bluuebunny/crossref_metadata_2025 huggingface dataset:
Postnatal development of primary visual projections in the tammar wallaby (Macropus eugenii)
Authors: Wye‐Dvorak Judith
Published: January 2005

The time course and pattern of retinal innervation of primary visual areas was traced in pouch‐young wallabies. Tritiated proline was injected into one eye of animals ranging in age from 1 to 72 days after birth. These results are compared to the 11 primary visual areas found in the adult wallaby, seven of which receive binocular input while four are monocular. At birth retinal ganglion cell axons have not reached any visual areas. Two to 4 days after birth, all of the axons are crossing to the contralateral optic tract. Nine to 12 days after birth axons begin to invade the contralateral lateral geniculate nucleus, the superior colliculus, and the medial terminal nucleus. Twenty to 21 days after birth, ipsilateral axons invade the lateral geniculate nucleus and superior colliculus. The contralateral projection precedes the ipsilateral projection in all binocular visual areas. By 25 days, ipsilateral and contralateral afferents share common territory in the lateral geniculate nucleus; however, afferents from each eye are initially concentrated in appropriate areas. Between 52 and 72 days, afferents to the dorsal lateral geniculate nucleus are gradually segregated into nine terminal bands. Four are contralateral while five are ipsilateral. By 72 days, the ipsilateral component to the superior colliculus is clustered beneath the contralateral projection a deeper layer. Projections to four monocular visual areas—lateral posterior nucleus, dorsal terminal nucleus, lateral terminal nucleus, and nucleus of the optic tract—are established later than binocular visual areas, except the suprachiasmatic nucleus.

The suprachiasmatic nucleus is the last to be bilaterally innervated even though it is situated closest to the optic chiasm. At the light microscope level a mature pattern of visual development is emerging by 72 days, although the eyes do not open until 140 days.
Thalamocortical connections in newborn mice
Authors: Crandall James E. , Caviness Verne S.
Published: January 2005

Thalamocortical axons reach the developing neocortex and become distributed within the cortical subplate during the third week of gestation. The present study is an analysis of the organization of connections that link thalamus and cortical subplate (corresponding to future layers V and VI) at birth. This age antedates the ascent of thalamic axons to contact cells of the supragranular layers, their principal targets in the adult cortex. At birth thalamic nuclear subdivisions are explicit; field‐characteristic cytoarchitectonic features, relating principally to the infragranular layers, delineate the majority of neocortical fields. The projection of principal relay nuclei upon the majority of fields of the cerebral convexity has been mapped by means of retrograde transport of HRP. Nucleus‐to‐field interrelationships as well as topologic order of the overall thalamic projection prove to be identical to that in the adult animal. The neonatal projection appears to be somewhat more divergent than that of the adult.
Laminar origins of visual corticocortical connections in the cat
Authors: Symonds Laura L. , Rosenquist Alan C.
Published: January 2005

The interconnections among visual areas in cat cortex were studied with respect to the specific laminae in which the cortically projecting neurons are located. Single injections of HRP were made through recording micropipettes into nine different visual areas. In 15 cortical areas the laminar distribution of neurons which were retrogradely filled with HRP was plotted. In this way we determined the laminar origins of the cortical projections to the nine separate cortical visual areas which were injected. There are three major observations. First, areas 17 and 18 are the only two visual areas in which layers II and III are the primary site of cortically projecting cells; in the other 13 areas the deeper layers of cortex provide a large percentage of such neurons. Second, within any one cortical area, cortically projecting neurons may be distributed among different layers; the specific layer depends upon the cortical target of those neurons. Third, any one cortical area receives projections from several different cortical layers, the specific layers being dependent upon the area from which the projection originates. An individual cortical area, therefore, contributes to several different cortical visual circuits, with each of these circuits defined by the laminar connections of its neurons.
The ultrastructure and organization of methionine‐enkephalin immunoreactive profiles in the interpeduncular nucleus of the cat
Authors: Kapadia Shanta E. , De Lanerolle Nihal C.
Published: January 2005

An ultrastructural analysis of the dorso‐intermediate (CDIZ) and dorsomedian zones (CDMZ) at the caudal end of the interpeduncular nucleus was undertaken. Serial vibratome sections were stained for metenkephalin‐like immunoreactivity by using the indirect antibody peroxidase‐antiperoxidase method of Sternberger, and ultrathin sections were examined electron microscopically, Met‐enkephalin‐like immunoreactivity was observed in two different types of somata in the two regions. The dendritic architecture of the dorso‐intermediate zone was characterized by the presence of many dendritic crests. A large number of these dendritic crests were immunostained for metenkephalin. A variety of terminals was also seen in the CDIZ and CDMZ and they are categorized according to their vesicular morphology into three classes. One class contained mainly clear round vesicles. The metenkephalin‐like immunoreactive (MELI) terminal profiles in both regions were of this class and contained small round vesicles which were less than 35 nm in diameter. These MELI terminals appeared in significant numbers, sometimes in close proximity to unlabeled somata and dendrites. The dorso‐median zone had, in addition, two more classes of terminals. One class was characterized by a large number of dense‐cored vesicles—class II, and the other group had a large proportion of flat clear vesicles—class III. The possible neurochemical identities of some of the unlabeled terminals in relation to the MELI dendritic structures are discussed in the light of known neurochemically established afferent projections to the CDIZ and CDMZ of the interpeduncular nucleus.
Afferent influences on brain stem auditory nuclei of the chicken: Time course and specificity of dendritic atrophy following deafferentation
Authors: Deitch Jeffrey S. , Rubel Edwin W
Published: January 2005

The time course and specificity of the changes in dendritic morphology following deafferentation were examined in nucleus laminaris of young chickens. The dendrites of nucleus laminaris neurons are segregated into dorsal and ventral domains, which are innervated separately from the ipsilateral and contralateral nucleus magnocellularis, respectively. Transection of the crossed dorsal cochlear tract deafferents the ventral dendrites of nucleus laminaris bilaterally without interrupting the matching input to the dorsal dendrites.

In 10‐day‐old chicks, atrophy of the ventral dendrites began immediately after transecting the tract; the ventral dendrites were 10% shorter by 1 hour and 16% shorter by 2 hours after deafferentation. The length of the ventral dendrites progressively decreased over the next 2 weeks, resulting in at least a 60% loss of ventral dendrite 16 days after surgery. The dorsal dendrites of the same cells, whose afferents remained intact, did not change in length during the time course of this study. However, 16 days after the lesion, spines appeared on the normally smooth dorsal and ventral dendrites. The time course of dendritic atrophy and its restriction to the deafferented postsynaptic surface are related to possible mechanisms by which afferents regulate and maintain their target neurons.
Central organization of eighth nerve and mechanosensory lateral line systems in the brainstem of ictalurid catfish
Authors: Finger Thomas E. , Tong Shang‐Liang
Published: January 2005

The octavolateral sensory systems in teleost fish comprise at least four distinct hair‐cell sensory modalities which are processed separately within the CNS. Two of these modalities, the mechanosensory lateral line system and the eighth nerve auditory system, have been implicated in the animal's ability to detect and localize underwater vibrations. Distinct mechanosensory lateral line and auditory nuclei are present within the torus semicircularis, the midbrain homologue of the inferior colliculus. The present study utilized horseradish peroxidase tracing techniques to delineate those areas of the lower brainstem which are involved in auditory as opposed to mechanosensory lateral line processes.

The primary mechanosensory nucleus of the medulla, n. medialis, projects directly to the optic tectum and to the mechanosensory nucleus of the torus semicircularis. Nucleus medialis receives input from primary lateral line nerve fibers as well as from a number of sites within the CNS: n. praeeminentialis pars ventralis, and the eminentia granularis and lobus caudalis of the cerebellum. The n. praeeminentialis itself receives a descending input from the mechanosensory nucleus of the torus semicircularis. These mechanosensory lateral line pathways are parallel to, but distinct from, those of the electrosensory lateral line system.

Auditory signals reach the midbrain via an entirely separate route. The octaval nerve terminates in a column of five medullary nuclei. Of these, only the anterior and descending octaval nuclei maintain a direct but sparse projection to the auditory nucleus of the midbrain. The bulk of the auditory input to the midbrain involves a newly described medullary nucleus, the medial auditory nucleus of the medulla. This nucleus receives input from the descending octaval nucleus and projects bilaterally to the auditory nucleus of the torus semicircularis. It is suggested that the medial auditory nucleus of the medulla is homologous to portions of the superior olivary complex of other vertebrates.
Reduced effects of monocular deprivation on a population of A‐laminae neurons in the cat's dorsal lateral geniculate nucleus
Authors: Peduzzi Jean D. , Hickey T. L.
Published: January 2005

The generation of nerve cells for the cat's dorsal lateral geniculate nucleus takes place between embryonic day (E) 22 and E32. Neurons generated before E28 exhibit a full range of soma sizes and morphological features, whereas neurons generated after E28 have only smaller somata and a more limited array of morphological features. We measured the effects of monocular deprivation on neurons in the cat's dorsal lateral geniculate nucleus that were generated at different times, with birthdates defined by injections of 3H‐thymidine. Whereas populations of nerve cells generated before E28 exhibit changes in cell size that are, on average, typical of those seen in monocularly deprived cats, populations of nerve cells generated after E28 are, on average, less affected by visual deprivation.
Thalamic projections of nucleus reticularis thalami of cat: A study using retrograde transport of horseradish peroxidase and fluorescent tracers
Authors: Steriade M. , Parent A. , Hada J.
Published: January 2005

The retrograde transport of horseradish peroxidase (HRP) and fluorescent tracers after injections in various thalamic nuclei was used to investigate the relative density of retrogradely labeled cells in different districts of reticularis thalami (RE) nuclear complex of cat. The RE nucleus was left virtually free of labeling only after injections localized into the anterior nuclear group; in those experiments, heavy retrograde labeling was obtained in mammillary nuclei. The major targets of RE cells proved to be centralis lateralis‐paracentralis (CL‐PC) and centrum medianum‐parafascicularis (CM‐PF) intralaminar nuclei. The projections to various intralaminar nuclei mainly arise in the rostral pole and rostrolateral part of RE nucleus and are reciprocal to intralaminar‐RE pathways disclosed by Jones ('75). The RE territories labeled following injections in relay and associational nuclei are more restricted and are located contiguously and slightly anteriorly to a given nucleus. There was a very small proportion of doubly labeled RE cells after injections with fluorescent tracers in different nuclei. This was not due to a technical failure since many double‐labeled neurons were found in the same material in medial globus pallidum after thalamic and midbrain injections (see companion paper by Parent and Steriade, '84). We conclude that most individual RE axons arborize in only one thalamic nucleus or nuclear group. An additional finding was the existence of intralaminar‐to‐relay (CL‐PC to VA‐VL) projections.
Efferent projections of the neonatal cat superior colliculus: Facial and cerebellum‐related brainstem structures
Authors: Stein Barry E. , Spencer Robert F. , Edwards Stephen B.
Published: January 2005

The superior colliculus develops its influence over eye and pinna movements gradually during postnatal maturation. Because superior colliculus cells respond earlier in postnatal life to nonvisual than to visual cues, it seemed likely that efferents involved in pinna movements would develop earlier than those involved in eye movements. In the present study, we examined the projections of the superior colliculus to structures related to the cerebellum and facial nucleus believed to be involved in eye‐head coordination and pinna movements. We did this by using the autoradiographic and horseradish peroxidase tracing techniques in 11 kittens, ranging in age from several hours to 14 days postnatal, and in seven adult cats.

Even in the youngest animals studied, a dense projection was observed from the superior colliculus to each of the target structures examined. These included the (1) parabigeminal nucleus, (2) paralemniscal zone, (3) dorsolateral pons, and (4) inferior olive. Surprisingly, the only projection observed to undergo any postnatal maturational changes was the one to the paralemniscal zone (involved in the pinna‐movement circuit of the superior colliculus), and the changes appeared as a reorganization of the terminal field rather than an increase in the density of transported label. Thus, no evidence was obtained to support our expectation that the superior colliculus efferents involved in orientation of the pinnae would develop earlier than those involved in visual orientation. Instead, each of the efferent projections of the superior colliculus examined in this study appears to be laid down prenatally and becomes adultlike long before functional maturity is reached. Presumably, then, the formation and elaboration of synaptic connections are the protracted postnatal processes that limit the functional properties of these neonatal efferent pathways.
The morphology of optic tract axons arborizing in the superior colliculus of the hamster
Authors: Sachs George M. , Schneider Gerald E.
Published: January 2005

Single axons innervating the superficial layers of the hamster's superior colliculus (SC) were visualized using an HRP‐filling technique. Five types of axons were distinguished. Experiments involving the removal of retinal and/or cortical input showed that three of these axon types originated in the contralateral retina with the fourth type most likely originating in the visual cortex. The origin of the fifth type, a widely branched varicose axon, is apparently subcortical.

The two major types of presumed retinotectal axons (types U and L1) project to the stratum griseum superficiale (SGS) in a bilaminar pattern. Type U axons take relatively direct paths from the layer of optic fibers to form dense terminal arbors in the upper half of the SGS. Terminal fields for type U fibers showed fairly consistent dimensions. Their rostrocaudal extent ranged from 90 μm to 190 μm, averaging about 120 μm.

Type L1 axons were thicker than type U axons and terminated in deeper regions of the SGS and in the stratum opticum (SO). Single axons of this type often gave rise to multiple branches which took separate, circuitous paths to a common terminal field. Terminal fields for type L1 axons varied more in extent than did type U fields, but 58% of them had fields 90–150 μm in extent.

Each of the axon types found can be related to previous studies of populations of tectal afferents. The two major types of retinofugal axons fit a scheme of parallel ascending pathways. The findings also have interesting implications for the study of axonal development.
Diameters and terminal patterns of retinofugal axons in their target areas: An HRP study in two teleosts (Sebastiscus and Navodon)
Authors: Ito Hironobu , Vanegas Horacio , Murakami Takeshi , Morita Yasuhiro
Published: January 2005

Studies in various vertebrate classes, particularly amphibians and mammals, have revealed that retinal ganglion cells with different functional properties project by means of axons of correspondingly different diameters onto specific target regions. Whether a similar pattern exists in teleosts is partly investigated in the present study. HRP was injected into the optic nerve of Sebastiscus and Navodon. The calibers of intraretinal HRP‐labeled axons were classed as fine (ca. 0.8 μm), medium (ca. 1.3 μm), and coarse (ca.2.5 μm). The calibers of HRP‐labeled retinofugal axons were then determined in their target areas, and these can be summarized as follows: Optic hypothalamus: fine, medium. Lateral geniculate nucleus: fine. Dorsolateral thalamic nucleus: fine, medium. Area pretectalis: fine. Nucleus of the posterior commissure: fine, medium. Area ventralis lateralis, contralateral: fine, medium, coarse; ipsilateral: coarse. Optic tectum, stratum opticum: fine, medium; stratum fibrosum et griseum superficiale: fine, medium, coarse, segregated in sublayers; stratum album contrale: fine, medium, coarse. Therefore, fine fibers were found to reach all target areas except the ipsilateral area ventralis lateralis, and these were the only fibers found in the lateral geniculate nucleus, area pretectalis, and stratum griseum centrale of the optic tectum. Coarse fibers, on the other hand, were found only in the area ventralis lateralis and the optic tectum (stratum fibrosum et griseum superficiale and stratum album centrale). Terminal patterns of these fibers were also studied. Most fine fibers take tortuous courses giving off a few branches and terminate with many varicosities, and medium and coarse fibers give off several finer branches and terminate with bulbous swellings. The physiological significance of these findings is discussed.

In addition, retrogradely labeled (retinopetal) cells were found in the olfactory bulb and the area ventralis pars ventralis of the telencephalon, as well as in the preoptic area and the dorsolateral thalamic nucleus.
Effects of strabismus and monocular deprivation on the eye preference of neurons in the visual claustrum of the cat
Authors: Perkel David J. , LeVay Simon
Published: January 2005

Visual response properties of neurons in the dorsocaudal claustrum were studied in two cats reared with convergent strabismus and three cats reared with monocular lid‐suture. In the normal claustrum, most cells respond about equally well to stimulation of either eye (Sherk and LeVay, '81). In the strabismic animals, there was a partial breakdown of binocularity: most cells remained binocular but were influenced more strongly by one eye (usually the contralateral eye) than the other. The loss of binocularity was less extreme in the claustrum than in area 17 of the same animals. In the monocularly deprived cats, claustral cells responded exclusively to the experienced eye. We interpret the changes observed in the claustrum as reflecting changes in the ocular dominance of cortical inputs to the claustrum, rather than as evidence for plasticity within the claustrum itself.

Autoradiography was used to study the return projection from claustrum to cortex in monocular deprivation. The cortical labeling pattern resembled that seen in normal cats. To examine whether this return projection might be involved in reducing cortical responsiveness to the deprived eye, recordings were made from area 17 of a monocularly deprived cat before and after ablation of the ipsilateral claustrum by injection of kainic acid. Following ablation, there was no unmasking of cortical responses to the deprived eye. Thus the cortico‐claustral loop does not appear to suppress cortical responses to the deprived eye.
FMRFamide immunoreactivity in the nervous system of the medusa Polyorchis penicillatus
Authors: Grimmelikhuijzen C. J. P. , Spencer A. N.
Published: January 2005

Three different antisera to the molluscan neuropeptide Phe‐Met‐Arg‐Phe‐amide (FMRFamide) and two different antisera to the fragment RFamide were used to stain sections or whole mounts of the hydrozoan medusa Polyorchis penicillatus. All antisera stained the same neuronal structures. Strong immunoreactivity was found in neurons of the ectodermal nerve nets of the manubrium and tentacles, in neurons of the sensory epithelium, and in neurons at the periphery of the sphincter muscle, Strong immunoreactivity was also present in processes and perikarya of the whole outer nerve ring, in the ocellar nerves, and in nerve cells lying at the periphery of the ocellus. The inner nerve ring contained a moderate number of immunoreactive processes and perikarya, which were distinct from the swimming motor neurons.

In contrast to the situation in the hydrozoan polyp Hydra attenuata, no immunoreactivity was found with several antisera to oxytocin/vasopressin and bombesin/gastrin‐releasing peptide.

The morphology and location of most FMRFamide‐immunoreactive neurons in Polyorchis coincides with two identified neuronal systems, which have been recently discovered from neurophysiological studies.
The axon reaction of the goldfish mauthner cell and factors that influence its morphological variability
Authors: Zottoli Steven J. , Hangen Donald H. , Faber Donald S.
Published: January 2005

The axon reaction of the goldfish Mauthner cell, elicited by spinal cord transection, included somatic swelling, nuclear eccentricity, chromatolysis, nuclear infolding, and a perinuclear buildup of basophilic material. The latter three changes were found most consistently and showed gradations which were ranked quantitatively.

The time of onset of chromatolysis and nucleus‐associated changes depended upon the distance of the wound from the Mauthner cell soma. Specifically, for Mauthner axons cut at 5, 10.5, and 20 mm distal to their somata, the approximate postoperative times of onset were 10, 20, and 40 days, respectively. Mauthner cells axotomized 42 mm distally did not display a consistent axon reaction. Cell atrophy and death were not found in cells axotomized 10.5, 20, or 42 mm from their somata up to 285 postoperative days, but were observed at the longer postoperative intervals (421 days) in neurons cut 5 mm distally and were consistently found in neurons axotomized less than 1.6 mm from their somata.

The axon reactions of Mauthner cells within a pair were frequently different. This variability cannot be explained by the influence of cut site or postoperative interval and is hypothesized to result from different metabolic conditions of the individual cells.
Immunoreactive pro‐enkephalin and pro‐dynorphin products are differentially distributed within the nucleus of the solitary tract of the rat
Authors: Lee Hyun Sook , Basbaum Allan I.
Published: January 2005

In this study we examined the distribution of two different endogenous opioid peptides in the nucleus of the solitary tract of the rat medulla. As a marker for immunoreactive enkephalin, we used an antiserum directed against one of the proenkephalin products, methionine enkephalin‐arg‐glyleu (m‐Enk). To identify immunoreactive dynorphin we used an antiserum directed against the prodynorphin product, dynorphin B (Dyn B). The PAP method was used on both colchicine and normal animals.

Caudal to the obex, within the commissural nucleus, there is extensive overlap of both immunoreactive m‐Enk and Dyn B terminals and cells. While the cells are morphologically similar, the immunoreactive dynorphin cells are somewhat larger. Rostral to the obex, there is a marked difference in the distribution of the two compounds. Immunoreactive m‐Enk terminals are concentrated medial to the solitary tract; there is minimal staining laterally. In contrast, immunoreactive Dyn B terminals are concentrated lateral to the solitary tract. The rostral cellular distribution of the two opioid peptides follows a similar pattern. The morphology of the medially located m‐Enk and laterally located Dyn B cells is also readily distinguished. The former are small, round cells with minimal dendritic labelling; the latter are larger, pyramidal neurons with prominent apical and basal dendrites. Since the medial and lateral nuclei of the solitary tract have been associated with cardiovascular and respiratory control, respectively, these data suggest that different endorphin families have different functional actions within the nucleus of the solitary tract.
An empirical assessment of stereological formulae applied to the counting of synaptic disks in the cerebral cortex
Authors: Colonnier Marc , Beaulieu Clermont
Published: January 2005

Known quantities of test objects approximating the parameters of cortical synapses were embedded in known volumes of a transparent embedding medium. The material was cut in slabs of appropriate thickness. The mean trace length (d) of the profiles of the test objects was measured and the number of profiles per unit area (NA) was calculated. Various stereological formulae were applied to these data to determine the number of test objects per unit volume (NV). For large numbers of those test objects most closely approximating the parameters of cortical synapses, the formula NV = NA/d and the DeHoff and Rhines formula ('61) for polydispersed circular disks NV = 8NAZ/π2 (where Z is the mean of the reciprocals of the trace lengths) gave accurate results (error ≤ 5%). Other popular formulae and procedures were not as accurate and underestimated their number by as much as 32%.
Synaptic organization of substance P‐like immunoreactive amacrine cells in goldfish retina
Authors: Yazulla Stephen , Studholme Keith M. , Zucker Charles L.
Published: January 2005

A class of amacrine cells in the goldfish retina displays substance P‐like immunoreactivity (SPIR). We studied the synaptic organization of SPIR amacrine cells by electron microscopical immunocytochemistry. Amacrine cells showing SPIR have processes which ramify in a very narrow band in layer 3 of the inner plexiform layer. SPIR is restricted to large dense‐cored vesicles (DCVs) which are distributed throughout the dendrites. Processes labeled with SPIR contain a mixture of DCVs and numerous small agranular vesicles. of 88 synaptic contracts analyzed, SPIR processes occurred as the presynaptic element 57 times and as the postsynaptic element 31 times. SPIR processes made synapses upon amacrine and ganglion cell dendrites with equal frequency and received synaptic input from both amacrine and bipolar cells. The stratification of SPIR amacrine cells in proximal sublamina α suggests that their synaptic interactions are restricted to “off” and “on‐off” neurons. However, this is in contrast to published electrophysiological data. Possible explanations for this discrepancy are discussed in detail.
Effects of age on meissner corpuscles: A study of silver‐impregnated neurites in mouse digital pads
Authors: Mathewson R. C. , Nava P. B.
Published: January 2005

Investigation focused on finding qualitative and quantitative evidence of age‐changes in the quantity of neural surface within Meissner corpuscles. These mechanoreceptors were studied in 53 mice (nine age‐groups) ranging from 1.7 to 24 months old. Forepaw digital pads were formalin‐fixed and frozen‐sectioned parallel to each digit and perpendicular to the skin. Serial sections were then silver‐impregnated to allow light microscopic examination of the neurites (axons) in corpuscles.

From young (1.7–7 months) to middle age (9–15 months), neurites became more coarse, tortuous, ramified, varicose, and thus more complex. At old age (18–24 months), neurites seemed attenuated and showed more of an irregular winding, twisted, or tangled pattern with less parallel orientation to the skin surface than the regular spiraled, looped, or arched pattern typical at young and middle ages. Corpuscle size appeared greatest at middle age, smallest at young age. Dermal papillae not occupied by corpuscular neurites were most abundant at old age.

The number of corpuscles per area and neurites per corpuscle decreased significantly with age, whereas the number of neurite bifurcations per corpuscle increased significantly. Morphometric analysis of neurites projected by a camera lucida onto a planimeter showed that the length of neurites meandering through a fixed interval of tissue increased significantly until age 12 months–evidence of increased tortuosity; the area of neurites measured within the same fixed interval, and the area of neurite terminals changed significantly as inverse parabolic functions of age–evidence of increased volume until middle age, which decreased thereafter.

The general trend of these changes implied growth at young age and atrophy at old age. Morphologic changes occurring mostly until middle age increased the surface area of each neurite, presumably to compensate for loss of neural surface caused by decreased number of corpuscles and neurites. However, this proposed compensatory response was lost after middle age as indicated by the morphologic changes thereafter.
Afferent influences on brain stem auditory nuclei of the chicken: Cessation of amino acid incorporation as an antecedent to age‐dependent transneuronal degeneration
Authors: Steward Oswald , Rubel Edwin W
Published: January 2005

Previous studies of the avian auditory system have revealed that removal of the peripheral receptor (the cochlea) leads to a transneuronal degeneration of auditory relay neurons in nucleus magnocellularis (NM) of the brain stem. An early manifestation of the degeneration which can be observed within 12 hours is a decrease of histochemical staining for RNA (Nissl staining); such a decrease could relect an alteration in protein synthetic activity within the NM neurons. The present study evaluates this possibility by determining whether the cochlea removal led to an alteration incorporation of protein precursors in the target neurons which exhibit transneuronal degeneration and if so, how early the changes appeared. The cochlea was removed unilaterally in seventeen 10‐day‐old chicks and two 66‐week‐old mature chickens, and incorporation of protein precursors was evaluated in the neurons of NM at 0.5, 1.5, 3, 6, 12, and 24 hours following the cochlea removal. Each chick received an intravenous injection of 3H leucine, and was allowed to survive for 30 minutes after the injection of precursor. The brains were then prepared for autoradiography. The extent of incorporation by neurons in NM was determined by counting grains overlying each cell body and determining grain density/μm2 of neuron cross‐sectional area.

We found that auditory relay neurons whose synaptic inputs have been silenced exhibit dramatic decreases in protein synthesis within 30 minutes after removal of the cochlea; leucine incorporation was reduced by about 50%. In chicks sacrificed 3 to 24 hours after removal of the cochlea, some neurons (about 1/3) were entirely unlabeled despite heavy labeling of their neighbors and heavy labeling of all NM neurons on the opposite side of the brain. The remaining neurons exhibited about a 15% reduction in incorporation in comparison with the cells in the contralateral (control) NM. While the decreases in incorporation were apparent at all survival intervals, there was no consistent decrease in Nissl staining until 6 hours after cochlea removal. There were no changes in protein precursor incorporation following removal of the cochlea in adult birds, a result which is in keeping with the relative absence of transneuronal degeneration following removal of the cochlea at maturity. The results suggest a very rapid transneuronal regulation of protein metabolism within target neurons in young animals, perhaps by activity‐related events.
Novel sources of descending input to the spinal cord of the hatchling chick
Authors: Gross Gayle H. , Oppenheim Ronald W.
Published: January 2005

Nuclear groups contributing supraspinal input to the spinal cord of the hatchling chick (Gallus domesticus) were determined by using the enzyme tracer horseradish peroxidase processed with tetramethylbenzidine histochemistry.

Five sources of projections to the spinal cord were found which have not been previously described in any species. All are probably related to autonomic function. They include ipsilateral hypothalamic projections from the lateral mamillary n., suprachiasmatic n., and n. of the lateral tubercle. There is a bilateral projection from the large interstitial cells of the mesencephalic posterior commissure, and in the myelencephalon, a mainly contralateral projection from interstitial cells of the vagus‐glossopharyngeal nerve.

Two other projections observed here have not been described in other avian species, one from the accessory vestibular n., the other, from the n. ambiguus. In the cerebellum, projections arise from the main and ventrolateral divisions of the fastigial n., and from “border cells” between the fastigial and interpositus n. The large‐celled submedial vestibular n. projects bilaterally.

Several projections previously described only in the pigeon, were confirmed here: the hypothalamic nucleus over the supramammilary decussation, the n. intercollicularis, the tangential n., and the n. alatus, a cell group between the hypoglossal and vagal nuclei.

Four sources of input projected only as far as mid‐cervical cord. These are n. intercollicularis, fastigial n., accessory vestibular n., and tangential n. All remaining projections reached to lower lumbosacral cord.

Sources of descending input are remarkably similar in mammals and avians. Where homologous nuclei exist, virtually identical projections to the cord are present.
Mapping and ultrastructure of serotonin‐immunoreactive neurons in the optic lobes of three insect species
Authors: Nässel Dick R. , Meyer Eric P. , Klemm Nikolai
Published: January 2005

With antibodies to serotonin (5‐HT) we have mapped immunoreactive neurons in the optic lobes of three insect species, the blowfly Calliphora, the desert ant Cataglyphis, and the worker bee Apis. The main emphasis in this investigation is on a system of 5‐HT‐positive neurons connecting the most peripheral neuropil of the optic lobes, the lamina, to more central neuropil regions. To aid in electron microscopical identification of these neurons we used immunocytochemistry at the EM‐level and Golgi‐EM for Calliphora and horseradish peroxidase (HRP) labelling for the other two insects.

The immunoreactive terminals in Calliphora and the HRP‐labelled ones in the other insects contain large (c. 100 nm) granular vesicles and smaller (c.60 nm) clear vesicles. In Cataglyphis and Apis the profiles with granular vesicles are presynaptic to second order neurons of the lamina, whereas in Calliphora no synaptic contacts were found. In this animal the 5‐HT‐positive terminals are situated distal in the synaptic layer of the lamina, in a region of retinal photoreceptor axons and perikarya of the lamina monopolar neurons.

In Catagylphis and Apis the interactions of the 5‐HT‐neurons with the laminar neurons might occur through chemical synapses, whereas in Calliphora neuroactive substance could be released non‐synaptically from varicosities distal to the synaptic layer. The possible involvement of 5‐HT in control of neuronal activity in the optic lobes is discussed.
Histological study of motor innervation of nuclear bag1 intrafusal muscle fibers in the cat
Authors: Kucera Jan
Published: January 2005

The nerve supply to spindles of the cat tenuissimus muscle was reconstructed with light and electron microscopy of serial transverse sections. Fifty‐two poles of the nuclear bag1 intrafusal muscle fiber were examined for motor innervation. The fiber poles were supplied by 71 myelinated motor axons that either terminated on bag1 fibers exclusively (93%) or coinnervated a chain fiber of the same intrafusal bundle (7%). No axons coinnervated both the bag1 and bag2 fibers. The unmyelinated preterminal segments of the axons were frequently short. Lengths and pre‐ and postsynaptic features of motor endings on bag1 fibers were variable. These features did not permit reliable classification of the endings into more than one morphological category. Moreover, the terminals of fusimotor (γ) and skeletofusimotor (β) axons on bag1 fibers appeared similar in cross‐section. The degree of indentation of axon terminals into the surface of bag1 fibers increased with increasing distance from the spindle equator. However, cross‐sectional areas of sole plates and axon terminals were relatively constant regardless of distance from the equator. The subjunctional membranes of both γ and β bag1 endings were typically smooth in contour. Bag1 endings differed from those on bag2 and typical chain fibers in having a thicker sole plate, frequently indented axon terminals, and unfolded subjunctional membranes. None of the bag1 endings resembled an extrafusal end plate. These observations indicated that (1) the dynamic (bag1) and static (bag2 and chain) intrafusal systems of the cat spindle are under separate motor control, and (2) the type of intrafusal fiber and the distance of the motor ending from the equator have a greater influence on the form and structure of bag1 endings than do supplying axons.
Ontogeny of the visual system in the cuttlefish, Sepiella japonica. I. Morphological differentiation of the visual cell
Authors: Yamamoto Masamichi
Published: January 2005

To provide morphological bases for functional studies, the differentiation of photoreceptors in the retina of a cuttlefish, Sepiella japonica, was examined by electron microscopy. Development of the retina occurs in four phases. In phase 1 (stages 21–23), the retinal epithelium consists of uniform columnar cells. In phase 2 (stages 24–29), the epithelial cells are classified into light and dark cells on the basis of the electron‐density of their cytoplasm. The perikarya of the light cells are located in the distal half of the epithelium, each extending proximally (i.e., sclerad) a thin foot, which protruded out of the epithelium through a narrow break in the basal lamina. The nuclei of the dark cells are distributed in the proximal half of the epithelium. Both cell types have a short cilium in the distal end. In phase 3 (stages 30–35), the light and the dark cells morphologically differentiate into receptor and supporting cells, respectively. The distal end of the light (receptor) cell begins to form an apical process, which gives off short irregular microvilli from its lateral surface. Beneath the basal lamina the feet of the receptor cells swell and the nuclei migrate into them through narrow breaks in the basal lamina. Thus, at the end of phase 3, each receptor cell becomes divided into an outer and inner segment. In phase 4 (stages 36–40), the receptor cells complete the specific structure as photoreceptive cells. The microvilli arising from the apical processes increase in length, density, and regularity to be organized into rhabdomes. The lamellated membranes of the myeloid bodies appear first in the outer segment and later increase in number in the inner segment. Morphometric data on the rhabdomeric microvilli in the adult and embryonic retinas are presented.
Selective retinal reinnervation of a surgically created tectal island in goldfish. II. Electron microscopic analysis
Authors: Edwards M. A. , Murray M.
Published: January 2005

In the preceding study (Edwards et al., 1985), we showed that regenerating optic axons reestablish a topographically restricted projection to a caudal tectal island created by surgical removal of a 1‐mm‐wide strip of caudal tectum in goldfish. In the present ultrastructural study, we evaluated the dependence of this axonal outgrowth on the presence of tectal target tissue caudal to the gap. Axon counts in the lesion zone were compared between cases with complete caudal tectal ablation and cases with ablation sparing a caudal tectal island (with and without optic nerve crush). During the postoperative interval of 20–50 days (early period), up to about 1,000 unmyelinated axons with features characteristic of optic axons were present in numerous small subpial bundles in both preparations. In the subsequent interval of 50–110 days (middle period), less than 200 axons were counted caudal to simple half‐tecta, whereas 4,000–14,000 myelinated and unmyelinated axons were present in a few large bundles which crossed the lesion zone of tectal island cases. In this period, optic terminals could be demonstrated in the tectal island using the anterograde horseradish peroxidase method. At 170–300 days after surgery (Late period), bridging bundles contained between 2,000 and 6,000 largely myelinated axons. We conclude that caudal tectal tissue is not necessary for the initial outgrowth of a small number of axons beyond a rostral half‐tectum. The target is essential, however, for the maintenance of these axon fascicles and for the subsequent massive outgrowth of axons to the island. The contributions of glial guidance, diffuse exploratory outgrowth, and target‐produced trophic factors to the formation of an initially exuberant projection to the island are discussed. A process of selective axon collateral withdrawal is proposed to account for the decrease in axon numbers within bridging bundles in the late period and for the late restriction in the retinal origin of the island projection indicated by results in the preceding study (Edwards et al., '85).
Ultrastructural characterization of gonadotropin‐releasing hormone (GnRH)‐producing neurons
Authors: Jennes Lothar , Stumpf Walter E. , Sheedy Mary E.
Published: January 2005

By means of preembedding immunohistochemistry, two types of gonadotropin‐releasing hormone (GnRH) positive neurons in the rat could be identified and characterized in the preoptic region and in the diagonal band: (1) a “smooth” GnRH neuron with relatively even cytoplasmic contours, and (2) a “spiny” GnRH neuron with thorn‐like protrusions of the perikaryon and cell processes. Both cell types contain the same organelles in similar number and distribution, but they differ in the number of synaptic contacts. In general, GnRH cell bodies have a large round or ovoid nucleus, well‐developed rough endoplasmic reticulum arranged in multilayered stacks or as individual cisternae, and several Golgi complexes. Lysosomes are not numerous under the conditions studied. Specializations include kinocilia, nematosomes, and lamellar whorls. Throughout the cytoplasm, scattered dense core vesicles with a diameter of 100 nm and clear vesicles with a diameter of 30–40 nm can be seen with a preferential localization close to the cell membrane. The cell processes of smooth GnRH cells close to the perikaryon appear as extensions of the perikaryal cytoplasm with all organelles except the nucleus. The two neurites originate from the perikaryon as tapering cones over a distance of 200–300 μm, until they reach a diameter of 0.5–3 μm. Cell processes of spiny GnRH cells show bifurcations, protrusions, or invaginations and contain clear and dense core vesicles in their spines. In areas distant from the perikaryon, immunoreactive fibers with a large number of dense core and clear vesicles can occasionally be seen to terminate synaptically or asynaptically on other neurons. The GnRH neurons show postsynaptic specializations at the level of the perikaryon and at cell processes, when apposed by a presynaptic terminal. Such synaptic contacts are seen less frequently on smooth cells than on spiny cells. Large areas of the GnRH cell may be covered by a thin glial lamella, which separates the cell body from the surrounding neuropil. The results indicate the existence of two populations of GnRH cell bodies with different patterns of innervation, which suggest different integrative capacities.
Cobalt injected into the right and left fasciculi retroflexes clarifies the organization of this pathway
Authors: Kemali M. , Làzàr G.
Published: January 2005

A cobaltic lysine complex was injected separately into the right and left fasciculi retroflexes of the frog. This tracing technique labeled, in a Golgi‐like manner, the neurons which initiate the fasciculi retroflexes and revealed details of their morphological pattern.

The fasciculi retroflexes originate from various neurons distributed in the diencephalon and mesencephalon, but their main source is the habenular nuclei. In the frog there are dorsal and ventral habenulae which are homologous to the medial and lateral habenulae, respectively, of mammals. In the frog the dorsal habenulae are strikingly asymmetric.

Our study shows that the fasciculus retroflexus is composed of several compact separated bundles of fibers and that the fibers originating from the dorsal habenular nuclei project to the interpeduncular nucleus, while those originating from the ventral habenular nuclei project beyond the interpeduncular nucleus, but so far we have not been able to show the exact site of their termination.

The labeling of cells within the interpeduncular nucleus raises the possibility that the habenulo‐interpeduncular tract is reciprocal in function.

The finds support our previously reported hypothesis on the theoretical interpretation of the functional circuitry of the frog habenulo‐interpeduncular system.
A morphological study of glial cells in the hypoglossal nucleus of the cat during nerve regeneration
Authors: Cova John L. , Aldskogius Håkan
Published: January 2005

The cat hypoglossal nerve and nucleus have been used as a model for the study of the occurrence and time course of modifications in the size and composition of the perineuronal glial cell population as they relate to cytological changes in the nerve cell body and the initiation and progress of axon regeneration. Animals were killed at 2, 5, 10, 20, 35, 65, and 115 days after crush injury to the hypoglossal nerve. At 5 days after surgery, growth cones and regenerating unmyelinated axons were present at the lesion site, but no conspicuous changes were apparent in the nerve cell bodies. At 10 days after surgery, the granular endoplasmic reticulum was disaggregated and depleted. The elongation phase appeared to be completed at 20 days, as judged by the bilateral retrograde labeling of the hypoglossal nuclei with horseradish peroxidase. By 35 days, the cytoarchitecture of the nerve cell bodies and maturation of axons, as determined by a comparison of the relative frequency distribution of cross sectional areas proximal and distal to the lesion, were completely restored. Comparative quantitative light microscopic examination of the hypoglossal nuclei of intact and experimental animals failed to reveal any statistically significant differences in the total number of glial cells, number of glial cells/unit area of neuropil, or relative proportions of glial cell types at any of the postoperative time intervals. Moreover, electron microscopic quantitation of the microglial cell population did not reveal any significant alterations in the number, density, location, or morphology of these cells. These results demonstrate that perineuronal glial cell proliferation or changes in the composition of the glial cell population are not attendant on retrograde changes in the cat hypoglossal nucleus or a necessary concomitant to successful axon regeneration.