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Biomedical subjects

S R Vincent

Publications and source records attributed to S R Vincent.

134 records · Page 8Linked to original sources
PubMed1978

The use of kainic acid in the localization of enzymes in the substantia nigra.

The selective destruction of neuronal perikarya via intracerebral injections of kainic acid was used to elucidate the cellular location of four neurotransmitter-related enzymes in the substantia nigra (SN). Two weeks after intranigral injections of kainic acid, dopamine-sensitive adenylate cyclase, glutamic acid decarboxylase (GAD), choline acetyltransferase (CAT) and acetylcholinesterase (AChE) were measured in the SN. Histological examination of the SN, and a reduction of striatal tyrosine hydroxylase (TH) activity by 94%, confirmed the extensive loss of neuronal cell bodies in the SN. Dopamine stimulation of adenylate cyclase was not reduced in the lesioned SN, supporting the view that dendritically-released dopamine can regulate cyclic AMP synthesis in afferent terminals to these dendrites. Nigral GAD activity was significantly reduced by the lesions, suggesting that there are GAD-containing perikarya in the SN. CAT activity was not affected by the kainic injections, indicating the absence of cholinergic perikarya in the SN. Nigral AChE activity was significantly decreased after kainic injections, thus confirming the presence of AChE within the nigral perikarya. The results suggest that dopamine-sensitive adenylate cyclase and CAT are located within afferents to the SN, while GAD and AChE are found, to some extent at least, in neuronal soma of the SN. The differentail effects of kainic acid on these enzymes suggest that this compound may be a useful neurochemical tool with which to determine the cellular distribution of enzyme systems in the central nervous system.

Acetylcholinesterase↗
PubMed1978

Insecticidal and neuroexcitant actions of DDT analogs on the cockroach, Periplaneta americana.

The American cockroach (Periplaneta americana) was used to test 14 DDT analogs for their ability to cause a) death and b) repetitive firing in the abdominal nerve cord. P,p' -DDT, p,p' -DDD, p,p' -methoxychlor, and o,p -DDT were all found to induce repetitive firing in the nerve cord after a twice threshold stimulus, but only p,p' -DDT, p,p' -DDD, and p,p' -methoxychlor produced mortality within 4 days from injection of the pesticides. Also, cockroaches exposed to sublethal doses of p,p' -DDT and p,p' -methoxychlor were found to exhibit repetitive firing in the abdominal nerve cord three weeks after injection of the pesticide. The 'cause and effect' relationship between neuroexcitation and lethality is therefore questioned, at least in the case of cockroaches.

Action Potentials↗
PubMedDate not supplied

Ultrastructure of cholinergic neurons in the laterodorsal tegmental nucleus of the rat: interaction with catecholamine fibers.

The ultrastructure of choline acetyltransferase (ChAT)-immunoreactive neurons in the laterodorsal tegmental nucleus (TLD) of the rat was investigated by immunohistochemical techniques. The immunoreactive neurons were medium to large in size, with a few elongated dendrites, contained well-developed cytoplasm, and a nucleus with deep infoldings. They received many nonimmunoreactive, mostly asymmetric synaptic inputs on their soma and dendrites. ChAT-immunoreactive, usually myelinated, axons were occasionally seen in TLD. Only one immunoreactive axon terminal was observed within TLD, and it made synaptic contact with a nonimmunoreactive neuronal perikaryon. The synaptic interactions between ChAT-immunoreactive neurons and tyrosine hydroxylase (TH)-immunoreactive fibers in the TLD were investigated with a double immunohistochemical staining method. ChAT-immunoreactivity detected with a beta-galactosidase method was light blue-green in the light microscope and formed dot-like electron dense particles at the electron microscopic level. TH-immunoreactivity, visualized with a nickel-enhanced immunoperoxidase method, was dark blue-black in the light microscope and diffusely opaque in the electron microscope. Therefore, the difference between these two kinds of immunoreactivity could be quite easily distinguished at both light and electron microscopic levels. In the light microscope, TH-positive fibers were often closely apposed to ChAT-immunoreactive cell bodies and dendrites in TLD. In the electron microscope, the cell soma and proximal dendrites of ChAT-immunoreactive neurons received synaptic contacts from TH-immunoreactive axon terminals. These results provide a morphological basis for catecholaminergic regulation of the cholinergic reticular system.

Animals↗
PubMedDate not supplied

Immunohistochemical localization of peptidylarginine deiminase in the rat brain.

The enzyme peptidylarginine deiminase is responsible for the post-translational modification of certain proteins by catalysing the deimination of arginine residues to citrullines. Recently, peptidylarginine deiminase has been purified from rat skeletal muscle and its primary structure determined by molecular cloning. We have used antibodies raised against this enzyme to examine its distribution in the rat central nervous system. A few discrete neuronal cell groups in the telencephalon were selectively stained. These were the septofimbrial nucleus, the anterior commissural nucleus of the hypothalamus, and the anterodorsal thalamic nucleus. The subcommissural organ was intensely stained; but other circumventricular organs were not. In addition, peptidylarginine deiminase-immunoreactivity was found in a large population of small cells throughout the grey and white matter of the rat brain. Some of these cells contained glial fibrillary acidic protein and could thus be identified as astrocytes. However, in many regions these peptidylarginine deiminase-positive cells appeared distinct from the glial fibrillary acidic protein-positive astrocytes. Light and electron microscopic examination indicated that these cells had the morphology of microglia, however they were not stained by a lectin marker for microglia. These cells often surrounded cerebral capillaries, and sent ramifying processes into the neuropil. Peptidylarginine deiminase has been suggested to be involved in the synthesis of the endothelium-derived relaxing factor nitric oxide from arginine-containing molecules. Thus the distinct peptidylarginine deiminase-positive glial cells surrounding cerebral blood vessels may be in a position to regulate local blood flow in response to neuronal activity.

Animals↗
PubMedDate not supplied

Substance P in the ascending cholinergic reticular system.

The neocortex receives a major cholinergic innervation from magnocellular neurones in the basal forebrain. However, an ascending cholinergic reticular system has also been postulated to arise from acetylcholinesterase (AChE)-containing neurones in the midbrain and pontine tegmentum. Lesions of this region decrease both AChE and choline acetyltransferase (ChAT) in various forebrain areas, and recent immunohistochemical studies have identified a group of ChAT-containing cell bodies in the midbrain reticular formation and dorsolateral pontine tegmentum. Here we have combined retrograde tracing with ChAT immunohistochemistry to demonstrate that this tegmental cholinergic cell group also directly innervates the cerebral cortex. Other immunohistochemical studies have indicated that the neuropeptide substance P is also present in certain cells in the laterodorsal tegmentum, and these too appear to project to the forebrain. We have therefore performed immunohistochemistry for both ChAT and substance P and have discovered that a subpopulation of the ascending cholinergic reticular neurones contains substance P. Thus, peptide-cholinergic coexistence, previously noted in peripheral neurones, also occurs in the brain.

Acetylcholine↗