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PubMedDate not supplied

Tracing neuronal connections in postmortem human hippocampal complex with the carbocyanine dye DiI.

This report describes the ability of the carbocyanine dye DiI to trace hippocampal complex connections in a paraformaldehyde immersion-fixed human postmortem brain. Six months after the placement of DiI crystals into the hilus of the dentate gyrus, the CA1 hippocampal subfield and the lateral entorhinal cortex, 50-microns thick, vibratome cut sections were examined using an epifluorescence microscope with a rhodamine filter. In association with DiI-labeled granule, pyramidal and multipolar type neurons, we observed dendrites containing dendritic spines and axons. DiI-labeled fibers were observed coursing within classically described hippocampal pathways for at least 8 mm distal to the injection site. Photoconversion of diaminobenzidine (DAB)-treated DiI sections produced a stable record of labeled profiles. These findings indicate that DiI is a useful method for investigating intrinsic local circuit connections in normal aldehyde-fixed postmortem human brain and suggests that DiI could be a powerful tool to examine altered neural connectivity in humans with neurological disease.

Aged↗
PubMed1998

[Structural organization and Lugaro neuron connections in the cat cerebellar cortex].

Two types of intermedial Lugaro cells are distinguished in the cat cerebellum: fusiform (horizontal, vertical and obliquely oriented at angles 60-70 to longitudinal axis of folia cerebelli at different levels of granular layer) and those with triangular somata, sparsely branching dendrites and small number of spines. Both fusiform and triangular neuron axons do not stretch out beyond the borders of cerebellar cortex and may be thought of as recurrent interneurons as they contain GABA and glycine. Lugaro cells form numerous contacts almost with all cortical nervous elements: piriform (Purkinje) and Golgi cells, granular and basket neurons, parallel and mossy fibres and even unipolar, (brush) cells. At light microscopic level they are represented as axosomatic and axodendritic contacts. Lugaro cells are the only cerebellar cortical interneurons with dendritic arborizarion oriented in horizontal plane in contrast to vertical orientation of the other interneurons of cerebellar cortex.

Animals↗
PubMed1973

Structure and development of neuronal connections in isogenic organisms: variations and similarities in the optic system of Daphnia magna.

It is readily apparent upon examination and comparison of organisms of the same and related species that to a large extent genes control morphological features. One means to ascertain the role and degree of genetic control is to study in detail the anatomy and development of a particular structure, say an identifiable neuron, in a population with a fixed genome, and at different stages of morphogenesis. The small crustacean, Daphnia, is well suited for this type of study, since it reproduces parthenogenically, its development is easily staged, and its nervous system is reasonably simple. In this paper comparisons of detailed morphology of neurons in the visual system of adult Daphnia magna are considered. Results indicate that gross features of the system are reproduced within the clone, but some of the finer details are not reproduced.

Animals↗
PubMed2001

Anatomy and in vivo activity of neurons connecting the crustacean stomatogastric nervous system to the brain.

In decapod crustaceans, the inferior ventricular nerve connects the cerebral ganglia (brain) with the stomatogastric nervous system (STNS). In the ivn of the crayfish, eight axons with diameters between 3.5 microm and 10 microm were found in close proximity to the oesophageal ganglion. Two of these axons terminate with their cell body within the ivn. The projections of the other six axons spread inside many neuropiles of the brain, mainly within the protocerebrum and the neuropils of the first and second antennae. Several fibers also send neurites via the circumoesophageal connectives toward the paired commissural ganglia and further down to the ventral nerve cord. The activity of motoneurons within the STNS and of axons in the ivn was recorded with implanted electrodes before, during and after times of feeding. At the beginning of feeding all tonically active ivn neurons accelerated their discharge rate and initially silent neurons also started to fire. Spike frequency was correlated with the quantity of food consumed. The ivn response was accompanied by a corresponding increase in pyloric frequency and an initiation of a gastric rhythm. The two motor rhythms showed a strong phasic interaction, but there was no phase coupling to the ivn activity.

Animals↗
PubMed1984

Hypertension induced changes in cerebral capillary permeability to water are mediated by afferent neuronal connections from the carotid sinus to the brain.

Mild acute hypertension was induced in rats pharmacologically and non-pharmacologically with metaraminol, angiotensin II or bilateral vagotomy. The extraction fraction of water (Ew) was measured in both hypertensive and normotensive animals. It was demonstrated that cerebral blood flow did not change during hypertensive states. Under constant flow conditions Ew becomes a direct index of the cerebral capillary permeability to water. Ew was significantly decreased (P less than 0.001) in all brain regions examined in the hypertensive animals as compared to normotensive controls. However, the decrease Ew induced by hypertension was not observed if the animal had previously received bilateral carotid sinus denervation. This observation indicated that the capillary permeability response induced by hypertension is mediated by a neurogenic mechanism involving information transfer from the peripheral baroreceptors in the carotid sinus along afferent connections into the central nervous system.

Afferent Pathways↗
PubMed2000

Oligodendrocyte lineage and the motor neuron connection.

One of the more surprising recent discoveries in glial biology has been that oligodendrocytes (OLs) originate from very restricted regions of the embryonic neural tube. This was surprising because myelinating OLs are widespread in the mature central nervous system, so there was no reason to suspect that their precursors should be restricted. What we now know about early OL development suggests that they might have as much (or more) in common with ventral neurons-specifically motor neurons (MNs)-as with other types of glia. This has implications for the way we think about glial development, function, and evolution. In this article we review the evidence for a shared MN-OL lineage and debate whether this is the only lineage that generates OLs. We decide in favour of a single embryonic lineage with regional variations along the anterior-posterior neuraxis.

Animals↗
PubMed1994

Regulation of N-methyl-D-aspartate (NMDA) receptor function during the rearrangement of developing neuronal connections.

There is evidence from a number of studies that the molecular and biophysical properties of NMDA receptors are altered during normal development. A temporal correlation with changes in NMDA receptor efficacy and periods of synaptic plasticity has been demonstrated in several systems, suggesting that NMDA receptors have a critical function in determining periods of synaptic plasticity. Data from our laboratory demonstrate reduced NMDA sensitivity of the tectal evoked potential following chronic application of NMDA to the tadpole tectum, a treatment that may mimic a naturally occurring mechanism for limiting neuronal plasticity to certain stages of development. Our analysis of the expression pattern of mRNA coding for various glutamate receptor subunits in the rat retinocollicular system establishes that differential regulation of NMDA receptor subunits at the mRNA level could be a molecular basis for changes in biophysical and pharmacological properties of the NMDA receptor complex. However, even though the NMDA receptor is the best studied candidate to function as a 'plasticity switch', there are large gaps in our understanding of the complete set of factors that control the ability of synapses to rearrange during development.

Animals↗
PubMedDate not supplied

[Evolution of neuronal connecting mechanisms: electrical, mixed and chemical synapses].

Investigation of the mechanisms of junctional transmission in the isolated spinal cord in cyclostomes, amphibians, reptilia and mammals reveals the decrease in the number of electrical synapses during evolution from primitive to more advanced vertebrates. Electrical transmission is lacking in reptilian and mammalian cord. On the basis of these data, the analysis of the unitary EPSPs evoked in motoneurons of the lamprey and frog by intracellular stimulation of reticulospinal axons and primary afferent fibers and dendrodendritic interaction between motoneurons, a hypothesis is advanced that neurons of similar type may communicate through pure electrical junctions, whereas successive synaptic articulations between different functional groups of neurons are formed by mixed or chemical synapses. The cellular mechanisms controlling interneuronal communications are discussed.

Amphibians↗
PubMed1988

Tracing of neuronal connections with cholera toxin subunit B: light and electron microscopic immunohistochemistry using monoclonal antibodies.

Subunit B of cholera toxin was used as a tracer substance in the central nervous system after being injected into various brain regions, mainly somatosensory relay structures. The tracer was localized with an immunoperoxidase technique, using monoclonal antibodies raised in mouse hybridomas. This method, which is applicable in both light and electron microscopic studies, is characterized by high contrast between specific labeling and unspecific background activity. It yields excellent retrograde labeling of the dendritic tree and is thus suitable for studying the neuronal cytoarchitecture and, on the ultrastructural level, the synaptic organization of identified projection neurons.

Animals↗
PubMed1988

Combined retrograde and anterograde tracing of neuronal connections: Fluoro-Gold and autoradiography.

We have combined the retrograde Fluoro-Gold (FG) and anterograde autoradiographic (AR) procedures to yield a sensitive high resolution technique by which afferent and efferent connections can be visualized from a single intracerebral injection site. Combined FG/AR sections show excellent results, with no apparent loss of signal compared to performing either procedure alone. Since the FG label is intense, the two labels may be viewed simultaneously by superimposing low level darkfield illumination from below the specimen with fluorescence illumination from above. This combined procedure is useful in the analysis of reciprocal connections involving small spatial domains, such as patchy corticocortical connections. Due to the high signal to noise ratio of both labels, this material is ideally suited for quantitative assessment using automated image analysis.

Afferent Pathways↗
PubMed1979

Neuronal connections in the ocellus of the wasp (Paravespula vulgaris L.).

Studies of the dorsal ocelli of the wasp Paravespula vulgaris (L.) led to the following results: Under a biconvex corneal lens, 150 microns in thickness, about 600 receptor cells are located. The rhabdomeres of two adjacent cells form a closed plate-like rhabdom (0.5--1.0 micron in thickness, 6 microns in width and 10--25 microns in depth or length). In the lateral ocellus the receptor cells synapse up to 8 ocellar nerve fibers, and in the median ocellus they synapse up to 16 (20--30 microns thick) ocellar nerve fibers. The ocellar synaptic plexus may display three types of synapses between the two types of neurons: (i) Receptor-cell axons are presynaptic to dendrites of the first-order interneurons. (ii) Dendrites of the first-order interneurons are presynaptic to receptor-cell axons. (iii) The subunits of a dendrite of first-order interneurons form synapses with each other.

Animals↗
PubMed1996

Neuronal connections of orbital cortex in rats: topography of cortical and thalamic afferents.

The cortical and thalamic afferent connections of rat orbital cortex were investigated using fluorescent retrograde axonal tracers. Each of the four orbital areas has a distinct pattern of connections. Corticocortical connections involving the ventral and ventrolateral orbital areas are more extensive than those of the medial and lateral orbital areas. The medial orbital area has cortical connections with the cingulate, medial agranular (Fr2) and posterior parietal (PPC) cortices. The ventral orbital area has connections with the cingulate area, area Fr2, secondary somatic sensory area Par2, PPC, and visual areas Oc2M and Oc2L. The ventrolateral orbital area (VLO) receives cortical input from insular cortex, area Fr2, somatic sensory areas Par1 and Par2, PPC and Oc2L. The lateral orbital area has cortical connections limited to the agranular and granular insular areas, and Par2. Thalamic afferents to the four orbital fields are also topographically organized, and are focused in the submedial and mediodorsal nuclei. The ventrolateral orbital area receives input from the entirety of the submedial nucleus, whereas the other orbital areas receive input from its periphery only. Each orbital area is connected with a particular segment of the mediodorsal nucleus. The medial orbital area receives its principal thalamic afferents from the parataenial nucleus, the dorsocentral portion of the mediodorsal nucleus, and the ventromedial portion of the submedial nucleus. The ventral orbital area receives input from the lateral segment of the mediodorsal nucleus, the rostromedial portion of the submedial nucleus, and the central lateral nucleus. Thalamic afferents to the ventrolateral orbital area arise from the entirety of the submedial nucleus and from the lateral segment of the mediodorsal nucleus. The lateral orbital area receives thalamic afferents from the central segment of the mediodorsal nucleus, the ventral portion of the submedial nucleus, and the ventromedial nucleus. The paraventricular, ventromedial, rhomboid and reuniens nuclei also provide additional input to the four orbital areas. The connections of the ventrolateral orbital area are interpreted in the context of its role in directed attention and allocentric spatial localization. The present findings provide anatomical support for the view that areas Fr2, PPC and VLO comprise a cortical network mediating such functions.

Animals↗
PubMed1982

Development of neuronal connections in chick embryonic retino-tectal system: an overview.

Synaptogenesis has been examined in the retino-tectal system of the chick embryo both biochemically and morphologically. We have evaluated the amount and the rate transport of glycoproteins synthetized in retinal ganglion cells and axonally transported to retinal nerve endings. The distribution of glycoproteins inside the tectum shows that they are part of the synaptosomal membrane either because they are incorporated in it "en route" or because they flow through an axolemmal flow. The role they might play in the building up of the synaptic membrane is discussed in relation to the maturation of synaptic contacts, observed either with E-PTA staining method or with routine fixation methods. The distribution of a carbohydrate binding protein was followed with histochemical techniques. This protein is synthesized by the matching tectal neurons, and its synthesis is developmentally regulated. It distribution is affected by innervation. All of these findings are discussed in relation to the hypothesis that three different steps are involved in embryonic synaptogenesis. These three steps are: 1) interneuronal recognition; 2) formation of initial contact, and 3) formation of synapses. The possibility that different kinds of cell surface macromolecules might play a different role is also discussed.

Animals↗