From the hierarchical organization of the central nervous system to the hierarchical aspects of biocodes.

The quite recent (at least on the evolutionary time scale) emergence of nervous systems in complex organisms enabled the living beings to build a wide-ranging model of the external world in order to predict and evaluate the outcomes of their actions. Such a process likely represents a real coding activity, since, by proper handling of information, it generates a mapping between the external environment and internal cerebral activity patterns. The patterns of neural activity that correspond to the final maps, however, emerge from the holistic assembly of a multilevel functional organization. Nerve tissue components, indeed, appear organized in compartments, also called functional modules (FM), that contain system components and circuits of different miniaturizations not only arranged to work together either in parallel or in series but also nested within each other. At least three levels can be recognized in a functional module and it is possible to point out that such a hierarchical organization of the brain circuits could be mirrored by a corresponding hierarchical organization of biocodes. This feature can also suggest the hypothesis that the same logic could operate also at system level to integrate FM into functional brain areas and to associate areas to generate the final map used by humans to image the external world and to imagine untestable worlds.

Dopamine D1 and D2 receptor immunoreactivities in the arcuate-median eminence complex and their link to the tubero-infundibular dopamine neurons.

Dopamine D1 and D2 receptor immunohistochemistry and Golgi techniques were used to study the structure of the adult rat arcuate-median eminence complex, and determine the distribution of the dopamine D1 and D2 receptor immunoreactivities therein, particularly in relation to the tubero-infundibular dopamine neurons. Punctate dopamine D1 and D2 receptor immunoreactivities, likely located on nerve terminals, were enriched in the lateral palisade zone built up of nerve terminals, while the densities were low to modest in the medial palisade zone. A codistribution of dopamine D1 receptor or dopamine D2 receptor immunoreactive puncta with tyrosine hydroxylase immunoreactive nerve terminals was demonstrated in the external layer. Dopamine D1 receptor but not dopamine D2 receptor immnunoreactivites nerve cell bodies were found in the ventromedial part of the arcuate nucleus and in the lateral part of the internal layer of the median eminence forming a continuous cell mass presumably representing neuropeptide Y immunoreactive nerve cell bodies. The major arcuate dopamine/ tyrosine hydroxylase nerve cell group was found in the dorsomedial part. A large number of tyrosine hydroxylase immunoreactive nerve cell bodies in this region demonstrated punctate dopamine D1 receptor immunoreactivity but only a few presented dopamine D2 receptor immunoreactivity which were mainly found in a substantial number of tyrosine hydroxylase cell bodies of the ventral periventricular hypothalamic nucleus, also belonging to the tubero-infundibular dopamine neurons. Structural evidence for projections of the arcuate nerve cells into the median eminence was also obtained. Distal axons formed horizontal axons in the internal layer issuing a variable number of collaterals classified into single or multiple strands located in the external layer increasing our understanding of the dopamine nerve terminal networks in this region.  Dopamine D1 and D2 receptors may therefore directly and differentially modulate the activity and /or Dopamine synthesis of substantial numbers of tubero-infundibular dopamine neurons at the somatic and terminal level. The immunohistochemical work also gives support to the view that dopamine D1 receptors and/or dopamine D2 receptors in the lateral palisade zone by mediating dopamine volume transmission may contribute to the inhibition of luteinizing hormone releasing hormone release from nerve terminals in this region.

Aspects on the integrative actions of the brain from neural networks to "brain-body medicine".

"Integration" is a key term in describing how nervous system can perform high level functions. A first condition to have "integration" is obviously the presence of efficient "communication processes" among the parts that have to be combined into the harmonious whole. In this respect, two types of communication processes, called wiring transmission (WT) and volume transmission (VT), respectively, were found to play a major role in the nervous system, allowing the exchange of signals not only between neurons, but rather among all cell types present in the central nervous system (CNS). A second fundamental aspect of a communication process is obviously the recognition/decoding process at target level. As far as this point is concerned, increasing evidence emphasizes the importance of supramolecular complexes of receptors (the so called receptor mosaics) generated by direct receptor-receptor interactions. Their assemblage would allow a first integration of the incoming information already at the plasma membrane level. Recently, evidence of two new subtypes of WT and VT has been obtained, namely the tunnelling nanotubes mediated WT and the microvesicle (in particular exosomes) mediated VT allowing the horizontal transfer of bioactive molecules, including receptors, RNAs and micro-RNAs. The physiological and pathological implications of these types of communication have opened up a new field that is largely still unexplored. In fact, likely unsuspected integrative actions of the nervous system could occur. In this context, a holistic approach to the brain-body complex as an indissoluble system has been proposed. Thus, the hypothesis has been introduced on the existence of a brain-body integrative structure formed by the "area postrema/nucleus tractus solitarius" (AP/NTS) and the "anteroventral third ventricle region/basal hypothalamus with the median eminence" (AV3V-BH). These highly interconnected regions operate as specialized interfaces between the brain and the body integrating brain-borne and body-borne neural and humoral signals.

GPCR heteromers and their allosteric receptor-receptor interactions.

The concept of intramembrane receptor-receptor interactions and evidence for their existences were introduced in the beginning of the 1980's, suggesting the existence of receptor heterodimerization. The discovery of GPCR heteromers and the receptor mosaic (higher order oligomers, more than two) has been related to the parallel development and application of a variety of resonance energy transfer techniques such as bioluminescence (BRET), fluorescence (FRET) and sequential energy transfer (SRET). The assembly of interacting GPCRs, heterodimers and receptor mosaic leads to changes in the agonist recognition, signaling, and trafficking of participating receptors via allosteric mechanisms, sometimes involving the appearance of cooperativity. The receptor interface in the GPCR heteromers is beginning to be characterized and the key role of electrostatic epitope-epitope interactions for the formation of the receptor heteromers will be discussed. Furthermore, a "guide-and-clasp" manner of receptor-receptor interactions has been proposed where the "adhesive guides" may be the triplet homologies. These interactions probably represent a general molecular mechanism for receptor-receptor interactions. It is proposed that changes in GPCR function (moonlighting) may develop through the intracellular loops and C-terminii of the GPCR heteromers as a result of dynamic allosteric interactions between different types of G proteins and other receptor interacting proteins in these domains of the receptors. The evidence for the existence of receptor heteromers opens up a new field for a better understanding of neurophysiology and neuropathology. Furthermore, novel therapeutic approaches could be possible based on the use of heteromers as targets for drug development based on their unique pharmacology.

Microvesicle and tunneling nanotube mediated intercellular transfer of g-protein coupled receptors in cell cultures.

Recent evidence shows that cells exchange collections of signals via microvesicles (MVs) and tunneling nano-tubes (TNTs). In this paper we have investigated whether in cell cultures GPCRs can be transferred by means of MVs and TNTs from a source cell to target cells. Western blot, transmission electron microscopy and gene expression analyses demonstrate that A(2A) and D(2) receptors are present in released MVs. In order to further demonstrate the involvement of MVs in cell-to-cell communication we created two populations of cells (HEK293T and COS-7) transiently transfected with D(2)R-CFP or A(2A)R-YFP. These two types of cells were co-cultured, and FRET analysis demonstrated simultaneously positive cells to the D(2)R-CFP and A(2A)R-YFP. Fluorescence microscopy analysis also showed that GPCRs can move from one cell to another also by means of TNTs. Finally, recipient cells pre-incubated for 24 h with A(2A)R positive MVs were treated with the adenosine A(2A) receptor agonist CGS-21680. The significant increase in cAMP accumulation clearly demonstrated that A(2A)Rs were functionally competent in target cells. These findings demonstrate that A(2A) receptors capable of recognizing and decoding extracellular signals can be safely transferred via MVs from source to target cells.

C2C12 myoblasts release micro-vesicles containing mtDNA and proteins involved in signal transduction.

Micro-vesicles can be released by different cell types and operate as 'safe containers' mediating inter-cellular communication. In this work we investigated whether cultured myoblasts could release exosomes. The reported data demonstrate, for the first time, that C2C12 myoblasts release micro-vesicles as shown by the presence of two exosome markers (Tsg101 and Alix proteins). Using real-time PCR analysis it was shown that these micro-vesicles, like other cell types, carry mtDNA. Proteomic characterization of the released micro-vesicle contents showed the presence of many proteins involved in signal transduction. The bioinformatics assessment of the Disorder Index and Aggregation Index of these proteins suggested that C2C12 micro-vesicles mainly deliver the machinery for signal transduction to target cells rather than key proteins involved in hub functions in molecular networks. The presence of IGFBP-5 in the purified micro-vesicles represents an exception, since this binding protein can play a key role in the modulation of the IGF-1 signalling pathway. In conclusion, the present findings demonstrate that skeletal muscle cells release micro-vesicles, which probably have an important role in the communication processes within skeletal muscles and between skeletal muscles and other organs. In particular, the present findings suggest possible new diagnostic approaches to skeletal muscle diseases.

Adenosine-dopamine interactions in the pathophysiology and treatment of CNS disorders.

Adenosine-dopamine interactions in the central nervous system (CNS) have been studied for many years in view of their relevance for disorders of the CNS and their treatments. The discovery of adenosine and dopamine receptor containing receptor mosaics (RM, higher-order receptor heteromers) in the striatum opened up a new understanding of these interactions. Initial findings indicated the existence of A(2A)R-D(2)R heterodimers and A(1)R-D(1)R heterodimers in the striatum that were followed by indications for the existence of striatal A(2A)R-D(3)R and A(2A)R-D(4)R heterodimers. Of particular interest was the demonstration that antagonistic allosteric A(2A)-D(2) and A(1)-D(1) receptor-receptor interactions take place in striatal A(2A)R-D(2)R and A(1)R-D(1)R heteromers. As a consequence, additional characterization of these heterodimers led to new aspects on the pathophysiology of Parkinson's disease (PD), schizophrenia, drug addiction, and l-DOPA-induced dyskinesias relevant for their treatments. In fact, A(2A)R antagonists were introduced in the symptomatic treatment of PD in view of the discovery of the antagonistic A(2A)R-D(2)R interaction in the dorsal striatum that leads to reduced D(2)R recognition and G(i/o) coupling in striato-pallidal GABAergic neurons. In recent years, indications have been obtained that A(2A)R-D(2)R and A(1)R-D(1)R heteromers do not exist as heterodimers, rather as RM. In fact, A(2A)-CB(1)-D(2) RM and A(2A)-D(2)-mGlu(5) RM have been discovered using a sequential BRET-FRET technique and by using the BRET technique in combination with bimolecular fluorescence complementation. Thus, other pathogenic mechanisms beside the well-known alterations in the release and/or decoding of dopamine in the basal ganglia and limbic system are involved in PD, schizophrenia and drug addiction. In fact, alterations in the stoichiometry and/or topology of A(2A)-CB(1)-D(2) and A(2A)-D(2)-mGlu5 RM may play a role. Thus, the integrative receptor-receptor interactions in these RM give novel aspects on the pathophysiology and treatment strategies, based on combined treatments, for PD, schizophrenia, and drug addiction.

beta-Amyloid fibrillation and/or hyperhomocysteinemia modify striatal patterns of hyaluronic acid and dermatan sulfate: Possible role in the pathogenesis of Alzheimer's disease.

A key event in Alzheimer's disease (AD) pathogenesis is the formation of insoluble peptides beta-amyloid aggregates and this process is favoured by a condition of hyperhomocysteinemia. To date, there is growing evidence that implicates glycosaminoglycans (GAGs) in the pathophysiology of amyloidosis but no data are available on the characterization of brain GAGs involved in the enhancing beta-amyloid fibrillogenesis in relationship to their structure and physico-chemical properties. Furthermore, few studies have been performed on the relationship between hyperhomocysteinemia and extracellular matrix (ECM) modifications. The aim of this study was to evaluate the amount and chemical structure of GAGs in rat striatal areas where beta-amyioid fibrillogenesis was induced, and in conditions of hyperhomocysteinemia. The intrastriatal injection of beta-amyloid produced a significant decrease (-40.8%) in the hyaluronic acid (HA) percentage and an increase (+14.5%) in the dermatan sulfate (DS) with a total charge density increasing of 14.9%. A significant decrease (-19.5%) in the HA percentage and an increase (+6.9%) in the DS % was also observed in striata obtained from the hyperhomocysteinemic animals. The total charge density increased by 6.8%. Quite the same trend was observed in rats after intrastriatal injection of beta-amyloid and in a condition of hyperhomocysteinemia. The observed increase of DS concentration and the correspondent decrease of the nonsulfated polymer HA after in vivo treatment with beta-amyloid and in a condition of hyperhocysteinemia support the hypothesis that an increase in local production of sulfated GAGs may reduce beta-amyloid neurotoxicity. However, the consequent modification of the ECM network might impair the extracellular diffusion pathways of different signal molecules and participate in the progression of AD.

A new hypothesis of pathogenesis based on the divorce between mitochondria and their host cells: possible relevance for Alzheimer's disease.

On the basis of not only the endosymbiotic theory of eukaryotic cell organization and evolution but also of observations of transcellular communication via Tunneling NanoTubes (TNTs), the hypothesis is put forward that when mitochondria, which were once independently living prokaryote-like organisms, are subjected to detrimental genetic, toxic, or environmental conditions, including age-related endogenous factors, they can regress towards their original independent state. At that point, they can become potentially pathogenic intruders within their eukaryotic host cell. Because of the protoplasmic disequilibrium caused by an altered, or mutated, mitochondral population, certain host cells with a minimal capacity for self-renewal, such as dopaminergic neurons, risk a loss of function and degenerate. It is also proposed that altered mitochondria, as well as their mutated mtDNA, can migrate, via TNTs, into adjacent cells. In this way, neurodegenerative states are propagated between cells (glia and/or neurons) of the Central Nervous System (CNS) and that this leads to conditions such as Alzheimer's and Parkinson's disease. This proposal finds indirect support from observations on rotenone-poisoned glioblastoma cells which have been co-cultured with non-poisoned cells. Immunocytochemical techniques revealed that mitochondria, moving along the TNTs, migrated from the poisoned cells towards the healthy cells. It has also been demonstrated by means of immunocytochemistry that, in glioblastoma cell cultures, Amyloid Precursor Protein (APP) is present in TNTs, hence it may migrate from one cell to neighbouring cells. This datum may be of high relevance for a better understanding of Alzheimer's Disease (AD) since molecular, cellular, and animal model studies have revealed that the formation of amyloid beta (Abeta) and other derivatives of the APP are key pathogenic factors in AD, causing mitochondrial dysfunction, free radical generation, oxidative damage, and inflammation. Furthermore, the present data demonstrate the presence of alpha-synuclein (alpha-syn) within TNTs, hence a similar pathogenic mechanism to the one surmised for AD, but centred on alpha-syn rather than on Abeta, may play a role in Parkinson's Disease (PD). As a matter of fact, alpha-syn can enter mitochondria and interact with complex I causing respiratory deficiency and increased oxygen free radical production. In agreement with this view, it has been demonstrated that, in comparison with normal subjects, PD patients show a significant accumulation of alpha-syn at Substantia Nigra and Striatal level, predominantly associated with the inner mitochondrial membrane,. These observations suggest that potentially neuropathogenic proteins, such as Abeta and alpha-syn, can not only diffuse via the extracellular space but also move from cell to cell also via TNTs where they can cause mitochondrial damage and cell degeneration. A mathematical model (see Appendix) is proposed to simulate the pathogenic consequences of the migration of altered mitochondria and/or of their mtDNA via TNTs. The results of the present simulation is compatible with the proposal that mutated mitochondrial agents behave as though they were infectious particles migrating through a continuum of interconnected cells.

Implications of the 'Energide' concept for communication and information handling in the central nervous system.

Recently a revision of the cell theory has been proposed, which has several implications both for physiology and pathology. This revision is founded on adapting the old Julius von Sach's proposal (1892) of the Energide as the fundamental universal unit of eukaryotic life. This view maintains that, in most instances, the living unit is the symbiotic assemblage of the cell periphery complex organized around the plasma membrane, some peripheral semi-autonomous cytosol organelles (as mitochondria and plastids, which may be or not be present), and of the Energide (formed by the nucleus, microtubules, and other satellite structures). A fundamental aspect is the proposal that the Energide plays a pivotal and organizing role of the entire symbiotic assemblage (see Appendix 1). The present paper discusses how the Energide paradigm implies a revision of the concept of the internal milieu. As a matter of fact, the Energide interacts with the cytoplasm that, in turn, interacts with the interstitial fluid, and hence with the medium that has been, classically, known as the internal milieu. Some implications of this aspect have been also presented with the help of a computational model in a mathematical Appendix 2 to the paper. Finally, relevances of the Energide concept for the information handling in the central nervous system are discussed especially in relation to the inter-Energide exchange of information.

Possible role of receptor heteromers in multiple sclerosis.

Recent results suggest that cytokine and glutamate receptors can interact directly and form receptor heteromers. Due to such heteromers, cytokines can act not only as classical neuromediators but also directly enhance glutamate gated ion channel activity via allosteric mechanisms. Our opinion is that such heteromers may lead to enhanced glutamate neurotoxicity in pathogenic processes of multiple sclerosis. Thus, agents targeting evolutionary conserved leucine-rich motifs responsible for such dimerization of receptors may represent a useful strategy to inhibit excitotoxicity in multiple sclerosis.

Common key-signals in learning and neurodegeneration: focus on excito-amino acids, beta-amyloid peptides and alpha-synuclein.

In this paper a hypothesis that some special signals ("key-signals" excito-amino acids, beta-amyloid peptides and alpha-synuclein) are not only involved in information handling by the neuronal circuits, but also trigger out substantial structural and/or functional changes in the Central Nervous System (CNS) is introduced. This forces the neuronal circuits to move from one stable state towards a new state, but in doing so these signals became potentially dangerous. Several mechanisms are put in action to protect neurons and glial cells from these potentially harmful signals. However, in agreement with the Red Queen Theory of Ageing (Agnati et al. in Acta Physiol Scand 145:301-309, 1992), it is proposed that during ageing these neuroprotective processes become less effective while, in the meantime, a shortage of brain plasticity occurs together with an increased need of plasticity for repairing the wear and tear of the CNS. The paper presents findings supporting the concept that such key-signals in instances such as ageing may favour neurodegenerative processes in an attempt of maximizing neuronal plasticity.

Cellular localization and distribution of dopamine D(4) receptors in the rat cerebral cortex and their relationship with the cortical dopaminergic and noradrenergic nerve terminal networks.

The role of the dopamine D(4) receptor in cognitive processes and its association with several neuropsychiatric disorders have been related to its preferential localization in the cerebral cortex. In the present work we have studied in detail the regional and cellular localization of the dopamine D(4) receptor immunoreactivity (IR) in the rat cerebral cortex and its relationship to the dopaminergic and noradrenergic nerve terminal networks, since both dopamine and noradrenaline have a high affinity for this receptor. High levels of D(4) IR were found in motor, somatosensory, visual, auditory, temporal association, cingulate, retrosplenial and granular insular cortices, whereas agranular insular, piriform, perirhinal and entorhinal cortices showed low levels. D(4) IR was present in both pyramidal and non-pyramidal like neurons, with the receptor being mainly concentrated to layers II/III. Layer I was observed to be exclusively enriched in D(4) IR branches of apical dendrites. Finally, mismatches were observed between D(4) IR and tyrosine hydroxylase and dopamine beta-hydroxylase IR nerve terminal plexuses, indicating that these receptors may be activated at least in part by dopamine and noradrenaline operating as volume transmission signals. The present findings support a major role of the dopamine D(4) receptor in mediating the transmission of cortical dopamine and noradrenaline nerve terminal plexuses.

On the key role played by altered protein conformation in Parkinson's disease.

On the basis of the previously proposed hierarchic organisation of the central nervous system (CNS) and of its syntropic behaviour, a view of neurodegenerative diseases focusing on the assemblage of abnormal multimeric proteins (pathologic protein mosaics (PMs)) is proposed. Thus, the main focus of the present paper is on Parkinson's disease (PD) as a neurodegenerative disease, which has as crucial feature protein conformational alterations and formation of pathological PMs. Two interconnected cellular dysfunctions are discussed as main pathogenic factors of PD syndromes, namely mitochondrial deficits (i.e. energy failure, especially critical for Substantia Nigra DA neurons) and conformational protein alterations (due to genetic or environmental causes). Conformational protein alterations can trigger pathological phenomena via the loss and/or the gain of new functions. In particular, altered proteins can lead to the formation of abnormal PMs, which can, inter alia, cause distortion of cellular structures, toxic functions and/or formation of improper membrane ion channels. In view of the fact that disordered proteins can easily acquire unwanted conformation, the "disorder index" (DI) for proteins involved in PD has been evaluated. It has been found that both alpha-synuclein and tau-protein have high DI. This datum is in agreement with the observation that these two proteins synergistically promote polymerisation of each other into amyloid fibrils, favouring the formation of Lewy bodies.

Receptor-receptor interactions within receptor mosaics. Impact on neuropsychopharmacology.

Future therapies for diseases associated with altered dopaminergic signaling, including Parkinson's disease, schizophrenia and drug addiction or drug dependence may substantially build on the existence of intramembrane receptor-receptor interactions within dopamine receptor containing receptor mosaics (RM; dimeric or high-order receptor oligomers) where it is believed that the dopamine D(2) receptor may operate as the 'hub receptor' within these complexes. The constitutive adenosine A(2A)/dopamine D(2) RM, located in the dorsal striato-pallidal GABA neurons, are of particular interest in view of the demonstrated antagonistic A(2A)/D(2) interaction within these heteromers; an interaction that led to the suggestion and later demonstration that A(2A) antagonists could be used as novel anti-Parkinsonian drugs. Based on the likely existence of A(2A)/D(2)/mGluR5 RM located both extrasynaptically on striato-pallidal GABA neurons and on cortico-striatal glutamate terminals, multiple receptor-receptor interactions within this RM involving synergism between A(2A)/mGluR5 to counteract D(2) signaling, has led to the proposal of using combined mGluR5 and A(2A) antagonists as a future anti-Parkinsonian treatment. Based on the same RM in the ventral striato-pallidal GABA pathways, novel strategies for the treatment of schizophrenia, building on the idea that A(2A) agonists and/or mGluR5 agonists will help reduce the increased dopaminergic signaling associated with this disease, have been suggested. Such treatment may ensure the proper glutamatergic drive from the mediodorsal thalamic nucleus to the prefrontal cortex, one which is believed to be reduced in schizophrenia due to a dominance of D(2)-like signaling in the ventral striatum. Recently, A(2A) receptors also have been shown to counteract the locomotor and sensitizing actions of cocaine and increases in A(2A) receptors have also been observed in the nucleus accumbens after extended cocaine self-administration, probably representing a compensatory up-regulation to counteract the cocaine-induced increases in dopamine D(2) and D(3) signaling. Therefore, A(2A) agonists, through antagonizing D(2) and D(3) signaling within A(2A)/D(2) and A(2A)/D(3) RM heteromers in the nucleus accumbens, may be found useful as a treatment for cocaine dependence. Furthermore, antagonistic cannabinoid CB(1)/D(2) interactions requiring A(2A) receptors have also been discovered and possibly operate in CB(1)/D(2)/A(2A) RM located principally on striatal glutamate terminals but also on some ventral striato-pallidal GABA neurons, thereby opening up a new mechanism for the integration of endocannabinoid, DA and adenosine mediated signals. Thus, A(2A), mGluR5 and/or CB(1) receptors can form integrative units with D(2) receptors within RM displaying different compositions, topography and localization. Also galaninR/5-HT(1A) RM probably participates in the transmission of the ascending 5-hydroxytryptamine neurons, where galanin receptors antagonize 5-HT(1A) recognition and signaling. Subtype specific galanin receptor antagonists may therefore represent novel antidepressant drugs. These results suggest the importance of a complete understanding of the function of these RM with regard to disease. Ultimately receptor-receptor interactions within RM that modify dopaminergic and serotonergic signaling may give new strategies for treatment of a wide range of diseases associated with altered dopaminergic and serotonergic signaling.

Structural plasticity in G-protein coupled receptors as demonstrated by the allosteric actions of homocysteine and computer-assisted analysis of disordered domains.

Structural plasticity of G-protein coupled receptors (GPCRs) is of basic importance for their interactions with ligands, in particular with other proteins such as receptors or receptor-modifying proteins that can lead to different functions for the same GPCR. In the present paper, structural plasticity of GPCRs has been investigated discussing allosteric modulatory actions of Homocysteine (Hcy) on D2 receptors together with data obtained by computer-assisted analysis of the presence of disordered domains in GPCRs. Previous evidence for a modulatory action of Hcy on D2 receptors has been further extended by means of experiments on the effects of Hcy local intrastriatal injection on rotational behaviour. Altogether the present data allow considering under a new angle the well known proposal of A2A antagonists as new therapeutic agents in Parkinson's disease (PD). Furthermore, they point out to not only the importance of drugs capable of reducing Hcy brain levels, but also to the potential therapeutic impact of drugs capable of regionally blocking (for PD) or enhancing (for some schizophrenic syndromes) Hcy allosteric action on D2 receptors. As far as the investigations on GPCR plastic domains, extracellular, intracellular and transmembrane domains of 14 GPCRs have been considered and propensity of each of these domains for a structured or unstructured conformation has been evaluated by means of ad hoc computer programs. It has been shown that the N- and C-terminals as well as intracellular loop 3 have a high propensity towards an unstructured conformation, hence they are potentially very plastic domains, which can undergo easily to interactions with other ligands, particularly with other protein domains. This aspect is obviously of the greatest importance not only for the function of single GPCRs, but also for their interactions either with other receptors (receptor-receptor interactions) or, more generally, for formation of clusters of membrane associated proteins, hence of "protein mosaics", where the GPCRs could represent the input unit of the supra-molecular device.

Opposite patterns of age-associated changes in neurons and glial cells of the thalamus of human brain.

In an autopsy series of 19 individuals, age-ranged 24-94, a relatively age-spared region, the anterior-ventral thalamus, was analyzed by immunohistochemical techniques to visualize neurons (neurofilament protein), astrocytes (glial fibrillary acidic protein), microglial cells (CD68) and amyloid precursor protein. The pattern of immunoreactivity was determined by surface fractal dimension and lacunarity, the size by the field area (FA) and the spatial uniformity by the uniformity index. From the normalized FA values of immunoreactivity for the four markers studied, a global parameter was defined to give an overall characterization of the age-dependent changes in the glio-neuronal networks. A significant exponential decline of the GP was observed with increasing age. This finding suggests that early in life (age<50 years) an adaptive response might be triggered, involving the glio-neuronal networks in plastic adaptive adjustments to cope with the environmental challenges and the continuous wearing off of the neuronal structures. The slow decay of the GP observed in a later phase (age>70 years) could be due to the non-trophic reserve still available.