Near-Infrared Spectroscopy: A Free-Living Neuroscience Tool to Better Understand Diabetes and Obesity

The human brain is the least accessible of all organs and attempts to study it in vivo rely predominantly on neuroimaging. Functional near-infrared spectroscopy (fNIRS) allows for the study of cortical neural activity in a non-invasive manner that may resemble free-living conditions. Moreover, compared to other neuroimaging tools, fNIRS is less expensive, it does not require the use of ionizing radiation, and can be applied to all study populations (patients suffering from claustrophobia, or neonates). In this narrative review, we provide an overview of the available research performed using fNIRS in patients with diabetes and obesity. The few studies conducted to date have presented controversial results regarding patients with diabetes, some reporting a greater hemodynamic response and others reporting a reduced hemodynamic response compared to the controls, with an unclear distinction between types 1 and 2. Subjects with obesity or a binge eating disorder have reduced prefrontal activation in response to inhibitory food or non-food stimuli; however, following an intervention, such as cognitive treatment, prefrontal activation is restored. Moreover, we discuss the potential of future applications of fNIRS for a better understanding of cortical neural activity in the context of metabolic disorders.

The Italian national surgical site infection surveillance programme and its positive impact, 2009 to 2011

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Polarization of caveolins and caveolae during migration of immortalized neurons

During CNS development neurons undergo directional migration to achieve their adult localizations. To study neuronal migration, we used a model cell line of immortalized murine neurons (gonadotropin-releasing hormone expressing neurons; GN11), enriched with caveolins and caveolae invaginations that show in vitro chemotaxis upon serum exposure. Cholesterol depletion with methyl-beta-cyclodextrin induced the loss of caveolae and the inhibition of chemotaxis, thus suggesting that GN11 migration depends upon the structural integrity of caveolae. Polarization of proteins and organelles is a hallmark of cell migration. Accordingly, GN11 cells transmigrating through filter pores exhibited a polarized distribution of caveolin-1 isoform (cav-1) in the leading processes. In contrast, during two-dimensional migration cav-1 and caveolae polarized at the trailing edge. As caveolae are enriched with signaling molecules, we suggest that asymmetrical localization of caveolae may spatially orient GN11 neurons to incoming migratory signals thereby transducing them into directional migration.

Caveolin-1 expression and membrane cholesterol content modulate N-type calcium channel activity in NG108-15 cells

Caveolins are the main structural proteins of glycolipid/cholesterol-rich plasmalemmal invaginations, termed caveolae. In addition, caveolin-1 isoform takes part in membrane remodelling as it binds and transports newly synthesized cholesterol from endoplasmic reticulum to the plasma membrane. Caveolin-1 is expressed in many cell types, including hippocampal neurons, where an abundant SNAP25-caveolin-1 complex is detected after induction of persistent synaptic potentiation. To ascertain whether caveolin-1 influences neuronal voltage-gated Ca2+ channel basal activity, we stably expressed caveolin-1 into transfected neuroblastoma x glioma NG108-15 hybrid cells [cav1(+) clone] that lack endogenous caveolins but express N-type Ca2+ channels upon cAMP-induced neuronal differentiation. Whole-cell patch-clamp recordings of cav1(+) cells demonstrated that N-type current density was reduced in size by approximately 70% without any significant change in the time course of activation and inactivation and voltage dependence. Moreover, the cav1(+) clone exhibited a significantly increased proportion of membrane cholesterol compared to wild-type NG108-15 cells. To gain insight into the mechanism underlying caveolin-1 lowering of N-current density, and more precisely to test whether this was indirectly caused by caveolin-1-induced enhancement of membrane cholesterol, we compared single N-type channel activities in cav1(+) clone and wild-type NG108-15 cells enriched with cholesterol after exposure to a methyl-beta-cyclodextrin-cholesterol complex. A lower Ca2+ channel activity was recorded from cell-attached patches of both cell types, thus supporting the view that the increased proportion of membrane cholesterol is ultimately responsible for the effect. This is due to a reduction in the probability of channel opening caused by a significant decrease of channel mean open time and by an increase of the frequency of null sweeps.

G-protein coupled receptors in lipid rafts and caveolae: how, when and why do they go there?

This review describes the advances in our understanding of the role of G-protein coupled receptor (GPCR) localisation in membrane microdomains known as lipid rafts and caveolae. The growing interest in these specialised regions is due to the recognition that they are involved in the regulation of a number of cell functions, including the fine-tuning of various signalling molecules. As a number of GPCRs have been found to be enriched in lipid rafts and/or caveolae by means of different experimental approaches, we first discuss the pitfalls and uncertainties related to the use of these different procedures. We then analyse the addressing signals that drive and/or stabilise GPCRs in lipid rafts and caveolae, and explore the role of rafts/caveolae in regulating GPCR trafficking, particularly in receptor exo- and endocytosis. Finally, we review the growing evidence that lipid rafts and caveolae participate in the regulation of GPCR signalling by affecting both signalling selectivity and coupling efficacy.

Attenuation of G protein-mediated inhibition of N-type calcium currents by expression of caveolins in mammalian NG108-15 cells

1. Caveolins are integral proteins of glycolipid/cholesterol-rich plasmalemmal caveolae domains, where, they may function as a plasma membrane scaffold onto which many classes of signalling molecules, including receptors and heterotrimeric G proteins, can assemble. To ascertain whether caveolins influence G protein-mediated signal transduction, we stably expressed caveolin-1 and -3 isoforms in the neuroblastoma x glioma NG108-15 hybrid cell line, lacking endogenous caveolins. Subsequently, using whole-cell voltage clamp methods, we examined whether the modulation of N-type voltage-gated Ca2+ channels by G(o) protein-coupled, delta-type opioid receptors might be affected by recombinant caveolin expression. 2. In transfected NG108-15 cells, caveolins localized at the plasma membrane and, upon subcellular fractionation on sucrose density gradients, they co-localized in Triton-resistant, low buoyancy fractions, with endogenous G(o) protein alpha-subunits. 3. The voltage-dependent inhibition of omega-conotoxin GVIA-sensitive Ba2+ currents following either activation of delta-opioid receptors by the agonist [o-pen2,o-pen5]-enkephalin (DPDPE), or direct stimulation of G proteins with guanosine 5'-O-(thiotriphosphate) (GTPgammaS) was significantly attenuated in caveolin-expressing cells. The kinetics of Ca2+ channel inhibition were also modified by caveolins. 4. Overall, these results suggest that caveolins may negatively affect G protein-dependent regulation of voltage-gated N-type Ca2+ channels, presumably by causing a reduction of the available pool of activated G proteins.

Thioacylation is required for targeting G-protein subunit G(o1alpha) to detergent-insoluble caveolin-containing membrane domains

alpha-Subunits of heterotrimeric G(i)-like proteins (alpha(i), alpha(o) and alpha(z)) associate with the cytoplasmic leaflet of the plasma membrane by means of N-terminally linked myristic acid and palmitic acid. An additional role for palmitate has been recently suggested by the observation that fusion with the palmitoylated N-terminus of alpha(i1) relocalizes cytosolic green-fluorescent-protein reporter to low buoyancy, Triton-insoluble membrane domains (TIFF; Triton-insoluble floating fraction), enriched with caveolin-1 [Galbiati, Volonté, Meani, Milligan, Lublin, Lisanti and Parenti (1999) J. Biol. Chem 274, 5843-5850]. Here we show that, upon transient expression in transfected COS-7 cells, myristoylated and palmitoylated alpha(o) (alpha(o)wt, where wt is wild-type) is exclusively found in TIFF, from where non-palmitoylated alpha(o)wt and alpha(o)C3S (Cys(3)-->Ser) mutant are excluded. Moreover, alpha(o) fused to N-terminally truncated human vasopressin V2 receptor (V2TR-alpha(o)), lacking myristate and palmitate, still localizes at the plasma membrane by means of first transmembrane helix of V2R, but is excluded from TIFF. Likewise, alpha(o)C3S does not partition into TIFF, even when its membrane avidity is enhanced by co-expression of betagamma-subunits. Thus membrane association, in the absence of added palmitate, is not sufficient to confer partitioning of alpha(o) within TIFF, suggesting that palmitoylation is a signal for membrane compartmentalization of dually acylated alpha-subunits.

Interaction between HIV-1 NEF and G(o) proteins in transfected COS-7 cells

Nef protein of HIV/SIV lentiviruses affects G-protein-mediated signaling, and physically associates to Lck, a myristoylated and palmitoylated Src-like tyrosine kinase. To assess whether Nef interacts with alpha-subunits of heterotrimeric G proteins (Galpha), carrying the same lipidation motif as Lck, we transiently expressed Nef and G(o)alpha (wild-type or nonpalmitoylated C3S mutant), individually or in combination, in transfected COS-7 cells. Recombinant Nef was mostly recovered in particulate fractions, and a Nef-Green Fluorescent Protein chimera was localized at the plasmalemma by in vivo fluorescence imaging. Moreover, Nef and C3S were entirely solubilized by cold Triton X-100, and excluded from low buoyant density sucrose gradient fractions, containing caveolin-1, whereas wild-type G(o)alpha was partially resistant to Triton extraction, and colocalized with caveolin-1. After coexpression, Nef recruited soluble C3S to membranes, and the two proteins were coimmunoprecipitated by G(o)alpha and Nef antisera. We conclude that Nef interacts with nonpalmitoylated G(o)alpha, presumably outside caveolin-rich microdomains of the plasma membrane.

Tubulin anchoring to glycolipid-enriched, detergent-resistant domains of the neuronal plasma membrane

After incubation of intact living cultured rat cerebellar granule cells at 37 degrees C with a new GM1 ganglioside analog, carrying a diazirine group and labeled with (125)I in the ceramide moiety, followed by photoactivation, a relatively small number of radiolabeled proteins were detected in a membrane-enriched fraction. A protein of about 55 kDa with a pI of about 5 carried a large portion of the radioactivity even if incubation and cross-linking were performed at 4 degrees C and in the presence of inhibitors of endocytosis, suggesting that it is cross-linked at the plasma membrane. Immunoprecipitation and Western blotting experiments showed the positivity of this protein for tubulin. Trypsin treatment of intact cells ruled out the involvement of a plasma membrane surface tubulin. Release of radioactivity from cross-linked tubulin after KOH treatment (but not hydroxylamine treatment) suggested that the photoactivated ganglioside reacts with an ester-linked fatty acid anchor of tubulin. Low buoyancy, detergent-resistant membrane fractions, isolated from cells after incubation with the GM1 analogue and photoactivation, proved their enrichment in endogenous and radioactive GM1 ganglioside, sphingomyelin, cholesterol, signal transduction proteins, and tubulin. It is noteworthy that radioactive tubulin was also detected in this fraction, indicating the presence of tubulin molecules carrying a fatty acid anchor in detergent-resistant, ganglioside-enriched domains of the plasma membrane. Parallel experiments carried out with a phosphatidylcholine analogue, also carrying a diazirine group and labeled with (125)I in the fatty acid moiety, showed the specificity of tubulin interaction with GM1. Taken together, these results indicate that some tubulin molecules are associated with a lipid anchor to detergent-resistant glycolipid-enriched domains of the plasma membrane. This novel feature of membrane domains can provide a key for a better understanding of their biological role.

The luteinizing hormone-releasing hormone receptor in human prostate cancer cells: messenger ribonucleic acid expression, molecular size, and signal transduction pathway

Evidence has accumulated indicating that LHRH might behave as an autocrine/paracrine growth inhibitory factor in some peripheral tumors. However, LHRH receptors in tumor cells have not been fully characterized, so far. The present experiments were performed to analyze: 1) the messenger RNA expression; 2) the molecular size; and 3) the signal transduction pathway of LHRH receptors in prostate cancer. For these studies, the human androgen-dependent LNCaP and androgen-independent DU 145 prostate cancer cell lines were used. 1) By RT-PCR, a complementary DNA product, which hybridized with a 32P-labeled oligonucleotide probe specific for the pituitary LHRH receptor complementary DNA, was found both in LNCaP and in DU 145 cells. 2) Western blot analysis, using a monoclonal antibody raised against the human pituitary LHRH receptor, revealed the presence of a protein band of approximately 64 kDa (corresponding to the molecular mass of the pituitary receptor) in both cell lines. 3) In LNCaP and DU 145 cells, pertussis toxin completely abrogated the antiproliferative action of a LHRH agonist (LHRH-A). Moreover, LHRH-A substantially antagonized the pertussis toxin-catalyzed ADP-ribosylation of a Galpha(i) protein. Finally, LHRH-A significantly counteracted the forskolin-induced increase of intracellular cAMP levels in both cell lines. These data demonstrate that the LHRH receptor, which is present in prostate cancer cells, independently of whether they are androgen-dependent or not, corresponds to the pituitary receptor, in terms of messenger RNA expression and protein molecular size. However, at variance with the receptor of the gonadotrophs, prostate cancer LHRH receptor seems to be coupled to the Galpha(i) protein-cAMP signal transduction pathway, rather than to the Galpha(q/11)-phospholipase C signaling system. This might be responsible for the different actions of LHRH in anterior pituitary and in prostate cancer.

Comparison of three assays for HIV antibodies detection in urine to be applied to epidemiological setting

Three immune-enzymatic tests for urinary HIV antibodies were examined in order to assess their sensibility, specificity and delta value. The highest sensibility was noticed for the Seradyn test (98.8%), followed by the Wellcozyme test (98.1%) and finally the SUDS rapid test (56.8%). The resultant specificity was 98.5% for the Seradyn test, 91.3% for the Wellcozyme test and 97.3% for the SUDS test. The measurement of delta value showed a higher capability of discrimination for Seradyn test, that could be considered the most reliable for epidemiological purposes.

The dually acylated NH2-terminal domain of gi1alpha is sufficient to target a green fluorescent protein reporter to caveolin-enriched plasma membrane domains. Palmitoylation of caveolin-1 is required for the recognition of dually acylated g-protein alpha subunits in vivo

Here we investigate the molecular mechanisms that govern the targeting of G-protein alpha subunits to the plasma membrane. For this purpose, we used Gi1alpha as a model dually acylated G-protein. We fused full-length Gi1alpha or its extreme NH2-terminal domain (residues 1-32 or 1-122) to green fluorescent protein (GFP) and analyzed the subcellular localization of these fusion proteins. We show that the first 32 amino acids of Gi1alpha are sufficient to target GFP to caveolin-enriched domains of the plasma membrane in vivo, as demonstrated by co-fractionation and co-immunoprecipitation with caveolin-1. Interestingly, when dual acylation of this 32-amino acid domain was blocked by specific point mutations (G2A or C3S), the resulting GFP fusion proteins were localized to the cytoplasm and excluded from caveolin-rich regions. The myristoylated but nonpalmitoylated (C3S) chimera only partially partitioned into caveolin-containing fractions. However, both nonacylated GFP fusions (G2A and C3S) no longer co-immunoprecipitated with caveolin-1. Taken together, these results indicate that lipid modification of the NH2-terminal of Gi1alpha is essential for targeting to its correct destination and interaction with caveolin-1. Also, a caveolin-1 mutant lacking all three palmitoylation sites (C133S, C143S, and C156S) was unable to co-immunoprecipitate these dually acylated GFP-G-protein fusions. Thus, dual acylation of the NH2-terminal domain of Gi1alpha and palmitoylation of caveolin-1 are both required to stabilize and perhaps regulate this reciprocal interaction at the plasma membrane in vivo. Our results provide the first demonstration of a functional role for caveolin-1 palmitoylation in its interaction with signaling molecules.

Expression of caveolin-1 and -2 in differentiating PC12 cells and dorsal root ganglion neurons: caveolin-2 is up-regulated in response to cell injury

Caveolae are cholesterol/sphingolipid-rich microdomains of the plasma membrane that have been implicated in signal transduction and vesicular trafficking. Caveolins are a family of caveolae-associated integral membrane proteins. Caveolin-1 and -2 show the widest range of expression, whereas caveolin-3 expression is restricted to muscle cell types. It has been previously reported that little or no caveolin mRNA species are detectable in the brain by Northern blot analyses or in neuroblastoma cell lines. However, it remains unknown whether caveolins are expressed within neuronal cells. Here we demonstrate the expression of caveolin-1 and -2 in differentiating PC12 cells and dorsal root ganglion (DRG) neurons by using mono-specific antibody probes. In PC12 cells, caveolin-1 expression is up-regulated on day 4 of nerve growth factor (NGF) treatment, whereas caveolin-2 expression is transiently up-regulated early in the differentiation program and then rapidly down-regulated. Interestingly, caveolin-2 is up-regulated in response to the mechanical injury of differentiated PC12 cells; up-regulation of caveolin-2 under these conditions is strictly dependent on continued treatment with NGF. Robust expression of caveolin-1 and -2 is also observed along the entire cell surface of DRG neurons, including high levels on growth cones. These findings demonstrate that neuronal cells express caveolins.

A cysteine-3 to serine mutation of the G-protein Gi1 alpha abrogates functional activation by the alpha 2A-adrenoceptor but not interactions with the beta gamma complex

Pertussis toxin-resistant (C351G) and also palmitoylation-negative (C3S/C351G), myristoylation-negative (G2A/C351G) and combined acylation-negative (G2A/C3S/C351G) forms of the G-protein Gi1 alpha were expressed in COS-7 cells along with the porcine alpha 2A-adrenoceptor. G2A/C3S/C351G Gi1 alpha and G2A/C351G Gi1 alpha were largely cytosolic and failed to interact with the agonist-occupied alpha 2A-adrenoceptor in membrane preparations. In contrast, C351G Gi1 alpha was almost entirely particulate and the alpha 2-adrenoceptor agonist UK14304 caused a marked stimulation of its GTPase activity and binding of [35S]GTP gamma S which was not prevented by pertussis toxin treatment of the cells. C3S/C351G Gi1 alpha was present in both the particulate and cytosolic fractions but the GTPase activity of the membrane bound fraction was only slightly activated by the alpha 2A-adrenoceptor. Coexpression of C3S/C351G Gi1 alpha and the alpha 2A-adrenoceptor along with beta 1 and gamma 2 subunits increased the P2 membrane complement of the alpha subunit and increased substantially the ratio of membrane bound to cytosolic protein. However, this also failed to allow marked stimulation of high-affinity GTPase activity by the alpha 2A-adrenoceptor despite the increased proportion of G-protein in the P2 membrane fraction. Despite the low fractional activation of C3S/C351G Gi1 alpha by the alpha 2A-adrenoceptor compared to C351G Gi1 alpha, the palmitoylation-resistant G-protein caused a marked reduction in pertussis toxin-resistant, agonist (UK14304)-mediated stimulation of adenylyl cyclase activity. UK14304 caused the same degree of effect on adenylyl cyclase activity in pertussis toxin-treated cells following transfection of the same amounts of C351G Gi1 alpha and C3S/C351G Gi1 alpha, as both appear to act to sequester beta gamma subunits. By contrast, neither G2A/C351G Gi1 alpha nor G2A/C3S/C351G Gi1 alpha resulted in effective regulation of adenylyl cyclase activity.

Interaction of the G-protein G11alpha with receptors and phosphoinositidase C: the contribution of G-protein palmitoylation and membrane association

Wild-type and palmitoylation defective mutants of the murine G protein G11alpha were transfected into HEK293 cells. Wild-type G11alpha was membrane associated, Cys9Ser Cys10Ser G11alpha was present in the soluble fraction whilst both Cys9Ser G11alpha and Cys10Ser G11alpha were distributed between the fractions. Expression of the rat TRH receptor resulted in agonist stimulation of inositol phosphate accumulation. The degree of stimulation produced by TRH following co-transfection of the palmitoylation-resistant forms of G11alpha compared to the wild-type protein correlated with the amount of membrane-associated G protein.

Targeting of a G alpha subunit (Gi1 alpha) and c-Src tyrosine kinase to caveolae membranes: clarifying the role of N-myristoylation

Many signaling molecules contain the consensus protein sequence Met-Gly at their N-termini that specifies N-myristoylation. Additionally, some of these proteins contain a cysteine at position-3 (Met-Gly-Cys) that can undergo palmitoylation. As many acylated proteins [G-protein subunits (alpha and beta gamma); c-Src and Src-family tyrosine kinases; H-Ras and Ras-related GTPases; endothelial nitric oxide synthase] are known to be targeted to caveolae membranes, it has been suggested that acylation is required or greatly facilitates this targeting event. However, it remains unclear whether myristoylation of Src-family kinases is necessary or sufficient for caveolar targeting. Our current study aims at clarifying the role of myristoylation in caveolar targeting using well-characterized acylation mutants of two model proteins, namely Gi1 alpha and c-Src. Here, we have used: i) detergent-free subcellular fractionation and ii) acylation mutants of Gi1 alpha and c-Src to systematically evaluate the relative contribution of myristoylation and palmitoylation to their caveolar targeting. Myristoylation (G2A) and palmitoytation (C3S) mutants of Gi1 alpha were poorly targeted to caveolae-enriched membrane fractions, while approximately 35% of total wild-type Gi1 alpha co-fractionated with caveolin, a caveolar marker protein. Similarly, a myristoylation minus mutant of c-Src was quantitatively excluded from caveolae. In contrast to a previous study, we conclude that myristoylation of Gi1 alpha and c-Src proteins is required for their correct caveolar targeting. However, the caveolar targeting of Gi1 alpha is dramatically augmented approximately 4-fold by palmitoylation. Our current studies are directly supported by the earlier in vivo observation that N-terminal myristoylation of v-Src is required for v-Src to phosphorylate caveolin on tyrosine residues in intact cells.

Chronic treatment with a synthetic cannabinoid CP-55,940 alters G-protein expression in the rat central nervous system

Prolonged exposure of rats to the synthetic cannabinoid receptor ligand, CP-55,940 (0.4 mg/kg, i.p. for 11 days), induced tolerance to analgesia, to the reduction in spontaneous locomotor activity and the incidence of splayed hind limbs. One hour after the last injection on day 11, the rats were killed and in situ hybridization was used to investigate the effect of treatment on G-protein alpha-subunit expression throughout the brain. Chronic cannabinoid exposure markedly reduced G alpha(s), G alpha(i) and G alpha(o) mRNA levels. The message for the alpha(s)-subunit was decreased in all the brain areas containing the basal autoradiographic signal; the decrease ranging from 25% in the thalamus to 45% in the mesencephalon. Also the basal G alpha(i) expression was reduced in tolerant rats showing the greatest decrease in the forebrain (63%) in the cerebellum (58%) and in the mesencephalon (38%). The reduction in G alpha(o) expression (25%) was more localized, being present only in the rostral portion of the brain (cortex, striatum and olfactory area). The alterations in alpha-subunits gene expression were not followed by any change in the amount of proteins. Our results indicate that, besides the receptor modification, alteration to the G-protein expression could be a molecular event associated with the development of cannabinoid tolerance.

Cholera toxin effects on body temperature changes induced by morphine

The present study evaluates the influence of cholera toxin and its B-subunit on thermic responses to morphine in the rats. The holotoxin (1 microg/rat) and the B-subunit (5 microg) were administered ICV and three days later rats were challenged ICV with morphine and tested for changes of body temperature. Cholera toxin, but not its B-subunit, modified the time course of the hyperthermic response induced by a low dose of morphine (2.5 microg), converted the hypothermia due to a higher dose of morphine (18 microg) to a consistent hyperthermia and only partially reduced the greater hypothermia induced by 36 microg of morphine. Cholera toxin-induced modifications of thermic responses to morphine were paralleled with a decreased Gs(alpha) immunoreactivity and a reduced ability for the toxin to catalyse the "in vitro" ADP-ribosylation of Gs(alpha) in hypothalamic membranes. In contrast, at the same time when morphine-induced effects on body temperature were assessed, no changes in pertussis toxin-mediated ADP-ribosylation of Gi(alpha)/Go(alpha), or basal adenylate cyclase activity, or binding of mu-opioid receptor selective ligand [3H]-DAMGO were observed in hypothalamic areas from rats treated with cholera toxin. These findings suggest that adaptative events secondary to prolonged activation of Gs(alpha) play a role in the modifications of thermic responses to morphine induced by CTX.

Pulmonary sporotrichosis with hyphae in a human immunodeficiency virus-infected patient. A case report

BACKGROUND

Pulmonary sporotrichosis is a rare event. Sporothrix schenckii is a dimorphic fungus and develops at 37 degrees C in yeast form. Usually hyphae are not observed in tissues, although their presence has been occasionally demonstrated in biopsies.

CASE

A 37-year-old man, human immunodeficiency virus-1 positive, with a CD4 cell count of 345/mm3, developed a productive cough. A sputum smear revealed the presence of a large amount of long, thin, septated micelia. The hyphae bore oval, sessile conidia. Cultures of sputum yielded numerous colonies of S schenckii.

CONCLUSION

This is the first report of hyphae of S schenckii in sputum. This case emphasizes the possibilities of cytology for the diagnosis of mycotic infections. Fungi have typical morphologies, and it is possible, on the basis of microscopic evidence, to suspect the nature of the infection early and thus to direct culture procedures.

Albendazole treatment of human hydatid tissue

The effect of albendazole was studied in 12 patients with cystic hydatid disease (CHD) of the liver. Six patients received albendazole continuously for 6 months, while 6 patients received albendazole for 6 courses of 4 weeks with a 2 week drug-free interval between cycles. The continuous therapy proved successful, with stable involution at the follow-up at 24 months, while the patients treated with discontinuous therapy showed improvement or relapse. In our experience, continuous therapy was more effective and can be considered to be a suitable alternative or percutaneous therapy in uncomplicated hydatid liver disease, as an initial treatment.

Chemical inhibition of myristoylation of the G-protein Gi1 alpha by 2-hydroxymyristate does not interfere with its palmitoylation or membrane association. Evidence that palmitoylation, but not myristoylation, regulates membrane attachment

The alpha-subunit of the G-protein Gi1 alpha is normally dually acylated at its N-terminus with the saturated fatty acids myristate and palmitate. Inhibition of protein myristoylation by treatment with 2-hydroxymyristate prevented neither the incorporation of [3H]palmitate nor the membrane association of this protein when expressed in the COS cells. Construction of a mutant of Gi1 alpha in which serine-6 was replaced by aspartic acid prevented both myristoylation and palmitoylation, and the expressed protein was found primarily in the cytoplasmic fraction. These data indicate the myristoylation is not an absolute requirement for palmitoylation of Gi1 alpha and that palmitoylation, but not myristoylation, plays a key role in membrane association of this G-protein alpha-subunit.

Morphine withdrawal syndrome and G protein expression: a study of the time course in the rat central nervous system

We followed the changes in G protein alpha subunit expression and levels throughout the brain during the naltrexone-precipitated withdrawal syndrome in morphine-dependent rats. Intraperitoneally injected naltrexone (10 mg/kg) in rats made tolerant to morphine resulted in sustained withdrawal. Additional naltrexone doses 6, 24 and 72 h later still induced a significant abstinence syndrome. At the fifth naltrexone injection (8 days later) counted signs were completely resolved but checked ones were not. Besides the behavioural modifications, opiate withdrawal affected G protein expression in the central nervous system. In situ hybridization showed that G alpha s and G alpha o mRNA, whose levels are increased in tolerance, changed further during opiate withdrawal. Specifically, as alpha s mRNA in the hypothalamus was reduced after the first naltrexone injection and reached the control level with subsequent doses. However, alpha a mRNA expression in the olfactory system remained elevated after repeated naltrexone injections, declining to the control value of only after the fifth dose. The amounts of G alpha s and G alpha o protein closely followed the time course of mRNA. The relationship between behavioural and biochemical parameters is discussed, together with the regional selectivity of the modifications.

Neuronal differentiation modifies the effect of ethanol exposure on voltage-dependent calcium channels in NG 108-15 cells

The effect of prolonged (72 h) ethanol (200 mM) exposure on the labeling of L-type (using tritiated PN 200-110) and N-type (using iodinated omega-conotoxin) voltage-dependent calcium channels was investigated in cultured NG 108-15 cells. In undifferentiated cells ethanol produced an 80% increase in PN 200-110 Bmax and no changes in omega-conotoxin binding. Differentiation had a profound effect on the response of cells to ethanol, which in differentiated neuron-like cells decreased omega-conotoxin binding (-53.5%) leaving PN 200-110 labeling of L-type channels unaffected. The effect was time dependent and reversible upon ethanol withdrawal. The decreased omega-conotoxin binding was accompanied by a reduced ability of omega-conotoxin to inhibit K+ -stimulated calcium uptake. The results demonstrate that in cultured NG 108-15 cells ethanol differentially affects DHP and omega-conotoxin-sensitive, voltage-dependent calcium channels and that the effect is also modulated by differentiation of the cell to a neuronal phenotype.

The role of palmitoylation of the guanine nucleotide binding protein G11 alpha in defining interaction with the plasma membrane

Mutations of Cys-9 to serine, Cys-10 to serine and a combination of both alterations were produced in a cDNA encoding murine G11 alpha to potentially interfere with the ability of the expressed polypeptides to act as substrates for post-translational palmitoylation. Each of these mutants and the wild-type protein were expressed in simian COS-1 cells. Mutation of either cysteine-9 or cysteine-10 decreased the degree of palmitoylation of the protein by some 80% compared with the wild-type, while the double mutant totally failed to incorporate [3H]palmitate. By contrast, in all transfections the endogenously expressed simian G11 alpha incorporated [3H]palmitate to similar levels. Particulate and cytoplasmic fractions from these cells were subjected to SDS/PAGE under conditions which allow resolution of primate and rodent forms of G11 alpha. Immunoblotting of these fractions demonstrated that in all cases the endogenously expressed simian G11 alpha was exclusively associated with the particulate fraction, as was the transfected and expressed wild-type murine G11 alpha. By contrast, each of the mutated forms of murine G11 alpha displayed a distribution in which approx. 70% of the expressed protein was present in the particulate fraction and 30% in the supernatant. To examine the conformation of the particulate expressed forms of murine G11 alpha, these fractions were treated with various concentrations of sodium cholate and immunoblots were subsequently performed on the solubilized and remaining particulate proteins. Whereas essentially all of the endogenous simian G11 alpha was solubilized by treatment with 1% (w/v) sodium cholate and some 50% with 0.32% cholate, expressed wild-type murine G11 alpha was more recalcitrant to solubilization. However, that fraction of wild-type murine G11 alpha which was solubilized behaved identically to the endogenous simian G11 alpha on Superose-12 gel-exclusion chromatography. The particulate fraction of the C9S/C10S double mutant of murine G11 alpha was highly resistant to solubilization by sodium cholate, whereas the particulate fractions of the two single cysteine to serine mutants were intermediate to the wild-type and double mutant in their ability to be solubilized by this detergent. These data demonstrate that the palmitoylation status of the cysteine residues at positions 9 and 10 in murine G11 alpha plays a central role in defining membrane association of this G-protein and indicate that much of the particulate fraction of the expressed palmitoylation-resistant mutants is likely to represent non-functional rather than correctly folded protein.(ABSTRACT TRUNCATED AT 400 WORDS)

BIMT 17, a 5-HT2A receptor antagonist and 5-HT1A receptor full agonist in rat cerebral cortex

In the search for antidepressant agents with a rapid onset of action, we have found that compound BIMT 17 (1-[2-[4-(3-trifluoromethylphenyl)piperazin-1- yl]ethyl]benzimidazol-[1H]-2-one) shows a good affinity for cerebral cortical 5-HT1A (pKi = 7.72) and 5-HT2A (pKi = 6.90) receptors, with no appreciable affinity for the other 5-HT receptor subtypes, including 5-HT2C. BIMT 17 reduced forskolin-stimulated cAMP accumulation in the cerebral cortex (pEC50 = 6.09) and in the hippocampus (pEC50 = 6.50), and antagonized 5-HT-induced phosphatidylinositol turnover (pKi = 6.96) in the cerebral cortex. The effect on cAMP accumulation was blocked by the 5-HT1A receptor antagonist tertatolol. Buspirone, 8-OH-DPAT and S 14671 (1-[2-(2-thenoylamino)ethyl]- 4[1-(7-methoxynaphtyl)]-piperazine), claimed to be 5-HT1A receptor agonists, did not reduce forskolin-stimulated cAMP formation in the cerebral cortex. On the basis of these data, it was concluded that BIMT 17 was the only compound that behaved as a full agonist with respect to the cAMP response in the cortex, while exerting concurrent agonism at 5-HT1A receptors and antagonism at 5-HT2A receptors. These characteristics might explain the peculiar behavior of BIMT 17 in mimicking the inhibitory action of 5-HT on the basal firing rate of the cortical neurons (see accompanying paper).

Behavioral and biochemical evidence of opioidergic involvement in cocaine sensitization

Chronic administration of cocaine produces sensitization to its behavioral effects in humans and experimental animals. In the present study, rats treated with cocaine (10 mg/kg, i.p.) once daily for 10 days showed an enhancement in the acute drug stimulation of locomotor activity and stereotypy. Biochemical analysis in the nucleus accumbens of chronic cocaine-treated animals indicated that sensitization of D1 dopamine (DA) receptors had also developed. In fact, stimulation of adenylyl cyclase activity by DA was increased in nucleus accumbens membranes from sensitized rats. Our findings suggest that a novel postsynaptic mechanism, i.e., an increased DA-D1 receptor function, may play a role in the sensitization. A causal relationship between the two events is supported by the observation that neither motor behavioral sensitization nor DA-dependent adenylyl cyclase hyperactivity developed when the opiate antagonist naltrexone (2 mg/kg, s.c.) was given daily for 10 days before cocaine. When given alone, naltrexone was inactive in all respects, which rules out any unspecific action and suggests that its effects may be due to competition at receptors with endogenous opioids mobilized by cocaine. This was indirectly supported by the finding that desensitization of opioid inhibition of adenylyl cyclase developed in nucleus accumbens membranes of cocaine-sensitized rats. Chronic blockade of opioid receptors by naltrexone also counteracted the reinforcing properties of cocaine; conditioned place preference, clearly displayed by cocaine-treated animals, was antagonized in a dose-related manner. Overall, these results confirm that endogenous opioid peptides play an important role in cocaine addiction.

The dynamic role of palmitoylation in signal transduction

Guanine nucleotide binding protein (G protein)-linked receptors, the alpha-subunits of heterotrimeric G proteins and members of the Src family of nonreceptor tyrosine kinases are among many polypeptides that are posttranslationally modified by the addition of palmitate, a long-chain fatty acid. Attachment of palmitate to these proteins is dynamic and may be regulated by their activation. The presence of palmitate appears to play a key role in the membrane localization of either the entire polypeptide or parts of it, and may regulate the interactions of these polypeptides with other proteins.

Somatotropic dysregulation in old mammals

In old mammals, including humans, the spontaneous growth hormone (GH) secretory pattern is markedly reduced resulting in lower amounts of GH released over 24 h, and the GH response to administration of GH-releasing hormone (GHRH) is reduced. In agreement with these in vivo findings, an impaired responsiveness to GHRH is evident in the pituitary of old male and female rats in vitro, and this is linked with a diminished stimulation of adenylate cyclase by GHRH. The poor GH responsiveness to GHRH in old mammals, which in the rat is coupled to a defective number of GHRH receptors in the somatotrophs, is likely due to a primary deficiency of GHRH availability, as implied by the diminished GHRH immunoreactivity and gene expression in and GHRH release from the hypothalamus of old rats. Attempts have been made to stimulate the sluggish somatotrophic function in elderly humans and dogs using GHRH; in either species positive results were obtained though, overall, it would seem that the GHRH hypofunction does not entirely account for the GH hyposecretory state during ageing. Concerning somatostatin, although the expression of this peptide decreases with age in the rat hypothalamus, secretion and activity of this hormone is increased, resulting in an altered relationship between GHRH and somatostatin gene expression and secretion. It is likely that defects, especially in catecholaminergic and cholinergic neurons, are instrumental in altering specific peptidergic neurons. Reportedly, catecholamines induce GH release by stimulating GHRH neurons and inhibiting somatostatin-releasing neurons; acetylcholine stimulates GH release via muscarinic receptors, in this way inhibiting the action of somatostatin neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

N-terminal fatty acylation of the alpha-subunit of the G-protein Gi1: only the myristoylated protein is a substrate for palmitoylation

The alpha-subunit of the G-protein Gi1 carries two fatty acyl moieties covalently bound to its N-terminal region: myristic acid is linked to glycine-2 and palmitic acid is linked to cysteine-3. Using site-directed mutagenesis on a cDNA construct of alpha i1 we have generated an alpha i1-G2A mutant, carrying alanine instead of glycine at position 2, and alpha i1-C3S mutant, in which serine replaced cysteine-3 and a double mutant with both substitutions (alpha i1-G2A/C3S). These constructs were individually expressed by transfection in Cos-7 cells, and incorporation of fatty acids into the various mutants was compared with wild-type alpha i1 monitoring metabolic labelling with [3H]palmitate or [3H]myristate. The disruption of the palmitoylation site in alpha i1-C3S did not influence myristoylation, whereas prevention of myristoylation in alpha i1-G2A also abolished palmitoylation. Co-translational myristoylation is thus an absolute requirement for alpha i1 to be post-translationally palmitoylated. The non-palmitoylated alpha i1-C3S showed reduced membrane binding to the same extent as the non-myristoylated/non-palmitoylated alpha i1-G2A and alpha i1-G2A/C3S mutants, indicating that the attachment of palmitic acid is necessary for proper interaction with the membrane.

Expression and regulation of calcium-independent protein kinase C in NG 108-15 cell differentiation

Protein, mRNA and activity levels of the calcium-independent protein kinase C (nPKC) isoenzymes were examined in NG108-15 cells. Western blot analyses reveal that proliferating NG 108-15 cells express the delta, epsilon, and eta, but not the theta species. The atypical species PKC zeta was also detected. Differentiation of these cells with dibutyryl cAMP was associated with increase in the levels of PKC epsilon, with no significant changes in its steady-state mRNA levels. The levels of the other isoforms were not altered by the differentiated state. Similarly, no changes in nPKC activity were discerned in either the soluble or particulate fractions when histone or other proteins were used as substrates. These data suggest that the PKC epsilon isoform may be important for the production and maintenance of the differentiated state in NG 108-15 cells.

The palmitoylation status of the G-protein G(o)1 alpha regulates its activity of interaction with the plasma membrane

Plasmids containing cDNAs encoding either the wild-type guanine-nucleotide-binding protein G(o)1 alpha or the palmitoylation-negative cysteine-3-to-serine (C3S) mutant of G(o)1 alpha were transfected into Rat 1 cells, and clones stably expressing immunoreactivity corresponding to these polypeptides were isolated. Clones C5B (expressing wild-type G(o)1 alpha) and D3 (expressing the mutant form) were selected for detailed study. Immunoprecipitation of whole cell lysates of each clone labelled with either [3H]palmitate or [3H]myristate demonstrated incorporation of [3H]myristate into both wild-type and the C3S mutant of G(o)1 alpha, but that incorporation of hydroxylamine-sensitive [3H]palmitate was restricted to the wild type. When membrane and cytoplasmic fractions were prepared from cells of either the C5B or D3 clones, although immunodetection of wild-type G(o)1 alpha was observed only in the membrane fraction, the C3S mutant was present in both membrane and cytoplasmic fractions. Furthermore, a significant proportion of the C3S G(o)1 alpha immunoreactivity was also detected in the cytoplasmic fraction if immunoprecipitation of recently synthesized G(o)1 alpha was performed from fractions derived from cells pulse-labelled with [35S]Trans label. Pretreatment of cells of both clones C5B and D3 with pertussis toxin led to complete ADP-ribosylation of the cellular population of G(o)1 alpha in both cell types, irrespective of whether the polypeptide was subsequently found in the membrane or cytoplasmic fraction following cellular disruption. By contrast, separation of membrane and cytoplasmic fractions before pertussis-toxin-catalysed [32P]ADP-ribosylation allowed modification only of the membrane-associated G(o)1 alpha (whether wild-type or the C3S mutant). This labelling was decreased substantially by incubation of the membranes with guanosine 5'-[beta gamma-imido]triphosphate. No cytoplasmic G-protein beta subunit was detected immunologically, and the non-membrane-associated C3S G(o)1 alpha from D3 cells migrated as an apparently monomeric 40 kDa protein on a Superose 12 gel-filtration column. Membrane-associated wild-type and C3S G(o)1 alpha appeared to interact with guanine nucleotides with similar affinity, as no alteration in the dose-response curves for guanine-nucleotide-induced maintenance of a stable 37 kDa tryptic fragment was noted for the two forms of G(o)1 alpha. Chemical depalmitoylation of membranes of clone C5B with neutral 1 M hydroxylamine caused a release of some 25-30% of each of G(o)1 alpha, Gi2 alpha and Gq alpha/G11 alpha from the membranes. Equivalent treatment of D3 cells caused an equivalent release of Gi2 alpha and Gq alpha/G11 alpha, but was unable to cause any appreciable release of the CS3 form of G(o)1 alpha, which was membrane-bound.

Prolonged very low calorie diet in highly obese subjects reduces plasma viscosity and red cell aggregation but not fibrinogen

Epidemiological studies have shown that obesity, as well as haemorheological changes are risk factors for cardiovascular disease. The aim of this study performed in grossly obese subjects was to investigate: (a) the effects on haemorheological parameters of a 3 month period of very low calorie diet (VLCD, 514 and 470 Kcal/day in women and men respectively), and (b) the relationship between haemorheological test results at baseline and the different types of body fat distribution. Fifty-two obese healthy subjects (31 women), with BMI > 30, were examined at baseline; 34 of these (19 women), compliant with the diet, were also examined after 3 months VLCD. At baseline, the results of haemorheological variables were not significantly different for patients in the highest waist-to-hip ratio (WHR) tertile vs those in the other two tertiles. After VLCD, body weight and BMI decreased markedly. The values of Ht, plasma viscosity (PV), erythrocyte aggregation index (EAI) values (P < 0.001) and white blood cell (WBC) counts (P < 0.01) significantly dropped. Globulin levels decreased, while albumin levels increased leading to significantly (P < 0.001) higher A/G ratios. No significant changes in fibrinogen (Fgn) levels were recorded after diet. In conclusion, the present study demonstrates that prolonged VLCD associated with slimming in grossly obese subjects is effective in improving related haemorheological disorders, mainly of plasmatic type, except Fgn. Second, we found that, at least in these grossly obese subjects, there is no clear evidence of a relationship between the degree of haemorheological changes and WHR values.

Neuroendocrine aging: its impact on somatotrophic function

In this paper, two different aspects of growth hormone neuroregulation during aging were considered. Twenty-month-old male rats had decreased growth hormone-releasing hormone mRNA levels and a slight reduction of somatostatin mRNA levels in the hypothalamus when compared to 8-month-old counterparts. Short-term administration of biosynthetic human growth hormone (125 micrograms rat twice daily, i.p.) to 8-month-old rats reduced hypothalamic growth hormone-releasing hormone mRNA and increased somatostatin mRNA levels. In old rats, growth hormone administration did not significantly change growth hormone-releasing hormone and somatostatin gene expression. Six old beagle dogs received short-term administration of growth hormone-releasing hormone alone or co-administered with clonidine, an alpha 2-adrenoceptor agonist, and the growth hormone secretory pattern was evaluated during a 6 h period by cluster analysis. In dogs given growth hormone-releasing hormone alone twice daily for 10 days, none of the GH secretory indices were modified except for the increase in the mean GH peak amplitude. By contrast, simultaneous administration of growth hormone-releasing hormone and clonidine, both given twice daily, significantly increased GH peak frequency and total peak area. Administration of clonidine (once daily) associated with growth hormone-releasing hormone (twice daily) further increased the GH secretory indices.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of protein kinase C in NG108-15 cell differentiation

The involvement of PKC in NG108-15 cell differentiation was investigated. Differentiation with dBcAMP was associated with a decrease in total cellular phorbol ester binding. The histone-directed PKC activity was decreased in the soluble fraction. Northern and Western blotting revealed the presence of only PKC alpha but not PKC beta and PKC gamma among the calcium-dependent isoforms. Differentiation induced a decrease of cytosolic PKC alpha immunoreactivity, with no changes of mRNA content or appearance of PKC beta and PKC gamma isoforms. The low levels of PKC alpha in the soluble fraction suggest that the mRNA for this species is less efficiently translated in differentiated NG108-15 cells. The data suggest that down-regulation of PKC alpha protein and kinase activity are associated with induction of neuronal morphology in NG108-15 cells.

Alterations of adenylyl cyclase-coupled growth hormone-releasing hormone (GHRH) pituitary receptors in different conditions of GHRH deprivation

Previous studies have clearly shown that the progressive decrease of growth hormone (GH) secretion occurring during ageing is coupled with a reduced responsiveness of pituitary GHRH receptors both in terms of GH secretion and activation of the adenylyl cyclase (AC), in the presence of increased basal values of the enzyme. The mechanism(s) subserving the age-associated alterations of GHRH-sensitive AC is likely related to the progressive decrease of hypothalamic GHRH function occurring with ageing. In this context, in old male rats, short-term administration of GHRH decreased the high basal AC activity and enhanced the GHRH-stimulated AC activity. Along this line, we decided to investigate whether experimentally induced abrogation of GHRH function in adult rats would induce the same alterations of AC-coupled GHRH receptors present in aged rats. Passive immunization of male young-adult rats with supra-maximal doses of GHRH antiserum (Ab-GHRH) significantly reduced the AC responsiveness to GHRH, an effect already evident 5 days post-injection and still present at 10 days. At this time interval, the treatment also evoked a significant increase of basal AC levels and of Gs alpha protein in the pituitary and completely blocked the GH-releasing effect of a bolus injection of GHRH. Furthermore, mechanical disruption of brain-pituitary links by complete stereotaxical ablation of the mediobasal hypothalamus induced a significant increase of basal AC levels and Gs alpha protein in the pituitary and a strikingly lower AC responsiveness to GHRH.(ABSTRACT TRUNCATED AT 250 WORDS)

[Measurement of C14 beta-radioactivity of stable natural origin taurine (2-aminoethanesulfonic acid) in bovine bile]

Taurine from natural sources has gained great importance as essential nutrient in milk for formula-fed infants. There is a strong request for a method capable of determining the natural origin of taurine. The measure of beta-radioactivity of 14C of taurine by means of liquid scintillation counting proved the most reliable. A simple method is reported.

Cholera toxin antagonizes morphine-induced catalepsy through a cyclic AMP-independent mechanism

We studied the effect of intracerebroventricular pretreatment with pertussis toxin and cholera toxin on morphine catalepsy in rats. Pertussis toxin (1 micrograms/rat, two, three and six days before) did not affect catalepsy evoked by central morphine. Cholera toxin (1 micrograms/rat) did not affect morphine catalepsy after 24 h and 48 h, but significantly reduced it (about 60%) after three and five days. Ten days later the morphine response had totally recovered. This effect was selective, since morphine analgesia was not modified. The reduction of catalepsy appeared unrelated to the ability of cholera toxin to raise cAMP levels, as demonstrated by the different time course of changes in striatal cholera toxin-stimulated adenylate cyclase activity. The effect required an intact cholera toxin molecule and did not occur with a similar dose of cholera toxin-B subunit. These findings demonstrate that catalepsy is an opioid effect not linked to pertussis toxin-sensitive G proteins and suggest that the Gs protein might be involved.

Growth hormone secretion is differently affected in genetically obese male and female rats

Growth hormone (GH) secretion is markedly blunted in obesity. Reportedly, genetically obese Zucker rats show a reduced GH secretion due to an impaired function of hypothalamic neurons producing the GH-releasing hormone (GHRH). The aim of this work was: (1) to compare the in vitro GH responsiveness to GHRH in genetically obese female versus male Zucker rats and, (2) to evaluate the function of hypothalamic GHRH and somatostatin and of pituitary receptors for these neurohormones as assessed by the effectiveness of GHRH and somatostatin on adenylate cyclase (AC) activity. Baseline GH secretion of pituitaries obtained from male and female obese rats was not different and similar to that present in lean counterparts. Stimulation with 10(-7) M GHRH elicited a significantly lower GH secretion from the pituitaries of obese male rats but induced a similar GH secretion from the pituitaries of lean and obese female rats. In these pituitaries, GH concentration was similar in obese versus lean male and female rats [corrected]. A sex-related difference was also evidenced when plasma concentrations of somatomedin C (IGF-I) were evaluated. Obese male rats had lower IGF-I concentrations than lean counterparts, while this was not the case for obese versus lean female rats. Evaluation of AC activity following GHRH disclosed a lower activation in obese than in lean male rats, whereas in the females the enzyme activation was higher in obese than in lean animals. Conversely, the inhibitory effect of somatostatin on forskolin-stimulated AC was similar in pituitary membranes of obese and lean rats of both sexes.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel N-terminal motif for palmitoylation of G-protein alpha subunits

We have examined the post-translational processing of G alpha subunits expressed endogenously in rat PC12 and NG108-15 rat/mouse hybrid cells, and after transfection of cDNA expression constructs into COS cells. Thioester-linked palmitoylation of alpha o, alpha s, alpha q/alpha 11 and alpha 12 has been detected by metabolic labelling with [3H]palmitate and immunoprecipitation. Palmitoylation of alpha o occurs post-translationally in cells treated with protein-synthesis inhibitors, suggesting possible dynamic acylation. Palmitoylation of the C-terminal CAAX motif has been excluded. Site-directed mutagenesis of alpha o has been used to implicate the site of modification as a cysteine residue next to the N-terminal myristoylated glycine, in a novel protein-lipid modification motif Met-Gly-Cys. The non-palmitoylated alpha o mutant is still myristoylated but shows reduced membrane binding, suggesting that reversible palmitoylation may regulate G alpha localization and function.

In situ hybridization reveals specific increases in G alpha s and G alpha o mRNA in discrete brain regions of morphine-tolerant rats

In situ hybridization histochemistry has been used to detect the basal distribution of mRNA encoding the alpha subunit of Gs, Go and Gi2 proteins throughout the rat brain. Based on these data we investigated the effect of chronic morphine on the content of these G protein alpha subunits mRNA. We observed an increase in the expression of alpha s and alpha o messages of chronically morphine-treated animals, while no changes were seen in alpha i2 mRNA. Specifically a 30% increase in expression for alpha s was seen only in the paraventricular nucleus of hypothalamus and a 20% elevation for alpha o was detected in the claustrum and endopiriform nucleus. Immunoblotting analysis was used to correlate the changes in alpha s and alpha o messages with equivalent changes in protein levels. Chronic morphine significantly increased alpha s amounts in the hypothalamus (70%), and produced a minor elevation (30%) in G alpha o levels in the olfactory area. Our results indicate that in discrete brain regions altered G protein expression is part of the adaptive changes underlying opiate tolerance.

Pharmacological characterization of the 5-hydroxytryptamine receptor coupled to adenylyl cyclase stimulation in human brain

Recently, a 5-hydroxytryptamine (5-HT) receptor has been described, whose pharmacology was distinct from that of the already known serotonergic receptors, so that it has been called 5-HT4. Because the lack of a high affinity radioligand, the identification of this receptor depends entirely on functional pharmacological analysis. Its stimulation leads to an increase in cyclic AMP accumulation in mouse embryo colliculi neurons, in guinea pig hippocampus and in human heart. We studied the effect of two indoleamines, 5-HT and 5-methoxytryptamine (5-MeO-T), and a benzimidazolone derivative, BIMU 8, in stimulating basal adenylyl cyclase activity in human frontal cortex, and characterized the receptor subtype involved. In membranes prepared from this tissue, 5-HT, 5-MeO-T and BIMU 8 dose-dependently stimulated (13-25%) the basal enzyme activity (220 pmoles cyclic AMP/min/mg protein). 5-MeO-T behaved as a full agonist, BIMU 8 elicited about 60% of the maximal 5-HT effect. The selective 5-HT1A agonist 8-OH-DPAT, was devoid of any stimulating activity. ICS 205-930, a low affinity 5-HT4 receptor antagonist, completely reversed the effect of all three agonists at high concentrations. Therefore, the present data are consistent with the 5-HT-mediated stimulation of adenylyl cyclase in human frontal cortex resulting by the activation of a 5-HT4 receptor subtype.