bluuebunny/crossref_metadata_2025 huggingface dataset:
Immunocytochemical investigation of L‐glutamic acid decarboxylase in the rat hippocampal formation: The influence of transient cerebral ischemia
Authors: Johansen Flemming‐Fryd , Lin Chin‐Tarng , Schousboe Arne , Wu Jang‐Yen
Published: January 2005

The hippocampus is especially vulnerable to ischemic damage. Neurons in the CA3c region and dentate hilus demonstrate fast progressive damage while CA1 pyramidal cells demonstrate delayed neuronal damage. The delayed CA1 pyramidal cell loss could be caused by postischemic neuronal hyperactivity if hippocampal interneurons are lost after ischemia. Therefore we have counted the L‐glutamic acid decarboxylase (GAD)‐immunoreactive neurons in the hippocampus from control rats and rats surviving 4 or 11 days after 20 minutes of cerebral ischemia. All rats were injected intraventricularly with colchicine before they were killed.

The hippocampal cell counts showed an increase in GAD‐immunoreactive somata visualized on the fourth postischemic day. Eleven days after ischemia, the number of GAD‐immunoreactive neurons visualized in the hippocampus CA1 and CA3c region decreased. GAD‐immunoreactive baskets were visualized in the pyramidal cell layer and the granule cell layer in controls and 4 days after ischemia, but not in the CA1 and CA3c pyramidal cell layer 11 days after ischemia.

We suggest the number of GAD‐immunoreactive neurons visualized on the fourth postischemic day increases because somatal GAD accumulation increases and, therefore, ischemia may enhance GAD production. Our previous counts of CA1 interneurons 21 days after ischemia in toluidine‐stained semithin sections demonstrated no interneuron loss. Therefore we suggest that the decreased number of CA1 and CA3c GAD‐immunoreactive neurons visualized 11 days after ischemia is related to a decreased GAD production. It is possible at this stage after ischemia that the interneurons have decreased their GAD production because they have lost their input and/or target cells.

We conclude that our counts of GAD‐immunoreactive neurons visualized after ischemia express changes in the content of somatal GAD rather than the actual number of GAD‐immunoreactive somata. Finally, we conclude that the delayed loss of CA1 pyramidal cells seen 4 days after ischemia is not preceded by loss of hippocampal GAD‐immunoreactive neurons.
Serotoninergic neurons in the mormyrid brain and their projection to the preelectromotor and primary electrosensory centers: Immunohistochemical study
Authors: Grant K. , Clausse S. , Libouban S. , Szabo T.
Published: January 2005

Serotonin‐containing neurons in the brain of the weak‐electric fish Gnathonemus petersii (mormyridae, teleostei) were studied with the aid of immunohistochemical labeling. Study of the central serotoninergic innervation was focused on the structures subserving the command of the electric organ and the first central relay of the electrosensory system.

In the midline raphe nuclei, serotoninergic neurons formed a column that stretched from the ventral caudal medulla to the dorsal midbrain, ending caudal to the cerebellar peduncle. In the dorsal tegmentum, serotoninergic neurons were found bilaterally at the anterior margin of the decussation of the lateral lemniscus. Labeled neurons were also present bilaterally immediately anterior to the cerebellar peduncle and also in the pretectal region. In the hypothalamus, many serotoninergic neurons were in contact with the ventricular wall, and a few were present in the preoptic area. This distribution of serotoninergic cell bodies showed many similarities to that in other fish and higher vertebrates but lacked the lateral spread of the serotoninergic raphe system found in the midbrain tegmentum in mammals.

Labeled fibers were found in both the preelectromotor medullary relay nucleus and the electromotor command nucleus. These serotoninergic projections were traced to the posterior raphe. Serotoninergic fibers also formed a dense network in the cortex and in the nucleus of the electrosensory lobe, both of which receive primary input from electroreceptors.

These results suggest that serotonin may have a role in the modulation of the intrinsic, rhythmic electromotor command and in the gating of electrosensory input.
Neurogenesis of glutamic acid decarboxylase immunoreactive cells in the hippocampus of the mouse. I: Regio superior and regio inferior
Authors: Soriano Eduardo , Cobas Alberto , Fairén Alfonso
Published: January 2005

The neurogenetic gradients of neurons showing glutamic acid decarboxylase (GAD) immunoreactivity were determined in the regio superior and in the regio inferior of the mouse hippocampus. Pregnant C57B1 mice received pulse injections of (3H)thymidine from E11 through E17 (E0 being the day of mating). Distributions of (3H)thymidine‐labeled, GAD‐positive neurons in the different strata of the hippocampus proper were recorded in adult animals. GAD‐positive neurons in this region are generated prenatally. Radial gradients of neurogenesis of GAD‐positive cells are characterized by two main features: (1) with the exception of the stratum lacunosum‐moleculare and its interface with the stratum radiatum, GAD‐positive neurons of the plexiform strata are generated before those destined for the pyramidal layer; (2) within the pyramidal layer, GAD‐positive cells are positioned according to an inside‐out sequence. In the transverse axis, neurogenesis of GAD‐positive cells follows a regio inferior to regio superior gradient. This gradient is due to prolonged neurogenesis of GAD‐positive cells for the pyramidal layer in the regio superior. Given the selective laminar disposition of the GABAergic interneurons in the hippocampus, the present authors explored whether or not the diverse types of these interneurons could have specific birth dates and concluded that no relationship exists between birth dates and adult phenotypes of GAD‐immunoreactive cells in the mouse hippocampus proper.
Structure‐function relationships in rat brainstem subnucleus interpolaris: III. Local circuit neurons
Authors: Jacquin Mark F. , Golden Judy , Rhoades Robert W.
Published: January 2005

Intracellular recording, electrical stimulation, receptive field mapping, and intracellular injection of horseradish peroxidase were used to assess the response properties, collateral projections, and morphology of 44 local circuit (LC) neurons in the subnucleus interpolaris (SpVi) of the trigeminal brainstem complex of the rat. LC neurons were defined as those with axons restricted to brainstem areas receiving trigeminal primary afferent fibers. Thus, none were antidromically activated from the thalamus, tectum, or cerebellum, and their axons could be seen terminating exclusively within the trigeminal brainstem complex or reticular formation. All neurons sampled were discharged by innocuous or noxious mechanical stimulation of a restricted portion of the face or mouth. They were classified functionally as sensitive to vibrissae (N = 22), nociceptors (N = 9), guard hairs (N = 7), hairy skin (N = 3), or periodontia (N = 3). Fifty percent of the stained neurons were vibrissa sensitive. Twenty‐one of these 22 responded to deflection of only one vibrissa. The remaining functional groups also had small receptive fields.

Intracellular staining revealed a consistency in vibrissa‐sensitive LC morphology. Somata were small to medium in size and multipolar. Their axons had an initial transverse trajectory and gave off recurrent collaterals which arborized extensively in the region of the soma. The parent axon then bifurcated. One branch traveled rostrally to subnucleus principalis while the other branch traveled caudally to subnucleus caudalis. The branches periodically sent collaterals into regions of the trigeminal complex corresponding to the transverse position of the soma. Dendrites extended 440 ± 140 μm rostrocaudally, forming a tree with a transverse perimeter of 459 ± 226 μm. Distal dendrites were thin and sinuous, had few spines, and extensively arborized adjacent to the soma. They ended in multiple swellings connected by slender processes.

The stereotyped morphology of vibrissa‐sensitive LC neurons differed from the variable morphologies of LC neurons activated by nociceptors, guard hairs, hairy skin, or periodontia. Although no group of neurons in one of these categories displayed a distinguishing morphological characteristic, they collectively had features which distinguished them from the vibrissa‐sensitive neurons. Non‐vibrissa‐responsive neurons generally had more expansive, but less circular, dendritic and recurrent axonal arbors; dendrites had more spines, and axons often sent endings into the reticular formation. Some did not display rostrally and caudally directed axon bifurcation, while others branched more extensively than vibrissa LC cells. Nociceptors tended to be located in the V spinal tract, rostrally displaced substantia gelatinosa, or in the border regions between SpVi and the reticular formation.
Light microscopic study of degenerating cobalt‐filled optic axons in goldfish: Role of microglia and radial glia in debris removal
Authors: Springer Alan D. , Wilson Bryan R.
Published: January 2005

Labeling severed axons with cobaltous‐lysine ultimately leads to the degeneration of their distal segments. The present study was designed to determine whether microglia and radial glia have comparable roles in the elimination of degenerating axons. Another purpose was to determine whether the cobalt could escape from degenerating axons and enter intact neuronal cells. Optic axons were filled with cobaltous‐lysine for 1 day and the retinal projections were examined from 1 to 106 days later. Optimal filling was obtained 1 day postlabeling. The number of filled axons in the optic tract was significantly reduced at the 2‐day time point, indicating that many axons had disintegrated. Many axons contained large swellings that resembled cells. However, transneuronally labeled neuronal cells were never observed. Labeled, rounded microglia appeared among the degenerating axons at the 3‐day time point, and the microglia changed shape at 5 days. They became elongated and manifested many processes. In addition, the microglia began to move toward, and entered, the ventricles and vasculature. Virtually all the labeled debris was removed between 17 and 28 days following the application of cobalt. The rapidity with which the axons were removed suggests that the cobalt accelerates the degenerative process either directly, or indirectly by accelerating the arrival of phagocytic cells.

Radial glia appeared to play a smaller role in debris elimination. They took up labeled debris to a lesser degree than microglia and were briefly labeled. Interestingly, radial glia did not take up cobalt when it was injected intracranially and diffused through the brain. A previous claim of an axosomatic retinotectal projection to cells deep in the stratum periventriculare of a teleost fish is reinterpreted to represent cobalt within radial glia.
Subcortical projections to the pontine nuclei in the cat
Authors: Aas Jan‐Erik
Published: January 2005

In a systematic attempt to trace all projections from the brainstem and diencephalon to the pontine nuclei of the cat, implantations and injections of horseradish peroxidase‐‐wheat germ agglutinin (HRP‐WGA) or Fluoro‐Gold were placed in the pontine nuclei of 21 cats. In most of the cases there was no evidence of spread of tracer outside the pontine nuclei. Retrogradely labeled cells in the brainstem and diencephalon were carefully mapped and counted.

The number of labeled cells in the brainstem and diencephalon ranged from 24 in cases with very small implantations to 3,490 in cases with large injections in the pontine nuclei (counts from every fifth section). The labeled cells are located bilaterally with an ipsilateral preponderance. After large injections, 25‐38% of the labeled cells were located in the brainstem reticular formation, 10‐16% in the pretectal nuclei, 10‐15% in the hypothalamus, 7‐9% in the zona incerta, 3‐9% in the fields of Forel, 4‐5% in the nucleus locus coeruleus, 3‐5% in the ventral lateral geniculate body, 2‐4% in the superior colliculus, 3% in the periaqueductal gray, and 14‐15% in other parts of the brainstem.

Judging from cases with small tracer deposits entirely confined to the pontine nuclei, there appear to be two types of subcortical inputs: Projections from the reticular formation, the nucleus locus coeruleus, the periaqueductal gray, and the raphe nuclei are widespread, presumably reaching all parts of the pontine nuclei, while projections from a diversity of other sources are localized, reaching limited parts of the pontine nuclei only or predominantly.
Effects of intraocular tetrodotoxin on the development of the retinocollicular pathway in the syrian hamster
Authors: Thompson Lan , Holt Christine
Published: January 2005

The developing uncrossed retinocollicular projection in the Syrian hamster undergoes a characteristic set of changes during the first 2 postnatal weeks. The retinal fibres, which initially project across the whole superior colliculus, withdraw from the caudal part and their terminals become clustered into deep, discrete clumps rostrally. Coincident with these afferent changes, there is substantial retinal ganglion cell death. To examine whether neuronal activity plays a role in these changes, we made daily injections of the sodium channel blocker tetrodotoxin (TTX) into one or both eyes from postnatal day 2 or 4 up to day 12.

Following TTX treatment, the uncrossed terminals retracted on schedule from the caudal and superficial parts of the superior colliculus and came to lie, as normal, in the deep layers rostrally. Within the rostral superior colliculus, however, the uncrossed terminals from TTX‐injected eyes lost their characteristic patchy distribution and were arranged diffusely. When only one eye received TTX injections, this inhibiting effect on terminal segregation was seen only in the projections from the TTX‐treated eye. The effect of TTX treatment on terminal segregation was much less severe than that of unilateral enucleation, after which uncrossed terminals persist throughout the entire superior colliculus.

TTX injections appeared to have little effect on overall ganglion cell death since the total number of ganglion cells in the crossed projection from TTX‐treated eyes was similar to that in normal eyes. However, the relative distribution of uncrossed cells in temporal and nasal retina was altered. In eyes that received TTX injections, the proportion of uncrossed cells in nasal retina was about 1.6 times that in normal animals and was close to the proportion seen in unilaterally enucleated animals. This increase in the treated eye occurred whether one or both eyes were injected with TTX.

We conclude that neuronal activity plays a role in the segregation of uncrossed terminals into discrete clumps in rostral colliculus and in the preferential elimination of uncrossed cells from the nasal retina. The inactive uncrossed projections from TTX‐treated eyes showed the greatest degree of disruption. The extent of the disruption was similar whether the crossed input from the other eye was active or inactive. This suggests that the activity‐driven interactions between ganglion cells within one eye are more significant than those between the two eyes in shaping the final form of the uncrossed retinocollicular projection.
Cytoarchitectural characteristic of the frontal eye fields in macaque monkeys
Authors: Stanton G. B. , Deng S.‐Y. , Goldberg E. M. , McMullen N. T.
Published: January 2005

The cytoarchitecture of the prearcuate gyrus, including the region of the physiologically defined frontal eye fields (FEF), was studied in four macaque monkeys (Macaca fascicularis, M. mulatta) to determine if the FEF could be anatomically identified. Brain sections were stained with standard Nissl and, in some cases, myelin stains.

Two nonstandard planes of section were used: one tangential to the prearcuate gyrus and the second normal to the most posterior bend of the prearcuate gyrus. The first plane of section was advantageous for studying the location of the FEF with reference to the entire medial‐lateral extent of the gyrus and the second allowed good comparisons of the FEF to adjacent anterior and posterior cortical areas. Frontal plane sections through the prearcuate gyrus were also examined in 15 macaque monkeys for comparison with sections cut normal to the posterior bend of the gyrus and tangential to the gyrus.

Intracortical microstimulation was performed in three monkeys. The FEF was defined as the area from which low‐threshold (≤50 μA) saccades could be evoked. The area extended about 10 mm along the anterior bank of the arcuate sulcus. Within the area, saccade amplitudes were represented in a mediolateral, large‐to‐small topography. No topography of saccade direction was noted within FEF but reversals of saccade direction for any given electrode pass were found. These results confirm the results from our earlier mapping study of FEF (Bruce et al.: J. Neurophysiol. 54:714‐734, '85).

Cell bodies of large pyramidal cells in layers III and V of the prearcuate gyri from three hemispheres were measured with the aid of an image‐combining computer microscope. The distribution of cells of >22 μm diameter or cross‐sectional areas of <500 μm2 were plotted. In one monkey, marker lesions made at microstimulation sites within the FEF or in adjacent non‐FEF areas were also plotted. The location of the FEF appeared to coincide with the concentration of large layer V pyramidal cells in the prearcuate gyrus rather than with any previously mapped cytoarchitectonic area. The numbers of large pyramids in layer V were noticeably reduced along the lip of the prearcuate gyrus and at dorsomedial and ventrolateral locations which were outside the physiologically defined FEF.
Laminar and areal differences in the origin of the subcortical projection neurons of the rat somatosensory cortex
Authors: Killackey Herbert P. , Koralek Katherine‐Ann , Chiaia Nicholas L. , Rhoades Robert W.
Published: January 2005

Fluorescent retrograde tracing techniques were employed in a double‐labelling paradigm to determine the distribution of corticospinal, corticotectal, and corticotrigeminal projection neurons in layer Vb of the adult and neonatal rat somatosensory cortex. The double‐labelling paradigm allowed a direct comparison of the cortical distribution of neurons projecting to each target and identification of neurons projecting to more than one target.

In the adult rat, each population of projection neurons was found to have a unique laminar and/or areal distribution. Corticospinal projection neurons were located throughout the width of layer Vb in the medial granular portion of somatosensory cortex, while corticotrigeminal projection neurons were distributed throughout the width of layer Vb in the more laterally located dysgranular portion of somatosensory cortex. Corticotectal projection neurons were located more superficially in layer Vb than either corticospinal or corticotrigeminal projection neurons and found scattered throughout both dysgranular and granular somatosensory cortex. Each combination of subcortical injections also resulted in double labelling a small percentage of uniquely distributed neurons. These distribution differences coupled with measurements of cell size allowed us to identify the parent population of the dual projection neurons. Subpopulations of corticotectal neurons also project to the brainstem trigeminal complex and to the spinal cord. Subpopulations of corticotrigeminal neurons also project to the spinal cord, and a proportion of corticotrigeminal neurons projects to at least two targets within the brainstem trigeminal complex (nucleus principalis and subnucleus interpolaris). In the adult rat, corticospinal neurons (as defined by either laminar position or somal size) did not appear to give off collaterals to either the superior colliculus or brainstem trigeminal complex.

In the neonatal rat, double‐labelled neurons which project to both the spinal cord and the tectum are distributed throughout the full width of layer Vb, rather than restricted to the superficial portion of the layer as in the adult rat. Further, it appears as if the ontogenetic change in the laminar distribution of corticospinal and tectal projection neurons is achieved by mechanisms of selective process elimination rather than cell death.

These results are discussed in terms of both the developmental factors which may contribute to the discrete distribution of cortical projection neurons found in the adult and the functional significance of bifurcating projection neurons.
Plasticity of frequency organization in auditory cortex of guinea pigs with partial unilateral deafness
Authors: Robertson Donald , Irvine Dexter R. F.
Published: January 2005

We have examined the effect of restricted unilateral cochlear lesions on the orderly topographic mapping of sound frequency in the auditory cortex of adult guinea pigs. These lesions, although restricted in spatial extent, resulted in a variety of patterns of histological damage to receptor cells and nerve fibres within the cochlea. Nevertheless, all lesions resulted in permanent losses of sensitivity of the cochlear neural output across a limited frequency range. Thirty‐five to 81 days after such damage to the organ of Corti, the area of contralateral auditory cortex in which the lesioned frequency range would normally have been represented was partly occupied by an expanded representation of sound frequencies adjacent to the frequency range damaged by the lesion. The thresholds at their new characteristic frequencies (CFs) of clusters of cortical neurones in these regions were close to normal thresholds at those frequencies (mean difference across all animals was 3.8 dB). In a second series of experiments, the responses of neurone clusters were examined within hours of making similar cochlear lesions. It was found that shifts in CF toward frequencies spared by the lesions could occur, but thresholds were greatly elevated compared to normal (mean difference was 31.7 dB in five animals). The emergence of sensitive drive in such regions after prolonged recovery periods in lesioned animals thus suggests that the auditory cortical frequency map undergoes reorganization in cases of partial deafness. Some features of this reorganization are similar to changes reported in somatosensory cortex after peripheral nerve injury, and this form of plasticity may therefore be a feature of all adult sensory systems.
Survey of noncortical afferent projections to the basilar pontine nuclei: A retrograde tracing study in the rat
Authors: Mihailoff G. A. , Kosinski R. J. , Azizi S. A. , Border B. G.
Published: January 2005

The retrograde transport of the conjugate wheat germ agglutinin–horseradish peroxidase (WGA‐HRP) was used in the rat to identify the cell bodies of origin for all subcortical projections to the basilar pontine nuclei (BPN). A parapharyngeal surgical approach was used to allow the injection micropipette to enter the BPN from the ventral aspect of the brainstem and thus avoid any potential for false‐positive labeling due to transection and injury‐filling of axonal systems located dorsal to the basilar pontine gray.

A surprisingly large number of BPN afferent cell groups were identified in the present study. Included were labeled somata in the lumbar spinal cord and a large variety of nuclei in the medulla, pons, and midbrain, as well as labeled cells in diencephalic and telencephalic nuclei such as the zona incerta, ventral lateral geniculate, hypothalamus, amygdala, nucleus basalis of Meynert, and the horizontal nucleus of the diagonal band of Broca.

Quite a number of cell groups known to project directly to the cerebellum also exhibited labeled somata in the present study. To explore the possibility that such neurons were labeled because their axons were transected and injury‐filled as they coursed through the BPN injection site to enter the cerebellum via the brachium pontis, a series of rats received complete, bilateral lesions of the brachium pontis followed 30‐60 minutes later with multiple, diffuse injections of WGA‐HRP (12‐16 placements per animal) throughout the cerebellar cortex. In another series of animals, the massive cerebellar WGA‐HRP injections were not preceded by brachium pontis lesions. In the latter cases, each of the cell groups in question that were known to project directly to the cerebellum exhibited labeled somata. However, when the cerebellar HRP injections were preceded by brachium pontis lesions, each of the cell groups in question continued to exhibit labeled somata in numbers comparable to that observed in the nonlesion cases. This implies that such neurons project to the BPN and the cerebellar cortex and that the axons of these particular neurons do not project to the cerebellum via the brachium pontis.
Collateral projections of predorsal bundle cells of the superior colliculus in the rat
Authors: Bickford Martha E. , Hall William C.
Published: January 2005

The deep layers of the superior colliculus contain cells which are premotor in the sense that they respond prior to the onset of shifts in gaze and send axons, by way of a pathway called the predorsal bundle, to the contralateral brainstem gaze centers and cervical spinal cord. Previous studies have suggested that these cells also contribute to other efferent pathways which arise in the deep layers. The present study examines the contributions of the cells of origin of the predorsal bundle to these additional pathways as a step toward understanding their roles in gaze mechanisms. In one series of experiments, retrograde tracers were used to compare the laminar distribution of predorsal bundle cells with the distributions of the cells of origin of three other pathways: those that project to the intralaminar region of the dorsal thalamus, those that project to the contralateral superior colliculus, and those that project to the ipsilateral brainstem tegmentum. Predorsal bundle cells were found primarily in stratum griseum intermedium sublayer b. This distribution overlaps extensively with the distribution of colliculus cells that project to the intralaminar region of the thalamus. In contrast, the majority of the colliculus cells that project to either the contralateral superior colliculus or the ipsilateral brainstem tegmentum do not overlap extensively with the predorsal bundle cells; instead, they are primarily located dorsal or ventral to sublayer b of stratum griseum intermedium. In a second series of experiments, two regions were injected with different retrograde fluorescent tracers in single animals in order to study the collateral projections of the cells of origin of these pathways. The results indicate that many predorsal bundle cells project to the intralaminar region of the dorsal thalamus but that only a few contribute to the tectotectal pathway. The results also indicate that few tectotectal cells contribute to the ipsilateral tectobulbar pathway.
Bed nucleus of the stria terminalis: Cytoarchitecture, immunohistochemistry, and projection to the parabrachial nucleus in the rat
Authors: Moga Margaret M. , Saper Clifford B. , Gray Thackery S.
Published: January 2005

The bed nucleus of the stria terminalis (BST) sends a dense projection to the parabrachial nucleus (PB) in the pons. The BST contains many different types of neuropeptidelike immunoreactive cells and fibers, each of which exhibits its own characteristic distribution within cytoarchitecturally distinct BST subnuclei. Corticotropin releasing factor (CRF)‐, neurotensin (NT)‐, somatostatin (SS)‐, and enkephalin (ENK)‐like immunoreactive (ir) neurons are particularly numerous within areas of the BST that project to the PB. In this study, we use the combined retrograde fluorescence‐immunofluorescence method to determine whether neurons in the BST that project to the PB contain these immunoreactivities. After Fast Blue injections into PB, retrogradely labeled neurons were numerous throughout the lateral part of the BST, particularly in the dorsal lateral (DL) and posterior lateral subnuclei. Retrogradely labeled neurons were also present in the preoptic, ventral lateral, and supracapsular BST subnuclei and in the parastrial nucleus. Many of the CRF‐ir, NT‐ir, and SS‐ir neurons in DL were retrogradely labeled. A few double‐labeled cells of each type were also found in the posterior lateral, ventral lateral and supracapsular BST subnuclei ENK‐ir neurons were never retrogradely labeled. Our results show that BST neurons that project to the PB stain for the same neuropeptides as those in the central nucleus of the amygdala (CeA) that project to the PB, demonstrating further the close anatomical relations between these two structures.
Morphology and distribution of neurons in the retina of the american garter snake Thamnophis sirtalis
Authors: Wong R. O. L.
Published: January 2005

American garter snake Thamnophis sirtalis, retina correspond to the retinal mosaic viewed in the living eye (Land and Snyder, Vision Res. 11:105–114, '85). The garter snake has three major morphological types of cones; large single cones, small single cones, and double cones. The brightly reflecting components seen in the living eye are large single cones and principal cones of double cones, whereas irregularly spaced dark regions within this mosiac mark the positions of small single cones. The “sparkle” of the retinal mosaic originates from the ellipsoid region of the cones where microdroplets of high refractive index are densely packed. Unlike conventional oil droplets, these microdroplets reside adjacent to mitochondrial cristae within the ellipsoid. However, the microdroplets may function collectively as a single large oil droplet to increase the angular sensitivity of the inner segments, thus reducing a potentially large Stiles–Crawford effect predicted for this geometrically small eye.

The ganglion cell layer of the garter snake comprises two morphologically distinct populations of presumed neurons; classical neurons and microneurons. Density distribution maps for neurons in the ganglion cell layer and the photoreceptor layer reveal the presence of a putative area centralis and a horizontal visual streak. The topography of large cones parallels that of classical neurons. Small single cones have a more circular distribution, but also peak in density at the area centralis. The convergence of cones to classical neurons is lowest at the area centralis, 2.5:1, and highest, 4:1, at the retinal edge.

With its interesting structural features, the garter snake retina provides helpful insight into different strategies in eye design.
Retrograde double‐labeling study of the marnmillothalamic and the mammillotegmental projections in the rat
Authors: Hayakawa Tetsu , Zyo Katuya
Published: January 2005

Collateral axonal branching from the medial or lateral mammillary nuclei to the anterior thalamus, Gudden's tegmental nuclei, the nucleus reticularis tegmenti pontis, and the medial pontine nucleus was studied using the fluores‐ cent retrograde double‐labeling method. One day after injection of Fast Blue into the anterior thalamic nuclei or Gudden's tegmental nuclei, Nuclear Yel‐ low was injected into Gudden's tegmental nuclei or the nucleus reticularis teg‐ menti pontis and the medial pontine nucleus. Following 1day survival, single‐ and double‐labeled neurons were examined in the mammillary nuclei.

The lateral mammillary nucleus contains neurons whose collateral fibers project to both the dorsal tegmental nucleus of Gudden and the ipsilateral or contralateral anterodorsal thalamic nucleus, to both the medial pontine nucleus and the anterodorsal thalamic nucleus, and to both the dorsal tegmen‐ tal nucleus of Gudden and the medial pontine nucleus. The pars medianus and pars medialis of the medial mammillary nucleus contain neurons whose collat‐ eral fibers project to both the anteromedial thalamic nucleus and the ventral tegmental nucleus of Gudden, to both the anteromedial thalamic nucleus and the medial part of the nucleus reticularis tegmenti pontis, and to both the ven‐ tral tegmental nucleus of Gudden and the medial part of the nucleus reticu‐ laris tegmenti pontis. The dorsal half of the pars posterior of the medial mam‐ millary nucleus contains a few neurons whose collateral fibers project to both the anteromedial thalamic nucleus and the rostral part of the ventral tegmen‐ tal nucleus of Gudden, and to both the caudal part of the anteroventral thal‐ amic nucleus and the rostral part of the ventral tegmental nucleus of Gudden, while the pars lateralis of the medial mammillary nucleus contains no double‐ labeled neurons and projects only to the anteroventral thalamic nucleus.
Anatomical study of the final common pathway for vocalization in the cat
Authors: Holstege Gert
Published: January 2005

Vocalization, the nonverbal production of sound, can be elicited in many vertebrates by stimulation in several regions of the limbic system but most easily in the caudal periaqueductal gray (PAG). This study shows that a specific cell group in the lateral part of the caudal PAG and in the tegmentum just lateral to it projects bilaterally to the nucleus retroambiguus (NRA) in the caudal medulla oblongata. Similar but much weaker projections are derived from the dorsal PAG. Neurons in the NRA in turn project via a contralateral pathway through the ventral funiculus of the spinal cord to motoneuronal cell groups, innervating intercostal and abdominal muscles. These projections are stronger on the contralateral side, although at lower thoracic and upper lumbar levels, many fibers recross to terminate in the ipsilateral motoneuronal cell groups. In the brainstem NRA neurons project to the motoneuronal cell groups innervating mouth‐opening and perioral muscles as well as to motoneurons innervating the pharynx, soft palate, and tongue, and probably to the larynx. All these muscles are active in vocalization. The present anatomical results, combined with the physiological results of others, indicate that the projections from PAG via NRA to vocalization motoneurons from the final common pathway in vocalization. The role of this pathway in the total framework of emotional behavior is discussed.
Generation of monoclonal antibodies against a nematode peptide extract: Another approach for identifying unknown neuropeptides
Authors: Sithigorngul Paisarn , Cowden Cynthia , Guastella John , Stretton Antony O.W.
Published: January 2005

Monoclonal antibodies that cross‐react with Ascaris neural antigens were generated in mice immunized with a conjugate made with keyhole limpet hemocyanin (KLH) linked to a crude peptide extract from Caenorhabditis elegans. The response to KLH was suppressed by injection of cyclophosphamide 3 days after immunization with a gamma‐aminobutyric acid (GABA)‐KLH conjugate. Screening of hybridomas was carried out by enzyme‐linked immunosorbent assay and whole mount immunocytochemistry. Two similar clones produced antibodies that recognized a small subset of Ascaris neurons. This result suggests that the monoclonal antibody technique might be useful for identifying new neuropeptides since the antibodies can be used for localization of the neuropeptidelike substances and, potentially, for immunoaffinity chromatography. As a by‐product of this experiment, monoclonal antibodies that recognize GABA‐like immunoreactivity in whole mounts and plastic sections were also obtained.
Development of the rat thalamus: V. The posterior lobule of the thalamic neuroepithelium and the time and site of origin and settling pattern of neurons of the medial geniculate body
Authors: Altman Joseph , Bayer Shirley A.
Published: January 2005

Long‐survival, sequential, and short‐survival thymidine radiograms of rat embryos, fetuses, and young pups were analyzed in order to examine the time of origin, site of origin, migratory route, and settling pattern of neurons of the medial geniculate body (MG). Quantitative evaluation of long‐survival radiograms established that the bulk of MG neurons are generated between embryonic (E) days E13 and E15, with a pronounced peak on day E14. There is an overall lateral‐to‐medial and caudal‐to‐rostral chronological gradient in MG neurogenesis. On the basis of significant regional differences in the birth dates of neurons, the MG was divided into several chronoarchitectonic areas. The earliest‐generated neurons (with close to 20% of the cells produced on day E13 and a negligible proportion on day E15) form the dorsal and ventral clusters far laterally. Next in sequential order are the neurons of the lateral shell, intermediate shell, and medial shell of the MG. The medial shell with it latest‐generated neurons (with over 30% produced rostrally on day E15) corresponds to the medial (magnocellular) subnucleus of the MG. There were no neurogenetic differences between the traditional dorsal and ventral divisions of the MG.

Examination of sequential radiograms in rats labeled with 3H‐thymidine on day E14 or E15 and killed on successive days brought supportive evidence for our earlier identification, in short‐survival radiograms, of a posteroventral thalamic neuropithelial evagination as the putative source, or committed cell line, of MG neurons. Wave fronts of apparently migrating unlabeled and labeled cells could be traced from this sublobule in a posterolateral direction to the future site of the MG.
Interaction between cholinergic neurons and substance P or calcitonin gene‐related peptide terminals of the rat sacral intermediolateral nucleus: Double immunostaining at the light and electron microscopic levels
Authors: Peng Yuwen , Kohno Johji , Shinoda Koh , Kawai Yoshinori , Ono Keiro , Jiang Wenhua , Shiotani Yahe
Published: January 2005

The relationships both between cholinergic neurons and substance P (SP) and between cholinergic neurons and calcitonin gene‐related peptide (CGRP) terminals were examined in the rat sacral intermediolateral nucleus at the light and electron microscopic levels by means of double‐immunostaining methods. Cholinergic neurons were labeled by a monoclonal antibody to choline acetyltransferase (CAT) with the avidin‐biotin technique and stained bluish‐green by indolyl‐β‐galactoside reaction products with β‐galactosidase as a marker. On the same sections, SP or CGRP fibers were labeled by polyclonal antisera to SP or CGRP after application of the peroxidase‐antiperoxidase (PAP) method and stained brown by the p‐dimethylaminoazobenzene (DAB) reaction. After embedding in Epon, light and electron microscopic sections were examined. At the light microscopic level, CGRP‐like immunoreactive (CGRP‐I) fibers and SP‐like immunoreactive (SP‐I) fibers were found to pass through the lateral edge of the dorsal horn and then into the dorsal region of the sacral intermediolateral nucleus. In addition, SP‐I fibers also extend from the dorsolateral funiculus into the entire sacral intermediolateral region. At the electron microscopic level, many axosomatic and axodendritic synapses were found between CAT‐I structures and SP‐I terminals in the intermediolateral nucleus, whereas most of the CGRP‐I terminals in this area made axodendritic synapses with CAT‐I dendrites. These results indicate that cholinergic neurons in the sacral intermediolateral nucleus receive direct synaptic input from SP‐I and CGRP‐I terminals. Therefore, it is likely that both SP‐I and CGRP‐I fibers from dorsal root ganglia and intrinsic SP‐I fibers make direct synapses with sacral parasympathetic preganglionic neurons and thus have great importance in the control of bowel and bladder reflexes.
Beta‐endorphin and gonadotropin‐releasing hormone synaptic input to gonadotropin‐releasing hormone neurosecretory cells in the male rat
Authors: Chen Wen‐Pin , Witkin Joan W. , Silverman Ann‐Judith
Published: January 2005

Physiological and pharmacological evidence has suggested that both endogenous opiates and gonadotropin‐releasing hormone (GnRH) itself can act centrally to exert a tonic inhibition on gonadotropin secretion via an inhibition of the neurosecretion of GnRH. To determine if the effects of these two peptides might be mediated via a direct synaptic input to the GnRH neuron, we undertook a double label ultrastructural study. We were able to localize in the same tissue section beta‐endorphin and GnRH. Analysis of serial sections through GnRH perikarya and dendrites in the male rat diagonal band/preoptic area revealed that almost 10% of the synapses impinging on the GnRH neuron contained beta‐endorphin; an additional 10% of the terminals contained GnRH. These data provide anatomical evidence in support of both a direct modulation of GnRH release by opiates and of the presence of an ultrashort feedback loop.
Alpha and delta ganglion cells in the rat retina
Authors: Peichl Leo
Published: January 2005

In the rat retina a distinctive class of large ganglion cell was demonstrated by intracellular staining with Lucifer Yellow and with reduced silver staining. They are referred to as alpha cells because they resemble the alpha cells of other mammalian retinae. A second class, called delta cells, is also described. Both classes belong to the type I group defined by Perry (Proc. R. Soc. Lond. [Biol.] 204:363–375, '79). The dendritic trees of both classes stratify in either an inner or outer lamina of the inner plexiform layer which presumably corresponds to an on/off dichotomy in the response to light.

Rat alpha cells constitute 2–4% of all ganglion cells, and their density, size, and detailed morphological appearance change with retinal location. Inner and outer stratifying alpha cells of the rat show significant differences compared to those of other mammals. In central retina (at the large cell density maximum) the densities and dendritic field sizes of inner and outer alpha cells are approximately equal. However, in peripheral retina outer alpha cells are up to three times more numerous and have dendritic field areas only one‐third the size of those of the inner alpha cells. The maximal density is about 110 alpha cells/mm2; peripheral densities are about 30/mm2. The smallest central dendritic field diameters are 220 μm. Peripheral dendritic field diameters are 350–550 μm for outer and 570–790 μm for inner alpha cells. Each subpopulation is distributed in a regular mosaic, and the territorial arrangement of the dendritic fields provides a homogeneous coverage of the retina. The dendritic coverage is three‐ to 3.6‐fold for each subpopulation, irrespective of their other quantitative differences. Eccentricity‐dependent receptive field sizes of the alpha cells are predicted from the morphological data.
Sound‐generating (sonic) motor system in a teleost fish (Porichthys notatus): Sexual polymorphisms and general synaptology of sonic motor nucleus
Authors: Bass Andrew H. , Marchaterre Margaret A.
Published: January 2005

The sonic motor nucleus of the plainfin midshipman, Porichthys notatus, is a midline nucleus located at the junction of the caudal medulla and rostral spinal cord. Its motoneurons innervate sonic “drumming” muscles that are attached to the lateral walls of the swimbladder. There are two classes of sexually mature males referred to as Type I and Type II. The Type I males are larger and generate sounds during the breeding season. The Type II males are smaller and, like adult females, have not yet been shown to generate sounds. This study examined possible sex differences in the size of sonic motoneurons, and the type and distribution of their afferent terminal boutons.

The average soma diameter of motoneurons of Type I males is about 50% larger than that of Type II males and females. There is also a small but significant difference in soma diameter between Type II males and females; they are smaller in the former class.

There were no sex differences in the presence or distribution of different classes of axosomatic and axodendritic terminal boutons, which included: (1) active zones with either clear, round, or pleomorphic vesicles, (2) active zones with both clear, round vesicles, and larger dense core vesicles, and (3) “mixed synapses” with gap junctions and active zones usually associated with pleomorphic vesicles.

The results are discussed within the context of sexual differentiation of vertebrate motor systems and the functional organization of the sonic motor system in fishes. Sex differences in soma diameter correlate with a number of sex differences in the gross and ultrastructural features that distinguish the sonic muscles of Type I males from those of Type II males and females, which are similar to each other. The absence of qualitative sex differences in synaptic morphology suggest that the central neuronal circuitry of the sonic motor system is similar among all three adult morphs.
Histaminergic system in the tree shrew brain
Authors: Airaksinen Matti S. , Flügge Gabriele , Fuchs Eberhard , Panula Pertti
Published: January 2005

This study mapped the histamine‐immunoreactive neuronal system in the brain of the tree shrew (Tupaia belangeri) and compared its structure with that of the rat and guinea pig. The histamine‐containing cell bodies lay in the posterior ventral hypothalamus in the tuberomammillary complex, as in the rodents. The morphology of this complex resembled that of the rat. The histaminergic axons projected to nearly all parts of the brain. The main ascending bundle ran ventromedially: the densest innervation was found in the ventral hypothalamus, preoptic area, septum, medial part of nucleus accumbens, and bed nucleus of the stria terminalis. High fiber densities were present in the amygdaloid nuclei and claustrum. Another pathway ran dorsomedially along the periventricular hypothalamus and sent fibers to all parts of the diencephalon. Part of these fibers followed the central gray to the midbrain and spread laterally below the inferior colliculus. Another descending pathway ran through the interfascicular and medial raphe nuclei to meet the pontine central gray. The densest fiber networks were seen in the dorsal tegmental and parabrachial nuclei, and around the locus coeruleus. Also the substantia nigra, interpeduncular and mesencephalic reticular nuclei, colliculi, and vestibular and raphe nuclei received a dense histaminergic innervation.

The organization of the fibers in the tree shrew brain resembled more that in the guinea pig than that in the rat. As compared with the guinea pig, more fibers were present, particularly in the globus pallidus, central thalamus, and deep cerebellar nuclei. No fibers were seen in the outer layer of the piriform cortex. In Tupaia, a laminar organization of the fibers was evident in the hippocampus, in contrast to the rodents. Also, a dense periventricular fiber plexus was prominent.
Morphometric and freeze‐fracture studies on peripheral nerve in shiverer mice
Authors: Panagopoulos G. , King R. H. M. , Gabriel G. , Stolinski C. , Sofer D. , Lachapelle F. , Thomas P. K.
Published: January 2005

Observations have been made on the peripheral nerves of shiverer (shi/shi) mice in comparison with control animals. Although this mutant lacks P1 myelin basic protein in peripheral and central myelin, myelin is defective only in the central nervous system. No ultrastructural abnormalities were observed in the shiverer nerves. Myelin spacing was normal. The density and distribution of intramembranous particles on the E and P faces of myelin and in the axolemma of myelinated and unmyelinated axons did not differ between the shiverer and control mice. Morphometric studies showed that external myelinated fiber diameter was significantly less and that myelin thickness was slightly but significantly greater in relation to axon diameter in the shiverer mice, suggesting a minor degree of axonal atrophy. It is concluded that P1 protein is not necessary for the formation and maintenance of the normal structure of peripheral myelin. The failure to detect differences in intramembranous particle density in myelin between shiverer and control mice indicates that P1 protein is not detected in freeze‐fracture preparations.