Hydrogen-bonding in the pyrimidine···NH3 van der Waals complex: experiment and theory.

The pyrimidineNH3 van der Waals complex has been studied using a combination of resonant two-photon ionisation (R2PI) spectroscopy, ab initio molecular orbital calculations and multidimensional Franck-Condon analysis. The R2PI spectrum is assignable to a single stable conformer in which the ammonia molecule binds via two hydrogen bonds within the plane of the ring, in a location which minimises repulsion between the ammonia nitrogen lone pair and that of the second, more remote pyrimidine nitrogen in the 3 position on the opposite side of the ring. Ground state estimated CCSD(T) interaction energies were extrapolated to the complete basis set limit: these calculations found the dissociation energy of the most stable conformer, σ(B), to be 20% larger than that of a second in-plane conformer, σ(A), in which the ammonia forms a similar pseudo five-membered ring, bridging the nitrogen at the 1 position with the carbon at the 2 position. This conformation in turn was found to have a dissociation energy 35% larger than that of a π-complex in which the ammonia binds above the plane of the aromatic ring. The results of multidimensional Franck-Condon simulations based on ab initio ground and excited state CASSCF and RICC2 geometry optimisations and vibrational frequency calculations showed good agreement with experiment. It is postulated that longer-range electrostatic interactions between the ammonia lone pair and the more distant of the two ring nitrogens on the pyrimidine, play a key role in determining which of the two in-plane structures is the more stable and which, therefore, is responsible for all of the spectral features observed in the R2PI spectrum.

Regional distribution of regulators of G-protein signaling (RGS) 1, 2, 13, 14, 16, and GAIP messenger ribonucleic acids by in situ hybridization in rat brain.

Regulators of G-protein signaling (RGS) proteins are a novel family of GTPase-activating proteins that interact with Galpha subunits of the Gi/o, Gz, Gq and G(12/13) subfamilies to dampen G-protein-coupled receptor (GPCR)-mediated signaling by accelerating intrinsic Galpha-GTPase activity. In the present study, we report on messenger ribonucleic acid (mRNA) localization in rat brain of six RGS genes by in situ hybridization. The distribution patterns of RGS2, RGS13, RGS14 and GAIP (Galpha interacting protein) overlapped in most brain regions examined. Highest regional expression was observed for RGS2 in the cerebral cortical layers, striatum, hippocampal formation, several thalamic and hypothalamic nuclei and hindbrain regions such as the pontine, interpeduncular and dorsal raphe nuclei. Levels of RGS14 mRNA closely paralleled those of RGS2 expression levels throughout most brain regions. RGS13 mRNA was enriched in the hippocampal formation, amygdala, mammillary nuclei as well as the pontine and interpeduncular nuclei. GAIP expression levels were highest in the hippocampal formation with moderate to low levels present in all other regions studied. Of the six RGS genes probed, RGS16 mRNA displayed a discrete localization predominantly in the thalamic midline/intralaminar and principal relay nuclei, and the hypothalamic suprachiasmatic nucleus. RGS1 mRNA signal was not detected in brain. In conclusion, the in situ hybridization studies for RGS2, RGS13, RGS14, RGS16 and GAIP mRNAs extend our knowledge of the distribution of RGS genes expressed in the rat central nervous system, and indicate overlapping RGS-enriched regions that may be indicative of functional diversification in GPCR signaling pathway modulation.

Applied genomics: integration of the technology within pharmaceutical research and development.

Multiple novel technologies have recently been developed to improve the analysis of genetic sequences, to rapidly assess RNA or protein levels in relevant tissues, and to validate function of potential new drug targets. The challenge facing pharmaceutical research is one of effective integration of these new technologies in ways that can maximally affect the discovery and development pipeline. Although database mining and transcriptional profiling clearly have increased the number of putative targets, the current focus is to assign function to new gene targets in a high-throughput manner. This requires a restructuring of the classical linear progression from gene identification, functional elucidation, target validation and screen development. New approaches are called for that can make this process non-linear and high-throughput.

RGS7 is palmitoylated and exists as biochemically distinct forms.

Regulator of G protein signaling (RGS) proteins are GTPase-activating proteins that modulate neurotransmitter and G protein signaling. RGS7 and its binding partners Galpha and Gbeta5 are enriched in brain, but biochemical mechanisms governing RGS7/Galpha/Gbeta5 interactions and membrane association are poorly defined. We report that RGS7 exists as one cytosolic and three biochemically distinct membrane-bound fractions (salt-extractable, detergent-extractable, and detergent-insensitive) in brain. To define factors that determine RGS7 membrane attachment, we examined the biochemical properties of recombinant RGS7 and Gbeta5 synthesized in Spodoptera frugiperda insect cells. We have found that membrane-bound but not cytosolic RGS7 is covalently modified by the fatty acid palmitate. Gbeta5 is not palmitoylated. Both unmodified (cytosolic) and palmitoylated (membrane-derived) forms of RGS7, when complexed with Gbeta5, are equally effective stimulators of Galpha(o) GTPase activity, suggesting that palmitoylation does not prevent RGS7/Galpha(o) interactions. The isolated core RGS domain of RGS7 selectively binds activated Galpha(i/o) in brain extracts and is an effective stimulator of both Galpha(o) and Galpha(i1) GTPase activities in vitro. In contrast, the RGS7/Gbeta5 complex selectively interacts with Galpha(o) only, suggesting that features outside the RGS domain and/or Gbeta5 association dictate RGS7-Galpha interactions. These findings define previously unrecognized biochemical properties of RGS7, including the first demonstration that RGS7 is palmitoylated.

NMR structure of free RGS4 reveals an induced conformational change upon binding Galpha.

Heterotrimeric guanine nucleotide-binding proteins (G-proteins) are transducers in many cellular transmembrane signaling systems where regulators of G-protein signaling (RGS) act as attenuators of the G-protein signal cascade by binding to the Galpha subunit of G-proteins (G(i)(alpha)(1)) and increasing the rate of GTP hydrolysis. The high-resolution solution structure of free RGS4 has been determined using two-dimensional and three-dimensional heteronuclear NMR spectroscopy. A total of 30 structures were calculated by means of hybrid distance geometry-simulated annealing using a total of 2871 experimental NMR restraints. The atomic rms distribution about the mean coordinate positions for residues 5-134 for the 30 structures is 0.47 +/- 0.05 A for the backbone atoms, 0. 86 +/- 0.05 A for all atoms, and 0.56 +/- 0.04 A for all atoms excluding disordered side chains. The NMR solution structure of free RGS4 suggests a significant conformational change upon binding G(i)(alpha)(1) as evident by the backbone atomic rms difference of 1. 94 A between the free and bound forms of RGS4. The underlying cause of this structural change is a perturbation in the secondary structure elements in the vicinity of the G(i)(alpha)(1) binding site. A kink in the helix between residues K116-Y119 is more pronounced in the RGS4-G(i)(alpha)(1) X-ray structure relative to the free RGS4 NMR structure, resulting in a reorganization of the packing of the N-terminal and C-terminal helices. The presence of the helical disruption in the RGS4-G(i)(alpha)(1) X-ray structure allows for the formation of a hydrogen-bonding network within the binding pocket for G(i)(alpha)(1) on RGS4, where RGS4 residues D117, S118, and R121 interact with residue T182 from G(i)(alpha)(1). The binding pocket for G(i)(alpha)(1) on RGS4 is larger and more accessible in the free RGS4 NMR structure and does not present the preformed binding site observed in the RGS4-G(i)(alpha)(1) X-ray structure. This observation implies that the successful complex formation between RGS4 and G(i)(alpha)(1) is dependent on both the formation of the bound RGS4 conformation and the proper orientation of T182 from G(i)(alpha)(1). The observed changes for the free RGS4 NMR structure suggest a mechanism for its selectivity for the Galpha-GTP-Mg(2+) complex and a means to facilitate the GTPase cycle.

Pindolol-insensitive [3H]-5-hydroxytryptamine binding in the rat hypothalamus; identity with 5-hydroxytryptamine7 receptors.

Pindolol-insensitive [3H]-5-hydroxytryptamine ([3H]-5-HT) binding to rat hypothalamic membranes was pharmacologically and functionally characterized to resolve whether this procedure selectively labels 5-HT7 receptors. Consistent with a previous report, 3 microM and not 100 nM pindolol was required to occupy fully 5-HT1A and 5-HT1B receptors. Remaining [3H]-5-HT binding was saturable (KD, 1.59+/-0.21 nM; Bmax, 53.8+/-3.1 fmol x mg protein(-1)). Displacement of [3H]-5-HT with metergoline and 5-CT revealed shallow Hill slopes (<0.5) but seven other compounds had slopes >0.8 and pKi values and the rank order of affinity were significantly correlated (r = 0.81 and 0.93, respectively) with published [3H]-5-HT binding to rat recombinant 5-HT7 receptors. In the presence of pindolol, 5-HT-enhanced accumulation of [32P]-cyclic AMP was unaffected by the 5-HT4 antagonist RS39604 (0.1 microM) or the 5-ht6 antagonist Ro 04-6790 (1 microM) but significantly attenuated by mesulergine (250 nM), ritanserin (450 nM) or methiothepin (200 nM) which have high affinity for the 5-HT7 receptor. Intracerebroventricular pretreatment with the serotonergic neurotoxin 5,7-dihydroxytryptamine, 5,7-DHT, elevated the [3H]-5-HT Bmax 2 fold, indicating that the hypothalamic 5-HT7 receptor is post-synaptic to 5-HT nerve terminals and regulated by synaptic 5-HT levels. These results suggest that, in the presence of 3 microM pindolol, [3H]-5-HT selectively labels hypothalamic binding sites consistent with functional 5-HT7 receptors.

Cloning and expression of the human kv4.3 potassium channel.

We report on the cloning and expression of hKv4.3, a fast inactivating, transient, A-type potassium channel found in both heart and brain that is 91% homologous to the rat Kv4.3 channel. Two isoforms of hKv4.3 were cloned. One is full length (hKv4.3 long), and the other has a 19 amino acid deletion (hKv4.3 short). RT-PCR shows that the brain contains both forms of the channel RNA, whereas the heart predominantly has the longer version. Both versions of the channel were expressed in Xenopus oocytes, and both contain a significant window or noninactivating current seen near potentials of -30 to -40 mV. The inactivation curve for hKv4.3 short is shifted 10 mV positive relative to hKv4.3 long. This causes the peak window current for the short version to occur near -30 mV and the peak for the longer version to be at -40 mV. There was little difference in the recovery from inactivation or in the kinetics of inactivation between the two isoforms of the channel.

Immunohistochemical distribution of RGS7 protein and cellular selectivity in colocalizing with Galphaq proteins in the adult rat brain.

Regulators of G protein signaling (RGS) proteins serve as potent GTPase-activating proteins for the heterotrimeric G proteins alphai/o and aq/11. This study describes the immunohistochemical distribution of RGS7 throughout the adult rat brain and its cellular colocalization with Galphaq/11, an important G protein-coupled receptor signal transducer for phospholipase Cbeta-mediated activity. In general, both RGS7 and Galphaq/11 displayed a heterogeneous and overlapping regional distribution. RGS7 immunoreactivity was observed in cortical layers I-VI, being most intense in the neuropil of layer I. In the hippocampal formation, RGS7 immunoreactivity was concentrated in the strata oriens, strata radiatum, mossy fibers, and polymorphic cells, with faint to nondetectable immunolabeling within the dentate gyrus granule cells and CA1-CA3 subfield pyramidal cells. Numerous diencephalic and brainstem nuclei also displayed dense RGS7 immunostaining. Dual immunofluorescence labeling studies with the two protein-specific antibodies indicated a cellular selectivity in the colocalization between RGS7 and Galphaq/11 within many discrete brain regions, such as the superficial cortical layer I, hilus area of the hippocampal formation, and cerebellar Golgi cells. To assess the ability of Galphaq/11-mediated signaling pathways to modulate dynamically RGS expression, primary cortical neuronal cultures were incubated with phorbol 12,13-dibutyrate, a selective protein kinase C activator. A time-dependent increase in levels of mRNA for RGS7, but not RGS4, was observed. Our results provide novel information on the region- and cell-specific pattern of distribution of RGS7 with the transmembrane signal transducer, Galphaq/11. We also describe a possible RGS7-selective neuronal feedback adaptation on Galphaq/11-mediated pathway function, which may play an important role in signaling specificity in the brain.

Technology evaluation: cystic fibrosis therapy, Genzyme.

Genzyme is developing therapies to replace the defective forms of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) protein in CF patients. The company is developing a gene therapy, as well as a recombinant production of CFTR for protein replacement therapy. Both approaches have been granted orphan drug status by the FDA [156348]. The results of several clinical trials were discussed at the first annual meeting of the American Society of Gene Therapy in May 1998. A single dose nasal administration was well tolerated by volunteers, but had disappointing efficacy. In a study completed at the Royal Brompton Hospital, London, a single dose aerosol application of GL-67:DOPE was administered to eight patients, while another eight received GL-67:DOPE plus pCF1-CFTR. In the second group, a moderate increase in the potential difference in the lung was observed, with a slight trend towards bacterial adherence normalization in the airway cells. Seven of the patients in the second group, and three patients who received lipid alone, developed, flu-like symptoms within 24 h. A trial at the University of Alabama, using the same formulation, showed that flu-like symptoms developed in six of eight patients by day two, and in all patients by day seven [290120]. In 1995, the company began a clinical safety trial involving delivery of a normal CF gene to the patient's lungs via an adenovirus vector. The administration involves the inhalation of an aerosol containing the vector or, separately, delivery to one lobe of the patient's lung via a bronchoscope [191678]. To evaluate additional delivery methods for the gene, Genzyme has an exclusive research agreement for the use of Vical's cytofectins as non-viral delivery vectors for CFTR. Also under investigation are delivery systems for the nasal epithelium using liposomes or lipid-DNA complexes. These protocols are being developed in collaboration with the National Heart & Lung Institute, London, and an undisclosed partner [162590], [177633]. Following in vitro screenings by the company, two T-shaped molecules were identified (GL-67 and GL-53), the gene transfer activities of which could be enhanced by dioleoyl-PE (DOPE). A recently-completed clinical trial in 16 CF patients demonstrated that the GL-67:DOPE:DMPE-PEG5000-pCF1-CFTR compound accumulated in the lung with minimal toxicity and resulted in a 25% correction of CF symptoms [268093]. Genzyme has also developed recombinant cell lines that synthesize CFTR and has used transgenic expression techniques to breed mice, rabbits and goats which secrete the protein in their milk. Protein replacement therapy is currently in preclinical investigation and research efforts have been reduced infavor of the gene therapeutic approach [177633].

Antisense oligonucleotide-induced reduction in 5-hydroxytryptamine7 receptors in the rat hypothalamus without alteration in exploratory behaviour or neuroendocrine function.

The effect of a 5-hydroxytryptamine7 (5-HT7) receptor-directed antisense oligonucleotide on rat behaviour and neuroendocrine function was investigated. Six days of intracerebroventricular 5-HT7 antisense oligonucleotide treatment significantly reduced [3H]5-HT binding to hypothalamic 5-HT7 receptors, whereas cortical 5-HT2C density remained unchanged. In rats on a food-restricted diet, both antisense and mismatch oligonucleotides reduced food intake and body weight compared with that in vehicle-treated controls by day 4 of administration. 5-HT7 antisense oligonucleotide administration did not affect exploratory or locomotor activity in photocell activity monitors on day 4 or elevated plus-maze behaviour on day 6 of intracerebroventricular treatment. 5-HT7 antisense oligonucleotide did not affect plasma corticosterone or prolactin levels or 5-HT turnover in either 5-HT cell body or terminal areas. These data demonstrate that intracerebroventricular 5-HT7 antisense oligonucleotide administration selectively reduced rat hypothalamic 5-HT7 receptor density without affecting any of the biochemical or behavioural measures. The results suggest that this antisense protocol could be a valuable tool to investigate central 5-HT7 receptor functions, and that this receptor is not critical for the control of neuroendocrine function or food intake.

Enhanced neuronal differentiation of NTera-2 cells expressing neuronally restricted beta2 adrenergic receptor.

NTera-2/D1 (NT2) is a human teratocarcinoma cell line which can be cultured as a dividing population of precursor cells that can be manipulated with retinoic acid (RA) to yield post-mitotic neurons. Precursor cells were transfected with the human beta2 adrenergic receptor, controlled by the neuronal cell specific rat synapsin-1 promoter. Transfected precursor cells did not display elevated expression of the beta2 adrenergic receptor. Upon differentiation to a neuronal phenotype with RA, betaSyn2 and betaSyn4 (beta2Syn-NT2; ATCC CRL-12356) displayed elevated beta2 adrenergic receptor levels, and an elevated coupling to cAMP production. It was also observed that the elevated expression of the beta2 adrenergic receptor in the neuronal NT2 cells resulted in an enhanced level of neuronal differentiation compared to the wild type cells. These results demonstrate that the neuronally restricted expression of the human beta2 adrenergic receptor in NT2 neurons results in increased receptor levels and receptor stimulated generation of cAMP, this may result in the observed improvement in neuronal differentiation.

Immunohistochemical localization of G protein beta1, beta2, beta3, beta4, beta5, and gamma3 subunits in the adult rat brain.

The regional distributions of the G protein beta subunits (Gbeta1-beta5) and of the Ggamma3 subunit were examined by immunohistochemical methods in the adult rat brain. In general, the Gbeta and Ggamma3 subunits were widely distributed throughout the brain, with most regions containing several Gbeta subunits within their neuronal networks. The olfactory bulb, neocortex, hippocampus, striatum, thalamus, cerebellum, and brainstem exhibited light to intense Gbeta immunostaining. Negative immunostaining was observed in cortical layer I for Gbeta1 and layer IV for Gbeta4. The hippocampal dentate granular and CA1-CA3 pyramidal cells displayed little or no positive immunostaining for Gbeta2 or Gbeta4. No anti-Gbeta4 immunostaining was observed in the pars compacta of the substantia nigra or in the cerebellar granule cell layer and Purkinje cells. Immunoreactivity for Gbeta1 was absent from the cerebellar molecular layer, and Gbeta2 was not detected in the Purkinje cells. No positive Ggama3 immunoreactivity was observed in the lateral habenula, lateral septal nucleus, or Purkinje cells. Double-fluorescence immunostaining with anti-Ggamma3 antibody and individual anti-Gbeta1-beta5 antibodies displayed regional selectivity with Gbeta1 (cortical layers V-VI) and Gbeta2 (cortical layer I). In conclusion, despite the widespread overlapping distributions of Gbeta1-beta5 with Ggamma3, specific dimeric associations in situ were observed within discrete brain regions.

Distribution of heterotrimeric G-protein beta and gamma subunits in the rat brain.

Heterotrimeric G-proteins, comprising alpha, beta and gamma subunits, have been shown to play a central role in coupling multiple receptors to a variety of enzymes and ion channels. In vitro studies have demonstrated the existence of selective interactions between various alpha, beta and gamma subunits, as well as between specific heterotrimers and target receptor and effector proteins. However, little is known of the physiological relevance of such associations, and the determinants of specificity in G-protein signaling within the brain remain largely unidentified. To investigate the possibility that specific heterotrimeric interactions result from discrete localizations of the G-protein subunits within the brain, we have used the technique of in situ hybridization to map the distribution of G-protein beta and gamma subunits in the rat brain. Beta1, beta2, beta3 and beta5 subunits were found to be widely expressed throughout the rat brain, whilst beta4 and the G-protein gamma subunit messenger RNAs generally showed more discrete expression patterns. The expression patterns for these subunits suggest that individual beta and gamma subunits may be co-expressed in certain cell types and brain regions; a particularly intriguing and striking co-localization was observed in the case of beta4 and gamma2 subunit messenger RNAs in layer VI of the occipital cortex. The localizations of the G-protein beta and gamma subunits, and their potential coupling to various receptor/effector systems, are discussed.

Cloning and tissue distribution of the human G protein beta 5 cDNA.

Heterotrimeric G proteins integrate signals between receptors and effector proteins. We have cloned the human beta 5 subunit from a human brain cDNA library. The clone has a 1059 bp open reading frame and is highly homologous to the murine clone. In contrast to the brain specific mouse beta 5, northern analysis showed it to be expressed in multiple tissues.

RGS7 attenuates signal transduction through the G(alpha q) family of heterotrimeric G proteins in mammalian cells.

The RGS proteins are a recently discovered family of G protein regulators that have been shown to act as GTPase-activating proteins (GAPs) on the G(alpha i) and G(alpha q) subfamilies of the heterotrimeric G proteins. Here, we demonstrate that RGS7 is a potent GAP in vitro on G(alpha i1), and G(alpha o) heterotrimeric proteins and that RGS7 acts to down-regulate G(alpha q)-mediated calcium mobilization in a whole-cell assay system using a transient expression protocol. This RGS protein and RGS4 are reported to be expressed predominantly in brain, and in situ hybridization studies have revealed similarities in the regional distribution of RGS and G(alpha q) mRNA expression. Our findings provide further evidence to support a functional role for RGS4 and RGS7 in G(alpha q)-mediated signaling in the CNS.

Selective uncoupling of RGS action by a single point mutation in the G protein alpha-subunit.

Heterotrimeric G proteins function as molecular relays, shuttling between cell surface receptors and intracellular effectors that propagate a signal. G protein signaling is governed by the rates of GTP binding (catalyzed by the receptor) and GTP hydrolysis. RGS proteins (regulators of G protein signaling) were identified as potent negative regulators of G protein signaling pathways in simple eukaryotes and are now known to act as GTPase-activating proteins (GAPs) for G protein alpha-subunits in vitro. It is not known, however, if Galpha GAP activity is responsible for the regulatory action of RGS proteins in vivo. We describe here a Galpha mutant in yeast (gpa1(sst)) that phenotypically mimics the loss of its cognate RGS protein (SST2). The gpa1(sst) mutant is resistant to an activated allele of SST2 in vivo and is unresponsive to RGS GAP activity in vitro. The analogous mutation in a mammalian Gqalpha is also resistant to RGS action in transfected cells. These mutants demonstrate that RGS proteins act through Galpha and that RGS-GAP activity is responsible for their desensitizing activity in cells. The Galphasst mutant will be useful for uncoupling RGS-mediated regulation from other modes of signal regulation in whole cells and animals.

Matrix metalloproteinases and metastatic cancer.

The rationale for matrix metalloproteinase (MMP) inhibition as a means to treat disease progression in breast cancer stems from the apparent involvement of MMPs in the hydrolysis of basement membranes during tumour cell invasion and subsequent metastasis. MMP-mediated matrix remodelling also appears to promote the growth of tumour cells, possibly by facilitating the proliferation and migration of endothelial cells and the neovascularization of tumour tissue. We found that transfection of the C127 breast cancer cell line by MMP-2 (gelatinase A), but not by MMP-1 or MMP-3 (collagenase and stromelysin respectively), gave rise to an invasive and metastatic phenotype. We were surprised to find that this phenotype depended not only on the catalytic properties of MMP-2 but also on properties associated with the MMP-2 non-catalytic C-terminal domain. Experiments with a synthetic gelatinase inhibitor revealed that a single dose could prevent the lungs of nude mice being colonized by the MMP-2 transfectants, and that the inhibitor had to be administered during or shortly after injection of the cells, indicating that an early event, such as the extravasation of the cells into the lung, is gelatinase-dependent in this system. In other studies employing long-term treatment with CT1746, an orally active gelatinase inhibitor, we have previously demonstrated a reduction in primary tumour growth rates, localized spread, and spontaneous metastasis, even when the treatment was commenced several days after tumour implantation. Furthermore, additive effects were recorded when gelatinase inhibitor therapy was combined with cytotoxic drug treatment. Since the gelatinase inhibitors can also inhibit bone resorption in vitro, these observations point to their potential for delaying disease recurrence and reducing rates of bone loss following conventional therapeutic strategies, in metastatic breast cancer.

CRIB (NGF delivery) Cyto Therapeutics Inc.

Cellular Replacement by Immunoisolatory Biocapsule (CRIB) is a technology under development by Cyto-Therapeutics for the delivery of therapeutic substances to the central nervous system (CNS). Preclinical studies with implants are underway for the potential treatment of Alzheimer's disease, Huntington's chorea and other neurodegenerative diseases [180367]. Theses implants contain cells that have been genetically engineered to secrete human nerve growth factor. Development of the CRIB implant is in collaboration with Genentech. CRIB consists of product-secreting cells encapsulated in a semipermeable polymer membrane. The device is surgically implanted into the target area of the brain, thus bypassing the blood-brain barrier, whilst isolating the foreign cells from the patient's immune system [180367]. CRIB implants secreting nerve growth factor (NGF) were effective in preventing nerve degeneration in a monkey model of Alzheimer's disease. The devices contained baby hamster kidney fibroblasts (genetically modified to secrete human NGF) and were implanted into brain ventricles of elderly rhesus monkeys whose cholinergic neurons had been cut. The monkeys treated with non-NGF secreting implants showed a decrease in the number of cholinergic neurons, while those treated with NGF-secreting implants showed a smaller loss of neurons and sprouting of cholinergic nerve fibres [200261]. CytoTherapeutics is working towards clinical trials with these implants in patients with Alzheimer's disease [168581]. Trials of NGF-secreting implants have also been carried out in animal models of Huntington's disease. The company demonstrated that in rodents whose brains had been lesioned with quinolinic acid to approximate the neuronal death which occurs in the disease, NGF-releasing implants protected many striatal neurons that would normally have died. In addition, it was shown that behaviors normally lost as a result of striatal neuron damage could be significantly attenuated. Further investigations are scheduled for the potential use of CRIB/NGF technology in Huntington's disease [180367]. The CRIB technology was originally developed at Brown University (Rhode Island, USA) which owns several patents that cover the technology. CytoTherapeutics has entered into collaborative agreements with the university for the use of the technology [199903] as well as with NeuroSpheres, Canada, for the use of their neural stem cells [199898].