bluuebunny/crossref_metadata_2025 huggingface dataset:
Different origins of cochlear efferents in some bat species, rats, and guinea pigs
Authors: Aschoff Andreas , Ostwald Joachim
Published: January 2005

The origin of olivocochlear efferents was studied in the rat, the guinea pig, and the bats Rhinolophus, Rhinopoma, Tadarida, and Phylostomus by retrograde labeling with HRP and the fluorescent dye fast blue. In all species with the exception of Rhinolophus rouxi two types of cochlear efferents could be found: small neurons located in the lateral superior olive (LSO) and larger ones located bilaterally in the periolivary region. In bats and rats small olivocochlear neurons (OCN) were found only in the ipsilateral LSO. In guinea pigs some small OCN were found also in the contralateral LSO. Large OCN were found in all animals except Rhinolophus. They were organized in a horseshoelike nucleus that extended in a rostrocaudal direction and bent rostrally around the medial superior olive (MSO). This nucleus contains several periolivary nuclei described separately by other authors.

In Rhinol rouxi somata of all olivocochlear efferents are concentrated in a single nucleus between the MSO and LSO, which we therefore call the nucleus olivocochlearis. This nucleus stains for acetylcholinesterase. We consider its neurons to be similar to small OCN, because they are small, associated with the LSO, and only ipsilaterally labeled. This fits well with the fact that Rhinolophus lacks an efferent innervation of outer hair cells (Bishop: Ph.D. Thesis, University of North Carolina, Chapel Hill, '86; Bruns and Schmieszek: Hear. Res. 3: 27–43, '80), which are normally innervated by large OCN (Guinan et al: J. Comp. Neurol. 221: 358–370, '83).
Ultrastructural identification of synaptic terminals from the axon of type 3 interneurons in the cat lateral geniculate nucleus
Authors: Montero V. M.
Published: January 2005

Synaptic terminals from the axons of type 3 neurons in the A‐laminae of the cat LGN impregnated with the Golgi gold‐toning procedure were examined at light and electron microscopic levels. The axons were identified by their somatic origin, thin diameter, and, in one of these cells, by dense undercoating beneath the axolemma, which is a known characteristic of the axon initial segment. The axon of one of the analyzed cells was profusely branched and extended throughout most of lamina A within the dendritic domains of the cell, and both types of processes were oriented along projection lines in LGN. This suggests that the dendrites and axons of type 3 cells receive inputs and exert effects, of probably inhibitory nature, within restricted retinotopic regions of LGN. The vast majority of the axon terminals of these cells were distributed in series along axonal branches. In one of the type 3 cells, however, a dense cluster of terminals arising from a secondary axonal branch was observed. Ultrastructurally, the analyzed synaptic terminals of the type 3 cells contained flattened or pleomorphic synaptic vesicles, dark mitochondria, and established synapses that appeared to be of symmetrical type when the membranes were perpendicularly cut. On the basis of these characteristics these terminals are classified as F boutons, following Guillery's (Z. Zellforsch. 96: 1–38, '69), nomenclature. The postsynaptic elements to the axon terminals were dendrites of small to medium size, which received “en passant” synaptic contacts in extraglomerular regions of the geniculate neuropil by the terminals distributed in series. The axon terminals located in clusters, however, made synapses with dendrites in glomerular regions of the neuropil, where they were not seen postsynaptic to retinal or other types of terminals. This is in contrast to the postsynaptic nature of F2 boutons in the same glomeruli, which have been identified as dendritic appendages of the GABA positive type 3 neurons in the cat LGN (Montero: J. Comp. Neurol 254: 223–245, '86). On the other hand, the axonal F terminals differ from F1 boutons in terms of synaptic relations and ultrastructure, since the latter have been shown to be presynaptic to F2s and sonata and to contain crowded populations of flat synaptic vesicles which give them a characteristic dark appearance. Terminals equivalent to F1 boutons have been shown to originate from perigeniculate cells in the rat LGN. From these observations it is suggested that the geniculate GABAergic interneurons support two morphologically and functionally different types of inhibitory terminals synapsing the dendrites of relay cells: the dendritic F2 terminals that in microcircuits are under the influence of retinal, cortical, perigeniculate, and cholinergic terminals from the midbrain, and the axonal F boutons, which would convey to the postsynaptic relay cell the unaltered output of these interneurons.
Cytoarchitecture of the avian ventral lateral geniculate nucleus
Authors: Guiloff Gloria D. , Maturana Humberto R. , Varela Francisco J.
Published: January 2005

The avian thalamic ventral lateral geniculate nucleus (GLv) was studied by light microscopic techniques in order to understand its anatomy, neuronal composition, and the nature of its retinal and tectal afferents. The avian GLv is of considerable interest because physiological experiments show that it is the brain structure with the highest percentage of color‐opponent responses (Maturana and Varela, '82).

We used adult pigeons and quail for the present study. With Nissl techniques a predominance of medium‐size neurons (58%) constitute the GLv. The shape, size, and orientation of the different neurons is highly variable throughout the GLv. With the Golgi methods, 5 classes of neurons are distinguished: I and IV (large), II (medium‐size), III and V (small). Some class IV large neurons have bifurcated axons; no axons were distinguished on the small neurons. Optic fibers penetrating the GLv are often collateral branches of retinal axons that continue elsewhere. Fink‐Heimer methods show that retinal axon terminals end around large and medium‐size neurons and also reach the internal lamina of the GLv. HRP tracing shows that the large and medium‐size neurons of the GLv project to the optic tectum.

On the basis of comparisons between the cytoarchitecture of the GLv described here and the physiological findings previously reported (Maturana and Varela, '82; Pateromichelakis, '79), we suggest that: (1) large GLv neurons are the color‐opponent units, (2) medium‐size neurons are the movement‐sensitive units, and (3) small neurons are either interneurons (local circuit neurons), or they might project to the area pretectalis or to some other GLv projection region not yet described.
Thalamic projections to fields A, AI, P, and VP in the cat auditory cortex
Authors: Morel Anne , Imig Thomas J.
Published: January 2005

Thalamocortical projections to four tonotopic fields (A, AI, P, and VP) of the cat auditory cortex were studied by using combined microelectrode mapping and retrograde axonal transport techniques. Horseradish peroxidase (HRP) or HRP combined with either tritiated bovine serum albumin or nuclear yellow was injected into identified best‐frequency sites of one or two different fields in the same brain. Arrays of labeled neurons were related to thalamic nuclei defined on the basis of their cytoarchitecture and physiology. In some cases, patterns of labeling were directly compared with thalamic best‐frequency maps obtained in the same brain. We compared only patterns of labeling resulting from injections into similar parts of the frequency representation in different fields to insure that observed differences in patterns of labeling did not simply reflect differences in the frequency representation at the injection sites.

The thalamic projection to the four fields is divided among seven nuclei, three tonotopic nuclei (ventral nucleus, V; lateral part of the posterior group of thalamic nuclei, Po; and dorsal cap nucleus, d) and four nontonotopic nuclei (caudodorsal nulceus, cd; ventrolateral nucleus, vl; and small, Ms, and medium‐large, Mg, cell regions of the medial division). Projections to each field differ, and each field receives inputs from tonotopic and nontonotopic nuclei. Field A receives its major inputs from Po and Mg, and a minor input from V. Field AI receives its major inputs from V, Po, and Mg, although Po and Mg have heavier projections to field A. Field P receives its major inputs from V, d, and vl; and minor inputs from cd, Ms, Mg, and Po. Field VP receives major inputs from V, vl, and cd; and minor inputs from d, Ms, and Mg.

There are segregated territories in V and Po in which most neurons project to one cortical field (major projection), and a smaller proportion projects to one or more other fields (minor projections). Field VP receives a major projection from the caudal pole of V. Field P receives a major projection from the caudal half of V, and from a thin band along the dorsal border of rostral V. Field AI receives a major projection from most of the rostral one‐half of V, and smaller areas in Po and the caudal half of V exclusive of its caudal pole. Field A receives a major projection from most of Po.

Neurons with collateral projections to at least two cortical fields have been found in small proportions in most areas projecting to tonotopic cortex. In V and Po at least one‐third of the minor‐projection fibers appear to be collaterals of major‐projection fibers.
Segmental origins of the cricket giant interneuron system
Authors: Jacobs Gwen A. , Murphey R. K.
Published: January 2005

The segmental origins of the cricket giant interneuron system have been studied by staining these neurons with cobalt during the last half of embryonic development. The results demonstrate that the interneurons are derived from three distinct clusters of embryonic neurons that form a serially repeating pattern in each abdominal ganglion. Some of the neurons previously described in adults (Mendenhall and Murphey, '74; Murphey, '85) have been identified in embryos and are described here with respect to this pattern. These neurons include both giant interneurons and several non‐giant mechanosensory interneurons that mediate several different sensory modalities. The anatomical organization of this system is compared to similar mechanosensory systems in other insects and crustacea.
Dopaminergic regulation of horizontal cell gap junction particle density in goldfish retina
Authors: Baldridge William H. , Ball Alexander K. , Miller Rodman G.
Published: January 2005

Light‐ or dark‐adapted goldfish (Carassius auratus) retinas were treated with dopamine, which is believed to uncouple horizontal cells via D1 receptors, or with the dopamine antagonist haloperidol. Aldehyde‐fixed retinas were freeze‐fractured and the replicas examined by electron microscopy to identify horizontal gap junctions. The density (number per μm2) of intra‐membrane particles of horizontal ceil soma gap junctions was significantly lower in light‐adapted and dopamine‐treated retinas than in dark‐adapted and haloperidol‐treated retinas. There was no statistically significant difference between gap junction particles densities in (I) light‐adapted (untreated) and in dopamine‐treated (light‐ or dark‐adapted) retinas, or between (II) dark‐adapted (untreated) and haloperidol‐treated (light‐ or dark‐adapted). These results suggest that the uncoupling of horizontal cell somas by dopamine is accompanied by a decrease in gap junction particle density and that there is a greater release of dopamine during light‐adaptation than dark‐adaptation. Unlike horizontal cell somas, horizontal cell axon terminals did not show consistent changes in gap junction particle density with light‐ or dark‐adaptation. Although the data suggests that there may be a reduction in axon terminal gap junction particle density with dopamine treatment, this effect is not reversible with haloperidol treatment. Our results suggest that the regulation of gap junctions may differ at two sites within the same cell.
Overlap in the distribution of cholinergic and catecholaminergic neurons in the upper brainstem of the ferret
Authors: Henderson Z.
Published: January 2005

The distribution of catecholaminergic and cholinergic neurons in the upper brainstem of the ferret were mapped by staining immunohistochemically two adjacent series of sections of brainstem for tyrosine hydroxylase and choline acetyltransferase, respectively. As in other species, large numbers of tyrosine‐hydroxylase‐positive neurons are localized in the ventral tegmental area (A10), the substantia nigra (A9), and in A8. Tyrosine‐hydroxylase‐positive neurons in the dorsolateral pontine tegmentum (A4, A6, and A7‐the locus coeruleus complex) of the ferret are rather diffusely distributed, as has been observed in other carnivore species such as the cat and the dog, but unlike in the cat, these cells in the ferret display a relative uniformity in size and morphology.

Choline‐acetyltransferase‐positive neurons which extend in the ferret's pedunculopontine tegmental nucleus and ventral parabrachial area (Ch5) are relatively large cells that stain intensely for choline acetyltransferase, and their dendrites form prominent bundles in regions where unstained fibre tracts are prevalent. Choline‐acetyltransferase‐positive neurons distributed in the laterodorsal tegmental nucleus (Ch6) are smaller than the cholinergic cells of Ch5, and they stain less intensely for choline acetyltransferase.

Rostrally, there is little overlap between the catecholaminergic cell groups A8, A9, and A10 and the cholinergic cell groups of Ch5 and Ch6. Caudally, the Ch5 neurons extend some considerable extent into the locus coeruleus complex. In the region of overlap, no cells with staining for both tyrosine hydroxylase and choline acetyltransferase were observed, as was ascertained with a double staining method employing a combination of tyrosine hydroxylase immunofluorescence and choline acetyltransferase peroxidase‐antiperoxidase immunohistochemistry.

In conclusion, the ferret has a typically carnivore pattern for the distribution of catecholaminergic cells in the upper brainstem, and there is a significant overlap between the catecholaminergic and cholinergic cell groups in the dorsolateral pontine tegmentum.
FMRFamidelike peptides of homarus americanus: Distribution, immunocytochemical mapping, and ultrastructural localization in terminal varicosities
Authors: Kobierski Linda A. , Beltz Barbara S. , Trimmer Barry Andrew , Kravitz Edward A.
Published: January 2005

The distribution of FMRFamidelike peptides was studied in the nervous system of the lobster Homarus americanus by using immunocytochemical and radioimmunological techniques. By radioimmunoassay FMRF‐amidelike immunoreactivity (FLI) was found in low levels (ca. 1 pmol/mg protein) throughout the ventral nerve cord and in much higher amounts (60–100 pmol/mg protein) in the neurosecretory pericardial organs. Immunocytochemical studies showed FLI in approximately 300–350 cell bodies, and in distinct neuropil regions, neuronal fiber tracts, and varicose endings. Specificity of the immunostaining was tested by preabsorbing the antiserum with FMRFamide, with peptides having similar carboxyl termini to FMRFamide (Met‐enkephalin‐Arg‐Phe, Phe‐Met‐Arg‐Tyr‐amide), with several amidated peptides (α‐melanocyte‐stimulating hormone, substance P, oxytocin), and with proctolin, a peptide found widely distributed in the lobster nervous system. Of these substances, only FMRFamide blocked the staining.

In addition to the pericardial organs, significant levels of FLI were found in neurosecretory regions associated with thoracic second roots and in the connective tissue sheath that surrounds the ventral nerve cord. In all three regions, immunocytochemical studies showed the FLI to be localized to fine fibers and associated terminal varicosities lying close to the surface of the tissue, with no obvious target in their immediate vicinity. When examined at the ultrastructural level, the immunoreactive varicosities of the thoracic second roots and of the ventral nerve cord sheaths were found a few microns from the surface of the tissue and contained electron‐dense granules. In the immunoreactive nerve cord sheath endings, in addition to the large, dense granules, small, clear vesicles were found. The appearance and location of these terminals suggest a neurohormonal role for FMRFamidelike peptides in lobsters. The observation that low levels of FLI are found in the hemolymph supports this suggestion. In addition, the localization of FLI to particular neuronal somata, fiber tracts, and neuropil regions suggests possible functional roles for these peptides in (1) integration of visual and olfactory information, (2) function of the anterior and posterior gut, and (3) the control of exoskeletal muscles.
Transection of the infraorbital nerve in newborn hamsters alters the somatosensory but not the visual representation in the superior colliculus
Authors: Mooney Richard D. , Nikoletseas Michael M. , Rhoades Robert W.
Published: January 2005

The experiments described in this report were designed to determine whether changing the somatosensory representation in the deep laminae of the hamster's superior colliculus would result in a corresponding reorganization in the visual map in the overlying superficial layers. The somatosensory representation was altered by transecting the infraorbital (IO) nerve on the day of birth. This trigeminal branch supplies, among other targets, the snout and mystacial vibrissa follicles. These peripheral structures compose a major portion of the somatosensory representation in the deep collicular laminae. The effects of these lesions were assessed in anatomical and physiological experiments when the animals reached adulthood.

Retrograde tracing with true blue demonstrated a 48% reduction in the number of trigeminocollicular neurons in the partially deafferented subnucleus interpolaris (the main source of trigeminal input to the rodent colliculus–e.g., Killackey and Erzurumlu: J. Comp. Neurol. 201:221–242, '81), but anterograde tracing with horseradish peroxidase (CHRP) and wheat germ agglutinin‐conjugated HRP showed that the terminal field of the trigeminocollicular projection from the deafferented subnucleus was essentially normal. This pathway terminated as a series of patches along the border between the stratum griseum intermediate and stratum album intermedium and encompassed approximately 75% of the rostrocaudal extent of the colliculus.

The electrophysiological experiments revealed a marked change in somatosensory collicular topography. There was an underrepresentation of the vibrissae and the entire IO peripheral field in the deep laminae of the nerve‐damaged animals, and neurons with trigeminal ophthalmic and mandibular receptive fields were recorded from portions of the colliculus in which only whisker‐sensitive neurons would be normally isolated. There were no corresponding changes in the organization of the visual representation.

These results support the conclusion that the organization of the visual representation in the superficial laminae and the organization of the somatosensory map in the deep layers of the mammalian superior colliculus follow independent developmental programs.
Distribution of GABA‐like immunoreactivity in the rat amygdaloid complex
Authors: Nitecka L. , Ben‐Ari Y.
Published: January 2005

The distribution of GABA‐like (GABA‐Li) immunoreactivity in the rat amygdaloid complex was studied by using an anti‐GABA antibody. GABA‐Li positive neurons and processes were present in every nucleus of the complex. Three patterns of immunoreactivity were revealed: (1) the intercalated masses and the lateral olfactory tract nucleus exhibited the most intense staining of the neuropil, and virtually every neuron was labeled, (2) the central and medial nuclei contained intensely labeled neuropil and moderately labeled neurons, and (3) in the remaining nuclei, the neuropil was weakly labeled, and relatively numerous GABA‐Li neurons were present. Our results suggest that: (1) the intercalated masses and lateral olfactory tract nucleus consist of large aggregates of GABA‐Li immunoreactive neurons, and (2) the lateral, basal dorsal, and the posterior cortical nuclei may constitute a significant source of GABAergic connections to other amygdaloid nuclei, in particular to the medial and central nuclei.
Distribution of specific intermediate‐filament proteins in the goldfish retina
Authors: Jones Paul S. , Schechter Nisson
Published: January 2005

The intermediate‐filament proteins expressed in the goldfish retina were investigated by immunohistochemistry and by immunoblotting. Polyclonal antibodies that previously had been raised against the goldfish optic nerve neurofilament (ON1 and ON2) and glial filament (ON3 and ON4) proteins were used in this study. Anti‐ON1/ON2 antiserum reacted on a retinal immunoblot with two proteins having molecular weights and isoelectric points corresponding to those of ON1 and ON2. Histologically, the most pronounced anti‐ON1/ON2 reactivity was observed in the ganglion cell layer of the goldfish retina. The anti‐ON3/ON4 antiserum reacted with a single protein on a retinal immunoblot. This protein had a molecular weight and isoelectric point which corresponded to the goldfish optic nerve glial filament proteins. This anti‐serum labeled horizontal cells in retina sections. Three previously unidentified goldfish visual‐pathway intermediate‐filament proteins sharing a molecular weight of 60K were observed on two‐dimensional gels of retinal cytoskeletal proteins and on retinal immunoblots which were probed with a monoclonal antibody which recognizes an epitope common to all intermediate Filament proteins.

The possible existence of homologs of mammalian GFAP and vimentin in the goldfish retina was also explored. Antibodies directed against mammalian GFAP and vimentin labeled the Müller fibers and the cone horizontal cells, respectively. However, immunoblot analysis and a comparison of the two‐dimensional gel electrophoresis patterns of goldfish retinal and rat spinal cord cytoskeletal proteins demonstrated a lack of goldfish proteins identical to the mammalian intermediate‐filament proteins.
Distribution of substance P‐like immunoreactive retinal ganglion cells and their pattern of termination in the optic tectum of chick (Gallus gallus)
Authors: Ehrlich D. , Keyser K. T. , Karten H. J.
Published: January 2005

Substance P‐like immunoreactive (SP‐LI) neurons were identified within the inner nuclear layer and ganglion cell layer of the chick retina. The SP‐LI cells in the inner nuclear layer consisted of several subtypes of neurons, differing in soma size and dendritic arborization. In the ganglion cell layer a population of moderately labelled SP‐LI neurons was also present. About 6–9 m̈m in diameter and spaced 50–80 m̈m apart, they formed a regular array across the entire retina, with a density of about 400 cells/mm2 in the superior temporal retina, declining to less than 100 cells/mm2 in the peripheral retina. The total number of SP‐LI cells in the ganglion cell layer was approximately 75,000. Individual axons could be followed toward the optic nerve head. Lesions near the optic nerve head resulted in axotomy of ganglion cells within a limited portion of the retina. Two days postaxotomy there were numerous SP‐LI swellings in the proximal segments of axotomized axons. SP‐LI neurons in the axotomized zone were larger, more numerous, and showed increased staining of their processes. Fourteen days following a retinal lesion, there was depletion of all SP‐LI cells in the ganglion cell layer within the axotomized zone, but the SP‐LI neurons in the inner nuclear layer were not noticeably affected.

Following a localized injection of rhodamine‐coupled latex beads into the optic tectum, a population of retinal ganglion cells (RGCs) in the contra‐lateral retina was retrogradely labelled. Many of these cells also exhibited SP‐like immunoreactivity.

Examination of the optic tectum indicated the presence of SP‐LI fibres in laminae 2–13 (nomenclature of Cajal: Histologie du Systems Nerveux. Vol. 2. Paris: Maloine, '11), with immunoreactive terminal regions present mainly in laminae 2–4, 7, and 9–13. SP‐LI cell bodies were found predominantly in laminae 10–12 and 13. Fourteen days following a retinal lesion, SP‐LI processes and terminals were depleted from laminae 2 and 3. Immunoreactive cells and processes in the remaining laminae of the optic tectum were not noticeably altered.

The present report confirms the existence of SP‐LI retinal ganglion cells in the chick retina and demonstrates their contribution to lamina specific SP‐LI arborization in the optic tectum.
Afferent and efferent connections of the primary octaval nuclei in the clearnose skate, Raja eglanteria
Authors: Barry Michael A.
Published: January 2005

Horseradish peroxidase techniques were employed to trace the central projections of afferents from the individual endorgans of the membranous labyrinth and to delineate the efferent projections from the primary octaval nuclei to the spinal cord and midbrain octavolateralis area in the clearnose skate, Raja eglanteria. First‐order octaval afferents project ipsilaterally to five primary octaval nuclei, namely: magnocellular, descending, posterior, anterior, and periventricular. Octaval afferents also terminate in the reticular formation, nucleus intermedius (primary mechanoreceptive lateral‐line nucleus), and vestibulolateral lobe of the cerebellum. Each primary octaval nucleus receives afferent input from each labyrinthine endorgan, with the possible exception of macula neglecta input to the magnacellular nucleus. Within the anterior, descending, and to a lesser extent posterior and magnocellular nuclei, this input is largely nonoverlapping. Semicircular canal cristae afferents terminate ventrally, saccular and lagenar afferents dorsally, utricular afferents laterally, and macula neglecta afferents course ventrally but terminate largely dorsally within these nuclei. In the vestibulolateral lobe of the cerebellum, cristae afferents project primarily to the pars medialis, whereas macular endorgan afferents terminate in the pars lateralis. Primary afferent input to the reticular formation is predominantly from the horizontal canal crista. The densest projections to nucleus intermedius are from the utriculus and sacculus. Vestibulospinal projections originate primarily from the magnocellular and descending nuclei. Secondorder auditory neurons are most likely located in dorsomedial parts of the descending and anterior nuclei. Cells in these nuclei project directly to the auditory area of the midbrain octavolateralis complex, but projections to this area originate predominantly from nuclei C1 and C2, which are possible superior olivary homologues.
Distribution of catecholaminergic cells in the retina of the rat, guinea pig, cat, and rabbit: Independence from ganglion cell distribution
Authors: Mitrofanis John , Vigny Annette , Stone Jonathan
Published: January 2005

By using an antibody against tyrosine hydroxylase (TH), the rate‐limiting enzyme in the production of catecholamines, we have examined the morphology and distribution of catecholaminergic cells in the retinas of the rat, guinea pig, cat, and rabbit. In the albino rat, as reported by others, most TH‐immunoreactive (TH‐IR) cells were amacrine cells, and formed two morphological classes. Cells of one class (class 1) are stellate amacrine cells, the somata of most being in the inner part of the inner nuclear layer (INL). Cells of the second class (class 2) were seen only as small somata, also in the inner part of the INL. Cells of both classes were found in all areas of the retina, with a distinct but broad concentration around the superior‐temporal margin of the retina. A small number of TH‐IR interplexiform cells was seen. In the pigmented rat, only class 1 cells were recognized, also concentrating at the superior‐temporal margin. In the guinea pig, cat, and rabbit, TH‐IR cells also seemed to form one morphological class of amacrine cells, which resembled the class 1 cells of the albino rat. In the guinea pig and cat, their distribution resembled that seen in the rat, with the cells concentrating at the superior‐temporal margin of the retina. In the rabbit, TH‐IR cells concentrated weakly in the visual streak, but at both ends of the streak the concentration of TH‐IR cells extended farther peripherally than the concentration of ganglion cells. Overall, the distribution of TH‐IR cells seems largely or (in the rabbit) partially independent of the distribution of ganglion cells. This independence raises questions of the development and function of this group of amacrine cells.
Morphology and ultrastructure of physiologically identified substantia gelatinosa (lamina II) neurons with axons that terminate in deeper dorsal horn laminae (III–V)
Authors: Light Alan R. , Kavookjian Anahid M.
Published: January 2005

In order to determine their local circuit function, we have examined physiologically characterized, intracellularly labeled neurons in laminae I and II with light and electron microscopes. Single neurons in the spinal substantia gelatinosa (lamina II) of the cat and monkey were recorded intracellularly and characterized physiologically. Following characterization, the neurons were labeled with horseradish peroxidase that was iontophoretically ejected from the recording micropipette. After fixation and sectioning, histochemical reaction allowed visualization of the neuron soma, dendrites, and axon. The four nociceptive neurons reported here (three from cats and one from a monkey) had axons that distributed terminal collaterals to deeper laminae of the spinal cord, including laminae III, IV, and V. Electron microscopy of the axons demonstrated that the parent axons were myelinated and that the terminal collaterals established synaptic contact with neurons in the deeper laminae. These results suggest that some substantia gelatinosa neurons relay nociceptive information to neurons in deeper regions of the spinal dorsal horn via myelinated axons.
Ultrastructural characterization of the synapses of the crossed temporodentate pathway in rats
Authors: Davis Lauren , Vinsant Sharon L. , Steward Oswald
Published: January 2005

The present, study was undertaken to define the ultrastructure of synapses of the crossed temporodentate pathway from the entorhinal cortex to the contralateral dentate gyrus and to compare the synapses of the sparse crossed pathway with those of the massive ipsilateral temporodentate pathway. The synapses of the crossed pathway were identified by using EM degeneration and EM autoradiographic techniques. For the degeneration studies, adult male Sprague‐Dawley rats were killed 1, 2, or 4 days following a unilateral entorhinal cortex lesion and prepared for electron microscopy. To identify the synapses by using autoradiographic techniques, four animals received injections of 3H‐proline into the entorhinal cortex, were allowed to survive for 3 days, and were prepared for EM autoradiography. Degenerating synapses of the crossed pathway that were found in the molecular layer of the dentate gyrus contralateral to a lesion formed asymmetric synapses on spines and possessed presynaptic organelles indistinguishable from synapses of the ipsilateral temporodentate pathway. The number of degenerating synapses was very low at all survival intervals (14.80 degenerating synapses/10,000μm2 at 1 day postlesion and 1.95 degenerating synapses/10,000μm2 at 2 days postlesion); no degenerating synapses were found at 4 days postlesion. Ninety‐eight percent of the degenerating synapses found at 1 day postlesion exhibited electron‐lucent degeneration. At 2 days postlesion 83% of the degenerating synapses in the dorsal blade and 18% of those in the ventral blade showed lucent degeneration; the remainder were electron dense. EM autoradiography confirmed the degeneration studies in terms of the type of terminals that were labeled and suggested that the density of the crossed pathway was higher than the degeneration results implied. We conclude that synapses of the crossed temporodentate pathway have a similar ultrastructure to synapses of the ipsilateral temporodentate pathway but exhibit a rapid form of degeneration such that they disappear very rapidly following the lesion.
Postnatal development of dendrites of relay neurons in the lateral geniculate nucleus of the marmoset (Callithrix jacchus): A quantitative Golgi study
Authors: Fritschy J. M. , Garey L. J.
Published: January 2005

Dendrites of multipolar relay neurons in the lateral geniculate nucleus of the marmoset (Callithrix jacchus), at various ages from birth to adulthood, were studied in rapid Golgi preparations. The dendrites were analyzed by means of three‐dimensional computer reconstructions and decomposed into intermediate and terminal segments, both of which were further classified according to their centrifugal order. Measurements were made of the number of segments per dendrite, the total length of dendrites, and the mean length of intermediate and terminal segments. In adult marmosets, there are four stem dendrites on average per neuron, and each dendrite divides into a mean of 14 segments. Between birth and 6 weeks of age, the mean dendritic length doubles, mainly because of changes in terminal segments. There is a significant decrease in dendritic length into adulthood. The total number of stem dendrites lose distal segments, after which there is a significant increase in the number of segments of orders 3 to 7. The mean length of intermediate segment does not change with age, nor with order, whereas the length of terminal segments increase from 50 to 120 μm from birth to 6 weeks of age, and then decrease to the adult value of 80μm. In conclusion, during the period of most rapid visual development, important morphological changes occur in geniculate relay‐cell dendrites, involving essentially terminal segments. These observations correlate well with changes of geniculate volume and neuronal density.
Demonstration of topographically organized projections from the hypothalamus to the pontine nuclei: An experimental anatomical study in the cat
Authors: Aas Jan‐Erik , Brodal Per
Published: January 2005

In 22 cats implantations and injections of horseradish peroxidase–wheat germ agglutinin (HRP‐WGA) or Fluoro‐Gold were placed in the pontine nuclei or the hypothalamus. The occurrence and distribution of labeled cells in the hypothalamus and of labeled terminal fibers in the pontine nuclei were mapped.

Following implantations of HRP‐WGA ventromedially in rostral parts of the pontine nuclei, 22–44% of all labeled cells in the brainstem and diencephalon are found in the medial mamillary nucleus ipsilateral to the implantation. Some labeled cells are also found in the supramamillary, premamillary, anterior mamillary, and tuberomamillary nuclei. Thus, labeled cells in the hypothalamus make up 33–54% of all labeled cells in the brainstem and diencephalon in such cases. In contrast, implantations and injections in mediocaudal parts of the pontine nuclei result in labeling of cells mainly in the posterior, dorsal, and lateral hypothalamic areas (terminology of Bleier: The Hypothalamus of the Cat. Baltimore: Johns Hopkins Press, '61). In these cases the labeled cells in the hypothalamus make up 16–25% of all labeled cells in the brainstem and diencephalon. Implantations in more lateral parts of the pontine nuclei label only a few cells in the hypothalamus.

Following implantations of HRP‐WGA in restricted parts of the hypothalamus, fibers from the medial mamillary nucleus were found to terminate ventromedially at all rostrocaudal levels of the pontine nuclei, ipsilateral to the implantation. In the rostralmost part of the pontine nuclei, the terminal labeling forms a dense, transversely oriented, c‐shaped band. Fibers from the posterior and dorsal hypothalamic areas terminate medially and dorsomedially in the caudal third of the pontine nuclei. Sparse terminal labeling is also seen in lateral parts of the pontine nuclei and medially at more rostral levels.

In two cases with small implantations of HRP‐WGA ventromedially in rostral parts of the pontine nuclei, labeled cells are found both in the medial mamillary nucleus and the cingulate gyrus. Thus, it seems possible that fibers from the medial mamillary nucleus and the cingulate gyrus converge upon a restricted area ventromedially in rostral parts of the pontine nuclei.
Tonotopic projection from the dorsal to the anteroventral cochlear nucleus of mice
Authors: Wickesberg Robert E. , Oertel Donata
Published: January 2005

To understand how auditory information is processed in the cochlear nuclei, it is crucial to know what circuitry exists and how it functions. In slice preparations, horseradish peroxidase (HRP) injections into the anteroventral cochlear nucleus (AVCN) reveal two circuits: a connection between the dorsal cochlear nucleus (DCN) and AVCN and a local circuit confined to the AVCN. Extracellular injection in the AVCN labels a band of cells in the DCN. The labeled cells in the DCN lie within a band of auditory nerve fiber terminals that are labeled by the same injection, showing that the connection from the DCN to the AVCN is frequency specific. The injections into the AVCN also labeled a cluster of neurons in the AVCN dorsal to the injection site. These cells may be interneurons that relay information from areas encoding higher frequencies to areas encoding lower frequencies within the AVCN. In the parasagittal plane, the AVCN is organized along two orthogonal axes that are indicated with HRP labeling of fibers and cell bodies. The tonotopic axis runs approximately dorsoventrally; the isofrequency axis runs approximately rostrocaudally. The axons of labeled DCN neurons and the cluster lie along the tonotopic axis, whereas the labeled auditory nerve fibers define the isofrequency axis. Where they cross is where HRP is taken up by the fibers. The area of uptake is small and lies in the middle of the darkly stained injection site.
Projections of the retinorecipient pretectal nuclei in the pigeon (columba livia)
Authors: Gamlin Paul D. R. , Cohen David H.
Published: January 2005

We have used anterograde autoradiographic and retrograde HRP techniques to investigate the efferent connections of the retinorecipient pretectal nuclei in the pigeon. In the accompanying paper we identified these nuclei in the pigeon as the nucleus lentiformis mesencephali–pars lateralis and pars medialis, the tectal gray, the area pretectalis, and pretectalis diffusus. Although there are reports of a few of the projections of these nuclei, they had not previously been the subject of a detailed study.

We found that different cell types in the lentiformis mesencephali, pars medialis and the lentiformis mesencephali, pars lateralis have descending projections to different targets. These targets include the inferior olive, the cerebellum, the lateral pontine nucleus, the nucleus papillioformis, the nucleus of the basal optic root, the nucleus mesencephalicus profundus, pars ventralis, the nucleus principalis precommissuralis, and the stratum cellulare externum. We found that a few cells in the lentiformis mesencephali project to the medial pontine nucleus, but that a much heavier projection arises from the nucleus laminaris precommissuralis, which is medial to the nucleus lentiformis mesencephali, pars medialis.

The tectal gray has predominantly ascending projections to the diencephalon. The nuclei that it projects to are the nucleus intercalatus thalami, the nucleus of the ventral supraoptic decussation, the nucleus posteroventralis, the ventral lateral geniculate nucleus, the nucleus dorsolateralis medialis, and the nucleus dorsolateralis anterior. The tectal gray also projects topographically to layers 4 and 8–13 of the optic tectum.

Area pretectalis has both ascending and descending projections. It has ipsilateral ascending projections to the nucleus dorsolateralis anterior, pars magnocellularis, the nucleus lateralis anterior, and the nucleus ventrolateralis thalami. It has ipsilateral descending projections to the central gray, the nucleus of the basal optic root, pars dorsalis, the lateral pontine nucleus, and the deep layers of the optic tectum. It has contralateral projections to the area pretectalis, the nucleus Campi Foreli, the interstitial nucleus of Cajal, the nucleus of Darkschewitsch, the cerebellum, and the Edinger‐Westphal nucleus.

The efferent projections of pretectalis diffusus are limited. It projects contralaterally to the pretectalis diffusus, and ipsilaterally to the nucleus of the ventral supraoptic decussation, the lateral pons, and the cerebellum.

Our results demonstrate that, by way of their ascending and descending projections, the retinorecipient pretectal nuclei can exert important influences on the range of visuomotor functions in which they participate. We know that area pretectalis mediates the pupillary light reflex (Gamlin et al., '84) and that the lentiformis mesencephali is involved in optokinetic nystagmus (McKenna and Wallman, '85). However, to our knowledge, other potential roles of the retinorecipient pretectal nuclei have not been identified.
Time of origin of cholinergic neurons in the rat basal forebrain
Authors: Semba Kazue , Fibiger Hans C.
Published: January 2005

The timing of the final mitotic division of basal forebrain cholinergic neurons was studied by injecting [3H]thymidine into timed pregnant rats and processing the brains of their progeny as young adults for immunohistochemistry with a monoclonal antibody to choline acetyltransferase (ChAT) followed by autoradiography. ChAT‐positive neurons located caudally in the basal forebrain were found to become postmitotic mostly on embryonic (E) days 12 and 13, whereas the peak final mitosis of more rostrally located ChAT‐positive neurons occurred increasingly later, with the most rostral ChAT‐immunoreactive neurons leaving their final mitotic cycles on E15 and E16. In all basal forebrain regions, cholinergic neurogenesis was complete by E17. These results indicate that the cholinergic neurons in the basal forebrain become postmitotic in a caudal‐to‐rostral gradient over about 5 days. The continuity of the gradient suggests that these cholinergic neurons may derive from the same germinal source.
Specificity of sensory projections to the spinal cord during development in bullfrogs
Authors: Smith Carolyn L. , Frank Eric
Published: January 2005

Sensory neurons in dorsal root ganglia of frogs project to areas of the spinal cord they do not normally innervate following removal of adjacent ganglia at tadpole stages (Frank and Westerfield, J. Physiol (Lond.) 324:495–505, '82b). A possible explanation of this phenomenon is that sensory neurons project to wider areas of the spinal cord in tadpoles than in adult frogs and that partial deafferentation causes the retention of these widespread projections. Therefore, the specificity of sensory projections to the spinal cord in tadpoles was assessed by staining individual dorsal roots with horseradish peroxidase. Thoracic sensory neurons project to thoracic segments of the spinal cord and to the brainstem in tadpoles, like thoracic sensory neurons in adult frogs. They rarely arborize in the brachial region even at stages when no other sensory fibers arborize at this level. Furthermore, their projections are restricted to the dorsal horn at all stages. Conversely, hypoglossal sensory neurons, which project into the intermediate gray matter in the adult, also project to this area in tadpoles. The finding that sensory neurons in tadpoles only project to areas of the spinal cord that they innervate in the adult suggests that the novel projections observed following partial deafferentation of the spinal cord are actually induced by the operation. An additional finding was that forelimb afferents, which project to an area extending from the obex to midthoracic levels in adult frogs, arborize at rostral spinal levels and at thoracic levels several stages before they form projections to the region around their own dorsal root. These differences in the stages at which projections to different levels of the spinal cord develop suggest that local properties of the spinal cord may control the timing of sensory fiber arborization.
Morphological diversity of displaced retinal ganglion cells in the rat: A lucifer yellow study
Authors: Buhl E. H. , Dann J. F.
Published: January 2005

Displaced retinal ganglion cells (DRGCs) were retrogradely labelled by injections of the fluorescent dye Fast Blue into the superior colliculi of pigmented rats. Following fixation these cells were intracellularly injected with Lucifer Yellow to determine their dendritic morphology and distribution.

Graphic reconstruction of Lucifer Yellow‐filled prelabelled neurones revealed a heterogeneous population of DRGCs. Their stratification within the inner plexiform layer was diverse and cells were classified according to their dendritic morphology.

The present sample consists largely of unistratifying neurones, the dendrites of which arborized within a narrow sublamina of the inner plexiform layer. They were characterized by a centrally located soma and densely branched dendritic network with little overlap within the branching pattern. In contrast, bistratifying DRGCs possessed a loose and sparsely branched dendritic structure, while diffusely stratifying neurones contained a high degree of dendritic crossing, culminating in a complex network, in which the soma position was biased toward the periphery.

One type of DRGC bore a striking resemblance to type 1 neurones (Perry, 1979; Proc. R. Soc. Lond. [Biol.] 204:363–375) in the ganglion cell layer. They were characterized by a large soma (15.8 μm ± 2.2 μm s.d.) and a dendritic field diameter averaging 288 μm (s.d. ± 62 μm) and were on average larger than the rest of the displaced population but smaller than type 1 cells in the ganglion cell layer. Since the stratification patterns of the displaced and nondisplaced type 1 neurones were indistinguishable, it is reasonable to assume that the Lucifer Yellow‐filled cells in the present study represent the displaced counterpart of regular type 1 ganglion cells. Therefore, it appears that despite the aberrant location of the soma within the inner nuclear layer, the dendritic morphology of the cell develops unimpeded into a normal stratification pattern, although both soma and dendritic field size are reduced. If displacement is a developmental aberration, this size decrease may arise from overcrowding within the inner nuclear layer where the soma becomes lodged erroneously during its migration to the ganglion cell layer. This would also account for the heterogeneity of displaced cells found in the present study, since the randomness of a developmental error would ensure that a variety of ganglion cell types was included in the displaced population.