Biomedical subjects

J G Valtschanoff

Publications and source records attributed to J G Valtschanoff.

32 records · Page 2Linked to original sources

PubMed1996

Colocalization of GABA and glycine in the rat dorsal column nuclei.

About half the neurons in the rat dorsal column nuclei were immunopositive for glycine or for GABA; these were smaller than immunonegative neurons. In double-stained material, 29% of stained neurons were immunopositive for GABA only, and 42% for both antigens. The results resemble those reported for spinal cord laminae that receive fast-conducting primary afferents, and suggest that glycine is an inhibitory neurotransmitter in the dorsal column nuclei.

Animals↗

PubMed1995

Ultrastructural and immunocytochemical characterization of terminals of postsynaptic ascending dorsal column fibers in the rat cuneate nucleus.

The morphology, synaptic contacts, and neurotransmitter enrichment of postsynaptic dorsal column terminals in the cuneate nucleus of rats were investigated and compared with those of identified primary afferents. For this purpose, anterograde transport of horseradish peroxidase-based tracers injected in the spinal cord was combined with postembedding immunogold labeling for glutamate and gamma-aminobutyric acid (GABA). Anterogradely labeled postsynaptic dorsal column terminals were morphologically homogeneous: they were small (mean area = 1.37 microns 2) and dome-shaped, contacted single dendritic shafts or cell bodies, and were not involved in axoaxonic synapses. The majority of them were not enriched in glutamate or GABA immunoreactivity compared with other tissue components. Their morphology, size, and neurotransmitter content thus differed from that of primary afferents. These differences are consistent with distinct functional roles for the two main afferent systems ascending to the cuneate nucleus.

Afferent Pathways↗

PubMed1995

Colocalization of neuronal nitric oxide synthase with GABA in rat cuneate nucleus.

Pre- and post-embedding immunocytochemistry were employed in this electron microscopic investigation of cuneate neurons that are enriched in GABA and in nitric oxide synthase, the enzyme responsible for the synthesis of nitric oxide. GABAergic neurons are local circuit interneurons; 10-20% of them also contain nitric oxide synthase. These are among the smallest GABA-positive perikarya. We describe a network of processes in the rat cuneate nucleus that are immunopositive for nitric oxide synthase. Axon terminals positive for nitric oxide synthase are small and make synapses mainly onto dendrites; they make only occasional axo-axonic contacts. Double-labelling immunocytochemistry verified that the large majority of terminals positive for nitric oxide synthase also contained GABA. However, most GABA-positive profiles were negative for nitric oxide synthase and GABA-positive terminals that are negative for nitric oxide synthase frequently made axo-axonic contacts. These results suggest that nitric oxide synthase is within a specialized subpopulation of interneurons in the cuneate nucleus.

Amino Acid Oxidoreductases↗

PubMed1995

Central release of tracer after noxious stimulation of the skin suggests non-synaptic signaling by unmyelinated fibers.

Injury to a peripheral nerve causes central changes of various nature and complexity reflecting activation of multiple signaling mechanisms. In a previous study we reported that nerve lesion triggers central release of a tracer, wheatgerm-agglutinin conjugated to horse-radish peroxidase, by unmyelinated fibers in the spinal cord. The released tracer occupies the space between nerve terminals and dendrites without extending into the synaptic cleft. We interpreted this to suggest release of unidentified endogenous factor(s) at nonsynaptic sites, which may contribute to the signaling of peripheral injury to the central nervous system. For such signaling to occur, a message must first be communicated along the axon. This message may depend on axonal transport and/or altered electrical activity. In pilot experiments we observed that application of tetrodotoxin (to block impulse conduction) to the intact nerve did not result in tracer release. We hypothesized that the message might be the sustained discharge of C fibers that occurs after injury. We show here that selective activation of C fibers (by applying mustard oil to the hindlimb of anesthetized rats) causes central release of tracer previously transported from the sciatic nerve to superficial laminae of the dorsal horn.

Animals↗

PubMed1995

Synaptic interactions between primary afferent terminals and GABA and nitric oxide-synthesizing neurons in superficial laminae of the rat spinal cord.

The superficial laminae (I and II) of the spinal dorsal horn receive small caliber primary afferent fibers responsive to noxious stimulation, and contain local circuit neurons that modulate afferent input. Many of these neurons are GABAergic; about a third of these also synthesize nitric oxide. We identified three main morphological types of primary afferent terminals in superficial laminae after injections of a tracer selective for small caliber afferents into the sciatic nerve of rats. The relative densities of the three types varied through the dorsoventral extent of laminae I and II. Synaptic contacts of each type with GABA- and nitric oxide synthase (NOS)-containing dendrites and axon terminals were determined by preembedding and postembedding immunocytochemistry. Nonglomerular primary afferent terminals, likely to originate from peptidergic unmyelinated fibers, were not seen in synaptic contact with either GABA- or NOS-containing neurons. Primary afferent terminals at the center of type 1 glomeruli (C1) and at the center of type 2 glomeruli (C2) are likely to originate from unmyelinated and small myelinated fibers, respectively. GABAergic terminals contacted more C2 than C1 terminals, suggesting more effective presynaptic inhibition of C2 terminals. Many GABAergic terminals were also positive for NOS, but all GABAergic terminals presynaptic to primary afferent terminals were negative for NOS. Only C2 terminals established frequent synapses with NOS-positive dendrites. (ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗

PubMed1994

Ultrastructural and immunocytochemical characterization of primary afferent terminals in the rat cuneate nucleus.

The cuneate nucleus is a relay center for somatosensory information by receiving tactile and proprioceptive inputs from primary afferent fibers that ascend in the dorsal funiculus. The morphology, synaptic contacts, and neurochemical content of primary afferent terminals in the cuneate nucleus of rats were investigated by combining anterograde transport of horseradish peroxidase conjugated to wheat-germ agglutinin or to cholera toxin (injected in cervical dorsal root ganglia) with postembedding immunogold labeling for glutamate and GABA. Both tracers gave similar results. Two types of terminals were labeled: type I terminals were irregularly shaped, had a mean area of 4.0 microns 2, synapsed on several dendrites, and were contacted by other terminals, some of which were GABA positive. Type II terminals were dome-shaped, had a mean area of 2.18 microns 2, and made synaptic contact on a single dendrite. All the anterogradely labeled terminals (interpreted as endings of primary afferents) were enriched in glutamate but not in GABA. The finding that identified primary afferent terminals are enriched in glutamate with respect to other tissue profiles strongly suggests a neurotransmitter role for glutamate in this afferent pathway to the rat cuneate nucleus.

Afferent Pathways↗

PubMed1994

Amino acid immunocytochemistry of primary afferent terminals in the rat dorsal horn.

We combined transganglionic tracing methods with postembedding electron microscopic immunocytochemistry to determine whether identified primary afferent fibers terminating in spinal laminae I-IV may use glutamate and aspartate as neurotransmitters. Sciatic injections of wheat-germ agglutinin conjugated to horseradish peroxidase labeled fine afferent fibers with terminals in laminae I-II of the lumbar spinal cord, whereas injections of the B subunit of cholera toxin conjugated to horseradish peroxidase labeled primary afferent terminals in deeper laminae. Many labeled primary afferent terminals in superficial laminae were involved in glomerular synaptic arrangements; others established nonglomerular contacts. Most glomerular arrangements were clearly immunopositive for glutamate, compared with dendrites, astrocytes, or terminals immunopositive for gamma-aminobutyric acid (GABA). The degree of enrichment varied in labeled terminals of different morphological types. Aspartate was enriched, though to a lesser degree than glutamate, in labeled central terminals of glomeruli in superficial laminae. Labeled primary afferent terminals in laminae III-IV were immunopositive for glutamate, though at lower levels than glomerular terminals in superficial laminae. Aspartate was not enriched in these terminals compared with dendrites, glia, and GABA-positive terminals. These results support a neurotransmitter role for glutamate in primary afferents to the dorsal horn. Quantitative differences in the content of glutamate in identified primary afferent terminals may be related to functional differences. Enrichment of aspartate in terminals in superficial but not deep laminae is compatible with a role for this amino acid in sustained, NMDA-mediated phenomena characteristic of activity in fine caliber afferents.

Afferent Pathways↗

PubMed1994

Tyrosine phosphorylation in rat spinal cord after sciatic nerve transection.

Immunocytochemistry using antibodies against phosphotyrosine was employed to identify changes in tyrosine phosphorylation in the rat spinal cord consequent to sciatic nerve injury. Increased immunostaining in the spinal gray matter, dorsal columns and gracile nucleus on the side of the lesion became evident after 3 days and was more pronounced with longer survival times up to 3 weeks (the longest survival tested). This increase was most prominent in the fourth lumbar segment (the focus of termination of sciatic nerve afferents). Immunostaining was ain astroglial cells and their processes in the dorsal horn; stained microglia were also seen. Immunopositivity also increased in glial cells surrounding motoneurons at the same levels. These changes suggest that a diffusible growth factor released centrally by injured nerve fibers activates tyrosine phosphorylation in glial cells via receptor tyrosine kinases.

Animals↗

PubMed1993

Neurons in rat cerebral cortex that synthesize nitric oxide: NADPH diaphorase histochemistry, NOS immunocytochemistry, and colocalization with GABA.

Neurons that stain for NADPH diaphorase, which colocalizes with nitric oxide synthase (NOS), are scattered uniformly across neocortex, and denser in entorhinal cortex. In the primary sensorimotor cortex, 0.5-2% of neurons contain NOS. These are most numerous in layers II-III, whereas NOS-positive fibers are concentrated in layers IV and VI. Most stained neurons are aspiny bipolar cells. Some in deep layers are multipolar; very few are pyramidal-shaped. In layer IV, NOS-positive neurons and their dendrites are confined to the septa between barrels. Retrograde tracing experiments demonstrate that NOS-positive cells are local circuit neurons. Double staining demonstrates that NOS-positive neurons also contain GABA.

Amino Acid Oxidoreductases↗

PubMed1993

Neurons in rat hippocampus that synthesize nitric oxide.

We studied the distribution and light- and electron-microscopic morphology of neurons in the hippocampal formation containing nitric oxide synthase (NOS), and thus likely to release nitric oxide, a freely diffusible neuromediator implicated in long-term potentiation. Only a small fraction of hippocampal neurons contained NOS or its marker, NADPH diaphorase. Most of the positive neurons were in the pyramidal layer of the subiculum, stratum radiatum of Ammon's horn, and subgranular zone of the dentate gyrus. Positive neurons were also conspicuous in the molecular layer of the dentate gyrus and in the pyramidal layer of CA3, sparse in the pyramidal layer of CA2 and CA1, and almost absent from presubiculum and parasubiculum. Numerous positive fibers were seen, especially in stratum radiatum and stratum lacunosum-moleculare of Ammon's horn. Double staining experiments demonstrated that nearly all NADPH diaphorase-positive neurons in the hippocampus also contained gamma-aminobutyric acid. On the basis of their morphology, distribution, and inhibitory neurotransmitter content, most NOS-positive cells in the hippocampus are probably local circuit neurons. These data suggest that nitric oxide in CA1 may function as a paracrine agent, rather than a spatially precise messenger, in long-term potentiation.

Amino Acid Oxidoreductases↗

PubMed1993

Amino acid immunoreactivity in corticospinal terminals.

Anterogradely labeled corticospinal axons and their terminals were identified after injections of wheat germ-agglutinin conjugated to horseradish peroxidase in the sensorimotor cortex of rats. Thin myelinated axons were labeled in the corticospinal tract. Terminal labeling was densest in the internal basilar nucleus and laminae III-IV of the dorsal horn throughout the spinal cord; electron microscopical observations were mainly from the cervical enlargement. Labeled terminals were most often small and dome-shaped with densely packed, clear round vesicles and sparse mitochondria. These terminals established asymmetric synapses with small dendrites or spines and were never involved in axoaxonic contacts. Postembedding immunocytochemistry was used to study the subcellular distribution of glutamate, aspartate, and gamma-aminobutyric acid (GABA). Corticospinal terminals appeared enriched in glutamate, but not GABA. Some corticospinal terminals appeared enriched in aspartate, though the labeling was less selective than in the case of glutamate. GABA immunolabeling was very dense in about 20% of terminals. These were most often small, rich in mitochondria, and made symmetric synapses; they were not anterogradely labeled from the cortex. Quantitative analysis on double immunolabeled material allowed a direct comparison of particle density for different antigens in the same section. Terminals with a high density of particles coding for glutamate were not enriched with GABA, and terminals immunolabeled for GABA were not enriched with glutamate. There was no significant correlation between glutamate and aspartate immunolabeling in corticospinal terminals; a subpopulation of these terminals may be enriched in aspartate. Aspartate immunolabeling was consistently higher in dendrites postsynaptic (in the plane of section) to corticospinal terminals than in other dendrites.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

PubMed1992

Nitric oxide synthase and GABA colocalize in lamina II of rat spinal cord.

A dense plexus of fibers in the substantia gelatinosa contains nitric oxide synthase (NOS). Using electron microscopic double-labeling immunocytochemistry for NOS combined with GABA or glutamate, we find that all NOS-positive terminals in this region also contain GABA but are not enriched in glutamate. In an attempt to verify that NOS-positive terminals do not originate from primary afferents, we combined NOS immunocytochemistry with anterograde tracing from the sciatic nerve. An intrinsic spinal origin for the NOS-positive plexus is suggested. The results are discussed in the light of the possible involvement of nitric oxide in hyperalgesia.

Afferent Pathways↗

PubMed1992

NADPH diaphorase in the spinal cord of rats.

To identify spinal neurons that may synthesize nitric oxide, cells and fibers histochemically stained for NADPH diaphorase (a nitric oxide synthase) were studied in the spinal cord of rats. The histochemical reaction gave an image similar to the best Golgi impregnations, staining cells down to their finest processes. Transverse, horizontal, and parasagittal 50 and 100 microns sections were used to follow dendritic and axonal arborizations of stained neurons. Major cell groups were identified in the superficial dorsal horn and around the central canal (at all spinal levels), and in the intermediolateral cell column (at thoracic and sacral levels). Scattered positive cells were also found in deeper dorsal horn, ventral horn, and white matter. In some cases, axons of cells in the dorsal horn could be traced into the white matter; many of these cells resembled neurons projecting to various supraspinal targets. Stained cells in the intermediolateral column, which sent their axons into the ventral root, were presumed to be preganglionic autonomic neurons. Dense plexes of fibers were stained in laminae I and II and in the intermediolateral column. A large number of NADPH diaphorase-positive neurons in the spinal cord appear to be involved in visceral regulation. Fibers of the intermediolateral system had a special relationship with vasculature, suggesting that nitric oxide may help to couple neural activity with regional blood flow in the spinal cord. The abundance of NADPH diaphorase-positive neurons and fibers in the superficial dorsal horn suggests that nitric oxide may also be involved in spinal sensory processing.

Amino Acid Oxidoreductases↗

PubMed1992

Peripheral injury and anterograde transport of wheat germ agglutinin-horse radish peroxidase to the spinal cord.

Previous observations have revealed labeling in the extracellular space surrounding boutons and unmyelinated fibers in superficial laminae of the spinal cord after injection of the tracer wheat germ agglutinin conjugated to horseradish peroxidase in dorsal root ganglia. The degree of extracellular labeling appeared related to the extent of the damage to the ganglia at the time of the injection. To determine whether injury might produce extracellular labeling, we investigated the effects of unilateral nerve crush or transection on spinal labeling after bilateral injections of the tracer into sciatic nerves. Confirming previous reports, labeling was confined to small dorsal root ganglion cells and to spinal laminae I and II, suggesting a selective affinity of this tracer for unmyelinated fibers. Labeling of both ganglion neurons and superficial spinal laminae was increased on the injured side, probably as a result of increased efficiency of receptor-mediated endocytosis. Electron microscopical observations revealed that the tracer was largely confined to unmyelinated dorsal root fibers bilaterally; a higher percentage of these fibers were labeled on the injured side. In the dorsal horn, the tracer was predominantly within unmyelinated axons and their terminals on the control side, whereas most of the labeling was extracellular and transneuronal on the injured side. The extracellular labeling surrounded unmyelinated fibers and their terminals in the spinal cord, but was excluded from the synaptic cleft. The demonstration that injury is accompanied by significantly increased release of this tracer from the terminals of unmyelinated fibers into the extracellular space suggests that endogenous substances may be released after peripheral lesions as a central signal of injury.

Animals↗