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A Contestabile

Publications and source records attributed to A Contestabile.

At least 73 records · Page 4Linked to original sources
PubMed1988

Depletion of cholinergic habenulo-interpeduncular neurons by selectively timed methylazoxymethanol acetate (MAM) treatment during pregnancy.

Methylazoxymethanol acetate (MAM) was injected to female rats at the beginning of the 17th day of gestation. Resulting offspring showed a remarkable decrease in the size of the medial habenula while the interpeduncular nucleus, whose neurons are generated before the time of MAM treatment, appeared anatomically unaffected. Choline acetyltransferase was significantly reduced in the habenulae and in the interpeduncular nucleus suggesting that MAM treatment had depleted a portion of the cholinergic neurons of the medial habenula which project to the interpeduncular nucleus. Aromatic amino acid decarboxylase significantly increased in the interpeduncular nucleus, a likely effect of monoaminergic hyperinnervation in response to partial cholinergic deprivation. MAM strategy can be usefully adopted for the study of general aspects of brain development when connected nuclei showing no overlapping in neuronal generation times are involved.

Acetylcholinesterase↗
PubMed1988

Effect of AF64A on the cholinergic systems of the retina and optic tectum of goldfish.

AF64A, a presumed selective cholinergic neurotoxin has been used to study the effect on cholinergic systems of the goldfish retina and optic tectum. Toxin injection in the vitreum and in the optic tectum caused a selective decrease of choline acetyltransferase activity in both areas, while no significant decrease of glutamate decarboxylase and D-3H aspartate uptake were observed at different times after the injections. The effect was particularly dramatic in the retina of long term-injected animals, where choline acetyltransferase dropped to practically zero level. The ultrastructural analysis showed selective degeneration of some neurons in the amacrine and ganglion cell layer of the retina as well as of synaptic terminals and neuronal cell bodies in the optic tectum. The results favour a selective cholinotoxicity of AF64A in fish nerve tissue at doses substantially higher than those found to have additional unselective effects in mammals.

Animals↗
PubMed1988

The effect of fluorocitrate on transmitter amino acid release from rat striatal slices.

In order to study the role of glutamine from glial cells for the synthesis of transmitter amino acids, the effect of the gliotoxic-substance fluorocitrate on amino acid release from slices was investigated. In vivo treatment with 1 nmol fluorocitrate reduced the Ca2+ dependent K+ evoked release of endogenous glutamate and GABA from the slices, whereas the glutamine efflux decreased and alanine efflux increased. The K+ evoked release of [3H]D-aspartate increased during fluorocitrate treatment. The latter is consistent with an inhibited uptake of D-aspartate into glial cells. Incubation of striatal slices with fluorocitrate (0.1 mM) decreased the glutamine efflux and increased the alanine efflux. Similar to the in vivo condition, fluorocitrate increased the K+ evoked [3H]D-aspartate release, but the K+ evoked release of endogenous glutamate and GABA increased rather than decreased. The ratio between the K+ evoked release of exogenous D-aspartate to endogenous glutamate increased in both cases. The results suggest an important role of glial cells in the synthesis and inactivation of transmitter amino acids.

Amino Acids↗
PubMed1988

Evolution of neurotransmitter-related markers in the vertebrate telencephalon. Comparative microchemical study in discrete brain regions of a frog and a turtle.

1. Neurochemical markers related to cholinergic, GABAergic and glutamatergic/aspartatergic neurotransmission have been measured in telencephalic areas obtained by microdissection from frog (Rana esculenta) and turtle (Pseudemys scripta elegans) brain. 2. In both species, pallial areas showed remarkably higher levels of synaptosomal D-3H-aspartate high affinity uptake than basal regions. Conversely, striatal and septal areas possessed higher levels of the GABAergic marker glutamate decarboxylase (GAD) than the pallium. 3. A differential distribution of GAD was noticed in striatal regions, highest levels of the enzyme being present in the ventral striatum, followed by the nucleus accumbens and the dorsal striatum. 4. Cholinergic markers choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) were rather uniformly distributed in the frog telencephalon, while, in the turtle, cholinergic markers were several-fold higher in the basal telencephalon, particularly in the striatum, than in the pallium. 5. The turtle dorsal ventricular ridge possessed ChAT levels more similar to the striatal than to the cortical ones. On the contrary, D-3H-aspartate uptake in the dorsal ventricular ridge was close to the highest levels found in cortical areas. 6. The quantitative neurochemical approach adopted for the present study appears to be a useful tool to investigate the problem of homologies and to gain new information on the evolution of neuron populations and neuronal connections in the vertebrate telencephalon.

Acetylcholinesterase↗
PubMed1988

Regional levels of neurotransmitter markers in the pigeon telencephalon: a comparison with possibly homologous areas of the rat telencephalon.

The levels of cholinergic, gamma-aminobutyric acidergic (GABAergic), and excitatory amino acid neurotransmitter markers have been measured in 18 regions of the pigeon telencephalon as well as in supposedly homologous areas of the rat telencephalon. Among the basal telencephalic areas, some similar patterns of regional distribution were observed, with the noticeable exception of the ratio of levels of cholinergic markers between the striatum and globus pallidus, which was much larger in the rat than in the pigeon. In the rat cortical areas, some interesting differences were noticed among the archicortex, the paleocortex, and various parts of the neocortex. In particular, the area identified as prefrontal cortex by previous studies was significantly richer in cholinergic and excitatory amino acid markers and poorer in GABAergic activity than other neocortical regions. In the pigeon, presumedly neocortical equivalent areas--in particular, those constituting the dorsal ventricular ridge--were quite variable in levels of cholinergic markers, and some apparently well-established areas homologous to mammalian neocortex showed exceptionally low levels of cholinergic markers. The higher variability in levels of neurotransmitter-related markers shown by cortically equivalent areas of the avian dorsal ventricular ridge, as compared with the more uniform pattern present in basal telencephalic regions, may be the result of a greater plasticity of these structures during evolution, in response to different selective pressures.

Acetylcholinesterase↗
PubMed1987

Cholinergic projections in the telencephalo-habenulo-interpeduncular system of the goldfish.

Experiments were performed in order to see whether acetylcholine is a neurotransmitter in the telencephalo-habenulo-interpeduncular system of the goldfish. After telencephalic ablation choline acetyltransferase decreased by 53% in the habenular nuclei but was unchanged in the interpeduncular nucleus. After combined telencephalic and habenular lesions, the enzyme level dropped by 95% in the interpeduncular nucleus. These results suggest the existence of a telencephalo-habenular and a habenulo-interpeduncular cholinergic projection in the goldfish, as previously demonstrated in mammals. Acetylcholinesterase histochemistry additionally demonstrates some similarities between the habenulae and the interpeduncular nucleus in the goldfish and in mammals.

Acetylcholinesterase↗
PubMed1987

Regional levels of neurotransmitter-related markers in the brain of the weakly electric fish Gnathonemus petersii.

The regional distribution of neurochemical markers for cholinergic, GABAergic and glutamatergic/aspartatergic transmission has been studied in several brain areas of the weakly electric fish Gnathonemus petersii. In particular, brain regions related to reception, relaying and processing of electrosensory modalities have been examined. The regional distribution of neurotransmitter-related markers is considered in the light of available anatomical data and is discussed with particular emphasis on differences among different parts of the hypertrophic valvula cerebelli and other cerebellar structures.

Acetylcholinesterase↗
PubMed1987

Topography of cholinergic and substance P pathways in the habenulo-interpeduncular system of the rat. An immunocytochemical and microchemical approach.

The topography of cholinergic and substance P containing habenulo-interpeduncular projections has been studied in the rat. The research has been carried out by combining choline acetyltransferase and substance P immunohistochemistry to experimental lesions and biochemical assays in microdissected brain areas. In addition, computer-assisted image analysis has been performed in order to obtain quantification of immunohistochemical data. The results show that cholinergic and substance P containing neurons have a different localization in the medial habenula and project to essentially different areas of the interpeduncular nucleus. Cholinergic neurons are crowded in the ventral two-thirds of the medial habenula while substance P containing cells are exclusively localized in the dorsal part of the nucleus. In most parts of the interpeduncular nucleus, choline acetyltransferase and substance P containing fibres and terminals are similarly segregated and no overlapping is apparent except for the rostralmost and the caudalmost ends of the nucleus. Cholinergic activity is largely concentrated in the central core of the nucleus, while substance P is preferentially localized in the peripheral subnuclei of the interpeduncular nucleus. In addition, both substance P and choline acetyltransferase levels show peculiar regional variations along the rostrocaudal axis of the interpeduncular nucleus. The results of experimental lesions demonstrate that the substance P projection carried by each fasciculus retroflexus is prevailingly ipsilateral in the rostral part of the interpeduncular nucleus and becomes progressively bilateral as far as more caudal regions of the nucleus are reached. By contrast, the cholinergic projections carried by each fasciculus retroflexus intermingle more rapidly and only show a slight ipsilateral dominance in the interpeduncular nucleus. The results of the study are discussed with reference to previous anatomical and neurochemical data which, in several instances, had given rise to discrepant interpretations.

Animals↗
PubMed1987

An in vivo model for studying function of brain tissue temporarily devoid of glial cell metabolism: the use of fluorocitrate.

The effect of intrastriatal injection of fluorocitrate on amino acid pattern, cell enzyme markers, and ultrastructural appearance was investigated. A dose of 1 nmol of fluorocitrate resulted in temporarily decreased levels of glutamine, glutamate, and aspartate, whereas the level of alanine was increased. The glutamine level was severely reduced after 4 h but was reversed after 24 h. The activity of different cellular enzyme markers did not change markedly after this dose. Ultrastructural changes in glial cells were observed, concomitant with the biochemical changes. A dose of greater than or equal to 2 nmol of fluorocitrate resulted in more marked and irreversible changes in amino acid levels. By 24-72 h after the injection of this dose, several marker enzyme activities decreased markedly. The ultrastructural changes affected the neurons as well as the glial cells and were not reversible. The use of microinjection of 1 nmol of fluorocitrate into the neostriatum of the rat to provide a model for studying transmitter amino acid metabolism in brain devoid of glial cell activity is discussed.

Amino Acids↗
PubMed1986

Ultrastructural and neurochemical effects of the presumed cholinergic toxin AF64A in the rat interpeduncular nucleus.

We have studied the effect of the presumptive cholinergic neurotoxin, ethylcholine mustard aziridinium ion (compound AF64A), on ultrastructure and neurochemical markers in the rat interpeduncular nucleus (IPN). Stereotaxic injections of 1 nmol of AF64A resulted in extensive degeneration of synaptic terminals within 40 h. Ultrastructural damage to neuronal cell bodies, dendrites and axons was also sometimes observed at this stage. Five days after the injection, more severe degenerative changes were observed in a larger number of neuronal cell bodies, axons and dendrites. High affinity uptake of [3H]choline, but not [3H]GABA, was significantly decreased 24 h after toxin injection. Five days after the injection, not only choline acetyltransferase but also glutamate decarboxylase levels were significantly decreased. Our results suggest that, in addition to presynaptic cholinergic neurotoxicity, AF64A also leads to degenerative alterations of non-cholinergic neurons. Our electron microscopic observations constitute the first ultrastructural report on neuropathological damage caused by AF64A.

Animals↗
PubMed1986

Modification of ultrastructural and neurochemical parameters in synaptosomes of the retino-deprived goldfish optic tectum.

Neurochemical parameters associated with cholinergic and excitatory amino acid transmission, were measured in synaptosomes of the goldfish optic tectum at different times after unilateral eye ablation. Significant decreases in choline acetyltransferase and acetylcholinesterase were measured 12 and 30 days after enucleation. The high affinity choline uptake did not parallel the decrease in cholinergic enzymes. Instead there was a significant increase of the uptake per unit of protein (though not relative to the total number of tectal synaptosomes). No decrease of the high affinity D-3H aspartate uptake was measured in the deafferentated optic tectum. Electron microscopic observations showed a correspondence between the time course of cholinergic enzyme decrease and the degeneration of retinal afferents to the tectum. The present results support the notion that acetylcholine is a better candidate than the excitatory amino acids for a neurotransmitter role in the fish optic tectum.

Acetylcholine↗
PubMed1986

Cholinergic, GABAergic and excitatory amino acidic neurotransmission in the goldfish vagal lobe.

Some neurotransmitter systems operating in the goldfish vagal lobe, an hypertrophied gustatory center, have been studied by means of experimental (kainic acid injection and vagal rhizotomy), neurochemical and ultrastructural methods. The use of the neurotoxin, kainic acid, revealed the existence of cholinergic and GABAergic neurons in the vagal lobe. The results of histochemical observations and biochemical assays performed after rhizotomy of sensory and motor vagal roots, suggest that the motor neurons of the vagal motor layer are cholinergic. The same experiments also indicate that the primary gustatory afferents distributing to the sensory layer of the vagal lobe are, at least in part, cholinergic. By contrast, no decrease of excitatory amino acid uptake was demonstrated following the experimental lesions. GABA is likely to play an important role in the goldfish vagal lobe, particularly in the sensory layer, where the highest level of its synthetic enzyme, glutamate decarboxylase, is recorded. The significant decrease of glutamate decarboxylase in the sensory layer after vagal rhizotomy suggests that either GABAergic primary afferents reach the vagal lobe, or that deafferentation results in a decreased GABA synthesis in intrinsic GABAergic neurons.

Acetylcholinesterase↗
PubMed1985

[3H] kainic acid binding sites in the synaptosomal-mitochondrial (P2) fraction from goldfish brain.

Binding of [3H]kainic acid to the synaptosomal-mitochondrial fraction (P2) of the goldfish brain was studied. Specific binding to this fraction represents about half of the total binding capability of the homogenate particulate material and is enriched in synaptic membranes; it is greater by about two orders of magnitude than those given for rat brain and pigeon optic tectum membranes. Association of the ligand-site complex has a time constant lower than 1 min and the same is true for the main component of the dissociation process. The binding equilibrium is apparently not affected by substances contained in the fraction material. The analysis of the dose-response data showed a main receptor population (B max = 139 pmol/mg protein) which displayed positive cooperativity (nH = 1.29). The same behaviour was shown by washed membranes from the same fraction but, in this case, the affinity for the ligand was lower (apparent affinity constants: K'D = 0.28 nM for the intact fraction and K'D = 0.38 nM for membranes). A smaller population of sites with higher affinity was also detected both in the intact fraction and in membranes. Among the substances tested as displacers of kainic acid from the synaptosomal sites, the most effective were quisqualate and L-glutamate. Folic acid and its dihydro and tetrahydro derivatives were half as potent as glutamate whereas methyltetrahydrofolic acid and folinic acid had a very weak action. The difference between these sites and those detected on rat brain membrane preparations is discussed.

Animals↗
PubMed1985

Neurotransmitter-related markers in the normal and experimentally lesioned telencephalon of the goldfish.

The telencephalon of teleost fish shows high affinity uptake for D-[3H]aspartate, intermediate levels of GABAergic markers and low levels of cholinergic enzymes. Experimental results (resection of the olfactory tracts or unilateral kainic acid administration in the telencephalon) suggest that: the projection from the olfactory bulbs to telencephalic targets is mediated by aspartate and/or glutamate; and a population of GABAergic neurons is present in a telencephalic area which is considered homologous to part of the striatal complex of land vertebrates. From the present results, it appears that the neurochemical approach can be used, in conjunction with neuroanatomical methods, to study evolutionary problems of telencephalic function.

Acetylcholinesterase↗
PubMed1985

Kainic acid differentially affects the synaptosomal release of endogenous and exogenous amino acidic neurotransmitters.

Presynaptic actions of kainic acid have been tested on uptake and release mechanisms in synaptosome-enriched preparations from rat hippocampus and goldfish brain. Kainic acid increased in a Ca2+-dependent way the basal release of endogenous glutamate and aspartate from both synaptosomal preparations, with the maximum effect (40-80%) being reached at the highest concentration tested (1 mM). In addition, kainic acid potentiated, in an additive or synergic way, the release of excitatory amino acids stimulated by high K+ concentrations. Kainic acid at 1 mM showed a completely opposite effect on the release of exogenously accumulated D-[3H]aspartate. The drug, in fact, caused a marked inhibition of both the basal and the high K+-stimulated release. Kainic acid at 0.1 mM had no clear-cut effect, whereas at 0.01 mM it caused a small stimulation of the basal release. The present results suggest that kainic acid differentially affects two neurotransmitter pools that are not readily miscible in the synaptic terminals. The release from an endogenous, possibly vesiculate, pool of excitatory amino acids is stimulated, whereas the release from an exogenously accumulated, possibly cytoplasmic and carrier-mediated, pool is inhibited or slightly stimulated, depending on the external concentration of kainic acid. Kainic acid, in addition, strongly inhibits the high-affinity uptake of L-glutamate and D-aspartate in synaptic terminals. All these effects appear specific for excitatory amino acids, making it likely that they are mediated through specific recognition sites present on the membranes of glutamatergic and aspartatergic terminals. The relevance of the present findings to the mechanism of excitotoxicity of kainic acid is discussed.

Animals↗