Biomedical subjects

L F Agnati

Publications and source records attributed to L F Agnati.

At least 73 records · Page 4Linked to original sources

PubMed1996

Wiring and volume transmission in the central nervous system: the concept of closed and open synapses.

During the past two decades, several revisions of the concepts underlying interneuronal communication in the central nervous system (CNS) have been advanced. Our group has proposed to classify intercellular communication in the CNS under two general frames: 'wiring' (WT) and 'volume' transmission (VT). WT is characterized by a single 'transmission channel' made by cellular (neuronal or glial) structures and with a region of discontinuity not larger than a synaptic cleft. VT is characterized by the diffusion from a cell source (neuronal or glial) of chemical and electrical signals in the extracellular fluid (ECF) for a distance larger than the synaptic cleft Based on morphological and functional characteristics, and in light of the distinction proposed, six main modes of intercellular communication can be recognized in the CNS: gap-junction, membrane juxtaposition, and closed synapse (which represent WT-type modes of communication); open synapse, paracrine transmission and endocrine-like transmission (which represent VT-type modes of communication). Closed and open synapses are distinguished on the basis of the sealing of the signal within or the leakage of the signal outside the synapse Intra-synaptic restriction or extra-synaptic diffusion of transmitters are insured by a number of anatomical arrangements (e.g. glial ensheathment of synapse, size of the synaptic cleft) and functional mechanisms (e.g. density and location of transmitter re-uptake sites and metabolic enzymes). Some central synapses can switch from closed to open state and vice versa, e.g. by changing the amount of transmitter released. Finally, a synapse containing several transmitters can work as an open synapse for one transmitter and as a closed synapse for another.

Animals↗

PubMed1996

Chronic continuous infusion of (-)nicotine reduces basic fibroblast growth factor messenger RNA levels in the ventral midbrain of the intact but not of the 6-hydroxydopamine-lesioned rat.

A negative correlation has been found between smoking and Parkinson's disease. There is evidence to suggest that this correlation appears to be associated with a neuroprotective role of nicotine for dopamine neurons at least in relation to mechanical injury. However, 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP) neurotoxicity to dopamine neurons is enhanced by chronic continuous (-)nicotine. More recently, basic fibroblast growth factor has been found to possess neurotrophic activities for many nerve cells including the dopamine cells in vivo and in vitro. Therefore, it is of interest to explore a possible effect of nicotine on basic fibroblast growth factor expression in the ventral midbrain of intact and 6-hydroxydopamine-lesioned rats and how treatment with nicotine can alter the 6-hydroxydopamine-induced injury of the nigral dopamine nerve cells as evaluated by dopamine biochemistry. In the present paper, an analysis of the effects of chronic continuous infusion of (-)nicotine via minipumps was carried out on basic fibroblast growth factor expression in the vental midbrain of the intact male rat and of the 6-hydroxydopamine lesioned rat. A quantitative messenger RNA protection assay analysis was used as well as an immunocytochemical analysis in the substantia nigra. Our findings give evidence that a two-week continuous infusion with (-)nicotine in the intact rat leads to substantial and dose-related (0.03-0.3 mg/kg per h) reductions of basic fibroblast growth factor messenger RNA levels in the ventral midbrain. These changes are not associated with changes in neuronal and glial basic fibroblast growth factor immunoreactivity in this region with the antibodies used. However, a one-week continuous infusion with (-)nicotine (0.125 mg/kg per h) failed to significantly alter the basic fibroblast growth factor messenger RNA levels in the ventral midbrain of solvent and 6-hydroxydopamine-injected rats and thus also the 6-hydroxydopamine-induced increase of basic fibroblast growth factor messenger RNA levels in the ventral midbrain of the lesioned side observed at this time-interval and known to be of astroglial origin [Chadi G. et al. (1994) Neuroscience 61, 891-910]. In agreement, the 6-hydroxydopamine-induced depletion of dopamine in the neostriatum was unaltered by the nicotine treatment (0.125 mg/kg per h). Thus, chronic continuous (-)nicotine treatment may lead to a reduced basic fibroblast growth factor trophic tone in the ventral midbrain of the intact but not of the 6-hydroxydopamine-lesioned rat neither on the lesioned nor on the unlesioned side of the ventral midbrain. It seems possible that chronic nicotine treatment mainly reduces basic fibroblast growth factor messenger RNA levels of neuronal origin, since the astroglial messenger RNA levels dominate after the 6-hydroxydopamine-induced lesions.

Animals↗

PubMed1996

Computer-assisted mapping of basic fibroblast growth factor immunoreactive nerve cell populations in the rat brain.

We have performed a mapping of basic fibroblast growth factor (bFGF) immunoreactive (ir) glial and nerve cell populations in the male rat brain using a rabbit antibody raised against a synthetic peptide of bovine bFGF. Regional morphometric and microdensitometric analysis of the bFGF ir neuronal profiles in coronal brain sections was carried out by means of an automatic image analyser. The density and intensity of the bFGF ir glial profiles were subjectively evaluated. The bFGF immunoreactivity (IR) was detected within the cytoplasm of neurons, except within the pyramidal neurons of hippocampal CA2 region, the fasciola cinerea and the indusium griseum, where bFGF IR was present in the nucleus. In contrast, in glial cells bFGF IR was always found in the nucleus. Neuronal and glial IR was no longer observed after absorption of the bFGF antiserum with recombinant bFGF. Basic FGF IR was found in neuronal and glial cell populations throughout the brain as well as in the choroid plexus and in the ependymal cells lining the ventricles. Basic FGF ir nerve cells were found in all layers of both the neocortex and allocortex. Within the caudate putamen and the nucleus accumbens a low density of weak bFGF ir neuronal profiles was detected. The majority of the thalamic nuclei showed medium to high densities of moderate to strong bFGF ir neuronal profiles. All the hypothalamic nuclei, with the exception of the anterior and lateral hypothalamic area and of the ventral hypothalamic nucleus, contained a high density of bFGF ir profiles. The pons and the medulla oblongata were characterized by the presence of a large number of nuclei containing moderate to high densities of strong bFGF ir profiles. The Purkinje cell layer of the cerebellar cortex contained a high density of moderately bFGF ir profiles. A moderate density of strong bFGF ir nerve cell profiles was observed within all the laminae of the spinal cord, except within the II and III laminae where a high density of strongly ir profiles was found. Histogram analysis of total immunoreactivity showed that the distribution of bFGF ir profiles within the telencephalon and mesencephalon tend to be similar with regard to the central tendency and spread. Using Kendall's tau, a significant correlation between intensity and density values was obtained only in the diencephalon. The cytoplasmic bFGF IR found in distinct nerve cell populations all over the rat brain and spinal cord may represent forms of bFGF which can be released from the nerve cells via non-exocytotic mechanisms in view of the absence of an intracellular signal peptide in bFGF. The presence of nuclear bFGF IR within the glial cells all over the central nervous system (CNS) suggests an intracellular function of bFGF, such as the promotion of mitogenesis and/or participation in the transcriptional regulation of various genes.

Animals↗

PubMed1996

The receptor mosaic hypothesis of the engram: possible relevance of Boolean network modeling.

In the past 15 years, several lines of evidence have shown that receptors for chemical signals can interact in domains of the plasma membrane and possibly form molecular circuits encoding logical operators. In this frame, the receptor mosaic hypothesis of the engram was advanced. According to this proposal, aggregates of different receptor species (mosaics) may form in neuronal membranes (typically synapses) and constitute a memory trace (engram) of its activity. In the present paper, we present an attempt to model the functioning of aggregates of interacting receptors in membrane domains by means of random Boolean networks.

Animals↗

PubMed1996

Effects of single and short-term administration of clonidine on hypothalamic-pituitary somatotropic function of the adult male rat: an in situ hybridization study.

The effects of the alpha-2 adrenoceptor agonist clonidine (CLO) on the growth hormone (GH) regulatory neuronal systems, growth hormone-releasing hormone (GHRH) and somatostatin (SS), were studied in adult male rats given a single or a short-term administration (1, 3 and 6 days) of the drug. Acute administration of CLO significantly decreased hypothalamic GHRH content [leaving unaltered GHRH messenger RNA (mRNA) levels] and increased plasma GH levels; hypothalamic SS content/mRNA levels and pituitary GH content/mRNA levels remained unchanged. In 1- and 3-day CLO-treated rats, by contrast, decreased hypothalamic GHRH content was coupled with a significant reduction in GHRH mRNA levels. In these rats, pituitary GH content and mRNA levels were also significantly increased, whereas hypothalamic SS content and mRNA levels remained unaltered. In 6-day CLO-treated rats, hypothalamic GHRH content and mRNA levels were still significantly reduced, plasma GH levels were increased, but to a lesser extent than in 1- and 3-day CLO-treated rats, and pituitary GH content and mRNA reverted to control levels. Hypothalamic SS content and mRNA levels remained unaltered. These results indicate that 1) functional activation of alpha-2 adrenergic receptors by CLO increases GHRH release from the hypothalamus, 2) CLO, via GHRH, increases GH secretion and biosynthesis, which in turn feeds back in the hypothalamus to reduce GHRH biosynthesis, and 3) reduction of hypothalamic GH-stimulatory activity tones down the initial pituitary somatotropic hyperfunction. Unaltered hypothalamic SS content and mRNA levels in all CLO-treated rats suggests that the somatostatinergic system is less sensitive than the GHRH system to changes in circulating GH levels.

Adrenergic alpha-2 Receptor Agonists↗

PubMed1995

Neurotensin-like immunoreactivity in odontoblasts and their processes in rat maxillary molar teeth and the effect of pulpotomy.

A strong neurotensin-like immunoreactivity (NT-like IR) was detected in the odontoblast cells of the rat teeth. 4 h after a partial pulpotomy performed in two maxillary molar teeth a decreased NT-like IR was observed in the odontoblast layer located at the vicinity of the lesion together with edema and nuclear pyknosis. NT-like IR became further decreased after 24 h. After 7 days NT-like IR had almost fully disappeared with signs of necrosis of the dental pulp and infiltration of polymorphonuclear lymphocytes. It seems possible that NT like peptides in the odontoblast cell layer may play a role, e.g., in dentinogenesis and/or nociception.

Animals↗

PubMed1995

Receptor-receptor interactions and their relevance for receptor diversity. Focus on neuropeptide/dopamine interactions.

Receptor diversity in combination with receptor-receptor subtype specific interactions, which can be antagonistic or synergistic in character, markedly increase plasticity in WT and VT in the nervous system. In this way switching among transmission lines for the various DA receptor subtypes becomes possible. Some of these aspects are supported by our work on selective modulation of D2 receptors by CCK and NT. Selective regulation of D2 receptors via CCK-8 receptor subtypes and NT receptors may underlie CCK/DA interactions and NT/DA interactions in the basal ganglia. These studies underline the importance of receptor-receptor interactions exerted at the membrane level between neuropeptide receptors and D2 receptors, which are determined at least in part by the ongoing activity at D1 receptors. In the case of both CCK/D2 and NT/D2 receptor interactions, it has been possible, by means of intrastriatal and intraaccumbens microdialysis, to obtain a functional correlate to the receptor interactions found in the membrane preparations from the striatum. Schizophrenia may be in part related to reduced release of CCK and/or NT peptides or to alterations in their receptor interactions with the D2 receptor. This view may lead to new therapeutic approaches.

Animals↗

PubMed1995

Long distance pathways of diffusion for dextran along fibre bundles in brain. Relevance for volume transmission.

Texas Red-labelled dextran with a mol. wt of 3000 g mol-1, a marker for the extracellular space, was injected unilaterally into the neostriatum of adult rats (0.3-30 micrograms microliter-1) and its distribution evaluated 1 min to 5 h later. Diffusion in the neuropil was observed with clearance starting after 30 min. After 10-15 min strong labelling along the myelinated fibre bundles was observed in the entire neostriatum. After about 20 min the labelling along the fibres reached into the corpus callosum and the overlaying deep layers of the cerebral cortex. A marked cellular uptake and accumulation of labelled dextran was found in putative perivascular pericytes. Thus, in the living brain preferential extracellular fluid pathways for diffusion exist, especially along fibre bundles, which allow the exchange of chemical signals between two distant regions. These may represent extracellular fluid pathways for volume transmission.

Animals↗

PubMed1995

On the cellular localization and distribution of carbonic anhydrase II immunoreactivity in the rat brain.

Evidence is provided that carbonic anhydrase-II is localized in the central nervous system to wide spread systems of oligodendrocytes and restricted astroglia populations, involving both fiber bundles and neuropil. It is suggested that CO2 formed in activated axons may, via carbonic anhydrase-II, give rise to protons controlling the excitability of surrounding neuropil. Thus, CO2 may represent an important, highly diffusible, signal in brain, involved in the tonic control of neuronal activity.

Animals↗

PubMed1995

Presynaptic A2-adrenoceptors and neuropeptide Y Y2 receptors inhibit [3H]noradrenaline release from rat hypothalamic synaptosomes via different mechanisms.

Presynaptic receptors may reduce transmitter release with different mechanisms. Both the alpha 2-agonist, clonidine and the Y2-agonist, neuropeptide Y fragment 13-36 (NPY 13-36), induce a concentration-dependent inhibition of the 4-aminopyridine (4-AP)-evoked [3H]noradrenaline ([3H]NA) release from hypothalamic synaptosomes. Changes in alpha 2- and Y2-modulation of noradrenaline (NA) release were observed by lowering the calcium influx with the use of omega-conotoxin (omega-CgTx), a calcium-channel blocking agent. In these experimental conditions, clonidine was less active, whereas NPY 13-36 preserved its efficacy. It therefore seems possible that presynaptic alpha 2-adrenoceptors can primarily inhibit NA release by reducing calcium influx via voltage-sensitive calcium channels (VSCC), while Y2-receptors may inhibit the intracellular release process with a mechanism independent of the calcium entry.

4-Aminopyridine↗

PubMed1995

Counteraction of NYP-induced c-Fos expression in the nucleus tractus solitarii by alpha 2 receptor agonists.

Neuronal c-Fos protein-like immunoreactivity (c-Fos IR) in parts of the nucleus tractus solitarii (NTS)-dorsal motor nucleus of the vagus nerve (dmnX) complex of the anaesthetized rat was studied 90 min after NTS microinjections of neuropeptide Y (NPY) and/or adrenergic receptor agonists in relevant cardiovascular doses. Microinjections of NPY and l-adrenaline alone into the NTS induced neuronal c-Fos IR in parts of the NTS-dmnX complex, while clonidine had no action. No double-labelled GFAP/c-Fos immunoreactive cells were found in the NTS-dmnX complex after the microinjection of NPY into the NTS. Coinjections of NPY and l-adrenaline or clonidine into the NTS reduced the NPY-induced increase in c-Fos IR. The results emphasize that during cardiovascular regulation NPY receptors can control neuronal gene expression in the NTS-dmnX complex via c-fos and that stimulation of alpha 2-adrenoceptors can attenuate NPY receptor transduction also in terms of induction of c-Fos IR in the NTS-dmnX complex via an antagonistic alpha 2/NPY receptor interaction.

Adrenergic alpha-2 Receptor Agonists↗

PubMed1995

Volume versus wiring transmission in the brain: a new theoretical frame for neuropsychopharmacology.

A volume transmission mode of communication in brain was implicit already in the early work of Golgi, who postulated the existence of electrical signals in the extracellular fluid (ECF) based on Volta's "wet conductor" made by solutions. The term volume transmission is taken from the term volume conduction describing the flow of ionic currents in the ECF as a basis for the electrocorticogram. The slow VT mode includes also chemical signals and is opposed to the fast synaptic (wiring) transmission. Every neuron may function in a dual mode, the synaptic and the volume transmission mode, when considering the autocrine and synaptic classes of communication. The paracrine- and neuroendocrine-like classes only involve the VT mode in the latter case including the CSF as a route. The chemical signals for VT are the neuropeptides, but also the classical transmitters, the monoamines, acetylcholine, GABA, and glutamate can participate, when they operate via slow, high affinity G protein coupled receptors. Ions such as K+, Ca++, and H+ also function as VT signals. The hypothesis is also introduced that CO2 can act as a multifacit long-distance VT and WT regulator besides being part of the CO2/HCO3 buffer. CO2 via regulating NMDA receptor sensitivity can also regulate NO formation, which represents a paracrine and fast VT signal. The therapy of CNS disorders is also discussed in the frame of the wiring and VT concept. Two therapeutical approaches can therefore be developed, one based on increasing WT and one based on increasing VT. In contrast to the WT therapy, which must preserve the electrotemporal code, the VT therapy can operate also with postsynaptic agonists. Therefore, a therapeutic effect with such a drug indicates that the deficiency in the communication process operates via VT. In view of the lack of very effective negative feedbacks in VT vs. WT, VT therapy may produce less tolerance and drug dependency.

Brain↗

PubMed1995

Effect of endothelin-1 induced ischemia on peroxidative damage and membrane properties in rat striatum synaptosomes.

Synaptosomes obtained from rat striata lesioned by central injection of endothelin-1 (ET-1) were analyzed for the levels of lipid peroxidation products, the susceptibility to lipid peroxidation, the phospholipid and free fatty acid composition and the activity of Na+,K(+)-ATPase one hour after ET-1 treatment. The intrastriatal injection of ET-1 promoted an increase of endogenous thiobarbituric reactive substances (TBARS), as index of free radical mediated lipid damage, and a greater susceptibility to iron/ascorbate-induced lipid peroxidation. The pattern of free fatty acids showed a significant decrease of arachidonic and docosahexaenoic acid consequent to ET-1 treatment. The analysis of lipid composition showed a significant loss of phospholipids: among phospholipid species, sphingomyelin and phosphatidylethanolamine plasmalogen were particularly reduced by ET-1 treatment. The activity of membrane-bound Na+,K(+)-ATPase was also significantly reduced in synaptosomes obtained from ET-1 lesioned striata. Taken together these results indicate a significant modification of synaptosomal membrane of ET-1 treated rat striata, possibly due to a free radical mediated damage.

Animals↗

PubMed1995

Changes in glucocorticoid receptor immunoreactivity after adrenalectomy and corticosterone treatment in the rat testis.

The distribution of glucocorticoid receptor (GR) in the rat testis was investigated by means of immunocytochemistry (IR) and computer-assisted image analysis. A monoclonal antibody against rat liver GR showed the presence of GR IR selectively in the nuclei of interstitial and tubular cells. The semiquantitative microdensitometry of GR IR revealed that 77% of the specific staining was localized in the tubular compartment of rat testis. After adrenalectomy, GR IR was greatly reduced both in interstitial and tubular cells, roughly at the same degree. Corticosterone treatment (50 mg/kg, for 5 d) of adrenalectomized animals yielded a recovery of nuclear immunopositivity without changing the cellular distribution of GR, as observed in control rats. Nevertheless, the high dose of corticosterone administered produced a significant (p < 0.01) decrease of GR IR with respect to control rats. These results provide evidence for a prevalent nuclear binding of GR in the tubular compartment in basal conditions. On the other hand, adrenalectomy or repeated corticosterone treatment seem to affect GR similarly in all positive cells without changing significantly the proportion of GR IR in the different testicular compartments. This uneven distribution of GR IR suggests that tubular cells can be a major target of corticosterone when affecting directly testicular functions in the rat.

Adrenalectomy↗

PubMed1995

A brief appraisal on some aspects of the receptor-receptor interaction.

Receptor-receptor interaction is being recognized as a key cellular mechanism responsible for the integration of signals between different transmission lines at the membrane level. Receptor-receptor interaction extends the classical concept of integration of depolarization and hyperpolarization effects to the integration of chemical events at membrane level. In the present paper only some hypotheses on the possible mechanistic aspects of the interactions between the membrane receptors will be discussed. Furthermore, possible functional consequences of receptor-receptor interaction will be explored. The limitations of the present experimental approaches to the study of receptor-receptor interaction will also be analysed.

Animals↗

PubMed1995

The concept of trophic units in the central nervous system.

The present paper proposes that trophic interplay among cells may represent the final common pathway for both genetic and environmental influences, and hence new criteria for the understanding of central nervous system (CNS) connectivity can be suggested. In particular, trophic signals may make up the common "language" through which genetic and epigenetic influences mold the CNS during development and the adult life. Furthermore, it will put forward the hypothesis that the developmental trophic interplay among cells leads to the formation of trophic units in the adult brain. A trophic unit is defined as the smallest set of cells, within the CNS, which act in a complementary way to support each other's trophism. The trophic units consist of neurons, glial cells, blood vessels, extracellular matrix (ECM). In particular, ECM gives support to the thin elongated cell processes and gives rise to selective chemical bridges between cell surfaces or between cell surfaces and the extracellular milieu. The trophic unit is a plastic device that not only assures neuronal survival, but also operates to adapt neuronal networks to new tasks by controlling extension of neuronal processes, synapse turnover and ECM characteristics. These plastic responses depend on the interplay of all the elements that constitute the trophic units. The concept of trophic unit may help to understand some features of neurodegenerative diseases, for example, the clustering of tangles in the neocortex and in the entorhinal cortex of Alzheimer's patients [corrected].

Animals↗

PubMed1995

Intercellular communication in the brain: wiring versus volume transmission.

During the past two decades several revisions of the concepts underlying interneuronal communication in the central nervous system have been advanced. We propose here to classify communicational phenomena between cells of the central neural tissue under two general frames: "wiring" and "volume" transmission. "Wiring" transmission is defined as intercellular communication occurring through a well-defined connecting structure. Thus, wiring transmission is characterized by the presence of physically identifiable communication channels within the neuronal and/or glial cell network. It includes synaptic transmission but also other types of intercellular communication through a connecting structure (e.g., gap junctions). "Volume" transmission is characterized by signal diffusion in a three-dimensional fashion within the brain extracellular fluid. Thus, multiple, structurally often not well characterized extracellular pathways connect intercommunicating cells. Volume transmission includes short- (but larger than synaptic cleft, i.e. about 20 nm) and long-distance diffusion of signals through the extracellular and cerebrospinal fluid. It must be underlined that the definitions of wiring and volume transmission focus on the modality of transmission and are neutral with respect to the source and target of the transmission, as well as type of informational substance transmitted. Therefore, any cell present in the neural tissue (neurons, astroglia, microglia, ependyma, tanycytes, etc.) can be a source or a target of wiring and volume transmission. In this paper we discuss the basic definitions and some distinctive characteristics of the two types of transmission. In addition, we review the evidence for different types of intercellular communication besides synaptic transmission in the central nervous system during phylogeny, and in vertebrates in physiological and pathological conditions.

Animals↗

PubMed1995

Temporal changes in sulphated glycoprotein-2 (clusterin) and ornithine decarboxylase mRNA levels in the rat testis after ethane-dimethane sulphonate-induced degeneration of Leydig cells.

Short- (3-24 h) and long-term (4-50 days) changes in sulphated glycoprotein-2 (SGP-2) and ornithine decarboxylase (ODC) mRNA levels in the adult rat testis were studied following a single dose of ethane-dimethane sulphonate (EDS), to destroy the Leydig cells. Distribution patterns of SGP-2 and ODC labelling were consistent with prevailing expression of the two transcripts in Sertoli cells and germ cells, respectively. This pattern did not show appreciable changes following EDS administration. No labelling of SGP-2 mRNA was noted in the interstitium of control and EDS-treated rats. This finding indicates that Leydig cell death induced by EDS is not associated with increased SGP-2 mRNA levels, a phenomenon related to apoptotic cell death in many tissues. Semi-quantitative densitometric analysis of the preparations demonstrated differential changes in SGP-2 and ODC mRNA levels in the tubular compartment following EDS treatment. At 6, but not at 3 and 12, h following EDS administration, SGP-2 mRNA levels showed a significant increase, possibly secondary to a direct effect of the alkylating agent on Sertoli cells. A significant decrease in ODC mRNA levels was observed from day 7 to day 28, matching degenerative changes in the seminiferous epithelium. In contrast, a decrease in SGP-2 transcript levels was observed from days 21-35 after treatment. In conclusion, our findings demonstrate that SGP-2 mRNA, a putative marker of apoptosis, is not altered in the testicular interstitium during EDS-induced degeneration of Leydig cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗