bluuebunny/crossref_metadata_2025 huggingface dataset:
Nerve growth factor receptor immunoreactive profiles in the normal, aged human basal forebrain: Colocalization with cholinergic neurons
Authors: Mufson Elliott J. , Bothwell Mark , Hersh Louis B. , Kordower Jeffrey H.
Published: January 2005

A monoclonal antibody raised against the receptor for nerve growth factor (NGF) has been used to map the distribution of NGF receptor‐containing profiles within the human basal forebrain of four male and three female elderly patients without neurologic or psychiatric illness. Immunohistochemically processed tissue reveals a continuum of NGF receptor‐positive neurons located within the medial septum, vertical and horizontal limb nuclei of the diagonal band, and nucleus basalis. NGF receptor‐containing neurons are also found within the bed nucleus of the stria terminalis, the anterior commissure, the internal capsule, and the internal and external medullary laminae of the globus pallidus. Virtually all (>95%) NGF receptor‐containing neurons colocalize with the specific cholinergic marker choline acetyltransferase (ChAT) or the nonspecific marker acetylcholinesterase (AChE). Conversely, a few cholinergic perikarya are found which are not NGF receptor positive (and vice versa). These findings demonstrate that human basal forebrain neurons on which NGF receptor immunoreactivity is detected are primarily cholinergic and analogous to the nonhuman primate Ch1–Ch4 subgroups of Mesulam et al. (J. Comp. Neurol., 214:170–197, '83). NGF receptor‐containing fiber tracts are observed emanating from the medial septum and vertical limb nucleus of the diagonal band coursing medially within the fornix. Another fascicle originating mainly from the nucleus basalis and travelling within the external capsule enroute to the cortex is observed innervating all cortical layers.

Comparison of NGF receptor‐ and ChAT‐containing neurons reveals cholinergic perikarya within the striatal complex, whereas virtually no NGF receptor‐containing neurons are found in these structures. An occasional displaced NGF receptor‐containing neuron is seen in the ventrolateral portion of the putamen and the white matter underlying the nucleus accumbens. These data are discussed in terms of the relationship of NGF receptor‐ and ChAT‐ containing neurons within the basal forebrain and in terms of the possible functional significance of NGF in normal and diseased brain.
Descending projections to the mammillary nuclei in the rat, as studied by retrograde and anterograde transport of wheat germ agglutinin–horseradish peroxidase
Authors: Shibata Hideshi
Published: January 2005

The cells of origin and projection fields of the descending afferents to the mammillary nuclei were studied in the rat with retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase.

The subiculum projects bilaterally to the entire medial mammillary nucleus (MM) in a topographic fashion along the two axes: (1) the proximal part of the subiculum along the presubiculo‐CA1 axis projects to the caudal and lateral regions of the MM whereas the more distal part of the subiculum projects to the medial region; (2) the septal part of the subiculum projects to the caudodorsal region of the MM whereas the more temporal part projects progressively to the more rostroventral regions. The ventral subiculum also projects ipsilaterally to the ventral and lateral margin of the lateral mammillary nucleus (LM). The presubiculum projects bilaterally to the dorsolateral region of the pars posterior of the MM and ipsilaterally to the LM. The infralimbic cortex projects bilaterally to the rostrodorsal region of the MM, whereas the retrosplenial cortex (areas 29a and 29b) projects bilaterally to the medial region at the midrostrocaudal and middorsoventral levels of the MM. The nucleus of the diagonal band projects bilaterally to the caudomedial region of the MM, whereas the lateral septal nucleus projects bilaterally to the pars mediana and the mammillary fiber capsule. A part of the anterior hypothalamic area ventromedial to the fornix projects predominantly ipsilaterally to the rostroventral part of the MM, whereas other basal forebrain regions such as the bed nucleus of the stria terminalis, the medial preoptic and anterior hypothalamic areas, and the area of the tuber cinereum send fibers predominantly ipsilaterally to the mammillary fiber capsule.

The results reveal a complex organization of the descending projections to the mammillary nuclei, which may reflect the complex functions of these nuclei within the limbic circuitry.
Quantitative Golgi study of anatomically identified subdivisions of motor thalamus in the rat
Authors: Sawyer Steven F. , Young Stephen J. , Groves Philip M.
Published: January 2005

A Golgi study of neurons in the ventroanterior‐ventrolateral complex (VAL) and ventromedial (VM) nucleus in the dorsal thalamus of rats was performed. To facilitate the delineation of subdivisions of these nuclei, some animals received injections of horseradish peroxidase (HRP) into the afferent and efferent fields of VAL and VM, and alternate sections were processed for the histochemical detection of HRP. As an adjunct to subjective observations, a multivariate statistical analysis of morphometric variables was performed to provide an objective assessment of neuronal morphology.

All Golgi‐stained neurons in VAL and VM were tentatively identified as projection neurons; no cells with morphological features commonly ascribed to thalamic interneurons were impregnated. Four classes of morphologically distinct neurons were identified in VAL. Type 1 neurons, the most commonly impregnated cell, were found throughout the extent of VAL and resembled “tufted” or “multipolar bush” neurons described previously in many thalamic nuclei. The remaining three neuronal types differed in a number of morphometric parameters and were differentially distributed throughout VAL. Type 2 neurons, distinguished in part by dendritic spine morphology and elongated bipolar dendritic fields, were found only in the rostral sector of the dorsal division of VAL (VALD). Type 3 neurons, characterized by a large and evenly distributed dendritic field, were situated in rostral VAL (all subdivisions). Type 4 neurons had small soma and dendritic dimensions and were located in the ventromedial aspect of the ventral division of VAL (VALV) adjacent to VM. In contrast, the vast majority of neurons in VM were considered to be a single morphological class (similar in form to type 4 neurons in VAL), although a rarely impregnated second type of neuron was also observed.

The apparent scarcity of interneurons in VAL and VM is consistent with previous evidence that the synaptic organization of motor thalamus in the rat is markedly different from that of higher‐order mammals. Speculation about the functional attributes of the neuronal types in VAL and VM is necessarily restricted to considerations of afferent and efferent relations, since “motor modality” functions of neurons in these nuclei have yet to be elucidated.
Cellular substrates for interactions between neurons containing phenylethanolamine N‐methyltransferase and GABA in the nuclei of the solitary tracts
Authors: Pickel V. M. , Chan J. , Milner T. A.
Published: January 2005

Adrenaline and γ‐aminobutyric acid (GABA) have been implicated in autonomic functions involving the intermediate and caudal portions of the medial nuclei of the solitary tracts (m‐NTS). We sought to determine whether there was a cellular basis for direct intracellular or synaptic interactions between these transmitters in neurons in the m‐NTS of rat brain by using dual‐labeling immunocytochemical methods. Light microscopy revealed immunoautoradiographic labeling for the adrenaline‐synthesizing enzyme phenylethanolamine N‐methyltransferase (PNMT) in perikarya and processes in close proximity to cells demonstrating peroxidase reaction product for GABA. Electron microscopy of the intermediate m‐NTS at the level of the area postrema further established the localization of immunoautoradiographic and peroxidase labels for PNMT and GABA in common as well as separate perikarya and dendrites. All axon terminals were labeled separately for PNMT and GABA. The PNMT‐labeled terminals formed both symmetric and asymmetric synapses, whereas the GABA‐labeled terminals formed exclusively symmetric synapses. Twenty‐four percent (n = 42) of the PNMT‐ and 39% (n = 128) of the GABA‐labeled terminals formed synaptic junctions on unlabeled soma and dendrites. Occasionally both types of terminals converged on a common unlabeled dendrite and on GABA‐labeled dendrites. Only 3% of the PNMT‐ and 12% of the GABA‐containing terminals formed synapses on PNMT‐labeled soma and dendrites, whereas 7% of each type formed synapses with GABA‐labeled profiles. The remaining labeled terminals lacked synaptic relations within the sections examined. The autoradiographic results were confirmed and extended by means of immunogold labeling for PNMT in combination with peroxidase‐antiperoxidase localization of the GABA‐synthesizing enzyme glutamic acid decarboxylase (GAD). GAD‐labeled terminals formed symmetric synapses with dendrites that were either unlabeled or contained low levels of PNMT (gold particles) or PNMT and GAD. We conclude that in caudal, more cardiovascular portions of the NTS, adrenaline and GABA may coexist, but they are more commonly detected in separate populations of neurons having receptive sites for both transmitters and innervating certain common target neurons.
Intrinsic synapses in the ventromedial nucleus of the hypothalamus: An ultrastructural study
Authors: Nishizuka Masako , Pfaff Donald W.
Published: January 2005

To test the ideas that neurons intrinsic to a hypothalamic region might participate in steroid hormone effects and that intrinsic synapses might have unusual morphological features, we deafferented the ventromedial nucleus of the hypothalamus (VMH) in ovariectomized female rats with a Halasz knife. Some rats were given estrogen; others were endocrine controls.

The main result of this study was that a large number of synapses in VMH survived the circumscribing cut. In fact, they comprised between one‐half and two‐thirds the number counted in unoperated controls. These were apparently from neuron cell bodies intrinsic to the medial basal hypothalamic island. Their morphology was not clearly different from that expected from unoperated controls or from other brain regions.

A significant estrogen effect, an increase in the number of axodendritic synapses per unit area as seen in animals without surgical transections, was not present in the deafferented groups. This suggests that the hormone effect is due to synapses on VMH neurons from cell groups outside the medial basal hypothalamic island. If functional effects of estrogen mediated through VMH do not rely on intrinsic neurons, they must use estrogen‐concentrating neurons that project to other brain regions.
Organization of the septal region in the rat brain: A Golgi/EM study of lateral septal neurons
Authors: Alonso Jose R. , Frotscher Michael
Published: January 2005

The combined Golgi/electron microscope (EM) technique was used to analyze the fine structure and synaptic organization of the various types of neurons in the rat lateral septum (LS), i.e., in the dorsolateral (LSd), intermediolateral (LSi), and ventrolateral (LSv) nuclei of the septal complex.

Two characteristic cell types were observed in the LSd: type I with thick, short dendrites densely covered with short spines, and type II with longer and thinner dendrites exhibiting fewer but longer spines. This latter type was by far the most frequently impregnated cell type in the LSd and was also present in the LSi. Synaptic contacts on spines of either cell type were asymmetric; the majority of the presynaptic boutons contained clear and dense‐core vesicles. Typical fusiform neurons with a low number of spines and rather long dendrites, sometimes invading other LS nuclei, were found in the LSi. The LSv contained numerous small neurons with small dendritic fields. A relatively large number of terminals with dense‐core vesicles were found to establish synaptic contacts with identified LSv neurons.

The morphological heterogeneity of LS neurons is discussed with regard to other studies on afferent and efferent fiber systems as well as immunohistochemical studies of this particular region of the septal complex.
Localization of serotoninlike‐immunoreactive amacrine cells in the larval tiger salamander retina
Authors: Yang Shu‐zhen , Lam Dominic M.‐K. , Watt Carl B.
Published: January 2005

Light microscopic immunocytochemistry was used to study the populations of serotoninlike‐immunoreactive cells in the larval tiger salamander retina. Of 1,135 serotonin‐immunostained cells observed in transverse cryosections, 87% were identified as amacrine cells, whereas 13% were tentatively designated as displaced amacrine cells. The somas of the vast majority of serotonin‐amacrine cells were situated in the innermost cell row of the inner nuclear layer. Only a few serotonin‐immunostained amacrine cell somas were observed in the second row of cells from the inner nuclear layer. Serotonin‐immunoreactive processes generally appeared as a diffuse plexus distributed evenly throughout all levels of the inner plexiform layer.

As determined in whole‐mount preparations, serotonin‐amacrine cells were divisible into two populations on the basis of the diameters of their somas. Large cells (45%) ranged from 16 to 19 μm in diameter with the vast majority measuring 17 to 18 μm. Smaller and sometimes less intensely stained cells ranged from 14 to 16 μm in diameter with the large majority measuring 15 μm. The diameters of serotonin‐displaced amacrine cells ranged from 19 to 22 μm with the large majority measuring 20 μm in diameter. An examination of whole‐mount retinas revealed that serotonin‐immunoreactive amacrine and displaced amacrine cells were distributed throughout the center and the periphery of the retina. The density of serotonin‐amacrine cells (large and small combined) was calculated to be 173 ± 4.5 (mean ± standard error) cells per mm2.
Thalamic and extrathalamic connections of the dysgranular unresponsive zone in the grey squirrel (Sciurus carolinensis)
Authors: Gould H. J. , Whitworth R. H. , LeDoux M. S.
Published: January 2005

The connections of the cortical dysgranular “unresponsive zone” (UZ) (Sur et al.: J. Comp. Neurol. 179:425–450, '78) in the grey squirrel were studied with horseradish peroxidase and autoradiographic techniques. The results of these experiments show that the major subcortical connections of the unresponsive zone are in large part reciprocal. Connections are distributed within the thalamus in a poorly defined region including restricted portions of several nuclei that lie along the rostral, dorsal, and caudal borders of the ventral posterior nucleus. Additional thalamic connections of the UZ terminate in the reticular nucleus and are reciprocally related to the paralaminar and central median nuclei. Extrathalamic terminations were observed in the zona incerta, the intermediate and deep layers of the superior colliculus, the red nucleus, and several subdivisions of the pontine nuclei. The similarity between the pattern of subcortical connections of the UZ in the grey squirrel and patterns reported for the parietal septal region in rats (Chapin and Lin: J. Comp. Neurol. 229:199–213, '84) and for area 3a in primates (Friedman and Jones: J. Neurophysiol. 45:59–85, '81), suggests that the UZ in the grey squirrel may represent a counterpart of at least part of area 3a as described in primates. The results are further discussed with respect to a possible role of the thalamus in control or modulation of interhemispheric circuits and of the UZ in the modulation of nociceptive and kinesthetic pathways through the thalamus. Finally, the term parietal dysgranular cortex (PDC) is proposed as an alternative to denote the region currently called the unresponsive zone.
Calcitonin gene‐related peptide immunoreactivity in the cat lumbosacral spinal cord and the effects of multiple dorsal rhizotomies
Authors: Traub Richard J. , Solodkin Ana , Ruda M. A.
Published: January 2005

This study determined the extent of the rostral projection of calcitonin gene‐related peptide‐like immunoreactive (CGRP‐IR) primary afferents in the cat lumbosacral spinal cord. To do this we examined the distribution of CGRP‐like immunoreactivity (CGRP‐LI) contralateral and ipsilateral to multiple dorsal rhizotomies. In the contralateral dorsal spinal cord, CGRP‐IR fibers dwere mostly observed in Lissauer's tract, the dorsal columns, and laminae I, II, and V. Fewer CGRP‐IR fibers were observed in laminae III, IV, and VI and the area around the central canal. The location of the CGRP‐LI suggests that the afferents arose from nociceptors. Unilateral dorsal rhizotomies of five consecutive segments in the lumbar enlargement caused a substantial although incomplete loss of CGRP‐LI in the rhizotomized dorsal spinal cord ipsilateral to the lesions. The majority of the remaining CGRP‐IR fibers were located in Lissauer's tract, the dorsal columns, and the lateral part of laminae I and V. Ventral rhizotomies or an ipsilateral hemisection in the most rostral rhizotomized segment, in addition to the dorsal rhizotomies, had no noticeable effect upon the density or location of the remaining CGRP‐LI. These results suggest that the majority of the CGRP‐LI within the rhizotomized region of spinal cord was contained within branches of small‐diameter primary afferents that entered the spinal cord through intact dorsal roots located caudal to the rhizotomized segments of spinal cord. It is concluded that CGRP‐IR small‐diameter primary afferents are capable of projecting at least five segments beyond their segment of entry and supplying collaterals to the superficial and deeper layers of the dorsal horn involved in the processing of nociceptive information.
Gap junction particle density of horizontal cells in goldfish retinas lesioned with 6‐OHDA
Authors: Baldridge W. H. , Ball A. K. , Miller R. G.
Published: January 2005

The I1 dopaminergic interplexiform cells of the fish retina are believed to modulate horizontal cell coupling by increasing gap junction resistance. Dopamine also modulates the morphology of horizontal cell gap junctions and mimics the effects of light adaptation. To determine whether the light‐dependent changes in gap junction morphology are due to endogenous dopamine release, horizontal cell gap junctions were studied in goldfish retinas lacking dopaminergic neurons.

Dopaminergic interplexiform cells were destroyed by intraocular injections of 6‐hydroxydopamine in both eyes. After lesioning, fish were treated in one of four ways: (1) light‐adapted, (2) dark‐adapted (1 hour), (3) light‐adapted and given and intraocular injection of dopamine, or (4) dark‐adapted (1 hour) and injected with dopamine. The effectiveness of lesioning was evaluated by autoradiographic detection of [3H]‐dopamine uptake in the retina of one eye. Retinas in which lesioning of the contralateral eye was deemed effective were processed for freeze‐fracture electron microscopy and the particle density of horizontal cell gap junctions determined.

Lesioned retinas, whether light‐ or dark‐adapted, had elevated horizontal cell soma gap junction particle densities compared to lesioned retinas treated with dopamine. These results demonstrate that high soma gap junction particle densities can be correlated with the absence of dopamine and low densities associated with the presence of dopamine. The differences in gap junction particle density between lesioned and lesioned + dopamine‐treatment were similar to differences between nonlesioned dark‐adapted (1 hour) and light‐adapted retinas, respectively. Therefore, the particle density of light‐ and dark‐adapted soma gap junctions suggests a greater release of dopamine in light‐adapted fish than in 1 hour dark‐adapted fish.

Gap junctions on axon terminals of horizontal cells in lesioned light‐ and dark‐adapted retinas had reduced particle densities compared to nonlesioned light‐adapted but not to nonlesioned dark‐adapted retinas. However, intraocular injections of dopamine into lesioned eyes did not alter axon terminal gap junction particle densities. This suggests that coupling at the horizontal cell soma and axon terminal may be regulated by different mechanisms.
Central acoustic tract in an echolocating bat: An extralemniscal auditory pathway to the thalamus
Authors: Casseday J. H. , Kobler J. B. , Isbey S. F. , Covey E.
Published: January 2005

To determine the sources and targets of auditory pathways that bypass the inferior colliculus in the mustache bat, we injected WGA‐HRP in the medial geniculate body and related auditory nuclei of the thalamus as well as in the lower brainstem. We used electrophysiological methods to verify that the injection electrode was in an area responsive to sound. The only thalamic injections that produced retrograde transport to cells in auditory nuclei caudal to the inferior colliculus were those that included the suprageniculate nucleus. These injections labeled a group of large multipolar cells lying between the ventral nucleus of the lateral lemniscus and the superior olivary complex. Neurons in this cell group have also been shown to project to the deep layers of the superior colliculus in the mustache bat. The pathway revealed by these studies is almost identical to the “central acoustic tract” in which fibers course medial to the lateral lemniscus and bypass the inferior colliculus to reach the deep superior colliculus and the suprageniculate nucleus.
GABA‐like immunoreactivity of neurons in the chicken diencephalon and mesencephalon
Authors: Granda Rita H. , Crossland William J.
Published: January 2005

The chick brain is a useful model system for studying the ontogeny and phylogeny of neural circuitry, especially that of the visual system. In this study the distribution of cells and processes showing GABA‐like immunoreactivity (GABA+) in the diencephalon and mesencephalon of the posthatch chick was determined immunohistochemically with a polyclonal antibody to GABA and compared with the results of similar studies in mammals. Most of the small GABA+ cells were found in the chick visual centers such as the nucleus lateralis anterior, suprachiasmatic nucleus, ventral lateral geniculate, optic tract, dorsolateralis anterior pars lateralis, lentiformis mesencephali, ectomammillary nucleus, area pretectalis, and the optic tectum. Large GABA+ cells were found in the following nuclei: reticularis superior, posteroventralis thalami, subpretectalis, isthmi pars magnocellularis, interstitiopretectosubpretectalis, mesencephalicus lateralis pars dorsalis. These large cell‐containing nuclei receive projections from visual or auditory centers. GABA+ axons were found throughout the diencephalon and mesencephalon but were especially prominent in the ansa lenticularis, fasciculus medialis longitudinalis, and optic tract. The distribution of GABA+ cells in the chick is more widespread than in rodents and exhibits an increased association with the visual centers suggesting a correlation with the specialized visual requirements of the bird.
GABAergic neurons in brainstem auditory nuclei of the chick: Distribution, morphology, and connectivity
Authors: Von Bartheld Christopher S. , Code Rebecca A. , Rubel Edwin W.
Published: January 2005

The second‐ and third‐order auditory nuclei in the brainstem of the chicken, nucleus magnocellularis (NM) and nucleus laminaris (NL), receive afferents that are immunoreactive to gamma‐aminobutyric acid (GABA). In order to investigate the source(s) of these GABAergic afferents, we examined the distribution, morphology, and connectivity of GABAergic neurons in and adjacent to NM and NL in chicks from 7 days of incubation to 12 days posthatch. Immunocytochemical techniques revealed the presence of approxi‐mately 150 GABA‐labeled neurons within the neuropil surrounding NM and NL on each side of the brainstem. Most of these neurons are located between NM and NL and along the lateral border of NM. GABAergic neurons are mul‐tipolar; their thick dendritic processes branch extensively and give rise to several thin, secondary processes. Frequently, the GABA‐labeled processes arbo‐rize within NM or NL. The morphology of these non‐NM/NL neurons was investigated further with Golgi impregnation and specific neuronal markers (antisera to microtubule‐associated protein). Our observations suggest that a considerable portion of GABAergic input to NM and NL originates from local GABAergic neurons.

In order to determine other possible sources of GABAergic input to NM and NL, we injected tracers unilaterally into NM/NL. A small number (20–30)of neurons were retrogradely labeled in the trapezoid body, almost exclusively ipsilaterally. No labeled cells were found in other regions of the brainstem, except for the contralateral NM, Unilateral injections of horseradish‐peroxi‐dase‐labeled wheat germ agglutinin into the paraflocculus revealed only minor terminal labeling in the lateral region of NL bilaterally. The number and dis‐tribution of GABAergic terminals in NM and NL appeared normalafter transection of the crossed dorsal cochlear tract.
Monoamine‐accumulating ganglion cell type of the cat's retina
Authors: Dacey Dennis M.
Published: January 2005

A monoamine‐accumulating ganglion cell type has been identified in an in vitro preparation of the cat's retina by a catecholamine‐like fluorescence that appears following intravitreal injections of dopamine and the indoleaminergic transmitter analog, 5,7‐dihydroxytryptamine (5,7‐DHT). A subpopulation of large, weakly fluorescing neurons were identified as composing a single, morphologically distinct ganglion cell type by intracellular injections of horseradish peroxidase (HRP). In a sample of 374 HRP‐filled cells soma diameter ranged from 13–21 μm (mean ± SD = 16.6 ± 1.3). Dendritic field size increased with increasing retinal eccentricity from 150–200 μm diameter at 0.5 mm from the area centralis to 600–800 μm diameter in the far retinal periphery. Dendrites are thin (∼1 μm diameter), show a characteristic branching pattern, and are narrowly stratified at the outer border of the inner plexiform layer. The monoamine‐accumulating ganglion cell and the outer (OFF‐center) alpha cell occupy distinct strata within sublamina a of the inner plexiform layer separated by a gap of about 5 μm.

The total number of monoamine‐accumulating (MA) ganglion cells was estimated at 5,400, about 3.5% of the total ganglion cell population. Spatial density of the MA ganglion cells, calculated from cell counts made in vitro, ranges from 60 cells/mm2 near the area centralis to 5 cells/mm2 in the far retinal periphery. A coverage factor (density x dendritic field area) of 2.2 was maintained from central to peripheral retina. The nature of the dendritic overlap was observed directly by making HRP injections into several neighboring ganglion cells. Five to seven neighboring dendritic trees extensively overlapped a given cell's dendritic field. However the dendritic processes did not intersect randomly but tended to interdigitate such that a uniform interdendritic spacing and density of dendritic processes was constructed locally within the dendritic plexus. Rotation of individual dendritic trees from their normal orientation produced a dramatic 4‐5‐fold increase in the number of dendritic intersections, suggesting that an active, local mechanism operates in the precise placement of individual dendrites within the plexus.

The monoamine‐accumulating ganglion cell appears morphologically equivalent to the delta ganglion cell (Boycott and Wässle; J. Physiol. (Lond.) 240: 397–419, '74; Kolb et al.; Vision Res. 21: 1081–1114, '81) and to the recently recognized indoleamine‐accumulating ganglion cell (Wässle et al: J. Neurosci. 7: 1574–1585, '87). Comparisons with previous studies indicate that they may be physiologically equivalent to the OFF‐center, sluggish sustained cells (also known as tonic W cells and Q cells) and probably project to the superior colliculus and/or the C‐lamina of the dorsal lateral geniculate nucleus.
Early neurogenesis of the mouse olfactory nerve: Golgi and electron microscopic studies
Authors: Marin‐Padilla Miguel , Amieva B. Manuel R.
Published: January 2005

The early neurogenesis of the mouse olfactory nerve, from its exit at the nasal epithelium to its entrance into the embryonic telencephalon, has been investigated by using the rapid Golgi method and electron microscopy. Previously unrecognized anatomical and possible functional interrelationships between developing olfactory nerve axons and their sheath cells have been observed: (1) at their exit from sensory epithelium (nasal compartment), (2) at their contact with the CNS surface (intracranial compartment), and 3) at their entrance into the embryonic telencephalon (central nervous tissue compartment). Based on these observations the anatomy of the mouse olfactory nerve is herein redefined. Exiting olfactory nerve axons and sheath cells from the same regions of the nasal epithelium establish an early association which is maintained up to their terminal glomerular neuropile. No disruptions have been found in either the olfactory nerve axons or in the continuity of their sheath cells from exit at the nasal epithelium to entrance into the developing olfactory bulb. Corresponding olfactory nerve axons with their sheath cells enter together and become incorporated into the developing olfactory bulb as units. Consequently, the cellular envelope of the olfactory glomerulus must be composed of olfactory sheath cells rather than of glial (astroglial) cells from the CNS. With this simple anatomical arrangement, a topographic map of the sensory epithelium could be established progressively in the developing olfactory bulb. Eventually, “regenerating” olfactory nerve axons from different nasal regions could be guided by their specific sheath cell conduits toward their target glomeruli; hence, the olfactory message may be maintained undisturbed throughout the life span of the animal. In addition, olfactory nerve axons establish synaptic‐like contacts with their corresponding sheath cells prior to or during the perforation of the CNS surface. Reciprocal recognition between corresponding axons and their sheath cells at this crucial stage in their neurogenesis may play a significant role in the establishment of their terminal glomerulus. This new concept of the anatomy of the mammalian olfactory nerve should provide insights helpful in clarifying some of the still‐unresolved questions regarding the structural and functional organizations of this primitive system.
Neuronal and synaptic measurements in the visual cortex of adult rats after undernutrition during normal or artificial rearing
Authors: Bedi K. S. , Massey R. F. , Smart J. L.
Published: January 2005

It is possible that the reported effects of early life undernutrition on brain morphology may be due to alterations in mother‐infant interactions and not directly to undernutrition. We have investigated this possibility by comparing artificially reared with mother‐reared rats. Four groups of black‐and‐white hooded male rats were reared. These consisted of mother reared control (MRC), mother reared undernourished (MRU), artificially reared control (ARC) and artificially reared undernourished (ARU). Artificially reared rats were raised in isolation away from their mothers from 5 to 21 days of postnatal age. They were fitted with a gastric cannula through which 'milk' was infused automatically. The period of undernutrition lasted from 5 to 25 postnatal days, following which the animals were fed ad libitum until 312 days of age. Rats from each group were then killed by perfusion with buffered 2.5% glutaraldehyde. Pieces of visual cortex from each rat were postfixed in osmium tetroxide and embedded in resin. Stereological procedures at the light and electron microscopical levels were used to estimate the synapse‐to‐neuron ratios in cortical layers II to IV.

Both MRC and ARC rats had about 7000 synapses per neuron. However, this ratio was about 8300 in MRU rats whilst it was only about 5000 in ARU animals. The rearing x nutrition interaction was statistically significant at the 0.1% level. These changes in the synapse‐to‐neuron ratio were mainly due to alterations in the numerical densities of the synapses rather than that of neurons.

These results demonstrate that environmental isolation, as a result of artificial rearing procedures, and concurrent undernutrition during the first three weeks of postnatal life, interact with one another to produce marked morphological changes in the adult rat brain. However, environmental isolation was not, by itself, sufficient to cause permanent changes in interneuronal connectivity.
Ultrastructural relationships of serotonin axon terminals in the cerebral cortex of the adult rat
Authors: Séguéla Philippe , Watkins Kenneth C. , Descarries Laurent
Published: January 2005

PAP immunocytochemistry with an antiserum against serotonin (5‐HT)‐glutaraldehyde‐protein conjugate (kindly donated by M. Geffard) was used to analyze the ultrastructural relationships of 5‐HT axon terminals (varicosities) in the frontal (Fr1‐Fr2), parietal (Par1), and occipital (Oc1M‐Oc2) cortex of adult rats. One hundred‐forty‐five immunostained varicosities from Fr1‐Fr2 (54 from layers I‐II; 91 from layer VI) and 97 each from the upper layers (I‐II) of Par1 and OcM1‐Oc2 were examined in groups of serial thin sections (mean number of sections in series: 3.2 to 7.3). These terminals were of comparable shape and size in the 4 cortical sectors examined, and averaged 0.66 ± 0.2 μm in mean diameter. The proportion of varicosities engaged in synaptic contact was evaluated by linear transformation of the relationship between the frequency of observed synaptic junctions and the number of thin sections available for examination. Reliability of the sampling was evidenced by a high coefficient of correlation (r> 0.95) in each cortical sector. The synaptic incidence extrapolated for whole varicosities ranged from 28% (layer VI of Fr1‐Fr2) to 46% (Par1), without statistically significant differences between the 4 sectors examined. The interregional mean could thus be evaluated at 38%. The synaptic 5‐HT terminals always made asymmetrical junctions, which were exclusively found on dendritic spines and shafts, and appeared more frequent on spines than shafts in the deep frontal and the upper occipital cortex. In all 4 sectors, dendritic shafts and spines and other axonal varicosities were frequently encountered in the immediate microenvironment of the immunostained varicosities. It is concluded that the cortical 5‐HT innervation is predominantly nonjunctional throughout the neocortex of the adult rat, which reinforces earlier views of a highly divergent afferent system with particular functional properties and perhaps capable of widespread, global and/or sustained influences in this part of the brain.
Cholinergic amacrine cells in the developing cat retina
Authors: Dann J. F.
Published: January 2005

Antiserum directed against the ACh‐synthesizing enzyme choline acetyltransferase (ChAT) was used to determine the development of cholinergic amacrine cell distributions in wholemounted kitten retinae. From birth (P0) two populations of cholinergic amacrine cells were immunolabelled; one population was located in the inner nuclear layer (INL) and the other was displaced to the ganglion cell layer (GCL). Dendrites from cholinergic amacrines in the INL stratified in the outer third of the inner plexiform layer (IPL), whilst those from displaced amacrines in the GCL stratified in the centre of the IPL. There was a centroperipheral gradient of development in both populations, and the total number of cholinergic amacrines in the GCL always exceeded that of the INL.

The most dramatic increase in the number of amacrines expressing ChAT was between P0 and P5 when the numbers doubled. During the same period there was an increase in the soma size of both populations in the peripheral retina. In the GCL, cholinergic amacrines did not attain adult size until P21 whereas those of the INL reached adult proportions by P5. Overall, between P0 and P21 there was a fivefold increase in the number of immunoreactive cholinergic amacrines in the GCL and a 3.5‐fold increase in those of the INL. In general, the distribution, soma size, percentage per layer, and total number of cholinergic amacrines in both populations resembled those of the adult by P21.
Crossed and uncrossed projections to cat sacrocaudal spinal cord: I. Axons from cutaneous receptors
Authors: Ritz Louis A. , Brown Paul B. , Bailey Steven M.
Published: January 2005

Intra‐axonal recording and horseradish peroxidase staining techniques were used to map terminal fields of primary afferent fibers from cutaneous receptors within the cat sacrocaudal spinal cord. It was hypothesized that projection patterns of cutaneous afferent fibers mirror the known somatotopic organization of sacrocaudal dorsal horn cells.

Forty‐three primary afferent fibers, innervating either slowly adapting type I receptors, hair follicles, or slowly adapting type II receptors, all on the tail, were recovered. All collaterals (N = 372) branched from parent axons in the dorsal columns. Most collaterals coursed rostromedially to the ipsilateral gray matter, penetrated the medial dorsal horn, and arborized within laminae III, IV, and to a lesser extent, V.

Ipsilateral projections to dorsal horn were as follows: axons with dorsal or dorsolateral receptive fields (RFs; n = 20) to the lateral portion, axons with lateral RFs (n = 4) to the central portion, and axons with ventral or ventro‐lateral RFs (n = 19) to the medial portion. Most axons (16 of 20) with dorsal or dorsolateral RFs also had contralateral projections to lateral dorsal horn and most axons (15 of 19) with ventral or ventrolateral RFs also had contralateral projections to medial dorsal horn. No axons with lateral RFs had crossed projections.

These data represent the first complete mapping of the somatotopic organization of primary afferent fiber projection patterns to a spinal cord level. The findings demonstrate that ipsilateral projection patterns of sacrocaudal primary afferent fibers are in register with the somatotopic organization of the dorsal horn. Our earlier suggestion that crossed projections of primary afferent fibers give rise to crossed components of dorsal horn RFs spanning the midline is supported by these results.
Morphology and somatotopic organization of the central terminals of hindlimb hair follicle afferents in the rat lumbar spinal cord
Authors: Shortland Peter , Woolf Clifford J. , Fitzgerald Maria
Published: January 2005

The morphology of the central collateral arborizations of 24 A‐beta hair follicle afferents (HFAs) innervating different regions of the skin of the hindlimb were studied by the intra‐axonal injection of horseradish peroxidase (HRP) in adult rats. A total of 236 collaterals were recovered. These fell into three classes—complex, simple, and blind‐ending—based on numbers of boutons and terminal branch patterns. The morphology of the HFA central arbors innervating the lateral and medial leg and dorsum of the foot was flameshaped. Afferents with receptive fields on the glabrous‐hairy skin border consistently had extra terminal branches running ventromedially into laminae IV/V. Differences in the width of terminal arbors were found. HFA terminals innervating the lateral leg formed narrower sheets than those innervating the dorsum of the foot and toes.

The somatotopic organization of the collaterals and terminal arborizations of individual afferents were analyzed both by considering all the collaterals along an axon's rostrocaudal extent and by only examining arbors with boutons (the complex and simple arbors). Thirty‐seven percent of blind‐ending and 18% of simple collaterals were found to overlap in the rostrocaudal direction with the complex arborizations of afferents whose receptive fields were in a different cutaneous nerve territory. There was no overlap between complex arborizations of afferents from different nerve territories. However, the complex arbors of afferents with receptive fields within a particular nerve territory showed considerable terminal overlap even if they had nonadjacent peripheral receptive fields. The topographical organization of the central terminals of HFAs, forms a coarse somatotopic map of overlapping terminals whereby a particular region of dorsal horn has a maximal, but not exclusive, input from a particular area of skin.
Early postnatal cellular proliferation and survival in the olfactory bulb and rostral migratory stream of normal and unilaterally odor‐deprived rats
Authors: Frazier‐Cierpial Lauren , Brunjes Peter C.
Published: January 2005

Unilateral naris occlusion in rats on postnatal Day 1 results in dramatic decreases in the size of specific olfactory bulb cell populations when pups are examined 30 days later (Frazier and Brunjes: J. Comp. Neurol. 269:355–370, '88). The observed reductions must result from alterations in cell proliferation and/or survival, alternatives examined in the present study.

During early postnatal development, most cells destined for the bulb are produced in regions caudal to the structure and migrate to the bulb in the massive rostral migratory stream. The dynamics of the stream were examined in both normal rats and pups with a single naris closed on Day 1. 3H‐thymidine injections were made on postnatal Days 2, 5, 10, 20, and 30. Groups of pups were killed 2 hours later to assess patterns of proliferation and 24 hours later to gauge initial stages of migration. A gradient of labeled cells was observed in the stream, with higher levels occurring at more caudal locations. The supply of cells to the bulb peaked on Day 5 and was still substantial as late as Day 30. The deprivation procedure did not affect patterns of cell labeling at any stage tested, indicating the procedure does not affect early cellular proliferation.

A third group of pups was examined 30 days after thymidine injection to assess both time of cell origin and survival rates. Dark granule cells and glia in the granule cell layer were produced at a consistent rate until Day 20 with cells added during the period evenly spread throughout the layer. Light granule and periglomerular cell production decreased dramatically after P5. Thirty days after injections on P2, fewer labeled dark granule cells and their associated glia were found in deprived bulbs, indicating that enhanced cell death plays a major role in the deprivation‐induced decrease in cell number.
Morphometric modifications associated with early sensory experience in the rat olfactory bulb: I. Volumetric study of the bulbar layers
Authors: Royet J. P. , Jourdan F. , Ploye H.
Published: January 2005

Current models of sensory coding in the olfactory bulb are based on the notion of topographical specificity in the processing of stimuli. Part of this hypothesis comes from studies of patterns of radiolabelled 2‐deoxyglucose uptake, and local morphometric variations of the mitral cell size observed following prolonged exposure to an odor. The present study explored the possibility that exposing young rats to a long‐term stimulation with an odor would induce spatially distributed volumetric variations of the bulbar layers. Three groups of 5 rats have been studied: (1) stimulated with ethyl acetoacetate from birth to 1 month of age, (2) unilaterally deprived following early cauterization of one nostril, and (3) normal animals of same age. Fourteen frontal histological sections uniformly distributed along the rostrocaudal axis of the olfactory bulb were used for this study. Areas of the bulbar layers were measured with the aid of an image analyser and the volume of the corresponding layers deduced by computation. Following complete sensory deprivation, the volume of all bulbar layers, except the periventricular core, was homogeneously reduced along the rostrocaudal axis of the olfactory bulb. Following long‐term stimulation with ethyl acetoacetate, volume reduction was significantly higher in anterior and middle regions than in the posterior part of the olfactory bulb. It is assumed that neuronal pathways activated by ethyl acetoacetate stimulation are mainly located in the posterior part of the olfactory bulb. Functional interpretations of these results are discussed with respect to the spatial dimension in olfactory coding.
Anatomical evidence of the projection of pontine omnipause neurons to midbrain regions controlling vertical eye movements
Authors: Ohgaki Tohru , Markham Charles H. , Schneider Jay S. , Curthoys Ian S.
Published: January 2005

Both anatomical and physiological studies have shown that pause neurons (PNs) in the medial pontine reticular formation project to two groups of burst neurons (BNs) involved in the genesis of horizontal saccadic eye movements: The excitatory burst neurons (EBNs), which lie rostral to the abducens nucleus, and the inhibitory burst neurons (IBNs), which lie caudal to the abducens. This study is concerned with the projection from PNs to a group of vertical BNs in the nucleus of the H field of Forel (H FF) in the caudomedial subthalamus. Three anatomical methods were used to demonstrate this connection.

First, intra‐axonal horseradish peroxidase (HRP) injection into physiologically identified PN axons demonstrated axonal branching and axonal terminations in and around the H FF. Second, micro‐injection of the tracer Phaseolus vulgaris leucoagglutinin (PHA‐L) into the pontine PN region labelled terminal axons and boutons in the nucleus of the H FF. Third, extracellular pressure injection of HRP into H FF yielded retrogradely labelled pontine PN neurons. These anatomical results confirmed the termination of PNs in areas controlling rapid vertical eye movements as physiologically demonstrated by Nakao et al.: Exp. Brain Res. 70:632–636, (88). This work points to the major role of pontine PNs in the synchronization of BN activity in rapid eye movements in all directions.
Organization of the projections from the trigeminal brainstem complex to the superior colliculus in the rat and hamster: Anterograde tracing with Phaseolus vulgaris leucoagglutinin and intra‐axonal injection
Authors: Rhoades Robert W. , Fish Stephen E. , Chiaia Nicolas L. , Bennett‐Clarke Carol , Mooney Richard D.
Published: January 2005

Anterograde tracing with Phaseolus vulgaris leucoagglutinin (PHA‐L) and intra‐axonal recording and injection techniques were employed to describe the projection from the trigeminal (V) brainstem complex to the deep laminae of the superior colliculus (SC) in the hamster and the rat. The organization of these projections was the same in the two species. Deposits of PHA‐L into V nucleus principalis (PrV) produced labelled axons and boutonlike swellings in the lower stratum griseum intermediale (SGI) and upper stratum album intermedium (SAI) in the SC bilaterally. Plots of boutonlike swellings indicated that the terminals of this projection were arrayed in clusters. Nucleus principalis also projected to the stratum griseum profundum (SGP) and stratum album profundum (SAP). This deeper projection did not terminate in clusters and it was most prominent in the lateral SC. The ipsilateral PrV‐SC projection appeared to arise mainly from axons that recrossed the midline at the level of the SC commissure. Reconstruction of individual PHA‐L labelled fibers demonstrated that single axons gave rise to terminals on both sides of the midline. Deposits of PHA‐L into V subnucleus interpolaris (SpI) yielded results that were identical to those obtained with PrV injections with one exception: none of these deposits produced any labelled terminals in the ipsilateral SC. Deposits of PHA‐L into V subnucleus caudalis (SpC) produced only sparse labelling in SC. Most labelled swellings were located in the SGP and SAP and they were visible only in the SC contralateral to the PHA‐L injection site. Single axons arising from cells in SpI were recorded and injected with horseradish peroxidase (HRP) in the hamster's SC. These fibers all responded to stimulation of multiple mystacial vibrissae and gave rise to 2–5 clusters of bouton‐like swellings in the lower SGI and upper SAI.