde transport techniques show that the nucleus reticularis gigantocellularis pars ventralis and the nucleus reticularis gigantocellularis project the entire length of the spinal cord. Double‐labelling methods show that some of the neurons in each area innervate both cervical and lumbar levels. There is evidence, however, that neurons in the lateral part of the nucleus reticularis gigantocellularis pars ventralis and the dorsal extreme of the nucleus reticularis gigantocellularis project mainly to cervical and thoracic levels. The autoradiographic method shows that the above nuclei supply direct innervation to somatic and autonomic motor columns as well as to laminae V–VIII and X. The nucleus reticularis gigantocellularis pars ventralis provides additional projections to lamina I and the outer part of lamina II.

Several areas of the medullary reticular formation project mainly, and in some cases exclusively, to cervical and thoracic levels. These areas include the nucleus reticularis parvocellularis, the nucleus reticularis lateralis, the nucleus retrofacialis, the nucleus ambiguus, the nucleus lateralis reticularis, caudal parts of the nuclei reticularis medullae oblongatee dorsalis and ventralis, and the nucleus supraspinalis. Autoradiographic experiments reveal that neurons in the ventrolateral medulla, particularly rostrally (the nucleus reticularis lateralis and neurons related to the nucleus lateralis reticularis), innervate sympathetic nuclei.

Our results indicate that spinal projections from bulbar areas of the reticular formation are more complicated than previously supposed. Axons from separate areas project to different spinal levels and in some cases to different nuclear targets. These data are in conformity with the evolving concept of reticular heterogeneity.
The monoamine‐containing neurons in avian brain: I. A study of the brain stem of the chicken (Gallus domesticus) by means of fluorescence and acetylcholinesterase histochemistry
Authors: Dubé Lorraine , Parent Andre
Published: January 2005

The distribution of monoamine (MA)‐containing nerve cell bodies in the brain stem of the chicken (Gallus domesticus) was studied by means of paraformaldehyde and glyoxylic acid fluorescent histochemical methods. The MA neurons were further characterized morphologically and histochemically in material prepared for the demonstration of acetylcholinesterase (AChE).

In the rostral midbrain of the chicken, two large collections of catecholamine (CA)‐containing cells are found: one located in the ventromedial and the other in the dorsolateral (pedunculopontine nucleus) portions of the tegmentum. On the basis of their topographic location, CA content, and fiber connections, these ventromedial and dorsolateral cell groups can be tentatively associated with the CA‐containing neuronal populations of the mammalian ventral tegmental area and pars compacta of the substantia nigra, respectively. In the caudal midbrain of the chicken, numerous CA‐containing cells are intermingled with serotonin (5HT)‐containing perikarya beneath as well as within the decussation of the superior cerebellar peduncles. At isthmus levels, abundant, closely‐packed CA‐containing cells are encountered along the lateral border of the central gray. These neurons, which display a very high AChE activity, appear to be equivalent to those of the mammalian locus coeruleus. A multitude of medium‐sized 5HT‐containing neuronal somata occurs within the raphe region of the isthmus. Some of these somata closely surround the medial longitudinal fasciculus. This 5HT‐containing cell group also massively invades the lateral tegmentum, where it be comes closely intermingled with the CA‐containing neurons of the locus coeruleus and subcoeruleus. All of these 5 HT‐containing neurons display a moderate to high AChE activity. In the medulla the number of MA‐containing neurons is much smaller than in the upper brain stem. Nevertheless, 5HT‐containing cells are present within the raphe region, particularly in the upper two‐thirds of the medulla, and CA‐containing perikarya can be found along the lateral border of the medulla and within the confines of the nucleus solitarius.

The findings of the present study reveal that the MA‐containing neuronal systems in the avain brain stem are organized according to a pattern that is much more complex than the one disclosed in reptiles or in other nonmammalian vertebrates. This complexity arises in large part from the fact that the 5HT‐containing systems undergo a prominent lateralization in birds, which leads to a close intermingling of 5HT‐containing and CA‐containing neuronal elements at various levels of the neuraxis.
Neurogenesis in the brain stem of the rabbit: An autoradiographic study
Authors: Oblinger Monica M. , Das Gopal D.
Published: January 2005

With the aid of (H3)‐thymidine autoradiography, neurogenesis was documented in the nuclear groups of the medualla oblongata, pons, and midbrain, as well as in the brain stem reticular formation of the rabbit. Following single injections of (H3)‐thymidine, counts were taken of intensely labeled neurons within the nuclei of the functional columns related to the cranial nerves, nuclei of several other functional classifications, and nuclei that did not fit into a functional category. In the brain stem as a whole, neurogenesis was found to occur between days 10.0 and 18.5 of gestation; however, the majority of nuclei studied contained intensely labeled neurons only between days 12.0 and 15.0. Only in the pontine nucleus and the tectum were intensely labeled cells observed as late as day 18.5. Directional gradients of histogenesis were often observed within, as well as between, various nuclei. Within the nuclear columns related to the cranial nerves, a clear mediolateral spread of neurogenesis was observable such that nuclei of the motor columns reached a peak in neurogenesis before those in the sensory columns. Likewise, a mediolateral proliferation pattern was seen in the brain stem reticular formation. Other individual directional gradients were discernible; however, in the brain stem as a whole, distinct overall gradients were not observable. In many individual nuclei, gradients in neuron size were observed such that large neurons preferentially arose prior to smaller neurons. Information pertaining to gradients in neurogenesis, as well as to relationships among functionally related nuclei, are disscussed.
Connections of the corticomedial amygdala in the golden hamster. I. Efferents of the “vomeronasal amygdala”
Authors: Kevetter Golda A. , Winans Sarah S.
Published: January 2005

The medial (M) and posteromedial cortical (C3) amygdaloid nuclei and the nucleus of the accessory olfactory tract (NAOT) are disignated the “vomeronasal amygdala” because they are the only components of the amygdala to receive a direct projection from the accessory olfactory bulb (AOB). The efferents of M and C3 were traced after injections of 3H‐proline into the amygdala in male golden hamsters. Frozen sections of the brains were processed for autoradiography.

The efferents of the “vomeronasal amygdala” are largely to areas which are primary and secondary terminal areas along the vomeronasal pathway, although the efferents from C3 and M terminate in different layers in these areas than do the projections from the vomeronasal nerve or the AOB. Specifically, C3 projects ipsilaterally to the internal granule cell layer of the AOB, the cellular layer of NAOT, and layer lb of M. Additional fibers from C3 terminate in a retrocommissural component of the bed nucleus of the stria terminalis (BNST) bilaterally, and in the cellular layers of the contralateral C3. The medial nucleus projects to the cellular layer of the ipsilateral NAOT, layer lb of C3, and bilaterally to the medial component of BNST.

Projections from M to non‐vomeronasal areas terminate in the medial preoptic area‐anterior hypothalamic junction, ventromedial nucleus of the hypothalamus, ventral premammillary nucleus and possibly in the ventral subiculum.

These results demonstrate reciprocal connections between primary and secondary vomeronasal areas and between the secondary areas themselves. They suggest that M, but not C3, projects to areas outside this vomeronasal network. The medial amygdaloid nucleus is therefore an important link between the vomeronasal organ and areas of the brain not receiving direct vomeronasal input.
Histogenesis of the cochlear nucleus of the mouse
Authors: Martin Michael R. , Rickets Christine
Published: January 2005

In Nissl‐stained preparations of the cochlear nucleus there are nine recognizable cell types. These cells are born during three periods of histogenesis prenatally. On gestation days 10.0, 10.5, and 11.0 the pyramidal, giant, and dark‐staining cells are born. The spherical, globular, multipolar, and horizontal cells are formed on gestation days 12.0, 12.5, and 13.0 and small cells follow on gestation day 14.5. The onset of granule cell formation is gestation day 14.5 and continues to birth on gestation day 19. At birth, and for at least the first 2 postnatal weeks, glial cells are born. There are no regional gradients in cell birth dates, cells from all birth dates being intermixed. Cell birth proceeds in an orderly sequence that is related only to cell size. Although there were no apparent spatiotemporal patterns, some clustering of labeled cells was evident. These observations do not support the hypothesis that Golgi Type I cells precede Golgi Type II cells in their order of birth since both large and small neurons project beyond the nucleus. There is, nonetheless, a sequential pattern in the onset of cell birth for the auditory system, with cochlear nucleus neurons preceding cochlear neurons.
Cerebellothalamic projections in the rat: An autoradiographic and degeneration study
Authors: Haroian Alan J. , Massopust Leo C. , Young Paul A.
Published: January 2005

The purpose of this study was to determine the topographical organization of cerebellothalamic projections in the rat. Following stereotaxic injections of 3H‐leucine or electrolytic lesions in the cerebellar nuclei, efferent fibers were observed to emerge from the cerebellum through two discrete routes. Fibers from the fastigial nucleus decussated within the cerebellum, formed the crossed ascending limb of the uncinate fasciculus, ascended in the dorsal part of the midbrain tegmentum, and entered the thalamus. Cerebellothalamic fibers from the interpositus and dentate nuclei coursed in the ipsilateral brachium conjuctivum, decussated in the caudal midbrain, and ascended to the thalamus via the crossed ascending limb of the brachium conjunctivum.

Cerebellar terminations were observed in the intralaminar, lateral, and ventral tier thalamic nuclei as well as in the medial dorsal nucleus. Projections to the intralaminar nuclei were more pronounced from the dentate and posterior interpositus than from the anterior interpositus and fastigial nuclei. The lateral thalamic nuclei received a projection from the dentate and posterior interpositus nuclei while the fastigial nucleus projected to the medial dorsal nucleus. Within the rostral ventral tier nuclei fastigiothalamic terminations were localized in the medial parts of the ventral medial and ventral lateral nuclei, whereas dentatothalamic projections were concentrated in the lateral parts of the ventral medial nucleus and the medial half of the ventral lateral nucleus. Terminations from the posterior interpositus nucleus were observed ventrally and laterally within the caudal two‐thirds of the ventral medial nucleus and throughout the ventral lateral nucleus, where they were densest in the lateral part of its lateral wing and within the central part of its cap. The anterior interpositus nucleus also projected to the central and lateral parts of the ventral lateral nucleus, but these terminations were considerably less dense than those from the posterior interpositus. A few fibers from the interpositus nuclei terminated in the medial part of the rostral pole of the ventral posterior nucleus.

A prominent recrossing of cerebellothalamic fibers from the fastigial, posterior interpositus, and dentate nuclei occurred through the central medial nucleus of the internal medullary lamina. These terminated within the ipsilateral ventral lateral and intralaminar nuclei.

These results show that each of the cerebellar nuclei project to the thalamus and that their terminations are topographically organized in the rostral ventral tier nuclei. The clustering of autoradiographic silver grains or terminal degeneration observed in the thalamic nuclei suggests a medial‐to‐lateral organization of this cerebellothalamic system.
The pontocerebellar system in the rat: An HRP study. I. Posterior vermis
Authors: Azizi S. A. , Mihailoff G. A. , Burne R. A. , Woodward D. J.
Published: January 2005

This study was undertaken to determine the origin of projections from the basilar pontine nuclei (BPN) and nucleus reticularis tegmentis pontis (NRTP) to the posterior vermal lobules VI‐IX of the rat cerebellum. We describe the topographical organization of this component of the pontocerebellar projection, and the congruence of the cells of origin in the basilar pons with some of the major pontine afferent systems including the corticopontine and tectopontine projections. Horseradish peroxidase (HRP) was injected into the midline cerebellar vermal zones of Long‐Evans hooded rats. The more sensitive chromogens, tetramethyl benzidine and benzidine dihydrochloride, were used to reveal the location of labeled neurons.

With injections located near the midline, groups of labeled cells were observed bilaterally within the BPN. The basic trend of the projections noted was: lobule VIa receives a nonfocal projection from nearly all subdivisions of the BPN throughout its rostrocaudal extent, as well as a substantial input from NRTP. Lobules VIb‐c receive input from NRTP, the rostral pons, and from the ventral, lateral, and medial groups of the middle BPN. A combination of lateral, medial, and dorsolateral groups of cells in the middle BPN project to lobule VII, in addition to projections from limited groups of cells in the rostral BPN. Lobule VIII receives afferents from the caudal aspect of the pontine gray. Lobules IXa‐b receive afferents from the medial and peduncular groups in the middle BPN, whereas lobule IXc receives inputs from a medial group and a small lateral cluster of cells in the caudal aspect of the BPN.

Pontine neurons projecting to the posterior vermis originate from areas which appear to receive descending inputs from visual, auditory, and somatosensory regions of the cerebral cortex. However, a large number of pontine and NRTP neurons projecting to lobules VI and VII are located within the terminal fields of tectal neurons, perhaps indicating a stronger input from the tectum rather than visual and auditory cerebral cortical regions.
Regeneration of axons and nerve cell bodies in the CNS of annelids
Authors: Hulsebosch C. E. , Bittner G. D.
Published: January 2005

The neuron addition hypothesis predicts that species that add CNS neurons during a particular ontogenetic stage should regenerate ablated somata better than species that add few, if any, neurons to the CNS during that same stage. We report that CNS nerve cells do not regenerate in three species of adult (reproductively competent) leeches (Hirudo medicinalis, Haemopus grande, and Macrobdella decora), which do not increase the number of neurons in any portion of the CNS. Nereis virens, a polychaete that adds CNS neurons to newly forming ganglia in the adult stage, also does not regenerate CNS neurons. Conversely, CNS neurons, including a pair of uniquely identifiable somata, do regenerate in Clymenella torquata, a polychaete that has a constant number of neurons in the adult stage. Hence, the results of our study suggest that several versions of the neuron addition hypothesis cannot predict CNS regenerative abilities in adult annelids. Finally, we report that severed stumps of CNS axons do not degenerate rapidly in Nereis or Clymenella, and that both species can regenerate severed CNS axons presumably by morphologic fusion or physiologic activation of surviving stumps.
Morphogenesis and synaptogenesis of the zebrafish mauthner neuron
Authors: Kimmel Charles B. , Sessions Stanley K. , Kimmel Reida J.
Published: January 2005

The shape of the Mauthner neuron (M‐neuron) and the distribution of its afferent synapses were studied between days 2 and 6 after fertilization in the zebrafish Brachydanio rerio. This interval is just after the outgrowth of M‐dendrites begins, and during this time the M‐cell acquires its definitive shape. The M‐cell has two large invariant dendrites: The lateral dendrite terminates in the sensory neuropil of the acoustico‐lateral area, and the ventral dendrite terminates in the neuropil of the motor tegmentum. Fine dendrites are present, and mostly arise from three regions; from the terminus of each major dendrite and from the ventral surface of the perikaryon. The number and position of fine dendrites within each of these sets is variable, even among animals from a single isogenic clone. M‐cells with improper numbers or positions of large dendrites were never encountered, even early in development. This suggests that their outgrowth is a highly directed process.

Large numbers of afferent synapses are formed on the M‐cell during the time of dendrite outgrowth. By day 6 there is a mosaic pattern of morphologically distinctive terminals that is similar to the pattern of the adult goldfish M‐cell. Identified categories of terminals include (1) myelinated club endings, on the distal part of the lateral dendrite, (2) boutons, on the dendrites and perikaryon, (3) unmyelinated club endings, on the dorsomedial portion of the perikaryon adjacent to the axon cap, and (4) spiral fiber terminals within the axon cap. The nonrandom nature of the input may be ascertained by observing the distribution of electrotonic or gap junctions on the cell surface. These are frequently encountered on the initial segment of the axon (spiral fiber terminals), ventral dendrite and ventral perikaryon (boutons), and distal lateral dendrite (myelinated club endings). Gap junctions are only rarely observed on the dorsal surface of the cell, although this region, like others of the cell, receives large numbers of chemical synaptic contacts. This pattern is similar at all stages studied, which suggests that no large rearrangements in synaptic contacts occur during this developmental period. We discuss these observations in relation to the hypothesis that patterned dendritic growth of the M‐cell is directed by synaptic interactions with the afferents.
Sensory control of dauer larva formation in Caenorhabditis elegans
Authors: Albert Patrice S. , Brown Susan J. , Riddle Donald L.
Published: January 2005

As a sensory response to starvation or overcrowding, Caenorhabditis elegans second‐stage larvae may molt into a developmentally arrested state called the dauer larva. When environmental conditions become favorable for growth, dauer larvae molt and resume development. Some mutants unable to form dauer larvae are simultaneously affected in a number of sensory functions, including chemotaxis and mating. The behavior and sensory neuroanatomy of three such mutants, representing three distinct genetic loci, have been determined and compared with wild‐type strain. Morphological abnormalities in afferent nerve endings were detected in each mutant. Both amphid and outer labial sensilla are affected in the mutant CB1377 (daf‐6)X, while another mutant, CB1387 (daf‐10)IV, is abnormal in amphidial cells and in the tips of the cephalic neurons. The most pleiotropic mutant, CB1379 (che‐3)I, exhibits gross abnormalities in the tips of virtually all anterior and posterior sensory neurons. The primary structural defect in CB1377 appears to be in the nonneuronal amphidial sheath cells. The disruption of neural organization in CB1377 is much greater in the adult than in the L2 stage. Of all the anterior sense organs examined, only the amphids are morphologically affected in all three mutants. Thus, one or more of the amphidial neurons may mediate the sensory signals for entry into the dauer larva stage in normal animals. Using temperature‐sensitive mutants we determined that the same defects which block entry into the dauer stage also prevent recovery of dauer larvae.
First somatosensory cortical columns and associated neuronal clusters of nucleus ventralis posterolateralis of the cat: An anatomical demonstration
Authors: Kosar Eva , Hand P. J.
Published: January 2005

Microlesions (30–275 microns in diameter) were placed in VLPm of the cat and the terminal axonal degeneration in SI cortex was stained using the Fink‐Heimer I technique. Following each of these microlesions, small, localized patches or subcolumns of degeneration, relativly light in density, were observed within laminae IIIb and IV of SI when viewed in the coronal plane. In addition, a few degenerating fibers ascended to lamina I. These multiple subcolumns had distinct radial boundaries and were narrow in the mediolateral plane (80–120 microns in width) but elongated rostro‐caudally (2500–3000 microns in length). Localized patches of degeneration were separated at their widest points by a distance of 500 microns medio–laterally, but at various rostro–caudal levels of SI were observed to merge into larger columns of degeneration (250–400 microns) and then separate again into smaller multiple patches (i.e., a “zebra‐like” pattern).

Small injections of HRP into the forelimb region of area 3b or rostral area 1–2 of SI resulted in the labeling of small, discrete clusters of neurons in the ventral regions of VPLm. The clusters examined ranged in size from 140–350 microns in medio–lateral diameter and were elongated rostro–caudally (up to 500 microns in extent); virtually all cells within a cluster appeared labeled, but not equally so.

A pattern of HRP labeling different from that observed following area 3b and rostral area 1–2 injections was observed following injections into more caudal regions of area 1–2 and into SII cortex. The labeling that resulted from these injections was not in the form of neuronal clusters but instead labeled cells tended to be scattered in more dorsal regions of VPLm. This scattering did not appear to be random since the labeled neurons were grouped within the same general area of VPLm. Labeling was distributed throughout a number of cell clusters, comprising only a small proportion of cells within each cluster. The pattern of labeling seen after caudal area 1–2 and SII injections differed only in its rostro–caudal extent within VPLm. SII injections generally resulted in labeling along the full rostro–caudal dimension of VPLm.

A differential organization of the anatomy of thalamocortical projections to the various subdivisions of SI and to SII was noted in this study. It is postulated that the multiple, discrete patches of degeneration in laminae IIIb and IV of SI represent a portion of the somatosensory cortical columns and that the HRP‐labeled clusters seen in VPLm following area 3b and rostral area 1–2 injections are the subcortical equivalents of these subcolumns.
Retinal recipient nuclei in the painted turtle, Chrysemys picta: An autoradiographic and HRP study
Authors: Bass Andrew H. , Northcutt R. Glenn
Published: January 2005

Retinofugal pathways in the painted turtle were examined with autoradiographic and HRP methods. The majority of the retinal fibers decussate at the optic chiasm and course caudally to terminate in 12 regions of the diencephalon and mesencephalon. The pars dorsalis of the lateral geniculate nucleus is the densest target in the thalamus. Two nuclei dorsal to pars dorsalis—the dorsal optic and dorsal central nuclei—receive optic input. Three nuclei ventral to pars dorsalis are retinal targets—the ventral geniculate nucleus, nucleus ventrolateralis pars dorsalis, and nucleus ventrolateralis pars ventralis. Contralateral fibers course through the pretectum where they terminate in nucleus geniculatis pretectalis, nucleus lentiformis mesencephali, nucleus posterodorsalis, and the external pretectal nucleus. Retinal fibers also terminate within the superficial zone of the optic tectum. HRP material demonstrates three optic fiber layers—laminae 9, 12, and 14. Optic fibers leave the main optic tract as a distinct accessory tegmental optic pathway and terminate in the basal optic nucleus. Ipsilateral retinal terminals occur in a pars dorsalis and a pars ventralis of the lateral geniculate nucleus, the dorsal optic nucleus, nucleus posterodorsalis, the basal optic nucleus, and in laminae 9 and 12 of the optic tectum. Rostrally, the ipsilateral tectal fibers occupy two zones along the medial and lateral tectal roof; these zones converge caudally and are continuous along the caudal wall of the tectum.