Purkinje-like cells in the cochlear nucleus of the Common Tree Shrew (Tupaia glis) identified by calbindin immunohistochemistry.

The dorsal cochlear nucleus (DCN) of Tree Shrews (Tupaia glis; n=2) was examined by calbindin (CB) immunohistochemistry for the presence of Purkinje-like cells (PLCs), detected previously in only four different mammals. We found up to eight CB-immunoreactive PLCs in the left and right DCN, and a few axons, likely of PLC origin, that appeared to leave the DCN. These findings suggest that PLCs may have a wider distribution through mammalian species, and may represent more than just misrouted cells.

Unipolar brush cells in the human cochlear nuclei identified by their expression of a metabotropic glutamate receptor (mGluR2/3).

Unipolar brush cells (UBCs) reside in the mammalian vestibulo-cerebellum and the ventral (VCN) and, particularly, dorsal cochlear nuclei (DCN). Human cerebellar UBCs are numerous too, but auditory UBCs have escaped detection. The human DCN, considered a degenerated structure, lost lamination and possibly neurons common in lower mammals, like UBCs. We searched for human auditory UBCs probing their immunoreactivity against the calcium-binding protein calretinin (CR-IR), and a metabotropic glutamate receptor (mGluR2/3-IR). We found: UBCs are constituents of the human DCN and VCN, though in small numbers. These auditory UBCs are not CR-IR, in contrast to human cerebellar UBCs and cerebellar and auditory UBCs in non-primate mammals, but display mGluR2/3-IR. The human DCN, thus, appears more complete than previously thought. This may be of interest regarding auditory brainstem electrode implantations in deaf patients.

Rabbit and monkey visual cortex: more than a year of recording with up to 64 microelectrodes.

In the visual cortex of rabbits and a marmoset monkey, 32 and 64 microwires, respectively, were chronically implanted by an indirect insertion method so that the cortex was penetrated from the white matter. For more than 1 year recordings of action potentials of good quality were obtained at most electrodes. Recording stability was judged by spike shape, spike train autocorrelograms, and spike rates: within recording sessions, stability was essentially perfect. Periods in which the signals of several electrodes were stable could last for several days. A method of in vivo reconstruction of the electrode locations by micro-X-rays and subsequent stereophotogrammetry is presented. The aspect of animal welfare is considered.

Unipolar brush cells in marmoset cerebellum and cochlear nuclei express calbindin.

Unipolar brush cells (UBCs) are excitatory neurons in the mammalian cerebellum and cochlear nuclei (CN), including the CN of primates, as shown only recently. UBCs are readily identified by their expression of the calcium-binding protein calretinin (CR), except for those of the primate CN that hardly immunostain for CR. The present findings corroborate the existence of UBCs in the CN of a primate, Callithrix. Furthermore, evidence is presented for UBCs, in the cerebellum and a small subpopulation of UBCs in the CN of Callithrix to express the calcium-binding protein calbindin (CB). This may be unique for Callithrix as CB-expressing UBCs have not been recognized in any other mammal. Presence of CB but not CR in UBCs of the Callithrix CN may indicate a certain interchangeability between these two calcium-binding proteins.

Unipolar brush cells in the cochlear nuclei of a primate (Callithrix jacchus).

Unipolar brush cells (UBCs) have been recognized in the cerebella of many species including primates. They have also been identified in the cochlear nuclei (CN) of many mammals, however, not in any primate. Our immunohistochemical study in the marmoset demonstrates the presence of abundant calretinin immunoreactive (CR-ir) UBCs in the cerebellum, as in other mammals. In the marmoset CN, in contrast, CR-ir UBCs could hardly be identified. The reverse pattern was evident in sections immunostained for a metabotropic glutamate receptor (mGluR2/3-IR): beautifully stained UBCs were present in the CN, but the stained cerebellar structures were difficult to identify as UBCs. The present findings indicate that UBCs are present in the CN of primates, as in other mammals, but that cerebellar and CN UBCs might differ in their molecular equipment in primates.

Sites of simian foamy virus persistence in naturally infected African green monkeys: latent provirus is ubiquitous, whereas viral replication is restricted to the oral mucosa.

Foamy viruses (FV), retroviruses of the genus Spumavirus, are able to infect a wide variety of animal species and replicate in nearly all types of cultured cells. To identify the cells targeted by FV in the natural host and define the sites of viral replication, multiple organs of four African green monkeys naturally infected with simian FV type 3 were investigated for the presence of FV proviral DNA and viral transcripts. All organs contained significant amounts of FV proviral DNA. In addition to proviruses containing the complete transactivator gene taf, proviral genomes carrying a specific 295-bp deletion in the taf gene were detected in all monkeys. As in the case of human foamy virus the deletion leads to the formation of the bet gene that is regarded to be instrumental in the regulation of viral persistence. FV RNA was detected by RT-PCR and in situ hybridization only in the oral mucosa of one monkey. No other samples contained detectable levels of viral transcripts. Histopathological changes were not observed in any of the tissue samples analyzed. Our results show that the natural history of FV is characterized by latent infection in all organs of the host and by minimal levels of harmless viral replication in the oral mucosa. The broad host cell range in vivo further encourages the development of FV-derived vectors for therapeutic gene delivery.

Transient molecular visualization of ocular dominance columns (ODCs) in normal adult marmosets despite the desegregated termination of the retino-geniculo-cortical pathways.

The activity-dependent immediate early gene protein Krox-24, expressed in the neocortex at high basal levels, decreases rapidly upon neuronal deactivation (Chaudhuri et al. [1995] Vis. Neurosci. 12:35-50). In infant marmosets, as in most primates, the geniculo-cortical terminations segregate into eye-specific anatomical ocular dominance columns (ODCs), which disappear, however, during adolescence (Spatz [1989] Brain Res. 488:376-380), resulting in balanced inputs from the two eyes (Sengpiel et al. [1996] Vis. Neurosci. 13:145-160). Nevertheless, we found, in adult marmosets, 24 hours after monocular retinal activity blockade by tetrodotoxin, distinct alternating compartments of potentiated and depressed Krox-24-like immunoreactivity (Krox-IR) in layer IV of area 17. This pattern of Krox-IR disappeared at 10 days of retinal silencing, but was still present at this survival time in stains for cytochrome oxidase or NADPH-diaphorase. After 20 days of retinal silencing, the pattern was not demonstrable with any of the three stains. We term these compartments physiological ODCs, in contrast to the anatomical ODCs of most primates. If the anatomical ODCs of infant marmosets disappear by collateral sprouting into the inappropriate ODCs, then the collateral geniculo-cortical synapses might differ slightly in their properties from the original ones. We silenced the sets of original and collateral synapses of the one ocularity. This apparently transiently initiated, at the synapses driven by the intact eye, two different complex processes leading to molecular potentiation at the original synapses and to molecular depression at the collateral synapses.

Differences between guinea pig and rat in the dorsal cochlear nucleus: expression of calcium-binding proteins by cartwheel and Purkinje-like cells.

This study describes differences between guinea pig and rat in the immunoreactivities for calbindin (CB-IR) and parvalbumin (PV-IR) in cartwheel (CWC) and Purkinje-like (PLC) cells of the dorsal cochlear nucleus (DCN). CWCs are the most important inhibitory interneurons of the DCN. Their soma and dendrites stain intensely for CB-IR in guinea pigs but only weakly and incompletely in rats. In both species, the CWCs do not show PV-IR. PLCs, a rare type of DCN cells often interpreted as displaced cerebellar Purkinje cells misrouted during migration, are known from rat and mouse and are here described for guinea pig DCN. PLCs are intensely and completely stained for CB-IR and PV-IR in guinea pigs. In rats, they stain with similar completeness only for CB-IR, PV-IR being weak and restricted to the cell's soma. Similar staining differences between the two species are seen with the cerebellar Purkinje cells, i.e., PLCs resemble the cerebellar Purkinje cells more than do the CWCs. Based on the present material (and preliminary findings in a primate (marmoset), we speculate that the PLCs have their place in the circuitry of the DCN receiving input via parallel fibers, like the CWCs, and possibly projecting their axon onto the cerebellum.

Morphology and connections of neurons in area 17 projecting to the extrastriate areas MT and 19DM and to the superior colliculus in the monkey Callithrix jacchus.

Neurons of area 17, the primary visual cortex, project to various anatomically and physiologically different extrastriate areas and subcortical regions. In the present investigation, we addressed the question of whether the efferent neurons in area 17 can contribute to functional diversity between these regions. We approached this question by analyzing the dendritic morphology of neurons in area 17 projecting to area MT, area 19DM, and the superior colliculus in the new world simian primate Callithrix jacchus, because dendritic morphology is an important factor in determining physiological properties of nerve cells. Retrograde transport of fluorochromes injected into the target regions, and intracellular injections of Lucifer yellow in the prelabelled neurons, revealed the following. 1) Morphologically identical large pyramidal cells in layer VI of area 17 project to all three targets. Some of them possess axon collaterals to two or all three targets, suggesting that they provide common information to all three areas. 2) Pyramidal cells in layer IIIc projecting to area MT form a morphologically homogeneous population. 3) Three small to medium-sized pyramidal cell types in layers IIIa-c, spiny stellate cells in layer IIIc, and another large pyramidal cell type in layer VI project to area 19DM. 4) Pyramidal cells in the lower two-thirds of layer V in area 17 project to the superior colliculus. In conclusion, we have shown that in Callithrix one efferent pathway may originate from several cell types. However, with the exception of the large cells in layer VI, efferent cells projecting to area MT, area 19DM, and the superior colliculus were morphologically distinct. This suggests that functional differences between brain regions could arise in part from morphological heterogeneity between and within the efferent cell populations.

Calcium-binding proteins in the spiral ganglion of the monkey, Callithrix jacchus.

Calcium-binding proteins can act as intermediaries between changing levels of free intracellular calcium ions and the physiological response of neurons. Some of these proteins, among them calbindin (CB), calretinin (CR) and parvalbumin (PV), can act as calcium buffers. A survey of previous studies in rodents and human fetuses leads to the impression that many spiral ganglion cells co-express CB, CR, and PV. The findings of the present study suggest that, in the adult marmoset, the expression of CB is restricted to a small number of cells, most likely type II ganglion cells, and that at least some of the numerous type I ganglion cells co-express CR and PV. In the neonate marmoset, large numbers of putative type I ganglion cells from the apical cochlear turn transiently expressed a light and granular labeling for CB-like immunoreactivity, in addition to the cells we believe to be type II ganglion cells exhibiting a strong and solid CB-like staining. The spiral ganglion cells in all developmental stages co-expressed the mitochondrial enzyme cytochrome oxidase. Furthermore, a small population of CB-LI axons of unknown origin was found to terminate near the CB-immunoreactive ganglion cells.

Structural dynamics of synapses and synaptic components.

Learning and memory formation are apparently based on cascades of molecular and cellular processes with increasing time constants (ms to days and weeks), but even the most long-lasting effects are transient. Memory traces may permanently modify the behavior (activity patterns, gene expression) of neurons and neuronal networks. Therefore the question is raised whether our current view on the stability of synapses under normal conditions is tenable. Evidence is reviewed suggesting that as direct or indirect effects of modifications in bioelectrical activity and chemical trophicity, synapses may be remodeled and removed within days and weeks, and possibly within hours. Accordingly, species-specific connectivity patterns are not restricted to the standard architecture of the CNS, but (morpho-)genetics allow for a considerable number of alternative wiring patterns, which appear under unusual conditions during ontogenesis and in adulthood. Our present knowledge suggests that, rather than the formation of synapses, they are a selective process. Until now there is no direct method of measuring either synaptic reorganization or the average life span of synapses. Specific cases, however, allow to estimate synapse turnover during ontogenesis, at its lowest possible level. Such data suggest that each synapse is on average remodeled or replaced several to many times during normal developmental, e.g. in the cerebral cortex of Marmoset monkeys at the very least 5 to 10 times (corresponding to 250 million synapses eliminated per hour in area 17!). It is discussed how the consequences of synapse turnover could be utilized by learning processes. Conclusions are followed by an outlook.

Distribution of cytochrome oxidase and parvalbumin in the primary visual cortex of the adult and neonate monkey, Callithrix jacchus.

The anatomical distributions of the mitochondrial enzyme cytochrome oxidase (CO) and of the calcium binding protein parvalbumin (PV) were studied in the striate cortex of adult and neonate New World monkeys (Callithrix jacchus). In the adult marmoset, both proteins were found in laminar arrangements similar to those described for the macaque monkey, with prominent bands of PV-like immunoreactive (PV-LI) puncta in layers IV and IIIb, and fairly evenly distributed PV-LI nonpyramidal neurons. Furthermore, the pattern of CO activity in area 17 of the neonate marmoset was almost identical to the CO pattern described in neonate macaque and squirrel monkeys. It came, therefore, as a surprise to find that the adult pattern of PV-like immunoreactivity (PV-LI) in the marmoset striate cortex arises from a neonatal pattern strikingly different from that seen in any developmental stage of the macaque, or in any other mammal studied so far. In the deep layers IV through VI of the neonate marmoset, a large number of PV-LI neurons was stained in bandlike patterns, their number in layers IV and V exceeding the number of PV-LI neurons present in these layers of the adult marmoset area 17. Staining of layers IV and VI was restricted to area 17 and involved nonpyramidal cells and their processes. The stained band of layer V, in contrast, continued throughout most of the neocortex. In area 17, an estimated 10 to 20% of the stained cells in layer V exhibited pyramidal shapes. The findings show that the expression of PV by visual cortical cells occurs before birth and suggest that the comparatively early onset of PV expression is not dependent on the onset of textured vision. The exuberant number of stained cells in some layers, and particularly the staining of pyramidal cells, in the neonate marmoset, suggest that a considerable number of cells possesses the stainability for PV-LI only transiently, i.e., in the marmoset, these cells have a specific demand for parvalbumin during this phase of their development.

Distribution of cytochrome oxidase in layers IV and V of the striate cortex in neonate monkeys.

The uniformly dense staining for cytochrome oxidase (CO) in layer IV of area 17 in adult monkeys has been described as developing from a bilaminar pattern in neonates being composed of a broad CO band in layer IV alpha and a narrow CO band attributed to the innermost zone of layer IV beta. Here we present evidence, in the neonate marmoset monkey, for the narrow CO band to be localized in the outermost rim of layer V, designated as sublayer Va.

Similarities and differences between cholinergic systems in the superior colliculus of guinea pig and rat.

We studied the distribution of acetylcholinesterase activity and choline acetyltransferase immunoreactivity in the superior colliculus of the guinea pig and the albino rat, using enzyme histochemical and immunohistochemical methods. Choline acetyltransferase-like immunoreactivity was localized in the neuropil throughout the colliculi, but the density of the immunoreactive neuropil varied among layers as well as between species. In the intermediate collicular layers the pattern of choline acetyltransferase immunoreactivity was closely matched by the distribution of acetylcholinesterase activity in guinea pig and rat, confirming our previous findings in the cat. Furthermore, in the guinea pig, but not in the rat, choline acetyltransferase-like immunoreactivity was localized in a prominent population of perikarya of the superficial gray layer.

Delineation of the striate cortex, and the striate-peristriate projections in the guinea pig.

The size and position of the guinea pig area 17 were determined by transneuronal labeling after intraocular injections of 3H-proline or WGA-HRP. Area 17 occupies a large region of the occipital cortex located between two shallow fissures, the fissura sagittalis lateralis and the lateral groove. Area 17 extends for about 6 mm rostral from the occipital pole of the hemisphere, and encroaches occipitally for more than 1 mm upon the ventromedial surface of the hemisphere; the lateral width is up to 4.5 mm. Single injections of WGA-HRP into area 17 produced eight patches of transported tracer which formed the same general pattern in the peristriate cortex, regardless of the position of the injection within the visual field representation of area 17. Two of these patches were found in anteromedial peristriate cortex; three patches were distributed anterolateral and lateral of area 17; and three patches were located in posterolateral peristriate cortex. For several reasons, each of these patches was interpreted as representing a single striate projection onto a separate peristriate area. Comparison of these results with published findings indicates that the parcellation of the peristriate cortex into a variety of different areas, the pattern formed by these areas around area 17, and their reciprocal connections with area 17 follow a common plan in all hitherto studied terrestrial Old World and New World rodents. Lucifer Yellow injections into striate cells projecting to one of the recipient areas (AM) indicated that the pyramidal cells of this set of striate neurons are characterized by a short apical dendrite, and that the basal dendrites of the layer V pyramidal cells branch more profusely than those of the layer III pyramids.

Parvalbumin in rat superior colliculus.

Parvalbumin-like immunoreactivity (PA-LI) has been studied in sections of the superior colliculus (SC) of the rat and its distribution compared to the patterns of acetylcholinesterase (AChE) and cytochrome oxidase (CO) staining. In the intermediate layers it was found that PA-LI is spatially associated with AChE only in the medial part of the SC, but assumes a complementary distribution further laterally. There was a positive correlation between PA-LI and CO. We conclude that the patterns of PA-LI and CO are not systematically related to collicular input known to be associated with the AChE-rich zones, but may reflect adherence to channel separation beyond the terminal fields of clustered afferents.

Release of met-enkephalin and its modulation through acetylcholine receptors in the rabbit superior colliculus.

This report presents evidence for the depolarization-dependent release of met-enkephalin from the superior colliculus of the rabbit. Collicular tissue was placed in superfusion chambers and met-enkephalin accumulation in the superfusate was measured by radioimmunoassay. Exposure to high potassium concentrations (30 mM and 56 mM) increased met-enkephalin release. This is the fourth transmitter shown to be released from collicular tissue. Furthermore, we have obtained the first evidence that suggests that met-enkephalin release is susceptible to muscarinic modulation. While the depolarization-dependent release of met-enkephalin was depressed in the presence of atropine (1 microM), hexamethonium (100 microM) did not block the increase of met-enkephalin release induced by high potassium.

Loss of ocular dominance columns with maturity in the monkey, Callithrix jacchus.

Previous studies have shown that adult marmosets lack ocular dominance columns (ODC) in area 17, but that ODCs can be demonstrated upon visual deprivation. The present results, obtained by transneuronal transport of WGA-HRP, indicate that ODCs normally develop in juvenile marmosets but disappear before the animal reaches maturity. The findings suggest that formation of ODCs during ontogenesis, and their persistence through adulthood, are different developmental processes depending on different mechanisms.

Differences in transneuronal transport of horseradish peroxidase conjugated wheat germ agglutinin in the visual system: marmoset monkey and guinea pig compared.

Conjugates of the lectin wheat germ agglutinin with horseradish peroxidase have been described as effective transneuronal tracers in different neuronal systems of various mammalian species. Here, the failure is described to detect any sign of transneuronal transport of the tracer in the visual system of adult marmoset monkeys (Callithrix jacchus), in spite of heavy anterograde labeling in the primary visual centers after intravitreous injections. In contrast, in the brains of guinea pigs processed by identical technical parameters, transneuronal anterograde labeling was readily recognized in the contralateral striate cortex, thalamic reticular nucleus, and parabigeminal nucleus. Furthermore, transneuronal retrograde labeling of cell bodies was evident in the thalamic reticular and paragibeminal nuclei, and in the striate cortico-geniculate and cortico-collicular cells. The transneuronal labeling of the cell bodies in the guinea pig striate cortex, which has not been demonstrated before, is taken as a measure for the sensitivity of the histological procedures applied. The failure to demonstrate transneuronal labeling in the marmoset monkey, thus, appears to indicate an interspecies difference in the mechanisms of transneuronal transfer of the tracer used. Positive results in other mammalian species such as other rodents, cat, and Old World monkeys, as obtained in this and other laboratories, further support this view.

Macro square wave jerks in a rhesus monkey: physiological and anatomical findings in a case of selective impairment of attentive fixation.

An otherwise normal female rhesus monkey executed large saccadic eye movements (macro square wave jerks) when required to attentively fixate a small visual target (fixation point). The jerks were observed exclusively in this specific testing situation. They occurred periodically at a frequency of 2.04 + - 0.18 Hz to the right side with an amplitude of 23.5 deg. Direction of the jerks was about 3-4 degrees downward from horizontal. These parameters remained constant throughout the several months of daily recording. No jerks were executed during periods when the behaviourally important target was absent or substituted by another, behaviourally non-relevant visual stimulus. The monkey could perform normal visually guided saccades as well as smooth pursuit eye movements, but with the jerks always superimposed, when the monkey paid attention to the visual target. Histologic inspection of the brain revealed the presence of an incapsulated nematode in the cortex of lobulus simplex of the right cerebellar hemisphere, i.e., in a region involved in oculomotor control.